BIOLOGY 
LIBRARY 


," 

A  TEXT-BOOK 


HUMAN    PHYSIOLOGY; 

DESIGNED  FOR  THE  USE  OF 

PRACTITIONERS  AND  STUDENTS  OF  MEDICINE. 


BY 

AUSTIN  FLINT,  JE.,  M.  D., 


PBOFE88OE  OF  PHYSIOLOGY  AND  PHYSIOLOGICAL  ANATOMY   IN  THE  BBLLBVTJE  HOSPITAL  MEDICAL  COLLEGE,  NEW 

YOBK;  FELLOW  OF  THE  NEW  YORK  ACADEMY  OF  MEDICINE;  MEMBEB  OF  THE  MEDICAL 

SOCIETY  OF  THE  COUNTY  OF  NEW   YOBK,  ETC.,  ETC. 


ILLUSTRATED  BY  THREE  LITHOGRAPHIC  PLATES  AND   THREE  HUNDRED  AND 
THIRTEEN  WOODCUTS. 


NEW  YOKE: 
D.    APPLETON    AND    COMPANY, 


549   &   551   BROADWAY. 
1876. 


f 


BIOLOGY 
LIBRARY 

G 


ENTEBED,  according  to  Act  of  Congress,  in  the  year  1875,  by 

D.   APPLETON   &  COMPANY, 
In  the  Office  of  the  Librarian  of  Congress,  at  "Washington. 


PEEF  AC  E. 


IN  preparing  this  text-book  for  the  use  of  students  and  practitioners  of 
medicine,  I  have  endeavored  to  adapt  it  to  the  wants  of  the  profession,  as 
they  have  appeared  to  me  after  a  considerable  experience  as  a  public  teacher 
of  human  physiology.  My  large  treatise  in  five  volumes  is  here  condensed, 
and  I  have  omitted  bibliographical  citations  and  matters  of  purely  historical 
interest.  Many  subjects,  which  were  considered  rather  elaborately  in  my 
larger  work,  are  here  presented  in  a  much  more  concise  form.  I  have 
added,  also,  numerous  illustrations,  which  I  hope  may  lighten  the  labors  of 
the  student.  A  few  of  these  are  original,  but  by  far  the  greatest  part  has 
been  selected  from  reliable  authorities.  I  have  thought  it  not  without 
historical  interest  to  reproduce  exactly  some  of  the  classical  engravings 
from  the  works  of  great  discoverers,,  such  as  illustrations  contained  in  the 
original  editions  of  Fabricius,  Harvey,  and  Asellius.  In  addition,  I  have 
reproduced  a  few  of  the  beautiful  microscopical  photographs  taken  at  the 
United  States  Army  Medical  Museum,  under  the  direction  of  Dr.  J.  J. 
Woodward,  to  whom  I  here  express  my  grateful  acknowledgments.  I  have 
also  to  thank  M.  Sappey  for  his  kindness  in  furnishing  electrotypes  of  many 
of  the  superb  engravings  with  which  his  great  work  upon  anatomy  is  illus- 
trated. 

My  work  in  five  volumes  was  intended  as  a  book  of  reference,  which  I 
hope  will  continue  to  be  useful  to  those  who  desire  an  account  of  the  litera- 
ture of  physiology,  as  well  as  a  statement  of  the  facts  of  the  science.  I 
have  always  endeavored,  in  public  teaching,  to  avoid  giving  undue  promi- 
nence to  points  in  which  I  might  myself  be  particularly  interested,  from 
having  made  them  subjects  of  special  study  or  of  original  research.  In  my 


iv  PREFACE. 

text-book,  I  have  carried  out  the  same  idea,  striving  to  teach,  systemati- 
cally and  with  uniform  emphasis,  what  students  of  medicine  are  expected 
to  learn  in  physiology,  and  avoiding  elaborate  discussions  of  subjects  not 
directly  connected  with  practical  medicine,  surgery,  and  obstetrics.  While 
I  have  referred  to  my  original  observations  upon  the  location  of  the  sense 
of  want  of  air  in  the  general  system,  the  new  excretory  function  of  the 
liver,  the  function  of  glycogenesis,  the  influence  of  muscular  exercise  upon 
the  elimination  of  urea,  etc.,  I  have  not  considered  these  subjects  with 
great  minuteness  and  have  generally  referred  the  reader  to  monographs  for 
the  details  of  my  experiments. 

Finally,  in  presenting  this  work  to  the  medical  profession,  I  cannot 
refrain  from  an  expression  of  my  acknowledgments  to  the  publishers,  who 
have  spared  nothing  in  carrying  out  my  views  and  have  devoted  special 
pains  to  the  mechanical  execution  of  the  illustrations. 

YORK,  November,  1875. 


CONTENTS. 


CHAPTER    I. 

THE  BLOOD. 

General  considerations— Transfusion— Quantity  of  blood— General  characters  of  the  blood— Blood-corpuscles— 
Development  of  the  blood-corpuscles — Leucocytes — Development  of  leucocytes — Composition  of  the  red  cor- 
puscles— Globuline— Haemaglobine — Analysis  of  the  blood — Composition  of  the  blood-plasma— Inorganic  prin- 
ciples— Organic  saline  principles — Organic  non-nitrogenized  principles — Excrementitious  matters — Organic  nitro- 
genized  principles — Plasmine,  fibrin,  metalbumen,  and  serine — Peptones — Coloring  matter — Coagulation  of  the 
blood — Characters  of  the  clot — Characters  of  the  serum — Circumstances  which  modify  coagulation — Coagulation 
of  the  blood  in  the  organism — Spontaneous  arrest  of  haemorrhage — Cause  of  the  coagulation  of  the  blood — So- 
called  fibrin-factors — Paraglobuline,  or  fibrinoplastic  matter — Fibrinogen, Page  1 


CHAPTER    II. 

CIRCULATION  OF   THE  BLOOD— ACTION  OF  THE  HEART. 

Discovery  of  the  circulation— Physiological  anatomy  of  the  heart— Valves  of  the  heart— Movements  of  the  heart- 
Impulse  of  the  heart — Succession  of  movements  of  the  heart — Force  of  the  heart's  action — Action  of  the  valves — 
Sounds  of  the  heart— Causes  of  the  sounds  of  the  heart— Frequency  of  the  heart's  action— Influence  of  age- 
Influence  of  digestion — Influence  of  posture  and  muscular  exertion — Influence  of  exercise — Influence  of  tem- 
perature— Influence  of  respiration  upon  the  action  of  the  heart — Cause  of  the  rhythmical  contractions  of  the 
heart  — Influence  of  the  nervous  system  upon  the  heart — Division  of  the  pneumogastrics — Galvanization  of  the 
pneumogastrics— Causes  of  arrest  of  action  of  the  heart— Blows  upon  the  epigastrium, 81 


CHAPTER   III. 

CIRCULATION   OF   THE  BLOOD  IN   THE    VESSELS. 

Physiological  anatomy  of  the  arteries— Course  of  blood  in  the  arteries  —Locomotion  of  the  arteries  and  production 
of  the  pulse — Pressure  of  blood  in  the  arteries— Pressure  in  different  parts  of  the  arterial  system— Depressor- 
nerve— Influence  of  respiration  upon  the  arterial  pressure— Kapidity  of  the  current  of  blood  in  the  arteries— Ra- 
pidity in  different  parts  of  the  arterial  system— Circulation  of  the  blood  in  the  capillaries— Physiological  anatomy 
of  the  capillaries— Capacity  of  the  capillary  system— Course  of  blood  in  the  capillaries— Relations  of  the  capil- 
lary circulation  to  respiration— Causes  of  the  capillary  circulation— Influence  of  temperature  upon  the  capillary 
circulation— Influence  of  direct  irritation  upon  the  capillary  circulation— Circulation  of  the  blood  in  the  veins- 
Physiological  anatomy  of  the  veins— Course  of  the  blood  in  the  veins— Pressure  of  blood  in  the  veins— Rapidity 
of  the  venous  circulation— Causes  of  the  venous  circulation— Air  in  the  veins— Function  of  the  valves— Condi- 
tions which  impede  the  venous  circulation — Regurgitant  venous  pulse— Circulation  in  the  cranial  cavity — Cir- 
culation in  erectile  tissues— Derivative  circulation— Pulmonary  circulation— Rapidity  of  the  circulation— Phe- 
nomena in  the  circulatory  system  after  death, 64 

CHAPTER   IV. 

RESPIRA  TION—RESPIRA  TOR  Y  MO  VEMENTS. 

General  considerations— Physiological  anatomy  of  the  respiratory  organs— Respiratory  movements  of  the  larynx- 
Epiglottis— Trachea  and  bronchial  tubes— Parenchyma  of  the  lungs— Movements  of  respiration— Inspiration- 
Muscles  of  inspiration— Expiration— Influence  of  the  elasticity  of  the  pulmonary  structure  and  walls  of  the  chest 
upon  expiration— Muscles  of  expiration— Action  of  the  abdominal  muscles  in  expiration— Types  of  respiration- 
Frequency  of  the  respiratory  movements— Relations  of  inspiration  and  expiration  to  each  other— The  respiratory 


vi  CONTENTS. 

sounds — Capacity  of  the  lungs  and  the  quantity  of  air  changed  in  the  respiratory  acts — Eesidual  air — Reserve 
air— Tidal,  or  breathing  air— Complemental  air— Extreme  breathing  capacity— Eelations  in  volume  of  the  expired 
to  the  inspired  air — Diffusion  of  air  in  the  lungs, Page  114 


CHAPTER    V. 

CHANGES  WHICH   THE  AIR  AND   THE  BLOOD    UNDERGO  IN  RESPIRATION. 

Composition  of  the  air — Consumption  of  oxygen — Exhalation  of  carbonic  acid — Influence  of  age — Relations  between 
the  quantity  of  oxygen  consumed  and  the  quantity  of  carbonic  acid  exhaled— Exhalation  of  watery  vapor— Ex- 
halation of  ammonia — Exhalation  of  organic  matter — Exhalation  of  nitrogen — Changes  of  the  blood  in  respira- 
tion (haematosis)— Difference  in  color  between  arterial  and  venous  blood— Comparison  of  the  gases  in  venous 
and  arterial  blood — Analysis  of  the  blood  for  gases — Relative  quantities  of  oxygen  and  carbonic  acid  in  venous 
and  arterial  blood— Nitrogen  of  the  blood — Condition  of  the  gases  in  the  blood— Mechanism  of  the  interchange 
of  gases  between  the  blood  and  the  air  in  the  lungs — Relations  of  respiration  to  nutrition,  etc. — Views  of  physi- 
ologists anterior  to  the  time  of  Lavoisier — Relations  of  the  consumption  of  oxygen  to  nutrition — Relations  of 
the  exhalation  of  carbonic  acid  to  nutrition — Essential  processes  of  respiration — The  respiratory  sense,  or  want 
on  the  part  of  the  system  which  induces  the  respiratory  movements — Respiratory  efforts  before  birth — Cuta- 
neous respiration— Asphyxia, .129 


CHAPTER    VI. 

ALIMENTATION. 

Appetite— Circumstances  which  modify  the  appetite— Influence  of  habit— Hunger— Seat  of  the  sense  of  hunger- 
Thirst — Seat  of  the  sense  of  thirst— Duration  of  life  in  inanition — Division  of  alimentary  principles— Nitrogeu- 
ized  alimentary  principles — Non-nitrogenized  alimentary  principles — Inorganic  alimentary  principles — Water — 
Alcohol— Distilled  liquors— Wines,  malt  liquors,  etc.— Coffee— Tea— Chocolate— Condiments  and  flavoring  articles 
— Quantity  and  variety  of  food  necessary  to  nutrition — Necessity  of  a  varied  diet, 171 


CHAPTER    VII. 

DIGESTION,  MASTICATION,  INSALIVATION,  AND  DEGLUTITION. 

General  arrangement  of  the  digestive  apparatus— Prehension  of  solids  and  liquids— Mastication— Physiological  anat- 
omy of  the  teeth — Anatomy  of  the  maxillary  bones — Temporo-in axillary  articulation — Muscles  of  mastication — 
Muscles  which  depress  the  lower  jaw— Action  of  the  muscles  which  elevate  the  lower  jaw  and  move  it  laterally 
and  antero-posteriorly — Action  of  the  tongue,  lips,  and  cheeks  in  mastication — Summary  of  the  process  of  masti- 
cation— Parotid  saliva — Submaxillary  saliva — Sublingual  saliva — Fluids  from  the  smaller  glands  of  the  mouth, 
tongue,  and  fauces — Mixed  saliva — Quantity  of  saliva — General  properties  and  composition  of  the  saliva — Action 
of  the  saliva  upon  starch— Mechanical  functions  of  the  saliva— Deglutition— Physiological  anatomy  of  the  parts  con- 
cerned in  deglutition — Muscles  of  the  pharynx — Muscles  of  the  soft  palate — Mucous  membrane  of  the  pharynx — 
(Esophagus— Mechanism  of  deglutition— First  period  of  deglutition— Second  period  of  deglutition— Protection  of 
the  posterior  nares  during  the  second  period  of  deglutition— Protection  of  the  opening  of  the  larynx— Function 
of  the  epiglottis— Study  of  deglutition  by  autolaryngoscopy— Third  period  of  deglutition— Intermittent  contrac- 
tion of  the  lower  third  of  the  esophagus— Nature  of  the  movements  of  deglutition— Deglutition  of  air,  .  195 


CHAPTER    VIII. 

STOMA  CH-DIGESTION. 

Physiological  anatomy  of  the  stomach— Glandular  apparatus  in  the  stomach— Gastric  juice— Mode  of  obtaining  the  gas- 
tric juice— Gastric  fistula  in  the  human  subject— Secretion  of  the  gastric  juice— Composition  of  the  gastric  juice- 
Source  of  the  acidity  of  the  gastric  juice— Ordinary  saline  constituents  of  the  gastric  juice— Action  of  the  gastric 
juice  in  digestion— Constituents  upon  which  the  activity  of  the  gastric  juice  depends — Action  of  the  gastric  juice 
upon  meats— Action  upon  albumen,  fibrin,  caseine,  and  gelatine— Action  upon  vegetable  nitrogenized  principles— 
Albuminose,  or  peptones — Action  of  the  gastric  juice  upon  fats — Action  upon  saccharine  and  amylaceous  principles 
—Duration  of  stomach-digestion— Digestibility  of  different  aliments  in  the  stomach— Action  of  the  gastric  juice 
upon  the  coats  of  the  stomach— Circumstances  which  influence  stomach-digestion— Character  of  the  contractions 
of  the  muscular  coat  of  the  stomach— Movements  in  the  cardiac  and  in  the  pyloric  portion— Mechanism  of  the 
movements  of  the  stomach— Rumination,  and  regurgitation  from  the  stomach— Rumination  in  the  human  sub- 
ject—Vomiting— Condition  of  the  stomach  during  the  act  of  vomiting— Action  of  the  diaphragm  in  vomiting— 
Action  of  the  abdominal  muscles  in  vomiting — Action  of  the  oesophagus  in  vomiting — Eructation,  .  .  226 


CONTENTS.  vii 

CHAPTER    IX. 

INTESTINAL   DIGESTION— DEF^CA  TION. 

Physiological  anatomy  of  the  small  intestine— Glands  of  Brunner— Intestinal  tubules,  or  follicles  of  Lieberkiihn— 
Solitary  glands,  or  follicles,  and  the  patches  of  Peyer — Intestinal  juice — General  properties  of  the  intestinal 

juice — Action  of  the  intestinal  juice  in  digestion — Pancreatic  juice — Action  of  the  pancreatic  juice  in  digestion 

Destruction  of  the  pancreas— Cases  of  fatty  diarrhoea— Action  of  the  pancreatic  juice  upon  starchy,  saccharine, 
and  nitrogenized  principles— Action  of  the  bile  in  digestion— Biliary  fistula— General  constitution  of  the  bile- 
Variations  in  the  flow  of  bile— Movements  of  the  small  intestine— Peristaltic  and  antiperistaltic  movements- 
Function  of  the  gases  in  the  small  intestine — Influence  of  the  nervous  system  upon  the  peristaltic  movements 

Physiological  anatomy  of  the  large  intestine— Digestion  La  the  large  intestine— Contents  of  the  large  intestine- 
Composition  of  the  faeces— Excretine  and  excretoleic  acid— Stercorine— Movements  of  the  large  intestine— Defse- 
cation — Gases  found  in  the  alimentary  canal Page  257 

CHAPTER   X. 

ABSORPTION— LYMPH  AND  CHYLE. 

General  considerations  of  absorption — Absorption  by  blood-vessels — Absorption  by  lacteal  and  lymphatic  vessels — 
Physiological  anatomy  of  the  lacteal  and  lymphatic  system — Absorption  by  the  lacteals — Absorption  from  parts 
not  connected  with  the  digestive  system— Absorption  of  fats  and  insoluble  substances— Variations  and  modifica- 
tions of  absorption — Imbibition  and  endosmosis — Imbibition  by  animal  tissues — Mechanism  of  the  passage  of 
liquids  through  membranes— Capillary  attraction — Endosmosis  through  porous  septa — Endosmosis  through  ani- 
mal membranes — Endosmosis  through  liquid  septa — Diffusion  of  liquids — Endosmotic  equivalents — Modifications 
of  endosmosis — Application  of  physical  laws  to  the  function  of  absorption — Transudation — Lymph  and  chyle — 
Mode  of  obtaining  lymph— Quantity  of  lymph — Properties  and  composition  of  lymph — Alterations  of  the  lymph 
—Corpuscular  elements  of  the  lymph— Leucocytes— Development  of  leucocytes  in  the  lymph  and  chyle— Glob- 
ulins— Origin  and  function  of  the  lymph — General  properties  of  the  chyle — Composition  of  the  chyle— Compara- 
tive analyses  of  the  lymph  and  the  chyle — Microscopical  characters  of  the  chyle — Movement  of  the  lymph  and 
chyle, 300 


CHAPTER    XI. 

SECRETION. 

General  considerations — Differences  between  the  secretions  and  fluids  containing  formed  anatomical  elements— Gassi- 
fication  of  the  secretions— Mechanism  of  the  production  of  the  true  secretions — Mechanism  of  the  production  of 
the  excretions — General  structure  of  secreting  organs — Anatomical  classification  of  glandular  organs— Classification 
of  the  secreted  fluids— Secretions  proper  (permanent  fluids ;  transitory  fluids)— Excretions— Fluids  containing 
formed  anatomical  elements — Physiological  anatomy  of  the  serous  and  synovial  membranes — Pericardial,  peri- 
toneal, and  pleural  secretions— Synovial  fluid—  Mucus— Mucous  membranes— Mechanism  of  the  secretion  of  mucus 
— Composition  and  varieties  of  mucus — Microscopical  characters  of  mucus — General  function  of  mucus — Non- 
absorption  of  certain  soluble  substances,  particularly  venoms,  by  mucous  membranes — Sebaceous  fluids— Physio- 
logical anatomy  of  the  sebaceous,  ceruminous,  and  Meibomian  glands— Ordinary  sebaceous  matter— Smegma  of 
the  prepuce  and  of  the  labia  minora — Vernix  caseosa— Cerumen— Meibomian  secretion — Function  of  the  Meibo- 
mian secretion — Mammary  secretion — Physiological  anatomy  of  the  mammary  glands — Condition  of  the  mam- 
mary glands  during  the  intervals  of  lactation— Structure  of  the  mammary  glands  during  lactation— Mechanism 
of  the  secretion  of  milk — Conditions  which  modify  the  lacteal  secretion — Quantity  of  milk — General  characters 
of  milk— Microscopical  characters  of  milk— Composition  of  milk— Variations  in  the  composition  of  milk— Colos- 
trum—Lacteal  secretion  in  the  newly -born, 341 


CHAPTER    XII. 

EXCRETION  BY   THE  SKIN  AND  KIDNEYS 

Differences  between  the  secretions  proper  and  the  excretions— Physiological  anatomy  of  the  skin— Physiological 
anatomy  of  the  nails  and  hairs— Sudden  blanching  of  the  hair— Uses  of  the  hairs— Perspiration—  Sudoriparous 
glands — Mechanism  of  the  secretion  of  sweat — Properties  and  composition  of  the  sweat — Peculiarities  of  the 
sweat  in  certain  parts— Physiological  anatomy  of  the  kidneys-Distribution  of  blood-vessels  in  the  kidneys 
—Lymphatics  and  nerves  of  the  kidneys— Mechanism  of  the  production  and  discharge  of  urine— Formation 
of  the  excrementitious  constituents  of  the  urine  in  the  tissues,  absorption  of  these  principles  by  the  blood, 
and  separation  of  them  from  the  blood  by  the  kidneys— Effects  of  removal  of  both  kidneys  from  a  living  animal 
—Effects  of  tying  the  ureters  in  a  living  animal— Extirpation  of  one  kidney— Influence  of  blood-pressure,  the 
nervous  system,  etc.,  upon  the  secretion  of  urine— Alternation  in  the  action  of  the  kidneys  upon  the  two  sides- 
Changes  in  the  composition  of  the  blood  in  passing  through  the  kidneys— Physiological  anatomy  of  the  urinary 
passages— Mechanism  of  the  discharge  of  urine— Properties  and  composition  of  the  urine -General  physical  prop- 


viii  CONTENTS. 

erties  of  the  urine— Quantity,  specific  gravity,  and  reaction  of  the  urine— Composition  of  the  urine— Gases  of 
the  urine — Variations  in  the  composition  of  the  urine — Variations  produced  by  food — Urina  potus,  urina  cibi, 
and  urina  sanguinis — Influence  of  muscular  exercise  upon  the  urine — Influence  of  mental  exertion,  .  Page  379 

CHAPTEE   XIII. 

FUNCTIONS   OF  THE  LIVER. 

Physiological  anatomy  of  the  liver — Distribution  of  the  portal  vein,  the  hepatic  artery,  and  the  hepatic  duct — 
Origin  and  course  of  the  hepatic  veins— Structure  of  a  lobule  of  the  liver— Arrangement  of  the  bile-ducts  in 
the  lobules— Anatomy  of  the  excretory  biliary  passages — Nerves  and  lymphatics  of  the  liver — Mechanism  of 
the  secretion  and  discharge  of  bile — Quantity  of  bile — Variations  in  the  flow  of  the  bile — Discharge  of  bile  from 
the  gall-bladder— General  properties  of  the  bile— Composition  of  the  bile— Origin  of  the  biliary  salts— Choles- 
terine— Biliverdine — Tests  for  bile — Excretory  function  of  the  liver — Origin  of  cholesterine — Experiments  show- 
ing the  passage  of  cholesterine  into  the  blood  as  it  circulates  through  the  brain— Elimination  of  cholesterine  by 
the  liver — Cholestersemia  — Production  of  sugar  in  the  liver — Evidences  of  a  glycogenic  function  in  the  liver — 
Does  the  liver  contain  sugar  during  life? — Mechanism  of  the  production  of  sugar  by  the  liver — Glycogenic  mat- 
ter—Variations in  the  glycogenic  function— Production  of  sugar  in  foetal  life— Influence  of  digestion  and  of  differ- 
ent kinds  of  food  upon  glycogenesis — Influence  of  the  nervous  system,  etc.,  upon  glycogenesis — Artificial  dia- 
betes—Destination of  sugar— Alleged  production  of  fat  by  the  liver— Changes  in  the  albuminoid  and  the  corpus- 
cular elements  of  the  blood  in  their  passage  through  the  liver, 431 


CHAPTER  XIV. 

THE  DUCTLESS   GLANDS. 

Probable  office  of  the  ductless  glands — Anatomy  of  the  spleen— Fibrous  structure  of  the  spleen  (trabeculae) — Malpi- 
ghian  bodies— Spleen-pulp— Vessels  and  nerves  of  the  spleen— Some  points  in  the  chemical  constitution  of  the 
spleen — State  of  our  knowledge  concerning  the  functions  of  the  spleen — Variations  in  the  volume  of  the  spleen 
—Extirpation  of  the  spleen— Anatomy  of  the  suprarenal  capsules— Cortical  substance— Medullary  substance 
— Vessels  and  nerves — Chemical  reactions  of  the  suprarenal  capsules — State  of  our  knowledge  concerning- 
the  functions  of  the  suprarenal  capsules — Extirpation  of  the  suprarenal  capsules — Addison's  disease — Anatomy 
of  the  thyroid  gland — State  of  our  knowledge  concerning  the  functions  of  the  thyroid  gland — Anatomy  of  the 
thymus — Pituitary  body  and  pineal  gland, 47'J 


CHAPTEE  XV. 

NUTRITION— ANIMAL   HEAT. 

Nature  of  the  forces  involved  in  nutrition— Definition  of  vital  properties— Life,  as  represented  in  development  and 
nutrition — Principles  which  pass  through  the  organism — Principles  consumed  in  the  organism — Development  of 
power  and  endurance  by  exercise  (training)— Formation  and  deposition  of  fat— Conditions  under  which  fat  exists 
in  the  organism— Physiological  anatomy  of  adipose  tissue— Conditions  which  influence  nutrition— Products  of 
disassimilation— Animal  heat — Limits  of  variation  in  the  normal  temperature  in  man — Variations  with  external 
temperature— Variations  in  different  parts  of  the  body— Variations  at  different  periods  of  life— Diurnal  variations 
—Relations  of  animal  heat  to  digestion— Influence  of  defective  nutrition  and  inanition— Influence  of  exercise, 
mental  exertion,  and  the  nervous  system,  upon  the  heat  of  the  body — Sources  of  animal  heat — Connection  of  the 
production  of  heat  with  nutrition— Seat  of  the  production  of  animal  heat— Eelations  of  animal  heat  to  the  different 
processes  of  nutrition— Eelations  of  animal  heat  to  respiration— Exaggeration  of  the  animal  temperature  in  par- 
ticular parts  after  division  of  the  sympathetic  nerve  and  in  inflammation— Intimate  nature  of  the  calorific  pro- 
cesses— Equalization  of  the  animal  temperature, 4S(i 


CHAPTEE    XVI. 

MOVEMENTS-VOICE  AND   SPEECH. 

Amorphous  contractile  substance — Ciliary  movements — Movements  due  to  elasticity — Varieties  of  clastic  tissue — 
Muscular  movements — Physiological  anatomy  of  the  involuntary  muscles — Mode  of  contraction  of  the  invol- 
untary muscular  tissue — Physiological  anatomy  of  the  voluntary  muscles — Fibrous  and  adipose  tissue  in  the 
voluntary  muscles— Connective  tissue— Blood-vessels  and  lymphatics  of  the  muscular  tissue— Connection  of 
the  muscles  with  the  tendons — Chemical  composition  of  the  muscles — Physiological  properties  of  the  mus- 
cles— Muscular  contractility,  or  irritability — Muscular  contraction — Changes  in  the  form  of  the  muscular 
fibres  during  contraction— Secomse,  Zuckung,  or  spasm— Mechanism  of  prolonged  muscular  contraction- 
Tetanus— Electrical  phenomena  in  the  muscles — Muscular  effort— Passive  organs  of  locomotion — Physiological 
anatomy  of  the  bones — Marrow  of  the  bones — Medullocells — Myeloplaxes — Periosteum — Physiological  anatomy 
of  cartilage — Fibro-cartilage — Voice  and  speech— Sketch  of  the  physiological  anatomy  of  the  vucal  organs — 


CONTENTS.  ix 

Vocal  chords— Muscles  of  the  larynx— Mechanism  of  the  production  of  the  voice— Appearance  of  the  glottis 
during  ordinary  respiration— Movements  of  the  glottis  during  phonation— Variations  in  the  quality  of  the 
voice,  depending  upon  differences  in  the  size  and  form  of  the  larynx  and  the  vocal  chords— Action  of  the 
intrinsic  muscles  of  the  larynx  in  phonation — Action  of  the  accessory  vocal  organs — Mechanism  of  the  differ- 
ent vocal  registers— Mechanism  of  speech, page  522 


CHAPTER  XVII. 

PHYSIOLOGICAL   DIVISIONS,  STRUCTURE,  AND   GENERAL   PROPERTIES   OF  THE 

NERVOUS  SYSTEM. 

General  considerations— Divisions  of  the  nervous  system— Physiological  anatomy  of  the  nervous  tissue— Anatomical 
divisions  of  the  nervous  tissue— Medullated  nerve-fibres— Simple,  or  non-medullated  nerve-fibres— Gelatinous 
nerve-fibres  (fibres  of  Kemak)— Accessory  anatomical  elements  of  the  nerves — Branching  and  course  of  the  nerves 
— Termination  of  the  nerves  in  the  muscular  tissue — Termination  of  the  nerves  in  glands — Terminations  of  the 
sensory  nerves — Corpuscles  of  Pacini,  or  of  Vater — Tactile  corpuscles — Terminal  bulbs— Structure  of  the  nerve- 
centres — Nerve-cells — Connection  of  the  cells  with  the  fibres  and  with  each  other — Accessory  anatomical  elements 
of  the  nerve-centres— Composition  of  the  nervous  substance— Kegeneration  of  the  nervous  tissue— Eeunion  of 
nerve-fibres — Motor  and  sensory  nerves — Distinct  seat  of  the  motor  and  sensory  properties  of  the  spinal  nerves — 
Experiments  of  Magendie  upon  the  roots  of  the  spinal  nerves— Properties  of  the  posterior  roots  of  the  spinal  nerves 
— Properties  of  the  anterior  roots  of  the  spinal  nerves — Eecurrent  sensibility — Mode  of  action  of  the  motor  nerves 
—Associated  movements— Mode  of  action  of  the  sensory  nerves— Sensation  in  amputated  members— General  prop- 
erties of  the  nerves — Nervous  irritability — Different  means  employed  for  exciting  the  nerves — Disappearance  of 
the  irritability  of  the  motor  and  sensory  nerves  after  exsection— Nerve-force— Sapidity  of  nervous  conduction— 
— Estimation  of  the  duration  of  acts  involving  the  nerve-centres — Action  of  electricity  upon  the  nerves — Induced 
muscular  contraction — Galvanic  current  from  the  exterior  to  the  cut  surface  of  a  nerve — Effects  of  a  constant  gal- 
vanic current  upon  the  nervous  irritability — Electrotonus,  anelectrotonus,  and  catelectrotonus — Neutral  point — 
Negative  variation, 563 


CHAPTER   XVIII. 

SPINAL  NERVES-MOTOR    CRANIAL   NERVES. 

Special  nerves  coming  from  the  spinal  cord— Cranial  nerves— Anatomical  classification— Physiological  classification- 
Motor  oculi  coinmunis  (third  nerve) — Physiological  anatomy — Properties  and  functions — Influence  upon  the 
movements  of  the  iris— Patheticus,  or  trochlearis  (fourth  nerve)— Physiological  anatomy— Properties  and  func- 
tions— Motor  oculi  externus,  or  abducens  (sixth  nerve) — Physiological  anatomy — Properties  and  functions — 
Motor  nerves  of  the  face— Nerve  of  mastication  (the  small,  or  motor  root  of  the  fifth)— Physiological  anatomy 
— Deep  origin — Distribution — Properties  and  functions  of  the  nerve  of  mastication — Facial  nerve,  or  nerve  of 
expression  (the  portio  dura  of  the  seventh)— Physiological  anatomy— Intermediary  nerve  of  Wrisberg— Decus- 
sation  of  the  fibres  of  origin  of  the  facial— Alternate  paralysis— Course  and  distribution  of  the  facial— Anasto- 
moses with  sensitive  nerves— Properties  and  functions  of  the  facial— Functions  of  the  branches  of  the  facial 
within  the  aqueduct  of  Fallopius— Functions  of  the  chorda  tympani— Influence  of  various  branches  of  the  facial 
upon  the  movements  of  the  palate  and  uvula — Functions  of  the  external  branches  of  the  facial — Spinal  accessory 
nerve  (third  division  of  the  eighth  nerve)— Physiological  anatomy— Properties  and  functions  of  the  spinal  ac- 
cessory— Functions  of  the  internal  branch  from  the  spinal  accessory  to  the  pneumogastric — Influence  of  the 
spinal  accessory  upon  the  heart — Functions  of  the  external,  or  muscular  branch  of  the  spinal  accessory— Sub- 
lingual,  or  hypoglossal  nerve  (ninth  nerve)— Physiological  anatomy— Properties  and  functions  of  the  sublin- 
gual— Glosso-labial  paralysis, 606 


CHAPTER    XIX. 

SENSORY  CRANIAL   NERVES. 

Trifacial,  or  trigeminal  nerve— Physiological  anatomy  of  the  trifacial — Properties  and  functions  of  the  trifacial — Divi- 
sion of  the  trifacial  within  the  cranal  cavity— Immediate  effects  of  division  of  the  trifacial— Remote  effects  of 
division  of  the  trifacial— Division  of  the-trifacial  before  and  behind  the  ganglion  of  Gasser— Communication  with 
the  sympathetic  at  the  ganglion  of  Gasser— Explanation  of  the  phenomena  of  disordered  nutrition  after  division 
of  the  trifacial — Cases  of  paralysis  of  the  trifacial  in  the  human  subject— Pneumogastric  nerve  (second  division  of 
the  eighth  nerve) — Physiological  anatomy — Properties  and  functions  of  the  pneumogastric— General  properties  of 
the  roots — Properties  and  functions  of  the  auricular  nerves — Properties  and  functions  of  the  pharyngeal  nerves — 
Properties  and  functions  of  the  superior  laryngeal  nerves— Properties  and  functions  of  the  inferior,  or  recurrent 
laryngeal  nerves— Properties  and  functions  of  the  cardiac  nerves,  and  influence  of  the  pneumogastrics  upon  the 
circulation— Depressor-nerve  of  the  circulation— Properties  and  functions  of  the  pulmonary  branches,  and  influ- 
ence of  the  pneumogastrics  upon  respiration— Properties  and  functions  of  the  O3sophageal  nerves— Properties  and 
functions  of  the  abdominal  branches, 634 


x  CONTENTS. 

CHAPTER   XX. 

FUNCTIONS   OF   THE  SPINAL    CORD. 

General  arrangement  of  the  cerebro-spinal  axis— Membranes  of  the  encephalon  and  spinal  cord— Cephalo-rachidian 
fluid— Physiological  anatomy  of  the  spinal  cord — Direction  of  the  fibres  after  they  have  penetrated  the  cord  by  the 
roots  of  the  spinal  nerves — General  properties  of  the  spinal  cord — Action  of  the  spinal  cord  as  a  conductor — Trans- 
mission of  motor  stimulus  in  the  cord — Decussation  of  the  motor  conductors  of  the  cord — Transmission  of  sen- 
sory impressions  in  the  cord — The  white  substance  of  the  posterior  columns  does  not  conduct  sensory  impres- 
sions— Action  of  the  gray  matter  as  a  conductor — Probable  function  of  the  cord  in  connection  with  muscular  co- 
ordination— Decussation  of  the  sensory  conductors  of  the  cord — Summary  of  the  action  of  the  cord  as  a  conductor 
—Action  of  the  spinal  cord  as  a  nerve-centre— Movements  in  decapitated  animals— Definition  and  applications 
•of  the  term  "reflex  " — Eeflex. action  of  the  spinal  cord — Question  of  sensation  and  volition  in  frogs  after  decapita- 
tion— Character  of  movements  following  irritation  of  the  surface  in  decapitated  animals — Dispersion  of  impres- 
sions in  the  cord — Conditions  essential  to  the  manifestation  of  reflex  phenomena — Exaggeration  of  reflex  excita- 
bility by  decapitation,  poisoning  with'  strychnine,  etc.  —  Eeflex  phenomena  observed  in  the  human  sub- 
ject,  Page  666 

CHAPTER    XXI. 

THE  ENCEPHALIC    GANGLIA. 

•Physiological  divisions  of  the  encephalon— Weight  of  different  parts  of  the  brain  and  of  the  entire  encephalon— Some 
points  in  the  physiological  anatomy  of  the  encephalon  and  its  connections— The  cerebrum—General  properties  of 
the  cerebrum— Functions  of  the  cerebrum— Extirpation  of  the  cerebrum  in  the  lower  animals— Pathological  facts 
bearing  upon  the  functions  of  the  cerebrum— Comparative  development  of  the  cerebrum  in  the  lower  animals- 
Development  of  the  cerebrum  in  different  races  of  men  and  in  different  individuals— Location  of  the  faculty  of  artic- 
ulate language  in  a  restricted  portion  of  the  anterior  cerebral  lobes— The  cerebellum— Some  points  in  the  physio- 
logical anatomy  of  the  cerebellum— Course  of  the  fibres  in  the  cerebellum— General  properties  of  the  cerebellum- 
Functions  of  the  cerebellum— Extirpation  of  the  cerebellum  in  animals— Pathological  facts  bearing  upon  the  func- 
tions of  the  cerebellum— Connection  of  the  cerebellum  with  the  generative  function— Development  of  the  cerebel- 
lum in  the  lower  animals— Ganglia  at  the  base  of  the  encephalon— Corpora  striata— Optic  thalami— Tubercula 
quadrigemina,  or  optic  lobes — Ganglion  of  the  tuber  annulare — Medulla  oblongata — Physiological  anatomy  of  the 
medulla  oblongata — Functions  of  the  medulla  oblongata — Connection  of  the  medulla  oblongata  with  respiration— 
Vital  point — Connection  of  the  medulla  oblongata  with  various  reflex  acts — Boiling  and  turning  movements  fol- 
lowing injury  of  certain  parts  of  the  encephalon— General  properties  of  the  peduncles, 688 


€HAPTER    XXII. 

SYMPATHETIC   NERVOUS  SYSTEM—SLEEP. 

General  arrangement  of  the  sympathetic  system— Peculiarities  in  the  intimate  structure  of  the  sympathetic  ganglia 
and  nerves — General  properties  of  the  sympathetic  ganglia  and  nerves — Functions  of  the  sympathetic  system — 
Vaso-motor  nerves— Eeflex  phenomena  operating  through  the  sympathetic  system— Trophic  centres  and  nerves 
(so  called) — Sleep — General  considerations — Condition  of  the  organism  during  sleep — Dreams — Eeflex  mental  phe- 
nomena during  sleep— Condition  of  the  brain  and  nervous  system  during  sleep— Theories  of  sleep— Anaesthesia 
and  sleep  produced  by  pressure  upon  the  carotid  arteries— Differences  between  natural  sleep  and  stupor  or 
coma — Eegeneration  of  the  brain-substance  during  sleep — Theory  that  sleep  is  due  to  a  want  of  oxygen — Condi- 
tion of  the  various  functions  of  the  organism  during  sleep, 729 


CHAPTER    XXIII. 

SPECIAL   SENSES— TOUCH,    OIF  ACTION,  AND   GUSTATION. 

General  characters  of  the  special  senses— Muscular  sense  (so  called)— Appreciation  of  weight— Sense  of  touch— Varia- 
tions in  tactile  sensibility  in  different  parts— Table  of  variations  measured  by  the  aesthesiometer— Connection 
between  the  variations  in  tactile  sensibility  and  the  distribution  of  the  tactile  corpuscles— Titillation— Apprecia- 
tion of  temperature— Venereal  sense— Olfaction— Nasal  fossae— Schneiderian  and  olfactory  membrane— Physio- 
logical anatomy  of  the  olfactory  nerves— Olfactory  bulbs— Olfactory  cells  and  terminations  of  the  olfactory  nerve- 
fibres— Properties  and  functions  of  the  olfactory  nerves— Mechanism  of  olfaction— Eelations  of  olfaction  to  the 
sense  of  taste— Eeflex  acts  through  the  olfactory  nerves— Gustation— Savory  substances— Eelations  between 
gustation  and  olfaction— Taste  and  flavor— Modifications  of  the  sense  of  taste— Nerves  of  taste— Chorda  tympani 
— Facial  paralysis  with  impairment  of  taste — Paralysis  of  general  sensibility  of  the  tongue  without  impairment  of 
taste— Glosso-pharyngeal  nerve  (first  division  of  the  eighth  nerve)— Physiological  anatomy— General  properties 
of  the  glosso-pharyngeal — Eelations  of  the  glosso-pharyngeal  nerves  to  gustation — Mechanism  of  gustation — 
Physiological  anatomy  of  the  organ 'of  taste — Papillae  of  the  tongue — Taste-buds,  or  taste-beakers — Connections 
of  the  nerves  with  the  organs  of  taste, 749 


CONTENTS.  xi 

CHAPTER    XXIY. 

VISION. 

General  considerations— Physiological  anatomy  and  general  properties  of  the  optic  nerves— Physiological  anatomy  of 
the  eyeball— Sclerotic  coat— Cornea— Membrane  of  Descemet,  or  of  Demours— Ligamentum  iridis  pectinatum— 
Choroid  coat — Ciliary  processes — Ciliary  muscle — Iris — Pupillary  membrane — Eetina — Crystalline  lens — Aqueous 
humor — Chambers  of  the  eye — Vitreous  humor— Summary  of  the  anatomy  of  the  globe — The  eye  as  an  optical 
instrument— Laws  of  refraction,  dispersion,  etc.,  bearing  upon  the  physiology  of  vision— Theories  of  light— Re- 
fraction by  lenses— Myopia  and  hypermetropia— Formation  of  images  in  the  eye— Mechanism  of  refraction  in  the 
eye — Astigmatism — Movements  of  the  iris — Direct  action  of  light  upon  the  iris — Action  of  the  nervous  system  upon 

the  iris — Mechanism  of  the  movements  of  the  iris — Accommodation  of  the  eye  to  vision  at  different  distances 

Changes  in  the  crystalline  lens  in  accommodation— Action  of  the  ciliary  muscle— Changes  in  the  iris  in  accom- 
modation— Erect  impressions  produced  by  images  inverted  upon  the  retina — Single  vision  with  both  eyes — Cor- 
responding points — The  horopter — Appreciation  of  distance  and  of  the  form  of  objects— Mechanism  of  the  stereo- 
scope— Duration  of  luminous  impressions— Irradiation — Movements  of  the  eyeball — Muscles  of  the  eyeball — Parts 
for  the  protection  of  the  eyeball — Eyelids — Muscles  which  open  and  close  the  eyelids — Conjunctival  mucous 
membrane — Lachrymal  apparatus — Composition  of  the  tears,  «... Page  767 


CHAPTER    XXV. 

AUDITION, 

Physiological  anatomy  of  the  auditory  nerves — General  properties  of  the  auditory  nerves — Topographical  anatomy 
of  the  parts  essential  to  the  appreciation  of  sound — The  external  ear — General  arrangement  of  the  parts  composing 
the  middle  ear— Anatomy  of  the  tympanum— Arrangement  of  the  ossicles  of  the  ear— Muscles  of  the  middle  ear 
— Mastoid  cells — Eustachian  tube — Muscles  of  the  Eustachian  tube — Mucous  membrane  of  the  middle  ear  and  of 
the  Eustachian  tube— General  arrangement  of  the  bony  labyrinth — Laws  of  sonorous  vibrations — Noise  and  musi- 
cal sounds — Intensity,  pitch,  and  quality  of  musical  sounds — Musical  scale — Harmonics,  or  overtones— Resonators 
of  Helmholtz — Resultant  tones— Summation  tones — Harmony— Discord— Tones  by  influence  (consonance) — Uses 
of  different  parts  of  the  auditory  apparatus— Uses  of  the  external  ear— Structure  of  the  membrana  tympani— Uses 
of  the  membrana  tympani — Vibrations  of  the  membrane  by  influence — Appreciation  of  the  pitch  of  tones — Mech- 
anism of  the  ossicles  of  the  ear — Physiological  anatomy  of  the  internal  ear — General  arrangement  of  the  mem- 
branous labyrinth— Vestibule— Semicircular  canals — Cochlea— Liquids  of  the  labyrinth— Distribution  of  nerves  in 
the  cochlea — Organ  of  Corti — Functions  of  different  parts  of  the  internal  ear — Functions  of  the  semicircular  canals 
— Functions  of  the  parts  contained  in  the  cochlea— Summary  of  the  mechanism  of  audition,  .  .  .  .815 


CHAPTER    XXVI. 

ORGANS  AND  ELEMENTS  OF  GENERATION. 

General  considerations — Sexual  generation — Spontaneous  generation  (so  called) — Female  organs  of  generation — Gen- 
eral arrangement  of  the  female  organs— External  and  internal  organs— The  ovaries— Development  of  the  Graa- 
flan  follicles — The  parovarium — The  uterus — The  Fallopian  tubes — Structure  of  the  ovum— Vitelline  membrane — 
Vitellus — Germinal  vesicle  and  germinal  spot — Discharge  of  the  ovum — Puberty  and  menstruation — Descrip- 
tion of  a  menstrual  period— Characters  of  the  menstrual  flow— Changes  in  the  uterine  mucous  membrane  during 
menstruation— Changes  in  the  Graafian  follicle  after  its  rupture  (corpus  luteum)— The  testicles— Tunica  vagi- 
nalis — Tunica  albuginea— Tunica  vasculosa — Seminiferous  tubes — Epididymis— Vas  deferens — Vesiculas  seminales 
—Prostate— Glands  of  the  urethra— Semen— Secretions  mixed  with  the  products  of  the  testicles— Spennatozoids— 
Development  of  the  spermatozoids— Seminal  fluid  in  advanced  age, 852 

CHAPTER    XXVII. 

FECUNDATION  AND  DEVELOPMENT  OF  THE  OVUM. 

Coitus— Action  of  the  male— Action  of  the  female— Entrance  of  spermatozoids  into  the  uterus— Course  of  the  sper- 
matozoids  through  the  female  generative  passages — Mechanism  of  fecundation — Determination  of  the  sex  of 
offspring — Hereditary  transmission — Snperfecundation — Influence  of  the  maternal  mind  upon  offspring — Union  of 
the  male  with  the  female  element  of  generation— Passage  of  the  spermatozoids  through  the  vitelline  membrane 
— Deformation  and  gyration  of  the  vitellus — Polar  globule — Vitelline  nucleus — Segmentation  of  the  vitellus— 
Primitive  trace  of  the  embryon— Blastodermic  layers— Formation  of  the  membranes— Amniotic  fluid— Umbili- 
cal vesicle— Formation  of  the  allantois  and  the  permanent  chorion  —Umbilical  cord — Menibranae  deciduse — 
Development  and  structure  of  the  placenta — General  view  of  the  development  of  the  embryon— Development 
of  the  cavities  and  layers  of  the  trunk  in  the  chick — External  blastodermic  membrane — Intermediate  mem- 
brane, in  two  layers — Internal  blastodermic  membrane — Neural  canal — Chorda  dorsalis — Primitive  aortse — Ver- 
tebrae—Origin of  the  Wolffian  bodies— Pleuro-peritoneal  cavity— Development  of  the  skeleton— Development  of 
the  muscles— Development  of  the  skin— Development  of  the  nervous  system— Development  of  the  encephalon 


xii  CONTENTS. 

— Development  of  the  organs  of  special  sense — Development  of  the  alimentary  system — Formation  of  the  me- 
sentery—Formation of  the  stomach— Development  of  the  large  intestine— Formation  of  the  pharynx  and  oesopha- 
gus — Development  of  the  anus — The  liver,  pancreas,  and  spleen — Development  of  the  respiratory  system— De- 
velopment of  the  face— Development  of  the  teeth— Development  of  the  genito-urinary  system— Development 
of  the  Wolffian  bodies— Ducts  of  the  Wolffian  bodies  and  ducts  of  M filler —Development  of  the  testicles  and 
ovaries — Development  of  the  urinary  apparatus — External  organs  of  generation — Hermaphroditism — Develop- 
ment of  the  circulatory  system — First,  or  vitelline  circulation— Second,  or  placental  circulation — Branchial  arches 
and  development  of  the  arterial  and  the  venous  system — Development  of  the  heart — Description  of  the  foetal 
circulation— Third,  or  adult  circulation, Page  887 


CHAPTER   XXVIII. 

F(ETAL   LIFE— DEVELOPMENT  AFTER   BIRTH— DEATH. 

Enlargement  of  the  uterus  in  pregnancy— Duration  of  pregnancy— Size,  weight,  and  position  of  the  fetus— The 
foetus  at  different  stages  of  intra-uterine  life — Multiple  pregnancy— Cause  of  the  first  contractions  of  the  uterus 
in  normal  parturition— Involution  of  the  uterus— Meconium— Dextral  preeminence— Development  after  birth- 
Ages— Death— Cadaveric  rigidity— Putrefaction,  938 


LIST  OF  ILLUSTRATIONS. 


PLATE  I.    (Haeckel.)     Fig.  A,  tortoise  (IV  weeks).  Fig.  B,  chick  (IV  days). 

"     E,  tortoise  (VI  weeks).  "    F,  chick  (VIII  days). 

PLATE  II.   (Haeckel.)    Fig.  C,  dog  (IV  weeks).  Fig.  D,  man  (IV  weeks). 

"     G,  dog  (VI  weeks).  u     H,  man  (VIII  weeks). 

Plates  I.  and  II.,  facing  page  920. 

PLATE  III.     (Erdl.)     Fig.  1,  human  embryon,  at  the  ninth  week. 

"     2,  human  embryon,  at  the  twelfth  week. 
Plate  III.,  facing  page  922. 


FIGURE  PAGE 

1.  Human  red  blood-corpuscles.     (United  States  Army  Medical  Museum.) 7 

2.  Human  red  blood-corpuscles  arranged  in  rows,  with  two  white  corpuscles,  or  leucocytes. .  7 

3.  Blood-corpuscles  of  the  frog.     (United  States  Army  Medical  Museum.) 8 

4.  Artificial  capillary  filled  with  a  sanguineous  mixture,  seen  under  a  micrometer.   (Malassez.)  1 1 

5.  Human  blood-corpuscles,  showing  post-mortem  alterations 11 

6.  Human  red  and  white  blood-corpuscles 15 

7.  Crystallized  haemaglobine.     (Gautier.) 18 

8.  Fibrinous  clot.     (Robin.) ». 80 

9.  Harvey's  observations  on  the  flow  of  blood  in  the  veins.     (Harvey.) 33 

10.  Diagram  of  the  four  cavities  of  the  heart.     (Bernard.) 34 

11.  Heart  in  situ.     (Dalton.) 35 

12.  Heart,  anterior  view.     (Bonamy  and  Beau.) 36 

13.  Left  cavities  of  the  heart.     (Bonamy  and  Beau.) 37 

14.  Right  cavities  of  the  heart.     (Bonamy  and  Beau) 38 

15.  Muscular  fibres  of  the  ventricles.     (Bonamy  and  Beau.) 39 

16.  Anastomosing  muscular  fibres  of  the  heart.     (Morel.) 39 

17.  Valves  of  the  heart.     (Bonamy  and  Beau.) 40 

18.  Diagram  showing  shortening  of  the  ventricles  during  systole 43 

19.  Cardiograph.     (Chauveau  and  Marey.) 45 

20.  Small  artery  from  the  mesentery  of  the  frog.     (United  States  Army  Medical  Museum.) . .  66 

21.  Apparatus  for  showing  the  action  of  the  elasticity  of  the  arteries.     (Marey.) 69 

22.  Sphygmograph  of  Marey , V2 

23.  Sphygmograph  applied  to  the  arm,  with  traces  of  the  pulse.     (Marey.) 72 

24.  Haemadynamometer  of  Poisseuille 75 

25.  (A)  Cardiometer  of  Magendie.     (B)  Compensating  instrument  of  Marey 76 

26.  Chauveau's  instrument  for  measuring  the  rapidity  of  the  flow  of  blood  in  the  arteries. . .  79 

27.  Capillary  blood-vessels.     (Eberth.) 81 

28.  Small  artery,  and  capillaries.     (United  States  Army  Medical  Museum.) 83 

29.  Web  of  the  frog's  foot.     (Wagner.) 85 

30.  Circulation  in  the  web  of  the  frog's  foot.     (Wagner.) 85 

31.  Small  artery  and  capillaries  from  the  lung  of  the  frog.     (United  States  Army  Medical 

Museum.) 86 


xiv  LIST  OF  ILLUSTRATIONS. 

FIGURE  PAGE 

32.  Portion  of  the  lung  of  a  live  triton.     (Wagner.). 88 

33.  Venous  radicles  uniting  to  form  a  small  vein.     (United  States  Army  Medical  Museum.). .  93 

34.  Valves  of  the  veins.     (Fabricius.) 97 

35.  Trachea  and  bronchial  tubes.     (Sappey.) 117 

36.  Lungs,  anterior  view.     (Sappey.) 118 

37.  Bronchi  and  lungs,  anterior  view.     (Sappey.) 119 

38.  Terminal  bronchus  and  air-cells.      (Robin.) 120 

39.  Section  of  the  parenchyma  of  the  human  lung,  injected  through  the  pulmonary  artery. 

(Schul  tze.) * .   1 2 1 

40.  Thorax,  anterior  view.     (Sappey.) 122 

41.  Thorax,  posterior  view.     (Sappey.). 122 

42.  Diaphragm.     (Sappey.) 124 

43.  Diagram  showing  the  elevation  of  the  ribs  in  inspiration.     (Beclard.) 126 

44.  Arrow-root  starch-granules.     (United  States  Army  Medical  Museum.) J.81 

45.  Crystals  of  margarine  and  margaric  acid.     (Funke.) 183 

46.  Crystals  of  stearine  and  stearic  acid.     (Funke.) 183 

47.  Stomach,  liver,  small  intestine,  etc.     (Sappey.) 196 

48.  Permanent  teeth.     (Le  Bon.) 198 

49.  Tooth  of  the  cat.     (Waldeyer.) 200 

50.  Inferior  maxilla.     (Sappey.) 201 

51.  Salivary  glands.     (Le  Bon.) 205 

52.  Cavities  of  the  mouth,  pharynx,  etc.     (Sappey.) 215 

53.  Muscles  of  the  pharynx,  etc.     (Sappey.) 216 

54.  Longitudinal  fibres  of  the  stomach.     (Sappey.) 227 

55.  Fibres  seen  with  the  stomach  everted.     (Sappey.) 228 

56.  Pits  in  the  mucous  membrane  of  the  stomach,  and  orifices  of  the  glands.     (Sappey.).  .  .  .  228 

57.  Peptic  and  mucous  glands.     (Sappey.) 230 

58.  Tube  for  gastric  fistula.     (Bernard.) 231 

59.  Gastric  fistula.     (Bernard.) 232 

60.  Dog  with  a  gastric  fistula.     (Beclard.) 232 

61.  Gastric  fistula  in  the  case  of  St.  Martin.     (Beaumont.) 233 

62.  Matters  taken  from  the  pyloric  portion  of  the  stomach.     (Bernard.) 244 

63.  Stomach,  liver,  small  intestine,  etc.     (Sappey.) 258 

64.  Gland  of  Brunner.     (Frey.) 260 

65.  Intestinal  tubules.     (Sappey.) 261 

66.  Intestinal  villus.     (Leydig.) 262 

67.  Capillary  net-work  of  an  intestinal  villus.     (Frey.) 262 

68.  Epithelium  of  the  small  intestine  of  the  rabbit.     (Fuuke.) 262 

69.  Patch  of  Peyer.     (Sappey.) 264 

70.  Patch  of  Peyer  seen  from  its  attached  surface.     (Sappey.) 264 

71.  Clamp  for  isolating  a  portion  of  the  intestine.     (Colin.) 265 

72.  Isolated  portion  of  the  intestine.     (Colin.) 266 

73.  Gall-bladder,  ductus  choledochus  and  pancreas.     (Le  Bon.) 268 

74.  Canula  for  pancreatic  fistula.     (Bernard.) 269 

75.  Canula  fixed  in  the  pancreatic  duct.     (Bernard.) 270 

76.  Pancreatic  fistula.     (Bernard.) 271 

77.  Crystals  of  glycocholate  of  soda.     (Robin.) 280 

78.  Dog  with  a  biliary  fistula 282 

79.  Stomach,  pancreas,  large  intestine,  etc.     (Sappey.) 288 

80.  Opening  of  the  small  intestine  into  the  caecum.     (Le  Bon.) 289 

81.  Stercorine  from  the  human  faeces 295 

82.  Stercorine  from  the  human  faeces 295 

83.  Superficial  lymphatics  of  the  skin  of  the  palmar  surface  of  the  finger.     (Sappey.) 304 

84.  Deep  lymphatics  of  the  skin  of  the  finger.     (Sappey.) 304 

85.  Same  finger,  lateral  view.     (Sappey.) ,  304 

86.  Superficial  lymphatics  of  the  arm.     (Sappey.) 305 


LIST  OF  ILLUSTRATIONS.  xv 

FIGURE  PAGE 

87.  Superficial  lymphatics  of  the  leg.     (Sappey.) 305 

88.  Lacteals.     (Asellius.) 307 

89.  Thoracic  duct.     (Mascagni.) 308 

90.  Valves  of  the  lymphatics.     (Sappey.) 309 

91.  Lymphatic  plexus,  showing  the  epithelial  lining  of  the  vessels.     (Belaieff,) 310 

92.  Lymphatics  and  lymphatic  glands.     (Sappey.) 311 

93.  Different  varieties  of  lymphatic  glands.     (Sappey.) 313 

94.  Epithelium  of  the  small  intestine  of  the  rabbit.     (Funke.) 318 

95.  Epithelium  filled  with  fat,  from  the  duodenum  of  the  rabbit.     (Funke.) 319 

96.  Villi  filled  with  fat,  from  the  small  intestine  of  an  executed  criminal.     (Funke.) 319 

97.  Egg  prepared  so  as  to  illustrate  endosmotic  action 323 

98.  Chyle  from  the  lacteals  and  thoracic  duct.     (Funke.) > 332 

99.  Sebaceous  glands.     (Sappey.) 359 

100.  Ceruminous  glands.     (Sappey.) 360 

101.  Meibomian  glands.     (Sappey.) 361 

102.  Mammary  gland  of  the  human  female.     (Liegeois.) 367 

103.  Human  milk-globules.     (Funke.) 872 

104.  Colostrum.     (Funke.) 377 

105.  Anatomy  of  the  nails.     (Sappey.) 383 

106.  Section  of  the  nail,  etc.     (Sappey.) 384 

107.  Hair  and  hair-follicle.     (Sappey.) 387 

108.  Root  of  the  hair.     (Sappey.) 387 

109.  Human  hair.     (United  States  Army  Medical  Museum.) 388 

110.  Transverse  section  of  a  human  hair.     (United  States  Army  Medical  Museum.) 388 

111.  Surface  of  the  palm  of  the  hand.     (Sappey.) 391 

112.  Sudoriparous  glands.     (Sappey.) 392 

113.  Vertical  section  of  the  kidney.     (Sappey.) 396 

114.  (A)  Longitudinal  section  of  the  pyramidal  substance  of  the  kidney.    (B)  Longitudinal  sec- 

tion of  the  cortical  substance  of  the  kidney.     (Sappey.) 397 

115.  Diagrammatic  view  of  the  Malpighian  bodies  and  tubes  of  the  kidney.     (Sappey.) 398 

116.  Blood-vessels  of  the  kidney.     (Sappey.) 401 

117.  Crystals  of  urea.     (Funke.) '. 414 

118.  Crystals  of  uric  acid.     (Funke.) 417 

119.  Urateof  soda.     (Funke.) 417 

120.  Crystals  of  hippuric  acid.     (Funke.) 418 

121.  Crystals  of  lactate  of  lime.     (Funke.) 418 

122.  Crystals  of  creatine.     (Funke.) 419 

123.  Crystals  of  creatinine.     (Funke.) 419 

124.  Crystals  of  oxalate  of  lime.     (Funke.) 420 

125.  Crystals  of  leucine.     (Funke.) 420 

126.  Crystals  of  tyrosine.     (Funke.) 421 

127.  Crystals  of  taurine.     (Funke.) 421 

128.  Crystals  of  chloride  of  sodium.     (Funke.) 422 

129.  Lobules  of  the  liver,  interlobular  vessels,  and  intralobular  veins.     (Sappey.) 433 

130.  Transverse  section  of  a  single  hepatic  lobule.     (Sappey.) 434 

131.  Liver-cells  from  a  human  fatty  liver.     (Funke.) 435 

132.  Portion  of  a  transverse  section  of  an  hepatic  lobule  of  the  rabbit.     (Kolliker.) 436 

133.  Anastomoses,  and  racemose  glands  attached  to  the  biliary  ducts.     (Sappey.) 437 

134.  Gall-bladder,  hepatic,  cystic,  and  common  ducts.     (Sappey.) 438 

135.  Crystals  of  glyeocholate  of  soda.     (Robin.) 445 

1 36.  Cholesterine  extracted  from  the  bile 447 

137.  Catheter  for  the  right  side  of  the  heart.     (Bernard.) 463 

138.  Double  sound,  used  for  collecting  blood  from  the  hepatic  veins.     (Bernard.) 463 

139.  Apparatus  for  extraction  of  glycogenic  matter.     (Bernard.) , 468 

140.  Instrument  for  puncturing  the  floor  of  the  fourth  ventricle.     (Bernard.) 470 

141.  Operation  of  puncturing  the  floor  of  the  fourth  ventricle.     (Bernard.) 471 


xvi  LIST   OF  ILLUSTRATIONS. 

FIGURE  PAGE 

142.  Malpighian  bodies  of  the  spleen  of  the  pig.     (Frey.) 474 

143.  Thymus  from  the  calf.     (Kolliker.) 484 

144.  Half  of  the  human  thymus,  laid  open.     (Kolliker.) 484 

145.  Adipose  vesicles.     (Kolliker.) 503 

146.  Amoeba  diffluens.     (Longet.) 522 

147.  Ciliated  epithelium.     (Le  Bon.) 523 

148.  Small  elastic  fibres.     (Kolliker.) 525 

149.  Larger  elastic  fibres.     (Robin.) 525 

150.  Large  elastic  fibres  (fenestrated  membrane).     (Kolliker.) 526 

151.  Muscular  fibres  from  the  urinary  bladder.     (Sappey.) 527 

152.  Muscular  fibres  from  the  aorta.     (Sappey.) 527 

153.  Muscular  fibres  from  the  uterus.     (Sappey.) 527 

154.  Striated  muscular  fibres.     (United  States  Army  Medical  Museum.) 529 

155.  Striated  muscular  fibres.     (Sappey.) 530 

156.  Fibres  of  tendon  from  the  human  subject.     (Rollett.) 531 

157.  Net-work  of  connective  tissue.     (Rollett.) 532 

158.  Frog's  leg  prepared  so  as  to  show  the  effects  of  woorara.     (Bernard.) 536 

159.  Apparatus  to  show  that  muscles  do  not  increase  in  volume  during  contraction.     (Marey.)  538 

160.  Diagram  of  the  muscular  wave.     (Aeby.) 540 

161.  Muscular  current  in  the  frog.     (Bernard.) 542 

162.  Longitudinal  section  of  bone.     (Sappey.) 544 

163.  Longitudinal  section  of  bone.     (United  States  Army  Medical  Museum.) 544 

164.  Transverse  section  of  bone.     (Sappey.) 545 

165.  Transverse  section  of  bone.     (United  States  Army  Medical  Museum.) 546 

166.  Bone-corpuscles.     (Rollett.) 546 

167.  Section  of  cartilage.     (United  States  Army  Medical  Museum.) 548 

168.  Section  of  diarthrodial  cartilage.     (Sappey.) 548 

169.  Section  of  the  cartilage  of  the  ear.     (Rollett.) 549 

170.  Longitudinal  section  of  the  human  larynx.     (Sappey.) 550 

171.  Posterior  view  of  the  muscles  of  the  larynx.     (Sappey.) 552 

172.  Lateral  view  of  the  muscles  of  the  larynx.     (Sappey.) 552 

173.  Glottis  seen  with  the  laryngoscope.     (Le  Bon.) 554 

174.  Nerve-fibres  from  the  human  subject.     (Kolliker.) 568 

175.  Fibres  of  Remak.     (Kolliker.) 569 

176.  Mode  of  termination  of  the  motor  nerves.     (Rouget.) 571 

177.  Termination  of  the  nerves  in  the  salivary  glands.     (Pfliiger.) 572 

178.  Pacinian  corpuscle.     (Sappey.) > 573 

179.  Papillae  of  the  skin.     (Sappey.) 574 

180.  Cutaneous  papilla  and  tactile  corpuscle.     (Kolliker.) 575 

181.  Corpuscles  of  Krause.     (Ludden.) 575 

182.  Multipolar  nerve-cell.     (Kolliker.) 577 

183.  Gray  matter  of  the  spinal  cord,  treated  with  nitrate  of  silver.     (Grandry.) 578 

184.  Multipolar  nerve-cell.     (Schultze.) 579 

185.  Multipolar  nerve-cell.     (Deiters.) 581 

186.  Connections  of  nerve-cells  and  nerve-fibres.     (Dean.) 582 

187.  Corpora  amylacea.     (Funke.) 585 

188.  Frog  prepared  so  as  to  show  that  woorara  destroys  the  properties  of  the  motor  nerves. 

(Bernard.) 595 

189.  Electric  forceps.     (Liegeois.) 600 

190.  Frog's  leg  prepared  so  as  to  show  the  contrasted  action  of  the  direct  and  the  inverse  cur- 

rent.   (Matteucci.) 601 

191.  Frog's  leg  prepared  so  as  to  show  induced  contraction.     (Liegeois.) 602 

192.  Cervical  portion  of  the  spinal  cord.     (Hirschfeld.) 607 

193.  Dorsal  portion  of  the  spinal  cord.     (Hirschfeld.) - 607 

194.  Inferior  portion  of  the  spinal  cord,  and  cauda  equina.     (Hirschfeld.) 607 

195.  Roots  of  the  cranial  nerves.     (Hirschfeld.) ' 608 


LIST  OF  ILLUSTRATIONS.  xvii 

FIGURE  PAGE 

196.  Distribution  of  the  motor  oculi  communis.     (Hirschfeld.) 610 

197.  Distribution  of  the  patheticus.     (Hirschfeld.) 614 

1 98.  Distribution  of  the  motor  oculi  externus.     (Hirschfeld.) 614 

199.  Distribution  of  the  small  root  of  the  fifth  nerve.     (Hirschfeld.) .  616 

200.  Incisors  of  the  rabbit  before  and  after  section  of  the  nerve  of  mastication.     (Bernard.).  617 

201.  Superficial  branches  of  the  facial  and  the  fifth.     (Hirschfeld.) 619 

202.  Chorda  tympani  nerve.     (Hirschfeld.) _  622 

203-208.  Expressions  of  the  face  produced  by  contractions  of  the  muscles  under  electrical 

excitation.     (Le  Bon,  after  Duchenne.) 626 

209.  Spinal  accessory  nerve.     (Hirschfeld.) 628 

210.  Sublingual  nerve.     (Sappey.) 633 

211.  Principal  branches  of  the  large  root  of  the  fifth  nerve.     (Robin.) 635 

212.  Ophthalmic  division  of  the  fifth.     (Hirschfeld.) 635 

213.  Superior  maxillary  division  of  the  fifth.     (Hirschfeld.) 636 

214.  Inferior  maxillary  division  of  the  fifth.     (Hirschfeld.) 637 

215.  Limits  of  cutaneous  distribution  of  the  sensory  nerves  to  the  face,  head, -and  neck. 

(Beclard.) 638 

216.  Instrument  for  dividing  the  fifth  nerve.     (Bernard.) 639 

217.  Operation  for  division  of  the  fifth  nerve.     (Bernard.) 640 

218.  Anastomoses  of  the  pneumogastric.     (Hirschfeld.) 645 

219.  Distribution  of  the  pneumogastric.     (Hirschfeld.) 646 

220.  Branches  of  the  pneumogastric  to  the  heart.     (Bernard) 654 

221.  Depressor-nerves.     (Cyon  and  Ludwig.) 656 

222.  Transverse  section  of  the  spinal  cord.     (Stilling.) 670 

223.  Transverse  section  of  the  spinal  cord.     (Gerlach.) 671 

224.  Frog  poisoned  with  strychnine.     (Liegeois.) 687 

225.  Vertical  section  of  the  encephalon.     (Hirschfeld.) 689 

226.  Direction  of  the  fibres  in  the  cerebrum.     (Le  Bon.) 691 

227.  Cerebellum  and  medulla  oblongata.     (Hirschfeld.) 707 

228.  Corpora  striata.     (Sappey.) 720 

229.  Anterior  view  of  the  medulla  oblongata.     (Sappey.) 725 

230.  Stylet  for  breaking  up  the  medulla  oblongata.     (Bernard.) 727 

231.  (A)  Cervical  and  thoracic  portion  of  the  sympathetic.     (Sappey.) 732 

231.  (B)  Lumbar  and  sacral  portions  of  the  sympathetic.     (Sappey.) 734 

232.  Sympathetic  ganglion,  with  multipolar  cells.     (Leydig.) 735 

233.  Olfactory  ganglion  and  nerve.     (Hirschfeld.) 755 

234.  Terminal  filaments  of  the  olfactory  nerves.     (Kolliker.) 756 

235.  Glosso-pharyngeal  nerve.     (Sappey.) 762 

236.  Papillae  of  the  tongue.     (Sappey.) 765 

237.  238.  Varieties  of  papillae  of  the  tongue.     (Sappey.) 766 

239.  Taste-buds.  (Engelmann.) 766 

240.  Optic  tracts,  commissure,  and  nerves.    (Hirschfeld.) 768 

241.  Diagram  of  the  decussation  at  the  optic  commissure 768 

242.  Choroid  coat  of  the  eye.     (Sappey.) 772 

243.  Ciliary  muscle.     (Sappey.) 773 

244.  Rods  of  the  retina.     (Schultze.) 777 

245.  (A)  Vertical  section  of  the  retina.     (H.  Miiller.) ) 

245.  (B)  Connection  of  the  rods  and  cones  of  the  retina  with  the  nervous  elements.   (Sappey.)  ) 

246.  Crystalline  lens,  anterior  view.     (Babuchin.) 779 

247.  Crystalline  lens,  posterior  view.     (Babuchin.) 780 

248.  Section  of  the  crystalline  lens.     (Babuchin.) 781 

249.  Zone  of  Zinn.     (Sappey.) 781 

250.  Section  of  the  human  eye.     (Helmholtz.) 783 

251.  Refraction  by  prisms 787 

252.  Refraction  by  convex  lenses 788 

253.  Section  of  the  lens,  etc.,  showing  the  mechanism  of  accommodation.     (Fick.) 800 


xviii  LIST   OF  ILLUSTRATIONS. 

FIGURE  PAGE 

254.  Muscles  of  the  eyeball.     (Sappey.) 808 

255.  Diagram  illustrating  the  action  of  the  muscles  of  the  eyeball.     (Fick.) 809 

256.  Lachrymal  and  Meibomian  glands.     (Sappey.) 813 

257.  Lachrymal  canals,  lachrymal  sac,  and  nasal  canal.     (Sappey.) 814 

258.  General  view  of  the  organ  of  hearing.     (Sappey.). 819 

259.  Ossicles  of  the  tympanum.     (Arnold.) 820 

260.  Ossicles  seen  from  within.     (Riidinger.) 820 

261.  Bony  labyrinth.     (Riidinger.) 823 

262.  Resonators  of  Helmholtz 831 

263.  Membrani  tympani.     (Riidinger.) 836 

264.  Diagram  of  the  labyrinth. — Vestibule  and  semicircular  canals.     (Riidinger.) 843 

265.  Otoliths  from  various  animals.     (Riidinger.) 844 

266.  Section  of  the  first  turn  of  the  spiral  canal. — Section  of  the  cochlea.     (Riidinger.) 845 

267.  Distribution  of  the  cochlear  nerve  in  the  spiral  canal.     (Sappey.) 847 

268.  The  two  pillars  of  the  organ  of  Corti.     (Sappey.) 848 

269.  Vertical  section  of  the  organ  of  Corti.     (Waldeyer.) 848 

270.  Uterus,  Fallopian  tubes,  and  ovaries.     ^Sappey.) 858 

271.  Section  of  the  ovary.     (Waldeyer.) 861 

272.  Graafian  follicle.     (Luschka.) 862 

273.  Virgin  uterus.     (Sappey.). 863 

274.  Muscular  fibres  of  the  uterus.     (Sappey.) 864 

275.  Superficial  muscular  fibres  of  the  uterus.     (Liegeois.) 865 

276.  Inner  layer  of  muscular  fibres  of  the  uterus.     (Liegeois.) 866 

277.  Blood-vessels  of  the  uterus  and  ovaries.     (Rouget.) 867 

278.  Fallopian  tube.     (Liegeois.) 868 

279.  External  erectile  organs  of  the  female.     (Liegeois.) 869 

280.  Ovum  of  the  rabbit.     (Waldeyer.) 871 

281.  Sections  of  two  corpora  lutea.     (Kolliker.) 877 

282.  Testicle  and  epididyrnis.     (Arnold.) 881 

283.  Vas  deferens,  vesiculae  seminales,  and  ejaculatory  duct.     (Liegeois.) 882 

284.  Human  spermatozoids.     (Luschka.) 885 

285.  Development  of  spermatozoids.     (Liegeois.) 886 

286.  Mulatto  woman  with  twins,  one  white  and  the  other  black  ;  from  a  photograph 895 

287.  Penetration  of  spermatozoids  through  the  vitelline  membrane.    (Haeckel.) 896 

288.  Formation  of  the  polar  globule.     (Robin.) 897 

289.  Segmentation  of  the  vitellus.     (Liegeois.) 898 

290.  Primitive  trace  of  the  embryon.     (Liegeois.) 899 

291.  Formation  of  the  membranes.     (Kolliker.) 902 

292.  Villi  of  the  chorion.     (Haeckel.) 905 

293.  Placenta  and  deciduse.     (Liegeois.) 910 

294-296.  Development  of  the  chick.     (Briicke.) 913 

297.  Development  of  the  notocorde.     (Robin.) 915 

298.  Human  embryon  one  month  old.     (Dalton.) 915 

299.  Development  of  the  nervous  system  of  the  chick.     (Wagner.) 917 

300.  Development  of  the  spinal  cord  and  brain  of  the  human  subject.     (Tiedemann.) 918 

301.  Fo3tal  pig,  showing  umbilical  hernia.     (Dalton.) 920 

302.  Development  of  the  bronchial  tubes  and  lungs.     (Rathke  and  Miiller.) 922 

303-305.  Development  of  the  face.     (Coste.) 924,  925 

306.  Temporary  and  permanent  teeth.     (Sappey.) 926 

307.  Foatal  pig,  showing  the  Wolffian  bodies.     (Dalton.) 927 

308.  Diagrammatic  representation  of  the  genito-urinary  system.     (Henle.) 929 

309.  Area  vasculosa.     (Bischoff.) 932 

310.  Aortic  arches  in  the  mammalia.      (Von  Baer.) 933 

311.  Diagram  of  the  foetal  circulation .  937 

312.  The  Siamese  twins 942 

313.  Cholesterine  extracted  from  meconium. . .  944 


HUMAN  PHYSIOLOGY. 


CHAPTER    I. 

THE  BLOOD. 

General  considerations— Transfusion— Quantity  of  blood— General  characters  of  the  blood— Blood-corpuscles— 
Development  of  the  blood-corpuscles — Leucocytes — Development  of  leucocytes — Composition  of  the  red  cor- 
puscles— Globuline— Haemaglobine — Analysis  of  the  blood — Composition  of  the  blood-plasma — Inorganic  prin- 
ciples—Organic saline  principles— Organic  non-nitrogenized  principles— Excrementitious  matters— Organic  nitro- 
genized  principles — Plasmine,  fibrin,  metalbumen,  and  seriue — Peptones — Coloring  matter — Coagulation  of  the 
blood — Characters  of  the  clot — Characters  of  the  serum — Circumstances  which  modify  coagulation — Coagulation 
of  the  blood  in  the  organism— Spontaneous  arrest  of  haemorrhage— Cause  of  the  coagulation  of  the  blood— So- 
called  fibrin-factors — Paraglobuline,  or  fibrinoplastic  matter — Fibrinogen. 

FKOM  the  earliest  periods  in  the  history  of  physiology,  the  importance  of  the  blood 
has  been  recognized;  and,  with  the  progress  of  knowledge,  this  great  nutritive  fluid  has 
been  shown  to  be  more  and  more  intimately  connected  with  the  phenomena  of  animal 
life.  It  is  now  known  to  be  the  most  abundant  and  highly  organized  of  the  fluids  of  the 
body,  providing  materials  for  the  regeneration  of  all  parts,  without  exception,  receiving 
the  products  of  their  waste  and  conveying  them  to  proper  organs,  by  which  they  are 
removed  from  the  system.  These  processes  require,  on  the  one  hand,  constant  regen- 
eration of  the  nutritive  constituents  of  the  blood,  and,  on  the  other,  its  constant  purifi- 
cation by  the  removal  of  effete  matters. 

Those  tissues  in  which  the  processes  of  nutrition  are  active  are  supplied  with  blood 
by  vessels;  but  some,  less  highly  organized,  like  the  epidermis,  hair,  cartilage,  etc., 
which  are  called  extra-vascular  because  they  are  not  penetrated  by  vessels,  are  none  the 
less  dependent  upon  the  blood,  as  they  imbibe  nutritive  material  from  the  blood  of  ad- 
jacent parts. 

The  importance  of  the  blood  in  the  processes  of  nutrition  is  evident ;  and,  in  animals 
in  which  nutrition  is  active,  death  is  the  immediate  result  of  its  abstraction  in  large 
quantity.  Its  importance  to  life  can  be  readily  demonstrated  by  experiments  upon  the 
inferior  animals.  If  we  take  a  small  dog,  introduce  a  canula  through  the  right  jugular 
vein  into  the  right  side  of  the  heart,  adapt  to  it  a  syringe,  and  suddenly  withdraw  a  great 
part  of  the  blood  from  the  circulation,  immediate  suspension  of  all  the  so-called  vital 
processes  is  the  result.  If  we  then  return  the  blood  to  the  system,  the  animal  is  as  sud- 
denly revived.  To  perform  this  experiment  satisfactorily,  we  must  accurately  adjust  the 
capacity  of  the  syringe  to  the  size  of  the  animal. 

Certain  causes,  one  of  which  is  diminution  in  the  force  of  the  heart's  action  after 
copious  ho3morrhage,  prevent  the  escape  of  all  the  blood  from  the  body,  even  after 
division  of  the  largest  arteries;  but,  after  the  arrest  of  the  functions  which  follows 
copious  discharges  of  this  fluid,  life  may  be  restored  by  injecting  into  the  vessels 
the  same  blood  or  the  fresh  blood  of  another  animal.  This  observation,  which  was  first 
1 


2  '  THE  BLOOD. 

made  on  the  inferior  animals,  has  been  applied  to  the  human  subject;  and  it  has  been 
ascertained  that,  in  patients  sinking  under  haemorrhage,  the  introduction  of  even  a  few 
ounces  of  fresh  blood  may  restore  the  functions  for  a  time,  and  sometimes  permanently. 
The  operation  of  transfusion,  which  consists  in  the  introduction  of  the  blood  of  one  indi- 
vidual into  the  vessels  of  another,  was  performed  upon  animals  in  the  middle  of  the 
seventeenth  century,  and  was  soon  after  attempted  in  the  human  subject.  So  great  was 
the  enthusiasm  with  which  some  regarded  these  experiments,  that  it  was  thought  pos- 
sible even  to  effect  a  renewal  of  youth  by  the  introduction  of  young  blood  into  the  veins 
of  old  persons ;  and  it  was  also  proposed  to  cure  certain  diseases,  such  as  insanity,  by 
actual  renewal  of  the  circulating  fluid.  These  ideas  were  not  without  apparent  foun- 
dation. It  was  stated,  in  1667,  that  a  dog,  old  and  deaf,  had  his  hearing  improved  and 
was  apparently  rejuvenated  by  transfusion  of  blood  from  a  young  animal.  A  year  later, 
Denys  and  Emmerets  published  a  case  of  a  maniac  who  was  restored  to  health  by  the 
transfusion  of  eight  ounces  of  blood  from  a  calf;  and  another  case  was  reported  of  a 
man  who  was  cured  of  leprosy  by  the  same  means.  But  the  case  of  insanity,  which  was 
apparently  cured,  suffered  a  relapse,  and  the  patient  died  during  a  third  attempt  at 
transfusion.  It  is  almost  unnecessary  to  say  that  these  extravagant  expectations  were 
not  realized.  In  fact,  some  operations  were  followed  by  such  disastrous  consequences, 
that  the  practice  was  forbidden  by  law  in  Paris  in  1668,  and  soon  fell  into  disuse. 

Transfusion,  with  more  reasonable  applications,  was  revived  in  the  early  part  of  this 
century  (1818)  by  Blundell,  who,  with  others,  demonstrated  its  occasional  efficacy  in 
desperate  haemorrhage  and  in  the  last  stages  of  some  diseases,  especially  cholera.  There 
are  now  quite  a  number  of  cases  on  record  where  life  has  been  saved  by  this  means ;  and 
oftentimes,  when  the  result  has  not  been  so  happy,  the  fatal  event  has  been  consider- 
ably delayed. 

Numerous  experiments  on  transfusion  in  animals  have  been  performed,  with  very 
interesting  results.  Prevost  and  Dumas  have  shown  that,  while  an  animal  may  be 
restored  after  haemorrhage  by  the  transfusion  of  defibrinated  blood,  no  such  effect  fol- 
lows the  introduction  of  the  serum ;  showing  that  the  vivifying  influence  in  all  prob- 
ability resides  in  the  corpuscles.  Brown-Se"quard  has  shown  that,  in  parts  detached 
from  the  body,  after  nervous  and  muscular  irritability  have  disappeared,  these  properties 
may  be  restored  for  a  time  by  the  injection  of  fresh  blood.  He  also  made  a  curious  ex- 
periment in  which  blood  was  passed  from  a  living  dog  into  the  carotid  of  a  dog  just  dead 
from  peritonitis.  The  animal  was  so  far  revived  by  this  operation  as  to  sustain  himself 
on  his  feet,  wag  his  tail,  etc.,  and  died  a  second  time,  twelve  and  a  half  hours  after.  In 
this  experiment,  insufflation  was  employed  in  addition  to  the  transfusion. 

It  may  be  considered  established  that,  in  animals,  after  haemorrhage,  life  may  be 
restored  by  injecting  the  blood,  defibrinated  or  not,  provided  it  be  introduced  slowly, 
without  admixture  with  air,  and  not  in  too  great  quantity.  In  the  human  subject,  es- 
pecially after  haemorrhage,  the  vital  processes  are  sometimes  restored  by  careful  trans- 
fusion of  human  blood,  with  the  above  precautions ;  remembering  that  a  very  small  quan- 
tity, three  or  four  ounces,  will  sometimes  be  sufficient. 

Quantity  of  Blood. — The  determination  of  the  entire  quantity  of  blood  contained  in 
the  body  is  a  question  of  great  interest,  and  has  long  engaged  the  attention  of  physiolo- 
gists, without,  however,  any  absolutely-definite  results.  Among  those  who  have  ex- 
perimented on  this  point,  may  be  mentioned  Allen-Moulins,  Herbst,  Fried.  Hoffmann, 
Valentin,  Blake,  Lehmann  and  Weber,  and  Vierordt.  The  fact  that  the  labors  of  these 
eminent  observers  have  so  far  been  unsuccessful  in  determining  definitely  the  entire  quan- 
tity of  blood  shows  the  extent  of  the  difficulties  to  be  overcome  before  the  question  can 
be  entirely  settled.  The  chief  difficulty  lies  in  the  fact  that  all  the  blood  is  not  discharged 
from  the  body  on  division  of  the  largest  vessels,  as  after  decapitation ;  and  no  perfectly- 
accurate  means  have  been  devised  for  estimating  the  quantity  which  remains  in  the 


QUANTITY   OF  BLOOD.  3 

vessels.  The  estimates  of  experimenters  present  the  following  wide  differences  :  Allen- 
Moulins,  who  was  one  of  the  first  to  study  this  question,  estimated  the  quantity  of  blood 
at  one-twentieth  the  weight  of  the  entire  hody.  The  estimate  of  Herbst  was  a  little 
higher.  Hoffmann  estimated  the  quantity  at  one-fifth  the  weight  of  the  body.  These 
observers  estimated  the  quantity  remaining  in  the  system  after  opening  the  vessels,  by 
mere  conjecture.  Valentin  was  the  first  who  attempted  to  overcome  this  difficulty  by 
experiment.  For  this  purpose  he  employed  the  following  process  :  He  took  first  a  small 
quantity  of  blood  from  an  animal  for  purposes  of  comparison;  then  he  injected  into  the 
vessels  a  known  quantity  of  a  saline  solution,  and,  taking  another  specimen  of  blood  some 
time  after,  he  ascertained  by  evaporation  the  proportion  of  water  which  it  contained, 
and  compared  with  the  proportion  in  the  first  specimen.  He  reasoned  that  the  excess  of 
water  in  the  second  specimen  over  the  first  would  give  the  proportion  of  the  water  intro- 
duced to  the  whole  mass  of  blood ;  and,  as  the  entire  quantity  of  water  introduced  was 
known,  the  entire  quantity  of  blood  could  be  deduced  therefrom.  Suppose,  for  example, 
that  the  excess  of  water  in  the  second  specimen  should  be  one  part  to  ten  of  the  blood, 
it  would  show  that  one  part  of  water  had  been  mixed  with  ten  of  the  blood;  and,  if 
we  had  injected  in  all  five  ounces  of  water,  we  should  have  the  whole  quantity  of  blood 
ten  times  that,  or  fifty  ounces.  This  method,  however,  is  open  to  the  objection  that  it  is 
impossible  to  take  note  of  the  processes  of  imbibition  and  exhalation  which  are  con- 
stantly in  operation. 

The  following  process,  which  is,  perhaps,  the  one  least  open  to  sources  of  error,  was 
employed  by  Lehmann  and  Weber,  and  applied  directly  to  the  human  subject,  in  the 
case  of  two  decapitated  criminals :  These  observers  estimated  the  blood  remaining  in 
the  body  after  decapitation,  by  injecting  the  vessels  with  water  until  it  came  through 
nearly  colorless.  The  liquid  was  carefully  collected,  evaporated  to  dryness,  and  the  dry 
residue  was  assumed  to  represent  a  certain  quantity  of  blood,  the  proportion  of  dry 
residue  to  a  definite  quantity  of  blood  having  been  previously  ascertained.  If  we  could 
be  certain  that  only  the  solid  matter  of  the  blood  was  thus  removed,  such  an  estimate 
would  be  tolerably  accurate.  As  it  is,  we  may  consider  it  as  approximating  very  nearly 
to  the  truth.  "We  quote  the  following  account  of  these  observations : 

"My  friend,  Ed.  Weber,  determined,  with  my  cooperation,  the  weights  of  two  crimi- 
nals both  before  and  after  their  decapitation.  The  quantity  of  blood  which  escaped 
from  the  body  was  determined  in  the  following  manner :  Water  was  injected  into  the 
vessels  of  the  trunk  and  head,  until  the  fluid  escaping  from  the  veins  had  only  a  pale-red 
or  yellow  color ;  the  quantity  of  the  blood  remaining  in  the  body  was  then  calculated, 
by  instituting  a  comparison  between  the  solid  residue  of  this  pale-red  aqueous  fluid,  and 
that  of  the  blood  which  first  escaped.  By  way  of  illustration,  I  subjoin  the  results 
yielded  by  one  of  the  experiments.  The  living  body  of  one  of  the  criminals  weighed 
60,140  grammes  (132'7  pounds),  and  the  same  body  after  decapitation,  54,600  grammes; 
consequently,  5,540  grammes  of  blood  had  escaped.  28-560  grammes  of  this  blood 
yielded  5-36  grammes  of  solid  residue ;  60-5  grammes  of  sanguineous  water  collected 
after  the  injection,  contained  3*724  grammes  of  solid  substances;  6,050  grammes  of  the 
sanguineous  water  that  returned  from  the  veins  were  collected,  and  these  contained 
37*24  grammes  of  solid  residue,  which  corresponds  to  1,980  grammes  of  blood;  conse- 
quently, the  body  contained  7,520  grammes  (16*59  pounds),  5,540  escaping  in  the  act  of 
decapitation,  and  1,980  remaining  in  the  body;  hence,  the  weight  of  the  whole  blood 
was  to  that  of  the  body  nearly  in  the  ratio  of  1  :  8.  The  other  experiment  yielded  a 
precisely  similar  result. 

"  It  cannot  be  assumed  that  such  experiments  as  these  possess  extreme  accuracy,  but 
they  appear  to  have  the  advantage  of  giving  in  this  manner  the  minimum  of  the  blood 
contained  in  the  body  of  an  adult  man  ;  for  although  some  solid  substances,  not  belong- 
ing to  the  blood,  may  be  taken  up  by  the  water  from  the  parenchyma  of  the  organs  per- 
meated with  capillary  vessels,  the  excess  thus  obtained  is  so  completely  counteracted  by 


4  THE  BLOOD. 

the  deficiency  caused  by  the  retention  of  some  blood  in  the  capillaries,  and  in  part  by 
transudation,  that  our  estimate  of  the  quantity  of  blood  contained  in  the  human  body 
may  be  considered  as  slightly  below  the  actual  quantity." 

The  process  just  described  gives  the  most  accurate  idea  of  the  probable  quantity  of 
blood  in  the  human  body ;  and,  although  more  recent  investigations  have  been  made 
upon  the  lower  animals,  by  different  methods,  they  are  all  more  or  less  open  to  objec- 
tion. We  may  assume,  then,  that,  in  a  person  of  ordinary  muscular  and  adipose  devel- 
opment, the  proportion  of  blood  to  the  weight  of  the  body  is  about  one  to  eight,  the 
entire  quantity  of  blood  in  the  body  being  from  sixteen  to  eighteen  pounds.  The  relative 
quantity  of  blood  is  said  to  be  less  in  the  infant  than  in  the  adult,  and  to  be  diminished 
in  old  age.  It  has  been  found,  also,  in  observations  on  the  inferior  animals,  to  be  greater 
in  the  male  than  in  the  female. 

Prolonged  abstinence  from  food,  except  when  large  quantities  of  liquid  are  ingested, 
has  a  notable  effect  in  diminishing  the  mass  of  blood,  as  indicated  by  the  small  quantity 
which  can  be  removed  from  the  body,  under  these  circumstances,  with  impunity  ;  and  it 
has  been  experimentally  demonstrated  that  the  entire  quantity  of  blood  is  considerably 
increased  during  digestion.  Bernard  drew  from  a  rabbit  weighing  about  two  and  a  half 
pounds,  during  digestion,  over  ten  and  a  half  ounces  of  blood  without  producing  death ; 
while  he  found  that  the  removal  of  half  that  quantity  from  an  animal  of  the  same  size, 
fasting,  was  followed  by  death.  Wrisberg  has  reported  a  case  of  a  female  criminal,  very 
plethoric,  from  whom  twenty-one  pounds,  seven  and  three-quarters  ounces  of  blood 
flowed  after  decapitation.  As  the  relations  of  the  quantity  of  blood  to  the  digestive 
function  are  so  important,  it  is  unfortunate  that  the  conditions  of  the  system  in  this 
respect  were  not  noted  in  the  observations  of  Lehmann  and  Weber.  It  is  evident,  there- 
fore, that  the  quantity  of  blood  in  the  body  is  considerably  increased  during  digestion ; 
but  as  regards  the  extent  of  this  increase,  we  cannot  form  any  very  definite  idea.  It  is 
only  shown  that  there  -is  a  marked  difference  in  the  effects  of  haamorrhage  in  animals, 
during  digestion  and  fasting. 

General  Characters  of  the  JBlood. 

Opacity. — The  opacity  of  the  blood  depends  upon  the  fact  that  it  is  not  a  homogene- 
ous fluid,  but  is  composed  of  two  distinct  elements,  a  clear  plasma  and  corpuscles,  which 
are  both  nearly  transparent,  but  which  have  a  different  refractive  power.  If  both  of  these 
elements  had  the  same  refractive  power,  the  mixture  would  present  no  obstacle  to  the 
passage  of  light ;  but,  as  it  is,  the  rays,  which  are  refracted  in  passing  from  the  air 
to  the  plasma,  are  again  refracted  when  they  enter  the  corpuscles,  and  again,  when 
they  pass  from  the  corpuscles  to  the  plasma,  so  that  they  are  lost,  even  in  a  thin  layer 
of  the  fluid.  This  loss  of  light  in  a  mechanical  mixture  of  two  transparent  liquids  of 
unequal  refractive  power  can  be  demonstrated  by  the  following  simple  experiment :  If 
to  a  little  chloroform  colored  red,  clear  water  be  added  in  a  test-tube,  these  liquids  re- 
main distinct  from  each  other,  and  both  are  transparent ;  but  if  we  agitate  them  vio- 
lently, the  chloroform  is  temporarily  subdivided  into  globules  and  mixed  with  the  water ; 
and,  as  they  refract  light  differently,  the  mixture  is  opaque. 

Odor,  Taste,  Reaction,  and  Specific  Gravity. — The  blood  has  a  faint  but  characteristic 
odor.  This  may  be  developed  so  as  to  be  very  distinct  by  the  addition  of  a  few  drops 
of  sulphuric  acid,  when  an  odor  peculiar  to  the  animal  from  which  the  blood  has  been 
taken  becomes  very  marked. 

The  taste  of  the  blood  is  faintly  saline,  on  account  of  the  presence  of  a  considerable 
proportion,  three  or  four  parts  per  thousand,  of  chloride  of  sodium  in  the  plasma. 

The  reaction  of  the  blood  is  always  distinctly  alkaline.  According  to  Zuntz,  the 
alkalinity  diminishes  rapidly  after  the  blood  is  drawn  from  the  vessels.  The  alkaline 
reaction  is  due  to  the  presence  of  basic  carbonate  and  phosphate  of  soda  in  the  plasma. 

The;  specific  gravity  of  defibrinated  blood  is  from  1052  to  1057  (Robin),  being  some- 


COLOR    OF   THE  BLOOD.  5 

what  less  in  the  female  than  in  the  male.     Its  density  varies  greatly  under  different  con- 
ditions of  digestion. 

Temperature. — The  temperature  of  the  blood  is  generally  given  as  from  98°  to  100° 
Fahr. ;  but  recent  experiments  have  shown  that  it  varies  considerably  in  different  parts 
of  the  circulatory  systsm,  independently  of  exposure  to  the  refrigerating  influence  of  the 
atmosphere.  By  the  use  of  very  delicate  registering  thermometers,  Bernard  has  suc- 
ceeded in  establishing  the  following  facts  with  regard  to  the  temperature  in  various 
parts  of  the  circulatory  system  in  dogs  and  sheep : 

1.  The  blood  is  warmer  in  the  right  than  in  the  left  cavities  of  the  heart. 

2.  It  is  warmer  in  the  arteries  than  in  the  veins,  with  a  few  exceptions. 

3.  It  is  generally  warmer  in  the  portal  vein  than  in  the  abdominal  aorta,  indepen- 
dently of  the  digestive  act. 

4.  It  is  constantly  warmer  in  the  hepatic  than  in  the  portal  veins. 

He  found  the  highest  temperature  in  the  blood  of  the  hepatic  vein,  where  it  ranged 
from  101°  to  107°.  In  the  aorta,  it  ranged  from  99°  to  105°. 

"We  may  assume,  then,  in  general  terms,  that  the  temperature  of  the  blood  in  the 
deeper  vessels  is  from  100°  to  107°  Fahrenheit. 

Color  of  the  Blood. — The  color  of  the  blood  is  due  to  the  corpuscles.  In  the  arterial 
system  it  is  uniformly  red.  In  the  veins  it  is  generally  dark  blue  and  sometimes  almost 
black.  This  difference  in  color  between  the  blood  in  the  arterial  and  in  the  venous  sys- 
tem was  a  matter  of  controversy  at  the  time  of  Harvey.  By  the  discoverer  of  the  cir- 
culation, the  difference,  which  is  now  universally  known  and  admitted  as  regards  most 
of  the  veins,  was  supposed  to  be  merely  accidental  and  dependent  on  external  causes. 
Fifty  years  later,  Lower  demonstrated  the  change  of  color  in  the  blood  as  it  passes 
through  the  lungs,  and  associated  it  with  the  true  cause ;  viz.,  the  absorption  of  oxygen. 
The  color  in  the  veins,  however,  is  not  constant.  Many  years  ago,  John  Hunter  ob- 
served, in  a  case  of  syncope,  that  the  blood  drawn  by  venesection  was  bright  red ;  and 
more  recently,  Bernard  has  demonstrated  that,  in  some  veins,  the  blood  is  nearly  if  not 
quite  as  red  as  in  the  arterial  system.  The  color  of  the  venous  blood  depends  upon  the 
condition  of  the  organ  or  part  from  which  it  is  returned.  The  red  color  was  first  no- 
ticed by  Bernard  in  the  renal  veins,  where  it  contrasts  very  strongly  with  the  black 
blood  in  the  vena  cava.  He  afterward  observed  that  the  redness  only  existed  during  the 
functional  activity  of  the  kidneys ;  and  when,  from  any  cause,  the  secretion  of  urine 
was  arrested,  the  blood  became  dark.  He  was  led,  from  this  observation,  to  examine 
the  venous  blood  from  other  glands ;  and,  directing  his  attention  to  those  which  he  was 
able  to  examine  during  their  functional  activity,  particularly  the  salivary  glands,  he  found 
the  blood  red  in  the  veins  during  secretion,  but  becoming  dark  as  soon  as  secretion  was 
arrested.  These  observations  may  be  easily  verified  by  opening  the  abdomen  of  a  living 
animal,  exposing  the  renal  veins,  and  introducing  a  canula  into  the  ureter,  so  as  to 
be  able  to  note  the  flow  or  arrest  of  the  urine.  So  long  as  the  urine  continues  to  flow, 
the  blood  in  these  vessels  is  bright  red ;  but  when  secretion  becomes  arrested,  as  it  soon 
does  after  exposure  of  the  organs,  it  presents  no  difference  from  the  blood  in  the 
vena  cava.  In  the  submaxillary  gland,  by  the  galvanization  of  a  certain  nerve  which  he 
calls  the  motor  nerve  of  the  gland,  Bernard  has  been  able  to  produce  secretion,  and,  by 
the  galvanization  of  another  nerve,  to  arrest  it ;  in  this  way  changing  at  will  the  color 
of  the  blood  in  the  vein.  It  has  J>een  found  by  the  same  observer  that  division  of  the 
sympathetic  in  the  neck,  which  dilates  the  vessels  and  increases  the  supply  of  blood  to 
one  side  of  the  head,  produces  a  red  color  of  the  blood  in  the  jugular.  He  has  also 
found  that  paralysis  of  a  member  by  division  of  the  nerve  has  the  same  effect  on  the 
blood  returning  by  the  veins. 

The  explanation  of  these  facts  is  evident  when  we  reflect  upon  the  reasons  why  the 
blood  is  red  in  the  arteries  and  dark  in  the  veins.  Its  color  depends  upon  the  corpus- 
cles ;  and  as  the  blood  passes  through  the  lungs  it  loses  carbonic  acid  and  gains  oxygen, 


6  THE  BLOOD. 

changing  from  black  to  red.  In  its  passage  through  the  capillaries  of  the  system,  in  the 
ordinary  processes  of  nutrition,  it  loses  oxygen  and  gains  carbonic  acid,  changing  from 
red  to  black.  During  the  intervals  of  secretion,  the  glands  receive  just  enough  blood 
for  their  nutrition,  and  the  ordinary  interchange  of  gases  takes  place,  with  the  con- 
sequent  change  of  color ;  but,  during  their  functional  activity,  the  blood  is  supplied 
in  greatly-increased  quantity,  in  order  to  furnish  the  watery  elements  of  the  secretions. 
Under  these  circumstances,  it  does  not  lose  oxygen  and  gain  carbonic  acid  in  any  great 
quantity,  as  has  been  demonstrated  by  actual  analysis,  and  consequently  there  is  no 
marked  change  in  color.  When  filaments  of  the  sympathetic  are  divided,  the  vessels 
going  to  the  part  are  dilated,  and  the  supply  of  blood  is  increased  to  such  an  extent, 
that  a  certain  proportion  passes  through  without  parting  with  its  oxygen  (a  fact  which 
has  also  been  demonstrated  by  analysis),  and  consequently  it  retains  its  red  color.  The 
explanation  in  cases  of  syncope  is  probably  the  same,  although  this  is  merely  a  suppo- 
sition. Even  during  secretion,  a  certain  quantity  of  carbonic  acid  is  formed  in  the 
gland,  which,  according  to  Bernard,  is  carried  off  in  solution  in  the  secreted  fluid. 

It  may  be  stated,  then,  in  general  terms,  that  the  color  of  the  blood  in  the  arteries  is 
bright  red ;  and,  in  the  ordinary  veins,  like  the  cutaneous  or  muscular,  it  is  dark  blue, 
almost  black.  It  is  red  in  the  veins  coming  from  glands  during  secretion,  and  dark  during 
the  intervals  of  secretion. 

Anatomical  Elements  of  the  Blood. 

In  1661,  the  celebrated  anatomist,  Malpighi,  in  examining  the  blood  of  the  hedgehog, 
with  the  imperfect  lenses  at  his  command,  discovered  little  floating  particles  which  he 
mistook  for  granules  of  fat,  but  which  were  the  blood-corpuscles.  He  did  not  extend  his 
observations  in  this  direction;  but,  a  few  years  later  (1673),  Leeuwenhoek,  by  the  aid 
of  simple  lenses  of  his  own  construction,  ranging  in  magnifying  power  from  forty  to  one 
hundred  and  sixty  diameters,  first  saw  the  corpuscles  of  human  blood,  which  he  minutely 
described  in  a  paper  published  in  the  Philosophical  Transactions,  in  1674.  To  Leeuwen- 
hoek is  generally  ascribed  the  honor  of  the  discovery  of  the  blood -corpuscles.1  About  a 
century  later,  "William  Hewson  described  another  kind  of  corpuscles  in  the  blood,  which 
are  much  less  abundant  than  the  red,  and  which  are  now  known  under  the  name  of  white 
globules,  or,  as  they  have  been  called  by  Robin,  leucocytes. 

Without  following  the  progress  of  microscopical  investigations  into  the  constitution 
of  the  blood,  it  may  be  stated  that  it  is  now  known  to  be  composed  of  a  clear  fluid,  the 
plasma,  or  liquor  sanguinis,  holding  certain  corpuscles  in  suspension.  These  corpuscles 
are  as  follows: 

1.  Red  corpuscles;  by  far  the  most  abundant,  constituting  a  little  less  than  one-half 
of  the  mass  of  blood. 

2.  Leucocytes,  or  white  corpuscles ;   much  less  abundant,  existing  only  in  the  pro- 
portion of  one  to  several  hundred  red  corpuscles-. 

3.  Granules;  exceedingly  minute,  called,  by  Milne-Edwards,  globulins,  and,  by  Kolli- 
ker,  elementary  granules.     These  are  few  in  number,  and  are  probably  fatty  particles 
from  the  chyle.     They  are  to  be  regarded  as  accidental  constituents  of  the  blood. 

Red  Corpuscles.— These  little  bodies  give  to  the  blood  its  red  color  and  its  opacity. 
They  are  true,  organized  structures,  containing  organic  nitrogenized  and  inorganic  ele- 
ments molecularly  united,  and,  as  an  exception  to  the  general  rule,  a  little  fatty  matter 
in  union  with  the  organic  principles.  They  constitute  a  little  less  than  one-half  the  mass 

i  Some  writers  give  the  credit  of  the  discovery  of  the  blood-corpuscles  to  Swammerdam.  In  165S,  Swammerdam 
studied  the  blood-corpuscles  of  the  frog  and  described  them  very  accurately;  but  his  researches  were  not  published 
until  1738,  a  number  of  years  after  his  death.  In  questions  of  priority,  it  is  usual  to  date  discoveries  from  the  time 
of  their  first  publication. 


BLOOD-CORPUSCLES. 


FIG.  1. — Human  blood-corpuscles  ;  magnified  370  diam- 
eters. (From  a  photograph  taken  at  the  United  States 
Army  Medical  Museum.) 


of  blood,  and,  according  to  the  observations  of  all  who  have  investigated  this  subject,  are 
more  abundant  in  the  male  than  in  the  female. 

The  form  of  the  blood -corpuscles  is  peculiar.  They  are  flattened,  biconcave,  circular 
disks,  with  a  thickness  of  from  one-fourth  to  one-third  of  their  diameter.  Their  edges 
are  rounded,  and  the  thin,  central  portion 
occupies  about  one-half  of  their  diameter. 
Their  consistence  is  not  much  greater  than 
that  of  the  plasma.  They  are  very  elastic, 
and,  if  deformed  by  pressure,  immediately 
resume  their  original  shape  when  the  press- 
ure is  removed.  Their  specific  gravity  is 
from  1088  to  1105,  considerably  greater 
than  the  specific  gravity  of  the  plasma, 
which  is  about  1028.  (Robin.) 

When  the  blood  has  been  drawn  from 
the  vessels  and  coagulates  slowly,  the  great- 
er density  of  the  red  corpuscles  causes  them 
to  gravitate  to  the  lower  portions  of  the 
clot,  leaving  the  white  corpuscles  and  fibrin 
at  the  surface.  This  is  the  cause  of  the 
"buffy-coat"  mentioned  by  some  writers. 
If  coagulation  be  prevented  by  the  addition 
of  a  small  quantity  of  sulphate  of  soda, 
there  is  quite  a  marked  gravitation  of  red  corpuscles  after  standing  for  some  hours. 

The  peculiar  form  of  the  blood-corpuscles  gives  them  a  very  characteristic  appearance 
under  the  microscope.  Examined  with  a  magnifying  power  of  from  three  hundred  to  five 
hundred  diameters,  those  which  present  their  flat  surfaces  have  a  shaded  centre  when  the 
edges  are  exactly  in  focus.  This  appearance  was  formerly  supposed  to  indicate  the  ex- 
istence of  a  nucleus  having  a  constitution  different  from  that  of  the  rest  of  the  corpuscle. 
It  is  now  understood  to  be  an  optical  effect,  the  result  of  the  form  of  the  corpuscles ;  their 
biconcavity  rendering  it  impossible  for  the  centre  and  edges  to  be  exactly  in  focus  at  the 
same  instant,  so  that,  when  the  edges  are  in  focus,  the  centre  is  dark,  and,  when  the  cenr 
tre  is  bright,  the  edges  are  shaded. 

As  the  blood-corpuscles  are  examined 
by  the  microscope  by  transmitted  light, 
they  are  nearly  transparent  and  of  a  pale- 
amber  color.  It  is  only  when  they  are  col- 
lected in  masses  that  they  present  the  red 
tint  characteristic  of  blood  as  it  appears 
to  the  naked  eye.  This  yellow  or  amber 
tint  is  quite  characteristic.  A  pretty  good 
idea  of  the  color  may  be  obtained  by  large- 
ly diluting  blood  in  a  test-tube  and  holding 
it  between  the  eye  and  the  light. 

In  examining  blood  under  the  micro- 
scope, the  corpuscles  are  seen  in  many 
different  positions  ;  some  flatr  some  on 
their  edges,  etc.  This  assists  us  in  recog- 
nizing their  peculiar  form. 


FIG.  2.  —Human  red  blood-corpuscles,  arranged  in  rows, 
with  two  white  corpuscles,  or  leucocytes. 


It  has  long  been  observed  that  the  blood- 
corpuscles  have  a  remarkable  tendency  to 
arrange  themselves  in  rows  like  rouleaux  of  coin.     This  appearance  has  attracted  univer- 
sal attention,  and  for  a  long  time  it  was  not  satisfactorily  explained.    Robin,  however,  has 


8 


THE   BLOOD. 


given  what  seems  to  be  the  true  explanation.  He  has  shown  that,  shortly  after  removal 
from  the  vessels,  there  exudes  from  the  corpuscles  an  adhesive  substance  which  smears 
their  surface  and  causes  them  to  stick  together.  Of  course  the  tendency  is  to  adhere  by 
their  flat  surfaces.  In  examining  a  specimen  of  blood  under  the  microscope,  the  presence 
of  this  adhesive  exudation  may  be  demonstrated  by  employing  firm  and  gradual  pressure 
on  the  glass  cover,  when  the  adherent  corpuscles  may  be  separated,  in  some  instances, 
and,  with  oblique  light,  we  can  see  a  little  transparent  filament  between  them,  which 
draws  them  together,  as  it  were,  when  the  pressure  is  removed.  This  phenomenon  is  due 
to  a  post-mortem  change ;  but  it  occurs  so  soon,  that  it  presents  itself  in  nearly  every 
specimen  of  fresh  blood,  and  is  therefore  mentioned  in  connection  with  the  normal  char- 
acters of  the  blood-corpuscles. 


Dimensions.  —  The  diameter  of  the  blood-corpuscles  has  a  more  than  ordinary  anatom- 
ical interest  ;  for,  varying  perhaps  less  in  size  than  other  anatomical  elements,  they  are 
often  taken  as  the  standard  by  which  we  form  an  idea  of  the  size  of  other  microscopic 
objects.  The  diameter  usually  given  is  -^Vo  of  an  inch.  The  exact  measurement  given 
by  Robin  is  .0073  of  a  millimetre,  or  F¥^-T  of  an  inch.  It  is  stated  by  some  authors  that 
the  size  of  the  corpuscles  is  very  variable,  even  in  a  single  specimen  of  blood.  We  have 
repeatedly  measured  them  and  found  a  diameter  of  ^Vo  °f  an  inch.  Very  few  are  to 
be  found  which  vary  from  this  measurement.  Kolliker,  who  gives  their  average  diame- 
ter as  s-^Vo  of  an  inch,  states  that  "at  least  ninety  -five  out  of  every  hundred  corpuscles 
are  of  the  same  size." 

"We  cannot  leave  the  subject  of  the  size  of  the  blood-corpuscles  without  a  notice  of  the 
measurements  in  the  blood  of  different  animals.  This  point  is  interesting,  from  the  fact 
that  it  is  often  an  important  question  to  determine  whether  a  given  specimen  of  blood  be 
from  the  human  subject  or  from  one  of  the  inferior  animals.  Comparative  measurements 
also  have  an  interest  on  account  of  a  relation  which  seems  to  exist  in  the  animal  scale 
between  the  size  of  the  blood-corpuscles  and  muscular  activity.  In  all  the  mammalia, 
with  the  exception  of  the  camel  and  llama,  in  which  the  corpuscles  are  oval,  the  blood 
has  nearly  the  same  anatomical  characters  as  in  the  human  subject.  In  only  two  animals, 
the  elephant  and  sloth,  are  the  red  corpuscles  larger  than  in  man  ;  in  all  others,  they  are 
smaller,  or  of  nearly  the  same  diameter.  By  reference  to  the  table,  it  will  be  seen  that, 

in  some  animals,  the  corpuscles  are  very  much 
smaller  than  in  man  ;  and,  by  accurate  meas- 
urements, we  are  enabled  to  distinguish  their 
blood  from  the  blood  of  the  human  subject. 
But,  in  forming  an  opinion  on  this  subject, 
it  must  be  remembered  that  there  is  some 
variation  in  the  size  of  the  corpuscles  of  the 
same  animal.  We  can  easily  distinguish  the 
blood  of  the  human  subject,  or  of  the  mam- 
mals generally,  from  that  of  birds,  fishes,  or 
reptiles  ;  for,  in  these  classes  of  animals,  the 
corpuscles  are  oval  and  contain  a  granular 
nucleus. 

Milne-Edwards  has  attempted  to  show, 
by  a  comparison  of  the  diameter  of  the 
blood-corpuscles  in  different  species,  that 

their  size  bears  an  inerSe  ratl°  tO  the 


FIG.  ^.-Blood-corpses  of  the  frog  ;  modified  370 

diameters.    (From  a  photograph  taken  at  the   cular  activity  of  the  animal.   Reference  to  the 

United  States  Army  Medical  Museum.)  ,   .  .         ...     ,  ,,     ,   ,,.         ,    ,.        111         ^j 

table  will  show  that  this  relation  holds  good 

to  some  extent,  while  there  certainly  exists  none  between  the  size  of  the  corpuscles  and 
the  size  of  the  animal.     In  deer,  animals  remarkable  for  muscular  activity,  the  corpuscles 


MAMMALS. 


9 


are  very  small,  -y^  of  an  inch ;  while  in  the  sloth  they  are  y^-,  and  in  the  ape,  which 
is  comparatively  inactive,  -j^Vo-  But,  on  the  other  hand,  in  the  dog,  which  is  quite 
active,  we  have  a  corpuscle  of  ^Yo  of  an  inch,  and  in  the  ox,  which  is  certainly  not  so 
active,  the  diameter  of  the  corpuscle  is  T^V<5-  °f  an  inch.  Although  this  relation  hetween 
the  size  of  the  blood-corpuscles  and  muscular  activity  is  not  invariable,  it  is  certain  that, 
the  higher  we  go  in  the  great  classes  of  animals,  the  smaller  are  the  blood-  corpuscles ; 
the  largest  being  found  in  the  lowest  orders  of  reptiles,  and  the  smallest,  in  the  mam- 
malia. The  blood  of  the  invertebrates,  with  a  few  exceptions,  contains  no  colored  cor- 
puscles. 

Table  of  Measurements  of  Red  Corpuscles. 

This  table  is  taken  from  the  table  of  Mr.  Gulliver,  published  in  the  Sydenham  edition  of  Hewson's 
Works,  page  237.  Nearly  five  hundred  measurements  were  made  by  Mr.  Gulliver ;  and  of  these, 
one  hundred  of  the  most  important  have  been  selected.  It  will  be  observed  that  the  diameter  of 
the  human  blood-corpuscle  is  greater  than  that  generally  given.  It  must  be  borne  in  mind  that  all 
these  measurements  are  mere  approximations ;  but  they  are  useful,  as  showing  the  relations  of  the 
corpuscles  in  different  animals,  and  enabling  us  to  distinguish  the  blood  of  the  human  subject  from 
that  of  some  of  the  inferior  animals.  The  measurements  are  all  given  in  fractions  of  an  English 
inch ;  and,  in  making  the  selections,  the  common  names  of  the  animals  have  been  substituted  for 
the  technical  names  given  in  the  original. 


Mammals. 


Corpuscles 

Circular. 

Diameter. 

Diameter. 

Man,    

ir/ou 

Weasel  

TijW 

Chimpanzee,     .... 

•       3^17 

Polecat,   .... 

•     Ti  6T 

Ourang-outang,     .... 

a"  aW 

Otter,  

•3TO¥ 

Black  monkey, 

.              jJgLj-y 

Seal,         .... 

•     WST 

Red  monkey,        .... 

inW 

Porpoise,     .... 

*»W 

Cape  baboon,  .... 

.       asV-H 

Whale, 

ffffS 

Brown  baboon,     .... 

•               34*93 

Hog,         .... 

'       41&TT 

Dog-faced  baboon,    . 

.   -J-4\T 

Indian  elephant,  . 

-$TT5 

Lazy  monkey,      .... 

Wsr 

Indian  rhinoceros,    . 

•     T^STf 

Bat,         

.         ^-fag 

Horse,          .... 

Two 

Long-eared  bat,   .... 

T&S 

Ass,         .        .        . 

'       4oW 

Mole,       

•        •    -thr 

Stag,   

TH^ST 

Hedgehog,  ..... 

TosF 

Fallow  deer,     . 

-     TsS'J 

Badger,   

.            ^j-fQ 

Virginia  deer, 

ToW 

Polar  bear,  

WTTF 

Giraffe,     .... 

'    T/{Vr 

Brown  bear  of  Europe,    . 

.    t-fa» 

Antelope,     .... 

rtW 

Black  bear  of  North  America. 

vlfa-5 

Gazelle,    .... 

•      4"9V? 

Raccoon,  

tf§  5  <T 

Goat,   

•sds* 

Dog,    

TFS  4"2" 

Sheep,      . 

•    FaW 

Fox,         

.      ^-Ipr 

Ox,       .         .         . 

fhr 

Jackal,         ...... 

38L6IT 

Buffalo,    .... 

-     ¥3W 

Wolf,       

•  ssW 

Musk  deer  of  Java, 

T?W 

Striped  hyena,      .... 

*           W~Ti~5 

Flying  squirrel, 

•      ¥^9^ 

Spotted  hyena, 

•       3  8  2"iJ 

Red  squirrel, 

WbTF 

Cat,     

440-T 

Black  squirrel, 

•     W4T 

Lion,        

.       .   Wn 

Gray  squirrel, 

ICMJTT 

Tiger,  

42W 

Marmot,  .... 

.    Ws* 

Leopard,  

Brown  rat,  .... 

WlT 

Panther,       

"46  .  fS 

Black  rat, 

.     -a-f^T 

Ferret,     

•     TTaT 

Mouse,         .... 

T814" 

10  THE   BLOOD. 

Diameter.  Diameter. 

Water  rat, ^i^     Opossum, ^T 

Porcupine, ^7    Kangaroo, ^3lr 

Beaver, ^IT 

Guinea-pig, ^^  L.  diam.  S.  diam. 

Rabbit, -3-gLjy  Dromedary  (oval),    .         .         .        T2V¥      -g^- 

Two-toed  sloth, Y-^T  Camel          (oval),        .         .         .    ^      Tfa 


Birds. 

Corpuscles  Oval, 

Long         Short 

Long 

Short 

Diameter.  Diameter. 

Diameter. 

Diameter. 

Eagle  (ring-tailed),  . 

T-sYir       3«V*     Pigeon,  . 

•     TTfW 

aeW 

Owl,    

•    T7W       40-7  o     Turtle-dove, 

•JlfoT 

aaVa 

Jay,         .         .  '       . 

YoVr       4-nrr    Peacock, 

.          ygLjY 

a-gW 

Raven,         .... 

•     TifdT         4  (fu  o      Cock,  • 

FuTa 

1T4  6^ 

Starling,  .... 

?hir      iriiW     Turkey,  . 

.          TfjJjy 

WW 

Wren,          .... 

•    FsV^       4"iVr     Guinea-fowl, 

_^  

T-A-T 

Sparrow, 

F&o       uifou     Quail, 

-                             SW 

4415 

Woodpecker, 

TS^TT 

¥o*rrrr 

.         5"T  3  -T       TUirir     Swan.      •         •         • 

.         y^r^ 

o  o  y 

Stork,          . 

•               •        1  8  0  to 

"nncpr 

y  E9^T 

Reptiles. 

*           •           i  y  <>  7 

Corpuscles  Oval. 

Long         Short 

Long 

Short 

Diameter.  Diameter. 

Diameter. 

Diameter. 

Green  turtle,    . 

•raW       TsVz     Lizard,    . 

•    "nrsT 

2-yL_ 

Land  tortoise, 

Tstrn 

Amphibia. 

Corpuscles  Oval. 

Long         Short 

Long 

Short 

Diameter.  Diameter. 

Diameter. 

Diameter. 

Frog, 

-i-A-ir      T«W     Toad, 

TTvj-7 

TTrtTfTT 

^'s/i65. 

Corpuscles  Oval. 

Long         Short  Long      Short 

Diameter.  Diameter.  Diameter.  Diameter. 

Perch, ToV?      T§W    Pike, FOIO'O'      irs^s" 

Carp, n'^fi     'wfas    Eel,  .         .         .         .         .         lA's"      W^F 

Enumeration  of  the  Blood- Corpuscles. — In  most  of  the  quantitative  analyses  of  the 
blood,  the  proportion  of  moist  corpuscles  to  the  entire  mass  of  blood  is  stated  to  be  a 
little  less  than  one-half.  This  estimate  is  necessarily  rather  rough ;  and  it  would  be  in- 
teresting to  ascertain,  if  possible,  the  normal  variations  in  the  proportion  of  corpuscles, 
under  different  conditions  of  the  system,  particularly  as  these  bodies  play  so  important  a 
part  in  many  of  the  functions  of  the  organism.  Estimates  of  this  kind  have  lately  been 
made  by  Malassez,  who  has  devised  a  method,  more  accurate  than  those  employed  before, 
for  the  actual  enumeration  of  the  red  corpuscles,  in  which,  it  is  stated,  the  error  does  not 
amount  to  more  than  two  or  three  per  cent.  The  process  employed  is  the  following : 


ENUMERATION   OF  THE   BLOOD-OOKPUSCLES. 


11 


The  blood  to  be  examined  is  diluted  with  ninety-nine  parts  of  a  liquid  composed  of 
one  volume  of  a  solution  of  gum-arabic  of  a  specific  gravity  of  1020  with  three  volumes 
of  a  solution  of  equal  parts  of  sulphate  of  soda  and  chloride  of  sodium,  also  of  a  spe- 
cific gravity  of  1020.  The  mixture,  containing  one  part  of  blood  in  one  hundred,  is  in- 
troduced into  a  small  thermometer-tube  with 
an  elliptical  bore,  the  sides  of  the  tube  being 
ground  flat  for  convenience  of  microscopical 
examination.  The  capacity  of  the  tube  is  to 
be  calculated,  by  estimating  the  weight  of  a 
volume  of  mercury  contained  in  a  given 
length.  The  tube  is  then  filled  with  the  di- 
luted blood,  and  the  number  of  corpuscles  in 
a  given  length  of  the  tube  is  counted  by 
means  of  a  microscope  fitted  with  an  eye- 
piece micrometer.  In  this  way,  the  number 
of  corpuscles  in  a  given  volume  of  blood  can 
be  readily  estimated.  In  man,  the  number 
in  a  cubic  millimeter  of  blood  (a  millimeter  = 
about  ^T  of  an  inch)  is  estimated  at  about 
four  million. 

According  to  the  observations  of  Malas- 
sez,  the  proportion  of  corpuscles  is  about  the 
same  in  all  parts  of  the  arterial  system.  In 
the  veins,  the  corpuscles  are  more  abundant  than  in  the  arteries.  In  the  venous  system, 
the  blood  of  the  splenic  veins  presents  the  largest  proportion  of  corpuscles,  and  the  pro- 
portion is  smallest  in  the  blood  of  the  hepatic  veins.  These  results  favor  the  idea 
that  the  red  corpuscles  are  formed,  to  a  certain  extent,  in  the  spleen,  and  that  some 
are  destroyed  in  the  liver ;  but  farther  observations  are  necessary  to  render  this  view 
certain. 


FIG.  4. — Artificial  capillary,  filled  with  a  sanguin- 
eous mixture,  seen  under  a  quadrilateral  mi- 
crometer. (Malassez.) 


Post-mortem  Changes  in  the  Blood- 
Corpuscles. — In  examining  the  fresh  blood 
under  the  microscope,  after  the  specimen 
has  been  under  observation  a  short  time, 
the  corpuscles  assume  a  peculiar  appear- 
ance, from  the  development,  on  their  sur- 
face, of  very  minute,  rounded  projections, 
like  the  granules  of  a  raspberry.  A  little 
later,  when  they  have  become  partly  de- 
siccated, they  present  a  shrunken  appear- 
ance, and  their  edges  are  more  or  less  ser- 
rated. Under  these  conditions,  their  orig- 
inal form  may  be  restored  by  adding  to 
the  specimen  a  liquid  of  about  the  den- 
sity of  the  serum.  When  they  have  been 
completely  dried,  as  in  blood  spilled  upon 
clothing  or  on  a  floor,  months  or  even 
years  after,  they  can  be  made  to  assume 
their  characteristic  form  by  carefully  moist- 
ening them  with  an  appropriate  liquid.  This  property  is  taken  advantage  of  in  exam- 
inations of  old  spots  supposed  to  be  blood ;  and,  if  the  manipulations  be  carefully  con- 
ducted, the  corpuscles  may  be  recognized  without  difficulty  by  the  microscope. 

If  pure  water  be  added  to  a  specimen  of  blood  under  the  microscope,  the  corpuscles 


FIG.  5. — Human  blood-corpuscles,  showing  post-mortem 
alterations. 


12  THE  BLOOD. 

swell  up,  become  spherical,  and  are  finally  lost  to  view  by  solution.      The  same  effect 
follows  almost  instantaneously  on  the  addition  of  acetic  acid. 

Structure. — The  structure  of  the  blood-corpuscles  is  very  simple.  They  are  perfectly 
homogeneous,  presenting,  in  their  normal  condition,  no  nuclei  or  granules,  and  are  not 
provided  with  an  investing  membrane.  A  great  deal  has  been  said  by  anatomists  con- 
cerning this  latter  point ;  and  some  are  of  the  opinion  that  the  corpuscles  are  cellular  in  their 
structure,  being  composed  of  a  membrane,  with  viscid,  semifluid  contents.  Without  going 
fully  into  the  discussion  of  this  question,  it  may  be  stated  that  few  have  assumed  to  have 
actually  demonstrated  this  membrane ;  but  certain  observers  have  inferred  its  existence 
from  the  fact  of  the  corpuscles  swelling,  and,  as  they  term  it,  bursting  on  the  addition 
of  water.  The  appearances  presented  upon  the  addition  of  iodine  to  blood  previously 
treated  with  water,  which  have  been  supposed  to  indicate  the  presence  of  shreds  of 
ruptured  vesicles,  are  not  sufficiently  distinct  to  demonstrate  the  existence  of  a  membrane. 
The  great  elasticity  of  the  corpuscles,  the  persistence  with  which  they  preserve  their 
biconcave  form,  and  their  general  appearance,  rather  favor  the  idea  that  they  are  homo- 
geneous bodies  of  a  definite  shape,  than  that  they  have  a  cell-wall  with  semifluid  con- 
tents ;  especially  as  the  existence  of  a  membrane  has  been  only  inferred  and  not  posi- 
tively demonstrated.  Their  mode  of  nutrition  is  like  that  of  other  anatomical  elements. 
They  are  bathed  in  a  nutritive  fluid,  the  plasma,  and,  as  fast  as  their  substance  becomes 
worn  out  and  effete,  new  material  is  supplied.  In  this  way,  they  undergo  the  same 
molecular  changes  as  other  anatomical  structures.  When  destroyed  or  removed  from  the 
body  in  hemorrhages,  new  corpuscles  are  gradually  developed,  until  their  quantity 
reaches  the  normal  standard. 

Development  of  the  Blood- Corpuscles. — Very  early  in  the  development  of  the  ovum, 
the  blood-vessels  appear,  constituting  what  is  called  the  area  vasculosa.  At  about  the 
same  time,  the  blood-corpuscles  are  developed,  it  may  be  before,  or  it  may  be  just  after  the 
appearance  of  the  vessels,  for  this  point  is  undetermined.  The  blood  becomes  red  when 
the  embryon  is  about  one-tenth  of  an  inch  in  length.  From  this  time  until  the  end  of 
the  sixth  or  eighth  week,  they  are  from  thirty  to  one  hundred  per  cent,  larger  than  in 
the  adult.  Most  of  them  are  circular,  but  some  are  ovoid,  and  a  few  are  globular.  At 
this  period,  nearly  all  of  them  are  provided  with  a  nucleus ;  but,  from  the  first,  there  are 
some  in  which  this  is  wanting.  The  nucleus  is  from  y^-g-  to  -g-^Vo  °f  an  mcn  m  diameter, 
globular,  granular,  and  insoluble  in  water  and  acetic  acid.  As  development  advances, 
these  nucleated  corpuscles  are  gradually  lost ;  but,  even  at  the  fourth  month,  we  may 
still  see  a  few  remaining.  After  this  time,  they  present  no  anatomical  differences  from 
the  blood-corpuscles  in  the  adult. 

In  many  works  on  physiology  and  general  anatomy,  we  find  accounts  of  the  develop- 
ment of  the  red  corpuscles  from  the  colorless  corpuscles,  or  leucocytes,  which  are  sup- 
posed to  become  disintegrated,  their  particles  becoming  developed  into  red  corpuscles ; 
but  there  seems  to  be  no  positive  evidence  that  such  a  process  takes  place.  The  red  cor- 
puscles appear  before  the  leucocytes  are  formed  ;  and  it  is  only  the  fact  that  the  two 
varieties  coexist  in  the  blood-vessels  which  has  given  rise  to  such  a  theory.  It  is  most 
reasonable  to  consider  that  the  red  corpuscles  are  formed  by  a  true  genesis  in  the  san- 
guineous blastema.  There  is,  farthermore,  no  sufficient  evidence  that  any  particular 
organ  or  organs  have  the  function  of  producing  the  blood-corpuscles.  It  is  regarded  by 
some  as  a  necessity  that  there  should  be  an  organ  for  the  destruction  of  the  corpuscles, 
and  one  for  their  formation.  Eegarding  them,  as  we  certainly  must,  as  organized  bodies 
which  are  essential  anatomical  elements  of  the  blood,  it  is  difficult  to  imagine  what 
reasons,  based  on  their  function,  should  lead  physiologists  to  seek  so  persistently  after  an 
organ  for  their  destruction.  The  hypothesis  that  they  are  used  in  the  formation  of  pig- 
mentary matter  seems  hardly  sufficient  to  account  for  this.  The  observations  of  Malassez, 


FUNCTION   OF  THE  BLOOD-COEPUSOLES.  13 

which  show  an  increase  in  the  number  of  corpuscles  in  the  blood  coming  from  the  spleen 
and  a  diminution  in  the  blood  of  the  hepatic  veins,  are  not  sufficiently  definite  to  serve 
as  a  demonstration  that  the  spleen  is  a  blood-forming  organ ;  and  the  same  remark 
may  be  applied  to  observations  upon  the  formation  of  blood-corpuscles  by  the  marrow 
of  the  bones. 

In  the  present  state  of  our  knowledge,  the  following  seem  to  be  the  most  rational 
views  with  regard  to  the  development  and  nutrition  of  the  blood-corpuscles: 

1.  At  the  time  of  their  first  appearance  in  the  ovum,  they  are  formed  by  no  special 
organs,  for  no  special  organs  then  exist ;  but  they  appear  by  genesis  in  the  sanguineous 
blastema. 

2.  When  fully  formed,  they  are  regularly-organized  anatomical  elements,  subject  to 
the  same  laws  of  gradual  molecular  waste  and  repair  as  any  of  the  anatomical  elements 
of  the  tissues. 

3.  They  are  generated  de  novo  in  the  adult,  when  diminished  in  quantity  by  haemor- 
rhage or  otherwise ;  and,  under  these  circumstances,  they  are  probably  formed  in  the 
liquor  sanguinis,  by  the  same  process  by  which  they  take  their  origin  in  the  ovum. 

Function  of  the  Blood-Corpuscles. — Although  the  albuminoid  constituents  of  the  plasma 
of  the  blood  are  essential  to  nutrition,  the  red  corpuscles  are  the  parts  most  immediately 
necessary  to  life.  We  have  already  seen,  in  treating  of  transfusion,  that  life  may  be  re- 
stored to  an  animal  in  which  the  functions  have  been  suspended  from  haemorrhage,  by  the 
introduction  of  fresh  blood ;  and,  while  it  is  not  necessary  that  this  blood  should  contain 
the  elements  of  fibrin,  it  has  been  shown  by  the  experiments  of  Prevost  and  Dumas  and 
others,  that  the  introduction  of  serum,  without  the  corpuscles,  has  no  restorative  effect. 
When  all  the  arteries  leading  to  a  part  are  tied,  the  tissues  lose  their  properties  of  con- 
tractility, sensibility,  etc.,  which  may  be  restored,  however,  by  supplying  it  again  with 
the  vivifying  fluid.  We  shall  see,  when  we  come  to  treat  of  the  function  of  respiration, 
that  one  great  distinction  between  the  corpuscular  and  fluid  elements  of  the  blood  is  the 
great  capacity  which  the  former  have  for  absorbing  gases.  Direct  observations  have 
shown  that  blood  will  absorb  from  ten  to  thirteen  times  as  much  oxygen  as  an  equal  bulk 
of  water ;  and  this  is  dependent  almost  entirely  on  the  presence  of  the  red  corpuscles.  As 
all  the  tissues  are  constantly  absorbing  oxygen  and  giving  off  carbonic  acid,  a  very  im- 
portant function  of  the  corpuscles  is  to  carry  oxygen  to  all  parts  of  the  body.  In  the 
present  state  of  our  knowledge,  this  is  the  only  well-defined  function  which  can  be 
attributed  to  the  red  corpuscles,  and  it  undoubtedly  is  the  principal  one.  They  have  an 
affinity,  though  not  so  great,  for  carbonic  acid,  which,  after  the  blood  has  circulated  in 
the  capillaries  of  the  system,  takes  the  place  ot  the  oxygen.  In  some  experiments  per- 
formed a  few  years  ago  on  the  effects  of  haemorrhage  and  the  seat  of  the  "  besoin  de  re- 
apirer"  we  demonstrated  that  one  of  the  results  of  removal  of  blood  from  the  system 
was  a  condition  of  asphyxia,  dependent  upon  the  absence  of  these  respiratory  elements. 

Leucocytes,  or  White  Corpuscles  of  the  Blood. — In  addition  to  the  red  corpuscles  of 
the  blood,  this  fluid  always  contains  a  number  of  colorless  bodies,  globular  in  form,  in  the 
substance  of  which  are  embedded  a  greater  or  less  number  of  minute  granules.  These 
have  been  called  by  Robin,  leucocytes.  This  name  seems  more  appropriate  than  that  ot 
white  or  colorless  blood-corpuscles,  inasmuch  as  they  are  not  peculiar  to  the  blood,  but 
are  found  in  the  lymph,  chyle,  pus,  and  various  other  fluids,  in  which  they  were  formerly 
known  by  different  names.  All  who  have  been  in  the  habit  of  examining  the  animal 
fluids  microscopically  have  noticed  the  great  similarity  between  the  corpuscular  elements 
found  in  the  above-mentioned  situations ;  and,  as  microscopes  have  been  improved  and 
investigations  have  become  more  exact,  the  varieties  of  corpuscles  have  been  narrowed 
down.  It  is  now  pretty  generally  acknowledged  that  the  corpuscles  found  in  mucus  and 
pus  are  identical ;  also,  that  there  is  no  difference  between  the  white  corpuscles  found  in 


14  THE  BLOOD. 

the  lymph,  chyle,  and  blood ;  and,  finally,  it  has  been  shown  that  all  of  these  bodies, 
which  were  formerly  supposed  to  present  marked  distinctive  characters,  belong  to  the 
same  class,  presenting  but  slight  differences  in  different  situations.  The  description  which 
will  be  given  of  the  white  corpuscles  of  the  blood,  and  the  effects  of  reagents,  will  an- 
swer, in  the  main,  for  all  the  corpuscular  bodies  that  are  grouped  under  the  name  of 
leucocytes. 

Leucocytes  are  normally  found  in  the  blood,  lymph,  chyle,  semen,  colostrum,  and 
vitreous  humor.  Pathologically,  they  are  found  in  the  secretion  of  mucous  mem- 
branes, following  irritation,  and  in  inflammatory  products,  when  they  are  called  pus- 
corpuscles. 

In  examining  a  specimen  of  blood  with  the  microscope,  we  immediately  notice  the 
marked  difference  between  the  leucocytes  and  red  corpuscles.  The  former  are  globular, 
with  a  smooth  surface,  somewhat  opaque  from  the  presence  of  more  or  less  granular 
matter,  white,  and  larger  than  the  red  corpuscles. 

In  examining  the  circulation  under  the  microscope,  we  are  struck  with  the  adhesive 
character  of  the  leucocytes  as  compared  with  the  red  corpuscles.  The  latter  circulate 
with  great  rapidity  in  the  centre  of  the  vessels,  while  the  leucocytes  have  a  tendency  to 
adhere  to  the  sides,  moving  along  slowly,  and  occasionally  remaining  for  a  time  entirely 
stationary,  until  they  are  swept  along  by  a  change  in  the  direction  or  force  of  the 
current. 

The  size  of  the  leucocytes  varies  somewhat,  even  in  any  one  fluid,  such  as  the  blood. 
Their  average  diameter  may  be  stated  as  -^-Q  of  an  inch.  It  is  in  pus,  where  they  exist  in 
greatest  abundance,  that  their  microscopical  characters  may  be  studied  with  greatest  ad- 
vantage. In  this  fluid,  after  it  is  discharged,  the  corpuscles  sometimes  present  remarkable 
deformities.  They  become  polygonal  in  shape,  and  sometimes  ovoid,  occasionally  presenting 
projections  from  their  surface,  which  give  them  a  stellate  appearance.  These  alterations, 
however,  are  only  temporary  ;  and,  after  from  twelve  to  twenty-four  hours,  they  resume 
their  globular  shape.  On  the  addition  of  acetic  acid,  they  swell  up,  become  transparent, 
with  a  delicate  outline,  and  present  in  their  interior  one,  two,  three,  or  even  four  rounded, 
nuclear  bodies,  generally  collected  in  a  mass.  This  is  rather  to  be  considered  as  a  coagu- 
lation of  a  portion  of  the  corpuscle,  than  a  nucleus  brought  out  by  the  action  of  the  acid 
which  renders  the  corpuscle  transparent ;  although  in  some  corpuscles  it  is  seen  without 
the  addition  of  any  reagent.  This  appearance  is  produced,  though  more  slowly,  by  the 
addition  of  water. 

Leucocytes  vary  considerably  in  their  external  characters  in  different  situations. 
Sometimes  they  are  very  pale  and  almost  without  granulations,  while  at  others  they  are 
filled  with  fatty  granules  and  are  not  rendered  clear  by  acetic  acid.  As  a  rule,  they 
increase  in  size  and  become  granular  when  confined  in  the  tissues.  In  colostrum,  where 
they  are  called  colostrum-corpuscles,  they  generally  undergo  this  change.  As  the  result 
of  inflammatory  action,  when  they  are  sometimes  called  inflammatory  or  exudation-cor- 
puscles, leucocytes  frequently  become  much  hypertrophied  and  are  filled  with  fatty 
granules. 

The  deformation  of  the  leucocytes,  to  which  allusion  has  already  been  made,  is  some- 
times so  rapid  and  changeable  as  to  produce  creeping  movements,  due  to  the  projection 
and  retraction  of  portions  of  their  substance.  These  movements  are  of  the  kind  called 
amoeboid,  and  are  supposed  to  be  important  in  the  process  of  migration  of  the  corpus- 
cles, which  has  lately  been  described. 

The  quantity  of  leucocytes  compared  to  the  red  corpuscles  can  only  be  given  approxi- 
matively.  It  has  been  estimated  by  counting  under  the  microscope  the  red  corpuscles  and 
leucocytes  contained  in  a  certain  space.  Moleschott  gives  the  proportion  as  1 : 335 ; 
others,  at  from  1  :  300  to  1  :  500.  It  has  been  found  by  Dr.  E.  Hirt,  of  Zittau,  whose 
observations  have  been  confirmed  by  others,  that  the  relative  quantity  of  leucocytes 
is  much  increased  during  digestion.  He  found,  in  one  individual,  a  proportion  of  1  :  1800 


DEVELOPMENT  OF  LEUCOCYTES. 


15 


\ 


before  breakfast ;  an  hour  after  breakfast,  which  was  taken  at  8  o'clock,  1  :  TOO ;  be- 
tween 11  and  1  o'clock,  1:1500;  after  dining,  at  1  o'clock,  1:400;  two  hours  after, 
1  :  1475 ;  after  supper,  at  8  P.  M.,  1  :  550 ;  at  11£  p.  M.,  1  :  1200.  The  leucocytes  are 
much  lighter  than  the  red  corpuscles,  and,  when  the  blood  coagulates  slowly,  are  fre- 
quently found  with  a  certain  amount  of  colorless  fibrin  forming  a  layer  on  the  surface  of 
the  clot,  which  is  called  the  "  buffy-coat." 
Their  specific  gravity  is  about  1070. 

Numerous  observers,  among  whom  may 
be  mentioned  Donne,  Kolliker,  Gray,  Hirt, 
and  Halassez,  have  noticed  a  great  in- 
crease in  the  number  of  leucocytes  in  the 
blood  coming  from  the  spleen,  and  have 
supposed  that  they  are  formed  chiefly  in 
this  organ.  It  is  inconsistent  with  the 
mode  of  development  of  these  corpuscles 
to  suppose  that  any  special  organ  is  exclu- 
sively engaged  in  their  production;  and 
their  persistence  in  animals  after  extirpa- 
tion of  the  spleen  shows  that  they  are  de- 
veloped in  other  situations. 

The  function  of  the  leucocytes  is  not 
understood.  The  supposition  that  they 


FIG.  6. — Human  red  and  while  blood-corpwcles. 


break  down  and  become  nuclei  for  the  de- 
velopment of  red  corpuscles,  which  at  one 
time  obtained,  is  a  pure  hypothesis,  which  has  no  positive  basis  in  fact. 


Development  of  Leucocytes. — These  corpuscles  appear  in  the  blood-vessels  very  early 
in  foetal  life,  before  the  lymphatics  can  be  demonstrated.  They  arise  in  the  same  way  as 
the  red  corpuscles,  by  genesis  from  materials  existing  in  the  vessels.  They  appear  in 
lymphatics,  before  these  vessels  pass  through  the  lymphatic  glands,  in  the  foetus  anterior 
to  the  development  of  the  spleen,  and  also  on  the  surface  of  mucous  membranes ;  so 
they  cannot  be  considered  as  produced  exclusively  by  the  lymphatic  glands,  as  has  been 
supposed.  There  is  no  organ  nor  class  of  organs  in  the  body  specially  charged  with  their 
formation ;  and,  although  they  frequently  appear  as  a  result  of  inflammation,  this  process 
is  by  no  means  necessary  for  their  production.  Robin  has  carefully  noted  the  phenom- 
ena of  their  development  in  recent  wounds.  The  first  exudation  consists  of  clear  fluid, 
with  a  few  red  corpuscles;  then,  a  finely  granular  blastema.  In  from  a  quarter  of  an 
hour  to  an  hour,  pale,  transparent  globules,  from  -g-^Vtr to  WW  °f  an  m°h  m  diameter, 
make  their  appearance,  which  soon  become  finely  granular  and  present  the  ordinary 
appearance  of  leucocytes.  They  are  thus  developed,  like  other  anatomical  elements,  by 
organization  of  the  necessary  elements  furnished  by  a  blastema,  and  not  by  the  action 
of  any  special  organ  or  organs. 

This  view  of  the  mode  of  development  of  leucocytes  seems  to  be  established  by  the 
following  very  elegant  experiments  of  Onimus,  showing  that  corpuscles  may  be  devel- 
oped, under  favorable  conditions,  in  a  perfectly  clear,  homogeneous  blastema : 

Onimus  used  the  clear  fluid  taken  without  delay  from  rapidly-developed  blisters, 
which  he  found  ordinarily  contained  no  leucocytes,  but  which  he  carefully  filtered  in 
order  to  remove  all  sources  of  error.  The  filtered  liquid  contained  no  morphological 
elements ;  but,  on  the  other  hand,  he  found  that,  if  the  liquid  were  allowed  to  remain 
for  an  hour  or  more  in  contact  with  the  derma,  it  always  contained  leucocytes  and  epi- 
thelial cells.  Under  these  circumstances,  even  after  filtration,  the  liquid  contained  a  few 
leucocytes ;  but,  after  six  or  seven  hours  of  repose  in  a  conical  vessel,  the  corpuscular 
elements  gravitated  to  the  bottom,  leaving  the  upper  portion  of  the  liquid  perfectly  clear. 


16  THE  BLOOD. 

This  liquid,  entirely  free  from  anatomical  elements,  was  enclosed  in  little  sacs  formed 
of  an  animal  membrane  (gold-beater's  skin)  and  introduced  under  the  skin  of  a  living 
rabbit.  At  the  end  of  twelve  hours,  a  few  small  leucocytes  and  granulations  had  made 
their  appearance ;  at  the  end  of  twenty-four  hours,  the  fluid  had  become  somewhat 
opaque,  and  contained  a  large  number  of  leucocytes  and  granulations ;  and,  at  the  end 
of  thirty-six  hours,  the  fluid  was  white,  milky,  and  composed  almost  entirely  of  leucocytes 
and  granulations.  The  leucocytes,  which  were  examined  also  by  Prof.  Kobin,  presented 
all  the  characters  by  which  these  corpuscles  are  ordinarily  recognized.  These  experi- 
ments were  repeated  with  more  than  forty  different  specimens  of  fluid  from  blisters. 

The  experiments  were  then  varied  in  order  to  show  the  influence  of  the  membrane 
and  the  composition  of  the  blastema  upon  the  development  of  leucocytes.  By  modify- 
ing the  membrane  in  which  the  blastema  was  enclosed,  it  was  found  that  the  corpuscles 
were  rapidly  developed  in  proportion  to  the  activity  of  the  osmotic  action.  When  thick 
animal  membranes  were  used,  their  development  was  slow,  and,  in  some  instances,  did 
not  take  place  at  all.  There  was  no  development  of  leucocytes  in  a  clear  blastema  en- 
closed in  a  sac  of  caoutchouc  or  in  glass  tubes  hermetically  sealed  ;  and  from  this  it  was 
concluded  that  osmotic  action  is  a  necessary  condition,  and  that  the  mere  heat  of  the 
body  is  not  sufficient  to  develop  these  corpuscles,  even  in  an  appropriate  blastema.  The 
influence  of  this  constant  molecular  movement  is  in  striking  contrast  to  the  conditions 
of  absolute  repose  which  are  so  essential  to  the  formation  of  crystals  from  ordinary 
saline  solutions. 

One  of  the  most  interesting  points  in  these  experiments  is  connected  with  the  influ- 
ence of  the  composition  of  the  blastema  upon  the  development  of  leucocytes.  It  was 
found  that  these  bodies  were  never  developed  in  a  blastema  in  which  the  fibrin  had  been 
coagulated.  Experimenting  with  two  liquids,  the  only  difference  in  their  constitution 
being  that  in  one  the  fibrin  had  been  coagulated  by  repeatedly  plunging  the  glass  tube  in 
which  it  was  contained  into  cool  water,  while  the  other  was  kept  at  the  ordinary  tem- 
perature, a  little  bicarbonate  of  soda  being  added  to  prevent  coagulation,  it  was  found 
that  leucocytes  were  developed  as  usual  in  the  fluid  which  contained  the  fibrinous  elements, 
and  that  none  appeared  in  the  other.  On  placing  the  liquid  with  its  coagulum  enclosed 
in  a  sac  under  the  skin,  it  was  found  that,  after  a  time,  the  fibrin  was  redissolved,  but 
no  leucocytes  made  their  appearance. 

The  theory  which  has  for  its  motto,  omnis  cellula  e  cellula,  receives  no  support  from 
these  experiments.  Onimus  added  to  fluids  which  had  been  deprived  of  fibrinous  matters, 
epithelial  cells  and  pus-corpuscles,  but,  even  after  thirty-six  hours,  he  never  found  any 
additional  development  of  corpuscular  elements.  Leucocytes  added  to  fluids  in  which 
the  fibrinous  elements  were  unchanged  did  not  seem  to  exert  any  influence  upon  the  de- 
velopment of  new  corpuscles. 

Elementary  Corpuscles. — Little  granules  are  found  in  the  blood,  especially  during 
digestion,  which,  as  they  were  supposed  to  take  part  in  the  formation  of  the  white  cor- 
puscles, have  been  called  elementary  granules  or  corpuscles.  They  probably  are  little 
fatty  particles  of  the  chyle  which  come  from  the  thoracic  duct,  and  are  not  positively 
known  to  have  any  connection  with  the  formation  of  the  other  corpuscular  elements  of 
the  blood. 

Composition  of  the  Red  Corpuscles. 

The  red  corpuscles  of  the  blood  contain  an  organic  nitrogenized  principle,  called 
globuline,  combined  with  inorganic  principles  and  a  coloring  matter.  The  composition 
of  the  leucocytes  has  not  been  accurately  determined.  The  inorganic  matters  contained 
in  the  red  corpuscles  are  in  a  condition  of  intimate  union  with  the  other  constituents. 
and  can  only  be  separated  by  incineration.  It  may  be  stated,  in  general  terms,  that 
most,  if  not  all  of  the  various  inorganic  constituents  of  the  plasma  exist  also  in  the  cor- 


H^MAGLOBINE. 


17 


puscles,  which  latter  are  particularly  rich  in  the  salts  of  potassa.  Iron  exists  in  the  col- 
oring matter  of  the  corpuscles.  In  addition,  the  corpuscles  contain  cholesterine,  lece- 
thine,  a  certain  amount  of  fatty  matter,  and  probably  some  of  the  organic  saline  princi- 
ples of  the  blood. 

Globuline. — Rollett,  by  alternately  freezing  and  thawing  blood  several  times  in  succes- 
sion in  a  platinum  vessel,  has  succeeded  in  separating  the  coloring  matter  from  the  red  cor- 
puscles. When  the  blood  is  afterward  warmed  and  liquefied,  the  fluid  is  no  longer  opaque, 
but  is  dark  and  transparent.  Microscopical  examination  then  reveals  the  corpuscles,  entire- 
ly decolorized  and  floating  in  a  red,  semitransparent  serum.  Denis  extracted  the  organic 
principle  of  the  corpuscles  by  adding  to  defibrinated  blood  about  one-half  its  volume  of 
a  solution  of  chloride  of  sodium  containing  one  part  in  ten  of  water.  Allowing  this  to 
stand  for  from  ten  to  fifteen  hours,  there  appears  a  viscid  mass,  which  is  very  carefully 
washed  with  water  until  all  the  coloring  matter  and  the  salt  added  has  been  removed. 
The  whitish,  translucid  mass  which  remains  is  called  globuline.  Denis  has  also  ex- 
tracted a  small  quantity  of  fibrin  from  the  corpuscles.  Globuline  is  readily  extracted 
from  the  blood  of  birds,  but  is  obtained  with  difficulty  from  the  blood  of  the  human 
subject. 

Hcemagloline. — This  is  the  coloring  matter  of  the  red  corpuscles.  It  has  been  called 
by  different  writers,  hfemaglobuline  or  hsematocrystalline ;  but  the  crystals  called  hsema- 
tine  and  hsematosine  are  derivatives  of  ha3maglobine  and  are  not  true  proximate  princi- 
ples. HaBmaglobine  may  be  extracted  from  the  red  corpuscles  by  adding  to  them,  when 
congealed,  ether,  drop  by  drop.  A  jelly-like  mass  is  then  formed,  which  is  passed  rap- 
idly through  a  cloth,  crystals  soon  appearing  in  the  liquid,  which  may  be  separated  by 
filtration.  (Gautier.) 

The  crystals  of  hsemaglobine  extracted  from  human  blood  are  in  the  form  of  four- 
sided  prisms,  elongated  rhomboids,  or  rectangular  tablets,  of  a  purplish-red  color.  They 
are  composed  of  carbon,  hydrogen,  oxygen,  nitrogen,  sulphur,  and  a  small  quantity  of 
iron.  They  are  soluble  in  water  and  in  very  dilute  alkaline  solutions,  and  the  haamaglo- 
bine  is  precipitated  from  these  solutions  by  ferrocyanide  of  potassium,  nitrate  of  mer- 
cury, chlorine,  or  acetic  acid.  The  proportion  of  this  coloring  matter  to  the  entire  mass 
of  blood  is  about  one  hundred  and  twenty-seven  parts  per  thousand.  It  constitutes 
from  if  to  .T9¥  of  the  dried  corpuscles.  A  solution  of  hsemaglobine  in  one  thousand 
parts,  examined  with  the  spectroscope,  gives  two  dark  bands  between  the  letters  D  and 
E  in  Frauenhofer's  scale. 

Treated  with  oxygen  or  prepared  in  fluids  in  contact  with  the  air,  there  occurs  a 
union  of  oxygen  with  the  coloring  matter,  forming  what  has  been  called  oxyhajmaglobine. 
There  can  be  no  doubt  that  the  oxygen  enters  into  an  intimate,  though  rather  unstable 
combination  with  hsemaglobine,  and  this  is  an  important  point  to  be  considered  in  con- 
nection with  the  absorption  of  oxygen  by  the  blood  in  respiration.  A  solution  of  oxy- 
hsemaglobine  presents  a  different  spectrum  from  a  solution  of  pure  haBmaglobine.  If 
we  examine  a  solution  of  oxyhsemaglobine  with  the  spectroscope  and  then  discharge 
the  oxygen  by  prolonged  ebullition  in  a  vacuum,  the  characteristic  bands  of  pure  hsema- 
globine  make  their  appearance.  The  union  of  oxygen  with  haemaglobine  is  unstable  and 
the  oxgen  can  be  removed  by  a  current  of  hydrogen,  nitrous  oxide,  or  carbonic  acid.  A 
current  of  carbonic  oxide  displaces  the  oxygen,  and  the  carbonic  oxide  forms  a  very  sta- 
ble combination  with  the  coloring  matter.  It  is  well  known  that  carbonic  oxide  is  a 
very  poisonous  gas,  which  becomes  fixed  in  the  corpuscles  so  that  they  become  inca- 
pable of  absorbing  oxygen. 

According  to  recent  observations,  oxygen  combined  with  haemaglobine  exists  in  the 
condition  of  ozone.     A  solution  of  oxyhsemaglobine  is  readily  decomposed  by  a  current 
of  sulphuretted  hydrogen,  forming,  like  ozone,  water  and  a  precipitate  of  sulphur. 
2 


18 


THE  BLOOD. 


Haamatine  may  be  produced  by  decomposition  of  haemaglobine,  by  a  process  which 
it  is  not  necessary  to  describe,  as  the  hasmatine  is  not  a  proximate  principle.  HaBmatoi- 
dine  is  also  a  product  of  decomposition  of  hsemaglobine,  but  it  does  not  contain  iron. 
Haematoidine  is  more  interesting,  however,  from  the  fact  that  it  is  frequently  found  in 
old  clots  that  have  been  long  extravasated  in  the  tissues.  Robin  found  a  notable  quan- 
tity of  crystals  of  hsematoidine  in  a  cyst  of  the  liver. 

Assuming,  as  we  certainly  may,  that  the 
bloo.d  furnishes  material  for  the  nourishment 
of  all  the  tissues  and  organs,  we  should  ex- 
pect to  find  entering  into  its  composition  all 
the  proximate  principles  existing  in  the  body 
which  undergo  no  change  in  nutrition,  like 
the  inorganic  principles,  and  organic  matters 
capable  of  being  converted  into  the  organic 
elements  of  every  tissue.  Farthermore,  as 
the  products  of  waste  are  all  taken  up  by  the 
blood  before  their  final  elimination,  these  also 
should  enter  into  its  composition.  "With  these 
facts  in  our  minds,  we  can  readily  appreciate 
the  importance  of  accurate  proximate  ana- 
lyses of  the  circulating  fluid. 

Notwithstanding 'the  immense  amount  of 
labor  bestowed  by  the  most  eminent  chemists 
of  the  day  upon  the  quantitative  analysis  of 
the  blood,  and  the  great  physiological  interest 
attaching  to  every  advance  in  our  knowledge 
in  this  direction,  the  chemical  difficulties  in- 
volved are  so  great,  that  even  now  there  are 
no  analyses  which  give  the  exact  quantities 
of  each  of  its  inorganic  constituents.  This  is 
owing  to  the  great  difficulty  in  the  analysis  of 
any  fluid  in  which  inorganic  and  organic  prin- 
ciples are  so  closely  united ;  for  there  is  no 
more  delicate  problem  in  analytical  chemistry 
than  the  determination  of  the  presence  and  the 
proportions  of  inorganic  substances  united  with 
organic  matter.  Of  the  animal  fluids  which  are  easily  obtained,  the  blood,  from  the  large 
proportion  of  different  organic  principles  which  enter  into  its  composition,  presents  the 
greatest  difficulties  to  the  analytical  chemist.  Another  difficulty  is  the  necessity  of  a 
proximate,  and  not  an  ultimate  analysis.  It  is  not  sufficient  to  give  the  amount  of  cer- 
tain chemical  elements  which  the  blood  contains;  we  must  ascertain  the  amount  of 
these  elements  in  the  state  of  union  with  each  other  to  form  proximate  principles. 

Most  of  the  constituents  of  the  blood  are  found  both  in  the  corpuscles  and  plasma. 
It  is  difficult  to  determine  all  of  the  different  constituents  of  these  two  parts  of  the  blood. 
It  has  been  shown,  however,  by  Schmidt,  of  Dorpat,  that  the  phosphorized  fats  are  more 
abundant  in  the  globules,  while  the  fatty  acids  are  more  abundant  in  the  plasma.  The 
salts  with  a  potash-base  have  been  found  by  the  same  observer  to  exist  almost  entirely 
in  the  corpuscles,  and  the  soda-salts  are  four  times  more  abundant  in  the  plasma  than  in 
the  corpuscles.  In  addition  to  the  nutritive  principles,  we  have,  entering  into  the  com- 
position of  the  blood,  urea,  cholesterine,  urate  of  soda,  creatine,  creatinine,  and  other 
substances  the  characters  of  which  are  not  yet  fully  determined,  belonging  to  the  class 
of  excrementitious  principles.  Their  consideration  comes  more  appropriately  under  the 
head  of  excretion,  and  they  will  be  fully  taken  up  in  the  chapters  devoted  to  that  subject. 


FIG.  7.— Crystallised  hcemaglobine.    (Gautier.) 
a,  &,  crystals  from  the  venous  blood  of  man ;  c,  blood 
of  the  cat ;  d,  blood  of  the  Guinea  pig ;  e,  blood 
of  the  marmot :  f.  blood  of  the  squirrel, 
tier.) 


(Gau- 


COMPOSITION  OF  THE  BLOOD-PLASMA.  19 


Analysis  of  the  Blood. 

In  the  analyses  given  in  the  older  works  on  physiology,  the  blood,  having  been  divided 
into  plasma  and  corpuscles,  was  supposed  to  contain,  in  the  plasma,  two  organic  princi- 
ples, called  albumen  and  fibrin.  Recent  investigations,  however,  have  shown  that  the 
organic  constituents  of  the  plasma  are  more  complex ;  and  the  more  modern  analyses  of 
the  blood  give  other  organic  principles,  which  have  been  separated  by  new  methods. 
As  these  have  been  very  generally  accepted  by  modern  writers,  it  becomes  necessary  to 
describe  them  in  detail,  and  we  shall  adopt  the  new  nomenclature,  as  far  as  the  different 
organic  principles  have  been  established  by  definite  observations.  An  argument  in  favor 
of  this  subdivision  of  the  matters  formerly  recognized  as  fibrin  and  albumen  is  the  fact, 
which  has  long  been  apparent,  that  the  organic  constituents  of  the  blood,  particularly 
albumen,  are  known  to  possess  certain  peculiar  properties  which  distinguish  them  from 
these  principles  as  they  are  found  elsewhere.  The  following  table,  which  we  have  care- 
fully compiled  from  recent  authorities,  particularly  Robin,  gives  approximative^  the  quan- 
tities of  the  different  constituents  of  the  blood-plasma.  These  may  be  divided  into  the 
following  classes:  1.  Inorganic  principles;  2.  Organic  saline  principles;  3.  Organic  non- 
nitrogenized  principles ;  4.  Excrementitious  matters ;  5.  Organic  nitrogenized  principles. 


Composition  of  the  Blood-Plasma. 
Specific  gravity,  1,028. 

Water,  779  parts  per  1,000  in  the  male ;  791  parts  per  1,000  in  the  female. 
Chloride  of  sodium,  3  to  4  parts  per  1,000. 
"         "  potassium,  0'359  parts  per  1,000. 
"         "  ammonium,  proportion  not  determined. 
Sulphate  of  potassa,  0'288  parts  per  1,000. 

"       "  soda,  proportion  not  determined. 
Carbonate  of  potassa,     "          "  " 

"  soda  (with  bicarbonate  of  soda),  1-200  parts  per  1,000. 
"  lime,  proportion  not  determined. 
"          "  magnesia,     "        "  " 

Phosphate  of  lime  of  the  bones,  and  neutral  phosphate, 
"  magnesia, 

"  potassa,  L  1-500  parts  per  1,000. 

"   iron  (probable), 

Basic  phosphates  and  neutral  phosphate  of  soda, 
Silica,  copper,  lead,  and  magnesia,  traces  occasionally. 
Lactate  of  soda,  proportion  not  determined. 

"       "  lime  (probable),  proportion  not  determined. 
Pneumate  of  soda,  "  «          " 

Oleate  of  soda, 


o 

.S       CQ 


Margarate  of  soda, 
Stearate      "      " 


Oleine, 

Margarine, 

Stearine, 

§  '§,  \    Lecethine,  containing' nitrogen  and  called  phosphorized  fatty  matter,  0'400  parts  per  1,000. 
.2  TJ        Glucose,  0-002  parts  per  1,000. 
go  -a    I    Glycogenic  matter,  proportion  not  determined. 
O   Sj   L  Inosite  (muscles),  "  "  " 


20  THE  BLOOD. 

Carbonic  acid  in  solution. 

Urea,  0*177  parts  per  1,000,  in  arterial  blood;  0'088,  in  the  blood  of  the  renal  vein. 

Urate  of  soda,  proportion  not  determined. 


"  potassa  (probable),  proportion  not  determined. 

"      "  lime,  "  "          "  " 

"      "  magnesia,    "  "          "  " 

"      "  ammonia,     "  "          "  " 

Sudorates  of  soda,  etc.,  "          "  " 

Inosates,  "          "  " 


u 


Oxalates, 
H  Creatinine,  " 

Leucine,  "          "  " 

Hypoxanthine,  "          "  " 

Cholesterine,  0'455  to  0'751  parts  per  1,000,  in  the  entire  blood. 

,,  .   ,,  ,    (    Fibrin,  3  parts  per  1,000. 

Plasmme,  25  parts  (dried)  per  1,000.  J    . 

|    Metalbumen,  22  parts  per  1,000. 

Serine,  53  parts  (dried)  per  1,000. 

(Moist  fibrin,  8'820  parts  per  1,000,  in  the  entire  blood. 

Metalbumen  and  serine  constitute  the  albumen  of  the  older  analyses.     Albumen, 

about  75  parts  [dried]  and  330  parts  [moist]  per  1,000,  in  the  entire  blood.) 

Peptones,  4  parts  (dried)  and  28  parts  (moist)  per  1,000. 

Coloring  matters  of  the  plasma,  proportion  and  characters  not  determined. 

We  shall  take  the  above  table  as  a  guide  for  our  study  of  the  individual  constituents 
of  the  blood-plasma.  As  regards  gases,  in  addition  to  carbonic  acid,  which  we  have 
classed  with  the  excrementitious  matters,  the  blood  contains  oxygen,  nitrogen,  and 
hydrogen.  The  nitrogen  and  hydrogen  are  not  important,  and  the  relations  of  oxygen 
will  be  fully  considered  under  the  head  of  respiration.  Most  of  the  coloring  matter  of 
the  blood  exists  in  the  red  corpuscles,  which  contain  a  peculiar  principle  which  we 
have  already  considered  in  connection  with  the  chemical  constitution  of  these  bodies. 

In  studying  the  composition  of  the  blood,  as  well  as  the  composition  of  food,  the 
tissues,  secreted  fluids,  etc.,  it  is  convenient  to  divide  its  constituents  into  classes,  and  this 
we  have  done  in  the  simplest  manner  possible. 

It  is  evident,  the  blood  receiving  all  the  products  of  disassimilation  as  well  as  the 
nutritive  principles  resulting  from  digestion,  that  there  should  be  a  division  of  its  con- 
stituents into  nutritive  and  excrementitious.  We  have  classed  certain  principles  together 
as  excrementitious.  These  are  the  various  products  of  disassimilation  of  the  organism, 
which  are  taken  up  by  the  blood  or  conveyed  to  the  blood-vessels  by  the  lymphatics, 
exist  in  the  blood  in  small  quantity,  and  are  constantly  being  separated  from  the  blood 
by  the  different  excreting  organs.  Their  constant  removal  from  the  blood  is  the  expla- 
nation of  the  excessively  minute  proportion  in  which  they  exist  in  this  fluid.  Their 
relations  to  the  organism  will  be  fully  considered  under  the  head  of  excretion. 

Excluding,  then,  for  the  present,  all  consideration  of  the  products  of  disassimilation, 
we  have  to  study  the  various  constituents  of  the  blood  that  are  more  or  less  directly 
concerned  in  nutrition. 

Physiological  chemists  recognize  certain  constituents  of  the  organism,  called  proxi- 
mate principles,  which  may  be  elementary  substances,  but  which  are  more  frequently 
compounds.  We  speak  of  chloride  of  sodium  as  a  proximate  principle  existing  in  the 
blood,  because,  as  chloride  of  sodium,  it  gives  to  the  blood  certain  properties.  We  do  not 
regard  the  chemical  elements,  chlorine  and  sodium,  as  proximate  principles,  because  they 
do  not  exist  in  the  blood  uncombined.  Still,  a  proximate  principle  may  be  a  chemical 
element,  as  in  the  case  of  oxygen,  which,  as  oxygen,  performs,  in  the  blood,  certain 
important  functions. 

Adopting,  in  the  main,  the  definition  given  by  Eobin,  we  may  regard  as  a  proximate 


COMPOSITION  OF  THE   BLOOD-PLASMA.  21 

principle,  a  substance  extracted  from  the  body,  winch  cannot  be  subdivided  without 
chemical  decomposition  and  loss  of  certain  characteristic  properties.  This  definition 
will  apply  to  all  classes  of  proximate  principles,  organic  as  well  as  inorganic. 

Taking  as  a  basis,  the  classification  proposed  by  Robin,  we  may  divide  the  proximate 
principles  of  the  blood,  and,  indeed,  of  the  entire  organism,  as  follows : 

1.  Inorganic  Principles. — This  class  is  of  inorganic  origin,  definite  chemical  compo- 
sition, and  crystallizable.     The  substances  forming  it  are  all  introduced  from  without, 
and  are  all  discharged  from  the  body  in  the  same  form  in  which  they  entered.     They 
never  exist  alone,  but  are  always  combined  with  the  organic  principles,  to  form  the 
organized  fluids  or  solids.     This  union  is  "  atom  to  atom,"  and  so  intimate  that  they  are 
taken  up  with  the  organic  elements,  as  the  latter  are  worn  out  and  become  effete,  and 
are  discharged  from  the  body,  although  themselves  unchanged.     To  supply  the  place  of 
the  principles  thus  thrown  off,  a  fresh  quantity  is  deposited  in  the  process  of  nutrition. 
They  give  to  the  various  organs  important  properties ;  and,  although  identical  with  sub- 
stances in  the  inorganic  world,  in  the  interior  of  the  body,  they  behave  as  organic  sub- 
stances.    They  require  no  special  preparation  for  absorption,  but  are  soluble  and  taken 
in  unchanged.     They  are  received  into  the  body  in  about  the  same  proportion  at  all 
periods  of  life,  but  their  discharge  is  notably  diminished  in  old  age,  giving  rise  to  cal- 
careous incrustations  and  deposits  and  a  considerable  increase  in  the  calcareous  matter 
entering  into  the  composition  of  the  tissues.     As  examples  of  this  class  we  may  cite 
water,  chloride  of  sodium,  the  carbonates,  sulphates,  phosphates,  and  other  inorganic 
salts. 

The  functions  of  water  in  the  blood  are  sufficiently  evident.  It  acts  as  a  solvent  for 
the  inorganic  salts,  the  organic  salts,  and  the  excrementitious  matters.  In  conjunction 
with  the  nitrogenized  principles,  it  constitutes  a  medium  in  which  the  corpuscles  are  sus- 
pended without  solution. 

The  various  salts  enumerated  in  the  table  exist  in  solution  in  water  and  are  more  or 
less  intimately  combined  with  the  coagulable  organic  principles.  Of  these,  the  chloride 
of  sodium  is  the  most  abundant.  It  undoubtedly  has  an  important  function  in  giving 
density  to  the  plasma  and  in  regulating  the  processes  of  endosmosis  and  exosmosis.  In 
connection  with  the  organic  salts  and  crystallizable  excrementitious  matters,  it  may  be 
stated,  in  general  terms,  that  the  blood  contains  from  14  to  10  parts  per  1,000  of  matters 
in  actual  solution,  of  which  from  6  to  8  parts  consist  of  inorganic  salts.  The  presence  of 
these  principles  in  solution,  with  the  organic  coagulable  principles,  prevents  the  solution 
of  the  corpuscular  elements  of  the  blood.  The  presence  of  the  chlorides  and  the  alka- 
line sulphates  assists  in  dissolving  the  sulphates,  carbonates,  and  the  calcareous  phos- 
phates. A  portion  of  the  carbonates  and  phosphates  are  decomposed  in  the  system  and 
furnish  bases  for  certain  of  the  organic  salts,  such  as  the  lactates,  nrates,  etc. 

2.  Organic  Saline  Principles. — These  principles  are  for  the  most  part  formed  in  the 
organism,  and  they  exist  in  the  blood  in  very  small  quantity.     The  lactates  are  probably 
produced  by  decomposition  of  a  portion  of  the  bicarbonates  and  the  union  of  the  bases 
with  lactic  acid,  the  lactic  acid  resulting  from  a  change  of  a  portion  of  the  saccharine 
matter  in  the  blood.     The  pneumate  of  soda  is  the  result  of  the  union  of  pneumic  acid, 
an  acid  principle  found  in  the  lungs,  with  the  base.     The  physiological  relations  of  these 
principles  are  little  understood.     The  salts  formed  by  the  union  of  fatty  acids  with  bases 
are  probably  produced  by  decomposition  of  the  fatty  principles,  a  great  part  of  which  is 
derived  from  the  food. 

3.  Organic  Non-nitrogenized  Principles. — These  usually  exist  in  the  blood  in  small 
quantity  and  are  derived  mainly  from  the  food.   Lecethine,  although  it  contains  nitrogen, 
is  introduced  into  this  class  because  it  presents  many  of  the  properties  of  the  fats.     It 
exists  in  the  blood,  bile,  nervous  substance,  and  the  yolk  of  egg.     This  principle  is  sup- 
posed by  Robin  to  be  almost  identical  with  protagon.     Its  chemical  properties  and 
physiological  relations  are  not  well  understood.     The  saccharine  principles  and  glyco- 


22  THE  BLOOD. 

genie  matter  are  derived  in  part  from  the  food  and  in  part  from  the  liver,  where  sugar 
and  glycogenic  matter  are  manufactured.  They  are  of  organic  origin,  definite  chemical 
composition,  and  crystallizable.  The  fats  and  sugars  are  distinguished  from  other  or- 
ganic principles  by  the  fact  that  they  are  composed  of  carbon,  hydrogen,  and  oxygen. 
In  the  sugars,  the  hydrogen  and  oxygen  exist  in  the  proportion  to  form  water,  which 
fact  has  given  them  the  name  of  hydrocarbons  or  hydrates  of  carbon.  The  principles 
of  this  class  play  an  important  part  in  development  and  nutrition.  One  of  them,  sugar, 
appears  very  early  in  foetal  life,  formed  first  by  the  placenta,  and  afterward  by  the  liver, 
its  formation  by  the  latter  organ  continuing  during  life.  Fat  is  a  necessary  element  of 
food,  and  is  also  formed  in  the  interior  of  the  body.  The  exact  influence  which  these 
substances  have  on  development  and  nutrition  is  not  known ;  but  experiments  and  obser- 
vation have  shown  that  this  influence  is  important.  They  will  be  considered  more  fully 
under  the  head  of  nutrition. 

4.  Excrementitious  Matters. — A  full  consideration  of  these  principles,  which  are  all 
formed  by  the  process  of  disassimilation  of  the  tissues  and  are  taken  up  by  the  blood  to 
be  eliminated  by  the  proper  organs,  belongs  to  excretion.     The  relations  of  carbonic 
acid  to  the  system  will  be  fully  considered  in  connection  with  respiration. 

5.  Organic  Nitrogenized  Principles. — This  class  of  proximate  principles  is  of  organic 
origin,  indefinite  chemical  composition,  and  non-crystallizable.     Substances  forming  this 
class  are  apparently  the  only  principles  which  are  endowed  with  so-called  vital  properties, 
taking  materials  for  their  regeneration  from  the  nutritive  fluids  and  appropriating  them  to 
form  part  of  their  own  substance.     Considered  from  this  point  of  view,  they  are  differ- 
ent  from  any  thing  which  is  met  with  out  of  the  living  body.     They  are  all,  in  the  body, 
in  a  state  of  continual  change,  wearing  out  and  becoming  effete,  when  they  are  trans- 
formed into  excrementitious  substances.     The  process  of  repair  in  this  instance  is  not 
the  same  as  in  inorganic  substances,  which  enter  and  are  discharged  from  the  body  with- 
out undergoing  any  change.     The  analogous  substances  which  exist  in  food  undergo  a 
very  elaborate  preparation  by  digestion,  before  they  can  even  be  absorbed  by  the  blood- 
vessels ;  and  still  another  change  takes  place  when  they  are  appropriated  by  the  various 
tissues.    They  exist  in  all  the  solids,  semisolids,  and  fluids  of  the  body,  never  alone,  but 
always  combined  with  inorganic  substances.     As  a  peculiarity  of  chemical  constitution, 
they  all  contain  nitrogen,  which  has  given  them  the  name  of  nitrogenized  or  azotized 
principles.    In  studying  their  properties  more  fully,  we  shall  see  that  they  are  by  far  the 
most  important  elements  in  the  organism.     The  elaborate  preparation  which  they  require 
for  absorption  involves  the  most  important  part  of  the  function  of  digestion.     Their  ab- 
solute integrity  is  necessary  to  the  operation  of  the  essential  functions  of  many  tissues, 
as  muscular  contraction  or  conduction  of  nervous  force.     An  exact  knowledge  of  all 
the  transformations  which  take  place  in  their  regeneration  and  the  process  by  which 
they  are  converted  into  effete  or  excrementitious  matters  would  enable  us  to  comprehend 
nutrition,  which  is  the  most  important  part  of  physiology ;  but  as  yet  we  know  little  of 
these  changes,  and  may  consider  ourselves  fortunate  in  understanding  a  few  of  the  laws 
in  accordance  with  which  they  are  regulated. 

Of  the  different  classes  of  proximate  principles  existing  in  the  blood,  it  is  at  once 
apparent  that  the  organic  nitrogenized  principles  are  more  complex  in  their  constitution, 
properties,  and  functions  than  the  other  classes.  These  principles,  as  they  exist  in  the 
blood,  possess  peculiar  and  characteristic  properties,  which  it  will  be  necessary  to  study 
in  detail. 

Plasmine,  Fibrin,  Metalbumen,  Serine. — The  name  plasmine  was  given  by  Denis  to  a 
peculiar  principle  which  he  extracted  from  the  blood  by  the  following  process :  The 
blood  drawn  directly  from  an  artery  or  vein  is  received  into  a  vessel  containing  one-sev- 
enth part  of  its  volume  of  a  concentrated  solution  of  sulphate  of  soda,  which  prevents 
coagulation ;  in  a  short  time  the  corpuscles  gravitate  to  the  bottom  of  the  vessel,  and 


PLASMIKE,  FIBRIN,  METALBUMEN,  SERINE,  PEPTONES,  ETC.        23 

the  plasma  may  be  separated  by  decantation ;  to  the  plasma  is  added  an  excess  of  pul- 
verized chloride  of  sodium,  when  a  soft,  pulpy  substance  is  precipitated,  which  is  plas- 
mine.  This  substance,  after  desiccation,  bears  a  proportion  of  about  twenty-five  parts 
per  thousand  of  blood.  It  is  soluble  in  from  ten  to  twenty  parts  of  water,  when  a  por- 
tion of  it  coagulates  and  may  be  removed  by  stirring  with  twigs  or  a  bundle  of  broom- 
corn,  in  the  way  in  which  fibrin  is  separated  from  the  blood.  The  fibrin  thus  separated 
is  called  by  Denis  concrete  fibrin,  and  the  substance  which  remains  in  solution,  dissolved 
fibrin.  By  most  writers  of  the  present  day,  the  dissolved  fibrin  of  Denis  is  called  metal- 
bumen,  a  name  which  we  shall  adopt. 

According  to  Denis,  plasmine  is  a  proximate  principle  of  the  blood,  and,  after  extrac- 
tion by  the  process  just  described,  is  decomposed  into  concrete  fibrin  and  dissolved 
fibrin,  or  metalbumen.  Having  removed  the  concrete  fibrin  from  the  solution  of  plas- 
mine, the  metalbumen  is  coagulated  by  the  addition  of  sulphate  of  magnesia,  which  does 
not  coagulate  ordinary  albumen.  The  proportion  of  dried  metalbumen  in  the  blood  is 
about  twenty-two  parts  per  thousand.  The  proportion  of  dried  fibrin  is  about  three 
parts  per  thousand. 

After  the  extraction  of  plasmine  from  the  blood,  another  coagulable  substance  re- 
mains, which  is  called  serine.  This  is  coagulated  by  heat,  the  strong  mineral  acids,  and 
absolute  alcohol,  but  is  not  coagulated  by  ether,  which  coagulates  albumen  of  the  white 
of  egg.  Serine  bears  a  close  resemblance  to  ordinary  albumen,  but  is  stated  to  be  much 
more  osmotic.  Its  proportion,  desiccated,  in  the  blood  is  about  fifty-three  parts  per 
thousand. 

We  cannot  admit  the  existence  of  new  coagulable  principles  in  the  blood  unless  it  be 
shown  that  the  processes  by  which  they  are  extracted  do  not  involve  decomposition  of 
established  proximate  constituents.  The  processes  just  described  do  not  seem  to  involve 
artificial  decomposition.  It  is  perfectly  proper,  in  analyzing  the  blood,  to  prevent  spon- 
taneous coagulation  by  the  addition  of  the  sulphate  of  soda,  as  this  salt  simply  keeps 
the  blood  fluid  without  apparently  changing  its  organic  constituents,  and  the  plasmine  is 
simply  precipitated  by  the  chloride  of  sodium.  It  is  evident,  also,  that  the  substance 
called  metalbumen,  being  coagulated  by  sulphate  of  magnesia,  is  not  albumen,  and 
serine  also  presents  some  important  points  of  difference  from  albumen.  Admitting  the 
existence,  then,  of  plasmine  and  serine,  it  is  important  to  understand  clearly  the  charac- 
ters of  these  principles  as  compared  with  what  were  formerly  called  fibrin  and  albumen. 

Instead  of  fibrin  and  albumen  in  the  blood,  we  now  recognize  two  new  principles,  in 
the  natural  condition  of  the  circulating  fluid,  which  are  called  plasmine  and  serine.  The 
substance  known  as  fibrin  is  one  of  the  products  of  decomposition  of  plasmine.  Metal- 
bumen and  serine  constitute  what  was  formerly  called  albumen.  Fibrin  is  not  a  proxi- 
mate principle,  but  is  formed  in  the  spontaneous  decomposition  of  plasmine.  Metalbu- 
men is  the  other  product  of  decomposition  of  plasmine.  The  fibrin  of  arterial  blood 
has  long  been  known  to  differ  somewhat  from  the  fibrin  of  venous  blood,  when  the  blood 
has  been  allowed  to  coagulate  spontaneously.  Arterial  fibrin  is  insoluble  in  a  solution 
of  chloride  of  sodium  which  will  dissolve  the  fibrin  of  venous  blood. 

Peptones,  etc. — A  certain  quantity  of  nitrogenized  matter,  distinct  from  the  principles 
just  described,  has  been  extracted  from  the  blood,  which  is  analogous  to  peptone  or 
albuminose.  This  is  separated  by  coagulating  the  serum  of  the  blood  with  hot  acetic 
acid  and  filtering,  when  the  peptones  pass  through  in  the  filtrate.  These  principles  are 
probably  derived  from  the  food.  Their  proportion  in  the  plasma  is  about  four  parts, 
dried,  per  thousand,  or  twenty-eight  parts  before  desiccation. 

A  small  quantity  of  coloring  matter  exists  in  the  plasma.  If  we  separate  the  corpus- 
cles as  completely  as  possible,  the  clear  liquid  still  has  a  reddish-amber  color.  This  col- 
oring matter  has  never  been  isolated  and  studied.  It  is  analogous  to  the  coloring  mat- 
ters of  the  red  corpuscles,  the  bile,  and  the  urine. 


24  THE  BLOOD. 

In  addition  to  the  organic  nitrogenized  principles  which  we  have  described,  some 
authors  recognize  a  substance  called  paraglobuline,  or  fibrinoplastic  matter,  and  fibrino- 
genic  matter.  These  are  supposed  to  be  factors  of  fibrin,  which  come  together  in  the 
coagulation  of  the  blood.  They  will  be  considered  in  connection  with  the  theories  of 
coagulation.  The  so-called  albuminates  of  soda  and  potassa  have  not  been  positively 
established  as  proximate  principles. 

Coagulation  of  the  Blood. 

The  remarkable  property  in  the  blood  of  spontaneous  coagulation  has  been  recog- 
nized almost  as  far  back  as  we  can  look  into  the  history  of  physiology ;  and,  since  the 
discovery  of  the  circulation,  there  have  been  few  subjects  connected  with  the  physiology 
of  the  blood  which  have  excited  more  universal  interest ;  but  the  ideas  with  regard  to 
the  cause  of  this  phenomenon  were  for  a  long  time  entirely  speculative.  The  first  defi- 
nite experiments  upon  this  subject  were  performed  by  Malpighi.  He  was  followed  by 
Borelli,  Kuysch,  and  a  host  of  others,  who  hold  conspicuous  places  in  the  history  of  our 
science,  among  whom  may  be  mentioned  Hunter,  Hew  son,  Muller,  Thackrah,  J.  Davy, 
Magendie,  Nasse,  and  Dumas.  Although  much  labor  has  been  expended  on  this  subject, 
the  final  cause  of  coagulation  is  by  no  means  definitely  settled. 

The  blood  retains  its  fluidity  while  it  remains  in  the  vessels  and  circulation  is  not 
interfered  with.  It  is  then  composed,  as  we  have  seen,  of  a  clear  plasma,  holding  cor- 
puscles in  suspension.  Shortly  after  the  circulation  is  interrupted,  or  after  blood  is 
drawn  from  the  vessels,  it  coagulates  or  "  sets  "  into  a  jelly-like  mass.  In  a  few  hours, 
we  find  that  contraction  has  taken  place,  and  a  clear,  straw-colored  fluid  has  been  ex- 
pressed, the  blood  thus  separating  into  a  solid  portion,  the  crassamentum,  or  clot,  and  a 
liquid,  which  is  called  serum.  The  serum  contains  all  the  elements  of  the  blood  except 
the  red  corpuscles  and  fibrin,  which  together  form  the  clot.  Coagulation  takes  place  in 
the  blood  of  all  animals,  commencing  a  variable  time  after  its  removal  from  the  vessels. 
In  the  human  subject,  according  to  Nasse,  when  the  blood  is  received  into  a  moderately- 
deep,  smooth  vessel,  the  phenomena  of  coagulation  present  themselves  in  the  following 
order : 

First,  a  gelatinous  pellicle  forms  on  the  surface,  which  occurs  in  from  one  minute  and 
forty-five  seconds  to  six  minutes ;  in  from  two  to  seven  minutes,  a  gelatinous  layer  has 
formed  on  the  sides  of  the  vessel ;  and  the  whole  mass  becomes  of  a  jelly -like  consistence,  in 
from  seven  to  sixteen  minutes.  Contraction  then  begins,  and,  if  we  watch  the  surface 
of  the  clot,  we  see  little  drops  of  clear  serum  making  their  appearance.  This  fluid  in- 
creases in  quantity,  and,  in  from  ten  to  twelve  hours,  separation  is  complete.  The  clot, 
which  is  heavier,  sinks  to  the  bottom  of  the  vessel,  unless  it  contain  bubbles  of  gas  or 
the  surface  be  very  concave.  In  most  of  the  warm-blooded  animals,  the  blood  coagulates 
more  rapidly  than  in  man.  It  is  particularly  rapid  in  the  class  of  birds,  in  some  of  which 
it  takes  place  almost  instantaneously.  Observations  have  shown  that  coagulation  is  more 
rapid  in  arterial  than  in  venous  blood.  In  the  former,  the  proportion  of  fibrin  formed  is 
notably  greater,  and,  as  we  have  seen,  the  characters  of  the  fibrin  are  somewhat  differ- 
ent. A  solution  of  chloride  of  sodium  dissolves  the  fibrin  of  venous  blood,  but  does  not 
dissolve  the  fibrin  of  an  arterial  clot. 

The  relative  proportions  of  the  serum  and  clot  are  very  variable,  unless  we  include  in 
our  estimate  of  the  serum  that  portion  which  is  retained  between  the  meshes  of  the  coag- 
ulated mass.  As  the  clot  is  composed  of  corpuscles  and  fibrin,  and  as  these  in  their 
moist  state  represent  in  general  terms  about  one-half  of  the  blood,  it  may  be  stated 
that,  after  coagulation,  the  actual  proportions  of  the  clot  and  serum  are  about  equal. 
If  we  take  simply  the  serum  which  separates  spontaneously,  we  have  a  large  quantity 
when  the  clot  is  densely  contracted,  and  a  very  small  quantity  when  it  is  loose  and 
soft.  Usually,  the  clot  retains  about  one-fifth  of  the  serum. 


COAGULATING  PRINCIPLE   OF  THE  BLOOD.  25 

Characters  of  the  Clot. — On  removing  the  clot,  after  the  separation  of  the  serum  is 
complete,  it  presents  a  gelatinous  consistence,  and  is  more  or  less  firm,  according  to  the 
degree  of  contraction  which  has  taken  place.  As  a  general  rule,  when  coagulation  has 
been  rapid,  the  clot  is  soft  and  but  slightly  contracted.  When,  on  the  other  hand,  coagu- 
lation has  been  slow,  it  contracts  for  a  long  time  and  is  much  denser.  When  coagulation 
is  slow,  the  clot  frequently  presents  what  is  known  as  the  cupped  appearance,  having  a 
concave  surface,  a  phenomenon  which  depends  merely  on  the  extent  of  its  contraction. 
It  also  presents  a  marked  difference  in  color  at  its  upper  portion.  The  blood  having 
remained  fluid  for  some  time,  the  red  corpuscles  settle,  by  virtue  of  their  greater  weight, 
leaving  a  colorless  layer  on  the  top.  This  is  the  buffy-coat  spoken  of  by  some  authors. 
Although  this  frequently  presents  itself  in  the  blood  drawn  in  inflammations,  it  is  by  no 
means  pathognomonic  of  this  condition,  and  is  liable  to  occur  whenever  coagulation  is 
slow  or  has  been  retarded  by  artificial  means.  It  is  always  present  in  the  blood  of  the 
horse.  Examined  microscopically,  the  buffy-coat  presents  fibrils  of  coagulated  fibrin 
with  some  of  the  white  corpuscles  of  the  blood.  On  removing  a  clot  of  venous  blood 
from  the  serum,  the  upper  surface  is  florid  from  contact  with  the  air,  while  the  rest  of  it 
is  dark ;  and,  on  making  a  section,  if  the  coagulation  have  not  been  too  rapid,  the  gravi- 
tation of  the  red  corpuscles  is  apparent.  The  section,  which  is  at  first  almost  black,  soon 
becomes  red  from  contact  with  the  atmosphere.  If  the  clot  be  cut  into  small  pieces,  it 
will  undergo  farther  contraction,  and  express  a  part  of  the  contained  serum.  If  the  clot 
be  washed  under  a  stream  of  water,  at  the  same  time  kneading  it  with  the  fingers,  we 
may  remove  almost  all  the  red  corpuscles,  leaving  the  meshes  of  fibrin,  which,  on  micro- 
scopical examination,  presents  the  fibrillated  appearance  to  which  we  have  already  referred. 

Characters  of  the  Serum. — After  coagulation,  if  the  serum  be  carefully  removed,  it 
is  found  to  be  a  fluid  of  a  color  varying  from  a  light  amber  to  quite  a  deep,  but  clear  red. 
This  depends  upon  a  peculiar  coloring  matter  which  has  never  been  isolated.  The  specific 
gravity  of  the  serum  is  about  1028,  somewhat  less  than  that  of  the  entire  mass  of  blood. 
It  contains  all  the  principles  found  in  the  plasma,  or  liquor  sanguinis,  with  the  exception 
of  the  elements  of  fibrin.  It  can  hardly  be  called  a  physiological  fluid,  as  it  is  formed 
only  after  coagulation  of  the  blood  and  never  exists  isolated  in  the  body.  The  effusions 
which  are  commonly  called  serum,  although  they  resemble  this  fluid  in  some  particulars, 
are  not  identical  with  it,  being  formed  by  a  process  of  transudation  rather  than  separa- 
tion from  the  blood,  as  in  coagulation.  The  serum  must  not  be  confounded  with  the 
plasma  or  liquor  sanguinis,  which  is  the  natural  clear  portion  of  the  blood. 

Coagulating  Principle  of  the  Blood. — Acquainted,  as  we  are,  with  the  properties  of 
fibrin,  it  is  evident  that  this  substance  is  the  agent  which  produces  coagulation  of  the 
blood.  In  fact,  whatever  coagulates  spontaneously  is  called  fibrin,  and  whatever  requires 
some  agent  to  produce  this  change  of  consistence  is  called  by  another  name.  But,  before 
the  properties  of  fibrin  were  fully  understood,  the  question  of  the  coagulating  principle 
was  a  matter  of  much  discussion.  Malpighi  was  probably  the  first  to  isolate  fibrin,  which 
he  did  by  washing  the  clot  in  a  stream  of  water,  which  removed  the  corpuscles  and  left  a 
whitish,  fibrous  net-work.  His  experiments  are  set  forth  in  an  article  in  which  he  at- 
tempted to  show  that  the  so-called  polypi  of  the  heart  were  formed  of  fibrin,  although  it 
was  not  then  called  by  that  name.  These  observations  were  soon  confirmed  by  others ; 
and  it  then  became  a  question  whether  this  substance  existed  as  a  fluid  in  the  liquor  san- 
guinis, or  was  furnished  by  the  corpuscles  after  the  removal  of  blood  from  the  vessels. 
This  was  decided  by  Hewson,  whose  simple  and  conclusive  experiments  leave  no  doubt 
that  coagulation  of  the  blood  is  due  to  fibrin,  and  that  this  substance  is  entirely  distinct 
from,  and  independent  of  the  corpuscles.  This  observer,  taking  advantage  of  the  prop- 
erty possessed  by  certain  saline  substances  of  preventing  the  coagulation  of  the  blood, 
was  the  first  to  separate  the  liquor  sanguinis  from  the  corpuscles.  He  mixed  fresh  blood 


26  THE  BLOOD. 

with  a  little  sulphate  of  soda,  which  prevented  coagulation,  and,  after  the  mixture  had 
been  allowed  to  stand  for  a  time,  the  corpuscles  gravitated  to  the  bottom  of  the  vessel. 
The  clear  fluid  was  then  decanted  and  diluted  with  twice  its  quantity  of  water,  when 
fibrin  became  coagulated. 

The  facts  thus  demonstrated  by  Hewson  were  confirmed  by  Miiller,  in  1832.  He  suc- 
ceeded in  separating  the  plasma  from  the  corpuscles  in  the  blood  of  the  frog  by  simple 
filtration,  first  diluting  it  with  a  saccharine  solution.  The  great  size  of  the  corpuscles  in 
this  animal  prevents  their  passage  through  a  filter,  and  the  clear  fluid  which  is  thus  sepa- 
rated soon  forms  a  colorless  coagulum. 

From  these  observations,  it  is  evident  that  the  coagulation  of  the  blood  is  due  to  the 
formation  of  fibrin.  Coagulation  of  this  substance  first  causes  the  whole  mass  of  blood 
to  assume  a  gelatinous  consistence ;  and,  by  virtue  of  its  contractile  properties,  it  soon 
expresses  the  serum,  while  the  red  corpuscles  are  retained.  One  of  the  causes  which 
operate  to  retain  the  corpuscles  in  the  clot  is  the  adhesive  matter  which  covers  their 
surface  after  they  escape  from  the  vessels,  which  produces  the  arrangement  in  rows  like 
piles  of  coin,  which  we  have  already  noted  under  the  head  of  microscopical  appearances. 
This  undoubtedly  prevents  those  which  are  near  the  surface  from  escaping  from  the  clot 
during  its  contraction. 

Circumstances  which  modify  Coagulation  out  of  the  Body. — The  conditions  which 
modify  coagulation  of  the  blood  have  been  closely  studied  by  Hewson,  Davy,  Thackrah, 
Kobin  and  Verdeil,  and  others.  They  are,  in  brief,  the  following : 

Blood  flowing  slowly  from  a  small  orifice  is  more  rapidly  coagulated  than  when  it 
is  discharged  in  a  full  stream  from  a  large  orifice.  If  it  be  received  into  a  shallow 
vessel,  it  coagulates  much  more  rapidly  than  when  received  into  a  deep  vessel.  If  the 
vessel  be  rough,  coagulation  is  more  rapid  than  if  it  be  smooth  and  polished.  If  the 
blood,  as  it  flows,  be  received  on  a  cloth  or  a  bundle  of  twigs,  it  coagulates  almost  in- 
stantaneously. In  short,  it  appears  that  all  circumstances  which  favor  exposure  of  the 
blood  to  the  air  hasten  its  coagulation.  The  blood  will  coagulate  more  rapidly  in  a  va- 
cuum than  in  the  air. 

Coagulation  of  the  blood  is  prevented  by  rapid  freezing,  but  it  takes  place  afterward 
when  the  fluid  is  carefully  thawed.  Between  32°  and  140°  Fahr.,  elevation  of  tempera- 
ture increases  the  rapidity  of  coagulation.  According  to  Eichardson,  agitation  of  the 
blood  in  closed  vessels  retards,  and  in  open  vessels  hastens  coagulation. 

Various  chemical  substances  retard  or  prevent  coagulation.  Among  them  we  may 
mention  the  following :  solutions  of  potash  and  of  soda ;  carbonate  of  soda ;  carbonate 
of  ammonia ;  carbonate  of  potash ;  ammonia ;  sulphate  of  soda.  In  the  menstrual  flow, 
the  blood  is  kept  fluid  by  mixture  with  the  abundant  secretions  of  the  vaginal  mucous 
membrane. 

Coagulation  of  the  Blood  in  the  Organism. — The  blood  coagulates  in  the  vessels  after 
death,  though  less  rapidly  than  when  removed  from  the  body.  As  a  general  proposition, 
it  may  be  stated  that  this  takes  place  in  from  twelve  to  twenty-four  hours  after  circula- 
tion has  ceased.  Under  these  circumstances,  the  blood  is  found  chiefly  in  the  venous 
system,  as  the  arteries  are  generally  emptied  by  post-mortem  contraction  of  their  mus- 
cular coat ;  but,  in  the  veins,  coagulation  is  slow  and  imperfect.  Coagula  are  found, 
however,  in  the  left  side  of  the  heart  and  in  the  aorta,  but  they  are  much  smaller  than 
those  in  the  right  side  of  the  heart  and  in  the  large  veins.  These  coagula  present  the 
general  characters  we  have  already  described.  They  are  frequently  covered  by  a  soft, 
whitish  film,  analogous  to  the  buffy-coat,  and  are  dark  in  their  interior. 

It  was  supposed  by  John  Hunter  that  coagulation  of  the  blood  did  not  take  place  in 
animals  killed  by  lightning,  or  by  prolonged  muscular  exertion,  as  when  hunted  to  death ; 
but  it  appears  from  the  observations  of  others  that  this  view  is  not  correct.  J.  Davy 


COAGULATION  OF  THE   BLOOD  IN  THE   ORGANISM.  27 

reported  a  case  of  death  by  lightning  where  a  loose  coagulum  was  found  in  the  heart 
twenty-four  hours  after.  In  this  case,  decomposition  was  very  far  advanced,  and  it  is 
probable  that  the  coagulum  had  become  less  firm  from  that  cause.  His  observations  also 
show  that  coagulation  occurs  after  poisoning  by  hydrocyanic  acid,  and  in  animals  hunted 
to  death. 

Coagulation  in  different  parts  of  the  vascular  system  is  by  no  means  unusual  during 
life.  In  the  heart,  we  sometimes  find  coagula  which  bear  evidence  of  having  existed  for 
some  time  before  death.  These  were  called  polypi  by  some  of  the  older  writers,  and  are 
often  formed  of  fibrin  almost  free  from  red  corpuscles.  They  generally  occur  when  death 
is  very  gradual  and  when  the  circulation  continues  for  some  time  with  greatly-diminished 
activity.  It  is  probable  that  a  small  coagulum  is  first  formed,  from  which  the  corpuscles 
are  washed  away  by  the  current  of  blood ;  that  this  becomes  larger  by  farther  depositions, 
until  we  have  large,  vermicular  masses  of  fibrin,  attached,  in  some  instances,  to  the 
chorda?  tendinese.  Clots  produced  in  this  way  may  be  distinguished  from  those  formed 
after  death  by  their  whitish  color,  dense  consistence,  and  the  closeness  with  which  they 
adhere  to  the  walls  of  the  heart. 

Bodies  projecting  into  the  caliber  of  a  blood-vessel  soon  become  coated  with  a  layer 
of  fibrin.  Rough  concretions  about  the  orifices  of  the  heart  frequently  induce  the  deposi- 
tion of  little  masses  of  fibrin,  which  sometimes  become  detached  and  are  carried  to  vari- 
ous parts  of  the  circulatory  system,  as  the  lungs  or  brain,  plugging  up  one  or  more  of  the 
smaller  vessels.  The  experiment  has  been  made  of  passing  a  thread  through  a  small 
artery,  allowing  it  to  remain  for  a  few  hours,  when  it  is  found  coated  with  a  layer  of 
coagulated  fibrin. 

Blood  generally  coagulates  when  effused  into  the  areolar  tissue  or  into  any  of  the 
cavities  of  the  body ;  although,  effused  into  the  serous  cavities,  the  tunica  vaginalis  for 
example,  it  has  been  known  to  remain  fluid  for  days  and  even  weeks,  and  coagulate  when 
let  out  by  an  incision.  In  the  Graafian  follicles,  after  the  discharge  of  the  ovum,  we 
sometimes  have  the  cavity  filled  with  blood,  which  forms  a  clot  and  is  slowly  removed 
by  absorption. 

Coagulation  thus  takes  place  in  the  vessels  as  the  result  of  stasis  or  of  very  great  retarda- 
tion of  the  circulation,  and  in  the  tissues  or  cavities  of  the  body,  whenever  it  is  accident- 
ally effused.  In  the  latter  case,  it  is  generally  removed  in  the  course  of  time  by  absorp- 
tion. This  takes  place  in  the  following  way :  First,  we  have  disappearance  of  the  red 
corpuscles,  or  decoloration  of  the  clot,  and  the  fibrin  is  then  the  only  substance  which 
remains.  This  becomes  reduced  from  a  fibrillated  to  a  granular  condition,  softens,  finally 
becomes  amorphous,  and  is  absorbed ;  although,  when  the  size  of  the  clot  is  considerable, 
this  may  occupy  weeks,  and  even  months,  and  may  never  be  completely  effected.  Effused 
in  this  manner,  the  constituents  of  the  blood  act  as  foreign  bodies ;  the  corpuscles  cease 
to  be  organized  anatomical  elements  capable  of  self-regeneration,  breakdown,  and  are 
absorbed.  The  fibrin  which  remains  undergoes  the  same  process,  the  stages  through 
which  it  passes  being  always  those  of  decay,  and  not  of  development.  In  other  words, 
the  clot  is  incapable  of  organization. 

Office  of  the  Coagulation  of  the  Blood  in  arresting  Hemorrhage. — The  property  of  the 
blood  under  consideration  has  a  most  important  office  in  the  arrest  of  haemorrhage.  The 
effect  of  an  absence  or  great  diminution  of  the  coagulability  of  the  circulating  fluid  is 
exemplified  in  instances  of  what  is  called  the  haemorrhagic  diathesis ;  a  condition  in  which 
slight  wounds  are  apt  to  be  followed  by  alarming,  and  it  may  be  fatal  haemorrhage.  This 
condition  of  the  blood  is  not  characterized  by  any  peculiar  symptoms  except  the  obsti- 
nate flow  of  blood  from  slight  wounds ;  and  this  may  continue  for  years.  In  a  case 
which  came  under  our  observation  a  few  years  since,  excision  of  the  tonsils  was  fol- 
lowed by  bleeding,  which  continued  for  several  days,  and  was  arrested  with  great  dif- 
ficulty. On  inquiry  it  was  ascertained  that  the  patient,  a  young  man  about  twenty 


28  THE  BLOOD. 

years  of  age,  in  other  respects  perfectly  healthy,  had  been  subject  from  early  life  to  per- 
sistent haemorrhage  from  slight  wounds. 

•Circumstances  which  accelerate  coagulation  have  a  tendency  to  arrest  haemorrhage. 
It  is  well  known  that  exposure  of  a  bleeding  surface  to  the  air  has  this  effect.  The  way 
in  which  the  vessel  is  divided  has  an  important  influence.  A  clean  cut  will  bleed  more 
freely  than  a  ragged  laceration.  In  division  of  large  vessels,  this  difference  is  sometimes 
very  marked.  Cases  are  on  record  in  which  the  arm  has  been  torn  off  at  the  shoulder- 
joint,  and  yet  the  haemorrhage  was,  for  a  time,  spontaneously  arrested ;  while  we  know 
that  division  of  an  artery  of  comparatively  small  size,  if  it  be  cut  across,  would  be  fatal 
if  left  to  itself.  Under  these  circumstances,  the  internal  coat  is  torn  in  shreds,  which 
retract,  their  curled  ends  projecting  into  the  caliber  of  the  vessel  and  having  the  same 
effect  on  the  coagulation  of  blood  as  a  bundle  of  twigs.  In  laceration  of  such  a  large 
vessel  as  the  axillary  artery,  the  arrest  cannot  be  permanent,  for,  as  soon  as  the  system 
recovers  from  the  shock,  the  contractions  of  the  heart  will  force  out  the  coagulated  blood 
which  has  closed  the  opening. 

From  the  foregoing  considerations,  it  is  evident  that  the  remarkable  phenomenon  of 
coagulation  of  the  blood,  which  has  so  much  engaged  the  attention  of  physiologists,  has 
rather  a  mechanical  than  a  vital  function ;  for  its  chief  office  is  in  the  arrest  of  haemor- 
rhage. Coagulation  never  takes  place  in  the  organism,  unless  the  blood  be  in  an  abnormal 
condition  with  respect  to  circulation.  Here  its  operations  are  mainly  conservative ;  but, 
as  almost  all  conservative  processes  are  sometimes  perverted,  clots  in  the  body  may  be 
productive  of  injury,  as  in  the  instances  of  cerebral  apoplexy,  clots  in  the  heart  occurring 
before  death,  the  detachment  of  emboli,  etc. 

Cause  of  the  Coagulation  of  the  Blood. — If  we  adopt  the  views  regarding  the  compo- 
sition of  the  blood  which  involve  the  production  of  fibrin  as  a  result  of  the  decomposition 
of  plasmine,  we  must  change  in  toto  our  ideas  of  the  cause  of  the  coagulation  of  the  blood. 
According  to  our  present  ideas,  fibrin  does  not  exist  as  a  proximate  principle,  and  plas- 
mine is  never  decomposed  in  the  body,  under  perfectly  normal  conditions ;  but,  if  the 
blood  be  drawn  from  the  body,  effused  from  the  vessels,  or  if  the  circulation  be  arrested 
for  a  certain  time,  plasmine  is  decomposed,  fibrin  is  formed,  and  the  blood  coagulates. 

In  another  work,  written  in  1864,  we  discussed  the  question  of  the  cause  of  the  co- 
agulation of  the  blood  quite  fully ;  but  fibrin  was  then  generally  regarded  as  a  proxi- 
mate principle  itself,  and  not  as  a  product  of  decomposition.  The  theory  that  we  then 
adopted  was  the  one  proposed  by  Kichardson,  in  1856  ;  viz.,  that  the  blood  normally 
contains  a  small  quantity  of  ammonia,  the  presence  of  which  keeps  the  fibrin  in  a  liquid 
state  ;  that  ammonia  is  constantly  being  taken  up  by  the  blood  from  the  tissues  and  ex- 
haled by  the  lungs,  and  that,  when  the  circulation  of  the  blood  is  arrested,  or  when  the 
blood  is  effused  or  drawn  from  the  vessels,  ammonia  is  exhaled  and  coagulation  takes 
place.  This  theory  has  been  formally  abandoned  by  Richardson,  who  adheres,  however, 
to  the  accuracy  of  his  experiments.  If  these  experiments  be  entirely  reliable,  they  seem 
to  prove  the  theory ;  but  it  is  stated  by  Eobin,  that,  using  chemical  processes  which  will 
detect  T.TnroMFw  °f  ammonia,  not  a  trace  of  this  substance  is  to  be  found  in  the  blood ; 
that  a  small  quantity  of  ammonia  added  to  the  blood  does  not  prevent  coagulation ;  and 
that  the  blood  secured  against  evaporation  will  nevertheless  coagulate.  The  chemical 
experiments  of  Eichardson  were  not  very  delicate,  and  the  objections  to  them,  made  by 
Robin,  are  probably  well-founded.  We  are  justified,  therefore,  in  abandoning  the  the- 
ory that  coagulation  of  the  blood  is  due  to  the  evolution  of  ammonia. 

We  may  take  the  same  position  with  regard  to  the  older  theories  of  coagulation, 
which  were  nearly  all  vague  and  unsatisfactory.  The  idea  that  exposure  to  the  air  is  the 
cause  of  coagulation,  which  was  held  by  Hewson,  is  disproved  by  the  simple  fact  that 
coagulation  takes  place  in  a  vacuum.  The  vital  theory  of  Hunter,  which  was  adopted 
by  most  physiologists  of  his  time,  is  too  indefinite  for  discussion  at  the  present  day,  and 


CAUSE   OF  THE   COAGULATION  OF  THE  BLOOD.  39 

really  expresses  utter  want  of  knowledge  on  the  subject.  The  theory  that  motion  is  the 
cause  of  the  fluidity  of  fibrin  in  the  body,  is  disproved  by  the  fact  that  violent  agitation 
of  the  blood  out  of  the  body  does  not  prevent  coagulation  ;  and  thus  it  is  with  nearly 
all  the  theories  that  have  been  advanced. 

The  idea  which  we  have  to  present  does  not  explain  why  the  blood  coagulates,  but 
it  gives  a  certain  notion  of  the  probable  conditions  under  which  plasmine  exists  in  the 
circulating  fluid : 

Plasmine,  circulating  in  the  blood-vessels,  under  normal  conditions,  is  a  liquid,  and 
its  decomposition  into  metalbumen  and  fibrin  is  abnormal.  Plasmine  is  undoubtedly  an 
important  nutritive  principle,  and  is  constantly  undergoing  change  as  it  is  used  in  the 
nutrition  of  the  nitrogenized  constituents  of  the  various  tissues  and  organs,  the  material 
thus  expended  being  supplied  by  the  nitrogenized  constituents  of  the  food.  It  is,  there- 
fore, like  other  nitrogenized  constituents  of  the  organism,  in  a  condition  of  constant 
metamorphosis  ;  and  all  that  we  can  say  is  that,  while  in  this  condition,  getting  material 
from  some  parts  and  giving  off  matters  in  others,  it  does  not  undergo  those  decomposing 
changes  which  are  observed  when  it  is  effused,  drawn  from  the  body,  or  the  circulation 
is  arrested,  which  involve  coagulation  of  the  blood. 

The  above  expresses  nearly  all  that  we  positively  know  of  the  cause  of  the  coagula- 
tion of  the  blood ;  but  the  question  in  fact  reduces  itself  to  the  rather  unsatisfactory 
proposition  that  the  blood  coagulates  because,  when  its  nitrogenized  principles  are  re- 
moved from  those  constant  molecular  changes  which  are  characteristic  of  the  class  of 
nitrogenized  principles  as  they  exist  in  the  living  organism,  decomposition  takes  place, 
which  results  in  the  production  of  a  coagulating  matter.  It  is  hardly  to  be  expected 
that  physiologists  would  be  satisfied  with  this,  which  is  indeed  little  more  than  a  confes- 
sion of  ignorance  ;  but  it  must  be  remembered  that  we  are  very  little  acquainted  with 
the  molecular  changes  taking  place  constantly  in  the  living  body.  When  we  understand 
these  more  thoroughly,  we  may  obtain  a  better  knowledge  of  the  causes  of  coagulation 
of  the  blood,  cadaveric  rigidity  of  muscles,  and  other  changes  which  take  place  when 
the  processes  of  nutrition  cease. 

Within  the  last  few  years,  A.  Schmidt  (1861)  has  proposed  a  theory  of  coagulation 
which  involves  the  coming  together  of  certain  principles  called  fibrin-factors.  This  the- 
ory has  been  adopted  and  more  or  less  modified  by  Ktihne,  Virchow,  and  others.  If 
blood-plasma,  rendered  neutral  with  acetic  acid,  be  diluted  with  ten  times  its  volume  of 
water  at  32°  Fahr.  and  then  be  treated  with  a  current  of  carbonic-acid  gas,  a  flocculent 
precipitate  is  formed,  which  has  been  called  paraglobuline,  or  fibrinoplastic  matter.  This 
substance  may  be  dissolved  in  water  containing  air  or  oxygen  in  solution.  After  this 
precipitate  has  been  separated,  if  the  clear  liquid  be  diluted  with  about  twice  its  volume 
of  ice-cold  water  and  be  again  treated  for  ar  long  time  with  a  current  of  carbonic  acid, 
a  viscid  scum  is  produced,  which  has  been  called  fibrinogen.  A  small  quantity  of  fibrin- 
ogen added  to  a  solution  of  paraglobuline  produces  coagulation  of  a  substance  like  fibrin. 
More  recently,  a  third  principle,  a  ferment,  has  been  described  by  Schmidt,  which  he 
considers  necessary  to  the  formation  of  fibrin. 

It  is  very  questionable  whether  the  substances  called  paraglobuline  and  fibrinogen  ex- 
ist in  the  blood  as  peculiar  principles.  Robin  considers  paraglobuline  as  identical  with 
metalbumen,  which  is  itself  one  of  the  products  of  the  decomposition  of  plasmine.  It 
is  true  that  the  so-called  fibrinogen  added  to  the  liquid  of  hydrocele  or  other  serosities 
not  spontaneously  coagulable  produces  coagulation,  but  this  occurs,  though  more  slowly, 
when  the  serum  separated  from  the  coagulated  blood  is  added  to  these  liquids. 

It  is  more  in  accordance  with  our  positive  knowledge  to  state  that  we  understand 
nothing  with  regard  to  the  cause  of  coagulation  of  the  blood  beyond  the  fact  that  plas- 
mine, when  removed  from  its  normal  condition  in  the  circulation,  decomposes  into  coag- 
ulating fibrin  and  metalbumen,  than  to  admit  the  existence  of  fibrinogen,  a  ferment,  and 
paraglobuline,  all  of  which  may  be  products  of  decomposition. 


30 


THE  BLOOD. 


It  is  a  curious  fact  that  leech-drawn  blood  remains  fluid  in  the  body  of  the  ani- 
mal. Richardson  has  observed,  also,  that  the  blood  flowing  from  a  leech-bite  presents 
the  same  persistent  fluidity,  which  explains  the  well-known  fact  that  the  insignificant 
wound  gives  rise  to  considerable  haemorrhage.  On  this  point  he  has  made  the  following 
curious  experiment : 

"  After  the  leech  was  removed  from  the  arm,  the  wound  it  had  produced  continued 
to  give  out  blood  very  freely.  I  caught  the  blood  thus  flowing  at  different  intervals, 
allowing  it  to  trickle  into  teaspoons  of  the  same  size  and  shape.  The  results  were  curi- 
ous. The  blood  which  was  received  into  the  first  spoon,  and  which  was  collected  imme- 
diately after  the  removal  of  the  leech,  was  dark,  and  showed  the  same  feebleness  of 
coagulation  as  the  blood  taken  from  the  leech  itself.  Another  portion  of  blood,  received 
into  a  second  spoon  five  minutes  later,  coagulated  in  twenty-five  minutes  with  moderate 
firmness.  A  third  portion  of  blood,  caught  ten  minutes  later  still,  coagulated  in  eight 
minutes ;  while  at  the  end  of  half  an  hour  the  blood  which  still  flowed  from  the  wound 
coagulated  firmly,  and  in  fine  red  clots,  in  two  minutes.  Ultimately  the  blood  coagu- 
lated as  it  slowly  oozed  from  the  wound,  so  that  the  wound  itself  was  sealed  up." 

The  existence  of  projections  into  the  caliber  of  vessels,  or  the  passage  of  a  fine  thread 
through  an  artery  or  vein,  will  determine  the  formation  of  a  small  coagulum  upon  the 
foreign  substance,  while  the  circulation  is  neither  interrupted  nor  retarded.  These  facts 
demand  explanation ;  but  all  we  can  say  with  regard  to  them  is,  that,  in  the  present 
state  of  our  knowledge,  explanation  is  difficult,  if  not  impossible.  The  process,  under 
these  circumstances,  cannot  be  subjected  to  direct  experiment,  as  in  the  case  of  blood 
coagulating  out  of  the  body ;  but  a  reasonable  inference  is  that  the  foreign  substance 
arrests  the  circulation  of  a  certain  portion  of  plasmine,  which  then  undergoes  decompo- 
sition. 

During  coagulation,  fibrin  assumes  a  filamentous  form,  presenting,  under  the  micro- 
scope, the  appearance  of  rectilinear  fibrillae.  These  fibrillas  gradually  increase  in  num- 
ber and,  as  contraction  of  the  clot  occurs,  becomes  irregularly  crossed.  They  are  always 


FIG.  8.— Coagulated  fibrin.    (Eobin.) 

Fibrinous  clot,  without  red  corpuscles,  and  containing1  leucocytes,  thrown  off  in  the  form  of  a  whitish  pseudo-mem- 
brane in  a  case  of  ulceration  of  the  neck  of  the  uterus  with  haemorrhage. 


straight,  however,  and  never  assume  the  undulating  appearance  characteristic  of  the 
white  fibrous  tissue.  The  appearance  just  described  does  not  indicate  a  process  of  or- 
ganization. When  fibrin  is  effused  into  any  of  the  tissues  or  organs  from  rupture  of 
vessels,  it  acts  as  a  foreign  substance,  and,  in  time,  becomes  entirely  or  in  part  absorbed. 
The  gradual  production  of  membranes  of  new  formation,  as  one  of  the  results  of  inflam- 
mation, these  becoming  organized,  is  entirely  different  from  sudden  hgemorrhagic 
effusions. 

The  blood  of  the  renal  and  hepatic  veins,  capillary  blood,  and  the  blood  which  passes 


DISCOVERY  OF  THE   CIRCULATION.  31 

from  the  capillary  system  into  the  veins  after  death,  does  not  generally  coagulate  or 
coagulates  very  imperfectly  ;  in  other  words,  these  varieties  of  hlood  do  not  readily  form 
fibrin.  The  reason  of  this  peculiarity  is  not  known ;  but  the  fact  affords  a  partial  ex- 
planation of  the  normal  fluidity  of  the  blood  ;  for  this  fluid,  passing  over  the  entire 
course  of  the  circulation  in  about  thirty  seconds,  seems  to  be  constantly  losing  its  coagu- 
lability in  its  passage  through  the  liver,  kidneys,  and  the  general  capillary  system,  as  fast 
as  its  coagulability  is  increased  in  the  other  parts.  Taking  into  consideration  the  rapidity 
of  the  circulation,  it  is  evident  that  the  blood  cannot  coagulate  while  the  normal  cir- 
culation is  maintained,  and  while  it  is  undergoing  the  constant  changes  incident  to  gen- 
eral nutrition. 


CHAPTER    II. 

CIRCULATION  OF  THE  BLOOD— ACTION  OF  THE  HEART. 

Discovery  of  the  circulation— Physiological  anatomy  of  the  heart— Valves  of  the  heart— Movements  of  the  heart- 
Impulse  of  the  heart — Succession  of  movements  of  the  heart — Force  of  the  heart's  action — Action  of  the  valves — 
Sounds  of  the  heart — Causes  of  the  sounds  of  the  heart — Frequency  of  the  heart's  action — Influence  of  age- 
Influence  of  digestion— Influence  of  posture  and  muscular  exertion— Influence  of  exercise— Influence  of  tem- 
perature— Influence  of  respiration  on  the  action  of  the  heart — Cause  of  the  rhythmical  contractions  of  the  heart 
—Influence  of  the  nervous  system  on  the  heart— Division  of  the  pneumogastrics— Galvanization  of  the  pneu- 
mogastrics — Causes  of  arrest  of  action  of  the  heart — Blows  upon  the  epigastrium. 

HAKVEY  discovered  the  circulation  of  the  blood  in  1616,  taught  it  in  his  public  lect- 
ures in  1619,  and,  in  1628,  published  the  "  Exercitatio  Anatomica  de  Motu  Cordis  et 
Sanguinis  in  Animalibm."  This  momentous  discovery,  from  the  isolated  facts  bearing 
upon  it  which  were  observed  by  anatomists,  to  its  grand  culmination  with  Harvey,  so 
fully  illustrates  the  gradual  development  of  most  great  physiological  truths,  that  it  does 
not  seem  out  of  place  to  begin  our  study  of  the  circulation  with  a  rapid  sketch  of  its 
history. 

The  facts  bearing  upon  the  circulation,  which  were  developed  before  the  time  of  Har- 
vey, were  chiefly  anatomical.  The  writings  of  Hippocrates  are  very  indefinite  upon  all 
points  connected  with  the  circulatory  system  ;  and  no  clear  and  positive  statements  are 
to  be  found  in  ancient  works  before  the  time  of  Aristotle.  The  work  of  Aristotle  most 
frequently  quoted  by  physiologists  is  his  "  History  of  Animals ;  "  and  in  this  occurs  a 
passage  which  seems  to  indicate  that  he  thought  that  air  passed  from  the  lungs  to  the 
heart ;  but  in  his  work,  De  Partibm  Animalium,  it  is  stated  that  there  are  two  great 
blood-vessels,  the  vena  cava  and  aorta,  arising  from  the  heart,  and  that  the  aorta  and 
its  branches  carry  blood.  Galen,  however,  demonstrated  experimentally  the  presence  of 
blood  in  the  arteries,  by  including  a  portion  of  one  of  these  vessels  between  two  liga- 
tures, in  a  living  animal ;  but  his  ideas  of  the  communication  between  the  arteries  and 
veins  were  erroneous,  for  he  believed  in  the  existence  of  small  orifices  in  the  septum  be- 
tween the  ventricles  of  the  heart,  a  mistake  that  was  corrected  by  Vesalius,  at  about  the 
middle  of  the  sixteenth  century. 

In  1553,  Michael  Servetus,  who  is  generally  regarded  as  the  discoverer  of  the  pas- 
sage of  the  blood  through  the  lungs,  or  the  pulmonary  circulation,  described  in  a  work 
on  theology  the  course  of  the  blood  through  the  lungs,  from  the  right  to  the  left  side  of 
the  heart.  This  description,  complete  as  it  is,  was  merely  incidental  to  the  development 
of  a  theory  with  regard  to  the  formation  of  the  soul,  and  the  development  of  what  were 
called  animal  and  vital  spirits  (spiritus).  The  same  year,  at  the  instigation  of  Calvin, 
Servetus  was  burned  alive  at  Geneva,  and  a  copy  of  his  book  was  also  committed  to  the 
flames.  But  one  or  two  copies  of  this  work  are  now  in  existence.  One  is  in  the  library 


32  CIRCULATION  OF  THE   BLOOD. 

of  the  Institute  of  France,  and  bears  evidence,  in  some  pages  that  are  partially  burned, 
of  the  fate  which  it  so  narrowly  escaped. 

A  few  years  later,  Columbo,  professor  of  anatomy  at  Padua,  and  Cesalpinus,  of  Pisa, 
described  the  passage  of  the  blood  through  the  lungs,  though  probably  without  any 
knowledge  of  what  had  been  written  by  Servetus.  To  Cesalpinus  is  attributed  the  first 
use  of  the  expression  circulation  of  the  blood.  He  also  remarked  that,  after  ligature  or 
compression  of  veins,  the  swelling  is  always  below  the  point  of  obstruction. 

The  history  of  the  discovery  of  the  valves  in  the  veins  is  quite  obscure,  although  pri- 
ority of  observation  is  almost  universally  conceded  to  Fabricius.  As  regards  this  point, 
we  can  depend  only  upon  the  dates  of  published  memoirs,  notwithstanding  the  assertion 
of  Fabricius,  that  he  had  seen  the  valves  in  1574.  In  1545,  Etienne  described,  in  branches 
of  the  portal  vein,  "  valves,  which  he  called  apophyses,  and  which  he  compared  to  the 
valves  of  the  heart."  In  1551,  Amatus  Lusitanus  published  a  letter  from  Cannanus,  in 
which  it  is  stated  that  he  had  found  valves  in  certain  of  the  veins.  In  1563,  Eustachius 
published  an  account  of  the  valves  of  the  coronary  vein.  In  1586,  a  clear  account,  by 
Piccolhominus,  of  the  valves  of  the  veins  was  published.  Fabricius  gave  the  most  accu- 
rate descriptions  and  delineations  of  the  valves,  and  his  first  publication  is  said  to  have 
appeared  in  1603.  He  demonstrated  them  to  Harvey,  at  Padua ;  and  it  is  probable  that 
this  was  the  origin  of  the  first  speculations  by  Harvey  on  the  mechanism  of  the  circula- 
tion. Shortly  after  the  return  of  Harvey  from  Padua  in  1602,  he  advanced  beyond  the 
study  of  inanimate  parts  by  dissections,  and  investigated  animated  nature  by  means  of 
vivisections.  As  is  evident,  when  we  consider  the  state  of  science  at  that  time,  anato- 
mists had  long  been  preparing  the  way  for  the  discovery  of  the  circulation,  although 
they  knew  little  of  the  functions  of  the  parts  they  described.  The  conformation  of  the 
heart  and  vessels,  and  even  the  arrangement  of  the  valves  of  the  veins,  did  not  lead  them 
to  suspect  the  course  of  the  blood;  but  a  few  well-conceived  experiments  on  living  ani- 
mals have  made  it  appear  so  simple,  that  we  now  wonder  it  remained  unknown  so  long. 
Farthermore,  these  experiments  made  it  evident  that  there  was  a  communication  at  the 
periphery  between  the  arteries  and  the  veins. 

In  the  work  of  Harvey  are  described,  first  the  movements  of  the  heart,  which  he 
exposed  and  studied  in  living  animals.  He  described  minutely  all  the  phenomena  which 
accompany  its  action ;  its  diastole,  when  it  is  filled  with  blood,  and  its  systole,  when  the 
fibres  of  which  the  ventricles  are  composed  contract  simultaneously,  and  "by  an  admi- 
rable adjustment  all  the  internal  surfaces  are  drawn  together,  as  if  with  cords,  and  so  is 
the  charge  of  blood  expelled  with  force."  From  the  description  of  the  action  of  the 
ventricles,  he  passes  to  the  auricles,  and  shows  how  these,  by  their  contraction,  fill  the 
ventricles  with  blood.  By  experiments  upon  serpents  and  fishes,  he  proved  that  the 
blood  fills  the  heart  from  the  veins,  and  is  sent  out  into  the  arteries.  Exposing  the  heart 
and  great  vessels  in  these  animals,  he  applied  a  ligature  to  the  veins,  which  had  the 
effect  of  cutting  off  the  supply  from  the  heart  so  that  it  became  pale  and  flaccid ;  and 
by  removing  the  ligature  the  blood  could  be  seen  flowing  into  the  organ.  When,  on  the 
contrary,  a  ligature  was  applied  to  the  artery,  the  heart  became  unusually  distended, 
which  continued  so  long  as  the  obstruction  remained.  "When  the  ligature  was  removed, 
the  heart  soon  returned  to  its  normal  condition. 

The  descriptions  given  by  Harvey  were  the  result  of  numerous  experiments  upon  liv- 
ing animals ;  exposing  the  heart  of  cold-blooded  animals,  in  which  the  movements  are 
comparatively  slow ;  studying,  also,  the  action  of  this  organ  in  warm-blooded  animals, 
after  its  movements  had  become  enfeebled.  As  we  shall  see  when  we  come  to  describe 
the  movements  of  the  heart,  nothing  can  exceed  the  simplicity  and  accuracy  of  the  de- 
scriptions of  Harvey,  which  are  universally  acknowledged  to  be  correct  in  almost  every 
particular. 

Harvey  completed  his  description  of  the  circulation,  by  experiments  showing  the 
course  of  the  blood  in  the  arteries  and  veins  and  the  uses  of  the  valves  of  the  veins. 


DISCOVERY  OF  THE   CIRCULATION. 


33 


These  experiments  are  models  of  simplicity  and  pertinence.  First,  he  showed  that  a 
ligature  tightly  applied  to  a  limb  prevented  the  blood  from  entering  the  artery  and 
arrested  pulsation.  The  ligature  then  relaxed  and  applied  with  moderate  tightness  so 
as  to  compress  only  the  superficial  veins  allowed  the  blood  to  pass  into  the  part  by  the 
arteries,  but  prevented  its  return  by  the  veins,  which  consequently  became  excessively 
congested.  The  ligature  being  removed,  the  veins  soon  emptied  themselves  and  the 
member  regained  its  ordinary  appearance.  He  observed  the  "  knots  "  in  the  veins  of  the 
arm  when  a  ligature  was  applied,  as  for  phlebotomy,  and  showed  that  the  space  be- 
tween these  knots,  which  are  formed  by  the  valves,  could  be  emptied  of  blood  by  press- 
ing toward  the  heart,  and  would  not  fill  itself  while  the  finger  was  kept  at  the  lower 
extremity.  It  was  impossible,  by  pressure  with  the  fingers,  to  force  the  blood  back 
through  one  of  the  valves. 


FIG.  9.— Harvey's  observations  on  the  flow  of  blood  in  the  veins.    (Harvey.) 

By  such  simple,  yet  irresistibly  conclusive  experiments  was  completed  the  chain  of 
evidence  establishing  the  fact  of  the  circulation  of  the  blood.     Truly  it  is  said  that  here 
commenced  an  epoch  in  the  study  of  physiology ;  for  then  the  scientific  world  began  to 
3 


34 


CIRCULATION  OF  THE  BLOOD. 


emancipate  itself  from  the  ideas  of  the  ancients,  which  had  held  despotic  sway  for  two- 
centuries,  and  to  study  Nature  for  themselves  by  means  of  experiments. 

Although  Harvey  described  so  perfectly  the  course  of  the  blood  and  left  not  a  shadow 
of  doubt  as  to  the  communication  between  the  arteries  and  veins,  it  was  left  to  others  to 
actually  see  the  blood  in  movement  and  follow  it  from  one  system  of  vessels  to  the  otheiv 
In  1661,  Malpighi  saw  the  blood  circulating  in  the  vessels  of  the  lung  of  a  living  frog, 
examining  it  with  magnifying  glasses ;  and,  a  little  later,  Leeuwenhoek  saw  the  circula- 
tion in  the  wing  of  a  bat.  The  great  discovery  was  then  completed. 

Enough  has  been  said  in  the  preceding  historical  sketch  to  give  a  general  idea  of  the 
course  of  the  great  nutritive  fluid  and  the  natural  anatomical  and  physiological  divisions 
of  the  circulatory  system.  There  is  a  constant  flow  from  the  central  organ  to  all  the 
tissues  and  organs  of  the  body,  and  a  constant  return  of  the  blood  after  it  has  passed 
through  these  parts.  But  before  the  blood,  which  has  thus  been  brought  back,  is  fit  to 
return  again  to  the  system,  it  must  pass  through  the  lungs  and  undergo  the  changes 
incident  to  respiration.  In  some  animals,  like  fishes,  the  same  force  sends  the  blood 
through  the  gills,  and  from  them  through  the  system.  In  others,  like  the  reptiles,  a 
mixture  of  aerated  and  non-aerated  blood  takes  place  in  the  heart,  and  the  general 
system  never  receives  blood  that  has  been  fully  arterialized.  But  in  man  and  all 
warm-blooded  animals,  the  organism  demands  blood  that  has  been  fully  purified  and 
oxygenated  by  its  passage  through  the  lungs,  and  here  we  find  the  first  great  and  com- 
plete divisions  of  the  circulation  into  the  pulmonary  and  systemic,  or,  as  they  have  been 
called,  the  lesser  and  greater  circulation.  The  heart  in  this  instance  is  double ;  hav- 
ing a  right  and  left  side  which  are  entirely  distinct  from  each  other.  The  right  heart 

receives  the  blood  as  it  is  brought 
from  the  system  by  the  veins  and 
sends  it  to  the  lungs ;  the  left  heart 
receives  the  blood  from  the  lungs 
and  sends  it  to  the  system.  It  mast 
be  borne  in  mind,  however,  that  al- 
though the  two  sides  of  the  heart 
are  distinct  from  each  other,  their 
action  is  simultaneous  ;  and,  in 
studying  the  motions  of  this  or- 
gan, we  shall  find  that  the  blood 
is  sent  simultaneously  from  the 
right  side  to  the  lungs,  and  from 
the  left  side  to  the  system.  It  will 
not  be  necessary,  therefore,  to  sep- 
arate the  two  circulations  in  our 
study  of  their  mechanism ;  for  the 
simultaneous  action  of  both  sides 
of  the  heart  enables  us  to  study 
its  functions  as  a  single  organ,  and 
the  constitution  and  operations  of 
the  two  kinds  of  vessels  do  not 
present  any  material  differences. 
For  convenience  of  study,  the  circulatory  system  may  be  divided  into  heart  and 
vessels,  the  latter  being  of  three  kinds:  the  arteries,  which  carry  blood  from  the 
heart  to  the  system ;  the  capillaries,  which  distribute  the  blood  more  or  less  abun- 
dantly in  different  parts  of  the  system ;  and  the  veins,  which  return  the  blood  from 
the  system  to  the  heart.  The  functions  of  each  of  these  divisions  may  be  considered 
separately. 


FIG.  10.— Diagram  of  the  four  carities  of  the  heart.  (Bernard.) 
od,  right  auricle ;  «cZ,  right  ventricle ;  og,  left  auricle ,  <vg,  left 
ventricle.  The  arrows  indicate  the  course  of  the  blood. 


ANATOMY  OF  THE  HEART. 


35 


Physiological  Anatomy  of  the  Heart. 

The  heart  of  the  human  subject  is  a  pear-shaped,  muscular  organ,  situated  in  the 
thoracic  cavity,  with  its  base  about  in  the  median  line  and  its  apex  at  the  fifth  inter- 
costal space   midway  between  the  median  line  and  a  perpendicular  dropped  through 
the  left  nipple.     Its  weight  is 
from  eight   to  ten  ounces  in 
the  female,  and  from  ten  to 
twelve  ounces  in  the  male.    It 
has  four   distinct  cavities;    a 
right  and  a  left  auricle,  and  a 
right  and  a  left  ventricle.     Of 
these,  the  ventricles  are   the 
more  capacious.     The  heart  is 
held  in  place,  or  may  be  said 
to  be  attached  by  the  great 
vessels  to  the   posterior  wall 
of  the  thorax,  while  the  apex    / 
is  free  and  capable  of  a  cer-    \ 
tain  degree  of  motion.      The    , 
whole  organ  is  enveloped  in  a   [ 
fibrous  sac  called  the  pericar-    \ 
dium.     This  sac  is  lined  by  a 
serous  membrane,  which  is  at-     ! 
tached  to  the  great  vessels  at 
the  base  and  reflected  over  its 
surface.     The  membrane  is  lu- 
bricated  by  a  drachm  or  two 

of  flnifl    qo  that  thp  movprnp-ntq    ai 
ll(1'  SC 

of  the  heart  are  normally  ac- 
complished without  any  friction.  The  serous  pericardium  does  not  present  any  dif- 
ferences from  serous  membranes  in  other  situations.  The  cavities  of  the  heart  are  lined 
by  a  smooth  membrane,  called  the  endocardium,  which  is  continuous  with  the  lining 
membrane  of  the  blood-vessels. 

The  right  auricle  receives  the  blood  from  the  vense  cavas  and  empties  it  into  the  right 
ventricle.  The  auricle  presents  a  principal  cavity,  or  sinus,  as  it  is  called,  with  a  little 
appendix,  called  from  its  resemblance  to  the  ear  of  a  dog,  the  auricular  appendix.  It  has 
two  large  openings  for  the  vena  cava  ascendens  and  the  vena  cava  descendens,  with  a 
small  opening  for  the  coronary  vein  which  brings  the  blood  from  the  substance  of  the 
heart  itself.  It  has,  also,  another  large  opening,  called  the  auriculo-ventricular  opening, 
by  which  the  blood  flows  into  the  ventricle.  The  walls  of  this  cavity  are  quite  thin  as 
compared  with  the  ventricles,  measuring  about  one  line.  They  are  composed  of  mus- 
cular fibres  arranged  in  two  layers,  one  of  which,  the  external,  is  common  to  both  auri- 
cles, and  the  other,  the  internal,  is  proper  to  each.  These  muscular  fibres,  although 
involuntary  in  their  action,  belong  to  the  striated,  or  what  is  termed  voluntary  variety, 
and  are  similar  in  structure  to  the  fibres  of  the  ventricles.  The  fibres  of  the  auricles  are 
much  fewer  than  those  of  the  ventricles.  Some  of  them  are  looped,  arising  from  a 
cartilaginous  ring  wljich  separates  the  auricles  and  ventricles,  and  passing  over  the 
auricles  ;  and  others  are  circular,  surrounding  the  auricular  appendages  and  the  open- 
ings of  the  veins,  extending,  also,  a  short  distance  along  the  course  of  these  vessels. 
One  or  two  valvular  folds  are  found  at  the  orifice  of  the  coronary  vein,  preventing  a 
reflux  of  blood,  but  there  are  no  valves  at  the  orifices  of  the  vense  cavse. 

The  left  auricle  receives  the  blood  which  comes  from  the  lungs  by  the  pulmonary 


FIG.  ll.—  Heart  in  situ.  (Dalton,  in  Flint,  "on  the  Heart.") 
c.  etc.,  ribs;  1,  2,  8,  etc.,  intercostal  spaces;  vertical  line,  median  line; 
triangle,  superficial  cardiac  region  ;   x  on  the  fourth  rib,  nipple. 


CIRCULATION  OF  THE  BLOOD. 


veins.     It  does  not  differ  materially  in  its  anatomy  from  the  right.     It  is  a  little  smaller, 
and  its  walls  are  thicker,  measuring  about  a  line  and  a  half.   It  has  four  openings  by  which 

it  receives  the  blood  from  the 
four  pulmonary  veins.  These 
openings  are  not  provided  with 
valves.  Like  the  right  auricle, 
it  has  a  large  opening,  by  which 
blood  flows  into  the  left  ven- 
tricle. The  arrangement  of  the 
muscular  fibres  is  essentially  the 
same  as  in  the  right  auricle.  In 
adult  life,  the  cavities  of  the  au- 
ricles are  entirely  distinct  from 
each  other.  Before  birth,  they 
communicate  by  a  large  open- 
ing, the  foramen  ovale,  and  the 
orifice  of  the  inferior  vena  cava 
is  provided  with  a  membranous 
fold,  the  Eustachian  valve, 
which  serves  to  direct  the 
blood  from  the  lower  part  of 
the  body  through  the  opening 
into  the  left  auricle.  After 
birth,  the  foramen  ovale  is 
closed  and  the  Eustachian  valve 
gradually  disappears. 

The  ventricles,  in  the  human 
subject  and  in  warm-blooded 
animals,  constitute  the  bulk  of 
the  heart.  They  have  a  ca- 
pacity somewhat  greater  than 
that  of  the  auricles  and  are 
provided  with  thick  muscular 
walls.  It  is  by  the  powerful 
action  of  this  portion  of  the 
heart  that  the  blood  is  forced, 
on  the  one  hand,  to  the  lungs  and  back  to  the  left  side,  and  on  the  other,  through  the 
entire  system  of  the  greater  circulation  to  the  right  side.  It  has  been  asserted  that  the 
capacity  of  the  right  ventricle  is  considerably  greater  than  that  of  the  left.  The  most 
recent  and  conclusive  observations  on  this  subject  are  those  of  Hiffelsheim  and  Robin. 
In  these  experiments,  the  cavities  were  filled  with  an  injection  of  wax,  and  the  estimates 
were  made  by  calculating  the  amount  of  liquid  displaced  by  the  moulds  of  the  different 
cavities.  Care  was  taken  to  make  the  injection  in  animals  before  cadaveric  rigidity  had 
set  in,  or  after  it  had  passed  away,  in  the  human  subject.  The  comparative  results  ob- 
tained by  these  observers  are  the  most  interesting,  for  the  cavities  were  undoubtedly  dis- 
tended by  the  injection  to  their  extreme  capacity,  and  contained  more  than  they  ever 
do  during  life.  They  found  the  capacity  of  the  right  auricle  from  one-tenth  to  one- 
eighth  greater  than  that  of  the  left.  The  capacity  of  the  right  ventricle  was  from 
one-tenth  to  one-eighth  greater  than  that  of  the  left,  but  more  frequently  there  was  less 
disparity  between  the  two  ventricles  than  between  the  auricles.  The  capacity  of  each 
ventricle  exceeded  that  of  the  corresponding  auricle  by  from  one-fourth  to  one-third. 
Nine  times  out  of  ten,  this  predominance  of  the  ventricle  >was  more  marked  on  the 
left  side.  The  absolute  capacity  of  the  left  ventricle,  according  to  these  observations, 


FIG.  12.— Heart,  anterior  view.    (Bonamy  and  Beau.) 
1,  right  ventricle;  2,  left  ventricle;  3,  4,  right  auricle;  5, 6,  left  auri- 
cle ;  7,  pulmonary  artery ;  8,  aorta ;  9,  superior  vena  cava ;  10,  ante- 
rior coronary  artery ;  ll'branch  of  the  coronary  vein ;  12, 12, 12,  lym- 
phatic vessels. 


ANATOMY  OF  THE   HEART. 


37 


16  v 


16 


is  from  143  to  212  cubic  centimeters,  or  from  about  4-8  to  7  ounces.     This  is  much 

greater  than  most  estimates,  which  place  the  capacity  of  the  various  cavities,  moderately 

distended,  at  about  2  ounces. 

Notwithstanding  the  disparity  in  the 

extreme  capacity  of  the  various  cavities, 

the  quantity  of  blood  which  enters  these 

cavities  is  necessarily  equal  to  that  which 

is  expelled.     This  has  been  stated  to  be 

a  little  more  than  two  ounces.     There 

are  no  means  of  estimating  with  exact- 
ness the   quantity  of  blood    discharged 

with  each  ventricular  contraction ;   and 

we  find  the  question  rather  avoided  in 

works  on  physiology.      All  we  can  say 

is  that,  from  observations  on  the  heart 

during  its  action,  it  never  seems  to  con- 
tain much  more  than  half  the  quantity  in 

all  its  cavities  that  it  does  when  fully 

distended  by  injection  ;  but  it  is  the  right 

cavities  which   are  most  dilatable,   and 

probably  the  ordinary  quantity  of  blood 

in  the  left  ventricle  is  from  four-fifths  to 

five-sixths  of  its  extreme  capacity. 

The   cavities   of   the  ventricles    are 

triangular  or  conoidal,   the  right   being 

broader  and  shorter  than  the  left,  which 

extends  to  the  apex.  The  inner  surface 
of  both  cavities  is  marked  by  peculiar 
ridges  and  papillae,  which  are  called 
columnae  earner.  Some  of  these  are 
mere  fleshy  ridges  projecting  into  the 
cavity;  others  are  columns  attached  by 
each  extremity  and  free  at  the  central 
portion;  and  others  are  papilla)  giving 
origin  to  the  chordae  tendineae,  which  are 
attached  to  the  free  edges  of  the  auriculo- 
ventricular  valves.  These  fleshy  columns 
interlace  in  every  direction  and  give  the  inner  surface  of  the  cavities  a  reticulated  ap- 
pearance. This  arrangement  evidently  facilitates  the  complete  emptying  of  the  ventri- 
cles during  their  contraction. 

The  walls  of  the  left  ventricle  are  uniformly  much  thicker  than  on  the  right  side. 
Bouillaud  found  the  average  thickness  of  the  right  ventricle  at  the  base  to  be  two  and 
a  half  lines,  and  the  thickness  of  the  left  ventricle  at  the  corresponding  part,  seven  lines. 
The  arrangement  of  the  muscular  fibres  constituting  the  walls  of  the  ventricles  is 
more  regular  than  in  the  auricles,  and  their  course  enables  us  to  explain  some  of  the  phe- 
nomena which  accompany  the  heart's  action.  The  direction  of  the  fibres  cannot  be 
well  made  out  unless  the  heart  have  been  boiled  for  a  number  of  hours,  when  part 
of  the  intermuscular  tissue  is  dissolved  out,  and  the  fibres  can  be  easily  separated  and 
followed.  Without  going  into  a  minute  description  of  their  direction,  it  is  sufficient  to 
state,  in  this  connection,  that  they  present  two  principal  layers ;  a  superficial  layer  com- 
mon to  both  ventricles,  and  a  deep  layer  proper  to  each.  The  superficial  fibres  pass 
obliquely  from  right  to  left  from  the  base  to  the  apex ;  here  they  take  a  spiral  course, 
become  deep,  and  pass  into  the  interior  of  the  organ  to  form  the  columnar  carneaa. 


FIG.  13.—  Left  cavities  of  the  heart,  (Bonamy  and  Beau.) 
1,  left  ventricular  cavity ;  2,  mitral  valve;  8,  4,  columnar, 
carnece;  5,  aortic  opening;  6,  aorta;  7,  8,  9,  aortic 
valves;  10,  right  ventricular  cavity;  11,  interventricular 
septum ;  12,  pulmonary  artery ;  13,  14,  pulmonic  valves ; 
15,  left  auricular  cavity;  16,  16,  right  pulmonary  veins, 
with  17, 17.  openings  of  the  veins ;  18,  section  of  the  cor- 
onary vein. 


38 


CIRCULATION   OF  THE   BLOOD. 


42 


These  fibres  envelop  both  Tentricles.  They  may  be  said  to  arise  from  cartilaginous  rings 
which  surround  the  auriculo- ventricular  orifices.  The  external  surface  of  the  heart  is 
marked  by  a  little  groove  which  indicates  the  division  between  the  two  ventricles.  The 

deep  fibres  are  circular,  or  transverse, 
and  surround  each  ventricle  separately. 
The  muscular  tissue  of  the  heart 
is  of  a  deep-red  color  and  resembles,  in 
its  gross  characters,  the  tissue  of  ordi- 
nary voluntary  muscles ;  but,  as  already 
intimated,  it  presents  certain  peculiar- 
ities in  its  minute  anatomy.  The  fibres 
are  considerably  smaller  and  more  gran- 
ular than  those  of  ordinary  muscles.  They 
are,  moreover,  connected  with  each  other 
by  short  inosculating  branches,  while  in 
the  voluntary  muscles  each  fibre  runs 
from  its  origin  to  its  insertion  enveloped 
in  its  proper  sheath,  or  sarcolemma.  The 
muscular  fibres  of  the  heart  have  no  sar- 
colemma. These  peculiarities,  particular- 
ly the  inosculation  of  the  fibres,  favor  the 
contraction  of  the  ventricular  walls  in 
every  direction  and  the  complete  expul- 
sion of  the  contents  of  the  cavities  with 
each  systole. 

The  distribution  of  the  nerves  to  the 
heart  and  the  arrangement  of  the  ganglia 
and  nerve-terminations  in  its  substance 
will  be  taken  up  in  connection  with  the 
influence  of  the  nervous  system  upon  he 
action  of  the  heart. 

Each  ventricle  has  two  orifices;  one 
by  which  it  receives  the  blood  from  the 
auricle,  and  the  other  by  which  the  blood 
passes  from  the  right  side  to  the  lungs 
and  from  the  left  side  to  the  system. 
All  of  these  openings  are  provided  with 
valves,  which  are  so  arranged  as  to  allow  the  blood  to  pass  in  but  one  direction. 

Tricuspid  Valve. — This  valve  is  situated  at  the  right  auriculo-ventricular  opening.  It 
has  three  curtains,  formed  of  a  thin  but  resisting  membrane,  which  are  attached  around 
the  opening.  The  free  borders  are  attached  to  the  chordae  tendineae,  some  of  which  arise 
from  the  papillae  on  the  inner  surface  of  the  ventricle,  and  others,  directly  from  the  walls 
of  the  ventricle.  When  the  organ  is  empty,  these  curtains  are  applied  to  the  walls  of 
the  ventricle,  leaving  the  auriculo-ventricular  opening  free ;  but  when  the  ventricle  is 
completely  filled  and  the  fibres  contract,  they  are  forced  up,  their  free  edges  become 
applied  to  each  other,  and  the  opening  is  closed. 

Pulmonic  Valves. — These  valves,  also  called  the  semilunar  or  sigmoid  valves  of  the 
right  side,  are  situated  at  the  orifice  of  the  pulmonary  artery.  They  are  strong  mem- 
branous pouches,  with  their  convexities,  when  closed,  looking  toward  the  ventricle. 
They  are  attached  around  the  orifice  of  the  pulmonary  artery  and  are  applied  very 
nearly  to  the  walls  of  the  vessel  when  the  blood  passes  in  from  the  ventricle ;  but  at 
other  times  their  free  edges  meet  in  the  centre,  opposing  the  regurgitation  of  blood.  At 
the  centre  of  the  free  edge  of  each  valve  is  a  little  corpuscle  called  the  corpuscle  of 


FIG.  14.— Right  cavities  of  the  heart.  (Bonamy  and  Beau.) 
I,  right  ventricular  cavity;  2,  posterior  curtain  of  the 
tricuspid  valve ;  3,  right  auricular  cavity ;  4,  colum- 
nce  camece  of  the  right  auricle  ;  5,  section  of  the  coro- 
nary vein ;  6,  Eustachian  valve ;  7,  ring  of  Vieussens ; 
8,  fossa  ovalis ;  9,  superior  vena  cava ;  10,  inferior  -vena 
cava ;  11,  aorta ;  12,  12,  right  pulmonary  veins. 


ANATOMY   OF  THE   HEART. 


39 


Arantius;  and,  just  above  the  margins  of  attachment  of  the  valves,  the  artery  presents 
three  little  dilatations,  or  sinuses,  called  the  sinuses  of  Valsalva.     The  corpuscles  of 
Arantius  probably  aid  in  the  adapta- 
tion of  the  valves  to  each  other  and 
in  the  effectual  closure  of  the  orifice. 

Mitral  Valve. — This  valve,  some- 
times called  the  bicuspid,  is  situated 
at  the  left  auriculo-ventricular  orifice. 
It  is  called  mitral  from  its  resem- 
blance, when  open,  to  a  bishop's  mi- 
tre. It  is  attached  to  the  edges  of  the 
opening,  and  its  free  borders  are  held 
in  place,  when  closed,  by  the  chords 
tendineas  of  the  left  side.  It  presents 
no  material  difference  from  the  tri- 
cuspid  valve,  with  the  exception  that 
it  is  divided  into  two  curtains  instead 
of  three. 

Aortic  Valves. — These  valves,  also 
called  the  semilunar  or  sigrnoid  valves 
of  the  left  side,  present  no  difference 
from  the  valves  at  the  orifice  of  the 
pulmonary  artery.  They  are  situated 
at  the  aortic  orifice. 

The  physiological  anatomy  of  the 
tricuspid  and  mitral  valves  may  be 
studied  by  cutting  away  the  auricles 
so  as  to  expose  the  auriculo-ventric- 
ular openings,  introducing  a  pipe  into 
the  pulmonary  artery  and  aorta,  after 
destroying  the  semilunar  valves,  and 
then  forcing  water  into  the  ventricles 

by  a  syringe  or  from  a  hydrant.     In  this  way  the  play  of  the  valves  may  be  strikingly 
exhibited. 

We  can  study  the  action  of  the  semilunar  valves  by  cutting  away  enough  of  the  ven- 
tricles to  expose  them  and  forcing  water  into  the  vessels.     These  experiments  give  an 


Fro.  15.— Muscular  fibres  of  the  ventricles.  (Bonamy  and  Beau.) 
1,  superficial  fibres,  common  to  both  ventricles ;  2,  fibres  of  the 
left  ventricle ;    3,  deep  fibres,  passing  upward  toward  the 
base  of  the  heart ;  4,  fibres  penetrating  the  left  ventricle. 


FIG.  16. — Anastomosing  muscular  fibres  of  the  heart.    (Morel.) 


idea  of -the  immense  strength  of  the  valves ;  for  they  can  hardly  be  ruptured  by  a  force 
which  is  not  sufficient  to  rupture  the  vessels  themselves. 


40  CIRCULATION"  OF  THE   BLOOD. 


FIG.  17. — Valves  of  the  heart.     (Bonamy  and  Beau.) 

1,  Eight  auriculo- ventricular  orifice,  closed  by  the  tricuspid  valve;  2,  fibrinous  ring;  3,  left  auriculo-ventricular 
orifice,  closed  by  the  mitral  valve;  4,  fibrinous  ring ;  5,  aortic  orifice  and  valves:  6,  pulmonic  orifice  and  valves ; 
7,  8,  9,  muscular  fibres. 

Movements  of  the  Heart. 

In  studying  the  phenomena  which  accompany  the  action  of  the  heart,  we  shall  fol- 
low the  course  of  the  blood,  beginning  with  it  as  it  flows  from  the  vessels  into  the  auri- 
cles. The  dilatation  of  the  cavities  of  the  heart  is  called  the  diastole,  and  the  contrac- 
tion of  the  heart,  the  systole.  When  these  terms  are  used  without  any  qualification, 
they  are  understood  as  referring  to  the  ventricles  ;  but  they  are  also  applied  to  the  action 
of  the  auricles,  as  the  auricular  diastole  or  systole,  which,  as  we  shall  see,  is  distinct 
from  the  action  of  the  ventricles. 

A  complete  revolution  of  the  heart  consists  in  the  filling  and  emptying  of  all  its  cavi- 
ties, during  which  they  experience  an  alternation  of  repose  and  activity.  As  these  phe- 
nomena occupy,  in  many  warm-blooded  animals,  a  period  of  time  less  than  one  second, 
it  will  be  appreciated  that  the  most  careful  study  is  necessary  in  order  to  ascertain  their 
exact  relations  to  each  other.  When  the  heart  is  exposed  in  a  living  animal,  the  most 
prominent  phenomenon  is  the  alternate  contraction  and  relaxation  of  the  ventricles ; 
but  this  is  only  one  of  the  operations  of  the  organ.  In  all  the  mammalia,  the  anatomy 
and  action  of  the  vascular  system  are  to  all  intents  and  purposes  the  same  as  in  the  hu- 
man subject ;  and,  although  the  exposure  of  the  heart  by  opening  the  chest  modifies  some- 
what the  force  and  frequency  of  its  pulsations,  the  various  phenomena  follow  each  other 
in  their  natural  order  and  present  essentially  their  normal  characters.  The  operation  of 
exposure  of  the  heart  may  be  performed  on  a  living  animal  without  any  great  difficulty ; 
and.  if  we  simply  take  care  to  keep  up  artificial  respiration,  the  action  of  the  heart  will 
continue  for  a  considerable  time.  We  may  keep  the  animal  quiet  by  the  administration 
of  ether  or  by  poisoning  with  woorara,  the  latter  agent  acting  upon  the  motor  nerves 
but  having  no  effect  upon  the  heart.  Having  opened  the  chest,  we  see  the  heart,  envel- 
oped in  its  pericardium,  contracting  regularly ;  and,  on  slitting  up  and  removing  this 
covering,  the  various  parts  are  completely  exposed.  The  right  ventricle  and  auricle  and 
a  portion  of  the  left  ventricle  can  be  seen  without  disturbing  the  position  of  the  parts ; 
but  the  greater  part  of  the  left  auricle  is  concealed.  As  both  auricles  and  ventricles  act 
together,  the  parts  of  the  heart  which  are  exposed  are  sufficient  for  purposes  of  study. 

Action  of  the  Auricles. — Except  the  short  time  occupied  in  the  contraction  of  the 
auricles,  these  cavities  are  continually  receiving  blood  on  the  right  side  from  the  system, 
by  the  vense  cavse,  and  on  the  left  side  from  the  lungs,  by  the  pulmonary  veins.  This 


MOVEMENTS   OF  THE   HEAET.  41 

continues  until  the  cavities  of  the  auricles  are  completety  filled,  the  blood  coming  in  by 
a  steady  current ;  and,  during  the  repose  of  the  heart,  the  blood  is  also  flowing  through 
the  auriculo- ventricular  orifices  into  the  ventricles.  When  the  auricles  have  become 
fully  distended,  they  contract  quickly  and  with  considerable  power  (the  auricular  sys- 
tole), and  force  the  blood  into  the  ventricles,  producing  complete  diastole  of  these  cavi- 
ties. During  this  contraction,  the  blood  not  only  ceases  to  flow  in  from  the  veins,  but 
some  of  it  is  regurgitated,  as  the  orifices  by  which  the  vessels  open  into  the  auricles  are 
not  provided  with  valves.  The  size  of  the  auriculo-ventricular  orifices  is  one  reason 
why  the  greater  portion  of  the  blood  is  made  to  pass  into  the  ventricles ;  and,  farther- 
more,  during  the  auricular  systole,  the  muscular  fibres  which  are  arranged  around  the 
orifices  of  the  veins  constrict  them  to  a  certain  extent,  which  tends  to  diminish  the  reflux 
of  blood.  There  can  be  no  doubt  that  some  regurgitation  takes  place  from  the  auricles 
into  the  veins,  but  this  prevents  the  possibility  of  over-distention  of  the  ventricles. 

It  has  been  shown  by  experiments  that  the  systole  of  the  auricles  is  not  immediately 
necessary  to  the  performance  of  the  circulation ;  and  the  contractility  of  the  auricles 
may  be  temporarily  exhausted  by  prolonged  irritation,  the  ventricles  continuing  to  act, 
keeping  up  the  circulation  of  blood. 

Action  of  the  Ventricles. — Immediately  following  the  contraction  of  the  auricles,  by 
which  the  ventricles  are  completely  distended,  we  have  contraction  of  the  ventricles. 
This  is  the  chief  active  operation  performed  by  the  heart  and  is  generally  spoken  of  as 
the  systole.  As  we  should  expect  from  the  great  thickness  of  the  muscular  walls,  the 
contraction  of  the  ventricles  is  very  much  more  powerful  than  that  of  the  auricles.  By 
their  action,  the  blood  is  forced  from  the  right  side  to  the  lungs  by  the  pulmonary  artery, 
and  from  the  left  side  to  the  system  by  the  aorta.  Eegurgitation  into  the  auricles  is  pre- 
vented by  the  closure  of  the  tricuspid  and  mitral  valves.  This  act  accomplished,  the 
heart  has  a  period  of  repose,  the  blood  flowing  into  the  auricles,  and  from  them  into  the 
ventricles,  until  the  auricles  are  filled  and  another  contraction  takes  place. 

Locomotion  of  the  Heart. — The  position  of  the  heart  after  death  or  during  the  re- 
pose of  the  organ  is  with  its  base  directed  slightly  to  the  right  and  its  apex  to  the  left 
side  of  the  body.  With  each  ventricular  systole,  it  raises  itself  up,  the  apex  is  sent  for- 
ward, and  is  moved  slightly  from  left  to  right.  The  movement  from  left  to  right  is  a 
necessary  consequence  of  the  course  of  the  superficial  fibres.  The  fibres  on  the  anterior 
surface  of  the  organ  are  longer  than  those  on  the  posterior  surface,  and  pass  from  the 
base,  which  is  comparatively  fixed,  to  the  apex,  which  is  ^movable.  As  a  consequence 
of  this  anatomical  arrangement,  the  heart  is  moved  upward  and  forward  during  its  sys- 
tole. The  course  of  the  fibres  from  the  base  to  the  apex  is  from  right  to  left ;  and,  a» 
they  shorten,  the  apex  is  of  necessity  slightly  moved  from  left  to  right. 

The  locomotion  of  the  entire  heart  forward  was  observed  by  Harvey,  in  the  case  of 
the  son  of  the  Viscount  Montgomery.  The  young  man,  aged  about  nineteen  years,  suf- 
fered a  severe  injury  to  the  chest,  resulting  in  an  abscess,  which  on  cicatrization  left 
an  opening  into  which  Harvey  could  introduce  three  fingers  and  the  thumb.  This 
opening  was  directly  over  the  apex  of  the  heart.  The  action  of  the  portion  of  the  heart 
thus  exposed  is  described  by  Harvey  in  the  following  words : 

"  We  also  particularly  observed  the  movements  of  the  heart,  viz. :  that  in  the  dias- 
tole it  was  retracted  and  withdrawn  ;  whilst  in  the  systole  it  emerged  and  protruded ; 
and  the  systole  of  the  heart  took  place  at  the  moment  the  diastole  or  pulse  in  the  wrist 
was  perceived.  To  conclude,  the  heart  struck  the  walls  of  the  chest,  and  became  promi- 
nent at  the  time  it  bounded  upward  and  underwent  contraction  on  itself." 

The  locomotion  of  the  heart  takes  place  in  the  direction  of  its  axis  and  is  due  to  the 
sudden  distention  of  the  -great  vessels  at  its  base.  These  vessels  are  eminently  elastic, 
and,  as  they  receive  the  charge  of  blood  from  the  ventricles,  become  enlarged  in  every 


42  CIRCULATION  OF  THE  BLOOD. 

direction  and  consequently  project  the  entire  organ  against  the  walls  of  the  chest.  This 
movement  is  aided  by  the  recoil  of  the  ventricles  as  they  discharge  their  contents.  The 
displacement  of  the  heart  during  its  systole  has  long  been  observed  in  vivisections  and 
may  be  demonstrated  in  any  of  the  mammals.  The  most  interesting  observations  on 
this  point  are  those  of  Chauveau  and  Faivre,  which  were  made  upon  a  monkey.  In  this 
animal,  in  which  the  position  of  the  heart  is  very  much  the  same  as  in  the  human  sub- 
ject, the  locomotion  of  the  organ  was  fully  established. 

Twisting  of  the  Heart. — The  spiral  course  of  the  superficial  fibres  would  lead  us  to 
look  for  another  phenomenon  accompanying  its  contraction  ;  namely,  twisting.  If  we 
attentively  watch  the  apex  of  the  heart,  especially  when  its  action  has  become  a  little 
retarded,  there  is  a  palpable  twisting  of  the  point  upon  itself  from  left  to  right  with  the 
systole,  and  an  untwisting  with  the  diastole. 

Hardening  of  the  Heart.— If  the  heart  of  a  living  animal  be  grasped  by  the  hand,  it 
will  be  observed  that  at  each  systole  it  becomes  hardened.  The  fact  that  it  is  composed 
almost  exclusively  of  fibres,  resembling  very  closely  those  of  the  voluntary  muscles, 
explains  this  phenomenon.  Like  any  other  muscle,  it  is  sensibly  hardened  during  con- 
traction. 

Shortening  and  Elongation  of  the  Heart. — The  phenomena  which  we  have  just  de- 
scribed are  admitted  by  all  writers  on  physiology  and  can  easily  be  observed ;  but  the 
change  in  length  of  the  heart  during  its  systole  has  been  a  matter  of  discussion.  All  who 
have  studied  the  heart  in  action  have  observed  changes  in  length  during  contraction  and 
relaxation  ;  but  the  contemporaries  of  Harvey  were  divided  as  to  the  periods  in  the  heart's 
action  which  are  attended  with  elongation  and  shortening.  Harvey  himself  is  not  abso- 
lutely definite  on  this  point.  In  one  passage  he  says,  in  describing  the  systole,  "  that  it  is 
everywhere  contracted,  but  especially  towards  the  sides,  so  that  it  looks  narrower,  a  lit- 
tle longer,  more  drawn  together."  In  his  description  of  the  case  of  the  son  of  the  Vis- 
count Montgomery,  who  suffered  from  ectopia  cordis,  he  states  that  during  the  systole 
the  heart  "emerged  and  protruded."  Vesalius,  Fontana,  and  some  others,  contended  for 
elongation  during  the  systole ;  but  Haller,  Steno,  Lancisi,  and  Bassuel  stated  that  it  be- 
comes shortened.  The  view  generally  entertained  at  the  present  day  is  that  the  heart  is 
shortened  during  its  systole.  There  is  no  doubt  that  the  point  of  the  heart  is  protruded 
during  the  ventricular  systole,  but  this  protrusion  is  not  due  to  elongation  of  the  ventricles. 
By  suddenly  cutting  the  heart  out  of  a  warm-blooded  animal  and  watching  the  phenom- 
ena which  accompany  the  few  regular  contractions  which  follow,  it  is  seen  that  the  ven- 
tricles invariably  shorten  during  the  systole.  This  can  easily  be  appreciated  by  the 
eye,  but  more  readily  if  the  point  of  the  organ  be  brought  just  in  contact  with  a  plane 
surface  at  right  angles,  when,  at  each  contraction,  it  is  unmistakably  observed  to  recede. 
The  following  experiments  we  have  frequently  repeated  before  the  class  of  the  Bellevue 
Hospital  Medical  College,  and  have  satisfied  ourselves  of  their  accuracy.  A  large  New- 
foundland pup,  about  nine  months  old,  was  poisoned  with  woorara,  artificial  respiration 
was  kept  up,  and  the  heart  exposed.  After  showing  the  protrusion  of  the  point  and 
the  apparent  elongation  of  the  heart  while  in  the  chest,  the  organ  was  rapidly  removed, 
placed  upon  the  table,  and  confined  by  two  long  needles  passed  through  the  base,  pinning 
it  to  the  wood.  It  contracted  for  one  or  two  minutes,  and  at  each  systole  the  ventricles 
were  manifestly  shortened.  The  point  was  then  placed  against  an  upright,  and  it  re- 
ceded with  each  systole  about  an  eighth  of  an  inch.  This  phenomenon  was  apparent  to 
all  present.  In  another  experiment,  performed  a  few  weeks  later,  the  heart,  which  had 
been  exposed  in  the  same  way,  was  examined  in  situ,  by  pinning  it  with  two  needles  to 
a  thin  board  passed  under  the  organ.  The  presence  of  the  needles  did  not  seem  to  in- 
terfere with  the  heart's  action,  and,  at  each  ventricular  systole,  the  point  evidently 
approached  the  base.  To  render  this  absolutely  certain,  a  knife  was  fixed  in  the  wood 


SUCCESSION   OF   THE  MOVEMENTS   OF  THE  HEART.  43 

at  right  angles  to  and  touching  the  point  during  the  diastole,  and  a  small  silver  tube 
was  introduced  through  the  walls  into  the  left  ventricle.  At  each  contraction,  a  jet 
of  blood  spurted  out  through  the  tube,  and  the  point  of  the  heart  receded  from  the 
knife  about  an  eighth  of  an  inch.  The  animal  experimented  upon  was  a  dog  a  little 
above  the  medium  size.  These  simple  experiments  demonstrate  that,  in  the  dog  at 
least,  the  ventricles  shorten  during 
their  systole.  The  arrangement  of 
the  muscular  fibres  is  too  nearly 
identical  in  the  heart  of  the  warm- 
blooded animals  to  leave  room  for 
doubt  that  it  also  shortens  in  the 
human  subject.  The  error  which 
has  arisen  in  this  respect,  and  which 
obtained  in  our  first  experiments 

made   in     1861     is   due   to    the   loco-    FlG>  ^-—Diagram  of  the  shortening  of  the  ventricles  during 

systole. 
motion  and  protrusion  of  the  entire    The  dotted  lines  show  the  position  of  the  heart  during  contraction. 

organ,  so  as  to  make  the  point  strike 

against  the  chest.  A  little  reflection  indicates  the  mechanism  of  this  phenomenon. 
During  the  intervals  of  contraction,  the  great  vessels,  particularly  the  aorta  and  pul- 
monary artery,  which  attach  the  base  of  the  heart  to  the  posterior  wall  of  the  thorax, 
are  filled  but  not  distended  with  blood;  at  each  systole,  however,  these  vessels  are 
distended  to  their  utmost  capacity ;  their  elastic  coats  permit  of  considerable  enlarge- 
ment, as  can  be  seen  in  the  living  animal,  and  this  enlargement,  taking  place  in  every 
direction,  pushes  the  whole  organ  forward.  We  have  also  considerable  locomotion  of 
the  heart  from  recoil.  It  is  for  this  reason  that,  observing  the  heart  in  situ,  the 
ventricles  seem  to  elongate.  It  is  only  when  we  examine  the  heart  firmly  fixed,  or 
contracting  after  it  is  removed  from  the  body,  that  we  can  appreciate  the  actual  changes 
which  occur  in  the  length  of  the  ventricles.  During  the  systole  the  ventricles  are  short- 
ened and  are  narrowed  in  their  transverse  diameter,  but  their  antero-posterior  diameter 
is  slightly  increased. 

In  addition  to  the  marked  changes  in  form,  position,  etc.,  which  the  heart  undergoes 
during  its  action,  we  observe,  on  careful  examination,  that  the  surface  of  the  ventricles 
becomes  marked  with  slight  longitudinal  ridges  during  the  systole.  This  was  not  noted 
by  Harvey  but  is  mentioned  by  Haller. 

Impulse  of  the  Heart. — Each  movement  of  the  heart  produces  an  impulse,  which  can 
be  readily  felt  and  sometimes  seen,  in  the  fifth  intercostal  space,  a  little  to  the  left  of  the 
median  line.  Vivisections  have  demonstrated  that  the  impulse  is  synchronous  with  the 
contraction  of  the  ventricles.  If  the  hand  be  introduced  into  the  chest  of  a  living  animal, 
and  the  finger  be  placed  between  the  point  of  the  heart  and  the  walls  of  the  thorax, 
every  time  that  we  have  a  hardening  of  the  point,  the  finger  will  be  pressed  against  the 
side.  If  the  impulse  of  the  heart  be  felt  while  the  finger  is  on  the  pulse,  it  is  evident 
that  the  heart  strikes  against  the  thorax  at  the  time  of  the  distention  of  the  arterial 
system.  The  impulse  is  due  to  the  locomotion  of  the  ventricles.  In  the  words  of  Harvey, 
"the  heart  is  erected,  and  rises  upwards  to  a  point,  so  that  at  this  time  it  strikes  against 
the  breast  and  the  pulse  is  felt  externally."  In  the  case  of  the  son  of  the  Viscount  Mont- 
gomery, already  referred  to,  Harvey  gives  a  most  graphic  description  of  the  manner  in 
which  the  heart  is  "retracted  and  withdrawn"  during  the  diastole,  and  "emerged  and 
protruded  "  during  the  systole. 

Succession  of  the  Movements  of  the  Heart. — "We  have  already  followed,  in  a  general 
way,  the  course  of  the  blood  through  the  heart  and  the  successive  action  of  the  various 
parts ;  but  we  have  yet  to  consider  these  points  more  in  detail,  and  to  ascertain,  if  possi- 
ble, the  relative  periods  of  activity  and  repose  in  each  portion  of  the  organ. 


44  CIRCULATION  OF   THE  BLOOD. 

The  great  points  in  the  succession  of  movements  are  readily  observed  in  the  hearts 
of  cold-blooded  animals,  in  which  the  pulsations  are  very  slow.  In  examining  the  heart 
of  the  frog,  turtle,  or  alligator,  the  alternations  of  repose  and  activity  are  very  strongly 
marked.  During  the  intervals  of  contraction,  the  whole  heart  is  flaccid,  and  the  ventricle 
is  comparatively  pale ;  we  then  see  the  auricles  slowly  filling  with  blood ;  when  they 
have  become  fully  distended,  they  contract  and  fill  the  ventricle,  which,  in  these  animals, 
is  single ;  the  ventricle  immediately  contracts,  its  action  following  upon  the  contraction 
of  the  auricles  as  if  it  were  propagated  from  them.  When  the  heart  is  filled  with  blood, 
it  has  a  dark-red  color,  which  contrasts  strongly  with  its  appearance  after  the  systole. 
This  operation  may  occupy  from  ten  to  twenty  seconds,  giving  an  abundance  of  time  for 
observation.  The  case  is  different,  however,  with  the  warm-blooded  animals,  in  which 
the  anatomy  of  the  heart  is  nearly  the  same  as  in  man.  Here  a  normal  revolution  may 
occupy  less  than  a  second ;  and  it  is  evident  that  the  varied  phenomena  we  have  just 
mentioned  are  followed  with  the  utmost  difficulty.  In  spite  of  this  rapidity  of  action,  it 
can  be  seen  that  a  rapid  contraction  of  the  auricles  precedes  the  ventricular  systole,  and 
that  the  latter  is  synchronous  with  the  impulse. 

Various  estimates  have  been  made  of  the  relative  time  occupied  by  the  auricular  and 
ventricular  contractions;  and  the  question  has  been  at  last  definitely  settled  by  the 
observations  of  Marey,  who  has  constructed  very  ingenious  and  delicate  instruments  for 
registering  the  form  and  frequency  of  the  pulse.  He  devised  a  series  of  most  interesting 
experiments,  in  which  he  was  enabled  to  register  simultaneously  the  pulsations  of  the 
different  divisions  of  the  heart,  and  has  succeeded  in  establishing  a  definite  relation  be- 
tween the  contractions  of  the  auricles  and  ventricles.  The  method  of  Marey  enables 
us  to  determine,  to  a  small  fraction  of  a  second,  the  duration  of  the  contraction  of  each 
of  the  divisions  of  the  heart. 

The  method  of  transmitting  the  movement  from  the  heart  to  a  registering  apparatus 
is  very  simple.  The  apparatus  consists  of  two  little  elastic  bags  connected  together  by 
an  elastic  tube,  the  whole  closed  and  filled  with  air.  A  pressure,  like  the  pressure  of 
the  fingers,  upon  one  of  these  bags  produces,  of  course,  an  instantaneous  and  correspond- 
ing dilatation  of  the  other.  If  we  suppose  one  of  these  bags  to  be  introduced  into  one 
of  the  cavities  of  the  heart,  and  the  other  placed  under  a  small  lever  arranged  on  a  pivot 
so  as  to  be  sensible  to  the  slightest  impression,  it  is  evident  that  any  compression  of  the 
bag  in  the  heart  would  produce  a  corresponding  change  in  volume  in  the  other  bag, 
which  would  be  indicated  by  a  movement  of  the  lever.  Marey  arranged  the  lever  with 
its  short  arm  on  the  elastic  bag,  and  the  long  arm,  provided  with  a  pen,  moving  against 
a  roll  of  paper,  which  passes  along  at  a  uniform  rate.  When  the  lever  is  at  rest  with  the 
paper  set  in  motion,  the  pen  will  make  a  horizontal  mark ;  but  when  the  lever  ascends 
and  descends,  a  corresponding  trace  will  be  made,  and  the  duration  of  any  movement 
can  readily  be  estimated  by  calculating  the  rapidity  of  the  motion  of  the  paper.  The  bag 
which  receives  the  impression  is  called  by  Marey  the  initial  bag,  and  the  other,  which  is 
connected  with  the  lever,  is  called  the  terminal  bag.  The  former  may  be  modified  in 
form  with  reference  to  the  situation  in  which  it  is  to  be  placed. 

The  experiments  of  M.  Marey,  with  reference  to  the  relations  between  the  systole  of 
the  auricles,  the  systole  of  the  ventricles,  and  the  impulse  of  the  heart,  were  performed 
upon  horses,  in  the  following  way  : 

A  sound  is  introduced  into  the  right  side  of  the  heart  through  the  jugular  vein,  an 
operation  which  may  be  performed  with  certainty  and  ease.  This  sound  is  provided  with 
two  initial  bags,  one  of  which  is  lodged  in  the  right  auricle,  while  the  other  passes  into 
the  ventricle.  The  bags  are  connected  with  distinct  tubes  which  pass  one  within  the 
other,  and  are  connected  by  elastic  tubing  with  the  registering  apparatus.  At  each  sys- 
tole of  the  heart,  the  bags  in  its  cavities  are  compressed  and  produce  corresponding 
movements  of  the  levers,  which  may  be  registered  simultaneously. 

To  register  the  impulse  of  the  heart,  an  incision  is  made  through  the  skin  and  the  ex- 


SUCCESSION   OF  THE   MOVEMENTS   OF   THE   HEART. 


45 


ternal  intercostal  muscle  over  the  point  where  the  apex-beat  is  felt.  A  little  bag,  stretched 
over  two  metallic  buttons  separated  by  a  central  rod,  is  then  carefully  secured  in  the 
cavity  thus  formed,  and  connected  by  an  elastic  tube  with  the  registering  apparatus. 
All  the  tubes  are  provided  with  stop-cocks,  so  that  each  initial  bag  may  be  made  to  com- 
municate with  its  lever  at  will.  When  the  operation  is  concluded  and  the  sound  firmly 
secured  in  place  by  a  ligature  around  the  vein,  the  animal  experiences  no  inconvenience, 
is  able  to  walk  about,  eat,  etc.,  and  there  is  every  evidence  that  the  circulation  is  not  in- 
terfered with.  The  cylinders  which  carry  the  paper  destined  to  receive  the  traces  are 
arranged  to  move  by  clock-work  at  a  given  rate.  The  paper  may  also  be  ruled  in  lines, 
the  distances  between  which  represent  certain  fractions  of  a  second.  Fig.  19  represents 
the  apparatus  reduced  to  one-sixth  of  its  actual  size.  Two  of  the  levers  are  connected 


FIG.  19.— Cardiograph.    (Chauveau  and  Marey.) 

The  instrument  is  composed  of  two  principal  elements :  A  E,  the  registering  apparatus,  and  A  S,  the  sphygtno- 
graphic  apparatus,  that  is  to  say,  which  receives,  transmits,  and  amplifies  the  movements  which  are  to  be 
studied."  The  compression  exerted  upon  the  bag  c,  which  is  placed  over  the  apex  of  the  heart  between  the  in- 
tercostal muscles,  is  conducted  by  the  tube  t  c,  which  is  filled  with  air,  to  the  first  lever.  The  compression  ex- 
erted upon  the  bags  o  and  ®,  in  the  double  sound,  is  conducted  by  the  tubes  t  o  and  tv  to  the  two  remaining  levers. 
The  movements  of  the  levers  are  registered  simultaneously  by  the  cylinders  A  E. 


with  the  double  sound  for  the  right  auricle  and  ventricle,  and  one  is  connected  with  the 
bag  destined  to  receive  the  impulse  of  the  heart.  In  an  experiment  upon  a  horse,  every 
thing  being  carefully  arranged  in  the  way  indicated,  the  clock-work  was  set  in  motion, 
and  the  movements  of  the  three  levers  produced  traces  upon  the  paper  which  were 
interpreted  as  follows : 

1.  The  paper  was  ruled  so  that  each  division  represented  one-tenth  of  a  second.    The 
traces  formed  by  the  three  levers  indicated  four  revolutions  of  the  heart.     The  first  revo- 
lution occupied  1TV  sec.,  the  second,  1^  sec.,  the  third,  1^  sec.,  and  the  fourth,  1  sec. 

2.  The  auricular  systole,  as  marked  by  the  first  lever,  immediately  preceded  the  ven- 
tricular systole,  and  occupied  about  two-tenths  of  a  second.     The  elevation  of  the  lever 
indicated  that  it  was  much  more  feeble  than  the  ventricular  systole,  and  sudden  in  its 
character ;  the  contraction,  when  it  had  arrived  at  the  maximum,  being  immediately  fol- 
lowed by  relaxation. 

3.  The  ventricular  systole,  as  marked  by  the  second  lever,  immediately  followed  the 
auricular  systole,  and  occupied  about  four-tenths  of  a  second.     The  almost  vertical  direc- 
tion of  the  trace  and  the  degree  of  elevation  showed  that  it  was  sudden  and  powerful  in 


46  CIRCULATION   OF  THE  BLOOD. 

its  character.  The  abrupt  descent  of  the  lever  showed  that  the  relaxation  was  almost 
instantaneous. 

4.  The  impulse  of  the  heart,  as  marked  by  the  third  lever,  was  shown  to  be  absolute- 
ly synchronous  with  the  ventricular  systole. 

Condensing  the  general  results  obtained  by  Marey,  which  are  of  course  subject  to  a 
certain  amount  of  variation,  we  have,  dividing  the  action  of  the  heart  into  ten  equal 
parts,  three  distinct  periods,  which  occur  in  the  following  order  : 

Auricular  Systole. — This  occupies  two-tenths  of  the  heart's  action.  It  is  feeble  as 
compared  with  the  ventricular  systole,  and  relaxation  immediately  follows  the  contraction. 

Ventricular  Systole. — This  occupies  four-tenths  of  the  heart's  action.  The  contrac- 
tion is  powerful  and  the  relaxation,  sudden.  It  is  absolutely  synchronous  with  the  im- 
pulse of  the  heart. 

Auricular  Diastole. — This  occupies  four-tenths  of  the  heart's  action. 

Force  of  the  Heart. — There  are  few  points  in  physiology  concerning  which  opinions 
have  been  more  widely  divergent  than  the  question  of  the  force  employed  by  the  heart  at 
each  contraction.  Borelli,  who  was  the  first  to  give  a  definite  estimate  of  this  force,  put 
it  at  180,000  pounds,  while  the  calculations  of  Keill  give  only  5  ounces.  These  estimates, 
however,  were  made  on  purely  theoretical  grounds.  Borelli  estimated  the  force  em- 
ployed by  the  deltoid  in  sustaining  a  given  weight  held  at  arm's  length,  and  formed  his 
estimate  of  the  power  of  the  heart  by  comparing  the  weight  of  the  organ  with  that  of 
the  deltoid.  Keill  made  his  estimate  from  a  calculation  of  the  rapidity  of  the  current 
of  blood  in  the  arteries.  Hales  was  the  first  to  investigate  the  question  experimentally, 
by  the  application  of  the  cardiometer.  He  showed  that  the  pressure  of  blood  in  the 
aorta  could  be  measured  by  the  height  to  which  the  fluid  would  rise  in  a  tube  connected 
with  that  vessel,  and  estimated  the  force  of  the  left  ventricle  by  multiplying  the  press- 
ure in  the  aorta  by  the  area  of  the  internal  surface  of  the  ventricle.  The  cardiometer 
has  undergone  various  improvements  and  modifications,  but  the  above  is  the  principle 
which  is  so  extensively  made  use  of  at  the  present  day  in  estimating  the  pressure  of  the 
blood  in  different  parts  of  the  circulatory  system.  First  we  have  the  improvement  of 
Poiseuille,  who  substituted  a  U-tube  partly  filled  with  mercury  for  the  long  straight  tube 
of  Hales;  and  then,  the  various  forms  of  cardiometers  constructed  by  Magendie,  Ber- 
nard, Marey,  and  others,  which  will  be  more  fully  discussed  in  connection  with  the  arte- 
rial circulation.  These  instruments  have  beeji  made  use  of  by  Marey,  with  very  good 
results,  in  investigating  the  relative  force  exerted  by  the  different  divisions  of  the  heart. 

Hales  estimated,  from  experiments  upon  living  animals,  the  height  to  which  the  blood 
would  rise  in  a  tube  connected  with  the  aorta  of  the  human  subject,  at  7  feet  6  inches, 
and  gives  the  area  of  the  left  ventricle  as  15  square  inches.  From  this  he  calculates  the 
force  of  the  left  ventricle  as  equal  to  51'5  pounds.  Although  this  estimate  is  only  an  ap- 
proximation, it  seems  to  be  based  on  more  reasonable  data  than  any  other. 

The  apparatus  of  Marey  for  registering  the  contractions  of  the  different  cavities  of 
the  heart  enabled  him  to  ascertain  the  comparative  force  of  the  two  ventricles  and  the 
right  auricle  ;  the  situation  of  the  left  auricle  precluding  the  possibility  of  introducing  a 
sound  into  its  cavity.  By  first  subjecting  the  bags  to  known  degrees  of  pressure,  the  de- 
gree of  elevation  of  a  lever  may  be  graduated  so  as  to  represent  the  degrees  of  the  car- 
diometer. In  analyzing  traces  made  by  the  left  ventricle,  the  right  ventricle,  and  right 
auricle,  in  the  horse,  Marey  found  that,  as  a  general  rule,  tjie  comparative  force  of  the 
right  and  left  ventricles  is  as  one  to  three.  The  force  of  the  right  auricle  is  comparatively 
insignificant,  being  in  one  case,  as  compared  with  the  right  ventricle,  only  as  one  to  ten. 

Action  of  the  Valves. — "We  have  already  indicated  the  course  of  the  blood  through 
the  cavities  of  the  heart,  and  it  has  been  apparent  that  the  necessities  of  the  circulation 
demand  some  arrangement  by  which  the  current  shall  always  be  in  one  direction.  The 


AUKIOULO-VENTRICULAR  VALVES.  47 

anatomy  of  the  valves  which  guard  the  orifices  of  the  ventricles  gives  an  idea  of  their 
function  ;  but  we  have  yet  to  consider  the  precise  mechanism  by  which  they  are  opened 
and  closed  and  the  way  in  which  regurgitation  is  prevented. 

In  man  and  the  warm-blooded  animals,  there  are  no  valves  at  the  orifices  by  which 
the  veins  open  into  the  auricles.  As  has  already  been  seen,  compared  with  the  ventri- 
cles, the  force  of  the  auricles  is  insignificant ;  and  it  has  farthermore  been  shown  by  ex- 
periment that  the  ventricles  may  be  filled  with  blood  and  the  circulation  continue,  when 
the  auricles  are  entirely  passive.  Although  the  orifices  are  not  provided  with  valves, 
the  circular  arrangement  of  the  fibres  about  the  veins  is  such,  that  during  the  contrac- 
tion of  the  auricles  the  openings  are  considerably  narrowed,  and  regurgitation  cannot 
take  place  to  any  great  extent.  The  force  of  the  blood  flowing  into  the  auricles  like- 
wise offers  an  obstacle  to  its  return.  There  is  really  no  valvular  apparatus  which  oper- 
ates to  prevent  regurgitation  from  the  heart  into  the  veins;  for  the  valvular  folds, 
which  are  so  numerous  in  the  general  venous  system,  and  particularly  in  the  veins  of 
the  extremities,  do  not  exist  in  the  venae  cavas.  The  continuous  flow  of  blood  from  the 
veins  into  the  auricles,  the  feeble  character  of  the  auricular  contractions,  the  arrange- 
ment of  the  fibres  around  the  orifices  of  the  vessels,  and  the  great  size  of  the  auriculo- 
ventricular  openings,  are  conditions  which  provide  sufficiently  for  the  flow  of  blood  into 
the  ventricles. 

Action  of  the  Auricula-  Ventricular  Valves. — After  the  ventricles  have  become  com- 
pletely distended  by  the  auricular  systole,  they  take  on  their  contraction,  which,  it  will 
be  remembered,  is  very  many  times  more  powerful  than  the  contraction  of  the  auricles. 
They  have  to  force  open  the  valves  which  close  the  orifices  of  the  pulmonary  artery  and 
aorta  and  empty  their  contents  into  these  vessels.  To  accomplish  this,  at  the  moment  of 
the  ventricular  systole,  there  is  an  instantaneous  and  complete  closure  of  the  auriculo- 
ventricular  valves,  leaving  but  one  opening  through  which  the  blood  can  pass.  That 
these  valves  close  at  the  moment  of  contraction  of  the  ventricles  is  demonstrated  by  the 
experiments  of  Chauveau  and  Faivre,  who  introduced  the  finger  through  an  opening  into 
the  auricle  and  actually  felt  the  valves  close  at  the  instant  of  the  ventricular  systole. 
This  tactile  demonstration,  and  the  fact  that  the  first  sound  of  the  heart,  which  is  pro- 
duced in  great  part  by  the  closure  of  the  auriculo- ventricular  valves,  is  synchronous 
with  the  ventricular  systole,  leave  no  doubt  as  to  the  mechanism  of  the  closure  of  these 
valves.  It  is  probable  that,  as  the  blood  flows  into  the  ventricles,  the  valves  are  slight- 
ly floated  out,  but  they  are  not  closed  until  the  ventricles  contract. 

If  a  bullock's  heart  be  prepared  by  cutting  away  the  auricles  so  as  to  expose  the 
mitral  and  tricuspid  valves,  securing  the  nozzles  of  a  double  syringe  in  the  pulmonary 
artery  and  aorta,  after  having  destroyed  the  semilunar  valves,  and  if  fluid  be  injected 
simultaneously  into  both  ventricles,  the  play  of  the  valves  will  be  exhibited.  The  mitral 
valve  effectually  prevents  the  passage  of  fluid,  its  edges  being  so  accurately  approxi- 
mated that  not  a  drop  passes  between  them  ;  but,  when  the  pressure  is  considerable,  a 
certain  quantity  of  fluid  passes  the  tricuspid  valve.  There  is,  indeed,  a  certain  amount 
of  insufficiency  at  the  right  auriculo-ventricular  orifice,  which  does  not,  exist  on  the 
opposite  side. 

The  fact  just  noted  was  first  pointed  out  by  Mr.  T.  W.  King,  and  is  called  by  him  the 
"  safety-valve  function  of  the  right  ventricle."  The  advantage  of  this  slight  insufficiency 
is  apparent  on  a  little  reflection.  The  right  ventricle  sends  its  blood  to  the  lungs,  where, 
in  order  to  facilitate  the  respiratory  processes,  the  walls  of  the  capillaries  are  very  thin. 
The  lungs  themselves  are  exceedingly  delicate,  and  an  effusion  of  blood,  or  considerable 
congestion,  would  be  liable  to  be  followed  by  serious  consequences.  To  prevent  this,  the 
right  ventricle  is  not  permitted  to  exert  all  its  force,  under  all  circumstances,  upon  the 
blood  going  into  the  pulmonary  artery ;  but,  when  the  action  of  the  heart  is  exaggerated 
from  any  cause,  the  lungs  are  relieved  by  a  slight  regurgitation,  which  takes  place  through 


48  CIRCULATION  OF  THE   BLOOD. 

the  tricuspid  valve.  The  lungs  are  still  farther  protected  by  the  sufficiency  of  the  mitral 
valve,  which  effectually  prevents  regurgitation  from  the  left  ventricle.  In  the  systemic 
circulation,  the  capillaries  are  less  delicate  ;  extravasation  of  blood  would  not  be  followed 
by  any  serious  results  ;  and  the  circulating  fluid  is  made  to  pass  through  a  considerable 
extent  of  elastic  vessels,  before  it  is  distributed  in  the  tissues.  It  is  evident  that,  on 
the  left  side,  there  is  no  necessity  for  such  a  provision,  and  it  does  not  exist. 

Action  of  the  Aortic  and  Pulmonic  Valves. — The  action  of  the  semilunar  valves  is 
nearly  the  same  upon  both  sides.  In  the  intervals  of  the  ventricular  contractions,  they 
are  closed  and  prevent  regurgitation  of  blood  into  the  ventricles.  The  systole,  however, 
overcomes  the  resistance  of  these  valves  and  forces  the  contents  of  the  ventricles  into  the 
arteries.  During  this  time,  the  valves  are  applied,  or  nearly  applied,  to  the  walls  of  the 
vessel ;  but,  so  soon  as  the  ventricles  cease  their  contraction,  the  constant  pressure  of  the 
blood,  which,  as  we  shall  see  hereafter,  is  very  great,  instantaneously  closes  the  openings. 

The  action  of  the  semilunar  valves  can  be  exhibited  by  cutting  away  a  portion  of  the 
ventricles  in  the  heart  of  a  large  animal,  securing  the  nozzles  of  a  double  syringe  in  the 
aorta  and  pulmonary  artery,  and  forcing  water  into  the  vessels.  In  performing  this  ex- 
periment, it  will  be  noticed  that,  while  the  aortic  semilunar  valves  oppose  the  passage  of 
the  liquid  so  effectually  that  the  aorta  may  be  ruptured  before  the  valves  will  give  way, 
a  considerable  degree  of  insufficiency  exists,  under  a  high  pressure,  at  the  orifice  of  the 
pulmonary  artery.  There  is  at  this  orifice  a  safety-valve  function  as  important  as  that 
ascribed  by  King  to  the  tricuspid  valve.  It  is  evident  that  the  slight  insufficiency  at  the 
pulmonic  orifice  may  be  even  more  directly  important  in  protecting  the  lungs  than  the 
insufficiency  of  the  tricuspid  valve.  The  difference  in  the  sufficiency  of  the  semilunar 
valves  on  the  two  sides  is  fully  as  marked  as  between  the  auriculo-ventricular  valves ; 
and  it  is  surprising  that,  since  the  observations  of  King,  this  fact,  which  we  demonstrated 
for  the  first  time  in  1864,  has  not  attracted  the  attention  of  physiologists. 

It  is  probable  that  the  corpuscles  of  Arantius,  which  are  situated  in  the  middle  of  each 
valvular  curtain,  assist  in  the  accurate  closure  of  the  orifice.  The  sinuses  of  Valsalva, 
situated  in  the  artery  behind  the  valves,  are  regarded  as  facilitating  the  closure  of  the 
valves  by  allowing  the  blood  to  pass  easily  behind  them. 

Sounds  of  the  Heart. — If  the  ear  be  applied  to  the  prsecordial  region,  it  will  be  found 
that  the  action  of  the  heart  is  accompanied  by  certain  sounds.  A  careful  study  of  these 
sounds  and  of  their  modifications  in  disease  has  enabled  the  practical  physician  to  distin- 
guish, to  a  certain  extent,  the  conditions  of  the  heart  by  auscultation.  This  increases 
the  interest  which  attaches  to  the  audible  manifestations  of  the  action  of  the  great  central 
organ  of  the  circulation. 

The  appreciable  phenomena  which  attend  the  heart's  action  are  connected  with  the 
systole  of  the  ventricles.  It  is  this  which  produces  the  impulse  against  the  walls  of  the 
thorax,  and,  as  we  shall  see  farther  on,  the  dilatation  of  the  arterial  system,  called  the 
pulse.  It  is  natural,  therefore,  in  studying  these  phenomena,  to  take  the  systole  as  a 
point  of  departure,  instead  of  the  action  of  the  auricles,  which  we  cannot  appreciate 
without  vivisections ;  and  the  sounds,  which  are  two  in  number,  have  been  called  first 
and  second,  with  reference  to  the  systole. 

The  first  sound  is  absolutely  synchronous  with  the  apex-beat.  The  second  sound 
follows  the  first  'with  scarcely  an  appreciable  interval.  Between  the  second  and  the 
first  sound,  there  is  an  interval  of  silence. 

Some  writers  have  attempted  to  represent  the  sounds  of  the  heart  and  their  relations 
to  each  other,  by  certain  syllables,  as,  "  lull-dup  or  lubb-tub  ;  "  but  it  seems  unnecessary 
to  attempt  to  make  such  a  comparison,  which  can  only  be  appreciated  by  one  who  is 
practically  acquainted  with  the  heart-sounds,  when  the  sounds  themselves  can  be  so 
easily  studied. 


CAUSES  OF  THE  SOUNDS  OF  THE  HEAET.         49 

Both  sounds  are  generally  heard  with  distinctness  over  any  part  of  the  prsecordia. 
The  first  sound  is  heard  with  its  maximum  of  intensity  over  the  body  of  the  heart,  a  little 
below  and  within  the  nipple,  between  the  fourth  and  fifth  ribs,  and  is  propagated  with 
greatest  facility  downward,  toward  the  apex.  The  second  sound  is  heard  with  its  maxi- 
mum of  intensity  at  the  base  of  the  heart,  between  the  nipple  and  the  sternum,  at  about  the 
locality  of  the  third  rib,  and  is  propagated  upward,  along  the  course  of  the  great  vessels. 

The  rhythm  of  the  sounds  bears  a  certain  relation  to  the  rhythm  of  the  heart's  action, 
which  we  have  already  discussed  ;  the  difference  being,  that  we  here  regard  the  heart's 
action  as  commencing  with  the  systole  of  the  ventricles,  while,  in  following  the  action  of 
different  parts  of  the  organ,  we  followed  the  course  of  the  blood  and  commenced  with 
the  systole  of  the  auricles.  Laennec  was  the  first  to  direct  special  attention  to  the  rhythm 
of  these  sounds,  although  they  had  been  recognized  by  Harvey,  who  compared  them  to  the 
sounds  made  by  the  passage  of  fluids  along  the  oesophagus  of  a  horse  when  drinking.  He 
divided  a  single  revolution  of  the  heart  into  four  parts :  the  first  two  parts  are  occupied 
by  the  first  sound ;  the  third  part,  by  the  second  sound  ;  and  in  the  fourth  part  there  is 
no  sound.  He  regarded  the  second  sound  as  following  immediately  after  the  first.  Some 
authors  have  described  a  "  short  silence  "  as  occurring  after  the  first  sound,  and  a  "  leng 
silence,"  after  the  second  sound.  The  short  silence,  if  appreciable  at  all,  is  so  indistinct 
that  it  may  practically  be  disregarded. 

Most  physiologists  regard  the  duration  of  the  first  sound  as  a  little  less  than  two-fourths 
of  the  heart's  action,  and  the  second  sound  as  a  little  more  than  one-fourth.  When  we 
come  to  consider  the  mechanism  of  the  production  of  the  two  sounds,  we  shall  see  that, 
if  our  views  on  that  point  be  correct,  the  first  sound  should  occupy  the  period  of  the  ven- 
tricular systole,  or  four-tenths  of  the  heart's  action,  the  second  sound  about  three-tenths, 
and  the  repose  three-tenths. 

The  first  sound  is  relatively  dull,  low  in  pitch,  and  is  made  up  of  two  elements ;  one, 
a  valvular  element,  in  which  it  resembles  in  character  the  second  sound,  and  the  other,  an 
element  which  is  due  to  the  action  of  the  heart  as  a  muscle.  It  has  been  ascertained  that 
all  muscular  contraction  is  attended  with  a  certain  sound.  To  this  is  added  an  impulsion 
element,  which  is  produced  by  the  striking  of  the  heart  against  the  walls  of  the  thorax. 

The  second  sound  is  relatively  sharp,  high  in  pitch,  and  has  but  one  clear  element, 
which  we  have  already  alluded  to  as  valvular. 

Causes  of  the  Sounds  of  the  Heart. — There  is  now  scarcely  any  difference  of  opinion 
with  regard  to  the  cause  of  the  second  sound  of  the  heart.  The  experiments  of  Rouanet, 
published  in  1832,  settled  beyond  a  doubt  that  it  is  due  to  a  closure  of  the  aortic  and 
pulmonary  semilunar  valves.  In  his  essay  upon  this  subject,  Rouanet  acknowledges  his 
indebtedness  for  the  first  suggestion  of  this  explanation  to  Mr.  Carswell,  who  was  at 
that  time  prosecuting  his  studies  in  Paris.  The  experiments  by  which  this  is  demon- 
strated are  as  simple  as  they  are  conclusive.  First  we  have  the  experiments  of  Rouanet, 
who  imitated  the  second  sound  by  producing  sudden  closure  of  the  aortic  valves  by  a 
column  of  water.  We  then  have  the  experiments,  even  more  conclusive,  of  the  British 
Commission,  in  which  the  semilunar  valves  were  caught  up  by  curved  hooks  introduced 
through  the  vessels  of  a  living  animal,  the  ass,  with  the  result  of  abolishing  the  second 
sound  and  substituting  for  it  a  hissing  murmur.  When  the  instruments  were  with- 
drawn and  the  valves  permitted  to  resume  their  action,  the  normal  sound  returned. 

It  is  unnecessary  to  discuss  the  various  theories  which  have  been  advanced  to  explain 
the  second  sound,  as  it  is  now  generally  acknowledged  to  be  due  to  the  sudden  closure 
of  the  semilunar  valves  at  the  orifices  of  the  aorta  and  pulmonary  artery.  We  remark, 
however,  that  the  sound  is  heard  with  its  maximum  of  intensity  over  the  site  of  these 
valves,  and  is  propagated  along  the  great  vessels,  to  which  they  are  attached.  It  also 
occurs  precisely  at  the  time  of  their  closure ;  viz.,  immediately  following  the  ventricular 
systole. 

4 


50  CIRCULATION   OF  THE  BLOOD. 

The  cause  of  the  first  sound  of  the  heart  has  not,  until  within  a  few  years,  been  so 
well  understood.  It  was  maintained  by  Rouanet  that  this  sound  was  produced  by  the 
sudden  closure  of  the  auriculo-ventricular  valves;  but  the  situation  of  these  valves  ren- 
dered it  difficult  to  demonstrate  this  by  actual  experiment.  We  have  already  seen,  that, 
while  the  second  sound  is  purely  valvular  in  its  character,  the  first  sound  is  composed  of 
a  certain  number  of  different  elements ;  but  auscultatory  experiments  have  been  made  by 
which  all  but  the  valvular  element  are  eliminated  and  the  character  of  the  first  sound 
made  to  resemble  that  of  the  second.  Conclusive  observations  on  this  point  were  made 
a  few  years  ago  by  Dr.  Austin  Flint,  constituting  part  of  an  essay  which  received  the 
prize  of  the  American  Medical  Association  in  1858.  In  this  essay,  the  following  points 
were  established : 

1.  If  a  folded  handkerchief  be  placed  between  the  stethoscope  and  integument,  the 
first  sound  is  divested  of  some  of  its  most  distinctive  features.     It  loses  the  quality  of  im- 
pulsion and  presents  a  well-marked  valvular  quality. 

2.  In  many  instances,  when  the  stethoscope  is  applied  to  the  prsecordia  while  the 
subject  is  in  a  recumbent  posture  and  the  heart  is  removed  by  force  of  gravity  from  the 
anterior  wall  of  the  thorax,  the  first  sound  becomes  purely  valvular  in  character  and  as 
short  as  the  second. 

3.  When  the  stethoscope  is  applied  to  the  chest  a  little  distance  from  the  point  where 
the  first  sound  is  heard  with  its  maximum  of  intensity,  it  presents  only  its  valvular  ele- 
ment. 

These  observations,  taken  in  connection  with  the  fact  that  the  first  sound  occurs  when 
the  ventricles  contract  and  necessarily  accompanies  the  closure  of  the  auriculo-ventricular 
valves,  show  pretty  conclusively  that  these  valves  produce  at  least  one  element  of  the 
sound.  In  farther  support  of  this  opinion,  we  have  the  fact  that  the  first  sound  is  heard 
with  its  maximum  of  intensity  over  the  site  of  the  valves  and  is  propagated  downward 
along  the  ventricles,  to  which  the  valves  are  attached.  Actual  experiments  are  not  want- 
ing to  confirm  this  view.  Chauveau  and  Faivre  have  succeeded  in  abolishing  the  first 
sound  by  the  introduction  of  a  wire  ring  into  the  auriculo-ventricular  orifice  through  a 
little  opening  in  the  auricle,  so  as  to  prevent  the  closure  of  the  valves.  When  this  is 
done,  the  first  sound  is  lost;  but  on  taking  it  out  of  the  opening  the  sound  returns. 
These  observers  also  abolished  the  first  sound  by  introducing  a  small  curved  tenotomy- 
knife  through  the  auriculo-ventricular  orifice  and  dividing  the  chordse  tendinea).  In 
this  experiment  a  loud  rushing  murmur  took  the  place  of  the  sound.  These  observations 
and  experiments  settle  beyond  question  the  fact  that  the  closure  of  the  auriculo-ven- 
tricular valves  produces  one  element  of  the  first  sound. 

The  other  elements  which  enter  into  the  composition  of  the  first  sound  are  not  so 
prominent  as  the  one  we  have  just  considered,  although  they  serve  to  give  it  its  pro- 
longed and  "  booming  "  character.  These  elements  are,  a  sound  like  that  produced  by 
any  large  muscle  during  its  contraction,  called  by  some  the  muscular  murmur,  and  the 
sound  produced  by  the  impulse  of  the  heart  against  the  walls  of  the  chest. 

There  can  be  no  doubt  but  that  the  muscular  murmur  is  one  of  the  elements  of  the 
first  sound ;  and  it  is  this  which  gives  its  prolonged  character  when  the  stethoscape  is 
applied  over  the  body  of  the  organ,  as  the  sound  produced  in  muscles  continues  during 
the  whole  period  of  their  contraction.  Admitting  this  to  be  an  element  of  the  first  sound, 
we  can  understand  how  its  duration  must  necessarily  coincide  with  that  of  the  ventricular 
systole.  We  can  appreciate,  also,  how  all  but  the  valvular  element  is  eliminated  when 
the  stethoscope  is  moved  from  the  body  of  the  heart,  the  muscular  sound  not  being  prop- 
agated as  completely  as  the  sound  made  by  the  closure  of  the  valves. 

The  impulse  of  the  heart  against  the  walls  of  the  thorax  also  contributes  to  produce 
the  first  sound.  This  is  demonstrated  by  noting  the  difference  in  the  sound  when  the 
subject  is  lying  upon  the  back,  and  when  he  is  upright,  by  interposing  any  soft  sub- 
stance between  the  stethoscope  and  the  chest,  or  by  auscultating  the  heart  after  the 


FREQUENCY   OF  THE  HEART'S  ACTION".  51 

sternum  has  been  removed.  Under  these  conditions,  the  first  sound  loses  its  booming 
character,  retaining,  however,  the  muscular  element,  when  the  instrument  is  applied  to 
the  exposed  organ. 

The  first  sound  of  the  heart  is  complex.  It  is  produced  by  the  sudden  closure  of  the 
auriculo- ventricular  valves  at  the  beginning  of  the  ventricular  systole,  to  which  are  super- 
added,  the  muscular  sound,  due  to  the  contraction  of  the  muscular  fibres  of  the  heart,  and 
the  impulsion-sound,  due  to  the  shock  of  the  organ  against  the  walls  of  the  thorax. 

The  second  sound  is  simple.  It  is  produced  by  the  sudden  closure  of  the  aortic  and 
pulmonic  semilunar  valves,  immediately  following  the  ventricular  systole. 

It  is  of  the  greatest  importance,  with  reference  to  pathology,  to  have  a  clear  idea  of 
the  currents  of  blood  through  the  heart,  with  their  exact  relation  to  the  sounds  and 
intervals.  At  the  commencement  of  the  first  sound,  the  blood  is  forcibly  thrown  from 
the  ventricles  into  the  pulmonary  artery  on  the  right  side  and  the  aorta  on  the  left, 
and  the  auriculo-ventricular  valves  are  suddenly  closed.  During  the  entire  period  oc- 
cupied by  this  sound,  the  blood  is  flowing  rapidly  through  the  arterial  orifices,  and  the 
auricles  are  receiving  blood  slowly  from  the  venae  cavas  and  the  pulmonary  veins.  When 
the  second  sound  occurs,  the  ventricles  having  become  suddenly  relaxed,  the  recoil  of 
the  arterial  walls,  acting  upon  the  column  of  blood,  immediately  closes  the  semilunar 
valves  upon  the  two  sides.  The  auricles  continue  to  dilate,  and  the  ventricles  are  slowly 
receiving  blood.  Immediately  following  the  second  sound,  during  the  first  part  of  the 
interval,  the  auricles  become  fully  dilated ;  and,  in  the  last  part  of  the  interval,  imme- 
diately preceding  the  first  sound,  the  auricles  contract  and  the  ventricles  are  fully 
dilated.  This  completes  a  single  revolution  of  the  heart. 

Frequency  of  the  Heart*  s  Action. — Physicians  have  always  attached  the  greatest  im- 
portance to  the  frequency  of  the  action  of  the  heart,  as  one  of  the  important  indications 
of  the  general  condition  of  the  system.  The  variations  which  are  met  with  in  health,  de- 
pending upon  age,  sex,  muscular  activity,  the  condition  of  the  digestive  system,  etc.,  point 
to  the  fact  that  the  action  of  the  heart  is  closely  allied  to  the  various  functions  of  the 
economy  and  readily  sympathizes  with  their  derangements.  As  each  ventricular  systole 
is  followed  by  an  expansion  of  the  arteries,  which  is  readily  appreciated  by  the  touch,  it 
is  more  convenient  to  study  the  succession  of  these  movements  by  exploring  the  vessels 
than  by  examination  of  the  heart  itself.  Leaving  out  certain  of  the  qualities  of  the  pulse, 
this  becomes  an  exact  criterion  of  the  acts  of  the  heart. 

The  number  of  pulsations  of  the  heart  is  not  far  from  seventy  per  minute  in  an  adult 
male  and  is  from  six  to  ten  more  in  a  female.  There  are  individual  cases,  however,  in 
which  the  pulse  is  normally  much  slower  or  more  frequent  than  this,  a  fact  which  must  be 
remembered  when  examining  the  pulse  in  disease.  It  is  said  that  the  pulse  of  Napoleon  I. 
was  only  forty  per  minute.  Dr.  Dunglison  mentions  a  case  which  came  under  his  own 
observation,  in  which  the  pulse  presented  an  average  of  thirty-six  per  minute.  The  same 
author  states  that  the  pulse  of  Sir  William  Congreve  was  never  below  one  hundred  and 
twenty-eight  per  minute,  in  health.  It  is  by  no  means  unfrequent  to  find  a  healthy  pulse 
of  a  hundred  or  more  a  minute ;  but,  in  the  cases  reported  in  which  the  pulse  has  been 
found  to  be  forty  or  less,  it  is  possible  that  every  alternate  beat  of  the  heart  was  so  feeble 
as  to  produce  no  perceptible  arterial  pulsation.  In  this  case,  the  fact  may  be  ascertained 
by  listening  to  the  heart  while  the  finger  is  placed  upon  the  artery.  Such  an  instance  has 
lately  come  under  our  observation,  in  which  the  pulse  was  apparently  but  thirty-five  per 
minute. 

Influence  of  Age  and  Sex. — In  both  the  male  and  female,  observers  have  constantly 
found  a  great  difference  in  the  rapidity  of  the  heart's  action  at  different  periods  of  life. 
The  observations  of  Dr.  Guy  on  this  point  are  very  numerous  and  were  made  with  the 
utmost  care  with  regard  to  the  conditions  of  the  system  at  the  time  the  pulse  was  taken 


52  CIKCULATION  OF  THE  BLOOD. 

in  each  case.  All  were  taken  at  the  same  hour  and  with  the  subject  in  a  sitting  posture. 
Dr.  Guy  found  the  pulsations  of  the  heart  in  the  fcfitus  to  be  pretty  uniformly  140  per 
minute.  At  birth,  the  pulse  is  136.  It  gradually  diminishes  during  the  first  year  to 
about  128.  The  second  year,  the  diminution  is  quite  rapid,  the  tables  of  Dr.  Guy  giving 
107  as  the  mean  frequency  at  two  years  of  age.  After  the  second  year,  the  frequency 
progressively  diminishes  until  adult  life,  when  it  is  at  its  minimum,  which  is  about  70  per 
minute.  It  is  a  common  but  erroneous  impression  that  the  pulse  diminishes  in  frequency 
in  old  age.  On  the  contrary,  numerous  observations  show  that  at  the  later  periods  of 
life  the  movements  of  the  heart  become  slightly  accelerated,  ranging  from  75  to  80. 

During  early  life  there  is  no  marked  and  constant  difference  in  the  rapidity  of  the 
pulse  in  the  sexes ;  but,  toward  the  age  of  puberty,  the  development  of  the  sexual  pecu- 
liarities is  accompanied  with  an  acceleration  of  the  heart's  action  in  the  female,  which 
continues  even  into  old  age.  The  differences  at  different  ages  are  shown  in  the  following 
table,  compiled  from  the  observations  of  Dr.  Guy : 


MALES. 
Average  pulsations. 
97        .... 

FEMALES. 
Average  pulsations. 
98 

.    84    . 

.    94 

76        .... 
.   73    . 

82 
.    80 

70       .... 
.    68    . 

78 
.    78 

70        .... 

77 

.    67    . 

.    76 

68        .... 
.        .        .    70    . 

77 
.    78 

67        .... 
.    71    . 

81 

.    82 

From  2  to    7  years 

"     8  "  14  " 

"  14  "  21  " 

"  21  "  28  " 

"  28  "  35  " 

"  35  "  42  " 

«  42  "  49  " 

«  49  "  56  " 

"  56  "  63  " 

"  63  "  70  " 

"  70  "  77  " 

"  77  "  84  " 

Influence  of  Digestion. — The  condition  of  the  digestive  system  has  a  marked  influence 
on  the  rapidity  of  the  pulse,  and  there  is  generally  an  increase  in  the  pulse  of  from  five 
to  ten  beats  per  minute  after  each  meal.  Prolonged  fasting  diminishes  its  frequency  by 
from  twelve  to  fourteen  beats.  Alcohol  first  diminishes  and  afterward  accelerates  the 
pulse.  Coffee  is  said  to  accelerate  the  pulse  in  a  marked  degree.  It  has  been  ascertained 
that  the  pulse  is  accelerated  to  a  greater  degree  by  animal  than  by  vegetable  food.  These 
variations  have  long  been  recognized  by  physiologists. 

Influence  of  Posture  and  Muscular  Exertion. — It  has  been  observed  that  the  position 
of  the  body  has  a  very  marked  influence  upon  the  rapidity  of  the  pulse.  Experiments 
of  a  very  interesting  character  have  been  made  by  Dr.  Guy  and  others,  with  a  view  to 
determine  the  difference  in  the  pulse  in  different  postures.  In  the  male,  there  is  a  differ- 
ence of  about  ten  beats  between  standing  and  sitting,  and  fifteen  beats  between  standing 
and  the  recumbent  posture.  In  the  female,  the  variations  with  position  are  not  so  great. 
The  average  given  by  Dr.  Guy  is,  for  the  male  standing,  81 ;  sitting,  71 ;  lying,  66  ;— 
for  the  female :  standing,  91 ;  sitting,  84 ;  lying,  80.  This  is  given  as  the  average  of  a 
large  number  of  observations.  There  were  a  few  instances,  however,  in  which  there  was 
scarcely  any  variation  with  posture,  and  some  in  which  the  variation  was  much  greater 
than  the  average.  In  the  inverted  posture,  the  pulse  was  found  to  be  reduced  about 
fifteen  beats. 

The  question  at  once  suggests  itself  whether  the  acceleration  of  the  pulse  in  sitting 
and  standing  may  not  be  due,  in  some  measure,  to  the  muscular  effort  required  in  mak- 
ing the  change  of  posture.  This  is  answered  by  the  farther  experiments  of  Dr.  Guy,  in 
which  the  subjects  were  placed  on  a  revolving  board,  and  the  posture  changed  without 


INFLUENCE   OF  EXERCISE   AND   TEMPERATURE.  53 

any  muscular  effort.  The  same  results  as  those  cited  above  were  obtained  in  these  ex- 
periments, showing  that  the  difference  is  due  to  the  position  of  the  body  alone.  In  a 
single  observation,  Dr.  Guy  found  the  pulse,  standing,  to  be  89 ;  lying,  77 ;  difference, 
12.  "With  the  posture  changed  without  any  muscular  effort,  the  results  were  as  follows : 
standing,  87 ;  lying,  74 ;  difference,  13.  Various  theoretical  explanations  of  these  vari- 
ations have  been  offered  by  physiologists ;  but  Dr.  Guy  seems  to  have  settled  experi- 
mentally the  fact  that  the  acceleration  is  due  in  part  to  the  muscular  effort  required  to 
maintain  the  body  in  the  sitting  and  standing  positions.  The  following  are  the  results 
of  experiments  which  bear  conclusively  on  this  point,  in  which  it  is  shown  that  when 
the  body  is  carefully  supported  in  the  erect  or  sitting  posture,  so  as  to  be  maintained 
without  muscular  effort,  the  pulse  is  less  frequent  than  when  the  subject  is  standing ; 
and,  farthermore,  that  the  pulse  is  accelerated,  in  the  recumbent  posture,  when  the  body 
is  only  partially  supported : 

"1.  Difference  between  the  pulse  in  the  erect  posture,  without  support,  and  leaning 
in  the  same  posture,  in  an  average  of  twelve  experiments  on  the  writer,  12  beats ;  and 
on  an  average  of  eight  experiments  on  other  healthy  males,  8  beats. 

"  2.  Difference  in  the  frequency  of  the  pulse  in  the  recumbent  posture,  the  body  fully 
supported,  and  partially  supported,  14  beats,  on  an  average  of  five  experiments. 

"  3.  Sitting  posture  (mean  of  ten  experiments  on  the  writer),  back  supported,  80 ; 
unsupported,  87 ;  difference,  7  beats. 

"4.  Sitting  posture  with  the  legs  raised  at  right  angles  with  the  body  (average  of 
twenty  experiments  on  the  writer),  back  unsupported,  86 ;  supported,  68 ;  difference,  18 
beats.  An  average  of  fifteen  experiments  of  the  same  kind  on  other  healthy  males  gave 
the  following  numbers:  back  unsupported,  80;  supported,  68;  a  difference  of  12  beats." 

Influence  of  Exercise,  etc.— It  is  a  fact  generally  admitted  that  muscular  exertion  in- 
creases the  frequency  of  the  pulsations  of  the  heart ;  and  the  experiments  just  cited  show 
that  the  difference  in  rapidity,  which  is  by  some  attributed  to  change  in  posture  (some 
positions,  it  is  fancied,  offering  fewer  obstacles  to  the  current  of  blood  than  others),  is 
mainly  due  to  muscular  exertion.  Every  one  knows,  indeed,  that  the  action  of  the  heart 
is  much  more  rapid  after  violent  exertion,  such  as  running,  lifting,  etc.  Experiments  on 
this  point  date  from  quite  a  remote  period.  Bryan  Robinson,  who  published  a  treatise 
on  the  "Animal  Economy"  in  1734,  states,  as  the  result  of  observation,  that  a  man  in 
the  recumbent  position  has  64  pulsations  per  minute ;  sitting,  68 ;  after  a  slow  walk,  78 ; 
after  walking  four  miles  in  an  hour,  100 ;  and  140  to  150  after  running  as  fast  as  he 
could.  This  general  statement,  which  has  been  repeatedly  verified,  shows  the  powerful 
influence  of  the  muscular  system  on  the  heart.  The  fact  is  so  familiar  that  it  need  not 
be  farther  dwelt  upon. 

The  influence  of  sleep  upon  the  action  of  the  heart  reduces  itself  almost  entirely  to 
the  proposition  that,  during  this  condition,  we  have  an  entire  absence  of  muscular  effort, 
and  consequently  the  number  of  beats  is  less  than  when  the  individual  is  aroused.  It 
has  been  found  that  there  is  no  difference  in  the  pulse  between  sleep  and  perfect  quiet  in 
the  recumbent  posture.  This  fact  obtains  in  the  adult  male ;  but  it  is  said  by  Quetelet 
that  there  is  a  marked  difference  in  females  and  young  children,  the  pulse  being  always 
slower  during  sleep. 

Influence  of  Temperature. — The  influence  of  extremes  of  temperature  upon  the  heart 
is  very  decided.  The  pulse  may  be  doubled  by  remaining  a  very  few  minutes  exposed 
to  extreme  heat.  Bence  Jones  and  Dickinson  have  ascertained  that  the  pulse  may  be 
very  much  reduced  in  frequency,  for  a  short  time,  by  the  cold  douche.  It  has  also  been 
remarked  that  the  pulse  is  habitually  more  rapid  in  warm  than  in  cold  climates. 

Although  many  circumstances  materially  affect  the  rapidity  of  the  heart's  action,  they 
do  not  complicate,  to  any  great  extent,  our  examinations  of  the  pulse  in  disease.  In 


54:  CIRCULATION  OF  THE   BLOOD. 

cases  which  present  considerable  febrile  movement,  the  patient  is  generally  in  the  recum- 
bent posture.  The  variations  induced  by  violent  exercise  are  easily  recognized,  while 
those  dependent  upon  temperature,  the  condition  of  the  digestive  system,  etc.,  are  so 
slight  that  they  may  practically  be  disregarded.  It  is  necessary  to  bear  in  mind,  how- 
ever, the  variations  which  exist  in  the  sexes  and  at  different  periods  of  life,  as  well  as 
the  possibility  of  individual  peculiarities,  when  the  action  of  the  heart  may  be  extraor- 
dinarily rapid  or  slow. 

Influence  of  Respiration  upon  the  Action  of  the  Heart. — The  relations  between  the 
functions  of  circulation  and  respiration  are  very  intimate,  and  one  function  cannot  go  on 
without  the  other.  If  circulation  be  arrested,  the  muscles,  being  no  longer  supplied  with 
fresh  blood,  soon  lose  their  contractile  power,  and  respiration  ceases.  We  shall  also  find 
that  circulation  is  impossible  if  respiration  be  permanently  arrested.  When  respiration 
is  imperfectly  performed,  the  action  of  the  heart  is  slow  and  labored.  All  physicians 
are  familiar  with  the  slow,  full  pulse,  indicating  labored  action  of  the  heart,  which 
occurs  in  profound  coma.  The  effects  of  arrest  of  respiration  are  marked  in  all  parts 
of  the  circulatory  system,  arteries,  capillaries,  and  veins ;  but  the  disturbances  thus  pro- 
duced all  react  upon  the  heart,  and  the  modifications  which  take  place  in  the  action  of 
this  organ  are  of  the  greatest  interest  and  importance. 

If  the  heart  be  exposed  in  a  living  animal  and  artificial  respiration  be  kept  up, 
although  the  pulsations  are  increased  in  frequency  and  diminished  in  force,  after  a  time 
they  become  perfectly  regular  and  continue  thus  so  long  as  air  is  adequately  supplied  to 
the  lungs.  Under  these  circumstances,  we  have  the  respiration  entirely  at  our  com- 
mand and  can  study  the  effects  of  its  arrest  upon  the  heart  with  the  greatest  facility. 
If  we  arrest  respiration,  we  observe  the  following  changes  in  the  action  of  the  heart  : 
For  a  few  seconds  pulsations  go  on  as  usual,  but  in  about  a  minute  they  begin  to 
diminish  in  frequency.  At  the  same  time,  the  heart  becomes  engorged  with  blood,  and 
the  distention  of  its  cavities  rapidly  increases.  For  a  time  its  contractions  are  com- 
petent to  discharge  the  entire  contents  of  the  left  ventricle  into  the  arterial  system,  and 
a  cardiometer  applied  to  an  artery  will  indicate  a  great  increase  in  the  pressure  of  blood. 
A  corresponding  increase  in  the  movements  of  the  mercury  will  be  noted  at  each 
action  of  the  heart,  indicating  that  the  organ  is  acting  with  abnormal  vigor.  If  respira- 
tion be  still  discontinued,  the  engorgement  becomes  intense,  the  heart  at  each  diastole 
being  distended  to  its  utmost  capacity.  It  now  becomes  incapable  of  emptying  itself, 
the  contractions  become  very  unfrequent,  perhaps  three  or  four  in  a  minute,  and  are 
progressively  enfeebled.  The  organ  is  dark,  almost  black,  owing  to  the  circulation  of 
venous  blood  in  its  substance.  If  respiration  be  not  resumed,  this  distention  continues, 
the  contractions  become  less  frequent  and  more  feeble,  and  in  a  few  minutes  they  en- 
tirely cease. 

The  arrest  of  the  action  of  the  heart,  under  these  circumstances,  is  chiefly  mechani- 
cal. The  unaerated  blood  passes  with  difficulty  through  the  capillaries  of  the  system, 
and,  as  the  heart  is  constantly  at  work,  the  arteries  become  immensely  distended.  This 
is  proven  by  the  great  increase  in  the  arterial  pressure  while  these  vessels  are  full  of 
black  blood.  If  we  now  closely  examine  the  heart  and  great  vessels,  we  are  able  to 
note  distinctly  the  order  in  which  they  become  distended.  These  phenomena  were  par- 
ticularly noticed  and  described  by  Prof.  Dalton,  and  they  demonstrate  conclusively  that, 
in  asphyxia,  the  obstruction  to  the  circulation  commences,  not  in  the  lungs,  as  is  com- 
monly supposed,  but  in  the  capillaries  of  the  system,  and  is  propagated  backward  to 
the  heart  through  the  arteries.  The  distention  of  the  heart  in  asphyxia  is  therefore  due 
to  the  fact  that  unaerated  blood  cannot  circulate  in  the  systemic  capillaries.  When  thus 
distended,  the  muscular  fibres  of  the  heart  become  paralyzed,  like  any  muscle  after  a 
severe  strain. 

If  respiration  be  resumed  at  any  time  before  the  heart's  action  has  entirely  ceased,  the 


RHYTHMICAL  CONTRACTIONS  OF  THE  HEART.         55 

organ  in  a  few  moments  resumes  its  normal  function.  We  first  notice  a  change  from  the 
dusky  hue  it  has  assumed  to  a  vivid  red,  which  is  owing  to  the  circulation  of  arterial 
blood  in  its  capillaries.  The  distention  then  becomes  gradually  relieved,  and,  for  a  few 
moments,  the  pulsations  are  abnormally  frequent.  If  we  now  open  an  artery,  it  will  be 
found  to  contain  red  blood.  An  instrument  applied  to  an  artery  will  show  a  diminution 
in  arterial  pressure  and  in  the  force  of  the  heart's  action,  if  the  arrest  of  respiration  have 
been  carried  only  far  enough  to  moderately  distend  the  heart ;  or  there  is  an  increase 
in  the  pressure  and  force  of  the  heart,  if  its  action  have  been  nearly  arrested.  A  few 
moments  of  regular  insufflation  will  cause  the  pulsations  to  resume  their  normal  char- 
acter and  frequency. 

In  the  human  subject,  the  effects  of  temporary  or  permanent  arrest  of  respiration  on 
the  heart  are  undoubtedly  the  same  as  those  observed  in  experiments  upon  the  warm- 
blooded animals.  In  the  same  way,  also,  it  is  possible  to  restore  the  normal  action  of  the 
organ,  if  respiration  be  not  too  long  suspended,  by  the  regular  introduction  of  fresh  air 
into  the  lungs.  The  numerous  examples  of  animation  restored  by  artificial  respiration,  in 
drowning,  etc.,  are  evidence  of  this  fact.  In  cases  of  asphyxia,  those  measures  by  which 
artificial  respiration  is  most  effectually  maintained  have  been  found  most  efficient. 

Certain  individuals  have  been  said  to  have  the  power  of  temporarily  arresting  the 
action  of  the  heart  by  a  voluntary  suspension  of  respiration.  The  most  remarkable  case 
of  this  kind  on  record  is  that  of  Colonel  Townshend,  which  is  quoted  in  many  works  on 
physiology.  Colonel  Townshend  was  said  to  be  able  to  arrest  respiration  and  the  action 
of  the  heart  so  completely  as  to  simulate  death.  When  in  this  condition,  the  pulse  was 
not  perceptible  at  the  wrist  or  over  the  pnecordia,  a  mirror  held  before  the  mouth  was 
not  tarnished,  and  he  was  to  all  appearances  dead.  On  one  occasion,  in  the  presence  of 
several  medical  gentlemen,  he  remained  in  this  condition  for  half  an  hour ;  afterward 
the  functions  of  respiration  and  circulation  becoming  gradually  reestablished.  This,  to 
say  the  least,  is  a  very  remarkable  case,  but  it  is  credited  by  many  physiologists. 

Cause  of  the  Rhythmical  Contractions  of  the  Heart. 

The  phenomena  attending  the  action  of  the  heart  present  few  difficulties  in  their 
investigation,  compared  with  the  study  of  the  cause  of  the  regular  contractions  and 
relaxations,  which  commence  early  in  fostal  development  to  terminate  only  with  life. 
This  interesting  question  has  long  engaged  the  attention  of  physiologists  and  has  been 
the  subject  of  numerous  experiments  and  speculations.  It  would  be  idle  to  follow  the 
various  theories  which  have  been  proposed  to  account  for  this  constant  action,  except  as 
a  subject  of  purely  historical  interest ;  for  many  of  them  are  based  upon  a  very  imperfect 
knowledge  of  the  phenomena  of  the  circulation.  At  the  present  day,  although  we  are 
perhaps  as  far  as  ever  from  a  knowledge  of  the  actual  cause  of  the  regular  movements, 
we  are  pretty  well  acquainted  with  the  various  conditions  by  which  they  are  regulated 
and  modified.  We  know,  for  example,  how  to  induce  contraction  in  a  living  muscle  or 
one  which  is  just  separated  from  the  organism  and  has  not  yet  lost  what  we  call  its  vital 
properties,  but  we  must  confess  our  utter  ignorance  when  we  ask  ourselves  why  it  acts 
in  response  to  a  stimulus.  The  advances  that  have  been  made  in  chemistry  and  micro- 
scopical anatomy  do  not  disclose  the  so-called  vital  principle ;  and  when  we  come  to 
examine  the  various  conditions  under  which  the  heart  will  continue  its  contractions,  we 
are  arrested  by  the  impossibility  of  fathoming  the  mystery  of  the  cause  of  contraction. 
The  heart  is,  anatomically,  very  much  like  the  voluntary  muscles  ;  but  it  has  a  constant 
function  to  perform  and  seems  to  act  without  any  palpable  excitation,  while  the  latter, 
which  have  an  occasional  function,  act  only  under  the  influence  of  a  natural  stimulus,  like 
the  nervous  force,  or  under  artificial  irritation.  The  movements  of  the  heart  are  not  the 
only  examples  of  what  seems  to  be  spontaneous  action.  The  ciliated  epithelium  is  in  mo- 
tion from  the  beginning  to  the  end  of  life,  and  will  continue  for  a  certain  time,  even  after 
the  cells  are  detached  from  the  organism.  This  motion  cannot  be  explained,  unless  we 


56  CIRCULATION  OF  THE  BLOOD. 

call  it  an  explanation  to  say  that  it  is  dependent  on  vital  properties.  But  if  we  are  yet 
ignorant  of  the  actual  cause  of  the  rhythmical  contraction  of  the  heart,  we  are  pretty 
well  acquainted  with  the  influences  which  render  its  action  regular,  powerful,  and 
sufficient  for  the  purposes  of  the  economy.  It  will  facilitate  our  comprehension  of  this, 
to  compare  the  action  of  the  heart  with  that  of  the  ordinary  voluntary  muscles. 

In  the  first  place,  every  one  knows  that  the  action  of  the  heart  is  involuntary.  We 
can  neither  arrest,  retard,  nor  accelerate  its  pulsations  by  a  direct  effort  of  the  will.  In 
this  statement,  we  of  course  except  those  examples  of  arrest  by  the  stoppage  of  respira- 
tion or  acceleration  by  violent  exercise,  etc.  In  this  respect  the  heart  differs  from  cer- 
tain muscles,  like  the  muscles  of  respiration,  which  act  involuntarily,  it  is  true,  but  the 
action  of  which  may  be  temporarily  arrested  or  accelerated  by  a  direct  voluntary  effort. 
The  last-mentioned  fact  gives  us  the  difference  between  the  heart  and  all  other  striated 
muscles.  All  of  them,  in  order  to  contract,  must  receive  a  stimulus,  either  natural  or 
artificial.  The  natural  stimulus  comes  from  the  nervous  centres  and  is  conducted  by  the 
nerves.  If  the  nerves  going  to  any  of  the  respiratory  muscles,  for  example,  be  divided, 
the  muscle  is  paralyzed  and  will  not  contract  without  some  kind  of  irritation.  Connec- 
tion with  the  nervous  system  does  not  seem  necessary  to  the  action  of  the  heart,  for 
it  will  contract,  especially  in  the  cold-blooded  animals,  some  time  after  its  removal  from 
the  body. 

When  a  muscle  has  been  removed  from  the  body  and  is  subjected  to  a  stimulus,  such 
as  galvanism  or  mechanical  or  chemical  irritation,  it  is  thrown  into  contraction ;  but,  if 
carefully  protected  from  irritation,  it  will  remain  quiescent.  Contraction  in  this  instance 
is  evidently  produced 'by  the  application  of  the  stimulus;  but  the  question  arises,  Why 
does  the  muscle  thus  respond  to  stimulation  ?  This  is  a  question  which  it  is  impossible  to 
answer  satisfactorily,  but  one  concerning  which  our  ideas,  since  the  time  of  Haller,  have 
assumed  a  definite  form.  This  great  physiologist  called  the  property  which  causes  the 
muscle  thus  to  contract,  irritability ;  which  is  nothing  more  nor  less  than  an  unexplained 
property  inherent  in  the  muscle  and  continuing  so  long  as  it  retains  its  absolute  physical 
and  chemical  integrity.  More  than  a  hundred  years  ago,  Haller  described  certain  tissues 
of  the  body  as  possessing  this  "  irritability,"  such  as  the  muscles,  stomach,  bladder,  etc., 
and  the  different  degrees  of  irritability  with  which  each  one  was  endowed.  He  ap- 
plied this  theory  to  the  action  of  the  heart,  which  he  considered  as  the  part  endowed 
with  irritability  to  the  highest  degree.  His  theory  of  the  action  of  the  heart  was  that  its 
rhythmical  contraction  depended  upon  the  irritability  inherent  in  its  muscular  fibres.  He 
was  far  from  denying  the  various  influences  which  modified  this  action,  but  regarded  its 
actual  power  of  contraction  as  independent. 

Experiments  have  shown  that  the  heart  will  pulsate  for  a  time  when  removed  from 
all  connection  with  other  parts  of  the  organism.1  In  the  cold-blooded  animals,  in  which 
the  irritability  of  the  tissues  remains  for  some  time  after  death,  this  is  particularly  marked. 
It  is  not  the  blood  in  the  cavities  of  the  heart  which  causes  it  to  contract,  for  it  will 
pulsate  when  its  cavities  have  been  emptied.  It  is  not  the  contact  of  the  air,  for  the 
heart  will  pulsate  in  a  vacuum.  The  heart  does  not  receive  its  irritability  from  the 
nervous  system,  for,  when  removed  from  the  body,  it  has  no  connection  with  the  nervous 
system ;  and  it  is  not  probable  that  it  receives  any  influence  from  sympathetic  ganglia 
which  have  lately  been  discovered  in  its  substance,  for  detached  portions  of  the  heart 
will  pulsate,  and  the  contractions  of  the  organ  will  continue  in  animals  poisoned  with 
woorara,  which  is  known  to  paralyze  the  motor  system  of  nerves.2 

1  Numerous  instances  of  contractions  of  the  heart  in  cold-blooded  animals  continuing  for  a  very  long  time  after 
excision  are  on  record.  Dr.  Dunglison,  in  his  work  on  Physiology,  mentions  several  instances  in  which  the  heart  pul- 
sated for  from  ten  to  twenty-four  hours  after  removal  from  the  body.  The  most  remarkable  examples  of  this  pro- 
longed action  were  in  the  heart  of  the  sturgeon.  In  one  instance,  in  an  experiment  on  a  large  alligator,  we  found  the 
heart  pulsating,  in  situ,  twenty-eight  hours  after  the  animal  had  been  killed  by  the  injection  of  a  solution  of  woorara. 
The  heart  was  then  excised  and  continued  to  beat  during  a  long  series  of  experiments,  until  it  was  arrested  by 
powerful  compression  with  the  hand  after  it  had  been  filled  with  water  and  the  vessels  tied. 

a  It  is  stated  by  Friedlander  that  no  portion  of  the  heart,  however  small,  will  contract  rhythmically  unless  it  con- 


RHYTHMICAL  CONTRACTIONS  OF  THE  HEART.         57 

It  is  unnecessary  to  refer  to  the  various  experiments  which  have  demonstrated  the 
independence  of  the  contractions  of  the  heart.  They  are  of  such  a  simple  nature  that 
they  may  be  verified  by  any  one  who  will  take  the  trouble  to  excise  the  heart  of  a  frog 
or  turtle,  place  it  under  a  small  bell-glass  so  that  it  will  not  be  subject  to  possible  irrita- 
tion from  currents  of  air,  and  watch  its  pulsations.  In  such  an  observation  as  this,  it  is 
evident  that,  for  a  certain  time,  contractions,  more  or  less  regular,  will  take  place;  and 
the  experiments  referred  to  above  show  that  they  occur  without  any  external  influ- 
ence. In  short,  it  is  evident  that  the  muscular  fibres  of  the  heart  possess  an  irritability, 
by  virtue  of  which  they  will  contract  intermittently  for  a  time,  although  no  stimulus  be 
applied ;  as  the  ordinary  striated  muscular  fibres  have  an  irritability,  by  virtue  of  which 
they  will  respond,  for  a  time,  to  the  application  of  a  stimulus. 

It  is  manifestly  necessary  that  the  action  of  the  heart  should  be  constant,  regular,  and 
powerful ;  and  when  we  say  that  the  irritability  inherent  in  its  muscular  tissue  is  such 
that  it  will  contract  for  a  time  without  any  external  stimulus,  we  by  no  means  assume 
that  this  is  the  cause  of  its  physiological  action.  It  is  only  an  important  and  incontestable 
property  of  the  muscular  fibres  of  the  heart,  and  its  regular  action  is  dependent  upon 
other  conditions. 

In  the  first  place,  we  have  to  inquire  what  makes  the  action  of  the  heart  regular. 
The  answer  to  this  is,  that  the  changes  of  nutrition,  by  which,  through  the  blood  circu- 
lating in  its  substance,  the  waste  of  its  tissue  is  constantly  supplied,  preserve  the  integrity 
of  the  fibres,  and  keep  them,  consequently,  in  a  condition  to  contract.  This  is  true, 
likewise,  of  the  ordinary  striated  muscular  fibres.  If  the  supply  of  blood  be  cut  off  from 
the  substance  of  the  heart,  especially  in  the  warm-blooded  animals,  the  organ  soon  loses 
its  irritability.  This  was  admirably  shown  by  the  experiments  of  Erichsen.  This 
observer,  after  exposing  the  heart  in  a  warm-blooded  animal  and  keeping  up  artificial 
respiration,  ligated  the  coronary  arteries,  thus  cutting  off  the  greatest  part  of  the  supply 
of  blood  to  the  muscular  fibres.  He  found,  as  the  mean  of  six  experiments,  that  the  heart 
ceased  pulsating,  although  artificial  respiration  was  continued,  in  23£  minutes.  After  the 
pulsations  had  ceased,  they  could  be  restored  by  removing  the  ligatures  and  allowing  the 
blood  to  circulate  again  in  the  substance  of  the  heart. 

In  the  second  place,  the  regular  and  powerful  contractions  of  the  heart  are  provided 
for  by  the  circulation  of  the  blood  through  its  cavities.  Although  the  heart,  removed 
from  the  body,  will  contract  for  a  time  without  a  stimulus,  it  can  be  made  to  contract 
during  the  intervals  of  repose  by  an  irritant,  such  as  the  point  of  a  needle  or  a  feeble 
current  of  galvanism.  For  a  certain  time  after  the  heart  has  ceased  to  contract  sponta- 
neously, contractions  may  be  induced  in  this  way.  This  can  easily  be  demonstrated  in 
the  heart  of  any  animal,  warm-blooded  or  cold-blooded.  This  irritability,  which  is 
manifested,  under  these  circumstances,  in  precisely  the  same  way  as  in  ordinary  muscles, 
is  different  in  degree  in  different  parts  of  the  organ.  Haller  and  others  have  shown  that 
it  is  greater  in  the  cavities  than  on  the  surface  ;  for,  long  after  irritation  applied  to  the 
exterior  fails  to  excite  contraction,  the  organ  will  respond  to  a  stimulus  applied  to  its 
interior.  The  experiments  of  Haller  also  show  that  fluids  in  the  cavities  of  the  heart 
have  a  remarkable  influence  in  exciting  and  keeping  up  its  contractions.  This  observa- 
tion is  of  much  interest,  as  showing  conclusively  that  the  presence  of  blood  is  necessary 
to  the  natural  and  regular  action  of  the  heart.  We  quote  one  of  the  experiments  on  this 
point  performed  upon  a  cat : 

"  .  .  .  .  The  superior  vena  cava  having  been  divided,  and  the  inferior  ligated, 
and  the  pulmonary  artery  opened,  and  the  right  ventricle  emptied  by  a  sufficient  com- 
pression, and  the  aorta  ligated,  all  with  promptitude,  I  saw  the  right  auricle  repose 
first,  the  right  ventricle  continued  to  beat  for  some  time  in  unison  with  the  left  ventri- 

tain  ganglia ;  but  this  point  cannot  be  regarded  as  definitively  settled  and  is  exceedingly  difficult  to  determine.  The 
fact  that  nervous  and  muscular  irritability  are  entirely  distinct  from  each  other  is  a  strong  argument  in  favor  of  the 
Independent  irritability  of  the  muscular  tissue  of  the  heart. 


58  CIRCULATION  OF  THE  BLOOD. 

cle,  and  its  walls  descended  toward  the  middle  line  of  the  heart :  but  this  ventricle  did 
not  delay  to  lose  its  movement  the  first.  As  for  the  other  ventricle,  which  could  no 
longer  empty  itself  into  the  aorta,  it  was  filled  with  blood  and  its  movement  continued 
for  four  hours.  .  .  ." 

This  experiment  was  confirmed  by  numerous  others.  It  will  be  observed  that  one 
side  of  the  heart  was  made  to  cease  its  pulsations,  while  the  other  side  continued  to  con- 
tract, by  simply  removing  the  blood  from  its  interior ;  which  conclusively  proves  that, 
although  the  heart  may  act  for  a  time  independently,  the  presence  of  blood  in  its  cavities 
is  a  stimulus  capable  of  prolonging  its  regular  pulsations.  Schiff  has  gone  still  farther, 
and  has  succeeded  in  restoring  the  pulsations  in  the  heart  of  a  frog,  which  had  ceased 
after  it  had  been  emptied,  by  introducing  a  few  drops  of  blood  into  the  auricle.  Our 
own  experiments  upon  the  hearts  of  alligators  and  turtles  show  that,  when  removed 
from  the  body  and  emptied  of  blood,  the  pulsations  are  feeble,  rapid,  and  irregular ;  but 
that  when  filled  with  blood,  the  valves  being  destroyed  so  as  to  allow  free  passage  in 
both  directions  between  the  auricles  and  ventricle,  the  contractions  become  powerful  and 
regular.  In  these  experiments,  when  water  was  introduced  instead  of  blood,  the  pulsa- 
tions became  more  regular,  but  were  more  frequent  and  not  so  powerful  as  when  blood 
was  used.  These  experiments  show  also  that  the  action  of  the  heart  may  be  affected  by 
the  character,  particularly  the  density,  of  the  fluid  which  passes  through  it,  which  may 
explain  its  rapid  and  feeble  action  in  anemia. 

It  seems  well  established  that  the  heart,  although  capable  of  independent  action,  is  ex- 
cited to  contraction  by  the  blood  as  it  passes  through  its  cavities.  A  glance  at  the  suc- 
cession of  its  movements,  particularly  in  cold-blooded  animals,  in  which  they  are  so  slow 
that  the  phenomena  can  be  easily  observed,  will  show  how  these  contractions  are  in- 
duced. If  Ave  look  at  the  organ  as  it  is  in  action,  we  see  first  a  distention  of  the  auri- 
cje,  and  this  is  immediately  followed  by  a  contraction  filling  the  ventricle,  which  in  its 
turn  contracts.  Undoubtedly,  the  tension  of  the  fibres,  as  well  as  the  contact  of  blood 
in  its  interior,  acts  as  a  stimulus ;  and,  as  all  the  fibres  of  each  cavity  are  put  on  the 
stretch  at  the  same  instant,  they  contract  simultaneously.  The  necessary,  regular 
distention  of  each  cavity  thus  produces  rhythmical  and  forcible  contractions ;  and  the 
mere  fact  that  the  action  of  the  heart  alternately  empties  and  dilates  its  cavities  in- 
sures regular  pulsations,  so  long  as  blood  is  supplied  and  no  disturbing  influences  are  in 
operation. 

The  muscular  fibres  of  the  heart  seem  to  be  endowed  with  an  inherent  property, 
called  irritability,  by  virtue  of  which  they  will  contract  for  a  certain  time  without  the 
application  of  a  stimulus.  Irritability,  manifested  in  this  way,  continues  so  long  as,  by 
the  processes  of  nutrition,  the  fibres  are  maintained  in  their  integrity.  The  muscular 
tissue,  however,  may  be  thrown  into  contraction,  during  the  intervals  of  repose,  by  the 
application  of  a  stimulus,  a  property  which  is  observed  in  all  muscular  fibres.  The  irri- 
tability manifested  in  this  way  is  much  more  marked  in  the  interior  than  on  the  exterior 
of  the  organ.  Blood  in  contact  with  the  lining  membrane  of  the  heart  acts  as  a  stimu- 
lus in  a  remarkable  degree  and  is  even  capable  of  restoring  irritability  after  it  has  be- 
come extinct.  The  passage  of  blood  through  the  heart  is  the  natural  stimulus  of  the 
organ  and  may  be  said  to  be  the  cause  of  its  regular  pulsations,  although  it  by  no  means 
endows  the  fibres  with  their  contractile  properties. 

Influence  of  the  Nervous  System  on  the  Heart. 

The  movements  of  the  heart,  as  we  have  seen,  are  not  directly  under  the  control  of 
the  will ;  and  observations  on  the  human  subject,  as  well  as  on  living  animals,  have 
shown  that  the  organ  is  devoid  of  general  sensibility.  The  latter  fact  was  demonstrated 
in  the  most  satisfactorv  manner  by  Harvey,  in  the  case  of  the  Viscount  Montgomery. 
In  this  case,  the  heart  was  exposed,  and  Harvey  found  that  it  could  be  touched  and 
handled  without  even  the  knowledge  of  the  subject.  This  has  been  verified  in  other  in- 


INFLUENCE  OF  THE  NERVOUS  SYSTEM  ON  THE  HEART.  59 

stances  in  the  human  subject.  Its  physiological  movements  are  capable  of  being  influ- 
enced in  a  remarkable  degree  through  the  nervous  system,  notwithstanding  this  insensi- 
bility and  in  spite  of  the  fact  that  the  muscular  fibres  composing  it  are  capable  of  con- 
traction when  removed  from  all  connection  with  the  body  and  that  the  regular  pulsa- 
tions can  be  kept  up  for  a  long  time  by  the  mere  passage  of  blood  through  its  cavities. 
The  influence  thus  exerted  is  so  great,  that  some  eminent  authorities  have  held  the  opin- 
ion that  the  cause  of  the  irritability  of  the  organ  was  derived  from  the  nerves.  One  of  the 
most  distinguished  advocates  of  this  opinion  was  Legallois.  This  observer  arrested  the 
action  of  the  heart  of  the  rabbit  by  suddenly  destroying  the  spinal  cord,  from  which  he 
drew  the  conclusion  that  the  heart  derived  its  contractile  power  from  the  cerebro-spinal 
system.  The  experiments  which  we  have  already  cited,  showing  the  continuance  of  the 
heart's  action  after  excision,  disprove  this  so  completely,  that  it  was  not  thought  worth 
while  to  discuss  this  view  while  treating  of  the  cause  of  its  rhythmical  contractions. 
The  same  may  be  said  with  regard  to  the  experiments  of  Brachet,  in  which  he  endeav- 
ored to  prove  that  the  contractility  of  the  heart  is  derived  from  the  cardiac  plexus  of  the 
sympathetic  system  of  nerves.  The  fact  that  the  heart  does  not  depend  for  its  contrac- 
tility upon  external  nervous  influence  may  be  regarded  as  long  since  definitely  settled ; 
but  within  a  few  years  the  discovery  in  its  substance  of  ganglia  belonging  to  the  sympa- 
thetic system  has  revived,  to  some  extent,  the  view  that  its  irritability  is  derived  from 
nerves.  It  is  not  necessary  to  follow  out  all  the  experiments  which  combine  to  demonstrate 
the  incorrectness  of  this  view.  Bernard,  by  a  series  of  admirably-conceived  experi- 
ments upon  the  effects  of  the  woorara  poison,  has  succeeded  in  demonstrating  the  dis- 
tinction between  muscular  and  nervous  irritability.  In  an  animal  killed  with  this  re- 
markable poison,  the  functions  of  the  motor  nerves  are  entirely  abolished,  so  that  gal- 
vanization or  other  irritation  does  not  produce  the  slightest  effect ;  yet  the  muscles  re- 
tain their  irritability,  and,  if  artificial  respiration  be  kept  up,  the  circulation  will  con- 
tinue for  a  long  time.  The  heart,  by  this  means,  seems  to  be  isolated  from  the  nervous 
system  as  completely  as  if  it  were  excised ;  and  galvanization  of  the  pneumogastric 
nerves  in  the  neck,  which,  in  a  living  animal,  will  immediately  arrest  its  action,  has  no 
effect.  On  the  other  hand,  poisoning  by  the  sulphocyanide  of  potassium  destroys  the 
muscular  irritability  and  leaves  the  nerves  intact.  By  these  experiments,  which  we 
have  frequently  repeated,  we  can  completely  separate  the  nervous  from  the  muscular 
irritability  and  show  their  entire  independence  of  each  other ;  and  there  is  every  rea- 
son to  suppose  that  the  heart,  like  the  other  muscles,  does  not  derive  its  contractility 
from  any  other  system.  It  is  evident,  however,  that  the  heart  is  often  powerfully  influ- 
enced through  the  nerves.  Sudden  and  violent  emotions  will  occasionally  arrest  its  ac- 
tion and  have  been  known  to  produce  death.  Palpitations  are  to  be  accounted  for  in 
the  same  way.  Some  of  the  modifications  which  we  have  already  considered,  depending 
on  exercise,  digestion,  etc.,  are  effected  through  the  nerves;  and  it  is  through  this  system 
that  the  heart  and  all  the  important  organs  of  the  body  are  made  to  a  certain  extent 
mutually  dependent.  It  becomes  interesting  and  highly  important,  then,  to  study  their 
influences  and  follow  out,  as  clearly  as  possible,  the  action  of  the  nerves  which  are  dis- 
tributed to  the  heart. 

The  anatomical  connections  of  the  heart  with  the  nervous  centres  are  mainly  through 
the  sympathetic  and  the  pneumogastric  nerves.  We  can  study  the  influence  of  these 
nerves  to  most  advantage  in  two-ways;  first,  by  dividing  them  and  watching  the  effect 
of  depriving  the  heart  of  their  influence,  and  second,  by  exciting  them  by  means  of  a 
feeble  current  of  galvanism.  It  is  well  known  that  in  an  animal  just  killed  the  "  nervous 
force  "  may  be  closely  imitated  by  galvanism,  which  is  better  than  any  other  means  of 
stimulation,  as  it  does  not  affect  the  integrity  of  the  nerves  and  the  amount  of  the  irrita- 
tion may  be  easily  regulated.1 

1  We  shall  not  discuss  the  effects  upon  the  heart  of  sudden  destruction  of  the  great  nervous  centres.    It  has  been 
shown  that  the  heart  becomes  arrested  when  the  brain  is  crushed,  as  by  a  blow  with  a  hammer,  when  the  medulla 


60  CIRCULATION   OF  THE  BLOOD. 

Experiments  on  the  influence  of  the  sympathetic  nerves  upon  the  heart  are  not  quite 
so  satisfactory  as  we  might  desire.  It  has  been  asserted  that  the  action  of  the  heart  is 
immediately  arrested  by  destroying  the  cardiac  plexus.  With  regard  to  this,  we  must 
take  into  account  the  difficulty  of  making  the  operation  and  the  disturbance  of  the  heart 
consequent  upon  the  necessary  manipulations.  It  has  been  shown  pretty  conclusively, 
however,  that  stimulation  of  the  sympathetic  in  the  neck  has  the  effect  of  accelerating  the 
pulsations  of  the  heart.  The  extreme  difficulty  of  dividing  all  the  branches  of  the  sympa- 
thetic going  to  the  organ  leaves  a  doubt  as  to  whether  such  an  operation  would  definitely 
abridge  its  action. 

We  have  next  to  consider  the  influence  of  the  pneumogastrics  upon  the  heart.  Ex- 
periments on  these  nerves  are  made  with  greater  facility  than  on  the  nerves  of  the  sym- 
pathetic system,  and  the  results  are  much  more  satisfactory.  Like  all  the  cerebro-spinal 
nerves,  the  influence  generated  in  the  nervous  centre  from  which  they  take  their  origin  is 
conducted  along  the  nerve  and  manifested  at  its  distribution.  When  they  are  divided, 
we  may  be  sure  that,  as  far  as  they  are  concerned,  all  the  organs  which  they  supply  are 
cut  off  from  nervous  influence  ;  and,  when  galvanized  in  their  course,  we  imitate  or  ex- 
aggerate the  influence  sent  from  the  nervous  centre. 

The  invariable  effect  on  the  heart  of  division  of  the  pneumogastric  nerves  in  the  neck 
is  an  increase  in  the  frequency  and  a  diminution  in  the  force  of  its  pulsations.  One  or  two 
writers  have  denied  this  fact,  but  it  is  confirmed  by  the  testimony  of  nearly  all  experi- 
menters. To  anticipate  a  little  in  the  history  of  the  pneumogastric  nerves,  it  may  be 
stated  that,  while  they  are  exclusively  sensitive  at  their  origin,  they  receive,  after  having 
emerged  from  the  cranial  cavity,  a  number  of  filaments  from  various  motor  nerves. 
That  they  influence  certain  muscles,  is  shown  by  the  paralysis  of  these  muscles  after  divi- 
sion of  the  nerves  in  the  neck,  as,  for  example,  the  arrest  of  the  movements  of  the  glottis. 
Having  this  double  property  of  motion  and  sensation,  and  being  distributed  in  part  to 
an  organ  composed  almost  exclusively  of  muscular  fibres,  which,  as  we  have  seen,  is  not 
endowed  with  general  sensibility,  we  should  expect  that  their  section  would  arrest,  or  at 
least  diminish,  the  frequency  of  the  heart's  action.  What  explanation,  then,  can  we  offer 
for  the  fact  that  this  seems  actually  to  excite  the  movements  of  the  heart?  We  shall  be 
better  prepared  to  answer  this  question  after  we  have  studied  the  effects  of  galvanization 
of  the  nerves  in  a  living  animal  or  in  one  in  which  the  action  of  the  heart  is  kept  up  by 
artificial  respiration. 

Numerous  experiments  have  been  made  with  reference  to  the  effects  on  the  heart  of 
galvanic  currents,  both  feeble  and  powerful,  passed  through  the  pneumogastrics  before 
division,  of  currents  passed  through  the  upper  and  lower  extremities  after  division,  etc., 
a  full  detail  of  which  belongs  properly  to  the  physiological  history  of  the  nervous  system. 
In  this  connection,  a  few  of  these  facts  only  need  be  stated. 

It  has  been  shown  by  repeated  experiments,  which  we  have  frequently  confirmed,  that 
a  moderately-powerful  interrupted  galvanic  current  passed  through  both  pneumogastrics 
will  arrest  the  action  of  the  heart,  and  that  the  organ  remains  quiescent  so  long  as  the 
current  is  continued.  This  experiment  has  been  performed  upon  living  animals,  both 
with  and  without  exposure  of  the  heart.  The  arrest  is  not  due  to  violent  and  continued 
contraction  of  the  muscular  fibres ;  on  the  contrary,  the  heart  is  relaxed,  its  ventricles 
are  flaccid,  and  its  fibres  are  for  the  time  paralyzed.  The  question  then  arises  whether 
this  action  be  exerted  directly  on  the  heart  through  the  nerves,  or  whether  an  influence 
be  conveyed  to  the  nervous  centre  and  transmitted  to  the  heart  in  another  way.  This 
is  settled  by  the  experiment  of  dividing  the  nerves  and  galvanizing  alternately  the  ex- 
tremities connected  with  the  heart  and  those  connected  with  the  nervous  centres.  It  has 

oblongata  or  the  spinal  cord  is  suddenly  destroyed,  and  even  the  crushing  of  a  foot,  in  the  frog,  has  been  known  to 
product  this  effect.  In  fine,  this  may  be  done  by  any  extensive  injury  to  the  nervous  system ;  but  this  fact  does  net 
teach  us  much  with  regard  to  the  physiological  influences  of  the  nerves.  For  example,  while  crushing  of  the  brain 
arrests  the  heart,  the  brain  may  be  removed  from  a  living  animal  and  the  heart  will  beat  for  days.  Experiments 
upon  the  influence  of  the  medulla  oblongata  and  spinal  cord  are  by  no  means  satisfactory. 


INFLUENCE   OF  THE   NERVOUS  SYSTEM  ON  THE  HEART.  61 

been  ascertained  that  galvanization  of  the  extremities  connected  with  the  heart  arrests 
its  action,  while  galvanization  of  the  central  extremities  has  no  such  effect.  Another 
interesting  fact  also  shows  that  the  influence  exerted  upon  the  heart  is  through  the  motor 
filaments  of  the  pneumogastrics.  It  has  been  demonstrated  by  Bernard,  in  a  very  curious 
series  of  experiments  which  we  shall  not  fully  discuss  in  this  connection,  that  the  woorara 
poison  paralyzes  only  the  motor  nerves,  leaving  the  sensory  nerves  intact.  If  we  expose 
the  heart  and  the  pneumogastric  nerves  in  a  warm-blooded  animal  poisoned  with  this  agent, 
and  continue  the  pulsations  by  keeping  up  artificial  respiration,  we  find  that  the  most 
powerful  current  of  galvanism  passed  through  the  pneumogastrics  has  no  effect  upon  the 
heart. 

When  we  come  to  the  study  of  the  nervous  system,  we  shall  see  that  the  inhibitory 
action  of  the  pneumogastrics  upon  the  heart  is  derived  from  the  spinal  accessory  nerves, 
a  fact  which  has  been  proven  beyond  question  by  a  very  ingenious  series  of  experiments, 
which  will  be  fully  described  hereafter. 

Although  galvanization  of  the  pneumogastrics  arrests  the  action  of  the  heart  in  nearly 
all  animals,  there  are  some  in  which  this  does  not  take  place,  as  in  birds ;  a  fact  which  is 
stated  by  Bernard,  but  for  which  he  offers  no  explanation.  In  some  experiments  insti- 
tuted on  this  subject  a  few  years  ago  on  alligators,  we  noticed  a  singular  peculiarity  which 
throws  some  light  on  the  question  we  are  now  considering.  Desiring  to  demonstrate  to 
the  class  at  the  New  Orleans  School  of  Medicine  the  action  of  the  heart  in  this  animal, 
an  alligator  six  feet  in  length  was  poisoned  with  woorara  and  the  heart  exposed.  The 
animal  came  under  the  influence  of  the  poison  in  about  thirty  minutes,  when  the  dissec- 
tion was  commenced,  and  was  quite  dead  when  the  heart  was  exposed.  The  pneumogas- 
trics were  then  exposed  and  galvanized,  with  the  effect  of  promptly  arresting  the  action 
of  the  heart.  This  observation  was  verified  in  another  experiment.  We  were  at  first  at  a 
loss  to  account  for  the  absence  of  effect  of  the  woorara  on  the  motor  filaments  of  the 
pneumogastric  nerves ;  but  on  reflection  we  thought  it  might  be  due  to  slow  absorption  of 
the  poison  in  so  large  a  cold-blooded  animal.  With  a  view  of  ascertaining  whether  there 
be  any  difference  in  the  promptness  with  which  different  nerves  in  the  body  are  affected 
by  this  agent,  we  made  the  following  experiment  upon  a  dog :  The  animal  was  brought 
under  the  influence  of  ether,  and  the  heart,  the  pneumogastrics,  and  the  sciatic  nerve 
were  exposed.  Galvanization  of  the  sciatic  produced  muscular  contraction,  and  stimula- 
tion of  the  pneumogastrics  arrested  the  heart  promptly.  A  grain  of  woorara,  dissolved  in 
water,  was  then  injected  under  the  skin  of  the  thigh.  One  hour  after  the  injection  of 
the  woorara,  the  sciatic  was  found  insensible  to  galvanism,  but  the  heart  could  be  ar- 
rested by  galvanization  of  the  pneumogastrics,  although  it  required  a  powerful  current. 
A  weaker  current  diminished  the  frequency  and  increased  the  force  of  its  pulsations. 
In  this  experiment,  the  operation  of  opening  the  chest  undoubtedly  diminished  the  ac- 
tivity of  absorption  of  the  poison  and  consequently  retarded  its  effects  upon  the  nervous 
system.  Taken  in  connection  with  the  observations  on  alligators,  it  shows  that  the  motor 
nerves  are  not  all  affected  at  the  same  time,  and  that  the  pneumogastrics  resist  the  action 
of  this  peculiar  poison  after  the  motor  nerves  generally  are  paralyzed. 

Our  knowledge  of  the  inherent  properties  of  the  muscular  fibres  of  the  heart  and  of 
the  effects  of  the  passage  of  blood  through  its  cavities,  which  together  are  competent  to 
keep  up  for  a  time  regular  pulsations  without  the  intervention  of  the  nervous  system, 
taken  in  connection  with  the  facts  just  stated  concerning  the  influence  of  section  or  gal- 
vanization of  the  pneumogastric  nerves,  enables  us  to  comprehend  pretty  well  the  influ- 
ence of  these  nerves  on  the  heart.  They  undoubtedly  perform  the  important  function 
of  regulating  the  force  and  frequency  of  its  pulsations.  Hardly  any  reflection  is  necessary 
to  convince  us  of  the  importance  of  such  a  function,  and  how  it  must  of  necessity  be 
accomplished  through  the  pneumogastrics.  It  is  important,  of  course,  that  the  heart 
should  act  at  all  times  with  nearly  the  same  force  and  frequency.  We  have  seen  that 
the  inherent  properties  of  its  fibres  are  competent  to  make  it  contract,  and  the  necessary 


62  CIRCULATION  OF  THE  BLOOD. 

intermittent  dilatation  of  its  cavities  makes  these  contractions  assume  a  certain  regular- 
ity ;  but  the  quantity  and  density  of  the  hlood  are  subject  to  very  considerable  variations 
within  the  limits  of  health,  which,  without  some  regulating  influence,  would  undoubtedly 
cause  variations  in  the  heart's  action,  so  considerable  as  to  be  injurious.  This  is  shown 
by  the  comparatively-inefficient  and  palpitating  action  of  the  heart  when  the  pneumogas- 
trics  are  divided.  These  nerves  convey  to  the  heart  a  constant  influence,  which  we  may 
compare  to  the  insensible  tonicity  imparted  to  voluntary  muscles  by  the  general  motor 
system.  For  we  know  that  when  a  set  of  muscles  on  one  side  is  paralyzed,  as  in  facial 
palsy,  their  tonicity  is  lost,  they  become  flaccid,  and  the  muscles  on  the  other  side,  with- 
out any  effort  of  the  will,  distort  the  features.  We  can  imitate  an  exaggeration  of  this 
force  by  a  feeble  current  of  galvanism,  which  renders  the  pulsations  of  the  heart  less 
frequent  and  more  powerful,  or  exaggerate  it  still  more  by  a  more  powerful  current, 
which  arrests  the  action  of  the  heart  altogether.  Phenomena  are  not  wanting  in  the 
human  subject  to  verify  these  views.  Causes  which  operate  through  the  nervous  sys- 
tem frequently  produce  palpitation  and  irregular  action  of  the  heart.  Cases  are  not 
uncommon  in  which  palpitation  habitually  occurs  after  a  full  meal.  There  are  instances 
on  record  of  immediate  death  from  arrest  of  the  heart's  action  as  a  consequence  of 
fright,  anger,  grief,  or  other  severe  mental  emotions.  Syncope  from  these  causes  is  by 
no  means  uncommon.  In  the  latter  instance,  when  the  heart  resumes  its  functions, 
the  nervous  shock  carried  along  the  pneumogastrics  is  only  sufficient  to  arrest  its  action 
temporarily.  When  death  takes  place,  the  shock  is  so  great  that  the  heart  never 
recovers  from  its  effects. 

Summary  of  certain  Causes  of  Arrest  of  the  Action  of  the  Heart. 

In  warm-blooded  animals,  the  heart's  action  speedily  ceases  after  it  is  deprived  ot 
its  natural  stimulus,  the  blood.  It  is  not  from  experiments  on  the  inferior  animals 
alone  that  we  derive  proof  of  this  fact.  It  is  well  known  that,  in  profuse  haemorrhage 
in  the  human  subject,  the  contractions  of  the  heart  are  progressively  enfeebled,  and, 
when  the  loss  of  blood  has  proceeded  to  a  certain  extent,  are  permanently  arrested. 
Cases  of  transfusion  after  haemorrhage  show  that  when  blood  is  introduced  the  heart 
may  be  made  to  resume  its  pulsations.  The  same  result  takes  place  in  death  by  asthe- 
nia ;  and  cases  are  on  record  in  which  life  has  been  prolonged,  as  in  haemorrhage,  by  trans- 
fusion of  even  a  small  quantity  of  healthy  blood.  These  facts  have  been  demonstrated 
on  the  inferior  animals  by  experiments  already  cited.  The  experiment  of  Haller,  in 
which  the  action  of  the  right  side  of  the  heart  of  a  cat  was  arrested  by  emptying  it  of 
blood,  while  the  left  side,  which  was  filled  with  blood,  continued  to  pulsate,  showed 
that  the  absence  of  blood  in  its  cavities  is  competent  of  itself  to  arrest  the  heart.  The 
experiments  of  Erichsen,  who  paralyzed  the  heart  by  ligating  the  coronary  arteries,  and 
of  Schiff,  who  produced  a  local  paralysis  by  ligating  the  vessel  going  to  the  right 
ventricle,  show  that  the  heart  may  also  be  arrested  by  cutting  off  the  circulation  of 
blood  in  its  substance.  Both  of  these  causes  must  operate  in  arrest  of  the  heart's 
action  in  haemorrhage. 

The  mechanical  causes  of  arrest  of  the  heart's  action  are  of  considerable  pathologi- 
cal importance.  The  heart,  in  common  with  other  muscles,  may  be  paralyzed  by  me- 
chanical injury.  A  violent  blow  upon  the  deltoid  paralyzes  the  arm ;  a  severe  strain 
will  paralyze  the  muscles  of  an  extremity ;  and,  in  the  same  way,  excessive  distention 
of  the  cavities  of  the  heart  will  arrest  its  pulsations.  This  is  shown  by  arrest  of  the 
circulation  in  asphyxia.  We  have  already  seen  that,  under  these  circumstances,  the  heart 
is  incapable  of  forcing  the  unaerated  blood  through  the  systemic  capillaries.  The  heart 
finally  becomes  enormously  strained  and  distended  and  is  consequently  paralyzed.  The 
same  result  follows  the  application  of  a  ligature  to  the  aorta.  This  effect  may  be  pro- 
duced, also,  in  the  cold-blooded  animals,  in  which,  if  the  heart  be  left  undisturbed,  the 


CAUSES   OF   AREEST   OF  THE   ACTION   OF  THE   HEART.  63 

pulsations  will  continue  for  a  long  time.  The  following  experiment  illustrating  this 
point  was  performed  upon  the  heart  of  an  alligator  six  feet  in  length : 

The  animal  was  poisoned  with  woorara,  and  twenty-eight  hours  after  death  the 
heart,  which  had  been  exposed  and  left  in  situ,  was  pulsating  regularly.  It  was  then 
removed  from  the  body,  and,  after  some  experiments  on  the  comparative  force,  etc.,  of 
the  pulsations  when  empty  and  when  filled  with  blood,  was  filled  with  water,  the 
valves  having  been  destroyed  so  as  to  allow  free  passage  of  the  fluid  through  the  cavi- 
ties, and  the  vessels  ligated.  The  ventricles,  still  filled  with  water  confined  in  their 
cavity,  were  then  firmly  compressed  with  the  hand,  so  as  to  subject  the  muscular  fibres 
to  powerful  compression.  From  that  time,  the  heart  entirely  ceased  its  contractions 
and  became  hard  like  a  muscle  in  a  state  of  cadaveric  rigidity.  This  experiment  shows 
how  completely  and  promptly  the  heart,  even  of  a  cold-blooded  animal,  may  be  ar- 
rested in  its  action  by  mechanical  injury. 

Cases  of  death  from  distention  of  the  heart  are  not  infrequent  in  practice.  It  is  well 
established  that  the  form  of  organic  disease  which  most  frequently  leads  to  sudden 
death  is  that  in  which  the  heart  is  liable  to  great  distention.  We  refer  to  disease  at  the 
aortic  orifice.  In  other  lesions  there  is  not  this  tendency ;  but,  when  the  aortic  orifice 
is  contracted  or  the  valves  are  insufficient,  any  great  disturbance  of  the  circulation  will 
cause  the  heart  to  become  engorged,  which  is  liable  to  produce  a  fatal  result. 

Most  persons  are  practically  familiar  with  the  distressing  sense  of  suffocation  which 
frequently  follows  a  blow  upon  the  epigastrium ;  and  a  few  cases  are  on  record  of  in- 
stantaneous death  following  a  comparatively  slight  concussion  in  this  region.  We  had  an 
opportunity,  in  the  winter  of  1854-'5,  of  witnessing  an  autopsy  in  a  case  of  this  kind.  A 
young  mulatto  man,  employed  as  a  waiter  at  the  Louisville  Hotel,  received  a  blow  in  the 
epigastrium  while  frolicking,  which  produced  instantaneous  death.  On  post-mortem  ex- 
amination, no  lesion  was  discovered.  Although  these  cases  are  rare,  they  are  well  recog- 
nized, and  the  effects  are  generally  attributed  to  injury  of  the  solar  plexus.  The  dis- 
tress is  precisely  what  would  occur  from  sudden  arrest  of  the  heart's  action ;  for  it  is 
the  blood  charged  with  oxygen  and  sent  by  the  heart  to  the  system,  which  supplies  the 
wants  of  the  tissues,  and  not  the  simple  entrance  of  air  into  the  lungs ;  and  arrest  of 
the  circulation  of  arterial  blood,  from  any  cause,  produces  suffocation  as  completely 
as  though  the  trachea  were  ligated.  This  fact  we  have  clearly  proven  by  experiments. 
It  is  a  question  whether  the  arrest  of  the  heart,  if  this  be  the  pathological  condition,  be 
due  to  concussion  of  the  nervous  centre  or  to  the  direct  effects  of  the  blow  upon  the 
organ  itself.  Our  present  data  do  not  enable  us  to  answer  this  question  definitely,  but 
they  rather  incline  us  to  the  opinion  that  in  such  accidents  the  symptoms  are  due  to 
direct  injury  of  the  heart.  An  additional  argument  in  favor  of  this  view  is  founded  on 
our  knowledge  of  the  mode  of  operation  of  the  sympathetic  system.  The  effects  of 
stimulation  or  irritation  of  this  system  are  not  instantaneously  manifested,  as  is  the  case 
in  the  cerebro-spinal  system,  but  are  developed  slowly  and  gradually. 

As  far  as  we  have  been  able  to  learn  by  experiment,  the  nervous  influences  which 
arrest  the  action  of  the  heart  operate  through  the  pneumogastrics  and  are  derived  from 
the  spinal  accessory  nerves.  As  we  have  just  seen,  we  can  closely  imitate  this  action  by 
galvanism.  The  causes  of  arrest  in  this  way  are  numerous.  Among  them  may  be  men- 
tioned, sudden  and  severe  bodily  pain  and  severe  mental  emotions.  With  the  exception 
of  arrest  of  the  heart  from  loss  of  blood  and  from  distention,  from  whatever  cause  it 
may-occur,  stoppage  of  the  heart  takes  place  from  influences  operating  through  the 
nervous  system.  It  may  be  temporary,  as  in  syncope,  or  it  may  be  permanent ;  and  ex- 
amples of  the  latter,  though  rare,  are  sufficiently  well  authenticated. 


64  CIRCULATION  OF  THE  BLOOD. 

CHAPTER    III. 

CIRCULATION  OF  THE  BLOOD  IN  THE  VESSELS. 

Physiological  anatomy  of  the  arteries— Course  of  blood  in  the  arteries — Locomotion  of  the  arteries  and  production 
of  the  pulse— Pressure  of  blood  in  the  arteries— Pressure  in  different  parts  of  the  arterial  system— Depressor 
nerve — Influence  of  respiration  on  the  arterial  pressure — Eapidity  of  the  current  of  blood  in  the  arteries — Eapid- 
ity  in  different  parts  of  the  arterial  system — Circulation  of  the  blood  in  the  capillaries — Physiological  anatomy 
of  the  capillaries— Capacity  of  the  capillary  system— Course  of  blood  in  the  capillaries— Eolations  of  the  capil- 
lary circulation  to  respiration — Causes  of  the  capillary  circulation — Influence  of  temperature  on  the  capillary  cir- 
culation—Influence of  direct  irritation  on  the  capillary  circulation— Circulation  of  the  blood  in  the  veins— Physio- 
logical anatomy  of  the  veins — Course  of  the  blood  in  the  veins — Pressure  of  blood  in  the  veins — Eapidity  of  the 
venous  circulation— Causes  of  the  venous  circulation— Air  in  the  veins— Function  of  the  valves— Conditions 
which  impede  the  venous  circulation— Eegurgitant  venous  pulse— Circulation  in  the  cranial  cavity— Circulation 
in  erectile  tissues— Derivative  circulation— Pulmonary  circulation— Eapidity  of  the  circulation— Phenomena  in 
the  circulatory  system  after  death. 

IN  man  and  in  all  animals  possessed  of  a  double  heart,  each  contraction  of  this  organ 
forces  a  charge  of  blood  from  the  right  ventricle  into  the  pulmonary  artery,  and  from 
the  left  ventricle  into  the  aorta.  We  have  seen  how  the  valves  which  guard  the  orifices 
of  these  vessels  effectually  prevent  regurgitation  during  the  intervals  of  contraction. 
There  is,  therefore,  but  one  direction  in  which  the  blood  can  flow  in  obedience  to  this 
intermittent  force  ;  and  the  fact  that,  even  in  the  smallest  arteries,  there  is  an  accelera- 
tion in  the  current  coincident  with  each  contraction  of  the  heart,  which  disappears  when 
the  action  of  the  heart  is  arrested,  shows  that  the  ventricular  systole  is  the  prime  cause 
of  the  arterial -circulation.  But  this  part  of  the  physiology  of  the  circulation  is  not  so 
simple  as  we  might  at  first  be  led  to  suppose.  The  arteries  have  the  important  function 
of  supplying  nutritive  matter  to  all  the  tissues,  of  furnishing  to  the  glands  materials  out 
of  which  the  secretions  are  formed,  and,  in  sliort,  are  the  vessels  of  supply  to  every  part 
of  the  organism.  The  supply  of  blood  regulates,  to  a  considerable  extent,  the  processes  of 
nutrition  and  has  an  important  bearing  on  the  general  and  special  functions ;  and  the 
various  physiological  processes  necessarily  demand  considerable  modifications  in  the 
quantity  of  arterial  blood  which  is  furnished  to  parts  at  different  times.  For  example, 
during  secretion,  the  glands  require  several  times  as  much  blood  as  in  the  intervals  of 
their  action.  The  force  of  the  heart,  we  have  seen,  varies  but  little  within  the  limits  of 
health  ;  and  the  conditions  necessary  to  the  proper  distribution  of  blood  in  the  economy 
are  regulated  almost  exclusively  by  the  arterial  system.  These  vessels  are  not  inert 
tubes,  but  are  endowed  with  elasticity,  by  which  the  circulation  is  considerably  facili- 
tated, and  with  contractility,  by  which  the  supply  to  any  part  may  be  modified,  inde- 
pendently of  the  action  of  the  heart.  Sudden  flushes  or  pallor  of  the  countenance  are 
examples  of  the  facility  with  which  this  may  be  effected.  It  is  evident,  therefore,  that 
the  properties  of  the  coats  of  the  arteries  are  of  great  physiological  importance.  We 
shall  then  commence  the  study  of  this  division  of  the  circulatory  system  with  a  consid- 
eration of  its  physiological  anatomy. 

Physiological  Anatomy  of  the  Arteries. 

The  vessels  which  carry  the  venous  blood  to  the  lungs  are  branches  of  a  great  trunk 
which  takes  its  origin  from  the  right  ventricle.  They  do  not  differ  in  structure  from  the 
vessels  which  carry  the  blood  to  the  general  system,  except  in  the  fact  that  their  coats 
are  somewhat  thinner  and  more  distensible.  The  aorta,  branches  and  ramifications  of 
which  supply  all  parts  of  the  body,  is  given  off  from  the  left  ventricle.  Just  at  its  ori- 
gin, behind  the  semilunar  valves,  the  aorta  has  three  sacculated  pouches,  called  the  si- 
nuses of  Valsalva.  Beyond  this  point  the  vessels  are  cylindrical.  As  we  recede  from 
the  heart,  the  arteries  branch,  divide,  and  subdivide,  until  they  are  reduced  to  micro- 


PHYSIOLOGICAL  ANATOMY   OF  THE  ARTERIES.  65 

scopic  size.  The  branches,  with  the  exception  of  the  intercostal  arteries,  which  make 
nearly  a  right  angle  with  the  thoracic  aorta,  are  given  off  at  an  acute  angle.  As  a  rule, 
the  arteries  are  nearly  straight,  taking  the  shortest  course  to  the  parts  which  they  sup- 
ply with  blood;  and,  while  the  branches  progressively  diminish  in  size,  but  few  are 
given  off  between  the  great  trunk  and  the  small  vessels  which  empty  into  the  capil- 
lary system.  Haller  counted  but  twenty  branches  of  the  mesenteric  artery  between  the 
aorta  and  the  capillaries  of  the  intestines.  So  long  as  a  vessel  gives  off  no  branches,  its 
caliber  does  not  progressively  diminish ;  as  the  common  carotids,  which  are  as  large  at 
their  bifurcation  as  they  are  at  their  origin.  There  are  one  or  two  instances  in  which 
vessels,  although  giving  off  numerous  branches  in  their  course,  do  not  diminish  in  size  for 
some  distance ;  as  the  aorta,  which  is  as  large  at  the  point  of  division  into  the  iliacs  as 
it  is  in  the  chest,  and  the  vertebral  arteries,  which  do  not  diminish  in  caliber  until  they 
enter  the  foramen  magnum.  With  these  exceptions,  as  we  recede  from  the  heart,  the 
caliber  of  the  vessels  progressively  diminishes.  It  has  long  been  remarked  that  the 
combined  caliber  of  the  branches  of  an  arterial  trunk  is  much  greater  than  that  of  the 
main  vessel ;  so  that  the  arterial  system,  as  it  branches,  increases  in  capacity. 

The  arrangement  of  the  arteries  is  such  that  the  requisite  supply  of  blood  is  sent  to 
all  parts  of  the  economy  by  the  shortest  course  and  with  the  least  expenditure  of  force 
from  the  heart.  Generally,  the  vessels  are  so  situated  as  not  to  be  exposed  to  pressure 
and  consequent  interruption  of  the  current  of  blood ;  but,  in  certain  situations,  as  about 
some  of  the  joints,  there  is  necessarily  some  liability  to  occasional  compression.  In 
certain  situations,  also,  as  in  the  vessels  going  to  the  brain,  particularly  in  some  of  the  in- 
ferior animals,  it  is  necessary  to  moderate  the  force  of  the  blood-current,  on  account  of 
the  delicate  structure  of  the  organs  in  which  they  are  distributed.  Here  Nature  makes 
a  provision  in  the  shape  of  anastomoses,  by  which,  on  the  one  hand,  compression  of  a 
vessel  simply  diverts,  and  does  not  arrest  the  current  of  blood,  and,  on  the  other  hand, 
the  current  is  rendered  more  equable  and  the  force  of  the  heart  is  moderated. 

The  arteries  are  provided  with  membranous  sheaths,  of  greater  or  less  strength,  as 
the  vessels  are  situated  in  parts  more  or  less  exposed  to  disturbing  influences  or  acci- 
dents. 

Researches  into  the  minute  anatomy  of  the  arteries  have  shown  that  they  are  pos- 
sessed of  three  pretty  well  marked  coats.  As  these  vary  very  considerably  in  arteries  of 
different  sizes,  it  will  be  convenient,  in  their  description,  to  divide  the  vessels  into  three 
classes : 

1.  The  largest  arteries  ;  in  which  are  included  all  that  are  larger  than  the  carotids 
and  common  iliacs. 

2.  The  arteries  of  medium  size ;   that  is,  between  the  carotids  and  iliacs  and  the 
smallest. 

3.  The  smallest  arteries  ;  or  those  less  than  ^  or  -fa  of  an  inch  in  diameter. 

The  largest  arteries  are  endowed  with  great  strength  and  elasticity.  Their  external 
coat  is  composed  of  white,  or  inelastic  fibrous  tissue,  with  a  few  longitudinal  and  oblique 
fasciculi  of  involuntary  muscular  fibres.  This  coat  is  no  thicker  in  the  largest  vessels 
than  in  some  of  the  vessels  of  medium  size ;  and  in  some  medium-sized  vessels  it  is 
actually  thicker  than  in  the  aorta.  This  is  the  only  coat  which  is  vascular. 

The  middle  coat,  on  which  the  thickness  of  the  walls  of  the  vessel  depends,  is  com- 
posed chiefly  of  the  yellow  elastic  tissue.  This  tissue  is  disposed  in  numerous  layers. 
First  we  have  a  thin  layer  of  ramifying  elastic  fibres,  and  then  a  number  of  layers  of 
elastic  membrane,  with  numerous  oval  longitudinal  openings,  which  has  given  it  the 
name  of  the  "  fenestrated  membrane."  Between  the  different  layers  of  this  membrane 
are  found  a  few  unstriped  or  involuntary  muscular  fibres.  These  muscular  fibres,  how- 
ever, are  not  numerous  and  have  but  little  physiological  importance.  A  small  portion 
of  the  aorta  and  pulmon ary^artery  next  the  heart  is  entirely  free  from  muscular  fibres. 
In  the  largest  arteries,  the/fibres  are  arranged  in  fasciculi,  with  amorphous  and  fibrous 
5 


66  CIRCULATION"   OF  THE  BLOOD. 

connective  tissue  running  in  a  circular,  longitudinal,  and  oblique  direction.  The  longi- 
tudinal and  oblique  fibres  exist  chiefly  in  the  outer  coat.  The  middle  coat  of  the  largest 
arteries  gives  them  their  yellowish  hue  and  the  elasticity  for  which  they  are  so  remark- 
able. 

The  internal  coat  of  the  largest  arteries  does  not  differ  materially  from  the  lining 
membrane  of  the  rest  of  the  arterial  system.  It  is  identical  in  structure  with  the  endo- 
cardium, the  membrane  lining  the  cavities  of  the  heart,  and  is  continued  through  the 
entire  vascular  system.  It  is  a  thin,  homogeneous,  elastic  membrane,  covered  with  a 
layer  of  elongated  epithelial  scales,  with  oval  nuclei,  their  long  diameter  following  the 
direction  of  the  vessel. 

The  arteries  of  medium  size  possess  considerable  strength,  some  elasticity,  and  very 
great  contractility.  In  the  outer  and  inner  coats  we  do  not  distinguish  any  great  differ- 
ence between  these  and  the  largest  arteries,  even  in  thickness.  The  essential  difference 


FIG.  20.— Small  artery  from  the  mesentery  of  the  frog,  showing  epithelium  and  circular  muscular  fibres  ,- 
magnified  500  diameters.    (From  a  photograph  taken  at  the  United  States  Army  Medical  Museum.) 

in  the  anatomy  of  these  vessels  is  found  in  the  middle  coat.  Here  we  have  a  continua- 
tion of  the  elastic  elements  found  in  the  largest  vessels,  but  relatively  diminished  in 
thickness  and  mingled  with  the  fusiform,  involuntary  muscular  fibres  arranged,  for  the 
most  part,  at  right  angles  to  the  course  of  the  vessel.  These  fibres  are  found  chiefly  in 
the  inner  layers  of  the  middle  coat,  and  only  in  arteries  smaller  than  the  carotids  and 
primitive  iliacs.  In  arteries  of  medium  size,  like  the  femoral,  profunda  femoris,  radial, 
or  ulnar,  they  exist  in  several  layers.  There  is  no  distinct  division,  as  regards  the  middle 
coat,  between  the  largest  arteries  and  those  of  medium  size.  As  we  recede  from  the 
heart,  muscular  fibres  gradually  make  their  appearance  between  the  elastic  layers,  pro- 
gressively increasing  in  quantity,  while  the  elastic  elements  are  diminished. 


ELASTICITY  OF  THE  ARTERIES.  67 

In  the  smallest  arteries,  the  external  coat  is  thin  and  disappears  just  before  the  ves- 
sels empty  into  the  capillary  system  ;  so  that  the  very  smallest  arterioles  have  only  the 
inner  coat  and  a  layer  of  muscular  fibres.  Although  the  greatest  part  of  the  muscular 
fibres  in  the  middle  coat  of  the  arteries  are  arranged  at  right  angles  to  the  course  of  the 
vessels,  nearly  all  of  the  arteries,  in  the  human  subject,  are  provided  with  longitudinal 
and  oblique  muscular  fasciculi,  which  are  sometimes  external,  sometimes  internal,  and 
sometimes  on  both  sides  of  the  circular  layers. 

The  middle  coat  is  composed  of  circular  muscular  fibres,  without  any  admixture  of 
elastic  elements.  In  vessels  -fa  of  an  inch  in  diameter,  we  have  two  or  three  layers  of 
fibres ;  but,  as  we  near  the  capillaries  and  as  the  vessels  lose  the  external  fibrous  coat, 
these  fibres  exist  in  a  single  layer. 

The  internal  coat  presents  no  essential  difference  from  the  coat  in  other  vessels,  with 
the  exception  that  the  epithelium  is  less  distinctly  marked. 

A  tolerably-rich  plexus  of  vessels  is  found  in  the  external  coats  of  the  arteries. 
These  are  called  the  vasa  vasorum  and  come  from  the  adjacent  arterioles,  having  no  di- 
rect connection  with  the  vessel  on  which  they  are  distributed.  A  few  vessels  penetrate 
the  external  layers  of  the  middle  coat,  but  none  are  ever  found  in  the  internal  coat. 

"Nervous  filaments,  principally  from  the  sympathetic  system,  accompany  the  arteries, 
in  all  probability  to  their  remotest  ramifications.  These  are  not  distributed  in  the  walls 
of  the  large  vessels,  but  rather  follow  them  in  their  course,  their  filaments  of  distribu- 
tion being  found  in  those  vessels  in  which  the  muscular  element  of  the  middle  coat  pre- 
dominates. When  we  come  to  treat  of  the  physiology  of  the  organic  system  of  nerves, 
we  shall  see  that  the  "  vaso-motor  "  nerves  play  an  important  part  in  regulating  the 
function  of  nutrition.  Lymphatics  have  not  been  found  in  the  coats  of  any  of  the  blood- 
vessels. 

Course  of  the  Blood  in  the  Arteries. — At  every  pulsation  of  the  heart,  all  the  blood 
contained  in  the  ventricles,  excepting,  perhaps,  a  few  drops,  is  forced  into  the  great  vessels. 
We  have  already  studied  the  valvular  arrangement  by  which  the  blood,  once  forced  into 
these  vessels,  is  prevented  from  returning  into  the  ventricles  during  the  diastole.  The 
sketch  we  have  given  of  the  anatomy  of  the  arteries  has  prepared  us  for  a  complexity 
of  phenomena  in  the  circulation  in  these  vessels,  which  would  not  obtain  if  they  were 
simple,  inelastic  tubes.  In  this  case,  the  intermittent  force  of  the  heart  would  be  felt 
equally  in  all  the  vessels,  and  the  arterial  circulation  would  be  subject  to  no  modifications 
which  did  not  come  from  the  action  of  the  central  organ.  As  it  is,  th*e  blood  is  received 
from  the  heart  into  vessels  endowed,  not  only  with  great  elasticity,  but  with  contractility. 
The  elasticity,  which  is  the  prominent  property  of  the  largest  arteries,  moderates  the 
intermittency  of  the  heart's  action,  providing  a  continuous  supply  to  the  parts ;  while 
the  contractility  of  the  smallest  arteries  is  capable  of  increasing  or  diminishing  the  supply 
in  any  part,  as  may  be  required  in  the  various  functions. 

Elasticity  of  the  Arteries. — This  property,  which  is  particularly  marked  in  large 
vessels,  has  long  been  recognized.  If,  for  example,  we  forcibly  distend  the  aorta  with 
water,  it  may  be  dilated  to  more  than  double  its  ordinary  capacity  and  will  resume  its 
original  size  and  form  as  soon  as  the  pressure  is  removed.  This  simple  experiment  teaches 
us  that,  if  the  force  of  the  heart  be  sufficient  to  distend  the  great  vessels,  their  elasticity 
during  the  intervals  of  its  action  must  be  continually  forcing  the  blood  toward  the 
periphery.  The  fact  that  the  arteries  are  distended  at  each  systole  is  abundantly  proven 
by  actual  experiment ;  although  the  immense  capacity  of  the  arterial  system,  as  compared 
with  the  small  charge  of  blood  which  enters  at  each  pulsation,  renders  the  actual  dis- 
tention  of  the  vessels  less  than  we  should  be  led  to  expect  from  the  force  of  the  heart's 
contraction.  The  most  satisfactory  experiments  on  this  subject  are  those  of  Poiseuille. 
This  observer  illustrated  the  dilatation  of  the  arteries  in  the  following  way :  Having 


68  CIRCULATION   OF  THE  BLOOD. 

exposed  a  considerable  extent  of  the  primitive  carotid  in  a  horse,  he  enclosed  a  portion 
in  a  tin  tube  filled  with  water  and  connected  with  a  small  upright  graduated  tube  of  glass. 
The  openings  around  the  artery,  as  it  passed  in  and  out  of  the  apparatus,  being  carefully 
sealed  with  tallow,  it  is  evident  that  any  dilatation  of  the  vessel  would  be  indicated  by 
an  elevation  of  the  water  in  the  graduated  tube.  This  experiment  invariably  showed  a 
marked  dilatation  of  the  artery  with  each  contraction  of  the  heart. 

It  being  fully  established  that  the  arteries  are  dilated  with  each  ventricular  systole,  it 
becomes  important  to  study  the  influence  of  their  elasticity  upon  the  current  of  blood. 
Division  of  an  artery  in  a  living  animal  exhibits  one  of  the  important  phenomena  due  to 
the  elastic  and  yielding  character  of  its  walls.  "We  observe,  even  in  vessels  of  consider- 
able size,  as  the  carotid  or  femoral,  that  the  flow  of  blood  is  not  intermittent  but  remit- 
tent. With  each  ventricular  systole,  there  is  a  sudden  and  marked  impulse ;  but,  during 
the  intervals  of  contraction,  the  blood  continues  to  flow  with  considerable  force.  As  we 
recede  from  the  heart,  the  impulse  becomes  less  and  less  marked ;  but  it  is  not  entirely 
lost,  even  in  the  smallest  vessels,  the  flow  becoming  constant  only  in  the  capillary  system. 
That  the  force  of  the  heart  is  absolutely  intermittent,  is  shown  by  the  following  experi- 
ment :  If  the  heart  be  exposed  in  a  living  animal,  and  a  canula  be  introduced  through  the 
walls  into  one  of  the  ventricles,  we  have  a  powerful  jet  at  each  systole,  but  no  blood  is 
discharged  during  the  diastole.  The  same  absolute  intermittency  of  the  current  will  be 
seen  if  the  aorta  be  divided.  It  is  evident  that  we  must  look  to  the  arteries  themselves 
for  the  force  which  produces  a  flow  of  blood  during  the  intervals  of  the  heart's  action. 
The  conversion  of  the  intermittent  current  in  the  largest  vessels  into  a  nearly-constant 
flow  in  the  smallest  arterioles  is  effected  by  the  physical  property  of  elasticity.  This  may 
be  illustrated  in  any  elastic  tube  of  sufficient  length.  If  we  connect  with  a  syringe  a  series 
of  rubber  tubes  progressively  diminishing  in  caliber  and  discharging  by  a  very  small  orifice, 
and  inject  water  in  an  intermittent  current,  if  the  apparatus  be  properly  adjusted,  the 
fluid  will  be  discharged  at  the  end  of  the  tube  in  a  continuous  stream.  Nearer  the 
syringe,  the  stream  will  be  remittent ;  and,  directly  at  the  point  of  connection  of  the 
syringe  with  the  tube,  the  stream  will  be  intermittent.  The  intermittent  impulse  may  be 
said,  in  this  case,  to  be  progressively  absorbed  by  the  elastic  walls  of  the  tube.  Each 
impulse  first  distends  that  portion  of  the  tube  nearest  to  it,  and  farther  on  the  distention 
is  diminished  until  it  becomes  inappreciable.  If  the  syringe  be  connected  with  two 
tubes,  one  elastic  and  the  other  inelastic,  the  current  will  be  either  remittent  or  contin- 
uous in  the  one,  and  intermittent  in  the  other.  This  modification  of  the  impulse  of  the 
heart  has  great  physiological  importance ;  for  it  is  evidently  essential  that  the  current  of 
blood,  as  it  flows  into  the  delicate  capillary  vessels,  should  not  be  alternately  intermitted 
and  impelled  with  the  full  power  of  the  ventricle.  After  all,  it  is  in  the  capillaries  that 
the  blood  performs  its  functions ;  and  here  we  should  have  a  constant  supply  of  the  fluid 
in  proper  quantity  and  in  proper  condition  to  meet  the  nutritive  and  other  requirements 
of  the  parts. 

The  elasticity  of  the  arteries  favors  the  flow  of  blood  toward  the  capillaries  by  a 
mechanism  which  is  easily  understood.  The  blood  discharged  from  the  heart  distends  the 
elastic  vessel,  which  reacts,  after  the  distending  force  ceases  to  operate,  and  compresses 
its  fluid  contents.  This  reaction  would  have  a  tendency  to  force  the  blood  in  two  direc- 
tions, were  it  not  for  an  instantaneous  closure  of  the  valves,  which  renders  regnrgitation 
with  the  heart  impossible.  The  influence,  then,  can  only  be  exerted  in  the  direction  of  the 
periphery ;  and,  if  we  can  imagine  as  divided  an  action  which  is  propagated  with  such 
rapidity,  the  reaction  of  that  portion  of  the  vessel  immediately  distended  by  the  heart 
distends  a  portion  farther  on,  which,  in  its  turn,  distends  another  portion,  and  so  the  wave 
passes  along  until  the  blood  is  discharged  into  the  capillaries.  In  this  way  we  can  see 
that,  in  vessels  removed  a  sufficient  distance  form  the  heart,  the  force  exerted  on  the 
blood  by  the  reaction  of  the  elastic  walls  is  competent  to  produce  a  very  considerable 
current  during  the  intervals  of  the  heart's  action.  This  theoretical  view  is  fully  carried 


CONTRACTILITY   OF  THE   ARTERIES. 


69 


out  by  the  following  simple  and  conclusive  experiment  of  Marey :  He  connected  two 
tubes  of  equal  size,  one  of  rubber  and  the  other  of  glass,  with  the  stop-cock  of  a  large 
vase  filled  with  water.  The  elastic  tube  was  provided  with  a  valve  near  the  stop-cock, 
which  prevented  the  reflux  of  fluid,  and  both  were  fitted  with  tips  of  equal  caliber. 
When,  by  alternately  opening  and  closing  the  stop-cock,  water  was  allowed  to  flow 
into  these  tubes  in  an  intermittent  stream,  it  was  found  that  a  greater  quantity  was 


Y  <EEfe 


FIG.  21. — Apparatus  for  showing  the,  action  of  the  elasticity  of  the,  arteries.    (Marey.) 
V,  vessel  of  water;  E,  stop-cock ;  T,  double  tube ;  S,  valve;  a,  a,  glass  tube;  &,  6,  rubber  tube. 

discharged  by  the  elastic  tube ;  but  an  equal  quantity  was  discharged  by  both  tubes 
when  the  stop-cock  was  left  open  and  the  fluid  allowed  to  pass  in  a  continuous  stream. 
This  simple  experiment  shows  that  not  only  does  the  elasticity  of  the  arteries  convert  the 
intermittent  current  in  the  largest  vessels  into  a  current  more  and  more  nearly  continuous 
as  we  approach  the  periphery,  but  that  when  reflux  is  prevented,  as  it  is  by  the  semilunar 
valves,  the  resiliency  of  the  arteries  assists  the  circulation. 

Contractility  of  the  Arteries. — It  is  a  well-established  anatomical  fact  that  the 
medium-sized  and  smallest  arteries  contain  contractile  elements ;  and  it  is  also  a  fact, 
proven  by  actual  experiment,  that,  as  a  consequence  of  the  condition  of  these  fibres, 
the  vessels  undergo  considerable  variation  in  their  caliber.  The  opinions  of  the  older 
physiologists  on  this  question  have  only  an  historical  interest  and  will  not,  therefore, 
be  discussed.  Among  the  more  recent  investigations  on  this  subject,  we  have  the  experi- 
ments of  Cl.  Bernard  and  of  Schiff,  which  have  been  repeatedly  confirmed,  showing  that, 
through  the  nervous  system,  the  muscular  coats  of  arteries  may  be  readily  made  to  con- 
tract or  become  relaxed.  If  the  sympathetic  be  divided  in  the  neck  of  a  rabbit,  in  a  very 
few  minutes  the  arteries  of  the  ear  on  that  side  are  notably  dilated.  If  the  divided  ex- 
tremity of  the  nerve  be  galvanized,  the  vessels  soon  take  on  contraction  and  may  become 
smaller  than  on  the  opposite  side.  These  experiments  demonstrate,  in  the  most  conclu- 
sive manner,  the  contractile  properties  of  the  small  arteries  and  give  us  an  idea  how  the 
supply  of  blood  to  any  particular  part  may  be  regulated.  The  vessels  may  be  most  ef- 
fectually excited  through  the  nervous  system ;  and  it  is  on  account  of  the  difficulty  in 
producing  marked  results  by  direct  irritation,  that  the  older  physiologists  were  divided 
on  the  subject  of  their  "irritability." 

The  contractility  of  the  arteries  has  great  physiological  importance.  As  their  func- 
tion is  simply  to  supply  blood  to  the  various  tissues  and  organs,  it  is  evident  that,  when 
the  vessels  going  to  any  particular  part  are  dilated,  the  supply  of  blood  is  necessarily  in- 
creased. This  is  particularly  well  marked  in  the  glands,  which,  during  the  intervals  of 
secretion,  receive  a  comparatively  small  quantity  of  blood.  Bernard  has  shown  that  gal- 
vanization of  what  he  calls  the  motor  nerve  of  a  gland  dilates  the  vessels,  largely  increases 


70  CIRCULATION   OF  THE   BLOOD. 

the  supply  of  blood,  and  induces  secretion ;  while  galvanization  of  the  sympathetic  fila- 
ments contracts  the  vessels,  diminishes  the  supply  of  blood,  and  arrests  secretion.  The 
pallor  of  parts  exposed  to  cold,  and  the  flush  produced  by  heat,  are  due,  on  the  one  hand, 
to  contraction,  and  on  the  other,  to  dilatation  of  the  small  arteries.  Pallor  and  blushing 
from  mental  emotions  are  examples  of  the  same  kind  of  action. 

The  ulterior  effects  on  nutrition,  which  result  from  dilatation  of  the  vessels  of  a  part, 
are  of  great  interest.  When  the  supply  of  blood  is  much  increased,  as  in  section  of  the 
sympathetic  in  the  neck,  nutrition  is  exaggerated,  and  the  temperature  of  the  part  is 
raised  beyond  that  of  the  rest  of  the  body. 

The  idea,  which  at  one  time  obtained,  that  the  arteries  were  the  seat  of  rhythmical 
contractions  which  had  a  favorable  influence  on  the  current  of  blood  is  entirely  erro- 
neous.1 It  is  hardly  necessary  to  repeat  that  the  prime  cause  of  the  arterial  circulation 
is  the  force  of  the  left  ventricle.  We  have  seen  that  the  elasticity  of  the  arteries  pro- 
duces a  flow  during  the  intervals  of  the  heart's  action,  and  the  question  now  arises 
whether  the  force  thus  exerted  be  simply  a  return  of  the  force  required  to  expand  the 
vessels,  which  has  been  borrowed,  as  it  were,  from  the  heart,  or  something  superadded 
to  the  force  of  the  heart.  The  experiment  of  Marey,  already  alluded  to,  settles  this  ques- 
tion. When  water  was  forced  in  an  intermittent  current  into  two  tubes,  one  elastic  and 
the  other  inelastic  but  discharging  by  openings  of  equal  size,  by  far  the  greater  quantity 
was  discharged  by  the  elastic  tube.  A  little  reflection  will  show  how  the  action  of  the 
elastic  arteries  must  actually  assist  the  circulation.  The  resiliency  of  the  vessel  is  con- 
tinually pressing  their  contents  toward  the  periphery,  as  regurgitation  is  rendered  impos- 
sible by  the  closure  of  the  semilunar  valves.  The  dilatation  of  the  vessels  with  each  sys- 
tole of  course  admits  an  increased  quantity  of  blood ;  and  it  has  been  experimentally 
demonstrated  that  the  same  intermittent  force  exerted  on  an  inelastic  tube  will  discharge 
a  less  quantity  of  liquid  from  an  opening  of  equal  caliber. 

Superadded,  then,  to  the  direct  action  of  the  heart,  we  must  recognize,  as  a  cause  in- 
fluencing the  flow  of  blood  in  the  arteries,  the  resiliency  of  the  vessels,  especially  of  those 
of  large  size,  this  force  being  derived  originally  from  the  heart.  Thus  it  will  be  seen  that 
the  arteries  are  constantly  kept  distended  with  blood  by  the  heart ;  and,  by  virtue  of 
their  elasticity  and  the  progressive  increase  in  the  capacity  of  this  system  as  they 
branch,  the  powerful  contractions  of  the  central  organ  only  serve  to  keep  up  an 
equable  current  in  the  capillaries.  The  small  vessels,  by  virtue  of  their  contractile 
walls,  regulate  the  distribution  of  the  blood,  acting  as  the  guards  or  sentinels  of 
the  process  of  nutrition,  and,  in  fact,  of  all  the  numerous  functions  in  which  the  blood 
is  concerned. 

Locomotion  of  the  Arteries  and  Production  of  the  Pulse. — At  each  contraction  of  the 
heart,  the  arteries  are  increased  in  length  and  many  of  them  undergo  a  considerable  loco- 
motion. This  may  be  readily  observed  in  vessels  which  are  tortuous  in  their  course  and 
is  frequently  very  marked  in  the  temporal  artery  in  old  persons.  The  elongation  may 
also  be  seen  if  we  watch  attentively  the  point  where  an  artery  bifurcates,  as  at  the  divis- 
ion of  the  common  carotid.  It  is  simply  the  mechanical  effect  of  sudden  distention, 
which,  while  it  increases  the  caliber  of  the  vessel,  causes  an  elongation  even  more 
marked. 

The  finger  placed  over  an  exposed  artery  or  one  which  lies  near  the  surface  expe- 
riences a  sensation  at  every  beat  of  the  heart  as  though  the  vessel  were  striking  against 
it.  This  has  long  been  observed  and  is  called  the  pulse.  Ordinarily  it  is  appreciated 
when  the  current  of  blood  is  subjected  to  a  certain  amount  of  obstruction,  as  in  the  radial, 

1  Schiff  has  noticed  rhythmical  contractions  in  the  superficial  arteries  of  the  ear  in  the  rabbit  and  in  some  other  ani- 
mals ;  but  this  phenomenon  is  exceptional,  and  the  movements  do  not  appear  to  favor  the  current  of  blood.  The 
recent  experiments  of  Dr.  J.  J.  Mason,  of  New  York,  show  conclusively,  to  our  mind  at  least,  that  there  is  not  a  peri- 
staitic  action  of  the  muscular  coats  of  the  small  arteries,  capable  of  assisting  the  circulation.  This  view,  however,  is 
opposed  to  the  ideas  of  Legros  and  Onimus  and  of  some  other  physiologists. 


FORM  OF  THE  PULSE.  71 

which  can  readily  be  compressed  against  the  bone.  In  an  artery  imbedded  in  soft  parts 
which  yield  to  pressure,  the  actual  dilatation  of  the  vessel  being  very  slight,  pulsation  is 
felt  with  difficulty,  if  at  all.  "When  obstruction  of  an  artery  is  complete,  as  in  ligation  of 
a  vessel,  the  pulsation  above  the  point  of  ligature  is  very  marked  and  can  be  readily  ap- 
preciated by  the  eye.  The  explanation  of  this  exaggeration  of  the  movement  is  the  fol- 
lowing: Normally,  the  blood  passes  freely  through  the  arteries  and  produces,  in  the 
smaller  vessels,  very  little  movement  or  dilatation ;  when,  however,  the  current  is  ob- 
structed, as  by  ligation  or  even  compression  with  the  finger,  the  force  of  the  heart  is  not  sent 
through  the  vessel  to  the  periphery  but  is  arrested  and  therefore  becomes  more  marked 
and  easily  appreciated.  In  vessels  which  have  become  undilatable  and  incompressible 
from  calcareous  deposits,  the  pulse  cannot  be  felt.  The  character  of  the  pulse  indicates, 
to  a  certain  extent,  the  condition  of  the  heart  and  vessels.  We  have  spoken,  when  treat- 
ing of  the  heart,  of  the  varying  rapidity  of  the  pulse,  as  it  is  a  record  of  the  rapidity  of 
the  action  of  this  organ ;  but  it  remains  for  us  to  consider  the  mechanism  of  its  produc- 
tion and  its  various  characters. 

Under  ordinary  circumstances,  the  pulse  may  be  felt  in  all  arteries  which  are  ex- 
posed to  investigation  ;  and,  as  it  is  due  to  the  movement  of  the  blood  in  the  vessels,  the 
prime  cause  of  its  production  is  the  contraction  of  the  left  ventricle.  The  experiments 
of  Marey  have  shown  that  the  impulse  given  to  the  blood  by  the  heart  is  not  felt  in  all 
the  vessels  at  the  same  instant.  By  ingenious  contrivances,  which  will  be  described 
farther  on,  this  observer  has  succeeded  in  registering  simultaneously  the  impulse  of  the 
heart,  the  pulse  of  the  aorta,  and  the  pulse  of  the  femoral  artery.  He  has  thus  ascer- 
tained that  the  contraction  of  the  ventricle  is  anterior,  in  point  of  time,  to  the  pulsation 
of  the  aorta,  and  that  the  pulsation  of  the  aorta  precedes  the  pulse  in  the  femoral.  This 
only  confirms  the  views  of  other  physiologists,  particularly  Weber,  who  described  this 
progressive  retardation  of  the  pulse  as  we  recede  from  the  heart,  estimating  the  difference 
between  the  ventricular  systole  and  the  pulsation  of  the  artery  in  the  foot  at  one-seventh 
of  a  second. 

It  is  evident  from  what  we  know  of  the  variations  which  occur  in  the  force  of  the 
heart's  action,  the  quantity  of  blood  in  the  vessels,  and  from  the  changes  which  may 
take  place  in  the  caliber  of  the  arteries,  that  the  characters  of  the  pulse  must  be  subject 
to  numerous  variations.  Many  of  these  may  be  appreciated  simply  by  the  sense  of  touch. 
We  find  writers  treating  of  the  soft  and  compressible  pulse,  the  hard  pulse,  the  wiry 
pulse,  the  thready  pulse,  etc.,  as  indicating  various  conditions  of  the  circulatory  system. 
The  character  of  the  pulse,  aside  from  its  frequency,  has  always  been  regarded  as  of  great 
importance  in  disease  ;  and  the  variations  which  occur  in  health  form  a  most  interesting 
subject  for  physiological  inquiry. 

Form  of  the  Pulse. — It  is  evident  that  few  of  the  characters  of  a  pulsation,  occupying 
as  it  does  but  one-seventieth  part  of  a  minute,  can  be  ascertained  by  the  sense  of  touch 
alone.  This  fact  has  been  appreciated  by  physiologists ;  and,  within  the  last  few  years, 
in  order  to  accurately  study  this  important  subject,  instruments  for  registering  the  pulse 
have  been  constructed,  to  enable  us  to  analyze  the  dilatation  and  movements  of  the 
vessels.  The  idea  of  such  an  instrument  was  probably  suggested  by  the  following 
simple  observation :  When  the  legs  are  crossed,  with  one  knee  over  the  other,  the  beating 
of  the  popliteal  artery  will  produce  a  marked  movement  in  the  foot.  If  we  could  apply 
to  an  artery  a  lever  provided  with  a  marking  point  in  contact  with  a  slip  of  paper  moving 
at  a  definite  rate,  this  point  would  register  the  movements  of  the  vessel  and  its  changes 
in  caliber.  The  first  physiologist  who  put  this  in  practice  was  Vierordt,  who  constructed 
quite  a  complex  instrument,  so  arranged  that  the  impulse  from  an  accessible  artery,  like 
the  radial,  was  conveyed  to  a  lever,  which  marked  the  movement  upon  a  revolving 
cylinder  of  paper.  This  instrument  was  called  a  "  sphygmograph."  The  traces  made  by 
it  were  perfectly  regular  and  simply  marked  the  extremes  of  dilatation,  exaggerated,  of 


CIRCULATION   OF  THE  BLOOD. 


course,  by  the  length  of  the  lever,  and  the  number  of  pulsations  in  a  given  time.  The 
latter  can  be  easily  estimated  by  more  simple  means ;  and,  as  the  former  did  not  convey 
any  very  definite  physiological  idea,  the  apparatus  was  regarded  rather  as  a  curiosity 
than  an  instrument  for  accurate  research. 


FIG.  22. — Sphygmograph  of  Marey. 

The  apparatus  is  securely  fixed  on  the  forearm,  so  that  the  spring  under  the  screw  V  is  directly  over  the  radial  artery. 
The  movements  of  the  pulse  are  transmitted  to  the  long  and  light  wooden  lever  L  and  registered  upon  the  sur- 
face P,  which  is  moved  at  a  known  rate  by  the  clock-work  H.  The  apparatus  is  so  adjusted  that  the  movements 
of  the  vessel  are  accurately  amplified  and  registered  by  the  extreme  point  of  the  lever. 


FIG.  23  (K).— Sphygmograph  of  Marey  applied  to  the  arm. 


FIG.  23  (B).— Trace  of  Tier  or  dt. 


FIG.  23  (C).— Trace  of  Marey. 
Portions  of  four  traces  taken  in  different  conditions  of  the  pulse. 


The  principle  on  which  the  instrument  of  Vierordt  was  constructed  was  correct ;  and 
it  only  remained  to  construct  one  which  would  be  easy  of  application  and  produce  a  trace 
representing  the  shades  of  dilatation  and  contraction  of  the  vessels,  in  order  to  lead  to 
important  practical  results.  These  indispensable  conditions  are  fully  realized  in  the 


FORM    OF  THE  PULSE.  73 

sphygmograph  of  Marey,  to  whose  researches  on  the  circulation  we  have  repeatedly 
referred.  The  instrument  simply  amplifies  the  changes  in  the  caliber  of  the  vessel;  and, 
although  its  application  is,  perhaps,  not  so  easy  as  to  make  it  generally  useful  in  practice, 
in  the  hands  of  Marey  it  has  given  us  a  definite  knowledge  of  the  physiological  character 
of  the  pulse  and  its  modifications  in  certain  diseases,  information  which  is  exceedingly 
desirable  and  which  could  not  be  arrived  at  by  other  means  of  investigation.  In  short 
its  mechanism  is  so  accurate  that,  when  skilfully  used,  it  gives  on  paper  the  actual 
"  form  of  the  pulse."  This  instrument,  applied  to  the  radial  artery,  gives  a  trace  very 
different  from  that  obtained  by  Vierordt,  which  was  simply  a  series  of  regular  eleva- 
tions and  depressions.  A  comparison  of  the  traces  obtained  by  these  two  observers 
gives  an  idea  of  the  defects  which  have  been  remedied  by  Marey ;  for  it  is  evident  that 
the  dilatation  and  contraction  of  the  arteries  cannot  be  so  regular  and  simple  as  would 
be  inferred  merely  from  the  trace  made  by  the  instrument  of  Vierordt. 

Analyzing  the  traces  of  Marey,  we  see  that  there  is  a  dilatation  following  the  systole 
of  the  heart,  marked  by  an  elevation  of  the  lever,  more  or  less  sudden,  as  indicated  by 
the  angle  of  the  trace,  and  of  greater  or  less  amplitude.  The  dilatation,  having  arrived 
at  its  maximum,  is  followed  by  reaction,  which  may  be  slow  and  regular,  or  may  be,  and 
generally  is,  interrupted  by  a  second  and  slighter  upward  movement  of  the  lever.  This 
second  impulse  varies  very  much  in  amplitude.  In  some  rare  instances,  it  is  nearly  as 
marked  as  the  first  and  may  be  appreciated  by  the  finger,  giving  the  sensation  of  a  double 
pulse  following  each  contraction  of  the  heart.  This  is  called  the  dicrotic  pulse.  As  a 
rule,  the  first  dilatation  of  the  vessel  is  sudden  and  is  indicated  by  an  almost  vertical 
line ;  this  is  followed  by  a  slow  reaction,  indicated  by  a  gradual  descent  of  the  trace, 
which  is  not,  however,  absolutely  regular,  but  is  marked  by  a  slight  elevation  indicating 
a  second  impulse.  The  amplitude  of  the  trace,  or  the  distance  between  the  highest  and 
the  lowest  points  marked  by  the  lever,  depends  upon  the  amount  of  constant  tension  of 
the  vessels.  Marey  has  found  that  the  amplitude  is  in  an  inverse  ratio  to  the  tension ; 
which  is  very  easily  understood,  for,  when  the  arteries  are  but  little  distended,  the  force 
of  the  heart  must  be  more  marked  in  its  effects  than  when  the  pressure  of  blood  is  very 
great.  Any  circumstance  which  facilitates  the  flow  of  blood  from  the  arteries  into  the 
capillaries  will,  of  course,  relieve  the  tension  of  the  arterial  system,  lessen  the  obstacle 
to  the  force  of  the  heart,  and  increase  the  amplitude  of  the  pulsation,  and  vice  versa. 
In  support  of  this  view,  Marey  has  found  that  cold  applied  to  the  surface  of  the  body 
contracting,  as  it  does,  the  smallest  arteries,  increases  the  arterial  tension  and  dimin- 
ishes the  amplitude  of  the  pulsation,  while  a  moderate  elevation  of  temperature  pro- 
duces an  opposite  effect. 

In  nearly  all  the  traces  given  by  Marey,  the  descent  of  the  lever  indicates  more  or  less 
oscillation  of  the  mass  of  blood.  The  physical  properties  of  the  larger  arteries  render 
this  inevitable.  As  they  yield  to  the  distending  influence  of  the  heart,  reaction  occurs 
after  this  force  is  taken  oft'  and,  if  the  distention  be  very  great,  gives  a  second  impulse  to 
the  blood.  This  is  quite  marked,  unless  the  tension  of  the  arterial  system  be  so  great  as 
to  offer  too  much  resistance.  One  of  the  most  favorable  conditions  for  the  manifestation 
of  dicrotism  is  diminished  tension,  which  is  always  found  coexisting  with  a  very  marked 
exhibition  of  this  phenomenon. 

The  delicate  instrument  employed  by  Marey  enabled  him  to  accurately  determine  and 
register  these  various  phenomena,-  by  observations  on  the  arteries  of  the  human  subject 
and  the  lower  animals ;  and,  by  means  of  an  ingeniously  constructed  "  schema,"  repre- 
senting the  arterial  system  by  elastic  tubes  and  the  left  ventricle  by  an  elastic  bag  pro- 
vided with  valves  and  acting  as  a  syringe,  he  satisfactorily  established  the  conditions  of 
tension,  etc.,  necessary  to  their  production.  In  this  schema,  the  registering  apparatus, 
simpler  in  construction  than  the  sphygmograph,  could  be  applied  to  the  tubes  with  more 
accuracy  and  ease.  He  demonstrated,  by  experiments  with  this  system  of  tubes,  that 
the  amplitude  of  the  pulsations,  the  force  of  the  central  organ  being  the  same,  is  greatest 


74  CIRCULATION"  OF   THE  BLOOD. 

when  the  tubes  are  moderately  distended,  or  when  the  tension  of  fluid  is  low,  and  vice  versa. 
He  demonstrated,  also,  that  a  low  tension  favors  dicrotism.  In  this  latter  observation, 
lie  diminished  the  tension  by  enlarging  the  orifices  by  which  the  fluid  was  discharged 
from  the  tubes,  imitating  the  dilatation  of  the  small  vessels,  by  which  the  tension  is  di- 
minished in  the  arterial  system.  He  also  demonstrated  that  an  important  and  essential 
element  in  the  production  of  dicrotism  is  the  tendency  to  oscillation  of  the  fluid  in  the 
vessels  during  the  intervals  between  the  contractions  of  the  heart.  This  can  only  occur 
in  a  fluid  which  has  a  certain  weight  and  acquires  a  velocity  from  the  impulse ;  for, 
when  air  was  introduced  into  the  apparatus,  dicrotism  could  not  be  produced  under  any 
circumstances,  as  the  fluid  did  not  possess  weight  enough  to  oscillate  between  the  im- 
pulses. Water  produced  a  well-marked  dicrotic  impulse  under  favorable  conditions; 
and  with  mercury,  the  oscillations  made  two,  three,  or  more  distinct  impulses.  By 
these  experiments  he  proved  that  the  blood  oscillates  in  the  vessels,  if  this  movement 
be  not  suppressed  by  too  great  pressure  or  tension.  This  oscillation  gives  the  successive 
rebounds  that  are  marked  in  the  descending  line  of  the  pulse,  and  is  capable,  in  some 
rare  instances  when  the  arterial  tension  is  very  slight,  of  producing  a  second  rebound 
of  sufficient  force  to  be  appreciated  by  the  finger. 

Without  treating  of  the  variations  in  the  character  of  the  pulse  in  disease,  due  to  the 
action  of  the  muscular  coat,  we  shall  consider  some  of  the  external  modifying  influences 
which  come  within  the  range  of  physiology.  The  smallest  vessels  and  those  of  medium 
size  possess  to  an  eminent  degree  what  is  called  tonicity,  or  the  property  of  maintaining 
a,  certain  continued  amount  of  contraction.  This  contraction  is  antagonistic  to  the  dis- 
tending force  of  the  blood,  as  is  shown  by  opening  a  portion  of  an  artery  included  be- 
tween two  ligatures  in  a  living  animal,  when  the  contents  will  be  forcibly  discharged  and 
the  caliber  of  that  portion  of  the  vessel  is  very  much  diminished.  Too  great  distention 
of  the  vessels  by  the  pressure  of  blood  seems  to  be  prevented  by  this  constant  action  of 
the  muscular  coat;  and  thus  the  conditions  are  maintained  which  give  the  pulse  the 
characters  we  have  just  described. 

By  excessive  and  continued  heat,  the  muscular  tissue  of  the  arteries  may  be  dilated 
so  as  to  offer  less  resistance  to  the  distending  force  of  the  heart.  Under  these  circum- 
stances, the  pulse,  as  felt  by  the  finger,  will  be  found  to  be  larger  and  softer  than  normal. 
Cold,  either  general  or  local,  has  an  opposite  effect;  the  arteries  become  contracted,  and 
the  pulse  assumes  a  harder  and  more  wiry  character.  Usually,  prolonged  contraction  of 
the  arteries  is  followed  by  relaxation,  as  is  seen  in  the  full  pulse  and  glow  of  the  surface 
which  accompany  reaction  after  exposure  to  cold. 

It  has  been  found,  also,  that  there  is  a  considerable  difference  in  the  caliber  of  the 
arteries  at  different  periods  of  the  day.  The  diameter  of  the  radial  has  been  found  very 
much  greater  in  the  evening  than  in  the  morning,  producing,  naturally,  a  variation  in  the 
character  of  the  pulse.  We  learn  from  these  physiological  variations,  how,  in  disease, 
when  they  become  more  considerable,  they  may  give  important  information  with  regard 
to  the  condition  of  the  system. 

Pressure  of  Blood  in  the  Arteries. 

The  reaction  of  the  elastic  walls  of  the  arteries  during  the  intervals  of  the  heart's 
action  gives  rise  to  a  certain  amount  of  constant  pressure,  by  which  the  blood  is  con- 
tinually forced  toward  the  capillaries.  The  discharge  of  blood  into  the  capillaries  has  a 
constant  tendency  to  diminish  this  pressure ;  but  the  contractions  of  the  left  ventricle, 
by  forcing  repeated  charges  of  blood  into  the  arteries,  have  a  compensating  action.  By 
the  equilibrium  between  these  two  agencies,  a  certain  degree  of  tension  is  maintained  in 
the  arteries,  which  is  called  the  arterial  pressure. 

The  first  experiments  with  regard  to  the  extent  of  the  arterial  pressure  were  made 
by  Hales,  an  English  physiologist,  more  than  a  hundred  years  ago.  This  observer, 
adapting  a-  long  glass  tube  to  the  artery  of  a  living  animal,  ascertained  the  height  of  the 


-c 


PRESSURE  OF  BLOOD  IN  THE  ARTERIES.  75 

column  of  blood  which  could  be  sustained  by  the  arterial  pressure.     In  some  experiments 
on  the  carotid  of  the  horse,  the  blood  mounted  to  the  height  of  from  eight  to  ten  feet. 

All  experiments  on  the  arterial  pressure  are  made 
on  the  principle  of  the  experiment  of  Hales,  which, 
with  reference  simply  to  the  constant  pressure  in  the 
arteries,  is  as  useful  as  those  of  later  date  and  much 
more  striking.  The  only  inconvenience  is  in  the  ma- 
nipulation of  the  long  tube ;  but  this  may  be  avoided 
by  setting  it  in  a  strip  of  wood,  when  it  can  be  easily 
handled.  If  a  large  artery,  as  the  carotid,  be  exposed 
in  a  living  animal,  and  a  metallic  point,  connected 
with  a  vertical  tube  of  small  caliber  and  from  seven 
to  eight  feet  long  by  a  bit  of  elastic  tubing,  be  secured 
in  the  vessel,  the  blood  will  rise  to  the  height  of  about 
six  feet  and  remain  at  this  point  almost  stationary, 
indicating,  by  a  slight  pulsatile  movement,  the  action 
of  the  heart.  On  carefully  watching  the  level  in  the 
tube,  in  addition  to  the  rapid  oscillation  coincident 
with  the  pulse,  another  oscillation  will  be  observed, 
which  is  less  frequent  and  which  corresponds  with 
the  movements  of  respiration.  The  pressure,  as  indi- 
cated by  an  elevation  of  the  fluid,  is  slightly  increased 
during  expiration  and  diminished  during  inspiration.1 

The  experiment  with  the  long  tube  gives  us  the 
best  general  idea  of  the  arterial  pressure,  which  will 
be  found  to  vary  between  five  and  a  half  and  six  feet 
of  blood,  or  a  few  inches  more  of  water.  The  oscil- 
lations produced  by  the  contractions  of  the  heart  are 
not  very  marked,  on  account  of  the  great  friction  in 
so  long  a  tube ;  but  this  is  favorable  to  the  study  of 
the  constant  pressure.  It  has  been  found  that  the 
estimates  above  given  do  not  vary  very  much  in  ani- 
mals of  different  sizes.  Bernard  found  the  pressure  in  the  carotid  of  a  horse  but  little 
more  than  in  the  dog  or  rabbit.  In  the  larger  animals,  it  is  the  force  of  the  heart  which 
is  increased,  and  not,  to  any  considerable  extent,  the  constant  pressure  in  the  vessels. 

The  experiments  of  Hales  were  made  with  a  view  of  calculating  the  force  of  the 
heart  and  were  not  directed  particularly  to  the  conditions  and  variations  of  the  arterial 
pressure.  It  is  only  since  the  experiments  performed  by  Poiseuille  with  the  hsemadyna- 
mometer,  in  1828,  that  we  have  any  reliable  data  on  this  latter  point.  Poiseuille's 
instrument  for  measuring  the  force  of  the  blood  is  a  simple  graduated  U-tube,  half  filled 
with  mercury,  with  one  arm  bent  at  a  right  angle,  so  that  it  can  easily  be  connected  with 
the  artery.  The  pressure  of  the  blood  is  indicated  by  a  depression  in  the  level  of  the 
mercury  on  one  side  and  a  corresponding  elevation  on  the  other.  This  instrument  is 
generally  considered  as  possessing  great  advantages  over  the  long  glass  tube;  but,  for 
estimating  simply  the  arterial  pressure,  it  is  much  less  useful,  as  it  is  more  sensitive  to 
the  impulse  of  the  heart.  For  the  study  of  the  cardiac  pressure,  it  has  the  disadvantage, 
in  the  first  place,  of  considerable  friction,  and,  again,  the  weight  of  the  column  of 
mercury  produces  an  extent  of  oscillation  by  its  mere  impetus,  greater  than  that  which 
would  actually  represent  the  force  of  the  heart. 

An  important  improvement  in  the  ha3madynamometer  was  made  by  Magendie.  This 
apparatus,  the  cardiometer,  in  which  Bernard  has  made  some  important  modifications,  is 

1  In  all  these  experiments  on  the  arterial  or  cardiac  pressure,  it  is  necessary  to  fill  part  of  the  tube,  or  whatever 
apparatus  we  may  use,  with  a  solution  of  carbonate  of  soda,  in  order  to  prevent  coagulation  of  the  blood  as  it  passes 
out  of  the  vessels. 


FIG.  24:.—Hmmadynamometer  of  Poiseuille. 
modified  by  Ludwig,  Syengler^  and 
Valentin. 

The  instrument  is  connected  with  the  ves- 
sel V  V,  in  such  a  manner  that  the 
circulation  is  not  interrupted.  The  ele- 
vation of  the  mercury  in  the  branch  B  C 
indicates  the  amount  of  pressure. 


76 


CIRCULATION  OF  THE  BLOOD. 


the  one  now  generally  used.  It  consists  of  a  small  but  thick  glass  bottle,  with  a  fine, 
graduated  glass  tube  about  twelve  inches  in  length,  communicating  with  it,  either  through 
the  stopper  or  by  an  orifice  in  the  side.  The  stopper  is  pierced  by  a  bent  tube  which  is 
to  be  connected  with  the  blood-vessel.  The  bottle  is  filled  with  mercury  so  that  it  will 
rise  in  the  tube  to  a  point  which  is  marked  zero.  It  is  evident  that  the  amount  of  press- 
ure on  the  mercury  in  the  bottle  will  be  indicated  by  an  elevation  in  the  graduated  tube ; 
and,  moreover,  from  the  fineness  of  the  column  in  the  tube,  we  avoid  some  of  the  in- 
conveniences which  are  due  to  the  weight  of  mercury  in  the  hsemadynamometer,  and  we 
also  have  less  friction.  This  instrument  is  appropriately  called  the  cardiometer,  as  it  in- 
dicates most  accurately,  by  the  extreme  elevation  of  the  mercury,  the  force  of  the  heart; 


FIG.  25  (A.).— Section  of  the  cardiometer  of  Jfagendie, 
as  modified  by  Bernard. 

A  strong  glass  bottle  is  perforated  at  each  side  and  fitted 
with  an  iron  tube,  with  an  opening,  T,  by  which  the 
mercury  enters.  One  end  of  the  iron  tube  is  closed, 
and  the  other  is  bent  upward  and  connected  with 
the  graduated  glass  tube  T',  which  has  a  caliber  of 
from  TV  to  |  of  an  inch.  The  bottle  is  filled  with 
mercury  until  it  rises  to  n'  in  the  tube  which  is 
marked  zero.  The  cork  is  perforated  by  the  tube  t, 
which  is  connected  by  a  rubber  tube  with  the  point 
C,  which  is  introduced  into  the  vessel. 


FIG.  25  (B).— Compensating  instrument  of  Marey. 


but  it  is  not  as  perfect  in  its  indications  of  the  mean  arterial  pressure,  for,  in  the  abrupt 
descent  of  the  mercury  during  the  diastole  of  the  heart,  the  impetus  causes  the  level  to 
fall  considerably  below  the  real  standard  of  the  constant  pressure.  Marey  has  succeeded 
in  correcting  this  difficulty  in  what  he  calls  the  "  compensating  "  instrument,  which  is 
constructed  on  the  following  principle :  Instead  of  a  simple  glass  tube  which  communi- 
cates with  the  mercury  in  the  bottle,  as  in  Magendie's  cardiometer,  he  has  two  tubes, 
one  of  which  is  like  the  one  already  described  and  represents  oscillations  produced  by 
the  heart,  while  the  other  is  larger,  and  has,  at  the  lower  part,  a  constriction  of  the 


INFLUENCE   OF   RESPIRATION.  77 

caliber,  which  is  here  reduced  to  capillary  fineness.  The  latter  tube  is  designed  to  give  the 
mean  arterial  pressure ;  the  constricted  portion  offering  such  an  obstacle  to  the  rise  of 
the  mercury  that  the  intermittent  action  of  the  heart  is  not  felt,  the  mercury  rising  slowly 
to  a  certain  level,  which  is  constant  and  varies  only  with  the  constant  pressure  in  the 
vessels. 

We  have  only  an  approximative  idea  of  the  average  pressure  in  the  arterial  system  in 
the  human  subject,  deduced  from  experiments  on  animals.  It  has  already  been  stated  to 
be  equal  to  about  six  feet  of  water  or  six  inches  of  mercury. 

The  most  interesting  questions  connected  with  the  subject  of  the  arterial  press- 
ure are  the  comparative  pressure  in  different  parts  of  the  arterial  system,  the  conditions 
which  modify  the  arterial  pressure,  and  its  influence  on  the  pulse.  These  points  have  all 
been  pretty  fully  investigated  by  experiments  on  animals  and  observations  on  systems  of 
elastic  tubes  arranged  to  represent  the  blood-vessels. 

Pressure  in  Different  Parts  of  the  Arterial  System. — The  experiments  of  Hales,  Poi- 
seuille,  Bernard,  and  others,  seem  to  show  that  the  constant  arterial  pressure  does  not 
vary  in  arteries  of  different  sizes.  These  physiologists  have  experimented  particularly 
on  the  carotid  and  crural,  and  have  found  the  pressure  in  these  two  vessels  about  the 
same.  From  their  experiments  they  conclude  that  the  force  is  equal  in  all  parts  of  the 
arterial  system.  The  experiments  of  Volkmann,  however,  have  shown  that  this  conclu- 
sion has  been  too  hasty.  With  the  registering  apparatus  of  Ludwig,  he  has  taken  the 
pressure  in  the  carotid  and  the  metatarsal  arteries  and  has  always  found  a  considerable 
difference  in  favor  of  the  former.  In  an  experiment  on  a  dog,  he  found  the  pressure  equal 
to  one  hundred  and  seventy-two  millimeters  in  the  carotid,  and  one  hundred  and  sixty- 
five  in  the  metatarsal.  In  an  experiment  on  a  calf,  the  pressure  was  one  hundred  and 
sixteen  mm.  in  the  carotid,  and  eighty-nine  mm.  in  the  metatarsal;  and  in  a  rabbit, 
ninety-one  mm.  in  the  carotid,  and  eighty-six  mm.  in  the  crural.  These  experiments  show 
that  the  pressure  is  not  absolutely  the  same  in  all  parts  of  the  arterial  system,  that  it  is 
greatest  in  the  arteries  nearest  the  heart,  and  that  it  gradually  diminishes  as  we  near  the 
capillaries.  The  difference  is  very  slight,  almost  inappreciable,  until  we  come  to  vessels  of 
very  small  size ;  but  here  the  pressure  is  directly  influenced  by  the  discharge  of  blood  into 
the  capillaries.  The  cause  of  this  diminution  of  pressure  in  the  smallest  vessels  is  the  prox- 
imity of  the  great  outlet  of  the  arteries,  the  capillary  system ;  for,  as  we  shall  see  farther 
on,  the  flow  into  the  capillaries  has  a  constant  tendency  to  diminish  the  pressure  in  the 
arteries.  It  is  obvious  that  this  influence  can  only  be  felt  in  a  very  marked  degree  in  the 
vessels  of  smallest  size. 

Influence  of  Respiration. — It  is  easy  to  see,  in  studying  the  arterial  pressure  with  any 
of  the  instruments  we  have  described,  that  there  is  a  marked  increase  with  expiration 
and  a  diminution  with  inspiration.  The  fact  that  expiration  will  increase  the  force  of  the 
jet  of  blood  from  a  divided  artery  has  long  been  observed  and  accords  perfectly  with  the 
above  statement.  In  tranquil  respiration,  the  influence  upon  the  flow  of  blood  is  due 
simply  to  the  mechanical  action  of  the  thorax.  With  every  inspiration,  the  air-cells  are 
enlarged,  as  well  as  the  blood-vessels  of  the  lungs,  the  air  rushes  in  through  the  trachea, 
and  the  movement  of  the  blood  in  the  veins  near  the  chest  is  accelerated.  At  the  same 
time,  the  blood  in  the  arteries  is  somewhat  retarded  in  its  flow  from  the  thorax,  or  at  least 
does  not  feel  the  expulsive  influence  which  follows  with  the  act  of  expiration.  The  arterial 
pressure  at  that  time  is  at  its  minimum.-  With  the  expiratory  act,  the  air  is  expelled  by 
compression  of  the  lungs,  the  flow  of  blood  into  the  thorax  by  the  veins  is  retarded  to  a 
certain  extent,  while  the  flow  of  blood  into  the  arteries  is  favored.  This  is  strikingly 
exhibited  in  the  augmented  force,  with  expiration,  in  the  jet  from  a  divided  artery. 
Under  these  circumstances  the  arterial  pressure  is  at  its  maximum.  In  perfectly  tranquil 
respiration,  the  changes  due  to  inspiration  and  expiration  are  slight,  presenting  a  differ- 


78  CIRCULATION"   OF  THE   BLOOD.   ' 

ence  of  not  more  than  half  an  inch  to  an  inch  in  the  cardiometer.  When  the  respiratory 
movements  are  exaggerated,  the  oscillations  are  very  much  more  marked. 

Interruption  of  respiration  is  followed  by  a  very  great  increase  in  the  arterial  press- 
ure. This  is  due,  not  to  causes  within  the  chest,  but  to  obstruction  to  the  circulation  in 
the  capillaries.  We  are  already  aware  of  the  influence  which  the  flow  of  bipod  into  the 
capillaries  is  constantly  exerting  upon  the  arterial  pressure.  This  tendency  to  diminish 
the  quantity  of  blood  in  the  arteries,  and  consequently  the  pressure,  is  constantly  coun- 
teracted by  the  blood  sent  into  the  arteries  by  the  contractions  of  the  heart.  With  an  in- 
terruption of  the  respiratory  function,  the  non-aerated  blood  passes  into  the  arteries  but 
cannot  flow  readily  through  the  capillaries ;  and,  as  a  consequence,  the  arteries  are  abnor- 
mally distended  and  the  pressure  is  greatly  increased.  If  respiration  be  permanently 
arrested,  the  arterial  pressure  becomes,  after  a  time,  diminished  below  the  normal 
standard,  and  is  finally  abolished,  on  account  of  the  stoppage  of  the  action  of  the  heart. 
If  respiration  be  resumed  before  the  heart  has  become  arrested,  the  pressure  soon  returns 
to  its  normal  condition. 

Muscular  effort  considerably  increases  the  arterial  pressure.  This  is  due  to  two  causes. 
In  the  first  place,  the  chest  is  generally  compressed,  favoring  the  flow  of  blood  into  the 
great  vessels.  In  the  second  place,  muscular  exertion  produces  a  certain  amount  of  ob- 
struction to  the  discharge  of  blood  from  the  arteries  into  the  capillaries.  Numerous 
experiments  upon  animals  have  shown  a  great  increase  in  pressure  in  the  struggles  which 
occur  during  severe  operations.  It  has  been  shown  that  galvanization  of  the  sympa- 
thetic in  the  neck  and  irritation  of  certain  of  the  cerebro-spinal  nerves  increase  the  arterial 
pressure,  probably  from  an  influence  on  the  muscular  coats  of  some  of  the  arteries,  caus- 
ing them  to  contract  and  thereby  diminishing  the  total  capacity  of  the  arterial  system. 

Effects  of  Haemorrhage. — Diminution  in  the  quantity  of  blood  has  a  remarkable  ef- 
fect upon  the  arterial  pressure.  If,  in  connecting  the  instrument  with  the  arteries,  we 
allow  even  one  or  two  jets  of  blood  to  escape,  the  pressure  will  be  found  diminished  per- 
haps one-half,  or  even  more.  It  is  hardly  necessary  to  discuss  the  mechanism  of  the  effect 
of  the  loss  of  blood  on  the  tension  of  the  vessels,  but  it  is  wonderful  how  soon  the  press- 
ure in  the  arteries  regains  its  normal  standard  after  it  has  been  lowered  by  haemorrhage. 
As  the  pressure  depends  largely  upon  the  quantity  of  blood,  as  soon  as  the  vessels  absorb 
the  serosities  in  sufficient  quantity  to  repair  the  loss,  the  pressure  is  increased.  This 
takes  place  in  a  very  short  time,  if  the  loss  of  blood  be  not  too  great. 

Experiments  on  the  arterial  pressure  with  the  cardiometer  have  verified  the  fact 
stated  in  treating  of  the  form  of  the  pulse ;  namely,  that  the  pressure  in  the  vessels  bears 
an  inverse  ratio  to  the  distention  produced  by  the  contractions  of  the  heart.  In  the  car- 
diometer, the  mean  height  of  the  mercury  indicates  the  constant,  or  arterial  pressure ; 
and  the  oscillations,  the  distention  produced  by  the  heart.  It  is  found  that  when  the 
pressure  is  great,  the  extent  of  oscillation  is  small,  and  vice  versa.  It  will  be  remembered 
that  the  researches  of  Marey  demonstrated  that  an  increase  of  the  arterial  pressure 
diminishes  the  amplitude  of  the  pulsations,  as  indicated  by  the  sphygmograph,  and  that 
the  amplitude  is  very  great  when  the  pressure  is  slight.  It  is  also  true,  as  a  general  rule, 
that  the  force  of  the  heart,  as  indicated  by  the  cardiometer,  bears  an  inverse  ratio  to  the 
frequency  of  its  pulsations. 

Depressor  Nerve  of  the  Circulation— Within  the  last  few  years,  an  important  discovery 
has  been  made  by  Cyon  and  Ludwig,  of  a  nerve  arising  in  the  rabbit  by  two  roots,  one 
from  the  main  trunk  of  the  pneumogastric  and  the  other  from  the  superior  laryngeal 
nerve,  which  joins  the  sympathetic  filaments  in  the  chest  and  passes  to  the  heart.  This 
nerve  has  a  reflex  action,  as  was  shown  by  the  experiments  of  Cyon,  its  galvanization 
reducing  the  arterial  pressure  by  one-third  or  one-half.  This  action  is  known  to  be 
reflex,  for,  when  the  nerve  is  divided,  galvanization  of  the  central  end  affects  the  arterial 


RAPIDITY   OF  THE   CURRENT   OF  BLOOD   IN  THE   ARTERIES.        79 


pressure,  while  no  such  result  follows  stimulation  of  the  peripheral  extremity ;  and  the 
effect  is  manifested  when  the  pneumogastrics  have  been  divided  and  no  direct  nervous 
influence  is  exerted  over  the  heart.  It  is  thought  that  the  reduction  in  the  arterial  press- 
ure following  galvanization  of  the  so-called  depressor  nerves  is  mainly  due  to  the  action 
of  the  splanchnic  nerves,  by  which  the  abdominal  vessels  become  largely  dilated.  If  the 
abdomen  be  opened  and  one  or  more  of  the  splanchnic  nerves  be  divided,  the  arterial 
pressure  is  immediately  diminished,  and  the  pressure  is  restored  if  the  divided  ends  of 
the  nerves  be  galvanized.  If,  after  division  of  the  splanchnic  nerves  and  the  conse- 
quent diminution  of  the  arterial  pressure,  the  depressor  nerves  be  galvanized,  the  press- 
ure still  undergoes  some  additional  diminution,  but  this  is  much  less  than  the  diminution 
which  follows  galvanization  of  the  depressor  nerves  without  section  of  the  splanchnic. 
The  action  of  these  nerves  will  be  more  fully  considered  in  connection  with  the  physiology 
of  the  nervous  system. 

Rapidity  of  the  Current  of  Blood  in  the  Arteries. — The  question  of  the  rapidity  of 
the  arterial  circulation  has  long  engaged  the  attention  of  physiologists;  but  the  experi- 
ments of  Volkmann,  with  his  hsemadrometer,  and  of  Yierordt,  with  a  peculiar  instru- 
ment which  he  devised  for  the  purpose,  did  not  lead  to  results  that  were  entirely 
satisfactory. 

The  best  instrument  for  measuring  the  rapidity  of  the  circulation  in  the  arteries  was 
devised  by  Ohauveau,  of  the  Veterinary  School  at  Lyons.  This  will  give,  by  calculation^ 
the  actual  rapidity  of  the  circulation  ;  and,  what  is  more  interesting,  it  marks  accurately 
the  rapid  variations  in  velocity  which  occur  at  different  periods  of  the  heart's  action. 

The  instrument  to  be  applied  to  the  carotid  of  the  horse  consists  of  a  thin  brass  tube, 
about  an  inch  and  a  half  in  length  and  of  the  diameter  of  the  artery  (about  three-eighths. 
of  an  inch),  which  is  provided  with  an 
oblong,  longitudinal  opening,  or  window, 
near  the  middle,  about  two  lines  long  and 
one  line  wide.  A  piece  of  thin  vulcan- 
ized rubber  is  wound  around  the  tube 
and  firmly  tied  so  as  to  cover  this  open- 
ing. Through  a  transverse  slit  in  the 
rubber,  is  introduced  a  very  light  metallic 
needle,  an  inch  and  a  half  in  length  and 
flattened  at  its  lower  part.  This  is  made 
to  project  about  half-way  into  the  caliber 
of  the  tube.  A  flat,  semicircular  piece 
of  metal,  divided  into  an  arbitrary  scale, 
is  attached  to  the  tube,  to  indicate  the 
deviations  of  the  point  of  the  needle. 

The  apparatus  is  introduced  carefully 
into  the  carotid  of  a  horse,  by  making  a 
slit  in  the  vessel,  introducing  first  one 
end  of  the  tube  directed  toward  the 


FIG.  W>—Cha,uveauls  instrument  for  measuring  the  ra- 
pidity of  the  flow  of  blood  in  the  arteries. 
The  instrument  viewed  in  face— a,  the  tube  to  be  fixed 
in  the  vessel ;  6,  the  dial  which  marks  the  extent  of 
movement  of  the  needle  d  ;  e,  a  lateral  tube  for  the  at- 
tachment of  a  cardiometer,  if  desired. 


heart,  then  allowing  a  little  blood  to 
enter  the  instrument,  so  as  to  expel  the 
air,  and,  when  full,  introducing  the  other 
end,  securing  the  whole  by  ligatures  above 
and  below. 

When  the  circulation  is  arrested,  the  needle  should  be  vertical,  or  mark  zero  on  the 
scale.     When  the  flow  is  established,  a  deviation  of  the  needle  occurs,  which  varies  in 
extent  with  the  rapidity  of  the  current.     Having  removed  all  pressure  from  the  vessel  s 
as  to  allow  the  current  to  resume  its  normal  character,  the  deviations  of  the  needle  are 
carefully  noted,  as  they  occur  with  the  systole  of  the  heart,  with  the  diastole,  etc.     After 


80  CIRCULATION"  OF  THE   BLOOD. 

withdrawing  the  instrument,  it  is  applied  to  a  tube  of  the  size  of  the  artery,  in  which  a 
current  of  water  is  made  to  pass  with  a  rapidity  which  will  produce  the  same  devia- 
tions as  occurred  when  the  instrument  was  connected  with  the  blood-vessel.  The  ra- 
pidity of  the  current  in  this  tube  may  be  easily  calculated  by  receiving  the  fluid  in  a 
graduated  vessel  and  noting  the  time  occupied  in  discharging  a  given  quantity.  By  this 
means  we  ascertain  the  rapidity  of  the  current  of  blood.  This  instrument  is  on  the  same 
principle  as  the  one  constructed  by  Vierordt,  but  in  sensitiveness  and  accuracy  it  is  much 
superior.  In  the  hands  of  Chauveau,  the  results,  particularly  those  with  regard  to  varia- 
tions in  the  rapidity  of  the  current,  are  very  interesting. 

Rapidity  of  the  Current  in  the  Carotid. — It  has  been  found  that  three  currents,  with 
different  degrees  of  rapidity,  may  be  distinguished  in  the  carotid : 

1.  At  each  ventricular  systole,  we  have,  as  the  average  of  the  experiments  of  Chau- 
veau, the  blood  moving  in  the  carotids  at  the  rate  of  20^-  inches  per  second.     After  this, 
the  rapidity  quickly  diminishes,  the  needle  returning  quite  or  nearly  to  zero,  which  would 
indicate  complete  arrest. 

2.  Immediately  succeeding  the  ventricular  systole,  we  have  a  second  impulse  given  to 
the  blood,  which  is  synchronous  with  the  closure  of  the  semilunar  valves,  the  blood  mov- 
ing at  the  rate  of  8T67  inches  per  second.     Chauveau  calls  this  the  dicrotic  impulse. 

3.  After  the  dicrotic  impulse,  the  rapidity  of  the  current  gradually  diminishes,  until 
just  before  the  systole  of  the  heart,  when  the  needle  is  nearly  at  zero.     The  average  rate, 
after  the  dicrotic  impulse,  is  5T97  inches  per  second. 

The  above  experiments  give  us,  for  the  first  time,  correct  notions  of  the  rapidity  and 
variations  in  the  flow  of  blood  in  the  larger  vessels ;  and  it  is  seen  that  they  correspond 
in  a  remarkable  degree  with  the  experiments  of  Marey  on  the  form  of  the  pulse.  Marey 
showed  that  there  is  a  marked  oscillation  of  the  blood  in  the  vessels,  due  to  a  reaction 
of  their  elastic  walls,  following  the  first  violent  distention  by  the  heart ;  that,  at  the  time 
of  closure  of  the  semilunar  valves,  the  arteries  experience  a  second,  or  dicrotic  distention, 
much  less  than  the  first;  and,  following  thisr  there  is  a  gradual  decline  in  the  distention 
until  the  minimum  is  reached.  Chauveau  shows  by  experiments  with  his  instrument 
that,  corresponding  to  the  first  dilatation  of  the  vessels,  the  blood  moves  with  great 
rapidity ;  following  this,  the  current  suddenly  becomes  nearly  arrested ;  this  is  followed  by  a 
second  acceleration  in  the  current,  less  than  the  first ;  and,  following  this,  we  have  a 
gradual  decline  in  the  rapidity  up  to  the  time  of  the  next  pulsation. 

Rapidity  in  Different  Parts  of  the  Arterial  System. — From  the  fact  that  the  arterial 
system  increases  in  capacity  as  we  recede  from  the  heart,  we  should  expect  to  find  a  cor- 
responding diminution  in  the  rapidity  of  the  flow  of  blood.  There  are,  however,  many 
circumstances,  aside  from  simple  increase  in  the  capacity  of  the  vessels,  which  modify 
the  blood-current  and  render  inexact  any  calculations  made  upon  purely  physical  principles. 
Such  are  the  tension  of  the  blood,  the  conditions  of  contraction  or  relaxation  of  the 
smallest  arteries,  etc.  It  is  necessary,  therefore,  to  have  recourse  to  actual  experiments 
to  arrive  at  any  definite  results  on  this  point.  The  experiments  of  Volkmann  showed  a 
great  difference  in  the  rapidity  of  the  current  in  the  carotid  and  metatarsal  arteries,  the 
averages  being  10  inches  per  second  in  the  carotid  and  2'2  inches  in  the  metatarsal.  The 
same  difference,  although  not  quite  so  marked,  was  found  by  Chauveau  between  the  carot- 
id and  the  facial.  The  last-named  observer  also  noted  an  important  modification  in  the 
character  of  the  current  in  the  smaller  vessels.  As  we  recede  from  the  heart,  the  sys- 
tolic impulse  becomes  rapidly  diminished,  being  reduced  in  one  experiment  about  two- 
thirds  ;  the  dicrotic  impulse  becomes  feeble  or  may  even  be  abolished  ;  but  the  constant 
flow  is  very  much  increased  in  rapidity.  This  fact  coincides  with  the  ideas  already 
advanced  with  regard  to  the  gradual  conversion,  by  virtue  of  the  elasticity  of  the  vessels, 
of  the  impulse  of  the  heart  into,  first,  a  remittent,  and,  in  the  very  smallest  arteries,  a 
nearly  constant  current. 

The  rapidity  of  the  flow  in  any  artery  must  be  subject  to  constant  modifications  due 


CIRCULATION  OF  THE   BLOOD  IN  THE  CAPILLARIES.  81 

to  the  condition  of  the  arterioles  which  are  supplied  by  it.  When  these  little  vessels  are 
dilated,  the  artery  of  course  empties  itself  with  greater  facility,  and  the  rapidity  is  in- 
creased. Thus  the  rapidity  bears  a  relation  to  the  arterial  pressure ;  as,  independently  of 
a  diminution  in  the  entire  quantity  of  the  circulating  fluid,  variations  in  the  pressure 
depend  chiefly  on  causes  which  facilitate  or  retard  the  flow  of  blood  into  the  capillaries. 
A  good  example  of  enlargement  of  the  capillaries  of  a  particular  part  is  in  mastication, 
when  the  salivary  glands  are  brought  into  activity  and  the  quantity  of  blood  which  they 
receive  is  greatly  increased.  Chauveau  found  an  immense  increase  in  the  rapidity  of  the 
flow  in  the  carotid  of  a  horse  during  mastication.  The  enlargement  of  the  vessels 
of  the  glands  during  their  function  has  been  conclusively  proven  by  the  experiments  of 
Bernard.  It  must  be  remembered  that,  in  all  parts  of  the  arterial  system,  the  rapidity 
of  the  current  of  blood  is  constantly  liable  to  increase  from  dilatation  of  the  small  ves- 
sels and  to  diminution  from  their  contraction. 

Circulation  of  the  Blood  in  the  Capillaries. 

Before  entering  upon  the  study  of  the  capillary  circulation,  we  should  define  what  we 
mean  by  the  capillary  vessels  as  distinguished  from  the  smallest  arteries  and  veins.  From 
a  strictly  physiological  point  of  view^  the  capillaries  are  to  be  regarded  as  commencing 


FIG.  27.— Capillary  blood-vessels  from  the  pecten  of  the  eye  of  the  bird.    (Ebertb.) 

o,  small  capillaries,  with  fusiform  cells ;  &,  capillaries  with  polygonal  cells ;  £>',  hyaloid  membrane  investing  the  capil- 
laries; c,  capillaries  from  the  intestine  of  the  snail. 

6 


82  CIRCULATION   OF  THE   BLOOD. 

at  the  point  where  the  blood  is  brought  near  enough  to  the  tissues  to  enable  them  to  sep- 
arate the  elements  necessary  for  their  regeneration  and  to  give  up  the  products  of  their 
physiological  decay.  With  our  present  knowledge,  it  is  impossible  to  assign  any  limit 
where  the  vessels  cease  to  be  simple  carriers  of  blood ;  and  it  does  not  seem  probable  that 
it  will  ever  be  known  to  what  part  of  the  vascular  system  the  processes  of  nutrition  are 
exclusively  confined.  The  divisions  of  the  blood-vessels  must  be,  to  a  certain  extent, 
arbitrarily  defined ;  and  we  should  feel  at  liberty  to  adopt  the  views  of  any  reliable  ob- 
server with  regard  to  the  kind  of  vessels  which  are  to  be  considered  as  capillaries.  The 
most  simple,  and  what  seems  to  be  the  most  physiological  view,  is  to  regard  as  capillaries 
those  vessels  which  have  but  a  single  tunic ;  for,  in  these,  the  blood  is  brought  in  closest 
proximity  to  the  tissues.  Vessels  which  are  provided,  in  addition,  with  a  muscular  or 
with  muscular  and  fibrous  coats  are  to  be  regarded  either  as  small  arteries  or  as  venous 
radicles.  This  view  is  favored  by  the  character  of  the  currents  of  blood  as  seen  in 
microscopical  observation  of  the  circulation  in  transparent  parts.  Here  an  impulse  is 
observed  with  each  contraction  of  the  heart,  until  we  come  to  vessels  which  have  but 
one  coat  and  are  so  narrow  as  to  allow  the  passage  of  but  a  single  line  of  blood- 
corpuscles. 

Physiological  Anatomy  of  the  Capillaries.  — If  the  arteries  be  followed  out  to  their 
minutest  ramifications,  they  will  be  found  progressively  diminishing  in  size  as  they  branch, 
and  their  coats,  especially  the  muscular,  becoming  thinner  and  thinner,  until  at  last  they 
present  an  internal  structureless  coat,  lined  by  epithelium  with  oval,  longitudinal  nuclei, 
a  middle  coat,  formed  of  but  a  single  layer  of  circular  muscular  fibres,  and  an  external 
coat,  composed  of  a  very  thin  layer  of  longitudinal  fibres  of  the  white  inelastic  tissue. 
These  vessels  are  from  ^i¥  to  -^  of  an  inch  in  diameter.  They  become  smaller  as  they 
branch,  and  undoubtedly  possess  the  property  of  contractility,  which  is  particularly 
marked  in  the  arterial  system.  Following  the  course  of  the  vessels,  when  they  are  re- 
duced in  size  to  about  ¥£7  of  an  inch,  the  external  fibrous  coat  is  lost,  and  the  vessel  then 
presents  only  the  internal  coat  and  a  single  layer  of  muscular  fibres.  These  become  smaller 
as  they  branch,  finally  lose  the  muscular  coat,  and  have  then  but  a  single  tunic.  These 
last  we  shall  consider  as  the  true  capillary  vessels. 

The  minute  structure  of  the  capillary  vessels  is  of  considerable  importance  and 
interest  and  has  been  very  closely  investigated  within  the  last  few  years.  It  was  for- 
merly thought  that  the  smallest  vessels,  which  we  describe  as  the  true  capillaries,  were 
composed  of  a  single,  homogeneous  membrane,  from  3-5-^0  to  yiiW  °f  an  mcn  thick,  with 
nuclei  embedded  in  its  substance,  but  not  provided  with  an  epithelial  lining.  Recent 
observations,  however,  have  shown  that  the  membrane  is  homogeneous,  elastic,  perhaps 
contractile,  and,  in  some  parts  at  least,  is  provided  with  fusiform  or  polygonal  epithelium 
of  excessive  tenuity.  The  borders  of  the  epithelial  cells  may  be  seen  by  staining  the  ves- 
sels with  nitrate  of  silver.  In  the  smallest  capillaries,  the  cells  are  narrow  and  elongated 
or  fusiform ;  and  in  the  larger  vessels,  they  are  more  polygonal,  with  very  irregular  borders. 
The  nuclei  which  have  been  observed  in  the  walls  of  the  vessels  belong  to  this  layer  of 
epithelium.  By  the  same  process  of  staining  with  nitrate  of  silver,  we  frequently  observe 
irregular,  non-nucleated  areas ;  and  it  has  been  supposed  by  some  that  these  indicate  the 
presence  of  stomata,  or  orifices  in  the  walls  of  the  vessels.  This  latter  point,  however, 
has  not  been  definitely  determined.  It  cannot  at  present  be  stated  positively  whether  or 
not.  orifices  normally  exist  in  the  walls  of  the  blood-vessels.  Most  of  the  anatomical 
points  we  have  just  mentioned  have  been  developed  by  observations  upon  the  vessels  of 
the  frog. 

The  diameter  of  the  capillaries  is  generally  as  small  as,  or  it  may  be  smaller  than 
that  of  the  blood-corpuscles ;  so  that  these  bodies  always  move  in  a  single  line  and 
must  become  deformed  in  passing  through  the  smallest  vessels,  recovering  their  natural 
shape,  however,  when  they  pass  into  vessels  of  larger  size.  The  capillaries  are  smallest 


PHYSIOLOGICAL  ANATOMY   OF  THE   CAPILLARIES. 


83 


in  the  nervous  and  muscular  tissue,  retina,  and  patches  of  Peyer,  where  they  have  a  di- 
ameter of  from  -g-oVo  to  ¥-oVo  of  an  inch.  In  the  mucous  layer  of  the  skin  and  in  the 
mucous  membranes,  they  are  from  ^-^  to  ^J7¥  of  an  inch  in  diameter.  They  are 
largest  in  the  glands  and  bones,  where  they  are  from  y^r  to  ^^Vff  of  an  inch  in  diam- 
eter. These  measurements  indicate  the  size  of  the  vessels  and  not  their  caliber.  Tak- 
ing out  the  thickness  of  their  walls,  it  is  only  the  very  largest  of  them  that  will  admit  of 
the  passage  of  a  blood-disk  without  a  change  in  its  form. 


-:_-_--  ~' —     "^ 

FIG.  28.— Small  artery  and  capillaries,  from  the  muscular  coats  of  the  urinary  bladder  of  the  frog;  magnified 

400  diameters.    (From  a  photograph  taken  at  the  United  States  Army  Medical  Museum.) 

This  preparation  shows  the  epithelium  of  the  vessels.    It  is  injected  with  nitrate  of  silver,  stained  with  carmine,  and 

mounted  in  Canada  balsam. 

Unlike  the  arteries,  which  grow  smaller  as  they  branch,  and  the  veins,  which  be- 
come larger,  as  we  follow  the  course  of  the  blood,  by  union  with  each  other,  the  capil- 
laries form  a  true  plexus  of  vessels  of  nearly  uniform  diameter,  branching  and  inosculat- 
ing in  every  direction  and  distributing  blood  to  the  parts  as  their  physiological  necessi- 
ties demand.  This  mode  of  inosculation  is  peculiar  to  these  vessels,  and  the  plexus  is  rich 
in  the  tissues,  as  a  general  rule,  -in  proportion  to  the  activity  of  their  nutrition.  Al- 
though their  arrangement  presents  certain  differences  in  different  organs,  the  capillary 
vessels  have  everywhere  the  same  general  characteristics,  the  most  prominent  of  which 
are  uniform  diameter  and  absence  of  any  positive  direction.  The  net-work  thus  formed  is 
very  rich  in  the  substance  of  the  glands  and  in  the  organs  of  absorption ;  but  the  vessels 
are  only  distended  with  blood  during  the  physiological  activity  of  these  parts.  In  the 
lungs,  the  meshes  are  particularly  close.  In  other  parts,  the  vessels  are  not  so  abundant, 
presenting  great  variations  in  different  tissues.  In  the  muscles  and  nerves,  in  which  nu- 
trition is  very  active,  the  supply  is  much  more  abundant  than  in  other  parts,  like  fibro- 


84  CIRCULATION  OF  THE  BLOOD. 

serous  membranes,  tendons,  etc.  In  none  of  the  tissues  do  we  find  capillaries  penetrat- 
ing the  anatomical  elements,  as  the  ultimate  muscular  or  nervous  fibres.  Some  tissues 
receive  no  blood,  at  least  they  contain  no  vessels  which  are  capable  of  carrying  red 
blood,  and  are  nourished  by  imbibition  of  the  nutrient  plasma  of  the  circulating  fluid. 
Examples  of  these,  which  are  called  extra-vascular  tissues,  are  cartilage,  nails,  and 
hair. 

The  foregoing  anatomical  sketch  gives  an  idea  of  how  near  the  blood  is  brought  to 
the  tissues  in  the  capillary  system,  and  how,  once  conveyed  there  by  the  arteries,  and  the 
supply  regulated  by  the  action  of  the  muscular  coat  of  the  smaller  vessels,  the  blood  is 
distributed  for  the  purposes  of  nutrition,  secretion,  absorption,  exhalation,  or  whatever 
function  the  part  has  to  perform.  This  will  be  still  more  apparent  when  we  come  to 
consider  the  course  of  the  blood  in  the  capillaries  and  the  immense  capacity  of  this  sys- 
tem, as  compared  with  the  arteries  or  veins. 

The  capacity  of  the  capillary  system  is  immense.  It  is  only  necessary  to  consider 
the  great  vascularity  of  the  skin,  mucous  membranes,  or  muscles,  to  realize  this  fact. 
In  injections  of  these  parts,  it  seems,  on  microscopical  examination,  as  though  they  con- 
tained nothing  but  capillaries.  In  preparations  of  this  kind,  the  elastic  and  yielding 
coats  of  the  capillaries  are  distended  to  their  utmost  limit.  Under  some  circumstances, 
in  health,  they  are  largely  distended  with  blood,  as  the  mucous  lining  of  the  alimentary 
canal  during  digestion,  the  whole  surface  presenting  a  vivid-red  color,  indicating  the 
great  richness  of  the  capillary  plexus.  Various  estimates  of  the  capacity  of  the  capil- 
lary, as  compared  with  the  arterial  system,  have  been  made,  but  they  are  simply  approxi- 
mative, and  there  seems  to  be  no  means  by  which  an  estimate,  with  any  pretensions  to 
accuracy,  can  be  formed.  The  various  estimates  which  are  given  are  founded  upon  cal- 
culations from  microscopical  examinations  of  the  rapidity  of  the  capillary  circulation  as 
compared  with  the  circulation  in  the  arteries.  In  this  way,  it  has  been  estimated  that 
the  entire  capacity  of  the  capillary  system  is  from  five  hundred  to  eight  hundred  times 
that  of  the  arterial  system.  It  must  be  evident  to  any  one  who  has  witnessed  the  capil- 
lary circulation  under  the  microscope,  that  the  conditions  under  which  the  animal  under 
examination  is  placed  are  liable  to  interfere  with  the  current  of  blood  ;  and  the  periodi- 
cal congestion  of  certain  parts,  the  fugitive  flushes  of  the  skin,  the  condition  of  the 
smallest  arteries  induced  by  changes  of  temperature,  exercise,  etc.,  make  it  evident  that 
the  current  of  blood  is  liable  to  great  variations.  It  is  impossible  to  strictly  apply  to 
the  capillary  circulation  in  the  various  parts  of  the  human  subject  observations  on  the 
wing  of  a  bat  or  the  mesentery  of  a  cat.  "We  must  consider,  then,  these  estimates  as 
mere  suppositions,  and  they  are  given  for  what  they  are  worth. 

Phenomena  of  the  Capillary  Circulation. — The  most  convenient  situation  for  the 
practical  study  of  the  capillary  circulation  is  the  tongue  or  the  web  of  the  frog.  Here 
may  be  studied,  not  only  the  movement  of  the  blood  in  the  true  capillaries,  but  the  cir- 
culation in  the  smallest  arteries  and  veins,  the  variations  in  caliber  of  these  vessels, 
especially  the  arterioles,  by  the  action  of  their  muscular  tunic,  and,  indeed,  the  action 
of  vessels  of  considerable  size.  This  has  been  a  most  valuable  means  of  studying  the 
circulation  in  the  capillaries  as  contrasted  with  the  flow  in  the  small  arteries  and  veins,  and 
the  only  one,  indeed,  which  could  give  us  any  definite  idea  of  the  action  of  these  vessels. 

The  magnificent  spectacle  of  the  capillary  circulation  was  first  observed  by  Malpighi, 
in  the  lungs,  and  afterward  by  Leeuwenhoek,  Spallanzani,  Haller,  Cowper,  and  others, 
in  other  parts.  We  see  the  great  arterial  rivers,  in  which  the  blood  flows  with  wonder- 
ful rapidity,  branching  and  subdividing,  until  the  circulating  fluid  is  brought  to  the  net- 
work of  fine  capillaries,  where  the  corpuscles  dart  along  one  by  one.  The  blood  is  then 
collected  by  the  veins  and  carried  in  great  currents  to  the  heart.  This  exhibition,  to 
the  student  of  Nature,  is  of  inexpressible  grandeur ;  and  our  admiration  is  not  dimin- 
ished when  we  come  to  study  the  phenomena  in  detail.  We  find  here  a  subject  as  inter- 


PHENOMENA  OF  THE  CAPILLARY   CIRCULATION.  85 

esting  as  was  the  action  of  the  heart  when  first  seen  by  Harvey,  involving  some  of  the 
most  important  phenomena  of  the  circulation.  It  can  be  seen  how  the  arterioles  regu- 
late the  supply  of  blood  to  the  tissues ;  how  the  blood  distributes  itself  by  the  capilla- 
ries: and,  finally,  having  performed  its  office,  how  it  is  collected  and  carried  off  by  the 


veins. 


FIG.  29.—  Web  of  the  frog's  hind-foot;  magnified.    (Wagner.) 
a,  a,  veins ;  &,  6,  &,  arteries. 

In  studying  the  circulation  under  the  microscope,  the  anatomical  division  of  the 
blood  into  corpuscles  and  a  clear  plasma  is  observed.  This  is  peculiarly  evident  in  cold- 
blooded animals,  the  corpuscles  being  comparatively  large  and  floating  in  a  plasma 
which  forms  a  distinct  layer  next  the  walls  of  the  vessel.  The  leucocytes,  which  are 
much  fewer  than  the  red  corpuscles,  are  generally  found  in  the  layer  of  plasma.  * 


FIG.  30.— Circulation  in  the  web  of  the  frog's  foot.    (Wagner.) 

,  are  pigmentary  matter.    <z,  a  venous  trunk,  composed  of  three  principal 
branches  (&,  6,  6),  and  covered  with  a  plexus  of  smaller  vessels  (c,  c). 

1  Various  methods  of  preparing  the  animal  for  examination  have  been  employed.    The  one  we  have  found  most 
convenient,  in  examining  the  circulation  in  the  frog,  is  to  break  up  the  medulla  with  a  needle,  an  operation  which 


86 


CIRCULATION   OF  THE  BLOOD. 


In  vessels  of  considerable  size,  as  well  as  in  some  capillaries,  the  corpuscles,  occupy- 
ing the  central  portion,  move  with  much  greater  rapidity  than  the  rest  of  the  blood, 
leaving  a  layer  of  clear  plasma  at  the  sides,  which  is  nearly  motionless.  This  curious 
phenomenon  is  in  obedience  to  a  physical  law  regulating  the  passage  of  liquids  through 
capillary  tubes  for  which  they  have  an  attraction,  such  as  exists,  for  example,  between 
the  blood  and  the  vessels.  Qn  tubes  reduced  to  a  diameter  approximating  that  of  the 
capillaries,  the  attractive  force  exerted  by  their  walls  upon  a  liquid,  causing  it  to  enter 
the  tube  to  a  certain  distance,  called  capillary  attraction,  becomes  an  obstacle  to  the  pas- 
sage of  fluid  in  obedience  to  pressure.  Of  course,  as  the  diameter  of  the  tube  is  re- 


FIG.  31.— Small  artery  and  capillaries  from  the  lung  of  a  frog ;  magnified  500  diameters.    (From  a  photograph 
taken  at  the  United  States  Army  Medical  Museum.) 

duced,  this  force  becomes  relatively  increased,  for  a  larger  proportion  of  the  liquid  con- 
tents is  brought  in  contact  with  it.  When  we  come  to  the  smallest  arteries  and  veins, 
and  still  more  the  capillaries,  the  capillary  attraction  is  sufficient  to  produce  the  mo- 
tionless layer,  called  the  "  still  layer  "  by  many  physiologists,  and  the  liquid  moves  only 
in  the  central  portion.  The  plasma  occupies  the  position  next  the  walls  of  the  vessels, 
for  it  is  this  portion  of  the  blood  which  is  capable  of  "  wetting  "  the  tubes.  The  trans- 
does  not  interfere  with  the  circulation,  and  to  attach  the  animal  by  pins  to  a  thin  piece  of  cork,  stretching  the  web  over 
an  orifice  in  the  cork,  to  allow  the  passage  of  light,  and  securing  it  with  pins  through  the  toes.  The  membrane  is 
then  moistened  with  water  and  covered  with  thin  glass,  and,  if  the  general  surface  be  kept  moist,  the  circulation  mny 
be  studied  for  hours.  By  gently  inflating  the  lungs  with  a  small  blow-pipe,  securing  the  air  by  a  ligature  passed 
around  the  larynx  beneath  the  mucous  membrane,  and  opening  the  chest,  the  pulmonary  circulation  may  be  studied. 
The  circulation  may  be  examined  in  the  tongue  (which  presents  a  magnificent  view  of  the  circulation  as  well  as  of  the 
nerves  and  muscular  fibres)  by  drawing  it  out  of  the  mouth  and  spreading  it  into  a  thin  sheet,  securing  it  with  pins. 
The  circulation  may  also  be  observed  in  the  mesentery  of  a  small,  warm-blooded  animal,  like  the  mouse,  by  fixing  it 
upon  the  frog-plate,  opening  the  abdomen,  and  drawing  out  the  membrane ;  but  it  is  not  seen  so  well  or  so  convenient- 
ly as  in  the  tongue  or  web  of  the  frog. 


PHENOMENA   OF  THE   CAPILLARY   CIRCULATION.  87 

parent  layer  was  observed  by  Malpighi,  Haller,  and  all  who  have  described  the  capillary 
circulation.  Poiseuille  recognized  its  true  relation  to  the  blood-current  and  explained 
the  phenomenon  of  the  still  layer  by  physical  laws,  which  had  been  previously  estab- 
lished with  regard  to  the  flow  of  liquids  in  tubes  of  the  diameter  of  from  one-twenty- 
fifth  to  one- eighth  of  an  inch,  bat  which  he  had  succeeded  in  applying  to  tubes  of  the 
size  of  the  capillaries. 

A  red  corpuscle  occasionally  becomes  involved  in  the  still  layer,  when  it  moves 
slowly,  turning  over  and  over,  or  even  remains  stationary  for  a  time,  until  it  is  taken  up 
again  and  carried  along  with  the  central  current.  A  few  white  corpuscles  are  con- 
stantly seen  in  this  layer.  They  move  along  slowly  and  apparently  have  a  tendency  to 
adhere  to  the  walls  of  the  vessel.  This  is  due  to  the  adhesive  character  of  the  surface  of 
the  white  corpuscles  as  compared  with  the  red,  which  can  easily  be  observed  in  examin- 
ing a  drop  of  blood  between  glass  surfaces,  the  red  corpuscles  moving  about  with  great 
facility,  while  the  white  have  a  tendency  to  adhere. 

Great  differences  exist  in  the  character  of  the  flow  of  blood  in  the  three  varieties  of 
vessels  which  are  under  observation.  In  the  arterioles,  which  may  be  distinguished  from 
the  capillaries  by  their  size  and  the  presence  of  the  muscular  and  fibrous  coats,  the  move- 
ment is  distinctly  remittent,  even  in  their  most  minute  ramifications.  The  blood  moves 
in  them  with  much  greater  rapidity  than  in  either  the  capillaries  or  veins.  They  become 
smaller  as  they  branch,  and  carry  the  blood  always  in  the  direction  of  the  capillaries. 
The  veins,  which  are  relatively  larger  than  the  arteries,  carry  the  blood  more  slowly 
and  in  a  continuous  stream  from  the  capillaries  toward  the  heart.  In  both  the  arteries 
and  veins,  the  current  is  frequently  so  rapid  that  the  form  of  the  corpuscles  cannot  be 
distinguished.  Only  a  portion  of  the  white  corpuscles  occupy  the  still  layer,  the  rest 
being  carried  on  in  the  central  current. 

The  circulation  in  the  true  capillaries  is  sui,generis.  Here  the  blood  is  distributed  in 
every  direction,  in  vessels  of  nearly  uniform  diameter.  The  vessels  are  generally  so  small 
as  to  admit  but  a  single  row  of  corpuscles,  which  move  almost  like  beings  endowed  with 
volition.  In  a  single  vessel,  a  line  of  corpuscles  may  be  seen  moving  in  one  direction  at 
one  moment,  a  few  moments  after,  taking  a  directly  opposite  course.  Spallanzani, 
in  one  of  his  observations,  describes  the  following  phenomenon :  Two  single  rows  of 
corpuscles,  passing  in  two  capillary  vessels  of  equal  size,  were  directed  toward  a  third 
capillary  vessel,  formed  by  the  union  of  the  two  others,  which  would  itself  admit  but  a 
single  corpuscle.  The  corpuscles  in  one  of  these  vessels  seemed  to  hold  back  until  those 
from  the  other  had  passed  in,  when  they  followed  in  their  turn.  "When  the  circulation  is 
normal,  the  movement  in  the  capillaries  is  always  quite  slow  as  compared  with  the  move- 
ment in  the  arterioles,  and  is  continuous.  Here,  at  last,  the  intermittent  impulse  of  the 
heart  is  lost.  The  corpuscles  do  not  necessarily  circulate  in  all  the  capillaries  which  are 
in  the  field  of  view.  Certain  vessels  may  not  receive  a  corpuscle  for  some  time,  but,  after 
a  while,  one  or  two  corpuscles  become  engaged  in  them  and  a  current  is  finally  established. 

Many  interesting  little  points  may  be  noticed  in  examining  the  circulation  for  a  suffi- 
cient length  of  time.  A  corpuscle  is  frequently  seen  caught  at  the  angle  where  a  vessel 
divides  into  two,  remaining  fixed  for  a  time,  distorted  and  bent  by  the  force  of  the  cur- 
rent. It  soon  becomes  released,  and,  as  it  enters  the  vessel,  it  regains  its  original  form. 
In  some  of  the  vessels  of  smallest  size,  the  corpuscles  are  slightly  deformed  as  they  pass 
through.  The  scene  is  changed  with  every  different  part  which  is  examined.  In  the 
tongue,  in  addition  to  the  arterioles  and  venules  with  the  rich  net-work  of  capillaries, 
dark-bordered  nerve-fibres,  striated  muscular  fibres,  and  pavement-epithelium  can  be 
distinguished.  In  the  lungs,  the  view  is  very  beautiful.  Large,  polygonal  air-cells  are 
observed,  bounded  by  capillary  vessels,  in  which  the  corpuscles  move  with  extreme 
rapidity.  It  has  been  observed  that  the  larger  vessels  are  crowded  to  their  utmost  capa- 
city with  corpuscles,  leaving  no  still  layer  next  the  walls,  such  as  is  seen  in  the  circula- 
tion in  other  situations. 


88  CIRCULATION  OF  THE  BLOOD. 

When  the  circulation  has  been  for  a  long  time  under  observation,  as  the  animal 
becomes  enfeebled,  very  interesting  changes  in  the  character  of  the  flow  of  blood  take 
place.  The  continuous  stream  in  the  smallest  vessels  diminishes  in  rapidity,  and,  after  a 
time,  when  the  contractions  of  the  heart  have  become  infrequent  and  feeble,  the  blood 
is  nearly  arrested,  even  in  the  smallest  capillaries,  during  the  intervals  of  the  heart's 
action,  and  the  current  becomes  remittent.  As  the  central  organ  becomes  more  and 
more  enfeebled,  the  circulation  becomes  intermittent,  and  the  blood  receives  an  impulse 
from  each  contraction,  remaining  stationary  during  the  intervals.  At  this  time,  the  cor- 
puscles cease  to  occupy  exclusively  the  central  portion  of  the  vessels,  and  the  clear  layer 


FIG.  32.— Portion  of  the  lung  of  a  live  triton,  drawn  under  tfie  microscope  and  magnified  150  diameters. 

(Wagner.) 

of  plasma  next  their  walls,  which  was  observed  in  the  normal  circulation,  is  no  longer 
apparent.  Following  this,  there  is  an  actual  oscillation  in  the  capillaries.  At  each  con- 
traction of  the  heart,  the  blood  is  forced  onward  a  little  distance,  but  it  almost  immediately 
returns  to  about  its  former  position.  This  phenomenon  has  long  been  observed  and  is 
explained  in.  the  following  way :  As  the  heart  has  become  enfeebled,  the  contractions 
are  so  infrequent  and  ineffectual,  that,  during  their  intervals,  the  constant  flow  in  the 
capillaries  is  entirely  arrested  ;  for  the  arterial  pressure,  which  is  its  immediate  cause 
and  which  is  maintained  by  the  successive  charges  of  blood  sent  into  the  arteries  at  each 
ventricular  systole,  is  lost.  But,  as  the  blood  is  contained  in  a  connected  system  of  closed 
tubes,  the  feeble  impulse  of  the  heart  is  propagated  through  the  vessels  and  produces  a 
slight  impulse,  even  in  the  smallest  capillaries,  which  dilates  them  and  forces  the  fluid  a 
little  distance.  As  soon,  however,  as  the  heart  ceases  to  contract,  the  current  is  arrested, 
and  the  blood,  meeting  with  a  certain  amount  of  obstruction  from  the  fluid  in  the  small 
veins,  which  are  still  farther  removed  from  the  heart,  is  made  to  return  to  its  former 
position.  This  phenomenon  continues  for  a  short  time  only,  for  the  heart  soon  loses  its 
contractility,  and  the  circulation  in  all  the  vessels  is  permanently  arrested. 

Rapidity  of  the  Capillary  Circulation.—  The  circulation  in  the  capillaries  of  a  part 


EAPIDITY  OF  THE  CAPILLARY   CIRCULATION.  89 

is  subject  to  such  great  variations,  and  the  differences  in  different  situations  are  so  con- 
siderable, that  it  is  impossible  to  give  any  definite  rate  which  will  represent  the  general 
rapidity  of  the  capillary  circulation.  It  is  for  this  reason  that  it  has  been  found  imprac- 
ticable to  estimate  the  capacity  of  the  capillary  as  compared  with  the  arterial  system. 
The  rapidity  of  the  flow  of  blood  is  by  no  means  so  great  as  it  appears  in  microscopical 
examinations,  being,  of  course,  exaggerated  in  proportion  to  the  magnifying  power 
employed.  It  is,  nevertheless,  to  microscopical  investigations  that  we  are  indebted  for 
the  scanty  information  we  possess  on  this  subject.  The  estimates  which  have  been  made 
by  various  observers  refer  generally  to  cold-blooded  animals  and  have  been  arrived  at  by 
simply  calculating  the  time  occupied  by  a  blood-corpuscle  in  passing  over  a  certain  dis- 
tance. Hales,  who  was  the  first  to  investigate  this  question,  estimated  that,  in  the  frog, 
a  corpuscle  moved  at  the  rate  of  an  inch  in  ninety  seconds.  The  estimates  of  Weber  and 
Valentin  are  considerably  higher,  being  about  one-fiftieth  of  an  inch  per  second.  Volk- 
mann  calculated  the  rapidity  in  the  mesentery  of  the  dog,  which  would  approximate 
more  nearly  to  the  human  subject,  and  found  it  to  be  about  one-thirtieth  of  an  inch 
per  second.  Yierordt  made  a  number  of  curious  observations  upon  himself,  by  which 
he  professed  to  be  able  to  estimate  the  rapidity  of  the  circulation  in  the  little  vessels  of 
the  eye.  He  states  that  when  the  eye  is  fatigued,  and  sometimes  when  the  nervous 
system  is  disordered,  compression  of  the  globe  in  a  certain  way  will  enable  one  to  see 
a  current  like  that  in  a  capillary  plexus.  This  he  believed  to  be  the  capillary  circula- 
tion, and,  by  certain  calculations,  he  formed  an  estimate  of  its  rapidity,  putting  it  at  from 
one-fortieth  to  one-twenty-eighth  of  an  inch  per  second.  The  latter  figure  accords  pretty 
nearly  with  the  observations  of  Volkmann  upon  the  dog.  How  far  these  observations 
are  to  be  relied  upon,  it  is  impossible  to  say.  Certainly  no  great  importance  would  be 
attached  to  them  if  they  did  not,  in  their  results,  approximate  to  the  estimates  of  Volk- 
mann, which  probably  represent,  more  nearly  than  any,  the  rapidity  of  the  current  in 
the  capillaries  of  the  human  subject.  After  what  has  been  said  of  the  variations  in  the 
capillary  circulation,  it  is  evident  that  the  foregoing  estimates  are  by  no  means  to  be 
considered  exact. 

Relations  of  the  Capillary  Circulation  to  Respiration. — In  treating  of  the  influence 
of  respiration  upon  the  action  of  the  heart,  the  arterial  pressure,  pulse,  etc.,  it  has  already 
been  stated  that  non-aerated  blood  cannot  circulate  freely  in  the  capillaries.  Various 
ideas  with  regard  to  the  effects  of  asphyxia  upon  the  circulation  have  been  advanced, 
which  will  be  again  discussed  in  connection  with  respiration.  The  fact  is  evident  that 
arrest  of  respiration  produces  arrest  of  circulation.  This  is  ordinarily  attributed  to  an 
impediment  to  the  passage  of  blood  through  the  lungs  when  they  no  longer  contain  the 
proper  quantity  of  oxygen.  This  view  is  entirely  theoretical  and  has  been  disproved  by 
experiments  dating  more  than  half  a  century  ago.  In  1789,  Goodwyn  advanced  the 
theory  that,  in  asphyxia,  the  blood  passes  through  the  lungs  but  is  incapable  of  exciting 
contractions  in  the  left  ventricle.  Bichat,  in  his  celebrated  essay  "  Sur  la  vie  et  la  mort" 
1805,  proved  by  experiment  that  black  blood  passes  through  the  lungs  in  asphyxia  and  is 
found  in  the  arteries.  His  theory  was  that  non-aerated  blood,  circulating  in  the  capilla- 
ries of  the  nervous  centres,  arrests  their  function,  thus  acting  indirectly  upon  the  circu- 
lation ;  and  that  finally  the  heart  itself  is  paralyzed  by  the  circulation  of  black  blood  in 
its  substance. 

The  immediate  effects  of  asphyxia  upon  the  circulation  are  referable  to  the  general 
capillary  system.  This  fact  we  demonstrated  conclusively  by  experiments  upon  the  frog, 
published  in  1857.  In  these  experiments,  the  medulla  oblongata  was  broken  up,  and  the 
web  of  the  foot  was  submitted  to  microscopical  examination.  This  operation  does  not  in- 
terfere with  the  circulation,  which  may  be  observed  for  hours  without  difficulty.  The  cu- 
taneous surface  was  then  coated  with  collodion,  care  only  being  taken  to  avoid  the  web 
under  observation.  The  effect  on  the  circulation  was  immediate.  It  instantlv  became  less 


90  CIKCULATION  OF  THE  BLOOD. 

rapid,  until,  at  the  expiration  of  twenty  minutes,  it  had  entirely  ceased.  The  entire 
coating  of  collodion  was  then  instantly  peeled  off.  Quite  a  rapid  circulation  immediately 
commenced,  but  it  soon  began  to  decline  and  in  twenty  minutes  had  almost  ceased.  In 
another  observation,  the  coating  of  collodion  was  applied  without  destroying  the  medulla. 
The  circulation  was  affected  in  the  same  manner  as  before  and  ceased  in  twenty-five 
minutes.  These  experiments,  taken  in  connection  with  observations  on  the  influence  of 
asphyxia  upon  the  arterial  pressure,  conclusively  show  that  non-aerated  blood  cannot 
circulate  freely  in  the  systemic  capillaries.  Venous  blood,  however,  can  be  forced 
through  them  with  a  syringe,  and,  even  in  asphyxia,  it  slowly  filters  through.  If  air  be 
admitted  to  the  lungs  before  the  heart  has  lost  its  contractility,  the  circulation  is  restored. 
No  differences  in  the  capillary  circulation  have  been  noticed  accompanying  the  ordinary 
acts  of  inspiration  and  expiration. 

Causes  of  the  Capillary  Circulation. — The  contractions  of  the  left  ventricle  are  evi- 
dently capable  of  giving  an  impulse  to  the  blood  in  the  smallest  arterioles ;  for  a  marked 
acceleration  of  the  current  accompanying  each  systole  can  be  distinguished  in  all  but  the 
true  capillaries.  It  has  also  been  shown  by  experiments  after  death,  that  blood  can  be 
forced  through  the  capillary  system  and  returned  by  the  veins  by  a  force  less  than  that 
exerted  by  the  left  ventricle.  This,  however,  cannot  rigidly  be  applied  to  the  natural 
circulation,  as  the  smallest  arteries  are  endowed  during  life  with  contractility,  which  is 
capable  of  modifying  the  blood-current.  Dr.  Sharpey  adapted  a  syringe,  with  a  heema- 
dynamometer  attached,  to  the  aorta  of  a  dog  just  killed,  and  found  that  fresh  defibrinated 
blood  could  be  made  to  pass  through  the  double  capillary  systems  of  the  intestines  and 
liver,  by  a  pressure  of  three  and  a  half  inches  of  mercury.  It  spurted  out  at  the  vein  in 
a  full  jet  under  a  pressure  of  five  inches.  In  this  observation,  the  aorta  was  tied  just 
above  the  renal  arteries.  The  same  pressure,  the  ligature  being  removed,  forced  the 
blood  through  the  capillaries  of  the  inferior  extremities.  This  is  much  less  than  the  arte- 
rial pressure,  which  is  equal  to  from  five  and  a  half  to  six  inches  of  mercury. 

It  is  thus  seen  that  the  pressure  in  the  arteries  which  forces  the  blood  toward  the 
capillaries  is  competent,  unless  opposed  by  excessive  contraction  of  the  arterioles,  not  only 
to  cause  the  blood  to  circulate  in  these  vessels,  but  to  return  it  to  the  heart  by  the  veins. 
This  fact  is  so  evident,  that  it  is  unnecessary  to  discuss  the  views  of  Bichat  and  some 
others,  who  supposed  that  the  action  of  the  heart  had  no  effect  upon  the  capillary  circu- 
lation. It  must  be  admitted  that  this  is  its  prime  cause ;  and  the  only  questions  to  be 
considered  are,  first,  whether  there  be  any  reason  why  the  force  of  the  heart  should  not 
operate  on  the  blood  in  the  capillaries,  and  second,  whether  there  be  any  force  in  these 
vessels  which  is  superadded  to  the  action  of  the  heart.  The  first  of  these  questions  is 
answered  by  microscopical  observations  on  the  circulation.  A  distinct  impulse,  follow- 
ing each  ventricular  systole,  is  observed  in  the  smallest  arteries ;  the  blood  flows  from 
them  directly  and  freely  into  the  capillaries ;  and  there  is  not  the  slightest  ground  for 
the  supposition  that  the  force  is  not  propagated  to  this  system  of  vessels. 

Various  writers  have  supposed  the  existence  of  a  "  capillary  power,"  which  they  have 
regarded  as  of  greater  or  less  importance  in  producing  the  capillary  circulation.  The 
ideas  of  some  are  purely  theoretical,  but  others  base  their  opinion  on  microscopical 
observations.  These  views  do  not  demand  extended  discussion.  There  is  a  force  in 
operation,  the  action  of  the  heart,  which  is  capable  of  producing  the  capillary  circula- 
tion ;  and  there  is  nothing  in  the  phenomena  of  the  circulation  in  these  vessels,  which  is 
inconsistent  with  its  full  operation.  Under  these  circumstances,  it  is  unphilosophical  to 
invoke  the  aid  of  the  currents  produced  in  capillary  tubes  in  which  liquids  of  different 
characters  are  brought  in  contact,  or  a  "  capillary  power "  dependent  upon  a  so-called 
vital  nutritive  attraction  between  the  tissues  and  the  blood,  unless  we  do  it  on  the  basis 
of  phenomena  observed  in  the  capillaries  when  the  action  of  the  heart  is  suppressed. 
When  the  heart  ceases  its  action,  movements  in  the  capillaries  are  sometimes  due  to  the 


CAUSES   OF   THE   CAPILLARY   CIRCULATION.  91 

contractions  of  the  arteries,  a  property  which  has  already  been  fully  considered.  Move- 
ments which  have  been  observed  in  membranes  detached  from  the  body  are  due  to  the 
mere  emptying  of  the  divided  vessels  or  to  simple  gravitation.  It  must  be  remembered 
that,  in  microscopical  examinations,  the  movements  observed  are  immensely  exaggerated 
by  the  magnifying  power,  and  we  receive,  at  first  sight,  an  erroneous  impression  of  their 
rapidity.  The  movements  of  the  blood  in  detached  membranes,  due  merely  to  gravitation, 
have  been  so  satisfactorily  explained  by  the  experiments  of  Poiseuille,  that  it  is  deemed 
unnecessary  to  refer  to  the  observations  of  those  who  have  attributed  this  phenomenon 
to  other  causes. 

Physiologists  who,  like  Bichat,  have  been  unable  to  explain  the  local  variations  in  the 
capillary  circulation  without  the  intervention  of  a  force  resident  in  these  vessels  or  in  the 
surrounding  tissues,  have  not  appreciated  the  action  of  the  arterioles.  These  little  vessels 
are  endowed  to  an  eminent  degree  with  contractility  and,  by  the  contractions  and  relaxa- 
tions of  their  muscular  walls,  they  regulate  the  supply  of  blood  to  the  capillaries  of  in- 
dividual parts.  Their  action  is  competent  to  produce  all  the  variations  which  are  ob- 
served in  the  capillary  circulation. 

It  is  evident,  then,  that  the  arterial  pressure,  which  is  itself  derived  from  the  action 
of  the  heart,  is  competent  to  produce  the  circulation  of  the  blood,  as  we  observe  it,  with 
all  its  variations,  in  the  capillary  vessels ;  that  there  is  no  evidence  of  the  intervention  of 
any  other  force ;  but,  on  the  contrary,  microscopical  observations  and  experiments  on  the 
arteries  and  veins,  thus  far,  show  that  there  is  no  other  force  in  operation. 

It  has  been  asserted  that  there  is  a  circulation  of  the  blood  in  the  area  vasculosa,  the 
first  blood-vessels  that  are  developed,  before  the  heart  is  formed ;  but  there  are  no  definite 
and  reliable  observations  which  show  that  there  is  any  regular  movement  of  the  blood, 
which  can  be  likened  to  the  circulation  as  it  is  observed  after  the  development  of  the 
heart,  anterior  to  the  appearance  of  a  contractile  central  organ.  Another  example  of 
what  is  supposed  to  be  circulation  without  the  intervention  of  the  heart  is  in  cases  of 
acardiac  foetuses.  Monsters  without  a  heart,  which  have  undergone  considerable  develop- 
ment and  which  present  systems  of  arteries,  capillaries,  and  veins,  have  been  described. 
All  of  these,  however,  are  accompanied  by  a  twin,  in  which  the  development  of  the  cir- 
culatory system  is  quite  or  nearly  perfect. 

Influence  of  Temperature  on  the  Capillary  Circulation. — Within  moderate  limits,  a 
low  temperature,  induced  by  local  applications,  has  been  found  to  diminish  the  quantity 
of  blood  sent  to  the  capillaries  and  retard  the  circulation,  while  a  high  temperature 
increases  the  supply  of  blood  and  accelerates  its  current.  The  mechanism  of  this  is 
beautifully  shown  by  the  experiments  of  Poiseuille.  This  observer  found  that  when  a 
piece  of  ice  was  applied  to  the  web  of  a  frog's  foot,  the  mesentery  of  a  small  warm-blooded 
animal,  or  to  any  part  in  which  the  capillary  circulation  can  be  observed,  the  number  of 
corpuscles  circulating  in  the  arterioles  became  very  much  diminished,  "  those  which  car- 
ried two  or  three  rows  of  corpuscles  giving  passage  to  but  a  single  row."  The  circulation 
in  the  capillaries  first  became  slower  and  then  entirely  ceased  in  parts.  On  removing 
the  ice,  in  a  very  few  minutes  the  circulation  regained  its  former  characters.  If,  on  the 
other  hand,  the  part  be  covered  with  water  at  104°  Fahr.,  the  rapidity  of  the  current  in 
the  capillaries  is  so  much  increased  that  we  can  hardly  distinguish  the  form  of  the  cor- 
puscles. 

Influence  of  Direct  Irritation  upon  the  Capillary  Circulation. — Experimental  re- 
searches on  the  effects  of  direct  irritation  of  the  capillaries,  in  parts  where  the  circulation 
can  be  observed  microscopically,  have  been  quite  numerous  since  Thompson  studied  the 
effects  of  saline  solutions  on  the  web  of  the  frog's  foot,  in  1813.  The  most  noticeable 
papers  on  this  subject  are  those  of  Dr.  Wilson  Philip  and  Mr.  Wharton  Jones.  The  latter 
paper,  which  receiv-ed  the  Astley  Cooper  prize  for  1850,  is  based  on  very  extended  and 


92  CIRCULATION  OF  THE  BLOOD. 

carefully- conducted  observations,  in  which  the  author,  by  means  of  various  irritants, 
succeeded  in  producing  very  curious  and  interesting  phenomena,  which  he  regarded  as 
inflammatory.  It  is  not  our  object  to  discuss  the  nature  of  inflammation  or  to  treat  of  the 
changes  in  the  character  of  the  capillary  circulation  which  are  supposed  to  attend  this 
condition,  as  this  subject  is  entirely  pathological ;  but  it  must  be  remembered,  in  con- 
sidering the  effects  of  direct  irritation  on  the  capillary  circulation,  that  the  phenomena 
thus  observed  in  cold-blooded  animals  cannot  be  taken  as  absolutely  representing  the 
characters  of  inflammation  in  the  human  subject.  When  an  irritation  is  applied  to  a 
transparent  part,  the  phenomena  observed  may  be  due  to  many  causes,  as  the  direct 
effects  upon  the  contractile  elements  of  the  blood-vessels,  reflex  action  through  the 
nervous  system,  and  the  direct  influence  of  the  application  upon  the  constitution  of  the 
blood.  Saline  or  other  fluids  are  competent  to  modify,  to  a  very  considerable  extent,  the 
composition  of  the  blood,  when  separated  from  it  only  by  the  thin,  permeable  walls  of  the 
vessels ;  and  the  phenomena  which  follow  their  application  are  necessarily  very  complex. 
The  process  of  inflammation  is  by  no  means  completely  understood ;  but  it  is  pretty  gen- 
erally acknowledged  to  be  a  modification  of  nutrition.  We  are  hardly  prepared  to  admit 
that  this  modification,  whatever  it  may  be,  can  be  induced  under  our  very  eyes,  simply 
by  the  application  of  irritants.  With  these  views,  microscopical  researches  on  the  "  state 
of  the  blood  and  blood-vessels  in  inflammation"  do  not  assume  the  importance  which  is 
attributed  to  them  by  many  authors.  Keeping  this  in  miDd,  we  may  state  the  following 
as  a  summary  of  the  phenomena  which  have  been  observed  in  the  capillary  circulation, 
as  the  result  of  irritation  applied  to  transparent  parts : 

The  application  of  the  irritant  is  immediately  followed  by  constriction  of  the  arterioles 
and  diminution  in  the  rapidity  of  the  current  in  them  as  well  as  in  the  capillaries. 

This  constriction  of  the  vessels  is  but  momentary,  if  a  powerful  irritant,  like  a  very 
strong  solution  of  a  salt,  be  used.  It  is  followed  by  a  dilatation  of  the  vessels  and  an 
increase  in  the  rapidity  of  the  circulation. 

Soon  after  the  vessels  have  become  dilated,  the  rapidity  of  the  circulation  becomes 
progressively  diminished,  until  oscillation  of  the  blood  in  the  vessels  takes  place,  which 
occurs  when  the  circulation  is  about  to  cease.  This  oscillation  finally  gives  place  to  com- 
plete stagnation;  and  the  vessels  become  crowded  with  blood,  so  that  the  transparent 
layer  next  their  walls  is  no  longer  observed.  In  this  condition,  it  has  often  been  noticed 
that  the  proportion  of  colorless  corpuscles  is  increased. 

Following  the  contraction  and  subsequent  dilatation  of  the  vessels,  there  are  stasis  and 
engorgement  of  the  parts  which  have  been  exposed  to  irritation.  If  the  irritation  be 
discontinued,  this  condition  is  gradually  relieved,  and  the  blood  resumes  its  normal 
current. 

In  inflammation,  as  it  is  observed  in  the  conjunctiva  and  in  other  vascular  parts,  there 
unquestionably  is  congestion  of  the  vessels ;  but  there  is  no  positive  evidence  of  stagnation 
of  blood  in  the  parts  as  a  constant  occurrence.  The  circulation  seems,  indeed,  to  be  more 
active  than  in  health.  With  regard  to  the  microscopical  phenomena  just  mentioned,  the 
contraction  of  the  arterioles  is  simply  the  effect  of  a  stimulus  upon  their  muscular  coats ; 
and  dilatation  takes  place  probably  in  consequence  of  the  excessive  contraction,  for  it  has 
been  shown  that  this  condition  of  the  muscular  fibres  is  pretty  constantly  followed  by 
unusual  relaxation.  It  has  never  yet  been  determined  how  far  the  stasis  of  the  blood  is 
due  to  an  osmotic  action  of  solutions  employed  in  the  experiments. 

Circulation  of  the  Blood  in  the  Veins. — The  blood,  distributed  to  the  capillaries  of  all 
the  tissues  and  organs  by  the  arteries,  is  collected  from  these  parts  in  the  veins  and 
carried  back  to  the  heart.  In  studying  the  anatomy  of  the  capillary  system  or  in  ob- 
serving the  passage  of  the  blood  from  the  capillaries  to  larger  vessels  in  parts  of  the 
living  organism  which  can  be  submitted  to  microscopical  examination,  it  is  seen  that  the 
capillaries,  vessels  of  nearly  uniform  diameter  and  anastomosing  in  every  direction,  give 


CIRCULATION  OF  THE   BLOOD   IN  THE  VEINS.  93 

origin,  so  to  speak,  to  a  system  of  vessels,  which,  by  union  with  others  as  we  follow  their 
course,  become  larger  and  larger,  and  carry  the  blood  away  in  a  uniform  current.  These 
are  called  the  venules,  or  venous  radicles.  They  are  the  peripheral  radicles  of  the 
numerous  vessels  which  transport  the  blood,'  after  it  has  served  the  purposes  of  nutrition 
or  secretion,  to  the  central  organ. 

The  venous  system  may  be  considered,  in  general  terms,  as  divided  into  two  sets  of 
vessels;  one,  which  is  deep-seated  and  situated  in  proximity  to  the  arteries,  and  the 


FIG.  33.—  Venous  radicles,  uniting  to  form  a  small  vein,  from  the  muscular  coat  o/tJie  urinary  bladder  of  the 

frog;  magnified  400  diameters.    (From  a  photograph  taken  at  the  United  States  Army  Medical  Museum.) 
This  preparation  shows  the  epithelium  of  the  vessels.    It  is  injected  with  nitrate  of  silver,  stained  with  carmine, 

and  mounted  in  Canada  balsam. 

other,  which  is  superficial  and  receives  for  the  most  part  the  blood  from  the  cutaneous 
surface.  The  entire  capacity  of  these  vessels,  as  compared  with  that  of  the  arteries,  is 
very  great.  As  a  general  rule,  each  vein,  when  fully  distended,  is  larger  than  its  adjacent 
artery.  Many  arteries  are  accompanied  by  two  veins,  as  the  arteries  of  the  extremities; 
while  certain  of  them,  like  the  brachial  or  spermatic,  have  more  than  two.  Added  to 
these  is  the  superficial  system  of  veins  which  have  no  corresponding  arteries.  It  is  true 
that  some  arteries  have  no  corresponding  veins,  but  examples  of  this  kind  are  not  suffi- 
ciently numerous  to  diminish,  in  any  marked  degree,  the  great  preponderance  of  the  veins, 
both  in  number  and  volume.  It  is  impossible  to  give  an  accurate  estimate  of  the  extreme 
capacity  of  the  veins  as  compared  with  the  arteries ;  but,  from  the  best  information  we 
have,  it  is  several  times  greater.  Borelli  estimated  that  the  capacity  of  the  veins  was  to 
the  capacity  of  the  arteries,  as  4  to  1 ;  and  Haller,  as  2J  to  1.  The  proportion  is  very 
variable  in  different  parts  of  the  body.  In  some  situations  the  capacity  of  the  veins  and 
arteries  is  about  equal ;  while  in  others,  as  in  the  pia  mater,  the  veins  will  contain,  when 
fully  distended,  six  times  as  much  as  the  arteries. 


94  CIRCULATION  OF  THE  BLOOD. 

In  attempting  to  compare  the  quantity  of  blood  normally  circulating  in  the  veins  with 
that  contained  in  the  arteries,  we  find  such  variations  in  the  venous  system  at  different 
times  and  in  different  parts,  both  in  the  quantity  of  blood,  rapidity  of  circulation,  pressure, 
etc.,  that  a  definite  estimate  is  impossible.  It  would  be  unphilosophical  to  attempt  even 
an  approximate  comparison,  as  the  variations  in  the  venous  circulation  constitute  one  of 
its  greatest  and  most  important  physiological  peculiarities,  which  must  be  fully  appreciated 
in  order  to  form  a  just  idea  of  the  function  of  the  veins.  The  arteries  are  always  full, 
and  their  tension  is  subject  to  comparatively  slight  variations.  Following  the  blood  into 
the  capillaries,  we  observe  the  immense  modifications  in  the  circulation  with  varying  physi- 
ological conditions  of  the  parts,  to  which  we  have  already  referred.  As  would  naturally  be 
expected,  the  condition  of  the  veins  varies  with  the  changes  in  the  capillaries,  from  which 
the  blood  is  taken.  In  addition  to  this,  there  are  independent  variations,  as  in  the  erectile 
tissues,  in  the  veins  of  the  alimentary  canal  during  absorption,  in  veins  subject  to  press- 
ure, etc. 

Following  the  veins  in  their  course,  it  is  observed  that  anastomoses  with  each  other 
form  the  rule,  and  not  the  exception  as  in  the  arteries.  There  are  always  a  number  of 
channels  by  which  the  blood  may  be  returned  from  a  part;  and,  if  one  vessel  be 
obstructed  from  any  cause,  the  current  is  simply  diverted  into  another.  The  vejns  do 
not  present  a  true  anastomosing  plexus,  such  as  exists  in  the  capillary  system,  but  simply 
an  arrangement  by  which  the  blood  can  readily  find  its  way  back  to  the  heart,  and  by 
which  the  vessels  may  accommodate  themselves  to  the  immense  variations  in  the  quan- 
tity of  their  fluid  contents.  This,  with  the  peculiar  valvular  arrangement  which  exists 
in  all  but  the  veins  of  the  cavities,  provides  against  obstruction  to  the  flow  of  blood 
through,  as  well  as  from  the  capillaries,  in  which  it  seems  essential  to  the  proper  nutri- 
tion and  function  of  parts  that  the  quantity  and  course  of  the  blood  should  be  regulated 
exclusively  through  the  arterial  system.  Special  allusion  to  the  different  venous  anas- 
tomoses belongs  to  descriptive  anatomy.  Physiologically,  the  communications  between  the 
different  veins  are  such  that  the  blood  can  always  find  a  way  to  the  heart,  and,  once 
fairly  out  of  the  capillaries,  it  cannot  react  and  influence  the  circulation  of  fresh  blood 
in  the  tissues. 

Collected  in  this  way  from  all  parts  of  the  body,  the  blood  is  returned  to  the  right 
auricle,  from  the  head  and  upper  extremities  by  the  superior  vena  cava,  from  the  trunk 
and  lower  extremities,  by  the  inferior  vena  cava,  and  from  the  substance  of  the  heart,  by 
the  coronary  veins. 

Structure  and  Properties  of  the  Veins. — The  structure  of  the  veins  is  somewhat  more 
complex  and  difficult  of  study  than  that  of  the  arteries.  Their  walls,  which  are  always 
much  thinner  than  the  walls  of  the  arteries,  may  be  divided  into  quite  a  number  of 
layers ;  but,  for  convenience  of  physiological  description,  we  shall  regard  them  as  pre- 
senting three  distinct  coats.  These  have  properties  which  are  tolerably  distinctive, 
although  not  as  much  so  as  the  three  coats  of  the  arteries. 

The  internal  coat  of  the  veins  is  a  continuation  of  the  single  coat  of  the  capillaries 
and  of  the  internal  coat  of  the  arteries.  It  is  a  simple,  homogeneous  membrane,  some- 
what thinner  than  in  the  arteries,  lined  by  a  delicate  layer  of  polygonal  epithelium. 

The  middle  coat  is  divided  by  some  into  two  layers ;  an  internal  layer,  which  is  com- 
posed chiefly  of  longitudinal  fibres,  and  an  external  layer,  in  which  the  fibres  have  a 
circular  direction.  These  two  layers  are  intimately  adherent  and  are  quite  closely 
attached  to  the  internal  coat.  The  longitudinal  fibres  are  composed  of  connective-tissue 
fibres  mingled  with  a  large  number  of  the  smallest  variety  of  the  elastic  fibres.  This 
layer  contains  a  large  number  of  capillary  vessels  (vasa  vasorum).  The  circular  fibres 
are  composed  of  elastic  tissue,  some  of  the  fibres  of  the  same  variety  as  is  found  in  the 
longitudinal  layer,  some  of  medium  size,  and  some  in  the  form  of  the  "fenestrated  mem- 
brane." In  addition,  there  are  inelastic  fibres  interlacing  in  every  direction  and  mingled 


STRUCTURE   AND   PROPERTIES   OF  THE   VEINS.  95 

with  capillary  blood-vessels,  and  the  unstriped  or  involuntary  muscular  fibres.  In  the 
human  subject,  in  the  veins  of  the  dura  and  pia  mater,  the  bones,  and  the  retina,  the 
vena  cava  descendens,  the  thoracic  portion  of  the  vena  cava  ascendens,  the  external  and 
internal  jugulars,  and  the  subclavian  veins,  there  are  no  muscular  fibres  in  the  middle  coat. 
In  the  larger  veins,  such  as  the  abdominal  vena  cava,  the  iliac,  crtiral,  popliteal,  mesen- 
teric,  and  axillary  veins,  the  fibres  are  both  circular  and  transverse.  In  the  smaller 
veins,  the  fibres  are  circular. 

The  external  coat  of  the  veins  is  composed  of  white  fibrous  tissue,  like  the  cor- 
responding coat  of  the  arteries.  In  the  largest  veins,  particularly  those  of  the  abdominal 
cavity,  this  coat  contains  a  layer  of  longitudinal  unstriped  muscular  fibres.  In  the  veins 
near  the  heart,  are  found  a  few  striated  fibres,  which  are  continued  on  to  the  veins  from 
the  auricles.  In  some  of  the  inferior  animals,  as  the  turtle,  these  fibres  are  quite  thick, 
and  pulsation  of  the  veins  in  the  immediate  vicinity  of  the  heart  is  very  marked.  In 
nearly  all  veins,  the  external  coat  is  several  times  thicker  than  the  internal.  This  is 
most  marked  in  the  larger  veins,  in  which  the  middle  coat,  particularly  the  layer  of 
muscular  fibres,  is  very  slightly  developed. 

In  what  are  called  the  venous  sinuses,  and  in  the  veins  which  pass  through  bony 
tissue,  we  have  only  the  internal  coat,  to  which  are  superadded  a  few  longitudinal  fibres, 
the  whole  being  closely  attached  to  the  surrounding  parts.  As  examples  of  this,  may  be 
mentioned  the  sinuses  of  the  dura  mater  and  the  veins  of  the  large  bones  of  the  skull. 
In  the  first  instance,  there  is  little  more  than  the  internal  coat  of  the  vein  firmly  attached 
to  the  surrounding  layers  of  the  dura  mater.  In  the  second  instance,  the  same  thin  mem- 
brane is  adherent  to  canals  formed  by  a  layer  of  compact  bony  tissue.  The  veins  are 
much  more  closely  adherent  to  the  surrounding  tissues  than  the  arteries,  particularly 
when  they  pass  between  layers  of  aponeurosis. 

The  above  peculiarities  in  the  anatomy  of  the  veins  indicate  considerable  differences 
in  their  properties  as  compared  with  the  arteries.  When  a  vein  is  cut  across,  its  walls 
fall  together,  if  not  supported  by  adhesions  to  surrounding  tissues,  so  that  its  caliber  is 
nearly  or  quite  obliterated.  The  yellow  elastic  tissue,  which  gives  to  the  larger  arteries 
their  great  thickness,  is  very  scanty  in  the  veins,  and  the  thin  walls  collapse  when  not 
sustained  by  liquid  in  the  interior  of  the  vessels.  Whenever  the  veins  remain  open  after 
section,  it  is  on  account  of  their  attachment  to  surrounding  tissues  and  is  not  due  to 
the  rigidity  of  the  vessels  themselves. 

Although  with  much  thinner  and  apparently  weaker  walls,  the  veins,  as  a  rule,  will 
resist  a  greater  pressure  than  the  arteries.  Observations  on  the  relative  strength  of 
the  arteries  and  veins  were  made  by  Hales,  but  the  most  extended  experiments  on  the 
subject  were  made  by  Clifton  Wintringham,  in  1740.  The  latter  observer  ascertained 
that  the  inferior  vena  cava  of  a  sheep,  just  above  the  opening  of  the  renal  veins,  was  rup- 
tured by  a  pressure  of  one  hundred  and  seventy-six  pounds,  while  the  aorta,  at  a  corre- 
sponding point,  yielded  to  a  pressure  of  one  hundred  and  fifty-eight  pounds.  The 
strength  of  the  portal  vein  was  even  greater,  supporting  a  pressure  of  nearly  five  atmos- 
pheres, bearing  a  relation  to  the  vena  cava  of  six  to  five;  yet  these  vessels  had  hardly 
one-fifth  the  thickness  of  the  arteries.  In  the  lower  extremities  in  the  human  subject,  the 
veins  are  much  thicker  and  stronger  than  in  other  situations,  a  provision  against  the 
increased  pressure  to  which  they  are  habitually  subjected  in  the  upright  posture.  Win- 
tringham noticed  one  singular  exception  to  the  general  rule  just  given.  In  the  vessels  of 
the  glands  and  of  the  spleen,  the  strength  of  the  arteries  was  much  greater  than  that  of 
the  veins.  The  splenic  vein  gave  way  under  a  pressure  of  little  more  than  one  atmos- 
phere, while  the  artery  supported  a  pressure  of  more  than  six  atmospheres. 

A  little  reflection  on  the  influences  to  which  the  venous  and  arterial  circulation  are 
subject  will  enable  us  to  understand  the  physiological  importance  of  the  great  difference 
in  the  strength  of  the  two  varieties  of  vessels.  It  is  true  that  in  the  arterial  system  the 
constant  pressure  is  greater  than  in  the  veins ;  but  it  is  nearly  the  same  throughout  the  ar- 


96  CIRCULATION  OF  THE  BLOOD. 

terial  system,  and  the  immense  extent  of  the  outlet  into  the  capillary  system  provides 
against  any  very  great  increase  in  pressure,  so  long  as  the  blood  is  in  a  condition  which 
enables  it  to  pass  into  the  capillaries.  The  muscular  fibres  of  the  left  ventricle  have  but 
a  limited  power,  and  when  the  pressure  in  the  arteries  is  so  great,  as  it  sometimes  is  in 
asphyxia,  as  to  close  the  aortic  valves  so  firmly  that  the  force  of  the  ventricle  will  not 
open  them,  it  cannot  be  increased.  At  the  same  time,  it  is  being  gradually  relieved  by  the 
capillaries,  through  which  the  blood  slowly  filters,  even  when  completely  unae  rated.  "With 
the  veins  it  is  different.  The  blood  has  a  comparatively  restricted  outlet  at  the  heart  and 
is  received  by  the  capillaries  from  all  parts  of  the  system.  The  vessels  are  provided  with 
numerous  valves,  which  render  a  general  backward  action  impossible.  Thus,  restricted 
portions  of  the  venous  system,  from  pressure  in  the  vessels,  increase  of  fluid  from  absorp- 
tion, accumulation  by  force  of  gravity,  and  other  causes,  may  be  subjected  to  great  and 
sudden  variations  in  pressure.  The  great  strength  of  these  vessels  enables  them  ordina- 
rily to  suffer  these  variations  without  injury ;  although  varicose  veins  in  various  parts 
present  examples  of  the  effects  of  repeated  and  continued  distention. 

The  veins  possess  a  considerable  degree  of  elasticity,  although  this  property  is  not  so 
marked  as  it  is  in  the  arteries.  If  we  include  between  two  ligatures  a  portion  of  a  vein 
distended  with  blood  and  make  a  small  opening  in  the  vessel,  the  blood  will  be  ejected 
with  some  force,  and  the  vessel  becomes  very  much  reduced  in  caliber. 

It  has  been  proven  by  direct  experiment  that  the  veins  are  endowed  with  the  peculiar 
contractility  characteristic  of  the  action  of  the  unstriped  muscular  fibres.  On  the  application 
of  galvanic  or  mechanical  excitation,  they  contract  slowly  and  gradually,  the  contraction 
being  followed  by  a  correspondingly-gradual  relaxation.  There  is  never  any  rhythmical 
or  peristaltic  movement  in  the  veins,  sufficient  to  assist  the  circulation.  The  only  regular 
movements  which  occur  are  seen  in  the  vessels  in  immediate  proximity  to  the  right 
auricle,  which  are  provided  with  a  few  fibres  similar  to  those  which  exist  in  the  walls  of 
the  heart. 

Nerves,  chiefly  from  the  sympathetic  system,  have  been  demonstrated  in  the  walls  of 
the  larger  veins  but  have  not  been  followed  out  to  the  smaller  ramifications. 

Valves  of  the  Veins. — The  discovery  of  the  valves  of  the  veins  has  already  been 
alluded  to  in  connection  with  the  history  of  the  discovery  of  the  circulation.  They  had 
undoubtedly  been  observed  in  various  parts  of  the  venous  system,  but  Fabricius,  the 
greatest  anatomist  of  his  day,  had  the  good  fortune  to  demonstrate  them  to  his  illustrious 
pupil,  William  Harvey,  whose  immortal  discovery  indicated  their  physiological  importance. 
Being  ignorant  of  the  observations  of  his  predecessors  on  this  subject,  Fabricius  an- 
nounced himself  as  their  discoverer  and  is  generally  so  regarded.  In  all  parts  of  the 
venous  system,  except,  in  general  terms  in  the  abdominal,  thoracic,  and  cerebral  cavities, 
there  exist  little  membranous,  semilunar  folds,  resembling  the  aortic  and  pulmonic  valves 
of  the  heart.  When  distended,  the  convexities  of  these  valves  look  toward  the  periph- 
ery. In  the  great  majority  of  instances,  the  valves  exist  in  pairs,  but  they  are  occa- 
sionally found  in  groups  of  three.  They  are  formed  in  part  of  the  lining  membrane  of 
the  veins,  with  fine  fibres  of  connective  tissue.  There  exists,  also,  a  fibrous  ring  follow- 
ing the  line  of  attachment  of  the  valvular  curtains  to  the  vein,  which  renders  the  vessel 
much  stronger  and  less  dilatable  here  than  in  the  spaces  between  the  valves.  The  valves 
are  by  far  the  most  numerous  in  the  veins  of  the  lower  extremities.  They  are  generally 
situated  just  below  the  point  where  a  small  vein  empties  into  one  of  larger  size,  so  that 
the  blood,  as  it  passes  in,  finds  an  immediate  obstacle  to  passage  in  the  wrong  direction. 
The  situation  of  the  valves  may  be  readily  observed  in  any  of  the  superficial  veins.  If 
the  flow  of  blood  be  obstructed,  little  knots  will  be  formed  in  the  congested  vessels, 
which  indicate  the  position  and  action  of  the  valves.  The  simple  experiment  of  Harvey, 
already  referred  to,  presents  a  striking  illustration  of  the  action  of  the  valves.  When  the 
vein  is  thus  congested  and  knotted,  if  the  finger  be  pressed  along  the  vessel  in  the  direc- 


VALVES   OF  THE   VEINS. 


97 


FIG.  84.—  Valve*  of  the  veins.   (Copied  and  reduced  from  a  figure  in  the  original  work  of  Fabricius,  published  in  1687.) 
A,  B,  vein;  L,  artery;  D,  E,  F,  G,  H,  I,  valves;  a,  ft,  y,  S,  e,  venous  branches. 

7 


98  CIKCULATION   OF  THE  BLOOD. 

tion  of  the  blood-current,  a  portion  situated  between  two  valves  may  be  emptied  of  blood ; 
but  it  is  impossible  to  empty  any  portion  of  the  vessel  by  pressing  the  blood  in  the  oppo- 
site direction.  On  slitting  open  a  vein,  we  observe  the  shape,  attachment,  and  extreme 
delicacy  of  structure  of  the  valves.  When  the  vessel  is  empty,  or  when  fluid  moves 
toward  the  heart,  they  are  closely  applied  to  the  walls ;  but  if  liquid  or  air  be  forced  in  the 
opposite  direction,  they  project  into  its  caliber,  and,  by  the  application  of  their  free  edges 
to  each  other,  effectually  prevent  any  backward  current.  Fabricius  noted  the  following 
peculiarity  in  the  arrangement  of  the  valves :  When  closed,  the  application  of  their  free 
edges  forms  a  line  which  runs  across  the  vessel ;  it  is  found  that,  in  successive  sets  of 
valves,  these  lines  are  at  right  angles  to  each  other,  so  that  if,  in  one  set,  this  line  have  a 
direction  from  before  backward,  in  the  sets  above  and  below  the  lines  run  from  side  to 
side. 

There  are  certain  exceptions  to  the  general  proposition  that  the  veins  of  the  great 
cavities  are  not  provided  with  valves.  Valves  are  found  in  the  portal  system  of  some  of 
the  inferior  animals,  as  the  horse.  They  do  not  exist,  however,  in  this  situation  in  the 
human  subject.  Generally,  in  following  out  the  branches  of  the  inferior  vena  cava,  no 
valves  are  found  until  we  come  to  the  crural  vein ;  but  occasionally  there  is  a  double 
valve  at  the  origin  of  the  external  iliac.  In  some  of  the  inferior  animals,  there  exists 
constantly  a  single  valvular  fold  in  the  vena  cava  at  the  openings  of  the  hepatic,  and  one 
at  the  opening  of  the  renal  vein.  This  is  not  constant  in  the  human  subject.  Valves 
are  found  in  the  spermatic,  but  not  in  the  ovarian  veins.  A  single  valvular  fold  has 
been  described  at  the  opening  of  the  right  spermatic  into  the  vena  cava.  There  are 
two  valves  in  the  azygos  vein  near  its  opening  into  the  superior  vena  cava.  There 
is  a  single  valve  at  the  orifice  of  the  coronary  vein.  There  are  no  valves  at  the 
openings  of  the  brachio-cephalic  into  the  superior  vena  cava ;  but  there  is  a  strong  double 
valve  at  the  point  where  the  internal  jugular  opens  into  the  brachio-cephalic.  Between 
this  point  and  the  capillaries  of  the  brain,  the  vessels  are  entirely  deprived  of  valves, 
except  in  very  rare  instances,  when  one  or  two  are  found  in  the  course  of  the  jugular. 

In  addition  to  the  double,  or  more  rarely  triple  valves  which  have  just  been  described, 
there  is  another  variety,  found  in  certain  parts,  at  the  point  where  a  tributary  vein  opens 
into  a  main  trunk.  This  consists  of  a  single  fold,  which  is  attached  to  the  smaller  vessel 
but  projects  into  the  larger.  Its  action  is  to  prevent  regurgitation,  by  the  same  mech- 
anism as  that  by  which  the  ileo-csecal  valve  prevents  the  passage  of  matters  from  the 
large  into  the  small  intestine.  These  valves  are  much  less  numerous  than  the  first  variety. 

The  veins  form  a  system  which  is  adapted  to  the  return  of  blood  to  the  heart  in  a 
comparatively  slow  and  unequal  current.  Distention  of  certain  portions  is  provided  for ; 
and  the  vessels  are  so  protected  with  valves,  that  whatever  influences  the  current  must 
favor  its  flow  in  the  direction  of  the  heart. 

Course  of  the  Blood: in  the  Veins.—  The  experiments  of  Hales  and  Sharpey,  showing 
that  defibrinated  blood  can  be  made  to  pass  from  the  arteries  into  the  capillaries  and  out 
at  the  veins  by  a  pressure  less  than  that  which  exists  in  the  arterial  system,  and  the 
observations  of  Magendie  upon  the  circulation  in  the  leg  of  a  living  dog,  showing  that 
ligation  of  the  artery  arrests  the  flow  in  the  vein,  points  which  have  already  been  fully 
discussed  in  treating  of  the  causes  of  the  capillary  circulation,  have  established,  beyond 
question,  the  fact  that  the  force  exerted  by  the  left  ventricle  is  sufficient  to  account  for 
the  venous  circulation.  The  heart  must  be  regarded  as  the  prime  cause  of  all  movement 
in  these  vessels.  Eegarding  this  as  definitely  ascertained,  there  remain  to  consider,  in 
the  study  of  the  course  of  the  blood  in  the  veins,  the  character  of  the  current,  the  influence 
of  the  vessels  themselves,  the  question  of  the  existence  of  forces  which  may  assist 
the  vis  a  tergo  from  the  heart,  and  circumstances  which  may  interfere  with  the  flow  of 
blood. 

As  a  rule,  in  the  normal  circulation,  the  flow  of  blood  in  the  veins  is  continuous.    The 


COURSE   OF   THE   BLOOD   IN   THE  VEINS.  99 

intermittent  impulse  of  the  heart,  which  progressively  diminishes  as  we  recede  from  this 
organ  but  is  still  felt  even  in  the  smallest  arteries,  is  lost,  as  we  have  seen,  in  the  capil- 
laries. Here,  for  the  first  time,  the  blood  moves  in  a  constant  current ;  and,  as  the  press- 
ure in  the  arteries  is  continually  supplying  fresh  blood,  that  which  has  circulated  in  the 
capillaries  is  forced  into  the  venous  radicles  in  a  steady  stream.  As  the  supply  to  the 
capillaries  of  different  parts  is  regulated  by  the  action  of  the  small  arteries,  and  as  this 
supply  is  subject  to  great  variations,  there  must  necessarily  be  corresponding  variations 
in  the  current  in  the  veins  and  in  the  quantity  of  blood  which  these  vessels  receive.  As  we 
should  anticipate,  then,  the  venous  circulation  is  subject  to  very  great  variations  arising 
from  irregularity  in  the  supply  of  blood,  aside  from  any  action  of  the  vessels  themselves 
or  any  external  disturbing  influences.  Great  variations  in  the  venous  current  are  observed 
in  the  veins  which  collect  the  blood  from  the  intestinal  canal.  During  the  intervals  of 
digestion,  these  vessels  carry  a  comparatively  small  quantity  of  blood ;  but,  during  diges- 
tion, they  are  laden  with  the  fluids  received  by  absorption,  and  the  quantity  is  largely 
increased. 

It  often  happens  that  a  vein  becomes  obstructed  from  some  cause  which  is  entirely 
physiological,  as  the  action  of  muscles.  The  immense  number  of  veins,  as  compared  with 
the  arteries,  and  their  free  communications  with  each  other,  provide  that  the  current, 
under  these  circumstances,  is  simply  diverted,  passing  to  the  heart  by  another  channel. 
When  any  part  of  the  venous  system  is  distended,  the  vessels  react  on  the  blood  and  exert 
a  certain  influence  on  the  current,  always  pressing  it  toward  the  heart,  for  the  valves 
oppose  a  flow  in  the  opposite  direction. 

The  intermittent  action  of  the  heart,  which  pervades  the  whole  arterial  system,  is 
generally  absorbed,  as  it  were,  in  the  passage  of  the  blood  through  the  capillaries ;  but, 
when  the  arterioles  of  any  part  are  very  much  relaxed,  the  impulse  of  the  central  organ 
may  extend  to  the  veins.  Bernard  has  shown  this  in  the  most  striking  manner,  in  his 
well-known  experiments  on  the  circulation  in  the  glands.  "When  the  glands  are  pouring 
out  their  secretions,  the  quantity  of  blood  which  they  receive  is  very  much  increased.  It 
is  then  furnished  to  supply  material  for  the  secretion,  and  not  exclusively  for  nutrition. 
If  the  vein  be  opened  at  such  a  time,  it  is  found  that  the  blood  has  not  lost  its  arterial 
character,  that  the  quantity  which  escapes  is  increased,  and  that  the  flow  is  in  an  inter- 
mittent jet,  as  from  a  divided  artery.  This  is  due  to  the  relaxed  condition  of  the  arteri- 
oles of  the  part,  and  the  phenomenon  thus  observed  constitutes  the  true  venous  pulse. 
What  thus  occurs  in  a  restricted  portion  of  the  circulatory  system  may  take  place  in  all 
the  veins,  though  in  a  less  marked  degree.  Physicians  have  frequently  noticed,  after  the 
blood  has  been  flowing  for  some  time  in  the  operation  of  venesection,  that  the  color 
changes  from  black  to  red,  and  the  stream  becomes  intermittent,  often  leading  the 
operator  to  fear  that  he  has  pricked  the  artery.  In  all  probability,  this  is  due  to 
the  relaxation  of  the  arterioles  as  one  of  the  effects  of  abstraction  of  blood,  producing 
the  same  condition  that  has  been  noted  in  some  of  the  glands  during  their  functional 
activity.  The  hypothesis  that  it  is  due  to  an  impulse  from  the  adjacent  artery  is  not  ad- 
missible. Except  in  the  veins  near  the  heart,  any  pulsation  which  occurs  is  to  be  attrib- 
uted to  the  force  of  the  heart,  transmitted  with  unusual  facility  through  the  capillary 
system.  A  nearly  uniform  current,  however,  is  the  rule,  and  a  marked  pulsation,  the 
rare  exception. 

Pressure  of  Blood  in  the  Veins. — The  pressure  in  the  veins  is  always  much  less  than 
in  the  arteries.  It  is  exceedingly  variable  in  different  parts  of  the  venous  system  and  in 
the  same  part  at  different  times.  As  a  rule,  it  is  in  inverse  ratio  to  the  arterial  pressure. 
Whatever  favors  the  passage  of  blood  from  the  arteries  into  the  capillaries  has  a  tendency 
to  diminish  the  arterial  pressure,  and,  as  it  increases  the  quantity  of  blood  which  passes 
into  the  veins,  must  increase  the  venous  pressure.  The  great  capacity  of  the  venous  sys- 
tem, its  numerous  anastomoses,  the  presence  of  valves  which  may  shut  off  a  portion  from 


100  CIRCULATION  OF  THE  BLOOD. 

the  rest,  are  circumstances  which  involve  great  variations  in  pressure  in  different  vessels. 
It  has  been  ascertained  that,  as  a  rule,  the  pressure  is  diminished  as  we  pass  from  the 
periphery  toward  the  heart.  In  an  observation  on  the  calf,  Volkmann  found  that,  with  a 
pressure  of  about  6*5  inches  of  mercury  in  the  carotid,  the  pressure  in  the  metatarsal  vein 
was  1*1  inch,  and  but  0*36  in  the  jugular.  Muscular  effort  has  a  marked  influence  on  the 
force  of  the  circulation  in  certain  veins  and  produces  an  elevation  in  the  pressure.  As 
the  reduced  pressure  in  the  veins  is  due,  in  a  measure,  to  the  great  relative  capacity  of 
the  venous  system  and  the  free  communications  between  the  vessels,  it  would  seem  that, 
if  it  were  possible  to  reduce  the  capacity  of  the  veins  in  a  part  and  force  all  the  blood  to 
pass  to  the  heart  by  a  single  vessel  corresponding  to  the  artery,  the  pressure  in  this  vessel 
would  be  greatly  increased.  Poiseuille  has  shown  this  to  be  the  fact  by  the  experiment 
of  ligating  all  the  veins  coming  from  a  part,  except  one  which  had  the  volume  of  the 
artery  by  which  the  blood  was  supplied,  forcing  all  the  blood  to  return  by  this  single 
channel.  This  being  done,  he  found  the  pressure  in  the  vein  immensely  increased,  becom- 
ing nearly  equal  to  that  in  the  artery. 

Rapidity  of  the  Venous  Circulation. — It  is  impossible  to  fix  upon  any  definite  rate  as 
representing  the  rapidity  of  the  current  Of  blood  in  the  veins.  It  will  be  seen  that  various 
circumstances  are  capable  of  increasing  very  considerably  the  rapidity  of  the  flow  in  cer- 
tain veins,  and  that,  under  certain  conditions,  the  current  in  some  parts  of  the  venous 
system  is  very  much  retarded.  Undoubtedly,  the  general  movement  of  blood  in  the  veins 
is  very  much  slower  than  in  the  arteries,  from  the  fact  that  the  quantity  of  blood  is  greater. 
If  it  be  assumed  that  the  quantity  of  blood  in  the  veins  is  double  that  contained  in  the 
arteries,  the  general  average  of  the  current  would  be  diminished  one-half.  As  we  near 
the  heart,  however,  the  flow  becomes  more  uniform  and  progressively  increases  in  rapidity. 

As  the  effect  of  the  heart's  action  upon  the  venous  circulation  is  subject  to  so  many 
modifying  influences  through  the  small  arteries  and  capillaries,  and  as  there  are  other 
forces  influencing  the  current,  which  are  by  no  means  uniform  in  their  action,  with  our 
present  knowledge,  estimates  of  the  general  rapidity  of  the  venous  circulation  or  the 
variations  in  different  vessels  would  be  founded  on  mere  speculations. 

Causes  of  the  Venous  Circulation. 

In  the  veins,  the  blood  is  farthest  removed  from  the  influence  of  the  contractions  of 
the  left  ventricle ;  and,  although  these  are  felt,  there  are  many  other  causes  which  com- 
bine to  carry  on  the  circulation,  and  many  influences  by  which  it  is  retarded  or  ob- 
structed. 

The  great  and  uniform  force  which  operates  on  the  circulation  in  these  vessels  is  the 
vis  a  tergo.  We  have  repeatedly  referred  to  the  entire  adequacy  of  the  arterial  pressure, 
propagated  through  the  capillaries,  to  account  for  the  movement  of  blood  in  the  veins, 
provided  there  be  no  great  obstacles  to  the  current.  There  are  no  facts  which  lead  us  to 
doubt  the  operation  of  this  force  as  the  prime  cause  of  the  venous  circulation  ;  and  the 
only  question  which  arises  is  whether  there  be  any  force  exerted  in  the  capillaries  them- 
selves which  is  superadded  to  the  force  of  the  heart.  In  discussing  the  capillary  circu- 
lation, we  stated  that  there  is  no  direct  proof  of  the  existence  of  a  distinct  "  capillary 
power "  influencing  the  movement  of  blood  in  these  vessels ;  and  consequently  the 
vis  a  tergo  operating  on  the  circulation  in  the  veins  must  be  attributed  mainly  to  the  ac- 
tion of  the  left  ventricle. 

The  other  forces  which  concur  to  produce  movement  of  blood  in  the  veins  are  the 
following : 

1.  Muscular  action,  by  which  many  of  the  veins  are  at  times  compressed,  thus  forcing 
the  blood  toward  the  heart,  regurgitation  being  prevented  by  the  action  of  the  valves. 

2.  A  suction  force  exerted  by  the  action  of  the  thorax  in  respiration,  operating, 
however,  only  on  the  veins  in  the  immediate  neighborhood  of  the  chest. 


COUKSE   OF  BLOOD   IN  TH£  'VEINS.:'  ;  101 

3.  A  possible  influence   from  contraction  of  the   coats  of  the  vessels  themselves. 
This  is  marked  in  the  veins  near  the  heart  in  some  of  the  inferior  animals. 

4.  The  force  of  gravity,  which  operates  only  on  vessels  which  carry  blood  from  above 
downward  to  the  heart,  and  a  slight  suction  force  which  may  be  exerted  upon  the  blood 
in  a  small  vein  as  it  passes  into  a  larger  vessel  in  which  the  current  is  more  rapid. 

The  obstacles  to  the  venous  circulation  are  :  Pressure  sufficient  to  obliterate  the  cali- 
ber of  a  vessel,  when,  from  the  free  communications  with  other  vessels,  the  current  is 
simply  diverted  into  another  channel ;  the  expulsive  efforts  of  respiration ;  the  contrac- 
tions of  the  right  side  of  the  heart ;  and  the  force  of  gravity,  which  operates,  in  the 
erect  posture,  on  the  current  in  all  excepting  the  veins  of  the  head,  neck,  and  in  parts 
of  the  trunk  above  the  heart. 

Influence  of  Muscular  Contraction. — That  the  action  of  muscles  has  considerable  in- 
fluence on  the  current  of  blood  in  the  veins  situated  between  them  and  in  their  sub- 
stance, has  long  been  recognized.  It  is  exemplified  in  the  operation  of  venesection, 
when  it  is  well  known  that  the  jet  from  the  vein  may  be  very  much  increased  in  force 
by  contraction  of  the  muscles  below  the  opening.  This  action  is  so  marked,  that  the 
parts  of  the  venous  system  which  are  situated  in  the  substance  of  muscles  have  been 
compared  by  Chassaignac  to  a  sponge  full  of  liquid,  vigorously  pressed  by  the  hand.  It 
must  always  be  remembered,  however,  that,  although  the  muscles  are  capable  of  acting 
on  the  blood  contained  in  veins  in  their  substance  with  great  vigor,  the  heart  is  fully 
competent  to  carry  on  the  venous  circulation  without  their  aid ;  a  fact  which  is  exempli- 
fied in  a  striking  manner  in  the  venous  circulation  in  paralyzed  parts. 

It  has  been  shown  by  actual  observations  with  the  haamadynamometer,  that  muscular 
action  is  capable  of  immensely  increasing  the  pressure  in  certain  veins.  The  first  defi- 
nite experiments  on  this  subject  were  made  by  Magendie,  who  showed  a  pressure  of  over 
two  inches  of  mercury  produced  by  a  general  muscular  contraction,  on  the  passage  of  a 
galvanic  current  from  a  needle  plunged  into  the  cervical  region  of  the  spinal  marrow  to 
one  fixed  in  the  muscles  of  the  thigh.  The  experiments  of  Bernard  have  shown  this 
more  accurately.  This  physiologist  found  that  the  pressure  in  the  jugular  of  a  horse, 
in  repose,  was  1-4  inch  ;  but  the  action  of  the  muscles  in  raising  the  head  increased  it  to 
a  little  more  than  five  inches,  or  nearly  four  times.  These  observations  show  at  once 
the  great  variations  in  the  current  and  the  important  influence  of  muscular  contraction 
on  the  venous  circulation. 

In  order  that  contractions  of  muscles  shall  assist  the  venous  circulation,  two  things 
are  necessary : 

1.  The  contraction  must  be  intermittent.     This  is  always  the  case  in  the  voluntary 
muscles.     It  is  a  view  entertained  by  many  that  each  muscular  fibre  relaxes  immediately 
after  its  contraction,  which  is  instantaneous,  and  that  a  certain  period  of  repose  is  neces- 
sary before  it  can  contract  again.     However  this  may  be,  it  is  well  known  that  all 
active  muscular  contraction,  as  distinguished  from  the  efforts  necessary  to  maintain  the 
body  in  certain  ordinary  positions,  is  intermittent  and  not  very  prolonged.     Thus  the 
veins,  which  are  partly  emptied  by  the  compression,  are  filled  again  during  the  repose  of 
the  muscle. 

2.  There  should  be  no  possibility  of  a  retrograde  movement  of  the  blood.     This  con- 
dition is  fulfilled  by  the  action  of  the  valves.     Anatomical  researches  have  shown  that 
these  valves  are  most  abundant  in  veins  situated  in  the  substance  of  or  between  the  mus- 
cles, and  that  they  do  not  exist  in  the  veins  of  the  cavities,  which  are  not  subject  to  the 
same  kind  of  compression.     It  is  thus  that  the  blood  is  prevented  from  passing  back- 
ward toward  the  capillary  system  ;  and,  when  the  caliber  of  a  vein  is  reduced  by  com- 
pression, part  of  its  contents  must  be  forced  toward  the  heart.     This  action  of  the  valves 
constitutes  their  most  important  function. 

Milne-Edwards  alludes  to  an  important  physiological  bearing  of  the  acceleration  of 


102  tflEQULATION  OF  THE   BLOOD. 

the  venous  circulation  by  contractions  of  muscles  on  their  nutrition.  It  is  apparently 
necessary  that  the  supply  of  blood  should  be  increased  in  a  muscle,  in  proportion  to  and 
during  its  activity ;  for  at  that  time  its  disassimilation  is  undoubtedly  augmented,  and 
there  is  an  increased  demand  on  the  blood  to  supply  the  waste.  It  is  apparently  a  pro- 
vision of  Nature  that  the  activity  of  a  muscle,  facilitating  the  passage  of  blood  in  its 
veins  and  consequently  its  flow  from  the  capillaries,  induces  an  increased  supply  of  the 
nutrient  fluid.  As  the  development  of  tissues  is  generally  in  proportion  to  their  vascu- 
larity,  this  may  account  for  the  increase  in  the  development  of  muscles  which  is  the  al- 
most invariable  result  of  exercise. 

Force  of  Aspiration  from  the  Thorax. — During  the  act  of  inspiration,  the  enlarge- 
ment of  the  thorax,  by  depression  of  the  diaphragm  and  elevation  of  the  ribs,  affects 
the  movements  of  fluids  in  all  the  tubes  m,its  vicinity.  The  air  rushes  in  by  the  trachea 
and  expands  the  lungs,  so  that  they  follow  the  movements  of  the  thoracic  walls.  The 
flow  of  blood  into  the  great  arteries  is  somewhat  retarded,  as  is  indicated  by  a  dimi- 
nution in  the  arterial  pressure ;  and,  finally,  the  blood  in  the  great  veins  passes  to  the 
heart  with  greater  facility  and  in  increased  quantity.  This  last-mentioned  phenomenon 
can  be  readily  observed,  when  the  veins  are  prominent,  in  profound  or  violent  inspira- 
tion. The  veins  at  the  lower  part  of  the  neck  are  then  seen  to  empty  themselves  of 
blood  during  inspiration,  and  they  become  distended  during  expiration,  producing  a  sort  of 
pulsation  which  is  synchronous  with  respiration.  This  can  always  be  observed  after  ex- 
posure of  the  jugular  in  the  lower  part  of  the  neck  in  an  inferior  animal.  After  this 
operation,  if  we  cause  the  animal  to  make  violent  respiratory  efforts,  the  vein  will  be 
almost  emptied  and  collapsed  with  inspiration  and  turgid  with  expiration.  The  move- 
ments of  the  veins  near  the  thorax  have  long  been  observed  and  have  been  described 
with  tolerable  accuracy.  Direct  observations  on  the  jugulars  show  conclusively  that  the 
influence  of  inspiration  cannot  be  felt  much  beyond  these  vessels.  They  are  seen  to 
collapse  with  each  inspiratory  act,  a  condition  which  limits  this  influence  to  the  veins 
near  the  heart.  The  flaccidity  of  the  walls  of  the  veins  will  not  permit  the  extended 
action  of  any  suction  force.  If  a  portion  of  a  vein  removed  from  the  body  be  attached 
to  the  nozzle  of  a  syringe  and  we  attempt  to  draw  a  liquid  through  it,  although  the  suc- 
tion force  be  applied  very  gently,  when  the  vessel  has  any  considerable  length  its  walls 
will  be  drawn  together.  In  the  circulation,  the  veins  are  moderately  distended  with 
blood  by  the  ms  a  tergo,  and,  to  a  certain  extent,  they  are  supported  by  connections  with 
surrounding  tissues,  so  that  the  force  of  aspiration  is  felt  farther  than  in  any  experiment 
on  vessels  removed  from  the  body.  The  blood,  as  it  approaches  the  thorax,  impelled  by 
other  forces,  is  considerably  accelerated  in  its  flow  ;  but  it  is  seen  by  direct  observation, 
that  beyond  a  certain  point,  and  that  very  near  the  chest,  ordinary  aspiration  has  no  in- 
fluence, and  violent  efforts  rather  retard  than  favor  the  venous  current. 

In  the  liver,  the  influence  of  inspiration  becomes  a  very  important  element  in  the 
mechanism  of  the  circulation.  This  organ  presents  a  vascular  arrangement  which  is 
exceptional.  The  blood,  distributed  by  the  arteries  in  a  capillary  plexus  in  the  mucous 
membrane  of  the  alimentary  canal  and  in  the  spleen,  instead  of  being  returned  directly 
to  the  heart  by  the  veins,  is  collected  into  the  portal  vein,  carried  to  the  liver,  and  is  there 
distributed  in  a  second  set  of  capillary  vessels.  It  is  then  collected  in  the  hepatic  veins 
and  carried  by  the  vena  cava  to  the  heart.  This  double  capillary  plexus  between  the 
left  and  the  right  side  of  the  heart  has  been  cited  as  an  argument  against  the  fact  that  the 
left  ventricle  is  capable  of  sending  the  blood  through  the  entire  circuit  of  the  vascular 
system.  The  three  hepatic  veins  open  into  the  inferior  vena  cava  near  the  point  where 
it  passes  the  diaphragm,  where  the  force  of  aspiration  from  the  thorax  would  materially 
assist  the  current  of  blood.  On  following  these  vessels  into  the  substance  of  the  liver,  it 
is  found  that  their  walls  are  so  firmly  adherent  to  the  tissue  of  the  organ,  that,  when  cut 
across,  they  remain  patulous;  and  it  is  evident  that  they  remain  open  under  all  con- 


FORCE   OF  ASPIRATION  FROM  THE  THORAX.  103 

ditions.  The  thorax  can  therefore  exert  a  powerful  influence  upon  the  hepatic  cir- 
culation ;  for  it  is  only  the  flaccidity  of  the  walls  of  the  vessels  which  prevents  this 
influence  from  operating  throughout  the  entire  venous  system.  Although  this  must  be  a 
very  important  element  in  the  production  of  the  circulation  in  the  liver,  the  fact  that  the 
blood  circulates  in  this  organ  in  the  foetus  before  any  movements  of  the  thorax  take 
place  shows  that  it  is  not  absolutely  essential.  All  the  influences  which  we  have  thus 
far  considered  are  merely  supplementary  to  the  action  of  the  great  central  organ  of  the 
circulation, 

A  farther  proof,  if  any  were  needed,  of  the  suction  force  of  inspiration  is  found  in  an 
accident  which  is  not  infrequent  in  surgical  operations  in  the  lower  part  of  the  neck. 
When  the  veins  in  this  situation  are  kept  open  by  a  tumor  or  by  induration  of  the  sur- 
rounding tissues,  an  inspiratory  effort  has  occasionally  been  followed  by  the  entrance  of 
air  into  the  circulation,  an  accident  which  is  liable  to  lead  to  the  gravest  results.  This 
occurs  only  when  a  divided  vein  is  kept  patulous ;  and  the  accident  proves  both  the 
influence  of  inspiration  on  liquids  in  the  veins  near  the  chest  and  its  restriction  to  the 
vessels  in  this  particular  situation  by  the  flaccidity  of  their  walls. 

A  full  discussion  of  the  subject  of  air  in  the  veins,  which  is  of  great  pathological  inter- 
est, does  not  belong  to  physiology.  The  blood  is  capable  of  dissolving  a  certain  quantity 
of  atmospheric  air ;  and  a  small  quantity,  very  gradually  introduced  into  a  vein,  can  be 
disposed  of  in  this  way.  When,  however,  a  considerable  quantity  suddenly  finds  its  way 
into  the  venous  system,  the  patient  experiences  a  sense  of  mortal  distress  and  almost 
immediately  falls  into  a  state  of  insensibility.  A  peculiar  whistling  sound  is  heard  when 
the  air  passes  in ;  and,  if  the  ear  be  applied  to  the  chest,  we  distinguish  the  labored 
efforts  of  the  heart,  accompanied  by  a  loud  churning  sound.  On  opening  the  chest  after 
death,  the  right  cavities  of  the  heart  are  invariably  found  distended  with  air  and  blood, 
the  blood  being  frothy  and  florid.  Generally  the  left  side  of  the  heart  is  nearly  or  quite 
empty. 

The  production  of  death  from  air  in  the  veins  is  purely  mechanical.  The  air,  finding 
its  way  to  the  right  ventricle,  is  mixed  with  the  blood  in  the  form  of  minute  bubbles  and 
is  carried  into  the  pulmonary  artery.  Once  in  this  vessel,  it  is  impossible  for  it  to  pass 
through  the  capillaries  of  the  lungs,  and  death  by  suffocation  is  the  inevitable  result,  if 
the  quantity  of  air  be  large.  It  is  because  no  blood  can  pass  through  the  lungs,  that  the 
left  cavities  of  the  heart  are  usually  found  empty. 

Air  injected  into  the  arteries  produces  no  such  serious  effects  as  air  in  the  veins.  It 
is  arrested  in  the  capillaries  of  certain  parts  and  in  the  course  of  time  is  absorbed  with- 
out producing  any  injury. 

Aside  from  the  pressure  exerted  by  the  contraction  of  muscles  and  the  force  of  as- 
piration from  the  thorax,  the  influences  which  assist  the  venous  circulation  are  very 
slight.  As  far  as  the  action  of  the  coats  of  the  vessels  themselves  is  concerned,  their 
contraction,  it  must  be  remembered,  is  slow  and  gradual,  like  the  contraction  of  the 
arteries  ;  and  it  is  hardly  possible  that,  in  the  general  venous  system,  this  should  operate  at 
all  on  the  blood-current,  beyond  the  simple  influence  of  the  reduction  of  the  caliber  of 
the  vessel.  There  is  a  slight  contraction  in  the  venaa  cava3  in  the  immediate  proximity 
of  the  heart,  which  is  very  much  more  extended  in  many  of  the  lower  vertebrate  ani- 
mals and  may  be  mentioned  as  having  an  influence,  very  insignificant  it  is  true,  on  the 
flow  of  blood  from  the  great  veins. 

In  the  veins  which  pass  from  above  downward,  the  force  of  gravity  favors  the  flow 
of  blood.  This  is  seen  by  the  turgescence  of  the  veins  of  the  neck  and  face,  when 
the  head  is  kept  for  a  short  time  below  the  level  of  the  heart.  If  the  arm  be  elevated 
above  the  head,  the  veins  of  the  back  of  the  hand  will  be  much  reduced  in  size,  from  the 
greater  facility  with  which  the  blood  passes  to  the  heart,  while  they  are  distended  when 
the  hand  is  allowed  to  hang  by  the  side  and  the  blood  has  to  mount  up  against  the  force 
of  gravity. 


104  CIRCULATION   OF  THE  BLOOD. 

In  the  extreme  irregularity  in  the  rapidity  of  the  circulation  in  different  veins,  it 
must  frequently  happen  that  a  vessel  empties  its  blood  into  another  of  larger  size,  in 
which  the  current  is  more  rapid.  In  such  an  instance,  as  a  physical  necessity,  the  more 
rapid  current  in  the  larger  vessel  exerts  a  certain  suction  force  on  the  fluid  in  the  vessel 
which  joins  with  it. 

Function  of  the  Valves  of  the  Veins. 

It  is  difficult  to  comprehend,  at  the  present  day,  how  any  anatomist  could  have  accu- 
rately described  the  valves  of  the  veins  and  yet  have  been  ignorant  of  their  function ;  and 
the  fact  that  their  use  was  not  understood  before  the  description  of  the  circulation  by  Har- 
vey shows  the  greatness  of  this  as  a  discovery  and  the  shallow  character  of  any  pretence 
that  men  of  science  had  any  definite  idea  of  the  motion  of  the  blood  before  his  time. 

With  our  present  knowledge  of  the  course  of  the  blood,  it  is  evident  that  the  great 
function  of  the  valves  is  to  present  an  obstacle  to  the  reflux  of  blood  toward  the 
capillary  system ;  and  it  only  remains  to  study  the  conditions  under  which  they  are 
brought  into  action. 

There  are  two  distinct  conditions  under  which  the  valves  of  the  veins  may  be  closed. 
One  of  them  is  the  arrest  of  circulation,  from  any  cause,  in  veins  in  which  the  blood  has 
to  mount  against  the  force  of  gravity ;  and  the  other,  compression  of  veins,  from  any 
cause  (generally  from  muscular  contraction)  which  tends  to  force  the  blood  from  the 
vessels  compressed  into  others,  when  the  valves  offer  an  obstruction  to  a  flow  toward  the 
capillaries  and  necessitate  a  current  in  the  direction  of  the  heart.  In  the  first  of  these 
conditions,  the  valves  are  antagonistic  to  the  force  of  gravity,  and,  when  the  caliber  of 
any  vessel  is  temporarily  obliterated,  they  aid  in  directing  the  current  into  anastomotic 
vessels.  It  is  but  rarely,  however,  that  they  act  thus  in  opposition  to  the  force  of  grav- 
ity ;  and  it  is  only  when  many  of  the  veins  of  a  part  are  simultaneously  compressed  that 
they  aid  in  diverting  the  current.  "When  a  single  vein  is  obstructed,  it  is  not  probable 
that  the  valves  are  necessary  to  divert  the  current  into  other  vessels,  for  this  would  take 
place  in  obedience  to  the  ms  a  tergo  ;  but  when  many  veins  are  obstructed  in  a  depend- 
ent part,  and  the  avenues  to  the  heart  become  insufficient,  the  numerous  valves  divide 
the  columns  of  blood,  so  that  the  pressure  is  equally  distributed  throughout  the  extent 
of  the  vessels.  For,  it  must  be  remembered,  the  strength  of  the  walls  diminishes  as 
we  pass  from  the  larger  veins  to  the  periphery,  and  the  smallest  vessels,  which,  were 
it  not  for  the  valves,  would  be  subjected  to  the  greatest  amount  of  pressure,  are  least 
calculated  to  bear  distention.  This  is  but  an  occasional  function  which  the  valves  are 
called  upon  to  perform ;  and  it  is  evident  that  their  influence  is  only  to  prevent  the 
weight  of  the  entire  column  of  blood,  in  vessels  thus  obstructed,  from  operating  on  the 
smallest  veins  and  the  capillaries.  It  cannot  make  the  labor  of  the  heart,  when  the 
blood  is  again  put  in  motion,  any  less  than  if  the  column  were  undivided,  as  this  organ 
must  have  sufficient  power  to  open  successively  each  set  of  valves,  when,  of  course, 
they  cease  to  have  any  influence  whatsoever. 

It  is  in  connection  with  the  intermittent  compression  of  the  veins  that  the  valves 
have  their  principal  and  almost- constant  function.  Their  situation  alone  would  lead  to 
this  supposition.  They  are  found  in  greatest  numbers  throughout  the  muscular  system, 
having  been  demonstrated  by  Sappey  in  the  smallest  venules  ;  they  are  also  found  in  the 
upper  parts  of  the  body,  where  they  certainly  do  not  operate  against  the  force  of  gravity ; 
while  they  do  not  exist  in  the  cavities,  where  the  venous  trunks  are  not  subject  to  com- 
pression. It  has  already  been  made  sufficiently  evident  that  the  action  of  muscles  sec- 
onds most  powerfully  the  contractions  of  the  heart.  The  vis  a  tergo  from  the  heart  is, 
doubtless,  generally  sufficient  to  turn  this  influence  of  muscular  compression  from  the 
capillary  system,  and  the  valves  of  the  veins  are  open ;  but  they  stand  ready,  neverthe- 
less, to  oppose  any  tendency  to  regurgitation. 

In  the  action  of  muscles,  the  skin  is  frequently  stretched  over  the  part,  and  the  cuta- 


CONDITIONS   WHICH  IMPEDE  THE  VENOUS   CIRCULATION.        105 

neous  veins  are  somewhat  compressed.  This  may  be  seen  in  the  hand,  by  letting  it  hang 
by  the  side  until  the  veins  become  somewhat  swollen,  and  then  contracting  the  muscles, 
when  the  skin  will  become  tense  and  the  veins  are  very  much  less  prominent.  Here  the 
valves  have  an  important  action.  The  compression  of  the  veins  is  much  greater  in  the 
substance  of  and  between  the  muscles  than  in  the  skin ;  but  the  blood  is  forced  from  the 
muscles  into  the  skin,  and  the  valves  act  to  prevent  it  from  taking  a  retrograde  course. 
The  fact  that  the  contraction  of  muscles  forces  blood  into  the  veins  of  the  skin  may  be 
seen  by  surrounding  the  upper  part  of  the  forearm  with  a  moderately-tight  ligature, 
which  will  distend  the  cutaneous  veins  below.  If  we  now  contract  the  muscles  vigor- 
ously, the  veins  below  will  become  sensibly  more  distended  and  knotted ;  showing,  at 
once,  the  passage  of  blood  into  the  skin  and  the  action  of  the  valves. 

When  a  vein  is  distended  by  the  injection  of  air  or  a  liquid  forced  against  the  valves, 
it  is  observed  that,  at  the  point  where  the  convex  borders  of  the  valves  are  attached,  the 
vessel  is  not  dilated  as  much  as  at  other  parts.  This  is  due  to  the  fact  that  the  valves 
are  bordered  with  a  fibrous  ring  which  strengthens  the  vessel  and  prevents  distention 
at  that  point,  which  would  otherwise  separate  the  free  borders  of  the  valves  and  render 
them  insufficient. 

A  full  consideration  of  the  venous  anastomoses  belongs  to  descriptive  anatomy. 
Suffice  it  to  say,  in  this  connection,  that  they  are  very  numerous  and  provide  for  a 
return  of  the  blood  to  the  heart  by  a  number  of  channels.  The  azygos  vein,  the  veins 
of  the  spinal  canal,  and  veins  in  the  walls  of  the  abdomen  and  thorax,  connect  the  infe- 
rior with  the  superior  vena  cava.  Even  the  portal  vein  has  lately  been  shown  to  have 
its  communications  with  the  general  venous  system.  Thus,  in  all  parts  of  the  organism, 
temporary  compression  of  a  vein  only  diverts  the  current  into  some  other  vessel,  and 
permanent  obliteration  of  a  vein  produces  enlargement  of  communicating  branches,  which 
soon  become  sufficient  to  meet  all  the  requirements  of  the  circulation. 

Conditions  which  impede  the  Venous  Circulation. 

Influence  of  Expiration. — The  influence  of  expiration  on  the  circulation  in  the  veins 
near  the  thorax  is  directly  opposed  to  that  of  inspiration.  As  the  act  of  inspiration  has 
a  tendency  to  draw  the  blood  from  these  vessels  into  the  chest,  the  act  of  expiration 
assists  in  forcing  the  blood  out  from  the  vessels  of  the  thorax  and  opposes  a  flow  in 
the  opposite  direction.  The  effect  of  prolonged  and  violent  expiratory  efforts  is  very 
marked,  being  followed  by  deep  congestion  of  the  veins  of  the  face  and  neck  and  a  sense 
of  fulness  in  the  head,  which  may  become  very  distressing.  The  opposition  to  the  venous 
current  generally  extends  only  to  vessels  in  the  immediate  vicinity  of  the  thorax,  or,  it 
may  be  stated  in  general  terms,  to  those  veins  in  which  the  flow  of  blood  is  assisted  by 
the  movements  of  inspiration ;  but,  while  the  inspiratory  influence  is  absolutely  confined 
to  a  very  restricted  circuit  of  vessels,  the  obstructive  influence  of  very  violent  and  pro- 
longed expiration  may  be  extended  very  much  farther,  as  is  seen  when  the  vessels  of  the 
neck,  face,  and  conjunctiva  become  congested  in  prolonged  vocal  efforts,  blowing,  etc. 
The  mechanism  of  this  is  not  what  we  might  at  first  be  led  to  suppose;  namely,  a 
mere  reflux  from  the  large  trunks  of  the  thoracic  cavity.  Were  this  the  case,  it  would 
be  necessary  to  assume  an  insufficiency  of  certain  valves,  which  does  not  exist.  In 
extreme  congestion,  reflux  of  blood  may  take  place  to  a  certain  extent  in  the  external 
jugular,  for  this  vessel  has  but  two  valves,  which  are  not  competent  to  prevent  regurgi- 
tation ;  the  chief  cause  of  congestion,  however,  is  due,  not  to  regurgitation,  but  to  accumu- 
lation from  the  periphery  and  an  obstruction  to  the  flow  of  blood  into  the  great  vessels. 

It  is  in  the  internal  jugular  that  the  influence  of  expiration  is  most  important,  both 
from  its  great  size  in  the  human  subject,  as  compared  with  the  other  vessels,  and  from 
the  importance  and  delicacy  of  the  parts  from  which  it  collects  the  blood.  At  the  open- 
ing of  this  vessel  into  the  innominate  vein,  is  a  pair  of  strong  and  perfect  valves,  which 
effectually  close  the  orifice  when  there  is  a  tendency  to  regurgitation.  These  valves  have 


106  CIRCULATION   OF  THE  BLOOD. 

attracted  much  attention  among  physiologists  since  the  discovery  of  the  circulation  has 
made  it  evident  how  important  they  may  be  in  protecting  the  brain  from  reflux  of 
blood.  When  the  act  of  expiration  arrests  the  onward  flow  in  the  veins  near  the  thorax, 
these  valves  are  closed  and  effectually  protect  the  brain  from  congestion  by  regurgita- 
tion.  The  blood  accumulates  behind  the  valves,  but  the  free  communication  of  the  inter- 
nal jugular  with  the  other  veins  of  the  neck  relieves  the  brain  from  congestion,  unless 
the  effort  be  extraordinarily  violent  and  prolonged. 

The  above  remarks  with  regard  to  the  influence  of  expiration  are  applicable  to  vocal 
efforts,  violent  coughing  or  sneezing,  or  any  unusual  muscular  efforts,  such  as  straining,  in 
which  the  glottis  is  closed. 

Eegurgitant  Venom  Pulse.— In  the  inferior  animals,  like  the  dog,  if  the  external 
jugular  be  exposed,  a  distention  of  the  vessel  is  seen  to  accompany  each  expiratory  act. 
This  is  sometimes  observed  in  the  human  subject,  when  respiration  is  exaggerated,  and 
has  been  called  improperly  the  venous  pulse.  There  is  no  sufficient  obstacle  to  the  regur- 
gitation  of  blood  from  the  thorax  into  the  external  jugular,  and  distinct  pulsations,  syn- 
chronous with  the  movements  of  respiration,  may  be  produced  in  this  way. 

It  is  evident  that  there  are  various  other  circumstances  which  may  impede  the  venous 
circulation.  Accidental  compression  may  temporarily  arrest  the  flow  in  any  particular 
vein.  When  the  whole  volume  of  blood  is  materially  increased,  as  after  a  full  meal  with 
copious  ingestion  of  liquids,  the  additional  quantity  of  blood  accumulates  chiefly  in  the 
venous  system  and  proportionately  diminishes  the  rapidity  of  the  venous  circulation. 

The  force  of  gravity  also  has  an  important  influence.  It  is  much  more  difficult  for  the 
blood  to  mount  from  below  upward  to  the  heart  than  to  flow  downward  from  the  head 
and  neck.  The  action  of  this  is  seen  if  comparison  be  made  between  the  circulation  in 
the  arm  elevated  above  the  head  and  hanging  by  the  side.  In  the  one  case  the  veins  are 
readily  emptied  and  contain  but  little  blood,  and  in  the  other  the  circulation  is  more 
difficult  and  the  vessels  are  moderately  distended.  The  walls  of  the  veins  are  thickest 
apd  the  valves  are  most  numerous  in  parts  of  the  body  which  are  habitually  dependent. 
The  influence  of  gravity  is  exemplified  in  the  production  of  varicose  veins  in  the  lower 
extremities.  This  disease  is  frequently  induced  by  occupations  which  require  constant 
standing;  but  the  exercise  of  walking,  aiding  the  venous  circulation,  as  it  does,  by  the 
muscular  effort,  has  no  such  tendency. 

Circulation  in  the  Cranial  Cavity. — In  the  encephalic  cavity,  there  are  certain  pecu- 
liarities in  the  anatomy  of  some  of  the  vessels,  with  exceptional  conditions  of  the  blood 
as  regards  atmospheric  pressure,  which  have  been  considered  capable  of  essentially  modi- 
fying the  circulation.  In  the  adult,  the  cranium  is  a  closed,  air-tight  box,  containing  the 
incompressible  cerebral  substance,  and  blood ;  conditions  which  are  widely  different  from 
those  presented  in  other  parts  of  the  system.  On  this  account  some  have  gone  so  far  as 
to  consider  that  any  change  in  the  quantity  of  circulating  fluid  in  the  brain  is  a  physical 
impossibility.  Pathological  facts  in  opposition  to  such  a  view  are  so  numerous  and  well 
established  that  the  question  does  not  now  demand  extended  discussion;  but  it  is  never- 
theless true  that  there  are  anatomical  peculiarities  in  these  parts,  the  effects  of  which 
on  the  circulation  present  important  and  interesting  points  for  study. 

In  the  brain,  the  venous  passages  which  correspond  to  the  great  veins  of  other  parts 
are  in  the  form  of  sinuses  between  the  folds  of  the  dura  mater  and  are  but  slightly 
dilatable.  In  the  perfectly-consolidated  adult  head,  the  blood  is  not  subjected  to 
atmospheric  pressure,  as  in  other  parts,  and  the  semisolids  and  liquids  which  com- 
pose the  encephalic  mass  cannot  increase  in  size  in  congestion  and  diminish  in  anae- 
mia. Notwithstanding  these  conditions,  the  fact  remains,  that  examinations  of  the 
vessels  of  the  brain  after  death  show  great  differences  in  the  quantity  of  blood  which 


CIRCULATION  IX  THE   CRANIAL  CAVITY.  107 

they  contain.  The  question  then  arises  as  to  what  is  displaced  to  make  room  for 
the  blood  in  congestion,  and  what  supplies  the  place  of  the  blood  in  anaemia.  An 
anatomical  peculiarity,  which  has  not  yet  been  considered,  offers  an  explanation  of 
these  phenomena.  Magendie  has  shown,  by  observations  on  living  animals,  confirmed 
by  dissections  of  the  human  body,  that  between  the  pia  mater  and  the  arachnoid  of  the 
brain  and  spinal  cord  there  exists  a  liquid,  the  cephalo-rachidian  fluid,  which  is  capable 
of  passing  from  the  surface  of  the  brain  to  the  spinal  canal  and  communicates  with  the 
fluid  in  the  ventricles.  This  he  has  conclusively  demonstrated  to  be  situated,  not 
between  the  layers  of  the  arachnoid,  as  was  supposed  by  Bichat,  but  between  the  inner 
layer  of  this  membrane  and  the  pia  mater.  The  communication  between  the  cranial 
cavity  and  the  spinal  canal  is  very  free.  This  has  been  demonstrated  by  exposing  the  dura 
mater  of  the  brain  and  of  the  cord,  making  an  opening  in  the  membranes  of  the  cord  so 
as  to  allow  the  liquid  to  escape  (which  it  does  in  quite  a  forcible  jet),  when  pressure  on  the 
membranes  of  the  brain  not  only  accelerated  the  flow  but  pressed  out  a  quantity  of  the  liquid 
after  all  that  would  escape  spontaneously  had  been  evacuated.  It  is  easy  to  see  one  of 
the  physiological  uses  of  this  liquid.  When  the  pressure  of  blood  in  the  arteries  leading 
to  the  brain  is  increased  or  when  there  is  an  obstacle  to  its  return  by  the  veins,  more  or 
less  congestion  takes  place,  and  the  blood  forces  the  liquid  from  the  cranial  into  the  spinal 
cavity ;  the  reverse  taking  place  when  the  supply  of  blood  to  the  brain  is  diminished. 
The  functions  of  all  highly-organized  and  vascular  parts  seem  to  require  certain  varia- 
tions in  the  supply  of  blood ;  and  there  is  no  reason  to  suppose  that  the  brain,  in  its 
varied  conditions  of  activity  and  repose,  is  any  exception  to  this  general  rule,  although 
the  physiological  conditions  of  its  vascularity  are  not  easily  studied. 

Physiologists,  even  before  the  time  of  Haller,  had  noticed  alternate  movements  of 
expansion  and  contraction  in  the  brain,  connected  with  the  acts  of  respiration.  This  is 
observed  in  children  before  the  fontanels  are  closed,  and  in  the  adult  when  the  brain  is 
exposed  by  an  injury  or  a  surgical  operation.  The  movements  are,  an  expansion  with  the 
act  of  expiration,  which,  in  violent  efforts,  is  sometimes  so  considerable  as  to  produce 
protrusion,  and  contraction  with  inspiration.  Magendie  also  studied  these  movements, 
which  he  explained  in  the  following  way :  With  the  act  of  expiration,  the  flow  of  blood 
in  the  arteries  is  favored,  and  the  current  in  the  veins  is  retarded.  If  the  effort  be 
violent,  the  valve  at  the  opening  of  the  internal  jugular  may  be  closed.  This  act  would 
produce  an  expansion  of  the  brain,  not  from  reflux  by  the  veins,  but  from  the  fact  that 
the  flow  into  the  chest  is  impeded,  and  the  blood,  while  passing  in  more  freely  by  the 
arteries,  is  momentarily  confined.  With  inspiration,  the  flow  into  the  thorax  is  mate- 
rially aided,  and  the  brain  is  in  some  degree  relieved  of  this  expanding  force. 

Robin,  His,  and  others  have  noted  a  peculiarity  in  the  small  vessels  of  the  brain, 
spinal  cord,  and  pia  mater,  which  is  curious,  but  the  physiological  significance  of  which  is 
not  yet  apparent.  These  vessels  are  surrounded  by  a  thin,  amorphous  sheath,  which  has 
a  diameter  of  from  y^j-  to  -^^  of  an  inch  greater  than  that  of  the  vessel  itself.  Be- 
tween this  and  the  blood-vessel  is  a  transparent  liquid.  This  structure,  which  has  been 
observed  in  no  other  part  of  the  circulatory  system,  is  regarded  by  Robin  as  the  com- 
mencement of  the  lymphatics  of  the  nervous  centres.  What  effect  this  disposition  of 
the  vessels  may  have  upon  the  facility  with  which  they  may  become  dilated  or  contracted, 
it  is  difficult  to  determine. 

Circulation  in  Erectile  Tissues.— In  the  organs  of  generation  of  both  sexes,  there 
exists  a  tissue  which  is  subject  to  great  increase  in  volume  and  rigidity  when  in  a  state 
of  what  is  called  erection.  The  parts  in  which  the  erectile  tissue  exists  are,  in  the  male, 
the  corpora  cavernosa  of  the  penis,  the  corpora  spongiosa,  with  the  glans  penis;  and,  in 
the  female,  the  corpora  cavernosa  of  the  clitoris,  the  gland  of  the  clitoris,  and  the  bulb 
of  the  vestibule.  In  addition,  Rouget  has  lately  demonstrated  the  presence  of  a  struct- 
ure analogous  to  erectile  tissue  in  the  body  of  the  uterus  and  in  a  bulb  annexed  to  the 


108  CIRCULATION  OF  THE  BLOOD. 

ovary  of  the  human  female.  He  has  shown  by  injections  that  the  uterus  is  capable  of 
erection  like  the  penis.  In  some  other  parts,  such  as  the  nipple  and  the  mucous  mem- 
brane of  the  vagina,  which  are  sometimes  described  as  erectile,  the  peculiar  vascular 
arrangement  which  is  characteristic  of  true  erectile  tissues  is  not  found.  In  the  nipple, 
the  hardness  which  follows  gentle  stimulation  is  simply  the  result  of  contraction  of  the 
smooth  muscular  fibres  with  which  this  part  is  largely  supplied,  and  it  is  analogous  to  the 
elevation  of  the  follicles  of  the  skin  from  the  same  cause,  in  what  is  called  goose-flesh. 
In  the  vagina,  congestion  may  occur,  as  in  other  mucous  membranes,  but  there  is  no 
proper  erection. 

The  vascular  arrangement  in  erectile  organs,  of  which  the  penis  may  be  taken  as  the 
type,  is  peculiar  to  them  and  is  not  found  in  any  other  part  of  the  circulatory  system. 
Taking  the  penis  as  an  example,  the  arteries,  which  have  an  unusually-thick  muscular 
coat,  after  they  have  entered  the  organ,  do  not  simply  branch  and  divide  dichotomously, 
as  in  most  other  parts,  but  send  off  large  numbers  of  arborescent  branches,  which  imme- 
diately become  tortuous  and  are  distributed  in  the  cavernous  and  spongy  bodies  in  nu- 
merous anastomosing  vessels,  with  but  a  single  thin,  homogeneous  coat,  like  the  true 
capillaries.  These  vessels  are  larger,  even,  than  the  arterioles  which  supply  them  with 
blood,  some  having  a  diameter  of  from  oV  to  T4T  of  an  inch.  The  cavernous  bodies  have 
an  external  investment  of  strong  fibrous  tissue  of  considerable  elasticity,  which  sends 
bands,  or  trabeculse,  into  the  interior,  by  which  it  is  divided  up  into  cells.  The  trabeculse 
are  composed  of  fibrous  tissue  mixed  with  a  large  number  of  smooth  muscular  fibres. 
These  cells  lodge  the  blood-vessels,  which  ramify  in  the  tortuous  manner  already  indicated 
and  finally  terminate  in  the  veins.  The  anatomy  of  the  corpora  spongiosa  is  essentially 
the  same,  the  only  difference  being  that  the  fibrous  envelope  and  the  trabeculse  are  more 
delicate  and  the  cells  are  of  smaller  size. 

Without  going  fully  into  the  mechanism  of  erection,  which  comes  more  properly 
under  the  head  of  generation,  it  may  be  stated  in  general  terms  that,  during  sexual 
excitement,  or  when  erection  occurs  from  any  cause,  the  thick  muscular  walls  of  the 
arteries  of  supply  relax  and  allow  the  arterial  pressure  to  distend  the  capacious  vessels 
lodged  in  the  cells  of  the  cavernous  and  spongy  bodies.  This  produces  the  characteristic 
change  in  the  volume  and  position  of  the  organ.  It  is  evident  that  erection  depends  upon 
the  peculiar  arrangement  of  the  blood-vessels,  and  is  not  simply  a  congestion,  such  as 
could  occur  in  any  vascular  part.  During  erection,  there  is  not  a  stasis  of  blood ;  but, 
if  it  continue  for  any  length  of  time,  the  quantity  which  passes  out  pf  the  part  by  the 
veins  must  be  equal  to  that  which  passes  in  by  the  arteries. 

Derivative  Circulation. — In  some  parts  of  the  circulatory  system,  there  exists  a  di- 
rect communication  between  the  arteries  and  the  veins,  so  that  all  the  blood  does  not 
necessarily  pass  through  the  minute  vessels  which  have  been  described  as  true  capilla- 
ries. This  peculiarity,  which  had  been  noted  by  Todd  and  Bowman,  Paget,  and  others, 
has  been  closely  studied  by  M.  Sucquet,  who  was  first  led  to  investigate  the  subject  by 
noticing  that  by  injecting  a  very  small  quantity  of  fluid,  entirely  insufficient  to  fill  all 
the  capillaries  of  a  member,  it  was  returned  by  certain  of  the  veins.  On  using  a  black, 
solidifiable  injection,  he  found  that  there  were  certain  parts  of  the  upper  and  lower  ex- 
tremities and  the  head  which  became  colored  by  the  injection,  while  other  parts  were 
not  penetrated.  Following  this  out  by  dissection,  he  showed  that,  in  the  upper  extrem- 
ity, the  skin  of  the  fingers  and  part  of  the  palm  of  the  hand  and  the  skin  over  the  ole- 
cranon  are  provided  with  vessels  of  considerable  size,  which  allowed  the  fluid  injected  by 
the  axillary  artery  to  pass  directly  into  some  of  the  veins,  while  in  other  parts  the  veins 
were  entirely  empty.  Extending  his  researches  to  the  lower  extremity,  he  found  analo- 
gous communications  between  the  vessels  in  the  knee,  toes,  and  parts  of  the  sole  of  the 
foot.  He  also  found  communications  in  the  nose,  cheeks,  lips,  forehead,  and  ends  of  the 
ears,  parts  which  are  particularly  liable  to  changes  in  color  from  congestion  of  vessels. 


PULMONARY   CIRCULATION.  100 

It  is  evident  that,  under  certain  circumstances,  a  larger  quantity  of  blood  than  usual 
may  pass  through  these  parts  without  'necessarily  penetrating  the  true  capillaries  and 
thus  exerting  a  modifying  influence  upon  nutrition.  The  changes  which  are  liable  to  oc- 
cur in  the  quantity  of  blood,  in  the  force  of  the  heart's  action,  etc.,  may  thus  take  place 
without  disturbing  the  circulation  in  the  capillaries,  a  provision  which  the  functions  of 
the  parts  would  seem  to  demand. 

Pulmonary  Circulation. — The  vascular  system  of  the  lungs  merits  the  name,  which 
is  frequently  applied  to  it,  of  the  lesser  circulation.  The  right  side  of  the  heart  acts 
simultaneously  with  the  left,  but  is  entirely  distinct  from  it,  and  its  muscular  walls  are 
very  much  less  powerful.  The  pulmonary  artery  has  thinner  and  more  distensible  coats 
than  the  aorta  and  distributes  its  blood  to  a  single  system  of  capillaries,  situated  very 
near  the  heart.  We  have  seen  that  the  orifice  of  the  pulmonary  artery  is  provided  with 
valves  which  prevent  regurgitation  into  the  ventricle.  In  the  substance  of  the  lungs, 
the  pulmonary  artery  is  broken  up  into  capillaries,  most  of  them  just  large  enough  to 
allow  the  passage  of  the  blood-corpuscles  in  a  single  row.  These  vessels  are  provided 
with  a  single  coat  and  form  a  very  close  net-work  surrounding  the  air-cells.  From  the 
capillaries  the  blood  is  collected  by  the  pulmonary  veins  and  conveyed  to  the  left  auri- 
cle. There  is  no  great  disparity  between  the  arteries  and  veins  of  the  pulmonary  system 
as  regards  capacity.  The  pulmonary  veins  in  the  human  subject  are  not  provided  with 
valves. 

The  blood  in  its  passage  through  the  lungs  does  not  meet  with  the  resistance  which 
is  presented  in  the  systemic  circulation.  This  fact  we  have  often  noticed  in  injecting 
defibrinated  blood  through  the  lungs  of  an  animal  just  killed.  We  have  also  observed 
that  an  injection  passes  through  the  lungs  as  easily  when  they  are  collapsed  as  when  they 
are  inflated.  The  anatomy  of  the  circulatory  system  in  the  lungs  and  of  the  right  side 
of  the  heart  shows  that  the  blood  must  pass  through  these  organs  with  comparative  fa- 
cility. The  power  of  the  right  ventricle  is  evidently  less  than  half  that  of  the  left,  and 
the  pulmonary  artery  will  sustain  a  much  less  pressure  than  the  aorta. 

The  two  sides  of  the  heart  act  simultaneously  ;  and  at  the  same  time  that  the  blood 
is  sent  by  the  left  ventricle  to  the  system  it  is  sent  by  the  right  ventricle  to  the  lungs. 
Some  physiologists  have  endeavored  to  measure  the  pressure  of  blood  in  the  pulmonary 
artery.  The  only  experiments  which  have  not  involved  opening  the  thoracic  cavity,  an 
operation  which  must  interfere  materially  with  the  pressure  of  blood  in  the  pulmonary 
artery,  as  it  does  with  the  general  arterial  pressure,  are  those  of  Chauveau  and  Faivre. 
These  observers  measured  the  pressure  by  connecting  a  cardiometer  with  a  trocar  intro- 
duced into  the  pulmonary  artery  of  a  living  horse  through  one  of  the  intercostal  spaces, 
and  found  it  to  be  about  one-third  as  great  as  the  pressure  in  the  aorta ;  an  estimate 
which  corresponds  pretty  nearly  with  the  comparative  power  of  the  two  ventricles,  as 
deduced  from  the  thickness  of  their  muscular  walls. 

Anatomy  teaches  us  that  the  capillaries  of  the  lungs  have  exceedingly  delicate  walls; 
and  it  is  evident  that  rupture  of  these  vessels  from  excessive  action  of  the  heart  would 
lead  to  grave  results.  It  has  already  been  noted  that  on  the  right  side  the  lungs  are  pro- 
tected by  an  insufficiency  of  the  auriculo-ventricular  valves,  which  does  not  exist  on  the 
left  side,  allowing  a  certain  degree  of  regurgitation  when  the  heart  is  acting  with  un- 
usual force,  and  thus  relieving,  to  a  certain  extent,  the  pulmonary  system.  This  was 
pointed  out  by  Mr.  King,  of  London,  and  is  called  the  safety-valve  function  of  the  right 
ventricle.  We  have  noticed,  in  the  heart  of  the  ox,  a  similar  difference  between  the 
aortic  and  the  pulmonic  semilunar  valves.  If  these  be  exposed  on  both  sides  by  cutting 
away  portions  of  the  ventricles,  and  if  a  current  of  liquid  be  forced  against  them  through 
the  vessels,  the  aortic  valves  will  be  found  to  entirely  prevent  the  passage  of  the  liquid, 
even  under  very  great  pressure,  while  the  pulmonic  valves  permit  regurgitation  under 
a  comparatively  inconsiderable  force.  A  little  reflection  will  make  it  evident  that, 


110  CIRCULATION  OF  THE   BLOOD. 

when  the  heart  is  acting  with  undue  vigor,  it  is  quite  as  important  to  relieve  the  lungs 
by  a  certain  amount  of  regurgitation  from  the  pulmonary  artery  as  by  insufficiency  of 
the  tricuspid  valves.  This  insufficiency  is  important,  both  at  the  auriculo-ventricular 
and  the  pulmonic  orifices,  in  protecting  the  delicate  structure  of  the  lungs  from  the  varia- 
tions in  force  to  which  the  action  of  both  ventricles  is  constantly  liable. 

On  microscopical  examination  of  the  circulation  in  the  lower  animals,  as  the  frog,  the 
movement  of  blood  in  the  capillaries  of  the  lungs  does  not  present  any  differences  from 
the  capillary  circulation  in  other  parts,  except  that  the  vessels  seem  more  crowded  with 
corpuscles  and  there  is  no  "  still  layer  "  next  their  walls. 

There  are  no  forces  of  any  importance  which  are  superadded  to  the  action  of  the 
right  ventricle  in  the  production  of  the  arterial,  capillary,  or  venous  circulation  in  the 
lungs ;  but  there  are  certain  conditions  which  may  obstruct  the  flow  of  blood  through 
these  parts.  "We  have  already  noted  the  effect  of  introduction  of  air  into  the  veins  in 
blocking  up  the  capillaries  of  the  lungs  and  preventing  the  passage  of  blood.  It  is  a  view 
pretty  generally  entertained  that  in  asphyxia  the  non-aeration  of  the  blood  obstructs  the 
pulmonary  circulation.  We  have  already  considered  this  subject  rather  fully  in  treating 
of  the  general  effects  of  arrest  of  respiration  on  the  circulation.  The  celebrated  experi- 
ments of  Bichat  demonstrated  the  passage  of  black  blood  through  the  lungs  in  asphyxia 
and  its  presence  in  the  arterial  system.  The  experiments  of  Dalton  and  others  have 
shown  that,  in  this  condition,  the  obstruction  to  the  circulation  occurs  first  in  the  sys- 
temic capillaries,  and  the  distention  is  propagated  backward  through  the  great  vessels 
and  the  left  cavities  of  the  heart  to  the  right  side.  When  the  heart  is  exposed  in  a  living 
animal  and  artificial  respiration  is  kept  up,  temporary  arrest  of  the  respiration  produces 
engorgement  and  labored  action  of  both  ventricles.  There  are  no  observations  which  show 
that  increase  of  pressure  in  the  pulmonary  artery  is  the  first  and  the  immediate  result 
of  asphyxia.  It  is  true  that,  after  death,  the  right  side  of  the  heart  is  engorged  ;  but  it 
is  well  known,  from  observations  after  death  and  experiments  on  living  animals,  that  the 
tonic  contraction  of  the  arteries  is  competent  to  empty  the  blood  into  the  veins ;  and 
the  facts  just  stated  regarding  the  insufficiency  of  the  pulmonic  semilunar  valves  explain 
how  the  right  side  of  the  heart  may  become  engorged  as  the  result  of  obstruction  to  the 
blood-current  in  the  left  side.  Established  facts  seem  to  show  that  asphyxia  does  not 
primarily  affect  the  pulmonary  circulation,  but  that  it  is  possible  for  venous  blood  to 
pass  through  the  lungs  without  undergoing  arterialization. 

Circulation  in  the  Walls  of  the  Heart. — The  fact  that  the  contractions  of  the  muscu- 
lar walls  of  the  heart,  by  which  the  blood  is  discharged  from  the  ventricles  into  the 
great  arteries,  necessarily  compress  the  vessels  in  the  substance  of  the  heart  itself 
would  lead  us  to  expect  certain  peculiarities  in  the  cardiac  circulation.  This  question  has 
been  lately  studied  by  Lannelongue,  who  has  arrived  at  the  following  results  : 

During  the  ventricular  systole,  which  discharges  the  blood  into  the  aorta,  the  vessels 
in  the  substance  of  the  ventricles  are  nearly  empty,  and  the  vessels  in  the  auricular  walls 
are  filled.  During  the  auricular  systole,  the  auricular  vessels  are  empty  and  the  ventricu- 
lar vessels  are  filled.  We  can  readily  understand  this  when  we  reflect  that  the  vessels 
in  the  substance  of  the  heart  must  be  compressed  when  the  muscular  fibres  contract. 

General  Rapidity  of  the  Circulation. 

Several  questions  of  considerable  physiological  interest  arise  in  connection  with  the 
general  rapidity  of  the  circulation  : 

1.  It  would  be  interesting  to  determine,  if  possible,  what  length  of  time  is  occupied 
by  the  blood  in  its  passage  through  the  entire  circuit  of  both  the  lesser  and  the  greater 
circulation. 

2.  What  is  the  time  required  for  the  passage  of  the  entire  mass  of  blood  through  the 
heart  ? 


GENERAL  RAPIDITY  OF  THE  CIRCULATION.  HI 

3.  "What  influence  has  the  number  of  pulsations  of  the  heart  on  the  general  rapidity 
of  the  circulation  ? 

The  first  of  these  questions  is  the  one  which  has  been  most  satisfactorily  answered  by 
experiments  on  living  animals.  In  1827,  Hering,  a  German  physiologist,  performed  the 
experiment  of  injecting  into  the  jugular  vein  of  a  living  animal  a  harmless  substance, 
which  could  be  easily  recognized  by  its  chemical  reactions,  and  noted  the  time  which 
elapsed  before  it  could  be  detected  in  the  blood  of  the  vein  of  the  opposite  side.  This 
gave  the  first  correct  idea  of  the  rapidity  of  the  circulation ;  for,  although  the  older 
physiologists  had  studied  the  subject,  their  estimates  were  founded  on  calculations  which 
had  no  accurate  basis  and  gave  very  varied  results.  The  experiment  of  Hering  is  often 
roughly  performed  as  a  physiological  demonstration ;  and  we  have  thus  had  frequent  oc- 
casions to  verify,  in  a  general  way,  its  accuracy.  If,  for  example,  we  expose  both  jugu- 
lars in  a  dog,  inject  into  one  a  solution  of  ferrocyanide' of  potassium  in  water,  and  draw 
a  specimen  of  blood  from  the  other  with  as  little  loss  of  time  as  possible,  it  will  be  found 
that,  within  twenty  or  thirty  seconds  after  the  injection,  the  salt  has  had  tune  to  pass 
from  the  jugular  to  the  right  heart,  thence  to  the  lungs  and  left  heart/  and  thence 
through  the  capillaries  of  the  head  and  face  back  to  the  jugular  on  the  opposite  side. 
Its  presence  can  be  determined  by  the  distinct  blue  color  produced  on  the  addition  of 
the  perchloride  of  iron  to  the  serum,  if  the  specimen  be  allowed  to  stand,  or  a  clear  ex- 
tract of  the  blood  may  be  made  by  boiling  with  a  little  sulphate  of  soda  and  filtering, 
treating  the  colorless  liquid  thus  obtained  with  the  salt  of  iron.  In  making  the  test  of 
the  blood-extract  or  serum,  the  addition  of  a  drop  of  nitric  acid  before  the  perchloride  of 
iron  is  added  will  render  the  blue  reaction  much  more  prompt  and  distinct  if  the  ferro- 
cyanide be  present. 

The  experiments  of  Hering  were  evidently  conducted  with  great  care  and  accuracy. 
He  drew  the  blood  at  intervals  of  five  seconds  after  the  commencement  of  the  injection, 
and  thus,  by  repeated  observations,  ascertained  pretty  nearly  the  rapidity  of  a  circuit  of 
blood  in  the  animals  on  which  he  experimented.  Others  have  taken  up  these  investiga- 
tions and  introduced  some  modifications  in  the  manipulations.  Yierordt  collected  the 
blood  as  it  flowed,  in  little  vessels  fixed  on  a  disk  revolving  at  a  known  rate,  which  gave 
more  exactness  to  the  observations  ;  but  this  method  is  essentially  the  same  as  that  em- 
ployed by  Hering,  and  the  results  obtained  by  these  two  observers  nearly  correspond. 

The  length  of  time  occupied  by  a  portion  of  blood  in  making  a  complete  circuit  of 
the  vascular  system,  in  the  human  subject,  is  only  to  be  deduced  from  observations  on 
the  inferior  animals ;  but,  before  this  application  is  made,  it  will  be  well  to  examine  the 
objections,  if  any  exist,  to  the  experimental  procedure  above  described. 

The  only  objection  which  could  be  made  is,  that  a  saline  solution,  introduced  into  the 
torrent  of  the  circulation,  would  have  a  tendency  to  diffuse  itself  throughout  the  whole 
mass  of  blood,  it  might  be,  with  considerable  rapidity.  This  objection  to  the  observa- 
tions of  Hering  has  been  made  by  Matteucci  and  is  considered  by  him  as  fatal  to  their 
accuracy.  It  certainly  is  an  element  which  should  be  taken  into  account ;  but,  from  the 
definite  data  which  have  been  obtained  concerning  the  rapidity  of  the  arterial  circula- 
tion and  the  inferences  which  are  unavoidable  with  regard  to  the  rapidity  of  the  venous 
circulation,  it  would  seem  that  the  saline  solution  must  be  carried  on  by  the  mere  rapid- 
ity of  the  arterial  flow  to  the  capillaries,  which  are  very  short,  taken  up  from  them,  and 
carried  on  by  the  veins,  and  thus  through  the  entire  circuit,  before  it  has  had  time  to 
diffuse  itself  to  any  considerable  extent.  It  is  not  apparent  how  this  objection  can  be 
overcome,  for  a  substance  must  be  used  which  will  mix  with  the  blood,  otherwise  it 
could  not  pass  through  the  capillaries. 

There  seems  no  reason  why,  with  the  above  restrictions,  the  results  obtained  by 
Hering  should  not  be  accepted,  and  their  application  be  made  to  the  human  subject. 

Hering  found  that  the  rapidity  of  the  circulation  in  different  animals  was  in  inverse 
ratio  to  their  size  and  in  direct  ratio  to  the  rapidity  of  the  action  of  the  heart. 


112  CIRCULATION  OF  THE  BLOOD. 

The  following  are  the  mean  results  in  certain  of  the  domestic  animals,  taking  the 
course  from  jugular  to  jugular,  when  the  blood  passes  through  the  lungs  and  through  the 
capillaries  of  the  face  and  head : 

In  the  Horse,  the  circulation  is  accomplished  hi  27'3  seconds. 
"      Dog,  «  "  15-2      " 

"      Goat,  "  "  12-8      " 

"      Rabbit,  "  "  6'9       " 

Applying  these  results  to  the  human  subject,  taking  into  account  the  size  of  the  body 
and  the  rapidity  of  the  heart's  action,  the  duration  of  the  circuit  from  one  jugular  to 
the  other  may  be  estimated  at  21 '4  seconds,  and  the  general  average  through  the  entire 
system,  at  23  seconds.  This  is  simply  approximative ;  but  the  results  in  the  inferior  ani- 
mals may  be  received  as  very  nearly,  if  not  entirely  accurate. 

Estimates  of  the  time  required  for  the  passage  of  the  whole  mass  of  blood  through, 
the  heart  are  even  less  definite  than  the  estimate  of  the  general  rapidity  of  the  circula- 
tion. To  arrive  at  any  satisfactory  result,  it  is  necessary  to  know  the  entire  quantity  of 
blood  in  the  body  and  the  exact  quantity  which  passes  through  the  heart  at  each  pulsa- 
tion. If  we  divide  the  whole  mass  of  blood  by  the  quantity  discharged  from  the  heart 
with  each  ventricular  systole,  we  ascertain  the  number  of  pulsations  required  for  the 
passage  of  the  whole  mass  of  blood  through  the  heart ;  and,  knowing  the  number  of 
beats  per  minute,  we  can  ascertain  the  length  of  time  thus  occupied.  The  objection  to 
this  kind  of  estimate  is  the  inaccuracy  of  the  data  respecting  the  quantity  of  blood  in 
the  system  as  well  as  the  quantity  which  passes  through  the  heart  with  each  pulsation. 
Nevertheless,  an  estimate  can  be  made,  which,  if  it  be  not  entirely  accurate,  cannot  be 
very  far  from  the  truth. 

The  entire  quantity  of  blood,  according  to  estimates  which  seem  to  be  based  on  the 
most  reliable  data,  is  about  one-eighth  the  weight  of  the  body,  or  eighteen  pounds,  in  a 
man  weighing  one  hundred  and  forty-four.  The  quantity  discharged  at  each  ventricular 
systole  is  estimated  by  Valentin  at  five  ounces,  and  by  Volkmann,  at  six  ounces.  In 
treating  of  the  capacity  of  the  different  cavities  of  the  heart,  it  has  been  noted  that  the 
left  ventricle,  when  fully  distended,  contains  from  five  to  seven  ounces.  Assuming  that, 
at  each  systole,  the  left  ventricle  discharges  all  its  blood,  except  perhaps  a  few  drops, 
and  that  this  quantity  in  an  ordinary-sized  man  is  five  ounces  (for  in  the  estimates  of 
Robin  and  Hiffelsheim,  the  cavities  were  fully  distended,  and  contained  more  than  under 
the  ordinary  conditions  of  the  circulation),  it  would  require  fifty-eight  pulsations  for  the 
passage  through  the  heart  of  the  entire  mass  of  blood.  Assuming  the  pulsations  to  be 
seventy-two  per  minute,  this  would  occupy  about  forty-eight  seconds. 

The  almost  instantaneous  action  of  certain  poisons,  which  must  act  through  the  blood, 
confirms  our  ideas  with  regard  to  the  rapidity  of  the  circulation.  The  intervals  between 
the  introduction  of  some  agents,  strychnine  for  example,  into  the  circulation,  and  the 
characteristic  effects  on  the  system,  have  been  carefully  noted  by  Blake,  whose  observa- 
tions coincide  pretty  closely  in  their  results  with  the  experiments  of  Hering. 

The  relation  of  the  rapidity  of  the  circulation  to  the  frequency  of  the  heart's  action  is 
a  question  of  considerable  interest,  which  was  not  neglected  in  the  experiments  of  Hering. 
It  is  evident  that,  if  the  charge  of  blood  sent  into  the  arteries  be  the  same,  or  nearly  the 
same,  under  all  circumstances,  any  increase  in  the  number  of  pulsations  of  the  heart  would 
produce  a  corresponding  acceleration  of  the  general  current  of  blood.  But  this  is  a  propo- 
sition which  cannot  be  taken  for  granted  ;  and  there  are  many  facts  which  favor  a  con- 
trary opinion.  It  may  be  enunciated  as  a  general  rule  that  when  the  acts  of  the  heart 
increase  in  frequency  they  diminish  in  force ;  which  renders  it  probable  that  the  ventricle1 
is  most  completely  distended  and  emptied  when  its  action  is  moderately  slow.  When, 
however,  the  pulse  is  very  much  accelerated,  the  increased  number  of  pulsations  of  the 
heart  might  be  sufficient  to  overbalance  the  diminished  force  of  each  act  and  would  thus 


PHENOMENA  IN   THE   CIRCULATORY   SYSTEM  AFTER  DEATH.       113 

actually  increase  the  rapidity  of  the  circulation.  Hering  has  settled  these  questions  ex- 
perimentally. His  observations  were  made  on  horses,  by  increasing  the  frequency  of 
the  pulse,  on  the  one  hand,  physiologically,  by  exercise,  and  on  the  other  hand,  patho- 
logically, by  inducing  inflammatory  action.  He  found,  in  the  first  instance,  that,  in  a 
horse,  with  the  heart  beating  at  the  rate  of  thirty -six  per  minute,  with  eight  respiratory 
acts,  ferrocyauide  of  potassium  injected  into  the  jugular  appeared  in  the  vessel  on  the 
opposite  side  after  an  interval  of  from  twenty  to  twenty-five  seconds.  By  exercise,  the 
number  of  pulsations  was  raised  to  one  hundred  per  minute,  and  the  rapidity  of  the  cir- 
culation was  from  fifteen  to  twenty  seconds.  The  observations  were  made  with  an 
interval  of  twenty-four  hours.  The  same  results  were  obtained  in  other  experiments. 
Here  there  is  a  considerable  increase  in  the  rapidity  of  the  circulation  following  a  physio- 
logical increase  in  the  number  of  beats  of  the  heart ;  but  the  value  of  each  beat  is  materi- 
ally diminished ;  otherwise,  the  rapidity  of  the  current  would  be  increased  about  three 
times,  as  the  pulse  became  three  times  as  frequent.  In  its  tranquil  action,  with  the  pulse 
at  thirty-six,  the  heart  contracted  thirteen  times  during  one  circuit  of  blood ;  while  it 
required  twenty-nine  pulsations  to  send  the  blood  over  the  same  course,  after  exercise, 
with  the  pulse  at  one  hundred ;  showing  a  diminution  in  the  value  of  the  ventricular  sys- 
tole of  more  than  one-half.  In  animals  suffering  under  inflammatory  fever,  either  spon- 
taneous or  produced  by  irritants,  the  same  observer  found  a  diminution  in  the  rapidity 
of  the  circulation,  accompanying  acceleration  of  the  pulse.  In  one  observation,  inflam- 
mation was  produced  in  the  horse  by  the  injection  of  ammonia  into  the  pericardium.  At 
the  commencement  of  the  experiment,  the  pulse  was  from  seventy-two  to  eighty-four 
per  minute,  and  the  duration  of  the  circulation  was  about  twenty -five  seconds.  The  next 
day,  with  the  pulse  at  ninety,  the  circulation  was  accomplished  in  from  thirty-five  to 
forty  seconds ;  and  the  day  following,  with  the  pulse  at  one  hundred,  the  rapidity  of  the 
circulation  was  diminished  to  from  forty  to  forty-five  seconds. 

If  we  be  justified  in  applying  the  above-mentioned  observations  to  the  human  subject 
(and  there  is  no  reason  why  this  should  not  be  done),  it  is  shown  that,  when  the  pulse  is 
accelerated  in  disease,  the  value  of  the  contractions  of  the  heart,  as  represented  by  the 
quantity  of  blood  discharged,  bears  an  inverse  ratio  to  their  number  and  is  so  much 
diminished  as  absolutely  to  produce  a  current  of  less  rapidity  than  normal. 

With  regard  to  the  relations  between  the  rapidity  of  the  heart's  action  and  the  gen- 
eral rapidity  of  the  circulation,  the  following  conclusions  may  be  given  as  the  results  of 
experimental  inquiry  : 

1.  In  physiological  increase  in  the  number  of  beats  of  the  heart,  as  the  result  of  exer- 
cise, for  example,  the  general  circulation  is  somewhat  increased  in  rapidity,  though  not 
in  proportion  to  the  increase  in  the  pulse. 

2.  In  pathological  increase  of  the  heart's  action,  as  in  febrile  movement,  the  rapidity 
of  the  general  circulation  is  generally  diminished,  it  may  be,  to  a  very  great  extent. 

3.  Whenever  the  number  of  beats  of  the  heart  is  considerably  increased  from  any 
cause,  the  quantity  of  blood  discharged  at  each  ventricular  systole  is  very  much  dimin- 
ished, either  from  lack  of  complete  distention  or  from  imperfect  emptying  of  the  cavities. 

Phenomena  in  the  Circulatory  System  after  Death. — We  do  not  believe  that  any  one 
has  proven  the  existence  of  a  force  in  the  capillaries  or  the  tissues  (capillary  power)  which 
materially  assists  the  circulation  during  life  or  produces  any  movement  immediately  after 
death ;  and  we  shall  not,  therefore,  discuss  the  extraordinary  post-mortem  phenomena 
of  circulation,  particularly  those  which  have  been  observed  by  Dr.  Dowler  in  subjects 
dead  of  yellow  fever.  But  nearly  every  autopsy  shows  that,  after  death,  the  blood  does 
not  remain  equally  distributed  in  the  arteries,  capillaries,  and  veins.  Influenced  by 
gravitation,  it  accumulates  in  and  discolors  the  most  dependent  parts  of  the  body.  The 
arteries  are  always  found  empty,  and  all  the  blood  in  the  body  accumulates  in  the  venous 
system  and  capillaries ;  a  fact  which  was  observed  by  the  ancients  and  gave  rise  to  the 
8 


114  RESPIRATION. 

belief  that  the  arteries,  as  their  name  implies,  were  air-bearing  tubes.  This  has  long 
engaged  the  attention  of  physiologists,  who  have  attempted  to  explain  it  by  various 
theories.  Without  discussing  the  views  on  this  subject  anterior  to  our  knowledge  of  the 
great  contractile  power  of  the  arteries  as  compared  with  other  vessels,  we  may  cite  the 
following  experiment  of  Magendie  as  offering  a  satisfactory  explanation.  If  the  artery 
and  vein  of  a  limb  be  exposed  in  a  living  animal  and  all  the  other  vessels  be  tied,  com- 
pression of  the  artery  does  not  immediately  arrest  the  current  in  the  vein,  but  the  blood 
will  continue  to  flow  until  the  artery  is  entirely  emptied.  The  artery,  when  relieved 
from  the  distending  force  of  the  heart,  reacts  on  its  contents  by  virtue  of  its  contractile 
coat  and  completely  empties  itself  of  blood.  An  action  similar  to  this  takes  place  after 
death  throughout  the  entire  arterial  system.  The  vessels  react  on  their  contents  and 
gradually  force  all  the  blood  into  and  through  the  capillaries,  which  are  very  short,  to 
the  veins,  which  are  capacious,  distensible,  and  but  slightly  contractile.  This  begins 
immediately  after  death,  while  the  irritability  of  the  muscular  coat  of  the  arteries  remains, 
and  is  seconded  by  the  subsequent  cadaveric  rigidity,  which  affects  all  the  involuntary, 
as  well  as  the  voluntary  muscular  fibres.  Once  in  the  venous  system,  the  blood  cannot 
return  on  account  of  the  valves.  Thus,  after  death,  the  blood  is  found  in  the  veins  and 
capillaries  of  dependent  parts  of  the  body. 


CHAPTER    IV. 

RESPIRA  TION-RESPIRA  TOR  Y  MO  VEHENTS. 

General  considerations— Physiological  anatomy  of  the  respiratory  organs— Kespiratory  movements  of  the  larynx- 
Epiglottis— Trachea  and  bronchial  tubes— Parenchyma  of  the  lungs— Movements  of  respiration— Inspiration- 
Muscles  of  inspiration — Expiration — Influence  of  the  elasticity  of  the  pulmonary  structure  and  walls  of  the  chest 
upon  expiration— Muscles  of  expiration— Action  of  the  abdominal  muscles  in  expiration— Types  of  respiration- 
Frequency  of  the  respiratory  movements — Relations  of  inspiration  and  expiration  to  each  other — The  respiratory 
sounds— Capacity  of  the  lungs  and  the  quantity  of  air  changed  in  the  respiratory  acts— Residual  air— Reserve 
air — Tidal,  or  breathing  air — Complemental  air — Extreme  breathing  capacity — Relations  in  volume  of  the  expired 
to  the  inspired  air— Diffusion  of  air  in  the  lungs. 

THE  characters  of  the  blood  are  by  no  means  identical  in  the  three  great  divisions  of 
the  vascular  system ;  but  physiologists  have  thus  far  been  able  to  investigate  only  the  dif- 
ferences which  exist  between  arterial  and  venous  blood,  for  the  capillaries  are  so  short, 
communicating  directly  with  the  arteries  on  the  one  side  and  the  veins  on  the  other,  that 
it  is  impossible  to  obtain  a  specimen  of  true  capillary  blood.  In  the  capillaries,  how- 
ever, the  nutritive  fluid,  which  is  identical  in  all  parts  of  the  arterial  system,  under- 
goes a  remarkable  change,  which  renders  it  unfit  for  nutrition.  Thus  modified  it  is 
known  as  venous  blood ;  and,  as  we  have  seen,  the  only  office  of  the  veins  is  to 
carry  it  back  to  the  right  side  of  the  heart,  to  be  sent  to  the  lungs,  where  it  loses 
the  vitiating  materials  it  has  collected  in  the  tissues,  takes  in  a  fresh  supply  of 
oxygen,  and  goes  to  the  left,  or  systemic  heart,  again  prepared  for  nutrition.  As  the 
processes  of  nutrition  vary  in  different  parts  of  the  organism,  there  are  of  necessity  cor- 
responding variations  in  the  composition  of  the  blood  throughout  the  venous  system. 

The  important  principles  which  are  given  off  by  the  lungs  are  exhaled  from  the 
blood;  and  the  gas  which  disappears  from. the  air  is  absorbed  by  the  blood,  mainly  by 
its  corpuscular  elements. 

A  proper  supply  of  oxygen  is  indispensable  to  nutrition  and  even  to  the  compara- 
tively-mechanical process  of  circulation ;  but  it  is  no  less  necessary  to  the  nutritive  pro- 
cesses that  carbonic  acid,  which  the  blood  acquires  in  the  tissues,  should  be  given  off. 

Respiration  may  be  defined  strictly  as  the  process  by  which  the  various  tissues  and 
organs  receive  and  appropriate  oxygen. 


GENERAL  CONSIDERATIONS.  115 

As  it  is  almost  exclusively  through  the  blood  that  the  tissues  and  organs  are  supplied 
with  oxygen,  and  as  the  blood  receives  and  exhales  most  of  the  carbonic  acid,  the  respira- 
tory process  may  be  said  to  consist  chiefly  in  the  change  of  venous  into  arterial  blood. 
But  experiments  have  demonstrated  that  the  tissues  themselves,  detached  from  the  body 
and  placed  in  an  atmosphere  of  oxygen,  will  absorb  this  gas  and  exhale  carbonic  acid. 
Under  these  circumstances,  they  certainly  respire ;  and  it  is  evident,  therefore,  that,  in 
this  process,  the  intervention  of  the  blood  is  not  an  absolute  necessity. 

The  tide  of  air  in  the  lungs  does  not  constitute  respiration,  as  we  now  understand  it. 
These  organs  merely  serve  to  facilitate  the  introduction  of  oxygen  into  the  blood  and  the 
exhalation  of  carbonic  acid.  If  the  system  be  drained  of  blood,  or  if  the  blood  be 
rendered  incapable  of  interchanging  its  gases  with  the  air,  respiration  ceases,  and  all  the 
phenomena  of  asphyxia  are  presented,  although  air  be  introduced  into  the  lungs  with 
perfect  regularity.  It  must  be  remembered  that  the  essential  processes  of  respiration 
take  place  in  all  the  tissues  and  organs  of  the  system  and  not  in  the  lungs.  Respiration 
is  a  process  similar  to  what  are  known  as  the  processes  of  nutrition ;  and,  although  it  is 
much  more  active  and  uniform  than  the  ordinary  nutritive  acts,  it  is  inseparably  con- 
nected with,  and  strictly  a  part  of  the  general  process.  As,  in  the  nutrition  of  the  sub- 
stance of  tissues,  the  nitrogenized  principles  of  the  blood  united  with  inorganic  matters 
are  used  up,  transformed  into  the  tissue  itself,  finally  changed  into  excrementitious  prod- 
ucts, such  as  urea  or  cholesterine,  and  discharged  from  the  body,  so  the  oxygen  of  the 
blood  is  appropriated,  and  carbonic  acid,  which  is  an  excrementitious  product,  is  produced, 
whenever  tissues  are  worn  out  and  regenerated.  There  is  a  necessary  and  inseparable 
connection  between  all  these  processes ;  and  they  must  be  considered,  not  as  distinct 
functions,  but  as  different  parts  of  the  one  great  function  of  nutrition.  As  we  are  as 
yet  unable  to  follow  out  all  the  intermediate  changes  which  take  place  between  the 
appropriation  of  nutritive  materials  from  the  blood  and  the  production  of  effete  or  ex- 
crementitious substances,  it  is  impossible  to  say  precisely  how  oxygen  is  used  by  the 
tissues  and  how  carbonic  acid  is  produced.  We  only  know  that  more  or  less  oxy- 
gen is  necessary  for  the  nutrition  of  all  tissues,  in  all  animals,  high  or  low  in  the  scale, 
and  that  the  tissues  produce  a  certain  quantity  of  carbonic  acid.  The  fact  that  oxygen  is 
consumed  with  much  greater  rapidity  than  any  other  nutritive  principle  and  that  the 
production  of  carbonic  acid  is  correspondingly  active,  as  compared  with  other  effete 
products,  points  pretty  conclusively  to  a  connection  between  the  absorption  of  the  one 
principle  and  the  production  of  the  other. 

In  some  of  the  lowest  of  the  inferior  animals,  there  is  no  special  respiratory  organ, 
the  interchange  of  gases  being  effected  through  the  general  surface.  Higher  in  the  ani- 
mal scale,  special  organs  are  found,  which  are  called  gills  when  the  animals  live  under 
water  and  respire  the  air  which  is  in  solution  in  the  water,  and  lungs  when  the  air  is 
introduced  in  a  gaseous  form.  Animals  possessed  of  lungs  have  a  tolerably-perfect  cir- 
culatory apparatus,  so  that  the  blood  is  made  to  pass  continually  through  the  respiratory 
organs.  In  the  human  subject  and  the  warm-blooded  animals  generally,  the  lungs  are 
very  complex  and  present  an  immense  surface  by  which  the  blood  is  exposed  to  the  air, 
separated  from  it  simply  by  a  delicate  and  permeable  membrane.  These  animals  are  like- 
wise provided  with  a  special  heart,  which  has  the  function  of  carrying  on  the  pulmonary 
circulation.  Although  respiration  is  carried  on  to  some  extent  by  the  general  surface,  the 
lungs  are  the  important  and  essential  organs  in  which  the  interchange  of  gases  takes  place. 

The  essential  conditions  for  respiration  in  animals  which  have  a  circulating  nutritive 
fluid  are :  air  and  blood,  separated  by  a  membrane  which  will  allow  the  passage  of  gases. 
The  effete  products  of  respiration  in  the  blood  pass  out  and  vitiate  the  air.  The  air  is 
deprived  of  a  certain  portion  of  its  oxygen,  which  passes  into  the  blood,  to  be  conveyed 
to  the  tissues.  Thus  the  air  must  be  changed  to  supply  fresh  oxygen  and  get  rid  of  the 
carbonic  acid.  The  rapidity  of  this  change  is  in  proportion  to  the  nutritive  activity  of 
the  animal  and  the  rapidity  of  the  circulation  of  the  blood. 


116  RESPIRATION. 

In  treating  in  detail  of  the  function  of  respiration,  it  will  be  convenient  to  make  the 
following  division  of  the  subject: 

1.  The  mechanical  phenomena  of  respiration ;  or  the  processes  by  which  the  fresh  air 
is  introduced  into  the  lungs  (inspiration),  and  the  vitiated  air  is  expelled  (expiration). 

2.  The  changes  which  the  air  undergoes  in  respiration. 

3.  The  changes  which  the  blood  undergoes  in  respiration. 

4.  The  relations  of  the  consumption  of  oxygen  and  the  production  of  carbonic  acid  to 
the  general  process  of  nutrition. 

5.  The  respiratory  sense ;  a  want,  on  the  part  of  the  system,  which  induces  the  re- 
spiratory acts  (besoin  de  respirer). 

6.  Cutaneous  respiration. 

7.  Asphyxia. 

The  study  of  these  questions  will  be  facilitated  by  a  brief  consideration  of  some 
points  in  the  anatomy  of  the  respiratory  organs. 

Physiological  Anatomy  of  the  Respiratory  Organs. 

Passing  backward  from  the  mouth  to  the  pharynx,  two  openings  are  observed; 
a  posterior  opening,  which  leads  to  the  oesophagus,  and  an  anterior  opening,  the  opening 
of  the  larynx,  which  is  the  commencement  of  the  passages  devoted  exclusively  to  respi- 
ration. The  structure  of  the  oesophagus  and  of  the  air-tubes  is  entirely  different.  The 
oesophagus  is  flaccid  and  destined  to  receive  and  convey  to  the  stomach  the  articles  of 
food,  which  are  introduced  by  the  constrictions  of  the  muscles  above.  The  trachea  and 
its  ramifications  are  exclusively  for  the  passage  of  air,  which  is  taken  in  by  a  suction 
force  produced  by  the  enlargement  of  the  thorax.  The  act  of  inhalation  requires  that 
the  tubes  should  be  kept  open  by  walls  sufficiently  rigid  to  resist  the  external  pressure 
of  the  air. 

Beginning  our  description  with  the  larynx,  it  is  seen  that  the  cartilages  of  which  it  is 
composed  are  sufficiently  rigid  and  unyielding  to  resist  the  pressure  produced  by  any  in- 
spiratory  effort.  Across  its  superior  opening  are  the  vocal  chords,  which  are  four  in  num- 
ber and  have  a  direction  from  before  backward.  The  two  superior  are  called  the  false  vocal 
chords,  because  they  are  not  concerned  in  the  production  of  the  voice.  The  two  inferior 
are  the  true  vocal  chords.  They  are  ligainentous  bands  covered  by  folds  of  mucous  mem 
brane,  which  is  quite  thick  on  the  superior  chords  and  very  thin  and  delicate  on  the  in- 
ferior. Anteriorly,  they  are  attached  to  a  fixed  point  between  the  thyroid  cartilages,  and 
posteriorly,  to  the  movable  arytenoid  cartilages.  Air  is  admitted  to  the  trachea  through 
an  opening  between  the  chords,  which  is  called  the  rima  glottidis.  Little  muscles,  arising 
from  the  thyroid  and  cricoid  and  attached  to  the  arytenoid  cartilages,  are  capable  of 
separating  and  approximating  the  points  to  which  the  vocal  chords  are  attached  posteri- 
orly, so  as  to  open  and  close  the  rima  glottidis. 

If  the  glottis  be  exposed  in  a  living  animal,  certain  regular  movements  are  presented, 
which  are  synchronous  with  the  acts  of  respiration.  The  larynx  is  opened  at  each  inspira- 
tion by  the  action  of  the  muscles  referred  to  above,  so  that  the  air  has  a  free  entrance  to 
the  trachea.  At  the  termination  of  the  inspiratory  act,  these  muscles  are  relaxed,  the 
vocal  chords  fall  together  by  their  own  elasticity,  and,  in  expiration,  the  chink  of  the 
glottis  returns  to  the  condition  of  a  narrow  slit.  These  respiratory  movements  of  the 
glottis  are  constant  and  are  essential  to  the  introduction  of  air  in  proper  quantity  into  the 
lungs.  The  expulsion  of  air  from  the  lungs  is  rather  a  passive  process  and  tends  in  it- 
self to  separate  the  vocal  chords ;  but  inspiration,  which  is  active  and  more  violent,  were 
it  not  for  the  movements  of  the  glottis,  would  have  a  tendency  to  draw  the  vocal  chords 
together.  The  muscles  which  are  concerned  in  producing  these  movements  are  animated 
by  the  inferior  laryngeal  branches  of  the  pneumogastric  nerves.  If  these  nerves  be 
divided,  the  movements  of  the  glottis  are  arrested,  and  respiration  is  very  seriously  inter- 


PHYSIOLOGICAL  ANATOMY   OF  THE  RESPIRATORY   ORGANS.     117 

fered  with.  This  is  particularly  marked  in  yonng  animals,  in  which  the  walls  of  the 
larynx  are  comparatively  yielding,  when  the  operation  is  frequently  followed  by  immedi- 
ate death  from  suffocation.  The  movements  of  the  glottis  enable  us  to  understand  how 
foreign  bodies  of  considerable  size  are  sometimes  accidentally  introduced  into  the  air- 
passages.  The  respiratory  movements  of  the  larynx  are  entirely  distinct  from  those  con- 
cerned in  the  production  of  the  voice  and  are  simply  for  the  purpose  of  facilitating  the 
entrance  of  air  in  respiration. 

Attached  to  the  anterior  portion  of  the  larynx,  is  the  epiglottis,  a  little,  leaf-shaped 
lamella  of  fibro-cartilage,  which,  during  ordinary  respiration,  projects  upward  and  lies 
against  the  posterior  portion  of  the  tongue.  During  the  act  of  deglutition,  respiration  is 
momentarily  interrupted,  and  the  air-passages  are  protected  by  the  tongue,  which  presses 
backward,  carrying  the  epiglottis  before  it  and  completely  closing  the  opening  of  the 


12 


FIG.  35.—  Trachea  and  bronchial  tubes.    (Sappey.) 

1,  2,  larynx;  3,3,  trachea;  4,  bifurcation  of  the  trachea;  5,  right  bronchus;  6,  left  bronchus;  7,  bronchial  division  to 
the  upper  lobe  of  the  right  lung;  8,  division  to  the  middle  lobe:  9,  division  to  the  lower  lobe ;  10.  division  to 
the  upper  lobe  of  the  left  lung;  11,  division  to  the  lower  lobe;  12,  12,  12,  12,  ultimate  ramifications  of  the 
bronchi;  13, 13, 13, 13,  lungs,  represented  in  contour;  14, 14,  summit  of  the  lungs;  15, 15,  base  of  the  lungs. 

larynx.  Physiologists  have  questioned  whether  the  epiglottis  be  necessary  to  the  com- 
plete protection  of  the  air-passages ;  and,  repeating  the  experiments  of  Magendie,  it  has 
been  frequently  removed  from  the  lower  animals  without  apparently  interfering  with  the 
proper  deglutition  of  solids  or  liquids.  We  have  been  satisfied,  from  actual  experiment, 
that  a  dog  will  swallow  liquids  and  solids  immediately  after  the  ablation  of  the  epiglottis, 
without  allowing  any  to  pass  into  the  trachea ;  but  it  becomes  a  question  whether  this 
experiment  can  be  absolutely  applied  to  the  human  subject.  In  a  case  of  loss  of  the 


118 


RESPIRATION. 


entire  epiglottis,  which  was  observed  in  the  Bellevue  Hospital,  the  patient  experienced 
slight  difficulty  in  swallowing,  from  the  passage  of  little  particles  into  the  larynx,  which 
produced  cough.  This  case  seemed  to  show  that  the  presence  of  the  epiglottis,  in  the 
human  subject  at  least,  is  necessary  to  the  complete  protection  of  the  air-passages  in 
deglutition. 

Passing  down  the  neck  from  the  larynx  toward  the  lungs,  is  a  tube,  from  four  to  four 
and  a  half  inches  in  length  and  about  three-quarters  of  an  inch  in  diameter,  which  is 
called  the  trachea.  It  is  provided  with  cartilaginous  rings,  from  sixteen  to  twenty  in 
number,  which  partially  surround  the  tube,  leaving  about  one-third  of  its  posterior  por- 
tion occupied  by  fibrous  tissue  mixed  with  a  certain  number  of  non-striated  muscular 
fibres.  Passing  into  the  chest,  the  trachea  divides  into  the  two  primitive  bronchi,  the 
right  being  shorter,  larger,  and  more  horizontal  than  the  left.  These  tubes,  provided,  like 
the  trachea,  with  imperfect  cartilaginous  rings,  enter  the  lungs,  divide  and  subdivide,  until 
the  minute  ramifications  of  the  bronchial  tree  open  directly  into  the  air-cells.  After 
penetrating  the  lungs,  the  cartilages  become  irregular  and  are  in  the  form  of  oblong, 
angular  plates,  which  are  so  disposed  as  to  completely  encircle  the  tubes.  In  tubes  of 
very  small  size,  these  plates  are  less  numerous  than  in  the  larger  bronchi,  until,  in  tubes 
of  a  less  diameter  than  TV  of  an  inch,  they  are  lost  altogether. 


FIG.  30. — Lungs,  anterior  view.    (Sappey.) 

1,  upper  lobe  of  the  left  lung ;  2,  lower  lobe ;  3,  fissure ;  4.  notch  corresponding  to  the,  apex  of  the  heart ;  5. 
pericardium;  6,  upper  lobe  of  the  right  lung;  7,  middle  lobe;  8,  lower  lobe;  $,  fissure  ;  10,  fissure;  11, 
diaphragm ;  12,  anterior  mediastinum ;  '13,  thyroid  gland  ;  14.  middle  cervical  aponeurosis  ;  15,  process  of  attach- 
ment of  the  mediastinum  to  the  pericardium;  16,  16,  seventh  ribs;  17,  17,  transversales  muscles;  18,  linea  alba. 


PHYSIOLOGICAL   ANATOMY   OF  THE   RESPIRATORY   ORGANS.     119 

The  walls  of  the  trachea  and  bronchial  tubes  are  composed  of  two  distinct  mem- 
branes ;  an  external  membrane,  between  the  layers  of  which  the  cartilages  are  situated 
and  a  lining  mucous  membrane.  The  external  membrane  is  composed  of  inelastic  and 
clastic  fibrous  tissue.  Posteriorly,  in  the  space  not  covered  by  cartilaginous  rings,  these 
fibres  are  mixed  with  a  certain  number  of  unstriped,  or  involuntary  muscular  fibres,  which 
exist  in  two  layers ;  a  thick  internal  layer,  in  which  the  fibres  are  transverse,  and  a  thinner 
longitudinal  layer,  which  is  external.  This  collection  of  muscular  fibres  is  sometimes 
called  the  trachealis  muscle.  Throughout  the  entire  system  of  bronchial  tubes,  there 
are  circular  fasciculi  of  muscular  fibres  lying  just  beneath  the  mucous  membrane,  with  a 
number  of  longitudinal  elastic  fibres.  The  character  of  the  bronchi  abruptly  changes 
in  tubes  less  than  ^  of  an  inch  in  diameter.  They  lose  the  cartilaginous  rings,  and 
the  external  and  the  mucous  membranes  become  so  closely  united  that  they  can  no 
longer  be  separated  by  dissection.  The  circular  muscular  fibres  continue  down  to  the  air- 
cells.  The  mucous  membrane  is  smooth,  covered  by  ciliated  epithelium,  the  movements 
of  the  cilia  being  always  from  within  outward,  and  it  is  provided  with  numerous  mucous 
glands.  These  glands  are  of  the  racemose  variety  and,  in  the  larynx,  are  of  considerable 
size.  In  the  trachea  and  bronchi,  racemose  glands  exist  in  the  membrane  on  the  posterior 
surface  of  the  tubes ;  but  anteriorly  are  small  follicles,  terminating  in  a  single,  and  some- 
times a  double,  blind  extremity.  These  follicles  are  lost  in  tubes  measuring  less  than  ^ 
of  an  inch  in  diameter. 


IS 


1G 


FIG.  37.— Bronchi  and  lungs,  posterior  mew.    (Sappey.) 

1,  1,  summit  of  the  lungs;  2,  2,  base  of  the  lungx ;  3,  trachea;  4,  right  bronchus;  5,  division  to  the  upper  lobs 
of  the-  lung  ;  6,  diciaion  to  the  lower  lobe ;  7,  left  bronchus ;  S,  division  to  the  upper  lobe ;  9,  division  to  the. 
lower  lobe;  10,  left  branch  of  the  pulmonary  artery  ;  11,  right  branch  ;  12.  left  auricle  of  the  heart;  13,  left  su- 
perior pulmonary  vein ;  14,  left  inferior  pulmonary  vein ;  15,  fight  superior  pulmonary  vein ;  16,  right  inferior  pul- 
monary vein;  17,  inferior  vena  cava ;  18,  left  ventricle  of  the  heart;  19,  right  ventricle. 

It  is  the  anatomy  of  the  parenchyma  of  the  lungs  which  possesses  the  most  physio- 
logical interest,  for  here  the  essential  processes  of  respiration  take  place.  When  mod- 
erately inflated,  the  lungs  have  the  appearance  of  irregular  cones,  with  rounded  apices, 
and  concave  bases  resting  upon  the  diaphragm.  They  fill  all  of  the  cavity  of  the  chest 
which  is  not  occupied  by  the  heart  and  great  vessels,  and  are  completely  separated  from 
each  other  by  the  mediastinum.  In  the  human  subject,  the  lungs  are  not  attached  to  the 


120 


RESPIRATION. 


thoracic  walls,  but  are  closely  applied  to  them,  each  covered  by  a  reflection  of  the  serous 
membrane  which  lines  the  cavity  of  the  corresponding  side.  Thus  they  necessarily  fol- 
low the  movements  of  expansion  and  contraction  of  the  thorax.  Deep  fissures  divide 
the  right  lung  into  three  lobes  and  the  left  lung  into  two.  The  surface  of  the  lungs  is 
divided  into  irregularly-polygonal  spaces,  from  |  of  an  inch  to  an  inch  in  diameter, 
which  mark  what  are  sometimes  called  the  pulmonary  lobules;  although  this  term  is  in- 
correct, as  each  of  these  divisions  includes  quite  a  number  of  the  true  lobules. 

Following  out  the  bronchial  tubes  from  the  diameter  of  ^  of  an  inch,  the  smallest, 
which  are  from  y^  to  TV  of  an  inch  in  diameter,  open  into  a  collection  of  oblong  vesicles, 

which  are  the  air-cells.  Each  collection 
of  vesicles  constitutes  one  of  the  true  pul- 
monary lobules  and  is  from  -^  to  -fa  of 
an  inch  in  diameter.  After  entering  the 
lobule,  the  tube  forms  a  sort  of  tortuous 
central  canal,  sending  off  branches  which 
terminate  in  groups  of  from  eight  to  fif- 
teen pulmonary  cells.  The  cells  are  a 
little  deeper  than  they  are  wide  and  have 
each  a  rounded,  blind  extremity.  Some 
are  smooth,  but  many  are  marked  by 
little  circular  constrictions,  or  rugae.  In 
the  healthy  lung  of  the  adult,  after  death, 
they  measure  from  ^-^  to  T|^T  or  -fa  of  an 
inch  in  diameter,  but  are  capable  of  very 
great  distention.  The  smallest  cells  are 
in  the  deep  portions  of  the  lungs,  and  the 
largest  are  situated  near  the  surface. 
There  are  considerable  variations  in  the 
size  of  the  cells  at  different  periods  of 
life.  The  smallest  cells  are  found  in  young 
children,  and  they  progressively  increase 
in  size  with  age.  The  walls  of  the  air- 
cells  contain  numerous  small  elastic  fibres, 

FIG.  38.-Mould  of  a  terminal  bronchm  and  a  group  of  which  do  not  form  distinCt  bundles  for 
air-cells  moderately  distended  by  injection,  from  the  each  air-cell,  but  anastomose  freely  with 
human  subject.  (Robin.)  * 

each  other,  so  that  the  same  fibres  belong 

to  two  or  more  cells.  This  structure  is  peculiar  to  the  parenchyma  of  the  lungs  and 
gives  to  these  organs  their  great  distensibility  and  elasticity,  properties  which  play  an  im- 
portant part  in  expelling  the  air  from  the  chest,  as  a  consequence  simply  of  cessation 
of  the  action  of  the  inspiratory  muscles.  Interwoven  with  these  elastic  fibres,  is  the 
richest  plexus  of  capillary  blood-vessels  found  in  the  economy.  The  vessels  are  larger 
than  the  capillaries  in  other  situations,  and  the  plexus  is  so  close  that  the  spaces  between 
them  are  narrower  than  the  vessels  themselves.  When  distended,  the  blood-vessels  form 
the  greatest  part  of  the  walls  of  the  cells. 

Lining  the  air-cells,  are  very  thin  scales  of  pavement-epithelium,  from  ^ginr  to  Wiro  °f 
an  inch  in  diameter,  which  are  applied  directly  to  the  walls  of  the  blood-vessels.  The 
epithelium  here  does  not  seem  to  be  regularly  desquamated,  as  in  other  situations.  Ex- 
amination of  injected  specimens  shows  that  the  blood-vessels  are  so  situated  between  the 
cells,  that  the  blood  in  the  greater  part  of  their  circumference  is  exposed  to  the  action  of 
the  air. 

The  entire  mass  of  venous  blood  is  distributed  in  the  lungs  by  the  pulmonary  artery. 
Arterial  blood  is  conveyed  to  these  organs  by  the  bronchial  arteries,  which  ramify  and 
subdivide  on  the  bronchial  tubes  and  follow  their  course  into  the  lungs,  for  the  nourish- 


MOVEMENTS   OF  RESPIRATION. 


121 


ment  of  these  parts.  It  is  possible  that  the  tissue  of  the  lungs  may  receive  some  nourish- 
ment from  the  blood  conveyed  there  by  the  pulmonary  artery ;  but,  as  this  vessel  does 
not  send  any  branches  to  the  bronchial  tubes,  it  is  undoubtedly  the  bronchial  arteries 
which  supply  the  material  for  their  nutrition  and  for  the  secretion  of  the  mucous  glands. 
This  is  one  of  the  anatomical  reasons  why  inflammatory  conditions  of  the  bronchial  tubes- 
do  not  extend  to  the  parenchyma  of  the  lungs,  and  vice  versa. 


FIG.  39.— Section  of  the  parenchyma  of  the  human  lung,  injected  through  the  pulmonary  artery.    (Schulze.) 
a,  a,  c,  c,  wall  of  the  air-eel  i ;  6,  small  arterial  branch. 

The  foregoing  anatomical  sketch  shows  the  admirable  adaptation  of  the  trachea  and 
bronchial  tubes  to  the  passage  of  the  air  by  inspiration  to  the  deep  portions  of  the  lungs> 
and  the  favorable  conditions  which  it  there  meets  with  for  an  interchange  of  the  elements 
of  the  air  and  blood.  It  is  also  evident,  from  the  enormous  number  of  air-cells,  that  the 
respiratory  surface  must  be  immense.1 

Movements  of  Respiration. 

In  man  and  in  the  warm-blooded  animals  generally,  inspiration  takes  place  as  a  con- 
sequence of  enlargement  of  the  thoracic  cavity  and  the  entrance  of  a  quantity  of  air 
through  the  respiratory  passages  corresponding  to  the  increased  capacity  of  the  lungs, 
In  the  mammalia,  the  chest  is  enlarged  by  the  action  of  muscles ;  and,  in  ordinary  respi- 
ration, inspiration  is  an  active  process,  while  expiration  is  comparatively  passive. 

A  glance  at  the  physiological  anatomy  of  the  thorax  in  the  human  subject  makes  it 
evident  that  the  action  of  certain  muscles  will  considerably  increase  its  capacity.  In  the 
first  place,  the  diaphragm  mounts  up  into  its  cavity  in  the  form  of  a  vaulted  arch.  By 
contraction  of  its  fibres,  it  is  brought  nearer  a  plane,  and  thus  the  vertical  diameter  of 
the  thorax  is  increased.  The  walls  of  the  thorax  are  formed  by  the  dorsal  vertebrae  and 

1  Hales  estimated  the  combined  surface  of  the  air-cells  at  289  square  feet;  Keill,  at  about  152  square  feet;  and1 
Lieberkuhn,  at  1,500  square  feet.  There  are  not  sufficient  data  on  this  point  for  us  to  form  any  thing  like  a  reliable 
estimate.  It  is  simply  evident  that  the  extent  of  surface  must  be  very  great.  In  passing  from  the  lower  to  the 
higher  orders  of  animals,  it  is  seen  that  Nature  provides  for  the  necessity  of  an  increase  in  the  activity  of  the  respira- 
tory process,  by  a  diminished  size  and  a  multiplication  of  the  air-cells. 


122 


RESPIRATION. 


ribs  posteriorly,  by  the  upper  ten  ribs  laterally,  and  by  the  sternum  and  costal  cartilages 
anteriorly.  The  direction  of  the  ribs,  their  mode  of  connection  wiiih  the  sternum  by  the 
costal  cartilages,  and  their  articulation  with  the  vertebral  column,  are  such  that,  by  their 
movements,  the  antero-posterior  and  transverse  diameters  of  the  chest  may  be  consider- 
ably modified. 

Inspiration. 

The  ribs  are  somewhat  twisted  upon  themselves  and  have  a  general  direction  forward 
and  downward.  The  first  rib  is  nearly  horizontal,  but  the  obliquity  of  the  ribs  progressively 
increases  from  the  upper  to  the  lower  parts  of  the  chest.  They  are  articulated  with  the 
bodies  of  the  vertebrae,  so  as  to  allow  of  considerable  motion.  The  upper  seven  ribs  are 
attached  by  the  costal  cartilages  to  the  sternum,  these  cartilages  Tunning  upward  and 


FIG.  40.  —  Thorax,  anterior  mew.    (Sappey.) 

1,  2,  3,  sternum ;  a.  circumference  of  the  upper  portion  of 
the  thorax:  5,  circumference  of  the  base  of  the 
thorax;  6,  first  rib;  7,  second  rib;  8,  8,  last  five  ster- 
nal ribs ;  9,  upper  three  false  ribs ;  10,  last  two,  or 
floating  ribs ;  11,  costal  cartilages. 


FIG.  41 .—  Thorax,  posterior  view.    (Sappey . ) 
1,  1,  spinous  processes  of  the  dorsal  vertebrse;    2,  '2, 
laminae  of  the  vertebrae  ;  8,  3,  transverse  processes ; 
4,  4,  dorsal  portions  of  the  ribs  ;  5,  5,  angles  of  the 
ribs. 


inward.  The  cartilages  of  the  eighth,  ninth,  and  tenth  ribs  are  joined  to  the  cartilage 
of  the  seventh.  The  eleventh  and  twelfth  are  floating  ribs  and  are  attached  only  to  the 
vertebrse. 

It  may  be  stated,  in  general  terms,  that  inspiration  is  effected  by  descent  of  the  dia- 
phragm and  elevation  of  the  ribs ;  and  expiration,  by  elevation  of  the  diaphragm  and 
descent  of  the  ribs. 

Arising  severally  from  the  lower  border  of  each  rib  and  attached  to  the  upper  border 
of  the  rib  below,  are  the  eleven  external  intercostal  muscles,  the  fibres  of  which  have 
an  oblique  direction  from  above  downward  and  forward.  Attached  to  the  inner  bor- 
ders of  the  ribs  are  the  internal  intercostals,  which  have  a  direction  from  above  downward 
and  backward,  nearly  at  right  angles  to  the  fibres  of  the  external  intercostals.  There  are 
also  a  number  of  muscles  attached  to  the  thorax  and  spine,  thorax  and  head,  upper  part 
of  humerus,  etc.,  which  are  capable  of  elevating  either  the  entire  chest  or  the  ribs. 
These  must  act  as  muscles  of  inspiration,  when  the  attachments  to  the  thorax  become 
the  movable  points.  Some  of  them  are  called  into  action  during  ordinary  respiration  ; 
others  act  as  auxiliaries  when  respiration  is  a  little  exaggerated,  as  after  exercise,  and  are 


MUSCLES   OF  INSPIRATION.  123 

called  ordinary  auxiliaries ;  while  others,  which  ordinarily  have  a  different  function,  are 
only  brought  into  play  when  respiration  is  excessively  difficult,  and  are  called  extraordi- 
nary auxiliaries. 

The  following  are  the  principal  muscles  concerned  in  inspiration : 

Muscles  of  Inspiration. 

Ordinary  Respiration. 
Muscle.  Attachments. 

Diaphragm Circumference  of  lower  border  of  thorax. 

Scalenus  anticus Transverse  processes  of  third,  fourth,  fifth,  and  sixth  cer- 
vical vertebrae tubercle  of  first  rib. 

Scalenus  medius Transverse  processes  of  lower  six  cervical  vertebrae 

upper  surface  of  first  rib. 

Scalenus  posticus Transverse  processes  of  lower  two  or  three  cervical  ver- 
tebrae  outer  surface  of  second  rib. 

External  intercostals Outer  borders  of  the  ribs. 

Sternal  portion  of  internal  intercostals.  .Borders  of  the  costal  cartilages. 

Twelve  levatores  costarum Transverse  processes  of  dorsal  vertebras ribs,  between 

the  tubercles  and  angles. 

Ordinary  Auxiliaries. 

Serratus  posticus  superior Ligamentum  nuchae,  spinous  processes  of  last  cervical 

and  upper  two  or  three  dorsal  vertebrae upper  bor- 
ders of  second,  third,  fourth,  and  fifth  ribs,  just  beyond 
the  angles. 

Sterno-mastoideus Upper  part  of  sternum mastoid  process  of  temporal 

bone. 

Extraordinary  Auxiliaries. 

Levator  anguli  scapulae Transverse  processes  of  upper  three  or  four  cervical 

vertebrae posterior  border  of  superior  angle  of 

scapula. 

Trapezius  (superior  portion) Ligamentum  nuchae  and  seventh  cervical  vertebra 

upper  border  of  spine  of  scapula. 

Pectoralis  minor. . Coracoid  process  of  scapula anterior  surface  and  up- 
per margins  of  third,  fourth,  and  fifth  ribs,  near  the 
cartilages. 

Pectoralis  major  (inferior  portion) Bicipital  groove  of  humerus costal  cartilages  and  low- 
er part  of  sternum. 

Serratus  magnus Inner  margin  of  posterior  border  of  scapula external 

surface  and  upper  border  of  upper  eight  ribs. 

Action  of  the  Diaphragm. — The  descriptive  and  general  anatomy  of  the  diaphragm 
gives  a  pretty  correct  idea  of  its  functions  in  respiration.  It  arises,  anteriorly,  from  the 
inner  surface  of  the  ensiforrn  cartilage,  laterally,  from  the  inner  surface  of  the  lower 
borders  of  the  costal  cartilages  and  the  six  or  seven  inferior  ribs,  passes  over  the  quadra- 
tus  lumborum  by  the  external  arcuate  ligament,  and  the  psoas  magnus  by  the  internal 
arcuate  ligament,  and  has  two  tendinous  slips  of  origin,  called  crurae  of  the  diaphragm, 
from  the  bodies  of  the  second,  third,  and  fourth  lumbar  vertebrae  and  the  intervertebral 
cartilages  on  the  right  side,  and  the  second  and  third  lumbar  vertebrae  and  the  interver- 
tebral cartilages  on  the  left  side.  From  this  origin,  which  extends  around  the  lower  cir- 
cumference of  the  thorax,  it  mounts  into  the  cavity  of  the  chest,  forming  a  vaulted 
arch,  or  dome,  with  its  concavity  toward  the  abdomen  and  its  convexity  toward  the 
lungs.  In  the  central  portion,  there  is  a  tendon  of  considerable  size  and  shaped  some- 


124 


RESPIRATION. 


thing  like  the  club  on  a  playing-card,  with  middle,  right,  and  left  leaflets.  The  remain- 
der of  the  organ  is  composed  of  radiating  fibres  of  voluntary  muscular  tissue.  The 
oesophagus,  aorta,  and  inferior  vena  cava  pass  through  the  diaphragm  from  the  thoracic 
to  the  abdominal  cavity,  by  three  openings. 

The  opening  for  the  oesophagus  is  surrounded  by  muscular  fibres,  by  which  it  is  par- 
tially closed  when  the  diaphragm  contracts  in  inspiration,  as  the  fibres  simply  surround 
the  tube,  and  none  are  attached  to  it. 


FIG.  42. — Diaphragm.    (Sappey.) 

1,  2,  8,  central  tendon ;  4,  right  pillar ;  5,  left  pillar ;  6,  7,  processes  between  the  pillars ;  8,  8,  openings  for  the  splanch- 
nic nerves;  9,  fibrous  arch  passing  over  the  psoas  magnus;  10,  fibrous  arch  passing  over  the  quadratus  lumbo- 
rum ;  11,  muscular  fibres  arising  from  these  two  arches ;  12,  12,  muscular  fibres  arising  from  the  lower  six  ribs  ; 
13,  fibres  from  the  ensiform  cartilage;  14,  opening  for  the  vena  cava;  15,  opening  for  the  oesophagus ;  16,  open- 
ing for  the  aorta;  17,  17,  part  of  the  transversalis  muscle;  18,  18,  aponeurosis;  19,  19,  quadratus  lumborum; 
20,  20,  psoas  magnus ;  21,  fourth  lumbar  vertebra. 

The  orifice  for  the  aorta  is  bounded  by  the  bone  and  aponeurosis  posteriorly,  and  in 
front,  by  a  fibrous  band  to  which  the  muscular  fibres  are  attached,  so  that  their  contrac- 
tion has  a  tendency  rather  to  increase  than  to  diminish  the  caliber  of  the  vessel. 

The  orifice  for  the  vena  cava  is  surrounded  entirely  by  tendinous  structure,  and  con- 
traction of  the  diaphragm,  although  it  might  render  the  form  of  the  orifice  more  nearly 
circular,  can  have  no  effect  upon  its  caliber. 

The  action  of  the  diaphragm  can  be  easily  studied  in  the  inferior  animals  by  vivisec- 
tions. If  the  abdomen  of  a  cat,  which,  from  the  conformation  of  the  parts,  is  well  adapted 
to  this  experiment,  be  largely  opened,  we  can  observe  the  descent  of  the  tendinous  por- 
tion and  the  contraction  of  the  muscular  fibres.  The  action  of  this  muscle  may  be  ren- 
dered more  apparent  by  compressing  the  walls  of  the  chest  with  the  hands,  so  as  to 
interfere  somewhat  with  the  movements  of  the  ribs.  By  putting  a  strong  ligature  around 
the  spinal  column  and  soft  parts  just  below  the  diaphragm  and  cutting  off  the  lower 
half  of  the  body,  as  was  done  by  the  assistant  to  the  chair  of  physiology  in  the  Bellevue 
Hospital  Medical  College,  Dr.  C.  F.  Roberts,  the  movements  of  the  diaphragm  may  be 
very  beautifully  exhibited  in  class-demonstrations. 

In  ordinary  respiration,  the  descent  of  the  diaphragm  and  its  approximation  to  a 
plane  are  the  chief  phenomena  observed ;  but,  as  there  is  a  slight  resistance  to  the  depres- 
sion of  the  central  tendon,  it  is  probable  that  there  is  also  a  certain  amount  of  elevation 


MUSCLES   OF   INSPIRATION.  125 

of  the  inferior  ribs,  the  diaphragm  assisting,  in  a  limited  degree  it  is  true,  the  action 
of  the  external  intercostals. 

The  phenomena  referable  to  the  abdomen,  which  coincide  with  the  descent  of  the 
diaphragm,  can  easily  be  observed  in  the  human  subject.  As  the  diaphragm  is  depressed, 
it  necessarily  pushes  the  viscera  before  it,  and  inspiration  is  therefore  accompanied  by 
protrusion  of  the  abdomen.  This  may  be  rendered  very  marked  by  a  forced  or  deep 
inspiration. 

The  action  of  the  diaphragm  may  be  illustrated  by  a  very  simple  yet  striking  experi- 
ment. In  an  animal  just  killed,  after  opening  the  abdomen,  if  we  take  hold  of  the  struct- 
ures which  are  attached  to  the  central  tendon  and  make  traction,  we  imitate,  in  a  rough 
way,  the  movements  of  the  diaphragm  in  respiration,  and  the  air  will  pass  into  the  lungs, 
sometimes  with  a  distinctly-audible  sound. 

The  effects  of  the  action  of  the  diaphragm  upon  the  size  of  its  orifices  are  chiefly 
limited  to  the  cesophageal  opening.  The  anatomy  of  the  parts  is  such  that  contraction 
of  the  muscular  fibres  has  a  tendency  to  close  this  orifice.  "When  we  come  to  treat  of 
the  digestive  system,  we  shall  see  that  the  contraction  of  the  diaphragm  is  auxiliary 
to  the  action  of  the  muscular  walls  of  the  oesophagus  itself,  by  which  the  cardiac  open- 
ing of  the  stomach  is  regularly  closed  during  inspiration.  This  may  become  important 
when  the  stomach  is  much  distended ;  for  descent  of  the  diaphragm  compresses  all  the 
abdominal  organs  and  might  otherwise  cause  regurgitation  of  food. 

The  contractions  of  the  diaphragm  are  animated  almost  exclusively,  if  not  exclu- 
sively, by  the  phrenic  nerve ;  a  nerve  which,  having  the  office  of  supplying  the  most 
important  respiratory  muscle,  derives  its  filaments  from  a  number  of  sources.  It  arises 
from  the  third  and  fourth  cervical  nerves,  receiving  a  branch  from  the  fifth  and  some- 
times from  the  sixth ;  it  passes  through  the  chest,  penetrates  the  diaphragm,  and  is  dis- 
tributed to  its  under  surface.  This  nerve  was  the  subject  of  numerous  experiments  by 
the  early  physiologists,  who  were  greatly  interested  in  the  minutiae  of  the  action  of  the 
diaphragm  and  of  other  muscles,  in  respiration.  Its  galvanization  produces  convulsive  con- 
tractions of  the  diaphragm,  and  its  section  paralyzes  the  muscle  almost  completely.  It 
was  noticed  by  Lower,  that  after  section  of  both  phrenic  nerves  the  movements  of  the 
abdomen  were  reversed,  and  it  became  retracted  in  inspiration.  This  is  explained  and 
illustrated  by  voluntary  suspension  of  the  action  of  the  diaphragm  and  exaggeration  of  the 
costal  movements.  As  the  ribs  are  raised,  the  atmospheric  pressure  causes  the  diaphragm 
to  mount  up  into  the  cavity  of  the  thorax,  and  of  course  the  abdominal  organs  follow. 

From  the  great  increase  in  the  capacity  of  the  chest  produced  by  the  action  of  the 
diaphragm  and  its  constant  and  universal  action  in  respiration,  it  must  be  regarded  as  by 
far  the  most  important  and  efficient  of  the  muscles  of  inspiration. 

Hiccough,  sobbing,  laughing,  and  crying,  are  due  mainly  to  the  action  of  the  dia- 
phragm, particularly  hiccough  and  sobbing,  which  are  produced  by  spasmodic  contrac- 
tions of  this  muscle,  generally  beyond  the  control  of  the  will. 

Action  of  the  Muscles  which  elevate  the  Ribs. — Scalene  Muscles. — In  ordinary  respira- 
tion, the  ribs  and  the  entire  chest  are  elevated  by  the  combined  action  of  a  number  of 
muscles.  The  three  scalene  muscles  are  attached  to  the  cervical  vertebrae  and  the  first 
and  second  ribs.  These  muscles,  which  act  particularly  upon  the  first  rib,  must  ele- 
vate with  it,  in  inspiration,  the  rest  of  the  thorax.  The  articulation  of  the  first  rib 
with  the  vertebral  column  is  very  movable,  but  it  is  joined  to  the  sternum  by  a  very 
short  cartilage,  which  allows  of  very  little  movement,  so  that  its  elevation  necessarily 
carries  with  it  the  sternum.  This  movement  increases  both  the  transverse  and  antero- 
posterior  diameters  of  the  thorax,  from  the  mode  of  articulation  and  direction  of  the 
ribs,  which  are  somewhat  rotated  as  well  as  rendered  more  horizontal. 

Intercostal  Muscles. — Concerning  the  mechanism  of  the  action  of  these  muscles,  there 
is  great  difference  of  opinion  among  physiologists ;  so  much,  indeed,  that  the  author  of 


126  RESPIRATION. 

a  late  elaborate  work  assumes  that  the  question  is  still  left  in  considerable  uncertainty. 
The  most  extended  researches  on  this  point  are  those  of  Beau  and  Maissiat  (Archives 
generales  de  medecine,  1843),  and  Sibson  (Philosophical  Transactions,  1846).  The  latter 
seem  to  settle  the  question  of  the  mode  of  action  of  the  intercostals  and  explain  satis- 
factorily certain  points  which  even  now  are  not  generally  appreciated.  More  recently, 
Onimus  has  shown,  by  experiments  upon  a  decapitated  animal,  that  the  external  inter- 
costals raise,  and  the  internal  intercostals  depress  the  ribs,  thus  confirming  the  views  of 
Sibson. 

We  shall  first  note  the  changes  which  take  place  in  the  direction  of  the  ribs  and  their 
relation  to  each  other  in  inspiration,  before  considering  the  way  in  which  these  move- 
ments are  produced. 

In  the  dorsal  region,  the  spinal  column  forms  an  arch  with  its  concavity  toward  the 
chest,  and  the  ribs  increase  in  length  progressively,  from  above  downward,  to  the  deep- 
est portion  of  the  arch,  where  they  are  longest  and  then  become  progressively  shorter. 
According  to  Sibson,  "  during  inspiration  the  ribs  approach  to  or  recede  from  each  other 
according  to  the  part  of  the  arch  with  which  they  articulate ;  the  four  superior  ribs  ap- 
proach each  other  anteriorly  and  recede  from  each  other  posteriorly ;  the  fourth  and 
fifth  ribs,  and  the  intermediate  set  (sixth,  seventh,  and  eighth),  move  further  apart  to  a 
moderate,  the  diaphragmatic  set  (four  inferior),  to  a  great  extent.  The  upper  edge  of 
each  of  these  ribs  glides  toward  the  vertebrse  in  relation  to  the  lower  edge  of  the  rib 
above,  with  the  exception  of  the  lowest  rib,  which  is  stationary."  These  movements 
increase  the  antero-posterior  and  transverse  diameters  of  the  thorax.  As  the  ribs  are 
elevated  and  become  more  nearly  horizontal,  they  must  push  forward  the  lower  portion 
of  the  sternum.  Their  configuration  and  mode  of  articulation  with  the  vertebrae  are 
such,  that  they  cannot  be  elevated  without  undergoing  a  considerable  rotation,  by  which 
the  concavity  looking  directly  toward  the  lungs  is  increased,  and  with  it  the  lateral 

diameter  of  the  chest.    All  the  intercostal  spaces  posteriorly 
are  widened  in  inspiration. 

The  ribs  are  elevated  by  the  action  of  the  external  inter- 
costals, the  sternal  portion  of  the  internal  intercostals,  and 
the  levatores  costarum.  The  external  intercostals  are  situ- 
ated between  the  ribs  only,  and  are  wanting  in  the  region 
of  the  costal  cartilages.  As  the  vertebral  extremities  of  the 
ribs  are  the  pivots  on  which  these  levers  move,  and  as  the 
sternal  extremities  are  movable,  the  direction  of  the  fibres 
of  the  intercostals  from  above  downward  and  forward 
renders  elevation  of  the  ribs  a  necessity  of  their  contrac- 
tion, if  it  can  be  assumed  that  the  first  rib  is  fixed  or  at 
least  does  not  move  downward.  The  scalene  muscles  ele- 
vate the  first  rib  in  ordinary  inspiration ;  and,  in  deep  in- 
FIG.  43.-Elevation  of  the  ribs  in  spiration,  this  takes  place  to  such  an  extent  as  to  palpably 
inspiration.  (Beciard.)  carrv  with  it  the  sternum  and  the  lower  ribs.  Theoreti- 

The  dark  lines  represent  the  ribs,  J  ,    ,  ,,  .         -, 

sternum,  and  costal  cartilages  in  cally,  then,  the  external  intercostals  can  do  nothing  but 
render  the  ribs  more  nearly  horizontal. 

If  the  external  intercostals  be  exposed  in  a  living  animal,  the  dog,  for  example,  in 
which  the  costal  type  of  respiration  is  very  marked,  close  observation  can  hardly  fail  to 
convince  any  one  that  these  muscles  enter  into  action  in  inspiration.  This  fact  has 
been  observed  by  Sibson  and  many  other  physiologists.  If  attention  be  directed  to  the 
sternal  portion  of  the  internal  intercostals,  situated  between  the  costal  cartilages,  their 
fibres  having  a  direction  from  above  downward  and  backward,  it  is  equally  evident  that 
they  enter  into  action  with  inspiration.  By  artificially  inflating  the  lungs  after  death, 
Sibson  confirmed  these  observations  and  showed  that,  when  the  lungs  are  filled  with 
air,  the  fibres  of  these  muscles  are  shortened.  In  inspiration,  the  ribs  are  all  separated 


MUSCLES   OF  INSPIRATION.  127 

posteriorly ;  but  laterally  and  anteriorly,  some  are  separated  (all  below  the  fourth),  and 
some  are  approximated  (all  above  the  fourth).  Thus  all  the  interspaces,  except  the 
anterior  portion  of  the  upper  three,  are  widened  in  inspiration.  Sibson  has  shown,  by 
inflation  of  the  chest,  that,  although  the  ribs  are  separated  from  each  other,  the  attach- 
ments of  the  intercostals  are  approximated.  The  ribs,  from  an  excessively  oblique  posi- 
tion, are  rendered  nearly  horizontal ;  and  consequently  the  inferior  attachments  of  the 
intercostals  are  brought  nearer  the  spinal  column,  while  the  superior  attachments  to  the 
upper  borders  of  the  ribs  are  slightly  removed  from  it.  Thus  these  muscles  are  short- 
ened. If,  by  separating  and  elevating  the  ribs,  the  muscles  be  shortened,  shortening  of 
the  muscles  will  necessarily  elevate  and  separate  the  ribs.  In  the  three  superior  inter- 
spaces, the  constant  direction  of  the  ribs  is  nearly  horizontal,  and  the  course  of  the 
intercostal  fibres  is  not  so  oblique  as  in  those  situated  between  the  lower  ribs.  These 
spaces  are  narrowed  in  inspiration.  The  muscles  between  the  costal  cartilages  have 
a  direction  opposite  to  that  of  the  external  intercostals  and  act  upon  the  ribs  from  the 
sternum,  as  the  others  do  from  the  spinal  column.  The  superior  interspace  is  narrowed, 
and  the  remainder  are  widened,  in  inspiration. 

Levatores  Costarum. — The  action  of  these  muscles  cannot  be  mistaken.  They  have 
immovable  points  of  origin,  the  transverse  processes  of  twelve  vertebras  from  the  last 
cervical  to  the  eleventh  dorsal,  and,  spreading  out  like  a  fan,  are  attached  to  the  upper 
edges  of  the  ribs  between  the  tubercles  and  the  angles.  In  inspiration,  they  contract 
and  assist  in  the  elevation  of  the  ribs.  They  are  more  developed  in  man  than  in  the 
inferior  animals. 

Auxiliary  Muscles  of  Inspiration. — The  muscles  which  have  just  been  considered  are 
competent  to  increase  the  capacity  of  the  thorax  sufficiently  in  ordinary  respiration; 
there  are  certain  muscles,  however,  which  are  attached  to  the  chest  and  the  upper  part 
of  the  spinal  column,  or  upper  extremities,  which  may  act  in  inspiration,  although  ordi- 
narily the  chest  is  the  fixed  point  and  they  move  the  head,  neck,  or  arms.  These 
muscles  are  brought  into  action  when  the  movements  of  respiration  are  exaggerated, 
When  this  exaggeration  is  but  slight  and  physiological,  as  after  exercise,  certain  of  them 
(the  ordinary  auxiliaries)  act  for  a  time,  until  the  tranquillity  of  the  movements  is 
restored.  But  when  there  is  obstruction  in  the  respiratory  passages  or  when  respiration 
is  excessively  difficult  from  any  cause,  threatening  suffocation,  all  the  muscles  which  can 
by  any  possibility  raise  the  chest  are  brought  into  action.  The  principal  ones  are  put 
down  in  the  table  under  the  head  of  extraordinary  auxiliaries.  Most  of  these  muscles 
can  voluntarily  be  brought  into  play  to  raise  the  chest,  and  the  mechanism  of  their 
action  can  in  this  way  be  demonstrated. 

Serratus  Posticus  Superior. — This  muscle  arises  from  the  ligamentum  nuchaa,  the 
spinous  processes  of  the  last  cervical  and  the  upper  two  or  three  dorsal  vertebras,  its  fibres 
passing  obliquely  downward  and  outward,  to  be  attached  to  the  upper  borders  of  the 
second,  third,  fourth,  and  fifth  ribs  just  beyond  their  angles.  By  reversing  its  action,  as 
we  have  reversed  the  description  of  its  origin  and  insertions,  it  is  capable  of  increasing 
the  capacity  of  the  thorax. 

Sterno-mastoideus. — That  portion  of  the  muscle  which  is  attached  to  the  mastoid 
process  of  the  temporal  bone  and  the  sternum,  when  the  head  is  fixed,  is  capable  of  act- 
ing as  a  muscle  of  inspiration.  It  does  not  act  in  ordinary  respiration,  but  its  contrac- 
tions can  be  readily  observed  whenever  respiration  is  hurried  or  exaggerated. 

The  following  muscles,  as  a  rule,  act  as  muscles  of  inspiration  only  when  respiration 
is  exceedingly  difficult  or  labored.  In  certain  cases  of  capillary  bronchitis,  for  example, 
the  anxious  expression  of  the  countenance  betrays  the  sense  of  impending  suffocation; 
the  head  is  thrown  back  and  fixed ;  the  shoulders  are  braced ;  and  every  available  muscle 
in  brought  into  action  to  raise  the  walls  of  the  thorax.1 

1  Under  these  circumstances,  some  muscles  which  we  have  not  thought  it  necessary  to  enumerate  may  act  in- 
directly as  muscles  of  inspiration. 


128  INSPIRATION. 

Letiator  Anguli  Scapula  and  Superior  Portion  of  the  Trapezius. — Movements  of  the 
scapula  have  often  been  observed  in  very  labored  respiration.  Its  elevation  during  in- 
spiration is  effected  chiefly  by  the  levator  anguli  scapulae  and  the  upper  portion  of  the 
trapezius.  The  former  muscle  arises  from  the  transverse  processes  of  the  upper  three  or 
four  cervical  vertebras  and  is  inserted  into  the  posterior  border  of  the  scapula  below  the 
angle.  It  is  a  thick,  flat  muscle  and,  when  the  neck  is  the  fixed  point,  assists  in  the  ele- 
vation of  the  thorax  by  raising  the  scapula.  The  trapezius  is  a  broad,  flat  muscle,  aris- 
ing from  the  occipital  protuberance,  part  of  the  superior  curved  line  of  the  occipital 
bone,  the  ligamentum  nuchas,  and  the  spinous  processes  of  the  last  cervical  and  all 
the  dorsal  vertebras,  to  be  inserted  into  the  upper  border  of  the  spine  of  the  scapula. 
Acting  from  its  attachments  to  the  occiput,  the  ligamentum  nuchas,  the  last  cervical 
vertebra,  and  perhaps  one  or  two  of  the  dorsal  vertebras,  this  muscle  may  elevate  the 
scapula  and  assist  in  inspiration. 

Pectoralis  Minor  and  Inferior  Portion  of  the  Pectoralis  Major. — These  muscles  act 
together  to  raise  the  ribs  in  difficult  respiration.  The  pectoralis  minor  is  the  more  effi- 
cient. Tracing  it  from  its  attachment  to  the  coracoid  process  of  the  scapula,  its  fibres 
pass  downward  and  forward  to  be  attached  by  three  indigitations  to  the  external  surface 
and  upper  margins  of  the  third,  fourth,  and  fifth  ribs  just  posterior  to  the  costal  cartilages. 
With  the  coracoid  process  as  the  fixed  point,  this  muscle  is  capable  of  powerfully  assist- 
ing in  the  elevation  of  the  ribs.  That  portion  of  the  pectoralis  major  which  is  attached 
to  the  lower  part  of  the  sternum  and  costal  cartilages  is  capable  of  acting  from  its  in- 
sertion into  the  bicipital  groove  of  the  humerus,  when  the  shoulders  are  fixed,  in  concert 
with  the  pectoralis  minor.  In  great  dyspncea,  it  is  frequently  observed  that  the  shoulders 
are  braced,  the  pectorals  acting  vigorously  to  raise  the  walls  of  the  chest. 

Serratus  Magnus.  —This  is  a  broad,  thin  muscle  covering  a  great  portion  of  the  lat- 
eral walls  of  the  thorax.  Attached  to  the  inner  margin  of  the  posterior  border  of  the 
scapula,  its  fibres  pass  forward  and  downward  and  are  attached  to  the  external  surface 
and  upper  borders  of  the  eight  superior  ribs.  Acting  from  the  scapula,  this  muscle  is 
capable  of  assisting  the  pectorals  in  raising  the  ribs  and  becomes  a  powerful  auxiliary  in 
difficult  inspiration. 

"We  have  thus  considered  the  functions  of  the  principal  inspiratory  muscles,  without 
taking  up  those  which  have  an  insignificant  or  undetermined  action.  In  many  animals, 
the  nares  are  considerably  distended  in  inspiration ;  and,  in  the  horse,  which  does 
not  -respire  by  the  mouth,  these  movements  are  as  essential  to  life  as  the  respiratory 
movements  of  the  larynx.  In  man,  as  a  rule,  the  nares  undergo  no  movement  unless 
respiration  be  somewhat  exaggerated.  In  very  difficult  respiration,  the  mouth  is  opened 
at  each  inspiratory  act.  We  have  not  thought  it  necessary  to  treat  of  the  action  of  those 
muscles  which  serve  to  fix  the  head,  neck,  or  shoulders  in  dyspnoea. 

The  division  into  muscles  of  ordinary  inspiration,  ordinary  auxiliaries,  and  extraor- 
dinary auxiliaries,  must  not  be  taken  as  absolute.  In  the  male,  in  ordinary  respiration, 
the  diaphragm,  intercostals,  and  levatores  costarum  are  the  great  inspiratory  muscles, 
and  the  action  of  the  scaleni,  with  the  consequent  elevation  of  the  sternum,  is  commonly 
very  slight  or  may  be  wanting.  In  the  female,  the  movements  of  the  upper  parts  of 
the  chest  are  very  marked,  and  the  scaleni,  the  serratus  posticus  superior,  and  sometimes 
the  stern o-mastoid,  are  brought  into  action  in  ordinary  respiration.  In  the  various  types 
of  respiration,  the  action  of  the  muscles  engaged  in  ordinary  respiration  necessarily  pre- 
sents considerable  variations. 

Expiration. 

The  air  is  expelled  from  the  lungs,  in  ordinary  expiration,  by  a  simple  and  compara- 
tively-passive process.  The  lungs  contain  a  great  number  of  elastic  fibres  surrounding 
the  air-cells  and  the  smallest  ramifications  of  the  bronchial  tubes,  which  give  them  great 
elasticity.  We  can  form  an  idea  of  the  extent  of  elasticity  of  these  organs,  by  simply 
removing  them  from  the  chest,  when  they  collapse  and  become  many  times  smaller  than 


MUSCLES   OF  INSPIRATION-.  139 

the  cavity  which  they  before  had  completely  filled.  The  thoracic  walls  are  also  very 
elastic,  particularly  in  young  persons.  After  the  muscles  which  increase  the  capacity 
of  the  thorax  cease  their  action,  the  elasticity  of  the  costal  cartilages  and  the  tonicitv 
of  the  muscles  which  have  been  put  on  the  stretch  will  restore  the  chest  to  what  we  may 
call  its  passive  dimensions.  This  elasticity  is  likewise  capable  of  acting  as  an  inspiratory 
force  when  the  chest  has  been  compressed  in  any  way.  There  are  also  certain  muscles, 
the  action  of  which  is  to  draw  the  ribs  downward  and  which,  in  tranquil  respiration, 
are  antagonistic  to  those  which  elevate  the  ribs.  Aside  from  this,  many  operations,  such 
as  speaking,  blowing,  singing,  etc.,  require  powerful,  prolonged,  or  complicated  acts  of 
expiration,  in  which  numerous  muscles  are  brought  into  play. 

Expiration  may  be  considered  as  depending  upon  two  causes,  as  follows : 

1.  The  passive  influence  of  the  elasticity  of  the  lungs  and  thoracic  walls. 

2.  The  action  of  certain  muscles,  which  either  diminish  the  transverse  and  antero- 
posterior  diameters  of  the  chest  by  depressing  the  ribs  and  sternum,  or  the  vertical  di- 
ameter, by  pressing  up  the  abdominal  viscera  behind  the  diaphragm. 

Influence  of  the  Elasticity  of  the  Pulmonary  Structure  and  Walls  of  the  Chest. — 
It  is  easy  to  understand  the  influence  of  the  elasticity  of  the  pulmonary  structure  in  ex- 
piration. From  the  collapse  of  the  lungs  when  openings  are  made  in  the  chest,  it  is  seen 
that,  even  after  the  most  complete  expiration,  these  organs  have  a  tendency  to  expel 
part  of  their  gaseous  contents,  which  cannot  be  fully  satisfied  until  the  chest  is  opened. 
They  remain  partially  distended,  from  the  impossibility  of  collapse  of  the  thoracic  walls 
beyond  a  certain  point ;  and,  by  virtue  of  their  elasticity,  they  exert  a  suction  force 
upon  the  diaphragm,  causing  it  to  form  a  vaulted  arch,  or  dome  above  the  level  of  the 
lower  circumference  of  the  chest.  When  the  lungs  are  collapsed,  the  diaphragm  hangs 
loosely  between  the  abdominal  and  thoracic  cavities.  In  inspiration  and  in  expiration, 
then,  the  relations  between  the  lungs  and  diaphragm  are  reversed.  In  inspiration,  the 
descending  diaphragm  exerts  a  suction  force  on  the  lungs,  drawing  them  downward ;  in 
expiration,  the  elastic  lungs  exert  a  suction  force  upon  the  diaphragm,  drawing  it  up- 
ward. This  antagonism  is  one  of  the  causes  of  the  great  power  of  the  diaphragm  as  an 
inspiratory  muscle. 

The  elasticity  of  the  lungs  operates  chiefly  upon  the  diaphragm  in  reducing  the  capa- 
city of  the  chest ;  for  the  walls  of  the  thorax,  by  virtue  of  their  own  elasticity,  have  a 
reaction  which  succeeds  the  movements  produced  by  the  inspiratory  muscles.  A  simple 
experiment,  which  we  have  often  performed  in  public  demonstrations,  illustrates  the 
expiratory  influence  of  the  elasticity  of  the  lungs.  If,  in  an  animal  just  killed,  we 
open  the  abdomen,  seize  hold  of  the  vena  cava  as  it  passes  through  the  diaphragm,  and 
make  traction,  we  imitate  the  action  of  this  muscle  sufficiently  to  produce  at  times  an 
audible  inspiration  ;  on  loosing  our  hold,  we  have  expiration,  as  it  is  in  a  measure  accom- 
plished in  natural  respiration,  by  virtue  of  the  resiliency  of  the  lungs,  carrying  the  dia- 
phragm up  into  the  thorax.  Although  this  is  the  main  action  of  the  lungs  themselves 
in  expiration,  their  relations  to  the  walls  of  the  thorax  are  important.  By  virtue  of 
their  elasticity,  they  assist  the  passive  collapse  of  the  chest.  "When  they  lose  this  prop- 
erty to  any  considerable  extent,  as  in  vesicular  emphysema,  they  offer  a  notable  resistance 
to  the  contraction  of  the  thorax ;  so  much,  indeed,  that  in  old  cases  of  this  disease  the 
movements  are  much  restricted,  and  the  chest  presents  a  characteristic  rounded  and  dis- 
tended appearance. 

Little  more  need  be  said  concerning  the  passive  movements  of  the  thoracic  walls. 
"When  the  action  of  the  inspiratory  muscle  ceases,  the  ribs  regain  their  oblique  direction, 
the  intercostal  spaces  are  narrowed,  and  the  sternum,  if  it  have  been  elevated  and  drawn 
forward,  falls  back  to  its  place  simply  by  virtue  of  the  elasticity  of  the  parts. 

Action  of  Muscles  in  Expiration. — The  following  are  the  principal  muscles  concerned 
in  expiration :  . 


130  EESPIRATION. 

Muscles  of  Expiration. 

Ordinary  Respiration. 

Muscle.  Attachments. 

Osseous  portion  of  internal  intercostal s .  .Inner  borders  of  the  ribs. 

Infracostales Inner  surfaces  of  the  ribs. 

Triangularis  sterni Ensiform  cartilage,  lower  borders  of  sternum,  lower  three 

or  four  costal  cartilages cartilages  of  the  second, 

third,  -fourth,  and  fifth  ribs. 

Auxiliaries. 

Obliquus  externus External  surface  and  inferior  borders  of  eight  inferior 

ribs anterior  half  of  the  crest  of  the  ileum,  Pou- 

:  .  part's  ligament,  linea  alba. 

Obliquus  internus Outer  half  of  Poupart's  ligament,  anterior  two-thirds  of 

the  crest  of  the  iLeum,  lumbar  fascia cartilages  of 

four  inferior  ribs,  linea  alba,  crest  of  the  pubis,  pec- 
tineal  line. 

Transversalis Outer  third  of  Poupart's  ligament,  anterior  two-thirds  of 

the  crest  of  the  ileum,  lumbar  vertebrae,  inner  surface 

of  cartilages  of  six  inferior  ribs crest  of  the  pubis, 

pectineal  line,  linea  alba. 

Sacro-lumbalis Sacrum angles  of  six  inferior  ribs. 

Internal  Intercostals. — The  internal  intercostals  have  different  functions  in  different 
parts  of  the  thorax.  They  are  attached  to  the  inner  borders  of  the  ribs  and  costal  carti- 
lages. Between  the  ribs,  they  are  covered  by  the  external  intercostals,  but,  between  the 
costal  cartilages,  they  are  covered  simply  by  aponeurosis.  Their  direction  is  from  above 
downward  and  backward,  nearly  at  right  angles  to  the  external  intercostals.  The  function 
of  that  portion  of  the  internal  intercostals  situated  between  the  costal  cartilages  has  al- 
ready been  noted.  They  assist  the  internal  intercostals  in  elevating  the  ribs  in  inspiration. 
Between  the  ribs,  these  muscles  are  directly  antagonistic  to  the  external  intercostals. 
They  are  more  nearly  at  right  angles  to  the  ribs,  particularly  in  that  portion  of  the  tho- 
rax where  the  obliquity  of  the  ribs  is  greatest.  The  observations  of  Sibson  have  shown 
that  they  are  elongated  when  the  chest  is  distended,  and  shortened  when  the  chest  is 
collapsed.  This  fact,  taken  in  connection  with  experiments  on  living  animals,  shows 
that  they  are  muscles  of  expiration.  Their  contraction  tends  to  depress  the  ribs  and 
consequently  to  diminish  the  capacity  of  the  chest.  If  we  bring  an  animal,  a  dog  for 
example,  completely  under  the  influence  of  ether,  expose  the  walls  of  the  chest,  dissect  off 
the  fascia  from  some  of  the  external  intercostals,  and  then  remove  carefully  a  portion  of 
one  or  two  of  these  muscles  so  as  to  expose  the  fibres  of  the  internal  intercostals,  it  is 
not  difficult,  on  close  examination,  to  observe  the  antagonism  between  the  two  sets  of 
muscles ;  one  being  brought  into  action  in  inspiration  and  the  other,  in  expiration. 

Infracostales. — These  muscles,  situated  at  the  posterior  part  of  the  thorax,  are  vari- 
able in  size  and  number.  They  are  most  common  at  the  lower  part  of  the  chest.  Their 
fibres  arise  from  the  inner  surface  of  one  rib  to  be  inserted  into  the  inner  surface  of  the 
first,  second,  or  third  rib  below.  The  fibres  follow  the  direction  of  the  internal  intercos- 
tals, and,  acting  from  their  lower  attachments,  their  contractions  assist  these  muscles  in 
drawing  the  ribs  downward. 

Triangularis  Sterni. — There  has  never  been  any  doubt  concerning  the  expiratory  func- 
tion of  the  triangularis  sterni.  From  its  origin,  the  ensiform  cartilage,  lower  borders  of 
the  sternum,  and  lower  three  or  four  costal  cartilages,  it  acts  upon  the  cartilages  of  the 
second,  third,  fourth,  and  fifth  ribs,  to  which  it  is  attached,  drawing  them  downward  and 
thus  diminishing  the  capacity  of  the  chest. 


TYPES   OF  RESPIRATION.  131 

The  above-mentioned  muscles  are  called  into  action  in  ordinary  tranquil  respiration, 
and  their  sole  function  is  to  diminish  the  capacity  of  the  chest.  In  labored  or  difficult 
expiration,  and  in  the  acts  of  blowing,  phonation,  etc.,  other  muscles,  which  are  called 
auxiliaries,  play  a  more  or  less  important  part.  These  muscles  all  enter  into  the  forma- 
tion of  the  walls  of  the  abdomen,  and  their  general  action  in  expiration  is  to  press  the 
abdominal  viscera  and  diaphragm  into  the  thorax  and  diminish  its  vertical  diameter. 
Their  action  is  voluntary ;  and,  by  an  effort  of  the  will,  it  may  be  opposed  more  or  less 
by  the  diaphragm,  by  which  means  the  duration  or  intensity  of  the  expiratory  act  is  regu- 
lated. They  are  also  attached  to  the  ribs  or  costal  cartilages,  and,  while  they  press  the 
diaphragm  upward,  depress  the  ribs  and  thus  diminish  the  antero-posterior  and  transverse 
diameters  of  the  chest.  In  this  action,  they  may  be  opposed  by  the  voluntary  contraction 
of  the  muscles  which  raise  the  ribs,  also  for  the  purpose  of  regulating  the  character  of  the 
expiratory  act.  The  importance  of  this  kind  of  action  in  declamation,  singing,  blowing, 
etc.,  is  evident ;  and  the  skill  exhibited  by  vocalists  and  performers  on  wind  instruments 
shows  how  delicately  this  may  be  regulated  by  practice. 

In  labored  respiration  in  disease  and  in  the  hurried  respiration  which  follows  violent 
exercise,  the  auxiliary  muscles  of  expiration,  as  well  as  of  inspiration,  are  called  into 
action  to  a  considerable  extent. 

Olliquus  Externus. — This  muscle,  in  connection  with  the  obliquus  internus  and  trans- 
versalis,  is  efficient  in  forced  or  labored  expiration,  by  pressing  the  abdominal  viscera 
against  the  diaphragm.  Its  fibres  run  obliquely  from  above  downward  and  forward. 
Acting  from  its  attachments  to  the  linea  alba,  the  crest  of  the  ileum,  and  Poupart's  liga- 
ment, by  its  attachment  to  the  eight  inferior  ribs,  it  draws  the  ribs  downward. 

Obliquus  Internus. — This  muscle  also  acts  in  forced  expiration,  by  compressing  the  ab- 
dominal viscera.  The  direction  of  its  fibres  is  from  below  upward  and  forward.  Acting 
from  its  attachments  to  the  crest  of  the  ileum,  Poupart's  ligament,  and  the  lumbar  fascia, 
by  its  attachments  to  the  cartilages  of  the  four  inferior  ribs,  it  draws  them  downward. 
The  direction  of  the  fibres  of  this  muscle  is  the  same  as  that  of  the  internal  intercostals. 
By  its  action  the  ribs  are  drawn  inward  as  well  as  downward. 

Transversalis. — The  expiratory  action  of  this  muscle  is  mainly  in  compressing  the  ab- 
dominal viscera. 

Sacro-lumbalis. — This  muscle  is  situated  at  the  posterior  portion  of  the  abdomen  and 
thorax.  Its  fibres  pass  from  its  origin  at  the  sacrum,  upward  and  a  little  outward,  to  be 
inserted  into  the  six  inferior  ribs  at  their  angles.  In  expiration  it  draws  the  ribs  down- 
ward, acting  as  an  antagonist  to  the  lower  levatores  costarum. 

There  are  some  other  muscles  which  may  be  brought  into  action  in  forced  expiration, 
assisting  in  the  depression  of  the  ribs,  such  as  the  serratus  posticus  inferior,  the  superior 
fibres  of  the  serratus  magnus,  the  inferior  portion  of  the  trapezius,  but  their  function  is 
unimportant. 

Types  of  Respiration. — In  the  expansive  movements  of  the  chest,  although  all  the 
muscles  which  have  been  classed  as  ordinary  inspiratory  muscles  are  brought  into  action 
to  a  greater  or  less  extent,  the  fact  that  certain  sets  may  act  in  a  more  marked  manner 
than  others  has  led  physiologists  to  recognize  different  types  of  respiration.  The  three 
following  types  are  generally  given-in  works  on  physiology  : 

1.  The  Abdominal  type. — In  this,  the  action  of  the  diaphragm  and  the  consequent 
movements  of  the  abdomen  are  most  prominent. 

2.  The  Inferior  Costal  type.— In  this,  the  action  of  the  muscles  which  expand  the 
lower  part  of  the  thorax,  from  the  seventh  rib  inclusive,  is  most  prominent. 

3.  The  Superior  Costal  type. — In  this,  the  action  of  the  muscles  which  dilate  the  thorax 
above  the  seventh  rib  and  which  elevate  the  entire  chest  is  most  prominent. 

The  abdominal  type  is  most  marked  in  children  under  the  age  of  three  years,  irrespec- 
tive of  sex.  In  them,  respiration  is  carried  on  almost  exclusively  by  the  diaphragm. 


132  RESPIRATION. 

At  a  variable  period  after  birth,  a  difference  in  the  types  of  respiration  in  the  sexes 
begins  to  show  itself.  In  the  male,  the  abdominal  conjoined  with  the  inferior  costal  type 
is  predominant,  and  this  continues  through  life.  In  the  female,  the  inferior  costal  type 
is  insignificant,  and  the  superior  costal  type  predominates.  Observers  differ  in  their  state- 
ments of  the  period  of  life  when  this  distinction  in  the  sexes  becomes  apparent.  .Without 
discussing  the  nice  question  as  to  the  exact  age  when  this  difference  in  the  sexes  first 
makes  its  appearance,  it  may  be  stated,  in  general  terms,  that,  shortly  before  the  age  of 
puberty  in  the  female,  the  superior  costal  type  becomes  more  marked  and  soon  predomi- 
nates ;  while,  in  the  male,  respiration  continues  to  be  carried  on  mainly  by  the  diaphragm 
and  lower  part  of  the  chest. 

The  cause  of  the  excessive  movements  of  the  upper  part  of  the  chest  in  the  female  has 
been  the  subject  of  considerable  discussion.  It  is  evident  that  it  is  not  due  to  the  mode 
of  dress  now  so  general  in  civilized  countries,  which  confines  the  lower  part  of  the  chest 
and  would  render  movements  of  expansion  somewhat  difficult,  for  the  same  phenomenon 
is  observed  in  young  girls  and  others  who  have  never  made  use  of  such  appliances.  But 
there  is  evidently  a  physiological  condition,  the  enlargement  of  the  uterus  in  gestation, 
which,  at  certain  times,  would  nearly  arrest  all  respiratory  movements,  except  those 
of  the  upper  part  of  the  chest.  The  peculiar  mode  of  respiration  in  the  female  is  a  pro- 
vision of  Nature  against  the  mechanical  difficulties  which  would  otherwise  follow  the 
physiological  enlargement  of  the  uterus.  In  pathology  it  is  observed  that,  in  consequence 
of  this  peculiarity,  females  are  able  to  carry,  without  great  inconvenience,  immense  quan- 
tities of  water  in  the  abdominal  cavity ;  while  a  much  smaller  quantity,  in  the  male,  pro- 
duces great  distress  from  difficulty  of  breathing. 

Frequency  of  the  Respiratory  Movements. — In  counting  the  respiratory  acts,  it  is  de- 
sirable that  the  subject  be  unconscious  of  the  observation,  otherwise  their  normal  char- 
acter is  apt  to  be  disturbed.  Of  all  who  have  written  on  this  subject,  Hutchinson  pre- 
sents the  most  numerous  and  convincing  collection  of  facts.  This  observer  ascertained 
the  number  of  respiratory  acts  per  minute,  in  the  sitting  posture,  in  1,897  males.  The 
results  of  his  observations,  with  reference  to  frequency,  are  given  in  the  following  table : 

Respirations  per  minute.                                                                                                     Number  of  cases. 
From     9  to  16.. 79 

16  239 

17 105 

18  195 

19  74 

20  561 

21 129 

22  143 

23  42 

24  243 

24  to  40 87 

Although  this  table  shows  considerable  variation  in  different  individuals,  the  great 
majority  (1,731)  breathed  from  sixteen  to  twenty-four  times  per  minute.  Nearly  a  third 
breathed  twenty  times  per  minute,  a  number  which  may  be  taken  as  the  average. 

The  relations  of  the  respiratory  acts  to  the  pulse  are  quite  constant  in  health.  It  has 
been  shown  by  Hutchinson  that  the  proportion  in  the  great  majority  of  instances  is  one 
respiratory  act  to  every  four  pulsations  of  the  heart.  The  same  proportion  generally 
obtains  when  the  pulse  is  accelerated  in  disease,  except  when  the  pulmonary  organs  are 
involved. 

Age  has  an  influence  on  the  frequency  of  the  respiratory  acts,  corresponding  with 
what  we  have  already  noted  with  regard  to  the  pulsations  of  the  heart. 


RESPIRATORY   SOUNDS.  133 

Quetelet  gives  the  following  as  the  results  of  observations  on  300  males  : 

44  respirations  per  minute,  soon  after  birth  ; 

26,  at  the  age  of  five  years  ; 

20,  at  the  age  of  fifteen  to  twenty  years  ; 

19,  at  the  age  of  twenty  to  twenty -five  years ; 

16,  about  the  thirtieth  year ; 

18,  from  thirty  to  fifty  years. 

The  influence  of  sex  is  not  marked  in  very  young  children.  The  same  observer  noted 
no  difference  between  males  and  females  at  birth ;  but  in  young  women  the  respirations 
are  a  little  less  frequent  than  in  young  men  of  the  same  age. 

The  various  physiological  conditions  which  have  been  noted  as  affecting  the  pulse 
have  a  corresponding  influence  on  respiration.  In  sleep,  the  number  of  respiratory  acts 
is  diminished  by  about  twenty  per  cent.  (Quetelet).  Muscular  effort  accelerates  the  re- 
spiratory movements  ^ari  passu  with  the  movements  of  the  heart. 

Relations  of  Inspiration  and  Expiration  to  each  other — The  Respiratory  /Sounds. — In 
ordinary  respiration,  inspiration  is  produced  by  the  action  of  muscles,  and  expiration,  in 
greatest  part,  by  the  passive  reaction  of  the  elastic  walls  of  the  thorax  and  the  lungs. 
The  inspiratory  and  expiratory  acts  do  not  immediately  follow  each  other.  Commencing 
with  inspiration,  it  is  found  that  this  act  maintains  about  the  same  intensity  from  its  be- 
ginning to  its  termination;  there  is  then  a  very  brief  interval,  when  expiration  follows, 
which  has  its  maximum  of  intensity  at  the  commencement  of  the  act  and  gradually  dies 
away.1  Between  the  acts  of  expiration  and  inspiration  is  an  interval,  which  is  somewhat 
longer  than  that  which  occurs  after  inspiration. 

The  duration  of  expiration  is  generally  somewhat  greater  than1  that  of  inspiration, 
although  they  may  be  nearly,  or  in  some  instances  quite  equal.  After  from  five  to  eight 
ordinary  respiratory  acts,  an  effort  generally  occurs  which  is  rather  more  profound  than 
the  rest,  and  by  which  the  air  in  the  lungs  is  more  effectually  changed.  The  temporary 
arrest  of  the  acts  of  respiration  in  violent  muscular  efforts,  in  straining,  in  parturition, 
etc.,  is  familiar  to  all. 

Ordinarily  respiration  is  not  accompanied  by  any  sound  which  can  be  heard  without 
applying  the  ear  directly,  or  by  the  intervention  of  a  stethoscope,  to  the  respiratory 
organs;  except  when  the  mouth  is  closed  and  breathing  is  carried  on  exclusively- 
through  the  nasal  passages,  when  a  soft,  breezy  murmur  accompanies  both  acts.  If  the 
mouth  be  sufficiently  opened  to  admit  the  free  passage  of  air,  no  sound  is  to  be  heard  in 
health.  In  sleep,  the  respirations  are  unusually  profound ;  and,  if  the  mouth  be  closed, 
the  sound  is  rather  more  intense. 

Snoring,  a  peculiar  sound,  more  or  less  marked,  which  sometimes  accompanies  the 
respiratory  acts  during  sleep,  occurs  when  the  air  passes  through  both  the  mouth  and  the 
nose.  It  is  more  marked  in  inspiration,  sometimes  accompanying  both  acts,  and  sometimes 
it  is  not  heard  in  expiration.  It  is  not  necessary  to  describe  the  characters  of  a  sound 
so  familiar.  Snoring  is  an  idiosyncrasy  with  many  individuals,  although  those  who  do  not 
snore  habitually  may  do  so  when  the  system  is  unusually  exhausted  and  relaxed.  It  only 
occurs  when  the  mouth  is  open,  and  the  sound  is  produced  by  vibration  and  a  sort  of 
flapping  of  the  velum  pendulum  palati,  between  the  two  currents  of  air  from  the  mouth 
and  nose,  together  with  a  vibration  in  the  column  of  air  itself. 

Applying  the  stethoscope  over  the  larynx  or  trachea,  a  sound  is  heard,  of  a  distinctly 
and  purely  tubular  character,  accompanying  both  acts  of  respiration.  In  inspiration, 
according  to  Dr.  Austin  Flint,  "  it  attains  its  maximum  of  intensity  quickly  after  the  de- 
velopment of  the  sound  and  maintains  the  same  intensity  to  the  close  of  the  act,  when 
the  sound  abruptly  ends,  as  if  suddenly  cut  off."  After  a  brief  interval,  the  sound  of  ex- 

1  In  listening  to  the  respiratory  murmur  over  the  substance  of  the  lungs,  the  expiratory  follows  the  inspiratory 
Bound  without  an  interval.  The  interval  between  the  acts  of  inspiration  and  expiration  is  only  appreciated  as  the  air 
passes  in  and  out  at  the  mouth. 


134  KESPIRATION. 

piration  follows.  This  is  also  tubular  in  quality ;  it  soon  attains  its  maximum  of  intensity, 
but,  unlike  the  sound  of  inspiration,  gradually  dies  away  and  is  lost  imperceptibly.  It  is 
seen  that  these  phenomena  correspond  with  the  nature  of  the  two  acts  of  respiration. 

Sounds  approximating  in  character  to  the  foregoing  are  heard  over  the  bronchial 
tubes  before  they  penetrate  the  lungs. 

Over  the  substance  of  the  lungs,  a  sound  may  be  heard  entirely  different  in  its  char- 
acter from  that  heard  over  the  larynx,  trachea,  or  bronchial  tubes.  In  inspiration,  the 
sound  is  much  less  intense  than  over  the  trachea  and  has  a  breezy,  expansive,  or  what 
is  called  in  auscultation  a  vesicular  character.  It  is  much  lower  in  pitch  than  the  trachea! 
sound.  It  is  continuous  and  rather  increases  in  intensity  from  its  commencement  to  its 
termination,  ending  abruptly,  like  the  tracheal  inspiratory  sound.  The  sound  is  produced 
in  part  by  the  movement  of  air  in  the  small  bronchial  tubes,  but  chiefly  by  the  expansion 
of  the  innumerable  air-cells  of  the  lungs.  It  is  followed,  without  an  interval,  by  the  sound 
of  expiration,  which  is  shorter,  one-fifth  to  one-fourth  as  long,  lower  in  pitch,  and  very 
much  less  intense.  A  sound  is  not  always  heard  in  expiration. 

The  variations  in  the  intensity  of  the  respiratory  sounds  in  different  individuals  are 
very  considerable.  As  a  rule  they  are  more  intense  in  young  persons ;  which  has  given 
rise  to  the  term  puerile  respiration,  when  the  sounds  are  exaggerated  in  parts  of  the  lung, 
in  certain  cases  of  disease.  The  sounds  are  generally  more  intense  in  females  than  in 
males,  particularly  in  the  upper  regions  of  the  thorax. 

It  is  difficult  by  any  description  or  comparison  to  convey  an  accurate  idea  of  the 
character  of  the  sounds  heard  over  the  lungs  and  air-passages,  and  it  is  superfluous  to 
make  the  attempt,  when  they  can  be  so  easily  studied  in  the  living  subject. 

Coughing,  Sneezing,  Sighing,  Yawning,  Laughing,  Sobbing,  and  Hiccough. — These 
peculiar  acts  demand  a  few  words  of  explanation.  Coughing  and  sneezing  are  gen- 
erally involuntary  acts,  produced  by  irritation  in  the  air-tubes  or  nasal  passages,  al- 
though coughing  is  often  voluntary.  In  both  of  these  acts,  there  is  first  a  deep  in- 
spiration, followed  by  a  convulsive  action  of  the  expiratory  muscles,  by  which  the 
air  is  violently  expelled  with  a  characteristic  sound,  in  the  one  case  by  the  mouth, 
and  in  the  other  by  the  mouth  and  nares.  Foreign  bodies  lodged  in  the  air-passages 
are  frequently  expelled  in  violent  fits  of  coughing.  In  hypersecretion  of  the  bron- 
chial mucous  membrane,  the  accumulated  mucus  is  carried  by  the  act  of  coughing 
either  to  the  mouth  or  well  into  the  larynx,  whence  it  is  expelled  by  the  act  of  ex- 
pectoration. When  either  of  these  acts  is  the  result  of  irritation  from  a  foreign  sub- 
stance or  secretions,  it  may  be  modified  or  partly  smothered  by  the  will,  but  is  not  com- 
pletely under  control.  The  exquisite  sensibility  of  the  mucous  membrane  at  the  summit 
of  the  air-passages,  under  most  circumstances,  protects  them  from  the  entrance  of  foreign 
matters,  both  liquid  and  solid ;  for  the  slightest  impression  received  by  the  membrane 
gives  rise  to  a  violent  and  involuntary  cough,  by  which  the  offending  matter  is  removed. 
The  glottis  is  also  spasmodically  contracted. 

In  sighing,  a  prolonged  and  deep  inspiration  is  followed  by  a  rapid  and  generally  an 
audible  expiration.  This  occurs,  as  a  general  rule,  once  in  from  five  to  eight  respiratory 
acts,  for  the  purpose  of  changing  the  air  in  the  lungs  more  completely,  and  it  is  due  to  an 
exaggeration  of  the  cause  which  gives  rise  to  the  ordinary  acts  of  respiration.  When  due 
to  depressing  emotions,  it  has  the  same  cause;  for,  at  such  times,  respiration  is  less 
effectually  performed.  Yawning  is  an  analogous  process,  but  differs  from  sighing  in  the 
fact  that  it  is  involuntary  and  cannot  be  produced  by  an  effort  of  the  will.  It  is  charac- 
terized by  a  wide  opening  of  the  mouth  and  a  very  profound  inspiration.  Yawning  is 
generally  assumed  to  be  an  evidence  of  fatigue,  but  it  often  occurs  from  a  sort  of  con- 
tagion. When  not  the  result  of  imitation,  it  has  the  same  exciting  cause  as  sighing,  viz., 
deficient  oxygenation  of  the  blood,  and  it  is  followed  by  a  sense  of  satisfaction,  which  shows 
that  it  meets  some  decided  want  on  the  part  of  the  system. 


CAPACITY   OF  THE  LUNGS.  135 

Laughing  and  sobbing,  though  expressing  opposite  conditions,  are  produced  by  very 
much  the  same  mechanism.  The  characteristic  sounds  accompanying  these  acts  are  the 
result  of  short,  rapid,  and  convulsive  movements  of  the  diaphragm,  accompanied  by  con- 
tractions of  the  muscles  of  the  face,  which  produce  the  expressions  characteristic  of 
hilarity  or  grief.  Although  to  a  certain  extent  under  the  control  of  the  will,  these  acts  are 
mainly  involuntary.  Violent  and  convulsive  laughter  may  be  excited  in  many  individuals 
by  titillation  of  certain  portions  of  the  surface  of  the  body.  Laughter  and  sometimes 
sobbing,  like  yawning,  may  be  the  result  of  involuntary  imitation. 

Hiccough  is  a  peculiar  modification  of  the  act  of  inspiration,  to  which  it  is  exclusively 
confined.  It  is  produced  by  a  sudden,  convulsive,  and  entirely  involuntary  contraction 
of  the  diaphragm,  accompanied  by  a  spasmodic  constriction  of  the  glottis.  The  contrac- 
tion of  the  diaphragm  is  more  extensive  than  in  laughing  and  sobbing  and  occurs  only 
once  every  four  or  five  respiratory  acts.  The  causes  which  give  rise  to  hiccough  are  nu- 
merous, and  many  of  them  are  referable  to  the  digestive  system.  Among  these  may  be 
mentioned  the  rapid  ingestion  of  a  quantity  of  dry  food  or  of  effervescing  or  alcoholic 
drinks.  It  occurs  frequently  in  cases  of  disease. 

Capacity  of  the  Lungs,  and  the  Quantity  of  Air  changed  in  the  Respiratory 

Acts. 

Several  points  of  considerable  physiological  interest  arise  in  this  connection.  It  is 
evident,  from  the  simple  experiment  of  opening  the  chest,  when  the  elastic  lungs  collapse 
and  expel  a  certain  quantity  of  air  which  cannot  be  removed  while  the  lungs  are  in  situ, 
that  a  part  of  the  gaseous  contents  of  these  organs  necessarily  remains  after  the  most 
complete  and  forcible  expiration.  After  an  ordinary  act,  there  is  a  certain  quantity 
of  air  in  the  lungs  which  can  be  expelled  by  a  forced  expiration.  In  ordinary  respi- 
ration, a  comparatively  small  volume  of  air  is  introduced  with  inspiration,  which  is  ex- 
pelled by  the  succeeding  expiration.1  By  the  extreme  action  of  all  the  inspiratory 
muscles  in  a  forced  inspiration,  a  supplemental  quantity  of  air  may  be  introduced  into  the 
lungs,  which  then  contain  much  more  than  they  ever  do  in  ordinary  respiration.  For 
convenience,  many  physiologists  have  adopted  the  following  names,  which  are  applied  to 
these  various  volumes  of  air : 

1.  Residual  Air  ;  that  which  is  not  and  cannot  be  expelled  by  a  forced  expiration. 

2.  Reserve  Air ;   that  which  remains  after  an  ordinary  expiration,  deducting  the 
residual  air. 

3.  Tidal,  or  ordinary  Breathing  Air ;  that  which  is  changed  by  the  ordinary  acts 
of  inspiration  and  expiration. 

4.  Gomplemental  Air ;  the  excess  over  the  ordinary  breathing  air,  which  may  be 
introduced  by  a  forcible  inspiration. 

The  questions  relating  to  the  above  divisions  of  the  respired  air  have  been  made  the 
subject  of  numerous  investigations;  but,  although  at  first  it  might  seem  easy  to  deter- 
mine all  of  them  by  a  sufficient  number  of  experiments,  the  necessary  observations  are 
attended  with  considerable  difficulty,  and  the  sources  of  error  are  numerous.  In  measur- 
ing the  air  changed  in  ordinary  breathing,  it  has  been  found  .that  the  acts  of  respiration 
are  so  easily  influenced  by  the  mind  and  it  is  so  difficult  to  experiment  on  any  individual 
without  his  knowledge,  that  the  results  of  many  good  observers  are  not  to  be  relied 
upon.  This  is  one  of  the  most  important  of  the  questions  under  consideration.  The 
difficulties  in  the  way  of  estimating  with  accuracy  the  residual,  reserve,  or  complemental 
volumes,  will  readily  suggest  themselves.  The  observations  on  these  points,  which  may 
be  taken  as  the  most  definite  and  exact,  are  those  of  Herbst,  of  Gottingen,  and  Hutchin- 
son,  of  England.  Those  of  the  last-named  observer  are  exceedingly  elaborate  and  were 

1  Experiments  have  shown  that  a  certain  volume  of  air  is  lost  in  the  lungs,  the  expired  air  being  a  little  less  in 
volume  than  the  quantity  inspired  (from  TV  to  ss)-    Tm's  is  not  taken  into  account  in  this  connection. 


136  KESPIRATION. 

made  on  an  immense  number  of  subjects  of  both  sexes  and  of  all  ages  and  occupations. 
They  are  generally  accepted  by  physiologists  as  the  most  extended  and  accurate. 

Residual  Air. — Perhaps  there  is  not  one  of  the  questions  under  consideration  more 
difficult  to  answer  definitely  than  that  of  the  quantity  of  air  which  remains  in  the  lungs 
after  a  forced  expiration ;  but  it  fortunately  is  not  one  of  any  great  practical  importance. 
The  residual  air  remains  in  the  lungs  as  a  physical  necessity.  The  lungs  are  always,  in 
health,  in  contact  with  the  walls  of  the  thorax ;  and,  when  this  cavity  is  reduced  to  its 
smallest  dimensions,  it  is  impossible  that  any  more  air  should  be  expelled.  The  volume 
which  thus  remains  has  been  variously  estimated  at  from  forty  cubic  inches  (Fontana)  to 
two  hundred  and  twenty  cubic  inches  (Jurin).  Dr.  Hutchinson,  who  has  carefully  con- 
sidered this  point,  estimates  the  residual  volume  at  about  one  hundred  cubic  inches,  but  he 
states  that  it  varies  very  considerably  in  different  individuals.  Taking  every  thing  into 
consideration,  we  may  assume  this  estimate  to  be  as  nearly  correct  as  any.  It  is  certain 
that  the  lungs  of  a  man  of  ordinary  size,  at  their  minimum  of  distention,  contain  more 
than  forty  cubic  inches  of  air;  and,  from  measurements  of  the  capacity  of  the  thorax, 
deducting  the  estimated  space  occupied  by  the  heart  and  vessels  and  the  parenchyma 
of  the  lungs,  it  is  shown  that  the  residual  air  cannot  amount  to  any  thing  like  two  hun- 
dred cubic  inches. 

There  is  no  special  division  of  the  function  of  respiration  connected  with  the  residual 
air.  It  remains  in  the  lungs  merely  as  a  physical  necessity,  and  its  volume  must  not  be 
taken  into  account  in  considering  the  volumes  which  are  changed  in  any  of  the  opera- 
tions connected  with  breathing. 

Reserve  Air. — This  name  is  appropriately  given  to  the  volume  of  air  which  may  be 
expelled  and  changed  by  a  voluntary  effort,  but  which  remains  in  the  lungs,  added  to  the 
residual  air,  after  an  ordinary  act  of  expiration.  It  may  be  estimated,  without  any 
reference  to  the  residual  air,  by  forcibly  expelling  air  from  the  lungs,  after  an  ordinary 
expiration.  The  average  volume  is  one  hundred  cubic  inches. 

The  reserve  air  is  more  or  less  changed  whenever  we  experience  a  necessity  for  a 
more  complete  renovation  of  the  contents  of  the  lungs  than  ordinary.  It  is  encroached 
upon  in  the  unusually  profound  inspiration  and  expiration  which  occur  every  five  or  six 
acts.  It  is  used  in  certain  prolonged  vocal  efforts,  in  blowing,  etc.  Added  to  the  residual 
air,  it  constitutes  the  minimum  capacity  of  the  lungs  in  ordinary  respiration.  As  it  is 
continually  receiving  watery  vapor  and  carbonic  acid,  it  is  always  more  or  less  vitiated, 
and,  when  reenforced  by  the  breathing  air,  which  enters  with  inspiration,  is  continually 
in  circulation,  in  obedience  to  the  law  of  the  diffusion  of  gases.  Those  who  are  in  the 
habit  of  arresting  respiration  for  a  time,  as  pearl-divers,  learn  to  change  the  reserve  air 
as  completely  as  possible  by  several  forcible  acts  and  then  fill  the  lungs  with  fresh  air. 
In  this  way  they  are  enabled  to  suspend  the  respiratory  acts  for  from  one  to  two  minutes 
without  inconvenience.  The  introduction  of  fresh  air  with  each  inspiration,  and  the 
constant  diffusion  which  is  going  on  and  by  which  the  proper  quantity  of  oxygen  finds 
its  way  to  the  air-cells,  give,  in  ordinary  breathing,  a  composition  to  the  air  in  the 
deepest  portions  of  the  lungs  which  insures  a  constant  aeration  of  the  blood. 

Tidal,  or  Ordinary  Breathing  Air. — The  volume  of  air  which  is  changed  in  the 
ordinary  acts  of  respiration  is  subject  to  immense  physiological  variations,  and  the 
respiratory  movements,  as  regards  intensity,  are  so  easily  influenced  by  the  mind,  that 
great  care  is  necessary  to  avoid  error  in  estimating  the  volume  of  ordinary  breathing  air. 
The  estimates  of  Herbst  and  of  Hutchinson  are  the  results  of  very  extended  observations 
made  with  great  care  and  are  generally  acknowledged  to  be  as  nearly  accurate  as  pos- 
sible. As  a  mean  of  these  observations,  it  has  been  found  that  the  average  volume  of 
breathing  air,  in  a  man  of  ordinary  stature,  is  twenty  cubic  inches.  According  to  Hutch- 


EXTREME   BREATHING  CAPACITY.  137 

inson,  in  perfect  repose,  when  the  respiratory  movements  are  hardly  perceptible,  not 
more  than  from  seven  to  twelve  cubic  inches  are  changed ;  while,  under  excitement,  he 
has  seen  the  volume  increased  to  seventy-seven  cubic  inches.  Of  course  the  latter  is 
temporary.  Herbst  noted  that  the  breathing  volume  is  constantly  increased  in  pro- 
portion to  the  stature  of  the  individual  and  bears  no  definite  relation  to  the  apparent 
capacity  of  the  chest. 

Complemental  Air. — The  thorax  may  be  so  enlarged  by  an  extreme  voluntary  in- 
spiratory  effort  as  to  contain  a  quantity  of  air  much  larger  than  after  an  ordinary  in- 
spiration. The  additional  volume  of  air  thus  taken  in  may  be  estimated  by  measuring 
all  the  air  which  can  be  expelled  from  the  lungs  after  the  most  profound  inspiration,  and 
deducting  the  sum  of  the  reserve  air  and  breathing  air.  This  quantity  has  been  found 
by  Hutchinson  to  vary  in  different  individuals,  bearing  a  close  relation  to  stature.  The 
mean  complemental  volume  is  one  hundred  and  ten  cubic  inches. 

The  complemental  air  is  drawn  upon  whenever  an  effort  is  made  which  requires  a 
temporary  arrest  of  respiration.  Brief  and  violent  muscular  exertion  is  generally  pre- 
ceded by  a  profound  inspiration.  In  sleep,  as  the  volume  of  breathing  air  is  somewhat 
increased,  the  complemental  air  is  encroached  upon.  A  part  or  the  whole  of  the  com- 
plemental air  is  also  used  in  certain  vocal  efforts,  in  blowing,  in  yawning,  in  the  deep 
inspiration  which  precedes  sneezing,  in  straining,  etc. 

Summary. — In  a  healthy  male  of  medium  stature,  the  residual  air,  which  cannot  be 
expelled  from  the  lungs,  amounts  to  about  one  hundred  cubic  inches. 

The  reserve  air,  which  can  be  expelled  but  which  is  not  changed  in  ordinary  respi- 
ration, amounts  to  about  one  hundred  cubic  inches. 

The  tidal  air,  which  is  changed  in  ordinary  respiration,  amounts  to  about  twenty 
cubic  inches. 

The  complemental  air,  which  may  be  taken  into  the  lungs  after  the  completion  of  an 
ordinary  act  of  inspiration,  amounts  to  about  one  hundred  and  ten  cubic  inches. 

Extreme  Breathing  Capacity. — By  the  extreme  breathing  capacity  is  meant  the  vol- 
ume of  air  which  can  be  expelled  from  the  lungs  by  the  most  forcible  expiration,  after 
the  most  profound  inspiration.  This  has  been  called  by  Dr.  Hutchinson  the  vital  capa- 
city, as  signifying  "  the  volume  of  air  which  can  be  displaced  by  living  movements." 
Its  volume  is  equal  to  the  sum  of  the  reserve  air,  the  breathing  air,  and  the  complemental 
air,  and  represents  the  extreme  capacity  of  the  chest,  deducting  the  residual  air.  Its 
physiological  interest  is  due  to  the  fact  that  it  can  readily  be  determined  by  an  appro- 
priate apparatus,  the  spirometer,  and  comparisons  can  thus  be  made  between  different 
individuals,  both  healthy  and  diseased.  The  number  of  observations  on  this  point  made 
by  Dr.  Hutchinson  is  enormous,  amounting  in  all  to  little  short  of  five  thousand. 

The  extreme  breathing  capacity  in  health  is  subject  to  variations  which  have  been 
shown  to  bear  a  very  close  relation  to  the  stature  of  the  individual.  Hutchinson  com- 
mences with  the  proposition  that,  in  a  man  of  medium  height  (five  feet  eight  inches),  it 
is  equal  to  two  hundred  and  thirty  cubic  inches.  He  has  shown  that  the  extreme  breath- 
ing capacity  is  constant  in  the  same  individual,  and  that  it  is  not  to  be  increased  by  habit 
or  practice. 

The  most  striking  result  of  the  experiments  of  Dr.  Hutchinson,  with  regard  to  the 
modifications  of  the  vital  capacity,  is  that  it  bears  a  definite  relation  to  stature,  without 
being  affected  in  a  very  marked  degree  by  weight  or  the  circumference  of  the  chest. 
This  is  especially  remarkable,  as  it  is  well  known  that  height  does  not  depend  so  much 
upon  the  length  of  the  body  as  upon  the  length  of  the  lower  extremities. 

It  has  been  ascertained  that  for  every  inch  in  height,  between  five  and  six  feet,  the 
extreme  breathing  capacity  is  increased  eight  cubic  inches. 


138 


RESPIRATION. 


The  following  table  shows  the  mean  results  of  the  immense  number  ot  observations 
on  which  this  conclusion  is  based  : 

Progression  of  the   Vital  Capacity  Volume  icith  the  Stature. 


Height. 

d 

C    °    oQ 

0 

Series  from 
observations  on 
1,923  cases. 

a  A, 

Sfet    0  inches)  Bf        n     } 

1st  result. 

175*0 

2d  result. 

176*0 

174-0 

5            2               ( 
5            2               j-5    «      3    «     . 

188*5 

191*0 

190*0 

o            4               J 

K                      4                            i 

U     "       5     " 

206*0 

207  0 

5            6               } 

h  5      "         7      u      . 

222*0 

228*0 

222*0 

58               [ 

5            8               t  g     4t            tj 

237*5 

241*0 

238'0 

10              j 

5      10        U  «  u  « 

254*5 

953-0 

254*0 

0              J 

Mean  of  all  Heights.  . 

214*0 

217*0 

214*0 

Age  has  an  influence,  though  less  marked  than  stature,  upon  the  extreme  breathing 
capacity.  As  the  result  of  4,800  observations  (males),  it  was  ascertained  that  the  volume 
increases  with  age  up  to  the  thirtieth  year,  and  progressively  decreases,  with  tolerable 
regularity,  from  the  thirtieth  to  the  sixtieth  year.  These  figures,  though  necessarily  sub- 
ject to  certain  individual  variations,  may  be  taken  as  the  basis  for  examinations  of  the 
extreme  breathing  capacity  in  disease,  which  frequently  give  important  information. 
Of  course,  the  breathing  capacity  is  modified  by  any  abnormal  condition  which  interferes 
with  the  mobility  of  the  thorax  or  the  dilatability  of  the  lungs. 

Relations  in  Volume  of  the  Expired  to  the  Inspired  Air. — A  certain  proportion  of  the 
inspired  air  is  lost  in  respiration,  so  that  the  air  expired  is  always  a  little  less  in  volume 
than  that  which  is  taken  into  the  lungs.  All  the  older  experimenters,  except  Magendie, 
were  agreed  upon  this  point.  The  loss  was  put  by  Davy  at  TV,  and  by  Cuvier  at  -^  of 
the  amount  of  air  introduced.  Observations  on  this  point,  to  be  exact,  must  include  a 
considerable  number  of  respiratory  acts ;  and,  from  the  difficulty  of  continuing  respira- 
tion in  a  perfectly  regular  and  normal  manner  when  the  attention  is  directed  to  that 
function,  the  most  accurate  results  may  probably  be  obtained  from  experiments  on  the 
lower  animals.  Despretz  caused  six  young  rabbits  to  respire  for  two  hours  in  a  confined 
space  containing  two  hundred  and  ninety-nine  cubic  inches  of  air,  and  ascertained  that 
the  volume  had  diminished  sixty-one  cubic  inches,  or  a  little  more  than  one-fiftieth.  We 
may  take  the  approximations  of  Davy  and  Cuvier,  as  applied  to  the  human  subject,  as 
nearly  correct,  and  assume  that,  in  the  lungs,  from  -fo  to  -fa  of  the  inspired  air  is  lost. 

Diffusion  of  Air  in  the  Lungs. — When  it  is  considered  that,  with  each  inspiration,  but 
about  twenty  cubic  inches  of  fresh  air  is  introduced,  sufficient  only  to  fill  the  trachea  and 
larger  bronchial  tubes,  it  is  evident  that  some  forces  must  act  by  which  this  fresh  air 
finds  its  way  into  the  air-cells  and  the  vitiated  air  is  brought  into  the  larger  tubes,  to  be 
expelled  with  the  succeeding  expiration.  The  expired  air  may  become  so  charged  with 
noxious  gases,  by  holding  the  breath  for  a  few  seconds,  that,  when  collected  in  a  receiver 
under  water,  it  is  incapable  of  supporting  combustion. 


DIFFUSION  OF  AIR  IN  THE  LUNGS.  139 

The  interchange  between  the  fresh  air  in  the  upper  portions  of  the  respiratory  appa- 
ratus and  the  air  in  the  deeper  parts  of  the  lungs  is  constantly  going  on,  in  obedience  to 
the  well-known  law  of  the  diffusion  of  gases,  aided  by  the  active  currents  or  impulses 
produced  by  the  alternate  movements  of  the  chest.  When  two  gases,  or  mixtures  of 
gases,  of  different  densities  are  brought  in  contact  with  each  other,  they  diffuse  or  mingle 
with  great  rapidity,  until,  if  undisturbed,  the  whole  mass  has  a  uniform  density  and  com- 
position. This  has  been  shown  to  take  place  between  very  light  and  very  heavy  gases 
in  opposition  to  the  laws  of  gravity,  and  even  when  two  reservoirs  are  connected  by  a 
small  tube  many  feet  in  length,  though  then  it  proceeds  quite  slowly.  In  the  respiratory 
apparatus,  at  the  termination  of  inspiration,  the  atmospheric  air,  composed  of  a  mixture 
of  oxygen  and  nitrogen,  is  introduced  into  the  tubes  with  a  considerable  impetus  and  is 
brought  into  contact  with  the  gas  in  the  lungs,  which  is  much  heavier,  as  it  contains  a 
considerable  quantity  of  carbonic  acid.  Diffusion  then  takes  place,  aided  by  the  elastic 
lungs,  which  are  gradually  forcing  the  gaseous  contents  out  of  the  cells,  until  a  certain 
portion  of  the  air  loaded  with  carbonic  acid  finds  its  way  to  the  larger  tubes,  to  be 
thrown  off  in  expiration,  its  place  being  supplied  by  the  fresh  air. 

Jn  obedience  to  the  law  established  by  Graham,  that  the  diffusibility  of  gases  is  in- 
versely proportionate  to  the  square  root  of  their  densities,  the  penetration  of  atmos- 
pheric air,  which  is  the  lighter  gas,  to  the  deep  portions  of  the  lungs  would  take  place 
with  greater  rapidity  than  the  ascent  of  the  air  charged  with  carbonic  acid ;  so  that 
eighty-one  parts  of  carbonic  acid  should  be  replaced  by  ninety-five  of  oxygen.  It  is 
found,  indeed,  that  the  volume  of  carbonic  acid  exhaled  is  always  less  than  the  volume 
of  oxygen  absorbed.  This  diffusion  is  constantly  going  on,  so  that  the  air  in  the  pul- 
monary vesicles,  where  the  interchange  of  gases  with  the  blood  takes  place,  maintains  a 
pretty  uniform  composition.  The  process  of  aSration  of  the  blood,  therefore,  has  none 
of  that  intermittent  character  which  attends  the  muscular  movements  of  respiration, 
which  would  undoubtedly  occur  if  the  entire  gaseous  contents  of  the  lungs  were  changed 
with  every  respiratory  act. 


CHAPTER    V. 

CHANGES  WHICH  THE  AIR  AND  THE  BLOOD   UNDERGO  IN  RESPIRATION. 

Composition  of  the  air— Consumption  of  oxygen— Exhalation  of  carbonic  acid— Influence  of  age— Eelations  between 
the  quantity  of  oxygen  consumed  and  the  quantity  of  carbonic  acid  exhaled— Exhalation  of  watery  vapor— Ex- 
halation of  ammonia— Exhalation  of  organic  matter— Exhalation  of  nitrogen— Changes  of  the  blood  in  respira- 
tion (hsematosis)— Difference  in  color  between  arterial  and  venous  blood— Comparison  of  the  gases  in  venous 
and  arterial  blood— Analysis  of  the  blood  for  gases— Relative  quantities  of  oxygen  and  carbonic  acid  in  venous 
and  arterial  blood— Nitrogen  of  the  blood— Condition  of  the  gases  in  the  blood— Mechanism  of  the  interchange 
of  gases  between  the  blood  and  the  air  in  the  lungs— Relations  of  respiration  to  nutrition,  etc.— Views  of  physi- 
ologists anterior  to  the  time  of  Lavoisier — Relations  of  the  consumption  of  oxygen  to  nutrition — Relations  of 
the  exhalation  of  carbonic  acid  to  nutrition— Essential  processes  of  respiration— The  respiratory  sense,  or  want 
on  the  part  of  the  system  which  induces  the  respiratory  movements— Respiratory  efforts  before  birth— Cuta- 
neous respiration— Asphyxia. 

FROM  the  allusions  which  we  have  already  made  to  the  general  process  of  respiration, 
it  is  apparent  that,  before  the  discovery  of  the  nature  of  the  gases  which  compose  the 
air  and  those  which  are  exhaled  from  the  lungs,  it  was  impossible  for  physiologists  to 
have  any  correct  ideas  of  the  nature  of  this  important  function.  It  is  not  surprising  that 
the  ancients,  observing  the  regular  introduction  of  air  into  the  lungs  and  noting  the  fact 
that  the  air  is  generally  much  cooler  than  the  body,  supposed  the  great  object  of  respi- 
ration to  be  the  cooling  of  the  blood.  It  is  also  evident  that  no  definite  knowledge  of 
any  of  the  processes  of  respiration  could  exist  prior  to  the  discovery  of  the  circulation 


140  KESPIRATION". 

of  the  blood  and  our  knowledge  of  the  composition  of  the  air  and  the  properties  of 
oxygen. 

The  discovery  of  the  properties  of  oxygen  and  carbonic  acid,  although  bearing  upon  the 
great  question  under  consideration,  were  simply  isolated  facts  and  failed  to  develop  any 
definite  idea  of  the  changes  of  the  air  and  blood  in  respiration.  The  application  of  these 
facts  was  made  by  the  great  chemist,  Lavoisier,  who  was  the  first  to  employ  the  delicate 
balance  in  chemical  investigation,  and  whose  observations  mark  the  beginning  of  an 
accurate  knowledge  of  the  function  of  respiration.  With  the  balance,  Lavoisier  showed 
the  nature  of  the  oxides  of  the  metals ;  he  discovered  that  carbonic  acid  is  formed  by  a 
union  of  carbon  and  oxygen ;  and,  noting  the  consumption  of  oxygen  and  the  produc- 
tion of  carbonic-  acid  in  respiration,  advanced,  for  the  first  time,  the  view  that  the  one 
was  employed  in  the  production  of  the  other.  Although,  as  would  naturally  be  expected, 
the  doctrines  of  this  great  observer  have  been  modified  with  the  advances  in  science,  he 
developed  facts  which  will  stand  forever,  and  which  have  served  as  the  starting-point  of 
all  our  knowledge  on  this  subject.  From  that  time,  physiologists  began  to  regard  respi- 
ration as  consisting  in  the  appropriation  of  oxygen  and  the  exhalation  of  carbonic  acid ; 
and  now  the  seat  of  this  process  is  simply  changed  from  the  lungs  to  the  tissues.  From  the 
limited  knowledge  of  the  intimate  phenomena  of  nutrition  which  obtained  in  his  day, 
Lavoisier  could  not  be  expected  to  entertain  any  other  view  than  that  the  carbonic  acid 
produced  was  the  result  of  a  direct  union  of  oxygen  with  carbon  in  the  blood.  It  is 
only  since  investigations  have  made  manifest  the  great  complexity  of  the  processes  of 
nutrition,  that  some  are  unwilling  to  believe  that  carbonic  acid  is  produced  in  so  simple 
a  way  as  it  appeared  to  Lavoisier. 

Composition  of  the  Air. — Pure  atmospheric  air  is  a  mechanical  mixture  of  79*19  parts 
of  nitrogen  with  20*81  parts  of  oxygen  (Dumas  and  Boussingault).  It  contains,  in  addi- 
tion, a  very  small  quantity  of  carbonic  acid,  about  one  part  in  2,000  by  volume.  The  air 
is  never  free  from  moisture,  which  is  very  variable  in  quantity,  being  generally  more 
abundant  at  a  high  than  at  a  low  temperature.  In  1840,  Schonbein  discovered  in  the 
air  a  peculiarly  odorous  principle  called  ozone,  which  he  conceived  to  be  a  compound  of 
oxygen  and  hydrogen,  but  which  is  now  pretty  well  shown  to  be  an  allotropic  form  of 
oxygen.  Oxygen  obtained  by  decomposing  water  by  the  Voltaic  pile  is  in  this  condition. 
It  exists  in  very  small  quantity  in  the  air,  and,  as  far  as  we  know,  plays  no  important 
part  in  the  function  of  respiration.  Its  chief  interest  has  been  in  its  theoretical  rela- 
tions to  epidemic  diseases.  Floating  in  the  atmosphere,  are  a  number  of  excessively- 
minute  organic  bodies.  Various  odorous  and  other  gaseous  matters  may  be  present  as 
accidental  constituents  of  the  atmosphere. 

In  considering  the  function  of  respiration,  it  is  not  necessary  to  take  account  of  any 
of  the  constituents  of  the  atmosphere  except  oxygen  and  nitrogen,  the  others  being 
either  inconstant  or  existing  in  excessively  minute  quantity.  It  is  necessary  to  the  regu- 
lar performance  of  the  function,  that  the  air  should  contain  about  four  parts  of  nitrogen 
to  one  of  oxygen  and  have  about  the  density  which  exists  on  the  general  surface  of  the 
globe.  When  the  density  is  very  much  increased,  as  in  mines,  respiration  is  usually 
more  or  less  disturbed.  By  exposure  to  a  rarefied  atmosphere,  as  in  the  ascent  of  high 
mountains  or  in  aerial  voyages,  respiration  may  be  very  seriously  interfered  with,  from  the 
fact  that  less  oxygen  than  usual  is  presented  to  the  respiratory  surface  and  the  reduced 
atmospheric  pressure  diminishes  the  capacity  of  the  blood  for  holding  gases  in  solution. 

Magendie  and  Bernard,  in  experimenting  on  the  minimum  proportion  of  oxygen  in 
the  air  which  is  capable  of  sustaining  life,  found  that  a  rabbit,  confined  under  a  bell- 
glass,  with  an  arrangement  for  removing  the  carbonic  acid  and  water  exhaled  as  fast  as 
they  were  produced,  died  of  asphyxia  when  the  quantity  of  oxygen  became  reduced  to 
from  three  to  five  per  cent. 

A  few  experiments  are  on  record  in  which  the  human  subject  and  animals  have  been 


CONSUMPTION   OF  OXYGEN.  141 

made  to  respire  for  a  time  pure  oxygen.  Although  this  is  the  gas  which  is  essential  in 
ordinary  respiration,  the  process  being  carried  on  about  as  well  in  a  mixture  of  oxygen 
with  hydrogen  as  with  nitrogen,  the  functions  do  not  seem  to  be  much  altered  when  the 
pure  gas  is  taken  into  the  lungs.  Allen  and  Pepys  confined  animals  for  twenty -four 
hours  in  an  atmosphere  of  pure  oxygen  without  any  notable  results ;  but,  as  is  justly 
remarked  by  Longet,  these  experiments  do  not  show  that  it  would  be  possible  to  respire 
unmixed  oxygen  indefinitely  without  inconvenience.  As  it  exists  in  the  air,  oxygen  is 
undoubtedly  in  the  best  form  for  the  permanent  maintenance  of  the  respiratory  func- 
tion. The  blood  seems  to  have  a  certain  capacity  for  the  absorption  of  oxygen,  which  is 
not  increased  when  the  pure  gas  is  respired. 

The  only  other  gas  which  has  the  power  of  maintaining  respiration,  even  for  a  time, 
is  nitrous  oxide.  This  is  absorbed  by  the  blood-corpuscles  with  great  avidity,  and,  for  a 
time,  it  produces  an  exaggeration  of  the  vital  processes,  with  delirium,  etc. — properties 
which  have  given  it  the  common  name  of  the  laughing  gas ;  but  this  condition  is  fol- 
lowed by  anaesthesia,  and  finally  asphyxia,  probably  because  the  gas  has  such  an  affinity 
for  the  blood-corpuscles  as  to  remain  to  a  certain  extent  fixed,  interfering  with  that  inter- 
change of  gases  which  is  essential  to  life.  Notwithstanding  this,  experimenters  have 
confined  with  impunity  rabbits  and  other  animals  in  an  atmosphere  of  nitrous  oxide  for 
a  number  of  hours.  In  all  cases  they  became  asphyxiated,  but  in  some  instances  were 
restored  on  being  brought  again  into  the  ordinary  atmosphere. 

Other  gases  which  may  be  introduced  into  the  lungs  either  produce  asphyxia,  nega- 
tively, from  the  fact  they  are  not  absorbed  by  the  blood  and  are  incapable  of  carrying  on 
respiration,  like  hydrogen  or  nitrogen,  or  positively,  by  a  poisonous  effect  on  the  system. 
The  most  important  of  the  gases  which  act  as  poisons  are,  carbonic  oxide,  sulphuretted 
hydrogen,  and  arseniuretted  hydrogen.  It  is  somewhat  uncertain  whether  carbonic  acid 
exert  its  deleterious  influence  as  a  poison  or  as  merely  taking  the  place  of  the  oxygen  in 
the  blood-corpuscles.  It  is  easily  displaced  from  the  blood  by  oxygen,  and  therefore 
does  not  seem  to  possess  the  properties  of  a  poison,  like  carbonic  oxide  and  some  other 
gases,  which  become  fixed  in  the  blood  and  are  not  readily  displaced  when  fresh  air  is 
introduced  into  the  lungs. 

Consumption  of  Oxygen. — The  determination  of  the  quantity  of  oxygen  which  is  re- 
moved from  the  air  by  the  process  of  respiration  is  a  question  of  great  physiological 
interest  and  one  which  engaged  largely  the  attention  of  Lavoisier  and  those  who  have 
followed  in  his  line  of  observation.  On  this  point,  there  is  an  accumulated  mass  of 
observations,  which  are  comparatively  unimportant  from  the  fact  that  they  were  made 
before  the  means  of  analysis  of  the  gases  were  as  perfect  as  they  now  are.  Although 
many  of  the  results  obtained  by  the  older  experimenters  are  interesting  and  instructive 
as  showing  the  comparative  quantities  of  oxygen  consumed  under  various  physiological 
conditions,  they  are  not  to  be  compared  with  the  more  recent  observations.  In  the 
observations  of  Eegnault  and  Reiset,  the  animal  to  be  experimented  upon  was  enclosed 
in  a  receiver  filled  with  air,  a  measured  quantity  of  oxygen  was  introduced  as  fast  as  it 
was  consumed  by  respiration,  and  the  carbonic  acid  was  constantly  removed  and  care- 
fully estimated.  In  most  of  the  experiments,  the  confinement  did  not  appear  to  inter- 
fere with  the  functions  of  the  animal,  which  ate  and  drank  in  the  apparatus  and  was  in 
as  good  condition  at  the  termination  as  at  the  beginning  of  the  observation.  This  method 
is  much  more  accurate  than  that  of  simply  causing  an  animal  to  breathe  in  a  confined 
space,  when  the  consumption  of  oxygen  and '  accumulation  of  carbonic  acid  and  other 
matters  must  interfere  more  or  less  with  the  proper  performance  of  the  respiratory  func- 
tion. As  employed  by  Eegnault  and  Reiset,  it  is  only  adapted  to  experiments  on  animals 
of  small  size.  These  give  but  an  approximate  idea  of  the  processes  as  they  take  place  in 
the  human  subject,  as  it  is  natural  to  suppose  that  the  relative  quantities  of  gases  con- 
sumed and  produced  in  respiration  vary  in  different  orders  of  animals. 


142  RESPIRATION. 

In  the  researches  on  respiration  by  Dr.  Max  Pettenkofer,  the  conditions  for  accurate 
observation  on  the  human  subject  seem  to  have  been  fulfilled.  Dr.  Pettenkofer  con- 
structed a  chamber  large  enough  to  admit  a  man  and  allow  perfect  freedom  of  motion, 
eating,  sleeping,  etc.,  into  which  air  could  be  constantly  introduced  in  definite  quantity, 
and  from  which  the  products  of  respiration  were  constantly  removed  and  estimated.  An 
incomplete  series  of  observations  is  published,  which  has  particular  reference  to  the  prod- 
ucts of  respiration ;  and,  thus  far,  the  subject  of  consumption  of  oxygen  has  not  been  fully 
considered.  This  method  was  adapted  to  the  human  subject  on  a  small  scale  in  1843,  by 
Scharling,  but  there  was  no  arrangement  for  estimating  the  quantity  of  oxygen  furnished. 

Estimates  of  the  absolute  quantities  of  oxygen  consumed,  or  of  carbonic  acid  ex- 
haled, based  on  analyses  of  the  inspired  and  expired  air,  calculations  from  the  average 
quantity  of  air  changed  with  each  respiratory  act,  and  the  average  number  of  respirations 
per  minute,  are  by  no  means  so  reliable  as  analyses  showing  the  actual  changes  in  the  air, 
like  those  of  Regnault  and  Reiset,  provided  the  physiological  conditions  be  fulfilled. 
When  there  is  so  much  multiplication  and  calculation,  a  very  slight  and  perhaps  unavoid- 
able inaccuracy  in  the  quantities  consumed  or  produced  in  a  single  respiration  will  make 
an  immense  error  in  the  estimate  for  a  day  or  even  an  hour.  Bearing  in  mind  all  these 
sources  of  error,  from  the  experiments  of  Valentin  and  Brunner,  Dumas,  Regnault  and 
Reiset,  and  others,  a  sufficiently-accurate  approximation  of  the  proportion  of  oxygen 
,  consumed  by  the  human  subject  may  be  formed.  The  air,  which  contains,  when  inspired, 
20'81  parts  of  oxygen  per  100,  is  found  on  expiration  to  contain  but  about  16  parts  per 
100.  In  other  words,  the  volume  of  oxygen  absorbed  in  the  lungs  is  five  per  cent,  or  -^ 
of  the  volume  of  air  inspired.  It  is  interesting  and  useful  to  extend  this  estimate  as  far 
as  possible  to  the  quantity  of  oxygen  absorbed  in  a  definite  time ;  for  the  regulation  of 
the  supply  of  oxygen  where  many  persons  are  assembled,  as  in  public  buildings,  hospi- 
tals, etc.,  is  a  question  of  great  practical  importance.  Assuming  that  the  average  respira- 
tions per  minute  are  eighteen,  and  that,  with  each  act,  twenty  cubic  inches  of  air  are 
changed,  fifteen  cubic  feet  of  oxygen  are  consumed  in  the  twenty-four  hours,  which  repre- 
sent three  hundred  cubic  feet  of  pure  air.  This  is  the  minimum  quantity  of  air  which  is 
actually  used,  making  no  allowance  for  any  increase  in  the  intensity  of  the  respiratory 
processes,  which  is  liable  to  occur  from  various  causes.  To  meet  all  the  respiratory  exi- 
gencies of  the  system,  in  hospitals,  prisons,  etc.,  it  has  been  found  necessary  to  allow  at 
least  eight  hundred  cubic  feet  of  air  for  each  person,  unless  the  situation  be  such  that  the 
air  is  changed  with  unusual  frequency ;  for,  beside  the  actual  loss  of  oxygen  in  the  respired 
air,  constant  emanations  from  both  the  pulmonary  and  cutaneous  surfaces  are  taking 
place,  which  should  be  removed.  In  some  institutions  as  much  as  twenty-five  hundred 
cubic  feet  of  air  is  allowed  to  each  person. 

The  quantity  of  oxygen  consumed  is  subject  to  great  variations,  depending  upon  tem- 
perature, the  condition  of  the  digestive  system,  muscular  activity,  etc.  The  following 
conclusions,  the  results  of  the  observations  of  Lavoisier  and  Se"guin,  give  at  a  glance  the 
variations  from  the  above-mentioned  causes : 

"1.  A  man,  in  repose  and  fasting,  with  an  external  temperature  of  90°  Fahr.,  con- 
sumes 1,465  cubic  inches  of  oxygen  per  hour. 

"2.  A  man,  in  repose  and  fasting,  with  an  external  temperature  of  59°  Fahr.,  con- 
sumes 1,627  cubic  inches  of  oxygen  per  hour. 

"  3.  A  man,  during  digestion,  consumes  2,300  cubic  inches  of  oxygen  per  hour. 

"  4.  A  man,  fasting,  while  he  accomplishes  the  labor  necessary  to  raise,  in  fifteen 
minutes,  a  weight  of  7,343  kil.  (about  16  Ib.  3  oz.  av.)  to  the  height  of  656  feet,  consumes 
3,874  cubic  inches  of  oxygen  per  hour. 

"5.  A  man,  during  digestion,  accomplishing  the  labor  necessary  to  raise,  in  fifteen 
minutes,  a  weight  of  7,343  kil.  (about  16  Ib.  3  oz.  av.)  to  the  height  of  700  feet,  consumes 
5,568  cubic  inches  of  oxygen  per  hour." 

All  who  have  experimented  on  the  influence  of  temperature  upon  the  consumption  of 


CONSUMPTION   OF  OXYGEN.  143 

oxygen,  in  the  warm-blooded  animals  and  in  the  human  subject,  have  noted  a  marked  in- 
crease at  low  temperatures.  Immediately  after  birth,  the  consumption  of  oxygen  in  the 
warm-blooded  animals  is  relatively  very  slight.  Buffon  and  Legallois  have  shown  that, 
just  after  birth,  dogs  and  other  animals  will  live  for  half  an  hour  or  more  under  water ;  and 
cases  are  on  record  where  life  has  been  restored  in  newly-born  children  after  seven,  and 
it  has  been  stated,  after  twenty-three  hours  of  asphyxia.  (Milne-Edwards.)  During  the 
first  periods  of  existence,  the  condition  of  the  newly-born  approximates  to  that  of  a  cold- 
blooded animal.  The  lungs  are  relatively  very  small,  and  it  is  some  time  before  they  fully 
assume  their  function.  The  muscular  movements  are  hardly  more  than  is  necessary  to  take 
the  small  amount  of  nourishment  consumed  at  that  period,  and  nearly  all  of  the  time  is 
passed  in  sleep.  There  is  also  very  little  power  of  resistance  to  low  temperature.  Although 
accurate  researches  regarding  the  comparative  quantities  of  oxygen  in  the  venous  and 
arterial  blood  of  the  foetus  are  wanting,  it  has  been  frequently  observed  that  the  differ- 
ence in  color  is  not  so  marked  as  it  is  after  pulmonory  respiration  becomes  established. 
The  direct  researches  of  W.  F.  Edwards  have  shown  that  the  absolute  consumption  of 
oxygen  by  very  young  animals  is  very  small ;  and  the  observations  of  Legallois  on  rabbits, 
made  every  five  days  during  the  first  month  of  existence,  show  a  rapidly-increasing  de- 
mand for  this  principle  with  age. 

Regnault  and  Reiset  have  shown  that  the  consumption  of  oxygen  is  greater  in  lean 
than  in  very  fat  animals,  provided  they  be  in  perfect  health.  They  have  also  shown  that 
the  consumption  is  much  greater  in  carnivorous  than  in  herbivorous  animals;  and,  in  ani- 
mals of  different  sizes,  it  is  relatively  much  greater  in  those  which  are  very  small.  In 
small  birds,  such  as  the  sparrow,  the  relative  quantity  of  oxygen  absorbed  was  ten 
times  greater  than  in  the  fowl. 

During  sleep  the  quantity  of  oxygen  consumed  is  considerably  diminished ;  and  in  hi- 
bernation it  is  so  small,  that  Spallanzani  could  not  detect  any  difference  in  the  composi- 
tion of  the  air  in  which  a  marmot,  in  a  state  of  torpor,  had  remained  for  three  hours. 
In  experiments  on  a  marmot  in  hibernation,  Regnault  and  Reiset  observed  a  reduction 
in  the  quantity  of  oxygen  consumed  to  about  -£$  of  the  normal  standard. 

It  has  been  shown  by  experiments,  that  the  consumption  of  oxygen  bears  a  pretty 
constant  ratio  to  the  production  of  carbonic  acid ;  and,  as  the  observations  upon  the  influ- 
ence of  sex,  number  of  respiratory  acts,  etc.,  on  the  activity  of  the  respiratory  processes, 
have  been  made  chiefly  with  reference  to  the  carbonic  acid  exhaled,  we  shall  consider 
these  influences  in  connection  with  the  products  of  respiration. 

Experiments  on  the  effect  of  increasing  the  proportion  of  oxygen  in  the  air  have  led 
to  varied  results  in  the  hands  of  different  observers.  Regnault  and  Reiset,  whose 
observations  on  this  point  are  generally  accepted,  did  not  discover  any  increase  in  the 
consumption  of  oxygen  when  this  gas  was  largely  in  excess  in  the  atmosphere. 

The  results  of  confining  an  animal  in  an  atmosphere  composed  of  twenty-one  parts  of 
oxygen  and  seventy-nine  parts  of  hydrogen  are  very  curious  and  instructive.  When 
hydrogen  is  thus  substituted  for  the  nitrogen  of  the  air,  the  consumption  of  oxygen  is 
largely  increased.  Regnault  and  Reiset  attribute  this  to  the  superior  refrigerating  power 
of  the  hydrogen ;  but  a  more  rational  explanation  would  seem  to  be  in  its  superior 
diffusibility.  Hydrogen  is  the  most  diffusible  of  all  gases ;  and,  when  introduced  into  the 
lungs  in  place  of  the  nitrogen  of  the  air,  the  vitiated  air,  charged  with  carbonic  acid, 
is  undoubtedly  more  readily  removed  from  the  deep  portions  of  the  lungs,  giving  place 
to  the  mixture  of  hydrogen  and  oxygen.  It  is  probably  for  this  reason  that  the 
quantity  of  oxygen  consumed  is  increased.  It  is  probable  that  the  nitrogen  of  the  air 
plays  an  important  part  in  the  phenomena  of  respiration  by  virtue  of  its  degree  of 
diffusibility. 

In  view  of  the  great  variations  in  the  consumption  of  oxygen  dependent  on  different 
physiological  conditions,  such  as  digestion,  exercise,  temperature,  etc.,  it  is  impossible  to 
fix  upon  any  number  which  will  represent,  even  approximatively,  the  average  quantity 


144  KESPIKATIOK 

consumed  per  hour.  The  estimate  arrived  at  by  Longet,  from  a  comparison  of  the  re- 
sults obtained  by  different  reliable  observers,  is  perhaps  as  near  the  truth  as  possible. 
This  estimate  puts  the  hourly  consumption  at  from  1,220  to  1,525  cubic  inches,  "in  an 
adult  male,  during  repose  and  in  normal  conditions  of  health  and  temperature." 

In  passing  through  the  lungs,  the  air,  beside  losing  a  proportion  of  its  oxygen, 
undergoes  the  following  changes : 

1.  Increase  in  temperature. 

2.  Gain  of  carbonic  acid. 

3.  Gain  of  watery  vapor. 

4.  Gain  of  ammonia. 

5.  Gain  of  a  small  quantity  of  organic  matter. 

6.  Gain,  and  occasionally  loss,  of  nitrogen. 

The  elevation  in  temperature  of  the  air  which  has  passed  through  the  lungs  has  been 
carefully  observed  by  Dr.  Grehant.  He  found  that,  with  an  external  temperature  of  72° 
Fahr.,  respiring  seventeen  times  per  minute,  the  air  taken  in  by  the  nares  and  expired  by 
the  mouth,  through  an  apparatus  containing  a  thermometer  carefully  protected  from  ex- 
ternal influences,  marked  a  temperature  of  95-4°.  Taking  in  the  air  by  the  mouth,  the 
temperature  of  the  expired  air  was  93°.  At  the  commencement  of  the  expiration,  Dr. 
Grehant  noted  a  temperature  of  94°.  After  a  prolonged  expiration,  the  temperature 
was  96°.  In  these  observations,  the  temperature  taken  beneath  the  tongue  was  98°. 

Exhalation  of  Carbonic  Acid. — The  production  of  carbonic  acid  in  the  respiratory 
process  is  as  universal  as  the  consumption  of  oxygen.  Experiments  have  shown  that  all 
animals  during  life  exhale  this  principle,  as  well  as  all  tissues,  so  long  as  they  retain  their 
irritability.  This  takes  place,  not  only  when  the  animals  or  tissues  are  placed  in  an 
atmosphere  of  oxygen  or  common  air,  but,  as  was  observed  by  Spallanzani,  in  an 
atmosphere  of  pure  nitrogen  or  hydrogen.  This  fact  has  since  been  noted  by  W.  F. 
Edwards,  J.  Miiller,  G.  Liebig,  Bert,  and  others. 

The  study  of  the  exhalation  of  carbonic  acid  presents  several  problems  of  great 
physiological  interest : 

1.  What  is  the  absolute  quantity  of  carbonic  acid  exhaled  by  the  lungs  in  a  given 
time? 

2.  What  are  the  variations  in  the  exhalation  of  this  principle  due  to  physiological 
influences  ? 

3.  What  is  the  relation  between  the  quantity  of  carbonic  acid  produced  and  the 
quantity  of  oxygen  consumed  ? 

On  account  of  the  variations  in  the  quantities  of  carbonic  acid  exhaled  at  different 
periods  of  the  day,  and  particularly  the  great  influence  of  the  rapidity  of  the  respiratory 
movements,  it  is  exceedingly  difficult  to  fix  upon  any  number  that  will  represent  the 
average  proportion  of  this  gas  contained  in  the  expired  air.  The  same  influences  were 
found  affecting  the  consumption  of  oxygen,  and  the  same  difficulties  were  experienced 
in  forming  an  estimate  of  the  proportion  of  this  gas  consumed.  As  we  assumed,  after 
a  comparison  of  the  results  obtained  by  different  observers,  that  the  volume  of  oxygen 
consumed  is  about  five  per  cent,  of  the  entire  volume  of  air,  it  may  be  stated,  as  an 
approximation,  that,  in  the  intervals  of  digestion,  in  repose,  and  under  normal  conditions 
as  regards  the  frequency  of  the  pulse  and  respiration,  the  volume  of  carbonic  acid 
exhaled  is  about  four  per  cent,  of  the  volume  of  the  expired  air.  As  the  volume  of 
oxygen  which  enters  into  the  composition  of  a  definite  quantity  of  carbonic  acid  is  pre- 
cisely equal  to  the  volume  of  the  carbonic  acid,  it  is  seen  that  a  certain  quantity  of 
oxygen  disappears  in  respiration  and  is  not  represented  in  the  carbonic  acid  exhaled. 

There  are  great  differences  in  the  proportion  of  carbonic  acid  in  the  expired  air, 
depending  upon  the  time  during  which  the  air  has  remained  in  the  lungs.  This  interest- 


EXHALATION  OF   CARBONIC  ACID.  145 

ing  point  has  been  studied  by  Yierordt,  in  a  series  of  ninety-four  experiments  made  upon 
his  own  person,  with  the  following  results : 

"When  the  respirations  are  frequent,  the  quantity  of  carbonic  acid  expelled  at  each 
expiration  is  much  less  than  in  a  slow  expiration ;  but  the  quantity  of  carbonic  acid  pro- 
duced during  a  given  time  by  frequent  respirations  is  greater  than  that  which  is  thrown 
off  by  slow  expirations." 

The  air  which  escapes  during  the  first  period  of  an  expiration  is  naturally  less  rich  in 
carbonic  acid  than  that  which  is  last  expelled  and  comes  directly  from  the  deeper  por- 
tions of  the  lungs.  Dividing,  as  nearly  as  possible,  the  expiration  into  two  equal  parts, 
Vierordt  found,  as  the  mean  of  twenty-one  experiments,  a  percentage  of  3'72  in  the 
first  part  of  the  expiration  and  5'44  in  the  second  part. 

Temporary  arrest  of  the  respiratory  movements,  as  we  should  expect,  has  a  marked 
influence  in  increasing  the  proportion  of  carbonic  acid  in  the  expired  air ;  although  the 
absolute  quantity  exhaled  in  a  given  time  is  diminished.  In  a  number  of  experiments 
on  his  own  person,  Vierordt  ascertained  that  the  percentage  of  carbonic  acid  becomes 
uniform  in  all  parts  of  the  respiratory  organs,  after  holding  the  breath  for  forty  seconds. 
Holding  the  breath  after  an  ordinary  inspiration,  for  twenty  seconds,  the  percentage 
of  carbonic  acid  in  the  expired  air  was  increased  1*73  over  the  normal  standard;  but  the 
absolute  quantity  exhaled  was  diminished  by  2*642  cubic  inches.  After  taking  the 
deepest  possible  inspiration  and  holding  the  breath  for  one  hundred  seconds,  the  per- 
centage was  increased  3 '08  above  the  normal  standard;  but  the  absolute  quantity  was 
diminished  more  than  fourteen  cubic  inches.  Allen  and  Pepys  state  that  air  which  has 
passed  nine  or  ten  times  through  the  lungs  contains  9'5  per  cent,  of  carbonic  acid. 

Vierordt  gives  the  following  formula  as  representing  the  influence  of  the  frequency  of 
the  respirations  on  the  production  of  carbonic  acid :  Taking  2-5  parts  per  hundred  as 
representing  the  constant  value  of  the  gas  exhaled  by  the  blood,  the  increase  over  this 
proportion  in  the  expired  air  is  in  exact  ratio  to  the  duration  of  the  contact  of  the  air 
and  blood. 

The  absolute  quantity  of  carbonic  acid  exhaled  in  a  given  time  is  a  more  important 
subject  of  inquiry  than  the  proportion  contained  in  the  expired  air ;  for  the  latter  is  con- 
stantly varying  with  every  modification  in  the  number  and  extent  of  the  respiratory  acts, 
and  the  volume  of  breathing  air  is  subject  to  great  fluctuations  and  is  very  difficult  of 
determination. 

Among  the  most  reliable  observations  on  the  quantity  of  carbonic  acid  exhaled  by  the 
human  subject  in  a  definite  time  and  the  variations  to  which  it  is  subject,  are  those  of 
Andral  and  Gavarret  and  of  Dr.  Edward  Smith.  The  observations  of  Lavoisier  and  SSguin, 
Prout,  Davy,  Dumas,  Allen  and  Pepys,  Scharling,  and  others,  have  none  of  them  seemed 
to  fulfil  the  necessary  experimental  conditions  so  completely.  Scharling's  method  was  to 
enclose  his  subject  in  a  tight  box,  with  a  capacity  of  about  twenty-seven  cubic  feet,  to 
which  air  was  constantly  supplied ;  but  the  observations  were  comparatively  few,  being 
made  on  only  six  persons.  In  his  observations,  the  quantities  of  gas  exhaled  must  have 
been  considerably  modified  by  the  elevation  of  temperature  and  exhalation  of  moisture  in 
so  small  a  space.  The  mental  condition  of  the  subject  of  an  experiment  has  an  influence 
upon  the  products  of  respiration,  and  the  function  is  sometimes  modified  from  the  mere 
fact  that  an  experiment  is  being  performed ;  an  influence  which  Scharling  did  not  fail  to 
recognize,  but  which  frequently  cannot  be  guarded  against. 

The  observations  of  Andral  and  Gavarret  were  made  on  sixty-two  persons  of  both 
sexes  and  different  ages  and  under  absolutely  identical  conditions  as  regards  digestion, 
time  of  the  day,  barometric  pressure,  and  temperature.  The  products  of  respiration  were 
collected  in  the  following  way :  A  thin  mask  of  copper  covering  the  face  and  large 
enough  to  contain  an  entire  expiration  was  fitted  to  the  face  by  its  edges,  which  were 
provided  with  India-rubber  so  as  to  make  it  air-tight.  At  the  upper  part  was  a  plate  of 
glass  for  the  admission  of  light,  and  at  the  lower  part,  an  opening,  which  allowed  the 
10 


146  KESPIKATIO^. 

entrance  of  air  but  was  provided  with  a  valve  preventing  its  escape.  By  another  open- 
ing, the  mask  was  connected  by  a  rubber  tube  with  three  glass  balloons,  capable  of  hold- 
ing 8,544  cubic  inches,  in  which  a  vacuum  had  been  previously  established.  "With  the  mask 
fixed  upon  the  face,  and  a  stopcock  opened,  connected  with  the  balloons,  so  as  to  gradu- 
ate the  current  of  air,  the  subject  respires  freely  in  the  current  which  comes  from  the 
exterior  into  the  receivers.  In  this  way,  although  the  quantity  of  air  respired  is  not  meas- 
ured, the  vacuum  in  the  receivers  draws  in  the  products  of  respiration.  The  current  will 
continue  for  from  eight  to  thirteen  minutes  and  is  so  regulated  that  the  air  is  respired 
but  once.  The  quantity  of  carbonic  acid  in  the  receivers  represents  the  quantity  pro- 
duced during  the  time  that  the  experiment  has  been  going  on.  By  carefully  fulfilling  all 
the  physiological  conditions,  regulating  the  number  of  respirations,  as  far  as  possible,  to 
the  normal  standard,  different  observations  on  the  same  subject,  at  different  times  and  under 
the  same  conditions,  were  attended  with  results  so  nearly  identical  as  to  give  every  con- 
fidence in  the  accuracy  of  the  process.  But  even  then,  these  observers  recognized  such 
immense  variations  in  the  exhalation  of  carbonic  acid  with  the  constantly-varying  physi- 
ological conditions,  that  they  did  not  feel  justified  in  taking  their  observations  as  a  basis 
for  calculations  of  the  entire  quantity  exhaled  in  the  twenty-four  hours. 

The  results  of  the  above-mentioned  observations  on  the  male,  between  the  ages  of  six- 
teen and  thirty,  between  1  and  2  p.  M.,  under  identical  conditions  of  the  digestive  and 
muscular  systems,  each  experiment  lasting  from  eight  to  thirteen  minutes,  showed  an 
exhalation  of  about  1,220  cubic  inches  of  carbonic  acid  per  hour. 

Dr.  Edward  Smith,  in  his  elaborate  paper  on  the  phenomena  of  respiration,  employed 
a  very  rigorous  method  for  the  estimation  of  the  carbonic  acid  exhaled.  lie  used  a  mask, 
fitting  closely  to  the  face,  which  covered  only  the  air-passages.  The  air  was  admitted  after 
being  measured  by  passing  through  an  ordinary  dry  gas-meter.  The  expired  air  was  passed 
through  a  drying  apparatus,  and  the  carbonic  acid  was  absorbed  by  a  solution  of  potash, 
arranged  in  a  number  of  layers  so  as  to  present  a  surface  of  about  seven  hundred  square 
inches,  and  carefully  weighed.  This  apparatus  was  capable  of  collecting  all  the  carbonic 
acid  exhaled  in  an  hour.  The  estimate  was  made  for  eighteen  waking  hours  and  six  hours 
of  sleep.  The  observations  for  the  eighteen  hours  were  made  on  four  persons;  namely, 
Dr.  Smith,  aat.  38  years,  weighing  196  pounds,  6  feet  high,  with  a  vital  capacity  of  280 
cubic  inches;  Mr.  Moul,  set.  48  years,  5  feet  9£  inches  high,  1V5  pounds  weight;  Dr. 
Murie,  set.  26  years,  5  feet  V£  inches  high,  133  pounds  weight,  vital  capacity  250  cubic 
inches ;  Prof.  Frankland,  a3t.  33  years,  5  feet  10£  inches  high,  and  136  pounds  weight. 
Breakfast  was  taken  at  8|-  A.  M.,  dinner  at  1£,  tea  at  5£,  and  supper  at  8£  p.  M.  The  ob- 
servations occupied  ten  minutes  and  were  made  every  hour  and  half-hour  for  eighteen 
hours.  The  average  for  the  eighteen  hours  gave  20,082  cubic  inches  of  carbonic  acid  for 
the  whole  period.  Observations  during  the  six  hours  of  sleep  showed  a  total  exhalation 
of  4,126  cubic  inches.  This,  added  to  the  quantity  exhaled  during  the  day,  gives  as  the 
total  exhalation  in  the  twenty-four  hours,  during  complete  repose,  24,208  cubic  inches 
/about  14'24  cubic  feet),  containing  V'144  oz.  av.  of  carbon.  Considering  the  great  varia- 
tions in  the  exhalation  of  carbonic  acid,  this  estimate  can  be  nothing  more  than  an  ap- 
proximation. One  of  the  great  modifying  influences  is  muscular  exertion,  by  which  the 
production  of  carbonic  acid  is  largely  increased.  This  would  indicate  a  larger  quantity 
during  ordinary  conditions  of  exercise,  and  a  much  larger  quantity  in  the  laboring  classes. 
Dr.  Smith  gives  the  following  approximate  estimates  of  these  differences: 

In  quietude 7*144  oz.  av.  of  carbon. 

Non-laborious  class 8'68        "  " 

Laborious  class 1T7          "  " 

In  studying  the  variations  in  the  exhalation  of  carbonic  acid,  important  information 
has  been  derived  from  experiments  by  many  observers  on  the  inferior  animals,  as  well  as 
Jrom  the  observations  of  Dumas,  Prout,  Scharling,  Pettenkofer,  and  others,  on  the 


EXHALATION  OF  CARBONIC  ACID.  147 

human  subject.  The  principal  conditions  which  influence  the  exhalation  of  this  principle 
are  the  following :  Age  and  sex ;  activity  or  repose  of  the  digestive  system ;  form  of 
diet ;  sleep  ;  muscular  activity  ;  fatigue  ;  moisture  and  surrounding  temperature ;  season 
of  the  year. 

Influence  of  Age. — In  treating  of  the  consumption  of  oxygen,  it  was  stated  that,  during 
the  first  few  days  of  extra-uterine  existence,  the  demand  for  oxygen  on  the  part  of  the 
system  is  very  slight.  At  this  period  there  is  a  correspondingly-feeble  exhalation  of 
carbonic  acid.  It  is  well  known  that,  during  the  first  hours  and  days  after  birth,  the  new 
being  has  little  power  of  generating  heat,  needs  constant  protection  from  changes  in  tem- 
perature, and  the  voluntary  movements  are  very  imperfect.  During  the  first  few  days, 
indeed,  the  infant  does  little  more  than  sleep  and  take  the  small  quantity  of  colostrum 
which  is  furnished  by  the  mammary  glands  of  the  mother.  While  the  animal  functions 
are  so  imperfectly  developed  and  until  the  nourishment  becomes  more  abundant  and  the 
child  begins  to  increase  rapidly  in  weight,  the  quantity  of  carbonic  acid  exhaled  is  very 
small. 

After  the  respiratory  function  has  become  fully  established,  it  is  probable,  from  the 
greater  number  of  respiratory  movements  in  early  life,  that  the  production  of  carbonic 
acid,  in  proportion  to  the  weight  of  the  body,  is  greater  in  infancy  than  in  adult  life. 
Direct  observations,  however,  are  wanting  on  this  point. 

The  observations  of  Andral  and  Gavarret  show  the  comparative  exhalation  of  carbonic 
acid  in  the  male,  from  the  age  of  twelve  to  eighty-two,  and  give  the  results  of  a  single 
observation  at  the  age  of  one  hundred  and  two  years.  They  show  an  increase  in  the 
absolute  quantity  exhaled,  from  the  age  of  twelve  to  thirty-two ;  a  slight  diminution, 
from  thirty-two  to  sixty;  and  a  considerable  diminution,  from  sixty  to  eighty -two.  These 
results  are  given  in  the  following  table : 

Carbonic  acid  exhaled  per  hour 

In  boys  from  twelve  to  sixteen  years 915  cubic  inches. 

In  young  men  from  seventeen  to  nineteen  years 1,220      "  ,      " 

In  men  from  twenty-five  to  thirty-two  years 1,343      "         " 

In  men  from  thirty-two  to  sixty  years 1,220      "         " 

In  men  from  sixty-three  to  eighty-two  years 933      "         " 

In  an  old  man  of  one  hundred  and  two  years 671      "        " 

Taking  into  consideration  the  increase  in  the  weight  of  the  body  with  age,  it  is  evident 
that  the  respiratory  activity  is  much  greater  in  youth  than  in  adult  life.  Andral  and 
Gavarret  do  not  give  the  weight  of  the  subjects  of  their  observations,  but,  as  the  weight 
generally  does  not  diminish  after  maturity,  there  can  be  no  doubt  that  there  is  a  rapid 
diminution  in  the  relative  quantity  of  carbonic  acid  produced  in  old  age. 

Scharling,  in  a  series  of  observations  on  a  boy  nine  years  of  age  and  weighing  48*5 
pounds,  an  adult  of  twenty-eight,  and  one  of  thirty-five  years,  the  latter  weighing  163-6 
pounds,  showed  that  the  respiratory  activity  in  the  child  was  nearly  twice  as  great,  in 
proportion  to  his  weight,  as  the  average  in  the  adults.  It  is  seen,  from  the  observations 
of  Andral  and  Gavarret,  that  the  absolute  increase  in  the  exhalation  of  carbonic  acid  from 
childhood  to  adult  life  is  very  slight  in  comparison  with  the  natural  increase  in  the 
weight  of  the  body;  showing  that,  proportionately,  the  exhalation  of  carbonic  acid  is 
greater  in  early  life. 

Influence  of  Sex. — All  observers  have  found  a  marked  difference  between  the  sexes,  in 
favor  of  the  male,  in  the  proportion  of  carbonic  acid  exhaled.  Andral  and  Gavarret  noted 
an  absolute  difference  of  about  forty-five  cubic  inches  per  hour  but  did  not  take  into 
consideration  the  differences  in  the  weight  of  the  body..  Scharling,  taking  the  proportion 
exhaled  to  the  weight  of  the  body,  noted  a  marked  difference  in  favor  of  the  male. 

The  difference  in  the  degree  of  muscular  activity  in  the  sexes  is  sufficient  to  account 
for  the  greater  evolution  of  carbonic  acid  in  the  male,  for  this  principle  is  exhaled  in  pro- 
portion to  the  muscular  development  of  the  individual ;  but  there  is  an  important  differ- 


148  RESPIRATION. 

ence  connected  with  the  variations  with  age,  which  depends  upon  the  condition  of  the 
generative  system  of  the  female. 

The  absolute  increase  in  the  evolution  of  carbonic  acid  with  age,  in  the  female,  is 
arrested  at  the  time  of  puberty  and  remains  stationary  during  the  entire  menstrual 
period,  provided  the  menstrual  flow  occur  with  regularity.  During  this  time,  the  average 
exhalation  per  hour  is  714  cubic  inches.  After  the  cessation  of  the  menses,  the  quantity 
gradually  increases,  until,  at  the  age  of  sixty,  it  amounts  to  915  cubic  inches  per  hour. 
From  the  age  of  sixty  to  eighty-two,  the  quantity  diminishes  to  793,  and  finally  to  670 
cubic  inches. 

When  the  menses  are  suppressed,  there  is  an  increase  in  the  exhalation  of  carbonic 
acid,  which  continues  until  the  flow  becomes  reestablished.  In  a  case  of  pregnancy 
observed  by  Scharling,  the  exhalation  was  increased  to  about  885  cubic  inches. 

Influence  of  Digestion, — Almost  all  observers  agree  that  the  exhalation  of  carbonic 
acid  is  largely  increased  during  digestion.  Lavoisier  and  Seguin  found  that,  in  repose 
and  fasting,  the  quantity  exhaled  per  hour  was  1,210  cubic  inches,  which  was  raised  to 
1,800  and  1,900  during  digestion.  Numerous  experiments  on  animals  have  confirmed 
this  statement.  A  very  interesting  series  of  observations  on  this  point  was  made  by 
Vierordt  upon  his  own  person.  Taking  his  dinner  at  from  12*30  to  1  P.  M.,  having  noted 
the  frequency  of  the  pulse  and  respirations  and  the  exhalation  of  carbonic  acid  at  12,  he 
found,  at  2  p.  M.,  the  pulse  and  respirations  increased  in  frequency,  the  volume  of  expired 
air  augmented,  and  that  the  carbonic  acid  exhaled  had  increased  from  15*77  to  18'22  cubic 
inches  per  minute.  In  order  to  ascertain  that  this  variation  did  not  depend  upon  the 
time  of  day  independently  of  the  digestive  process,  he  made  a  comparison  at  12  M.,  at  1 
and  at  2  p.  M.  without  taking  food,  which  showed  no  notable  variation,  either  in  the 
pulse,  number  of  respirations,  volume  of  expired  air,  or  quantity  of  carbonic  acid  exhaled. 
There  can  be  no  doubt  that  the  exhalation  of  carbonic  acid  is  notably  increased  during 
the  functional  activity  of  the  digestive  system. 

The  effect? of  inanition  is  to  gradually  diminish  the  exhalation  of  carbonic  acid.  Bidder 
and  Schmidt  noted  the  daily  production  of  carbonic  acid  in  a  cat  which  was  subjected  to 
eighteen  days  of  inanition,  at  the  end  of  which  time  it  died.  The  quantity  diminished 
gradually  from  day  to  day,  until,  just  before  death,  it  was  reduced  a  little  more  than  one- 
half.  Dr.  Smith  noted,  in  his  own  person,  the  influence  of  a  fast  of  twenty-seven  hours. 
There  was  a  marked  diminution  in  the  quantity  of  air  respired,  in  the  quantity  of  vapor 
exhaled,  in  the  number  of  respirations,  and  in  the  rapidity  of  the  pulse.  The  exhalation 
of  carbonic  acid  was  diminished  one-fourth.  An  interesting  point  in  this  observation  was 
the  fact  that  the  quantity  was  as  small  four  and  a  half  hours  after  eating  as  at  the  end 
of  the  twenty-seven  hours.  "  An  increase  of  carbonic  acid  in  the  absence  of  food,  at  or 
near  the  period  when  it  is  usually  increased  by  food,"  was  also  noted  in  the  experiment 
by  Dr.  Smith. 

Influence  of  Diet. — Eegnault  and  Reiset,  in  their  experiments  on  animals,  studied  the 
effect  of  different  kinds  of  diet  upon  the  relations  of  the  quantity  of  oxygen  absorbed  to 
the  carbonic  acid  exhaled.  About  the  only  conclusive  and  extended  series  of  investiga- 
tions on  the  influence  of  diet  upon  the  absolute  quantity  of  carbonic  acid  exhaled  are 
those  of  Dr.  Smith.  This  observer  made  a  large  number  of  experiments  on  the  influence 
of  various  kinds  of  food  and  extended  his  inquiries  into  the  influence  of  certain  beverages, 
such  as  tea,  coffee,  cocoa,  malt  and  fermented  liquors.  We  have  already  fully  described 
the  method  employed  in  these  experiments,  and  the  conclusions,  which  are  of  great 
interest  and  importance,  are  very  exact  and  reliable. 

Dr.  Smith  divides  food  into  two  classes,  one  which  increases  the  exhalation  of  carbonic 
acid,  which  he  calls  respiratory  excitants,  and  the  other,  which  diminishes  the  exhalation, 
he  calls  non-exciters. 

The  following  are  the  results  of  a  large  number  of  carefully-conducted  observations 
upon  four  persons : 


EXHALATION   OF  CARBONIC  ACID.  149 

"  The  excito-respiratory  are  nitrogeneous  food,  milk  and  its  components,  sugars,  rum, 
beer,  stout,  the  cereals,  and  potato. 

"  The  non-exciters  are  starch,  fat,  certain  alcoholic  compounds,  the  volatile  elements 
of  wines  and  spirits,  and  coffee-leaves. 

"  Respiratory  excitants  have  a  temporary  action ;  hut  the  action  of  most  of  them 
commences  very  quickly,  and  attains  its  maximum  within  one  hour. 

"  The  most  powerful  respiratory  excitants  are  tea  and  sugar ;  then  coffee,  rum,  milk, 
cocoa,  ales,  and  chiccory ;  then  casein  and  gluten,  and  lastly,  gelatin  and  albumen.  The 
amount  of  action  was  not  in  uniform  proportion  to  their  quantity.  Compound  aliments, 
as  the  cereals,  containing  several  of  these  substances,  have  an  action  greater  than  that 
of  any  of  their  elements. 

u  Most  respiratory  excitants,  as  tea,  coffee,  gluten,  and  casein,  cause  an  increase  in 
the  evolution  of  carbon  greater  than  the  quantity  which  they  supply,  while  others,  as 
sugar,  supply  more  than  they  evolve  in  this  excess,  that  is,  above  the  basis.  No  sub- 
stance containing  a  large  amount  of  carbon  evolves  more  than  a  small  portion  of  that 
carbon  in  the  temporary  action  occurring  above  the  basis-line,  and  hence  a  large  portion 
remains  unaccounted  for  by  these  experiments." 

The  comparative  observations  of  Dr.  Smith  upon  the  four  persons  who  were  the  sub- 
jects of  experiment  demonstrated  one  very  important  fact ;  namely,  that  the  action  of 
different  kinds  of  food  upon  respiration  is  modified  by  idiosyncrasies  and  the  tastes  of 
different  individuals.  For  example,  in  experiments  on  his  own  person,  certain  articles 
which  were  agreeable  to  him  excited  the  exhalation  of  carbonic  acid ;  but  in  experi- 
menting with  the  same  articles  upon  Mr.  Moul,  to  whom  they  were  distasteful,  he  found 
the  respiratory  action  diminished. 

Quite  a  number  of  observers  have  noted  the  influence  of  alcohol  upon  the  products 
of  respiration ;  but  the  results  of  experiments  have  not  been  entirely  uniform.  Prout 
observed  a  constant  diminution  in  the  quantity  of  carbonic  acid  exhaled,  under  the  in- 
fluence of  alcohol.  This  has  been  confirmed  by  the  observations  of  Horn,  Yierordt,  and 
many  others ;  but  Hervier  and  Saint-Lager  assert  that  the  use  of  alcohol  increases  the 
exhalation  of  carbonic  acid.  In  the  experiments  of  Prout,  a  small  quantity  of  wine  taken 
fasting  caused  the  proportion  of  carbonic  acid  in  the  expired  air  to  fall  immediately 
from  4  to  3  parts  per  100.  During  the  four  hours  following,  it  oscillated  between  3-40, 
3-10,  and  3.  The  administration  of  a  second  dose,  followed  by  some  symptoms  of  in- 
toxication, diminished  the  proportion  to  2 '70  per  100.  Dr.  Fyfe,  of  Edinburgh,  showed 
that  the  depressing  effects  of  an  alcoholic  excess  were  continued  into  the  following  day. 
Dr.  Fyfe  also  noted  a  fact,  important  in  this  connection,  namely,  that  the  prolonged  use 
of  nitric  acid  and  the  condition  of  the  system  induced  by  the  administration  of  mer- 
curials were  attended  with  a  considerable  diminution  in  the  daily  amount  of  carbonic 
acid  exhaled  by  the  lungs.  In  addition,  Prout  demonstrated  that  the  exhalation  of  car- 
bonic acid  was  diminished  by  the  use  of  a  concentrated  infusion  of  tea,  and  Horn  noted 
the  same  effect  attending  slight  narcotism  produced  by  smoking  tobacco. 

The  observations  of  Dr.  Smith,  which  were  all  made  fasting,  show  a  certain  variation 
in  the  effects  of  different  alcoholic  beverages.  His  results  are  briefly  the  following : 

"  Brandy,  whiskey,  and  gin,  and  particularly  the  latter,  almost  always  lessened  the 
respiratory  changes  recorded,  while  rum  as  commonly  increased  them.  Rum-and-milk 
had  a  very  pronounced  and  persistent  action,  and  there  was  no  effect  on  the  sensorium. 
Ale  and  porter  always  increased  them,  while  sherry  wine  lessened  the  quantity  of  air 
inspired,  but  slightly  increased  the  carbonic  acid  evolved. 

"  The  volatile  elements  of  alcohol,  gin,  rum,  sherry,  and  port- wine,  when  inhaled, 
lessened  the  quantity  of  carbonic  acid  exhaled,  and  usually  lessened  the  quantity  of  air 
inhaled.  The  effect  of  fine  old  port-wine  was  very  decided  and  uniform ;  and  it  is 
known  that  wines  and  spirits  improve  in  aroma  and  become  weaker  in  alcohol  by  age. 
The  excito-respiratory  action  of  rum  is  probably  not  due  to  its  volatile  elements." 


150  RESPIRATION. 

From  these  facts,  it  would  seem  that  the  most  constant  effect  of  alcohol  and  of  alcoholic 
liquors,  such  as  wines  and  spirits,  is  to  diminish  the  exhalation  of  carbonic  acid.  This 
effect  is  almost  instantaneous,  when  the  articles  are  taken  into  the  stomach  fasting ;  and 
when  taken  with  the  meals,  the  increase  in  carbonic  acid  which  habitually  accompanies 
the  process  of  digestion  is  materially  lessened.  Eum,  which  Dr.  Smith  found  to  be  a 
respiratory  excitant,  is  an  exception  to  this  rule.  Malt  liquors  seem  to  increase  the  ex- 
halation of  carbonic  acid.  With  regard  to  alcohol  itself,  Dr.  Smith  says:  "The  action 
of  pure  alcohol  was  much  more  to  increase  than  to  lessen  the  respiratory  changes,  and 
sometimes  the  former  effect  was  well  pronounced." 

Kegarding  as  one  of  the  great  sources  of  carbonic  acid  the  development  of  this  prin- 
ciple in  the  tissues,  whence  it  is  taken  up  by  the  blood,  Dr.  Smith  attributes  the  grateful 
and  soothing  influence  of  tea,  coffee,  eau  sucree,  and  the  other  beverages  which  he  classes 
as  respiratory  excitants,  to  their  action  in  facilitating  the  removal  of  this  principle  from 
the  system.  The  presence  of  carbonic  acid  in  the  tissues  and  in  the  blood  produces  a 
sense  of  malaise,  or  depression,  which  we  should  suppose  would  be  relieved  by  any  thing 
which  facilitates  its  elimination.  It  is  undoubtedly  this  indefinite  sense  of  discomfort 
which  induces  the  act  of  sighing,  by  which  the  air  in  the  lungs  is  more  effectually  reno- 
vated. This  view  is  sustained  by  the  fact  that  intellectual  fatigue  and  mental  emotions 
diminish  the  exhalation  of  carbonic  acid.  Apjohn  cites  an  instance  in  which  the  pro- 
portion of  carbonic  acid  in  the  expirations  was  reduced  to  2'9  parts  per  100  under  the 
influence  of  mental  depression. 

We  have  already  alluded  to  the  modification  in  the  exhalation  of  carbonic  acid  pro- 
duced by  tobacco. 

Influence  of  Sleep. — All  who  have  directed  attention  to  the  influence  of  sleep  upon 
the  respiratory  products  have  noted  a  marked  diminution  in  the  exhalation  of  carbonic 
acid ;  but  we  again  recur  to  the  experiments  of  Dr.  Smith  for  exact  information  on  this 
point.  Dr.  Smith  estimated  the  quantity  of  carbonic  acid  exhaled  during  six  hours  of 
sleep,  at  night,  at  4,126  cubic  inches.  According  to  this  observer,  the  quantity  during 
the  night  is  to  the  quantity  during  the  day,  in  complete  repose,  as  ten  is  to  eighteen. 
During  a  light  sleep,  the  exhalation  was  10*32,  and  during  profound  sleep,  9'52  cubic 
inches  per  minute. 

We  have  alluded  to  the  great  diminution  in  the  quantity  of  oxygen  consumed  in  hiber- 
nating animals  while  in  a  torpid  condition.  Regnault  and  Reiset  found  that  a  marmot 
in  hibernation  consumed  only  -^  of  the  oxygen  which  he  used  in  his  active  condition. 
In  the  same  animal  they  noted  an  exhalation  of  carbonic  acid  equal  to  but  little  more 
than  half  the  weight  of  oxygen  absorbed;  so  that  in  this  condition  the  diminution  in  the 
exhalation  of  carbonic  acid  is  proportionately  even  greater  than  in  the  consumption  of 
oxygen. 

Influence  of  Muscular  Activity, — Nearly  all  observers  are  agreed  that  there  is  a  con- 
siderable increase  in  the  exhalation  of  carbonic  acid  during  and  immediately  following 
muscular  exercise.  In  insects,  Mr.  Newport  has  found  that  a  greater  quantity  is  some- 
times exhaled  in  an  hour  of  violent  agitation  than  in  twenty-four  hours  of  repose.  In  a 
drone,  the  exhalation  in  twenty-four  hours  was  0'30  of  a  cubic  inch,  and  during  vio- 
lent muscular  exertion  the  exhalation  in  one  hour  was  0-34.  Lavoisier  recognized  the 
great  influence  of  muscular  activity  upon  the  respiratory  changes.  In  treating  of  the 
consumption  of  oxygen,  we  have  quoted  his  observations  on  the  relative  quantities  of  air 
vitiated  in  repose  and  activity. 

Yierordt,  in  a  number  of  observations  on  the  human  subject,  ascertained  that  moder- 
ate exercise  increased  the  average  quantity  of  air  respired  per  minute  by  nearly  nineteen 
cubic  inches,  and  that  there  was  an  increase  of  1'197  cubic  inch  per  minute  in  the  ab- 
solute quantity  of  carbonic  acid  exhaled. 

The  following  results  of  the  experiments  of  Dr.  Edward  Smith  on  the  influence  of 
exercise  are  very  definite  and  satisfactory : 


EXHALATION  OF   CARBONIC  ACID.  151 

In  walking  at  the  rate  of  two  miles  an  hour,  the  exhalation  of  carbonic  acid  during 
one  hour  was  equal  to  the  quantity  produced  during  If  hour  of  repose  with  food,  and  2£ 
hours  of  repose  without  food. 

Walking  at  the  rate  of  three  miles  per  hour,  one  hour  was  equal  to  2£-  hours  with, 
and  3£  hours  without  food. 

One  hour's  labor  at  the  tread-wheel,  while  actually  working  the  wheel,  was  equal  to 
4£  hours  of  rest  with  food,  and  6  hours  without  food. 

The  various  observers  we  have  cited  have  remarked  that,  when  muscular  exertion  is 
carried  so  far  as  to  produce  great  fatigue  and  exhaustion,  the  exhalation  of  carbonic  acid 
is  notably  diminished. 

Influence  of  Moisture  and  Temperature. — Lehmann  has  shown  that  the  exhalation  of 
carbonic  acid  is  much  greater  in  a  moist  than  in  a  dry  atmosphere.  This  conclusion 
was  the  result  of  a  number  of  experiments  on  birds  and  animals  confined  in  air  at  differ- 
ent temperatures  and  different  degrees  of  moisture.  He  found  that  35-J-  oz.  av.  weight  of 
rabbits,  at  a  temperature  of  about  100°  Fahr.,  exhaled  during  an  hour  before  noon,  in  a 
dry  air,  about  15  cubic  inches  of  carbonic  acid ;  while,  in  a  moist  air  at  the  same  tempera- 
ture, the  exhalation  was  about  22  cubic  inches. 

Disregarding  observations  on  the  influence  of  temperature  in  cold-blooded  animals  as 
inapplicable  to  the  human  subject,  it  has  been  ascertained  that  the  exhalation  of  carbonic 
acid  is  much  greater  at  low  than  at  high  temperatures,  within  the  limits  of  heat  and  cold 
that  are  easily  borne  by  the  human  subject ;  thus  following  the  rule  which  governs  the 
consumption  of  oxygen. 

The  experiments  of  Yierordt  on  the  human  subject  show  that  there  is  an  increase  in 
the  exhalation  of  carbonic  acid  of  about  one-sixth,  under  the  influence  of  a  moderate 
diminution  in  temperature.  In  these  observations,  the  low  temperatures  ranged  between 
37-5°  and  59°,  and  the  high  temperatures  between  60-5°  and  75'5°  Fahr.  He  found  the 
quantity  of  air  taken  into  the  lungs  slightly  increased  at  low  temperatures.  The  abso- 
lute quantity  of  carbonic  acid  exhaled  per  minute  was  18-27  cubic  inches  for  the  low 
temperatures,  and  15 '73  cubic  inches  for  the  high  temperatures. 

Influence  of  the  Season  of  the  Year. — It  has  been  pretty  well  established  by  the  re- 
searches of  Dr.  Smith,  that  spring  is  the  season  of  the  greatest,  and  fall  the  season  of 
the  least  activity  of  the  respiratory  function. 

The  months  of  maximum  are :  January,  February,  March,  and  April. 

The  months  of  minimum  are :  July,  August,  and  a  part  of  September. 

The  months  of  decrease  are :  June  and  July. 

The  months  of  increase  are :  October,  November,  and  December. 

W.  F.  Edwards,  in  1819,  showed  in  a  marked  manner  the  influence  of  the  seasons 
upon  the  respiratory  phenomena  in  birds.  In  a  series  of  very  curious  observations,  which 
he  repeatedly  verified,  it  was  demonstrated  that  the  increase  in  the  activity  of  respiration 
during  the  winter  was  to  a  certain  extent  independent  of  the  immediate  influence  of  the 
surrounding  temperature.  In  the  month  of  January,  he  confined  six  yellow-hammers  in 
a  receiver  containing  71 '4  cubic  inches  of  air,  carrying  the  temperature  from  69°  to  70° 
Fahr.  The  mean  duration  of  their  life  was  62  minutes  25  seconds.  In  the  months  of 
August  and  September,  he  repeated  the  experiment  on  thirteen  birds  of  the  same  species, 
at  the  same  temperature.  The  mean  duration  of  life  was  82  minutes.  These  experiments 
have  an  important  bearing  on  our  views  concerning  the  essential  nature  of  the  respira- 
tory function.  They  seem  to  indicate  that  the  respiratory  processes  are  intimately  con- 
nected with  nutrition.  Like  the  other  nutritive  phenomena,  they  undoubtedly  vary  at 
different  seasons  of  the  year  and  are  to  a  certain  extent  independent  of  sudden  and 
transitory  conditions.  During  the  winter,  more  air  is  habitually  used  than  in  summer, 
and  the  respiratory  processes  cannot  be  immediately  brought  down  to  the  summer 
standard  by  a  mere  elevation  of  temperature. 

Observations  on  the  influence  of  barometric  pressure  are  not  sufficiently  definite  in 
their  results  to  warrant  any  exact  conclusions. 


153  RESPIRATION. 

Some  physiologists  have  attempted  to  fix  certain  hours  of  the  day  when  the  exhalation 
of  carbonic  acid  is  at  its  maximum  or  at  its  minimum ;  but  the  respiratory  activity  is 
influenced  by  such  a  variety  of  conditions,  that  it  is  impossible  to  do  this  with  any  degree 
of  accuracy. 

Relations  between  the    Quantity  of  Oxygen  consumed  and  the  Quantity  of 

Carbonic  Acid  exhaled. 

Oxygen  unites  with  carbon  in  certain  proportions  to  form  carbonic-acid  gas,  the  vol- 
ume of  which  is  precisely  equal  to  the  volume  of  the  oxygen  which  enters  into  its  com- 
position. In  studying  the  relations  of  the  volumes  of  these  gases  in  respiration,  we  have 
a  guide  in  the  comparison  of  the  volumes  of  the  inspired  and  expired  air.  It  is  now 
generally  recognized  that  the  volume  of  air  expired  is  less,  at  an  equal  temperature,  than 
the  volume  of  air  inspired.  Assuming,  then,  that  the  changes  in  the  expired  air,  as  re- 
gards nitrogen  and  all  gases  except  oxygen  or  carbonic  acid,  are  insignificant,  it  must  be 
admitted  that  a  certain  quantity  of  the  oxygen  consumed  by  the  economy  is  unaccounted 
for  by  the  oxygen  which  enters  into  the  composition  of  the  carbonic  acid  exhaled.  We 
have  already  noted  that  from  TV  to  ^,  or  about  1*4  to  2  per  cent,  of  the  inspired  air  is 
lost  in  the  lungs ;  or  it  may  be  stated,  in  general  terms,  that  the  oxygen  absorbed  is  equal 
to  about  five  per  cent,  of  the  volume  of  air  inspired,  and  the  carbonic  acid  exhaled,  only 
about  four  per  cent.  A  certain  amount  of  the  deficiency  in  volume  of  the  expired  air  is 
to  be  accounted  for,  then,  by  a  deficiency  in  the  exhalation  of  carbonic  acid. 

The  experiments  of  Regnault  and  Reiset,  to  which  frequent  reference  has  been  made, 
have  a  most  important  bearing  on  the  question  under  consideration.  As  these  observers 
were  able  to  accurately  measure  the  entire  quantities  of  oxygen  consumed  and  carbonic 
acid  produced  in  a  given  time,  the  relation  between  the  two  gases  was  kept  constantly  in 
view.  They  found  great  variations  in  this  relation,  mainly  dependent  upon  the  regimen 
of  the  animal.  The  total  loss  of  oxygen  was  found  to  be  much  greater  in  carnivorous 
than  in  herbivorous  animals  ;  and,  in  animals  that  could  be  subjected  to  a  mixed  diet,  by 
regulating  the  food,  this  was  made  to  vary  between  the  two  extremes.  The  mean  of 
seven  experiments  on  dogs  showed  that,  for  every  1,000  parts  of  oxygen  consumed,  Y45 
parts  were  exhaled  in  the  form  of  carbonic  acid.  In  six  experiments  on  rabbits,  the 
mean  was  919  for  every  1,000  parts  of  oxygen. 

In  animals  fed  on  grains,  the  proportion  of  carbonic  acid  exhaled  was  greatest,  some- 
times passing  a  little  beyond  the  volume  of  oxygen  consumed. 

"  The  relation  is  nearly  constant  for  animals  of  the  same  species  which  are  subjected 
to  a  perfectly  uniform  alimentation,  as  is  easy  to  realize  as  regards  dogs ;  but  it  varies 
notably  in  animals  of  the  same  species,  and  in  the  same  animal,  submitted  to  the  same 
regimen,  but  in  which  we  cannot  regulate  the  alimentation,  as  in  fowls." 

When  herbivorous  animals  were  entirely  deprived  of  food,  the  relation  between  the 
gases  was  the  same  as  in  carnivorous  animals. 

The  final  result  of  the  experiments  of  Regnault  and  Reiset  was,  that  the  "relation 
between  the  oxygen  contained  in  the  carbonic  acid  and  the  total  oxygen  consumed,  varies, 
in  the  same  animal,  from  0*62  to  1-04,  according  to  the  regimen  to  which  it  is  subjected." 
These  observations  on  animals  have  been  confirmed  in  the  human  subject  by  M.  Doyere, 
who  found  a  great  variation  in  the  relations  of  the  two  gases  in  respiration ;  the  volume 
of  carbonic  acid  exhaled  varying  between  1*087  and  0*862  for  1  part  of  oxygen  consumed. 

The  destination  of  the  oxygen  which  is  not  represented  in  the  carbonic  acid  exhaled 
is  obscure.  Some  have  thought  that  it  unites  with  hydrogen  to  form  water ;  but  there  is 
no  satisfactory  evidence  of  the  formation  of  water  in  the  economy,  and  researches  have 
failed  to  show  that  there  is  more  thrown  off  from  the  body  than  is  taken  in  with  food  and 
drink. 

The  variations  in  the  relative  volumes  of  oxygen  consumed  and  carbonic  acid  produced 


EXHALATION  OF  WATERY   VAPOR.  153 

in  respiration  are  not  favorable  to  the  hypothesis  that  the  carbonic  acid  is  the  result  of  a 
direct  action  of  oxygen  upon  carbonaceous  matters.  We  should  hardly  expect  a  definite 
relation  to  exist  between  these  two  gases  in  respiration,  when  we  find  carbonic  acid  ex- 
haled in  the  absence  of  oxygen. 

Many  of  the  points  which  we  have  considered  with  relation  to  the  variations  in  the 
exhalation  of  carbonic  acid  have  been  investigated  by  experiments  in  Pettenkofer's  cham- 
ber, and  the  results  very  nearly  correspond  with  the  observations  of  Scharling,  Smith,  and 
others  which  we  have  quoted. 

"Sources  of  Carbonic  Acid,  in  the  Expired  Air. — All  the  carbonic  acid  in  the  expired 
air  comes  from  the  venous  blood,  where  it  exists  in  two  forms ;  in  a  free  state  in  simple 
solution,  or  at  least  in  a  state  of  very  feeble  combination,  and  in  union  with  bases,  form- 
ing the  carbonates  and  bicarbonates.  That  which  exists  in  solution  in  the  blood  is  simply 
exhaled.  The  alkaline  carbonates  and  bicarbonates  of  the  blood,  coming  to  the  lungs, 
meet  with  pneumic  acid  (discovered  by  Verdeil  in  1851),  and  are  decomposed,  giving  rise 
to  a  farther  evolution  of  gas.  It  is  pneumic  acid  which  gives  the  constant  acid  reaction 
to  the  tissue  of  the  lungs.  This  principle  is  found  in  the  pulmonary  parenchyma  at  all 
periods  of  life,  from  which  it  may  be  extracted  by  the  proper  manipulations  and  obtained 
in  a  crystalline  form.  Its  quantity  is  not  very  great.  The  lungs  of  a  female  who  suffered 
death  by  decapitation  contained  about  O77  of  a  grain. 

The  action  of  pneumic  acid  upon  the  bicarbonates  in  the  blood  has  been  illustrated 
in  a  marked  manner  by  Bernard.  When  bicarbonate  of  soda  is  injected  into  the  jugular 
of  a  living  animal,  a  rabbit,  for  example,  it  is  decomposed  as  fast  as  it  gets  to  the  lungs, 
and  carbonic  acid  is  evolved.  This  experiment  produces  no  inconvenience  to  the  animal 
when  the  bicarbonate  is  introduced  slowly ;  but,  when  it  is  injected  in  large  quantity, 
the  evolution  of  gas  in  the  lungs  is  so  great  as  to  fill  the  pulmonary  structure  and  even 
the  heart  and  great  vessels,  and  death  is  the  result. 

Exhalation  of  Watery  Vapor. — The  fact  that  the  expired  air  contains  a  considerable 
quantity  of  watery  vapor  has  long  been  recognized ;  and  most  of  the  earlier  experimenters 
who  directed  their  attention  to  the  phenomena  of  respiration  made  the  estimation  of  the 
quantity  exhaled,  and  the  laws  which  regulate  pulmonary  transpiration,  the  subject  of 
investigation.  It  is  evident  that  there  must  be  many  circumstances  materially  influencing 
this  process,  such  as  the  hygrometric  condition  of  the  atmosphere,  temperature,  extent 
of  respiratory  surface,  etc.,  which  are  of  sufficient  importance  to  demand  special  con- 
sideration. In  many  points  of  view,  also,  it  is  interesting  to  know  the  absolute  quantity 
of  aqueous  exhalation  from  the  lungs. 

When  the  surrounding  atmosphere  has  a  temperature  below  40°  or  43°  Fahr.,  a  distinct 
cloud  is  produced  by  the  condensation  of  the  vapor  of  the  breath.  By  breathing  upon 
any  polished  surface,  it  is  momentarily  tarnished  by  the  condensed  moisture.  Although  the 
fact  that  watery  vapor  is  contained  in  the  breath  is  thus  easily  demonstrated,  the  estimation 
of  its  absolute  quantity  presents  difficulties  which  were  not  overcome  by  the  older  physi- 
ologists. With  the  present  improved  methods  of  analysis,  however,  there  are  many  very 
accurate  means  of  estimating  watery  vapor.  One  method  is  by  the  use  of  Liebig's  bulbs 
filled  with  sulphuric  acid,  or  tubes  filled  with  chloride  of  calcium,  both  of  which  sub- 
stances have  a  great  avidity  for  water.  From  a  large  number  of  observations  on  his  own 
person  and  eight  others,  collecting  the  water  by  sulphuric  acid,  Valentin  made  the  fol- 
lowing estimate  of  the  weight  of  water  exhaled  from  the  lungs  in  twenty-four  hours : 

In  his  own  person,  the  exhalation  in  twenty-four  hours  was  6,055  grains. 

In  a  young  man  of  small  size,  the  quantity  was  5,042  grains. 

In  a  student  rather  above  the  ordinary  height,  the  quantity  was  11,930  grains. 

The  mean  of  his  observations  gave  a  daily  exhalation  of  8,333  grains,  or  about  1£ 
Ib.  av. 


154  RESPIRATION. 

The  extent  of  respiratory  surface  has  a  very  marked  influence  on  the  quantity  of 
watery  vapor  exhaled.  This  fact  is  very  well  shown  by  a  comparison  of  the  exhalation 
in  the  adult  and  in  old  age,  when  the  extent  of  respiratory  surface  is  much  diminished- 
Barral  found  the  exhalation  in  an  old  man  less  than  half  that  of  the  adult.  It  is  evident 
that  the  absolute  quantity  of  vapor  exhaled  is  increased  when  respiration  is  accelerated. 
The  quantity  of  water  in  the  blood  also  exerts  an  important  influence.  Valentin  found 
that  the  pulmonary  transpiration  was  more  than  doubled  in  a  man  immediately  after 
drinking  a  large  quantity  of  water. 

The  vapor  in  the  expired  air  is  derived  from  the  entire  surface  which  is  traversed  in 
respiration,  and  not  exclusively  from  the  air-cells.  The  air  which  passes  into  the  lungs 
derives  a  certain  amount  of  moisture  from  the  mouth,  nares,  and  trachea.  The  great  vas- 
cularity  of  the  mucous  membranes  in  these  situations  as  well  as  of  the  air-cells,  and  the 
great  number  of  mucous  glands  which  they  contain,  serve  to  keep  the  respiratory  sur- 
faces constantly  moist.  This  is  important,  for  only  moist  membranes  allow  the  free 
passage  of  gases,  which  is  of  course  essential  to  the  process  of  respiration. 

Exhalation  of  Ammonia,  Organic  Matter,  etc. — Ammonia  has  long  been  recognized 
as  an  exhalation  from  the  human  body  in  health,  from  the  skin  as  well  as  the  lungs.  Dr. 
Richardson  calls  attention,  in  his  essay  on  the  "  Coagulation  of  the  Blood,"  to  the  obser- 
vations of  Mr.  Reade,  Dr.  Reuling,  Viale  and  Latini,  and  others,  on  this  point.  Reuling 
has  shown  that  the  quantity  of  ammonia  in  the  expired  air  is  increased  in  certain  diseases, 
particularly  in  uraemia.  Its  characters  in  the  expired  air  are  frequently  so  marked,  that 
patients  who  are  entirely  unacquainted  with  the  pathology  of  uremia  sometimes  recog- 
nize an  ammoniacal  odor  in  their  own  breath. 

The  pulmonary  surface  exhales  a  small  quantity  of  organic  matter.  This  has  never 
been  collected  in  sufficient  quantity  to  enable  us  to  recognize  in  it  any  peculiar  or  dis- 
tinctive properties,  but  its  presence  may  be  demonstrated  by  the  fact  that  a  sponge  com- 
pletely saturated  with  the  exhalations  from  the  lungs,  or  the  vapor  from  the  lungs 
condensed  in  a  glass  vessel,  will  undergo  putrefaction,  which  is  a  property  distinctive 
of  organic  substances. 

It  is  well  known  that  certain  substances  which  are  only  occasionally  found  in  the 
blood  may  be  eliminated  by  the  lungs.  Certain  odorous  principles  in  the  breath  are 
pretty  constant  in  those  who  take  liquors  habitually  in  considerable  quantity.  The  odor 
of  garlics,  onions,  turpentine,  and  many  other  principles  which  are  taken  into  the  stom- 
ach, may  be  recognized  in  the  expired  air. 

The  action  of  the  lungs  in  the  elimination  of  certain  gases,  which  are  poisonous  in 
very  small  quantities  when  they  are  absorbed  in  the  lungs  and  carried  to  the  general 
system  in  the  arterial  blood,  is  very  well  shown  by  the  experiments  of  Bernard.  Sulphu- 
retted hydrogen,  which  produces  death  in  a  bird  when  it  exists  in  the  atmosphere  in  the 
proportion  of  one  to  eight  hundred,  may  be  taken  in  solution  into  the  stomach  with 
impunity  and  even  be  injected  into  the  venous  system;  in  both  instances  being  elimi- 
nated by  the  lungs  with  great  promptness  and  rapidity.  The  lungs,  wrhile  they  present 
an  immense  and  rapidly  absorbing  surface  for  volatile  poisonous  substances,  are  capable 
of  relieving  the  system  of  some  of  these  substances  by  exhalation  when  they  find  their 
way  into  the  veins. 

Exhalation  of  Nitrogen. — The  most  accurate  direct  experiments,  particularly  those  of 
Regnault  and  Reiset,  show  that  the  exhalation  of  a  small  quantity  of  nitrogen  is  a  pretty 
constant  respiratory  phenomenon.  From  a  large  number  of  experiments  on  dogs,  rabbits, 
fowls,  and  birds,  these  observers  came  to  the  conclusion  that,  when  animals  are  subjected 
to  their  habitual  regimen,  they  exhale  a  quantity  of  nitrogen  equal  in  weight  to  from  yfg- 
to  -^5-  of  the  weight  of  oxygen  consumed.  In  birds,  during  inanition,  they  sometimes 
observed  an  absorption  of  nitrogen,  but  this  was  rarely  seen  in  mammals.  Boussingault, 


CHANGES   IN   THE  BLOOD  IN  RESPIRATION.  155 

estimating  the  nitrogen  taken  into  the  body  and  comparing  it  with  the  entire  quantity 
discharged,  arrived  at  the  same  results  in  experiments  upon  a  cow.  Barral,  by  the  same 
method,  confirmed  these  observations  by  experiments  on  the  human  subject.  Notwith- 
standing the  conflicting  testimony  of  the  older  physiologists,  there  can  now  be  no  doubt 
that,  under  ordinary  physiological  conditions,  there  is  an  exhalation  by  the  lungs  of  a 
small  quantity  of  nitrogen. 

Changes  of  the  Blood  in  Respiration  (Hcematosis). 

It  is  to  be  expected  that  the  blood,  receiving,  on  the  one  hand,  all  the  products  of 
digestion,  and,  on  the  other,  the  products  of  disassimilation  or  decay  of  the  tissues,  con- 
nected with  the  lymphatic  system,  and  exposed  to  the  action  of  the  air  in  the  lungs, 
should  present  important  differences  in  composition  in  different  parts  of  the  vascular 
system. 

In  the  first  place,  there  is  a  marked  difference  in  color,  composition,  and  properties, 
between  the  blood  in  the  arteries  and  in  the  veins ;  the  change  from  venous  to  arterial 
blood  being  effected  almost  instantaneously  in  its  passage  through  the  lungs.  The  blood 
which  goes  to  the  lungs  is  a  mixture  of  the  fluid  collected  from  all  parts  of  the  body ;  and 
we  have  seen  that  it  presents  great  differences  in  its  composition  in  different  parts  of  the 
venous  system.  In  some  veins  it  is  almost  black,  and  in  some,  nearly  as  red  as  in  the 
arteries.  In  the  hepatic  vein  it  contains  sugar,  and  its  nitrogenized  constituents  and  cor- 
puscles are  diminished ;  in  the  portal  vein,  during  digestion,  it  contains  materials  absorbed 
from  the  alimentary  canal ;  and,  finally,  there  is  every  reason  to  suppose  that  parts  which 
require  different  materials  for  their  nutrition  and  produce  different  excrementitious  prin- 
ciples exert  different  influences  on  the  constitution  of  the  blood  which  passes  through 
them.  After  this  mixture  of  different  kinds  of  blood  has  been  collected  in  the  right  side 
of  the  heart  and  passed  through  the  lungs,  it  is  returned  to  the  left  side  and  sent  to  the 
system,  thoroughly  changed  and  renovated,  and,  as  arterial  blood,  it  has  a  nearly  uniform 
composition,  as  far  as  can  be  ascertained,  in  all  parts  of  the  system.  The  change,  there- 
fore, which  the  blood  undergoes  in  its  passage  through  the  lungs,  is  the  transformation 
of  the  mixture  of  venous  blood  from  all  parts  of  the  organism  into  a  fluid  of  uniform 
character,  which  is  capable  of  nourishing  and  sustaining  the  function  of  every  tissue  and 
organ  of  the  body. 

The  capital  phenomena  of  respiration,  as  regards  the  air  in  the  lungs,  are  loss  of  oxygen 
and  gain  of  carbonic  acid,  the  other  phenomena  being  accessory  and  comparatively  un- 
important. As  the  blood  is  capable  of  holding  gases  in  solution,  in  studying  the  essential 
changes  which  this  fluid  undergoes  in  respiration,  we  look  for  them  in  connection  with 
the  proportions  of  oxygen  and  carbonic  acid  before  and  after  it  has  passed  through  the 
lungs.  In  respiration,  the  most  marked  effect  on  the  venous  blood  is  change  in  color. 

Difference  in  Color  between  Arterial  and  Venous  Blood. — "We  have  already  considered 
this  in  treating  of  the  properties  of  the  blood,  and  shall  take  up  in  this  connection  only 
the  cause  of  the  remarkable  change  in  the  color  of  the  blood  in  the  lungs.  This  change 
is  instantaneous,  and,  long  before  the  discovery  of  oxygen  by  Priestley,  was  recognized 
by  Lower,  Goodwyn,  and  others,  as  due  to  the  action  of  the  air. 

The  influence  of  air  in  changing  the  color  of  venous  blood  may  be  noted  in  blood 
which  has  been  drawn  from  the  body,  as  is  exemplified  by  the  red  color  of  that  portion 
of  a  clot,  or  the  surface  of  defibrinated  venous  blood,  which  is  exposed  to  the  air.  If  we 
cut  into  a  clot  of  venous  blood,  the  interior  is  almost  black,  but  it  becomes  red  on  ex- 
posure to  the  air  for  a  very  few  seconds. 

We  have  been  in  the  habit  of  illustrating  the  physiological  influence  of  the  air  on 
venous  blood  by  the  following  simple  experiment :  Removing  the  lungs  of  an  animal  (a 
dog)  just  killed,  the  nozzle  of  a  syringe  is  secured  in  the  pulmonary  artery  by  a  ligature, 
and  a  canula,  connected  with  a  rubber  tube  which  empties  into  a  glass  vessel,  is  secured 


156  RESPIRATION. 

in  the  pulmonary  vein.  Adapting  a  bellows  to  the  trachea,  we  imitate  the  process  of 
respiration ;  and,  if  defibrinated  venous  blood  be  carefully  injected  through  the  lungs,  it 
will  be  returned  by  the  pulmonary  vein,  presenting  the  bright-red  color  of  arterial  blood. 
When  the  artificial  respiration  is  interrupted,  the  blood  passes  through  the  lungs  without 
change.1  In  exposing  the  thoracic  organs  and  keeping  up  artificial  respiration,  repeating 
the  celebrated  experiment  of  Robert  Hook,  made  before  the  Royal  Society,  in  1664,  we 
can  see,  through  the  thin  walls  of  the  auricles,  the  red  color  of  the  blood  on  the  left  side 
contrasting  with  the  dark  venous  blood  on  the  right. 

Since  the  discovery  of  oxygen,  it  has  been  ascertained  that  this  is  the  only  constituent 
of  the  air  which  is  capable  of  arterializing  the  blood.  Priestley  showed  that  venous  blood 
is  not  changed  in  color  by  nitrogen,  hydrogen,  or  carbonic  acid ;  while  all  these  gases, 
by  displacing  oxygen,  will  change  the  arterial  blood  from  red  to  black.2 

The  elements  of  the  blood  which  absorb  the  greater  part  of  the  oxygen  are  the  red 
corpuscles.  While  the  plasma  will  absorb,  perhaps,  twice  as  much  gas  as  pure  water,  it 
has  been  shown  by  Magnus  and  by  Gay-Lussac  that  the  corpuscles  will  absorb  from  ten  to 
thirteen  times  as  much.  By  some  the  proportion  is  put  much  higher.  According  to  the 
late  researches  of  Fernet,  which  have  been  confirmed  by  Lothar  Meyer,  the  volume  of 
oxygen  fixed  by  the  corpuscles  is  about  twenty-five  times  that  which  is  dissolved  in  the 
plasma. 

Comparison  of  the  Gases  in  Venous  and  Arterial  Blood. — The  demonstration  of  the 
fact  that  free  oxygen  and  carbonic  acid  exist  in  the  blood,  with  a  knowledge  of  the  rela- 
tive proportion  of  these  gases  in  the  blood  before  and  after  its  passage  through  the  lungs, 
is  a  point  hardly  second  in  importance  to  the  relative  composition  of  the  air  before  and 
after  respiration.  The  idea  enunciated  by  Mayow,  about  two  hundred  years  ago,  that 
"  there  is  something  in  the  air,  absolutely  necessary  to  life,  which  is  conveyed  into  the 
blood,"  except  that  the  vivifying  principle  is  not  named  or  its  other  properties  described, 
expresses  what  we  now  consider  one  of  the  great  objects  of  respiration.  This  is 
even  more  strictly  in  accordance  with  facts  than  the  idea  of  Lavoisier,  who  supposed 
that  all  the  chemical  processes  of  respiration  took  place  in  the  lungs.  Mayow  also  de- 
scribed the  evolution  of  gas  from  blood  placed  in  a  vacuum.  Many  observers  have  since 
succeeded  in  extracting  gases  from  the  blood  by  various  processes.  Sir  Humphry  Davy 
induced  the  evolution  of  carbonic  acid  by  raising  arterial  blood  to  the  temperature  of  200° 
Fahr.,  and  venous  blood  to  a  temperature  of  112°;  Stevens  and  others  disengaged  gas 
by  displacement  with  hydrogen,  nitrogen,  or  the  ordinary  atmosphere;  but,  notwith- 
standing this,  before  the  experiments  of  Magnus,  in  1837,  many  denied  the  existence  in 
the  blood  of  any  free  gas  whatsoever. 

Analysis  of  the  Blood  for  Oases. — There  were  certain  grave  sources  of  error  in  the 
method  employed  by  Magnus,  which  render  his  observations  of  little  value,  except  as 
demonstrating  that  oxygen,  carbonic  acid,  and  nitrogen  may  be  extracted  by  the  air- 
pump  from  both  arterial  and  venous  blood.  The  only  source  of  error  in  the  results 
which  he  fully  recognized  lay  in  the  difficulty  in  extracting  the  entire  quantity  of  gas  in 
solution ;  but  a  careful  study  of  his  essay  shows  another  element  of  inaccuracy  which  is 
even  more  important.  The  relative  quantities  of  oxygen  and  carbonic  acid  in  any  single 

1  This  demonstration  is  very  striking,  especially  if  we  use  a  syringe  with  a  double  nozzle,  one  point  secured  in  the 
pulmonary  artery,  and  the  other  simply  carrying  the  blood  by  a  rubber  tube  into  a  glass  vessel.    Keceiving  the  blood 
which  passes  through  the  lungs  and  that  which  simply  passes  through  the  tube,  into  two  tall  glass  vessels,  the  one 
is  of  a  bright  red,  and  the  other  retains  its  dark  color.    In  preparing  for  the  experiment  it  is  necessary,  immediately 
after  removing  the  lungs  from  the  animal,  to  inject  them  with  a  little  defibrinated  blood,  so  as  to  remove  the  coagu- 
lating blood  from  the  pulmonary  capillaries,  which  would  otherwise  become  obstructed.    The  injection  should  be 
made  gently  and  gradually,  to  avoid  extravasation.    Defibrinated  ox-blood  may  be  used.    The  most  convenient  way 
to  secure  the  canulse  in  the  vessels  is  to  push  them  into  the  pulmonary  artery  through  the  right  ventricle,  and  into 
the  pulmonary  vein  through  the  left  auricle. 

2  Carbonic  oxide  and  nitrous  oxide  have  a  strong  affinity  for  the  blood-corpuscles  and  become  fixed  in  them,  the 
former  giving  the  blood  a  vivid  red  color.    Sugar  and  many  salts  will  also  redden  venous  blood.    These  agents,  how- 
ever, do  not  impart  the  physiological  properties  of  arterial  blood. 


ANALYSIS  OF  THE  BLOOD  FOR   GASES.  157 

specimen  of  blood  present  great  variations,  dependent  upon  the  length  of  time  that  the 
blood  has  been  allowed  to  stand  before  the  estimate  of  the  gases  is  made.  As  it  is  im- 
possible to  make  this  estimate  immediately  after  the  blood  is  drawn,  on  account  of  the 
froth  produced  by  agitation  with  a  gas  when  the  method  by  displacement  is  employed, 
and  the  bubbling  of  the  gas  when  extracted  by  the  air-pump,  this  objection  is  fatal.  It 
is  necessary  to  wait  until  the  froth  has  subsided  before  attempting  to  make  an  accurate 
estimate  of  the  volume  of  gas  given  off.  The  following  observation  of  Magnus  illus- 
trates this  fact.  The  observation  was  on  the  human  blood,  six  hours  after  it  had  been 
thoroughly  mixed  with  hydrogen  : 

Blood  of  Man.  Carbonic  Add. 

4-077  cubic  inches.  -013  cubic  inches. 

3-650  "  0-781  " 

3-838  «  1-355 

After  twenty-four  hours,  at  the  end  of  which  time  the  blood  had  no  odor  : 

4*077  cubic  inches.  1*517  cubic  inches. 

3-650  "  1-456          " 

3-833  "  2-075  " 

The  excess  of  carbonic  acid  found  twenty-four  hours  after  over  the  quantity  found 
six  hours  after,  in  the  first  and  third  specimens,  is  a  little  more  than  fifty  per  cent.,  while 
in  the  second  specimen  it  is  very  nearly  one  hundred  per  cent.  In  these  analyses,  the  pro- 
portion of  oxygen  is  not  given.  The  question  naturally  arises  as  to  the  source  of  the  car- 
bonic acid  which  was  evolved  during  the  last  eighteen  hours  of  the  observation.  This  is 
evident,  when  we  consider  one  of  the  important  properties  of  the  blood.  A  number  of 
years  ago,  Spallanzani  demonstrated  that,  in  common  with  other  parts  of  the  body,  fresh 
blood  removed  from  the  body  has,  of  itself,  the  property  of  consuming  oxygen ;  and 
W.  F.  Edwards  has  shown  that  the  blood  will  exhale  carbonic  acid.  In  1856,  Harley, 
by  a  series  of  ingenious  experiments,  found  that  blood,  kept  in  contact  with  air  in  a 
closed  vessel  for  twenty -four  hours,  consumed  oxygen  and  gave  off  carbonic  acid.  More 
recently,  Bernard  has  shown  that,  for  a  certain  time  after  the  blood  is  drawn  from  the 
vessels,  it  will  continue  to  consume  oxygen  and  exhale  carbonic  acid.  If  all  the  carbonic 
acid  be  removed  from  a  specimen  of  blood  by  treating  it  with  hydrogen,  and  if  it  be 
allowed  to  stand  for  twenty-four  hours,  another  portion  of  gas  can  be  removed  by  again 
treating  it  with  hydrogen,  and  still  another  quantity  by  treating  it  with  hydrogen  a  third 
time.  From  these  facts  it  is  clear  that,  in  the  experiment  of  Magnus,  the  excess  of  car- 
bonic acid  involved  a  post-mortem  consumption  of  oxygen ;  and  no  analyses  made  in  the 
ordinary  way,  by  displacement  with  hydrogen  or  by  the  air-pump,  in  which  the  blood 
must  necessarily  be  allowed  to  remain  in  contact  with  oxygen  for  a  number  of  hours,  can 
be  accurate.  The  only  process  which  can  give  us  a  rigorous  estimate  of  the  relative  quan- 
tities of  oxygen  and  carbonic  acid  in  the  blood  is  one  in  which  the  gases  can  be  esti- 
mated without  allowing  the  blood  to  stand,  or  in  which  the  formation  of  carbonic  acid 
in  the  specimen,  at  the  expense  of  the  oxygen,  is  prevented.  All  others  will  give  a  less 
quantity  of  oxygen  and  a  greater  quantity  of  carbonic  acid  than  exists  in  the  blood  cir- 
culating in  the  vessels  or  immediately  after  it  is  drawn  from  the  body. 

A  solution  of  this  important  and  difficult  problem  in  the  analysis  of  the  blood  has  been 
attained  by  Bernard.  This  observer  made  a  great  number  of  experiments  in  the  hope  of 
discovering  some  means  by  which  the  post-mortem  consumption  of  oxygen  by  the  blood- 
corpuscles  could  be  arrested.  He  found,  finally,  that  carbonic  oxide,  one  of  the  most  active 
of  the  poisonous  gases,  had  a  remarkable  affinity  for  the  blood-corpuscles.  When  taken 
into  the  lungs,  it  is  absorbed  by  and  becomes  fixed  in  the  corpuscles,  effectually  prevent- 
ing the  consumption  of  oxygen  and  the  production  of  carbonic  acid,  which  normally 


158  KESPIRATION. 

takes  place  in  the  capillary  system  and  which  is  one  of  the  indispensable  conditions  of 
nutrition.  The  mechanism  of  poisoning  by  the  inhalation  of  this  gas  is  by  its  fixation  in 
the  blood-corpuscles,  their  consequent  paralysis,  and  the  arrest  of  their  function  as  re- 
spiratory organs.  As  it  is  the  continuance  of  this  transformation  of  oxygen  into  carbonic 
acid,  after  the  blood  is  drawn  from  the  vessels,  which  interferes  with  the  ordinary  analy- 
sis of  the  blood  for  gases,  we  might  expect  to  extract  all  the  oxygen  if  we  could  imme- 
diately saturate  the  blood  with  carbonic  oxide.  The  preliminary  experiments  of  Ber- 
nard on  this  point  are  conclusive.  He  ascertained  that,  by  mixing  carbonic  oxide  in  suf- 
ficient quantity  with  a  specimen  of  fresh  arterial  blood,  in  about  two  hours,  all  the  oxy- 
gen which  it  contained  was  displaced.  Introducing  a  second  quantity  of  carbonic  oxide 
after  two  hours,  and  leaving  it  in  contact  with  the  blood  for  an  hour,  a  quantity  of  oxy- 
gen was  removed  so  small  that  it  might  almost  be  disregarded.  A  third  experiment  on 
the  same  blood  failed  to  disengage  any  oxygen  or  carbonic  acid. 

The  view  entertained  by  Bernard  of  the  action  of  carbonic  oxide  in  displacing  the 
oxygen  of  the  blood  is,  that  the  former  gas  has  a  remarkable  affinity  for  the  blood-corpus- 
cles, in  which  nearly  all  the  oxygen  is  contained,  and  when  brought  in  contact  with 
them  unites  with  the  organic  matter,  setting  free  the  oxygen,  in  the  same  way  that  the 
acid  entering  into  the  composition  of  a  salt  is  set  free  by  any  other  acid  which  has  a 
stronger  affinity  for  the  base.  There  is  every  reason  to  suppose  that  this  view  is  correct, 
as  carbonic  oxide  is  much  less  soluble  than  oxygen  and  as  it  has  the  property  of  dis- 
engaging this  gas  only  from  the  blood,  leaving  the  other  gases  still  in  solution. 

As  carbonic  oxide  displaces  the  oxygen  alone,  it  is  necessary  to  resort  to  some  other 
process,  in  addition  to  this,  to  disengage  the  other  gases  contained  in  the  blood.  It  is 
only  necessary  to  arrest  the  action  of  the  corpuscles  upon  the  oxygen,  and  then  the 
gases  may  be  set  free  by  the  air-pump  or  any  method  which  may  be  convenient.  The 
method  adopted  by  Lothar  Meyer,  Bernard,  Ludwig,  and  Grehant  for  the  disengagement 
of  all  the  gases  contained  in  the  blood  is  first  to  displace  the  oxygen  by  carbonic  oxide, 
using  about  two-thirds  of  gas  by  volume  to  one-third  of  blood,  then  to  attach  the  tube 
to  a  column  of  mercury  and  subject  the  blood  to  the  barometric  vacuum,  which  sets  free 
the  carbonic  acid  and  the  nitrogen.  The  results  obtained  by  this  method  correspond 
with  our  ideas  concerning  the  nature  of  the  respiratory  process ;  and  analyses  of  the 
blood  taken  at  different  periods  show  variations  in  the  quantities  of  oxygen  in  the  ar- 
terial, and  carbonic  acid  in  the  venous  blood,  corresponding  with  some  of  the  variations 
which  we  have  noted  in  the  loss  of  oxygen  and  gain  of  carbonic  acid  in  the  air  in  res- 
piration. 

In  drawing  the  blood  for  analysis,  Bernard  takes  the  fluid  directly  from  the  vessels  by 
a  syringe  and  passes  it  under  mercury  into  a  tube,  in  such  a  way  that  it  does  not  come  in 
contact  with  the  air.  In  this  tube,  which  is  graduated,  the  blood  is  brought  in  contact 
with  carbonic  oxide,  which  displaces  the  oxygen  from  the  corpuscles  and  prevents  the 
formation  of  carbonic  acid  at  the  expense  of  a  portion  of  the  oxygen.  The  tube  is  then 
connected  with  an  apparatus  by  which  the  atmospheric  pressure  is  removed.  In  this  way, 
nearly  all  the  gases  contained  in  the  blood  are  disengaged ;  but,  according  to  most  ob- 
servers, a  small  quantity  of  carbonic  acid  remains  in  the  blood  in  combination.  This  may 
be  removed  by  the  introduction  into  the  apparatus  of  a  small  quantity  of  tartaric  acid. 
It  is  justly  remarked  by  Bert,  in  his  admirable  work  on  respiration,  that,  as  the  appa- 
ratus for  the  exhaustion  of  air  has  been  made  more  and  more  nearly  perfect,  the  quantity 
of  carbonic  acid  in  combination  has  seemed  less  and  less.  By  far  the  greatest  quantity  of 
the  excrementitious  carbonic  acid  in  the  blood  is  extracted  by  the  removal  of  atmospheric 
pressure  in  the  most  carefully-perfected  apparatus. 

The  analyses  of  Bernard,  who  obtained  from  fifteen  to  twenty  per  cent,  of  oxygen  in 
volume  from  the  arterial  blood,  show  the  great  imperfection  of  the  process  employed  by 
Magnus,  who  obtained  from  the  arterial  blood  of  horses  and  calves  a  mean  of  but  2-44 
per  cent,  of  oxygen.  It  does  not  seem  necessary,  therefore,  to  discuss  the  criticisms  of 


ANALYSIS   OF  THE  BLOOD  FOR  GASES.  159 

the  results  obtained  by  Magnus  which  were  made  by  Gay-Lussac  and  Magendie,  soon 
after  their  publication,  and  more  recently  by  Harley  and  others.1 

Bernard's  experiments  were  made  chiefly  on  dogs  and  had  special  reference  to  the 
proportion  of  oxygen  in  the  blood.  In  two  specimens  taken  from  a  dog  in  good  con- 
dition, a  specimen  of  arterial  blood,  drawn  from  the  vessels  by  a  syringe  and  put  in  con- 
tact with  carbonic  oxide  without  being  exposed  to  the  air,  was  found  to  contain  18*28 
per  cent.,  and  a  specimen  of  venous  blood,  taken  in  the  same  way,  8-42  per  cent.,  in  vol- 
ume, of  oxygen.  The  proportion  of  gases  in  the  blood  is  found  to  vary  very  considerably 
under  different  conditions  of  the  system,  particularly  with  reference  to  the  digestive 
process.  The  following  are  the  general  results  of  later  observations,  showing  the  differ- 
ences and  variations  in  the  proportions  of  all  the  gases  in  arterial  and  venous  blood. 

Arterial  blood,  while  an  animal  is  fasting,  contains  from  nine  to  eleven  parts  per 
hundred  of  oxygen.  In  full  digestion,  the  proportion  is  raised  to  seventeen,  eighteen,  or 
even  twenty  parts  per  hundred.  The  proportion  varies  in  different  animals,  being  much 
greater,  for  example,  in  birds  than  in  mammals. 

The  quantity  of  carbonic  acid  is  even  more  variable  than  the  quantity  of  oxygen. 
During  digestion  there  are  from  five  to  six  parts  per  hundred  of  free  carbonic  acid  in  the 
arterial  blood.  During  the  intervals  of  digestion  this  quantity  is  reduced  to  almost  noth- 
ing; and,  after  fasting  for  twenty-four  hours,  frequently  not  a  trace  is  to  be  discovered.* 

Venous  blood  always  contains  a  large  quantity  of  carbonic  acid,  both  free  in  solution 
and  combined  with  bases.  This  quantity  varies  in  different  parts  of  the  venous  system 
and  bears  a  relation  to  the  color  of  the  blood.  It  is  well  known  that  the  venous  blood 
coming  from  some  glands  is  dark  during  the  intervals  of  secretion  and  nearly  as  red  as 
arterial  blood  during  their  functional  activity.  In  the  venous  blood  from  the  submax- 
illary  gland  of  a  dog,  Bernard  found  18'07  per  cent,  of  carbonic  acid  during  repose  and 
10-14  per  cent,  during  secretion.  The  blood  coming  from  the  muscles  is  the  darkest  in 
the  body  and  contains  the  greatest  quantity  of  free  carbonic  acid.  The  quantity  of  free 
carbonic  acid  is  immensely  increased  in  the  venous  blood  during  digestion.  It  is  owing 
to  this  fact  that  the  gas  then  exists  in  quantity  in  the  arterial  blood.  Bearing  in  mind 
the  fact  that  the  proportion  of  gases  in  the  arterial  and  venous  blood  varies  considerably 
under  different  conditions  of  the  system  and  that  it  is  especially  variable  in  the  blood 
of  different  veins,  we  may  take  the  following,  which  we  quote  from  Bert,  as  the  average 
results  obtained  by  the  most  recent  German  observers : 

0.  C03  C02  C03  N.  Total  gas 

disengaged  in  combi-  total.  in  volume 

by  a  vacuum.  nation.  per  100. 

"  Arterial  blood  ..   15'03  27'99  1-15  2914  1-60  45'77 

Venous  blood. . .     8'17  31-27  2'38  33'65  1'37  43*19 

"If  we  now  examine  the  blood  coming  from  different  parts  of  the  body,  we  find  that 
the  blood  of  the  hepatic  veins  is  poorer  in  oxygen  and  richer  in  carbonic  acid  than  the 
general  venous  blood ;  that  the  blood  of  the  portal  vein  presents  the  same  characters  to 
a  higher  degree;  that  the  blood  of  the  muscles  in  contraction  presents  the  same  relations 
as  compared  with  the  blood  of  muscles  in  repose  or  paralyzed ;  that,  on  the  other  hand, 
the  blood  of  the  glands  has  more  oxygen  during  their  activity  than  during  their  repose. 

1  To  Magnus  belongs  the  credit  of  demonstrating  the  important  fact  that  oxygen,  carbonic  acid,  and  nitrogen  can 
be  extracted  from  the  blood  by  removing  the  atmospheric  pressure.    Before  his  observations,  Gmelin,  Mitscherlich, 
and  Tiedemann  placed  venous  blood  in  a  tube  over  mercury  in  the  receiver  of  an  air-pump,  and,  by  removing  the  press- 
ure as  far  as  possible,  caused  the  mercury  to  descend.    On  admitting  air  into  the  receiver  and  restoring  the  press- 
ure, the  mercury  ascended,  with  the  blood,  again  filling  the  tube  completely.    From  this  they  reasoned  that  there 
was  no  free  carbonic  acid  in  the  blood.    By  passing  up  a  little  acetic  acid,  carbonic  acid  was  set  free,  which  led  them 
to  believe  that  all  the  carbonic  acid  was  in  combination.    Magnus  showed  that  the  reason  why  other  observers  had 
failed  to  extract  gas  by  means  of  the  air-pump  was  that  the  rarefaction  of  the  air  was  not  carried  sufficiently  far. 

2  These  results  are  quoted  from  Bernard  and  were  given  in  his  lectures  delivered  at  the  College  of  France  in  the 
summer  of  1861.    More  recent  observations  by  German  physiologists  have  shown  that  Bernard's  estimates  of  the 
proportions  of  carbonic  acid  were  much  too  low. 


160  RESPIRATION. 

"  If  we  compare  the  venous  blood  of  the  right  side  of  the  heart  with  the  arterial 
blood  of  the  left  side,  we  find  that  the  latter  is  richer  in  oxygen  and  poorer  in  carbonic 
acid.  In  examining  this  more  closely,  we  see  that  the  difference  in  the  oxygen  is  greater 
than  in  the  carbonic  acid ;  this  being  in  accordance  with  the  well-known  fact  that  ani- 
mals absorb  more  oxygen  than  is  equivalent  to  the  carbonic  acid  exhaled." 

These  facts  coincide  with  the  views  which  are  now  held  regarding  the  essential  pro- 
cesses of  respiration.  The  blood  going  to  the  lungs  contains  carbonic  acid  and  but  a 
small  proportion  of  oxygen.  In  the  lungs,  carbonic  acid  is  given  off,  appearing  in  the 
expired  air,  and  the  oxygen  which  disappears  from  the  air  is  carried  away  by  the  ar- 
terial blood. 

Nitrogen  of  the  Blood. — As  far  as  is  known,  nitrogen  has  no  very  important  office  in 
the  process  of  respiration.  There  is  sometimes  a  slight  exhalation  of  this  gas  by  the 
lungs,  and  analyses  have  demonstrated  its  existence  in  solution  in  the  blood.  Magnus 
found  generally  a  larger  proportion  in  the  arterial  than  in  venous  blood,  although,  in  one 
instance,  there  was  a  larger  proportion  in  the  venous  blood.  It  is  not  absolutely  certain 
whether  the  nitrogen  which  exists  in  the  blood  be  derived  from  the  air  or  from  the 
tissues.  Its  almost  constant  exhalation  in  the  expired  air  would  lead  to  the  supposition 
that  it  is  produced  in  small  quantity  in  the  system  or  supplied  by  the  food.  There  is  no 
evidence  that  nitrogen  enters  into  combination  with  the  blood-corpuscles ;  it  exists  sim- 
ply in  solution  in  the  blood,  which  is  capable  of  absorbing  about  ten  times  as  much  as 
pure  water.  Nothing  is  known  with  regard  to  the  relations  of  the  free  nitrogen  of  the 
blood  to  the  processes  of  nutrition. 

Condition  of  the  Gases  in  the  Blood. — It  is  now  pretty  generally  admitted  that  the 
oxygen  of  the  blood  exists,  not  in  simple  solution,  but  in  a  condition  of  feeble  combina- 
tion with  certain  of  the  constituents  of  the  blood-corpuscles,  particularly  the  coloring 
matter.  In  studying  the  composition  of  the  corpuscles,  we  have  seen  that,  when  air  is 
admitted  to  venous  blood,  oxygen  unites  with  the  hseinaglobine,  forming  oxyhsema- 
globine.  Carbonic  oxide,  which  has  a  great  affinity  for  the  corpuscles,  displaces  almost 
immediately  all  the  oxygen  which  the  blood  contains.  When  the  corpuscles  are  de- 
stroyed, as  they  may  be  readily  by  receiving  fresh  blood  into  a  quantity  of  pure  water, 
the  red  color  is  instantly  changed  to  black. 

Carbonic  acid  is  more  easily  exhaled  from  the  blood  than  oxygen.  It  was  this 
principle  which  was  obtained  by  those  who  first  succeeded  in  extracting  gas  from  the 
blood.  While  there  is  every  reason  to  suppose  that  oxygen  is  in  combination  with  the 
blood-corpuscles,  carbonic  acid  seems  to  be  in  a  condition  of  simple  solution  and  is  con- 
tained more  especially  in  the  plasma.  What  may  be  considered  as  the  free  carbonic  acid 
of  the  blood  behaves  in  all  regards  like  a  gas  simply  held  in  solution.  The  view  that  it  is 
held  in  solution  chiefly  in  the  plasma  is  sustained  by  the  fact  that  serum  will  absorb 
more  carbonic  acid  than  an  equal  volume  of  defibrinated  blood. 

Liebig  has  shown  that  the  phosphate  of  soda,  one  of  the  constituents  of  the  blood, 
influences  to  a  remarkable  degree  the  quantity  of  carbonic  acid  which  can  be  held  in 
solution  by  any  liquid.  One  hundredth  of  a  part  of  this  salt  in  pure  water  will  double 
its  capacity  for  dissolving  carbonic  acid.  When  blood  is  in  contact  with  a  certain 
quantity  of  air,  oxygen  is  consumed  and  carbonic  acid  is  exhaled.  The  fact  that  car- 
bonic oxide,  which  has  such  a  remarkable  affinity  for  the  corpuscles,  displaces  oxygen 
almost  exclusively,  is  another  argument  in  favor  of  the  view  that  the  carbonic  acid  is 
contained  mainly  in  the  plasma. 

The  carbonic  acid  which  is  formed  in  the  tissues  and  is  taken  up  by  the  blood  in  its 
passage  through  the  capillaries  exists  in  this  fluid  in  two  forms :  ,one,  in  simple  solution, 
chiefly  in  the  plasma,  and  the  other,  in  a  state  of  such  loose  chemical  combination  in 
the  bicarbonates  that  it  may  be  disengaged  by  displacement  by  another  gas  and  is 


CONDITION  OF  THE   GASES  IN  THE  BLOOD.  161 

readily  set  free  by  pneumic  acid.  This  gas  is  a  product  of  excretion  and  is  not  engaged 
in  any  of  the  vital  functions ;  while  oxygen,  which  has  an  all-important  function  to  per- 
form, unites  immediately  with  the  blood-corpuscles  and  is  not  easily  disengaged  except 
when  it  undergoes  transformation  in  the  process  of  nutrition.  In  addition  to  this 
excrementitious  carbonic  acid,  there  is  another  portion  which  is  a  permanent  constituent 
of  the  blood,  in  the  carbonates,  and  cannot  be  set  free  without  the  use  of  reagents. 

Nitrogen  exists  in  the  blood  in  the  same  condition  of  solution  in  the  plasma  as 
carbonic  acid. 

Mechanism  of  the  Interchange  of  Gases  between  the  Blood  and  the  Air  in  the  Lungs. — 
The  gases  from  the  air  pass  into  the  blood,  and  the  gases  of  the  blood  are  exhaled 
through  the  delicate  membrane  which  separates  these  two  fluids,  in  accordance  with 
laws  which  are  now  well  understood.  The  first  to  point  out  the  power  of  gases  thus 
to  penetrate  and  pass  through  membranes  was  the  late  Dr.  J.  K.  Mitchell,  of  Philadel- 
phia. His  attention  was  first  directed  to  this  subject  by  noticing  the  escape  of  gas  from 
gum-elastic  balloons  filled  with  hydrogen.  Observations  on  the  lungs  of  the  snapping 
turtle  filled  with  air  and  placed  in  an  atmosphere  of  carbonic  acid  or  nitrous  oxide, 
showed  a  very  rapid  passage  of  gas  from  the  exterior  to  the  interior.  Dr.  Mitchell 
recognized  the  passage  of  gases  through  membranes  into  liquids  and  the  exhalation  of 
gases  which  were  in  solution  in  these  liquids.  He  noted  this  action  in  the  absorption  of 
oxygen  and  the  exhalation  of  carbonic  acid  in  the  lungs,  although  he  fell  into  the  error  of 
supposing  that  there  was  no  carbonic  acid  in  solution  in  the  blood  and  that  it  was  ex- 
haled as  soon  as  formed.  A  few  years  later,  Dr.  Eogers,  of  Philadelphia,  enclosed  a 
fresh  pig's  bladder,  filled  with  venous  blood,  in  a  bell-glass  of  oxygen.  In  two  hours  a 
quantity  of  oxygen  had  been  consumed  and  a  large  quantity  of  carbonic  acid  had  made 
its  appearance. 

We  have  already  seen  that  the  blood  is  exposed  to  the  air  in  the  lungs,  separated 
from  it  only  by  a  very  delicate  membrane,  over  an  immense  surface.  The  membrane, 
far  from  interfering  with  the  interchange  of  gases,  actually  favors  it ;  and  thus,  in 
obedience  to  the  laws  which  regulate  endosmosis  between  gases  and  liquids,  the  oxygen 
is  continually  passing  into  the  blood  and  the  free  carbonic  acid  is  exhaled. 

General  Differences  in  the  Composition  of  Arterial  and  Venous  Blood. — All  observers 
agree  that  there  are  certain  marked  differences  in  the  composition  of  arterial  and  venous 
blood,  aside  from  their  free  gases.  The  arterial  blood  contains  less  water  and  is  richer 
in  organic  and  most  inorganic  constituents  than  the  venous  blood.  It  also  contains  a 
larger  proportion  of  corpuscles.  It  is  more  coagulable  and  offers  a  larger  and  firmer 
clot  than  venous  blood.  The  only  principles  which  are  constantly  more  abundant  in 
venous  blood  are  water  and  the  alkaline  carbonates.  According  to  Longet,  10,000  parts 
of  venous  blood  contained  12'3  parts  of  carbonic  acid  combined,  and  the  same  quantity 
of  arterial  blood  contained  but  8'3  parts.  The  deficiency  of  water  in  the  blood  which 
comes  from  the  lungs  is  readily  explained  by  the  escape  of  watery  vapor  in  the  expired  air. 

An  important  distinction  between  arterial  and  venous  blood  is  one  to  which  we  have 
already  incidentally  alluded;  viz.,  that  the  former  has  a  uniform  composition  in  all  parts 
of  the  arterial  system,  while  the  composition  of  the  latter  varies  very  much  in  the  blood 
coming  from  different  organs.  Arterial  blood  is  capable  of  carrying  on  the  processes  of 
nutrition,  while  venous  blood  is  not  and  cannot  even  circulate  freely  in  the  systemic 
capillaries. 

Relations  of  Respiration  to  Nutrition,  etc. — It  has  been  demonstrated  that  all  tissues, 
so  long  as  they  retain  their  absolute  integrity  of  composition,  have  the  property  of  appro- 
priating oxygen  and  exhaling  carbonic  acid,  independently  of  the  presence  of  blood;  and 
that  the  arterial  blood  carries  oxygen  from  the  lungs  to  the  tissues,  there  gives  it  up,  and 
receives  carbonic  acid,  which  is  carried  by  the  venous  blood  to  the  lungs,  to  be  exhaled. 
11 


162  RESPIRATION. 

From  this  fact  alone,  it  is  more  than  probable  that  respiration  is  inseparably  connected 
with  the  general  act  of  nutrition.  Its  processes  must  be  studied,  therefore,  as  they  take 
place  in  the  tissues  and  organs  of  the  body.  In  the  present  state  of  the  science,  the 
questions  which  naturally  arise  in  connection  with  the  essential  processes  of  respiration 
are  the  following : 

1.  In  what  way  is  oxygen  consumed  in  the  system? 

2.  How  is  carbonic  acid  produced  by  the  system? 

3.  What  is  the  nature  of  the  processes  which  take  place  between  the  disappearance 
of  oxygen  and  the  evolution  of  carbonic  acid  ? 

"When  these  questions  are  satisfactorily  answered,  we  shall  understand  the  essence  of 
respiration ;  but,  in  reasoning  on  this  subject,  we  must  not  fall  into  the  error  of  assimilat- 
ing the  respiratory  phenomena  too  closely  to  those  with  which  we  are  acquainted  as 
they  occur  in  inorganic  bodies.  It  must  be  remembered  that  in  the  organism  we  are 
dealing  with  principles  which  have  the  remarkable  property  of  self-regeneration,  and 
which,  as  a  simple  condition  of  normal  existence,  consume  oxygen,  when  it  is  presented 
to  them,  and  exhale  carbonic  acid.  Without  a  proper  supply  of  oxygen,  the  tissues  die, 
lose  these  peculiar  properties,  and  finally  disappear  by  putrefactive  decomposition.  This 
consumption  of  oxygen  cannot  be  regarded  in  any  other  light  than  as  the  appropriation, 
by  a  living  part,  of  an  element  necessary  to  supply  waste,  in  the  same  way  as  those  ma- 
terials which  are  ordinarily  called  nutritive  are  appropriated.  That  waste  is  continually 
going  on  there  can  be  no  doubt;  and,  as  the  production  of  urea,  creatine,  creatinine, 
cholesterine,  etc.,  is,  to  a  certain  extent,  independent  of  the  absorption  of  food,  so  the 
production  of  carbonic  acid  is  in  a  certain  degree  independent  of  the  absorption  of  oxy- 
gen. How  different  are  these  phenomena  from  those  which  attend  the  combinations  and 
decompositions  of  inorganic  matters !  As  an  example,  let  oxygen  be  brought  in  contact, 
under  proper  conditions,  with  iron.  Under  these  circumstances,  a  union  of  iron  and 
oxygen  takes  place,  and  a  new  substance,  oxide  of  iron,  is  formed,  which  has  peculiar 
and  distinct  properties.  In  the  «ame  -  way,  carbonic  acid  may  be  disengaged  from  its 
combinations  by  the  action  of  a  stronger  acid,  which  unites  with  the  base  and  forms  a 
new  substance  in  no  way  resembling  the  original  salt.  To  make  the  contrast  still  more 
striking,  let  fat  be  heated  in  oxygen  or  in  the  air  until  it  undergoes  combustion;  it  is 
then  changed  into  carbonic  acid  and  water,  by  a  definite  chemical  reaction,  and  is  utterly 
destroyed  as  fat. 

In  the  living  body  the  organic  nitrogenized  principles  are  in  a  condition  of  continual 
change,  breaking  down  and  forming  various  excrementitious  principles,  at  the  head  of 
which  may  be  placed  carbonic  acid.  It  is  essential  to  life  that  these  principles  be  main- 
tained in  their  chemical  integrity,  which  requires  a  supply  of  fresh  matter  as  food,  and, 
above  all,  a  supply  of  oxygen.  We  put  ourselves  in  the  position  of  ignoring  well-estab- 
lished facts  and  principles  when  we  assimilate  without  reserve  the  process  of  the  con- 
sumption of  oxygen  and  production  of  carbonic  acid  by  living  organic  bodies,  to  simple 
combustion  of  sugar  or  fat.  The  ancients  saw  that  the  breath  was  warmer  than  the  sur- 
rounding air,  that  in  the  lungs  the  air  took  heat  from  the  body,  and,  as  they  knew  of  no 
other  changes  in  the  air  produced  by  respiration,  they  assumed  that  its  object  was  simply 
to  cool  the  blood.  Lavoisier  discovered  that  the  air,  containing  oxygen,  lost  a  portion 
of  this  principle  in  respiration  and  gained  carbonic  acid  and  watery  vapor.  He  saw  that 
this  might  be  imitated  by  the  combustion  of  hydro-carbons,  such  as  exist  in  the  blood. 
He  called  respiration  a  slow  combustion  and  regarded  as  its  principal  office  the  mainte- 
nance of  animal  temperature.  When  it  was  shown  by  analyses  of  the  blood  for  gases, 
that  oxygen  is  not  consumed  in  the  lungs,  but  is  taken  up  by  the  circulating  fluid  and 
carried  all  over  the  body,  and  that  carbonic  acid  is  brought  from  all  parts  by  the  blood 
to  the  lungs,  these  facts,  taken  in  connection  with  the  fact  that  the  tissues  have  the  prop- 
erty of  consuming  oxygen  and  exhaling  carbonic  acid,  led  physiologists  to  change  the 
location  of  the  combustive  process  from  the  lungs  to  the  tissues. 


RELATIONS  OF  RESPIRATION  TO   NUTRITION.  163 

"We  cannot  stop  at  this  point.  Now  it  is  known  that  the  organic  principles  of  the 
body,  which  form  the  basis  of  all  tissues  and  organs,  are  continually  undergoing  change 
as  a  condition  of  existence ;  that  they  do  not  unite  with  any  substance  in  definite  chemi- 
cal proportions,  but  that  their  particles,  after  a  certain  period  of  existence,  degenerate 
into  excrementitious  substances  and  are  regenerated  by  an  appropriation  and  change  of 
materials  furnished  by  the  blood.  As  far  as  the  respiration  of  these  parts  is  concerned, 
we  can  only  say,  that,  in  this  process,  carbonic  acid  is  produced  and  oxygen  is  consumed. 
These  facts  show  that  respiration  is  essentially  a  phenomenon  of  nutrition,  possessing  a 
degree  of  complexity  certainly  equal  to  that  of  the  other  nutritive  processes.  It  must 
be  acknowledged  that  thus  far  its  cause  and  intimate  nature  have  eluded  investigation. 
In  respiration  by  the  tissues,  no  one  has  yet  been  able  to  give  the  cause  of  the  absorption 
of  oxygen  or  the  exhalation  of  carbonic  acid,  or  to  demonstrate  the  condition  in  which 
oxygen  exists  when  once  appropriated,  or  the  particular  changes  which  take  place  and 
the  principles  which  are  lost,  in  the  formation  of  carbonic  acid. 

The  views  of  physiologists  with  regard  to  the  essential  processes  of  respiration,  be- 
fore the  time  of  Lavoisier,  have  barely  an  historical  interest  at  the  present  day,  except 
the  remarkable  idea  of  Mayow,  which  comprehended  nearly  the  whole  process  and 
which  was  unnoticed  for  about  a  hundred  years.  It  is  not  our  object  to  dwell  upon  the 
various  theories  which  have  been  advanced  from  time  to  time,  or  even  to  fully  discuss,  in 
this  connection,  the  combustion-theory  as  proposed  by  Lavoisier  and  modified  by  Liebig 
and  others.  Although  this  theory  is  nominally  received  by  many  physiologists  of  the  pres- 
ent day,  it  will  be  found  that  most  of  them,  in  accordance  with  the  facts  which  have 
since  been  developed,  really  regard  respiration  as  connected  with  nutrition.  They  only 
differ  from  those  who  reject  the  combustion-theory,  in  their  definition  of  the  term  com- 
bustion. Lavoisier  regarded  respiration  as  a  slow  combustion  of  carbon  and  hydrogen ; 
and,  if  every  rapid  or  slow  combination  of  oxygen  with  any  other  body  be  considered  a 
combustion,  this  view  is  absolutely  correct  and  was  proven  when  it  was  shown  that 
oxygen  united  with  any  of  the  tissues.  Longet  says  that  since  the  time  of  Lavoisier  it  is 
agreed  to  give  the  above  signification  to  the  word  combustion;  but  this  must  simply  be 
for  the  purpose  of  retaining  the  name  applied  by  Lavoisier  to  the  respiratory  process, 
while  its  signification  is  altered  to  suit  the  facts  which  have  since  taken  their  place  in 
science.  There  is  no  doubt  that  combustion  is  generally  regarded  as  signifying  the  direct 
and  active  union  of  oxygen  with  certain  principles  which  commonly  contain  carbon  and 
hydrogen ;  and  the  immediate  products  of  this  union  are  carbonic  acid,  water,  and,  inci- 
dentally, heat  and  light.  It  is  certain  that  oxygen  does  not  unite  in  the  body  directly 
with  carbon  and  hydrogen,  although  it  is  consumed  and  carbonic  acid  and  water  are  pro- 
duced in  respiration.  Important  intermediate  phenomena  take  place,  and  we  do  not 
therefore  fully  express  the  respiratory  process  by  the  term  combustion.  The  researches 
of  Spallanzani,  W.  F.  Edwards,  Oollard  de  Martigny,  and  others,  who  have  demonstrated 
the  abundant  exhalation  of  carbonic  acid  by  animals  and  by  tissues  deprived  of  oxygen, 
show  that  it  is  not  a  product  of  combustion  of  any  of  the  principles  of  the  organism. 
Rejecting  this  hypothesis  as  insufficient  to  explain  the  intimate  nature  of  the  respira- 
tory process,  it  remains  to  be  seen  how  satisfactorily,  in  the  present  state  of  the  science, 
it  is  possible  to  answer  the  several  questions  we  have  proposed. 

1.  In  what  way  is  the  oxygen  consumed  in  the  system?  Oxygen  taken  from  .the  air 
is  immediately  absorbed  by,  and  enters  into  the  composition  of  the  red  corpuscles.  Part 
of  the  oxygen  disappears  in  the  red  corpuscles  themselves,  and  carbonic  acid  is  given 
off.  To  how  great  an  extent  this  takes  place  it  is  impossible  to  say ;  but  it  is  evident, 
even  from  a  study  of  the  methods  of  analysis  of  the  blood  for  gases,  that  the  property 
of  absorbing  oxygen  and  giving  off  carbonic  acid,  which  .Spallanzani  demonstrated  to 
belong  to  the  tissues,  is  possessed  as  weft  by  the  red  corpuscles.  During  life  it  is  not 
possible  to  determine  how  far  this  takes  place  in  the  blood  and  how  far  in  the  tissues. 
The  theory  has  been  proposed  that  all  the  respiratory  change  takes  place  in  the  blood  as 


164  EESPIKATIOK 

it  circulates ;  but  the  avidity  of  the  tissues  for  oxygen  and  the  readiness  with  which 
they  exhale  carbonic  acid  leave  no  room  for  doubt  that  much  of  this  change  is  effected 
in  their  substance. 

Oxygen,  carried  by  the  blood  to  the  tissues,  is  appropriated  and  consumed  in  their 
substance,  together  with  the  nutritive  materials  with  which  the  circulating  fluid  is 
charged.  We  are  acquainted  with  some  of  the  laws  which  regulate  its  consumption  but 
have  not  been  able  to  follow  it  out  and  ascertain  the  exact  nature  of  the  changes  which 
take  place.  All  that  we  can  say  definitely  on  this  point  is,  that  it  unites  with  the  organic 
principles  of  the  system,  satisfying  the  "  respiratory  sense  "  and  supplying  an  imperative 
want  which  is  felt  by  all  animals  and  which  extends  to  all  parts  of  the  organism.  After 
being  absorbed,  it  is  lost  in  the  intricate  processes  of  nutrition.  There  is  no  evidence  in 
favor  of  the  view  that  oxygen  unites  directly  with  carbonaceous  matters  in  the  blood 
which  it  meets  in  the  lungs,  and,  by  direct  union  with  carbon,  forms  carbonic  acid. 

2.  How  is  carbonic  acid  produced  by  the  system?     That  carbonic  acid  makes  its 
appearance  in  the  blood  itself,  produced  in  the  red  corpuscles,  has  been  abundantly  proven 
by  observations  already  cited,  although  it  is  impossible  to  determine  to  what  extent  this 
takes  place  during  life.     It  is  likewise  a  product  of  the  physiological  decomposition  of 
the  tissues,  whence  it  is  absorbed  by  the  blood  circulating  in  the  capillaries  and  conveyed 
by  the  veins  to  the  right  side  of  the  heart.     It  has  been  experimentally  demonstrated 
that  its  production  is  not  immediately  dependent  upon  the  absorption  of  oxygen,  for  its 
formation  continues  in  an  atmosphere  of  hydrogen  or  of  nitrogen.     It  is  most  reasonable 
to  consider  the  carbonic  acid  thus  formed  as  a  product  of  excretion  or  disassimilation, 
like  urea,  creatine,  or  cholesterine.     The  fact  that  it  may  easily  be  produced  artificially, 
out  of  the  body,  does  not  demonstrate  that  its  formation  in  the  body  is  as  simple  as  when 
it  is  formed  by  the  process  of  combustion.    We  may  be  able  at  some  future  time  to  pro- 
duce artificially  all  the  excrementitious  principles,  as  has  already  been  done  in  the  case 
of  urea ;  but  we  are  hardly  justified  in  supposing  that  the  mode  of  formation  of  carbonic 
acid,  as  one  of  the  phenomena  of  nutrition,  is  precisely  the  same  as  when  it  is  made  by 
our  chemical  manipulations. 

As  expressing  nearly  all  that  is  known,  even  at  the  present  day,  regarding  the  mode 
of  formation  of  carbonic  acid  in  the  economy,  we  may  take  the  following  concluding 
passage  from  the  paper  of  Collard  de  Martigny,  published  in  1830 : 

"  The  carbonic  acid  expired  is  a  product  of  assimilative  decomposition,  secreted  in 
the  capillaries  and  excreted  by  the  lungs." 

The  carbonic  acid  thus  produced  is  taken  up  by  the  blood,  part  of  it  in  a  free  state  in 
solution,  particularly  in  the  plasma,  and  a  part  which  has  united  with  the  carbonates  to 
form  bicarbonates.  Carried  thus  to  the  lungs,  the  free  gas  is  removed  by  simple  dis- 
placement, and  that  which  exists  in  combination  is  set  free  by  the  acids  found  in  the 
pulmonary  substance. 

3.  What  is  the  nature  of  the  intermediate  processes,  from  the  disappearance  of 
oxygen  to  the  evolution  of  carbonic  acid?     A  definite  answer  to  this  question  would 
complete  our  knowledge  of  the  respiratory  process ;  but  this,  in  the  present  state  of  the 
science,  we  are  not  prepared  to  give.     We  can  only  repeat  what  has  already  been  so 
frequently  referred  to,  that  oxygen  must  be  considered  as  a  nutritive  principle,  and 
carbonic  acid,  as  a  product  of  excretion.    The  intermediate  processes  belong  to  the  general 
function  of  nutrition,  with  the  intimate  nature  of  which  we  are  unacquainted.     We 
have  not  sufficient  evidence  for  supposing  that  this  process  is  identical  with  what  is 
generally  known  as  combustion. 

The  Respiratory  Sense,  or  Want  on  the  part  of  the  System  which  induces  the 
Respiratory  Movements.     (Besoin  de  respirer.) 

We  are  all  familiar  with  the  peculiar  and  distressing  sense  of  suffocation  which 
attends  an  interruption  in  the  respiratory  process.  Under  ordinary  conditions,  the  act 


THE  RESPIRATORY  SENSE.  165 

of  breathing  takes  place  without  our  knowledge;  but  even  when  the  air  is  but  little 
vitiated,  when  its  entrance  into  the  lungs  is  slightly  interfered  with  or  when  a  consider- 
able portion  of  the  pulmonary  structure  is  involved  in  disease,  we  experience  a  certain 
sense  of  uneasiness  and  become  conscious  of  the  necessity  of  respiratory  efforts.  This 
gradually  merges  into  the  sense  of  suffocation,  and,  if  the  obstruction  be  sufficient,  is 
followed  by  convulsions,  insensibility,  and  finally  by  death. 

Although  we  are  not  sensible  of  any  want  of  air  under  ordinary  conditions,  it  was 
proven  by  the  celebrated  experiment  of  Robert  Hook,  in  1664,  that  there  is  a  want 
always  felt  by  the  system,  and  that,  if  this  want  be  effectually  supplied,  no  respiratory 
movements  will  take  place.  "We  have  often  repeated  the  experiment  demonstrating  this 
fact.  If  a  dog  be  brought  completely  under  the  influence  of  ether,  the  chest  and  abdo- 
men opened,  and  artificial  respiration  be  carefully  kept  up  by  means  of  a  bellows  fixed 
in  the  trachea,  even  after  the  animal  has  come  from  under  the  influence  of  the  anaesthetic, 
so  as  to  look  around  and  wag  his  tail  when  spoken  to,  he  will  frequently  cease  all 
respiratory  movements  when  the  air  is  adequately  supplied  to  the  lungs.  This  fact  can  be 
very  satisfactorily  observed,  as  the  diaphragm  and  other  important  respiratory  muscles 
are  denuded  and  exposed  to  view.  If  the  artificial  respiration  be  interrupted  or  im- 
perfectly performed,  the  animal  almost  immediately  feels  the  want  of  air,  and  the  exposed 
respiratory  muscles  are  thrown  into  violent  but  ineffectual  contraction. 

It  is  generally  admitted,  indeed,  that  there  exists  in  the  system  what  may  appropri- 
ately be  regarded  as  a  respiratory  sense,  or,  as  it  is  called  by  the  French,  fiesoin  de  respirer, 
which  is  conveyed  to  the  respiratory  nervous  centre  and  gives  rise  to  the  ordinary  reflex 
and  involuntary  movements  of  respiration,  that  this  sense  is  exaggerated  by  any  thing 
which  interferes  with  respiration,  and  is  then  carried  on  to  the  brain,  where  it  is 
appreciated  as  dyspnoaa  and  finally  as  the  overpowering  sense  of  suffocation.  An 
exaggeration  of  the  respiratory  sense  constitutes  an  oppression,  which  is  referred  to  the 
lungs.  It  has  been  demonstrated,  however,  that  the  sensation  of  hunger,  which  is  felt 
in  the  stomach,  and  of  thirst,  which  is  felt  in  the  throat  and  fauces,  have  their  seat 
really  in  the  general  system,  and  are  instinctively  referred  to  the  parts  mentioned, 
because  they  are  severally  relieved  by  the  introduction  of  food  into  the  stomach  and  the 
passage  of  liquid  along  the  throat  and  oesophagus.  It  cannot,  therefore,  be  assumed, 
from  sensations  only,  that  the  sense  of  want  of  air  is  really  situated  in  the  lungs.  The 
question  of  its  seat  and  its  immediate  cause  is  one  of  the  most  interesting  of  the  physio- 
logical points  connected  with  respiration. 

Many  physiologists  accept  the  view  of  Marshall  Hall,  that  the  respiratory  sense  is 
located  in  the  lungs,  is  carried  to  the  medulla  oblongata  by  the  pulmonary  branches  of 
the  pneumogastric  nerves,  and  is  due  to  the  accumulation  of  carbonic  acid  in  the 
pulmonary  vesicles ;  but  there  are  facts  in  physiology  and  pathology  which  are  incon- 
sistent with  such  an  exclusive  view. 

In  cases  of  disease  of  the  heart,  when  the  system  is  imperfectly  supplied  with 
oxygenated  blood,  the  sense  of  suffocation  is  frequently  most  distressing,  although  the 
lungs  be  unaffected  and  receive  a  sufficient  supply  of  pure  air.  This  and  other  similar 
facts  led  Berard  to  adopt  the  view  that  the  respiratory  sense  has  its  point  of  departure 
in  the  right  cavities  of  the  heart  and  is  due  to  their  distention  as  the  result  of  obstruc- 
tion to  the  passage  of  blood  through  the  lungs.  John  Reid  thought  it  was  due  in  a 
measure  to  the  circulation  of  venous  blood  in  the  medulla  oblongata.  What  has  been 
shown  to  be  the  correct  explanation  was  given  by  Yolkmann  in  1841.  He  regarded  the 
sense  of  want  of  air  as  dependent  on  a  deficiency  of  oxygen  in  the  tissues,  producing  an 
impression  which  is  conveyed  to  the  medulla  oblongata  by  the  nerves  of  general 
sensibility.  By  a  series  of  experiments,  this  observer  disproved  the  view  that  this  sense 
resides  in  the  lungs  and  is  transmitted  along  the  pneumogastric  nerves ;  and,  by  exclusion, 
he  located  it  in  the  general  system  and  showed  that  such  a  supposition  is  sufficient  to 
explain  all  the  phenomena  connected  with  the  respiratory  movements.  In  the  hope  of 


166  KESPIKATICXNT. 

settling  some  of  these  questions,  which  might  be  regarded  as  somewhat  uncertain,  we 
instituted,  a  few  years  ago,  a  series  of  experiments  upon  the  situation  and  cause  of  the 
respiratory  sense.  In  these  observations,  the  following  facts,  some  of  which  had  been 
previously  noted,  were  demonstrated : 

1.  If  the  chest  be  opened  in  a  living  animal,  and  artificial  respiration  be  carefully 
performed,  inflating  the  lungs  sufficiently  but  cautiously  and  taking  care  to  change  the 
air  in  the  bellows  every  few  moments,  as  long  as  this  is  continued,  the  animal  will  make 
no  respiratory  effort;  showing  that,  for  the  time,  the  respiratory  sense  is  abolished. 

2.  When  the  artificial  respiration  is  interrupted,  the  respiratory  muscles  are  thrown 
into  contraction,  and  the  animal  makes  regular,  and  at  last  violent  efforts.     If  we  now 
expose  an  artery  and  note  the  color  of  the  blood  as  it  flows,  it  will  be  observed  that  the 
respiratory  efforts  commence  only  when  the  blood  in  the  vessel  begins  to  be  dark.    "When 
artificial  respiration  is  resumed,  the  respiratory  efforts  cease  only  when  the  blood  becomes 
red  in  the  arteries.     The  invariable  result  of  this  experiment  seems  to  show  that  the 
respiratory  sense  is  connected  with  a  supply  of  blood  containing  little  oxygen  and  charged 
with  carbonic  acid  to  the  systemic  capillaries  by  the  arteries,  and  that  it  varies  in  intensity 
with  the  degree  of  change  in  the  blood. 

3.  If,  while  artificial  respiration  is  regularly  performed,  a  large  artery  be  opened  and 
the  system  be  thus  drained  of  blood,  when  the  hemorrhage  has  proceeded  to  a  certain 
extent,  the  animal  makes  respiratory  efforts,  which  become  more  and  more  violent,  until 
they  terminate,  just  before  death,  in  general  convulsions.     The  same  result  follows  when 
the  blood  is  prevented  from  getting  to  the  system  by  applying  a  ligature  to  the  aorta. 

These  facts,  which  may  be  successively  observed  in  a  single  experiment,  remain  pre- 
cisely the  same  if  we  previously  divide  both  pneumogastric  nerves  in  the  neck ;  showing 
that  these  are  by  no  means  the  only  nerves  which  convey  the  respiratory  sense  to  the 
medulla  oblongata. 

The  conclusions  which  may  legitimately  be  drawn  from  the  above-mentioned  facts  are 
the  following : 

The  respiratory  sense  has  its  seat  in  the  system  and  is  transmitted  to  the  medulla 
oblongata  by  the  general  sensory  nerves.  It  does  not  originate  in  the  lungs,  for  it 
operates  when  the  lungs  are  regularly  filled  with  pure  air,  if  the  system  be  drained  of  the 
oxygen-carrying  fluid. 

The  respiratory  sense  is  due  to  a  want  of  oxygen  on  the  part  of  the  system,  and  not  to 
any  fancied  irritant  properties  of  carbonic  acid ;  for,  when  the  lungs  are  filled  with  air, 
and  the  system  is  gradually  drained  of  blood,  although  all  the  blood  which  finds  its  way 
to  the  capillaries  is  fully  oxygenated,  as  the  quantity  becomes  insufficient  to  supply  the 
required  amount  of  oxygen,  the  sense  of  want  of  air  is  felt,  and  respiratory  efforts  take 
place.  The  experimental  results  on  which  these  conclusions  are  based  are  invariable, 
and  we  have  demonstrated  them  repeatedly;  so  that  the  location  of  the  respiratory 
sense  in  the  general  system,  and  the  fact  that  it  is  an  expression  of  a  want  of  oxygen, 
seem  as  certain  as  that  oxygen  is  taken  up  by  the  blood  from  the  lungs  and  distributed 
to  the  tissues  by  the  arteries.  With  this  view  we  can  explain  all  the  reflex  phenomena 
which  are  connected  with  the  respiratory  function. 

The  supposition  of  Berard  that  the  respiratory  sense  is  due  to  distention  of  the  right 
cavities  of  the  heart  is  disproved  by  the  simple  experiment  of  sudden  excision  of  this 
organ.  In  that  case,  as  the  system  is  drained  of  blood,  efforts  at  respiration  invariably 
take  place,  though  the  supply  of  air  to  the  lungs  be  continued. 

Sense  of  Suffocation. — We  must  separate,  to  a  certain  extent,  the  respiratory  sense 
from  the  sense  of  distress  from  want  of  air,  and  its  extreme  degree,  the  sense  of  suffoca- 
tion. The  first  is  not  a  sensation,  but  an  impression  conveyed  to  the  medulla  oblongata, 
giving  rise  to  involuntary  reflex  movements.  The  necessities  for  oxygen  on  the  part  of 
the  system  regulate  the  supply  of  air  to  the  lungs.  We  have  already  seen  that,  once  in 


SENSE.  OF   SUFFOCATION.  167 

every  five  to  eight  respirations,  or  when  the  respiratory  movements  are  a  little  restricted 
under  the  influence  of  depressing  emotions,  an  involuntary  deep  or  sighing  inspiration  is 
made,  for  the  purpose  of  changing  the  air  in  the  lungs  more  completely.  The  increased 
consumption  of  oxygen  and  a  certain  amount  of  interference  with  the  mechanical  process 
of  respiration  during  violent  muscular  exercise  put  us  "  out  of  breath,"  and  for  a  time 
the  respiratory  movements  are  exaggerated.  This  is  perhaps  the  first  physiological  way 
in  which  the  want  of  air  is  appreciated  by  the  senses.  A  deficiency  in  hsematosis,  either 
from  a  vitiated  atmosphere,  mechanical  obstruction  in  the  air-passages,  or  grave  trouble 
in  the  general  circulation,  produces  all  grades  of  sensations,  from  the  slight  oppression 
which  is  felt  in  a  crowded  room,  to  the  intense  distress  of  suffocation.  When  haamatosis 
is  but  slightly  interfered  with,  only  an  indefinite  sense  of  oppression  is  experienced,  and  the 
respiratory  movements  are  a  little  increased,  the  most  marked  effect  being  an  increase  in 
the  number  and  extent  of  sighing  inspirations.  In  the  experiments  upon  animals  to  which 
we  have  referred,  when  artificial  respiration  was  interrupted,  we  first  noticed  regular  and 
not  violent  contractions  of  the  respiratory  muscles ;  but,  as  the  sense  of  want  of  air  be- 
came exaggerated,  every  muscle  which  could  be  used  to  raise  the  chest  was  brought  into 
action.  In  the  human  subject  in  this  condition,  the  countenance  has  a  peculiar  expres- 
sion of  anxiety  and  distress,  and  the  movements  soon  extend  to  the  entire  muscular  sys- 
tem, resulting  in  general  convulsions,  and,  finally,  in  insensibility. 

Bearing  in  mind  the  fact  that,  although  these  sensations  are  referred  to  the  lungs, 
indicating  increased  respiratory  effort  as  the  common  means  for  their  relief,  they  have 
their  real  point  of  departure  in  the  general  system,  we  can  understand  the  operation  of 
various  abnormal  conditions  of  the  circulation,  when  the  lungs  are  adequately  supplied 
with  fresh  air.  The  first  subjective  symptom  of  air  in  the  veins  is  a  sense  of  impending 
suffocation.  There  is  no  want  of  air  hi  the  lungs,  but  the  circulation  is  instantaneously 
interrupted,  and  oxygenated  blood  is  not  supplied  to  the  tissues.  The  same  effect,  practi- 
cally, follows  abstraction  of  the  circulating  fluid  or  the  absorption  of  any  poisonous  agent 
which  destroys  the  function  of  the  corpuscles  as  carriers  of  oxygen;  although,  in  haemor- 
rhage, the  effects  are  not  so  marked,  as  generally  the  system  is  gradually  debilitated  by 
the  progressive  loss  of  blood.  It  was  invariably  noticed,  in  the  experiments  above  referred 
to,  that,  after  the  division  of  a  large  artery,  although  artificial  respiration  was  carefully 
performed,  respiratory  efforts  took  place  when  the  system  became  nearly  drained  of  blood. 
As  the  hasmorrhage  continued,  these  efforts  became  more  violent  and  resulted,  just  before 
death,  in  general  convulsions.  A  comparison  of  this  experiment  with  those  in  which 
artificial  respiration  was  simply  interrupted  shows  that,  in  sudden  haemorrhage,  there  can 
be  no  doubt  that  the  system  feels  the  want  of  oxygen ;  and,  when  the  loss  of  blood  is 
very  great,  this  is  increased  until  it  amounts  to  a  sense  of  suffocation.  In  gradual  haemor- 
rhage, there  is  a  conservative  provision  of  Nature,  by  which  faintness  and  diminution  in 
the  force  of  the  heart's  action  favor  the  arrest  of  the  flow  of  blood. 

Poisoning  by  carbonic  oxide  is  generally  accompanied  with  convulsions,  which  arise 
from  the  sense  of  suffocation  and  are  due  to  a  fixation  of  this  gas  in  the  blood-corpuscles, 
by  which  they  are  rendered  incapable  of  carrying  oxygen  to  the  system.  Convulsions  also 
attend  poisoning  by  hydrocyanic  acid,  in  cases  in  which  the  system  is  not  overpowered 
immediately  by  a  large  dose  of  this  agent  and  the  muscular  irritability  is  destroyed. 

Experiments  have  failed  to  show  that  the  respiratory  sense,  or  the  sense  of  suffocation, 
is  due  to  irritation  produced  by  carbonic  acid  in  the  non-oxygenated  blood. 

Respiratory  Efforts  before  Birth. 

It  is  generally  admitted  that  one  of  the  most  important  functions  of  the  placenta>  and 
the  one  which  is  most  immediately  connected  with  the  life  of  the  foetus,  is  a  respiratory 
interchange  of  gases,  analogous  to  that  which  takes  place  in  the  gills  of  aquatic  animals. 
The  vascular  prolongations  from  the  foetus  are  continually  bathed  in  the  blood  of  the 
mother,  and  this  is  the  only  way  in  which  it  can  receive  oxygen.  Notwithstanding  the 


168  KESPIEATIOK 

statements  of  those  who  have  been  unable  to  note  any  difference  in  color  between  the 
blood  contained  in  the  umbilical  arteries  and  the  vein,  there  are  direct  observations 
showing  that  such  a  difference  does  exist.  Legallois  frequently  observed  a  bright-red 
color  in  the  blood  of  the  umbilical  vein ;  and,  on  alternately  compressing  and  releasing  the 
vessel,  he  saw  the  blood  change  in  color  successively  from  red  to  dark  and  from  dark  to  red. 
As  oxygen  is  thus  adequately  supplied  to  the  system,  the  foetus  is  in  a  condition  similar  to 
that  of  the  animals  in  which  artificial  respiration  was  effectually  performed.  The  want 
of  oxygen  is  fully  met,  and  therefore  no  respiratory  efforts  take  place.  Eespiratory 
movements  will  take  place,  however,  even  in  very  young  animals,  when  there  is  a  defi- 
ciency of  oxygen  in  the  system.  It  has  been  observed  that  the  liquor  amnii  occasionally 
finds  its  way  into  the  respiratory  passages  of  the  foetus,  where  it  could  only  enter  during 
efforts  at  respiration.  Winslow,  in  the  latter  part  of  the  last  century,  first  noticed  respir- 
atory efforts  in  the  foetuses  of  cats  and  dogs  in  the  uterus  of  the  mother  during  life ;  and 
many  others  have  observed  that,  when  foetuses  are  removed  from  vascular  connection 
with  the  mother,  they  will  make  vigorous  efforts  at  respiration.  This  fact  we  have  fre- 
quently had  occasion  to  demonstrate  in  making  operations  upon  pregnant  animals.  After 
the  death  of  the  mother,  the  foetus  always  makes  a  certain  number  of  respiratory  efforts, 
which  are  not  uncertain  in  their  character,  but  distinct,  accompanied  by  great  elevation 
of  the  ribs,  opening  of  the  mouth,  and  following  each  other  at  regular  intervals,  inde- 
pendently of  irritation  of  the  general  surface. 

From  what  has  been  experimentally  demonstrated  with  regard  to  the  seat  and  cause 
of  the  respiratory  sense  after  birth,  it  is  evident  that  want  of  oxygen  is  the  cause  of  re- 
spiratory movements  in  the  foetus.  When  the  circulation  in  the  maternal  portion  of  the 
placenta  is  interrupted  from  any  cause,  or  when  the  blood  of  the  foetus  is  obstructed  in 
its  course  to  and  from  the  placenta,  the  impression  due  to  want  of  oxygen  is  conveyed 
to  the  medulla  oblongata,  and  efforts  at  respiration  are  the  result.  This  cannot  be  due 
to  an  accumulation  of  carbonic  acid  in  the  lungs  and  is  entirely  consistent  with  our 
views,  locating  the  respiratory  sense  in  the  general  system. 

Cutaneous  Respiration. 

This  mode  of  respiration,  although  very  important  in  many  of  the  lower  orders  of  ani- 
mals, is  insignificant  in  the  human  subject  and  is  even  more  slight  in  animals  covered 
with  hair  or  feathers.  Still,  an  appreciable  quantity  of  oxygen  is  absorbed  by  the  skin 
of  the  human  subject,  and  an  amount  of  carbonic  acid,  which  is  proportionately  larger, 
is  exhaled.  Exhalation  of  carbonic  acid,  which  is  connected  rather  with  the  functions 
of  the  skin  as  a  general  eliminating  organ  and  is  by  no  means  an  essential  part  of  the  re- 
spiratory process,  will  be  more  fully  considered  under  the  head  of  excretion.  Carbonic 
acid  is  given  off  with  the  general  emanations  from  the  surface,  being  found  at  the  same 
time  in  solution  in  the  urine  and  in  most  of  the  secretions.  It  is  well  known  that  death 
follows  the  application  of  an  impermeable  coating  to  the  entire  cutaneous  surface ;  but 
this  is  by  no  means  due  to  a  suppression  of  its  respiratory  function  alone.  The  skin  has 
other  offices,  particularly  in  connection  with  regulation  of  the  animal  temperature,  which 
are  infinitely  more  important. 

An  estimate  of  the  extent  of  the  cutaneous,  as  compared  with  pulmonary  respiration, 
has  been  made  by  Scharling,  by  comparing  the  relative  quantities  of  carbonic  acid  exhaled 
in  the  twenty -four  hours.  According  to  this  observer,  the  skin  performs  from  -fa  to  -fa  of 
the  respiratory  function.  It  is  exceedingly  difficult  to  collect  all  the  carbonic  acid  given 
off  by  the  skin  under  perfectly  normal  conditions.  In  some  recent  observations  by  Au- 
bert,  the  -estimate  is  very  much  lower  than  that  given  by  Scharling. 

Asphyxia. 

The  effects  of  cutting  off  the  supply  of  oxygen  from  the  lungs  are  mainly  referable  to 
the  circulatory  system  and  have  already  been  considered  under  the  head  of  the  influ- 


ASPHYXIA. 


169 


ence  of  respiration  upon  the  circulation.  It  will  be  remembered  that,  in  asphyxia  the 
non-aerated  blood  passes  with  so  much  difficulty  through  the  systemic  capillaries  as 
finally  to  arrest  the  action  of  the  heart.  It  is  the  experience  of  those  who  have  experi- 
mented on  this  subject,  that  the  movements  of  the  heart,  once  arrested  in  this  way,  can- 
not be  restored,  but  that  while  the  slightest  regular  movements  continue,  its  functions 
will  gradually  return  if  air  be  readmitted  to  the  lungs. 

A  remarkable  power  of  resisting  asphyxia  exists  in  newly-born  animals  that  have 
never  breathed.  This  was  noticed  by  Haller  and  others  and  has  been  the  subject  of  nu- 
merous experiments,  among  which  we  may  mention  those  of  Buffon,  Legallois,  and  W.  F. 
Edwards.  Legallois  found  that  young  rabbits  would  live  for  fifteen  minutes  deprived  of 
air  by  submersion,  but  that  this  power  of  resistance  diminished  rapidly  with  age.  W. 
F.  Edwards  has  shown  that  there  exists  a  great  difference  in  this  regard  in  different 
classes  of  animals.  Dogs  and  'cats,  which  are  born  with  the  eyes  shut  and  in  which  there 
is  at  first  a  very  slight  development  of  animal  heat,  will  show  signs  of  life  after  submer- 
sion for  more  than  half  an  hour ;  while  Guinea-pigs,  which  are  born  with  the  eyes  open, 
are  much  more  active,  and  produce  a  greater  amount  of  heat,  will  not  live  more  than 
seven  minutes.  The  cause  of  this  peculiarity  has  been  attributed  to  the  existence  of 
the  foramen  ovale,  enabling  the  blood  to  get  to  the  system  without  passing  through 
the  lungs,  by  those  who  regard  the  arrest  of  the  circulation  in  asphyxia  as  due  to  ob- 
struction to  the  pulmonary  circulation ;  but  this  explanation  is  not  sufficient,  as  blood 
passes  easily  through  the  lungs  in  asphyxia  and  is  obstructed  only  in  the  systemic  capil- 
laries. The  true  explanation  seems  to  be  that,  in  most  warm-blooded  animals,  during  the 
very  first  periods  of  extra-uterine  life,  the  demands  on  the  part  of  the  system  for  oxygen 
are  comparatively  slight.  At  this  time,  there  is  very  little  activity  in  the  processes  of 
nutrition,  and  the  actual  consumption  of  oxygen  and  exhalation  of  carbonic  acid  are 
much  below  the  usual  regular  standard  in  animals  of  this  class.  In  fact,  their  condition  is 
somewhat  like  that  of  cold-blooded  animals.  The  actual  difference  in  the  consumption 
of  oxygen  immediately  after  birth  and  at  the  age  of  a  few  days  is  sufficient  to  explain 
the  remarkable  power  of  resisting  asphyxia  just  after  birth. 

One  of  the  most  interesting  questions,  in  a  practical  point  of  view,  connected  with 
the  subject  of  asphyxia,  is  the  effect  on  the  system  of  air  vitiated  from  breathing  in  a 
confined  space.  There  are  here  several  joints  which  present  themselves  for  considera- 
tion. The  effect  of  respiration  on  the  air  is  to  take  away  a  certain  proportion  of  oxygen 
and  to  add  certain  principles  which  are  regarded  as  deleterious.  The  emanation  which  is 
generally  regarded  as  having  the  most  decided  influence  upon  the  system  is  carbonic  acid. 
A  careful  review  of  the  most  reliable  observations  on  this  subject  shows  that  the  in- 
fluence of  carbonic  acid  is  generally  very  much  over-estimated.  In  poisoning  by  char- 
coal-fumes, it  is  generally  carbonic  oxide  which  is  the  active  principle.  Regnault  and 
Reiset  exposed  dogs  and  rabbits  for  many  hours  to  an  atmosphere  containing  twenty- 
three  parts  per  hundred  of  carbonic  acid  artificially  introduced,  and  thirty  to  forty  parts 
of  oxygen,  without  any  ill  effects.  They  took  care,  however,  to  keep  up  a  constant  sup- 
ply of  oxygen.  These  experiments  are  at  variance  with  the  results  obtained  by  others, 
but  Regnault  and  Reiset  explain  this  difference  by  the  supposition  that  the  gases  in  other 
observations  were  probably  impure,  containing  a  little  chlorine  or  carbonic  oxide.  There 
is  no  reason  to  doubt,  from  the  high  reputation  of  these  observers  for  skill  and  accuracy, 
that  their  experiments  are  perfectly  reliable ;  and,  in  that  case,  they  prove  that  carbonic 
acid  does  not  act  upon  the  system  as  a  poison.  This  view  is  sustained  by  the  observa- 
tions of  Bernard  with  carbonic  oxide,  which  is  known  to  be  excessively  poisonous.  In 
animals  killed  by  this  gas,  the  blood,  both  venous  and  arterial,  is  of  a  bright-red  color, 
which  is  due  to  the  fixation  of  the  gas  by  the  blood-corpuscles.  In  this  way,  the  red 
corpuscles,  which  act  normally  as  respiratory  agents  carrying  oxygen  to  the  tissues,  are 
paralyzed,  and  the  animal  dies  from  asphyxia.  We  have  already  referred  to  this  remark- 
able affinity  of  the  red  corpuscles  for  carbonic  oxide  and  its  action  in  arresting  the  trans- 


170  KESPIKATIOK 

formation  of  oxygen  into  carbonic  acid  in  the  blood,  in  treating  of  the  different  methods 
of  analysis  of  the  blood  for  gases,  and  have  shown  that  this  gas  is  the  proper  agent  to 
use  in  the  method  of  analysis  by  displacement. 

In  breathing  in  a  confined  space,  the  distress  and  the  fatal  results  are  produced,  in 
all  probability,  more  by  animal  emanations  and  a  deficiency  of  oxygen  than  by  the  pres- 
ence of  carbonic  acid.  When  the  latter  gas  is  removed  as  fast  as  it  is  produced,  the  effects 
of  diminution  in  the  proportion  of  oxygen  are  soon  very  marked,  and  they  progressive- 
ly increase  until  death  occurs.  Bernard  has  shown  that  birds  enclosed  in  a  confined  space, 
from  which  the  carbonic  acid  is  carefully  removed,  will  gradually  consume  oxygen,  un- 
til, when  death  occurs,  the  proportion  is  reduced  to  from  three  to  five  parts  per  hun- 
dred. "When  the  carbonic  acid  is  allowed  to  remain,  the  increased  density  of  the  atmos- 
phere interferes  with  the  diffusion  between  the  gases  of  the  blood  and  the  air,  and  death 
supervenes  with  greater  rapidity. 

The  influence  on  animals  of  emanations  from  the  lungs  and  general  surface  is  un- 
doubtedly very  considerable ;  and  this  fact,  which  almost  all  have  experienced  more  or 
less,  has  been  fully  and  painfully  illustrated  in  several  instances  of  large  numbers  of  per- 
sons confined  without  proper  change  of  air.  Overcrowding  is  one  of  the  most  prolific 
sources  of  disease  among  the  poorer  classes  of  society  ;  and  there  are  many  forms  of  dis- 
ease prevalent  in  large  cities,  that  are  almost  unknown  in  the  rural  districts  and  that  can 
be  alleviated  only  by  proper  sanitary  regulations,  which,  unfortunately,  are  often  very 
difficult  to  enforce. 

In  crowded  assemblages,  the  slight  diminution  of  oxygen,  the  elevation  of  temperature, 
increase  in  moisture,  and  particularly  the  presence  of  organic  emanations,  combine  to 
produce  unpleasant  sensations.  The  terrible  effects  of  this  carried  to  an  extreme  degree 
were  exemplified  in  the  confinement  of  the  one  hundred  and  forty-six  English  prisoners, 
for  eight  hours  only,  in  the  *'  Black  Hole  "  of  Calcutta,  a  chamber  eighteen  feet  square, 
with  only  two  small  windows,  and  those  obstructed  by  a  veranda.  Out  of  this  number, 
ninety-six  died  in  six  hours,  and  one  hundred-and  twenty-three,  at  the  end  of  the  eight 
hours.  Many  of  those  who  immediately  survived  died  afterward  of  putrid  fever.  This 
frightful  tragedy  has  frequently  been  repeated  on  emigrant  and  slave  ships,  by  confining 
great  numbers  in  the  hold  of  the  vessel,  where  they  were  entirely  shut  out  from  the 
fresh  air.  This  subject  possesses  great  pathological  interest ;  the  effects  of  an  insufficient 
supply  of  air  and  the  accumulation  in  the  atmosphere  of  animal  emanations  being  very 
important  in  connection  with  the  cause  and  prevention  of  many  diseases. 

The  condition  of  the  system  has  a  marked  and  "important  influence  on  the  rapidity 
with  which  the  effects  of  vitiated  atmosphere  are  manifested,  as  we  should  anticipate 
from  what  we  know  of  the  variations  in  the  consumption  of  oxygen  under  different  con- 
ditions. As  a  rule,  the  immediate  effects  of  confined  air  are  not  so  rapidly  manifested  in 
weak  and  debilitated  persons  as  in  those  who  are  active  and  powerful.  It  has  sometimes 
been  observed,  in  cases  where  a  male  and  female  have  attempted  suicide  together  by  the 
fumes  of  charcoal,  that  the  female  may  be  restored  some  time  after  life  is  extinct  in  the 
male.  This  is  probably  owing  to  the  greater  demand  for  oxygen  on  the  part  of  the  male. 

The  following  interesting  fact  is  reported  by  Bernard,  showing  the  relative  power  of 
resisting  asphyxia  in  health  and  disease : 

"  Two  young  persons  were  in  a  chamber  warmed  by  a  stove  fed  with  coke.  One  of 
them  was  seized  with  asphyxia  and  fell  unconscious.  The  other,  at  that  time  suffering 
with  typhoid  fever  and  confined  to  the  bed,  resisted  sufficiently  to  be  able  to  call  for  help. 
We  know  already  that  this  resistance  to  toxic  influences  is  manifested  in  animals,  when 
they  are  made  sick ;  we  here  have  the  proof  of  the  same  phenomenon  in  man.  As  for  the 
one  who,  in  good  health,  had  experienced  the  effects  of  the  commencement  of  poisoning, 
she  had  a  paralysis  of  the  left  arm,  which  was  not  completely  cured  at  the  end  of  six 
months." 

When  poisoning  by  confined  air  is  gradual,  the  system  becomes  somewhat  accustomed 


ALIMENTATION. 


171 


to  the  toxic  influence,  the  temperature  of  the  body  is  lowered,  and  an  animal  will  live  in 
an  atmosphere  which  will  produce  instantaneous  death  in  one  that  is  fresh  and  vigorous. 
Bernard  has  made  a  number  of  curious  and  instructive  experiments  on  this  point.  In 
one  of  them  a  sparrow  was  confined  under  a  bell-glass  for  one  hour  and  a  half,  at  the 
end  of  which  time  another  was  introduced,  the  first  being  still  quite  vigorous.  The  second 
became  instantly  much  distressed  and  died  in  five  minutes;  but,  ten  minutes  after,  the 
sparrow  which  had  been  confined  for  more  than  an  hour  and  a  half  was  released  and  flew 
away.  The  points  to  which  we  have  alluded  have  been  confirmed  and  the  observations 
somewhat  extended  by  the  more  recent  researches  of  Bert.  This  is  simply  demonstrating, 
with  experimental  accuracy,  a  fact  of  which  we  are  all  conscious;  for  it  is  well  known 
that,  going  from  the  fresh  air  into  a  close  room,  we  experience  a  malaise  which  is  not 
felt  by  those  who  have  been  in  the  room  for  a  length  of  time  and  whose  emanations  have 
vitiated  the  atmosphere. 


CHAPTER    VI. 

ALIMENT  A  TION. 

Appetite — Circumstances  which  modify  the  appetite — Influence  of  habit — Hunger — Seat  of  the  sense  of  hunger — 
Thirst— Seat  of  the  sense  of  thirst— Duration  of  life  in  inanition— Division  of  alimentary  principles— Nitrogen- 
ized  alimentary  principles — Non-nitrogenized  alimentary  principles — Inorganic  alimentary  principles — Water — 
Alcohol — Distilled  liquors — Wines,  malt  liquors,  etc. — Coffee — Tea — Chocolate — Condiments  and  flavoring  articles 
—Quantity  and  variety  of  food  necessary  to  nutrition— Necessity  of  a  varied  diet. 

IN  the  organism  of  animals,  every  part  is  continually  undergoing  what  may  be  called 
physiological  decay ;  the  organic  nitrogenized  principles  are  being  constantly  transformed 
into  effete  matter ;  and,  as  these  constituents  never  exist  without  inorganic  principles,  with 
which  they  are  closely  and  inseparably  united,  it  is  found  that  the  products  of  their  decay 
are  always  discharged  from  the  body  in  combination  with  inorganic  matters.  This  pro- 
cess of  molecular  change  is  a  necessary  and  an  inevitable  condition  of  life.  Its  activity  may 
be  increased  or  retarded  by  various  means,  but  it  cannot  be  arrested.  The  excremen- 
titious  principles  which  are  thus  formed  are  produced  constantly  by  the  tissues  and  must 
be  continually  removed  from  the  organism,  otherwise  they  accumulate  and  induce  serious 
toxic  conditions.  Examples  of  this  are  found  in  those  diseases  of  the  kidneys  which  in- 
terfere with  the  elimination  of  urea,  producing  urasmic  poisoning,  and  in  diseases  of  the 
liver  which  interfere  with  the  elimination  of  cholesterine,  giving  rise  to  cholestersemia. 

It  is  evident,  from  the  amount  of  matter  that  is  daily  discharged  from  the  body, 
that  the  process  of  disassimilation,  as  it  is  called,  must  be  very  active.  Its  constant 
operation  necessitates  a  constant  appropriation  of  new  matter  by  the  parts,  in  order  that 
they  may  maintain  their  integrity  of  composition  and  be  always  ready  to  perform  their 
functions  in  the  economy.  The  blood  contains  all  the  principles  necessary  for  the  regen- 
eration of  the  organism.  Its  inorganic  constituents  are  generally  found  in  the  form  in 
which  they  exist  in  the  substance  of  the  tissues ;  but  the  organic  principles  of  the  parts 
are  formed  in  the  substance  of  the  tissues  themselves,  by  a  transformation  of  material 
furnished  by  the  blood.  The  physiological  decay  of  the  organism  is,  therefore,  being 
constantly  repaired  by  the  blood ;  but,  in  order  to  keep  the  great  nutritive  fluid  from 
becoming  impoverished,  the  materials  which  it  is  constantly  losing  must  be  supplied  from 
some  source  out  of  the  body,  and  this  necessitates  the  ingestion  of  matters  which  are 
known  as  food.  Food  is  taken  into  the  body  in  obedience  to  a  want  on  the  part  of  the 
system,  which  is  expressed  by  the  sensation  of  hunger,  when  it  relates  to  solid  or  semi- 
solid  matters,  and  thirst,  when  it  relates  to  water.  As  these  sensations  constitute  the 
first  cause  of  the  introduction  of  materials  capable  of  regenerating  the  blood,  their 


172  ALIMENTATION. 

consideration  naturally  precedes  the  study  of  digestion,  the  process  by  which  the  articles 
of  food  are  prepared  for  absorption  and  appropriation  by  the  circulating  fluid. 

Hunger  and  Thirst. 

The  term  hunger  may  be  applied  to  all  degrees  of  that  peculiar  want  felt  by  the  sys- 
tem which  induces  the  ingestion  of  nutritive  principles.  Its  first  manifestations  are,  per- 
haps, best  expressed  by  the  term  appetite ;  a  sensation  by  no  means  disagreeable,  and 
one  which  may  be  excited  by  the  sight,  smell,  or  even  the  recollection  of  savory  articles, 
at  times  when  it  does  not  absolutely  depend  on  a  want  in  the  system.  In  the  ordinary 
and  moderate  development  of  the  appetite,  it  is  impossible  to  say  that  the  sensation  is 
referable  to  any  distinct  part  or  organ.  It  is  influenced  in  some  degree  by  habit ;  in 
many  persons,  the  feeling  being  experienced  at  or  near  the  hours  when  food  is  ordinarily 
taken.  If  not  soon  gratified,  the  appetite  is  rapidly  intensified  until  it  becomes  actual 
hunger.  Except  when  the  quantity  of  food  taken  is  unnecessarily  large,  the  appetite 
simply  disappears  on  the  introduction  of  food  into  the  stomach  and  gives  place  to  the 
sense  of  satisfaction  which  accompanies  the  undisturbed  and  normal  action  of  the  diges- 
tive organs ;  or,  in  those  who  are  in  the  habit  of  engaging  in  absorbing  occupations  at 
that  time,  the  only  change  experienced  is  the  absence  of  desire  for  food.  The  sense  of 
oppression  and  fulness  which  attends  over-distention  of  the  stomach  is  simply  superadded 
to  the  feeling  of  satisfaction  of  the  appetite,  of  which  it  is  not  a  necessary  part. 

In  man,  the  appetite  is  usually  manifested  in  a  marked  degree  at  least  twice,  and 
generally  three  times  in  the  twenty-four  hours.  In  this  country,  food  is  commonly 
taken  three  times  daily.  In  childhood,  when  the  system  demands  material,  not  only  for 
the  repair  of  worn-out  parts  but  for  growth,  food  is  generally  taken  oftener  and  in 
larger  relative  quantity  than  in  the  adult.  The  infant  should  satisfy  the  appetite  at  least 
six  or  seven  times  in  the  twenty-four  hours ;  and  nothing  has  a  more  serious  influence 
upon  the  development  of  the  growing  child  than  bad  quality  or  a  restricted  quantity  of 
food. 

It  has  been  observed  that  children  and  old  persons  do  not  endure  deprivation  of  food 
so  well  as  adults.  This  fact  was  noted  by  M.  Savigny,  in  the  case  of  the  wreck  of  the 
frigate  Medusa.  After  the  wreck,  one  hundred  and  fifty  persons,  of  all  ages,  were 
exposed  on  a  raft  for  thirteen  days  with  hardly  any  food.  Out  of  this  number  only 
fifteen  survived,  among  them  M.  Savigny ;  and  the  children,  young  persons,  and  the  aged, 
were  the  first  to  succumb. 

Important  modifications  in  the  appetite  are  due  to  temperature.  In  cold  climates, 
and  during  the  winter  season  in  all  climates,  the  desire  for  food  is  notably  increased,  and 
the  tastes  are  somewhat  modified.  Animal  food,  and  particularly  fats,  are  more  agree- 
able at  that  time,  and  the  quantity  of  nutriment  which  is  demanded  by  the  system  is 
then  considerably  greater.  In  many  persons,  the  difference  in  the  appetite  in  warm  and 
cold  seasons  is  very  marked. 

Exercise  and  occupation,  both  mental  and  physical,  when  not  pushed  to  the  point  of 
exhaustion,  increase  the  desire  for  food  and  undoubtedly  facilitate  digestion.  Certain 
articles,  especially  the  vegetable  bitters,  taken  into  the  stomach  immediately  before  the 
time  when  food  is  habitually  taken,  frequently  have  the  same  effect ;  while  other  articles, 
which  do  not  satisfy  the  requirements  of  the  system,  have  a  tendency  to  diminish  the 
desire  for  food.  Many  articles  of  the  materia  medica,  especially  preparations  of  opium, 
have,  in  some  persons,  a  marked  influence  in  diminishing  the  appetite.  The  abuse  of 
alcoholic  stimulants  will  sometimes  take  away  all  desire  for  food.  When  hunger  is 
pressing,  it  has  been  observed  that  tobacco,  in  those  who  are  accustomed  to  its  use,  will 
frequently  allay  the  sensation  for  a  time.  "When  the  system  has  been  badly  nourished 
from  any  cause,  as  after  prolonged  abstinence  or  in  recovery  from  an  exhausting  dis- 
ease, hunger  is  generally  pressing  and  almost  constant;  and  this  continues  until  the 
organism  has  regained  its  normal  condition.  Under  these  circumstances,  the  ingestion 


HUNGER  AND   THIRST.  173 

of  food,  even  in  unusually  large  quantity,  has  but  a  momentary  effect  in  appeasing  the 
appetite ;  showing  that,  although  the  feeling  of  satiety  which  follows  the  introduction  of  a 
sufficient  quantity  of  food  into  the  stomach  is  experienced,  the  system  still  feels  the  want 
of  nourishment,  and  this  want  is  expressed  by  an  almost  immediate  recurrence  of  the 
appetite. 

If  food  be  not  taken  in  obedience  to  the  demands  of  the  system  as  expressed  by  the 
appetite,  the  sensation  of  hunger  becomes  most  distressing.  It  is  then  manifested  by  a 
peculiar  and  indescribable  sensation  in  the  stomach,  which  soon  becomes  devoloped  into 
actual  pain.  This  is  generally  accompanied  by  intense  pain  in  the  head  and  a  feeling  of 
general  distress,  which  soon  render  the  satisfaction  of  this  imperative  demand  on  the 
part  of  the  system  the  absorbing  idea  of  existence.  Starvation  overcomes,  in  many 
instances,  every  moral  and  intellectual  feeling  and  gives  full  play  to  the  purely  animal 
instincts.  Furious  delirium  frequently  supervenes  after  a  few  days  of  complete  absti- 
nence ;  and  this  is  generally  the  immediate  precursor  of  death.  It  is  unnecessary  to  cite 
any  of  the  numerous  instances  in  which  murder  and  cannibalism  are  resorted  to  when 
starvation  is  imminent ;  suffice  it  to  say,  that  the  extremity  of  hunger  or  of  thirst,  like 
the  sense  of  impending  suffocation,  is  a  demand  on  the  part  of  the  system  so  imperative, 
that  it  must  be  satisfied  if  within  the  range  of  possibility.  There  have  been  instances  of 
sublime  resignation  in  the  face  of  this  terrible  agony,  but  these  are  rare  in  comparison 
with  the  examples  of  frightful  expedients  to  satisfy  the  demands  of  Nature. 

The  question  of  the  seat  of  the  sense  of  hunger  is  one  of  considerable  physiological 
interest.  When  we  say  that  it  is  instinctively  referred  to  the  stomach,  it  is  simply 
expressing  the  fact  that  the  sensation  is  of  a  nature  to  demand  the  introduction  of  food 
into  the  alimentary  canal.  The  sense  of  the  want  of  air  demands  the  introduction  of  fresh 
air  into  the  lungs ;  but,  though  air  be  inspired,  if  any  thing  interfere  with  its  passage  to 
the  system  by  the  blood,  the  demand  for  oxygen  is  unsatisfied.  It  has  been  shown  that  the 
real  seat  of  the  respiratory  sense  is  in  the  general  system,  and  that  this  is  referred  to  the 
lungs  because  it  is  necessarily  by  the  introduction  of  air  into  these  organs  that  the  want 
is  met.  The  same  principle  is  manifested,  in  a  manner  no  less  distinct,  with  regard  to 
the  ingestion  and  assimilation  of  food.  When  the  system  is  suffering  from  defective 
nutrition,  as  after  prolonged  abstinence  or  during  recovery  from  diseases  which  have 
been  accompanied  by  lack  of  assimilation,  the  mere  filling  of  the  stomach  produces  a 
sensation  of  repletion  of  this  organ,  but  the  sense  of  hunger  is  not  relieved ;  but  if,  on  the 
other  hand,  the  nutrition  be  active  and  sufficient,  the  stomach  is  frequently  entirely 
empty  for  a  considerable  time  without  the  development  of  the  sense  of  hunger.  The 
following  observation  bears  strongly  on  this  point :  In  a  dog  with  a  fistula  into  the  gall- 
bladder, the  bile-duct  having  been  tied  and  partly  exsected,  digestion  was  so  much  inter- 
fered with  that  death  from  inanition  took  place  in  thirty-eight  days ;  and,  although  the 
animal  took  food  abundantly,  the  appetite  was  voracious  and  never  satisfied.  The  same 
phenomenon  has  sometimes  been  observed  in  cases  of  diabetes  accompanied  with  great 
deficiency  of  assimilation.  The  appetite  is  preserved  and  hunger  is  felt  by  persons  who 
suffer  from  extensive  organic  disease  of  the  stomach,  and  the  sensation  has  been  occa- 
sionally relieved  by  nutritious  enemata  or  by  injections  into  the  veins. 

An  interesting  and  curious  case  has  been  reported  by  Prof.  Busch,  of  Bonn,  which 
points  almost  conclusively  to  a  want  of  assimilation  of  nutritive  matter  by  the  gen- 
eral system  as  the  main  cause  of  the  sensation  of  hunger.  In  this  case,  which  will  be 
more  fully  detailed  hereafter,  there  existed  a  fistula  into  what  appeared  to  be  the  upper 
third  of  the  small  intestine.  The  patient  was  a  woman,  thirty-one  years  of  age,  who, 
in  the  sixth  month  of  her  fourth  pregnancy,  received  the  injury  which  resulted  in  the 
fistulous  opening,  by  being  tossed  by  a  bull,  one  of  the  horns  penetrating  the  abdomen. 
She  was  seen  by  Prof.  Busch  six  weeks  after  the  injury,  at  which  time  every  thing  taken 
into  the  stomach  passed  at  the  upper  opening  of  the  fistula.  Although  the  patient  took 
food  in  large  quantity,  she  became  extremely  emaciated  and  weak.  "The  patient  at 


174  ALIMENTATION. 

first  had  a  most  voracious  appetite ;  she  never  felt  satisfied.  She  continued  to  eat,  even 
when  the  first  portions  of  food  which  she  had  taken  were  escaping  through  the  opening. 
She  would  then  say  that  she  felt  better,  but  was  still  hungry.  Prof.  Busch  infers  that 
hunger  is  composed  of  two  separate  sensations — one  general,  the  other  local ;  the  former 
resulting  from  the  want  of  material  to  supply  the  waste  of  tissue."  Such  facts  render 
it  certain  that  the  appetite  and  the  sense  of  hunger  are  expressions  of  a  general  want  on 
the  part  of  the  system,  referred  by  our  sensations  to  the  stomach,  but  really  located  in 
the  general  system.  This  want  can  only  be  completely  satisfied  oy  the  absorption  of 
digested  alimentary  matter  by  the  blood  and  its  assimilation  by  the  tissues. 

The  sense  of  hunger  is  undoubtedly  appreciated  by  the  cerebrum,  and  it  has  been  a 
question  whether  there  be  any  special  nerves  which  have  the  function  of  conveying  this 
impression  to  the  great  nervous  centre.  The  nerve  which  would  naturally  be  supposed  to 
possess  this  function  is  the  pneumogastric ;  but,  notwithstanding  certain  observations  to 
the  contrary,  it  has  been  proven  that  section  of  both  of  these  nerves  by  no  means  abolishes 
the  desire  for  food.  Longet  has  observed  that  dogs  eat,  apparently  with  satisfaction, 
after  section  of  the  glosso-pharyngeal  and  lingual  nerves.  This  observer  is  of  the  opinion 
that  the  sensation  of  hunger  is  conveyed  to  the  brain  through  the  sympathetic  system. 
Although  there  are  various  considerations  which  render  this  somewhat  probable,  it  is 
not  apparent  how  it  could  be  demonstrated  experimentally.  It  is  undoubtedly  the  sym- 
pathetic system  of  nerves  which  presides  specially  over  nutrition ;  and  hunger,  which 
depends  upon  deficiency  of  nutrition,  is  certainly  not  conveyed  to  the  brain  by  any  of  the 
cerebro-spinal  nerves. 

Thirst  is  the  special  sensation  which  induces  the  ingestion  of  water.  In  its  moderate 
development,  this  is  usually  an  indefinite  feeling,  accompanied  with  more  or  less  sense 
of  dryness  and  heat  of  the  throat  and  fauces,  and  sometimes,  after  the  ingestion  of  a 
quantity  of  very  dry  food,  by  a  peculiar  sensation  referred  to  the  stomach.  When  the 
sensation  of  thirst  has  become  intense,  the  immediate  satisfaction  which  follows  the 
ingestion  of  a  liquid,  particularly  water,  is  very  great.  Thirst  is  very  much  under  the 
influence  of  habit,  some  persons  experiencing  a  desire  to  take  liquids  only  two  or  three 
times  daily,  while  others  do  so  much  more  frequently.  The  sensation  is  also  sensibly 
influenced  by  the  condition  of  the  atmosphere,  as  regards  moisture,  by  exercise,  and 
by  other  circumstances  which  influence  the  discharge  of  water  from  the  body,  particularly 
by  the  skin.  A  copious  loss  of  blood  is  always  followed  by  great  thirst.  This  we  have 
frequently  noticed  in  the  inferior  animals.  After  an  operation  involving  hasmorrhage, 
they  nearly  always  drink  with  avidity  as  soon  as  released.  In  diseases  which  are  charac- 
terized by  increased  discharge  of  liquids,  thirst  is  generally  excessive. 

The  demand  on  the  part  of  the  system  for  water  is  much  more  imperative  than  for 
solids ;  in  this  respect  being  only  second  to  the  demand  for  oxygen.  Animals  will  live 
much  longer  deprived  of  solid  food  but  allowed  to  drink  freely  than  if  deprived  of  both 
food  and  drink.  A  man,  supplied  with  dry  food  but  deprived  of  water,  will  not  survive 
more  than  a  few  days.  Water  is  necessary  to  the  function  of  nutrition,  and  acts,  more- 
over, as  a  solvent  in  removing  from  the  system  the  products  of  disassimilation. 

After  deprivation  of  water  for  a  considerable  time,  the  intense  thirst  becomes  most 
agonizing.  The  dryness  and  heat  of  the  throat  and  fauces  are  increased  and  accom- 
panied by  a  distressing  sense  of  constriction.  A  general  febrile  condition  supervenes,  the 
blood  is  diminished  in  quantity  and  becomes  thickened,  the  urine  is  sca'nty  and  scalding, 
and  there  seems  to  be  a  condition  of  the  principal  viscera  approaching  inflammation. 
Death  takes  place  in  a  few  days,  generally  preceded  by  delirium. 

The  sensation  of  thirst  is  instinctively  referred  to  the  mouth,  throat,  and  fauces;  but 
it  is  not  necessarily  appeased  by  the  passage  of  water  over  these  parts,  and  it  may  be 
effectually  relieved  by  the  introduction  of  water  into  the  system  by  other  channels,  as  by 
injecting  it  into  the  veins.  Bernard  has  demonstrated,  by  the  following  experiment,  that 
water  must  be  absorbed  before  the  demands  of  the  system  can  be  satisfied :  He  made  an 


HUNGER  AND  THIKST.  175 

opening  into  the  resophagus  of  a  horse,  tied  the  lower  portion,  and  allowed  the  animal 
to  drink  after  he  had  been  deprived  of  water  for  a  number  of  hours.  The  animal  drank 
an  immense  quantity,  but  the  water  did  not  pass  into  the  stomach,  and  the  thirst  was 
not  relieved.  He  modified  this  experiment  by  causing  dogs  to  drink  with  a  fistulous 
opening  into  the  stomach  by  which  the  water  was  immediately  discharged.  They  con- 
tinued to  drink  without  being  satisfied,  until  the  fistula  was  closed  and  the  water  could 
be  absorbed.  "We  have  often  repeated  the  latter  experiment  in  public  demonstrations.  In 
one  of  these  particularly,  the  animal  drank  repeatedly  until  he  had  taken  several  quarts 
of  water,  only  ceasing  from  fatigue  and  soon  recommencing ;  but,  so  soon  as  the  fistula 
was  closed,  he  drank  a  moderate  quantity  and  was  satisfied. 

In  a  case  reported  by  Dr.  Gairdner,  of  Edinburgh,  in  the  human  subject,  all  the 
liquids  swallowed  passed  out  at  a  wound  in  the  neck  by  which  the  oasophagus  had  been  cut 
across.  The  thirst  in  this  case  was  insatiable,  although  buckets-full  of  water  were  taken  in 
the  day;  but,  on  injecting  water,  mixed  with  a  little  spirit,  into  the  stomach,  the  sen- 
sation was  soon  relieved.  This  observation  was  made  in  1820,  long  before  the  experi- 
ments just  referred  to  upon  the  inferior  animals. 

Although  the  sensation  of  thirst  is  referred  to  special  parts,  it  is  an  expression  of  the 
want  of  fluids  in  the  system  and  is  to  be  effectually  relieved  only  by  the  absorption  of 
fluids  by  the  blood.  There  are  no  nerves  belonging  to  the  cerebro-spinal  system  which 
have  the  office  of  carrying  this  sensation  to  the  brain,  division  of  which  will  abolish  the 
desire  for  liquids.  Experiments  show  that  no  effectual  relief  of  the  sensation  is  afforded 
by  simply  moistening  the  parts  to  which  the  heat  and  dryness  are  referred.  As  a  demand 
on  the  part  of  the  system,  it  is  entirely  analogous  to  the  sense  of  want  of  air  and  of 
hunger,  differing  only  in  the  way  in  which  it  is  manifested. 

After  a  certain  period  of  inanition,  febrile  movement  and  general  agitation  occur, 
and  there  is  almost  always  disturbance  of  the  mental  faculties,  amounting  sometimes  to 
furious  delirium.  Frequently,  however,  the  delirium  is  of  a  mild  character,  with  hallu- 
cinations. There  are  cases  in  which  there  is  no  marked  mental  disturbance,  but  these 
are  generally  in  persons  who  voluntarily  suffer  starvation. 

The  length  of  time  that  life  continues  after  complete  deprivation  of  food  and  drink  is 
very  variable.  The  influences  of  age  and  obesity  have  already  been  referred  to.  With- 
out citing  the  numerous  individual  instances  of  starvation  in  the  human  subject  which 
have  been  reported,  it  may  be  stated,  in  general  terms,  that  death  occurs  after  from  five 
to  eight  days  of  total  deprivation  of  food.  In  1816,  one  hundred  and  fifty  persons, 
wrecked  on  the  frigate  Medusa,  were  exposed  on  a  raft  in  the  open  sea  for  thirteen  days. 
At  the  end  of  this  time  only  fifteen  were  found  alive.  One  of  the  survivors,  M.  Savigny, 
gave,  in  an  inaugural  thesis,  a  very  instructive  and  accurate  account  of  this  occurrence, 
which  has  been  very  generally  quoted  in  works  of  physiology.  Authentic  instances  are 
on  record  in  which  life  has  been  prolonged  much  beyond  the  period  above  mentioned ;  but 
they  generally  occurred  in  persons  who  were  so  situated  as  not  to  suffer  from  cold, 
which  the  system,  under  this  condition,  has  very  little  power  to  resist.  In  these  cases, 
also,  there  was  no  muscular  exertion,  and  water  was  generally  taken  in  abundance.  All 
of  these  circumstances  have  an  important  influence  in  prolonging  life. 

Berard  quotes  the  example  of  a  convict  who  died  of  starvation  after  sixty-three  days, 
but  in  this  case  water  was  taken.  An  instance  of  eight  miners  who  survived  after  five 
days  and  sixteen  hours  of  almost  complete  deprivation  of  food  is  referred  to  in  works 
upon  physiology.  Berard  also  quotes  from  various  authorities  instances  of  deprivation 
of  food  for  periods  varying  from  four  months  to  sixteen  years.  All  of  the  subjects  were 
females,  and  the  histories  of  such  cases,  reports  of  which  are  by  no  means  uncommon, 
belong  properly  to  psychology,  as  they  undoubtedly  are  examples  of  that  morbid  desire 
to  excite  sympathy  and  interest,  which  is  sometimes  observed  and  which  leads  to  the 
most  adroit  and  persevering  efforts  at  deception. 

From  thirty  to  thirty-five  days  may  be  taken  as  the  average  duration  of  life  in  dogs 


176  ALIMENTATION. 

deprived  entirely  of  food  and  drink.     This  fact  it  is  important  to  bear  in  mind  in  con- 
nection with  observations  on  the  nutritive  value  of  different  articles  of  food. 

Alimentation. 

Under  the  name  of  aliment,  in  its  widest  signification,  it'Ms  proposed  to  include  all 
articles  composed  of  or  containing  elements  in  a  form  which  enables  them  to  be  used 
for  the  nourishment  of  the  body,  either  by  being  themselves  appropriated  by  the  or- 
ganism, by  influencing  favorably  the  process  of  nutrition,  or  by  retarding  disassimila- 
tion.  Those  principles  which  are  themselves  appropriated  may  be  called  direct  aliments ; 
and  those  which  simply  assist  nutrition  without  contributing  reparative  material, 
together  with  those  which  retard  disassimilation,  may  be  termed  accessory  aliments. 
By  this  definition  of  aliment,  nothing  is  excluded  which  contributes  to  nutrition.  The 
air  must  be  considered  in  this  light,  as  well  as  water  and  all  articles  which  are  com- 
monly called  drinks. 

In  the  various  articles  used  as  food,  nutritious  elements  are  frequently  combined  with 
each  other  and  with  indigestible  and  non-nutritious  matters.  The  elements  of  the 
food  which  are  directly  used  in  nutrition  are  the  true  alimentary  principles,  embracing, 
thus,  only  those  principles  which  are  capable  of  absorption  and  assimilation.  The 
ordinary  food  of  the  warm-blooded  animals  contains  alimentary  principles  united  with 
innutritious  substances  from  which  they  are  separated  in  digestion.  This  necessitates  a 
complicated  digestive  apparatus.  In  some  of  the  inferior  animals,  the  quantity  of  nu- 
tritious material  forms  so  small  a  part  of  the  food  that  the  digestive  apparatus  is  even 
more  complicated  than  in  the  human  subject.  This  is  especially  marked  in  the  herbivora, 
the  flesh  of  which  forms- an  important  part  of  the  diet  of  man.  In  addition  to  what  are 
distinctly  recognized  as  alimentary  principles,  food  contains  many  substances  having  an 
important  influence  on  nutrition,  which  have  never  been  isolated  and  analyzed,  but 
which  render  it  agreeable.  Many  of  these  principles  are  developed  in  the  process  of 
cooking.  They  will  be  considered,  as  far  as  practicable,  in  connection  with  the  different 
articles  of  diet. 

The  alimentary  principles  belong  to  the  inorganic,  vegetable,  and  animal  kingdoms, 
and  are  generally  divided  into  the  following  classes: 

1.  Organic  nitrogenized  principles  (albumen,  fibrin,  caseine,  musculine,  etc.),  belong- 
ing to  the  animal  kingdom,  and  vegetable  nitrogenized  principles,  such  as  gluten  and 
legumine. 

2.  Organic  non-nitrogenized  principles  (sugars,  fats,  and  starch). 

3.  Inorganic  principles. 

Nitrogenized  Alimentary  Principles. 

In  the  nutrition  of  certain  classes  of  animals,  these  principles  are  derived  exclusively 
from  the  animal  kingdom,  and  in  others,  exclusively  from  the  vegetable  kingdom ;  but 
in  man,  who  is  omnivorous,  both  animals  and  vegetables  contribute  nitrogenized  material. 
In  both  animal  and  vegetable  food,  these  principles  are  always  found  combined  with 
inorganic  matters  (water,  chloride  of  sodium,  the  phosphates,  sulphates,  etc.),  and  fre- 
quently with  non-nitrogenized  principles  (sugar,  starch,  and  fat). 

MwcuUne. — Of  the  different  nitrogenized  principles  used  as  food,  musculine,  albumen, 
caseine,  and  fibrin  are  the  most  important.  Musculine,  the  organic  principle  which  forms 
the  bulk  of  the  muscular  substance,  is  perhaps  the  most  important  and  abundant  article 
of  this  class.  This  substance  is  always  united  with  more  or  less  inorganic  matter,  which 
cannot  be  separated  without  incineration.  The  flesh  of  different  animals  presents  wide 
differences  in  general  appearance,  in  nutritive  properties,  and  in  flavor,  which  become 
more  marked  after  the  formation  of  the  odorous,  empyreumatic  substances  which  are 


NITROGENIZED   ALIMENTARY  PRINCIPLES.  177 

developed  in  cooking;  but  the  organic  principle  of  all  of  them  is  musculine.  Muscular 
tissue  is  rendered  much  more  digestible  by  cooking,  a  process  which  serves  to  disin- 
tegrate, to  a  certain  extent,  the  intermuscular  areolar  tissue  and  facilitates  the  action  of 
the  digestive  fluids.  The  savors  developed  in  this  process  have  a  decidedly  favorable 
influence  on  the  secretion  of  the  gastric  juice.  It  is  doubtful  whether  pure  musculine 
would  be  capable  of  supporting  life  for  a  long  period ;  but  the  muscular  tissue  has  been 
shown  by  experiment  to  be  sufficient  for  the  purposes  of  nutrition,  in  the  carnivora,  and 
it  undoubtedly  is  in  man. 

Of  all  kinds  of  muscular  tissue,  beef  possesses  the  greatest  nutritive  power.  Other 
varieties  of  flesh,  even  that  of  birds,  fishes,  and  animals  in  a  wild  state,  do  not  present 
an  appreciable  difference,  as  far  as  can  be  ascertained  by  chemical  analysis ;  but  when 
taken  daily  for  a  long  time,  they  become  distasteful,  the  appetite  fails,  and  the  system 
seems  to  demand  a  change  of  diet.  The  flesh  of  carnivorous  animals  is  rarely  used  as 
food;  and  animals  that  feed  upon  animal  as  well  as  vegetable  food,  such  as  pigs  or 
ducks,  acquire  a  disagreeable  flavor  when  the  diet  is  not  strictly  vegetable. 

Albumen. — This  is  an  alimentary  principle  hardly  second  in  importance  to  musculine. 
As  an  article  of  diet,  it  is  chiefly  found  in  the  white  of  egg,  where  it  exists  in  great 
quantity  and  is  combined  with  a  variety  of  inorganic  substances.  Although  an  important 
alimentary  principle,  it  cannot  meet  all  the  nutritive  requirements  of  the  organism. 
Numerous  observations  on  the  inferior  animals  have  shown  that  pure  albumen  will  not 
sustain  life.  The  egg  of  the  fowl,  however,  containing,  in  addition  to  albumen,  a  large 
quantity  of  inorganic  matter,  the  fatty  matter  of  the  yolk,  and  other  organic  principles, 
is  a  most  nutritious  article  of  food.  The  albuminoid  matters  constitute  the  great 
nutritive  nitrogenized  principles  of  the  blood  and  are  the  substances  into  which  all  the 
principles  of  this  class  which  exist  in  food  are  converted  before  they  are  applied  to  the 
nutrition  of  the  tissues. 

Gaseine. — At  a  certain  period  of  life,  caseine  constitutes  essentially  the  sole  nitrogenized 
article  of  food.  It  is  found  only  in  milk,  and  it  exists  largely  in  the  great  variety  of 
cheeses,  which  are  manufactured  from  milk.  In  addition  to  caseine,  milk  contains  butter, 
sugar,  and  a  variety  of  inorganic  principles.  Milk  is  capable  of  supplying  material  for 
the  nourishment  of  all  parts  of  the  organism,  caseine  furnishing  the  nitrogenized  prin- 
ciple. In  the  form  of  cheese,  caseine  constitutes  an  important  article  of  food. 

Fibrin. — Fibrin  is  by  no  means  so  important  an  article  of  diet  as  those  just  considered, 
and  it  very  seldom  forms  any  considerable  part  of  our  food  The  same  may  be  said  of 
some  other  principles  of  this  class,  such  as  globuline,  which  is  the  organic  principle  of  the 
blood-corpuscles,  vitelline,  a  principle  peculiar  to  the  yolk  of  the  egg,  osteine  and  car- 
tilagine.  The  last  two  substances  are  generally  taken  after  they  have  undergone  peculiar 
modifications  in  cooking,  when  they  are  known  by  other  names. 

Gelatine  and  Chondrine,  etc. — After  prolonged  boiling,  the  organic  principles  of  the 
bones,  integuments,  areolar  tissue,  tendons,  and  other  structures  composed  of  the  white 
fibrous  tissue,  are  dissolved  and  transformed  into  a  new  substance  which  is  called  gelatine. 
Cartilage  treated  in  the  same  way  is  in  great  part  converted  into  chondrine.  The  prin- 
ciples thus  formed  are  soluble  in  hot  water,  rendering  it  slightly  viscid,  but  on  cooling  the 
whole  mass  becomes  of  a  more  or  less  gelatinous  consistence,  according  to  the  quantity  of 
gelatine  that  is  present.  A  considerable  quantity  of  inorganic  matter,  particularly  phos- 
phate of  lime,  is  always  present  in  combination  with  gelatine. 

Gelatine  and  chondrine  present  slight  differences  as  regards  their  chemical  reactions, 
in  other  respects  being  nearly  identical.  The  sulphate  of  alumina,  alum,  and  the  sulphate 
of  iron,  will  precipitate  chondrine  but  have  no  influence  on  a  solution  of  gelatine.  Tan- 
12 


178  ALIMENTATION. 

nin,  or  infusion  of  galls,  added  to  a  solution  of  gelatine,  produces  a  brownish  precipitate. 
This  reaction  is  marked  in  a  solution  containing  but  one  part  of  gelatine  to  five  thousand 
parts  of  water.  Both  gelatine  and  chondrine  are  of  indefinite  chemical  composition  and  un- 
crystallizable.  By  the  action  of  sulphuric  acid,  gelatine  is  %ransformed  into  a  crystallizable 
substance  called  glycocolle,  which  has  a  sweetish  taste,  is  soluble  in  water,  and  is  insoluble 
in  alcohol  and  ether.  According  to  some,  this  is  capable  of  being  separated  into  alcohol 
and  carbonic  acid  by  fermentation. 

A  great  deal  of  interest  was  at  one  time  attached  to  gelatine  as  an  article  of  food, 
from  the  fact  that  it  is  formed  and  extracted  from  parts,  particularly  the  bones,  which 
were  before  regarded  as  comparatively  useless.  Indeed,  the  experiment  of  diminishing 
the  quantity  of  meat  and  supplying  in  its  place  the  extract  of  bones  was  made  in  several 
hospitals  and  manufacturing  establishments  in  France ;  but  this  change  in  diet  led  so  uni- 
versally to  complaints  of  insufficiency  of  food,  that  experiments  were  soon  instituted  with 
a  view  of  determining  whether  gelatine  really  possessed  any  nutritive  power.  "Without 
entering  into  a  full  discussion  of  these  experiments,  it  may  be  stated  that  the  introduction 
of  gelatine  as  an  article  of  diet,  to  the  exclusion  of  other  principles  which  were  known  to 
be  nutritive,  was  always  followed  by  loss  of  weight  and  the  indications  of  more  or  less  de- 
fective nutrition.  In  other  words,  the  introduction  of  gelatine  did  not  permit  any  diminu- 
tion in  the  quantity  of  ordinary  articles  of  food.  The  whole  question  was  finally  settled 
by  the  researches  of  Magendie,  the  reporter  of  the  French  committee  on  gelatine,  in  1841. 
This  report  embodied  the  results  of  numerous  experiments  on  the  effects  of  various  nitro- 
genized  principles,  but  the  conclusions  with  regard  to  gelatine  were  very  striking.  When 
taken  alone,  it  was  distasteful  in  the  highest  degree,  even  to  animals  on  the  verge  of 
starvation ;  even  the  agreeable  jelly  formed  of  different  parts  of  the  pig  and  the  giblets 
of  fowl,  prepared  by  the  charcuticrs  of  Paris,  which  were  at  first  taken  by  the  animals 
with  apparent  satisfaction,  was  refused  after  a  few  days ;  and,  when  animals  were  con- 
fined exclusively  to  this  article,  death  took  place  about  the  twentieth  day,  with  all  the 
symptoms  of  inanition. 

The  flavor  of  meat  was  formerly  supposed  to  depend  chiefly  on  a  peculiar  principle,, 
called,  by  Thenard,  osmazome.  This  name  is  now  seldom  used,  as  the  substance  which 
was  so  called  is  known  to  be  composed  of  various  empyreumatic  nitrogenized  products, 
with  lactic  acid,  the  lactate  of  soda,  the  inosate  of  potash,  creatiiie,  creatinine,  and 
other  principles  the  nature  of  which  has  not  been  determined. 

Most  of  the  vegetable  articles  of  food  contain  more  or  less  nitrogenized  matters 
which  resemble  very  closely  their  analogues  in  the  animal  kingdom.  Some  of  these  vege- 
table principles  resemble  those  above  considered  so  closely  that  they  have  been  called 
respectively,  vegetable  albumen,  fibrin,  and  caseine.  They  all,  however,  present  certain 
distinguishing  peculiarities. 

Vegetable  Albumen. — In  the  juice  of  most  vegetables  which  are  used  as  food,  there 
exists  a  substance,  coagulable  by  heat  and  by  alcohol,  and  having  the  same  composition  as 
ordinary  albumen  with  the  exception  of  the  equivalents  of  phosphorus  and  sulphur. 
This  is  found  most  abundantly  in  the  juice  of  turnips,  carrots,  cabbages,  and  vegetables  of 
this  class.  In  wh  eaten  flour,  which  contains  nearly  all  classes  of  alimentary  principles, 
it  is  also  found,  but  in  small  quantity. 

There  is  every  reason  to  suppose  that,  as  nutritive  principles,  vegetable  and  animal 
albumen  are  nearly  identical.  Many  of  the  largest  and  strongest  animals  are  nourished 
exclusively  from  the  vegetable  kingdom.  The  human  subject  and  many  of  the  inferior 
animals  may  be  nourished  at  will  by  vegetable  or  by  animal  food.  There  is,  however, 
always  a  physiological  difference  in  the  various  nitrogenized  principles,  which  is  not  ap- 
preciable by  chemical  analysis.  The  flesh  of  the  carnivora,  when  used  as  food,  is  not  the 
same  as  the  flesh  of  the  herbivora;  and  the  quality  of  the  meat  may  be  modified  in  many 
animals  by  changing  them  from  vegetable  to  animal  food.  Although  the  muscular  tissue 


NITROGENIZED   ALIMENTARY   PRINCIPLES.  179 

of  one  animal  may  be  used  for  the  nourishment  of  another,  the  flesh  of  an  animal  thus 
nourished  is  not  an  appropriate  food  for  man.  We  should  live  upon  vegetable  principles  • 
taking  them  in  part  directly,  and  in  part  indirectly,  or  after  they  have  been  prepared  and 
assimilated  by  animals.  As  a  rule,  the  nutritive  principles  in  vegetables  are  relatively 
less  abundant  than  in  animal  food,  and  the  indigestible  residue  is  therefore  greater;  but 
man,  and  even  the  carnivorous  animals,  may  be  nourished  for  an  indefinite  period  by  ap- 
propriate articles  derived  from  the  vegetable  kingdom. 

Vegetable  Fibrin  and  Caseine. — Many  of  the  vegetable  juices  contain  a  spontaneously- 
coagulable  substance  which  has  been  called  vegetable  fibrin.  This  is  particularly  abun- 
dant in  the  cereals.  What  has  been  said  concerning  fibrin  as  an  alimentary  principle  is 
applicable  to  this  substance.  Its  proportion  in  vegetables  is  small,  unless  we  consider  as 
vegetable  fibrin,  gluten,  one  of  the  most  abundant  and  important  of  the  nutritive  principles 
contained  in  ordinary  flour. 

A  principle  may  be  extracted  from  beans,  peas,  and  other  vegetables  of  this  class, 
which  is  thought  by  many  to  be  identical,  in  all  respects,  with  caseine  and  has  been 
called  vegetable  caseine.  The  article  called  tao-foo,  made  by  the  Chinese  from  peas,  is 
apparently  identical  with  cheese.  The  peas  are  reduced  to  a  pulp  by  boiling  and  the 
vegetable  caseine  is  coagulated  by  rennet,being  afterward  treated  in  the  same  way  as  the 
analogous  substance  manufactured  from  milk.  Vegetable  and  animal  caseine  have,  as  far 
as  we  know,  identical  physiological  relations.  Vegetable  caseine  is  sometimes  called 
leguinine.  It  is  sparingly  soluble  in  water,  is  insoluble  in  alcohol,  is  not  coagulated  by 
heat,  and  is  precipitated  by  the  mineral  acids  and  some  of  the  mercurial  and  calcareous 
salts.  It  is  dissolved  by  the  vegetable  acids. 

Another  substance,  supposed  by  some  to  be  identical  with  vegetable  caseine,  is  aman- 
dine. This  is  found  widely  distributed  in  the  vegetable  kingdom,  but  it  hardly  presents 
points  of  distinction  from  leguinine,  sufficient  to  mark  it  as  a  distinct  principle. 

Gluten. — In  many  of  the  vegetable  grains  known  as  cereals,  there  exists,  in  variable 
proportions,  a  highly-nutritive  nitrogenized  substance  called  gluten.  This  is  found  in 
great  abundance  (from  ten  to  thirty-five  per  cent.)  in  wheat.  Its  proportion  in  other 
grains  is  insignificant.  It  may  be  easily  extracted  from  ordinary  wheaten  flour,  by  knead- 
ing under  a  stream  of  water,  when  the  starch,  a  little  sugar,  vegetable  albumen,  mucilage, 
and  some  soluble  matters  are  removed,  and  the  gluten  remains  in  the  form  of  an  adhesive, 
elastic,  grayish -white  mass.  Gluten  is  capable  of  acting  as  a  ferment,  transforming  starch 
first  into  dextrine  and  then  into  sugar.  It  is  the  substance  which  gives  the  peculiar  con- 
sistence and  porous  character  to  bread. 

The  nutritive  power  of  gluten  is  so  great,  and  it  contains  such  a  variety  of  alimentary 
principles,  that  dogs  are  well  nourished  and  can  live  indefinitely  on  it  when  taken  as  the 
sole  article  of  food.  This  experiment  was  actually  made  by  the  gelatine  committee ;  and 
the  fact  will  be  easily  understood  when  we  consider  that  it  is  a  compound  of  no  less 
than  three  distinct  nitrogenized  principles,  together  with  fatty  and  inorganic  matters. 
In  one  of  the  methods  of  treatment  of  diabetes  mellitus,  in  which  all  saccharine  and 
amylaceous  matters  are  excluded  from  the  food,  it  has  been  found  difficult  to  nourish  the 
body  sufficiently  and  give  proper  variety  to  the  diet  without  bread  ;  and,  under  these 
circumstances,  the  use  of  bread  composed  almost  exclusively  of  gluten  has  been  highly 
successful.  With  proper  care,  a  bread  can  be  made  in  this  way,  which  is  eminently 
nutritive  and  not  unpalatable. 

Gluten  obtained  by  washing  flour  under  a  stream  of  water  contains  vegetable  fibrin, 
vegetable  albumen,  and  a  substance  soluble  in  alcohol,  called  glutine.  This  latter  sub- 
stance is  found  in  quantity  only  in  wheaten  flour. 

In  the  different  articles  of  food  belonging  to  the  vegetable  kingdom,  there  are  un- 
doubtedly many  nitrogenized  matters  with  the  distinguishing  properties  of  which  we 


180  ALIMENTATION. 

are  not  yet  familiar.  In  their  relations  to  the  body  as  alimentary  principles,  these  would 
not  possess  much  practical  interest,  even  if  they  had  all  been  isolated  and  studied ;  for  all 
articles  of  this  class  are  apparently  transformed  into^the  same  nutritive  principles, 
namely,  the  albuminoid  constituents  of  the  blood. 

Non- Nitrogenized  Alimentary  Principles. 

The  important  principles  belonging  to  the  class  of  non-nitrogenized  matters  are  the 
sugars,  starch,  and  fat.  From  the  fact  that  these  are  supposed  by  some  to  be  exclusively 
concerned  in  keeping  up  the  animal  temperature  by  the  oxidation  of  carbon,  they  are 
frequently  spoken  of  as  the  carbonaceous  or  calorific  elements  of  food.  They  are  some- 
times called  hydro-carbons.1 

In  many  respects  there  are  marked  and  important  differences  between  the  nitro- 
genized  and  non-nitrogenized  articles  of  food ;  and  whether  or  not  these  differences  relate 
to  the  nutrition  of  the  organism  is  a  question  which  will  be  considered  in  its  appropriate 
place.  The  production  of  animal  heat,  which  is  supposed  by  some  to  be  due  entirely  to 
the  action  of  non-nitrogenized  substances,  is  closely  connected  with  the  function  of  nutri- 
tion, and  all  that  is  at  present  known  of  this  general  process  must  be  taken  into  con- 
sideration in  connection  with  calorification.  It  is  certain,  however,  that  all  alimentary 
and  proximate  principles  which  contain  nitrogen,  excluding  the  inorganic  and  some 
cry stalliz able  organic  substances,  have  very  different  properties  from  those  which  contain 
no  nitrogen.  While  the  nitrogenized  principles  are  in  a  state  of  continual  change,  so  that 
it  is  impossible  to  fix  upon  any  formula  as  representing  their  exact  ultimate  composition, 
the  non-nitrogenized  principles  are  not  changed,  unless  by  the  influence  of  some  other  sub- 
stance known  as  a  ferment,  and  have  a  distinct  and  definite  chemical  composition.  The 
latter  not  only  differ  greatly  from  the  nitrogenized  principles,  but  most  of  the  individual 
articles  of  this  class  present  distinctive  peculiarities  in  their  general  properties,  reactions, 
and  ultimate  composition.  Treating  of  them  as  alimentary  principles,  we  have  now  only 
to  do  with  their  general  properties  and  the  changes  which  they  may  be  made  to  under- 
go out  of  the  body. 

Sugar. — A  great  many  varieties  of  sugar  occur  in  food,  and  this  principle  may  be 
derived  from  both  the  animal  and  the  vegetable  kingdom.  The  most  common  varieties 
derived  from  animals  are  sugar  of  milk,  and  honey,  beside  a  small  quantity  of  liver-sugar, 
which  is  taken  whenever  the  liver  is  used  for  food.  The  sugars  derived  from  the  vege- 
table kingdom  are  cane-sugar,  under  which  head  may  be  classed  all  varieties  of  sugar 
except  that  obtained  from  fruits,  and  grape-sugar,  which  comprises  all  the  varieties  exist- 
ing in  fruits.  In  addition,  an  impure,  uncrystallizable  residue,  obtained  in  the  manu- 
facture of  the  different  varieties  of  cane-sugar,  called  molasses,  is  a  common  article  of 
food.  The  following  are  the  formulae  for  the  different  varieties  of  sugar  in  a  crystalline 
form: 

Cane- Sugar,  da  Hn  On 

Milk-Sugar,  012  H12  O12 

Grape-Sugar  (Glucose),  Ci2  Hi4  OJ4 

All  varieties  of  sugar  have  a  peculiar  sweet  taste ;  they  are  soluble  in  water  and  in 
alcohol ;  they  are  inflammable,  leaving  an  abundant  carbonaceous  residue  and  giving  off 
a  peculiar  odor  of  caramel ;  they  are  capable  of  being  converted,  in  contact  with  fer- 
ments or  with  nitrogenized  principles,  into  alcohol  and  carbonic  acid  and  into  lactic 
acid;  they  are  also  capable  of  other  modifications  when  treated  with  the  mineral  acids, 
or  with  alkalies,  which  are  interesting  more  in  a  chemical  than  a  physiological  point  of 
view.  Of  all  the  varieties  of  sugar,  that  made  from  the  sugar-cane  is  the  most  soluble, 


1  The  name  hydro-carbon  is  strictly  applicable  only  to  the  sugars  and  starch,  which  are,  chemically,  hydrates  of 
carbon,  containing  as  they  do,  carbon,  with  hydrogen  and  oxygen  in  the  proportions  to  form  water. 


NON-NITROGENIZED   ALIMENTARY   PRINCIPLES.  181 

the  sweetest,  and  the  most  agreeable.    Beet-root  sugar,  so  extensively  used  in  France,  is 
perhaps  as  agreeable,  but  is  not  so  sweet. 

Much  of  the  sugar  used  in  the  nutrition  of  the  organism  is  formed  in  the  body  from 
the  digestion  of  starch.  This  transformation  of  starch  may  be  effected  artificially.  The 
sugar  thus  formed  is  called  glucose  and  is  identical  in  composition  with  grape-sugar. 
Except  in  the  milk  during  lactation,  this  is  the  only  form  in  which  sugar  exists  in  the 
organism,  all  the  sugar  of  the  food  being  converted  into  glucose  before  it  is  taken  into 
the  blood. 

Starch. — A  non-nitrogenized  principle,  closely  resembling  sugar  in  its  ultimate  com- 
position (Ci2  Hio  Oio),  is  contained  in  abundance  in  a  great  number  of  vegetables.  It  is 
found  particularly  in  the  cereals  (wheat,  rye,  corn,  barley,  rice,  and  oats),  in  the  potato, 
chestnuts,  and  in  the  grains  of  leguminous  plants  (beans,  peas,  lentils,  and  kidney-beans),  in 
the  tuberous  roots  of  the  yam,  tapioca,  and  sweet-potato,  in  the  roots  of  the  Maranta 
arundinacea*  in  the  sago-plant,  and  in  the  bulbs  of  orchis.  In  the  cereals,  after  desicca- 
tion, the  proportion  of  starch  is,  in  general  terms,  between  sixty  and  seventy  parts  per 
hundred.  It  is  most  abundant  in  rice,  which  contains,  after  desiccation,  88'65  parts  per 
100. 

Starch  may  be  separated  from  many  plants  by  simple  washing,  but  in  others,  in  which 
it  exists  in  connection  with  a  considerable  proportion  of  gluten,  a  more  elaborate  process 
is  employed  in  commerce.  The  different  varieties  of  manufactured  starch,  such  as  corn- 
starch,  potato-starch,  arrow-root,  tapioca,  and  sago,  differ  only  in  the  presence  of  a 
minute  quantity  of  odorous  and  flavoring  principles. 

When  extracted  in  a  pure  state,  starch  is  in  the  form  of  granules,  varying  in  size  from 
nmnr  to  ¥iro  °f  an  inch,  and  presenting,  in  most  varieties,  certain  peculiarities  of  form. 
The  granule  is  frequently  marked  by  a 
little  conical  excavation  called  the  hilum, 
and  the  starch-substance  is  arranged  in  the 
form  of  concentric  laminae,  the  outlines 
of  which  are  frequently  quite  distinct. 
"When  starch  is  rubbed  between  the  fingers, 
these  little  hard  bodies  give  it  rather  a 
gritty  feel  and  produce  a  crackling  sound. 
The  different  varieties  of  starch  may  be 
recognized  microscopically  by  the  peculiar 
appearance  of  the  granules. 

The  presence  of  even  a  minute  quan- 
tity of  starch  in  any  mixture  which  is  not 
alkaline  may  be  readily  determined  by 
the  addition  of  iodine,  which  unites  with 
the  starch,  producing  an  intense-blue  color. 
The  color  may  be  destroyed  by  the  addi- 
tion of  an  alkali  or  by  the  application  of  FIG  44.— Arrow-root  starch-granules ;  magnified  370 

heat.     It  may  be  restored,  however,  by 

the  addition  of  an  acid  or,  in  the  latter 

instance,  it  returns  when  the  mixture  is  allowed  to  cool,  if  the  temperature  have  not 

been  carried  to  212°  Fahr. 

Starch  is  insoluble  in  water,  but,  when  boiled  with  several  times  its  volume  of  water, 
the  granules  swell  up,  become  transparent,  and  finally  fuse  together,  mingling  with  the 
water  and  giving  it  a  mucilaginous  consistence.  The  mixture  on  cooling  forms  a  jelly- 
like  mass  of  greater  or  less  consistence.  This  change  in  starch  is  called  hydration  and 
is  interesting  as  one  of  the  transformations  which  takes  place  in  the  process  of  digestion, 

1  The  creeping  roots  from  which  the  substance  known  as  arrow-root  is  manufactured. 


182  ALIMENTATION. 

when  starch  is  taken  uncooked.     This  change  is  generally  effected,  however,  in  the  pro- 
cess of  cooking. 

The  most  interesting  properties  ot  starch  are  connected  with  its  transformation,  first 
into  dextrine  and  finally  into  glucose.  This  always  takes  place  in  digestion,  before  starch 
can  be  absorbed.  In  the  digestive  apparatus,  the  change  into  sugar  is  almost  instan- 
taneous, and  the  intermediate  substance,  dextrine,  is  not  recognized.  By  boiling  starch 
for  a  number  of  hours  with  dilute  sulphuric  acid,  it  gradually  loses  its  property  of  striking 
a  blue  color  with  iodine,  and  is  transformed,  without  any  change  in  chemical  composition, 
into  the  soluble  substance  called  dextrine.  If  the  action  be  continued,  it  assumes  four  atoms 
of  water  and  is  converted  into  glucose.  If  dextrine  be  perfectly  pure,  no  coloration  is 
produced  by  the  addition  of  iodine,  but  it  ordinarily  contains  starch  imperfectly  trans- 
formed, and  iodine  produces  a  reddish  color.  The  change  of  starch  into  dextrine  may  be 
effected  by  a  dry  heat  of  about  400°  Fahr.,  a  process  which  is  commonly  employed  in 
commerce.  The  most  effectual  method  of  producing  this  transformation  of  starch,  aside 
from  the  process  of  digestion,  is  by  the  action  of  a  peculiar  vegetable  substance  called 
diastase.  This  substance  is  produced  in  the  process  of  germination  of  many  of  the  vege- 
tables containing  starch.1  One  part  of  diastase  will  effect  the  transformation  of  one  hun- 
dred parts  of  starch,  which  would  require  thirty  times  the  quantity  of  sulphuric  acid. 
What  has  been  said  regarding  sugar  as  an  alimentary  principle  will  apply  to  starch. 
Although  an  abundant  and  important  article  of  diet,  it  is  insufficient  of  itself  for  the  pur- 
poses of  nutrition. 

Vegetable  Principles  resembling  Starch. — In  certain  vegetables,  substances  isomeric 
with  starch,  but  presenting  slight  differences  as  regards  general  properties  and  reactions, 
have  been  described,  but  they  possess  no  very  great  interest  as  alimentary  principles  and 
demand  only  a  passing  mention.  These  are,  inuline,  lichenine,  cellulose,  pectose,  mannite, 
mucilages,  and  gums.  Inuline  is  found  in  certain  roots.  It  is  capable  of  being  converted 
into  sugar  but  does  not  pass  through  the  intermediate  stage  of  dextrine.  It  differs  from 
starch  in  being  very  soluble  in  hot  water  and  in  striking  a  yellow  instead  of  a  blue  color 
with  iodine.  Lichenine  is  found  in  many  kinds  of  edible  mosses  and  lichens.  It  differs 
from  starch  only  in  its  solubility. 

Cellulose  is  a  substance,  generally  regarded  as  identical  in  all  plants,  which  forms  the 
basis  of  the  walls  of  the  vegetable  cells.  It  exists  in  greater  or  less  abundance  in  all 
vegetables.  It  is  less  easily  acted  upon  by  acids  than  starch,  but  is  capable,  when  treated 
with  concentrated  sulphuric  acid,  of  being  converted  first  into  dextrine,  and  finally  into 
sugar.  It  is  only  in  soft  and  recent  vegetable  products  that  it  can  be  regarded  as  an  ali- 
mentary principle. 

Pectose  is  a  principle  which  exists,  mingled  with  cellulose,  in  unripe  fruits,  carrots, 
turnips,  and  some  other  vegetables  of  this  class.  Its  composition  has  not  been  deter- 
mined. In  ripe  fruits,  it  is  found  transformed  into  a  soluble  substance  called  pectine. 
This  transformation  may  be  effected  artificially  by  the  action  of  acids  and  heat.  Pectine 
may  be  precipitated  in  a  gelatinous  form  by  alcohol  from  the  juices  of  fruits. 

Mannite  is  a  sweetish  principle  found  in  manna,  mushrooms,  celery,  onions,  and 
asparagus.  Manna  in  tears  is  composed  of  this  principle  in  nearly  a  pure  state.  It  is 
perhaps  more  analogous  to  sugar  than  to  starch,  but  it  is  not  capable  of  fermentation  and 
has  no  influence  on  polarized  light. 

Gums  and  mucilages  may  enter  to  a  certain  extent  into  the  composition  of  food,  but 
they  can  hardly  be  considered  as  alimentary  principles.  Gums  are  found  exuding  from 
certain  trees,  first  in  a  fluid  state,  but  becoming  hard  on  exposure  to  the  air.  A  viscid, 
stringy  mucilage  is  found  surrounding  many  grains,  such  as  the  flax-seed  and  quince-seeds, 
and  exists  in  various  kinds  of  roots  and  leaves.  Both  gums  and  mucilages  mix  readily 

1  Diastase  is  a  white,  amorphous,  nitrogenized  substance,  insoluble  in  alcohol,  soluble  in  water,  and  is  extracted 
from  barley,  oats,  grain,  and  potatoes,  in  process  of  germination.  Its  action  upon  starch  is  most  energetic  at  from  150* 
to  167°  Fahr. 


FATS  AND   OILS. 


183 


with  water,  giving  it  a  consistence  called  mucilaginous.    They  have  the  same  composition 
as  starch. 

Experiments  have  shown  that  gum  passes  through  the  alimentary  canal  unchanged 
and  has  no  nutritive  power.  It  is  said  that  gummy  exudations  from  trees  form  an  im- 
portant part  of  the  food  of  certain  savage  African  tribes ;  but  it  must  be  remembered 
that  in  this  condition  the  exudation  is  impure  and  contains  many  other  substances.  Gum 
is  mentioned  in  this  connection  from  the  fact  that  it  is  frequently  used  in  the  treatment 
of  disease  and  is  thought  by  many  to  possess  nutritive  properties. 

Fats  and  Oils. — Fatty  or  oily  matters,  derived  from  both  the  animal  and  the  vegetable 
kingdom,  constitute  an  important  division  of  the  articles  of  food.  As  a  proximate  prin- 
ciple, fat  is  found  in  all  parts  of  the  body,  with  the  exception  of  the  bones,  teeth,  and 
fibrous  tissues.  It  necessarily  constitutes  an  important  part  of  all  animal  food  and  is 
taken  in  the  form  of  adipose  tissue,  infiltrated  in  the  various  tissues  in  the  form  of  globules 
and  granules  of  oil,  and  in  suspension  in  the  caseine  and  water  in  milk.  Animal  fat  is  a 
mixture  of  oleine,  margarine,  and  stearine,  in  varied  proportions,  and  possesses  a  con- 
sistence which  depends  upon  the  relative  quantities  of  these  principles.  More  or  less  fat 
always  enters  into  the  composition  of  food,  but,  as  a  rule,  it  is  more  abundantly  taken  in 
cold  than  in  warm  climates.  The  ordinary  diet  of  the  Greenlander  contains  what  would 
be  considered  in  temperate  climates  as  an  enormous  quantity  of  fat  and  oil,  frequently  in 
a  disgusting  form,  and  often  taken  unmixed  with  other  articles. 

The  different  varieties  of  animal  fats  do  not  demand  special  consideration  as  articles 
of  diet.  Butter,  an  important  article  of  food,  is  somewhat  different  from  the  fat  extracted 
from  adipose  tissue,  but  most  varieties  of  fat  lose  their  individual  peculiarities  in  the  pro- 
cess of  digestion  and  are  apparently  identical  when  they  find  their  way  into  the  lacteal 
vessels. 


FIG.  45. — Crystals  of  margarine  and  mar- 
garic  acid.  (Funke.)  a,  a,  a,  margarine ; 
&,  margaric  acid. 


FIG.  4C. — Crystals  of  stearine  and  stearic 
acid.  (Funke.)  a,  a,  a,  stearine ;  6, 
stearic  acid. 


In  the  vegetable  kingdom,  fat  is  particularly  abundant  in  seeds  and  grains,  but  it 
exists  in  quantity  in  some  fruits,  as  the  olive.  Here  it  is  generally  called  oil.  Its  pro- 
portion in  linseed  is  20  per  cent. ;  in  rape-seed,  35  to  40  per  cent. ;  in  hemp-seed,  25  per 
cent. ;  and  in  poppy-seed,  47  to  50  per  cent.  It  exists  in  considerable  proportion  in  nuts 
and  in  certain  quantity  in  the  cereals,  particularly  Indian  corn.  Its  proportion  in  the 
different  varieties  of  wheat  is  from  1-87  to  2-61  per  cent. ;  in  rye,  2'25  per  cent. ;  in 
barley,  2'76  per  cent. ;  in  oats,  5 -5  per  cent. ;  in  Indian  corn,  8-8  per  cent. ;  and  in  rice, 
0-8  per  cent.  The  above  is  the  proportion  in  the  grains  after  desiccation. 

Fat,  both  animal  and  vegetable,  may  be  either  liquid  or  solid.     It  has  a  peculiar  oily 


184  ALIMENTATION. 

feel,  a  neutral  reaction,  and  is  insoluble  in  water  and  soluble  in  alcohol  (particularly  hot 
alcohol),  chloroform,  ether,  benzine,  and  solutions  of  soaps.  The  solid  varieties  are  exceed- 
ingly soluble  in  the  oils.  Treated  with  alkalies,  at  a  high  temperature  and  in  the  presence 
of  water,  the  fats  are  decomposed  into  fatty  acids  and  glycerine,  the  acid  uniting  with  the 
base  to  form  a  soap.  Alkaline,  mucilaginous,  and  some  animal  fluids  (particularly  the 
pancreatic  juice)  are  capable  of  holding  fat  in  a  state  of  minute  and  permanent  subdivision 
and  suspension,  forming  what  are  known  as  emulsions. 

The  composition  of  many  of  the  fats  and  oils  has  never  been  definitely  ascertained,  on 
account  of  the  difficulty  in  obtaining  them  in  a  state  of  absolute  purity.  They  contain 
carbon,  hydrogen,  and  oxygen,  but  the  latter  elements  do  not  exist  in  the  proportions  to 
form  water. 

As  alimentary  principles,  fats  and  oils  are  undoubtedly  of  great  importance.  They 
are  supposed  by  many  to  be  particularly  concerned  in  the  function  of  calorification.  It 
has  been  proven  by  repeated  experiments  that  fat,  as  a  single  article  of  diet,  is  insufficient 
for  the  purposes  of  nutrition. 

Inorganic  Alimentary  Principles, 

Physiological  chemistry  has  shown  that  all  the  organs,  tissues,  and  fluids  of  the 
body  contain  inorganic  matter  in  greater  or  less  abundance.  The  same  is  true  of  vege- 
table products.  All  the  organic  nitrogenized  principles  contain  mineral  substances  which 
cannot  be  removed  without  incineration  and  which  must  be  considered  as  actually  part 
of  their  substance.  When  new  organic  matter  is  appropriated  by  the  tissues  to  supply 
the  place  of  that  which  has  become  effete,  the  mineral  substances  are  deposited  with 
them ;  and  the  organic  principles,  as  they  become  effete  or  are  transformed  into  excre- 
mentitious  substances  and  discharged  from  the  body,  are  always  thrown  off  in  connection 
with  the  mineral  substances  which  enter  into  their  composition.  This  constant  dis- 
charge of  inorganic  principles,  forming,  as  they  do,  an  essential  part  of  the  organism, 
necessitates  their  introduction  with  the  food,  in  order  to  maintain  the  normal  constitu- 
tion of  the  parts.  As  these  principles  are  as  necessary  to  the  proper  constitution  of  the 
body  as  any  other,  they  must  be  considered  as  belonging  to  the  class  of  alimentary  sub- 
stances. 

Water. — This  is  one  of  the  most  important  of  the  proximate  principles  of  the  organ- 
ism, is  found  in  every  tissue  and  part  without  exception,  is  introduced  with  all  kinds 
of  food,  and  is  the  basis  of  all  drinks.  As  a  rule,  it  is  taken  in  greater  or  less  quantity 
in  a  nearly  pure  state.  Although,  as  a  drink,  water  should  be  colorless,  odorless,  and 
nearly  tasteless,  it  always  contains  more  or  less  saline  and  other  matters  in  solution, 
with  a  certain  quantity  of  air.  The  air  and  gases  may  be  evolved  by  boiling  or  removing 
the  atmospheric  pressure.  Pure  water  does  not  exist  in  Nature.  Even  rain-water  always 
contains  salts  and  frequently  a  little  ammonia  and  organic  matter.  The  waters  of  the 
mineral  springs,  which  are  so  abundant  in  parts  of  this  country,  are  very  rich  in  saline 
constituents  and  generally  contain  a  notable  quantity  of  carbonic  acid ;  but  the  consid- 
eration of  their  properties  does  not  belong  to  physiology.  The  demand  on  the  part  of 
the  system  for  water  is  regulated,  to  a  certain  extent,  by  the  quantity  discharged  from 
the  organism,  and  this  is  subject  to  great  variations.  The  quantity  taken  as  drink  also 
depends  very  much  on  the  constitution  of  the  food  as  regards  the  water  which  enters  into 
its  composition. 

Chloride  of  Sodium. — Of  all  saline  substances,  chloride  of  sodium  is  the  one  most 
widely  distributed  in  the  animal  and  the  vegetable  kingdom.  It  exists  in  all  varieties  of 
food ;  but  the  quantity  which  is  taken  in  combination  with  other  principles  is  usually 
insufficient  for  the  purposes  of  the  economy,  and  common  salt  is  generally  added  to  cer- 
tain articles  of  food  as  a  condiment,  when  it  improves  their  flavor,  promotes  the  seere- 


ALCOHOL.  185 

tion  of  certain  of  the  digestive  fluids,  and  meets  a  positive  nutritive  demand  on  the  part 
of  the  system.  Numerous  experiments  and  observations  have  shown  that  a  deficiency 
of  chloride  of  sodium  in  the  food  has  an  unfavorable  influence  on  nutrition. 

Phosphate  of  Lime. — This  is  almost  as  common  a  constituent  of  vegetable  and  animal 
food  as  chloride  of  sodium.  It  is  seldom  taken  except  in  combination,  particularly  with 
the  nitrogenized  alimentary  principles.  Its  importance  as  an  alimentary  principle  has 
been  experimentally  demonstrated,  it  having  been  shown  that,  in  animals  deprived  as 
completely  as  possible  of  this  substance,  the  nutrition  of  the  body,  particularly  in  parts 
which  contain  it  in  considerable  quantity,  as  the  bones,  is  seriously  affected. 

Iron. — Hsemaglobine,  the  coloring  matter  of  the  blood,  contains,  intimately  united 
with  organic  matter,  a  considerable  proportion  of  iron.  Examples  of  anaemia,  which 
are  daily  met  with  in  practice  and  are  almost  always  relieved  in  a  short  time  by  the  ad- 
ministration of  iron,  are  proof  of  the  importance  of  this  substance  as  an  alimentary 
principle.  The  quantity  of  iron  which  is  discharged  from  the  body  is  very  slight,  a 
trace  only  being  discoverable  in  the  urine.  A  small  quantity  of  iron  is  frequently  intro- 
duced in  solution  in  the  water  taken  as  drink,  and  it  is  a  constant  constituent  of  milk 
and  eggs.  When  its  supply  in  the  food  is  insufficient,  it  is  necessary,  in  order  to  restore 
the  processes  of  nutrition  to  their  normal  condition,  to  administer  it  in  some  form,  until 
its  proportion  in  the  organism  reaches  the  proper  standard. 

It  is  hardly  necessary  even  to  enumerate  the  other  inorganic  alimentary  principles,  as 
nearly  all  are  in  a  state  of  such  intimate  combination  with  nitrogenized  principles  that 
they  may  be  regarded  as  part  of  their  substance.  Suffice  it  to  say,  that  all  the  inorganic 
matters  which  exist  in  the  organism  as  proximate  principles  are  found  in  the  food.  That 
these  are  essential  to  nutrition,  cannot  be  doubted ;  but  it  is  evident  that,  by  themselves, 
they  are  incapable  of  supporting  life,  as  they  cannot  be  converted  into  either  nitrogen- 
ized or  non-nitrogenized  organic  principles. 

Alcohol. 

All  distilled  and  fermented  liquors  and  wines  contain  a  greater  or  less  proportion  of 
alcohol.  As  these  are  so  generally  used  as  beverages,  and  as  the  effects  of  their  exces- 
sive use  are  so  serious,  the  influence  of  alcohol  upon  the  organism  has  become  one  of  the 
most  important  questions  connected  with  alimentation.  In  the  discussion  of  this  subject, 
it  is  not  proposed  to  enter  into  the  great  moral  questions  involved,  but  to  consider,  from 
a  purely  physiological  point  of  view,  the  immediate  and  remote  influences  of  the  various 
alcoholic  beverages  upon  nutrition  and  the  animal  functions.  Some  alcoholic  beverages 
influence  the  functions  solely  through  the  alcohol  which  they  contain  ;  while  others,  as 
beer  and  porter,  with  a  comparatively  small  proportion  of  alcohol,  contain  a  consider- 
able quantity  of  solid  matters  which  may  act  as  alimentary  principles. 

Alcohol  (C4H6O2),  from  its  composition,  is  to  be  classed  with  the  non-nitrogenized 
principles,  more  especially  the  fats,  in  which  the  hydrogen  and  oxygen  do  not  exist  in 
the  proportion  to  form  water.  We  have  seen  that  sugar  and  fat  are  essential  to  proper 
nutrition  and  that  they  undergo  important  changes  in  the  organism.  Alcohol  is  capable 
of  being  absorbed  and  taken  into  the  blood ;  and  it  becomes  a  question  of  great  interest 
to  determine  whether  it  be  consumed  in  the  economy  or  whether  it  be  discharged  un- 
changed by  the  various  emunctories. 

Alcohol  has  long  since  been  recognized  in  the  expired  air  after  it  has  been  taken  into 
the  stomach  ;  and  late  researches  have  confirmed  the  earlier  observations  with  regard  to 
its  elimination  in  its  original  form  and  have  shown  that,  after  it  has  been  taken  in  quan- 
tity, it  exists  in  the  blood  and  all  the  tissues  and  organs,  particularly  the  liver  and  ner- 


186  'ALIMENTATION. 

vous  system.1  Lallemand,  Perrin,  and  Duroy  have  sta*fcd,  also,  that  there  is  a  consider- 
able elimination  of  alcohol  by  the  lungs,  skin,  and  kidneys ;  but  the  accuracy  of  the  ex- 
periments by  which  these  results  were  arrived  at  has  lately  been  questioned.  The  re- 
cent observations  of  Drs.  Anstie  and  Dupre  have,  indeed,  thrown  great  doubt  upon  the 
chromic-acid  test  for  alcohol,  which  was  employed  by  the  French  observers  above  men- 
tioned. Anstie  and  Dupre  have  clearly  shown  that  the  color-test  applied  to  the  urine  of 
persons  who  do  not  drink  alcohol  at  all  not  only  acts  with  chromic  acid  in  the  same 
way  as  does  alcohol,  but  that  the  substance  in  the  urine,  whatever  it  may  be,  "  is  capa- 
ble of  being  similarly  oxidized  into  an  acid  which  is  apparently  identical  with  acetic  acid, 
and  similarly  converted  to  iodoform  by  boiling  with  iodine  and  an  alkali."  Nevertheless, 
when  alcohol  has  been  taken  in  narcotic  doses,  there  is  a  certain  amount  of  alcoholic  elimi- 
nation in  the  urine,  as  was  shown  long  ago  by  Percy.  We  are  not,  however,  considering 
at  present  the  elimination  of  alcohol  when  the  ingestion  of  this  principle  has  been  pushed 
to  extreme  intoxication,  but  only  the  question  whether  moderate  doses  of  alcohol  be 
eliminated  in  totality  or  be  consumed  in  the  organism  in  the  same  way  as  sugar  or  albu- 
men. It  is  possible  to  administer,  for  example,  such  quantities  of  sugar  that  a  certain 
amount  will  pass  off  in  the  urine ;  and  no  one  supposes  that  moderate  quantities  of  sugar 
are  not  consumed  in  the  organism.  As  the  result  of  the  final  experiments  of  Anstie,  it 
is  absolutely  certain  that  most  of  the  alcohol  which  is  taken  in  quantities  not  sufficient 
to  produce  alcoholic  intoxication  is  consumed  in  the  organism,  and  but  a  trivial  amount 
is  thrown  off,  either  in  the  urine,  the  faeces,  the  breath,  or  the  cutaneous  transpiration. 
This  question  is  of  the  greatest  importance  with  regard  to  the  moderate  use  of  alcohol 
under  normal  conditions,  and  especially  in  its  bearing  upon  the  therapeutical  action  of 
the  various  alcoholic  drinks  administered  in  cases  of  disease. 

Taken  in  moderate  quantity,  alcohol  generally  produces  a  certain  amount  of  nervous 
exaltation,  which  gradually  passes  off.  In  some  individuals  the  mental  faculties  are 
sharpened  by  alcohol,  while  in  others  they  are  blunted.  There  is  nothing,  indeed,  more 
variable  than  the  immediate  effects  of  alcohol  on  different  persons.  In  large  doses,  the 
effects  are  the  well-known  phenomena  of  intoxication,  delirium;  more  or  less  anaesthesia, 
coma,  and  sometimes,  if  the  quantity  be  excessive,  death.  As  the  rule,  the  mental  exal- 
tation produced  by  alcohol  is  followed  by  reaction  and  depression,  except  in  debilitated 
or  exhausted  conditions  of  the  system,  when  the  alcohol  seems  to  supply  a  decided 
want. 

The  views  of  physiologists  concerning  the  influence  of  a  moderate  quantity  of  alcohol 
on  the  nervous  system  are  somewhat  conflicting.  That  it  may  temporarily  give  tone  and 
vigor  to  the  system  when  the  energies  are  unusually  taxed,  cannot  be  doubted ;  but  this 
effect  is  not  produced  in  all  individuals.  The  constant  use  of  alcohol  may  create  an  ap- 
parent necessity  for  it,  producing  a  condition  of  the  system  which  must  be  regarded  as 
pathological. 

The  immediate  effects  of  the  ingestion  of  a  moderate  quantity  of  alcohol,  continued 
for  a  few  days,  are  decided.  It  notably  diminishes  the  exhalation  of  carbonic  acid  and 
the  discharge  of  other  excrementitious  principles,  particularly  urea.  These  facts  have 
long  since  been  experimentally  demonstrated.  The  proper  amount  of  mental  and  physi- 
cal exercise,  tranquillity  of  the  nervous  system,  and  all  circumstances  which  favor  the 
vigorous  nutrition  and  development  of  the  organism  physiologically  increase,  rather  than 
diminish,  the  amount  of  the  excretions,  correspondingly  increase  the  demand  for  food, 
and,  if  continued,  are  of  permanent  benefit.  Alcohol,  on  the  other  hand,  diminishes  the 
activity  of  nutrition.  If  its  use  be  long  continued,  the  assimilative  powers  of  the  system 

1  It  was  formerly  a  question  considerably  discussed  whether  alcohol  exist  in  the  brain  and  in  the  fluid  found  in  the 
ventricles,  in  intoxicated  persons.  This  was  settled  by  Percy,  who  found  alcohol  in  the  brain,  liver,  and  sometimes 
in  the  urine,  in  dogs  poisoned  with  alcohol  and  in  men  who  had  died  after  excessive  drinking.  In  these  experi- 
ments, the  presence  of  alcohol  was  determined  by  distillation,  the  distilled  substances  being  inflammable  and  capable 
of  dissolving  camphor.— PERCY,  Prize  TJiesis.  An  Experimental  Inquiry  concerning  the  Presence  of  Alcohol  in 
the  Ventricles  of  the  Brain,  etc.,  London,  1839. 


ALCOHOL.  187 

become  so  weakened  that  the  proper  quantity  of  food  cannot  he  appropriated,  and  alcohol 
is  craved  to  supply  a  self-engendered  want.  The  organism  may,  in  many  instances,  be 
restored  to  its  physiological  condition  by  discontinuing  the  use  of  alcohol ;  but  it  is  gen- 
erally some  time  before  the  nutritive  powers  become  active,  and  alcohol,  meanwhile, 
seems  absolutely  necessary  to  existence. 

Under  ordinary  conditions,  when  the  organism  can  be  adequately  supplied  with  food, 
alcohol  is  undoubtedly  injurious.  When  the  quantity  of  food  is  insufficient,  alcohol  may 
supply  the  want  for  a  time  and  temporarily  restore  the  powers  of  the  body^  but  the 
effects  of  its  continued  use,  conjoined  with  insufficient  nourishment,  show  that  it  can- 
not take  the  place  of  assimilable  matter.  These  effects  are  too  well  known  to  the 
physician,  particularly  in  hospital-practice,  to  need  farther  comment.  Notwithstand- 
ing these  undoubted  physiological  facts,  alcohol,  in  some  form,  is  used  by  almost  every 
people  on  the  face  of  the  earth,  civilized  or  savage.  Whether  this  be  in  order  to 
meet  some  want  occasionally  felt  by  and  peculiar  to  the  human  organism,  is  a  ques- 
tion upon  which  physiologists  have  found  it  impossible  to  agree.  That  alcohol,  at 
certain  times,  taken  in  moderation,  soothes  and  tranquillizes  the  nervous  system  and 
relieves  exhaustion  dependent  upon  unusually  severe  mental  or  physical  exertion,  cannot 
be  doubted.  It  is  by  far  too  material  a  view  to  take  of  existence,  to  suppose  that  the 
highest  condition  of  man  is  that  in  which  the  functions,  possessed  in  common  with  the 
lower  animals,  are  most  perfectly  performed.  Inasmuch  as  temporary  insufficiency  of 
food,  great  exhaustion  of  the  nervous  system,  and  various  conditions  in  which  alcohol 
seems  to  be  useful,  must  of  necessity  often  occur,  it  is  hardly  proper  that  this  agent 
should  be  utterly  condemned ;  but  it  is  the  article,  par  excellence,  which  is  liable  to  abuse, 
and  the  effects  of  which  on  the  mind  and  body,  when  taken  constantly  in  excess,  are 
most  serious. 

Although  alcohol  imparts  a  genial  warmth  when  the  system  is  suffering  from  ex- 
cessive cold,  it  is  not  proven  that  it  enables  men  to  endure  a  very  low  temperature  for  a 
great  length  of  time.  This  end  can  be  effectually  accomplished  only  by  an  increased 
quantity  of  food.  The  testimony  of  Dr.  Hayes,  the  Arctic  explorer,  is  very  strong  upon 
this  point.  He  says :  "  While  fresh  animal  food,  and  especially  fat,  is  absolutely  essen- 
tial to  the  inhabitants  and  travellers  in  Arctic  countries,  alcohol  is,  in  almost  any  shape, 
not  only  completely  useless  but  positively  injurious.  .  .  .  Circumstances  may  occur 
under  which  its  administration  seems  necessary;  such,  for  instance,  as  great  pros- 
tration from  long-continued  exposure  and  exertion,  or  from  getting  wet;  but  then  it 
should  be  avoided,  if  possible,  for  the  succeeding  reaction  is  always  to  be  dreaded ;  and, 
if  a  place  of  safety  is  not  near  at  hand,  the  immediate  danger  is  only  temporarily 
guarded  against,  and  becomes,  finally,  greatly  augmented  by  reason  of  decreased  vitality. 
If  given  at  all,  it  should  be  in  very  small  quantities  frequently  repeated,  and  continued 
until  a  place  of  safety  is  reached.  I  have  known  the  most  unpleasant  consequences  to 
result  from  the  injudicious  use  of  whiskey  for  the  purpose  of  temporary  stimulation, 
and  have  also  known  strong  able-bodied  men  to  have  become  utterly  incapable  of  resist- 
ing cold  in  consequence  of  the  long-continued  use  of  alcoholic  drinks." 

It  is  not  demonstrated  that  alcohol  increases  the  capacity  to  endure  severe  and  pro- 
tracted bodily  exertion.  Its  influence  as  a  therapeutic  agent,  in  promoting  assimilation 
in  certain  conditions  of  defective  nutrition,  in  relieving  shock  and  nervous  exhaustion,  in 
sustaining  the  powers  of  life  in  acute  diseases  characterized  by  rapid  emaciation  and 
abnormally  active  disassimilation,  etc.,  is  undoubted;  but  the  consideration  of  these 
questions  does  not  belong  to  physiology. 

Coffee. 

Coffee  is  an  article  consumed  daily  by  many  millions  of  human  beings  in  all  quarters 
of  the  globe.  In  armies  it  has  been  found  almost  indispensable,  enabling  men  on  moderate 
rations  to  perform  an  amount  of  labor  which  would  otherwise  be  impossible.  After 


188  ALIMENTATION. 

exhausting  efforts  of  any  kind,  there  is  no  article  which  relieves  the  overpowering  sense 
of  fatigue  so  completely  as  coffee.  Army-surgeons  say  that  at  night,  after  a  severe 
inarch,  the  first  desire  of  the  soldier  is  for  coffee,  hot  or  cold,  with  or  without  sugar,  the 
only  essential  being  a  sufficient  quantity  of  the  pure  article.  This  has  been  the  universal 
experience  in  the  late  civil  war ;  the  rations  of  coffee  issued  by  the  United  States  Govern- 
ment being  abundant  and  pure,  though  not,  of  course,  of  the  quality  possessing  the  most 
delicate  flavor.  Almost  every  one  can  bear  testimony  from  personal  experience  to  the 
effects  of  coffee  in  relieving  the  sense  of  fatigue  after  mental  or  bodily  exertion  and  in 
increasing  the  capacity  for  labor,  especially  mental,  by  producing  wakefulness  and  clear- 
ness of  intellect.  From  these  facts,  the  importance  of  coffee,  either  as  an  alimentary 
article  or  as  taking  the  place,  to  a  certain  extent,  of  aliment,  is  apparent. 

Except  in  persons  who,  from  idiosyncrasy,  are  unpleasantly  affected  by  it,  coffee, 
taken  in  moderate  quantity  and  at  proper  times,  produces  an  agreeable  sense  of  tran- 
quillity and  comfort,  with,  however,  no  disinclination  to  exertion,  either  mental  or 
physical.  Its  immediate  influence  upon  the  system,  which  is  undoubtedly  stimulant,  is 
peculiar  and  is  not  followed  by  reaction  or  unpleasant  after-effects.  Habitual  use  renders 
coffee  almost  a  necessity,  even  in  those  who  are  otherwise  well  nourished  and  subjected  to 
no  extraordinary  mental  or  bodily  strain.  Taken  in  excessive  quantity,  or  in  those  unac- 
customed to  its  use,  particularly  when  taken  at  night,  it  produces  persistent  wakeful- 
ness.  These  effects  are  so  well  known  that  it  is  often  taken  for  the  purpose  of  prevent- 
ing sleep. 

Experimental  researches  have  shown  that  the  use  of  coffee  permits  a  reduction  in 
the  quantity  of  food,  in  workingmen  especially,  much  below  the  standard  which  would 
otherwise  be  necessary  to  maintain  the  organism  in  proper  condition.  In  the  observa- 
tions of  De  Gasparin  upon  the  regimen  of  the  Belgian  miners,  it  was  found  that  the 
addition  of  a  quantity  of  coffee  to  the  daily  ration  enabled  them  to  perform  their  arduous 
labors  on  a  diet  which  was  even  below  that  found  necessary  in  prisons  and  elsewhere 
where  this  article  was  not  employed.  Numerous  experiments  have  shown  that  coffee 
diminishes  the  absolute  quantity  of  urea  discharged  by  the  kidneys.  In  this  respect,  as 
far  as  has  been  ascertained,  the  action  of  coffee  is  like  that  of  alcohol  and  may  reason- 
ably be  supposed  to  retard  disassimilation,  with  the  important  difference  that  it  is 
followed  by  no  unfavorable  after-effects  and  can  be  used  in  moderation  for  an  indefinite 
time  with  advantage. 

A  study  of  the  composition  of  coffee  shows  a  considerable  proportion  of  what  must 
be  considered  as  alimentary  matter.  The  following  is  the  result  of  the  analyses  of  Payen : 

Composition  of  Coffee. 

Cellulose 34-000 

Water  (hygroscopic) 12-000 

Fatty  substances 10  to  13-000 

Glucose,  dextrine,  indeterminate  vegetable  acid 15-500 

Legumine,  caseine,  etc 10-000 

Chlorolignate  of  potash,  and  caffeine 3'5  to  5-000 

Nitrogenized  organic  matter 3'000 

Free  caffeine 0-800 

Concrete,  insoluble  essential  oil O'OOl 

Aromatic  essence,  of  agreeable  odor,  soluble  in  water 0-002 

Mineral  substances;  potash,  magnesia,  lime,  phosphoric,  silicic,  and  sulphuric  acid  and 

chlorine  .  .  6'697 


100-000 


The  above  is  the  composition  of  raw  coffee,  but  the  berry  is  seldom  used  in  that 
form,  being  usually  subjected  to  torrification  before  an  infusion  is  made.     The  roasting 


COFFEE,    TEA,   AND   CHOCOLATE. 


189 


should  be  conducted  slowly  and  gently,  until  the  grains  assume  a  chestnut-brown  color. 
During  this  process,  the  grains  are  considerably  swollen,  but  they  lose  from  sixteen  to 
seventeen  per  cent,  in  weight.  A  peculiar  aromatic  principle  is  also  developed  by  roasting. 
If  the  torrification  be  pushed  too  far,  much  of  the  agreeable  flavor  is  lost,  and  an  acrid 
empyreumatic  principle  is  produced.  An  infusion  of  fifteen  hundred  grains  of  roasted 
and  ground  coffee  in  about  a  quart  of  boiling  water,  the  infusion  made  by  simple  per- 
colation, contains  about  three  hundred  grains  of  the  soluble  principles.  According  to 
Payen,  this  contains  about  one  hundred  and  forty  grains  of  nitrogenized  matters  and 
one  hundred  and  fifty-three  grains  of  fatty,  saccharine,  and  saline  substances.  There  is 
every  reason  to  suppose  that  that  these  principles  are  assimilated;  and  an  infusion  of 
coffee,  with  milk  and  sugar,  presents,  therefore,  a  considerable  variety  and  quantity  of 
alimentary  matter.  The  peculiar  stimulant  effects  of  coffee  are  probably  due  to  the 
caffeine  and  volatile  oil. 

In  the  countries  where  coffee  is  grown,  the  leaves  of  the  shrub,  roasted  and  made  into 
an  infusion,  are  quite  commonly  used.  Their  effects  upon  the  system  are  similar  to  those 
of  coffee,  and  it  is  said  that  the  natives  prefer  the  leaves  to  the  berry. 

Tea. 

An  infusion  of  the  dried  and  prepared  leaves  of  the  tea-plant  is  perhaps  as  common  a 
beverage  as  coffee,  and,  taking  into  consideration  its  immense  consumption  in  China  and 
Japan,  it  is  actually  used  by  a  greater  number  of  persons.  Its  effects  upon  the  system  are 
similar  to  those  of  coffee,  but  are  generally  not  so  marked.  Ordinary  tea,  taken  in 
moderate  quantity,  like  coffee,  relieves  fatigue  and  increases  mental  activity,  but  does  not 
usually  induce  such  persistent  wakefulness. 

It  is  unnecessary  to  describe  all  the  varieties  of  tea  in  common  use.  There  are,  how- 
ever, certain  varieties,  called  green  teas,  which  present  important  differences,  as  regards 
composition  and  physiological  effects,  from  the  black  teas,  which  are  more  commonly 
used.  The  following  is  a  comparative  analysis  of  these  two  varieties  by  Mulder: 

Composition  of  Tea. 


CONSTITUENTS. 

CHINESB. 

JAVANESE. 

Hyson. 

Congou. 

Hyson. 

Congou. 

Volatile  oil  ... 

0-79 

2-22 
0-28 
2-22 
8-56 
17-80 
0-43 
22-80 

23-60 
3-00 
17-08 

0-60 
1-84 

3-64 
7-28 
12-88 
0-46 
19-88 
1-48 
19-12 
2-80 
28-32 

0-98 
3-24 
0-32 
1-64 
12-20 
17'56 
0-60 
21-68 

20-36 
3-64 
18-20 

0-65 
1-28 

2-44 
11-08 
14-80 
0-65 
18-64 
1-64 
18-24 
1-28 
27-00 

Chlorophylle  .  .             ...              .  .        

Resin  

Gum  .        .                      

Tannin  

Theine  

Extractive  .  .                      

Apotheme  

Extract  obtained  by  hydrochloric  acid                       .            

Albumen  .'...'.      

Fibrous  matter  

Salts  included  in  the  above  

98-78 
5-56 

98-30 
5-24 

100-42 
4-76 

97-70 
5-36 

Both  tea  and  coffee  possess  peculiar  organic  principles.  The  active  principle  of  tea  is 
called  theine,  and  the  active  principle  of  coffee,  caffeine.  As  they  are  supposed  to  be 
particularly  active  in  producing  the  peculiar  effects  upon  the  nervous  system  which  are 
characteristic  of  both  tea  and  coffee,  there  is  good  reason  to  suppose  that  they  are  nearly 
identical  in  their  physiological  effects.  Theine  (or  caffeine)  exists  in  greater  proportion 
in  tea  than  in  coffee ;  but,  as  a  rule,  much  more  soluble  matter  is  employed  in  the  prepara- 
tion of  coffee,  which  may  account  for  its  more  marked  effects  upon  the  system. 


190  ALIMENTATION. 

Green  tea,  especially  in  those  unaccustomed  to  its  use,  frequently  produces  nervous 
tremor,  wakefulness,  and  disturbed  sleep — when  sleep  can  be  obtained — palpitations,  and 
other  disturbances  usually  termed  nervous.  In  some  persons  these  unpleasant  effects  may 
be  overcome  by  habit ;  and  many  constantly  use  a  mixture  of  equal  parts  of  black  and 
green  tea  with  no  unpleasant  effects.  The  peculiar  effects  of  green  tea  are  attributed  to 
the  volatile  oil,  which  it  contains  in  great  abundance. 

Tea  is  prepared  for  drinking  by  rapidly  making  an  infusion  of  the  leaves  with  hot 
water.  The  aroma  is  impaired  by  boiling.  The  proportion  generally  used  is  about 
three  hundred  grains  of  tea  to  a  quart  of  water.  The  tea  is  first  covered  with  boiling 
water  and  allowed  to  steep,  or  "  draw,"  for  from  ten  to  fifteen  minutes,  in  a  warm 
place;  boiling  water  is  then  added  in  the  quantity  desired.  Green  tea,  treated  in  this 
way,  yields  about  twenty  per  cent,  of  soluble  matters,  and  black  tea,  about  twenty- 
three  per  cent. 

Chocolate. 

Chocolate  is  made  from  the  seeds  of  the  cocoa-tree,  roasted,  deprived  of  their  husks, 
and  ground  with  warm  rollers  into  a  pasty  mass  with  sugar,  flavoring  substances  being 
sometimes  added.  It  is  then  made  into  cakes,  cut  into  small  pieces  or  scraped  to  a  pow- 
der, and  boiled  with  milk  or  milk  and  water,  when  it  forms  a  thick,  gruel-like  drink, 
which  is  highly  nutritive  and  has  some  of  the  exhilarating  properties  of  coffee  or  tea. 
Beside  containing  a  large  proportion  of  nitrogenized  matter  resembling  albumen,  the 
cocoa-seed  is  particularly  rich  in  fatty  matter  and  contains  a  peculiar  principle,  theobro- 
mine,  analogous  to  caffeine  and  theine,  which  is  supposed  to  possess  similar  physiological 
properties. 

The  following  is  an  analysis  by  Payen  of  the  cocoa-seeds  freed  from  the  husks  but 
not  roasted.  Torrification  has  the  effect  of  developing  the  peculiar  aromatic  principle, 
and  moderating  the  bitterness,  which  is  always  more  or  less  marked : 

Composition  of  Kernels  of  Cocoa. 

Fatty  matter  (cocoa-butter) '• 48  to  50 

Albumen,  fibrin,  and  other  nitrogenized  matter 21  "  20 

Theobromine 4  "     2 

Starch  (with  traces  of  saccharine  matter) 11   "  10 

Cellulose 3  "     2 

Coloring  matter,  aromatic  essence traces. 

Mineral  substances 3  to    4 

Hygroscopic  water 10  "  12 

100     100 

It  is  evident,  from  the  above  table,  that  cocoa  with  milk  and  sugar,  the  ordinary  form 
in  which  chocolate  is  taken,  must  form  a  very  nutritious  mixture.  Taken  with  a  little 
bread,  it  readily  relieves  hunger  and  supplies  nearly  all  the  principles  absolutely  necessary 
to  nutrition.  Its  influence  as  a  stimulant,  supplying  the  place  of  matter  which  is  directly 
assimilated  and  retarding  disassimilation,  is  dependent,  if  it  exist  at  all,  upon  the  theobro- 
mine ;  but  its  stimulating  properties  are  slight  as  compared  with  those  of  coffee  and  tea. 

A  drink  called  cocoa  is  sometimes  made  of  the  seeds  roasted  entire  and  mixed  with  a 
little  starchy  matter,  but  this  is  not  so  delicate  in  flavor  as  chocolate.  A  brown,  mucilagi- 
nous infusion  is  sometimes  made  of  the  husks  (shells).  This  has  a  slight  chocolate-flavor, 
but  it  does  not  possess  the  nutrient  properties  of  the  kernels  of  cocoa. 

Condiments  and  Flavoring  Articles. 

The  refinements  of  modern  cookery  involve  the  use  of  numerous  articles  which  can- 
not be  classed  as  alimentary  principles.  Pepper,  capsicum,  vinegar,  mustard,  spices,  and 


QUANTITY   OF  FOOD   NECESSARY   TO   NUTRITION.  191 

articles  of  this  class,  which  are  so  commonly  used,  with  the  various  compound  sauces 
have  no  decided  influence  on  nutrition,  except  in  so  far  as  they  promote  the  secretion  of 
the,  digestive  fluids.  Common  salt,  however,  as  we  have  already  seen,  is  very  important, 
and  this  has  been  considered  under  the  head  of  inorganic  alimentary  principles.  The 
various  flavoring  seeds  and  leaves,  truffles,  mushrooms,  etc.,  have  no  physiological  impor- 
tance except  as  they  render  articles  of  food  more  palatable. 

Quantity  and   Variety  of  Food  necessary  to  Nutrition. 

The  inferior  animals,  especially  those  not  subjected  to  the  influence  of  man,  regulate 
by  instinct  the  quantity  and  kind  of  food  which  they  consume.  The  same  is  true  of  man 
during  the  earliest  periods  of  his  existence  ;  but,  later  in  life,  the  diet  is  variously  modi- 
fied by  taste,  habit,  climate,  and  what  may  be  termed  artificial  wants.  It  is  usually  a 
safe  rule  to  follow  the  appetite  with  regard  to  quantity,  and  the  tastes,  when  they  are 
not  manifestly  vitiated  or  morbid,  with  regard  to  variety.  The  cravings  of  Nature  indi- 
cate when  to  change  the  form  in  which  nutriment  is  taken ;  and  that  a  sufficient  quan- 
tity has  been  taken  is  manifested  by  a  sense,  not  exactly  of  satiety,  but  of  evident  satis- 
faction of  the  demands  of  the  system.  During  the  first  periods  of  life,  the  supply  must 
be  a  little  in  excess  of  the  actual  loss,  in  order  to  furnish  materials  for  growth  ;  during 
the  later  periods,  the  quantity  of  nitrogenized  matter  assimilated  is  somewhat  less  than 
the  loss  ;  but,  in  adult  age,  the  system  is  maintained  at  a  tolerably  definite  standard  by 
the  assimilation  of  material  about  equal  in  quantity  to  that  which  is  discharged  in  the 
form  of  excretions. 

Although  the  loss  of  substance  by  disassimilation  creates  and  regulates  the  demand  for 
food,  it  is  an  important  fact,  never  to  be  lost  sight  of,  that  the  supply  of  food  has  a  very 
great  influence  upon  the  quantity  of  the  excretions.  As  an  illustration  of  this,  we  may 
take  the  influence  of  food  upon  the  exhalation  of  carbonic  acid ;  and  this  is  but  an 
example  of  what  takes  place  with  regard  to  other  excretions.  The  quantity  of  the 
excretions  is  even  more  strikingly  modified  by  exercise,  which,  within  physiological 
limits,  increases  the  vigor  of  the  system,  provided  the  increased  quantity  of  food  required 
be  supplied. 

While  a  certain  amount  of  waste  of  the  system  is  inevitable,  it  is  a  conservative  pro- 
vision of  Nature,  that,  when  the  supply  of  new  material  is  diminished,  life  is  preserved — 
not,  indeed,  in  all  its  vigor — by  a  corresponding  reduction  in  the  quantity  of  excre- 
tions ;  and,  in  the  same  way,  the  forces  are  retained  after  complete  deprivation  of  food 
much  longer  than  if  disassimilation  proceeded  always  with  the  same  activity. 

As  regards  the  quantity  of  food  necessary  to  maintain  the  system  in  proper  condition, 
it  is  evident  that  this  must  be  greatly  modified  by  habit,  climate,  the  condition  of  the 
muscular  system,  age,  sex,  etc.,  as  well  as  idiosyncrasies. 

The  daily  loss  of  substance  which  must  be  supplied  by  material  introduced  from  with- 
out is  very  great.  A  large  portion  of  this  discharge  takes  place  by  the  lungs,  and  a  con- 
sideration of  the  mode  of  introduction  of  gaseous  principles  to  supply  part  of  this  waste  be- 
longs to  the  subject  of  respiration.  The  most  abundant  discharge  which  is  compensated  by 
absorption  from  the  alimentary  canal  is  that  of  water,  both  in  a  liquid  and  vaporous  con- 
dition. The  entire  quantity  of  water  daily  removed  from  the  system  has  been  estimated 
at  about  four  and  a  half  pounds  ;  and,  assuming  that  there  is  no  evidence  of  the  produc- 
tion of  water  in  the  organism,  an  equal  quantity  must  necessarily  be  introduced.  The 
quantity  which  is  taken  in  the  form  of  drink  varies  with  the  character  of  the  food.  When 
the  solid  articles  contain  a  large  proportion  of  water,  the  quantity  of  drink  may  be  di- 
minished ;  and  it  is  possible,  by  taking  a  large  proportion  of  the  watery  vegetables,  to 
exist  entirely  without  drink.  There  is  no  article  the  consumption  of  which  is  so  much 
a  matter  of  habit  as  water,  any  excess  which  may  be  taken  being  readily  removed  by  the 
kidneys,  skin,  and  lungs.  Prof.  Dalton  estimates  the  daily  quantity  necessary  for  a  full- 
grown,  healthy  male,  at  fifty-two  fluid  ounces,  or  3'38  Ibs.  avoirdupois. 


192  ALIMENTATION. 

The  quantity  of  solid  food  necessary  to  the  proper  nourishment  of  the  body  is  shown 
by  estimating  the  solid  matter  in  the  excretions  ;  and  the  facts  thus  ascertained  corre- 
spond very  closely  with  the  quantity  of  material  which  the  system  lias  been  found,  to 
actually  demand.  The  estimates  of  Pay  en,  the  quantity  of  carbon  and  of  nitrogenized 
matter  in  a  dry  state  being  given,  are  generally  quoted  and  adopted  in  works  on  physiol- 
ogy. According  to  this  observer,  the  following  are  the  daily  losses  of  the  organism  : 


Carton  (o,  its  equiva.ent).  ...  j  ^±?  ><™^  \  4,««4  gr,  (,0,3  o,  a,) 

Nitrogenized  substances  ......     (with  308-68  grs.  of  nit.)      2,006-42  grs.  (  4*58  oz.  av.) 

6,800-96  grs.  (15'51  oz.  av.) 

From  this  he  estimates  that  the  normal  ration,  supposing  the  food  to  consist  of  lean 
meat  and  bread,  is  as  follows  : 

Nitrogenized  substances.  Carbon. 

Bread  .............   15,434       grs.  (35'27  oz.)  =  1,080-38  grs.         and         4,630'2    grs. 

Meat  ..............     4,412-12  grs.  (10*09  oz.)  =     930'05  grs.         and  485'55  grs. 

19,846-12  grs.  (45'36  oz.)        2,010'43  grs.  6,115-75  grs. 

This  daily  ration,  which  is  purely  theoretical,  is  shown  by  actual  observation  to  be 
nearly  correct.  Prof.  Dalton  says  :  "  From  experiments  performed  while  living  on  an 
exclusive  diet  of  bread,  fresh  meat,  and  butter,  with  coffee  and  water  for  drink,  we  have 
found  that  the  entire  quantity  of  food  required  during  twenty-four  hours  by  a  man  in 
full  health  and  taking  free  exercise  in  the  open  air,  is  as  follows  : 

Meat  ..........................................   16    ounces,  or  I'OO  Ib.  avoirdupois. 

Bread  ......  ...................................   19         "         "1-19" 

Butter  or  fat  ...................................     3£       "         "  0'22  "  " 

Water  .........................................   52    fluid  oz.  "  3'38  "  " 

That  is  to  say,  rather  less  than  two  and  a  half  pounds  of  solid  food,  and  rather  over 
three  pints  of  liquid  food." 

Bearing  in  mind  the  great  variations  in  the  nutritive  demands  of  the  system  in  differ- 
ent persons,  it  may  be  stated,  in  general  terms,  that,  in  an  adult  male,  from  ten  to  twelve 
ounces  of  carbon  and  from  four  to  five  ounces  of  nitrogenized  matter  (estimated  dry) 
are  discharged  from  the  organism  and  must  be  replaced  by  the  ingesta  ;  and  this  de- 
mands a  daily  consumption  of  from  two  to  three  pounds  of  solid  food,  the  quantity  of 
food  depending,  of  course,  greatly  on  its  proportion  of  solid,  nutritive  principles. 

It  is  undoubtedly  true  that  the  daily  ration  has  frequently  been  diminished  consider- 
ably below  the  physiological  standard  in  charitable  institutions,  prisons,  etc.  ;  but,  when 
there  is  complete  inactivity  of  body  and  mind,  this  produces  no  other  effect  than  that  of 
slightly  diminishing  the  weight  and  strength.  The  system  then  becomes  reduced  with- 
out any  actual  disease,  and  there  is  simply  a  diminished  capacity  for  labor.  But  in  the 
alimentation  of  large  bodies  of  men  subjected  to  exposure  and  frequently  called  upon 
to  perform  severe  labor,  the  question  of  food  is  of  vital  importance,  and  the  men  collec- 
tively are  like  a  powerful  machine  in  which  a  certain  quantity  of  material  must  be  fur- 
nished in  order  to  produce  the  required  amount  of  force.  This  important  physiological 
fact  is  most  strikingly  exemplified  in  armies  ;  and  the  history  of  the  world  presents  few 
examples  of  warlike  operations  in  which  the  efficiency  of  the  men  has  not  been  impaired 
by  insufficient  food. 

The  influence  of  diet  upon  the  capacity  for  labor  was  well  illustrated  by  a  compari- 
son of  the  amount  of  work  accomplished  by  English  and  French  laborers  in  1841,  on 
a  railroad  from  Paris  to  Kouen.  The  French  laborers  engaged  on  this  work  were 


NECESSITY   OF  A   VARIED  DIET.  193 

able  at  first  to  perform  only  about  two-thirds  of  the  labor  accomplished  by  the  English. 
It  was  suspected  that  this  was  due  to  the  more  substantial  diet  of  the  English,  which 
proved  to  be  the  fact ;  for,  when  the  French  laborers  were  subjected  to  a  similar  regi- 
men, they  were  able  to  accomplish  an  equal  amount  of  work.  In  all  observations  of  this 
kind,  and  they  are  very  numerous,  it  has  been  shown  that  an  animal  diet  is  much  more 
favorable  to  the  development  of  the  physical  forces  than  one  consisting  mainly  of  vege- 
tables. 

Climate  has  an  important  influence  on  the  quantity  of  food  demanded  by  the  system. 
It  is  generally  acknowledged  that  the  consumption  of  all  kinds  of  food  is  greater  in  cold 
than  in  warm  climates,  and  almost  every  one  has  experienced  in  his  own  person  a  con- 
siderable difference  in  the  appetite  at  different  seasons  of  the  year.  Travelers'  accounts 
of  the  quantity  of  food  taken  by  the  natives  of  the  frigid  zone  are  almost  incredible. 
They  speak  of  men  consuming  over  a  hundred  pounds  of  meat  in  a  day ;  and  a  Eussian 
admiral,  Saritcheff1,  mentions  an  instance  of  a  man  who,  in  his  presence,  ate  at  a  single 
meal  a  mess  of  boiled  rice  and  butter  weighing  twenty-eight  pounds.  Although  it  is 
difficult  to  regard  these  statements  with  entire  confidence,  the  general  opinion  that  the 
appetite  is  greater  in  cold  than  in  warm  climates  is  undoubtedly  well  founded.  Dr. 
Hayes,  the  Arctic  explorer,  states,  from  his  personal  observation,  that  the  daily  ration 
of  the  Esquimaux  is  from  twelve  to  fifteen  pounds  of  meat,  about  one-third  of  which  is 
fat.  On  one  occasion  he  saw  an  Esquimau  consume  ten  pounds  of  walrus-flesh  and 
blubber  at  a  single  meal,  which  lasted,  however,  several  hours.  The  continued  low 
temperature  he  found  had  a  remarkable  effect  on  the  tastes  of  his  own  party.  With  the 
thermometer  ranging  from  —60°  to  —70°  Fahr.,  there  was  a  continual  craving  for  a 
strong  animal  diet,  particularly  fatty  substances.  Some  members  of  the  party  were  in 
the  habit  of  drinking  the  contents  of  the  oil-kettle  with  evident  relish. 

Necessity  of  a  Varied  Diet. 

In  considering  the  nutritive  value  of  the  various  alimentary  principles,  the  fact  that 
no  single  one  of  them  is  capable  of  supplying  all  the  material  for  the  regeneration  of  the 
organism  has  frequently  been  mentioned.  The  normal  appetite,  which  is  our  best  guide 
as  regards  the  quantity  and  the  selection  of  food,  indicates  that  a  varied  diet  is  necessary 
to  proper  nutrition.  This  fact  is  also  exemplified  in  a  marked  degree  in  long  voyages 
and  in  the  alimentation  of  armies,  when,  from  necessity  or  otherwise,  the  necessary 
variety  of  aliment  is  not  presented.  Analytical  chemistry  fails  to  show  why  this  change 
in  alimentary  principles  is  necessary,  or  in  what  the  deficiency  in  a  single  kind  of  diet 
consists ;  but  it  is  nevertheless  true  that,  after  the  organic  constituents  of  the  organism 
have  appropriated  the  nutritious  elements  of  particular  kinds  of  food  for  a  certain  time, 
they  lose  the  power  of  inducing  the  changes  necessary  to  proper  nutrition,  and  a  supply 
of  other  material  is  imperatively  demanded.  This  fact  is  particularly  well  marked  when 
the  diet  consists  in  great  part  of  salted  meats,  although  it  is  also  the  case  when  any  single 
variety  of  fresh  meat  is  constantly  used.  After  long  confinement  to  a  diet  restricted  as 
regards  variety,  a  supply  of  other  material,  such  as  fresh  vegetables,  the  organic  acids, 
and  articles  which  are  called  generally  anti-scorbutics,  becomes  indispensable  ;  otherwise, 
the  modifications  in  nutrition  and  in  the  constitution  of  the  blood  incident  to  the  scor- 
butic condition  are  almost  sure  to  be  developed. 

It  is  thus  apparent  that  adequate  quantity  and  proper  quality  of  food  are  not  all 
that  are  required  in  alimentation ;  and  those  who  have  the  responsibility  of  regulating 
the  diet  of  a  large  number  of  persons  must  bear  in  mind  the  fact  that  the  organism  de- 
mands considerable  variety.  Fresh  vegetables,  fruits,  etc.,  should  be  taken  at  the  proper 
seasons.  It  is  almost  always  found,  when  there  is  of  necessity  some  sameness  of  diet, 
that  there  is  a  general  craving  for  particular  articles,  and  these,  if  possible,  should  be 
supplied.  This  was  frequently  exemplified  in  the  late  war.  At  times  when  the  diet  was 
13 


194  ALIMENTATION. 

necessarily  somewhat  monotonous,  there  was  an  almost  universal  craving  for  onions  and 
raw  potatoes,  which  were  found  by  the  surgeons  to  be  excellent  anti-scorbutics. 

With  those  who  supply  their  own  food,  the  question  of  variety  of  diet  generally 
regulates  itself;  and  in  institutions,  it  is  a  good  rule  to  follow  as  far  as  possible  the 
reasonable  tastes  of  the  inmates.  In  individuals,  particularly  females,  it  is  not  uncommon 
to  observe  marked  disorders  in  nutrition  attributable  to  want  of  variety  in  the  diet  as 
well  as  to  an  insufficient  quantity  of  food,  as  a  matter  of  education  or  habit. 

The  physiological  effects  of  a  diet  restricted  to  a  single  alimentary  principle  or  to  a 
few  articles  have  been  pretty  closely  studied  both  in  the  human  subject  and  in  the  inferior 
animals.  Magendie  demonstrated  long  ago  that  animals  subjected  to  a  diet  composed 
exclusively  of  non-nitrogenized  articles  die  in  a  short  time  with  all  the  symptoms  of 
inanition.  The  same  result  followed  in  dogs  confined  to  white  bread  and  water ;  but 
these  animals  lived  very  well  on  the  military  brown  bread,  as  this  contains  a  greater 
variety  of  alimentary  principles.  Facts  of  this  nature  were  multiplied  by  the  "  gelatine 
commission,"  and  the  experiments  were  extended  to  nitrogenized  substances  and  articles 
containing  a  considerable  variety  of  alimentary  principles.  In  these  experiments,  it  was 
shown  that  dogs  could  not  live  on  a  diet  of  pure  musculine,  the  appetite  entirely  failing,  at 
from  the  forty-third  to  the  fifty -fifth  day.  They  were  nourished  perfectly  well  by  gluten, 
which,  as  we  have  seen,  is  composed  of  a  number  of  different  alimentary  principles. 
Among  the  conclusions  arrived  at  by  this  commission,  which  bear  particularly  on  the 
questions  under  consideration,  were  the  following : 

"  Gelatine,  albumen,  fibrin,  taken  separately,  do  not  nourish  animals  except  for  a  very 
limited  period  and  in  a  very  incomplete  manner.  In  general,  these  substances  soon 
excite  an  insurmountable  disgust,  to  the  point  that  animals  prefer  to  die  of  hunger  rather 
than  touch  them. 

"  The  same  principles  artificially  combined  and  rendered  agreeably  sapid  by  season- 
ing are  accepted  more  readily  and  longer  than  if  they  were  isolated,  but  ultimately  they 
have  no  better  influence  on  nutrition,  for  animals  that  take  them,  even  in  considerable 
quantity,  finally  die  with  all  the  signs  of  complete  inanition. 

"  Muscular  flesh,  in  which  gelatine,  albumen,  and  fibrin  are  united  according  to  the 
laws  of  organic  nature,  and  when  they  are  associated  with  other  matters,  such  as  fat> 
salts,  etc.,  suffices,  even  in  very  small  quantity,  for  complete  and  prolonged  nutri- 
tion." 

In  Burdach's  treatise  on  physiology,  is  an  account  of  some  interesting  experiments  by 
Ernest  Burdach  on  rabbits,  showing  the  influence  of  a  restricted  diet  upon  nutrition. 
Three  young  rabbits  from  the  same  litter  were  experimented  upon.  One  was  fed  with 
potato  alone  and  died  on  the  thirteenth  day  with  all  the  appearances  of  inanition. 
Another  fed  on  barley  alone  died  in  the  same  way  during  the  fourth  week.  The  third 
was  fed  alternately  day  by  day  with  potato  and  barley,  for  three  weeks,  and  afterward 
with  potato  and  barley  given  together.  This  one  increased  in  size  and  was  perfectly 
well  nourished. 

In  1769,  long  before  any  of  the  above-mentioned  experiments  were  performed,  Dr. 
Stark,  a  young  English  physiologist,  fell  a  victim  at  an  early  age  to  ill-judged  experiments 
on  his  own  person  on  the  physiological  effects  of  different  kinds  of  food.  He  lived  for 
forty -four  days  on  bread  and  water,  for  twenty-nine  days  on  bread,  sugar,  and  water,  and 
for  twenty-four  days  on  bread,  water,  and  olive-oil ;  until  finally  his  constitution  became 
broken,  and  he  died  from  the  effects  of  his  experiments. 


DIGESTION.  195 


CHAPTER    VII. 

DIGESTION,  MASTICATION,  INSALIVATION,  AND  DEGLUTITION. 

General  arrangement  of  the  digestive  apparatus — Prehension  of  solids  and  liquids — Mastication — Physiological  anat- 
omy of  the  teeth— Anatomy  of  the  maxillary  bones— Temporo-maxillary  articulation— Muscles  of  mastication- 
Muscles  which  depress  the  lower  jaw — Action  of  the  muscles  which  elevate  the  lower  jaw  and  move  it  laterally 
and  antero-posteriorly — Action  of  the  tongue,  lips,  and  cheeks  in  mastication — Summary  of  the  process  of  masti- 
cation— Parotid  saliva — Submaxillary  saliva — Sublingual  saliva — Fluids  from  the  smaller  glands  of  the  mouth, 
tongue,  and  fauces — Mixed  saliva — Quantity  of  saliva — General  properties  and  composition  of  the  saliva — Action 
of  the  saliva  on  starch — Mechanical  functions  of  the  saliva — Deglutition — Physiological  anatomy  of  the  parts  con- 
cerned in  deglutition— Muscles  of  the  pharynx— Muscles  of  the  soft  palate— Mucous  membrane  of  the  pharynx— 
(Esophagus — Mechanism  of  deglutition — First  period  of  deglutition — Second  period  of  deglutition — Protection  of 
the  posterior  nares  during  the  second  period  of  deglutition — Protection  of  the  opening  of  the  larynx — Function 
of  the  epiglottis— Study  of  deglutition  by  autolaryngoscopy— Third  period  of  deglutition— Intermittent  contrac- 
tion of  the  lower  third  of  the  oesophagus — Nature  of  the  movements  of  deglutition — Deglutition  of  air. 

THE  inorganic  alimentary  principles  are,  with  few  exceptions,  introduced  in  the  form 
in  which  they  exist  in  the  blood  and  require  no  preparation  or  change  before  they  are 
absorbed ;  but  the  organic  nitrogenized  principles  are  always  united  with  more  or  less 
matter  possessing  no  nutritive  properties,  from  which  they  must  be  separated,  and,  even 
when  pure,  they  always  undergo  certain  changes  before  they  become  part  of  the  great 
nutritive  fluid.  The  non-nitrogenized  principles  also  undergo  changes  hi  constitution  or 
in  form  preparatory  to  absorption.  With  the  varied  forms  in  which  food  is  taken  by 
different  animals,  we  find  great  differences  in  the  arrangement  of  the  digestive  apparatus, 
from  the  simple  pouch  with  a  single  orifice,  which  constitutes  the  entire  digestive  system 
of  many  of  the  infusorial  animalcules,  to  the  immense  length  of  intestine,  with  its  numer- 
ous glandular  appendages,  found  in  the  mammalia.  In  the  higher  classes  of  animals, 
great  differences  exist  in  the  anatomy  of  the  digestive  organs,  particularly  as  regards  the 
length  and  capacity  of  the  alimentary  canal.  In  the  carnivora,  in  which  the  food  con- 
tains comparatively  little  indigestible  residue,  the  intestine  is  but  three  or  four  times  the 
length  of  the  body  (i.  e.  from  the  mouth  to  the  anus),  and  the  colon,  which  receives  the 
residue  of  digestion,  is  of  small  capacity ;  while  in  the  herbivora,  in  which  the  bulk  of 
food,  compared  with  its  nutritious  principles,  is  enormous,  there  are  frequently  four  dis- 
tinct cavities  to  the  stomach,  and  the  intestine  is  ten,  twelve,  and  in  some  (the  sheep) 
twenty-eight  times  the  length  of.  the  body,  with  a  colon  of  very  large  size.  The  food  of 
man  is  derived  from  both  the  animal  and  the  vegetable  kingdom,  and,  in  relative  length 
and  capacity,  the  alimentary  canal  is  between  that  of  the  carnivora  and  the  herbivora, 
being  from  six  to  seven  times  the  length  of  the  body. 

A  full  meal  probably  occupies  from  two  to  four  hours  in  its  digestion,  this  depending, 
of  course,  upon  the  kind  of  food,  the  fineness  of  its  comminution  by  mastication,  etc.  The 
matters  taken  into  the  stomach  consist  generally  of  all  varieties  of  alimentary  principles, 
and  they  are  exposed  to  certain  mechanical  processes  in  the  mouth  and  alimentary  canal 
and  to  the  action  of  various  secreted  fluids. 

In  the  mouth,  the  food  is  divided,  as  occasion  demands,  by  the  incisor  teeth,  and 
is  then  passed,  by  the  action  of  the  cheeks  and  tongue,  between  the  molars,  where  it  is 
subjected  to  mastication.  During  this  process,  it  is  mixed  with  the  various  fluids  which 
compose  the  saliva  and  becomes  more  or  less  coated  with  the  tenacious  secretions  of  the 
mucous  follicles  of  the  buccal  cavity.  It  is,  or  should  be,  reduced  in  the  mouth  to  a  pul- 
taceous  mass,  with  which  the  saliva,  particularly  that  from  the  parotid  gland,  is  thoroughly 
incorporated.  The  secretion  of  the  submaxillary  and  the  sublingual  gland,  being  more 
viscid,  has  a  tendency  to  coat  the  exterior  of  the  alimentary  bolus. 

By  the  action  of  the  tongue,  the  alimentary  bolus,  after  mastication,  is  passed  back  to 


196 


DIGESTION. 


the  pharynx,  where,  by  the  successive  action  of  the  constrictor  muscles,  it  is  forced 
into  the  oesophagus.  This  tube  leads  from  the  pharynx  to  the  stomach  and  is  provided 
with  thick  muscular  walls,  by  the  contraction  of  which  the  food  is  passed  into  this  cavity, 
which  serves  at  once  as  a  receptacle  for  the  food  and  an  important  active  organ  in 
digestion. 


FIG.  47. — Stomach,  liver,  small  intestine,  etc.    (Sappey.) 

1,  inferior  surface  of  the  liver  ;  2,  round  ligament  of  the  liver;  8,  gall-bladder;  4,  superior  surface  of  the  right 
lobe  of  the  liver ;  5,  diaphragm;  6,  lower  portion  of  the  oesophagus;  7,  stomach;  8,  gastro-hepatic  omentum;  9, 
spleen;  10,  gastro-splenic  omentum ;  11,  duodenum  ;  12,12,  small  intestine;  IS,  caecum;  14,  appendix  ver- 
miformis;  15, 15,  transverse  colon;  16,  sigmoid  flexure  of  the  colon;  17, urinary  bladder. 

The  stomach  is  covered  externally  by  the  general  peritoneal  covering  of  the  abdominal 
organs.  It  is  provided  with  a  mucous  membrane,  which  secretes  the  gastric  juice  and 
absorbs  the  water  with  inorganic  and  other  principles  in  solution.  The  stomach  also  has 
muscular  walls,  composed  of  unstriped  muscular  fibres  arranged  in  two  principal  layers. 
Nearly  all  the  principles  contained  in  food  are  modified  by  the  gastric  juice,  and  some  are 
completely  liquefied  and  absorbed  in  the  stomach.  By  the  action  of  the  gastric  juice,  the 
food,  comminuted  and  incorporated  with  the  fluids  of  the  mouth,  is  farther  reduced  to  a 
pultaceous  mass,  which  was  formerly  called  the  chyme,  the  muscular  movements  of  the 
stomach  turning  it  over  and  over,  so  that  it  becomes  thoroughly  incorporated  with  the 
fluids.  These  movements  have  a  tendency  to  force  the  food,  as  it  becomes  sufficiently 
liquefied,  into  the  small  intestine ;  and  a  collection  of  circular  muscular  fibres,  called 
sometimes  the  pyloric  muscle,  stands  at  the  pylorus  as  a  guard,  allowing  the  liquid  por- 
tions to  pass  gradually  through,  but  sending  back  the  larger  masses  to  be  farther  acted 
upon  in  the  stomach.  By  these  movements,  a  great  portion  of  the  food,  prepared  by  the 


PREHENSION   OF   SOLIDS  AND  LIQUIDS.  197 

action  of  the  stomach,  is  slowly  forced  into  the  small  intestine.  This  tube,  from  fifteen 
to  twenty  feet  in  length,  is  covered  with  peritoneum  and  loosely  hound  to  the  spinal 
column  by  the  mesentery,  which  is  formed  of  the  two  folds  of  the  peritoneum  and  is 
sufficiently  long  to  allow  of  free  movements  of  the  intestines  over  each  other  and  in  the 
abdominal  cavity,  except  the  first  few  inches,  where  it  is  pretty  firmly  attached  to  the 
posterior  abdominal  wall.  The  small  intestine  commences  by  a  dilated  portion  eight  or 
ten  inches  in  length,  called  the  duodenum.  The  remainder  is  divided  into  the  jejunum 
and  the  ileum.  The  former  embraces  the  upper  two-fifths  of  the  intestine,  but  there  is 
no  distinct  line  of  separation  between  it  and  the  ileum.  The  mucous  membrane  lining 
the  small  intestine  is  thick,  provided  with  an  immense  number  of  villi,  and,  particularly 
in  the  upper  portion,  is  thrown  into  transverse  folds,  which  are  called  the  valvulaa  con- 
niventes.  The  valvula3  conniventes  disappear  in  the  lower  part  of  the  ileum.  They  are 
peculiar  to  the  human  subject.  Thickly  set  in  the  upper  part  of  the  duodenum  and  scat- 
tered through  its  lower  portion  and  the  upper  part  of  the  jejunum,  are  small  compound 
follicles  called  the  glands  of  Brunner ;  and  throughout  the  whole  of  the  intestine  are 
simple  follicles,  called  the  follicles  of  Lieberkuhn.  These  glandular  organs  secrete  the 
intestinal  juice.  As  the  food  passes  from  the  stomach  into  the  intestine,  it  imbibes 
the  bile  and  pancreatic  juice,  which  are  poured  into  the  duodenum,  as  well  as  the  intes- 
tinal juice. 

Between  the  mucous  membrane  of  the  small  intestine  and  the  peritoneum,  are  two 
layers  of  unstriped  muscular  fibres,  by  the  progressive  peristaltic  action  of  which  the 
food  is  passed  slowly  on  toward  the  large  intestine.  The  alimentary  principles,  liquefied 
and  prepared  by  digestion,  are  gradually  absorbed  by  the  blood-vessels  of  the  intestinal 
mucous  membrane  and  by  the  lacteals. 

The  indigestible  residue  of  the  food  is  passed  by  peristaltic  action  into  the  large  intes- 
tine. This  portion  of  the  alimentary  canal  is  from  four  to  six  feet  in  length  ;  and,  like 
the  small  intestine,  it  has  a  peritoneal,  mucous,  and  muscular  coat.  Under  ordinary  con- 
ditions the  large  intestine  is  not  concerned  in  digestion.  It  simply  retains  the  residue  of 
food,  with  certain  excrementitious  substances,  until  its  contents  are  expelled  by  the  act 
of  def 03 cation. 

Prehension  of  Solids  and  Liquids. 

The  different  modes  of  prehension  form  a  very  interesting  part  of  the  physiology  of 
digestion  in  the  inferior  animals;  but,  in  the  human  subject,  the  process  is  so  simple  and 
well  known  that  it  demands  nothing  more  than  a  passing  mention.  The  mechanism  of 
sucking  in  the  infant  and  of  drinking  is  a  little  more  complicated.  In  sucking,  the  lips 
are  closed  around  the  nipple,  the  velum  pendulum  palati  is  applied  to  the  back  of  the 
tongue  so  as  to  close  the  buccal  cavity  posteriorly,  and  the  tongue,  acting  as  a  piston, 
produces  a  tendency  to  a  vacuum  in  the  mouth,  by  which  the  liquids  are  drawn  in  with 
considerable  force.  This  may  be  done  independently  of  the  act  of  respiration,  which  is 
necessarily  arrested  only  during  deglutition ;  for  the  mere  act  of  suction  has  never  any 
thing  to  do  with  the  condition  of  the  thoracic  walls.  The  mechanism  of  drinking  from 
a  vessel  is  essentially  the  same.  The  vessel  is  inclined  so  that  the  lips  are  kept  covered 
with  the  liquid  and  are  closed  around  the  edge.  By  a  gentle,  sucking  action  the  liquid  is 
then  introduced.  This  is  the  ordinary  mechanism  of  drinking;  but  sometimes  the  head 
is  thrown  back  and  the  liquid  is  poured  into  the  mouth,  as  in  "tossing  off"  the  contents 
of  a  small  vessel  as  a  wine-glass.  - 

Mastication. 

In  the  human  subject,  mechanical  division  of  food  in  the  mouth  is  neither  so  com- 
pletely and  laboriously  effected  as  in  the  herbivora,  particularly  the  ruminants,  nor  is  the 
process  so  rapid  and  imperfect  as  in  the  carnivora.  In  order  that  digestion  may  take 
place  in  a  perfectly  natural  manner,  it  is  necessary  that  the  food,  as  it  is  received  into 
the  stomach,  should  be  so  far  comminuted  and  incorporated  with  the  fluids  of  the  mouth 


198 


DIGESTION. 


as  to  be  readily  acted  upon  by  the  gastric  juice ;  otherwise  stomach-digestion  is  pro- 
longed and  difficult.  Non-observance  of  this  physiological  law  is  a  frequent  cause  of 
what  is  generally  called  dyspepsia.  In  animals  that  do  not  masticate,  as  in  some  which 
live  exclusively  on  flesh,  the  process  of  stomach-digestion  is  much  more  prolonged  than  in 
the  human  subject,  even  when  the  diet  is  the  same ;  and  it  is  found  that  while  man  must, 
as  a  rule,  take  food  two  or  three  times  in  the  day,  the  carnivorous  animals  are  generally 
best  nourished  when  food,  in  proper  quantity,  is  taken  but  once  in  the  twenty-four  hours. 
In  the  carnivora,  the  proportionate  quantity  of  food  is  greater  than  in  man,  and  diges- 
tion is  much  more  prolonged. 

The  comparative  anatomy  of  the  organs  of  mastication  makes  it  evident  that  the 
human  race  is  designed  to  live  on  a  mixed  diet ;  but  experience  has  shown  that  man  can 
be  nourished  for  an  indefinite  period  on  a  diet  composed  exclusively  of  either  animal 
or  vegetable  principles. 

Physiological  Anatomy  of  the  Organs  of  Mastication. — In  the  adult,  each  jaw  is  pro- 
vided with  sixteen  teeth,  all  of  which  are  about  equally  well  developed.  The  canines, 
so  largely  developed  in  the  carnivora  but  which  are  rudimentary  in  the  herbivora,  and 


FIG.  ^.—Permanent  teetJi.    (Le  Bon.) 
The  external  portions  of  the  maxillary  bones  have  been  removed  to  show  the  roots  of  the  teeth. 

the  incisors  and  molars,  so  perfectly  developed  in  the  herbivora,  are,  in  man,  of  nearly 
the  same  length.  Each  tooth  presents  for  anatomical  description  a  crown,  a  neck,  and 
a  root,  or  fang.  The  crown  is  that  portion  which  is  entirely  uncovered  by  the  gums ; 
the  root  is  that  portion  embedded  in  the  alveolar  cavities  of  the  maxillary  bones ;  and 


MASTICATION.  199 

the  neck  is  the  portion,  sometimes  slightly  constricted,  situated  between  the  crown  and 
the  root,  covered  by  the  edge  of  the  gum.  Thin  sections  of  the  teeth  show  that  they 
are  composed  of  several  distinct  structures. 

Enamel  of  the  Teeth.— The  crown  is  covered  by  the  enamel,  which  is  by  far  the 
hardest  structure  in  the  economy.  This  is  white  and  glistening  and  is  thickest  on  the 
lower  portion  of  the  tooth,  especially  over  the  surfaces  which,  from  being  opposed  to 
each  other  on  either  jaw,  are  most  exposed  to  wear.  It  here  exists  in  several  concentric 
layers.  The  incrustation  of  enamel  becomes  gradually  thinner  toward  the  neck,  where 
it  ceases.  Microscopical  examination  shows  that  the  enamel  is  made  up  of  pentagonal  or 
hexagonal  rods,  one  end  resting  upon  the  subjacent  structure,  and  the  other,  when  there 
exists  but  a  single  layer  of  enamel,  terminating  just  beneath  the  cuticle  of  the  teeth. 
The  hardness  of  the  enamel  varies  in  different  persons.  In  some  it  is  so  soft  that  in  mid- 
dle life  it  becomes  worn  away  from  the  opposing  surfaces,  and  occasionally  the  teeth  are 
worn  down  almost  to  the  gums ;  while  in  others  the  enamel  remains  over  the  crown  of 
the  tooth  even  in  old  age. 

The  exposed  surfaces  of  the  teeth  are  still  farther  protected  by  a  membrane,  from 
g^¥oi7  ^0  f  S6oo  °f  an  mcn  in  thickness,  closely  adherent  to  the  enamel,  called  the  cuticle 
of  the  enamel.  This  delicate  membrane  may  be  demonstrated  in  thin  sections  of  young 
teeth  by  the  addition,  under  the  microscope,  of  weak  hydrochloric  acid.  The  acid  at- 
tacks the  enamel,  producing  little  bubbles  of  gas  which  press  out  the  membrane  from 
the  edge  of  the  preparation  and  thus  render  it  apparent.  The  cuticle  presents  a  strong 
resistance  to  reagents  and  is  undoubtedly  very  useful  in  protecting  the  teeth  from  the 
action  of  acids  which  may  find  their  way  into  the  mouth. 

Dentine. — The  largest  portion  of  the  teeth  is  composed  of  a  peculiar  structure  called 
dentine,  or  ivory.  In  many  respects,  particularly  in  its  composition,  this  resembles 
bone  ;  but  it  is  much  harder,  and  does  not  possess  the  lacunae  and  canaliculi  which  are 
characteristic  of  the  true  osseous  structure.  The  dentine  bounds  and  encloses  the  cen- 
tral cavity  of  the  tooth,  extending  in  the  crown  to  the  enamel  and  in  the  root,  to  the 
cement.  It  is  formed  of  a  homogeneous  fundamental  substance,  which  is  penetrated 
by  an  immense  number  of  canals  radiating  from  the  pulp-cavity  toward  the  exterior. 
These  are  called  the  dentinal  tubules  or  canals.  They  are  from  ^-^5-0  to  12^06  of  an 
inch  in  diameter,  with  walls  of  a  thickness  a  little  less  than  their  caliber.  Their  course 
is  slightly  wavy  or  spiral.  Commencing  at  the  pulp-cavity,  into  which  these  canals  open 
by  innumerable  little  orifices,  they  are  found  to  branch  and  occasionally  anastomose, 
their  communications  and  branches  becoming  more  numerous  as  they  approach  the  ex- 
ternal surface  of  the  tooth.  The  canals  of  largest  diameter  are  found  next  the  pulp-cav- 
ity, and  they  become  smaller  as  they  branch.  The  structure  which  forms  the  walls  of 
these  tubules  is  somewhat  denser  than  the  intermediate  portion,  which  is  sometimes 
called  the  inter-tubular  substance  of  the  dentine  ;  but,  in  some  portions  of  the  tooth,  the 
tubules  are  so  numerous  that  their  walls  touch  each  other,  and  there  is,  therefore,  no 
inter-tubular  substance.  Near  their  origin  and  near  the  peripheral  terminations  of  the 
dentinal  tubules,  are  sometimes  found  solid  globular  masses  of  dentine,  called  dentine- 
globules,  which  irregularly  bound  triangular  or  stellate  cavities  of  very  variable  size. 
These  cavities  have  been  considered  as  lacunae,  like  the  lacunae  of  true  bone ;  but  this 
view  is  not  held  by  the  best  and  most  recent  observers.  Sometimes  these  cavities  are 
very  numerous  and  form  regular  zones  near  the  peripheral  termination  of  the  tubules. 
The  dentine  is  sometimes  marked  by  concentric  lines,  indicating  a  lamellated  arrange- 
ment. In  the  natural  condition,  the  dentinal  tubules  are  filled  with  a  clear  liquid,  which 
penetrates  from  the  vascular  structures  in  the  pulp-cavity. 

Cement. — Covering  the  dentine  of  the  root,  is  a  thin  layer  of  true  bony  structure, 
called  the  cement,  or  crusta  petrosa.  This  is  thickest  at  the  summit  and  the  deeper  por- 
tions of  the  root,  where  it  is  sometimes  lamellated,  and  it  becomes  thinner  near  the  neck. 
It  finally  becomes  continuous  with  the  enamel  of  the  crown,  so  that  the  dentine  is  every- 


200 


DIGESTION. 


where  completely  covered.  The  cement  contains  true  bone-lacunae  and  canaliculi,  and,  in 
very  old  teeth,  a  few  Haversian  canals,  except  near  the  neck,  where  the  layer  is  very  thin. 
It  is  closely  adherent  to  the  dentine  and  to  the  periosteum  lining  the  alveolar  cavities. 

Pulp- Cavity. —In  the  interior  of  each  tooth,  extending  from  the  apex  of  the  root  or 
roots  into  the  crown,  is  the  pulp-cavity,  which  contains  a  collection  of  minute  blood- 
vessels and  nervous  filaments,  held  together  by  longitudinal  fibres  of  white  fibrous  tis- 
sue. This  is  the  only  portion  of  the  tooth  endowed  with  sensibility.  Its  blood-vessels 
and  nerves  penetrate  by  a  little  orifice  at  the  extremity  of  the  root. 

The  dentine  and  enamel  of  the  teeth  must  be  regarded  as  perfected  structures ;  for, 
when  the  second  or  permanent  teeth  are  lost,  they  are  never  reproduced,  and  when  these 
parts  are  invaded  by  wear  or  by  decay,  they  are  incapable  of  regeneration.  The  integrity 

of  the  pulp,  even,  is  not  necessary  to  the 
stability  of  the  teeth ;  for  examples  are 
numerous  in  which  the  pulp  loses  its 
vitality  from  various  causes,  and  yet  the 
tooth  remains  and  is  as  serviceable  as 
ever,  being  only  discolored  by  the  decom- 
position of  the  structures  in  the  pulp- 
cavity,  which  can  neither  escape  nor 
become  absorbed. 

The  descriptive  anatomy  of  the  teeth 
in  the  human  subject  shows  how  well 
calculated  they  are  to  perform  their  va- 
ried functions,  and  how  admirably  they 
are  adapted  to  a  diet  composed  of  articles 
derived  from  both  the  animal  and  the 
vegetable  kingdom.  The  thirty-two  per- 
manent teeth  are  divided  as  follows  : 

1.  Eight  incisors,  four  in  each  jaw, 
called  the  central  and  lateral  incisors. 

2.  Four  canines,  or  cuspidati,  two  in 
each  jaw,  just  back  of  the  incisors.    The 
upper  canines  are  sometimes  called  the 
eye-teeth,  and  the  lower  canines,  the 
stomach-teeth. 

3.  Eight  bicuspid — the  small,  or  false 
molars — just  back  of  the  canines ;  four 
in  each  jaw. 

4.  Twelve   molars,    or  multicuspid, 
situated  just  back  of  the  bicuspid;  six 
in  each  jaw. 

The  incisors  are  wedge-shaped,  flat- 
tened antero-posteriorly,  and  bevelled 
at  the  expense  of  the  posterior  face,  giv- 
ing them  a  sharp,  cutting  edge,  which  is 
sometimes  perfectly  straight  but  is  gen- 


FIG.  49.—  Tooth  of  the  cat,  in  situ.    fWaldeyer.) 
1,  enamel;  2,  dentine;  3,  cement;  4,  periosteum  of  the  alveo- 
lar cavity ;  5,  lower  jaw ;  6,  pulp-cavity. 


erally  more  or  less  rounded.  The  upper 
incisors  are  generally  larger  and  strong- 
er than  the  lower.  In  the  upper  jaw  the  central  incisors  are  larger  than  the  lateral ; 
while  in  the  lower  jaw  the  lateral  incisors  are  larger  than  the  central.  Each  of  the  incisors 
has  but  a  single  root.  The  special  function  of  the  incisor  teeth  is  to  divide  the  food  as  it 
is  taken  into  the  mouth.  The  permanent  incisors  make  their  appearance  from  the  sev- 
enth to  the  eighth  year. 


MASTICATION.  201 

The  canines  are  more  conical  and  pointed  than  the  incisors  and  have  longer  and 
larger  roots,  especially  those  in  the  upper  jaw.  Their  roots  are  single.  They  are  used 
to  some  extent,  in  connection  with  the  incisors,  in  dividing  the  food ;  but  they  have  no 
prominent  function  in  tearing  the  food,  as  in  the  carnivora,  in  which  they  are  extraor- 
dinarily developed.  The  permanent  canines  make  their  appearance  from  the  eleventh 
to  the  twelfth  year. 

The  bicuspid  teeth  are  shorter  and  thicker  than  the  canines.  Their  opposed  surfaces 
are  rather  broad  and  are  marked  by  two  eminences.  The  upper  bicuspids  are  somewhat 
larger  than  the  lower.  The  roots  are  single,  but  in  the  upper  jaw  they  are  slightly  bifur- 
cated at  their  extremities.  They  are  used,  with  the  true  molars,  in  triturating  the  food. 
The  permanent  bicuspids  make  their  appearance  from  the  ninth  to  the  tenth  year. 

The  molar  teeth,  called  respectively — counting  from  before  backward — the  first,  sec- 
ond, and  third  molars,  are  the  largest  of  all  and  are,  par  excellence,  the  teeth  used  in 
mastication.  Their  form  is  that  of  a  cube,  rounded  laterally  and  provided  with  four  or 
five  eminences  on  their  opposed  surfaces.  The  first  molars  are  the  largest.  They  have 
generally  three  roots  in  the  upper  jaw  and  two  in  the  lower,  although  they  sometimes 
have  four  or  even  five  roots.  The  second  molars  are  but  little  smaller  than  the  first 
and  resemble  them  in  nearly  every  particular.  The  third  molars,  called  frequently  the 
wisdom-teeth,  are  much  smaller  than  the  others  and  are  by  no  means  so  useful  in  masti- 
cation. In  the  upper  jaw  the  root  is  grooved  or  imperfectly  divided  into  three  branches ; 
but  in  the  lower  jaw  it  generally  has  two  distinct  branches.  The  first  molars  are  the 
first  of  the  permanent  teeth,  making  their  appearance  between  the  sixth  and  the  seventh 
year.  The  second  molars  appear  from  the  twelfth  to  the  thirteenth  year ;  and  the  third 
molars,  from  the  seventeenth  to  the  twenty-first  year,  and  sometimes  even  much  later. 
In  some  instances  the  third  molars  are  never  developed. 

The  upper  jaw  has  ordinarily  a  somewhat  longer  and  broader  arch  than  the  lower  ; 
so  that  when  the  mouth  is  closed  the  teeth  are  not  brought  into  exact  apposition,  but  the 
upper  teeth  overlap  the  lower  teeth  both  in  front  and  laterally.  The  lower  teeth  are  all 
somewhat  smaller  than  the  corresponding  teeth 
in  the  upper  jaw  and  generally  make  their  ap- 
pearance a  little  earlier. 

The  physiological  anatomy  of  the  maxillary 
bones  and  of  the  temporo-maxillary  articulation 
necessarily  precedes  the  study  of  the  muscles  of 
mastication  and  the  mechanism  of  their  action. 

The  superior  maxillary  bones  are  immovably 
articulated  with  the  other  bones  of  the  head  and 
do  not  usually  take  any  active  part  in  mastica- 
tion ;  but  their  inferior  borders,  with  the  upper 
teeth  embedded  in  the  alveolar  cavities,  present 

~       i         f  .  i  •  i       ,,.-,.  FIG-  50.— Inferior  maxilla.    (Sappey.) 

hxed  surfaces  against  which  the  food  is  pressed      3    body.  2  ramus;  3<  8ymphysl8.  4,  ^ 
by  the  action  of  the  muscles  which  move  the  lower  f°ssa;.  5>  mental  foramen ;  6,  attachment  of 

the  digastric  muscle,  7,  depression  at  the 
jaw.  site  of  the  facial  artery ;  8,  angle;  9,  attach- 

The  inferior  maxilla  is  a  single  bone.  Its 
body  is  horizontal,  of  a  horseshoe  shape,  and,  in 

the    alveolar   cavities    in    its    Superior   border,  are  muscle;  1 5,  alveolar  border ;  i, incisor  teeth: 

.,,,,..  c,  canine  teeth ;  b,  bicuspid  teeth ;  m,  molars. 

embedded  the  lower  teeth.      Below  the  teeth, 

both  externally  and  internally,  are  surfaces  for  the  attachments  of  the  muscles  concerned 

in  the  various  movements  of  the  jaw,  and  for  one  of  the  muscles  of  the  tongue. 

Behind  the  body  of  the  inferior  maxilla,  on  either  side,  is  a  vertical  portion  called  the 
ramus.  In  the  adult,  this  forms  nearly  a  right  angle  with  the  body,  making  what  is  called 
the  angle  of  the  jaw.  Superiorly,  the  ramus  terminates  in  two  processes,  separated  by  a 
deep  groove  called  the  sigmoid  notch.  The  posterior  process  is  the  condyle,  or  condyloid 


DIGESTION. 

process,  the  anatomy  of  which  will  be  considered  farther  on  in  treating  of  the  temporo- 
maxillary  articulation.  The  anterior  process,  called  the  coronoid  process,  is  for  the  at- 
tachment of  the  temporal  muscle,  one  of  the  most  powerful  of  the  muscles  of  mastication. 
The  greater  portion  of  the  external  surface  of  the  ramus,  extending  down  to  the  angle,  is 
for  the  attachment  of  the  masseter  muscle.  The  internal  surface  of  the  ramus  gives  at- 
tachment to  several  muscles ;  viz.,  the  external  pterygoid,  attached  to  the  neck  just  be- 
low the  condyle,  the  temporal,  the  attachment  to  the  coronoid  process  being  much 
more  extensive  on  the  internal  than  on  the  external  surface,  and  the  internal  pterygoid, 
which  has  its  attachment  at  the  angle. 

T emp  or  o- Maxillary  Articulation. — The  various  classes  of  mammalia  present  great 
differences  in  the  temporo-maxillary  articulation,  differences  which  indicate,  to  a  great 
extent,  their  natural  diet.  In  the  carnivora,  the  long  diameter  of  the  condyle  is  trans- 
verse, and  it  is  so  firmly  embedded  in  the  deep  glenoid  cavity  of  the  temporal  bone  as 
to  admit  of  extended  movements  in  but  one  direction.  In  these  animals,  lateral  and 
antero-posterior  sliding  movements  of  the  jaw  are  impossible,  and  there  is  very  little 
mastication  of  the  food.  In  the  rodentia,  the  long  diameter  of  the  condyle  is  antero- 
posterior,  the  peculiar  gnawing  movements  in  these  animals  requiring  a  considerable 
sliding  movement  of  the  lower  jaw  in  this  direction.  In  the  herbivora,  particularly  the 
ruminants,  the  condyle  is  small  and  slightly  concave  instead  of  convex  as  in  most  other 
animals.  It  moves  on  a  large  projecting  surface  on  the  temporal  bone,  and  the  entire 
jaw  is  capable  of  remarkably  extensive  lateral  movements. 

In  man,  the  articulation  of  the  lower  jaw  with  the  temporal  bone  is  such  as  to  allow, 
to  a  considerable  extent,  of  an  antero-posterior  sliding  movement  and  a  lateral  move- 
ment, in  addition  to  the  ordinary  movements  of  elevation  and  depression.  The  condy- 
loid  process  is  convex,  with  an  ovoid  surface,  the  general  direction  of  its  long  diameter 
being  transverse  and  slightly  oblique  from  without  inward  and  from  before  backward. 
This  process  is  received  into  a  cavity  of  corresponding  shape  in  the  temporal  bone,  called 
the  glenoid  fossa,  which  is  bounded,  anteriorly,  by  a  rounded  eminence  (eminentia  articu- 
laris),  the  uses  of  which  will  be  more  rally  described  in  connection  with  the  movements 
of  the  jaw. 

Between  the  condyle  of  the  lower  jaw  and  the  glenoid  fossa,  is  an  oblong,  inter-ar- 
ticular disk  of  fibro-cartilage.  This  disk  is  thicker  at  the  edges  than  in  the  centre.  It  is 
pliable  and  so  situated  that  when  the  lower  jaw  is  projected  forward,  making  the  lower 
teeth  project  beyond  the  upper,  it  is  applied  to  the  convex  surface  of  the  eminentia  ar- 
ticularis  and  presents  a  concave  surface  for  articulation  with  the  condyle.  One  of  the 
uses  of  this  cartilage  is  to  constantly  present  a  proper  articulating  surface  upon  the  artic- 
ular eminence  and  thus  admit  of  the  antero-posterior  sliding  movement  of  the  lower  jaw. 
It  is  also  important  in  the  lateral  movements  of  the  jaw,  in  which  one  of  the  condyles 
remains  in  the  glenoid  cavity  and  the  other  is  projected,  so  that  the  bone  undergoes  a 
slight  rotation. 

Muscles  of  Mastication. — To  the  lower  jaw  are  attached  certain  muscles,  by  which  it  is 
depressed,  and  others  by  which  it  is  elevated,  projected  forward  and  drawn  backward, 
and  moved  from  side  to  side.  The  following  are  the  principal  muscles  concerned  in  the 
production  of  these  varied  movements : 

Muscles  of  Mastication. 

Muscles  which  depress  the  lower  jaw. 
Muscle.  Attachments. 

Digastric. .  < Mastoid  process  of  the  temporal   bone  —  Lower 

border  of  the  inferior  maxilla  near  the  sym- 
physis,  with  its  central  tendon  held  to  the  side 
of  the  body  of  the  hyoid  bone. 


MASTICATION.  203 

Muscle.  Attachments. 

Mylo-hyoid Body  of  the  hyoid  bone — Mylo-hyoid  ridge  on  the 

internal  surface  of  the  inferior  maxilla. 

Genio-hyoid Body  of  the  hyoid  bone — Inferior  genial  tubercle 

on  the  inner  surface  of  the  inferior  maxilla  near 
the  symphysis. 

Platysma  myoides Clavicle,  acromion,  and  fascia — Anterior  half  of 

the  body  of  the  inferior  maxilla  near  the  in- 
ferior border. 

Muscles  which  elevate  the  lower  jaw  and  move  it  laterally  and  antero-posteriorly. 

Temporal Temporal  fossa — Coronoid  process  of  the  inferior 

maxilla. 

Masseter Malar  process  of  the  superior  maxilla,  lower  border 

and  internal  surface  of  the  zygomatic  arch — 
Surface  of  the  ramus  of  the  inferior  maxilla. 

Internal  pterygoid Pterygoid  fossa — Inner  side  of  the  ramus  and  angle 

of  the  inferior  maxilla. 

External  pterygoid Pterygoid  ridge  of  the  sphenoid,  the  surface  be- 
tween it  and  the  pterygoid  process,  external 
pterygoid  plate,  and  the  tuberosity  of  the  palate 
and  the  superior  maxillary  bone — Inner  surface 
of  the  neck  of  the  condyle  of  the  inferior 
maxilla  and  the  inter-articular  fibro-cartilage. 

Action  of  the  Muscles  which  depress  the  Lower  Jaw. — The  most  important  of  these 
muscles  have  for  their  fixed  point  of  action  the  hyoid  bone,  which,  under  these  circum- 
stances, is  fixed  by  the  muscles  which  extend  from  it  to  the  upper  part  of  the  chest. 
The  central  tendon  of  the  digastric,  as  it  perforates  the  stylo-hyoid,  is  connected  with  the 
hyoid  bone  by  a  loop  of  fibrous  tissue ;  and,  acting  from  this  bone  as  the  fixed  point,  the 
anterior  belly  must  of  necessity  tend  to  depress  the  jaw.  The  attachments  of  the  raylo- 
hyoid  and  the  genio-hyoid  render  their  action  in  depressing  the  jaw  sufficiently  evident, 
which  is  also  the  case  with  the  platysma  myoides,  acting  from  its  attachments  to  the 
upper  part  of  the  thorax. 

It  has  been  a  disputed  question  whether  the  upper  jaw  does  or  does  not  participate 
in  the  act  of  opening  the  mouth.  That  depression  of  the  lower  jaw  is  the  main  action 
in  ordinary  mastication  is  sufficiently  evident;  but  it  is  possible,  by  fixing  the  lower  jaw, 
to  perform  the  acts  of  mastication — laboriously  and  imperfectly  it  is  true — by  movements 
of  the  upper  jaw.  In  ordinary  mastication,  however,  the  upper  jaw  undergoes  a  slight 
movement  of  elevation  in  opening  the  mouth ;  and  this  becomes  somewhat  exaggerated 
when  the  mouth  is  opened  to  the  fullest  possible  extent. 

Action  of  the  Muscles  which  elevate  the  Lower  Jaw  and  move  it  laterally  and  antero- 
posteriorly. — The  temporal,  masseter,  and  internal  pterygoid  muscles  are  chiefly  con- 
cerned in  the  simple  act  of  closing  the  jaws.  As  this  is  almost  the  only  movement  of 
mastication  in  many  of  the  carnivora,  in  this  class  of  animals  these  muscles  are  most 
largely  developed.  Their  anatomy  alone  gives  a  sufficiently  clear  idea  of  their  mode  of 
action  ;  and  their  immense  power,  even  in  the  human  subject,  is  explained  by  the  number 
of  their  fibres,  by  the  attachments  of  many  of  these  fibres  to  the  strong  aponeuroses  by 
which  they  are  covered,  and  the  fact  that  the  distance  from  their  origin  to  their  insertion 
is  very  short. 

The  attachments  of  the  internal  and  external  pterygoids  are  such  that,  by  their  alter- 
nate action  on  either  side,  the  jaw  may  be  moved  laterally,  as  their  points  of  origin  are 
situated  in  front  of  and  internal  to  the  temporo-maxillary  articulation.  The  articulation 
of  the  lower  jaw  is  of  such  a  nature  that,  in  its  lateral  movements,  the  condyles  themselves 


204  DIGESTION. 

cannot  be  sufficiently  displaced  from  side  to  side,  but,  with  the  condyle  on  one  side  fixed 
or  moved  slightly  backward,  the  other  may  be  brought  forward  against  the  articular 
eminence,  producing  a  movement  of  rotation.  The  pterygoid  muscles  are  largely  de- 
veloped in  the  herbivora,  in  which  the  lateral  movements  of  mastication  are  so  important. 
The  above  explanation  of  the  lateral  movements  of  the  jaw  presupposes  the  possi- 
bility of  movements  in  an  antero-posterior  direction.  Movements  in  a  forward  direction, 
so  as  to  make  the  lower  teeth  project  beyond  the  upper,  are  effected  by  the  pterygoids, 
the  oblique  fibres  of  the  masseter,  and  the  anterior  fibres  of  the  temporal.  By  the 
combined  action  of  the  posterior  fibres  of  the  temporal,  the  digastric,  mylo-hyoid,  and 
genio-hyoid,  the  jaw  is  brought  back  to  its  position.  By  the  same  action  it  may  also  be 
drawn  back  slightly  from  its  normal  position  while  at  rest. 

Action  of  the  Tongue,  Lips,  and  Cheeks,  in  Mastication. —  Experiments  on  living 
animals  and  phenomena  observed  in  cases  of  lesions  of  the  nervous  system  in  the  human 
subject  have  fully  demonstrated  the  importance  of  the  tongue  and  cheeks  in  mastication. 
The  following  observations  of  Panizza  on  the  effects  of  section  of  both  hypoglossal 
nerves  in  dogs  show  the  importance  of  the  tongue,  both  in  mastication  and  deglutition : 
"  After  the  section  of  the  hypoglossal  the  movements  of  the  tongue  cease  immediately, 
but  the  general  sensibility  of  that  organ  and  the  taste  was  not  less  marked.  Indeed,  if 
milk,  or  bread  moistened  in  the  liquid,  were  presented  to  the  dog,  he  made  ineffectual 
efforts  to  lap  and  to  masticate,  moving  the  head  and  the  lower  jaw ;  the  tongue,  when 
displaced,  remaining  in  the  same  position,  and  even  when  a  bolus  of  meat  or  bread  was 
put  on  its  anterior  surface,  it  was  found  for  a  long  time  after  in  the  same  place,  which 
proves  that  section  of  the  hypoglossals  destroys  not  only  the  movements  necessary  to 
mastication,  but  also  those  of  deglutition."  We  have  lately  had  occasion  to  verify  most 
of  these  observations  in  a  dog  in  which  both  sublingual  nerves  were  divided.  The  experi- 
ment, however,  was  made  chiefly  with  reference  to  the  action  of  the  tongue  in  deglutition. 

Section  of  the  facial  nerves  is  now  a  common  physiological  experiment.  Opera- 
tions of  this  kind  and  cases  of  facial  palsy,  which  are  not  uncommon  in  the  human 
subject,  show  that  when  the  cheek  is  paralyzed  the  food  accumulates  between  it  and  the 
teeth,  producing  great  inconvenience.  In  animals,  like  the  herbivora,  which  use  the  lips 
and  tongue  extensively  in  the  prehension  of  food,  division  of  the  facial  and  hypoglossal 
nerves  interferes  materially  with  this  function. 

The  tongue  is  a  muscular  organ  which,  by  virtue  of  the  complex  arrangement  of  its 
fibres,  is  capable  of  a  great  variety  of  important  movements.  By  the  action  of  what  are 
called  the  extrinsic  muscles  of  the  tongue,  the  organ  is  moved  in  various  directions,  while 
the  intrinsic  muscles  are  capable  at  the  same  time  of  producing  many  changes  in  its  form. 
For  example,  by  the  action  of  those  fibres  of  the  genio-hyo-glossal  muscles  which  are 
attached  to  the  chin  and  the  posterior  part  of  the  tongue,  the  whole  organ  is  carried  for- 
ward and  may  be  protruded  to  a  considerable  extent.  At  the  same  time  the  whole  length 
of  the  muscles  may  act  upon  the  middle  line  of  the  tongue,  to  which  they  are  attached, 
and  depress  the  centre  so  as  to  render  it  concave  from  side  to  side ;  or  the  transverse 
fibres  of  the  tongue  may  act  so  as  to  make  it  longer  and  narrower.  The  tongue  is  drawn 
into  the  mouth  by  the  action  of  the  anterior  fibres  of  the  genio-hyo-glossus  on  either  side, 
and  may  be  still  farther  shortened  by  the  contraction  of  the  stylo-glossus  and  the  interior 
fibres  of  the  hyo-glossus.  The  general  action  of  the  hyo-glossus,  on  either  side,  is  to 
draw  down  the  sides  of  the  tongue  and  make  it  convex  from  side  to  side.  The  stylo- 
glossus  and  the  palato-glossns  draw  the  back  of  the  tongue  upward  and  backward  toward 
the  pharnyx,  and  they  are  thus  useful  in  the  first  processes  of  deglutition.  By  the  com- 
bined and  varied  actions  of  these  and  other  muscles,  the  tongue  is  made  to  perform  the 
numerous  movements  which  take  place  in  connection  with  phonation,  suction,  mastica- 
tion, deglutition,  etc. 

The  varied  and  complicated  movements  of  the  tongue  during  mastication  are  not 


SALIVA. 


205 


easily  described.  After  solid  food  is  taken  into  the  mouth,  the  tongue  prevents  its  escape 
from  between  the  teeth,  and,  by  its  constant  movements,  rolls  the  alimentary  bolus  over 
and  over  and  passes  it  at  times  from  one  side  to  the  other,  so  that  the  food  may  undergo 
thorough  trituration.  Aside  from  the  functions  of  the  tongue  as  an  organ  of  taste,  its  sur- 
face is  endowed  with  peculiar  sensibility  as  regards  the  consistence,  size,  and  form  of  dif- 
ferent articles  ;  and  this  property  is  undoubtedly  important  in  determining  when  mastica- 
tion is  completed,  although  the  thoroughness  with  which  mastication  is  accomplished  is 
very  much  influenced  by  habit. 

Tonic  contraction  of  the  orbicularis  oris  is  necessary  to  keep  the  fluids  within  the  mouth 
during  repose  ;  and  this  muscle  is  sometimes  brought  into  action  when  the  mouth  is  very 
full,  to  assist  in  keeping  the  food  between  the  teeth.  This  latter  function,  however,  is 
mainly  performed  by  the  buccinator  ;  the  action  of  which  is  to  press  the  food  between 
the  teeth  and  keep  it  in  place  during  mastication,  assisting,  from  time  to  time,  in  turning 
the  alimentary  bolus  so  as  to  subject  new  portions  to  trituration. 

The  process  of  mastication  is  regulated  to  a  very  great  extent  by  the  exquisite  sensi- 
bility of  the  teeth  to  the  impressions  of  hard  and  soft  substances.  It  is  only  necessary 
to  call  attention  to  the  ease  and  certainty  with  which  we  recognize  the  presence  and  the 
consistence  of  the  smallest  substance  between  the  teeth,  in  order  to  appreciate  the 
advantages  of  this  tactile  sense  in  mastication.  It  is  in  this  way,  mainly,  that  we  be- 
come aware  that  the  process  of  mastication  is  completed  ;  and  it  is  this  sense  which  ad- 
monishes us  instantly  of  the  presence  of  bodies  too  hard  for  mastication,  which,  if  allowed 
to  remain  in  the  mouth,  might  seriously  injure  the  teeth. 

One  of  the  most  important  of  the  digestive  processes  which  take  place  in  the  mouth 
is  the  incorporation  of  the  saliva  with  the  food,  or  insalivation.  Not  only  has  the  saliva 
a  mechanical  function,  assisting  to  reduce  the  food  to  the  proper  form  and  consistence  to 
be  easily  swallowed,  but  it  seems  to  be 
necessary  to  the  proper  performance  of 
the  subsequent  processes  of  digestion 
and  is  concerned  to  a  certain  extent  in 
the  transformation  of  starch  into  sugar. 
That  the  saliva  is  necessary  to  digestion 
is  proven  by  the  grave  effects  upon  the 
general  function  of  nutrition  which  fol- 
low its  loss  in  any  considerable  quan- 
tity. This  occasionally  occurs  from  the 
habit  of  excessive  spitting  or  as  the  re- 
sult of  salivary  fistula.  It  becomes  im- 
portant, therefore,  to  study  the  physical 
and  chemical  properties  of  the  saliva, 
the  sources  from  which  it  is  derived, 
and  its  mechanical  and  chemical  func- 
tions in  digestion. 

Saliva. 

The  fluid  which  is  mixed  with  the 

food  in  mastication,  which  moistens  the 

i  ,,  ,  ,  , 

mucous  membrane  of  the  mouth,  and 

which  may  be  collected  at  anv  time  in 

...     ,      ,,        .        , 
smaJl  quantity  by  the  Simple  act  OI  spu- 

tatirm    iq  pnmnn^prl  nf  thp  «AnrAfinn«  r»f 
tation,  IS 

a  considerable  number  and  variety  of 

glands.      The  most  important  of  these  are  the  parotid,  submaxillary,  and  sublingual, 

which  are  usually  called  the  salivary  glands.     In  addition,  we  have  the  labial  and  buccal 


FIG.  51.  —  Salivary  glands.    (Le  Bon.) 
^parotid.  ^duct  of  st,J.  ^  submayAttary  ;  s,  »uUin- 

gual;  6,  mylo-hyoid  muscle;  7,  lingual  branch  of  the  fifth 
nerve;  8,  duct  of  Wharton  ;  9,  digastric  muscle;  10. 
sterno-mastoid  muscle;  11,  external  jugular  vein;  12,  iacial 
vein'  13'  temporal  vein;  14,  15,  internal  jugular  vein  ;  16, 
branch  Qf  the  ceryica]  plexu3  .  17(  subiinguai  nerve. 


206  DIGESTION. 

glands,  the  follicular  glands  of  the  tongue  and  general  mucous  surface,  and  certain 
glandular  structures  in  the  mucous  membrane  of  the  pharynx.  The  liquid  which  he- 
comes  more  or  less  incorporated  with  the  food  before  it  descends  to  the  stomach,  and 
which  must  be  considered  as  the  digestive  fluid  of  the  mouth,  is  known  as  the  mixed 
saliva ;  but  the  study  of  the  composition  and  properties  of  this  fluid  as  a  whole  should  be 
prefaced  by  a  consideration  of  the  different  secretions  of  which  it  is  composed. 

The  salivary  glands  belong  to  the  variety  of  glands  called  racemose.  They  closely 
resemble  the  other  glands  belonging  to  this  class,  and  their  structure  will  be  considered 
more  particularly  under  the  head  of  secretion. 

Parotid  Saliva. — The  parotid  is  the  largest  of  the  three  salivary  glands.  It  is  sit- 
uated below  and  in  front  of  the  ear  and  opens  by  the  duct  of  Steno  into  the  mouth,  at 
about  the  middle  of  the  cheek.  The  papilla  which  marks  the  orifice  of  the  duct  is 
situated  opposite  the  second  large  molar  tooth  of  the  upper  jaw. 

Numerous  opportunities  have  presented  themselves,  in  cases  of  salivary  fistula,  for  the 
study  of  the  properties  of  the  pure  parotid  saliva  in  the  human  subject ;  and  the  situation 
of  the  duct  of  Steno,  in  the  herbivora  especially,  is  such  that  this  fluid  can  easily  be  ob- 
tained by  operations  on  the  inferior  animals.  Prof.  J.  C.  Dalton  has  obtained  the  pure 
parotid  saliva  from  the  human  subject  by  simply  introducing  a  silver  tube,  of  from  -fa 
to  ^  of  an  inch  in  diameter,  into  the  duct  by  its  opening  into  the  mouth. 

The  following  facts  with  regard  to  the  properties  of  the  parotid  saliva  observed  by 
Dalton  are  given  in  his  own  words,  in  a  communication  kindly  made  in  answer  to  certain 
inquiries : 

"  On  the  28th  of  July,  1863,  I  obtained,  from  a  strong,  healthy  man,  about  two 
drachms  of  the  mixed  saliva  of  the  mouth,  by  causing  him  to  hold  in  his  mouth  for  a 
short  time  a  clean  glass  stopper,  and  collecting  the  secretion  as  it  was  discharged. 

"  One  hour  afterward  I  obtained,  from  the  same  man,  four  drachms  of  pure  parotid 
saliva,  by  introducing  a  long  silver  canula  into  the  natural  orifice  of  Steno's  duct,  on  the 
left  side,  and  collecting  the  saliva  as  it  flowed  from  the  outer  extremity  of  the  canula. 

"  The  two  kinds  of  saliva  compared  as  follows : 

"  Both  were  distinctly  alkaline  in  reaction ;  the  parotid  saliva  rather  the  more  so. 

"  The  parotid  saliva  was  rather  clear  and  watery  in  appearance ;  the  saliva  of  the  mouth 
was  quite  opaline,  with  admixture  of  buccal  epithelium,  but  became  clear  on  filtration. 

"  The  parotid  saliva  was  rendered  turbid  by  the  action  of  heat,  and  by  the  addition  of 
nitric  acid,  as  well  as  sulphate  of  soda  in  excess ;  but  not  by  sulphate  of  magnesia,  nor  by 
ferro-cyanide  of  potassium  with  acetic  acid. 

"  The  saliva  of  the  mouth,  filtered  clear,  became  turbid  by  heat  and  by  nitric  acid, 
but  showed  no  precipitate  by  either  sulphate  of  soda  or  sulphate  of  magnesia  in  excess. 
There  was  also  a  slight  precipitate  on  the  addition  of  pure  acetic  acid,  which  did  not  take 
place  in  the  parotid  saliva, 

"  The  parotid  saliva  showed  no  traces  of  sulpho-cyanogen  on  the  addition  of  the  per- 
chloride  of  iron,  but  they  were  distinctly  marked  in  the  buccal  saliva. 

"  On  mixing  the  two  kinds  of  saliva  with  boiled  starch,  and  keeping  the  mixture  at 
the  temperature  of  100°  Fahr.,  sugar  was  present  in  both  specimens  at  the  end  of  five 
minutes.  There  was  no  marked  difference  between  them  in  this  respect. 

"  While  making  some  similar  experiments  to  the  above  on  a  previous  patient,  in  April, 
1863,  I  found  that  with  the  canula  introduced  into  Steno's  duct,  not  only  was  the  dis- 
charge of  parotid  saliva  increased  by  the  mastication  of  food,  but  that  it  ran  from  the 
canula  very  much  faster  than  in  a  state  of  rest,  whenever  the  patient  smiled,  spoke,  or 
moved  his  lips  or  cheeks  in  any  way." 

The  organic  matter  of  the  parotid  saliva  is  coagulable  by  heat  (212°  Fahr.),  alcohol, 
and  the  strong  mineral  acids.  Dalton  found,  in  the  human  saliva,  that  it  was  also  coagu- 
lated by  an  excess  of  sulphate  of  soda ;  but  Bernard  states  that,  in  the  parotid  saliva  of 


SALIVA. 


207 


the  horse,  the  organic  matter  passed  through  .a  mixture  of  sulphate  of  soda  but  was 
coagulated  by  sulphate  of  magnesia.  Almost  all  physiologists  agree  that  this  organic 
matter  is  not  identical  in  its  properties  with  albumen  or'  with  the  peculiar  principle 
described  by  Miahle  in  the  mixed  saliva,  under  the  name  of  animal  diastase. 

A  compound  of  sulpho-cyanogen  is  now  generally  acknowledged  to  be  a  constant 
constituent  of  the  parotid  saliva.  This  cannot  be  recognized  by  the  ordinary  tests  in  the 
fresh  saliva  taken  from  the  duct  of  Steno,  but  in  the  clear,  filtered  fluid  which  passes 
after  the  precipitation  of  the  organic  matter,  there  is  always  a  distinct  red  color  on  the 
addition  of  the  persulphate  of  iron.  As  this  reaction  is  more  marked  in  the  mixed  saliva,, 
the  methods  by  which  the  presence  of  a  sulpho-cyanide  is  to  be  demonstrated  will  be 
considered  in  connection  with  that  fluid. 

In  the  human  subject,  the  parotid  secretion  is  more  abundant  than  that  of  any  other 
of  the  salivary  glands.  The  entire  quantity  in  the  twenty-four  hours  has  not  been 
directly  estimated ;  but  Prof.  Dalton  found  that,  during  mastication,  the  quantity  secreted 
in  twenty  minutes  on  one  side  was  127'5  grains,  and  on  the  other  side,  374'4  grains. 

A  curious  fact  with  regard  to  the  influence  of  mastication  upon  the  flow  from  the 
parotids  was  observed  by  Colin  in  the  horse,  ass,  and  ox.  He  found  that,  when  mastica- 
tion was  performed  on  one  side  of  the  mouth,  the  flow  from  the  gland  on  that  side  was 
greatly  increased,  exceeding  by  several  times  the  quantity  produced  upon  the  opposite 
side.  This  fact  was  confirmed  by  Dalton,  as  already  indicated,  in  the  human  subject. 

The  flow  of  saliva  from  the  parotid  takes  place  with  greatly-increased  activity  during 
the  process  of  mastication.  The  orifice  of  the  parotid  duct  is  so  situated  that  the  fluid  is 
poured  directly  upon  the  mass  of  food  as  it  is  undergoing  trituration  by  the  teeth ;  and, 
as  the  secretion  is  more  abundant  on  the  side  on  which  mastication  is  going  on,  and  the 
consistence  of  the  fluid  is  such  as  to  enable  it  to  mix  readily  with  the  food,  the  function 
of  this  gland  is  supposed  to  be  particularly  connected  with  mastication.  This  is  undoubt- 
edly the  fact ;  although  its  flow  is  not  absolutely  confined  to  the  period  of  mastication, 
but  continues,  in  small  quantity,  during  the  intervals.  Its  quantity  is  regulated  some- 
what by  the  character  of  the  food,  being  much  greater  when  the  articles  taken  into  the 
mouth  are  dry  than  when  they  contain  considerable  moisture.  There  is  a  great  difference 
in  different  animals  as  regards  the  stimulation  of  the  salivary  glands  by  substances  intro- 
duced into  the  mouth.  In  the  human  subject,  the  stimulus  produced  by  sapid  sub- 
stances will  sometimes  induce  a  great  increase  in  the  flow  of  the  parotid  saliva.  Mits- 
cherlich  and  Eberle  observed  this  in  persons  suffering  from  salivary  fistula  and  noted, 
furthermore,  that  the  mere  sight  or  odor  of  food  produced  the  same  effect. 

The  supposition,  which  has  been  entertained  by  some  authors,  that  the  flow  from  the 
parotid  is  dependent  upon  the  mechanical  pressure  of  the  muscles  or  of  the  condyle  of 
the  lower  jaw  during  mastication  has  no  foundation  in  fact.  It  is  now  well  established 
that  one  of  the  indispensable  conditions  in  the  production  of  a  secretion  is  a  great  increase 
in  the  quantity  of  blood  circulating  in  the  gland,  and  that  the  vascular  supply  is  regulated 
through  the  nervous  system.  The  fact  that  an  alternation  in  the  parotid  secretion  accom- 
panies an  alternation  in  the  act  of  mastication  is  also  an  argument  against  this  mechanical 
theory  ;  for  it  is  not  to  be  supposed  that  during  mastication  there  exists  a  difference  in 
the  pressure  of  the  muscles  or  of  the  condyles  on  the  two  sides,  corresponding  with  the 
differences  which  have  been  noted  in  the  secretion  from  the  glands  on  either  side.  In 
the  horse  and  in  the  dog,  it  has  been  observed  that  the  secretion  of  the  parotids  is  com- 
pletely arrested  during  the  deglutition  of  liquids,  while  the  flow  from  the  other  salivary 
glands  is  not  affected. 

To  sum  up  the  functions  of  the  parotid  saliva — aside  from  any  chemical  action  which 
it  may  have  upon  the  food,  which  will  be  fully  considered  in  connection  with  the  mixed 
saliva — it  evidently  has  an  important  mechanical  office.  It  is  discharged  in  large  quan- 
tity during  the  entire  process  of  mastication  and  is  poured  into  the  mouth  in  such  a 
manner  as  to  become  of  necessity  thoroughly  incorporated  with  the  food.  Its  function 


208  DIGESTION. 

is  chiefly,  although  not  exclusively,  connected  with  mastication  and  indirectly,  with  deglu- 
tition ;  for  it  is  only  by  becoming  incorporated  with  this  saliva,  that  the  deglutition  of 
dry,  pulverulent  substances  is  rendered  possible.  Facts  in  comparative  physiology,  show- 
ing a  great  development  of  the  parotids  in  animals  that  masticate  very  thoroughly,  par- 
ticularly the  ruminants,  a  slight  development  in  those  that  masticate  but  slightly,  and  the 
absence  of  these  glands  in  animals  that  do  not  masticate  at  all,  are  additional  arguments 
in  favor  of  these  views. 

Submaxillary  Saliva. — In  the  human  subject,  the  submaxillary  is  the  second  of  the 
salivary  glands  in  point  of  size.  Its  minute  structure  is  the  same  as  that  of  the  parotid. 
As  its  name  implies,  it  is  situated  below  the  inferior  maxillary  bone.  It  is  in  the  anterior 
part  of  what  is  known  as  the  submaxillary  triangle  of  the  neck.  Its  excretory  duct,  called 
sometimes  the  duct  of  Wharton,  is  about  two  inches  in  length  and  passes  from  the 
gland,  beneath  the  tongue,  to  open  by  a  small  papilla  by  the  side  of  the  frenum.  This 
gland  is  relatively  very  small  in  the  herbivora  but  is  largely  developed  in  the  carnivora, 
in  the  latter  being  larger  than  the  parotid. 

The  pure  submaxillary  saliva  presents  many  important  points  of  difference  from  the 
secretion  of  the  parotid.  It  was  first  studied  as  a  distinct  fluid  by  Bernard.  It  may  be 
obtained  by  exposing  the  duct  and  introducing  a  fine  silver  tube,  when,  on  the  introduc- 
tion of  any  sapid  substance  into  the  mouth,  the  secretion  will  flow  in  large,  pearly  drops. 
Bernard  found  this  variety  of  saliva  much  more  viscid  than  the  parotid  secretion.  It  is 
perfectly  clear,  and,  on  cooling,  frequently  becomes  of  a  gelatinous  consistence.  Its 
organic  matter  is  not  coagulable  by  heat.  In  the  dog,  it  is  rather  more  strongly  alkaline 
than  the  parotid  saliva.  According  to  Bernard,  it  does  not  contain  the  sulpho-cyanide 
of  potassium. 

The  submaxillary  gland  pours  out  its  secretion  in  greatest  abundance  when  sapid  sub- 
stances are  introduced  into  the  mouth.  In  the  solipeds  and  ruminants,  Colin  has  ob- 
served that  the  quantity  of  submaxillary  saliva  secreted  is  much  increased  during  eating; 
but,  unlike  the  parotids,  the  secretion  does  not  alternate  on  the  two  sides  with  the  alter- 
nation in  mastication.  He  has  found,  in  all  the  domestic  animals,  that  the  flow  is  greatly 
influenced  by  the  degree  of  sapidity  of  the  food.  Although  sapid  articles  induce  an 
abundant  secretion  from  the  submaxillary  glands,  they  also  produce  an  increase  in  the 
secretions  from  the  parotids  and  sublinguals ;  and,  on  the  other  hand,  movements  of 
mastication  increase  somewhat  the  flow  from  the  submaxillaries,  and  these  glands  secrete 
a  certain  amount  of  fluid  during  the  intervals  of  digestion.  The  viscid  consistence  of  the 
submaxillary  saliva  renders  it  less  capable  of  penetrating  the  alimentary  mass  during 
mastication  than  the  parotid  secretion,  so  that  it  remains  chiefly  near  the  surface  of  the 
alimentary  mass. 

Sullingual  Saliva. — The  sublinguals,  the  smallest  of  the  salivary  glands,  are  situated 
beneath  the  tongue,  on  either  side  of  the  frenum.  In  minute  structure  they  resemble  the 
parotid  and  the  submaxillary  glands.  Each  gland  has  a  number  of  excretory  ducts,  from 
eight  to  twenty,  which  open  into  the  mouth  by  the  side  of  the  frenum ;  and  one  of  the 
ducts,  larger  than  the  others,  joins  the  duct  of  the  submaxillary  gland  near  its  termina- 
tion in  the  mouth. 

The  secretion  of  the  sublingual  glands  is  more  viscid  even  than  the  submaxillary  sali- 
va, but  it  differs  in  the  fact  that  it  does  not  gelatinize  on  cooling.  It  is  so  glutinous  that 
it  adheres  strongly  to  any  vessel  and  flows  with  difficulty  from  a  tube  introduced  into 
the  duct.  Like  the  secretion  from  the  other  salivary  glands,  its  reaction  is  distinctly  al- 
kaline. Its  organic  matter  is  not  coagulable  by  heat,  acids,  or  the  metallic  salts.  Ac- 
cording to  Bernard,  after  desiccation  it  is  redissolved  by  water  and  its  viscid  properties 
are  then  restored. 

In  accordance  with  the  view  entertained  by  Bernard  concerning  the  function  of  this 


SALIVA. 

variety  of  saliva  and  its  special  connection  with  deglutition,  it  is  supposed  to  be  secreted 
immediately  before  and  during  the  act  of  swallowing.  The  experiments  which  are  ad- 
vanced in  support  of  this  view  are  mostly  those  in  which  a  tube  was  fixed  in  each  of  the 
three  salivary  ducts  in  a  dog,  when  the  animal  was  caused  to  make  movements  of  the 
jaw,  movements  of  deglutition,  and  at  the  same  time  the  gustatory  nerves  were  stimu- 
lated by  the  introduction  of  vinegar  into  the  mouth.  In  an  experiment  of  this  kind  it 
was  observed  that  fluid  was  secreted  by  all  the  glands,  but  in  unequal  proportions;  "the 
submaxillary  saliva  flowed  very  abundantly,  the  parotid  saliva  much  less,  and  the  sublin- 
gual  saliva  flowed  very  feebly."  Although  the  animal  made  movements  of  mastication, 
experienced  a  gustatory  impression,  and  made  movements  of  deglutition,  it  is  by  no  means 
evident  from  this  observation,  or  from  others  reported  by  Bernard,  that  the  flow  of  the 
sublingual  saliva  had  any  special  connection  with  the  act  of  deglutition.  The  observa- 
tions of  Colin  on  this  subject  show  that,  in  the  domestic  ruminants,  there  is  a  constant 
flow  of  the  sublingual  saliva  during  the  time  occupied  in  eating. 

It  has  been  experimentally  demonstrated  that  the  sublingual  glands  may  be  excited 
to  secretion  by  impressions  made  by  sapid  substances  upon  the  nerves  of  taste,  although 
the  flow  is  always  less  than  from  the  submaxillary  glands.  The  great  viscidity  of  the 
sublingual  saliva  renders  it  less  easily  mixed  with  the  alimentary  bolus  than  the  secre- 
tions from  the  parotid  or  the  submaxillary  glands. 

Fluids  from  the  Smaller  Glands  of  the  Mouth,  Tongue,  and  Pharynx. — Beneath  the 
mucous  membrane  of  the  inner  surface  of  the  lips,  are  small,  rounded,  glandular  bodies, 
opening  by  numerous  ducts  into  the  buccal  cavity,  called  the  labial  glands ;  and,  in  the 
submucous  tissue  of  the  cheeks,  are  similar  bodies,  called  the  buccal  glands.  The  latter 
are  somewhat  smaller  than  the  labial  glands.  Two  or  three  of  the  buccal  glands  are  of 
considerable  size  and  have  ducts  opening  opposite  the  last  molar  tooth.  These  are 
sometimes  distinguished  as  the  molar  glands.  There  are  also  a  few  small  glands  in  the 
mucous  membrane  of  the  posterior  half  of  the  hard  palate ;  but  the  glands  on  the  under 
surface  of  the  soft  palate  are  larger  and  more  numerous  and  here  form  a  continuous 
layer.  The  glands  of  the  tongue  (lingual  glands)  are  situated  beneath  the  mucous  mem- 
brane, mainly  on  the  posterior  third  of  the  dorsum ;  but  a  few  are  found  at  the  edges 
and  the  tip.  All  of  these  are  small,  racemose  glands,  similar  in  structure  to  those  which 
have  been  called  the  true  salivary  glands.  In  addition  to  these  structures,  the  mucous 
membrane  of  the  tongue  is  provided  with  a  number  of  simple  and  compound  follicular 
glands,  which  extend  over  its  entire  surface  but  are  most  abundant  at  the  posterior  por- 
tion, behind  the  circumvallate  papilla?. 

In  the  pharynx  and  the  posterior  portion  of  the  buccal  cavity,  are  found  the  pharyn- 
geal  glands  and  the  tonsils.  In  the  pharynx,  particularly  the  upper  portion,  racemose 
glands,  like  those  found  in  the  mouth,  exist  in  large  numbers.  The  mucous  membrane  is 
provided,  also,  with  numerous  simple  and  compound  mucous  follicles.  The  tonsils,  situ- 
ated on  either  side  of  the  fauces  between  the  pillars  of  the  soft  palate,  consist  of  an  ag- 
gregation of  compound  follicular  glands,  held  together  by  fibrous  tissue.  The  number  of 
glands  entering  into  the  composition  of  each  tonsil  is  from  ten  to  twenty. 

The  secretion  from  the  glands  and  follicles  above  enumerated  cannot  be  obtained,  in 
the  human  subject,  unmixed  with  the  fluids  from  the  true  salivary  glands.  It  has  been 
obtained,  however,  in  small  quantity,  from  the  inferior  animals,  after  ligature  of  all  the 
salivary  ducts.  This  secretion  is  simply  a  grayish,  viscid  mucus,  containing  a  number  of 
leucocytes  and  desquamated  epithelial  scales.  It  is  this  which  gives  the  turbid  and  opa- 
line character  to  the  mixed  saliva,  as  the  secretions  of  the  various  salivary  glands  are  all 
perfectly  transparent.  The  fluid  from  these  glands  in  the  mouth  is  mixed  with  the  sali- 
vary secretions ;  and  that  from  the  posterior  part  of  the  tongue,  the  tonsils,  and  the 
pharyngeal  glands  passes  down  to  the  stomach  with  the  alimentary  bolus.  This  secretion, 
consequently,  forms  a  constant  and  essential  part  of  the  mixed  saliva. 
14 


210  DIGESTION. 

Mixed  Saliva. — Although  the  study  of  the  distinct  secretions  discharged  into  the 
mouth  possesses  considerable  physiological  interest  and  importance,  it  is  only  the  fluid 
resulting  from  a  union  of  them  all,  which  can  properly  be  considered  in  connection  with 
the  general  process  of  insalivation.  In  man  it  is  necessary  that  the  cavity  of  the  mouth 
should  be  continually  moistened,  if  for  nothing  else,  to  keep  the  parts  in  a  proper  condi- 
tion for  phonation.  A  little  reflection  will  make  it  apparent  that  the  flow,  from  some  of 
the  glands  at  least,  is  constant,  and  that,  from  time  to  time,  a  certain  quantity  of  saliva 
is  swallowed.  This  is  even  more  marked  in  some  of  the  inferior  animals,  as  the  rumi- 
nants. The  discharge  of  fluid  into  the  mouth,  though  diminished,  is  not  arrested  during 
sleep.  In  the  review  of  the  different  kinds  of  saliva,  it  has  been  seen  that  the  flow  from 
none  of  the  glands  is  absolutely  intermittent ;  unless  it  be  so  occasionally  from  the  pa- 
rotid, the  secreting  function  of  which  is  most  powerfully  influenced  by  the  act  of  masti- 
cation and  the  impression  of  sapid  substances. 

Upon  the  introduction  of  food,  the  quantity  of  saliva  is  enormously  increased  ;  and 
we  have  already  noted  the  influence  of  the  sight,  odor,  and  occasionally  even  the  thought 
of  agreeable  articles.  Many  persons  present  a  marked  increase  in  the  flow  of  saliva  at 
the  sight  of  a  lemon ;  and  we  are  all  familiar,  in  a  general  way,  with  the  impressions 
which  bring  "  water  into  the  mouth."  The  experiments  of  Frerichs  on  dogs  with  gas- 
tric fistulae,  and  the  observations  of  Gardner  on  a  patient  with  a  wound  in  the  oesopha- 
gus, have  demonstrated  that  the  flow  of  saliva  may  be  excited  by  the  stimulus  of  food 
introduced  directly  into  the  stomach  without  passing  through  the  mouth. 

Quantity  of  Saliva. — It  is  not  easy  to  estimate,  in  the  human  subject,  the  entire 
quantity  of  saliva  secreted  in  the  twenty-four  hours  ;  and  great  variations  in  this  regard 
undoubtedly  exist  in  different  persons,  and  even  in  the  same  individual  at  different  times. 
An  approximate  estimate  may  be  arrived  at  by  noting,  as  nearly  as  possible,  the  average 
quantity  secreted  during  the  intervals  of  digestion  and  adding  to  it  the  quantity  ab- 
sorbed by  the  various  articles  of  food.  Some  of  the  earlier  physiologists  investigated 
this  subject  with  much  patience.  Be"rard  quotes  the  experiments  of  Siebold,  who  col- 
lected the  saliva  by  holding  the  mouth  open  with  the  head  inclined,  receiving  the 
fluid  in  a  vessel  as  fast  as  it  was  secreted.  An  estimate  of  this  kind  can  only  be  ap- 
proximative, and  those  made  by  Dalton  are  apparently  the  most  satisfactory.  This  ob- 
server found  that  he  was  able  to  collect  from  the  mouth,  without  any  artificial  stimulus, 
about  five  hundred  and  fifty-six  grains  of  saliva  per  hour ;  and  he  also  found  that  wheaten 
bread  gained  in  mastication  fifty-five  per  cent.,  and  lean  meat,  forty-eight  per  cent,  in 
weight.  Assuming  the  daily  allowance  of  bread  to  be  nineteen  ounces  and  the  allow- 
ance of  meat  to  be  sixteen  ounces,  and  estimating  the  quantity  of  saliva  secreted  during 
twenty-two  hours  of  interval,  the  entire  quantity  in  twenty-four  hours  would  amount  to 
20,164  grains,  or  a  little  less  than  three  pounds  avoirdupois,  of  which  rather  more  than 
one-half  is  secreted  during  the  intervals  of  eating. 

Eemembering  that  the  quantity  of  saliva  must  necessarily  be  subject  to  great  varia- 
tions, this  estimate  may  be  taken  as  giving  a  sufficiently  close  approximation  of  the  quan- 
tity of  saliva  ordinarily  secreted.  It  must  be  borne  in  mind,  however,  with  reference 
to  this  and  the  other  digestive  secretions,  that  this  immense  quantity  of  fluid  is  at  no 
one  time  removed  from  the  blood,  but  is  reabsorbed  nearly  as  fast  as  secreted,  and  that, 
normally,  none  of  it  is  discharged  from  the  organism. 

General  Properties  and  Composition  of  Saliva. — The  mixed  fluid  taken  from  the 
mouth  is  colorless,  somewhat  opaline,  frothy,  and  slightly  viscid.  It  generally  has  a  faint 
and  somewhat  disagreeable  odor  very  soon  after  it  is  discharged.  If  it  be  allowed  to 
stand,  it  deposits  a  whitish  sediment,  composed  mainly  of  desquamated  epithelial  scales, 
with  a  few  leucocytes,  leaving  the  supernatant  fluid  tolerably  clear.  Its  specific  gravity 
is  variable,  ranging  from  1004  to  1006  or  1008.  Its  reaction  is  almost  constantly  alka- 


COMPOSITION   OF  HUMAN  SALIVA.  211 

line  ;  although,  under  certain  abnormal  conditions  of  the  system,  it  has  occasionally  been 
observed  to  be  neutral,  and  sometimes,  though  rarely,  acid.  We  have  occasionally  ob- 
served a  distinctly  acid  taste  in  the  saliva  after  very  severe,  prolonged,  and  exhausting 
muscular  exertion.  The  saliva  becomes  slightly  opalescent  by  boiling  or  on  the  addition 
of  the  strong  acids.  The  addition  of  absolute  alcohol  produces  an  abundant  whitish, 
flocculent  precipitate.  Almost  invariably  the  mixed  saliva  presents  a  more  or  less  intense 
blood -red  tint  on  the  addition  of  a  per-salt  of  iron,  which  is  due  to  the  presence  of  a 
sulpho-cyanide  either  of  potassium  or  sodium. 

A  number  of  analyses  of  the  human  mixed  saliva  have  been  made  by  different  chem- 
ists, presenting,  however,  few  differences,  except  in  the  relative  proportions  of  water 
and  solid  ingredients,  which  are  probably  quite  variable.  One  of  the  most  reliable  of 
these  analyses  is  the  following,  by  Bidder  and  Schmidt : 

Composition  of  Human  Saliva. 

Water 995'16 

Epithelium 1'62 

Soluble  organic  matter 1-34 

Sulpho  cyanide  of  potassium 0*06 

Phosphates  of  soda,  lime,  and  magnesia 0*98 

Chloride  of  potassium    ) 
Chloride  of  sodium        \  ' 

1,000-00 

The  organic  principle  of  the  mixed  saliva,  called  by  Berzelius  ptyaline,  is  not  affected 
by  heat  or  the  acids,  but,  on  the  addition  of  an  excess  of  absolute  alcohol,  is  coagulated 
in  the  form  of  whitish  flakes,  which  may  be  readily  separated  by  filtration.  This  sub- 
stance has  been  closely  studied  by  Mialhe  and  is  described  by  him  under  the  name  of 
animal  diastase.  This  author  regards  it  as  the  active  principle  of  the  saliva.  It  is  ob- 
tained from  the  human  saliva  by  the  following  simple  process : 

The  fluid  from  the  mouth  is  first  filtered,  then  treated  with  five  or  six  times  its  weight 
of  absolute  alcohol,  by  which  a  white  or  grayish-white  precipitate  is  formed.  This  sub- 
stance is  collected  on  a  filter  and  is  dried  in  thin  layers  on  a  plate  of  glass  in  a  current 
of  air  at  from  100°  to  120°  Fahr.  It  may  then  be  preserved  indefinitely  in  a  well-stop- 
pered bottle.  The  principle  thus  prepared  may  be  dissolved  in  water,  when  it  is  insipid, 
neutral,  and  becomes  readily  decomposed,  giving  rise  to  a  substance  resembling  butyric 
acid.  It  has  no  influence  upon  the  nitrogenized  alimentary  principles,  but,  when  brought 
in  contact  with  raw  or  hydrated  starch,  readily  transforms  it,  first  into  dextrine,  and 
afterward  into  glucose.  According  to  Mialhe,  the  energy  of  this  action  is  such  that  one 
part  is  sufficient  to  effect  the  transformation  of  more  than  two  thousand  parts  of  starch. 

The  presence  of  a  certain  quantity  of  sulpho-cyanide  of  potassium  in  the  mixed  saliva 
can  be  demonstrated  by  the  addition  of  a  per-salt,  especially  the  perchloride  of  iron. 
That  this  is  a  constant  and  normal  ingredient  of  the  human  saliva  cannot  be  doubted. 
We  have  frequently  had  occasion  to  apply  this  test  to  the  saliva  of  different  persons,  and 
the  results  have  been  invariably  the  same. 

It  has  been  a  question  whether  the  red  color  produced  by  the  perchloride  of  iron  be 
really  due  to  the  presence  of  a  sulpho-cyanide  in  the  saliva ;  or,  if  it  exist  at  all,  whether 
this  salt  be  a  normal  constituent  or  be  developed  accidentally  as  a  pathological  condi- 
tion, or  produced,  as  has  been  suggested,  by  the  action  of  reagents.  The  elaborate  in- 
vestigations of  Longet  seem  to  have  settled  these  questions  conclusively.  He  obtained 
nearly  three  quarts  of  human  saliva,  which  he  collected  in  half  an  hour  from  forty  sol- 
diers, fasting,  who,  after  having  rinsed  and  cleaned  the  mouth,  excited  the  secretion  by 
chewing  pieces  of  India-rubber.  The  fluid  was  then  concentrated  so  that  all  the  sulpho- 
cyanide  was  brought  into  a  few  drops,  which  showed,  in  an  intense  degree,  the  peculiar 


212  DIGESTION. 

reaction  with  the  perchloride  of  iron.  By  suitable  manipulations,  the  presence  of  sul- 
phur was  also  established. 

Longet  states,  farthermore,  that  he  has  examined  the  saliva  from  a  great  number  of 
persons,  under  all  conditions,  and  has  never  failed  to  demonstrate  the  presence  of  the 
sulpho-cyanide.  Its  proportion  he  found  very  variable,  and  in  some  cases  it  was  so 
slight  that  the  reaction  with  the  perchloride  of  iron  did  not  immediately  manifest  itself; 
but,  by  slowly  evaporating  the  liquid  to  one-half  or  one-third  of  its  original  volume, 
the  reaction  was  observed  in  all  cases. 

It  is  probable  that  the  sulpho-cyanide  of  potassium  is  a  constant  ingredient  of  each 
of  the  three  varieties  of  saliva.  It  has  been  found  in  the  parotid,  in  cases  of  salivary 
fistula,  and  was  noted  by  Dalton  in  the  saliva  taken  from  the  duct  of  Steno,  although,  in 
this  case,  the  saliva  contained  an  organic  principle  which  interfered  with  the  test,  but 
which  could  be  precipitated  by  alcohol  and  separated  by  filtration.  Longet  found  the 
sulpho-cyanide  in  the  saliva  from  the  submaxillary  and  sublingual  glands,  taken  from  the 
floor  of  the  mouth  behind  the  inferior  incisor  and  canine  teeth. 

Very  little  need  be  said  concerning  the  remaining  inorganic  constituents  of  saliva, 
except  that  they  are  of  such  a  nature  as  almost  invariably  to  render  the  fluid  distinctly 
alkaline.  They  exist  in  small  proportion  and  do  not  appear  to  be  connected  in  any  way 
with  the  functions  of  the  saliva  as  a  digestive  fluid. 

Functions  of  the  Saliva. 

Physiologists  are  not  entirely  agreed  concerning  some  of  the  most  important  questions 
relating  to  the  function  of  the  mixed  saliva  in  digestion.  Bernard,  from  observations  on 
the  lower  animals,  particularly  on  dogs,  concludes  that  the  operation  of  the  saliva  is  simply 
mechanical ;  while  others,  in  view  of  its  property  of  rapidly  transforming  starch  into 
sugar,  attribute  to  it  an  important  chemical  function.  The  experiments  on  which  the 
view  of  Bernard  is  based  are  conclusive,  so  far  as  they  go.  He  has  shown  that  none  of 
the  distinct  varieties  of  saliva  from  the  dog  affect  starch ;  that  a  mixture  of  the  fluids 
from  the  three  salivary  glands  is  likewise  inoperative ;  and  that  the  mixed  saliva  from 
the  mouth  of  the  dog,  containing  the  secretion  of  the  mucous  glands  of  the  mouth,  con- 
verts starch  into  sugar  with  difficulty.  At  the  same  time,  however,  he  mentions  the 
well-known  fact  that  the  human  mixed  saliva  changes  starch  into  sugar  with  great 
rapidity,  and  that  the  same  effect  is  produced  by  the  unmixed  parotid  or  submaxillary 
secretion.  In  the  dog,  amylaceous  principles  taken  by  the  mouth  are  always  found  un- 
altered in  the  stomach  and  are  only  transformed  into  sugar  in  the  small  intestines ;  but 
observations  have  shown  that  this  is  not  the  case  in  the  human  subject.  These  facts  are 
a  sufficient  argument  against  the  direct  application  of  experiments  made  on  an  exclusive- 
ly carnivorous  animal,  like  the  dog,  to  the  digestive  process  in  man.  While  there  is  no 
reason  to  suppose  that  there  is  any  material  difference  in  the  mammalia,  as  regards  the 
general  operation  of  some  of  the  functions,  such  as  circulation  or  respiration,  it  is  evident 
that  differences  exist  in  the  properties  of  the  digestive  fluids,  as  well  as  in  the  teeth  and 
jaws,  corresponding  with  the  great  differences  in  the  character  and  conditions  of  the 
alimentary  principles.  In  the  study  of  digestion,  therefore,  the  results  of  experiments 
on  the  inferior  animals  cannot  always  be  taken  without  reserve,  and  they  should  be  con- 
firmed by  observations  on  the  human  subject ;  but,  fortunately,  the  properties  of  nearly 
all  of  the  digestive  fluids  which  have  been  studied  minutely  by  vivisections  have  been 
investigated  more  or  less  fully  in  man. 

In  1831,  Leuchs  discovered  that  hydrated  starch,  mixed  with  fresh  saliva  and  warmed, 
became  liquid  in  the  space  of  several  hours  and  was  converted  into  sugar.  This  fact  has 
since  been  repeatedly  confirmed ;  and  it  is  now  a  matter  of  common  observation  that 
hydrated  starch  or  unleavened  bread,  taken  into  the  mouth,  almost  instantly  loses  the 
property  of  striking  a  blue  color  with  iodine  and  responds  to  the  ordinary  tests  for  sugar. 
Of  the  rapidity  of  this  action  any  one  can  easily  convince  himself  by  the  simple  experi- 


FUNCTIONS   OF  THE   SALIVA.  213 

ment  of  taking  a  little  cooked  starch  into  the  mouth,  mixing  it  well  with  the  saliva,  and 
testing  in  the  ordinary  way  for  sugar.  This  can  hardly  be  done  so  rapidly  that  the  reac- 
tion is  not  manifested,  and  the  presence  of  sugar  is  also  indicated  by  the  taste.  Although 
the  human  mixed  saliva  will  finally  exert  the  same  action  on  uncooked  starch,  the  trans- 
formation takes  place  much  more  slowly.  It  has  been  shown  by  experiment  that  all  the 
varieties  of  human  saliva  have  the  same  effect  on  starch  as  the  mixed  fluids  of  the  mouth. 
Dalton  found  no  difference  in  the  pure  parotid  saliva  and  the  mixed  saliva  of  the  human 
subject,  as  regards  the  power  of  transforming  starch  into  sugar.  Bernard  obtained  the 
pure  secretions  from  the  parotid  and  from  the  submaxillary  glands  in  the  human  subject, 
by  drawing  it  out  of  the  ducts,  as  they  open  into  the  mouth,  with  a  small  syringe  with 
the  nozzle  arranged  so  as  to  fit  over  the  papillae,  and  demonstrated  their  action  on  starch. 
Longet  showed  that  a  mixture  of  the  secretions  of  the  submaxillary  and  the  sublingual 
glands  had  the  same  property. 

It  is  unnecessary,  in  this  connection,  to  recite  the  numerous  experiments  on  the  in- 
fluence of  the  saliva  of  the  inferior  animals  on  starch;  but  it  may  be  stated,  as  an  estab- 
lished and  generally-accepted  fact,  that  the  mixed  saliva  and  the  secretion  of  the  different 
salivary  glands,  in  the  human  subject,  invariably  transform  cooked  starch  into  sugar  with 
great  rapidity  in  the  mouth,  and  also,  at  the  proper  temperature,  out  of  the  body.  It 
has  been  also  shown  by  Mialhe  that  the  starch,  although  it  is  converted  rapidly  into  sugar 
in  this  process,  is  first  transformed  into  dextrine.  This  point  being  settled,  there  arises 
the  important  question  whether  the  action  of  the  saliva  be  important  in  the  digestion  of 
starch,  or  whether  this  transformation  be  merely  accidental ;  for  it  has  been  shown  that 
other  fluids,  among  which  may  be  mentioned  the  serum  of  the  blood,  the  fluid  found  in 
cysts,  and  mucus,  have  the  same  property,  although  none,  except  the  intestinal  juices,  are 
nearly  so  efficient  as  the  saliva.  And,  again,  the  quantity  of  starch  contained  in  the  food 
is  so  great  that  it  would  require,  apparently,  a  longer  contact  with  the  saliva  than  usually 
takes  place  in  the  mouth  to  make  this  action  very  efficient.  These  considerations  make 
it  necessary  to  follow  the  amylaceous  principles  of  food  into  the  stomach  and  to  ascer- 
tain, if  possible,  whether  the  transformation  into  sugar  be  continued  in  this  organ. 

Bernard,  after  feeding  a  dog  with  starch,  drew  off  the  contents  of  the  stomach  by  a 
gastric  fistula  and  found  the  starch  unchanged,  with  no  traces  of  sugar.  This  experi- 
ment we  have  often  repeated  in  public  demonstrations,  with  the  same  results ;  but  the 
differences  already  noted  in  the  properties  of  the  saliva  of  the  human  subject  and  of  the 
inferior  animals  destroy  much  of  the  value  of  such  observations.  Longet  and  others  have 
shown  that  the  addition  of  gastric  juice  to  the  saliva  does  not  interfere  with  the  action 
of  the  latter  on  starch,  but  it  has  been  found  that  the  reaction  of  the  sugar  thus  resulting 
from  the  transformation  of  the  starch  is  masked  by  the  presence  of  other  principles  con- 
tained in  the  stomach.  The  question  of  the  continuance,  in  the  stomach,  of  the  digestion 
of  starch  by  the  saliva  is  settled  by  the  following  observation  by  Grtinewaldt  and 
Schroder,  in  1853,  on  a  woman  with  a  gastric  fistula: 

"  After  a  meal  of  raw  starch,  no  sugar  was  found  in  the  contents  of  the  stomach,  the 
acid  juice  was  drawn  by  the  fistula,  and  was  mixed  with  paste  ;  the  transformation  into 
sugar  commenced  immediately.  As  Bidder  has  observed,  the  transforming  property  of 
the  saliva  persists,  even  in  the  presence  of  free  acids. 

"  A  few  ounces  of  starch  swelled  with  boiling  water  were  introduced  in  the  stomach, 
fasting,  by  the  fistula ;  immediately  after,  a  portion  of  the  starch  was  expelled  again ; 
already  it  contained  sugar.  A  quarter  of  an  hour  after,  a  great  deal  of  sugar  was  found 
in  the  stomach,  and  the  paste  had  become  entirely  fluid." 

There  can  be  no  doubt  that  the  saliva,  in  addition  to  its  important  mechanical  func- 
tions, transforms  a  considerable  portion  of  the  cooked  starch,  which  is  the  common  form 
in  which  this  principle  is  taken  by  the  human  subject,  into  sugar;  but  it  is  by  no  means 
the  only  fluid  engaged  in  its  digestion,  similar  properties  belonging,  as  we  shall  see  here- 
after, to  the  pancreatic  and  the  intestinal  juice.  The  last-named  fluids  are  probably  more 


214  DIGESTION. 

active,  even,  than  the  saliva.  The  saliva  acts  slowly  and  imperfectly  on  raw  starch, 
which  becomes  hydrated  in  the  stomach  and  is  digested  mainly  by  the  fluids  of  the  small 
intestine.  In  all  probability,  the  saliva  does  not  digest  all  the  hydrated  starch  taken  as 
food,  the  greater  part  passing  unchanged  from  the  stomach  into  the  intestine.  Those  who 
attribute  merely  a  mechanical  function  to  the  saliva  draw  their  conclusions  entirely  from 
experiments  on  the  lower  animals,  particularly  the  carnivora ;  and  it  is  evident  that  such 
observations  cannot  be  strictly  applied  to  the  human  subject. 

The  principle  which  is  specially  active  in  the  digestion  of  starch,  in  the  human  subject 
at  least,  must  exist  in  the  pure  secretion  from  the  various  glands  as  well  as  in  the  mixed 
saliva.  It  has  been  isolated  and  studied  by  Mialhe,  under  the  name  of  animal  diastase. 
Its  properties  and  its  action  on  starch  have  already  been  noted  in  treating  of  the  com- 
position of  the  mixed  saliva. 

In  treating  of  the  various  fluids  which  are  combined  to  form  the  mixed  saliva,  their 
mechanical  functions  have  necessarily  been  touched  upon.  To  sum  up  this  subject,  how- 
ever, it  may  be  stated  that  the  fluids  of  the  mouth  and  pharnyx  have  quite  as  important  an 
office  in  preparing  the  food  for  deglutition  and  for  the  action  of  the  juices  in  the  stomach 
as  in  the  digestion  of  starch.  Indeed,  the  former  is  probably  the  more  important  function 
in  man  and  the  herbivora.  It  is  a  matter  of  common  experience  that  the  rapid  degluti- 
tion of  very  dry  articles  is  impossible ;  and  the  experiments  of  Bernard  and  others  on 
horses  furnish  very  striking  illustrations  of  the  importance  of  the  saliva  as  a  purely  me- 
chanical agent.  In  the  human  subject,  although  mastication  and  insalivation  are  by  no 
means  so  complete  as  in  some  of  the  lower  animals,  the  quantity  of  saliva  absorbed  by  the 
various  articles  of  food  is  enormous.  It  seems  impossible  that  the  fluid  thus  incorporated 
with  the  alimentary  principles  should  not  have  an  important  influence  on  the  changes 
which  take  place  in  the  stomach,  although  it  must  be  confessed  that  our  information  on 
this  point  is  very  meagre,  except  as  regards  the  digestion  of  starch. 

It  is  undoubtedly  the  abundant  secretion  of  the  parotid  glands  which  becomes  most 
completely  incorporated  with  the  food  during  mastication  and  which  serves  to  unite  the  dry 
particles  into  a  single  coherent  mass.  In  an  experiment  on  a  horse,  Bernard  found  that, 
after  the  ducts  of  Steno  had  been  divided,  the  portions  of  food,  which  were  collected  by 
an  opening  into  the  oesophagus  as  they  were  swallowed,  were  not  coherent  and  were 
passed  into  the  stomach  with  great  difficulty.  The  time  occupied  in  eating  about  three- 
quarters  of  a  pound  of  oats  was  twenty-five  minutes ;  while,  before  the  section  of  the 
salivary  ducts,  a  pound  of  oats  was  eaten  in  nine  minutes. 

The  secretions  from  the  submaxillary  and  sublingual  glands  and  from  the  small  glands 
and  follicles  of  the  mouth,  being  more  viscid  and  less  in  quantity  than  the  parotid  secre- 
tion, penetrate  the  alimentary  bolus  less  easily  and  have  rather  a  tendency  to  form  a  glairy 
coating  on  its  exterior,  agglutinating  the  particles  on  the  surface  with  peculiar  tenacity. 

When  the  process  of  mastication  and  insalivation  is  completed  and  the  food  is  passed 
back  into  the  pharynx,  it  meets  with  the  secretion  of  the  pharyngeal  glands,  which  still 
farther  coats  the  surface  with  the  viscid  fluid  which  covers  the  mucous  membrane  in  this 
situation,  thus  facilitating  the  first  processes  of  deglutition. 

It  has  been  observed  that  the  saliva  has  a  remarkable  tendency  to  entangle  bubbles  of 
air  in  the  alimentary  mass.  In  mastication,  a  considerable  quantity  of  air  is  mixed  with 
the  food,  and  this  undoubtedly  facilitates  the  penetration  of  the  gastric  juice.  It  is  well 
known  that  moist,  heavy  bread,  and  articles  that  cannot  become  impregnated  in  this  way 
with  air,  are  not  easily  acted  upon  in  the  stomach. 

Deglutition. 

Deglutition  is  the  act  by  which  solid  and  liquid  articles  are  forced  from  the  mouth 
into  the  stomach.  The  process  involves  first,  the  passage,  by  a  voluntary  movement,  of 
the  alimentary  mass  through  the  isthmus  of  the  fauces  into  the  pharynx ;  then  a  rapid 
contraction  of  the  constrictors  of  the  pharynx,  by  which  it  is  forced  into  the  oesophagus ; 


DEGLUTITION. 


215 


and,  finally,  a  peristaltic  action  of  the  muscular  walls  of  the  oesophagus,  extending  from 
its  opening  at  the  pharynx  to  the  stomach. 

Physiological  Anatomy  of  the  Parts  concerned  in  Deglutition. — The  parts  concerned 
in  this  function  are  the  tongue,  the  muscular  walls  of  the  pharynx,  and  the  oesophagus. 
In  the  passage  of  food  and  drink  through  the  pharynx,  it  is  necessary  to  completely  pro- 
tect from  the  entrance  of  foreign  matters  a  number  of  openings  which  are  exclusively  for 
the  passage  of  air.  These  are  above,  the  posterior  nares  and  the  Eustachian  tubes,  and 
below,  the  opening  of  the  larynx.  The  mechanism  by  which  these  passages  are  closed 
during  the  acts  of  deglutition  is  one  of  the  most  interesting  subjects  connected  with  this 
function  and  has  long  engaged  the  attention  of  physiologists. 

The  tongue — a  muscular  organ  capable  of  a  great  variety  of  movements,  and  en- 
dowed, as  we  have  seen,  with  highly  important  functions  connected  with  mastication — 
is  the  chief  agent  in  the  first  processes  of  deglutition.  Its  physiological  anatomy  has 
already  been  considered. 


FIG.  52.— Cavities  of  the  mouth  and  pharynx,  etc.    (Sappey.) 

Section  in  the  median  line  of  the  face  and  the  superior  portion  of  the  neck,  designed  to  show  the  mouth  in  its  rela- 
tions to  the  nasal  fossae,  the  pharynx,  and  the  larynx :  1,  sphenoidal  sinuses ;  2,  internal  orifice  of  the  Eustachian 
tube ;  3,  palatine  arch  ;  4,  velum  pendulum  palati ;  5,  anterior  pillar  of  the  soft  palate  ;  6.  posterior  pillar  of  the 
soft  palate ;  7,  tonsil ;  8.  lingual  portion  of  the  cavity  of  the  pharynx  ;  9,  epiglottis ;  10,  section  of  the  hyoid 
bone ;  11,  laryngeal  portion  of  the  cavity  of  the  pharynx ;  12,  cavity  of  the  larynx. 


The  pharynx,  in  which  the  most  vigorous  and  complex  of  the  movements  of  degluti- 
tion take  place,  is  an  irregular,  funnel-shaped  cavity,  its  longest  diameter  being  trans- 
verse and  opposite  the  cornua  of  the  hyoid  bone,  with  its  smallest  portion  at  the  opening 
into  the  oesophagus.  Its  length  is  about  four  and  a  half  inches.  It  is  connected  superiorly 
and  posteriorly  with  the  basilar  process  of  the  occipital  bone  and  the  upper  cervical  verte- 


216 


DIGESTION. 


brae.  It  is  imperfectly  separated  from  the  cavity  of  the  mouth  by  the  velum  pendulum 
palati,  a  movable  musculo-membranous  fold  continuous  with  the  roof  the  mouth  and 
marked  by  a  line  in  the  centre,  which  indicates  its  original  development  by  two  lateral 
halves.  This,  which  is  called  the  soft  palate,  when  relaxed,  presents  a  concave  surface 
looking  toward  the  mouth,  a  free,  arched  border,  and  a  conical  process  hanging  from  the 
centre,  called  the  uvula.  On  either  side  of  the  soft  palate,  are  two  curved  pillars  or  arches. 

The  anterior  pillars  of  the  fauces  are  formed  by  the  palato-glossus  muscle  on  either 
side  and  run  obliquely  downward  and  forward,  the  mucous  membrane  which  covers 
them  becoming  continuous  with  the  membrane  over  the  base  of  the  tongue.  The  posterior 
pillars  are  more  closely  approximated  to  each  other  than  the  anterior.  They  run  obliquely 
downward  and  backward,  their  mucous  membrane  becoming  continuous  with  the  mem- 
brane covering  the  sides  of  the  pharynx.  Between  the  lower  portion  of  the  anterior  and 
posterior  pillars,  are  the  tonsils ;  and  in  the  substance  of,  and  beneath  the  mucous  mem- 
brane of  the  palate  and  pharynx,  are  small  glands,  which  have  already  been  described. 

In  Fig.  52  are  shown  the  cavities  of  the  mouth  and  pharynx  with  their  relations  to 
the  nares  and  the  larynx. 


17 


FIG.  53. — Muscles  of  the  pharynx,  etc.    (Sappey.) 

1,  2,3,  4,  4,  superior  constrictor;  5,  6,  7,  8,  middle  constrictor;  9,  10,  11,  12,  inferior  constrictor;  18,  13,  stylo- 
pharyngeus ;  14,  stylo-hyoid  muscle ;  15,  stylo-glossus ;  16,  hyo-glossus ;  17,  mylo-hyoid  muscle ;  18,  buccinator 
muscle ;  19,  tensor  palati ;  20,  levator  palati. 

The  isthmus  of  the  fauces,  or  the  strait  through  which  the  food  passes  from  the  mouth 
to  the  pharynx,  is  bounded  above,  by  the  soft  palate  and  the  uvula ;  laterally,  by  the  pil- 
lars of  the  palate  and  the  tonsils ;  and  below,  by  the  base  of  the  tongue. 


DEGLUTITION.  217 

The  openings  into  the  pharynx  above  are  the  posterior  nares  and  orifices  of  the  Eusta- 
chian  tubes.  Below,  are  the  openings  of  the  oesophagus  and  the  larynx. 

The  muscles  of  the  pharynx  are  the  superior  constrictor,  the  stylo-pharyngeus,  the 
middle  constrictor,  and  the  inferior  constrictor  ;  and  it  is  easy  to  see,  from  the  situation  of 
these  muscles,  how,  by  their  successive  action  from  above  downward,  the  food  is  passed 
into  the  oesophagus. 

The  superior  constrictors  form  the  muscular  wall  of  the  upper  part  of  the  pharynx. 
Their  origin  extends  from  the  lower  third  of  the  margin  of  the  internal  pterygoid  plate  of 
the  sphenoid  bone  to  the  alveolar  process  of  the  last  molar  tooth,  the  intermediate  line  of 
attachment  being  to  tendons  and  ligaments.  The  fibres  then  pass  backward  and  meet  in 
the  median  raphe,  which  is  attached  by  aponeurotic  fibres  to  a  ridge  on  the  basilar  process 
of  the  occipital  bone,  called  the  pharyngeal  spine. 

The  stylo-pharyngeus  muscle  has  a  rounded  portion  above,  by  which  it  arises  from  the 
inner  surface  of  the  base  of  the  styloid  process  of  the  temporal  bone.  It  passes  between 
the  superior  and  middle  constrictors  of  the  pharynx,  becomes  thin,  and  spreading  out,  its 
fibres  mingle  in  part  with  the  fibres  of  the  constrictors  and  the  palato-pharyngeus,  and  a 
few  pass  to  be  inserted  into  the  upper  border  of  the  thyroid  cartilage. 

Tho  middle  constrictor  is  a  flattened  muscle,  arising  from  the  cornuaof  the  hyoid  bone 
and  the  stylo-hyoid  ligament,  its  fibres  passing  backward,  spreading  into  a  fan-shape,  and 
meeting  in  the  median  raphe. 

The  inferior  constrictor  is  the  most  powerful  of  the  muscles  of  the  pharynx.  It  arises 
by  thick,  fleshy  masses  from  the  sides  of  the  thyroid  and  cricoid  cartilages  of  the  larynx. 
The  inferior  fibres  curve  backward,  and  the  superior  fibres,  backward  and  upward,  to 
meet  in  the  median  raphe. 

The  muscles  which  form  the  fleshy  portions  of  the  soft  palate  are  likewise  important 
in  deglutition. 

The  levator  palati,  a  long  muscle  of  considerable  thickness,  arises  from  the  apex  of  the 
petrous  portion  of  the  temporal  bone  and  the  adjacent  cartilaginous  portion  of  the  Eusta- 
chian  tube ;  and,  spreading  out  in  the  posterior  portion  of  the  soft  palate,  as  its  name 
implies,  it  raises  the  velum. 

The  tensor  palati,  sometimes  called  the  circumflexus,  is  a  broad,  thin  muscle,  consist- 
ing of  a  vertical  portion,  which  is  fleshy,  and  a  horizontal  portion,  which  is  tendinous. 
The  fleshy  fibres  arise  from  the  scaphoid  fossa  of  the  sphenoid  bone,  pass  downward,  be- 
come tendinous,  and  wind  around  the  hamular  process ;  after  which  the  muscle  spreads 
out  into  a  thin  aponeurosis,  which  passes  to  the  median  line  on  the  anterior  portion  of 
the  soft  palate.  Its  action  is  to  render  the  palate  tense. 

The  palato-glossus  forms  the  anterior  pillar  of  the  soft  palate.  It  arises  from  the  side 
of  the  palate  near  the  uvula  and  passes  to  be  inserted  into  the  side  and  dorsum  of  the 
tongue.  The  action  of  this  muscle  is  to  constrict  the  isthmus  of  the  fauces,  by  drawing 
down  the  soft  palate  and  elevating  the  base  of  the  tongue. 

The  palato-pharyngeus  forms  the  posterior  pillar  of  the  soft  palate.  It  arises  from  the 
soft  palate  by  two  fasciculi,  and  joins  with  the  fibres  of  the  stylo-pharyngeus,  to  be  in- 
serted into  the  posterior  border  of  the  thyroid  cartilage.  Its  action  is  to  approximate  the 
posterior  pillars  of  the  palate  and  depress  the  velum; 

The  azygos  uvulae  is  the  small  muscle,  consisting  of  two  fasciculi,  one  on  either  side, 
which  forms  the  fleshy  portion  of  the  uvula.  It  has  no  very  marked  or  important  action 
in  deglutition. 

The  mucous  membrane  of  the  pharynx,  aside  from  the  various  glands  situated  beneath 
it  and  in  its  substance,  which  have  already  been  described,  presents  some  peculiarities, 
which  are  interesting  more  from  an  anatomical  than  a  physiological  point  of  view.  In 
the  superior  portion,  which  forms  a  cuboidal  cavity  just  behind  the  posterior  nares,  the 
membrane  is  darker  and  much  richer  in  blood-vessels  than  in  other  parts.  Its  surface  is 
smooth  and  provided  with  ciliated,  columnar  epithelium,  like  that  which  covers  the  mem- 


218  DIGESTION. 

brane  of  the  posterior  nares.  It  is  marked  by  a  deep  antero-posterior  groove  in  the 
median  line ;  and,  on  either  side,  parallel  with  the  median  line,  are  four  smaller  grooves. 
In  the  horizontal  portions,  the  mucous  membrane  in  the  central  groove  adheres  to  the 
periosteum  of  the  basilar  process,  particularly  at  its  posterior  extremity.  Laterally,  be- 
low the  level  of  the  opening  of  the  Eustachian  tubes,  and  posteriorly,  at  the  point  where 
it  becomes  vertical,  the  mucous  membrane  abruptly  changes  its  character.  The  epithelial 
covering  is  here  composed  of  cells  of  the  pavement-variety,  similar  to  those  which  cover 
the  mucous  membrane  of  the  oesophagus.  The  membrane  is  also  paler  and  is  less  rich 
in  blood-vessels.  It  is  provided  with  papillae,  some  of  which  are  simple,  conical  eleva- 
tions, while  others  present  from  two  to  six  conical  processes  with  a  single  base.  These 
papillae  are  rather  thinly  distributed  over  all  of  that  portion  of  the  mucous  surface  which 
is  covered  with  pavement-epithelium. 

The  contractions  of  the  muscular  walls  of  the  pharynx  force  the  alimentary  bolus  into 
the  oesophagus,  a  tube  possessed  of  thic^mjis^ula^walls^  extending  to  the  stomach.  The 
oesophagus  is  about ^in^jn^]^sjii_length^.  It  is  Cylindrical,  and  rather  constricted  at  its 
^superior  and  mferiox^ejtomitigs.  It  commences  in  the  niedian  line_  behind  the  lower 
border  of  the  cricoid  cartilage  and  opposite  the  ^fth^eimc^ljrej^tebra.  At  first,  as  it  de- 
scends, it  pasjiejtsJMtleutQ  thgj^t^of  the  cervical  vertebra).  It  then  passes  from  left  to 
right  from  the  fourth  or  fifth  to  the  ninth  dorsal  vertebra,  to  give  place  to  the  aorta.  It 
finally  passes  a  little  to  the  left  again,  and  from  behind  forward,  to  its  opening  into  the 
stomach.  In  its  passage  through  the  diaphragm,  it  is  surrounded  byjmigcujar^  fibres^  so 
that  when  this  muscle  is  contracted  in  inspiration,  its  action  has  a  tendency  to  close  the 
opening. 

The  coats  of  the  oesophagus  are  two  in  number,  unless  we  include,  as  a  third  coat,  the 
fibrous  tissue  which  attaches  the  mucous  membrane  to  the  subjacent  muscular  tissue. 

The  external  coat  is  composed  of  an  external  longitudinal,  and  an  internal  circular  or 
transverse  layer  of  muscular  fibres.  In  the  superior  portion,  the  longitudinal  fibres  are 
arranged  in  three  distinct  fasciculi ;  one  in  front,  which  passes  downward  from  the  pos- 
terior surface  of  the  cricoid  cartilage,  and  one  on  either  side,  extending  from  the  inferior 
constrictors  of  the  pharynx.  As  the  fibres  descend,  the  fasciculi  become  less  distinct 
and  are  finally  blended  into  a  uniform  layer.  The  circular  layer  is  somewhat  thinner 
than  the  external  layer.  Its  fibres  are  transverse  near  the  superior  and  inferior  extrem- 
ities of  the  tube  and  are  somewhat  oblique  in  the  intermediate  portion.  The  muscular 
coat  is  from  ^  to  T^  of  an  inch  in  thickness. 

In  the  upper  third  of  the  oesophagus,  the  muscular  fibres  are  exclusively  of  the  red  or 
striated  variety,  with  some  anastomosing  bundles ;  but,  lower  down,  there  is  a  mixture  of 
non-striated  fibres,  which  appear  first  in  the  circular  layer.  These  latter  fibres  become 
gradually  more  numerous,  until,  in  the  lower  fourth,  they  largely  predominate.  A  few 
striated  fibres,  however,  are  found  as  low  down  as  the  diaphragm. 

The  mucous  membrane  of  the  oesophagus  is  attached  to  the  muscular  tissue  by  a  dense, 
fibrous  layer.  It  is  quite  vascular  and  reddish  above,  but  becomes  gradually  paler  in  the 
inferior  portion.  The  mucous  membrane  is  ordinarily  thrown  into  longitudinal  folds, 
which  are  obliterated  when  the  tube  is  distended.  Its  epithelium  is  thick,  of  the  pave- 
ment-variety, and  is  continuous  with,  and  similar  to  the  covering  of  the  lower  portion  of 
the  pharynx.  It  is  provided  with  papillae  of  the  same  structure  as  those  found  in  the 
pharynx,  the  conical  variety  predominating.  Numerous  small,  racemose  glands  are  found 
throughout  the  tube,  forming  by  their  aggregation  at  the  lower  extremity,  just  before  it 
opens  into  the  stomach,  a  glandular  ring. 

Mechanism  of  Deglutition. — For  convenience  of  description,  physiologists  have  gen- 
erally divided  the  process  of  deglutition  into  three  periods.  The  first  period  is  occupied 
by  the  passage  of  the  alimentary  bolus  backward  to  the  isthmus  of  the  fauces.  This  may 
appropriately  be  considered  as  a  distinct  period,  because  the  movements  are  effected  by 


DEGLUTITION.  219 

the  action  of  muscles  under  the  control  of  the  will.  The  second  period  is  occupied  hy  the 
passage  of  the  food  from  the  isthmus  of  the  fauces,  through  the  pharynx,  into  the  upper 
part  of  the  oesophagus.  The  third  period  is  occupied  by  the  passage  of  the  food  through 
the  oesophagus  into  the  stomach. 

In  the  first  period,  the  tongue  is  the  important  agent.  After  mastication  has  been 
completed,  the  mouth  is  closed  and  the  tongue  becomes  slightly  increased  in  width,  and, 
with  the  alimentary  bolus  behind  it,  is  pressed  from  before  backward  against  the  roof  of 
the  mouth.  The  act  of  swallowing  is  always  performed  with  difficulty  when  the  mouth 
is  not  completely  closed ;  for  the  tongue,  from  its  attachments,  must  follow,  to  a  certain 
extent,  the  movements  of  the  lower  jaw.  The  first  part  of  the  first  period  of  deglutition, 
therefore,  is  simple  ;  but,  when  the  food  has  passed  beyond  the  hard  palate,  it  comes  in 
contact  with  the  hanging  velum,  and  the  muscles  are  brought  into  action  which  render 
this  membrane  tense  and  oppose  it  in  a  certain  degree  to  the  backward  movement  of  the 
base  of  the  tongue.  This  is  effected  by  the  action  of  the  tensor-palati  and  the  palato- 
glossus.  The  moderate  tension  of  the  soft  palate  admits  of  its  being  applied  to  the  smaller 
morsels,  while  the  opening  is  dilated  somewhat  forcibly  by  masses  of  greater  size. 

It  is  easy  to  appreciate,  in  analyzing  the  first  period  of  deglutition,  that  liquids  and 
the  softer  articles  of  food  are  assisted  in  their  passage  to  the  isthmus  of  the  fauces  by  a 
slight  suction  force.  This  is  effected  by  the  action  of  the  muscles  of  the  tongue,  elevating 
the  sides  and  depressing  the  centre  of  the  dorsum,  while  the  soft  palate  is  accurately 
applied  to  the  base. 

The  importance  of  the  movements  of  the  tongue  during  the  first  period  of  deglutition 
is  shown  by  experiments  on  the  inferior  animals  and  by  cases  of  loss  of  this  organ  in 
the  human  subject.  In  the  experiments  of  Panizza,  which  have  already  been  referred  to 
in  connection  with  mastication,  it  was  found  that  paralysis  of  the  tongue  by  section  of 
the  hypoglossal  nerves  in  dogs  deprived  the  animals  of  the  power  of  swallowing,  even 
when  a  bolus  of  meat  or  bread  was  put  upon  its  dorsal  surface.  In  an  observation  on  a 
young  dog,  in  which  we  divided  both  hypoglossal  nerves,  the  effect  upon  deglutition  was 
very  marked.  The  animal  ate  with  difficulty,  the  pieces  of  meat  which  were  given  him 
frequently  dropping  from  the  mouth.  He  was  able  to  swallow  only  by  jerking  the  head 
suddenly  upward,  so  as  to  throw  the  meat  past  the  base  of  the  tongue ;  and,  even  when 
deglutition  commenced,  the  first  steps  took  place  slowly  and  with  apparent  difficulty. 
The  process  of  drinking  was  very  curious.  The  animal  made  the  usual  noise  in  attempt- 
ing to  drink,  but  the  tongue  did  not  come  out  of  the  mouth,  and  the  only  way  he  seemed 
to  get  any  water  was  by  jerking  the  head  and  moving  the  jaw  so  as  to  throw  some  of  the 
liquid  into  the  mouth.  On  causing  him  to  drink  from  a  graduated  glass,  it  was  found 
that  he  drank  four  fluidounces  in  four  minutes.  In  the  case  of  a  young  girl,  reported  to 
the  Academy  of  Science,  in  1718,  by  De  Jussieu,  in  which  there  was  congenital  absence 
of  the  tongue,  deglutition  was  impossible  until  the  food  had  been  pushed  with  the  finger 
far  back  into  the  mouth.  In  cases  of  amputation  of  the  tongue,  a  portion  of  its  base  gen- 
erally remains  sufficient  to  press  against  the  palate  and  thus  act  in  the  first  period  of  deg- 
lutition. 

The  movements  in  the  first  period  of  deglutition  are  under  the  control  of  the  will  but 
are  generally  involuntary.  When  the  food  has  been  sufficiently  masticated,  it  requires 
an  effort  to  prevent  the  act  of  swallowing.  In  this  respect,  the  movements  are  like  the 
acts  of  respiration,  except  that  the  imperative  necessity  of  air  in  the  system  must,  in  a 
short  time,  overcome  any  voluntary  effort  by  which  respiration  has  been  arrested. 

The  second  period  of  deglutition  involves  more  complex  and  important  muscular 
action  than  the  first.  By  a  rapid  and  almost  convulsive  series  of  movements,  the  food  is 
made  to  pass  through  the  pharynx  into  the  oesophagus.  The  movements  are  then  entirely 
beyond  the  control  of  the  will,  and  belong  to  the  kind  usually  called  reflex.  After  the 
alimentary  mass  has  passed  beyond  the  isthmus  of  the  fauces,  it  is  easy  to  observe  a  sud- 
den and  peculiar  movement  of  elevation  of  the  larynx  by  the  action  of  muscles  which 


220  DIGESTION. 

usually  depress  the  lower  jaw,  but  which  are  now  acting  from  this  bone  as  the  fixed 
point.  The  muscles  which  produce  this  movement  act  chiefly  upon  the  hyoid  bone. 
They  are  the  digastric  (particularly  the  anterior  belly),  the  mylo-hyoid,  the  genio-hyoid, 
the  stylo-hyoid,  and  some  of  the  fibres  of  the  genio-glossus.  It  is  probable,  also,  that  the 
thyro-hyoid  acts  at  this  time  to  draw  the  larynx  toward  the  hyoid  bone.  With  this  ele- 
vation of  the  larynx,  there  is  necessarily  an  elevation  of  the  anterior  and  inferior  portions 
of  the  pharynx,  which  are,  as  it  were,  slipped  under  the  alimentary  bolus  as  it  is  held  by 
the  constrictors  of  the  isthmus  of  the  fauces. 

Contraction  of  the  constrictor  muscles  of  the  pharynx  takes  place  almost  simulta- 
neously with  the  movement  of  elevation ;  and  the  superior  constrictor  is  so  situated  as  to 
grasp  the  morsel  of  food,  and  with  it  the  soft  palate.  The  muscles,  the  constrictors  act- 
ing from  the  median  raphe,  assist  to  elevate  the  anterior  and  inferior  walls  of  the  pharynx 
and  pass  the  food  rapidly  into  the  upper  part  of  the  oesophagus.  All  these  complex 
movements  are  accomplished  with  great  rapidity,  and  the  larynx  and  pharynx  are  then 
immediately  returned  to  their  original  position. 

Protection  of  the  Posterior  Nares  during  the  Second  Period  of  Deglutition. — When 
the  act  of  deglutition  is  performed  with  regularity,  no  portion  of  the  liquids  and  solids 
swallowed  ever  finds  its  way  into  the  air-passages.  The  entrance  of  foreign  substances 
into  the  posterior  nares  is  prevented  in  part  by  the  action  of  the  superior  constrictors  of 
the  pharynx,  which,  as  we  have  seen,  embrace,  during  their  contraction,  not  only  the  ali- 
mentary mass,  but  the  velum  pendulum  palati  itself,  and  in  part,  also,  by  contraction  of 
the  muscles  which  form  the  posterior  pillars  of  the  soft  palate. 

During  the  first  part  of  the  second  period  of  deglutition,  the  soft  palate  is  slightly 
raised,  being  pressed  upward  by  the  morsel  of  food.  This  fact  has  been  observed  in  cases 
in  which  the  parts  have  been  exposed  by  surgical  operations,  and  its  mechanism  has  also 
been  observed  in  the  human  subject,  by  Bidder  and  Kobelt.  In  one  case — that  of  a  young 
man  who  had  lost  the  superior  maxillary  bone,  as  well  as  the  zygoma — the  soft  palate 
could  be  observed  from  its  superior  surface ;  and,  at  each  movement  of  deglutition,  the 
palate,  which  is  naturally  inclined  downward,  became  more  horizontal,  and  the  posterior 
wall  of  the  pharynx  came  forward  to  meet  it.  The  same  movement  of  the  pharynx  was 
observed  by  Kobelt  in  the  case  of  a  soldier  who  received  a  severe  sabre-cut  in  the  neck. 

While  the  food  is  passing  through  the  pharynx,  the  palato-pharyngeal  muscles,  which 
form  the  posterior  pillars  of  the  soft  palate,  are  in  a  state  of  contraction  by  which  the 
edges  of  the  pillars  are  nearly  approximated,  forming,  with  the  uvula  between  them, 
almost  a  complete  diaphragm  between  the  postero-superior  and  the  antero-inferior  parts 
of  the  pharynx.  This,  with  the  application  of  the  posterior  wall  of  the  pharynx  to  the 
superior  face  of  the  soft  palate,  completes  the  protection  of  the  posterior  openings  of 
the  nasal  fossae.  The  fact  that  the  posterior  pillars  are  thus  contracted  and  approximated 
during  deglutition  may  be  easily  verified  by  simply  watching  these  parts  with  a  mirror 
during  an  effort  at  swallowing.  In  a  case,  observed  by  Berard,  it  was  shown  that  the 
muscular  action  of  the  soft  palate  was  absolutely  necessary  to  the  protection  of  the  nares, 
particularly  in  swallowing  liquids.  In  this  instance,  a  young  lady  was  affected  with 
complete  paralysis  of  the  velum,  which  allowed  liquids  to  return  so  freely  by  the  nose  in 
swallowing  that  she  was  obliged  to  retire  from  observation  whenever  she  drank. 

Protection  of  the  Opening  of  the  Larynx,  and  Uses  of  the  Epiglottis  in  Deglutition. — 
The  entrance  of  the  smallest  quantity  of  solid  or  liquid  foreign  matter  into  the  larynx 
produces  violent  and  distressing  cough.  This  accident  is  of  not  infrequent  occurrence, 
especially  when  an  act  of  inspiration  is  inadvertently  performed  while  solids  or  liquids 
are  in  the  pharynx.  During  inspiration,  the  glottis  is  opened,  and  at  that  time  only  can 
a  substance  of  any  considerable  size  find  its  way  into  the  respiratory  passages.  Respira- 
tion is  interrupted,  however,  during  each  and  every  act  of  deglutition ;  and  there  can, 


DEGLUTITION.  221 

therefore,  be  hardly  any  tendency  at  that  time  to  the  entrance  of  foreign  substances  into 
the  larynx.  During  a  regular  act  of  swallowing,  nothing  can  find  its  way  into  the  respir- 
atory passages,  so  complete  is  the  protection  of  the  larynx  during  the  period  when  the 
food  passes  through  the  pharynx  into  the  oesophagus. 

The  situation  of  the  epiglottis  has  naturally  led  physiologists  to  attribute  to  it  great 
importance  in  preventing  the  entrance  of  particles  of  food  and  liquids  into  the  larynx.  It 
will  be  remembered  that  this  cartilaginous,  leaf-like  process  is  attached  to  the  anterior 
portion  of  the  larynx,  and  is  usually  erect,  lying  against  the  base  of  the  tongue.  In  the 
movements  of  the  tongue  and  larynx  incident  to  deglutition,  the  epiglottis  is  necessarily 
applied  to  the  superior  face  of  the  larynx  so  as  to  close  the  opening.  Although,  during 
deglutition,  the  glottis  is  covered  in  this  way,  it  is  necessary  to  study  closely  all  the  con- 
ditions which  are  involved  and  to  ascertain  what  is  the  actual  value  of  each  of  the  various 
means  by  which  entrance  of  foreign  bodies  into  the  air-passages  is  prevented,  for  this 
protection  is  accomplished  by  several  distinct  provisions. 

It  is  evident,  from  the  anatomy  of  the  parts  and  the  necessary  results  of  the  contrac- 
tions of  the  muscles  of  deglutition,  that,  while  the  food  is  passing  through  the  pharynx, 
the  larynx,  by  its  elevation,  passes  under  the  tongue  as  it  moves  backward,  and  the  soft 
base  of  this  organ  is,  as  it  were,  moulded  over  the  glottis.  With  the  parts  removed  from 
the  human  subject  or  from  one  of  the  inferior  animals,  we  can  imitate  the  natural  move- 
ments of  the  tongue  and  larynx,  and  it  is  evident  that  this  provision  alone  must  be  suffi- 
cient to  protect  the  larynx  from  the  entrance  of  solid  or  semisolid  particles  of  food, 
particularly  when  we  remember  how  the  alimentary  particles  are  agglutinated  by  the 
saliva  and  how  easy  their  passage  becomes  over  the  membrane  coated  with  a  slimy 
mucus.  Experiments  on  the  inferior  animals  and  observations  upon  the  human  subject 
have  conclusively  settled  the  question  that  the  deglutition  of  all  articles,  except  liquids,  is 
generally  effected  without  difficulty  when  the  epiglottis  has  been  removed,  or  lost  by 
accident  or  disease.  The  same  is  true  when,  in  addition,  the  intrinsic  muscles  of  the 
larynx  have  been  paralyzed  by  the  section  of  nerves,  or  even  when  closure  of  the  rima 
glottidis  is  forcibly  prevented.  It  has  been  shown,  however,  by  the  experiments  of 
Longet,  that,  when  the  larynx  is  in  part  prevented  from  performing  its  movement  of 
ascension,  the  deglutition  of  a  moist  mass  of  alimentary  matter  is  effected  with  difficulty 
and  is  followed  by  a  sharp  cough,  indicating  the  entrance  of  a  certain  quantity  of  foreign 
matter  into  the  air-passages. 

It  is  impossible  for  the  muscles  of  the  pharynx  to  contract  without  drawing  together 
the  sides  of  the  larynx,  to  which  they  are  attached,  and  assisting  to  close  the  glottis.  At 
the  same  time,  as  the  movements  of  respiration  are  arrested  during  deglutition,  the  lips 
of  the  glottis  fall  together,  as  they  always  do  except  in  inspiration.  This  fact  we  have 
repeatedly  observed  in  demonstrating  the  respiratory  movements  of  the  glottis;  for, 
when  the  larynx  is  thus  exposed,  the  animal  makes  frequent  efforts  at  deglutition.  In 
addition  to  this  passive  and  incomplete  approximation  of  the  vocal  chords,  it  has  repeat- 
edly been  observed  that  the  lips  of  the  glottis  are  accurately  and  firmly  closed  during 
each  act  of  deglutition. 

Longet  justly  attaches  great  importance  to  the  exquisite  sensibility  of  the  top  of  the 
larynx  in  preventing  the  entrance  of  foreign  substances.  His  experiments  of  dividing  all 
the  nervous  filaments  distributed  to  the  intrinsic  muscles  show  that  their  action  is  not 
essential.  But,  on  division  of  the  superior  laryngeal,  the  nerve  which  gives  sensibility 
to  the  parts,  he  found  that  liquids  occasionally  passed  in  small  quantity  into  the  trachea. 
This  is  attributed  to  the  want  of  sensibility  in  the  mucous  membrane  above  the  glottis : 
"for  the  animal  is  not  aware  in  time  of  the  presence  of  liquid  which  may  accidentally 
get  into  the  supra-laryngeal  cavity,  the  occlusion  of  the  glottis  is  sometimes  too  tardy 
and  does  not  take  place  until  after  the  passage  of  the  liquid ;  or,  again,  the  animal,  in- 
stead of  then  making  a  sudden  expiration,  makes  an  unseasonable  inspiration  which 
facilitates  the  introduction  of  the  foreign  substance  into  the  air-passages,  and  the  cough 


222  DIGESTION. 

does  not  take  place  until  this  is  already  in  contact  with  the  tracheal  or  bronchial  mucous 
membrane."  These  experiments  strikingly  illustrate  the  conservative  function  of  the 
acute  sensibility  of  the  mucous  membrane  above  the  glottis.  No  foreign  substance  can 
find  its  way  into  the  air-passages  by  simply  dropping  into  the  cavity  situated  above  the 
vocal  cords  when  respiration  is  interrupted,  but  can  only  enter  by  being  drawn  in  forcibly 
and  suddenly  with  an  act  of  inspiration,  when  the  glottis  is  widely  opened.  It  is  now 
well  known  to  the  practical  physician  that  direct  applications  cannot  be  made  to  the  in- 
terior of  the  larynx,  unless  an  instrument  be  suddenly  introduced  with  the  inspiratory  act ; 
and,  at  this  time,  a  little  dexterity  will  enable  an  operator  to  introduce  bodies  of  consider- 
able size  below  the  vocal  chords. 

Before  the  experiments  of  Magendie,  in  1813,  physiologists  were  generally  of  the 
opinion,  judging  from  anatomical  relations,  that  the  epiglottis  had  the  function  of  pro- 
tecting the  larynx  from  the  entrance  of  particles  of  food  during  the  second  period  of  deg- 
lutition. Magendie  extirpated  the  entire  epiglottis  in  dogs  and  found  that  the  animals 
swallowed  liquids  and  solids  without  difficulty,  the  act  being  very  seldom  followed  by 
cough.  The  observations  on  deglutition  were  made  an  hour  after  the  removal  of  the 
epiglottis.  In  other  animals,  the  superior  and  inferior  laryngeal  nerves  were  divided, 
thus  paralyzing  the  muscles  of  the  glottis.  The  deglutition  of  liquids  especially  be- 
came difficult  and  was  followed  generally  by  cough.  As  the  result  of  these  observations, 
Magendie  came  to  the  conclusion  that  the  larynx  is  protected  during  deglutition  by  clos- 
ure of  the  glottis  itself. 

Although  the  experiments  on  animals  were  apparently  conclusive,  observations  on 
the  human  subject  have  been  cited,  in  which,  after  destruction  of  the  epiglottis  by  dis- 
ease, there  existed  persistent  difficulty  in  swallowing  liquids.  As  numerous  pathological 
observations  of  this  character  have  been  reported,  the  question  could  not  be  regarded  as 
entirely  settled  by  the  researches  of  Magendie.  It  was  with  the  view  of  determining 
this  more  rigorously,  that  farther  experiments  were  instituted  in  1841,  by  Longet. 

In  investigating  this  question,  Longet  removed  the  epiglottis  from  six  dogs.  He  found 
that,  in  the  animals  kept  until  the  parts  were  perfectly  cicatrized,  more  or  less  cough 
followed  the  deglutition  of  liquids.  One  of  these  he  kept  for  six  months  and  found  that 
when  he  drank  milk  or  water  cough  never  failed  to  follow.  The  same  fact  was  noted  in 
three  of  the  animals  that  were  killed  on  the  nineteenth  day  and  in  one  that  was  killed 
on  the  thirtieth  day.  In  all,  the  complete  excision  of  the  epiglottis  was  verified  by  post- 
mortem examination.  In  one  of  the  animals,  killed  two  days  after  the  operation,  that 
generally  swallowed  liquids  without  coughing,  there  was  found  a  swelling  at  the  base  of 
the  tongue  which  projected  over  the  larynx. 

Several  cases  of  loss  of  the  epiglottis  in  the  human  subject  are  quoted  by  Longet  in 
support  of  his  view  that  this  part  is  necessary  to  the  complete  protection  of  the  air-pas- 
sages, particularly  in  the  deglutition  of  liquids.  Two  of  the  most  striking  of  these  cases 
were  observed  by  Larrey,  in  Egypt.  One  of  these  was  the  case  of  General  Murat,  who 
was  wounded  by  a  ball  passing  through  the  neck  from  one  angle  of  the  jaw  to  the  other, 
cutting  off  the  epiglottis,  which  was  expelled  by  the  mouth.  In  this  instance,  the  diffi- 
culty in  the  deglutition  of  liquids  was  so  great,  that  it  became  necessary  to  introduce 
them  through  a  tube  passed  into  the  oesophagus.  In  the  other  case,  the  epiglottis  was 
entirely  removed  by  a  wound  and  was  preserved  and  presented  to  the  surgeon.  In 
this  instance,  the  difficulty  in  the  deglutition  of  liquids  was  even  greater  than  in  the 
former;  each  effort  at  swallowing  being  followed  by  convulsive  and  suffocating  cough. 
This  difficulty  persisted  after  the  parts  had  become  completely  cicatrized.  In  these  cases, 
it  is  possible  that  the  injury  to  muscles  and  other  parts  from  such  severe  wounds  might 
interfere  with  the  movements  of  the  larynx  or  the  closure  of  the  glottis  and  thus  disturb 
deglutition.  In  a  case  in  which  the  epiglottis  had  entirely  sloughed  away  as  a  conse- 
quence of  syphilitic  disease,  observed  by  Dr.  Austin  Flint,  the  difficulty  in  swallowing 
liquids,  although  sufficiently  well  marked,  was  by  no  means  so  great  as  in  the  cases  men- 


DEGLUTITION.  333 

tioned  above.  The  difficulty  in  swallowing  was  noted  as  not  great,  but  the  patient  swal- 
lowed liquids  more  easily  than  solids.  The  difficulty  consisted  of  cough  and  loss  of  breath, 
as  the  patient  described  it.  It  was  less  when  articles  were  swallowed  while  the  patient 
was  in  the  recumbent  posture,  and  food  and  drink  were  habitually  taken  in  that  position. 
At  the  time  that  this  patient,  a  female,  was  in  the  Belle vue  Hospital  under  the  observa- 
tion of  Dr.  Flint,  the  deglutition  was  improving.  Dr.  Flint  noted  that,  after  she  had  been 
in  the  hospital  a  few  days,  on  causing  her  to  swallow  in  his  presence,  the  act  of  degluti- 
tion was  performed  with  a  certain  deliberation  but  without  difficulty.  An  examination 
of  the  parts  with  the  laryngoscope  was  made  by  Dr.  Church,  in  the  presence  of  Dr.  Flint 
and  Dr.  Dalton :  "  The  absence  of  the  epiglottis  was  determined  by  sight.  The  vocal 
chords  were  distinctly  seen.  The  little  excrescences  described  as  apparent  to  the  touch 
were  visible." 

In  the  case  just  described,  there  was  not  a  constant  and  considerable  difficulty  in 
deglutition  ;  but  it  is  stated  that  difficulty  had  existed,  undoubtedly  from  the  passage  of 
articles  into  the  larynx,  and  when  no  such  accident  took  place  the  act  was  performed 
with  a  "  certain  deliberation."  It  is  a  curious  fact,  also,  that,  when  the  difficulty  in  swal- 
lowing was  considerable,  deglutition  was  accomplished  most  easily  in  the  recumbent 
posture,  in  which  the  tendency  of  particles  of  food  to  pass  into  the  larynx  must  have  been 
much  lessened. 

While,  with  attention  on  the  part  of  the  subject,  the  larynx  may  frequently,  and  per- 
haps generally,  be  protected  from  the  entrance  of  foreign  substances  during  deglutition, 
after  loss  of  the  epiglottis  when  other  parts  are  not  affected,  a  study  of  the  numerous 
cases  of  this  lesion  as  the  result  of  disease  or  injury  shows  that  the  epiglottis  is  by  no 
means  so  inefficient  in  the  protection  of  the  larynx  as  was  supposed  by  Magendie.  Still, 
it  is  but  one  of  the  means  which  have  been  provided  for  this  end. 

Since  the  air-passages  have  been  so  fully  explored  by  means  of  the  laryngoscope,  this 
instrument  has  been  used  to  a  certain  extent  in  the  study  of  the  phenomena  of  degluti- 
tion. In  July,  1865,  a  note  was  presented  to  the  French  Academy  of  Sciences,  giving 
the  results  of  experiments  by  Dr.  Krishaber  on  the  mechanism  of  deglutition  as  studied 
by  autolaryngoscopy,  followed  by  a  note  on  the  same  subject  by  M.  H.  Guinier.  Dr. 
Krishaber,  as  the  result  of  his  observations,  gave  the  following  conclusions : 

"  1st.  In  the  act  of  deglutition  the  alimentary  bolus  passes  in  one  of  the  pharyngeal 
grooves,  over  one  of  the  sides  of  the  epiglottis  tilted  by  the  elevation  of  the  larynx ;  the 
bolus  thus  arrives  at  the  oesophagus  at  the  moment  when,  by  the  contraction  of  the  con- 
strictor muscles,  the  pharynx  is  shortened  and  brought  in  front  of  the  mass. 

"  2d.  The  deglutition  of  liquids  is  effected  in  the  same  manner ;  these  passing,  how- 
ever, quite  frequently  upon  the  epiglottis  itself,  which  happens  very  rarely  with  solid  ali- 
ments. 

u  3d.  A  quantity — extremely  small,  it  is  true — of  liquid  engages  itself  during  normal 
deglutition  around  the  border  of  the  epiglottis  and  moistens  the  mucous  membrane  of 
the  larynx  and  even  of  the  vocal  chords. 

"  4th.  In  gargling,  the  larynx  being  widely  opened,  a  larger  quantity  finds  its  way 
into  the  vocal  organ. 

"  5th.  An  alimentary  bolus  may  be  easily  tolerated  in  the  respiratory  passages ;  that 
is  to  say,  in  the  larynx,  as  far  as  the  vocal  chords  and  even  in  the  interior  of  the  trachea. 

"  6th.  The  sensibility  of  the  trachea  to  the  impression  of  foreign  bodies  is  infinitely 
less  than  that  of  the  larynx. 

"  Yth.  Hard  and  cold  bodies,  as,  for  example,  a  sound,  are  not  tolerated  in  the  respir- 
atory passages ;  while  any  soft  body,  which  can  adhere  to  the  mucous  membrane  and 
has  a  temperature  like  that  of  the  parts  touched,  is  easily  tolerated  in  the  respiratory 
passages  and  kept  in  the  trachea  many  minutes  without  producing  the  slightest  cough." 

These  observations  confirm  the  views  of  Longet  and  others  concerning  the  passage  of 
alimentary  substances  down  the  pharynx  by  the  sides  of  the  epiglottis ;  and,  in  that  case, 


224  DIGESTION. 

liquids  would  almost  certainly  pass  around  the  borders  in  quantity  sufficient  to  moisten 
the  mucous  membrane  below.  It  must  be  remembered,  however,  that  the  sensibility  of 
the  air-passages  is  very  unequal  in  different  persons,  and  that  it  may  be  considerably 
modified  by  education  of  the  parts.  This  should  make  us  hesitate  to  accept  the  view 
that,  in  gargling,  the  larynx  receives  a  quantity  of  liquid,  and  that  an  alimentary  bolus 
may  be  tolerated  in  the  trachea  for  many  minutes  without  coughing. 

To  sum  up  the  mechanism  by  which  the  opening  of  the  larynx  is  protected  during  the 
deglutition  of  solids  and  liquids,  we  have  only  to  carefully  follow  the  articles  as  they  pass 
over  the  inclined  plane  formed  by  the  back  of  the  tongue  and  the  anterior  and  inferior 
part  of  the  pharynx.  As  the  food  is  making  this  passage  in  obedience  to  the  contraction 
of  the  muscles  which  carry  the  tongue  backward,  draw  up  the  larynx,  and  constrict  the 
pharynx,  the  soft  base  of  the  tongue  and  the  upper  part  of  the  larynx  are  applied  to  each 
other,  with  the  epiglottis,  which  is  now  inclined  backward,  between  them ;  at  the  same 
time  the  glottis  is  closed,  in  part  by  the  action  of  the  constrictor  muscles  attached  to  the 
sides  of  the  thyroid  cartilages,  and  in  part  by  the  action  of  its  intrinsic  muscles.  If  the 
food  be  tolerably  consistent  and  united  into  a  single  bolus,  it  slips  easily  from  the  back 
of  the  tongue  along  the  membrane  covering  the  anterior  and  inferior  part  of  the  phar- 
ynx ;  but  if  it  be  liquid  or  of  little  consistence,  a  portion  takes  this  course,  while  another 
portion  passes  over  the  epiglottis,  being  directed  by  it  into  the  two  grooves  or  gutters  by 
the  side  of  the  larynx.  It  is  by  these  means,  together  with  those  by  which  the  posterior 
nares  are  protected,  that  all  solids  and  liquids  are  passed  into  the  oesophagus,  and  the 
second  period  of  deglutition  is  safely  accomplished. 

The  third  period  of  deglutition  is  the  most  simple  of  all.  It  involves  merely  contrac- 
tions of  the  muscular  walls  of  the  oesophagus,  by  which  the  food  is  forced  into  the  stom- 
ach. The  longitudinal  fibres  shorten  the  tube  and  slip  the  mucous  membrane,  lubricated 
by  its  glairy  secretion,  above  the  bolus  ;  while  the  circular  fibres,  by  a  progressive  peri- 
staltic contraction  from  above  downward,  propel  the  food  into  the  stomach.  The  pas- 
sage of  food  down  the  oesophagus  was  for  the  first  time  closely  studied  by  Magendie, 
who  noted,  in  this  connection,  many  curious  and  important  facts.  In  numerous  experi- 
ments on  the  lower  animals,  he  observed  that,  while  the  peristaltic  contractions  of  the 
upper  two-thirds  of  the  tube  were  immediately  followed  by  a  relaxation,  which  contin- 
ued till  the  next  act  of  deglutition,  the  lower  third  remained  contracted  generally  for 
about  thirty  seconds  after  the  passage  of  the  food  into  the  stomach.  During  its  contrac- 
tion, this  part  of  the  oesophagus  was  hard,  like  a  cord  firmly  stretched.  This  was  fol- 
lowed by  relaxation  ;  and  this  alternate  contraction  and  relaxation  continued  constantly, 
even  when  the  stomach  was  empty,  although,  during  digestion,  the  contractions  were  fre- 
quent in  proportion  to  the  quantity  of  food  in  the  stomach.  The  contraction  was  always 
increased  by  pressing  the  stomach  and  attempting  to  pass  some  of  its  contents  into  the 
oesophagus.  This  provision  is  undoubtedly  important  in  preventing  regurgitation  of  the 
contents  of  the  stomach,  especially  when  the  organ  is  exposed  to  pressure,  as  in  urina- 
tion or  defsecation.  We  have  already  noted  the  action  of  the  crura  of  the  diaphragm, 
which  has  a  tendency  to  close  the  cesophageal  opening  during  inspiration. 

The  length  of  time  occupied  in  the  third  period  of  deglutition  was  noted  by  Magendie 
in  the  inferior  animals,  but  we  have  been  unable  to  find  any  definite  observations  on  this 
point  in  the  human  subject,  although  this  would  have  been  easy  in  the  cases  of  gastric 
fistula  which,  from  time  to  time,  have  come  under  the  observation  of  physiologists.  Ma- 
gendie found  that  the  alimentary  bolus  sometimes  occupied  two  or  three  minutes  in  its 
passage,  and  that  it  was  often  momentarily  arrested  in  its  course.  It  frequently  seems  as 
though  we  were  ourselves  conscious  of  a  very  slow  passage  of  food  down  the  oesophagus, 
and  not  infrequently  a  piece  of  bread  or  a  mouthful  of  liquid  is  taken  to  hasten  it ;  but 
it  is  not  probable  that  every  alimentary  bolus  remains  for  two  or  three  minutes  in  the 
oesophagus,  and  liquids  undoubtedly  are  swallowed  with  considerable  rapidity,  as  they 


DEGLUTITION.  225 

•can  soon  be  recognized  in  the  stomach  by  their  temperature.  As  the  lower  part  of  the 
•oesophagus  is  composed  chiefly  of  unstriped  muscular  fibres,  it  is  probable  that  here  the 
contractions  are  more  gradual  than  in  the  upper  portions. 

As  we  have  already  had  occasion  to  remark,  the  muscular  movements  which  take  place 
during  all  the  periods  of  deglutition  are  peculiar.  The  first  act  is  generally  involuntary  from 
inattention,  but  it  is  under  the  control  of  the  will.  The  second  act  is  involuntary  when 
once  commenced,  but  may  be  excited  by  the  voluntary  passage  of  solids  or  liquids  beyond 
the  velum  pendulum  palati.  It  is  impossible  to  perform  the  second  act  of  deglutition  un- 
less there  be  some  article,  either  solid  or  liquid,  in  the  pharynx.  It  is  easy  to  make  three 
or  four  successful  efforts  consecutively,  in  which  there  is  elevation  of  the  larynx  with  all 
the  other  characteristic  movements ;  but  a  little  attention  will  show  that  with  each  act 
a  small  quantity  of  saliva  is  swallowed.  When  the  efforts  have  been  frequently  repeat- 
ed, the  movements  become  impossible,  until  time  enough  has  elapsed  between  them  for 
the  saliva  to  collect.  This  fact  we  personally  verified  before  writing  this  paragraph, 
and  it  was  demonstrated  to  be  due  to  the  absence  of  liquid ;  for,  immediately  after,  an 
ounce  of  water  was  swallowed  without  difficulty  by  sixteen  successive  movements  of 
deglutition.  This  experiment  also  shows  the  small  quantity  of  liquid  (only  half  a  drachm) 
necessary  to  excite  the  contraction  of  the  muscles  concerned  in  the  second  act. 

All  the  movements  of  deglutition,  except  those  of  the  first  period,  must  be  regarded  as 
essentially  reflex,  depending  upon  an  impression  made  upon  the  afferent  nerves  distrib- 
uted to  the  mucous  membrane  of  the  pharynx  and  oesophagus. 

The  position  of  the  body  has  little  to  do  with  the  facility  with  which  deglutition  is 
effected.  Liquids  or  solids  may  be  swallowed  indifferently  in  all  postures.  Berard  states 
that  a  juggler,  in  his  presence,  passed  an  entire  bottle  of  wine  from  the  mouth  to  the 
stomach,  while  standing  on  his  head.  The  same  feat  we  have  lately  seen  accomplished 
with  apparent  ease,  by  a  juggler  who  drank  three  glasses  of  beer  while  standing  on  his 
hands  in  the  inverted  posture. 

Deglutition  of  Air. — In  the  celebrated  essay  of  Magendie  on  the  mechanism  of  vom- 
iting, it  is  stated  that  as  soon  as  nausea  commenced  the  stomach  began  to  fill  with  air,  so 
that,  before  vomiting  occurred,  the  organ  became  tripled  in  size.  Magendie  showed,  far- 
therm  ore,  that  the  air  entered  the  stomach  by  the  oesophagus,  for  the  distention  occurred 
when  the  pylorus  was  ligated.  In  a  subsequent  memoir,  the  question  of  the  deglutition 
of  air,  aside  from  the  small  quantity  which  is  incorporated  with  the  food  during  mastica- 
tion and  insalivation,  was  farther  investigated.  It  was  found  that  some  persons  had  the 
faculty  of  swallowing  air,  and,  by  practice,  Magendie  himself  was  able  to  acquire  it, 
although  it  occasioned  such  distress  that  it  was  discontinued.  Out  of  a  hundred  students 
of  medicine,  eight  or  ten  were  found  able  to  swallow  air. 

It  is  not  very  uncommon  to  find-  persons  who  have  gradually  acquired  this  habit  in 
order  to  relieve  uncomfortable  sensations  in  the  stomach ;  and,  when  -confirmed,  it  occa- 
sions persistent  disorder  in  the  process  of  digestion.  Quite  a  number  of  cases  of  this 
kind  are  reported  by  Magendie,  and  in  several  it  was  carried  to  such  an  extent  as  to  pro- 
duce great  distention  of  the  abdomen.  A  curious  case  of  habitual  air-swallowing  is  re- 
ported by  Dr.  Austin  Flint,  in  his  work  on  the  Practice  of  Medicine. 

Although  the  subject  of  air-swallowing  properly  belongs  to  pathology,  the  fact  that 
the  muscles  of  deglutition  are  capable,  in  some  individuals,  of  forcing  air  into  the  stom- 
ach, is  not  without  physiological  interest. 

15 


226  DIGESTION. 

CHAPTER    VIII. 

8TOMA  CH-DIGESTION. 

Physiological  anatomy  of  the  stomach — Glandular  apparatus  in  the  stomach — Gastric  juice — Mode  of  obtaining  the  gas- 
tric juice— Gastric  fistula  in  the  human  subject— Secretion  of  the  gastric  juice— Composition  of  the  gastric  juice- 
Source  of  the  acidity  of  the  gastric  juice — Ordinary  saline  constituents  of  the  gastric  juice — Action  of  the  gastric 
juice  in  digestion— Constituents  on  which  the  activity  of  the  gastric  juice  depends— Action  of  the  gastric  juice 
upon  meats — Action  upon  albumen,  fibrin,  caseine,  and  gelatine — Action  upon  vegetable  nitrogenized  principles — 
Albuminose,  or  peptones — Action  of  the  gastric  juice  upon  fats — Action  upon  saccharine  and  amylaceous  principles 
—Duration  of  stomach-digestion— Digestibility  of  different  aliments  in  the  stomach— Action  of  the  gastric  juice 
upon  the  coats  of  the  stomach— Circumstances  which  influence  stomach-digestion — Character  of  the  contractions 
of  the  muscular  coat  of  the  stomach— Movements  in  the  cardiac  and  in  the  pyloric  portion— Mechanism  of  the 
movements  of  the  stomach — Rumination,  and  regurgitation  from  the  stomach — Rumination  in  the  human  sub- 
ject—Vomiting— Condition  of  the  stomach  during  the  act  of  vomiting— Action  of  the  diaphragm  in  vomiting- 
Action  of  the  abdominal  muscles  in  vomiting — Action  of  the  oesophagus  in  vomiting — Eructation. 

Physiological  Anatomy  of  the  Stomach. 

THE  most  dilated  portion  of  the  alimentary  canal,  in  man,  is  the  stomach.  It  serves 
the  double  purpose  of  a  receptacle  for  the  food  and  an  organ  in  which  certain  important 
digestive  processes  take  place.  It  is  situated  in  the  upper  part  of  the  abdominal  cavity 
and  is  held  in  place  by  folds  of  the  peritoneum  and  by  the  oesophagus.  Its  form  is  not 
easily  described.  It  has  been  compared  to  a  bagpipe,  which  it  resembles  somewhat, 
when  moderately  distended.  As  we  should  naturally  suppose  from  the  fact  that  the 
stomach  periodically  receives  considerable  quantities  of  solids  and  liquids,  its  form  and 
position  are  subject  to  great  variations.  When  empty,  it  is  flattened,  and  in  many  parts 
its  opposite  walls  are  in  contact.  When  moderately  distended,  its  length  is  from  thirteen 
to  fifteen  inches,  its  widest  diameter,  about  five  inches,  and  its  capacity,  one  hundred  and 
seventy-five  cubic  inches,  or  about  five  pints.  The  parts  usually  noted  in  anatomical  de- 
scriptions are :  a  greater  and  a  lesser  curvature  ;  a  greater  and  a  lesser  pouch ;  a  cardiac, 
or  cesophageal  opening  ;  and  a  pyloric  opening,  which  leads  to  the  intestinal  canal.  The 
great  pouch  is  sometimes  called  the  fundus. 

The  coats  of  the  stomach  are  three  in  number ;  the  peritoneal,  muscular,  and  mucous. 
By  some,  the  fibrous  tissue  which  unites  the  mucous  to  the  muscular  coat  is  regarded  as 
a  distinct  covering  and  is  called  the  fibrous  coat. 

Peritoneal  Coat. — This  is  simply  a  process  of  the  peritoneum,  similar  in  structure  to 
the  membrane  which  covers  the  other  abdominal  viscera.  It  is  a  reflection  of  the  mem- 
brane which  lines  the  general  abdominal  cavity,  which,  on  the  viscera,  is  somewhat  thin- 
ner than  it  is  on  the  walls  of  the  cavity.  Over  the  stomach,  the  peritoneum  is  from  ¥^ 
to  iroT  °f  an  mcn  m  thickness.  It  belongs  to  the  class  of  serous  membranes  and  con- 
sists'of  fibres  of  the  white  inelastic  tissue,  mingled  with  a  considerable  number  of  elastic 
fibres.  It  is  closely  adherent  to  the  subjacent  muscular  coat  and  is  not  very  abundantly 
supplied  with  blood-vessels  and  nerves.  Lymphatics  have  been  demonstrated  only  in  the 
subserous  structure.  The  surface  of  the  peritoneum  is  everywhere  covered  with  regu- 
larly-polygonal, flattened  cells  of  pavement  or  tessellated  epithelium,  closely  adherent  to 
each  other  and  presenting  a  perfectly  smooth  surface  which  is  continually  moistened 
with  a  small  quantity  of  watery  secretion.  An  important  function  of  this  membrane  is 
to  present  a  smooth  surface  covering  the  abdominal  parietes  and  viscera,  so  as  to  allow 
of  free  movements  of  the  organs  over  each  other  and  against  the  walls  of  the  abdomen. 

Muscular  Coat. — Throughout  the  whole  of  the  alimentary  canal,  from  the  cardiac 
opening  of  the  stomach  to  the  anus,  the  muscular  fibres  forming  the  middle  coat  are  of 


PHYSIOLOGICAL  ANATOMY   OF  THE   STOMACH.  227 

the  involuntary,  pale,  or  unstriped  variety.  These  fibres,  called  sometimes  muscular 
fibre-cells,  are  very  pale,  with  faint  outlines,  fusiform  or  spindle-shaped,  and  contain  each 
an  oval,  longitudinal  nucleus.  They  are  very  closely  adherent  by  their  sides,  and  are  so 
arranged  as  to  dovetail  into  each  other,  forming  sheets  of  greater  or  less  thickness, 
depending  upon  the  number  of  their  layers.  The  muscular  coat  of  the  stomach  varies  in 
thickness  in  different  animals.  In  the  human  subject,  it  is  thickest  in  the  region  of  the 
pylorus  and  is  thinnest  at  the  fundus.  Its  average  thickness  is  about  -^  of  an  inch.  In 
the  pylorus,  it  is  from  ^  to  T^  of  an  inch  thick,  and  in  the  fundus,  from  ^  to  -£%  of  an  inch. 
The  muscular  fibres  exist  in  the  stomach  in  two  principal  layers ;  an  external,  longi- 
tudinal layer  and  an  internal,  circular  layer,  with  a  third  layer  of  oblique  fibres  extending 
over  the  great  pouch  only,  which  is  internal  to  the  circular  layer.  The  direction  of  the 
fibres  in  these  layers  can  generally  be  seen  in  a  stomach  which  has  been  dried  and  inflated. 
The  longitudinal  fibres  are  continued  from  the  oesophagus  and  are  most  marked  over  the 
lesser  curvature.  They  are  not  continued  very  distinctly  over  the  rest  of  the  stomach. 
The  circular  and  oblique  fibres  are  best  seen  when  the  organ  has  been  everted  and  the 
mucous  membrane  carefully  removed.  The  circular  layer  is  not  very  distinct  to  the  left 
of  the  cardiac  opening,  over  the  great  pouch,  but  in  other  parts  it  is  tolerably  regular. 
Toward  the  pylorus,  the  fibres  become  more  numerous,  and,  at  the  opening  into  the 
duodenum,  they  form  a  powerful  muscular  ring,  which  is  sometimes  called  the  sphincter 
of  the  pylorus,  or  the  pyloric  muscle.  At  this  point  they  project  considerably  into  the 
interior  of  the  organ  and  cease  abruptly  at  the  opening  into  the  duodenum,  so  as  to  form 
a  sort  of  valve,  presenting,  when  contracted,  a  flat  surface  looking  toward  the  intestine. 
The  oblique  layer  takes  the  place,  in  great  part,  of  the  circular  fibres  over  the  great 
pouch.  It  extends  obliquely  over  the  fundus  from  left  to  right  and  ceases  at  a  distinct 
line  extending  from  the  left  margin  of  the  oesophagus  to  about  the  junction  of  the  middle 
with  the  last  third  of  the  great  curvature.  This  anatomical  fact  is  interesting,  for  it 
is  at  about  the  point  where  the  oolique  layer  of  fibres  ceases  that  the  stomach  becomes 
constricted  during  the  movements  which  are  incident  to  digestion,  dividing  the  organ  into 
two  tolerably  distinct  compartments. 


FIG.  54.— Longitudinal  fibres  of  the  stomach.    (Sappey.) 

1,  lesser  curvature ;  2,  2,  greater  curvature ;  3,  greater  pouch ;  4,  lesser  pouch ;  5, 6, 6,  lower  end  of  the  oesophagus ;  7,T, 
pylorus ;  8,  8,  longitudinal  fibres  at  the  lesser  curvature ;  9,  fibres  extending  over  the  greater  curvature ;  10, 10, 
a  very  thin  layer  of  longitudinal  fibres  over  the  anterior  surface  of  the  stomach;  11,  circular  fibres  seen  through 
the  thin  layer  of  longitudinal  fibres. 


228 


DIGESTION. 


The  blood-vessels  of  the  muscular  coat  are  quite  numerous  and  are  arranged  in  a 
peculiar,  rectangular  net-work,  which  they  always  present  in  the  non-striated  muscular 
tissue.  The  nerves  belong  chiefly  to  the  sympathetic  system  and  are  demonstrated  with 
difficulty. 


FIG.  55. — Fibres  seen  with  the  stomach  everted.   (Sappey.) 

1, 1,  oesophagus ;  2,  circular  fibres  at  the  cesophageal  opening;  3,  8,  circular  fibres  at  the  lesser  curvature ;  4,  4,  circu- 
lar fibres  at  the  pylorus ;  5,  5,  6,  7,  8,  oblique  fibres ;  9,  10,  fibres  of  this  layer  covering  the  greater  poxich ;  11,  por- 
tion of  the  stomach  from  which  these  fibres  have  been  removed  to  show  the  subjacent  circular  fibres. 

Mucous  Coat. — Passing  from  the  oesophagus  to  the  stomach,  a  very  marked  change 
takes  place  in  the  character  of  the  mucous  membrane.  The  white,  hard  appearance  of 
the  cesophageal  lining,  due  to  its  covering  of  pavement-epithelium,  abruptly  ceases,  pre- 
senting a  sharply-defined,  dentated  border;  and  the  membrane  of  the  stomach  is  soft, 

velvety  in  appearance,  and  of  a  reddish-gray 
color.  In  some  of  the  inferior  animals,  as  the 
horse,  the  characteristic  membrane  of  the  oesoph- 
agus is  prolonged  into  the  stomach  and  forms 
a  large,  white  zone  around  the  cardiac  opening, 
with  abruptly-defined  edges,  contrasting  strong- 
ly with  the  rest  of  the  lining  membrane  of  the 
stomach. 

The  mucous  lining  of  the  stomach  is  loosely 
attached  to  the  submucous  muscular  tissue  and 
is  thrown  into  large,  longitudinal  folds,  which 
become  effaced  as  the  organ  is  distended.  When 
the  muscular  coat  of  the  stomach  is  in  a  condi- 
tion of  cadaveric  rigidity,  the  longitudinal  fold- 
ing of  the  mucous  membrane  is  very  marked. 

FIG.  56.— Pits  in  the  mucous  membrane  of  the   if  the  mucous  membrane  be  stretched  or  if  the 
stomach,  and  orifices  of  the  glands ;  mag- 
nified 20  diameters.   (Sappey.)  stomach  be    everted    and    distended,    and    the 

^'ofthe^ast^^  mucus,  which   always  exists  in  greater  or  less 

abundance  over  the  surface,  be  gently  removed 

under  a  stream  of  water,  the  membrane  will  be  found  marked  with  innumerable  po- 
lygonal pits  or  depressions,  enclosed  by  ridges,  which,  in  some  parts  of  the  organ,  are 
quite  regular.  These  are  best  seen  with  the  aid  of  a  simple  lens,  as  many  of  them  are 


PHYSIOLOGICAL   ANATOMY   OF   THE   STOMACH.  339 

quite  small.  The  size  of  the  pits  is  very  variable,  but  the  average  is  about  ^  of  an 
inch.  This  appearance  is  not  distinct  toward  the  pylorus ;  the  membrane  here  present- 
ing irregular,  conical  projections  and  well-marked  villi  resembling  those  found  in  the 
small  intestine.  The  surface  of  the  mucous  membrane  is  covered  with  columnar  or  pris- 
moidal  epithelium,  the  cells  being  tolerably  regular  in  shape,  each  with  a  clear  nucleus 
and  a  distinct  nucleolus. 

The  thickness  of  the  mucous  membrane  of  the  stomach  varies  in  different  parts.  It 
is  usually  thinnest  near  the  oesophagus  and  thickest  near  the  pylorus.  Its  thinnest  portion 
measures  from  ^  to  -fa  of  an  inch ;  its  thickest  portion,  from  j1^  to  -XV  of  an  inch ;  and 
the  intermediate  portion,  about  ^  of  an  inch. 

Glandular  Apparatus  of  the  Stomach. — Extending  from  the  bottoms  of  the  pits  in  the 
mucous  membrane  of  the  stomach  to  the  submucous  connective  tissue,  are  immense  num- 
bers of  racemose  glands.  These  are  generally  arranged  in  tolerably  distinct  groups,  sur- 
rounded by  fibrous  tissue,  each  group  belonging  to  one  of  the  polygonal  depressions. 
The  tissue  which  connects  the  tubes  is  dense  but  not  abundant.  There  are  marked  dif- 
ferences in  the  anatomy  of  the  glands  of  the  stomach  in  different  parts  of  the  organ, 
which  are  particularly  interesting,  as  they  are  supposed  to  correspond  with  differences  in 
the  function  of  various  parts  of  the  mucous  membrane.  There  are,  indeed,  two  distinct 
varieties  of  glands;  the  gastric  glands,  found  throughout  the  organ,  except  in  the  pyloric 
portion,  and  the  mucous  glands  found  chiefly  in  the  pyloric  portion,  with  a  few  scattered 
irregularly  through  the  other  portions  of  the  mucous  membrane.  These  demand  special 
consideration,  as  the  former  are  supposed  to  secrete  the  gastric  juice  and  are  active  only 
during  digestion,  while  the  latter  secrete  a  glairy  mucus,  which  is  not  produced  specially 
during  digestion  and  which  has  no  distinct  digestive  function  with  which  we  are  ac- 
quainted. 

Gastric,  or  Peptic  Glands. — These  glands  are  found  throughout  the  entire  extent  of 
the  mucous  membrane  of  the  stomach,  except  around  the  pyloric  orifice  and  in  the  lesser 
pouch.  In  the  human  subject,  their  distribution,  as  compared  with  that  of  the  mucous 
glands,  is  much  wider  than  in  most  of  the  inferior  animals.  They  vary  in  their  length 
with  the  variations  in  the  thickness  of  the  mucous  membrane.  Recent  researches  have 
shown  that  all  of  these  glands  are  racemose.  They  present,  in  the  upper  fourth  or  fifth  of 
their  length,  a  single  tube,  lined  by  a  continuation  of  the  columnar  epithelium  covering  the 
surface  of  the  mucous  membrane.  Below  this,  they  divide  into  several  branches,  prir 
mary  and  secondary,  and  are  lined  with  rounded  cells  of  glandular  epithelium,  having  the 
appearance  of  simple  racemose  glands.  The  cells  lining  the  branching  tubes  are  some- 
times called  peptic  cells.  They  each  have  a  nucleus  and  a  nucleolus,  contain  numerous 
granules,  and  are  about  T^^  of  an  inch  in  diameter.  This  is  the  general  character  of  the 
glands  in  the  greater  part  of  that  portion  of  the  mucous  membrane  wrhich  secretes  the 
gastric  juice.  They  readily  undergo  post-mortem  alteration,  and,  in  the  human  subject, 
are  only  to  be  seen  satisfactorily  in  the  fresh  stomachs  of  subjects  who  have  died  sud- 
denly, having  previously  been  in  a  condition  of  perfect  health. 

Mucous  Glands. — Near  the  pyloric  extremity  of  the  stomach  and  in  the  lesser  pouch, 
where  the  mucous  membrane  is  decidedly  paler  than  over  the  rest  of  the  organ,  the 
character  of  the  glands  is  peculiar.  As  a  rule,  the  glands  in  these  situations  are  com- 
pound ;  but  they  do  not  present  more  than  two  or  three  divisions  until  they  have  passed 
through  about  one-half  of  the  thickness  of  the  mucous  membrane,  when  they  break  up 
into  numerous  small  secondary  tubes.  The  important  peculiarity  of  these  glands  is 
that  they  are  lined  throughout  with  columnar  epithelium  and  are  everywhere  deprived 
of  the  cells  found  in  the  true  peptic  glands.  The  structure  of  the  glands  from  different 
portions  of  the  stomach  is  shown  in  Fig.  57. 

Closed  Follicles. — In  the  substance  of  the  mucous  membrane,  between  the  tubes  and 
near  their  coecal  extremities,  are  occasionally  found  closed  follicles,  like  the  solitary  glands 


230 


DIGESTION. 


and  patches  of  Peyer  of  the  intestines.  These  are  not  always  present  in  the  adult,  but 
are  generally  found  in  children.  They  are  usually  most  abundant  over  the  greater  curva- 
ture, though  they  may  be  found  in  other  situations.  In  their  anatomy  they  are  identical 
with  the  closed  follicles  of  the  intestines  and  do  not  demand  special  consideration  in  this 
connection. 


FIG.  57. — Peptic  and  mucous  glands ;  magnified  100  diameters.    (Sappey.) 

A.  Peptic  gland  from  the  middle  portion  of  the  stomach :   1,  excretory  canal;   2, 2,  2,  the  three  principal  branches  of 

the  gland ;  3,  8,  3,  secondary  branches  filled  with  rounded  cells. 

B.  Peptic  gland  from  the  pyloric  portion:    1,  excretory  canal;  2,  2,  the  two  principal  branches;   3,  3,  terminal  culs- 

de-sac. 

C.  Mucous  gland  from  the  pyloric  portion :    1,  excretory  canal;  2, 2,  the  two  branches;  3, 3, 3,  3, 3,  secondary  branches ; 

4,  4,  4,  small,  terminal,  racemose  glands. 

Gastric  Juice. 

At  the  present  day  it  seems  profitless  to  argue  the  question  of  the  existence  of  a 
digestive  fluid  in  the  stomach ;  and  the  discussions  of  the  earlier  physiologists  as  regards 
the  possibility  of  the  existence  of  a  fluid  capable  of  dissolving  the  articles  of  food  have 
only  an  historical  interest.  Our  definite  knowledge  of  the  most  important  physiological 
properties  of  this  fluid  dates  from  the  celebrated  observations  of  Dr.  Beaumont  on  Alexis 
St.  Martin,  the  Canadian,  who  had  a  large  fistulous  opening  into  the  stomach.  These 
observations  were  commenced  in  May,  1825,  and  were  continued  for  a  number  of  years. 
The  first  publication  of  them  was  in  the  Philadelphia  Medical  Recorder,  in  1826. 

Mode  of  obtaining  the  Gastric  Juice. — The  ingenious  experiments  of  Dr.  Beaumont 
upon  the  case  of  St.  Martin  gave  an  impulse  to  the  study  of  digestion  and  pointed  out 
the  way  in  which  the  action  of  the  gastric  juice  could  be  investigated.  The  fact  that  Dr. 
Beaumont  noted  the  action  of  human  gastric  juice  upon  all  the  ordinary  articles  of  food 
enabled  physiologists  to  compare  with  it  the  properties  of  the  secretion  obtained  from  the 


GASTRIC  JUICE. 


231 


Inferior  animals,  an  indispensable  condition  in  the  study  of  the  digestive  fluids.  In  1843, 
Blondlot  published  a  treatise  on  digestion,  in  which  he  gave  the  results  of  experiments 
on  dogs  with  fistulous  openings  into  the  stomach.  This  observer  is  generally  spoken  of 
.as  the  first  to  obtain  the  gastric  juice  by  the  establishment  of  a  fistula  into  the  stomach 
in  the  inferior  animals ;  but  Longet  states  that,  in  December,  1842,  Dr.  JBassow  read  a 
paper  before  the  Imperial  Society  of  Naturalists  of  Moscow,  which  was  published  in  the 
Bulletin  for  that  year,  in  which  he  gave  an  account  of  a  number  of  successful  attempts 
to  establish  gastric  fistulae  in  dogs.  In  the  animals  operated  upon  by  Bassow,  the 
fistula  was  not  kept  open  by  a  canula,  and  he  was  much  annoyed  by  its  tendency  to 
close.  There  is  no  reason  to  suppose  that  Blondlot  was  aware  of  the  experiments  of 
Bassow,  which,  as  Longet  remarks,  were  little  known  to  physiologists  and,  as  far  as  we 
are  aware,  were  not  quoted  in  works  on  physiology  before  the  publication  of  Longet's 
treatise,  in  1861.  With  some  slight  modifications  in  the  operative  procedure,  the  method 
of  Blondlot  is  the  one  now  in  common  use. 

The  establishment  of  a  permanent  gastric  fistula  is  now  one  of  the  simplest  and  most 
oommon  of  the  physiological  experiments.  The  dog  is  the  animal  generally  used ;  and, 
from  the  fact  that  he  is  not  very  subject  to  peritonitis,  the  operation  almost  always  ends 
in  recovery,  and  the  animal  can  be  trained  so  that  the  juice  may  be  obtained  in  quantity 
and  with  great  facility.  The  operative  procedure  which  we  have  found  most  convenient 
is  the  following : 

It  is  best  to  choose  a  dog  of  medium  size,  young,  but  nearly,  if  not  entirely  full  grown, 
in  perfect  health,  and  of  good  disposition.  Bringing  the  animal  under  the  influence  of 
ether,  he  is  to  be  held  firmly  on  the  back,  and  an  incision 
about  two  inches  in  length  is  made  in  the  median  line  into  the 
abdominal  cavity.  This  incision  should  be  commenced  from 
half  an  inch  to  an  inch  below  the  ensiforrn  cartilage.  Intro- 
ducing the  finger  into  the  abdominal  cavity,  the  stomach  can 
readily  be  felt,  especially  if  it  be  moderately  distended ;  and, 
with  a  pair  of  hooked,  or  bull-dog  forceps,  that  portion  of  the 
stomach  nearest  the  wound  may  be  seized  and  drawn  out  of 
the  abdomen.  It  is  important  to  make  the  fistula  into  that 
portion  of  the  anterior  wall  of  the  stomach  which  is  nearest 
the  wound,  in  order  to  avoid  disturbance  in  the  position  of  the 
viscera;  and  the  organ  is  in  the  most  favorable  position  for 
the  operation  if  it  be  moderately  distended  with  food. 

A  portion  of  the  stomach  being  drawn  out  of  the  abdomen, 
a  slit  is  made  parallel  to  the  longitudinal  fibres,  just  large 
enough  to  admit  the  canula. 

A  silver  canula,  about  an  inch  and  a  quarter  in  length,  half 
an  inch  in  diameter,  and  provided  with  a  straight  rim  or  flange 
at  each  end  about  half  an  inch  in  width,  is  now  introduced  into 
the  stomach  and  firmly  secured  in  place  by  a  ligature  sur- 
rounding it  and  passed  in  and  out  through  the  coats  of  the 
stomach  near  the  lips  of  the  wound,  like  the  string  of  a  purse. 
This  canula  may  be  single  or,  as  suggested  by  Bernard,  double, 
one  half  screwing  into  the  other  so  that  it  may  be  elongated  to 
twice  the  length  it  has  when  closed.  This  is  somewhat  con- 
venient, as  the  tube  may  be  introduced  elongated,  and,  when 
the  swelling  of  the  parts  has  subsided,  it  may  be  shortened  by  a 
key,  so  as  not  to  project  beyond  the  abdominal  walls. 

After  the  canula  has  been  firmly  fixed  in  the  stomach,  the 
tube,  w^th  one  of  its  flanged  ends  projecting,  should  be  drawn  to  the  upper  part  of  the 
•opening  in  the  abdomen,  and  the  wound  closed  by  sutures  passed  through  the  integument, 
muscles,  and  peritoneum. 


3.— Tube  for  gastric  fis- 
tula. (Bernard.) 
A,  B,  section  of  the  silver  tube 
partly  unscrewed;  C,  projec- 
tion to  receive  the  key  used 
in  turning  the  screw ;  D,  head 
of  the  key;  E,  extremity  of 
the  tube. 


232 


DIGESTION. 


FiG.  59.— Gastric  fistula.    (Bernard.) 

E,  stomach ;  D,  duodenum ;  M,  muscles  of  the  abdomen,  di- 
vided ;  O,  opening  of  the  fistula. 


The  dog  will  generally  eat  on  the  second  or  third  day  after  the  operation  ;  and  perito- 
nitis— aside  from  the  inflammatory  action  which  agglutinates  the  stomach  at  the  site  of 
the  operation  to  the  walls  of  the  abdomen — rarely  follows.  It  is  best  to  feed  the  animal 
sparingly  a  short  time  before  operating,  as  there  is  some  difficulty  in  seizing  the  stomach 
when  it  is  entirely  empty. 

Having  established  a  permanent  fistula  into  the  stomach,  after  the  wound  has  cica- 
trized around  the  canula,  the  animal  suffers  no  inconvenience  and  may  serve  indefi- 
nitely for  experiments  on  the  gastric 
juice.  Many  physiologists  have  been  in 
the  habit  of  exciting  the  flow  of  this 
fluid  by  the  introduction  into  the  stom- 
ach of  pieces  of  tendon  or  hard,  indi- 
gestible articles,  on  the  ground  that  the 
fluid  taken  from  the  fistula,  under  these 
circumstances,  is  unmixed  with  the  pro- 
ducts of  stomach-digestion ;  but  it  has 
been  shown  that  the  quantity  and  char- 
acter of  the  juice  are  influenced  by  the 
nature  of  the  stimulus  which  causes  its 
secretion,  and  it  is  proper,  therefore,  to 
excite  the  action  of  the  stomach  by  ar- 
ticles which  are  relished  by  the  animal. 
For  this  purpose,  lean  meat  may  be 
given,  cut  into  pieces  so  small  that  they 
will  be  swallowed  entire,  and  first 
thrown  into  boiling  water  so  that  their  exterior  may  become  somewhat  hardened.  The 
cork  is  then  removed  from  the  tube,  which  is  freed  from  mucus  and  debris,  when 

the  gastric  juice  will  begin  to  flow,  sometimes  immediately 
and  sometimes  in  from  three  to  five  minutes  after  the  food 
has  been  taken.  It  flows  in  clear  drops  or  in  a  small  stream 
for  about  fifteen  minutes,  nearly  free  from  the  products  of 
digestion.  At  the  end  of  this  time  it  is  generally  accom- 
panied with  grumous  matter,  and  the  experiment  should 
be  concluded  if  it  be  desired  simply  to  obtain  the  pure  se- 
cretion. In  fifteen  minutes,  from  two  to  three  ounces  of 
fluid  may  be  obtained  from  a  good-sized  dog,  which,  when 
filtered,  is  perfectly  clear;  and  this  operation  may  be  re- 
peated three  or  four  times  a  week  without  interfering  with 
the  quality  of  the  secretion  or  injuring  the  health  of  the 
animal. 

Although  instances  of  gastric  fistula  in  the  human  sub- 
ject had  been  reported  before  the  case  of  St.  Martin  and 
have  been  observed  since  that  time,  the  remarkably  healthy 
condition  of  the  subject  and  the  extended  experiments  of 
so  competent  and  conscientious  an  observer  as  Dr.  Beau- 
mont have  rendered  this  case  memorable  in  the  history  of 
physiology.  It  is  undoubtedly  the  fact  that  this  is  the  only 
instance  on  record  in  which  pure,  normal  gastric  juice  has 
been  obtained  from  the  human  subject;  and  it  served  a 
most  important  purpose  as  the  standard  for  comparison  of 
subsequent  experiments  on  the  inferior  animals.  The  de- 
tails of  this  case,  condensed  from  the  monograph  of  Beau- 
mont, are  briefly  the  following : 
Alexis  St.  Martin,  a  Canadian  voyageur  in  the  service  of  the  American  Fur  Company, 


FIG.  60. — Dog  with  a  gastric  fistula. 
(Beclard.) 


GASTRIC  JUICE. 


233 


eighteen  years  of  age,  of  good  constitution  and  perfectly  healthy,  was  wounded  in  the 
left  side  by  the  accidental  discharge  of  a  gun  loaded  with  duck-shot.  The  wound  was 
received  on  the  6th  of  June,  1822,  and  the  muzzle  of  the  gun  was  not  more  than  a  yard 
distant  from  the  body.  The  contents  of  the  gun  entered  posteriorly,  carrying  away 
integument  and  muscles  from  a  space  the  size  of  the  hand,  with  the  anterior  half  of  the 
sixth  rib,  fracturing  the  fifth  rib,  lacerating  the  lower  portion  of  the  left  lobe  of  the 
lung  and  the  diaphragm,  and  perforating  the  stomach.  The  patient  was  seen  by  Dr. 
Beaumont  twenty -five  or  thirty  minutes  after  the  accident,  when  the  above  facts  were 
noted,  and  an  opening  into  the  stomach  was  discovered  large  enough  to  admit  the  fore- 
finger. Extensive  sloughing  took  place,  and  for  seventeen  days  every  thing  that  was 
swallowed  passed  out  at  the  wound,  and  nourishment  was  administered  by  the  rectum. 
In  the  spring  of  1824,  the  wound  had  cicatrized,  and  the  patient  had  perfectly  recovered 
his  health ;  but,  in  the  process  of  cure,  seven  pieces  of  cartilage  had  come  away,  and  three 
or  four  inches  of  the  sixth  rib,  with  about  half  of  the  lower  edge  of  the  fifth  rib,  had  been 
removed  by  an  operation.  The  perforation  into  the  stomach  was  irregularly-circular  in 
form  and  about  two  and  a  half  inches  in  circumference.  This  opening  was  closed  by  a 
protrusion  of  the  mucous  membrane  of  the  stomach  in  the  form  of  a  valve,  which  could 
readily  be  depressed  by  the  finger  so  as  to  expose  the  interior  of  the  organ.  This  valve 
effectually  prevented  the  discharge  of  the  contents  of  the  stomach,  which  had  annoyed 
the  patient  previous  to  the  winter  of  1823-'24. 


A,  A,  A,  B, 


FIG.  61.— Gastric  fistu  lain  Hie  ease  of  St.  Martin.    (Beaumont.) 

IB  ui  ihe  opening  into  the  stomach ;  C,  left  nipple ;  D,  chest ;  E,  cicatrices  from  the  wound  made 
for  the  removal  of  a  piece  of  cartilage;  F,  F,  F,  cicatrices  of  the  original  wound. 


From  May,  1825  until  August  of  the  same  year,  St.  Martin  was  under  the  observation 
of  Dr.  Beaumont  and  submitted  to  numerous  experiments.  At  the  end  of  that  time,  he 
returned  to  Canada  and  was  lost  sight  of  for  four  years,  during  which  time  he  married 
and  became  the  father  of  two  children,  "  worked  hard  to  support  his  family,  and  enjoyed 
robust  health  and  strength."  He  then  came  again  under  the  observation  of  Dr.  Beau- 
mont and  continued  in  his  service,  doing  the  work  of  a  common  servant,  until  March, 
1831.  After  this  he  was  under  observation  from  time  to  time  until  1836  ;  all  this  time 
enjoying  perfect  health,  with  good  digestion,  and  having  become  the  father  of  several 
more  children.  The  la?t  published  observations  made  upon  this  case  were  in  1856. 

The  following  was  the  method  employed  by  Dr.  Beaumont  in  extracting  the  juice : 


234  DIGESTION. 

The  subject  was  placed  on  the  right  side  in  the  recumbent  posture,  the  valve  was  de- 
pressed within  the  aperture,  and  a  gum-elastic  tube,  of  the  size  of  a  large  quill,  was 
passed  into  the  stomach  to  the  extent  of  five  or  six  inches.  On  turning  him  upon  the  left 
side  until  the  opening  became  dependent,  the  stimulation  of  the  tube  caused  the  secretion 
to  flow,  sometimes  in  drops  and  sometimes  in  a  small  stream.  The  quantity  of  fluid  or- 
dinarily obtained  was  from  four  drachms  to  an  ounce  and  a  half.  The  usual  time  for 
collecting  the  juice  was  early  in  the  morning,  before  he  had  eaten.  It  was  remarked 
that  under  these  circumstances  there  was  never  an  accumulation  of  gastric  juice  in  the 
stomach,  and  its  flow  was  only  excited  by  the  stimulus  of  the  tube.  It  was  also  repeat- 
edly observed  that  the  introduction  of  alimentary  principles,  while  the  tube  was  in  the 
stomach,  produced  an  almost  instantaneous  increase  in  the  flow. 

Thanks  to  these  opportunities  for  observing  the  action  of  the  human  stomach,  followed 
by  the  experiments  of  Blondlot  and  others  on  the  inferior  animals,  now  so  common, 
physiologists  have  become  pretty  well  acquainted  with  the  phenomena  which  attend  the 
secretion  of  the  gastric  juice. 

Secretion  of  the  Gastric  Juice. — As  the  earlier  observers  were  unacquainted  with  the 
laws  which  regulate  the  production  of  secreted  fluids  as  distinguished  from  those  which 
contain  only  excrementitious  principles,  their  ideas  concerning  the  secretion  of  the  gastric 
juice  were  necessarily  indefinite.  One  of  the  most  important  facts  developed  by  Beau- 
mont was  that  the  normal  solvent  fluid  of  the  stomach  is  only  produced  in  obedience  to 
the  stimulus  of  food,  during  the  natural  process  of  digestion.  Eecent  advances  in  physio- 
logical chemistry  have  enabled  experimenters  to  correct  many  errors  in  the  observations 
of  Beaumont  concerning  the  properties  and  action  of  the  gastric  juice,  but  his  descrip- 
tions of  the  phenomena  which  accompany  its  secretion  have  been  repeatedly  verified. 

During  the  intervals  of  digestion,  the  mucous  membrane  is  comparatively  pale,  "  and 
is  constantly  covered  with  a  very  thin,  transparent,  viscid  mucus,  lining  the  whole  inte- 
rior of  the  organ."  On  the  application  of  any  irritation,  or,  better,  on  the  introduction 
of  food,  the  membrane  changes  its  appearance.  It  now  becomes  red  and  turgid  with 
blood ;  small  pellucid  points  begin  to  appear  in  various  parts,  which  are,  in  reality,  drops 
of  gastric  juice ;  and  these  gradually  increase  in  size  until  the  fluid  trickles  down  the 
sides  in  small  streams.  The  membrane  is  now  invariably  of  a  strongly  acid  reaction, 
while  at  other  times  it  is  either  neutral  or  faintly  alkaline.  The  thin,  watery  fluid  thus 
produced  is  the  true  gastric  juice.  Although  the  stomach  may  contain  a  clear  fluid  at 
other  times,  this  is  generally  abnormal,  is  but  slightly  acid,  and  does  not  possess  the 
marked  solvent  properties  characteristic  of  the  natural  secretion.  It  has  been  shown  by 
Beaumont,  and  his  observations  have  been  repeatedly  confirmed  by  experiments  on  the 
inferior  animals,  that  the  gastric  juice  is  secreted  in  greatest  quantity  and  possesses  the 
most  powerful  solvent  properties,  when  food  has  been  introduced  into  the  stomach  by 
the  natural  process  of  deglutition.  Under  these  circumstances  the  stimulation  of  the 
mucous  membrane  is  general,  and  secretion  takes  place  from  the  entire  surface  capable 
of  producing  the  fluid.  "When  any  foreign  substance,  as  the  gum-elastic  tube  used  in 
collecting  the  juice,  is  introduced,  the  stimulation  is  local,  and  the  flow  of  fluid  is  com- 
paratively slight.  It  has  been  also  observed  that  the  quantity  immediately  secreted  on 
the  introduction  of  food,  after  a  long  fast,  is  always  much  greater  than  when  food  has 
been  taken  after  the  ordinary  interval. 

While  natural  food  is  undoubtedly  the  proper  stimulus  for  the  stomach,  and  while,  in 
normal  digestion,  the  quantity  of  gastric  juice  is  perfectly  adapted  to  the  work  it  has  to 
perform,  it  has  been  noted  that  savory  and  highly-seasoned  articles  generally  produce  a 
more  abundant  secretion  than  those  which  are  comparatively  insipid.  An  abundant 
secretion  is  likewise  excited  by  some  of  the  vegetable  bitters. 

Impressions  made  on  the  nerves  of  gustation  have  a  marked  influence  in  exciting  the 
action  of  the  mucous  membrane  of  the  stomach.  Blondlot  found  that  sugar,  introduced 


GASTRIC  JUICE.  235 

into  the  stomach  of  a  dog  by  a  fistula,  produced  a  flow  of  juice  much  less  abundant  than 
when  the  same  quantity  was  taken  by  the  mouth.  To  convince  himself  that  this  did  not 
depend  upon  the  want  of  admixture  with  the  alkaline  saliva,  he  mixed  the  sugar  with  saliva 
and  passed  it  in  by  the  fistula,  when  the  same  difference  was  observed.  It  is  a  curious 
fact  that,  in  some  animals,  particularly  when  they  are  very  hungry,  the  sight  and  odor 
of  food  will  induce  secretion  of  gastric  juice. 

The  gastric  juice  is  probably  one  of  the  most  sensitive  of  the  secreted  fluids  to  dis- 
turbing influences.  It  was  remarked  by  Beaumont  that  a  febrile  condition  of  the  system, 
the  depression  resulting  from  an  excess  in  eating  and  drinking,  or  even  purely  mental 
conditions,  such  as  anger  or  fear,  vitiated,  diminished,  and  sometimes  entirely  suppressed 
secretion  by  the  stomach.  At  some  times  the  mucous  membrane  became  red  and 
dry,  and  at  others  it  was  pale  and  moist.  In  such  morbid  conditions,  it  is  stated  that 
drinks  were  immediately  absorbed,  but  that  food  remained  in  the  stomach  undigested  for 
twenty-four  or  forty-eight  hours. 

The  influence  of  the  nervous  system  on  the  secretion  of  gastric  juice,  exerted  particu- 
larly through  the  pneumogastric  nerves,  is  very  marked  and  important,  but  its  considera- 
tion belongs  properly  to  the  section  on  the  nervous  system. 

After  the  food  has  been  in  part  liquefied  and  absorbed  and  in  part  reduced  to  a  pulta- 
ceous  consistence,  the  secretion  of  gastric  juice  ceases ;  the  movements  of  the  stomach 
having  gradually  forced  that  portion  of  the  food  which  is  but  partially  acted  upon  in  this 
organ  or  is  digested  only  in  the  small  intestines,  out  at  the  pylorus.  The  stomach  is  thus 
entirely  emptied,  the  mucous  membrane  becomes  pale,  its  reaction  loses  its  marked  acid 
character  and  becomes  neutral  or  faintly  alkaline. 

Secretion  in  Different  Parts  of  the  Stomach. — The  differences  already  noted  in  the 
anatomy  of  the  mucous  membrane  of  the  stomach  in  different  parts  of  the  organ  point 
to  the  important  question  of  a  possible  difference  in  the  physiological  action  of  the  secre- 
tions of  different  parts,  particularly  the  pyloric  portion  and  the  rest  of  the  general  surface. 
We  can  learn  but  little  that  is  definite  with  regard  to  this  point  from  observations  on 
the  inferior  animals,  unless  they  be  confirmed  in  the  human  subject.  The  observations, 
however,  of  Kolliker,  Goll,  and  Bonders,  on  the  pig,  are  very  satisfactory,  and  subse- 
quently they  were  fully  confirmed  as  regards  the  human  subject.  It  is  well  known  that  an 
acidulated  infusion  of  the  mucous  membrane  of  the  stomach  possesses,  if  properly  pre- 
pared, all  the  digestive  properties  of  the  true  gastric  juice,  and  that  this  is  not  the  case 
with  similar  infusions  of  the  mucous  membrane  from  any  other  parts.  Kolliker,  in  ex- 
periments on  artificial  digestion  made  in  conjunction  with  Dr.  Goll,  "  on  the  gastric  mu- 
cous membrane  of  the  pig,  clearly  showed  that  the  two  kinds  of  glands  entirely  differ  in 
respect  of  their  solvent  power ;  inasmuch  as  those  with  the  round  cells  dissolved  acidu- 
lated coagulated  protein-compounds  in  a  very  short  time  ;  those  with  cylindrical  epithe- 
lium, on  the  contrary,  either  did  not  operate  at  all,  or  produced  a  slight  effect  only  after 
a  longer  period."  The  same  author  farther  states  that  these  observations  were  confirmed 
by  Bonders  and  himself  in  the  human  stomach. 

Although  the  character  of  the  secretion  in  different  parts  of  the  stomach  is  not  the 
same  in  all  animals,  it  must  be  admitted  that,  in  man,  the  mucous  membrane  of  the  stom- 
ach, in  what  is  called  the  pyloric  zone,  does  not  secrete  the  true,  acid,  solvent,  gas- 
tric juice.  In  other  words,  this  fluid  is  produced  only  in  those  portions  of  the  stomach 
in  which  the  mucous  membrane  is  provided  with  tubes  lined  with  cells  of  glandular  epi- 
thelium, or  what  have  been  called  the  stomach-cells. 

In  most  of  the  modern  works  on  physiology,  allusion  is  made  to  the  probable  quantity 
of  gastric  juice  secreted  in  the  twenty -four  hours.  The  estimates  on  this  point  can  be 
only  approximative,  even  in  the  inferior  animals,  and  they  give  no  definite  information 
concerning  the  normal  quantity  in  the  human  subject.  Bidder  and  Schmidt,  Lehmann, 
Corvisart,  and  others,  have  made  calculations  of  the  probable  quantity,  either  by  collect- 
ing the  juice  for  a  certain  time  and  multiplying  the  quantity  thus  obtained  by  a  number 


236  DIGESTION. 

to  represent  the  whole  twenty-four  hours,  or  by  ascertaining  the  amount  of  fluid  required 
to  digest  a  certain  weight  of  food  and  estimating  from  this  the  quantity  necessary  to  dis- 
pose of  all  the  food  taken  during  the  day.  Both  of  these  methods  are  manifestly  incor- 
rect. In  the  first,  the  intermittency  of  the  secretion  is  not  taken  into  account ;  and,  in 
the  second,  it  is  incorrectly  assumed  that  digestion  out  of  the  body  is  accomplished  pre- 
cisely as  it  takes  place  in  the  stomach. 

Dr.  Beaumont  was  sometimes  able  to  collect,  in  from  ten  to  fifteen  minutes,  two 
ounces  of  pure  gastric  juice,  simply  by  the  stimulation  produced  by  the  gum-elastic 
catheter  used  in  the  operation  ;  but  he  expressly  states  that,  in  this  case,  only  a  part  of  the 
mucous  membrane  is  excited  to  secretion,  while  the  flow  is  very  much  increased  by  the 
introduction  of  food  by  the  mouth,  which  produces  a  general  excitation  of  the  secreting 
membrane.  Estimates  like  those  of  Bidder  and  Schmidt,  which  put  the  quantity  of  gas- 
tric juice  secreted  in  twenty-four  hours  by  a  healthy  man  of  ordinary  size  at  six  thou- 
sand four  hundred  grammes,  or  about  fourteen  pounds,  are  probably  not  exaggerated, 
although  they  are  of  necessity  merely  approximative. 

The  enormous  quantity  of  fluid  daily  secreted  by  the  mucous  membrane  of  the  stom- 
ach would  excite  surprise  were  it  not  considered  that,  after  this  fluid  has  performed  its 
office  in  digestion,  it  is  immediately  reabsorbed,  and  but  a  small  quantity  of  the  secretion 
exists  in  the  stomach  at  any  one  time.  During  digestion,  a  circulation  of  material  is 
going  on,  in  which  the  stomach  is  continually  producing,  out  of  materials  furnished  by 
the  blood,  a  fluid  which  liquefies  certain  elements  of  the  food  and,  as  fast  as  this  is  ac- 
complished, is  absorbed  again  by  the  blood,  together  with  the  principles  that  have  been 
thus  digested. 

Composition  of  the   Gastric  Juice. 

The  gastric  juice  is  mixed  in  the  stomach  with  more  or  less  mucus  secreted  by  the 
lining  membrane.  When  drawn  by  a  fistula,  it  generally  contains  particles  of  food,  which 
have  become  triturated  and  partially  disintegrated  in  the  mouth,  and  is  always  mixed 
with  a  certain  quantity  of  saliva,  which  is  swallowed  during  the  intervals  of  digestion  as 
well  as  when  the  stomach  is  in  a  state  of  functional  activity.  By  adopting  certain  pre- 
cautions, however,  the  fluid  may  be  obtained  nearly  free  from  impurities,  except  the  ad- 
mixture of  saliva.  The  juice  taken  from  the  stomach  during  the  first  moments  of  its 
secretion  and  separated  from  mucus  and  foreign  matters  by  filtration  is  a  clear  fluid,  of 
a  faint  yellowish  or  amber  tint,  and  possessing  little  or  no  viscidity.  Its  reaction  is 
always  strongly  acid ;  and  it  is  now  a  well-established  fact  that  any  fluid,  secreted  by 
the  mucous  membrane  of  the  stomach,  which  is  either  alkaline  or  neutral,  is  not  the  nor- 
mal gastric  juice. 

The  specific  gravity  of  the  gastric  juice  in  the  case  of  St.  Martin,  according  to  the 
observations  of  Beaumont  and  Silliman,  was  1005  ;  but  later,  Dr.  F.  G.  Smith  found  it 
in  one  instance,  1008,  and  in  another,  1009.  There  is  every  reason  to  suppose  that  the 
fluid,  in  the  case  of  St.  Martin,  was  perfectly  normal,  and  from  1005  to  1009  may  be 
taken  as  the  range  of  the  specific  gravity  of  the  gastric  juice  in  the  human  subject. 
There  is  undoubtedly  considerable  variation,  as  regards  specific  gravity,  in  the  inferior 
animals. 

The  gastric  juice  is  described  by  Beaumont  as  inodorous,  when  taken  directly  from 
the  stomach  ;  but  it  has  rather  an  aromatic  and  a  not  disagreeable  odor  when  it  has  been 
kept  for  some  time.  It  is  a  little  saltish,  and  its  taste  is  similar  to  that  of  "thin,  mu- 
cilaginous water  slightly  acidulated  with  muriatic  acid."  The  gastric  juice  from  the  dog 
has  something  of  the  odor  peculiar  to  this  animal. 

It  has  been  found  by  Beaumont,  in  the  human  subject,  and  by  those  who  have  experi- 
mented on  the  gastric  juice  of  the  lower  animals,  that  this  fluid,  if  kept  in  a  well- 
stoppered  bottle,  will  retain  its  chemical  and  physiological  properties  for  an  indefinite  pe- 
riod. The  only  change  which  it  undergoes  is  the  formation  of  a  pellicle,  consisting  of  a 


COMPOSITION   OF  THE   GASTRIC  JUICE.  337 

vegetable,  confervoid  growth,  upon  the  surface,  some  of  which  breaks  up  and  falls  to  the 
bottom  of  the  vessel,  forming  a  whitish,  flocculeut  sediment.  We  have  now  (1875)  a 
specimen  of  gastric  juice  which  was  taken  from  a  dog  with  a  gastric  fistula  in  January, 
1862.  It  has  no  putrefactive  odor  and  is  apparently  in  the  same  condition  as  when  it 
was  first  drawn.  In  addition  to  this  remarkable  faculty  of  resisting  putrefaction,  this 
process  is  arrested  in  decomposing  animal  substances,  both  when  taken  into  the  stomach 
and  when  exposed  to  the  action  of  the  gastric  juice  out  of  the  body. 

There  are  on  record  no  minute  quantitative  analyses  of  the  human  gastric  juice, 
except  those  by  Schmidt,  of  the  fluid  from  the  stomach  of  a  woman  with  gastric  fistula; 
and  in  this  case  there  is  reason  to  suppose  that  the  secretion  was  not  normal.  The  analysis 
of  the  gastric  juice  of  St.  Martin  by  Berzelius  was  not  minute.  The  analyses  of  Schmidt 
give  less  than  six  parts  per  thousand  of  solid  matter,  while  Berzelius  found  over 
twelve  parts  per  thousand.  In  all  the  comparatively  recent  analyses,  there  have  been 
found  a  free  acid  or  acids ;  a  peculiar  organic  matter,  generally  called  pepsin  ;  and  various 
inorganic  salts,  among  which  may  be  mentioned  as  most  important,  the  chlorides  of 
sodium,  potassium,  and  calcium,  with  the  phosphates  of  lime,  magnesia,  and  iron.  Of 
these  constituents,  the  salts  possess  little  physiological  importance  as  compared  with  the 
organic  matter  and  the  acid  principles. 

The  following  analysis  by  Bidder  and  Schmidt  gives  the  mean  of  nine  observations 
upon  dogs : 

Table  of  Solid  Constituents  of  the   Gastric  Juice  of  the  Dog. 
(Bidder  and  Schmidt.) 

Ferment  (pepsin.) 17'127 

Free  hydrochloric  acid  (?) ~ 3'050 

Chloride  of  potassium 1*125 

Chloride  of  sodium 2*507 

Chloride  of  calcium 0*624 

Chloride  of  ammonium 0'468 

Phosphate  of  lime 1'729 

Phosphate  of  magnesia 0*226 

Phosphate  of  iron 0*082 


26*938 

In  another  series  of  three  experiments,  in  which  the  saliva  was  allowed  to  pass  into 
the  stomach,  the  proportion  of  free  acid  was  2*337,  and  the  proportion  of  organic  matter 
was  somewhat  increased. 

Organic  Principle  of  the  Gastric  Juice. — This  principle,  called  pepsin  or  gasterase,  is 
an  organic  nitrogenized  body,  peculiar  to  the  gastric  juice,  and,  as  we  shall  see  farther  on, 
is  essential  to  its  digestive  properties.  When  the  gastric  fluid  was  first  obtained,  even  by 
the  imperfect  methods  employed  anterior  to  the  observations  of  Beaumont  and  of  Blond- 
lot,  an  organic  matter  was  spoken  of  as  one  of  its  constituents. 

Experiments  on  artificial  digestive  fluids,  by  Eberle,  Schwann  and  Mtiller,  Wasmann, 
and  others,  have  demonstrated  that  acidulated  infusions  of  the  mucous  membrane  of  the 
stomach,  possessing  all  the  physiological  properties  of  the  gastric  juice,  contain  an  organic 
matter,  first  isolated  by  Wasmann,  on  which  the  solvent  powers  of  these  acid  fluids  seem 
to  depend.  Mialhe,  who  has  obtained  this  substance  in  great  purity  by  the  process  recom- 
mended by  Vogel,  describes  the  following  properties  as  characteristic  of  the  organic 
matter  in  artificial  gastric  juice  :  Dried  in  thin  slices  on  a  plate  of  glass,  it  is  in  the  form 
of  small,  grayish,  translucent  scales,  with  a  faint  and  peculiar  odor  and  a  feebly  bitter 
and  nauseous  taste.  It  is  soluble  in  water  and  in  a  weak  alcoholic  mixture,  but  is  in- 
soluble in  absolute  alcohol.  A  solution  of  it  is  rendered  somewhat  turbid  by  a  tempera- 


238  DIGESTION. 

tare  of  212°  Fahr.,  but  it  is  not  coagulated,  although  it  loses  its  specific  properties.  It  is 
not  affected  by  acids  but  is  precipitated  by  tannin,  creosote,  and  a  great  number  of  the 
metallic  salts.  This  substance  dissolved  in  water  slightly  acidulated  possesses,  in  a  very 
marked  degree,  the  peculiar  solvent  properties  of  the  gastric  juice;  but  it  has  been  found 
by  Pay  en  and  Mialhe  not  to  be  so  active  as  the  principle  extracted  from  the  gastric  juice 
itself,  which  is  described  by  Payen  under  the  name  of  gasterase.  In  the  abattoirs  of 
Paris,  Mialhe  collected  from  the  secreting  stomachs  of  calves  as  they  were  killed,  from 
six  to  ten  pints  of  gastric  juice ;  and  from  this  he  extracted  the  pure  pepsin  by  the  pro- 
cess recommended  by  Payen,  which  consists  merely  in  one  or  two  precipitations  by 
alcohol.  This  substance  he  found  to  be  identical  with  the  principle  obtained  by  Payen 
from  the  gastric  juice  of  the  dog.  Its  action  upon  albuminoid  matters  was  precisely  the 
same  as  that  of  pepsin  extracted  from  artificial  gastric  juice,  except  that  it  was  more 
powerful. 

Source  of  the  Acidity  of  the  Gastric  Juice. — Eeaumur  and  Spallanzani  recognized 
that  the  fluid  from  the  stomach  has,  at  certain  times,  an  acid  reaction  ;  and  subsequent 
observations  have  confirmed  this  fact  and  have  shown  that  this  reaction  is  invariable 
during  digestion.  But,  although  the  most  distinguished  and  skilful  chemists  of  the  day 
have  attempted  to  ascertain  the  source  of  this  acidity,  from  Prout,  in  1823,  to  Blondlot, 
in  1858,  embracing  Leuret  and  Lassaigne,  Tiedemann  and  Gmelin,  Berzelius,  Chevreul, 
Bidder  and  Schmidt,  Dumas,  Lehmann,  Bernard  and  Barreswil,  with  a  host  of  others, 
the  question  has  not  yet  received  a  solution  which  is  generally  accepted. 

The  method  made  use  of  by  some  of  those  who  profess  to  have  found  free  hydrochloric 
acid  in  the  gastric  juice  has  been  to  subject  the  fluid  to  distillation,  testing  the  acid  fluid 
which  passes  over  with  nitrate  of  silver ;  but  the  experiments  of  Bernard  and  Barreswil 
on  the  gastric  juice  from  dogs,  and  the  more  recent  observations  of  Dr.  F.  G.  Smith  on 
the  gastric  juice  from  St.  Martin,  have  shown  that  this  process  is  really  of  little  value. 
The  following  observations  by  Bernard  and  Barreswil  seem  to  show  that,  although 
hydrochloric  acid  may  be  obtained  from  gastric  juice  by  distillation,  it  does  not  neces- 
sarily exist  in  the  fluid  in  a  free  state  ;  which  is  a  very  important  consideration  in  a  ques- 
tion in  which  every  thing  depends  upon  the  absolute  accuracy  of  modes  of  analyses  : 

In  subjecting  the  gastric  juice  of  the  dog  to  distillation  at  a  low  temperature,  with  all 
the  necessary  precautions,  it  was  found  that  the  first  products  did  not  present  an  acid  re- 
action. It  was  at  first  thought  that  this  would  be  a  ground  for  the  exclusion  of  hydrochloric 
acid,  which  is  considered  to  be  volatile  ;  but  it  was  found  that,  in  the  distillation  of  water 
which  had  been  slightly  acidulated  with  hydrochloric  acid,  the  first  products  were  neu- 
tral, and  the  acid  was  disengaged  only  in  the  fluid  which  passed  over  toward  the  last 
periods  of  the  process.  On  again  distilling  the  gastric  juice,  it  was  found  that  the  prod- 
uct was  neutral,  presenting  no  precipitate  with  the  nitrate  of  silver,  until  about  four- 
fifths  of  the  fluid  had  passed  over ;  that  afterward,  the  fluid  which  passed  over  was  distinct- 
ly acid,  but  did  not  precipitate  with  the  salts  of  silver ;  and  "  finally,  only  toward  the  last 
instants,  when  there  remained  only  a  few  drops  of  gastric  juice  to  evaporate,  the  acid 
liquid  which  was  produced  gave  a  marked  precipitate  with  the  salts  of  silver,  which  was 
not  dissolved  by  concentrated  nitric  acid."  It  was  found  that  the  addition  to  the  gastric 
juice  of  a  small  quantity  of  oxalic  acid  produced  a  marked  opacity  due  to  the  formation 
of  the  insoluble  oxalate  of  lime,  while  an  equal  quantity  of  the  same  reagent  produced  no 
opacity  in  water  containing  a  proportion  of  two  thousandths  of  hydrochloric  acid,  to 
which  chloride  of  calcium  had  been  added.  From  this  experiment,  Bernard  concluded 
that  the  hydrochloric  acid  in  the  gastric  juioe  exists  in  the  condition  of  a  chloride  and 
not  in  a  free  state. 

Prof.  F.  G.  Smith,  who  had  an  opportunity  of  examining  the  gastric  juice  from  St. 
Martin,  in  1856,  took  the  fluid  from  the  stomach  after  two  ounces  of  dry  bread  had  been 
chewed  and  swallowed,  and  subjected  it  to  distillation.  The  first  fluid  which  passed  over 


COMPOSITION   OF  THE   GASTKIC  JUICE.  239 

was  neutral,  and  the  residue,  after  the  temperature  had  been  somewhat  raised,  produced 
a  slight  precipitate  with  the  nitrate  of  silver,  which  was  soluble  in  ammonia.  In  an- 
other experiment,  a  mixture  of  lactic  acid  and  chloride  of  sodium  in  solution  was  sub- 
jected to  distillation,  and  the  product  formed  a  slight  precipitate  with  the  nitrate  of  sil- 
ver, which  was  soluble  in  ammonia.  In  another  experiment,  a  mixture  of  lactic  acid 
and  chloride  of  sodium  in  solution  was  subjected  to  distillation,  and  the  product  formed 
a  slight  precipitate  with  the  nitrate  of  silver.  The  precipitation,  in  this  instance,  was 
attributed  to  the  passage  of  a  small  quantity  of  chloride  of  sodium  with  the  vapors,  and 
it  is  to  this,  also,  that  he  attributes  the  opalescence  of  the  products  of  distillation  of  the 
gastric  juice,  when  treated  with  the  nitrate  of  silver.  These  experiments  are  of  great 
interest  in  so  far  as  they  confirm  the  observations  of  Bernard,  Villefranche,  and  Bar- 
reswil,  on  the  gastric  juice  of  the  dog. 

The  experiments  of  Lehmann  are  even  more  conclusive.  He  found  that  pure  gastric 
juice,  when  evaporated  in  vacuo,  develops  hydrochloric  acid ;  but  he  also  found  that 
chloride  of  calcium  is  decomposed  during  evaporation  with  lactic  acid  in  vacuo  and 
attributes  the  generation  of  hydrochloric  acid  in  the  gastric  juice  to  the  decomposition 
with  this  salt,  and  not  the  chloride  of  sodium,  as  was  thought  by  Bernard,  Villefranche, 
and  Barreswil. 

The  addition  of  a  small  quantity  of  oxalic  acid  to  gastric  juice  produces  a  precipitate 
of  the  insoluble  oxalate  of  lime,  which  does  not  take  place  in  the  presence  of  free  hydro- 
chloric acid,  even  when  it  exists  in  very  minute  quantity.  No  one  has  denied  that  this- 
reaction  always  takes  place  in  the  gastric  juice ;  but,  in  this  fluid,  is  it  inconsistent  with 
the  presence  of  a  small  quantity  of  hydrochloric  acid  ?  We  have  found  that  the  addition 
of  two  drops  of  ordinary  hydrochloric  acid  to  half  a  fluidounce  of  gastric  juice  does  not 
prevent  the  precipitation  of  the  oxalate  of  lime,  which,  in  the  single  observation  referred 
to,  was  prevented  only  when  the  quantity  of  acid  was  increased  to  five  drops.  On  adding 
oxalic  acid  to  fresh  urine,  the  precipitate  of  oxalate  of  lime  was  marked ;  but,  after  the 
addition  of  two  drops  of  ordinary  hydrochloric  acid,  this  reaction  did  not  take  place. 
Taken  in  connection  with  the  fact  that  many  of  the  ordinary  chemical  reactions  are  pre- 
vented or  modified  in  fluids  containing  organic  substances,  this  would  lead  us  to  inquire 
whether  free  hydrochloric  acid  may  not  exist  in  small  quantity  in  the  gastric  juice,  and, 
as  an  exceptional  phenomenon,  the  reaction  between  the  oxalic  acid  and  the  soluble  salts 
of  lime  still  take  place,  or  whether  the  acid  may  not  unite  with  the  organic  principle, 
forming,  as  was  suggested  by  Schiff,  chlorohydropeptic  acid.  In  support  of  this  latter 
view,  it  is  to  be  remembered  that  Mulder  has  formed  combinations  of  organic  principles 
with  various  of  the  mineral  acids,  such  as  the  sulphuric  and  the  hydrochloric.  In  these 
compounds,  the  acid  character  remains,  but  the  ordinary  reactions  of  the  acid  are  lost. 

With  the  abundant  opportunities  which  have  been  presented  for  the  chemical  study 
of  the  gastric  juice,  not  only  in  the  inferior  animals  but  in  man,  and  in  view  of  the  nu- 
merous elaborate  researches  into  the  nature  of  this  fluid  by  the  most  skilful  physiological 
chemists  of  the  day,  it  is  a  matter  of  surprise  that  the  question  of  the  existence  of  free 
hydrochloric  acid,  or  its  condition  as  regards  combination  with  the  organic  matter,  is 
not  settled.  It  certainly  cannot  now  be  regarded  as  determined  beyond  question.  If, 
as  is  supposed  by  Bidder  and  Schmidt,  there  be  a  proportion  of  chlorine  which  cannot  be 
accounted  for  by  the  quantity  of  ordinary  bases  in  the  gastric  juice,  it  probably  does  not 
exist  as  free  hydrochloric  acid,  but  it  is  in  some  way  united  with  organic  matter. 

In  1786,  Macquart  indicated  the  presence  of  lactic  acid  in  the  gastric  juice  of  the  calf, 
attributing  the  acidity  of  the  gastric  juice  of  the  ox  and  the  sheep  to  free  phosphoric 
acid.  Since  then  there  have  been  numerous  analyses  in  which  this  principle  has  been 
said  to  be  found.  Among  those  who  early  adopted  this  view,  may  be  mentioned  Che- 
vreul,  Graves,  and  Leuret  and  Lassaigne.  After  the  analyses  by  Prout,  in  1823,  and  the 
observations  of  Beaumont  on  the  fluid  obtained  from  St.  Martin,  and  until  the  publication 
of  the  experiments  of  Bernard,  Villefranche,  and  Barreswil,  in  1844,  hydrochloric  acid 


240  DIGESTION. 

was  generally  supposed  to  be  the  free  acid  of  the  gastric  juice.  It  is  chiefly  on  the  last- 
named  observations — which  have  been  supported  by  Bernard  in  his  later  publications  and 
by  the  confirmatory  experiments  of  Lehmann  and  others — that  those  who  admit  the 
presence  of  free  lactic  acid  in  quantity  in  the  gastric  juice  rest  their  belief. 

We  have  already  referred  to  the  experiments  of  Bernard,  which  show  that  an  artificial 
fluid  containing  chloride  of  sodium  and  lactic  acid  in  solution  behaves,  during  distillation, 
in  every  way  like  the  normal  gastric  juice.  These  show,  also,  how  hydrochloric  acid 
may  be  produced  during  the  last  period  of  the  distillation  by  decomposition  of  the 
chlorides.  We  have  seen  that  this  observation  was  confirmed  by  Lehmann,  who  noted 
the  same  reaction  during  evaporation  at  the  ordinary  temperature,  in  vacuo,  although  he 
supposed  the  action  in  the  gastric  juice  to  be  upon  the  chloride  of  calcium  instead  of  the 
chloride  of  sodium.  Lehmann  found  in  the  acid  residue,  free  lactic  acid,  lactate  of  lime, 
and  alkaline  chlorides.  Bernard  and  Lehmann  have  brought  forward  other  experimental 
facts  to  show  that  the  gastric  juice  contains  lactic  acid.  If  starch  be  boiled  in  a  solution 
containing  hydrochloric  acid,  it  soon  loses  its  property  of  forming  a  blue  compound  with 
iodine ;  while  if  it  be  boiled  with  lactic  acid,  no  such  change  is  observed.  If  starch  be 
boiled  with  a  solution  containing  hydrochloric  acid,  to  which  has  been  added  a  soluble 
lactate  in  excess,  it  remains  unaltered ;  which  shows,  according  to  Bernard,  that  hydro- 
chloric acid  in  a  free  state  cannot  exist  in  the  presence  of  an  excess  of  a  salt  of  lactic 
acid.  By  similar  experiments,  the  same  observer  assumes  to  prove  that  the  existence  of 
hydrochloric  acid  is  inadmissible  in  the  presence  of  a  phosphate  or  an  acetate  in  excess. 
Lehmann  has  found  that  starch  boiled  with  gastric  juice  retains  the  property  of  being 
colored  blue  by  iodine.  These  experiments  are  considered  by  Bernard  as  positive  proof 
that  the  acid  of  the  gastric  juice  is  the  lactic;  and  the  fact  "seems  to  him  to  be  at  the 
present  day  beyond  contestation."  The  facts  adduced  by  Lehmann,  however,  are  even 
stronger.  By  operating  upon  a  large  quantity  of  gastric  juice,  he  formed  the  lactates  in 
such  a  quantity  that  he  was  enabled  to  subject  them  to  ultimate  analysis  and  determine 
positively  the  nature  of  the  acid.  He  found  that  the  acid  had  the  composition  of  lactic 
acid  formed  from  sugar,  and  not  that  of  the  acid  formed  from  the  juice  of  the  muscular 
tissue. 

In  view  of  the  facts  above  mentioned  and  the  somewhat  uncertain  basis  on  which 
the  supposition  of  the  presence  of  free  hydrochloric  acid  is  founded,  it  seems  almost  cer- 
tain that  the  principal  free  acid  of  the  gastric  juice  is  the  lactic.  It  is  important  to  re- 
member that,  while  the  experiments  of  Bernard  and  Lehmann  were  made  on  gastric 
juice  from  the  dog,  they  have  been  confirmed,  in  their  essential  particulars,  by  the  more 
recent  observations  of  Prof.  F.  G.  Smith  on  the  normal  gastric  juice  from  the  human 
subject. 

It  now  only  remains  to  discuss  the  question  of  the  existence  in  the  gastric  juice  of  the 
acid  phosphate  of  lime,  to  the  exclusion  altogether  of  free  acids ;  a  theory  first  proposed 
by  Blondlot  in  1843,  and  entertained  and  defended  by  him,  as  late  as  1858,  notwithstand- 
ing the  fact  that  this  view  ha's  met  with  no  favor  among  physiologists. 

To  Blondlot  belongs  the  rare  merit  of  having  been  one  of  the  first,  if  not  the  very 
first,  to  propose  and  execute  an  experiment  by  which  the  normal  gastric  juice  could  be 
obtained  in  quantity  from  a  living  animal.  In  his  first  analysis  of  the  fluid  thus  obtained, 
he  denied  the  existence  of  any  acid  principles  except  the  biphosphate  of  lime.  This 
view  he  holds  at  the  present  day ;  and,  notwithstanding  the  elaborate  researches  of  the 
most  distinguished  physiological  chemists,  in  all  of  which  a  free  acid  of  some  kind  has 
been  recognized,  he  still  ardently  defends  his  original  position.  The  question  of  the  exist- 
ence in  the  gastric  juice  of  the  acid  phosphate  of  lime,  to  the  exclusion  of  free  acids,  may 
be  discussed  in  a  few  words. 

Assuming  that  the  gastric  juice  contains  a  free  acid,  a  view  which  the  arguments  of 
Blondlot  fail  to  disprove,  the  question  arises  whether  the  biphosphate  of  lime  may  not 
also  exist  in  this  fluid.  On  this  point  there  can  be  no  doubt.  All  the  modern  analyses 


COMPOSITION   OF  THE   GASTRIC  JUICE.  241 

of  the  gastric  juice  give  the  phosphate  of  lime  as  one  of  its  constituents;  and  Blondlot 
justly  remarks  that  it  is  strange  to  see,  in  certain  analyses,  the  neutral  phosphate  of  lime 
and  hydrochloric  or  lactic  acid  put  down  as  existing  together,  as  though  the  phosphoric 
acid  were  able  to  retain  the  two  equivalents  of  the  base  in  the  presence  of  either  of  these 
two  acids.  The  fact  is,  that  basic  phosphate  of  lime,  a  salt  insoluble  in  pure  water  but 
soluble  in  acid  solutions,  is  invariably  decomposed  in  the  presence  of  acids  as  powerful  as 
the  hydrochloric  or  the  lactic.  It  then  loses  two  equivalents  of  the  base  and  is  trans- 
formed into  an  acid  phosphate. 

There  can  be  no  doubt  of  the  constant  presence  of  the  acid  phosphate  of  lime  in  the 
gastric  juice,  at  least  in  the  dog,  and  its  quantity  is  undoubtedly  increased  in  this  animal 
during  the  digestion  of  bones,  by  the  action  of  the  acid  fluid  upon  their  phosphatic  con- 
stituents ;  but  the  arguments  of  Blondlot  against  the  existence  of  a  free  acid  have  little 
or  no  weight.  One  of  those  on  which  most  stress  is  laid  is  that  the  gastric  juice  does  not 
act  upon  the  carbonates,  which  would  undoubtedly  be  the  case  if  it  contained  a  free 
acid.  The  simple  reply  to  this  is  that  there  is  sufficient  evidence  to  show  that  it  is 
not  the  fact.  Melsens,  using  a  specimen  of  fluid  obtained  by  Blondlot  from  the  dog  and 
given  to  Dumas,  found  that  seventy-three  grammes  of  juice  dissolved,  in  twenty-four 
hours,  0-108  of  a  gramme  of  calcareous  spar  (crystallized  carbonate  of  lime).  He  con- 
firmed this  observation  by  several  experiments,  so  that  there  can  be  no  doubt  as  to  its 
accuracy. 

It  is  plain,  therefore,  that,  while  the  acid  phosphate  of  lime  has  been  shown  to  be  a 
constant  constituent  of  the  pure  gastric  juice,  contributing,  in  a  certain  degree,  to  its 
acidity,  it  is  not  by  any  means  to  be  regarded  as  the  sole  acid  principle ;  the  phosphate 
probably  existing  in  this  form  by  virtue  of  the  presence  in  this  fluid  of  a  free  acid. 

On  what  does  the  acidity  of  the  gastric  juice  depend?  This  is  the  simple  question  to 
which  the  foregoing  discussion  naturally  leads ;  and  it  is  one  which  can  be  answered 
almost  with  positiveness,  although  it  is  not  settled  to  the  satisfaction  of  all  physiologists 
and  there  are  some  conflicting  observations  which  can  be  harmonized  only  by  new  re- 
searches. 

Aside  from  the  conditions  under  which  acids,  such  as  butyric,  acetic,  or  lactic,  are 
developed  from  articles  of  food  taken  into  the  stomach,  the  evidence  is  strongly  in 
favor  of  free  lactic  acid  as  the  principle  on  which  the  gastric  juice  mainly  and  constantly 
depends  for  its  acidity.  There  also  exists  a  certain  quantity  of  biphosphate  of  lime;  and 
this  is  the  only  condition  in  which  a  phosphate  of  lime  can  exist  in  the  presence  of  free 
lactic  acid. 

The  observations  of  Bidder  and  Schmidt  indicate,  apparently,  a  quantity  of  chlorine 
in  the  gastric  juice  not  to  be  accounted  for  by  the  proportion  of  bases  obtained  by  ulti- 
mate analysis.  There  is  evidence  sufficiently  positive  to  show  that  there  is  no  hydro- 
chloric acid  in  the  gastric  juice,  in  a  condition  which  allows  the  fluid  to  present  the  re- 
actions which  are  observed  when  this  acid  exists  in  a  free  state.  If  there  be  any  hydro- 
chloric acid  not  in  combination  with  metallic  bases,  it  is  united  with  organic  matter  in 
such  a  way  as  to  prevent  the  manifestations  of  its  ordinary  properties,  except  that  of 
acidity.  The  fact  that  some  of  the  mineral  acids  can  be  made  to  unite  in  this  way  with 
albuminoid  substances  lends  color  to  this  supposition ;  although  farther  investigations 
are  necessary  to  demonstrate  that  this  takes  place  in  the  gastric  juice. 

Ordinary  Saline  Constituents  of  the  Gastric  Juice. — It  has  been  experimentally  de- 
monstrated that  artificial  fluids,  containing  the  organic  principle  of  the  gastric  juice  and 
the  proper  proportion  of  free  acid,  are  endowed  with  all  the  digestive  properties  of  the 
normal  secretion  from  the  stomach,  and  that  these  properties  are  rather  impaired  when 
an  excess  of  its  normal  saline  constituents  is  added  or  when  the  relation  of  the  salts  to 
the  water  is  disturbed  by  concentration.  Boudault  and  Corvisart  evaporated  two  hun- 
dred grammes  of  the  gastric  juice  of  the  dog  to  dryness  and  added  to  the  residue  fifty 
16 


242  DIGESTION. 

grammes  of  water.  They  found  that  the  fluid  thus  prepared,  containing  four  times  the 
normal  proportion  of  saline  principles,  did  not  possess  by  any  means  the  energy  of  action 
on  alimentary  substances  of  the  normal  secretion.  These  facts  have  led  physiologists  to 
attach  little  importance  to  the  ordinary  saline  principles  found  in  the  gastric  juice. 

In  the  various  analyses  of  the  pure  juice  from  the  human  subject  and  the  inferior 
animals,  particularly  dogs,  chemists  have  discovered  the  chlorides  of  sodium,  calcium, 
potassium,  and  ammonium,  the  phosphate  of  lime  (necessarily  in  the  form  of  the 
biphosphate),  magnesia,  and  a  small  proportion  of  phosphate  of  iron.  Of  these  princi- 
ples, the  chloride  of  sodium  has  always  been  found  to  exist  in  greatest  abundance. 

Action  of  the   Gastric  Juice  in  Digestion. 

In  treating  of  the  composition  of  the  gastric  juice,  frequent  allusion  has  been  made  to 
its  solvent  action  in  digestion  and  to  the  constituents  on  which  this  property  depends. 
Certain  of  the  principles  most  readily  attacked  by  this  fluid  are  acted  upon  by  weak  acid 
solutions  containing  no  organic  matter ;  but,  although  some  physiologists  have  been  dis- 
posed to  regard  the  processes  of  solution  which  take  place  in  the  stomach  as  dependent 
merely  on  the  presence  of  a  free  acid,  it  is  now  well  established  that  the  presence  of  a 
peculiar  organic  principle  is  an  indispensable  condition  to  the  performance  of  real  diges- 
tion by  the  gastric  fluid.  It  has  also  been  fully  established  that  fluids  containing  the  or- 
ganic principle  of  the  gastric  juice  have  no  digestive  properties  unless  they  also  possess 
the  proper  degree  of  acidity  ;  and  it  is  as  well  settled  that  fluids  containing  acids  alone 
have  no  action  on  albuminoids  similar  to  that  which  takes  place  in  digestion,  and  that 
when  these  principles  are  dissolved  by  them  it  is  simply  accidental. 

It  is  a  curious  fact  that  the  presence  of  any  one  particular  acid  does  not  seem  essen- 
tial to  the  digestive  properties  of  the  gastric  juice,  so  long  as  the  proper  degree  of  acidity 
is  preserved.  In  the  experiments  of  Bernard,  Villefranche,  and  Barreswil,  after  saturating 
the  gastric  juice  with  neutral  phosphate  of  lime  and  adding  acetic,  phosphoric,  or  hydro- 
chloric acid  in  such  quantity  that  it  certainly  existed  in  a  free  state,  the  digestive  proper- 
ties of  the  fluid  were  retained.  These  authors  regard  it  as  essential  that  the  normal  acid 
of  the  gastric  juice  should  be  thus  capable  of  being  replaced  indifferently  by  other  acids ; 
for,  they  say,  in  case  any  salt  were  introduced  into  the  stomach  which  would  be  decom- 
posed by  the  lactic  acid  of  the  gastric  juice,  digestion  would  be  interfered  with,  unless  the 
liberated  acid  could  take  its  place.  It  can  readily  be  appreciated  that  transient  disturb- 
ances might  occur  from  this  cause,  were  the  existence  of  any  one  acid  principle  indispen- 
sable to  the  digestive  properties  of  the  gastric  juice;  while,  if  only  a  certain  degree  of 
acidity  were  required,  this  condition  might  be  produced  by  any  acid,  either  derived  from 
the  food  or  secreted  by  the  stomach. 

Enough  has  already  been  said,  under  the  head  of  the  organic  principle  of  the  gastric 
juice,  to  show  that  the  presence  of  this  substance  is  likewise  a  condition  indispensable  to 
digestion. 

As  far  as  has  been  ascertained  by  experiments  upon  artificial  digestion,  the  mucus, 
which  always  exists  in  greater  or  less  quantity  in  the  stomach,  does  not  seem  to  be  im- 
portant. It  is  usual  in  these  experiments  to  separate  mucus  and  extraneous  matters  from 
gastric  juice  by  filtration  before  it  is  used ;  and  the  digestive  properties  of  the  fluid  thus 
treated  are  not  sensibly  affected  when  the  mucus  is  allowed  to  remain. 

In  studying  the  physiological  action  of  the  gastric  juice,  it  must  always  be  borne  in 
mind  that  the  general  process  of  digestion  is  accomplished  by  the  combined,  as  well  as 
the  successive  action  of  the  different  digestive  fluids.  The  act  should  be  viewed  in  its  en- 
semble, rather  than  as  a  process  consisting  of  several  successive  and  distinct  operations,  in 
which  different  classes  of  principles  are  dissolved  by  distinct  fluids.  The  food  meets  with 
the  gastric  juice,  after  having  become  impregnated  with  a  large  quantity  of  saliva ;  and  it 
passes  from  the  stomach  to  be  acted  upon  by  the  intestinal  fluids,  having  imbibed  both 
saliva  and  gastric  juice.  By  studying  the  different  digestive  fluids  in  too  exclusive  a 


ACTION  OF  THE  GASTRIC  JUICE  IN  DIGESTION.  243 

manner,  many  physiologists,  while  professing  to  assign  definite  and  distinct  properties  to 
each,  thus  investing  the  function  of  digestion  with  the  attraction  of  simplicity,  have 
necessarily  ignored  or  distorted  facts  and  have  assumed  a  completeness  for  the  sum  of 
our  information  on  this  subject,  which  does  not  exist. 

"When  the  acts  which  take  place  in  the  mouth  are  properly  performed,  the  following 
alimentary  substances,  comminuted  by  the  action  of  the  teeth  and  thoroughly  insalivated, 
are  taken  into  the  stomach :  muscular  tissue,  containing  the  muscular  substance  envel- 
oped in  its  sarcolemma,  blood-vessels,  nerves,  white  fibrous  tissue  holding  the  muscular 
fibres  together,  interstitial  fat,  and  a  small  quantity  of  albumen,  fibrin,  and  corpuscles 
from  the  blood,  all  combined  with  a  considerable  quantity  of  inorganic  saline  matters; 
albumen,  sometimes  unchanged,  but  generally  in  a  more  or  less  perfectly  coagulated  con- 
dition ;  fatty  matter,  sometimes  in  the  form  of  oil  and  sometimes  enclosed  in  vesicles, 
constituting  adipose  tissue ;  gelatine  and  animal  matters  in  a  liquid  form  extracted  from 
meats,  as  in  soups ;  caseine,  in  its  liquid  form  united  with  butter  and  salts  in  milk,  and 
coagulated  in  connection  with  various  other  principles  in  cheese ;  vegetable  nitrogenized 
principles,  of  which  gluten  may  be  taken  as  the  type ;  vegetable  fats  and  oils ;  saccharine 
principles,  both  from  the  animal  and  the  vegetable  kingdom,  but  chiefly  from  vegeta- 
bles ;  the  different  varieties  of  amylaceous  principles ;  and,  finally,  organic  acids  and  salts, 
derived  chiefly  from  vegetables.  These  principles,  particularly  those  from  the  vegetable 
kingdom,  are  united  with  more  or  less  innutritions  matter,  such  as  cellulose.  They  are 
also  seasoned  with  aromatic  principles,  condiments,  etc.,  which  are  not  directly  used  in 
nutrition. 

The  various  articles  coming  under  the  head  of  drinks  are  taken  without  any  consider- 
able admixture  with  the  saliva.  They  embrace  water,  the  various  nutritious  or  stimulant 
infusions  (including  alcoholic  beverages),  with  a  small  proportion  of  inorganic  salts  in 
solution. 

All  the  articles  enumerated  above  are  more  or  less  modified  in  the  stomach  ;  and  the 
action  of  the  gastric  juice  upon  them  will  now  be  taken  up  in  detail. 

Action  of  the  Gastric  Juice  upon  Meats. — There  are  three  ways  in  which  the  action 
of  the  gastric  juice  upon  the  various  articles  of  food  may  be  studied.  One  is  to  subject 
them  to  the  action  of  the  pure  fluid  taken  from  the  stomach,  as  was  done  by  Beaumont,  in 
the  human  subject,  and  by  Blondlot  and  others,  in  experiments  upon  the  inferior  animals  ; 
another  is  to  make  use  of  properly-prepared  acidulated  infusions  of  the  mucous  membrane 
of  the  stomach,  which  have  been  shown  to  have  sensibly  the  same  properties  as  the  gastric 
juice,  differing  only  in  activity  ;  and  another  is  to  examine  from  time  to  time  the  contents 
of  the  stomach  after  food  has  been  taken.  By  all  of  these  methods  of  study,  it  has  been 
shown  that  the  digestion  of  meat  in  the  stomach  is  far  from  being  complete.  The  parts  of 
the  muscular  structure  most  easily  attacked  are  the  fibrous  tissue  which  holds  the  muscular 
fibres  together,  with  the  sarcolemma,  or  sheath  of  the  fibres  themselves.  If  the  gastric 
juice  of  the  dog  be  placed  in  a  vessel  with  finely-chopped  lean  meat  and  be  kept  in  contact 
with  it  for  a  number  of  hours  at  from  80°  to  100°  Fahr.,  agitating  the  vessel  occasionally 
so  as  to  subject,  as  far  as  possible,  every  particle  of  the  meat  to  its  action,  the  filtered  fluid 
will  be  found  increased  in  density,  its  acidity  diminished,  and  presenting  all  the  evidences 
of  having  dissolved  a  considerable  portion  of  the  tissue.  There  always,  however,  will 
remain  a  certain  portion  which  has  not  been  dissolved.  Its  constitution  is  nevertheless 
materially  changed  ;  for  it  no  longer  possesses  the  ordinary  character  of  muscular  tissue, 
but  easily  breaks  down  between  the  fingers  into  a  pultaceous  mass.  On  subjecting  this 
residue  to  microscopical  examination,  it  is  found  not  to  contain  any  of  the  white  inelastic 
fibres;  and  the  fibres  of  muscular  tissue,  although  presenting  the  well-marked  and  char- 
acteristic striffl,  are  broken  into  short  pieces  and  possess  very  little  tenacity.  It  is  evi- 
dently only  the  muscular  substance  which  remains;  the  connective  tissue  and  the  sarco- 
lemma having  been  dissolved.  These  facts  we  have  repeatedly  noted,  and,  even  on  adding 


244 


DIGESTION. 


fresh  juice  to  the  undigested  matter,  we  have  been  unable  to  dissolve  it  to  any  considerable 
extent,  the  residue  not  being  sensibly  diminished  in  quantity,  and  the  muscular  substance 
always  presenting  its  characteristic  striae,  on  microscopical  examination. 

Although  it  is  stated  by  many,  in  a  general  way,  that  the  nitrogenized  alimentary 
principles  are  digested  by  the  gastric  juice,  a  review  of  actual  experiments  will  show  that 
the  digestion  of  meat  in  the  stomach  is  substantially  such  as  we  have  just  indicated. 
Beaumont,  in  his  experiments  on  artificial  digestion,  while  he  frequently  states  that  the 
meat  is  completely  digested,  describes  the  mixture,  after  a  digestion  of  eight  or  nine  hours, 
as  about  the  color  of  whey  and  depositing  a  fine  sediment  of  a  reddish  color  after  standing 
for  a  few  minutes.  In  no  case  does  he  distinctly  state  that  meat  is  ever  completely  dis- 
solved. Pappenheim  examined  animal  matters,  especially  muscular  tissue,  in  various 
stages  of  digestion  by  the  gastric  juice,  and  noted  the  disintegration  of  the  tissue  and 
division  of  the  muscular  fibres  into  fragments,  but  not  the  solution  of  the  true  muscular 
substance.  Burdach  describes  the  digestion  of  meat  as  consisting  in  the  solution  of  its 
cellular  tissue,  which  is  dissolved,  first  separating  the  muscular  fibres,  and  finally  being 
converted  into  a  pultaceous  mass,  more  or  less  brown.  The  same  facts,  essentially,  have 
been  noted  by  Bernard  in  experiments  with  the  gastric  juice  of  different  animals.  This 
observer  has  found  that  the  fluid  from  the  stomach  of  the  rabbit  or  the  horse  is  much 
inferior,  as  regards  the  activity  of  its  action  upon  meat,  to  the  gastric  juice  of  the  dog. 
He  compares  the  disintegrating  process  which  takes  place  in  the  stomach  to  the  action 
of  boiling  water  in  cooking. 

I 
l 

fe&V/ft>«&i 

•OT?^&Y«tt 


~Fis.  62. — Matters  taken  from  the  pylorie  portion  of  the  stomach,  of  a  dog  during  digestion  of  mixed  food. 

(Bernard.) 

a,  disintegrated  muscular  fibres,  the  striae  having  disappeared  ;  &,  c.  muscular  fibres,  in  which  the  striae  have  partly 
disappeared ;  d,  d,  d,  globules  of  fat ;  e,  e,  e,  starch  ;  g,  molecular  granules. 

"Whether  the  gastric  juice  be  entirely  incapable  of  acting  upon  the  muscular  substance 
or  not,  the  above-mentioned  facts  clearly  show  that  muscular  tissue  is  usually  not  com- 
pletely digested  in  the  stomach.  The  action  in  this  organ  is  to  dissolve  out  the  inter- 
muscular  fibrous  tissue  and  the  sarcolemma,  or  sheath  of  the  muscular  fibres,  setting  the 
true  muscular  substance  free  and  breaking  it  up  into  small  particles.  The  mass  of  tissue 
is  thus  reduced  to  the  condition  of  a  thin,  pultaceous  fluid,  which  passes  into  the  small 
intestine,  where  the  process  of  digestion  is  completed.  As  far  as  a  great  part  of  the  true 
muscular  substance  is  concerned,  the  action  in  the  stomach  is  preparatory  and  not  final. 


ACTION  OF  THE   GASTRIC  JUICE  IN  DIGESTION.  245 

The  constituents  of  the  blood  (albumen,  corpuscles,  etc.),  which  may  be  introduced 
in  small  quantity  in  connection  with  muscular  tissue,  are  probably  completely  dissolved 
in  the  stomach. 

Action  upon  Albumen,  Fibrin,  Caseine,  and  Gelatine. — Dr.  Beaumont  thought  that 
raw  albumen,  or  white  of  egg,  became  first  coagulated  in  the  stomach  and  was  afterward 
dissolved  ;  but  this  has  been  disproved  by  numerous  other  observers,  who,  however,  have 
experimented  chiefly  on  dogs.  Reference  to  the  experiments  of  Beaumont  will  show  that 
the  phenomena  which  he  described  as  taking  place  in  a  mixture  of  equal  parts  of  white 
of  egg  and  gastric  juice,  kept  at  the  temperature  of  the  body  for  three  hours,  do  not  really 
indicate  coagulation.  He  states  that  "  in  ten  or  fifteen  minutes,  small,  white  flocculi  began 
to  appear,  floating  about ;  and  the  mixture  became  of  an  opaque  and  whitish  appearance. 
This  continued  slowly  and  uniformly  to  increase  for  three  hours,  at  which  time  the  fluid 
had  become  of  a  milky  appearance ;  the  small  flocculi,  or  loose  coagula,  had  mostly  dis- 
appeared, and  a  light-colored  sediment  subsided  to  the  bottom."  If  white  of  egg  be  mixed 
with  equal  parts  of  pure  water  and  be  gently  stirred  with  a  glass  rod,  the  same  small, 
white  flocculi  will  make  their  appearance,  and  the  mixture  will  become  opaque  and 
whitish.  This  is  due  to  the  disengagement  of  shreds  of  the  membranes  in  which  the 
clear  albumen  is  contained  ;  these  being  invisible  in  pure  white  of  egg,  from  the  fact  that 
the  two  substances  have  the  same  refractive  power.  A  very  different  appearance  is 
presented  when  water  containing  even  a  small  quantity  of  nitric  acid  is  added  to  a  liquid 
containing  albumen.  True  coagulation  then  takes  place,  and  the  mixture  becomes  imme- 
diately filled  with  large,  dense  clots  ;  or  the  mass  may  become  nearly  solidified,  if  the  acid 
be  added  in  sufficient  quantity.  Longet  and  Schiff  injected  a  filtered  watery  mixture  of 
albumen  into  the  stomach  of  a  dog  through  a  fistulous  opening  and  found  that  no  coagu- 
lation took  place. 

The  action  of  the  gastric  juice  upon  uncooked  white  of  egg  is  to  disintegrate  its 
structure,  separating  and  finally  dissolving  the  membranous  sacs  in  which  the  pure 
albumen  is  contained.  It  also  acts  upon  the  albumen  itself,  forming  a  new  fluid  substance, 
called  albuminose,  or  albumen-peptone,  which,  unlike  albumen,  is  not  coagulated  by  heat 
or  acids,  but  is  precipitated  by  alcohol,  tannin,  and  many  of  the  metallic  salts. 

The  digestion  of  raw  or  imperfectly-coagulated  albumen  takes  place  with  considerable 
rapidity  in  the  stomach.  Beaumont  gave  St.  Martin  the  white  of  two  eggs  when  the 
stomach  was  empty  and  found  that  it  had  been  completely  disposed  of  in  an  hour  and  a 
half.  The  digestion  of  albumen  in  this  form  is  more  rapid  than  when  it  has  been  com- 
pletely coagulated  by  heat. 

Coagulated  white  of  egg  is  almost  if  not  entirely  dissolved  by  the  gastric  juice.  If  a 
cube  of  albumen  in  this  condition  be  subjected  to  the  action  of  the  gastric  juice  at  the 
temperature  of  the  body,  taking  care  to  agitate  it  occasionally,  the  edges  and  corners 
gradually  become  rounded,  and  nearly  the  whole  mass  finally  breaks  down  and  is  dissolved, 
having  previously  become  softened  so  that  it  may  be  easily  crushed  between  the  fingers. 
Usually,  one  or  two  points  appear  in  the  mass,  which  are  acted  upon  with  difficulty  or 
may  resist  solution  entirely.  It  is  a  matter  of  common  as  well  as  scientific  observation, 
that  eggs  when  hard-boiled  are  less  easily  digested  than  when  they  are  soft-boiled  or  raw. 

The  products  of  the  digestion  of  raw  or  of  coagulated  albumen  (albumen-peptone) 
are  essentially  the  same.  It  is  probable  that  the  entire  process  of  digestion  and  absorp- 
tion of  albumen  takes  .place  in  the  stomach,  and,  if  any  pass  out  of  the  pylorus,  the 
quantity  is  exceedingly  small. 

Fibrin,  as  distinguished  from  the  so-called  fibrin  of  the  muscular  tissue,  pr  musculine, 
is  not  a  very  important  article  of  diet.  The  action  of  the  gastric  juice  upon  it  is  more 
rapid  and  complete  than  upon  albumen.  The  well-known  action  upon  fibrin  of  water 
slightly  acidulated  with  hydrochloric  acid  has  led  some  physiologists  to  assume  that  the 
acid  is  the  only  constituent  in  the  gastric  juice  necessary  to  the  digestion  of  this  principle ; 


246  DIGESTION. 

but  careful  observations  on  the  comparative  action  of  acidulated  water  and  of  artificial 
or  natural  gastric  juice  show  that  the  presence  of  the  organic  matter  is  necessary  to 
the  digestion  of  this  as  well  as  of  other  nitrogenized  alimentary  principles.  The  action  of 
water  containing  a  small  proportion  of  acid  is  to  render  fibrin  soft  and  transparent,  fre- 
quently giving  to  the  entire  mass  a  jelly-like  consistence.  The  result  of  the  digestion  of 
fibrin  in  the  gastric  juice,  or  in  an  acidulated  fluid  to  which  pepsin  has  been  added,  is 
its  complete  solution  and  transformation  into  a  substance  which  is  not  affected  by  heat, 
acids,  or  by  rennet. 

The  substance  resulting  from  the  action  of  gastric  juice  upon  fibrin,  called  by  Leh- 
mann,  fibrin-peptone,  presents  many  points  of  similarity  with  the  albumen-peptone,  but 
nevertheless  has  certain  distinctive  characters.  Lehrnann,  indeed,  supposes  that  there  are 
differences  between  the  products  of  the  digestion  of  all  the  various  nitrogenized  aliment- 
ary principles,  sufficiently  well  marked  to  distinguish  them  from  each  other. 

Liquid  caseine  is  immediately  coagulated  by  the  gastric  juice,  by  virtue  both  of  the 
free  acid  and  the  organic  matter.  Once  coagulated,  caseine  is  acted  upon  in  the  same 
way  as  coagulated  albumen.  The  caseine  which  is  taken  as  an  ingredient  of  cheese  is 
digested  in  the  same  way.  According  to  Lehmann,  coagulated  caseine  requires  a  longer 
time  for  its  solution  in  the  stomach  than  most  other  nitrogenized  substances ;  and  it  is 
stated  by  the  same  author,  on  the  authority  of  Elsasser,  that  the  caseine  of  human  milk, 
which  coagulates  only  into  a  sort  of  jelly,  is  more  easily  digested  than  caseine  from  cow's 
milk.  The  product  of  the  digestion  of  caseine  is  a  soluble  substance,  not  coagulable  by 
heat  or  the  acids,  called  by  Lehmann,  caseine-peptone. 

Gelatine  is  rapidly  dissolved  in  the  gastric  juice,  when  it  loses  the  characters  by 
which  it  is  ordinarily  recognized,  and  no  longer  forms  a  jelly  on  cooling.  This  substance 
is  much  more  rapidly  disposed  of  than  the  tissues  from,  which  it  is  formed,  and  the  prod- 
ucts of  its  digestion  in  the  gastric  juice  resemble  the  substances  resulting  from  the  di- 
gestion of  the  albuminoids  generally. 

Action  on  Vegetable  Nitrogenized  Principles. — These  principles,  of  which  gluten  may 
be  taken  as  the  type,  undoubtedly  are  chiefly,  if  not  entirely  digested  in  the  stomach. 
Eaw  gluten  is  acted  upon  very  much  in  the  same  way  as  fibrin,  and  cooked  gluten  be- 
haves like  coagulated  albumen.  Vegetable  articles  of  food  generally  contain  gluten  in 
greater  or  less  quantity,  or  principles  resembling  it,  as  well  as  various  non-nitrogenized 
principles,  and  cellulose.  The  fact  that  these  articles  are  not  easily  attacked  in  any  por- 
tion of  the  alimentary  canal,  unless  they  have  been  well  comminuted  in  the  mouth,  is 
shown  by  the  passage  of  grains  of  corn,  beans,  etc.,  in  the  faeces.  "When  properly  pre- 
pared by  mastication  and  insalivation,  the  action  of  the  gastric  juice  is  to  disintegrate 
them,  dissolving  out  the  nitrogenized  principles,  freeing  the  starch  and  other  matters  so 
that  they  may  be  more  easily  acted  upon  in  the  intestines,  and  leaving  the  hard,  indi- 
gestible matters,  such  as  cellulose,  to  pass  away  in  the  faeces.  The  nitrogenized  portions 
of  bread  are  probably  acted  upon  in  the  stomach  in  the  same  way  and  to  the  same  ex- 
tent as  albumen,  fibrin,  and  caseine. 

Albuminose,  or  Peptones. 

The  product  or  the  sum  of  the  products  of  the  digestion  of  nitrogenized  alimentary 
principles  in  the  stomach  was  first  closely  studied  by  Mialhe,  who  regarded  the  action 
of  the  gastric  juice  on  all  principles  of  this  class  as  resulting  in  their  transformation  into 
a  new  substance  which  he  called  albuminose.  Lehmann  has  since  investigated  the  prin- 
ciples resulting  from  the  action  of  the  gastric  juice  on  various  nitrogenized  matters  and 
describes  them  under  the  name  of  peptones.  It  has  been  conclusively  shown  that  stom- 
ach-digestion is  not  merely  a  solution  of  certain  alimentary  principles,  but  that  these 
substances  undergo  very  marked  changes  and  lose  the  properties  by  which  they  are  gen- 
erally recognized.  That  the  different  principles  resulting  from  this  transformation  re- 


ALBUMINOSE,  OR  PEPTONES.  347 

semble  each  other  very  closely  is  also  undoubted  ;  but  there  are  differences  in  the  chemi- 
cal composition  of  the  products  of  digestion  of  different  principles,  as  well  as  differences, 
which  have  lately  been  noted,  as  regards  their  behavior  with  reagents. 

Albuminose  is  a  colorless  liquid,  with  a  feeble  odor  resembling  that  of  meat.  It  is 
not  coagulable  by  heat,  acids,  or  by  pepsin  ;  a  property  which  distinguishes  it  from  almost 
all  of  the  nitrogenized  principles  of  food.  It  is  coagulated,  however,  by  many  of  the 
metallic  salts,  by  chlorine,  and  by  a  solution  of  tannin,  after  it  has  been  acidulated  by 
nitric  acid.  On  evaporating  albuminose  to  dryness,  the  residue  consists  of  a  yellowish- 
white  substance,  resembling  desiccated  white  of  egg.  This  is  soluble  in  water,  when  it 
regains  its  characteristic  properties  ;  but  it  is  entirely  insoluble  in  alcohol. 

Lehmann  found  a  great  similarity  between  the  substances  resulting  from  the  digestion 
of  the  various  albuminoid  bodies,  and  even  those  produced  by  the  digestion  of  gluten, 
chondrine,  and  gelatinous  tissues.  He  was  unable  to  obtain  the  peptones  free  from  min- 
eral substances.  In  the  condition  of  greatest  purity  in  which  they  have  been  obtained, 
they  have  been  found  to  be  white,  amorphous,  odorless,  with  a  mucous  taste,  very  solu- 
ble in  water,  and  insoluble  in  alcohol.  Their  watery  solutions  redden  litmus.  They 
combine  readily  with  bases,  forming  neutral  salts  soluble  in  water.  The  differences  be- 
tween the  various  peptones  are  not  as  yet  very  well  defined.  Lehmann  states  that  they 
always  contain  the  same  proportion  of  sulphur  that  existed  in  the  albuminoid  substances 
from  which  they  are  formed.  According  to  this  observer,  the  gastric  juice  transforms  the 
various  nitrogenized  alimentary  principles  into  these  liquid  substances,  which  are  not  easily 
coagulable  and  which  present  slight  differences  in  chemical  composition  and  general  prop- 
erties, varying  with  the  principles  from  which  they  are  formed.  Those  which  have  been 
most  particularly  described  are  fibrin-peptone,  albumen-peptone,  and  caseine-peptone. 

With  even  the'  imperfect  knowledge  which  we  have  of  the  properties  of  albuminose, 
it  is  evident  that  stomach-digestion,  aside  from  its  function  in  preparing  certain  articles 
for  the  action  of  the  intestinal  fluids,  does  not  simply  liquefy  certain  of  the  alimentary 
principles,  but  changes  them  in  such  a  way  as  to  render  them  endosmotic  and  provides 
against  the  coagulation  which  is  so  readily  induced  in  ordinary  nitrogenized  bodies. 
Albuminose  passes  through  membranes  with  great  facility,  and,  as  we  have  seen,  is  not 
coagulable  by  heat  or  the  acids. 

Another,  the  most  important  and  the  essential  change  which  is  exerted  by  the  gastric 
juice  upon  the  albuminoids,  is  that  by  which  they  are  rendered  capable  of  assimilation 
by  the  system  after  their  absorption.  The  important  fact  that  pure  albumen  and  gela- 
tine, when  injected  into  the  blood,  are  not  assimilable,  but  are  rejected  by  the  kidneys, 
was  first  demonstrated  by  Bernard  and  Barreswil.  These  observers  found,  also,  that  albu- 
men and  gelatine  which  had  previously  been  digested  in  gastric  juice  were  assimilated  in 
the  same  way  as  though  they  had  penetrated  by  the  natural  process  of  absorption  from 
the  alimentary  canal.  The  same  is  true  of  caseine  and  fibrin.  These  facts,  showing  that 
something  more  is  necessary  in  stomach-digestion  than  mere  solution,  point  to  pepsin  as 
the  important  active  principle  in  producing  the  peculiar  modifications  so  necessary  to 
proper  assimilation  of  nitrogenized  alimentary  substances.  The  action  which  takes  place 
is  one  of  those  ordinarily  termed  catalytic,  in  which  the  pepsin,  acting  as  a  ferment,  in- 
duces certain  peculiar  changes.  They  are,  however,  an  essential  and  the  most  important 
part  of  the  action  of  the  gastric  juice,  and  the  transformation  into  albuminose  takes 
place  in  all  nitrogenized  principles  which  are  liquefied  in  the  stomach.  As  it  is  impossible 
for  two  catalytic  processes  to  take  place  at  the  same  time  in  any  single  organic  substance, 
the  more  powerful  always  overcoming  and  taking  the  place  of  the  weaker,  it  is  evident 
that,  when  nitrogenized  principles  in  process  of  decomposition  are  introduced  into  the 
stomach,  the  catalytic  process  of  putrefaction  must  cease  when  the  changes  which  occur 
in  digestion  become  established.  This  explains  the  antiseptic  properties  of  the  gastric 
juice  and  the  frequent  innocuousness  of  animal  substances  in  various  stages  of  decom- 
position, when  taken  into  the  stomach. 


248  DIGESTION. 

Action  of  the  Gastric  Juice  on  Fats,  Sugars,  and  Amylaceous  Substances. — Beaumont 
does  not  say  mucli  with  regard  to  the  changes  which  fatty  substances  undergo  in  the  stom- 
ach, except  that  they  are  u  digested  with  great  difficulty."  All  the  recent  observations 
on  this  subject  show  that  these  principles,  when  taken  in  the  condition  of  oil,  pass  out 
at  the  pylorus  unchanged.  Most  of  the  fatty  constituents  of  the  food  are  liquefied  at  the 
temperature  of  the  body ;  and,  when  taken  in  the  form  of  adipose  tissue,  the  little  vesi- 
cles in  which  the  oleaginous  matter  is  contained  are  dissolved,  the  fat  is  set  free  and 
melted,  and  floats  in  the  form  of  great  drops  of  oil  on  the  alimentary  mass.  The  action 
of  the  stomach,  then,  seems  to  be  to  prepare  the  fats  for  digestion,  chiefly  by  dissolving 
the  adipose  vesicles,  for  the  complete  digestion  which  takes  place  in  the  small  in- 
testine. 

The  varieties  of  sugar  of  which  glucose  is  the  type  undergo  little  if  any  change  in 
digestion  and  are  probably  for  the  most  part  directly  absorbed  by  the  mucous  membrane 
of  the  stomach.  This  is  not  the  case,  however,  with  the  varieties  of  sugar  classed  with 
cane-sugar.  It  has  been  shown  that  cane-sugar  injected  into  the  veins  of  a  living  animal 
is  not  assimilated  by  the  system  but  is  immediately  rejected  by  the  kidneys.  When, 
however,  it  has  been  changed  into  glucose  by  the  action  of  a  dilute  acid  or  by  digestion 
in  the  gastric  juice,  it  no  longer  behaves  as  a  foreign  substance  and  does  not  appear  in  the 
urine.  This  leads  to  a  consideration  of  the  changes  which  cane-sugar  undergoes  in  the 
stomach.  Experiments  have  shown  that  this  variety  of  sugar,  after  being  digested  for 
several  hours  in  the  gastric  juice,  is  slowly  converted  into  glucose.  This  action  does  not 
depend  upon  any  constituent  of  the  gastric  juice  except  the  free  acid  ;  and  an  exceedingly 
dilute  mixture  of  hydrochloric  acid  had  an  equally  marked  effect.  Experiments  in  arti- 
ficial digestion  have  shown  that  cane-sugar  is  transformed  into  glucose  by  the  gastric 
juice  very  slowly,  the  action  of  this  fluid  in  no  way  differing  from  that  of  very  dilute 
acids.  In  the  natural  process  of  digestion,  this  action  may  take  place  to  a  certain  ex- 
tent ;  but  it  is  not  shown  to  be  constant  or  important,  and  we  must  look  to  intestinal  di- 
gestion for  the  rapid  and  efficient  transformation  of  cane-sugar. 

The  action  of  gastric  juice,  unmixed  with  saliva,  upon  starch  is  entirely  negative,  as 
far  as  any  transformation  into  sugar  is  concerned.  When  the  starch  is  enclosed  in  vege- 
table cells,  it  is  set  free  by  the  action  of  the  gastric  juice  upon  the  nitrogenized  parts. 
Eaw  starch,  in  the  form  of  granules,  becomes  hydrated  in  the  stomach,  on  account  of 
the  elevated  temperature  and  the  acidity  of  the  contents  of  the  organ.  This  is  not  the 
form,  however,  in  which  starch  is  generally  taken  by  the  human  subject ;  but  when  it  is 
so  taken,  the  stomach  evidently  assists  in  preparing  it  for  the  more  complete  processes 
of  digestion  which  are  to  take  place  in  the  small  intestine. 

Cooked  or  hydrated  starch,  the  form  in  which  it  exists  in  bread,  farinaceous  prepara- 
tions generally,  and  ordinary  vegetables,  is  not  affected  by  the  pure  gastric  juice  and 
passes  out  at  the  pylorus  unchanged.  It  must  be  remembered,  however,  that  the  gastric 
juice  does  not  prevent  a  continuance  of  the  action  induced  by  the  saliva ;  and  experi- 
ments have  shown  that  gastric  juice  taken  from  the  stomach,  when  it  contains  a  notable 
quantity  of  saliva,  has,  to  a  certain  extent,  the  power  of  transforming  starch  into  sugar. 
It  has  already  been  remarked  that,  with  regard  to  this  question,  experiments  on  dogs,  as 
these  animals  do  not  naturally  take  starch  as  food,  do  not  correspond  with  observations 
on  the  human  subject. 

The  changes  which  vegetable  acids  and  salts,  the  various  inorganic  constituents  of 
food,  and  the  liquids  which  come  under  the  head  of  drinks  undergo  in  the  stomach  are 
very  slight.  Most  of  these  principles  can  hardly  be  said  to  be  digested ;  for  they  are 
either  liquid  or  in  solution  in  water  and  are  capable  of  direct  absorption  and  assimila- 
tion. With  regard  to  most  of  the  inorganic  salts,  they  either  exist  in  small  quantity  in 
the  ordinary  water  taken  as  drink  or  are  united  with  organic  nitrogenized  principles. 
In  the  latter  case,  they  become  intimately  combined  with  the  organic  principles  result- 
ing from  stomach-digestion.  We  have  already  seen  that  the  various  peptones  have  been 


DURATION  OF  STOMACH-DIGESTION.  349 

found  to  contain  the  same  inorganic  constituents  which  existed  in  the  nitrogenized  prin- 
ciples from  which  they  are  formed. 

Some  discussion  has  arisen  with  regard  to  the  action  of  the  fluids  of  the  stomach  upon 
the  phosphate  and  the  carbonate  of  lime,  salts  which  are  considered  nearly  if  not  en- 
tirely insoluble.  The  action  upon  these  principles  is  interesting,  as  they  are  essential 
constituents  of  the  osseous  tissues.  Observations  in  both  natural  and  artificial  digestion 
have  shown  that  the  calcareous  constituents  of  bone  are,  to  a  certain  extent,  dissolved 
in  the  gastric  juice.  Bones  are  digested  to  a  considerable  extent  in  the  stomach,  although 
the  greater  part  passes  through  the  alimentary  canal  and  is  discharged  unchanged  in  the 
faeces.  Beaumont  has  shown  this  to  be  true  in  the  human  subject  by  experiments  which 
he  performed,  out  of  the  body,  with  gastric  juice  taken  from  St.  Martin.  In  these  ob- 
servations, after  a  certain  portion  of  the  bone  had  been  dissolved,  the  action  was  in- 
creased by  the  addition  of  fresh  gastric  juice.  In  the  natural  process  of  digestion,  the 
solution  of  the  calcareous  elements  of  bone  is  more  rapid  than  in  artificial  digestion, 
from  the  fact  that  the  juice  is  being  continually  absorbed  and  secreted  anew  by  the  mu- 
cous membrane  of  the  stomach. 

Duration  of  Stomach-Digestion. 

Now  that  the  relative  importance  of  the  stomach  and  the  small  intestines  in  digestion 
is  more  fully  understood,  less  interest  is  attached  to  the  length  of  time  required  for  the 
action  of  the  gastric  juice  upon  different  articles  of  food  than  formerly,  when  the  stom- 
ach was  regarded  as  the  principal,  if  not  the  sole  digestive  organ.  It  was  thought  at 
one  time  that  the  food  was  converted  in  the  stomach  into  a  pultaceous  mass  called  chyme, 
which  passed  into  the  intestine,  where  the  assimilable  portion,  the  chyle,  was  separated 
and  absorbed  by  the  lacteals.  Beaumont,  in  preparing  the  elaborate  table  which  has 
been  so  much  quoted,  conceived  that  the  simple  action  of  the  gastric  juice  represented 
the  chief  part  of  the  digestive  process;  and  that  it  was  possible,  from  experiments  with 
this  fluid,  to  ascertain  the  digestibility  of  different  articles.  From  this  point  of  view,  he 
regarded  fatty  substances,  which  are  now  known  to  be  digested  exclusively  in  the  small 
intestines,  as  requiring  a  very  long  time  for  their  digestion. 

Understanding,  as  we  do,  that  comparatively  few  articles,  and  these  belonging  exclu- 
sively to  the  class  of  organic  nitrogenized  principles,  are  completely  dissolved  in  the 
stomach,  it  is  evident  that  the  length  of  time  during  which  food  remains  in  this  organ,  or 
the  time  occupied  in  the  solution  of  food  by  gastric  juice,  out  of  the  body,  does  not  rep- 
resent the  absolute  digestibility  of  different  articles.  It  is,  nevertheless,  an  interesting  and 
an  important  question  to  ascertain,  as  nearly  as  possible,  the  duration  of  stomach-digestion. 

There  has  certainly  never  been  presented  so  favorable  an  opportunity  for  determining 
the  duration  of  stomach-digestion  as  in  the  case  of  St.  Martin.  From  a  great  number 
of  observations  made  on  digestion  in  the  stomach  itself,  Beaumont  came  to  the  con- 
clusion that  "  the  time  ordinarily  required  for  the  disposal  of  a  moderate  meal  of  the 
fibrous  parts  of  meat,  with  bread,  etc.,  is  three  to  three  and  a  half  hours."  The  obser- 
vations of  Prof..  F.  G.  Smith,  made  upon  St.  Martin  many  years  later,  give  two  hours  as 
the  longest  time  that  aliments  remained  in  the  stomach.  In  a  remarkable  case  of  intes- 
tinal fistula,  reported  by  Prof.  Busch,  of  Bonn,  it  was  noted  that  food  began  to  pass  out 
of  the  stomach  into  the  intestines  fifteen  minutes  after  its  ingestion  and  continued  to 
pass  for  three  or  four  hours,  until  the  stomach  was  emptied. 

Undoubtedly,  the  duration  of  stomach-digestion  varies  in  different  individuals  and  is 
greatly  dependent  upon  the  kind  and  quantity  of  food  taken,  conditions  of  the  nervous 
system,  exercise,  etc.  As  a  mere  approximation,  the  average  time  that  food  remains  in 
the  stomach  after  an  ordinary  meal  may  be  stated  to  be  from  two  to  four  hours. 

Digestibility  of  Different  Aliments  in  the  Stomach.— We  are  indebted  to  Beaumont 
for  nearly  all  that  is  positively  known  regarding  the  facility  with  which  different  articles 


250 


DIGESTION. 


are  disposed  of  in  the  stomach.  While  it  is  fully  understood  that  most  of  the  substances 
experimented  upon  by  him  are(not  completely  digested  by  the  gastric  juice,  and  although 
he  was  often  wrong  in  assuming  that  articles  of  food  were  digested  when  they  had  not 
become  completely  liquefied  and  consequently  endosmotic,  the  table  which  he  prepared 
with  so  much  care  was  the  result  of  such  conscientious  and  extended  research,  that  it 
must  always  be  recognized  as  of  great  value.  Nearly  all  of  the  results  given  in  the  table 
are  derived  from  experiments  frequently  repeated  and  "  performed  under  the  naturally 
healthy  condition  of  the  stomach  and  ordinary  exercise."  They  show  the  mean  time 
employed  in  the  digestion,  in  the  stomach,  of  most  of  the  ordinary  articles  of  food,  in  the 
person  of  a  healthy  young  man  of  good  digestive  powers.  Of  course  it  must  be  under- 
stood that  there  are  important  peculiarities  in  different  individuals,  which  could  not  be 
considered.  As  many  of  the  alimentary  substances  experimented  upon  are  but  slightly 
acted  on  by  the  gastric  juice,  it  has  been  thought  proper,  in  making  the  selections  from 
the  table,  to  discard  all  articles  which  are  mainly  digested  in  the  small  intestine. 
With  these  modifications,  therefore,  the  following  table  may  be  taken  as  representing 
the  comparative  rapidity  with  which  most  of  the  ordinary  nitrogenized  articles  are  acted 
upon  in  the  stomach ;  they  being  either  completely  dissolved,  and  probably  directly  ab- 
sorbed by  its  mucous  membrane,  or  prepared  for  the  action  of  the  intestinal  fluids,  passing 
gradually  out  at  the  pylorus.  It  must  be  remembered,  however,  that  slow  digestion  does 
not  always  indicate  that  the  process  is  difficult,  and  the  action  of  the  gastric  fluids  upon 
many  articles  which  apparently  give  no  trouble  in  digestion  is  by  no  means  rapid. 

Table  showing  the  Digestibility  of  various  Alimentary  Substances  in  the 

Stomach.     (Beaumont.) 


Articles  of  Diet. 

Mode  of  Prepara- 
tion. 

ii 

B    S 

Articles  of  Diet. 

Mode  of  Prepara- 
tion. 

B     R 

1    * 

Milk... 

Boiled 

2-00 

Chicken  full  grown        .  . 

Kricasseed 

2'45 

do.                                     .  . 

Raw 

2-15 

Fowls   domestic 

Boiled 

4-00 

E^s,  fresh     

do. 

2*00 

do           do. 

Roasted 

4*00 

do       do 

Whipped 

1-30 

Ducks  domesticated 

do 

4-00 

do.      do  

Roasted 

2-15 

do      wild 

do. 

4'30 

do.      flo 

Soft-boiled 

3-00 

Boiled 

1-30 

do.      do  

Hard-boiled 

3-80 

do.      bean 

do. 

3-00 

do       do 

Fried 

3'30 

do. 

3'00 

Custard  

Baked 

2-45 

do.      mutton 

do. 

3-30 

Codfish  cured  dry 

Boiled 

2-00 

do 

3'30 

Trout,  salmon,  fr?sh  
do.        do.        do  
Bass,  striped,     do  
Flounder,             do  

do. 
Fried 
Broiled 
Fried 

1-30 
1-30 
3-00 
3-30 

do.      beef,      vegetable?,  I 
and  bread  j 
do.      marrow-bones  
Piys'  feet   soused 

do. 

do. 
do. 

4-00 
4-15 

i-oo 

Catfish                 do. 

do. 

3'30 

Tripe             do 

do. 

1-00 

Boiled 

4'00 

do 

1-45 

Oysters  fresh                

Raw 

2'55 

Spinal  marrow  animal 

do 

2'40 

do.       do  

Roasted 

3'15 

Liver,  beeves',  fresh 

Broiled 

2-00 

do        do          .            ... 

Stewed 

3-30 

Aponeurosis 

Boiled 

3-00 

Venisou  steak  

Broiled 

1-35 

Heart,  animal.  ... 

Fried 

4-00 

Pig   suckinf                

Roasted 

2-30 

Cartilage 

Boiled 

4'15 

Lamb,  fresh  

Broiled 

2-30 

Tendon  

do. 

5-30 

Beef  fresh  lean  rare 

Roasted 

3-00 

Hash  meat  and  vegetables 

Warmed 

2-30 

Beef-steak  

Broiled 

3'00 

Sausage,  fresh  

Broiled 

3-20 

Beef  fresh  lean  drj 

Roasted 

3'30 

Gelatine       

Boiled 

2'SO 

do.    with  mustard,  etc  
do.  with  salt  only 

Boiled 
do. 

3-10 
3'36 

Cheese,  old,  strong  
Green  corn  and  bean" 

Raw 
Boiled 

3-30 
3-45 

Fried 

4'00 

Beans  pod 

2'30 

Mutton    fresh 

Broiled 

3-00 

Parsnips 

do. 

2-30 

do.        do  

Boiled 

3'00 

Potatoes,  Irish  

Roasted 

2-30 

do.        do. 

Roasted 

3'15 

do.         do.  .  . 

Baked 

2'  30 

Veal,  fresh  

Broiled 

4'00 

do.         do  

Boiled 

3  'SO 

do       do. 

Fried 

4'30 

Cabbage   head 

Raw 

2-30 

Pork   steak  

Broiled 

3-15 

do.         do.  with  vinegar 

do. 

2-00 

do.      fat  and  lean 

Roasted 

5-15 

do.         do.  . 

Boiled 

4-30 

do.      recently  salted  
do.                 do. 

Raw 

Stewed 

3-00 
3-00 

Carrot,  orange  ; 
Turnips  flat  

do. 
do. 

3-13 
8-30 

Broiled 

3'15 

Beets                                       ! 

do 

3-45 

do.                 do 

Fried 

4-15 

Bread,  corn  j 

Baked 

3'15 

do.                 do.          

Turkey  wild                  .  ... 

Boiled 
Roasted 

4-30 
2-18 

do.     wheat,  fresh  
Apples,  sweet,  mellow  

do. 
Raw 

3-30 
1-30 

do.      domesticated  
do.                do  
Goose,  wild  

Boiled 
Roasted 
do. 

2-25 

2-30 
2  30 

do.     sour,        do  
do.       do.     hard  

do. 

do. 

2-00 
2-50 

CIRCUMSTANCES  WHICH  INFLUENCE   STOMACH-DIGESTION.       251 

Most  of  the  facts  recorded  in  the  above  table  are  in  accordance  with  the  popular  ideas 
regarding  the  digestibility  of  various  articles,  based  upon  general  experience.  With  these 
as  a  guide,  the  following  may  be  taken  as  a  summary  of  what  is  known  regarding  the 
facility  with  which  different  articles  are  disposed  of  in  the  stomach  : 

Milk  is  one  of  the  articles  digested  in  the  stomach  with  greatest  ease.  Its  highly -nu- 
tritive properties  and  the  variety  of  principles  which  it  contains  render  it  extremely  valu- 
able as  an  article  of  diet,  particularly  when  the  digestive  powers  are  impaired  and  when 
it  is  important  to  supply  the  system  with  considerable  nutriment.  Eggs  are  likewise 
highly  nutritious  and  are  easily  digested.  Raw  and  soft-boiled  eggs  are  more  easily 
digested  than  hard-boiled.  Whipped  eggs  are  apparently  disposed  of  with  great  facility. 
As  a  rule,  the  flesh  of  fish  is  more  easily  digested  than  that  of  the  warm-blooded  animals. 
Oysters,  especially  when  raw,  are  quite  easy  of  digestion.  The  flesh  of  mammals  seems 
to  be  more  easily  digested  than  the  flesh  of  birds.  Of  the  different  kinds  of  meat,  veni- 
son, lamb,  beef,  and  mutton  are  easily  digested,  while  veal  and  fat  roast-pork  are  digested 
with  difficulty.  Soups  are  generally  very  easily  digested.  The  animal  substances  which 
were  found  to  be  digested  most  rapidly,  however,  were  tripe,  pigs'  feet,  and  brains. 
Vegetable  articles  are  represented  in  the  table  as  being  digested  in  about  the  same  time 
as  ordinary  animal  food ;  but  a  great  part  of  the  digestion  of  these  substances  takes  place 
in  the  small  intestine.  Bread  is  digested  in  about  the  time  required  for  the  digestion  of 
the  ordinary  meats. 

Circumstances  which  influence  Stomach-Digestion. 

The  various  conditions  which  influence  stomach-digestion,  except  those  which  relate 
exclusively  to  the  character  or  the  quantity  of  food,  operate  mainly  by  influencing  the 
quantity  and  quality  of  the  gastric  juice.  It  is  seldom,  if  ever,  that  temperature  has  any 
influence ;  for  the  temperature  of  the  stomach  in  health  does  not  present  variations  suffi- 
cient to  have  any  marked  effect  upon  digestion.  Experiments  in  artificial  digestion  have 
shown  that  alimentary  substances  are  most  vigorously  acted  upon  when  maintained  in 
contact  with  gastric  juice  at  or  near  100°  Fahr. 

As  a  rule,  gentle  exercise,  conjoined  with  repose  or  agreeable  and  tranquil  occupation 
of  the  mind,  is  more  favorable  to  digestion  than  absolute  rest.  Violent  exercise  or  severe 
mental  or  physical  exertion  is  always  undesirable  immediately  after  the  ingestion  of  a 
large  quantity  of  food,  and,  as  a  matter  of  common  experience,  has  been  found  to  retard 
digestion.  Sleep,  if  light  and  taken  in  the  sitting  posture,  seems  almost  necessary  to  easy 
digestion  in  many  persons  ;  but  it  should  be  continued  for  only  a  few  minutes.  A  pro- 
longed and  deep  sleep  immediately  after  a  full  meal  is  almost  always  injurious,  and  ex- 
traordinary heaviness  at  that  time  is  generally  an  indication  that  too  much  food  has  been 
taken. 

The  effects  of  sudden  and  considerable  loss  of  blood  upon  stomach-digestion  are  very 
marked.  After  a  full  meal,  the  whole  alimentary  tract  is  deeply  congested,  and  this  con- 
dition is  undoubtedly  necessary  to  the  secretion,  in  proper  quantity,  of  the  various  diges- 
tive fluids.  When  the  entire  quantity  of  blood  in  the  economy  is  greatly  diminished  from 
any  cause,  there  is  a  difficulty  in  supplying  the  amount  of  gastric  juice  necessary  for  a 
very  full  meal,  and  disorders  of  digestion  are  apt  to  occur,  especially  if  a  large  quantity 
of  food  have  been  taken.  This  is  also  true  in  inanition,  when  the  quantity  of  blood  is 
greatly  diminished.  In  this  condition,  although  the  system  constantly  craves  nourish- 
ment and  the  appetite  is  frequently  enormous,  food  should  be  taken  in  small  quantities  at 
a  time. 

As  a  rule,  children  and  young  persons  digest  food  which  is  adapted  to  them  more 
easily  and  in  larger  relative  quantity  than  those  in  adult  life  or  in  old  age  ;  but,  ordina- 
rily, in  old  age,  the  digestive  processes  are  carried  on  with  more  vigor  and  regularity 
than  the  other  vegetative  functions,  such  as  general  assimilation,  circulation,  or  respiration. 


252  DIGESTION. 

Influence  of  the  Nervous  System  on  the  Stomach. — It  is  well  known  that  mental 
emotions  frequently  have  a  marked  influence  on  digestion,  and  this,  of  course,  can  take 
place  only  through  the  nervous  system.  Of  the  two  nerves  which  are  distributed  to  the 
stomach,  the  pneumogastric  has  been  the  more  carefully  studied,  experiments  upon  the 
sympathetic  being  difficult  and  unsatisfactory.  Although  the  complete  history  of  the 
influence  of  the  pneumogastric  nerves  upon  digestion  belongs  to  the  section  on  the  nervous 
system,  it  will  be  interesting  in  this  connection  to  consider  briefly  some  of  the  facts 
which  have  been  ascertained  with  regard  to  the  influence  which  these  nerves  exert  upon 
the  stomach. 

After  section  of  the  pneumogastric  nerves  in  the  neck,  acts  of  deglutition  are  apparent- 
ly performed,  but  the  food  usually  collects  in  and  distends  the  paralyzed  oesophagus  and 
does  not  pass  to  the  stomach.  It  is  not  surprising,  therefore,  that  the  first  experiments 
upon  the  influence  of  the  pneumogastrics  on  digestion  should  have  been  contradictory,  some 
contending  that  section  of  the  nerves  arrested  stomach-digestion,  while  others  maintained 
that  the  nerves  had  little  or  no  influence  upon  the  stomach.  It  is  evident  that,  without 
an  appreciation  of  the  effects  of  section  of  the  pneumogastrics  upon  deglutition,  observa- 
tions on  the  influence  of  their  section  upon  stomach-digestion  would  be  of  little  value. 

The  experiments  of  Lon get  seem  to  show  that,  while  section  of  the  pneumogastrics  in 
the  neck  undoubtedly  diminishes  the  secretion  of  gastric  juice,  the  production  of  this  fluid 
is  not  entirely  arrested.  He  states  that  in  dogs,  one  or  two  days  after  section  of  the 
nerves,  he  found  the  lacteals  filled  with  chyle  after  milk  had  been  passed  into  the  stom- 
ach ;  but  it  is  now  well  known  that  chyle  is  in  great  part,  if  not  entirely  formed  in  the 
intestinal  canal,  without  the  intervention  of  the  stomach.  Another  experiment,  however, 
is  more  interesting.  After  section  of  the  pneumogastrics,  having  exposed  the  mucous 
membrane  of  the  stomach,  he  found  that  an  acid  fluid  appeared  in  parts  which  were  sub- 
jected to  mechanical  or  galvanic  irritation.  The  general  results  of  his  experiments  on 
this  subject  were  that,  after  the  division  of  both  pneumogastric  nerves,  small  quantities  of 
food  could  be  digested  in  the  stomach,  but  that  a  considerable  mass  was  only  chymitied 
on  the  surface,  the  centre  not  undergoing  any  alteration.  This  he  attributes,  not  so  much 
to  arrest  of  secretion  of  the  gastric  juice,  as  to  paralysis  of  the  movements  of  the  stomach, 
which,  when  the  mass  of  food  is  considerable,  are  necessary  in  order  to  expose  all  purts 
to  the  action  of  the  gastric  juice. 

The  experiments  of  Bernard  on  this  subject  are  very  clear  and  satisfactory.  When 
the  mucous  membrane  of  the  stomach  was  turgid  with  blood,  the  animal  (a  dog)  being  in 
full  digestion  and  provided  with  a  large  gastric  fistula  so  that  the  changes  which  might 
take  place  in  the  stomach  could  be  readily  observed,  the  pneumogastrics  were  divided  in 
the  neck.  At  once  the  mucous  membrane  became  pale  and  flaccid,  and  the  secretion  of 
gastric  juice  was  arrested.  When  the  animal  died  after  section  of  the  pneumogastrics 
during  digestion,  it  was  remarked  that  the  absorption  of  chyle  seemed  to  have  been  ar- 
rested, the  lacteals  being  found  to  contain  coagulated  chyle  even  as  far  as  the  villi  of  the 
intestines.  According  to  these  experiments,  the  action  of  gastric  juice  which  might  exist 
in  the  stomach  at  the  time  of  section  of  the  pneumogastrics  would  continue,  but  no  new 
fluid  is  secreted ;  and,  if  the  fluid  thus  remaining  in  the  stomach  be  neutralized,  digestion 
is  immediately  arrested.  In  one  experiment  in  which  the  pneumogastrics  had  been 
divided,  having  previously  emptied  the  stomach,  Bernard  introduced  meat  finely  divided. 
The  next  day,  the  meat  had  a  distinctly-ammoniacal  odor  and  an  alkaline  reaction,  the 
result  of  spontaneous  decomposition.  These  experiments  show  only  an  immediate  arrest 
of  the  secretion  of  the  gastric  juice.  In  certain  exceptional  instances,  in  which  animals 
survive  the  section  of  both  nerves  for  a  number  of  days  or  sometimes  even  recover,  it 
has  been  noted  that,  after  a  few  days,  an  acid  secretion  again  takes  place  in  the  stomach. 
Although  much  confusion  exists  in  the  earlier  observations  on  the  effects  of  section  of 
the  pneumogastrics  upon  the  stomach,  the  conclusions  to  be  drawn  from  recent  experi- 
ments are  tolerably  definite. 


MOVEMENTS   OF  THE   STOMACH.  253 

There  can  be  no  doubt  that  division  of  both  these  nerves  produces  immediate  and 
grave  disorder  in  the  process  of  stomach-digestion,  amounting,  it  is  more  than  probable, 
to  complete  arrest  of  the  secretion  of  the  gastric  juice.  Its  secretion  may  be  induced 
again  by  local  stimulation,  but  the  quantity  is  always  greatly  diminished.  Under  these 
circumstances,  it  is  possible  that  very  small  quantities  of  food  may  be  digested  in  the 
stomach  a  day  or  two  after  the  operation ;  and,  if  the  animal  survive  for  a  considerable 
time,  the  secretion  may  be  to  a  certain  extent  reestablished.  Serious  trouble  in  stomach- 
digestion  is  produced  by  the  paralysis  of  the  muscular  coats  of  the  stomach  consequent 
upon  section  of  both  pneumogastrics. 

Movements  of  the  Stomach.— As  the  articles  of  food  are  passed  into  the  stomach  by 
the  acts  of  deglutition,  the  organ  gradually  changes  its  form,  size,  and  position.  When 
the  stomach  is  empty,  the  opposite  surfaces  of  its  lining  membrane  are  in  contact  in 
many  parts  and  are  thrown  into  numerous  longitudinal  folds.  As  the  organ  is  distended, 
these  folds  are  effaced,  the  stomach  itself  becoming  more  rounded ;  and,  as  the  two  ends 
with  the  lesser  curvature  are  comparatively  immovable,  the  whole  organ  undergoes  a 
movement  of  rotation,  by  which  the  anterior  face  becomes  superior  and  is  applied  to  the 
diaphragm.  At  this  time  the  great  pouch  has  nearly  filled  the  left  hypochondriac  region, 
the  greater  curvature  looks  anteriorly,  and  comes  in  contact  with  the  abdominal  walls. 
Aside  from  these  changes,  which  are  merely  due  to  the  distention,  the  stomach  under- 
goes important  movements,  which  continue  until  its  contents  have  been  dissolved  and 
absorbed  or  have  passed  out  at  the  pylorus.  But  while  these  movements  are  taking 
place,  the  two  orifices  are  guarded,  so  that  the  food  shall  remain  for  the  proper  time 
exposed  to  the  action  of  the  gastric  juice.  We  have  already  noted  the  rhythmical  con- 
tractions of  the  lower  extremity  of  the  oesophagus,  by  which  regurgitation  of  food  is 
prevented ;  and  the  circular  fibres,  which  form  a  thick  ring  at  the  pylorus,  are  constantly 
contracted,  so  that,  at  least  during  the  first  periods  of  digestion,  only  liquids  and  that 
portion  of  food  which  has  been  reduced  to  a  pultaceous  consistence  can  pass  into  the 
small  intestine.  It  is  well  known  that  this  resistance  at  the  pylorus  does  not  endure  in- 
definitely, for  indigestible  articles  of  considerable  size,  such  as  stones,  have  been  passed 
by  the  anus  after  having  been  introduced  into  the  stomach  ;  but  observation  has  shown 
that  masses  of  digestible  matter  are  passed  by  the  movements  of  the  stomach  to  the 
pylorus,  over  and  over  again,  and  that  they  do  not  find  their  way  into  the  intestine  until 
they  have  become  softened  and  broken  down. 

The  contractions  of  the  walls  of  the  stomach  are  of  the  kind  characteristic  of  the 
non-striated  muscular  fibres.  If  the  finger  be  introduced  into  the  stomach  of  a  living 
animal  during  digestion,  it  is  gently  but  rather  firmly  grasped  by  a  contraction,  which  is 
slow  and  gradual,  enduring  for  a  few  seconds,  and  as  slowly  and  gradually  relaxing  and 
extending  to  another  part.  The  movements  during  digestion  undoubtedly  present  certain 
differences  in  different  animals ;  but  there  can  be  no  doubt  that  the  phenomenon  is  univer- 
sal. In  dogs,  when  the  abdomen  is  opened  soon  after  the  ingestion  of  food,  the  stomach 
appears  pretty  firmly  contracted  on  its  contents.  In  a  case  reported  by  Todd  and  Bow- 
man, in  the  human  subject,  in  which  the  stomach  was  very  much  hypertrophied  and  the 
walls  of  the  abdomen  were  very  thin,  the  vermicular  movements  could  be  distinctly 
seen.  These  movements  were  active,  resembling  the  peristaltic  movements  of  the  intes- 
tines, for  which,  indeed,  they  were  mistaken,  as  the  nature  of  the  case  was  not  recog- 
nized during  life.  No  argument,  therefore,  seems  necessary  to  show  that,  during  diges- 
tion, the  stomach  is  the  seat  of  tolerably  active  movements. 

A  peculiarity  in  the  movements  of  the  stomach,  which  has  been  repeatedly  observed 
in  the  lower  animals,  particularly  dogs  and  cats,  and  in  certain  cases  has  been  confirmed 
in  the  human  subject,  is  that,  at  about  the  junction  of  the  cardiac  two-thirds  with  the 
pyloric  third,  there  is  frequently  a  transverse  band  of  fibres  so  firmly  contracted  as  to 
divide  the  cavity  into  two  almost  distinct  compartments.  It  has  also  been  noted  that  the 


254  DIGESTION. 

contractions  in  the  cardiac  division  are  much  less  vigorous  than  near  the  pylorus ;  the 
stomach  seeming  simply  to  adapt  itself  to  the  food  by  a  gentle  pressure  as  it  remains  in 
the  great  pouch,  while,  in  the  pyloric  portion,  divided  off  as  it  is  by  the  hour-glass  con- 
traction above-mentioned,  the  movements  are  more  frequent,  vigorous,  and  expulsive. 
We  must  again  refer,  however,  to  the  observations  of  Beaumont  for  the  only  accurate 
description  of  the  movements  of  the  stomach,  as  they  take  place  during  digestion  in  the 
human  subject. 

The  experiments  of  Beaumont  were  generally  made  with  the  subject  lying  on  the 
right  side,  and  the  movements  of  the  stomach  were  observed  by  following  with  the  eye  a 
particular  morsel  of  food  as  it  passed  along,  or  by  introducing  the  bulb  of  a  thermometer 
into  the  organ  and  allowing  it  to  move  with  the  alimentary  mass.  It  was  invariably 
found  that  the  movements  of  the  thermometer-bulb  were  the  same  as  those  observed  by 
identifying  and  following  a  particular  portion  of  food.  As  the  alimentary  bolus  enters 
by  the  cardiac  opening,  it  turns  to  the  left,  descends  into  the  greater  pouch,  and  follows 
the  greater  curvature  to  the  pyloric  end.  It  then  returns  to  the  cardiac  orifice  by  the 
lesser  curvature  and  takes  again  the  same  course  as  before.  While  these  revolutions,  so 
to  speak,  of  the  alimentary  mass  are  going  on,  the  food  is  turned  over  and  over,  so  that 
it  becomes  intimately  mixed  with  the  digestive  fluids  and  subjected  to  a  certain  amount 
of  trituration.  This  action  is  undoubtedly  of  great  importance,  as  fresh  portions  of  food 
are  thereby  successively  exposed  to  the  action  of  the  gastric  juice,  and  the  boluses,  with 
their  particles  agglutinated  to  a  certain  extent  in  the  mouth,  are  disintegrated  and  pene- 
trated with  the  gastric  fluid  in  every  part. 

A  marked  difference  was  observed  between  the  movements  in  the  cardiac  and  in  the 
pyloric  portion.  When  the  thermometer-bulb  arrived  at  the  contracted  septum,  which 
was  three  or  four  inches  from  the  pyloric  end,  it  was  at  first  stopped  by  the  forcible  con- 
traction ;  but,  in  a  short  time,  there  was  a  gentle  relaxation  which  allowed  it  to  pass, 
when  it  was  drawn  quite  forcibly  for  three  or  four  inches  toward  the  pyloric  opening. 
When  in  this  portion  of  the  stomach,  the  bulb  was  firmly  grasped  and  made  to  undergo 
a  spiral  motion ;  and,  if  drawn  forcibly  out,  it  gave  to  the  fingers  the  sensation  of  being 
held  by  a  strong  suction  force.  As  soon  as  relaxation  occurs,  the  bulb  is  passed  back  to 
the  seat  of  stricture,  and,  when  pulled  through  this,  it  moves  freely  in  the  great  cavity. 
Each  one  of  these  revolutions  was  found  to  occupy  from  one  to  three  minutes.  They 
were  slower  at  first  than  after  digestion  had  been  somewhat  advanced. 

The  mechanism  of  the  movements  of  the  stomach  is  easily  appreciated  when  we  con- 
sider the  number  and  varied  direction  of  the  fibres  which  form  the  muscular  coat  of  the 
stomach,  and  the  fact  that  the  stomach,  when  distended,  is  more  or  less  displaced  with 
every  movement  of  the  diaphragm.  It  is  easy  to  understand,  also,  how,  in  the  pyloric 
portion,  where  the  muscular  fibres  are  thickest  and  the  cavity  is  elongated  and  compara- 
tively small,  the  movements  should  be  more  vigorous  and  expulsive  than  in  the  rest  of  the 
organ.  We  have  already  alluded  to  the  fact  that  the  movements  of  the  stomach  are 
animated  by  the  pneumogastric  nerves  and  become  arrested  when  both  these  nerves  are 
divided. 

As  the  result  chiefly  of  the  observations  of  Beaumont,  the  following  may  be  taken  as 
a  summary  of  the  physiological  movements  of  the  stomach  in  digestion : 

The  stomach  normally  undergoes  no  movements  until  food  is  passed  into  its  cavity. 
When  food  is  received,  at  the  same  time  that  the  mucous  membrane  becomes  congested 
and  the  secretion  of  gastric  juice  commences,  contractions  of  the  muscular  coat  begin, 
which  are  slow  and  irregular  during  the  commencement  of  stomach-digestion,  but  become 
more  vigorous  and  regular  as  the  process  advances.  After  digestion  has  become  fully 
established,  the  stomach  is  generally  divided,  by  the  firm  and  almost  constant  contraction 
of  a  transverse  band  of  fibres,  into  a  cardiac  and  a  pyloric  portion ;  the  former  occupying 
about  two-thirds,  and  the  latter,  one-third  of  the  length  of  the  organ.  The  contractions 
of  the  cardiac  division  of  the  stomach  are  uniform  and  rather  gentle ;  while,  in  the 


REGURGITATION   OF  FOOD,  AND  ERUCTATION.  255 

pyloric  division,  they  are  intermittent  and  more  expulsive.  The  effect  of  the  contractions 
of  the  stomach  upon  the  food  contained  in  its  cavity  is  to  subject  it  to  a  tolerably  uniform 
pressure,  with  a  certain  amount  of  trituration  and  agitation,  in  the  cardiac  portion,  the 
general  tendency  of  the  movement  being  toward  the  pylorus  along  the  greater  curvature, 
and  back  from  the  pylorus  toward  the  great  pouch  along  the  lesser  curvature.  At  the 
constricted  part,  which  separates  the  cardiac  from  the  pyloric  portion,  there  is  an  ob- 
struction to  the  passage  of  the  food  until  it  has  been  sufficiently  acted  upon  by  the  secre- 
tions in  the  cardiac  division  to  have  become  reduced  to  a  pultaceous  consistence.  The  ali- 
mentary mass  then  passes  into  the  pyloric  division,  and,  by  a  more  powerful  contraction 
than  occurs  in  other  parts  of  the  stomach,  it  is  passed  into  the  small  intestine.  This 
completes  the  distinction  between  the  two  portions  of  the  stomach,  the  cardiac  division 
only,  as  we  have  already  seen,  possessing  a  mucous  membrane  capable  of  secreting  the 
true  solvent  gastric  juice. 

The  revolutions  of  the  alimentary  mass,  thus  accomplished,  take  place  slowly,  by  gen- 
tle and  persistent  contractions  of  the  muscular  coat ;  the  food  occupying  from  one  to 
three  minutes  in  its  passage  entirely  around  the  stomach.  Every  time  that  a  revolution 
is  accomplished,  the  contents  of  the  stomach  are  somewhat  diminished  in  quantity ; 
probably,  in  a  slight  degree,  from  absorption  of  digested  mater  by  the  stomach  itself,  but 
chiefly  by  the  gradual  passage  of  the  softened  and  disintegrated  mass  into  the  small  intes- 
tine. This  process  continues  until  the  stomach  is  emptied,  occupying  a  period  of  from 
two  to  four  hours  ;  after  which,  the  movements  of  the  stomach  cease  until  food  is  again 
introduced. 

Regurgitation  of  Food,  and  Eructation. 

Regurgitation  of  part  of  the  contents  of  the  stomach,  in  the  human  subject,  although 
of  frequent  occurrence,  particularly  in  early  life,  is  not  strictly  a  physiological  act ;  and 
this  is  always  due  either  to  overloading  of  the  stomach  or  to  some  pathological  condition. 
Hut  in  some  of  the  inferior  animals  this  is  habitual ;  a  certain  class,  called  ruminants, 
regularly  passing  the  food,  after  the  first  deglutition,  in  small  quantities  from  the  paunch 
into  the  mouth,  where  it  undergoes  a  second  mastication  and  is  only  then  permitted  to 
pass  to  the  secreting  stomach  and  the  rest  of  the  alimentary  canal.  Animals  of  this 
class,  examples  of  which  are  the  ox,  sheep,  goat,  camel,  and  the  deer  tribe,  are  invari- 
ably herbivorous  and  take  into  the  stomach  a  large  bulk  of  matter  from  which  is  elabo- 
rated a  comparatively  small  quantity  of  nutriment.  During  the  period  when  they  are 
nourished  by  milk,  rumination  does  not  take  place. 

Considerable  interest  is  attached  to  the  function  of  rumination  in  the  inferior  ani- 
mals, in  connection  with  human  physiology,  from  the  fact  that  an  analogous  process  has 
sometimes  been  observed  in  the  human  subject ;  though  this  is  rare  and  is  generally  con- 
nected with  a  pathological  condition.  Such  cases  have  been  often  quoted,  and,  in  the 
earlier  works  on  physiology,  were  frequently  exaggerated  ;  but,  a  few  instances,  well  au- 
thenticated, are  on  record  in  which  rumination  had  become  habitual.  A  very  remark- 
able case  of  this  kind  is  reported  by  Home.  The  subject  was  an  idiot-boy,  aged  nineteen 
years,  who  had  an  appetite  so  ravenous  that  it  became  necessary  to  restrict  the  quantity 
of  food.  At  dinner  he  ordinarily  ate  about  a  pound  and  a  half  of  meat  and  vegetables, 
swallowing  the  whole  in  two  minutes.  He  began  to  chew  the  cud  at  the  end  of  a  quar- 
ter of  an  hour.  The  muscles  of  the  throat  could  be  seen  to  contract  when  the  bolus  was 
passed  back  to  the  mouth.  He  chewed  the  food  by  two  or  three  movements  of  the  jaws 
and  then  swallowed  it  again.  This  was  repeated  at  internals  for  half  an  hour,  during 
which  time  he  was  always  more  quiet  than  usual.  The  intellect  was  so  feeble  that  it  was 
impossible  to  ascertain  whether  the  rumination  were  voluntary  or  involuntary.  One  of 
the  cases  of  rumination  most  frequently  referred  to  is  that  of  M.  Cambay,  who  studied 
the  phenomena  in  his  own  person  and  made  it  the  subject  of  an  inaugural  thesis ;  and 
another  is  the  case  of  the  brother  of  M.  P.  Berard.  In  these  instances,  as  far  as  could 


256  DIGESTION. 

be  ascertained  from  the  sensations  during  the  act,  the  regurgitation  of  food  was  effected 
by  persistent  contractions  of  the  muscular  walls  of  the  stomach,  assisted  by  a  slight  and 
almost  involuntary  contraction  of  the  abdominal  muscles  and  diaphragm.  It  is  stated  by 
Cambay  that,  in  his  case,  the  taste  of  the  articles  of  food  was  not  modified,  "  but  that  it 
is  with  something  of  a  sense  of  pleasure  that  the  ruminator  thus  causes  to  return  to  the 
mouth  the  aliments  that  he  has  taken  into  the  stomach,  which  makes  them  undergo  a 
new  trituration." 

Rumination  in  the  human  subject  is  not  a  physiological  act.  It  is  evident  that  the  sub- 
stances returned  to  the  mouth  are  not  usually  impregnated  with  the  gastric  juice,  for  they 
have  not  the  disagreeable  acid  taste  of  ordinary  vomited  matters.  The  acts  are  generally 
preceded  by  a  sense  of  fulness  in  the  stomach,  and  their  mechanism  is  probably  nearly 
the  same  as  that  of  the  regurgitation  of  small  quantities  of  milk  from  the  distended 
stomachs  of  young  children,  which  is  so  common.  In  the  person  of  Cambay,  the  first 
act  was  said  to  be  voluntary,  but  succeeding  ones  were  not  under  the  control  of  the  will. 
Undoubtedly,  the  faculty  of  regurgitating  the  food  may  be  improved  by  practice,  and 
we  have  known  of  an  instance  in  which  it  was  apparently  cultivated  as  an  accom- 
plishment. 

The  mechanism  of  regurgitation  of  portions  of  the  contents  of  the  stomach,  aside 
from  instances  simulating  rumination,  has  been  so  often  alluded  to  that  it  demands  in  this 
connection  but  a  passing  mention.  In  some  persons,  this  act  may  be  accomplished  by  a 
voluntary  muscular  effort,  especially  when  the  stomach  is  overloaded.  It  occasionally 
happens,  when  the  stomach  is  somewhat  distended,  that  a  small  portion  of  its  contents 
suddenly  finds  its  way  to  the  mouth  without  even  the  consciousness  of  the  individual. 
The  muscular  contraction  which  produces  this  slight  regurgitation  is  so  insignificant  that 
there  must  necessarily  have  been  some  relaxation  at  the  cardiac  opening  of  the  stomach, 
which  under  ordinary  conditions  is,  as  we  know,  firmly  closed.  The  act  is  then  produced, 
in  part  by  a  slight  contraction  of  the  abdominal  muscles  and  diaphragm,  and  in  part  by 
contractions  of  the  stomach  itself  and  anti-peristaltic  movements  of  the  oesophagus.  It 
has  nothing  of  the  violent,  expulsive  character  of  true  vomiting,  which  is  produced  by 
the  spasmodic  and  involuntary  contraction  of  the  abdominal  muscles  and  diaphragm,  the 
stomach  being  passive. 

The  discharge  of  gases  from  the  oesophagus  by  the  mouth,  accompanied  with  a  pe- 
culiar and  characteristic  sound,  is  very  common.  This  is  usually  accomplished  without 
any  marked  contraction  of  the  muscles  concerned  in  vomiting  and  evidently  requires  very 
little  force.  Usually,  the  cardia  is  so  effectually  closed  as  to  prevent  the  passage  even  of 
gases  ;  and,  in  eructation,  there  must  be  a  temporary  relaxation  of  this  opening.  When 
thus  relaxed,  the  act  is  accomplished  chiefly  by  contractions  of  the  stomach  and  oesopha- 
gus. It  is  generally  accompanied  or  preceded  by  sensible  convulsive  movements  of  the 
oesophagus,  involving,  possibly,  contractions  of  its  longitudinal  fibres,  which  would  favor 
relaxation  of  the  cardiac  opening.  Although  it  is  usually  involuntary,  this  act  is  some- 
times under  the  control  of  the  will.  When  it  occurs,  while  it  is  difficult  or  impossible  to 
prevent  the  discharge  of  the  gas,  the  accompanying  sound  may  be  readily  suppressed. 
Eructation  is  frequently  a  matter  of  habit,  which  in  many  persons  becomes  so  developed 
by  practice  that  the  act  may  be  performed  voluntarily  at  any  time. 


INTESTINAL  DIGESTION.  357 


CHAPTER    IX. 

INTESTINAL  DIGESTION.— DEF^HC A  TION. 

Physiological  anatomy  of  the  small  intestine — Glands  of  Brunner — Intestinal  tubules,  or  follicles  ot  Lieberkuhn — 
Solitary  glands,  or  follicles,  and  the  patches  of  Peyer — Intestinal  juice — General  properties  of  the  intestinal 
juiee — Action  of  the  intestinal  juice  in  digestion — Pancreatic  juice — Action  of  the  pancreatic  juice  in  digestion — 
Destruction  of  the  pancreas — Cases  of  fatty  diarrhoea — Action  of  the  pancreatic  juice  upon  starchy,  saccharine, 
and  nitrogenized  principles — Action  of  the  bile  in  digestion — Biliary  fistula — General  constitution  of  the  bile — 
Variations  in  the  flow  of  bile — Movements  of  the  small  intestine — Peristaltic  and  antiperistaltic  movements — 
Function  of  the  gases  in  the  small  intestine — Influence  of  the  nervous  system  upon  the  peristaltic  movements — 
Physiological  anatomy  of  the  large  intestine— Digestion  in  the  large  intestine— Contents  of  the  large  intestine- 
Composition  of  the  faeces— Excretine  and  excretoleic  acid — Stercorine — Movements  of  the  large  intestine — Defse- 
cation — Gases  found  in  the  alimentary  canal. 

Physiological  Anatomy  of  the  Small  Intestine. 

THE  small  intestine,  so  called  on  account  of  its  small  size  as  compared  with  the  rest 
of  the  intestinal  tract,  is  the  long,  cylindrical  tuhe  which  occupies  the  greatest  part  of 
the  abdominal  cavity.  This  must  now  be  regarded  as  the  most  important  division  of  the 
digestive  system ;  and  its  physiological  anatomy,  together  with  that  of  the  great  glands 
which  discharge  their  secretions  into  its  cavity,  is  indispensable  as  an  introduction  to 
the  study  of  intestinal  digestion.  As  it  is  in  the  small  intestine  that  the  final  elaboration 
of  most  of  the  alimentary  principles  takes  place,  and  here,  also,  that  these  principles  are 
taken  into  the  circulating  fluid,  we  shall  find,  in  our  study  of  its  anatomy,  certain  parts 
which  are  concerned  in  digestion,  and  others  which,  as  far  as  we  know,  are  connected 
only  with  the  function  of  absorption.  It  will  be  most  convenient,  however,  to  consider, 
in  this  connection,  all  the  structures  found  in  the  small  intestine  which  possess  physio- 
logical interest. 

The  small  intestine,  extending  from  the  pyloric  extremity  of  the  stomach  to  the  ileo- 
c£ccal  valve,  is  held  to  the  spinal  column  by  a  double  fold  of  serous  membrane,  called  the 
mesentery.  As  the  peritoneum  which  lines  the  cavity  of  the  abdomen  passes  from 
either  side  to  the  spinal  column  it  comes  together  in  a  double  fold  just  in  front  of  the 
great  vessels  along  the  spine,  and,  passing  forward,  splits  again  into  two  layers,  which 
become  continuous  with  each  other  and  enclose  the  intestine,  forming  its  external  coat. 
The  width  of  the  mesentery  is  usually  from  three  to  four  inches;  but,  at  the  commence- 
ment and  the  termination  of  the  small  intestine,  it  suddenly  becomes  shorter,  binding  the 
duodenum  and  that  portion  of  the  intestine  which  opens  into  the  caput  coli  closely  to  the 
subjacent  parts.  The  mesentery  thus  keeps  the  intestine  in  place  but  allows  of  a  certain 
amount  of  motion,  so  that  the  tube  may  become  convoluted,  accommodating  itself  to  the 
size  and  form  of  the  abdominal  cavity.  The  form  of  these  convolutions  is  irregular  and 
is  continually  changing.  * 

The  length  of  the  small  intestine,  in  situ,  is  probably  from  fifteen  to  eighteen  feet 
(Sappey) ;  but  the  canal  is  very  distensible,  and  its  dimensions  are  subject  to  constant 
variations.  When  separated  from  the  mesentery  and  measured  without  stretching,  its 
length  has  been  found  to  be,  on  an  average,  about  twenty  feet.  Its  diameter  is  about 
one  and  a  quarter  inch. 

The  small  intestine  has  been  divided  into  three  portions,  which  present  anatomical 
:  and  physiological  peculiarities,  more  or  less  marked.     These  are  the  duodenum,  the  jeju- 
num, and  the  ileum. 

The  duodenum  has  received  its  name  from  the  fact  that  it  is  about  the  length  of  the 
breadth  of  twelve  fingers,  or  from  eight  to  ten  inches.     This  portion  of  the  intestine  is 
considerably  wider  than  the  constricted,  pyloric  end  of  the  stomach,  with  which  it  is  con- 
17 


258 


DIGESTION. 


tinuous,  and  is  also  much  wider  than  its  continuation,  the  jejunum.  It  presents  a  curve,, 
which  is  ordinarily  described  by  anatomists  as  consisting  of  three  portions.  The  first, 
called  the  hepatic  or  ascending  portion,  is  about  two  inches  in  length.  This  is  much  less 
firmly  fixed  by  its  peritoneal  attachment  than  the  other  portions  and  is  nearly  covered 
by  the  serous  membrane.  Its  direction  is  outward,  backward,  and  slightly  upward. 
Turning  downward,  and  a  little  inward,  it  merges  into  the  second,  called  the  descending 


FKJ.  C3.— Stomach,  liver,  small  intestine,  etc.    (Sappey.) 

1,  inferior  surface  of  the  liver;  ground  ligament  of  tJie  liver;  3,  gall-bladder;  4,  superior  surface  of  the 
right  lobe  of  the  liver  ;  5,  diaphragm;  6,  lower  portion  of  the  oesophagus;  7,  stomach;  8,gastro-hepatic  omen- 
turn,'  9,  spleen;  10,  gastro-splenic  omentum;  11,  duodenum;  12,  12,  small  intestine;  13,  ececum .;  14, 
appendix  vermiformis  ;  15, 15,  transverse  colon  ;  lQ,sigmoid  flexure  of  the  colon;  17,  urinary  bladder. 

or  vertical  portion,  the  length  of  which  is  about  three  inches.  This  is  covered  with 
peritoneum  only  on  its  anterior  surface  and  is  somewhat  more  firmly  attached  than  the 
ascending  portion.  The  intestine  then  makes  a  second  bend,  and  the  third  or  the  trans- 
verse portion  is  horizontal  in  its  course,  passing  across  the  spine  to  the  left  hypochon- 
drium.  This  portion  is  about  five  inches  in  length.  It  is  narrower  than  the  others,  is 
but  partially  covered  by  peritoneum,  and  is  more  firmly  bound  down  than  any  other  part 
of  the  small  intestine. 

The  coats  of  the  duodenum,  like  those  of  the  other  divisions  of  the  intestinal  tube,  are 
three  in  number.  Commencing  externally,  we  have  the  serous^  or  peritoneal  coat,  which 
has  already  been  described.  The  middle,  or  muscular  coat  is  composed  of  the  involuntary, 
or  unstriped  muscular  fibres,  such  as  exist  in  the  stomach,  arranged  in  two  layers.  The 
external,  longitudinal  layer  is  not  very  thick,  and  the  direction  of  its  fibres  can  be  made 


PHYSIOLOGICAL  ANATOMY   OF  THE   SMALL  INTESTINE.          259 

out  easily  only  at  the  outer  portions  of  the  tube  opposite  the  attachment  of  the  mesen- 
tery. Near  the  mesenteric  border,  the  fibres  are  very  faint.  This  is  true  throughout  the 
whole  of  the  small  intestine;  although  the  fibres  are  most  numerous  in  the  duodenum. 
The  internal,  circular,  or  transverse  layer  of  fibres  is  considerably  thicker  than  the  longi- 
tudinal layer.  These  fibres  encircle  the  tube,  running,  for  the  most  part,  at  right  angles 
to  the  external  layer,  but  some  of  them  having  rather  an  oblique  direction.  The  circu- 
lar layer  is  thickest  in  the  duodenum,  diminishing  gradually  in  thickness  to  the  middle 
of  the  jejunum,  but  after  that  maintaining  a  nearly  uniform  thickness  throughout  the 
canal  to  the  ileo-caecal  valve. 

The  jejunum,  the  second  division  of  the  small  intestine,  is  continuous  with  the  duo- 
denum. It  presents  no  well-marked  line  of  separation  from  the  third  division,  but  is 
generally  considered  to  include  the  upper  two-fifths  of  the  small  intestine,  the  lower 
three-fifths  being  called  the  ileum.  It  has  received  the  name  jejunum  from  the  fact 
that  it  is  almost  always  found  empty  after  death.  This  portion  of  the  intestine  presents 
no  important  peculiarities  as  regards  its  peritoneal  and  muscular  coat. 

The  ileum  is  somewhat  narrower  and  thinner  than  the  jejunum,  otherwise  possessing 
no  marked  peculiarities  except  in  the  structure  of  its  mucous  membrane.  This  opens 
into  the  commencement  of  the  colon  and  is  the  termination  of  the  small  intestine. 

Mucous  Membrane  of  the  Small  Intestine. — The  mucous  coat  of  the  small  intestine  is 
somewhat  thinner  than  the  lining  membrane  of  the  stomach.  It  is  thickest  in  the  duo- 
denum and  gradually  becomes  thinner  until  we  reach  the  ileum.  It  is  highly  vascular, 
presenting,  like  the  mucous  membrane  of  the  stomach,  a  great  increase  in  the  quantity 
of  blood  during  the  process  of  digestion.  It  has  a  peculiar  soft  and  velvety  appearance, 
and,  during  digestion,  it  is  of  a- vivid-red  color,  being  pale-pink  during  the  intervals.  It 
presents  for  anatomical  description  the  following  parts:  1,  folds  of  the  membrane,  called 
valvulaa  conniveutes ;  2,  duodenal  racemose  glands,  or  the  glands  of  Brunner ;  3,  intesti- 
nal tubules,  or  follicles  of  Lieberkuhn ;  4,  intestinal  villi ;  5,  solitary  glands,  or  follicles ; 
6,  agminated  glands,  or  patches  of  Peyer. 

The  valvulaa  conniventes,  simple  transverse  duplicatures  of  the  mucous  membrane 
of  the  intestine,  are  particularly  well  marked  in  man,  although  they  are  found  in  some 
of  the  inferior  animals  belonging  to  the  class  of  mammals,  as  the  elephant  and  the  camel. 
They  render  the  extent  of  the  mucous  membrane  much  greater  than  that  of  the  other 
coats  of  the  intestine.  Commencing  at  about  the  middle  of  the  duodenum,  they  extend, 
with  no  diminution  in  number,  throughout  the  jejunum.  In  the  ileum  they  become  pro- 
gressively more  and  more  scanty,  until  they  are  lost  at  about  its  lower  third.  Sappey 
.found  about  six  hundred  of  these  folds  in  the  first  half  of  the  small  intestine  and  from  two 
hundred  to  two  hundred  and  fifty  in  the  lower  half.  He  estimates  that,  in  those  portions 
of  intestine  where  they  are  most  abundant,  they  increase  the  length  of  the  mucous  mem- 
brane to  about  double  that  of  the  tube  itself;  but  in  the  ileum  they  do  not  increase  the 
length  more  than  one-sixth.  The  folds  are  always  transverse  and  occupy  usually  from 
one-third  to  one-half  of  the  circumference  of  the  tube,  although  a  few  may  extend  entirely 
around  it.  The  greatest  width  of  each  fold  is  in  the  centre,  where  it  measures  from  a 
quarter  to  half  an  inch.  From  this  the  width  gradually  diminishes  until  the  folds  are 
lost  in  the  membrane  as  it  is  attached  to  the  muscular  coat.  Between  the  folds  are 
found  fibres  of  connective  tissue  similar  to  those  which  attach  the  membrane  throughout 
the  whole  of  the  alimentary  tract.  This,  though  loose,  is  constant,  and  it  prevents  the 
folds  from  being  effaced,  even  when  the  intestine  is  distended  to  its  utmost.  Between 
the  folds  are  also  found  blood-vessels,  nerves,  and  lymphatics. 

The  position  and  arrangement  of  the  valvula3  conniventes  is  such  that  they  move  freely 
in  both  directions  and  may  be  applied  to  the  inner  surface  of  the  intestine  either  above 
or  below  their  line  of  attachment.  It  is  evident  that  the  food,  as  it  passes  along  in  obe- 
dience to  the  peristaltic  movements,  must,  by  insinuating  itself  beneath  the  folds  and 


260  DIGESTION. 

passing  over  them,  be  exposed  to  a  greater  extent  of  mucous  membrane  than  if  these 
valves  did  not  exist.  This  is  about  the  only  definite  use  that  can  be  assigned  to  them. 
They  cannot,  as  has  been  supposed  by  some,  have  any  considerable  influence  upon  the 
rapidity  of  the  passage  of  the  alimentary  mass  along  the  intestinal  canal. 

Thickly  set  beneath  the  mucous  membrane  in  the  first  half  of  the  duodenum,  and 
scattered  here  and  there  throughout  the  rest  of  its  extent,  are  the  duodenal  racemose 
glands,  or  the  glands  of  Brnnner.  These  are  not  found  in  other  parts  of  the  intestinal 

canal.  In  their  structure,  they  closely 
resemble  the  racemose  glands  of  the 
oesophagus.  On  dissecting  the  muscu- 
lar coat  from  the  mucous  membrane, 
they  may  be  seen  with  the  naked  eye, 
in  the  areolar  tissue,  in  the  form  of  lit- 
tle, rounded  bodies,  about  one-tenth  of 
an  inch  in  diameter.  Examined  micro- 
scopically, these  bodies  are  found  to 
consist  of  a  large  number  of  short,  blind 
tubes  branching  in  every  direction  and 
held  together  by  a  few  fibres  of  con- 
nective tissue.  The  tubes  have  blood- 
vessels ramifying  on  their  exterior  and 
are  lined  with  glandular  epithelium. 

They  collect  together  to  terminate  in 
FIG.  W.— GlandofBmnner,  from  the  human  subject.  (Frey.)  .,  ,  .  ,  ,, 

an  excretory  duct  which  penetrates  the 

mucous  membrane  and  opens  into  the  intestinal  cavity.  When  these  structures  are  ex- 
amined in  a  perfectly  fresh  preparation,  the  excretory  duct  is  frequently  found  to  contain 
a  clear,  viscid  mucus,  of  an  alkaline  reaction.  This  secretion  has  never  been  obtained  in 
quantity  sufficient  to  admit  of  the  determination  of  its  chemical  or  physiological  proper- 
ties. Its  quantity  must  be  infinitely  small  as  compared  with  the  secretion  produced 
by  the  glandular  tubes  found  in  such  immense  numbers  throughout  the  intestinal  tract, 
and  it  cannot  be  regarded  as  constituting  an  important  part  of  the  fluid  known  as  the 
intestinal  juice. 

The  intestinal  tubules,  or  the  follicles  of  Lieberkuhn,  the  most  important  glandular 
structures  in  the  intestinal  mucous  membrane,  are  found  throughout  the  whole  of  the 
small  and  large  intestine.  In  examining  a  thin  section  of  the  mucous  membrane,  these 
little  tubes  are  seen  closely  packed  together,  occupying  nearly  the  whole  of  its  structure. 
From  the  great  extent  of  the  membrane,  it  can  readily  be  conceived  that  their  number 
must  be  immense.  Between  the  tubules,  are  blood-vessels,  embedded  in  a  dense  stroma 
of  fibrous  tissues  with  numerous  unstriped  muscular  fibres.  In  a  vertical  section  of 
the  mucous  membrane,  the  only  situations  where  the  tubules  are  not  seen  are  in  that 
portion  of  the  duodenum  where  the  space  is  occupied  by  the  ducts  of  the  glands  of  Brun- 
ner  and  immediately  over  the  centre  of  the  larger  solitary  glands  and  some  of  the  closed 
follicles  which  are  collected  to  form  the  patches  of  Peyer.  The  tubes  are  not  entirely 
absent  in  the  patches  of  Peyer,  but  are  here  collected  in  rings,  twenty  or  thirty  tubes  deep, 
which  surround  each  of  the  closed  follicles.  A  microscopical  examination  of  the  surface 
of  the  mucous  membrane  by  reflected  light  shows  that  the  openings  of  the  tubules  are 
between  the  villi. 

The  tubules  are  usually  simple,  though  sometimes  bifurcated,  are  composed  externally 
of  a  structureless  basement-membrane,  and  are  lined  with  a  single  layer  of  columnar  epi- 
thelium like  the  cells  which  cover  the  villi,  the  only  difference  being  that,  in  the  tubes, 
the  cells  are  a  little  shorter.  These  cells  never  contain  fatty  granules,  even  during  the  di- 
gestion of  fat.  The  central  cavity  which  the  cells  enclose,  which  is  about  one-fourth  of 
the  diameter  of  the  tube,  is  filled  with  a  clear,  viscid  fluid,  which  is  the  most  important 


PHYSIOLOGICAL  ANATOMY   OF  THE  SMALL  INTESTINE. 


261 


.constituent  of  the  intestinal  juice.  The  length  of  the  tubules  is  equal  to  the  thickness  ol 
the  mucous  membrane  and  is  about  Js  of  an  inch.  Their  diameter  is  about  ^  of  an 
inch.  In  man,  they  are  cylindrical,  terminating  in  a  single,  rounded,  blind  extremity, 
which  is  frequently  a  little  larger  than  the  rest  of  the  tube.  These  tubules  are  the  chief 
agents  concerned  in  the  production  of  the  fluid  known  as  the  intestinal  juice. 


FiG.  ^.—Intestinal  tubules;  magnified  100  diameters.    (Sappey.) 

A.  From  the  dog.    1,  excretory  canal ;  2,  2,  primary  branches  ;  8,  3,  secondary  branches ;  4,  4,  terminal  cuU-de-sac. 

B.  From  the  ox.    1,  excretory  canal ;   2,  principal  branch,  dividing  into  two ;  3,  branch  undivided ;  4,  4,  terminal 

culs-de-sac. 

C.  From  the  sheep.    1,  trunk;  2,  2,  branches. 
1).  Single  tube,  from  the  pig. 

E.  From  the  rabbit  and  hare.    1,  simple  gland ;  2,  3,  4,  bifid  glands ;  5,  compound  gland  from  the  duodenum. 


The  intestinal  villi,  though  chiefly  concerned  in  absorption,  are  most  conveniently 
considered  in  this  connection.  These  exist  throughout  the  whole  of  the  small  intestine 
but  are  not  found  beyond  the  ileo-csecal  valve,  although  they  cover  that  portion  of  the 
valve  which  looks  toward  the  ileum.  Their  number  is  very  great,  and  they  give  to  the 
membrane  its  peculiar  and  characteristic  velvety  appearance.  They  are  found  on  the 
valvulaa  conniventes  as  well  as  on  the  attached  portions  of  the  mucous  membrane.  In 
the  duodenum  and  jejunum,  they  are  most  numerous.  In  these  parts,  there  are  from 
fifty  to  ninety  villi  to  a  square  line,  and,  in  the  ileum,  from  forty  to  seventy  to  a  square 
line.  Sappey  estimates,  on  an  average,  about  fifty  to  the  square  line  and  more  than  ten 
millions  (10,125,000)  throughout  the  whole  of  the  small  intestine.  The  form  of  the  villi 
varies  somewhat  in  different  animals.  In  the  human  subject,  they  are  flattened  cylinders 
or  cones.  In  the  duodenum,  where  they  resemble  somewhat  the  elevations  found  in  the 
pyloric  portion  of  the  stomach,  they  are  shorter  and  broader  than  in  other  situations 
and  are  more  like  flattened,  conical  folds.  In  the  jejunum  and  ileum,  they  are  in  the 
form  of  long,  flattened  cones  and  cylinders.  As  a  rule,  the  cylindrical  form  predominates 
in  the  lower  portion  of  the  intestine.  In  the  jejunum  they  attain  their  greatest  length, 


262 


DIGESTION. 


measuring  here  from  ^5  to  2*6  of  an  inch  in  length  by  ^  to  ^  of  an  inch  in  breadth  at 
their  base. 

The  structure  of  the  villi  shows  them  to  be  simple  elevations  of  the  mucous  mem- 
brane, provided  with  blood-vessels,  and  probably  also  with  lacteals,  or  intestinal  lym- 
phatics. Externally  is  found  a  single  layer  of  long,  columnar  epithelial  cells,  resting  on 


. 

FIG.  ^.—Intestinal  villus.    (Leydig.)  FIG.  67.— Capillary  net-work  of  an  intestinal  villus.  (Frey.) 

«,  cr,  a,  epithelial  covering ;    6,  &,  capillary  net-work  ;  a,  venous  trunk ;  6,  arterial  trunk, 

c,  c,  longitudinal  muscular  fibres  ;  d,  lacteal. 

a  structureless  basement-membrane.  These  cells,  though  closely  adherent  to  the  sub- 
jacent parts  during  life,  are  easily  detached  after  death  and  are  almost  always  destroyed 
and  removed  in  injected  preparations.  They  adhere  firmly  to  each  other  and  are  isolated 
with  difficulty  in  microscopical  preparations.  Kolliker  has  shown  that  the  membranes  on 
the  free  surfaces  of  these  cells  are  thickened  and  finely  striated,  forming,  as  it  were,  a 

special  membrane  covering  the  villus  and  exter- 
nal to  the  cells.  This  membrane  may  be  raised 
up  from  the  cells  and  exhibited  by  the  action 
of  water. 

The  substance  of  the  villus  is  composed  of  a 
stroma  of  amorphous  matter,  in  which  are  em- 
bedded nuclei  and  a  few  fibres,  fibro-plastic 
cells,  and  numerous  non- striated  muscular 
fibres.  The  blood-vessels  are  very  numerous ; 
four  or  five,  and  sometimes  as  many  as  twelve 
or  fifteen  arterioles  entering  at  the  base,  ram- 
ifying through  the  substance  of  the  villus, 
but  not  branching  or  anastomosing,  or  even 
diminishing  in  caliber  until,  by  a  slightly  wavy 
turn  or  loop,  they  communicate  with  the  ven- 
ous radicles,  each  of  which  is  somewhat  larger 
than  the  arterioles.  The  veins  all  converge 

to  two  or  three  branches,  finally  emptying  into  a  large  trunk  situated  nearly  in  the 
axis  of  the  villus. 


FIG. 


-Epithelium  of  the  small  intestine  of  the 
rabbit.     (Funke.) 


PHYSIOLOGICAL   ANATOMY   OF   THE   SMALL   INTESTINE.  263 

The  nuclei  of  the  muscular  fibres  of  the  villi  may  be  shown  by  treating  them  with 
acetic  acid  after  the  epithelium  has  been  removed.  These  fibres  appear  to  be  longi- 
tudinal, forming  a  thin  layer  surrounding  the  villus,  about  half-way  between  the  pe- 
riphery and  the  centre  and  continuous  with  the  muscular  coat  of  the  intestine.  The  mus- 
cular fibres,  from  their  arrangement,  would  seem  to  be  capable  of  shortening  the  villus ; 
and  this  has  actually  been  observed  in  specimens  taken  from  the  intestine  shortly  after 
death. 

The  anatomy  of  the  lacteals  as  they  originate  in  the  villi  has  been  the  subject  of  much 
controversy ;  but  almost  all  anatomists  are  now  agreed  that  these  vessels  commence  by 
blind  extremities,  which  are  either  single  or  present  a  few  short,  rounded  cliverticula 
leading  to  a  single  tube. 

Owing  to  the  excessive  tenuity  of  the  walls  of  the  lacteals  in  the  villi,  it  has  been 
found  impossible  to  fill  them  with  an  artificial  injection,  although  the  lymphatics  sub- 
jacent to  them  may  be  easily  distended  and  studied  in  this  way.  Those  who  profess  to 
have  seen  the  single  lacteal  in  the  villus  have  done  so  by  examining  the  parts  when  the 
lacteal  system  has  been  engorged  with  chyle. 

We  must  still  regard  the  question  of  the  origin  of  the  lacteals  in  the  intestinal  villi  as 
one  of  great  obscurity.  They  may  originate  by  a  delicate,  anastomosing  plexus,  just  be- 
neath the  epithelium,  as  is  thought  probable  by  Sappey,  or  the  chyle  may  pass  through 
the  epithelial  layer  and  a  part  of  the  substance  of  the  villus,  according  to  the  view  pre- 
sented by  Eecklinghausen,  without  the  intervention  of  distinct  vessels,  until  the  particles 
reach  the  central  tube. 

No  satisfactory  account  has  ever  been  given  of  nerves  in  the  intestinal  villi.  If  any 
exist  in  these  structures,  they  probably  are  derived  from  the  sympathetic  system,  which 
is  largely  distributed  to  the  intestinal  canal. 

The  solitary  glands  or  follicles  and  the  patches  of  Peyer,  or  agminated  glands,  have 
one  and  the  same  structure,  the  only  difference  being  that  those  called  solitary  are  scat- 
tered singly  in  very  variable  numbers  throughout  the  small  and  large  intestine,  while  the 
agminated  glands  consist  of  numbers  of  these  follicles  collected  into  patches  of  different 
sizes.  These  patches  are  generally  found  in  the  ileum.  The  number  of  the  solitary 
glands  is  so  variable  that  it  is  impossible  to  give  any  general  estimate  of  it.  They  are 
sometimes  absent.  The  patches  of  Peyer  are  always  situated  in  that  portion  of  the  intes- 
tine opposite  the  attachment  of  the  mesentery.  They  are  likewise  variable  in  number 
and  are  irregular  in  size.  They  usually  are  irregularly-oval  in  form,  and  measure  from 
half  an  inch  to  an  inch  and  a  half  in  length  by  three-fourths  of  an  inch  in  breadth. 
Sometimes  they  are  three  or  four  inches  long,  but  the  largest  are  always  found  in 
the  lower  part  of  the  ileum.  Their  number  is  about  twenty,  and  they  are  generally 
confined  to  the  ileum ;  but  when  they  are  very  numerous — for  they  sometimes  exist 
to  the  number  of  sixty  or  eighty — they  may  be  found  in  the  jejunum  or  even  in  the 
duodenum. 

Two  varieties  of  the  patches  of  Peyer  have  been  lately  described  by  anatomists.  In 
one  of  these  varieties,  the  patch  is  quite  prominent,  its  surface  being  slightly  raised 
above  the  general  mucous  surface,  while,  in  the  other,  the  surface  is  smooth,  and  the 
patch  is  distinguished  at  first  with  some  difficulty.  The  more  prominent  patches  are  cov- 
ered with  mucous  membrane  arranged  in  folds  something  like  the  convolutions  on  the 
surface  of  the  brain.  The  valvular  conniventes  are  arrested  at  or  very  near  their  borders. 
These  are  the  only  patches  which  are  generally  described  as  the  glands  of  Peyer,  the 
others,  which  may  be  called  the  smooth  patches,  being  generally  overlooked.  The  latter 
are  covered  with  a  smooth,  thin,  and  closely-adherent  mucous  membrane.  Their  follicles 
are  small  and  numerous.  The  borders  of  these  patches  are  much  less  strongly  marked  than 
those  of  the  first  variety.  As  they  are  evident  only  upon  close  examination  and  as  they 
are  the  only  patches  present  in  certain  individuals,  it  is  said  that  sometimes  the  patches 
of  Peyer  are  entirely  w  an  ting.  They  are  generally  less  numerous  than  the  first  variety 


264 


DIGESTION. 


FIG.  69.— Patch  of  Peyer.  (Sappey.) 
1, 1, 1,  patch  of  Peyer;  2,  2,  folds  seen 
on  the  surface;  3,  3,  grooves  be- 
tween the  folds ;  4,  4,  fossettes  be- 
tween some  of  the  folds  :  5,  5,  5, 
5,  5,  5,  5,  5,  valvute  coriniventes; 
(5,  6, 6,  6,  solitary  glands;  7, 7,  7,  7, 
smaller  solitary  glands :  8,  8,  soli- 
tary glands  upon  the  valvulse  con- 
niventes. 


and,  according  to  Sappey,  are  most  abundant  in  persons  of  feeble  constitution.     The 
villi  are  very  large  and  prominent  on  the  mucous  membrane  covering  the  first  variety 

of  Peyer's  patches,  especially  at  the  summit  of  the  folds. 
In  the  second  variety,  the  villi  are  the  same  as  over  other 
parts  of  the  mucous  membrane,  except  that  they  are 
placed  more  irregularly  and  are  not  so  numerous. 

The  intimate  structure  of  the  patches  of  Peyer  has.  not 
been  definitely  settled  in  all  its  particulars.  It  is  well  deter- 
mined, however,  that  the  follicles  which  compose  them  are 
completely  closed,  the  openings  which  have  been  said  to 
exist  being  undoubtedly  accidental  ruptures  made  in  pre- 
paring specimens  for  microscopical  examination.  These 
follicles  are  somewhat  pear-shaped,  with  their  pointed 
projections  directed  toward  the  cavity  of  the  intestine. 
Just  above  the  follicle,  there  is  generally  a  small  opening 
in  the  mucous  membrane,  surrounded  by  a  ring  of  intes- 
tinal tubules,  and  leading  to  a  cavity,  the  base  of  which 
is  convex  and  formed  by  the  conical  projection  of  the 
follicle.  The  diameter  of  the  follicles  is  from  fa  to 
fa  or  even  fa  of  an  inch.  The  small-sized  follicles  are 
generally  covered  by  mucous  membrane  and  have  no 
opening  leading  to  them.  Each  follicle  consists  of  a  rather 
strong  capsule  composed  of  an  almost  homogeneous  or 
very  slightly  fibrous  membrane,  enclosing  a  semifluid, 
grayish  substance,  cells,  blood-vessels,  and  probably  lym- 
phatics. The  semifluid  matter  is  of  an  albuminoid  character.  The  cells  are  very  small, 
rounded,  and  mingled  with  numerous  small,  free  nuclei.  The  blood-vessels  have  rather  a 
peculiar  arrangement.  In  the  first  place  they  are  distributed  between  the  follicles,  so  as 
to  form  a  rich  net-work  surrounding  each  one.  Numerous  capillary  branches  are  sent 
from  these  vessels  into  the  interior  of  the  follicle,  returning  in  the  form  of  loops. 
The  obscurity  in  the  anatomy  of  the  follicles  is  chiefly  with  regard  to  the  arrangement 

of  their  lymphatic  vessels.  These  have  not  been  dis- 
tinctly traced  within  the  investing  membrane.  They 
have  been  demonstrated  surrounding  the  follicles,  but  it 
is  still  doubtful  whether  they  exist  in  their  interior. 
This  question  is  so  unsettled  that  it  is  impossible  to 
make  a  definite  statement  on  the  subject.  All  that  is 
known  is  that,  during  digestion,  the  number  of  lacteals 
coming  from  the  Peyerian  patches  is  greater  than  in 
other  parts  of  the  mucous  membrane  ;  but  vessels  con- 
taining a  milky  fluid  are  never  seen  within  the  follicles. 
The  mucous  membrane  covering  the  prominent 
patches  is  generally  so  thick  and  folded  that  the  closed 
follicles  cannot  be  seen  from  above  and  are  only  dis- 
cernible from  the  under  surface.  In  the  smooth  patch- 
es, the  follicles  are  generally  well  brought  out  by  macer- 
ation in  acetic  acid. 

The  description  of  the  follicles  which  compose  the 
patches  of  Peyer  answers,  in  general  terms,  for  the  soli- 
patch;  s  ,8,  fibrous  coat,  of  the  inte"s-   tary  glands,  except  that  the  latter  are  found  in  both 

tine  ;  4, 4,  patch  ;  5,  5,  5,  5.  5,  5,  5.  5,     ,  i 

vaivute  conniventes.  the  small  and  the  large  intestine. 


FIG.  70.— Patch  of  Peyer,  seen  from,  its 
attached  surface.    (Sappey.) 


INTESTINAL  JUICE.  265 

Intestinal  Juice. 

Of  the  three  fluids  with  which  the  food  is  brought  in  contact  in  the  intestinal  canal 
namely,  the  bile,  the  pancreatic  juice,  and  the  intestinal  juice,  the  last,  the  secretion  of 
the  mucous  membrane  of  the  small  intestine,  presents  the  greatest  difficulties  in  the  in- 
vestigation of  its  properties  and  function.  If  it  be  admissible  to  reason  from  the  known 
mechanism  of  secretion  in  other  parts,  it  is  fair  to  suppose  that  the  normal  secretion 
from  the  mucous  membrane  of  the  small  intestine  can  only  take  place  in  obedience  to 
the  stimulus  of  food.  The  same  cause  induces  the  secretion  of  the  pancreatic  juice  and 
increases  the  flow  of  bile.  As  we  have  already  seen,  the  food,  as  it  passes  from  the 
stomach  into  the  duodenum,  is  to  a  great  extent  disintegrated  and  is  mingled  with  the 
secretions  from  both  the  mouth  and  the  stomach.  Under  these  circumstances,  it  is  evi- 
dently impossible  to  collect  the  intestinal  juice  under  perfectly  physiological  conditions, 
in  a  state  of  purity  sufficient  to  allow  of  extended  experiments  regarding  its  composition, 
properties,  and  action  in  digestion. 

Bidder  and  Schmidt  experimented  upon  dogs  and  cats,  shutting  off  from  the  intestine 
the  bile  and  pancreatic  juice,  and  found  that  starch  introduced  into  the  canal  became 
transformed  into  sugar.  They  also  observed  that  fat  was  emulsified  to  a  considerable 
degree,  and  that  albumen  and  meat  were  partially  disintegrated  and  digested.  These 
observers  were  unable  to  collect  the  intestinal  juice  in  quantity  sufficient  for  analysis. 
That  which  they  obtained  was  found  to  be  colorless,  very  viscid,  and  strongly  alkaline 
in  its  reaction. 

As  far  as  the  composition  and  general  properties  of  the  intestinal  juice  are  concerned, 
the  observations  of  Colin  upon  horses  are  the  most  definite,  although  it  is  questionable 
whether  he  succeeded  in  obtaining  the  fluid  in  a  normal  state.  To  collect  the  fluid,  an 
incision  was  made  into  the  abdominal  cavity,  and  from  four  and  a  half  to  six  feet  of  the 
small  intestine  were  drawn  out. 

This  portion  was  emptied  by  gen-  £ 

tly  pressing  with  the  finger  from 
above  downward,  while,  with  the 
other  hand,  the  upper  portion  was 
kept  closed.  Without  removing 
the  fingers,  two  soft  clamps  were  r 

&       '  .  Fir,.  71.— Clamp  for  isolating  a  portion  of  the  ^ntestlnG.    (Colin.) 

then  applied,  thus  Shutting  Ott  the  A,  lower  plate;  B,  upper  plate;  <7,  fixed  screw;  D,  movable  screw  in 
exposed  part  of  the  intestine  from  place;  ^',  screw  turned  so  as  to  allow  the  clamp  to  be  passed 

the  rest  of  the  canal.    The  gut  was 

then  returned  and  the  wound  in  the  abdomen  closed.  At  the  end  of  half  an  hour,  the 
animal  was  killed  by  bleeding,  and  the  contents  of  the  isolated  portion  of  the  intestine 
were  examined.  The  quantity  of  juice  obtained  was  considerable,  being  from  1,235  to 
1,852  grains  for  about  six  and  a  half  feet  of  intestine.  It  was  always  found  to  be  much 
less  when  intestinal  digestion  had  been  suspended,  and  its  quantity  could  be  increased  by 
the  injection  into  the  loop  of  a  little  solution  of  manna,  sulphate  of  soda,  or  aloes.  The 
fluid  thus  obtained  was  clear,  slightly  yellowish,  with  a  saline  taste  and  an  alkaline  re- 
action. It  was  mixed  with  mucus,  which  formed  a  sediment  when  the  fluid  was  allowed 
to  stand,  and  could  be  separated  by  filtration.  Notwithstanding  the  care  with  which 
these  observations  were  conducted,  it  is  not  probable  that  the  fluid  thus  obtained  by 
Colin  was  the  normal  intestinal  juice ;  and  it  certainly  does  not  correspond  in  its  gen- 
eral characters  with  the  fluids  which  have  been  studied  by  other  experimenters. 

It  becomes  an  interesting  question,  in  this  connection,  to  determine  whether  the  soli- 
tary and  the  agminated  glands  produce  any  secretion  which  is  discharged  into  the  intes- 
tinal cavity.  Although  these  follicles  are  closed,  the  observations  of  Colin  have  shown 
pretty  conclusively  that  they  are  capable  of  producing  a  secretion ;  but  the  precise  mode 
of  its  formation  is  not  so  apparent.  The  experiment  by  which  this  was  demonstrated 


266 


DIGESTION. 


was  made  on  a  pig,  an  animal  in  which  there  is  an  enormous  agminate  gland,  ribbon- 
shaped  and  over  six  feet  in  length.  That  portion  of  the  ileum  in  which  the  gland  is 
situated  was  emptied,  and  about  four  and  a  half  feet  of  it  were  isolated  by  two  ligatures 
from  the  rest  of  the  canal.  At  the  end  of  an  hour  the  animal  was  killed  and  the  intestine 
examined.  The  surface  of  the  gland  was  found  covered  with  a  layer  of  mucus,  thicker 
and  more  consistent  than  over  other  portions  of  the  membrane.  The  only  way  in  which 
it  could  reasonably  be  supposed  that  this  secretion  was  produced  is  by  exhalation  through 
the  membranes  of  the  follicles,  as  there  is  no  evidence  that  their  contents  are  discharged 
by  rupture. 


FIG.  72.— Isolated  portion  of  the  intestine,    (Colin.) 

Taking  only  into  consideration  experiments  upon  the  inferior  animals,  little  definite 
information  has  been  obtained  concerning  the  composition  and  properties  of  the  intestinal 
juice.  We  can  readily  see  that  this  must  be  the  case,  since  it  has  thus  far  been  impossi- 
ble, in  observations  of  this  kind,  to  fulfil  the  necessary  physiological  conditions.  Farther 
facts  are  evidently  needed  to  harmonize  the  opposite  results  arrived  at  by  different  ex- 
perimenters. It  was  the  same  in  the  progress  of  the  physiology  of  stomach-digestion, 
which  was  unsettled  and  obscure  until  the  normal  gastric  juice  was  obtained  by  Beau- 
mont. The  following  case  of  intestinal  fistula,  reported  by  Busch,  has  done  much  to  elu- 
cidate this  subject : 

The  case  referred  to  was  that  of  a  woman,  thirty-one  years  of  age,  who,  in  the  sixth 
month  of  her  fourth  pregnancy,  was  injured  in  the  abdomen  by  being  tossed  by  a  bull. 
The  wound  was  between  the  umbilicus  and  the  pubes,  presenting  two  contiguous  open- 
ings connected  with  the  intestinal  canal.  It  was  supposed  that  the  openings  were  into 
the  upper  third  of  the  small  intestine.  At  the  time  the  patient  first  came  under  observa- 
tion, every  thing  that  was  taken  into  the  stomach  was  discharged  by  the  upper  opening, 
and  all  attempts  to  establish  a  communication  between  the  two  by  a  surgical  operation 
had  failed.  At  this  time,  the  patient  was  extremely  emaciated,  had  a  voracious  appetite, 
and  was  evidently  suffering  from  defective  nutrition  resulting  from  the  constant  dis- 
charge of  alimentary  matter  from  the  fistula.  Having  been  treated,  however,  by  the 
introduction  of  cooked  alimentary  substances  into  the  opening  connected  with  the  lower 


ACTION   OF  THE   INTESTINAL  JUICE   IN  DIGESTION.  267 

end  of  the  intestine,  she  soon  improved  in  her  nutrition  and  was  then  made  the  subject 
of  extended  and  interesting  observations  upon  intestinal  digestion. 

With  regard  to  the  general  properties  of  the  intestinal  juice,  the  observations  of  Busch 
upon  his  case  of  intestinal  fistula  agree  with  those  of  Bidder  and  Schmidt  upon  the  lower 
animals.  He  never,  in  the  natural  condition,  found  a  large  quantity  of  secretion  in  the  in- 
testine. The  fluid  was  white  or  of  a  pale  rose-color,  consistent,  and  always  strongly  alka- 
line. The  maximum  proportion  of  solid  matter  which  it  contained  was  7*4  and  the  mini- 
mum, 3-87  per  cent.  The  secretion  apparently  could  not  be  obtained  in  sufficient  quantity 
for  ultimate  analysis.  No  better  opportunity  than  this  could  be  presented  for  studying 
the  intestinal  juice  in  its  pure  state.  The  nature  of  the  case  made  it  impossible  that  there 
should  be  any  admixture  of  food,  pancreatic  juice,  bile,  or  the  secretion  of  the  duodenal 
glands ;  and,  during  the  process  of  digestion,  the  lower  part  of  the  intestine  undoubtedly 
produced  a  fluid  of  perfectly  normal  character.  When  we  come  to  consider  the  action 
of  the  intestinal  juice  upon  the  various  articles  of  food,  our  most  reliable  facts  will  be 
drawn  from  the  observations  made  upon  this  case. 

From  what  has  been  ascertained  by  experiments  upon  the  lower  animals  and  observa- 
tions on  the  human  subject,  the  intestinal  juice  has  been  shown  to  possess  the  following 
characters : 

Its  quantity  in  any  portion  of  the  mucous  membrane  which  can  be  examined  is  small ; 
but,  when  the  extent  of  the  canal  is  considered,  it  is  evident  that  the  entire  quantity  of 
intestinal  juice  must  be  great,  although,  beyond  this,  no  reliable  estimate  can  be  made. 

The  intestinal  juice  is  viscid  and  has  a  tendency  to  adhere  to  the  mucous  membrane. 
It  is  generally  either  colorless  or  of  a  faint  rose-tint,  and  its  reaction  is  invariably  alkaline. 

With  regard  to  the  composition  of  the  intestinal  juice,  little  of  a  definite  character  has 
been  learned.  All  that  can  be  said  is  that  its  solid  constituents  exist  in  the  proportion 
of  about  5 '47  parts  per  hundred.  In  most  analyses  of  fluids  from  the  intestine,  there  is 
reason  to  believe  that  the  normal  intestinal  juice  was  not  obtained. 

The  organs  which  secrete  the  fluid  known  as  the  intestinal  juice  are  the  follicles  of 
Lieberkuhn,  the  glands  of  Brunner,  and  possibly  the  solitary  follicles  and  patches  of  Peyer. 
The  fluid,  however,  is  chiefly  secreted  by  the  follicles  of  Lieberkuhn,  which,  as  we  have 
seen,  exist  in  the  mucous  membrane  of  the  intestine  in  immense  numbers.  Although  the 
other  organs  mentioned  do  not  contribute  much  to  the  secretion,  they  produce  a  certain 
quantity  of  fluid;  and  the  intestinal  juice  must  be  regarded  as  a  compound  fluid,  like  the 
saliva,  and  not  the  product  of  a  single  variety  of  glands,  like  the  gastric  juice. 

Action  of  the  Intestinal  Juice  in  Digestion. 

The  physiological  action  of  the  intestinal  juice  has  been  closely  studied  in  the  inferior 
animals  by  Frerichs  and  by  Bidder  and  Schmidt,  but  their  experiments  have  been  some- 
what contradictory.  All  observers,  however,  are  agreed  that  this  fluid  is  more  or  less 
active  in  transforming  starch  into  sugar.  We  must  turn  finally  to  the  observations  of 
Busch,  on  the  case  of  intestinal  fistula  in  the  human  subject,  for  the  most  satisfactory  and 
definite  information  on  this  subject.  In  many  points,  it  is  true,  these  observations  sim- 
ply confirm  those  which  have  been  made  upon  the  inferior  animals,  but  they  are  of  great 
value,  as  they  establish  conclusively  many  important  facts  regarding  the  physiological 
action  of  the  intestinal  juice  in  the  human  subject. 

In  the  case  reported  by  Busch,  starch,  both  raw  and  hydrated,  when  introduced  into 
the  lower  opening,  where  it  came  in  contact  only  with  the  intestinal  juice,  was  invariably 
changed  into  glucose.  Cane-sugar  was  not  transformed  into  glucose  but  appeared  in 
the  faeces  as  cane-sugar.  This  is  important,  with  reference  both  to  the  want  of  action 
of  the  intestinal  juice  upon  cane-sugar  and  the  fact  that  cane-sugar,  as  such,  is  not  ab- 
sorbed in  quantity  by  the  intestinal  mucous  membrane. 

Coagulated  albumen  and  cooked  meat  were  always  more  or  less  digested  by  the  intes- 
tinal juice.  This  fact  coincides  with  the  observations  of  Bidder  and  Schmidt. 


268 


DIGESTION. 


The  observations  which,  were  made  on  fats,  melted  butter,  and  cod-liver  oil,  showed 
that  the  pure  intestinal  juice  had  little  or  no  action  upon  them.  These  substances  always 
appeared  in  the  fasces  unchanged.  When,  however,  fatter  matters  were  taken  into  the 
stomach,  they  were  discharged  from  the  upper  opening  in  the  intestine,  in  the  form  of  a 
very  fine  emulsion,  and  could  not  be  recognized  as  fat. 

It  is  evident,  from  these  facts,  that  the  intestinal  juice  is  important  in  digestion,  more 
as  a  fluid  which  aids  the  general  process  as  it  takes  place  in  the  small  intestine  than  as 
one  which  has  a  peculiar  action  upon  any  distinct  class  or  classes  of  alimentary  princi- 
ples. It  undoubtedly  assists  in  completing  the  digestion  of  albuminoid  substances  and  in 
transforming  starch  into  sugar.  Although,  in  the  latter  process,  its  action  is  very 
marked,  the  same  property  belongs  to  the  saliva  and  the  pancreatic  juice.  Intimately 
mingled — as  it  always  is  during  digestion — with  the  bile  and  the  pancreatic  juice  as  well 
as  with  various  alimentary  substances,  the  intestinal  juice  should  be  studied  as  it  operates 
upon  the  food,  in  connection  with  the  other  fluids  found  in  the  small  intestine,  the  diges- 
tive action  of  all  being  most  intimately  associated. 

Pancreatic  Juice. 

The  physiological  anatomy  of  the  pancreas  does  not  demand  a  very  extended  consid- 
eration, as  most  of  the  points  of  its  descriptive  anatomy  have  no  direct  relation  to  its 
physiology,  and  its  minute  anatomy  belongs  properly  to  the  subject  of  secretion.  The 
pancreas  is  a  glandular  organ,  situated  transversely  id  the  upper  part  of  the  abdominal 
cavity,  and  closely  applied  to  its  posterior  wall.  Its  form  is  elongated,  with  an  enlarged, 
thick  portion,  called  the  head  (which  is  attached  to  the  duodenum),  a  body,  and  a  pointed 
extremity,  which  is  in  close  relation  to  the  hilum  of  the  spleen.  Its  average  weight  is 
from  four  to  five  ounces  ;  its  length  is  about  seven  inches  ;  its  greatest  breadth,  about  an 
inch  and  a  half;  and  its  thickness,  three-quarters  of  an  inch.  It  lies  behind  the  perito- 
neum, which  covers  only  its  anterior  surface. 


FIG.  73. — G all-bladder,  ductus  choledochus,  and  pancreas.    (Lc  Bon.) 

a,  gall-bladder;  &,  hepatic  duct;  c,  opening  of  the  second  duct  of  the  pancreas;  d,  opening  of  tho  pancreatic  and 
the  bile-duct;  e,  e,  duodenum ;  /,  ductus  choledochus;  p,  pancreas. 

According  to  Bernard,  who  has  made  numerous  investigations  into  the  anatomy  of 
this  gland,  there  are  nearly  always,  in  the  human  subject,  two  ducts  opening  into  the 
duodenum ;  one  which  opens  in  common  with  the  ductus  communis  choledochus,  and 
one  which  opens  about  an  inch  above  the  main  duct,  called  by  Bernard  the  recurrent  or 


PANCREATIC   JUICE. 


269 


accessory  duct.  The  main  duct  is  about  an  eighth  of  an  inch  in  diameter  and  extends 
along  the  body  of  the  gland,  becoming  larger  as  it  approaches  the  opening.  The  sec- 
ond duct  is  smaller  and  becomes  diminished  in  caliber  as  it  nears  the  duodenum.  Many 
anatomists  describe  but  a  single  duct,  regarding  the  other  as  anomalous.  The  dissections 
of  Bernard,  however,  were  very  numerous  and  show  the  almost  constant  occurrence  of 
two  ducts. 

In  general  appearance  and  minute  structure,  the  pancreas  is  like  the  parotid  and  sub- 
maxillary  glands.  By  the  older  anatomists  it  was  known  as  the  "  abdominal  salivary 
gland,"  on  account  of  this  resemblance  in  structure  and  an 
assumed  similarity  in  the  nature  of  their  secretions.  Recent 
developments  in  the  physiology  of  the  pancreatic  juice  have 
caused  this  name  to  be  discarded. 

Bernard  was  the  first  to  obtain  normal  pancreatic  juice 
from  a  living  animal  and  to  give  a  definite  idea  of  its  properties 
and  functions ;  a  point  which  it  is  proper  to  particularly  insist 
upon,  inasmuch  as,  since  his  discovery,  some  have  pretended 
that  the  facts  which  he  established  had  been  demonstrated 
before.  The  following  method  for  collecting  the  pancreatic 
juice  from  a  living  animal,  one  which  we  have  repeatedly  em- 
ployed with  success,  is  essentially  that  recommended  by  Ber- 
nard : 

The  animal  generally  employed  by  Bernard  in  these  ex- 
periments is  the  dog.  Selecting  one  of  tolerably  large  size, 
he  is  secured  to  the  operating-table  and  placed  upon  his  left 
side.  An  incision  from  three  to  four  inches  in  length  is  then 
made  in  the  right  hypochondrium,  just  below  and  parallel 
with  the  border  of  the  last  rib.  The  parts  are  first  divided 
down  to  the  fascia  transversalis  and  the  peritoneum.  An 
opening  is  then  made  into  the  abdominal  cavity  about  half 
the  length  of  the  incision  through  the  skin  and  muscles, 
which  brings  to  view  the  duodenum  and  a  portion  of  the  pan- 
creas. The  duodenum,  with  the  pancreas  attached  to  it,  is 
then  carefully  drawn  out  of  the  abdomen.  The  next  step  is 
to  introduce  a  small  canula  into  the  principal  pancreatic  duct. 
In  the  dog,  there  are  always  two  pancreatic  ducts ;  a  small 
duct,  which  opens  into  the  intestine  at  or  near  the  opening  of 
the  bile-duct,  and  a  principal  duct,  which  is  situated  about  an 
inch  below.  To  collect  the  juice,  the  tube  should  be  intro- 
duced into  the  principal  duct.  This  is  found  by  turning  the 
duodenum  and  pancreas  so  as  to  expose  the  posterior  surface 
of  the  gland,  when  the  duct,  which  is  very  short  and  almost 
concealed  by  the  tissue  of  the  pancreas,  may  be  seen  oblique- 
ly penetrating  the  intestinal  wall.  In  the  dog,  the  pancreas 
is  composed  of  two  portions ;  one,  called  the  horizontal  por- 
tion, which  is  attached  to  the  duodenum,  and  a  vertical  por- 
tion, which  passes  away  from  the  intestine  between  the  folds 
of  the  mesentery.  The  duct  is  generally  situated  near  the 
point  where  the  pancreas  ceases  to  be  attached  to  the  intes- 
tine. The  tissue  of  the  pancreas  is  to  be  carefully  pushed 
away  from  the  duct  with  the  end  of  the  canula  or  the  point 
of  a  knife,  a  small  longitudinal  slit  is  made  in  it  with  the 
scissors,  and  a  silver  canula,  about  one-twelfth  of  an  inch  in  diameter  and  four  inches  in 
length,  is  introduced  and  firmly  secured  in  place  by  a  ligature  which  has  previously  been 


FIG.  74.— Canula  for  a  pancre- 
atic fistula.  (Bernard.) 

A,  stylet,  the  extremity  of  which 
should  pass  a  little  beyond 
the  end  of  the  canula  B,  to 
facilitate  its  introduction  into 
the  pancreatic  duct ;  B,  can- 
ula, provided  with  little 
grooves  c,  c,  to  hold  the 
threads  for  attachment  into 
the  duct  and  into  the  bladder 
used  to  collect  the  pancreatic 
juice. 


270  DIGESTION. 

thrown  around  the  duct.  The  canula  should  be  provided  with  a  well-fitting  stylet,  with 
the  point  rounded  so  that  it  may  be  introduced  into  the  duct  with  ease  ;  and  the  end  of 
the  canula  should  be  somewhat  roughened,  so  that  the  ligature  may  secure  it  well  in 
place.  The  canula  will  enter  the  duct  for  a  short  distance  only,  and  it  should  not  be  in- 
troduced forcibly.  After  this  has  been  accomplished,  the  canula  may  be  steadied  by  at- 
taching it  with  a  single  stitch  to  the  wall  of  the  intestine.  The  stylet  is  now  to  be  with- 
drawn and  the  parts  carefully  returned  to  the  abdomen,  leaving  the  end  of  the  canula 
projecting  at  the  anterior  portion  of  the  wound,  which  should  be  carefully  closed.  Ber- 
nard recommends  to  first  raise  up  the  fascia  and  peritoneum  with  hooks  and  carefully 
attach  their  edges  with  sutures,  and  then  to  close,  in  the  same  way,  the  incision  in  the 
muscles  and  integument.  The  animal  may  now  be  kept  upon  the  table,  and  the  fluid 
which  is  discharged  from  the  tube  collected  in  a  test-tube,  or  a  thin  gum-elastic-bag  may 
be  attached.  This  may  be  provided  with  a  stopcock,  so  that  the  fluid  may  be  drawn  off 
at  will. 

L 


FJG.  75. — Canula  fixed  in  the  pancreatic  duct.    (Bernard.) 

A,  principal  pancreatic  duct  of  the  dog ;  B,  smaller  pancreatic  duct ;  C,  ligature  securing  a  canula  in  the  principal  duct ; 
D,  D,  ligature  attaching  the  canula  to  the  intestine,  for  security;  E,  canula;  F,  bladder,  provided  with  a  stop- 
cock G,  to  collect  the  pancreatic  juice ;  P,  P,  pancreas ;  I,  I,  intestine. 

Like  the  other  digestive  fluids,  the  pancreatic  juice  is  secreted  in  abundance  only 
during  the  process  of  digestion.  It  is  therefore  necessary  to  feed  the  animal  moderately 
about  an  hour  before  the  operation,  so  that  the  pancreas  may  be  in  full  activity.  When 
it  is  exposed  at  that  time,  it  is  filled  with  blood  and  has  a  rosy  tint,  contrasting  strongly 
with  its  pale  appearance  during  the  intervals  of  digestion. 

In  performing  the  above  experiment,  it  is  generally  better  not  to  employ  an  anaes- 
thetic agent,  as  this  very  frequently  produces  vomiting,  arrests  digestion  for  a  time,  and 
consequently  interferes  with  the  secretion  of  the  pancreatic  juice.  This,  however,  is  not. 
always  the  case.  We  have  sometimes  performed  the  operation  with  the  aid  of  ether  and 
have  obtained  a  fair  amount  of  fluid.  It  is  also  necessary  to  avoid  traction  upon  the  duo- 
denum as  much  as  possible,  for  this  is  almost  sure  to  produce  vomiting.  To  obtain  the 
best  results,  the  operation  should  be  performed  rapidly  and  with  very  little  exposure  of 
the  pancreas.  In  some  very  successful  experiments,  Bernard  has  obtained  from  sixty 
to  one  hundred  grains  of  juice  in  an  hour,  from  a  dog  of  medium  size. 

Some  of  the  most  interesting  facts  developed  by  Bernard  concerning  the  pancreatic 
juice  relate  to  phenomena  connected  with  its  secretion.  It  is  important  to  remember 


PANCREATIC  JUICE.  37! 

that  the  secretion  of  the  pancreas  is  entirely  suspended  during  the  intervals  of  digestion. 
This  fact  has  been  definitely  settled  by  Bernard  and  can  easily  be  observed  by  opening 
animals  in  digestion  and  while  fasting.  In  the  first  instance,  the  pancreatic  duct  will  be 
found  full  of  normal  secretion,  and,  in  the  other,  it  will  be  almost,  if  not  entirely,  empty. 
Bernard  has  also  found  that  the  pancreatic  juice  begins  to  flow  into  the  duodenum  during 
the  first  periods  of  stomach-digestion,  before  alimentary  matters  have  begun  to  pass  in 
quantity  into  the  intestine. 


FIG.  76. — Pancreatic  jixtula.    (Bernard.) 

Full-grown  shepherd-do?  (female),  in  which  a  pancreatic  fistula  has  been  established  A,  silver  tube  to  which  a 
bladder  has  been  attached;  B,  bladder;  C,  stopcock  for  the  purpose  of  collecting  the  juice  which  accumulates 
in  the  bladder. 

Another  important  fact  determined  by  Bernard  is  that  the  secretion  of  the  pancreas 
is  readily  modified  by  irritation  and  inflammation  following  the  operation.  When  we 
come  to  treat  of  the  general  properties  of  the  normal  pancreatic  fluid,  it  will  be  seen  that 
its  characteristics  are,  decided  alkalinity,  viscid  consistence,  and  coagulability  by  heat. 
It  is  almost  always  the  case  that,  a  few  hours  after  the  canula  is  fixed  in  the  duct,  the 
juice  loses  some  of  these  characters  and  flows  in  abnormal  quantity.  With  respect  to 
susceptibility  to  irritation,  the  pancreas  is  peculiar ;  and  its  secretion  is  sometimes  ab- 
normal from  the  first  moments  of  the  experiment,  especially  if  the  operative  procedure 
have  been  prolonged  and  difficult.  That  the  properties  above  described  are  characteristic 
of  the  normal  pancreatic  secretion,  there  can  be  no  doubt ;  as,  in  all  instances,  fluid  taken 
from  the  pancreatic  duct  of  an  animal  suddenly  killed  while  in  full  digestion  is  strongly 
alkaline,  viscid,  and  coagnlable  by  heat.  This  excessive  sensitiveness  of  the  pancreas  has 
rendered  fruitless  all  the  attempts  of  Bernard  to  establish  a  permanent  pancreatic  fistula 
from  which  the  normal  juice  could  be  collected ;  and  we  are  not  disposed  to  admit  that 
the  fluid  collected  by  recent  German  observers,  from  permanent  fistulas,  represents  phys- 
iological conditions. 

General  Properties  and  Composition  of  the  Pancreatic  Juice.— In  all  the  inferior  ani- 
mals from  which  the  pancreatic  secretion  has  been  obtained  in  a  normal  condition,  the 
fluid  has  been  found  to  present  pretty  uniform  characters.  It  is  viscid,  slightly  opaline, 


272  DIGESTION. 

and  has  a  distinctly  alkaline  reaction.  Bernard  found  the  specific  gravity  of  the  fluid 
from  the  dog  to  be  1040.  The  quantity  of  organic  matter  which  the  normal  secretion 
contains  is  very  great,  so  that  the  fluid  is  completely  solidified  on  the  application  of  heat. 
This  great  coagulability  is  one  of  the  properties  by  which  the  normal  fluid  may  be  distin- 
guished from  that  which  has  undergone  alteration. 

Composition  of  the  Pancreatic  Juice  of  the  Dog.     (Bernard.) 

Water 900  to     920 

Organic  matter,  precipitable  by  alcohol  and  containing  )  7^-An 

always  a  little  lime  (pancreatine) }*' 

Carbonate  of  soda,         1 

Chloride  of  sodium,         !  10  to         f/40 

Chloride  of  potassium,  | 

Phosphate  of  lime,  1'000      1'000 

Most  of  the  analyses  which  have  been  made  of  the  pancreatic  fluid  are  not  to  be  relied 
upon,  as  the  manner  in  which  the  juice  was  obtained  shows  generally  that  it  was  not 
normal.  There  is  no  doubt,  however,  that  the  fluid  which  was  obtained  from  the  dog 
and  analyzed  by  Bernard  possessed  all  of  its  characteristic  physiological  properties. 

The  chemical  properties  of  the  organic  principle  of  the  pancreatic  juice  are  distinctive. 
Although,  like  albumen,  it  is  coagulated  by  heat,  the  strong  mineral  acids,  and  absolute 
alcohol,  it  differs  from  albumen  in  the  fact  that  its  dried  alcoholic  precipitate  can  be  re- 
dissolved  in  water,  giving  to  the  solution  all  the  physiological  properties  of  the  normal 
pancreatic  secretion.  Bernard  has  also  found  that  pancreatine  is  coagulated  by  an  excess 
of  sulphate  of  magnesia,  which  will  coagulate  caseine  but  has  no  effect  upon  albumen. 
It  is  important  to  recognize  this  distinction  between  pancreatine  and  other  nitrogenized 
principles,  especially  albumen,  from  the  fact  that  the  last-named  substance  has  the  prop- 
erty of  forming  an  emulsion  with  fats,  though  not  so  readily  and  completely  as  the  pan- 
creatic juice;  and  it  is  essential  to  decide  whether  the  organic  principle  be  a  peculiar 
and  distinct  substance,  or  albumen  transuded  pathologically,  perhaps,  from  the  blood. 
There  can  be  no  doubt,  in  view  of  the  marked  chemical  and  physiological  peculiarities  of 
pancreatine,  that  this  is  a  distinct  proximate  principle,  which  is  characteristic  of  the 
pancreatic  secretion  and  found  in  no  other  fluid. 

Kesearches  have  shown  that  pancreatine  is  the  essential  physiological  constituent  of 
the  pancreatic  juice  and  the  only  one  which  gives  this  fluid  its  peculiar  digestive  proper- 
ties. The  contents  of  the  duodenum,  as  the  partly  digested  matters  pass  from  the  stomach, 
are  generally  acid ;  but  this  does  not  at  all  interfere  with  the  action  of  the  pancreatic 
juice.  Although  the  secretion  itself  is  alkaline,  it  retains  its  physiological  properties 
when  it  has  been  rendered  acid  by  admixture  with  gastric  juice. 

The  inorganic  constituents  of  the  pancreatic  juice  do  not  possess  any  great  physiologi- 
cal interest,  inasmuch  as  they  do  not  seem  to  be  essential  to  its  peculiar  digestive  proper- 
ties. It  has  been  shown,  indeed,  by  Bernard,  that  the  organic  principle  alone,  extracted 
from  the  pancreatic  juice  and  dissolved  in  water,  is  capable  of  imparting  to  the  fluid  all 
the  physiological  characters  of  the  normal  secretion. 

The  entire  quantity  of  pancreatic  juice  secreted  in  the  twenty-four  hours  has  been 
variously  estimated  by  different  authors.  After  what  has  been  said  concerning  the  varia- 
tions to  which  the  secretion  is  subject,  it  is  not  surprising  that  these  estimates  should 
present  great  differences.  Bernard  was  able  to  collect  from  a  dog  of  medium  size  from 
eighty  to  one  hundred  grains  in  an  hour ;  but  it  must  be  remembered  that  only  one  of  the 
ducts  was  operated  upon,  and  that  the  gland  is  always  very  susceptible  to  irritation. 
There  is  no  accurate  basis  for  an  estimate  of  the  quantity  of  pancreatic  fluid  secreted  in 
the  twenty-four  hours  in  the  human  subject,  or  of  the  quantity  necessary  for  the  digestion 
of  a  definite  amount  of  food. 


ACTION   OF  THE   PANCREATIC  JUICE  IN  DIGESTION. 


273 


Unlike  the  gastric  juice,  the  secretion  of  the  pancreas,  under  ordinary  conditions  of 
heat  and  moisture,  rapidly  undergoes  decomposition.  In  warm  and  stormy  weather  the 
alteration  is  marked  in  a  few  hours ;  but,  at  a  temperature  of  from  50°  to  70°  Fahr.,  it 
decomposes  gradually  in  from  two  to  three  days.  The  changes  which  the  fluid  thus 
undergoes  are  interesting,  from  the  fact  that  some  physiologists,  having  experimented 
with  an  altered  or  an  abnormal  secretion,  have  failed  to  recognize  certain  of  the  charac- 
teristic properties  of  the  normal  fluid.  As  it  thus  undergoes  decomposition,  the  fluid 
acquires  a  very  offensive,  putrefactive  odor,  and  its  coagulability  diminishes,  until  finally 
it  is  not  affected  by  heat.  The  alkalinity,  however,  increases  in  intensity ;  and,  when 
neutralized  with  an  acid,  there  is  a  considerable  evolution  of  carbonic  acid,  which  does 
not  occur  in  fresh  pancreatic  juice. 

Action  of  the  Pancreatic  Juice  in  Digestion. 

It  is  only  since  the  observations  of  Bernard,  in  1848,  that  the  pancreatic  juice  has  been 
regarded  as  a  fluid  of  any  great  importance  in  digestion.  It  has  now  been  demonstrated, 
both  by  cases  of  disorganization  of  the  pancreas  in  man  and  by  experiments  on  animals 
in  which  the  tissue  of  the  organ  has  been  destroyed,  that  the  pancreatic  juice  is  essential 
to  digestion  and  to  life,  animals  dying  of  inanition  when  its  function  has  been  abolished. 

The  most  striking  feature  in  the  discovery  made  by  Bernard  was  the  action  of  the 
pancreatic  juice  in  the  digestion  of  fats;  it  being  shown  that  these  principles  are  acted 
upon  almost  exclusively  by  the  pancreas,  and  that  they  pass  through  the  alimentary  canal 
undigested  when  this  organ  has  been  destroyed.  For  this  reason,  probably,  the  action 
of  the  pancreas  in  the  digestion  of  fatty  substances  has  received  an  undue  prominence ; 
and  its  action  upon  other  articles  of  food,  though  not  at  the  present  day  overlooked,  does 
not  always  receive  proper  consideration.  We  shall  find  that  the  pancreatic  juice  has  an 
important  action  in  the  digestion  of  nearly  all  the  alimentary  principles  as  they  pass  out 
from  the  stomach. 

Action  upon  Fats. — Even  before  the  publication  of  Bernard's  researches,  it  was  pretty 
generally  admitted  that  the  digestion  of  fat  consisted  in  its  minute  subdivision  and  sus- 
pension in  the  form  of  an  emulsion.  This  view  was  adopted  from  the  fact  that,  during 
the  absorption  of  fats  from  the  intestinal  canal,  the  lacteals  and  thoracic  duct  always 
contain  innumerable  small,  fatty  globules ;  but  the  ideas  of  physiologists  as  to  the  par- 
ticular fluid  by  which  the  emulsification  of  fats  is  accomplished  were  not  very  well 
settled.  The  most  generally-received  opinion,  however,  was  that  this  was  effected  by 
the  bile ;  but  experiments  on  this  subject  were  very  contradictory. 

One  of  the  most  remarkable  facts  observed  by  Bernard  was  that,  in  the  rabbit,  after 
the  ingestion  of  fatty  matters,  vessels  filled  with  white  chyle  do  not  make  their  appearance 
at  the  commencement  of  the  small  intestine,  as  in  other  animals,  but  are  first  seen  from 
twelve  to  twenty  inches  below  the  pylorus.  The  anatomical  peculiarity  in  these  animals 
is  that  the  pancreatic  duct,  instead  of  opening  into  the  intestine  with  the  bile-duct  at  the 
upper  part  of  the  small  intestine,  has  its  opening  from  twelve  or  twenty  inches  below, 
just  at  the  point  where  the  chyliferous  vessels  are  observed.  This  fact,  which  we  have 
frequently  confirmed,  points  directly  to  the  pancreatic  juice  as  the  agent  principally,  if 
not  exclusively,  concerned  in  emulsifying  the  fats ;  while  it  shows  that  the  bile  possesses 
Jittle  or  no  immediate  efficiency  in  this  regard.  Following  out  this  line  of  inquiry,  and 
operating  with  fresh,  coagulable  pancreatic  juice  and  the  liquid  fats  or  those  capable  of 
being  liquefied  by  gentle  heat,  it  was  found  that  slight  agitation  of  this  fluid  with  the  fats 
produced  a  very  fine  and  permanent  emulsion,  similar  in  every  respect  to  the  milky  fluid 
found  in  the  lacteals  during  digestion.  In  fact,  comparative  analyses  of  the  lymph  and 
chyle  have  shown  that  the  latter  liquid  is  nothing  more  than  lymph  with  the  addition  of 
fatty  emulsion.  As  soon  as  the  absorption  of  fat  is  completed,  the  lacteal  vessels  lose 
their  opaque,  white  contents  and  carry  nothing  but  colorless  lymph.  This  is  one  of  the 
18 


274  DIGESTION. 

great  experimental  facts  upon  which  is  based  the  view  that  the  pancreatic  juice  has  the 
property  of  digesting  the  fats.  Concerning  the  accuracy  of  this  observation  there  can  be 
no  doubt.  The  fact  has  been  so  frequently  confirmed,  that  it  must  now  be  considered  as 
established  beyond  question,  and  we  can  add  our  testimony  to  its  accuracy  from  personal 
observation.  It  is  true  that  some  of  the  German  physiologists  have  been  unable  to  con- 
firm these  experiments ;  but,  by  carefully  following  out  the  process  indicated  by  Ber- 
nard, which  is  detailed  with  great  care,  we  have  invariably  found  his  observations  to  be 
correct.  It  is  well  known  that  many  of  the  German  experimenters  operated  with  pan- 
creatic juice  which  was  not  coagulable  and  which  Bernard  regards  as  abnormal  and  in- 
capable of  digesting  fat. 

The  pancreatic  juice  is  the  only  one  of  the  digestive  fluids  which  is  capable  of  forming 
a  complete  and  permanent  emulsion  with  fats.  The  fact  that  the  other  digestive  fluids 
will  not  accomplish  this  is  easily  demonstrated  as  regards  the  saliva,  gastric  juice,  and  bile. 
The  intestinal  juice  is  then  the  only  one  which  might  be  supposed  to  have  this  property. 
The  observations  of  Busch  on  this  point,  in  his  case  of  intestinal  fistula,  are  conclusive. 
He  found  that  fatty  matters  taken  into  the  stomach  were  discharged  from  the  upper 
opening  in  the  intestine  in  the  form  of  a  fine  emulsion  and  were  never  recognizable  as 
oil ;  but  that  fat  introduced  into  the  lower  intestinal  opening  was  not  acted  upon  and 
was  discharged  unchanged  in  the  fsBces. 

Another  peculiarity  noted  by  Bernard  in  the  emulsion  resulting  from  the  action  of 
pancreatic  juice  upon  fats  is  that  it  persists  when  diluted  with  water  and  will  pass 
through  a  moistened  filter  like  milk.  This  does  not  take  place  in  the  imperfect  emulsion 
formed  by  a  mixture  of  oil  with  any  other  of  the  digestive  fluids. 

Although  the  normal  pancreatic  juice  is  constantly  alkaline,  this  is  not  an  indispensa- 
ble condition  as  regards  its  peculiar  action  upon  fats ;  for  the  emulsion  is  none  the  less 
complete  when  the  fluid  has  been  previously  neutralized  with  gastric  juice. 

Bernard  has  shown  that  the  pancreatic  juice  and  the  tissue  of  the  pancreas  have  the 
property  of  saponifying  fats,  or  decomposing  them  into  a  fatty  acid  and  glycerine,  and  that 
this  property  is  not  possessed  by  any  other  tissue  or  liquid  of  the  economy.  The  question 
naturally  arises,  then,  whether  this  be  an  accidental  property  of  the  tissue  and  the  secre- 
tion of  the  pancreas  or  whether  partial  saponification  of  fat  take  place  in  digestion.  Con- 
cerning this  point  there  is  no  difference  of  opinion  among  physiological  chemists.  The 
fat  which  is  contained  in  the  lacteal  vessels  is  always  neutral ;  and  the  absence  of  any 
fatty  acid  has  been  recognized  by  Bernard  as  well  as  by  others.  The  inevitable  conclu- 
sion to  be  drawn  from  this  fact  is,  that,  while  fat  may  be  in  part  decomposed  into  an  acid 
and  glycerine  by  the  pancreatic  juice,  out  of  the  body,  in  the  natural  process  of  digestion, 
either  this  does  not  take  place  or  the  acid  is  not  absorbed  by  the  lacteals.  The  greatest 
part,  if  not  the  whole,  of  the  fat  which  is  digested  in  the  small  intestine  is  simply  formed 
into  an  emulsion  by  the  pancreatic  juice  and  undergoes  no  chemical  alteration. 

To  complete  the  experimental  evidence  of  the  action  of  the  pancreatic  juice  in  the 
digestion  of  fats,  Bernard  attempted  to  extirpate  or  destroy  the  pancreas  in  a  living  ani- 
mal. This  he  found  very  difficult.  All  attempts  to  extirpate  the  organ  with  the  knife 
being  unsuccessful,  the  injection  of  foreign  matters  into  the  duct  was  resorted  to.  After 
a  great  number  of  unsuccessful  experiments,  in  two  instances,  the  functions  of  the  gland 
were  suspended  for  a  time  and  its  tissue  was  partly  destroyed  by  the  injection  of  melted 
tallow.  In  both  of  these  observations,  the  effects  upon  digestion  were  very  marked. 
Although  the  appetite  was  voracious,  the  animals  became  gradually  emaciated,  and  the 
fa3ces  contained  a  large  quantity  of  rancid,  undigested  fat.  At  the  same  time,  other  ali- 
mentary principles,  incompletely  digested,  were  recognized  in  the  discharges.  In  two 
dogs  operated  upon  by  Bernard,  in  which  the  experiments  were  successful,  the  nutrition 
and  the  alvine  discharges  became  normal  at  the  thirteenth  and  the  seventeenth  day. 
After  the  animals  had  completely  recovered,  they  were  killed,  and  the  pancreas  in  both 
instances  was  found  partially  destroyed. 


ACTION  OF  THE  PANCREATIC  JUICE  IN  DIGESTION.  275 

Now  that  the  action  of  the  pancreatic  juice  upon  fats  is  so  well  understood  it  is  a 
matter  of  surprise  that  the  cases  of  fatty  diarrhoea  connected  with  disorganization  of  the 
pancreas,  which  were  reported  by  Dr.  Richard  Bright,  in  1832,  did  not  direct  the  atten- 
tion of  physiologists  to  the  function  of  this  organ.  These  cases,  with  others  of  a  similar 
character  which  have  been  reported  from  time  to  time,  are  now  brought  forward  as 
strong  evidence  of  the  action  of  the  pancreas  in  the  digestion  of  fats.  Many  of  them  pre- 
sented a  train  of  symptoms  analogous  to  those  observed  in  animals  after  partial  destruc- 
tion of  the  gland.  The  presence  of  fat  in  the  alvine  dejections  was  most  marked ;  and 
as  is  now  well  known,  this  could  be  nothing  but  the  undigested  fatty  principles  of  the 
food.  In  the  three  cases  observed  by  Bright,  the  pancreas  was  found  so  disorganized 
that  its  secreting  function  must  have  been  almost,  if  not  entirely,  abolished.  In  the  case 
reported  by  Mr.  Lloyd,  the  condition  was  the  same ;  and,  in  the  case  reported  by  Dr. 
Elliotson,  "  the  pancreatic  duct  and  the  larger  lateral  branches  were  filled  with  white 
calculi."  Another  interesting  case  of  disease  of  the  pancreas  is  described  in  the  catalogue 
of  the  Anatomical  Museum  of  the  Boston  Society  for  Medical  Improvement,  in  1847.  In 
this  case,  it  was  observed  by  the  patient  that  fatty  discharges  from  the  bowels  did  not 
take  place  unless  fatty  articles  of  food  had  been  taken.  After  death,  a  large  tumor  was 
found  in  the  situation  of  the  pancreas,  but  all  trace  of  the  normal  structure  of  the  organ 
had  been  destroyed.  Many  more  cases  of  this  character  are  quoted  by  Bernard  and 
others,  and  they  fully  confirm  the  observations  and  experiments  which  have  been  made 
upon  the  lower  animals.  They  all  seem  to  show  that  the  function  of  the  pancreas  in 
digestion  is  essential  to  life,  but  that  one  of  the  chief  disorders  in  digestion  incident  to  the 
destruction  of  this  gland  relates  to  the  digestion  of  fats. 

Taking  into  consideration  all  the  facts  bearing  upon  this  subject,  the  conclusion  is  in- 
evitable that  the  chief  agent  in  the  digestion  of  fats  is  the  pancreatic  juice ;  and  that  this 
fluid  acts  by  forming  with  the  fat  a  very  fine  emulsion,  thus  reducing  it  to  a  form  in 
which  it  can  be  absorbed.  How  far  the  bile  may  assist  in  this  process  is  a  question  which 
will  come  up  for  consideration  hereafter ;  but  the  facts  with  regard  to  the  pancreatic 
juice  are  conclusive. 

Action  upon  Starchy  and  Saccharine  Principles. — All  physiologists  are  agreed  with 
regard  to  the  action  of  the  pancreatic  juice  in  transforming  starch  into  sugar.  This  was 
first  observed,  in  1844,  by  Valentin,  who  experimented  with  an  artificial  fluid  made  by 
infusing  pieces  of  the  pancreas  in  water.  Bouchardat  and  Sandras  first  noted  this  prop- 
erty in  the  normal  pancreatic  secretion. 

The  property  of  converting  starch  into  sugar  is  possessed  by  several  of  the  digestive 
fluids.  We  have  seen  that  the  starchy  elements  of  food  are  acted  upon  by  the  saliva, 
that  this  action  is  not  necessarily  arrested  as  these  principles,  mixed  with  the  saliva, 
pass  into  the  stomach,  and  that  the  intestinal  juice  of  itself  is  capable  of  effecting  the 
transformation  of  starch  into  sugar  to  a  considerable  extent.  It  therefore  becomes  an 
important  question  to  determine  precisely  how  far  the  pancreas  is  actually  concerned  in 
the  digestion  of  this  class  of  principles. 

Bernard  places  the  pancreatic  juice  at  the  head  of  the  list  of  the  digestive  fluids  which 
act  upon  starch.  This  view  is  undoubtedly  correct ;  although  he  goes  a  little  too  far 
in  claiming  that  starch  is  almost  exclusively  digested  by  the  pancreas.  Bernard's  ex- 
periments, however,  were  made  chiefly  on  dogs,  and  these  animals  do  not  naturally  take 
starch  as  food.  In  man,  some  of  the  starchy  principles  of  the  food  are  acted  upon  by 
the  saliva,  but,  undoubtedly,  most  of  the  starch  taken  as  food  is  digested  in  the  small  in- 
testine. Although  the  intestinal  juice  is  capable  of  effecting  the  transformation  of  starch 
into  sugar,  the  experimental  evidence  is  conclusive  that  in  this  it  is  subordinate  to  the 
pancreatic  juice,  which  latter  effects  this  transformation,  at  the  temperature  of  the  body, 
with  extraordinary  activity.  There  is  no  positive  evidence  that  the  bile  has  any  thing  to 
do  with  this  action. 


276  DIGESTION. 

To  sum  up  the  whole  process  of  the  digestion  of  starch,  it  may  be  stated,  in  general 
terms,  that  this  principle,  when  hydrated,  which  is  the  usual  condition  in  which  it  is 
taken  into  the  stomach  of  the  human  subject,  is  slightly  acted  upon  by  the  saliva,  both 
in  the  mouth  and  after  it  has  passed  into  the  stomach ;  when  it  is  taken  raw,  it  is  hy- 
drated in  the  stomach  and  usually  undergoes  no  transformation  into  sugar  until  it  has 
passed  into  the  small  intestine ;  and,  when  it  passes  out  at  the  pylorus,  mainly  by  the  ac- 
tion of  the  pancreatic  juice  but  with  the  assistance  of  the  intestinal  juice,  it  is  transformed 
into  glucose  and  in  this  form  is  absorbed. 

We  have  already  followed  out  the  digestion  of  sugar  as  far  as  the  small  intestine. 
Glucose  undergoes  no  change  in  the  stomach  and  is  taken  directly  into  the  circulation. 
It  is  probable,  also,  that  a  small  quantity  of  cane-sugar  may  in  like  manner  be  taken  up 
by  the  blood-vessels  of  the  intestinal  mucous  membrane.  It  has  been  shown  that  a  small 
quantity  of  cane-sugar  is  transformed  into  glucose  in  the  stomach,  but,  as  we  noted  in 
treating  of  stomach-digestion,  the  quantity  is  inconsiderable,  and  the  transformation  de- 
pends simply  upon  the  presence  of  a  free  acid  in  the  gastric  juice. 

As  most  of  the  saccharine  principles  of  food  exist  in  the  form  of  cane-sugar,  it  is  the 
action  of  the  digestive  fluids  upon  this  variety  of  sugar  which  possesses  the  greatest  phys- 
iological interest.  As  cane-sugar  passes  from  the  stomach  into  the  duodenum  it  is  al- 
most instantly  transformed  into  glucose.  This  fact  has  lately  received  additional  con- 
firmation in  the  case  of  intestinal  fistula  observed  by  Bnsch.  In  this  case,  when  cane- 
sugar  was  introduced  in  quantity  into  the  stomach,  fasting,  the  fluid  which  escaped  from 
the  upper  end  of  the  intestine  contained  a  small  quantity  of  glucose  but  never  any  cane- 
sugar. 

It  now  becomes  a  question  whether  the  transformation  of  cane-sugar  into  glucose  be 
effected  by  the  bile,  the  intestinal  juice,  or  the  pancreatic  juice.  The  pancreatic  juice 
and  the  intestinal  juice  are  the  two  fluids  which  might  be  supposed  to  have  this  effect ; 
for  it  has  been  repeatedly  demonstrated  that  the  bile  has  of  itself  no  direct  action  upon 
any  of  the  alimentary  principles.  This  point  is  settled  by  the  experiments  of  Busch  upon 
the  lower  end  of  the  intestine,  in  his  case  of  fistula.  Matters  introduced  into  this  lower 
opening  came  in  contact  with  the  intestinal  juice  only.  He  found  that  cane-sugar,  ex- 
posed thus  to  the  action  of  the  intestinal  juice,  was  not  converted  into  glucose,  but  a 
large  portion  of  it  was  found  in  the  faeces.  His  observations  also  indicate  that  cane- 
sugar  is  not  readily  absorbed  by  the  intestinal  mucous  membrane  until  it  has  been  trans- 
formed into  glucose. 

Out  of  the  body,  the  pancreatic  juice  is  capable,  if  kept  but  for  a  short  time  in  con- 
tact with  any  of  the  saccharine  principles,  of  transforming  them  into  lactic  acid.  The 
contents  of  the  small  intestine  are  sometimes  alkaline  or  neutral  and  are  sometimes  acid. 
When  a  very  large  quantity  of  sugar  has  been  taken,  a  part  of  it  may  be  converted  in  the 
intestine  into  lactic  acid,  and  this  may  happen  with  the  sugar  which  results  from  the 
digestion  of  starch ;  but,  under  ordinary  conditions,  starch  and  cane-sugar  are  readily 
changed  into  glucose  and  are  absorbed  without  undergoing  farther  transformation.  All 
the  varieties  of  sugar,  after  they  have  been  absorbed  by  the  portal  vein  and  carried  to 
the  liver,  are  here  transformed  into  glucose,  the  only  form,  apparently,  under  which  they 
can  be  used  in  nutrition. 

Action  of  the  Pancreatic  Juice  upon  Nitrogenized  Principles. — We  have  frequently  had 
occasion  to  insist  upon  the  great  relative  importance  of  intestinal  digestion,  and  it  has 
been  apparent  that,  in  the  stomach,  the  process  of  disintegration  of  food  is  not  final, 
even  as  regards  many  of  the  nitrogenized  principles,  but  is  rather  preparatory  to  the 
complete  liquefaction  of  these  principles,  which  takes  place  in  the  small  intestine.  The 
experiments,  already  referred  to,  of  Bernard,  in  which  the  pancreas  has  been  partially 
destroyed  in  dogs,  show  rapid  emaciation,  with  great  voracity,  and  the  passage,  not  only 
of  unchanged  fats  and  starch,  but  of  undigested  nitrogenized  matter  in  the  dejections. 


ACTION   OF  THE   BILE  IN  DIGESTION. 


277 


In  some  instances,  pieces  of  tripe  which  had  been  fed  to  the  animal  were  recognizable  in 
the  fasces  "  by  their  aspect,  because  of  their  slight  alteration."  The  voracious  appetite, 
progressive  emaciation,  and  the  passage  of  all  classes  of  alimentary  substances  in  the 
faeces,  after  this  operation,  demonstrate  conclusively  the  great  importance  of  the  pancre- 
atic juice  in  digestion.  But,  when  we  inquire  into  the  precise  mode  of  action  of  this 
fluid  upon  the  albuminoids,  the  question  becomes  one  of  great  difficulty.  If  the  bile  be 
shut  off  from  the  intestine  and  discharged  externally  by  a  fistulous  opening,  the  same 
voracity  and  emaciation  are  observed ;  and  yet  there  is  no  single  alimentary  substance 
upon  which  the  bile,  of  itself,  can  be  shown  to  exert  a  decided  digestive  action.  Farther- 
more,  the  pancreatic  juice  is  evidently  calculated  to  act  upon  alimentary  principles  after 
they  have  been  subjected  to  the  action  of  the  stomach,  a  preparation  which  is  absolutely 
essential  to  proper  intestinal  digestion;  and,  once  passed  into  the  intestine,  the  food 
comes  in  contact  with  a  mixture  of  pancreatic  juice,  intestinal  juice,  and  bile.  We  have 
to  study,  therefore,  the  special  action  of  the  pancreatic  secretion  upon  the  albuminoids, 
as  far  as  it  can  be  isolated,  and  its  action  in  conjunction  with  the  other  intestinal  fluids 
and  in  the  presence  of  other  alimentary  principles  in  process  of  digestion.  The  first 
definite  observations  upon  these  points  were  made  by  Bernard.  He  found  that  the  albu- 
minoid substances  generally,  exposed  to  the  action  of  the  pancreatic  juice  out  of  the 
body,  became  rapidly  softened  and  dissolved  in  some  of  their  parts,  but  soon  passed  into  a 
condition  of  putrefaction.  An  analogous  change,  it  will  be  remembered,  also  takes  place 
in  starchy  and  fatty  matters  when  exposed  to  the  action  of  the  pancreatic  juice  out  of 
the  body,  and  they  pass  through  the  various  stages  of  transformation  respectively  into 
lactic  acid  and  the  fatty  acids.  This  putrefactive  action  does  not  take  place  in  albuminoids 
which  have  been  precipitated  after  having  been  cooked,  or  in  raw  gluten  or  caseine.  The 
presence  of  fat  also  interferes  with  putrefaction  ;  so  that  Bernard  concludes  that  the  fats 
have  an  important  influence  in  the  intestinal  digestion  of  nitrogenized  principles. 

Taking  into  consideration  what  has  been  positively  ascertained  concerning  the  action 
of  the  pancreatic  juice  upon  the  albuminoids,  there  can  be  no  doubt  with  regard  to  the 
importance  of  its  function  in  the  digestion  of  these  principles  after  they  have  been  ex- 
posed to  the  action  of  the  gastric  juice.  Experiments  upon  the  digestion  of  these  sub- 
stances after  they  have  passed  out  of  the  stomach  show  that  they  undergo  important  and 
essential  changes  as  they  pass  down  the  intestinal  canal.  While  the  bile  and  the  intesti- 
nal juice  are  by  no  means  inert,  they  seem  to  be  only  auxiliary  in  their  action  to  the  pan- 
creatic juice.  When  meat  is  taken  into  the  stomach  or  is  exposed  even  for  a  long  period 
to  the  action  of  the  gastric  juice,  there  is  always  more  or  less  insoluble  residue,  which  can 
be  shown  by  microscopical  examination  to  consist  of  the  muscular  substance. 

The  preparation  which  the  albuminoids  undergo  in  the  stomach  is  undoubtedly  neces- 
sary to  the  easy  digestion,  in  the  small  intestine,  of  that  portion  which  is  not  dissolved  by 
the  gastric  juice.  ,  This  fact  has  been  conclusively  demonstrated  by  experiments  on  in- 
testinal digestion  in  the  inferior  animals  and  by  the  observations  of  Busch  in  the  case  of 
intestinal  fistula  in  the  human  subject. 

Action  of  the  Bile  in  Digestion. 

A  great  deal  of  diversity  of  opinion  has  existed  among  physiologists  concerning  the 
functions  of  the  bile.  It  is  now  pretty  generally  acknowledged  that  this  fluid  has,  of 
itself,  no  marked  influence  upon  any  of  the  different  classes  of  alimentary  principles, 
such  as  we  have  observed  in  the  other  secretions  discharged  into  the  alimentary  canal. 
This  being  the  case,  it  is  important  to  decide  whether  the  bile  be  essential  in  assisting  or 
modifying  the  action  of  other  secretions  or  whether  it  be  entirely  inert  in  the  digestive 
process.  From  the  fact  that  it  is  poured  into  the  upper  part  of  the  small  intestine,  it 
would  seem  that  it  must  have  some  office,  either  in  modifying  the  digestion  and  absorp- 
tion of  food  or  in  the  passage  of  alimentary  substances  or  their  residue  down  the  intes- 
tinal tract.  It  is  difficult  to  suppose  that  a  fluid  which  is  brought  in  contact  with  the  ali- 


278  DIGESTION. 

mentary  mass  in  that  portion  of  the  intestine  where  the  most  important  digestive  pro- 
cesses commence  should  be  simply  excrementitious ;  yet  this  is  the  view  entertained  by 
some  experimentalists.  In  this  position  of  the  subject,  naturally  the  first  question  to 
decide  relates  to  the  excrementitious  or  recrementitious  character  of  the  bile  ;  or  whether, 
in  other  words,  the  bile  be  separated  from  the  blood  simply  to  be  discharged  from  the 
body  or  have  some  important  function  to  perform  as  a  secretion.  An  apparently  simple 
method  of  settling  this  question  has  been  employed  by  many  experimenters,  but  with  re- 
sults which  are  not  satisfactory,  unless  they  can  be  in  some  way  harmonized.  Schwann, 
Nasse,  Bidder  and  Schmidt,  and  Bernard,  whose  observations  will  be  more  fully  consid-' 
ered  hereafter,  have  performed  experiments  upon  animals  in  which  the  bile  was  entirely 
shut  off  from  the  intestine  and  discharged  from  the  body  by  a  fistula.  If  the  bile  be  sim- 
ply excrementitious,  it  should  follow  that  animals  operated  upon  in  this  way  would  not 
suffer  from  the  discharge  of  the  bile  by  a  fistula  and  its  diversion  from  the  intestine  ;  but, 
in  all  of  them,  death  occurred  with  symptoms  pointing  to  defective  nutrition  consequent 
upon  grave  disorder  of  digestion.  The  same  result  followed  our  own  experiments  on  this 
subject.  On  the  other  hand,  Blondlot  attempts  to  show  that  the  bile  is  simply  an  excre- 
tion, and  that  animals  thrive  and  will  live  for  an  indefinite  period,  when  the  bile  is 
diverted  from  its  natural  course  and  is  discharged  from  the  body. 

In  the  experiments  of  those  who  simply  closed  the  ductus  communis  choledochus,  the 
effects  of  shutting  off  the  bile  from  the  intestine  were  modified  by  the  consequent  undue 
accumulation  of  this  fluid  in  the  biliary  passages.  The  only  way  to  obviate  this  difficulty 
was  to  discharge  the  bile  by  a  fistula,  as  was  first  done  by  Schwann.  The  first  experi- 
ments reported  by  Schwann  were  made  upon  sixteen  dogs  and  one  rabbit.  Of  these, 
only  six  can  be  regarded  as  successful ;  and,  in  the  others,  the  animals  either  died  of 
peritonitis  resulting  from  the  operation,  or  recovered,  the  fistulous  opening  into  the  gall- 
bladder becoming  closed  and  the  communication  between  the  liver  and  the  intestine  re- 
establishing itself.  These  six  animals  died,  apparently  of  inanition,  respectively,  after 
seven,  thirteen,  seventeen,  twenty-five,  sixty-four,  and  eighty  days.  In  all,  except  the 
two  animals  that  lived  for  sixty -four  and  eighty  days  respectively,  there  was  gradual 
diminution  in  weight  from  the  date  of  the  operation,  notwithstanding  that  a  large  quan- 
tity of  food  was  taken.  In  the  two  exceptions,  there  was  first  diminution  in  weight,  then 
the  flesh  was  partially  regained,  but  it  subsequently  diminished  until  death  occurred.  In 
these  six  animals,  there  was  every  reason  to  believe  that  death  occurred  from  the  aboli- 
tion of  the  digestive  function  of  the  bile,  and  the  disturbances  in  nutrition  were  very  much 
like  those  produced  by  Bernard  by  destruction  of  the  pancreas.  These  experiments 
were  confirmed  in  their  essential  particulars  by  Bidder  and  Schmidt,  Nasse,  and  Bernard. 
These  facts  seem  to  show  that  the  bile  is  not  simply  an  excrementitious  fluid,  and  that 
its  function,  after  it  is  discharged  into  the  intestine,  is  not  only  important  but  absolutely 
essential  to  life.  The  only  experiment  which  is  opposed  to  this  view  is  one  reported  by 
Blondlot. 

The  experiment  by  Blondlot  was  made  upon  a  dog.  The  fistula  was  established  in 
the  fundus  of  the  gall-bladder,  the  ductus  communis  having  been  tied  and  a  portion  ex- 
sected.  Fifteen  days  after  the  operation,  the  animal  had  become  extremely  thin,  but  ate 
well,  and,  according  to  the  report  of  the  experimenter,  was  in  perfect  health.  During  all 
this  time,  however,  he  habitually  licked  the  bile,  but  he  was  finally  prevented  from  doing 
this  by  a  muzzle.  From  the  moment  when  the  dog  ceased  to  swallow  the  bile,  the  nutri- 
tion began  to  improve,  and  in  three  months  he  had  recovered  the  natural  amount  of 
flesh.  A  farther  account  of  this  experiment  is  given  by  Blondlot  in  another  memoir. 
The  animal,  while  in  perfect  health  aside  from  the  existence  of  the  fistula,  was  claimed 
by  the  owner,  from  whom  it  had  been  stolen  before  it  passed  into  the  hands  of  the  ex- 
perimenter. With  the  fistula  still  open,  the  dog  was  used  by  its  owner  for  hunting  and 
lived  for  five  years.  At  the  end  of  this  time  it  was  returned  to  M.  Blondlot,  but  died 
while  in  his  possession,  two  months  after. 


ACTION   OF  THE  BILE  IN  DIGESTION.  379 

The  important  question  then  to  determine  was  that  the  bile  had  been  completely  shut 
off  from  the  intestinal  canal.  An  examination  of  the  parts  was  consequently  made  in 
the  presence  of  a  number  of  physicians  and  students.  On  the  most  minute  dissection,  it 
was  impossible  to  find  any  communication  between  the  bile-duct  and  the  duodenum; 
and  the  conclusion  arrived  at  was  that  the  animal  had  lived  for  five  years  without  a  drop 
of  bile  passing  into  the  intestine,  and,  consequently,  that  this  fluid  was  useless  in  digestion. 

The  facts  obtained  by  all  other  observers  are  in  direct  opposition  to  the  above  experi- 
ment. After  a  number  of  trials,  we  succeeded  in  establishing  a  biliary  fistula  in  a  dog, 
the  operation  being  followed  by  no  inflammation  of  the  peritoneum,  and,  notwithstanding 
that  the  animal  was  voracious  and  consumed  daily  large  quantities  of  food,  it  died  in 
thirty-eight  days,  of  inanition.  If  our  own  observation  and  those  of  other  experimenters 
be  correct,  it  is  impossible  that  an  animal  should  live  in  perfect  health  for  years  with  all 
the  bile  discharged  by  a  fistula. 

There  is  reason  to  believe  that  the  experiment  of  Blondlot  was  inaccurate,  and  that  a 
communication  existed  between  the  bile-duct  and  the  duodenum,  which  was  not  discov- 
ered at  the  dissection  after  death.  The  following  observation  strengthens  us  in  this 
opinion : 

We  made  an  attempt  on  one  occasion  to  ascertain  the  total  amount  of  bile  secreted  in 
twenty-four  hours;  and,  with  this  view,  the  ductus  communis  choledochus  was  exposed 
in  a  dog,  the  bile  contained  in  the  gall-bladder  was  pressed  out,  a  canula,  with  an  elastic 
bag  attached,  was  fixed  in  the  duct,  and  the  external  wound  was  closed,  leaving  the  end 
of  the  canula,  with  the  bag  attached,  protruding  from  the  abdomen.  The  bag  ruptured 
twenty-three  hours  after,  and  the  experiment  was  consequently  unsuccessful  in  the  end 
for  which  it  was  undertaken.  The  tube  dropped  out  at  the  end  of  forty-eight  hours,  and 
the  external  wound  quickly  healed.  Thirty  days  after  the  operation  the  animal  was 
killed.  He  had  then  entirely  recovered,  and  no  bile  had  been  discharged  externally  for 
a  long  time.  The  alvine  dejections  were  perfectly  normal,  and  there  could  be  no  doubt 
that  the  bile  was  regularly  discharged  into  the  duodenum.  On  dissection  after  death, 
the  liver  was  found  normal,  and  the  papilla  which  marks  the  opening  of  the  bile-duct 
into  the  duodenum  was  natural  in  appearance.  It  was  with  the  greatest  difficulty,  how- 
ever, that  the  communication  between  the  bile-duct  and  the  duodenum  could  be  found ; 
yet,  after  patient  searching  for  more  than  an  hour,  a  small,  tortuous  tract  was  discovered. 
Had  it  not  been  certain  that  bile  had  been  constantly  discharged  into  the  intestine,  it 
might  have  been  assumed,  even  after  careful  examination,  that  no  such  communication 
existed.  This  examination  convinced  us  that  it  was  possible  that  the  communication 
between  the  duct  and  the  intestine  had  been  reestablished  in  Blondlot's  case,  and  that  it 
had  escaped  observation  in  the  dissection  after  death. 

The  isolated  experiment  of  Blondlot  does  not  therefore  invalidate  the  results  obtained 
by  Schwann  and  confirmed  by  so  many  eminent  physiologists.  The  bile  is  not  simply  an 
excretion  but  has  an  important  and  essential  office  to  perform  in  the  process  of  intestinal 
digestion.  We  have,  however,  conclusively  shown  that,  in  addition  to  its  recrementitious 
function,  it  separates  from  the  blood  an  important  excrementitious  principle,  cholesterine, 
which,  under  a  modified  form,  is  discharged  in  the  faeces.  This  function  of  the  liver  will 
be  fully  considered  under  the  head  of  excretion.  It  is  sufficient  for  our  present  purposes 
to  show  that  the  bile,  unlike  any  other  fluid  in  the  organism,  has  two  distinct  functions, 
dependent  upon  two  distinct  classes  of  constituents.  The  peculiar  principles  known  as 
the  biliary  salts,  which  are  produced  in  the  liver,  give  to  it  its  digestive  properties ;  and 
the  cholesterine,  which  is  simply  separated  from  the  blood  by  the  liver,  gives  it  its  ex- 
crementitious character. 

As  we  are  much  better  acquainted  with  the  excrementitious  than  with  the  digestive 
function  of  the  bile,  we  shall  consider,  in  this  connection,  only  a  few  of  the  points  con- 
cerning the  chemistry  of  this  fluid,  deferring  a  full  account  of  its  composition  until  we 
come  to  treat  of  it  as  an  excretion. 


280 


DIGESTION. 


The  bile  varies  in  color  and  consistence  in  different  animals.  It  usually  has  a  greenish, 
yellowish,  or  brownish  hue.  In  the  human  subject,  it  has  a  dark,  golden-brown  color 
and  is  somewhat  viscid  in  consistence,  chiefly  from  admixture  with  the  mucus  of  the  gall- 
bladder. The  specific  gravity  of  human  bile  has  been  found  to  be  about  1018.  Its  reac- 
tion is  faintly  alkaline. 

Physiological  chemists  have  long  since  recognized  in  the  bile  peculiar  principles, 
which  are  found  in  no  other  part  of  the  organism ;  but  the  exact  nature  of  these  con- 
stituents was  first  described  by  Strecker,  in  1848,  who  obtained  from  the  bile  of 'the  ox 
two  principles,  cholic  and  choleic  acid,  which  he  found  to  exist  in  this  fluid  in  combina- 
tion with  soda.  The  cholic  acid  of  Strecker,  which  may  be  decomposed  into  a  new  acid 
and  a  principle  called  glycine,  and  the  choleic  acid,  from  which  may  be  formed  a  new 
acid  and  taurine,  are  called  by  Lehinann,  respectively,  glycocholic  and  taurocholic  acid. 
In  the  bile  of  the  ox,  these  are  found  combined  with  soda,  and  the  peculiar  proximate 
principles  of  this  fluid  are  now  recognized  as  the  glycocholate  of  soda,  a  crystalline  sub- 
stance, and  the  taurocholate  of  soda,  which  is  of  a  resinous  consistence  and  is  stated  to 
be  uncrystallizable.  In  the  human  bile,  Dalton  has  found  a  resinous  substance,  which, 
from  its  behavior  with  various  reagents,  is  undoubtedly  analogous  to  the  taurocholate 
of  soda  of  ox-bile,  but  which  he  could  not  obtain  in  a  crystalline  form. 


FIG.  77.— Crystals  of  glycocholate  of  soda.    (Robin.) 

In  addition  to  the  biliary  salts,  the  bile  contains  the  ordinary  inorganic  salts,  found 
in  nearly  all  the  animal  fluids,  a  small  quantity  of  fat,  the  oleates,  margarates,  and  stea- 
rates  of  soda  and  potassa,  mucus  from  the  gall-bladder,  and  cholesterine ;  the  last  being 
an  excrementitious  product.  The  action  of  the  bile  in  digestion,  whatever  its  nature  may 


ACTION   OF  THE  BILE   IN  DIGESTION.  281 

be,  undoubtedly  depends  chiefly  upon  the  biliary  salts,  and  perhaps  to  some  extent  upon 
its  saponaceous  constituents. 

Experiments  with  regard  to  the  action  of  the  bile  upon  different  alimentary  substances 
out  of  the  body  have  not  led  to  any  definite  results.  It  is  only  in  connection  with  the  other 
digestive  fluids  that  the  bile  seems  to  be  efficient ;  and  the  only  observations  which  have 
thrown  any  light  upon  the  subject  are  those  made  upon  digestion  in  the  living  organism. 
Simple  ligation  of  the  bile-duct  has  taught  us  very  little  regarding  the  effects  of  shutting  off 
the  bile  from  the  intestine  ;  for  the  immediate  effects  of  the  operation  generally  interfered 
with  the  process  of  digestion,  and  subsequently  the  experiment  was  necessarily  disturbed 
by  the  effects  of  the  retention  of  bile  in  the  excretory  passages.  As  would  naturally  be 
expected,  these  observations  have  been  quite  contradictory.  The  most  satisfactory  ex- 
periments upon  the  digestive  function  of  the  bile  have  followed  the  establishment  of  a 
fistulous  opening  into  the  gall-bladder,  the  flow  of  bile  at  the  same  time  being  completely 
shut  off  from  the  intestine.  In  all  experiments  of  this  kind  in  which  fatal  inflammation 
did  not  follow  the  operation,  death  has  taken  place  from  inanition,  notwithstanding  an 
increase  in  the  quantity  of  food  taken.  This  result  is  not  due  simply  to  the  loss  of  the 
solid  matter  discharged  in  the  bile,  which  is  small  in  proportion  to  the  total  daily  loss  of 
weight ;  but  it  undoubtedly  proceeds  from  disordered  nutrition,  which  has  its  starting- 
point  in  disordered  digestion. 

Observations  on  a  Dog  with  a  Biliary  Fistula. — We  have  now  to  study  the  modifica- 
tions in  digestion  and  nutrition  which  are  the  result  of  simply  diverting  the  bile  from  the 
intestine.  With  that  view,  we  followed  carefully  these  changes  in  an  animal  with  a 
biliary  fistula  that  was  under  our  own  observation.  This  experiment  confirmed,  in  all 
important  particulars,  those  of  Schwann  and  of  Bidder  and  Schmidt.  It  is  given  here 
somewhat  in  detail,  for,  inasmuch  as  no  inflammation  followed  the  operation  and  nothing 
occurred  to  complicate  the  effects  of  the  diversion  of  the  bile  from  the  intestine,  we  re- 
garded the  experiment  as  remarkably  successful. 

November  15,  1861,  a  biliary  fistula  was  established  in  a  young  cur-dog  weighing 
twelve  pounds.  The  abdominal  organs  were  very  little  exposed,  and  the  experiment, 
from  the  first,  promised  to  be  very  satisfactory.  The  bile-duct  was  first  ligated  next  the 
intestine  and  at  its  junction  with  the  cystic  duct,  and  the  intermediate  portion  was  ex- 
sected.  The  incision  in  the  abdomen  was  in  the  median  line  just  below  the  ensiform 
cartilage,  and  was  about  three  inches  long.  The  fundus  of  the  gall-bladder  was  then 
drawn  to  the  upper  portion  of  the  wound,  and  the  bile  was  evacuated  by  a  small  opening, 
the  edges  of  which  were  attached  to  the  abdominal  parietes.  The  wound  in  the  abdo- 
men was  then  closed,  except  the  opening  into  the  gall-bladder,  into  which  a  few  shreds 
of  lamp-wicking  were  introduced. 

The  animal  appeared  to  do  perfectly  well  after  the  operation  and  ate  the  usual  quan- 
tity the  next  day.  He  was  kept  in  a  warm  room,  although  the  weather  was  mild  ;  and 
a  careful  record  was  made  of  his  condition  every  day.  The  fistula  occasionally  showed  a 
tendency  to  close,  but  it  was  kept  open  by  the  occasional  introduction  of  a  glass  rod. 
From  time  to  time,  while  the  animal  was  under  observation,  he  licked  the  bile  as  it 
flowed  from  the  fistula.  This  was  afterward  prevented  by  a  long  wire-muzzle,  the  sides 
of  which  were  covered  with  oil-silk. 

The  abdomen  was  somewhat  tumid,  with  some  rumbling  in  the  bowels,  for  five  days 
after  the  operation.  The  first  alvine  discharge  took  place  on  the  evening  of  the  second 
day.  The  faeces  seemed  in  all  regards  normal.  After  that  time,  they  became  very  infre- 
quent, although  the  animal  ate  well  every  day.  The  fasces  that  were  passed  after  the 
third  day  were  of  a  grayish  color  and  moderately  soft.  They  had  an  exceedingly  offensive 
and  penetrating  odor.  At  about  the  fifteenth  day,  the  fasces  became  more  frequent,  and, 
from  that  time,  were  passed  three  or  four  times  a  day.  Generally,  they  were  clay-col- 
ored ;  but  on  one  or  two  occasions  they  were  quite  dark.  They  always  had  a  peculiarly 
offensive  odor. 


282  DIGESTION". 

The  weight  of  the  animal  remained  stationary  for  about  four  days.  On  the  sixth  day 
(November  20th),  the  weight  began  to  diminish.  He  weighed  on  that  day,  before  feed- 
ing, eleven  and  one-quarter  pounds.  November  22d,  he  weighed  but  little  over  eleven 
pounds.  November  24th,  he  weighed  ten  pounds.  He  maintained  this  weight  until 
December  1st,  when  the  weight  again  began  to  diminish.  On  December  6th,  the  weight 
was  nine  pounds.  On  December  7th,  the  weight  was  reduced  to  eight  and  a  half  pounds, 
and  the  strength  began  to  fail  manifestly.  December  10th  and  llth,  he  gained  a  little, 
on  those  days  weighing  nine  pounds;  but,  after  that,  he  progressively  diminished  in 
strength  and  in  weight  until  death  occurred,  thirty-eight  days  after  the  operation.  The 
weight  was  then  seven  and  a  half  pounds,  showing  a  total  loss  of  four  and  a  half  pounds, 
or  37-J-  per  cent. 

During  the  first  nine  days  of  the  observation,  the  animal  ate  well  but  not  ravenously, 
taking  about  three-quarters  of  a  pound  of  beef-heart  daily.  On  the  tenth  day,  the  appe- 
tite increased.  He  ate  on  that  day,  at  one  time  a  pound,  and  at  another,  half  a  pound  of 
meat.  He  ate  on  an  average  about  a  pound  and  a  half  of  beef-heart  daily,  until  the  day 
before  his  death.  During  the  last  five  or  six  days,  he  seemed  very  ravenous  and  was  not 
allowed  to  eat  all  that  he  would  at  one  time.  At  this  time  he  was  ordinarily  fed  twice  a 
day.  He  would  not  eat  fat,  even  when  very  hungry.  During  the  last  day,  when  too 


FIG.  78.— Dog  with  a  'biliary  fistula. 

From  a  rough  sketch  made  the  fourteenth  day  after  the  operation.  A  small  glass  vessel  is  tied  around  the  body 
to  collect  the  bile,  and  a  wire  muzzle,  the  lower  part  of  which  is  covered  with  oil-silk,  is  placed  over  the  mouth  to 
prevent  the  animal  from  licking  the  bile.  The  dog  is  considerably  emaciated. 

weak  to  stand,  he  attempted  to  eat  while  lying  down.  During  the  last  twelve  days  of 
the  observation,  he  attempted  constantly  to  eat  the  faeces.  During  the  last  days  of  the 
experiment,  when  the  dog  had  become  much  reduced  in  weight,  he  became  very  cross 
and  snapped  at  every  animal  that  came  near  him.  There  was  never  any  icterus,  fetor 
of  the  breath,  or  falling  off  of  the  hair. 

A  careful  examination  of  the  animal  was  made  after  death.  The  gall-bladder  was 
somewhat  contracted  but  not  obliterated,  and  the  fistula  would  admit  a  large-sized 
male  catheter.  Both  ends  of  the  divided  bile-duct  were  found  impervious,  and  there  was 
no  passage  of  bile  into  the  intestine.  The  abdominal  organs  were  normal,  with  the 
exception  of  evidences  of  slight  peritoneal  inflammation  around  the  wound  and  over  the 
convex  surface  of  the  liver.  There  was  no  fat  in  the  omentum  or  anywhere  in  the  body, 
except  a  very  small  quantity  at  the  bottom  of  the  orbit. 

The  above  observation  is  a  type  of  the  instances— which  are  not  very  numerous — in 


ACTION   OF  THE  BILE   IN  DIGESTION.  283 

which  the  bile  has  been  completely  shut  off  from  the  intestine  and  discharged  externally 
by  a  fistula  into  the  gall-bladder.  As  far  as  could  be  ascertained,  this  animal,  from  the 
first,  presented  no  disturbances  which  were  not  due  solely  to  the  absence  of  the  bile  from 
the  intestine  and  its  discharge  externally.  Although  the  phenomena  here  presented  do 
not  teach  us  much  that  is  definite  concerning  the  digestive  action  of  the  bile,  taken  in 
connection  with  what  has  been  ascertained  concerning  the  general  properties  of  this  se- 
cretion, they  throw  some  light  upon  its  functions. 

One  of  the  functions  which  has  been  ascribed  to  the  bile  is  that  of  regulating  the  peris- 
taltic movements  of  the  small  intestine  and  of  preventing  putrefactive  changes  in  the 
intestinal  contents  and  the  abnormal  development  of  gas.  Experiments  on  this  point  are 
somewhat  conflicting.  Our  own  observations  would  lead  us  to  doubt  the  constant  influ- 
ence of  the  bile  upon  the  peristaltic  movements.  During  the  first  few  days  of  our  experi- 
ment, the  dejections  were  very  rare ;  but  they  afterward  became  regular,  and,  at  one 
time,  even,  there  was  a  tendency  to  diarrhoea.  There  can  be  no  doubt,  however,  that 
the  bile  retards  the  putrefaction  of  the  contents  of  the  intestinal  canal,  particularly  when 
animal  food  has  been  taken.  The  faeces  in  the  dog  were  always  extremely  offensive. 
Bidder  and  Schmidt  found  this  to  be  the  case  in  dogs  fed  entirely  on  meat ;  but  the  faeces 
were  nearly  odorless  when  the  animals  were  fed  on  bread  alone.  In  the  case  of  intes- 
tinal fistula  in  the  human  subject,  the  evacuations  which  took  place  after  the  intro- 
duction of  alimentary  substances  into  the  lower  portion  of  the  intestine  had  an  unnaturally 
offensive  and  putrid  odor.  In  this  case,  as  it  was  impossible  for  matters  to  pass  from  the 
portions  of  the  intestine  above  the  fistula  to  those  below,  the  food  introduced  into  the 
lower  opening  was  completely  removed  from  the  action  of  the  bile. 

As  far  as  the  digestion  of  the  different  alimentary  principles  is  concerned,  it  has  been 
shown  that  the  bile,  of  itself,  has  no  particular  action  upon  any  of  them.  In  the  faeces 
of  animals  with  biliary  fistula,  the  only  peculiarity  which  has  been  observed,  aside  from 
the  putrefactive  odor  and  the  absence  of  the  coloring  matter  of  the  bile,  has  been  the 
presence  of  an  abnormal  proportion  of  fat.  "We  have  observed  this  in  the  faeces  of  a  pa- 
tient suffering  under  jaundice  apparently  due  to  temporary  obstruction  of  the  bile-duct. 
This  fact  was  noted  in  the  dogs  experimented  upon  by  Bidder  and  Schmidt. 

The  various  experiments  which  have  been  performed  upon  animals  render  it  almost 
certain  that  the  bile  has  an  important  influence,  either  upon  the  digestion  or  upon  the  ab- 
sorption of  fats.  Bidder  and  Schmidt  noted  in  animals  with  biliary  fistula  that  the  chyle 
contained  very  much  less  fat  than  in  health.  In  an  animal  with  a  fistula  and  the  bile-duct 
obliterated,  the  proportion  of  fat  was  1'90  parts  to  1,000  parts  of  chyle  ;  while,  in  an  ani- 
mal with  the  biliary  passages  intact,  the  proportion  was  32*79  parts  per  1,000.  In  ani- 
mals operated  upon  in  this  way,  there  is  frequently  a  great  distaste  for  fatty  articles  of 
food.  In  our  own  observation,  the  dog  refused  fat  meat,  even  when  very  hungry  and 
when  lean  meat  was  taken  with  great  avidity. 

Experiments  concerning  the  influence  of  the  bile  upon  the  absorption  of  fats  have  re- 
sulted in  hardly  any  thing  definite.  We  know  only  the  fact  that,  when  the  bile  is  diverted 
from  the  intestine,  the  proportion  of  fat  in  the  chyle  is  greatly  reduced,  and  a  large  pro- 
portion of  the  fat  taken  with  the  food  passes  through  the  intestine  and  is  found  in  the 
faeces. 

The  action  of  the  bile  in  exciting  muscular  contraction,  particularly  in  the  smooth 
muscular  fibres,  is  pretty  well  established.  It  has  been  shown  by  Schiff  that  this  fluid 
acts  upon  the  muscular  fibres  situated  in  the  substance  of  the  intestinal  villi,  causing 
them  to  contract,  and,  according  to  his  view,  assisting  in  the  absorption  of  chyle  by  emp- 
tying the  lacteals  of  the  villi.  The  whole  subject,  however,  of  the  absorption  of  fats  is 
exceedingly  difficult  of  investigation  ;  and  our  knowledge  of  it  has  not  been  sensibly  ad- 
vanced by  the  experiments  upon  the  influence  exerted  by  the  bile.  Notwithstanding  the 
obscurity  in  which  this  subject  is  involved,  it  is  certain  that  the  progressive  emaciation, 
loss  of  strength,  and  final  death  of  animals  deprived  of  the  action  of  the  bile  in  the  intes- 


284 


DIGESTION. 


tine,  are  due  to  defective  digestion  and  assimilation.  In  spite  of  the  great  quantities  of  food 
taken  by  these  animals,  the  phenomena  which  precede  the  fatal  result  are  simply  those 
of  starvation.  It  may  be  that  the  biliary  salts  are  absorbed  by  the  blood  and  are  neces- 
sary to  proper  assimilation  ;  but  there  is  no  experimental  basis  for  this  supposition,  and 
it  is  impossible  to  discover  these  salts  in  the  blood  of  the  portal  system  by  the  ordinary 
tests.  It  is  more  probable  that  the  biliary  salts  influence  in  some  way  the  digestive  pro- 
cess and  are  modified  and  absorbed  with  the  food. 

The  observations  of  Bidder  and  Schmidt  show  conclusively  that  the  characteristic 
constituents  of  the  bile  are  absorbed  in  their  passage  down  the  alimentary  canal.  Hav- 
ing arrived  at  a  pretty  close  estimate  of  the  quantity  of  bile  daily  produced  in  dogs,  they 
collected  and  analyzed  all  the  faecal  matter  passed  by  a  dog  in  five  days.  Of  the  dry 
residue  of  the  faeces,  the  proportion  which  could  by  any  possibility  represent  the  biliary 
matters  did  not  amount  to  one-fourth  of  the  dry  residue  of  the  bile  which  must  have  been 
secreted  during  that  time.  They  also  estimated  the  total  quantity  of  sulphur  contained 
in  the  faeces  and  found  that  the  entire  quantity  was  hardly  one-eighth  of  that  which 
was  discharged  into  the  intestine  in  the  bile ;  and,  inasmuch  as  nearly  one-half  of  that 
found  in  the  faeces  came  from  hairs  which  had  been  swallowed  by  the  animal,  the  experi- 
ment showed  that  nearly  all  the  sulphur  contained  in  the  non-crystallizable  element  of 
the  bile  (the  taurocholate  of  soda)  had  been  taken  up  again  by  the  blood.  These  obser- 
vations show  conclusively  that  the  greater  part  of  the  bile,  with  the  biliary  salts,  is  ab- 
sorbed by  the  intestinal  mucous  membrane.  Prof.  Dalton  has  attempted  to  follow  these 
principles  into  the  blood  of  the  portal  system,  but  has  never  been  able  to  detect  the  bili- 
ary salts,  by  the  most  careful  analysis.  Like  the  peculiar  principles  of  other  secretions 
which  are  reabsorbed  in  the  alimentary  canal,  these  substances  become  changed  and  are 
not  to  be  recognized  by  the  ordinary  tests,  after  they  are  taken  into  the  blood. 

Although  it  is  the  digestion  and  absorption  of  fatty  substances  which  seem  to  be 
most  seriously  interfered  with  in  cases  of  biliary  fistula  in  the  inferior  animals,  the  rapid 
loss  of  weight  and  strength  indicates  great  disturbance  in  the  digestion  and  absorp- 
tion of  other  articles  of  food.  A  fact  which  indicates  a  connection  between  the  bile  and 
the  process  of  digestion  is  that  the  flow  of  this  secretion,  although  constant,  is  greatly 
increased  when  food  passes  into  the  intestinal  canal.  This  has  been  noted  by  all  who 
have  experimented  on  the  subject.  The  following  observations  on  the  dog,  showing  the 
variations  in  the  flow  of  bile  from  the  fistula,  were  made  twelve  days  after  the  fistula  had 
been  established,  when  the  weight  of  the  animal  had  been  reduced  from  twelve  to  ten 
pounds. 

Table  of  Variations  in  the  Flow  of  Bile  with  Digestion. 

(At  each  observation,  the  bile  was  drawn  for  precisely  thirty  minutes.) 


Time  after  Feeding. 

Fresh  Bile. 

Dried  Bile. 

Percentage  of 
Dry  Kesidue. 

Immediately  

Grains. 

8-103 

Grains. 

0-370 

4-566 

One  hour  

20-527 

0-586 

2-854 

Two  hours  

35-760 

1-080 

3-023 

Four  hours  

38-939 

1-404 

'  3-605 

Six  hours  

22-209 

0-987 

4-450 

Eight  hours  

36-577 

1-327 

3-628 

Ten  hours  

24-447 

0-833 

3-407 

Twelve  hours  

5-710 

0-247 

4-325 

Fourteen  hours  

5-000 

0-170 

3-400 

Sixteen  hours  

8-643 

0-309 

3-575 

Eighteen  hours  

9-970 

0-277 

2-778 

Twenty  hours  

4-769 

0-170 

3-565 

Twenty-two  hours  

7-578 

0-293 

3-866 

MOVEMENTS   OF  THE   SMALL  INTESTINE.  285 

Disregarding  slight  variations  in  this  table,  which  might  be  accidental,  it  may  be 
stated,  in  general  terms,  that  the  bile  commences  to  increase  in  quantity  immediately 
after  eating ;  that  its  flow  is  at  its  maximum  from  the  second  to  the  eighth  hour,  during 
which  time  the  quantity  does  not  vary  to  any  great  extent ;  after  the  eighth  hour  it 
begins  to  diminish,  and,  from  the  twelfth  hour  to  the  time  of  feeding,  it  is  at  is  minimum. 

Although  it  has  been  pretty  satisfactorily  demonstrated  that  the  presence  of  the  bile 
in  the  small  intestine  is  necessary  to  proper  digestion  and  even  essential  to  life,  and 
although  the  variations  in  the  flow  of  bile  with  digestion  are  now  well  established,  it 
must  be  confessed  that  we  have  scarcely  any  definite  information  concerning  the  mode 
of  action  of  the  bile  in  intestinal  digestion  and  absorption.  Nearly  all  that  we  can  say  on 
this  point  is  that  its  action  seems  to  be  auxiliary  to  that  of  the  other  digestive  fluids. 

Movements  of  the  Small  Intestine. 

By  the  contractions  of  the  muscular  coat  of  the  small  intestine,  the  alimentary  mass 
is  made  to  pass  along  the  canal,  sometimes  in  one  direction  and  sometimes  in  another ; 
the  general  tendency,  however,  being  toward  the  c^cum.  The  partially-digested  matters 
which  pass  out  at  the  pylorus  are  prevented  from  returning  to  the  stomach  by  the  pecul- 
iar arrangement  of  the  fibres  which  constitute  the  pyloric  muscle.  The  passage  from 
the  stomach  to  the  intestine,  as  we  have  seen,  becomes  constricted  gradually,  so  that 
food  of  the  proper  consistence  finds  its  way  easily  into  the  duodenum  ;  but,  viewed 
from  the  .duodenal  side,  the  constriction  is  abrupt,  so  that  regurgitation  is  generally 
difficult. 

Once  in  the  intestine,  the  food  is  propelled  along  the  canal  by  peculiar  move- 
ments, which  have  been  called  peristaltic,  when  its  direction  is  toward  the  large 
intestine,  and  antiperistaltic,  when  the  direction  is  reversed.  These  movements  are 
of  the  character  peculiar  to  the  unstriped  muscular  fibres ;  viz.,  slow,  gradual,  the 
contraction  enduring  for  a  certain  time  and  being  followed  by  a  correspondingly  slow 
and  gradual  relaxation.  Both  the  circular  and  the  longitudinal  muscular  layers  par- 
ticipate in  these  movements.  If  we  carefully  watch  this  action  in  the  intestines  of 
an  animal  after  the  abdomen  has  been  opened,  we  can  sometimes  see  a  gradual  constric- 
tion produced  by  the  action  of  the  circular  fibres  at  a  certain  point,  which  is  slowly 
propagated  along  the  tube,  while,  at  the  same  time,  the  longitudinal  fibres  are  alternate- 
ly contracted  and  relaxed  in  the  same  gradual  manner,  shortening  and  elongating  the 
tube  and  facilitating  the  onward  passage  of  its  contents.  It  can  readily  be  appreciated 
how  movements  of  this  kind  are  capable  of  propelling  the  alimentary  mass  slowly  but 
certainly  along  the  intestinal  tract,  even  when  the  direction  is  in  opposition  to  the  force 
of  gravity  ;  and  we  can  see  how  admirably  these  movements  are  calculated  to  thorough- 
ly incorporate  the  food  with  the  digestive  fluids  and  to  expose  those  parts  which  have 
been  completely  liquefied  to  the  absorbent  action  of  the  mucous  membrane. 

Although  the  mechanism  of  the  propulsive  movements  of  the  intestine  may  be  studied 
in  living  animals  after  opening  the  abdomen,  or,  better  still,  in  animals  just  killed,  the 
movements  thus  observed  do  not  entirely  correspond  with  those  which  take  place  under 
natural  conditions.  In  vivisections,  no  movements  are  observed  at  first ;  but,  soon  after 
exposure  of  the  parts,  nearly  the  whole  intestine  moves  like  a  mass  of  worms.  In  the 
normal  process  of  digestion,  the  movements  are  never  so  general  or  so  active ;  they  take 
place  more  regularly  and  consecutively  in  those  portions  in  which  the  contents  are  most 
abundant,  and  the  movements  are  generally  intermittent,  being  interrupted  by  long  inter- 
vals of  repose.  In  Prof.  Busch's  case  of  intestinal  fistula,  there  existed  a  large  ventral 
hernia,  the  coverings  of  which  were  so  thin  that  the  peristaltic  movements  could  be  readily 
observed.  In  this  case,  the  general  character  of  the  movements  corresponded  with  what 
has  been  observed  in  the  inferior  animals.  It  was  noted  that  the  movements  were  not 
continuous,  and  that  there  were  often  intervals  of  rest  for  more  than  a  quarter  of  an  hour. 


286  DIGESTION. 

It  was  also  observed  that  the  movements,  as  indicated  by  flow  of  chymous  matter  from 
the  upper  end  of  the  intestine,  were  intermitted  with  considerable  regularity  during  part 
of  the  night.  Antiperistaltic  movements,  producing  discharge  of  matters  which  had  been 
introduced  into  the  lower  end  of  the  intestine,  were  frequently  observed. 

As  far  as  has  been  ascertained  by  observations  upon  the  human  subject  and  warm- 
blooded animals,  the  regular  intestinal  movements  are  excited  by  the  passage  of  alimen- 
tary matter  from  the  stomach  through  the  tube  during  the  natural  process  of  digestion. 
By  a  very  slow  and  gradual  action  of  the  muscular  coat  of  the  intestine,  its  contents  are 
passed  along,  occasionally  the  action  being  reversed  for  a  time,  until  the  indigestible 
residue,  mixed  with  a  certain  quantity  of  intestinal  secretion,  more  or  less  modified,  is 
discharged  gradually  into  the  caput  coli.  These  movements  are  apparently  not  continu- 
ous, and  they  depend  somewhat  upon  the  quantity  of  matter  contained  in  different  parts  of 
the  intestinal  tract.  If  we  are  to  judge  from  the  movements  in  the  inferior  animals  after 
the  abdomen  has  been  opened,  the  intestines  are  constantly  changing  their  position,  prin- 
cipally by  the  action  of  their  longitudinal  muscular  fibres,  so  that  the  force  of  gravity  does 
not  oppose  the  onward  passage  of  their  contents  as  much  as  if  the  relative  position  of  the 
parts  were  constant.  There  are  no  definite  observations  concerning  the  relative  activity 
of  the  peristaltic  movements  in  different  portions  of  the  intestine ;  but,  from  the  fact  that 
the  jejunum  is  constantly  found  empty,  while  the  ileum  contains  a  considerable  quantity 
of  pultaceous  matter,  it  would  seem  that  the  movements  must  be  more  vigorous  and 
efficient  in  the  upper  portions  of  the  canal. 

The  gases  which  are  constantly  found  in  the  intestine  have  an  important  mechanical 
function.  They  are  useful,  in  the  first  place,  in  keeping  the  canal  constantly  distended 
to  the  proper  extent,  thus  avoiding  the  liability  to  disturbances  in  the  circulation  and 
facilitating  the  passage  of  the  alimentary  mass  in  obedience  to  the  peristaltic  contrac- 
tions. They  also  support  the  walls  of  the  intestine  and  protect  these  parts  against  con- 
cussions in  walking,  leaping,  etc.  The  gases  are  useful,  likewise,  in  offering  an  elastic 
but  resisting  mass  upon  which  the  compressing  action  of  the  abdominal  muscles  may  be 
exerted  in  the  acts  of  straining  and  expiration.  If  we  could  suppose  the  intestinal  tube 
to  be  entirely  free  from  gaseous  contents,  it  is  evident  that  the  functions  above  mentioned 
would  be  performed  imperfectly  and  with  difficulty. 

There  can  be  hardly  any  question  that  the  normal  movements  of  the  intestine  are 
due  principally  to  the  impression  made  upon  the  mucous  membrane  by  the  alimentary 
matters,  to  which  is  added,  perhaps,  the  stimulating  action  of  the  bile.  It  is  difficult  to 
determine  with  accuracy  what  part  the  bile  plays  in  the  production  of  these  movements, 
from  the  fact  that  the  normal  action  of  the  intestine  is  not  easily  observed.  In  the  case 
of  intestinal  fistula  so  often  referred  to,  when  food  was  introduced  into  the  lower  end  of 
the  canal,  there  was  at  first  an  abundant  evacuation  every  twenty -four  hours ;  but  sub- 
sequently it  became  necessary  to  use  enemeta.  As  there  was  no  communication  between 
the  lower  and  the  upper  end  of  the  intestine,  this  fact  is  an  evidence  that  the  peristaltic 
movements  can  take  place  without  the  action  of  the  bile.  Experiments  upon  the  inferior 
animals  concerning  the  influence  of  the  bile  upon  the  peristaltic  movements  are  somewhat 
contradictory.  When  the  abdomen  is  opened  during  life,  vigorous  movements  may  some- 
times be  excited  by  pressing  bile  into  the  intestine  from  the  gall-bladder ;  and  the  same 
result  is  occasionally  observed  when  the  bile  is  applied  to  the  peritoneal  surface  in  an 
animal  recently  killed.  But  the  various  experiments  in  which  the  bile  has  been  diverted 
from  the  intestine  and  discharged  by  a  fistula,  taking  the  frequency  of  the  alvine  dejec- 
tions as  a  test,  show  that  regular  peristaltic  movements  may  take  place  without  the  in- 
tervention of  the  bile. 

The  vigorous  peristaltic  movements  which  occur  soon  after  death  have  been  explained 
in  various  ways.  It  has  been  shown  that  these  movements  are  not  due  to  a  lower- 
ing of  the  temperature  or  to  exposure  of  the  intestines  to  the  air.  The  latter  fact 
may  be  easily  verified  by  killing  a  rabbit,  when  vigorous  movements  may  be  seen  through 


PHYSIOLOGICAL  ANATOMY   OF   THE  LARGE  INTESTINE.          287 

the  thin  abdominal  walls,  even  while  the  cavity  is  unopened.  According  to  Schiff,  the 
only  cause  of  these  exaggerated  movements  is  diminution  or  arrest  of  the  circulation. 
This  physiologist,  by  compressing  the  abdominal  aorta  in  a  living  animal,  was  able  to  ex- 
cite peristaltic  movements  in  the  intestine  as  vigorous  as  those  which  take  place  after 
death ;  and,  on  ceasing  the  compression,  the  movements  were  arrested. 

The  nerves  distributed  to  the  small  intestine  are  derived  from  the  sympathetic,  and 
from  branches  of  the  pneumogastric,  which  latter  come  from  the  nerve  of  the  right  side 
and  are  distributed  to  the  whole  of  the  tract,  from  the  pylorus  to  the  ileo-cgecal  valve. 
The  intestine  receives  no  filaments  from  the  left  pneumogastric.  The  experiments  of 
Brachet,  by  which  he  attempted  to  prove  that  the  movements  of  the  intestines  were 
under  the  control  of  the  pneumogastric  and  nerves  emanating  from  the  spinal  cord,  have 
not  been  verified  by  other  observers.  Eecent  experiments  render  it  probable  that  an 
influence,  derived  from  the  cerebro-spinal  system,  is  essential  to  the  functions  of  the 
sympathetic  ganglia,  which  may  account  for  some  of  the  results  obtained  by  Brachet 
after  dividing  the  spinal  cord.  The  experiments  of  Mtiller,  however,  render  it  certain 
that  the  peristaltic  movements  are  to  some  extent  under  the  influence  of  the  sympathetic 
system.  In  these  experiments,  movements  of  the  intestine  were  produced  by  galvaniza- 
tion of  filaments  of  the  sympathetic  distributed  to  its  muscular  coat,  after  the  ordinary 
post-mortem  movements  had  ceased.  The  same  results  followed  the  application  of  caustic 
potash  to  the  semilunar  ganglia,  the  movements  reappearing  when  the  potash  was  applied, 
"  with  extraordinary  vivacity  "  in  the  rabbit,  after  the  abdomen  had  been  opened  and  the 
movements  had  entirely  ceased.  These  experiments  have  been  confirmed  by  Longet, 
who  found,  however,  that  the  movements  did  not  take  place  unless  alimentary  matters 
were  contained  in  the  intestine. 

It  must  be  acknowledged  that  very  little  is  known  concerning  the  reflex  actions  which 
take  place  through  the  sympathetic  system ;  but  there  is  certainly  good  ground  for  sup- 
posing that  certain  reflex  functions  are  performed  by  this  system  of  nerves,  one  of  the 
most  important  of  which  is  the  production  of  peristaltic  movements  in  obedience  to  the 
impression  made  by  alimentary  substances  upon  the  mucous  membrane.  This  impression 
is  probably  conveyed  to  the  semilunar  ganglia  and  reflected  back  through  the  motor  nerves 
to  the  muscular  coat  of  the  intestine. 

Physiological  Anatomy  of  the  Large  Intestine. 

The  large  intestine,  so  called  because  its  diameter  is  greater  than  that  of  the  rest  of 
the  intestinal  tract,  receives  for  the  most  part  only  the  indigestible  residue  of  the  food, 
mingled  with  certain  of  the  secretions  which  are  discharged  into  the  small  intestine.  In 
the  human  subject,  the  processes  of  digestion  which  take  place  in  this  part  of  the  ali- 
mentary canal  are  unimportant ;  and  it  is  probable  that,  under  physiological  conditions, 
hardly  any  thing  but  water  is  absorbed  by  its  lining  membrane.  Matters  are,  however, 
stored  up  in  the  large  intestine  for  a  number  of  hours,  and  a  certain  amount  of  secretion 
takes  place  from  its  follicular  glands. 

The  entire  length  of  the  large  intestine  is  from  four  to  six  feet.  Its  diameter  is  great- 
est at  its  commencement,  where  it  measures,  when  moderately  distended,  from  two  and  a 
half  to  three  and  a  half  inches.  According  to  the  observations  of  Brinton,  the  average 
diameter  of  the  tube  beyond  the  caBCum  is  from  one  and  two-thirds  to  two  and  two- 
thirds  inches.  Passing  from  the  caecum,  the  canal  diminishes  in  caliber,  gradually  and 
very  slightly,  to  where  the  sigmoid  flexure  opens  into  the  rectum.  This  is  the  narrowest 
portion  of  the  canal.  Beyond  this,  the  rectum  gradually  increases  in  diameter,  forming 
a  kind  of  pouch,  which  abruptly  diminishes  in  size  near  the  external  opening,  to  form  the 
anus. 

The  general  direction  of  the  large  intestine  is  from  the  coBcum  in  the  right  iliac  fossa 
to  the  left  iliac  fossa,  thus  encircling  the  convoluted  mass  formed  by  the  small  in- 


288 


DIGESTION. 


testine,  in  the  form  of  a  horseshoe.      From  the  caecum  to  the  rectum,  the  canal  is 
known  as  the  colon.      The  first  division   of  the  colon,  called  the  ascending   colon, 

passes  almost  directly  upward 
to  the  under  surface  of  the  liver ; 
the  canal  here  turns  at  nearly 
a  right  angle,  passes  across  the 
upper  part  of  the  abdomen,  and 
is  called  the  transverse  colon ; 
it  then  passes  downward  at 
nearly  a  right  angle,  forming 
the  descending  colon.  The 
last  division  of  the  colon,  called 
the  sigmoid  flexure,  is  situated 
in  the  left  iliac  fossa  and  is  in 
the  form  of  the  italic  letter  S. 
This  terminates  in  the  rectum, 
which  is  not  straight,  as  its 
name  would  imply,  hut  presents 
at  least  three  distinct  curva- 
[20  tures,  as  follows :  it  passes  first 

in  an  oblique  direction  from  the 
left  sacro-iliac  symphysis  to  the 
median  line  opposite  the  third 
piece  of  the  sacrum;  it  then 
passes  downward,  in  the  me- 
dian line,  following  the  con- 
cavity of  the  sacrum  and  coc- 
cyx ;  and  the  lower  portion, 
which  is  about  an  inch  in  length, 
turns  backward  to  terminate  in 
the  anus. 

The  form  of  the  large  intes- 
tine is  peculiar.  The  c&cum, 
or  caput  coli,  presents  a  round- 
ed, dilated  cavity,  continuous 
with  the  colon  above  and  com- 
municating by  a  transverse  slit 
with  the  ileum.  At  its  lower 
portion,  is  a  small,  cylindrical 
tube,  from  one  to  five  inches  in 
length,  opening  below  and  a  little  posterior  to  the  opening  of  the  ileum,  called  the  ver- 
miform appendix.  This  is  covered  with  peritoneum  and  is  possessed  of  a  muscular  and 
a  mucous  coat.  It  is  sometimes  entirely  free  and  is  sometimes  provided  with  a  short 
fold  of  mesentery  for  a  part  of  its  length.  The  coats  of  the  appendix  are  very  thick. 
The  muscular  coat  consists  of  longitudinal  fibres  only.  The  mucous  membrane  is  pro- 
vided with  tubules  and  closed  follicles,  the  latter  frequently  being  very  numerous.  This 
little  tube,  which  is  only  about  one-third  of  an  inch  in  diameter,  generally  contains  a 
quantity  of  clear,  viscid  mucus.  The  uses  of  the  vermiform  appendix  are  unknown. 

Ileo-ccBcal  Valve. — The  most  interesting  anatomical  peculiarity  of  the  ca3cum  is  the 
opening  by  which  it  receives  the  contents  of  the  small  intestine.  This  opening  is  ar- 
ranged in  the  form  of  a  valve,  known  as  the  ileo-csecal  valve,  situated  at  the  inner  and 
posterior  portion  of  the  caecum.  The  small  intestine,  at  its  termination,  presents  a 


FIG.  79.— Stomach,  pancreas,  large  intestine,  etc.  (Sappey.) 
1,  anterior  surface  of  the  liver:  2,  gall-bladder;  3,3,  section  of  the  dia- 
phragm ;  4,  posterior  surface  of  the  stomach ;  5,  lobus  Spigelii  of  the 
liver ;  6,  cceliac  axis ;  7,  coronary  artery  of  the  stomach ;  8,  splenic 
artery;  9,  spleen;  10,  pancreas;  11,  superior  mesenteric  vessels;  12, 
duodenum ;  18,  upper  extremity  of  the  small  intestine ;  14,  lower  end 
of  the  ileum;  15,  15,  mesentery;  1 6.  ccecum ;  17,  appendix  vermi- 
tormis;  18,  ascending  colon;  19,  19,  transverse  colon;  20,  de- 
scending colon;  21,  sigmoid  Jlexwe  of  the  colon;  22,  rectum;  23, 
urinary  bladder. 


PHYSIOLOGICAL  ANATOMY   OF   THE   LARGE   INTESTINE. 


289 


shallow  concavity,  which  is  provided  with  a  horizontal,  button-hole  slit  opening  into 
the  c?3cum.  The  surface  of  the  valve  which  looks  toward  the  small  intestine  is  cov- 
ered with  a  mucous  membrane  provided  with  villi  and  in  all  respects  resembling  the 
general  mucous  lining  of  the  small  intestine.  Viewed 
from  the  caecum,  a  convexity  is  observed  corresponding 
to  the  concavity  upon  the  other  side.  The  cascal  surface 
of  the  valve  is  covered  with  a  mucous  membrane  identi- 
cal with  the  general  mucous  lining  of  the  large  intestine. 
It  is  evident,  from  an  examination  of  these  parts,  that 
pressure  from  the  ileum  would  open  the  slit  and  allow 
the  easy  passage  of  the  semifluid  contents  of  the  intes- 
tine;  but  pressure  from  the  cascal  side  approximates 
the  lips  of  the  valve,  and  the  greater  the  pressure  the 
more  firmly  is  the  opening  closed.  The  valve  itself  is 
composed  of  folds  formed  of  the  white  fibrous  tissue  of 
the  intestine  (the  cellular  tunic  of  some  anatomists),  and 
circular  muscular  fibres  from  both  the  small  and  the 
large  intestine,  the  whole  being  covered  with  mucous 
membrane.  The  lips  of  the  valve  unite  at  either  extrem- 
ity of  the  slit  and  are  prolonged  on  the  inner  surface  of 
the  csecum,  forming  two  raised  bands  or  bridles;  and 

these  become  gradually  effaced  and  are  thus  continuous  FIG.  so.— Opening  of  the  small  intes 
with  the  general  lining  of  the  canal.  The  posterior  bridle 
is  a  little  longer  and  more  prominent  than  the  anterior. 
These  assist  somewhat  in  enabling  the  valve  to  resist 
pressure  from  the  csecal  side.  The  longitudinal  layer  of 
muscular  fibres  and  the  peritoneum  pass  directly  over  the 
attached  edge  of  the  valve  and  are  not  involved  in  its  folds.  These  give  strength  to  the 
part,  and,  if  they  be  divided  over  the  valve,  gentle  traction  will  suffice  to  draw  out  and 
obliterate  the  folds,  leaving  a  simple  and  unprotected  communication  between  the  large 
and  the  small  intestine. 


tine  into  the  cnecum.    (Le  Bon.) 
1,  small  intestine;  2,  ileo-ca-cal  valve; 
8,  csecum  ;  4,  opening  of  the  appen- 
dix vermiformis;  5,  mucous  fold  at 


the 

intes 

membrane. 


opening  of  the  appendi 
stine  ;  7,  7,  folds  of  t 


x  ;  6,  large 
the  mucous 


Peritoneal  Coat. — Like  most  of  the  other  abdominal  viscera,  the  large  intestine  is 
covered  by  peritoneum.  The  caacum  is  covered  by  this  membrane  only  anteriorly  and 
laterally.  It  is  usually  bound  down  closely  to  the  subjacent  parts,  and  its  posterior  sur- 
face is  without  a  serous  investment;  although  sometimes  it  is  completely  covered,  and 
there  may  be  even  a  short  mesocoscum.  The  ascending  colon  is  likewise  covered  with 
peritoneum  only  in  front  and  is  closely  attached  to  the  subjacent  parts.  The  same  ar- 
rangement is  found  in  the  descending  colon.  The  transverse  colon  is  almost  completely 
invested  with  peritoneum  ;  and  the  two  folds  forming  the  transverse  mesocolon  separate 
to  pass  over  the  tube  above  and  below,  uniting  again  in  front  to  form  the  great  omentum. 
The  transverse  colon  is  consequently  quite  movable.  In  the  course  of  the  colon  and  the 
upper  part  of  the  rectum,  particularly  on  the  transverse  colon,  are  found  a  number  of 
little  sacculated  pouches  filled  with  fat,  called  the  appendices  epiploicaa.  The  sigmoid 
flexure  of  the  colon  is  invested  with  peritoneum,  except  at  the  attachment  of  the  iliac 
mesocolon.  This  division  of  the  intestine  is  capable  of  considerable  motion.  The  upper 
portion  of  the  rectum  is  almost  completely  covered  by  peritoneum  and  is  but  loosely  held 
in  place.  The  middle  portion  is  closely  bound  down,  and  is  covered  with  peritoneum  only 
anteriorly  and  laterally.  The  lowest  portion  of  the  rectum  has  no  peritoneal  covering. 

Muscular  Coat.— The  muscular  fibres  of  the  large  intestine  have  an  arrangement  quite 
different  from  that  which  exists  in  the  small  intestine.     The  external,  longitudinal  layer, 
instead  of  extending  over  the  whole  tube,  is  arranged  in  three  distinct  bands,  which  com- 
19 


290  DIGESTION. 

mence  in  the  caecum  at  the  vermiform  appendix.  Passing  along  the  ascending  colon, 
one  of  the  bands  is  situated  anteriorly,  and  the  others,  latero-posteriorly.  In  the  trans- 
verse colon,  the  anterior  band  becomes  inferior  and  the  two  latero-posterior  bands  be- 
come respectively  postero-superior  and  postero-inferior.  In  the  descending  colon  and 
the  sigmoid  flexure,  the  muscular  bands  resume  the  relative  position  which  they  had  in 
the  ascending  colon.  As  these  longitudinal  fibres  pass  to  the  rectum,  the  anterior  and 
the  external  bands  unite  to  pass  down  on  the  anterior  surface  of  the  canal,  while  the 
posterior  band  passes  down  on  its  posterior  surface.  Thus  the  three  bands  are  here 
formed  into  two.  These  two  bands  as  they  pass  downward,  though  remaining  distinct, 
become  much  wider;  and  longitudinal  muscular  fibres  commencing  at  the  rectum  are 
situated  between  them,  so  that  this  part  of  the  canal,  especially  in  its  lower  portion,  is 
covered  with  longitudinal  fibres  in  a  pretty  uniform  layer. 

The  arrangement  of  the  muscular  fibres  of  the  rectum  has  been  closely  studied  by  Sap- 
pey.  He  has  found  that,  as  far  as  their  terminations  are  concerned,  the  fibres  may  be 
divided  into  an  external,  a  middle,  and  an  internal  layer.  The  posterior  fibres  of  the  ex- 
ternal layer  pass  away  from  the  lower  portion  of  the  rectum,  are  reflected  backward 
along  the  concavity  of  the  sacrum,  and  are  attached  to  the  promontory.  These  fibres, 
which  are  generally  pale,  Sappey  proposes  to  designate  as  retractors  of  the  anus.  A  few 
of  the  posterior  fibres  are  attached  to  the  aponeurosis  and  the  parts  between  the  coccyx 
and  the  promontory.  In  front,  the  external  fibres  are  attached  to  the  aponeurosis  which 
covers  the  vesiculee  seminales,  and  laterally  they  are  inserted  into  the  deep  pelvic  fascia. 
The  termination  of  the  middle  layer  of  the  fibres  is  less  clearly  made  out.  Those  situated  at 
the  sides  of  the  rectum  are  inserted  into  "  a  very  dense  cellulo-fibrous  band,  which,  by  its 
opposite  surface,  gives  insertion  to  a  great  number  of  fibres  of  the  levator  ani."  The 
others  are  many  of  them  continuous  with  the  fibres  of  the  levator  ani  as  they  pass  along 
the  floor  of  the  pelvis.  Some  of  the  fibres  of  the  deep  layer  are  attached  by  little  tendons, 
which  pass  between  the  external  and  the  internal  sphincter,  to  the  deep  portions  of  the 
skin  encircling  the  anus.  The  importance  of  closely  studying  the  attachments  of  these 
fibres  will  be  appreciated  when  we  come  to  treat  of  defaecation. 

Over  the  cascum  and  the  colon,  the  anterior  band  of  muscular  fibres  is  from  one-third 
to  one-half  an  inch  in  width.  The  postero-external  band  is  not  more  than  half  so  wide, 
and  the  postero-internal  band  is  even  narrower.  The  muscular  bands  are  much  shorter 
than  the  canal  itself,  and  their  attachment  to  the  walls  gives  the  intestine  a  peculiar  sac- 
culated  appearance.  That  this  is  produced  by  the  arrangement  of  the  muscular  fibres, 
may  be  demonstrated  by  dividing  them  in  various  places  or  by  removing  them  entirely, 
when  the  canal  may  be  extended  to  double  its  original  length.  Between  the  bands  there 
are  no  longitudinal  muscular  fibres;  but  circular  or  transverse  muscular  fibres  exist 
throughout  the  whole  length  of  the  large  intestine.  In  the  csecum  and  the  colon,  the  cir- 
cular fibres  are  so  pale  and  the  layers  are  so  thin  that  their  presence  is  demonstrated  with 
great  difficulty.  In  the  rectum  they  are  somewhat  more  numerous.  About  an  inch 
above  the  anus,  the  circular  fibres  are  collected  into  a  pretty  well-marked  muscular  ring, 
which  has  been  called  the  internal  sphincter. 

Mucous  Coat. — The  mucous  lining  of  the  large  intestine  presents  several  important 
points  of  difference  from  that  which  is  found  in  the  small  intestine.  It  is  paler,  somewhat 
thicker  and  firmer,  and  is  more  closely  adherent  to  the  subjacent  parts.  In  no  part  of  this 
membrane  are  there  any  folds,  like  those  which  form  the  valvulse  conniventes  of  the  small 
intestine ;  and  the  surface  is  perfectly  smooth  and  free  from  villosities. 

Throughout  the  entire  mucous  membrane,  from  the  ileo-caacal  valve  to  the  anus,  are 
innumerable  orifices  which  lead  to  simple  follicular  glands.  These  structures  resemble  in 
all  respects  the  follicles  of  the  small  intestine,  except  that  they  are  a  little  longer,  owing 
to  the  greater  thickness  of  the  membrane,  are  wider,  and  are  rather  more  numerous. 
Among  these  small  follicular  openings  are  found,  scattered  irregularly  throughout  the 


PHYSIOLOGICAL  ANATOMY   OF  THE  LARGE  INTESTINE.          291 

membrane,  larger  openings  which  lead  to  utricular  glands,  resembling  the  closed  follicles, 
in  general  structure,  except  that  they  have  an  orifice  opening  into  the  cavity  of  the  in- 
testine, which  is  sometimes  so  large  as  to  be  visible  to  the  naked  eye.  The  number  of 
these  glands  is  very  variable,  and  they  are  irregularly  disseminated  throughout  the  intes- 
tine, in  company  with  the  closed  follicles,  except  in  the  rectum,  where  they  are  absent. 
In  the  ca3cum  and  colon,  numerous  isolated,  closed  follicles  are  generally  found,  which 
are  identical  in  structure  with  the  solitary  glands  of  the  small  intestine.  These  are  ex- 
ceedingly variable,  both  in  number  and  size. 

The  mucous  membrane  of  the  rectum,  in  the  upper  three-fourths  of  its  extent,  does 
not  differ  materially  from  that  of  the  colon.  In  the  lower  fourth,  the  fibrous  tissue  by 
which  the  lining  membrane  is  united  to  the  subjacent  muscular  coat  is  loose,  and  the 
membrane,  when  the  canal  is  empty,  is  thrown  into  a  great  number  of  irregular  folds. 
At  the  site  of  the  internal  sphincter,  five  or  six  little  semilunar  valves  have  been  observed, 
with  their  concavities  directed  toward  the  colon.  These  form  an  irregular,  festooned 
line,  which  surrounds  the  canal ;  their  folds,  however,  are  small  and  have  no  tendency 
to  obstruct  the  passage  of  fascal  matters.  The  simple  follicles  are  particularly  abundant 
in  the  rectum,  and  the  membrane  is  constantly  covered  with  a  thin  coating  of  mucus. 
Another  peculiarity  to  be  noted  in  the  mucous  membrane  of  the  lower  portion  of  the 
rectum,  is  its  great  vascularity,  the  veins,  especially,  being  very  numerous. 

Finally,  the  rectum  terminates  in  the  anus,  a  button-hole  orifice,  situated  a  little  in 
front  of  the  coccyx,  which  is  kept  closed  and  somewhat  retracted,  except  during  the  pas- 
sage of  the  faeces,  by  the  powerful  external  sphincter.  This  muscle  is  composed  entirely 
of  red,  or  striated  fibres,  which  are  arranged  in  the  form  of  an  ellipse,  its  long  diameter 
being  antero-posterior. 

It  is  now  almost  universally  admitted  that  the  digestion  of  all  classes  of  alimentary  sub- 
stances is  completed  either  in  the  stomach  or  in  the  small  intestine,  and  that  the  mucous 
membrane  of  the  large  intestine  does  not  secrete  a  fluid  endowed  with  any  well-marked 
digestive  properties.  The  simple  follicles,  the  closed  follicles,  and  the  utricular  glands, 
produce  a  glairy  mucus,  which,  as  far  as  we  know,  serves  merely  to  lubricate  the  canal. 
This  has  never  been  obtained  in  sufficient  quantity  to  admit  of  any  accurate  investigation 
into  its  properties. 

In  studying  the  changes  which  the  alimentary  mass  undergoes  in  its  passage  through 
the  small  intestine,  we  have  seen  that,  in  this  portion  of  the  canal,  the  greatest  part  of  all 
the  nutritive  material  is  not  only  liquefied  but  is  absorbed.  Sometimes  fragments  of  mus- 
cular fibre,  oil-globules,  and  other  matters  in  a  state  of  partial  disintegration,  are  to  be 
detected  in  the  faBces  by  the  microscope ;  but  generally  this  is  either  the  result  of  taking 
an  excessive  quantity  of  these  substances  or  it  depends  upon  some  derangement  of  the 
digestive  apparatus.  When  intestinal  digestion  takes  place  with  regularity,  the  trans- 
formation of  the  alimentary  mass  into  faecal  matter  is  slow  and  gradual.  As  the  con- 
tents of  the  stomach  are  passed  little  by  little  into  the  duodenum,  the  chymous  mass  be- 
comes of  a  bright-yellow  color,  and  its  fluidity  is  increased,  from  the  admixture  of  bile 
and  pancreatic  fluid.  In  passing  along  the  canal,  the  consistence  of  the  mass  gradually 
diminishes,  from  the  absorption  of  its  liquid  portions,  and  the  color  becomes  darker; 
and,  by  the  time  that  the  contents  of  the  ileum  are  ready  to  pass  into  the  caBcum,  the 
greatest  part  of  those  substances  which  we  have  recognized  as  alimentary  principles  , 
have  become  changed  and  absorbed.  The  various  forms  of  starchy  and  saccharine  prin- 
ciples, unless  they  have  been  taken  in  excessive  quantity,  soon  disappear  from  the  in- 
testine ;  and  the  glucose,  which  is  the  result  of  their  digestion,  may  be  recognized  in  the 
blood  of  the  portal  system.  As  a  rule,  fatty  matters  are  not  found  in  the  lower  part  of 
the  ileum,  having  passed  into  the  lacteals  in  the  form  of  an  emulsion.  Neither  fibrin, 
albumen,  nor  caseine,  can  be  detected  in  the  ileum ;  and,  as  we  have  seen,  the  muscular 
substance,  as  recognized  by  its  microscopical  characters,  becomes  gradually  disintegrated 


292  DIGESTION. 

and  is  lost — except  a  few  isolated  fragments  deeply  colored  with  bile — some  time  before 
the  indigestible  residue  passes  into  the  large  intestine. 

In  the  human  subject,  those  portions  of  the  food  which  resist  the  successive  and  com- 
bined action  of  the  different  digestive  secretions  are  derived  chiefly  from  the  vegetable 
kingdom.  Hard,  vegetable  seeds,  the  cortex  of  the  cereals,  spiral  vessels,  and,  in  fine, 
all  parts  which  are  composed  largely  of  cellulose,  pass  through  the  intestinal  canal  with- 
out much  change.  These  substances  form,  in  the  faeces,  the  greatest  part  of  what  can  be 
recognized  as  the  residue  of  matters  taken  as  food.  It  is  well  known  that  an  exclusively 
animal  diet,  particularly  if  the  nutritious  principles  be  taken  in  a  concentrated  and  read- 
ily-assimilable form,  leaves  very  little  undigested  matter  to  pass  into  the  large  intestine, 
and  gives  to  the  fasces  a  character  quite  different  from  that  which  is  observed  in  herbiv- 
orous animals  or  in  man  when  subjected  to  an  exclusively  vegetable  diet.  The  charac- 
ters of  the  residue  of  the  digestion  of  albuminoid  substances  are  not  very  distinct.  As  a 
rule,  none  of  the  albuminoids  are  to  be  recognized  in  the  healthy  fasces  by  the  ordinary 
tests. 

Many  insoluble  inorganic  substances  are  taken  with  the  food  and  appear  unchanged 
in  the  fasces.  The  fasces  of  dogs  fed  exclusively  on  bones,  which  were  formerly  adminis- 
tered internally  as  a  remedy  for  epilepsy,  under  the-name  of  album  Grcecum,  are  composed 
almost  entirely  of  calcareous  matter.  With  regard  to  the  ordinary  inorganic  constituents 
of  the  fasces,  however,  it  is  difficult  to  say  how  much  is  derived  from  the  ingesta  and 
how  much  from  the  different  intestinal  secretions. 

Contents  of  the  Large  Intestine. 

When  the  contents  of  the  small  intestine  have  passed  the  ileo-cascal  valve,  they  be- 
come changed  in  their  general  character,  partly  from  admixture  with  the  secretions  of 
this  portion  of  the  canal,  and  are  then  known  as  the  fasces.  The  most  palpable  of  these 
changes  relate  to  consistence,  color,  and  odor. 

Fascal  matter  has  a  much  firmer  consistence  than  the  contents  of  the  ileum,  which  is 
due  to  a  constant  absorption  of  the  liquid  portions.  As  a  rule,  the  consistence  is  great  in 
proportion  to  the  length  of  time  that  the  fasces  remain  in  the  large  intestine  ;  and  this  is 
variable  in  different  persons  and  in  the  same  person,  in  health,  depending  somewhat  upon 
the  character  of  the  food.  The  color  changes  from  the  yellow,  more  or  less  bright, 
which  is  observed  in  the  ileum,  to  the  dark  yellowish-brown,  characteristic  of  the  fasces. 
Although  the  bile-pigment  cannot  usually  be  recognized  by  the  ordinary  tests,  it  is  this 
which  gives  to  the  contents  of  the  large  intestine  their  peculiar  color,  which  is  lost  when 
the  bile  is  not  discharged  into  the  duodenum.  In  a  specimen  of  healthy  human  fasces, 
which  had  been  dried,  extracted  with  alcohol,  the  alcoholic  solution  precipitated  wi!;li 
ether,  and  the  precipitate  dissolved  in  distilled  water,  we  failed  to  detect  the  slightest 
trace  of  the  biliary  salts  by  Pettenkofer's  test.  In  a  watery  extract  of  the  same  fasces, 
the  addition  of  nitric  acid  also  failed  to  show  the  reaction  of  the  coloring  matter  of  the 
bile.  The  color  of  the  fasces,  however,  has  been  found  to  vary  considerably  with  the  diet. 

The  odor  of  the  fasces,  which  is  characteristic  and  quite  different  from  that  of  the 
contents  of  the  ileum,  is  somewhat  variable  and  is  due  in  part  to  the  peculiar  decompo- 
sition of  the  residue  of  the  food,  in  part  to  the  decomposition  of  the  bile,  and  in  part  to 
matters  secreted  by  the  mucous  membrane  of  the  colon  and  of  the  glands  near  the  anus. 

The  entire  quantity  of  fasces  in  the  twenty-four  hours  was  found  by  Wehsarg  to  be 
about  4'6  ounces.  This  was  the  mean  of  seventeen  observations ;  the  largest  quantity 
being  10'8  ounces,  and  the  smallest,  2'4  ounces. 

The  reaction  of  the  fasces  is  undoubtedly  very  variable,  depending  chiefly  upon  the 
character  of  the  food.  Marcet  found  the  human  excrements  always  alkaline.  Wehsarg, 
on  the  other  hand,  found  the  reaction  generally  acid,  but  very  frequently,  alkaline  or 
neutral. 


CONTENTS   OF  THE  LARGE  INTESTINE.  293 

The  first  accurate  analyses  of  the  faeces  were  made  by  Berzelius ;  but  the  great  ad- 
vances which  have  been  made  in  physiological  chemistry  since  that  time  have  enabled 
later  observers  to  arrive  at  results  much  more  definite  and  satisfactory.  Marcet  has  lately 
discovered  a  crystallizable  substance  peculiar  to  the  human  faeces ;  and  we  have  recently 
shown  that  probably  the  most  important  excrement! tious  principle  discharged  by  the 
rectum  is  derived  from  the  bile  and  is  a  peculiar  modification  of  cholesterine.  Most  of 
our  statements  concerning  the  composition  of  the  faeces  in  health  will  be  derived  from 
the  researches  of  Wehsarg  and  of  Marcet  and  from  our  own  observations. 

The  proportions  of  water  and  solid  matter  in  the  faeces  is  variable.  Berzelius  found, 
in  the  healthy  human  faeces,  V3'3  parts  of  water  and  26'7  parts  of  solid  residue.  The 
average  of  seventeen  observations  by  Wehsarg  was  precisely  the  same.  In  the  observa- 
tions of  Wehsarg,  the  mean  quantity  of  solid  matter  discharged  in  the  fasces  in  the  twenty- 
four  hours  was  463  grains,  the  extremes  being  882'8  grains  and  251-6  grains.  The  pro- 
portion of  undigested  matters  in  the  solid  residue  was  very  small,  averaging  but  little 
more  than  ten  per  cent.,  the  mean  quantity  in  the  twenty-four  hours  in  ten  observations 
being  but  52'5  grains.  This  was  found,  however,  to  be  exceedingly  variable  ;  the  largest 
quantity  being  126*5  grains,  and  the  smallest,  12'5  grains. 

Microscopical  examination  of  the  faeces  reveals  the  various  vegetable  and  animal  struct- 
ures which  we  have  referred  to  as  escaping  the  action  of  the  digestive  fluids.  Wehsarg 
also  found  a  "finely  divided  faecal  matter"  of  indefinite  structure,  but  containing  partly 
disintegrated  intestinal  epithelium.  Crystals  of  cholesterine  were  never  observed.  When- 
ever the  matter  is  neutral  or  alkaline,  crystals  of  the  ammonio-magnesian  phosphate  are 
found.  Mucus  is  also  found  in  variable  quantity  in  the  fasces,  with  desquamated  epithe- 
lium, and  a  few  leucocytes. 

The  quantity  of  inorganic  salts  in  the  faeces  is  not  great.  In  addition  to  the  ammonio- 
magnesian  phosphate,  phosphate  of  magnesia,  phosphate  of  lime,  and  a  small  quantity  of 
iron  have  been  found.  The  chlorides  are  either  absent  or  are  present  only  in  small 
quantity. 

Marcet  has  pretty  generally  found  in  the  human  faeces  a  substance  possessing  the 
characters  of  margaric  acid,  and  volatile  fatty  acids;  the  latter  free,  however,  from 
butyric  acid.  Cystine  is  mentioned  as  an  occasional  constituent  of  the  faeces.  He  also 
found  a  coloring  matter,  which  is  probably  a  modification  of  biliverdine. 

In  1854,  Marcet  described  a  new  substance  in  the  human  fasces,  which  he  called  excre- 
tine,  and  an  acid  called  excretoleic  acid,  which  he  supposed  to  be  a  compound  of  excre- 
tine.  These  substances  and  the  one  which  we  described  in  1862,  under  the  name  of  ster- 
corine,  are,  as  far  as  we  know,  the  only  principles  that  have  been  recognized  as  charac- 
teristic of  the  normal  faeces ;  and  the  stercorine  we  have  found  to  be  one  of  the  most  dis- 
tinct and  important  of  the  excrementitious  principles  in  the  body.  The  relations  of 
excretine  to  the  process  of  disassimilation  of  the  tissues  have  not  been  so  clearly  indicated. 

Excretine  and  Excretoleic  Acid.—  Excretine  was  obtained  by  Marcet  from  the  healthy 
human  fasces  in  the  following  way  :  The  fseces  were  first  treated  with  boiling  alcohol 
until  nothing  more  could  be  extracted.  This  alcoholic  solution  was  acid  and  deposited 
a  sediment  on  cooling.  Milk  of  lime  was  then  added  to  the  solution,  producing  a  yel- 
lowish-brown precipitate  and  leaving  the  fluid  of  a  clear  straw-color.  The  precipitate 
was  then  collected  on  a  filter,  dried,  afterward  agitated  with  ether  and  filtered,  forming 
a  clear,  yellow  solution.  In  from  one  to  three  days,  beautiful,  long,  silky  crystals  of  ex- 
cretine were  formed,  generally  collected  into  tufts  adhering  to  the  sides  of  the  vessel. 
Examined  by  the  microscope,  these  were  found  to  consist  of  acicular,  four-sided  prisms 
of  variable  size.  This  substance  is  insoluble  in  water,  slightly  soluble  in  cold  alcohol,  but 
is  very  soluble  in  ether  and  in  hot  alcohol.  Its  alcoholic  solutions  are  faintly  though  dis- 
tinctly alkaline.  Its  fusing-point  is  from  203°  to  205°  Fahr.  It  may  be  boiled  with 
potash  for  hours  without  undergoing  saponification.  Apparently,  the  quantity  of  excre- 


294  DIGESTION. 

tine  contained  in  the  fasces  is  not  very  great,  as  only  12*6  grains  were  obtained  by  Marcet 
from  nine  evacuations. 

We  have  very  little  definite  information  concerning  the  production  of  excretine. 
Marcet  examined,  on  one  occasion,  the  contents  of  the  small  intestine  of  a  man  that  had 
died  of  disease  of  the  heart,  without  finding  any  excretine.  It  is  probable  that  this 
principle  is  formed  in  the  large  intestine,  although  farther  observations  are  wanting  on 
this  point. 

The  substance  called  excretoleic  acid  is  very  indefinite  in  its  composition  and  proper- 
ties. It  is  described  as  an  olive-colored  fatty  acid,  insoluble  in  water,  non-saponifiable, 
and  very  soluble  in  ether  and  in  hot  alcohol.  It  fuses  at  from  77°  to  79°  Fahr. 

Stercorine. — This  principle,  which  we  discovered  in  the  fasces  in  1862,  was  described 
by  Boudet  in  1833,  as  existing  in  excessively  minute  quantity  in  the  serum  of  the  blood, 
and  was  called  by  him  seroline.  As  we  found  it  to  be  the  most  abundant  and  character- 
istic constituent  of  the  stercoraceous  matter,  we  proposed  to  call  it  stercorine ;  particu- 
larly as  our  researches  led  us  to  the  opinion  that  it  really  does  not  exist  in  the  serum,  but 
is  formed  from  cholesterine  by  the  processes  employed  for  its  extraction. 

Stercorine  may  be  extracted  in  the  following  way  :  The  fasces  are  first  evaporated  to 
dryness,  pulverized,  and  treated  with  ether.  The  ether-extract  is  then  passed  through 
animal  charcoal,  fresh  ether  being  added  until  the  original  quantity  of  the  ether-extract 
has  passed  through.  It  is  impossible  to  decolorize  entirely  the  solution  by  this  process  ; 
but  it  should  pass  through  perfectly  clear  and  of  a  pale-amber  color.  The  ether  is  then 
evaporated,  and  the  residue  is  extracted  with  boiling  alcohol.  This  alcoholic  solution  is 
evaporated,  and  the  residue  is  treated  with  a  solution  of  caustic  potash  for  one  or  two 
hours  at  a  temperature  a  little  below  the  boiling-point,  by  which  all  the  saponifiable  fats 
are  dissolved.  The  mixture  is  then  largely  diluted  with  water,  thrown  upon  a  filter,  and 
is  washed  until  the  fluid  which  passes  through  is  neutral  and  perfectly  clear.  The  filter  is 
then  carefully  dried,  and  the  residue  is  washed  out  with  ether.  The  ether  solution  is  then 
evaporated,  extracted  with  boiling  alcohol,  and  the  alcoholic  solution  is  evaporated.  The 
residue  of  this  last  evaporation  is  composed  of  pure  stercorine. 

When  first  obtained,  stercorine  is  a  clear,  slightly  amber,  oily  substance,  about  the 
consistence  of  Canada  balsam  used  in  microscopical  preparations.  In  four  or  five  .days 
it  begins  to  show  the  characteristic  crystals.  These  are  few  in  number  at  first,  but  soon 
the  entire  mass  assumes  a  crystalline  form.  In  one  analysis,  we  obtained,  from  seven 
and  a  half  ounces  of  normal  human  fasces  (the  entire  quantity  for  the  twenty -four  hours), 
10-417  grains  of  stercorine,  the  extract  consisting  of  nothing  but  crystals.  This  was  all 
the  stercorine  to  be  extracted  from  the  regular,  daily  evacuation  of  a  healthy  male 
twenty-six  years  of  age  and  weighing  about  one  hundred  and  sixty  pounds.  In  the  ab- 
sence of  other  investigations,  the  daily  quantity  of  this  substance  excreted  may  be  as- 
sumed to  be  not  far  from  ten  grains. 

In  many  regards,  stercorine  bears  a  close  resemblance  to  cholesterine.  It  is  neutral, 
inodorous,  and  insoluble  in  water  and  in  a  solution  of  potash.  It  is  soluble  in  ether  and  in 
hot  alcohol,  but  is  almost  insoluble  in  cold  alcohol.  A  red  color  is  produced  when  it  is 
treated  with  strong  sulphuric  acid.  It  may  be  easily  distinguished  from  cholesterine, 
however,  by  the  form  of  its  crystals.  It  fuses  at  a  low  temperature,  96*8°  Fahr.,  while 
cholesterine  fuses  at  293°  Fahr. 

Stercorine  crystallizes  in  the  form  of  thin,  delicate  needles,  frequently  mixed  with 
clear,  rounded  globules,  which  are  probably  composed  of  the  same  substance  in  a  non- 
crystalline  form.  When  the  crystals  are  of  considerable  size,  the  borders  near  their  ex- 
tremities are  split  longitudinally  for  a  short  distance.  The  crystals  are  frequently  ar- 
ranged in  bundles,  as  in  Fig.  81,  in  which  they  are  represented  as  seen  under  a  T\-inch 
objective.  In  Fig.  82,  the  crystals  are  represented  as  seen  under  a  £-inch  objective. 
These  crystals  cannot  be  confounded  with  excretine,  which  crystallizes  in  the  form  of 


CONTENTS   OF  THE  LARGE  INTESTINE. 


295 


regular,  four-sided  prisms,  or  with  the  thin  rhomboidal  or  rectangular  tablets  of 
cholesterine.  They  are  identical  with  the  crystals  of  seroline  figured  by  Robin  and 
Ver-diel. 

There  can  be  no  doubt  with  regard  to  the  origin  of  the  stercorine  which  exists  in  the 
faeces.  We  have  found  that,  whenever  the  bile  is  not  discharged  into  the  duodenum  as 
is  probably  the  case,  for  a  time,  in  icterus  accompanied  with  clay-colored  evacuations, 
stercorine  is  not  to  be  discovered  in  the  dejections.  In  one  case  of  this  kind,  in  which 
the  faeces  were  subjected  to  examination,  the  matters  extracted  with  hot  alcohol  were 
entirely  dissolved  by  boiling  for  fifteen  minutes  with  a  solution  of  potasht  showing  the 


FIG.  81.—  Stercorine  from  the  human  fceces. 


FIG.  82. — Stercorine  from  the  same  specimen  after  it 
had  been  melted,  placed  upon  a  glass  slide,  cov- 
ered with  thin  glass,  and  allowed  to  crystallize. 

The  crystallization  was  very  slow,  occupying  some  weeks- 


absence  of  cholesterine  and  stercorine.  In  another  examination  of  the  faeces  from  this 
patient,  made  nineteen  days  after,  when  the  icterus  had  almost  entirely  disappeared  and 
the  evacuations  had  become  normal,  stercorine  was  discovered.  These  facts  show  that 
the  cholesterine  of  the  bile,  in  its  passage  through  the  intestine,  is  changed  into  ster- 
corine. Both  of  these  principles  are  crystalline,  non-saponifiable,  are  extracted  by  the 
same  chemical  manipulations,  and  behave  in  the  same  way  when  treated  with  sulphuric 
acid.  The  stercorine  must  be  regarded  as  a  slight  modification  of  cholesterine,  which 
is  the  excrementitious  principle  of  the  bile.1 

We  have  found  that  the  change  of  cholesterine  into  stercorine  is  directly  connected 
with  the  process  of  intestinal  digestion.  If  an  animal  be  kept  for  some  days  without 
food,  cholesterine  will  be  found  in  the  faeces,  although,  for  a  few  days,  stercorine  is  also 
present.  It  is  a  fact  generally  recognized  by  those  who  have  analyzed  the  faeces,  that 
cholesterine  does  not  exist  in  the  normal  evacuations ;  but,  whenever  digestion  is  arrested, 
the  bile  being  constantly  discharged  into  the  duodenum,  cholesterine  is  found  in  large  quan- 
tity. For  example,  in  hibernating  animals,  cholesterine  is  always  present  in  the  faaces. 
The  same  is  true  of  the  contents  of  the  intestines  during  foatal  life ;  the  meconium  always 

1  Our  researches  into  the  functions  of  cholesterine  have  left  no  doubt  that  this  is  an  excrementitious  principle 
hardly  second  in  importance  to  urea.  We  have  found  that  cholesterine  is  always  more  abundant  in  the  blood  com- 
ing from  the  brain  than  in  the  blood  of  the  general  arterial  system  or  in  the  venous  blood  from  other  parts ; 
that  its  quantity  is  hardly  appreciable  in  venous  blood  from  ihe  paralyzed  side  in  hemiplegia;  and  that  it  is  sep- 
arated from  the  blood  by  the  liver.  We  have  also  shown  that,  in  cases  of  serious  structural  disease  of  the  liver 
accompanied  by  symptoms  pointing  to  blood-poisoning,  cholesterine  accumulates  in  the  blood,  constituting  a  con- 
dition which  we  have  called  cholestersemia.  This  subject  will  be  fully  discussed  under  the  head  of  excretion.  For 
a  full  account  of  our  observations  upon  the  functions  of  cholesterine,  see  The  American  Journal  of  the  Medical 
Sciences,  October,  1362. 


296  DIGESTION. 

containing  a  large  quantity  of  cholesterine,  which  disappears  from  the  evacuations  when 
the  digestive  function  becomes  established. 

Movements  of  the  Large  Intestine. 

Movements  of  the  general  character  which  we  have  noted  in  the  small  intestine  occur 
in  the  large  intestine,  although  the  peculiarities  in  the  arrangement  of  the  muscular  fibres 
and  the  more  solid  consistence  of  the  contents  render  these  movements  in  the  large  in- 
testine somewhat  distinctive.  In  all  instances  where  the  movements  have  been  observed 
in  the  human  subject  or  in  the  lower  animals,  they  have  been  found  to  be  less  vigorous  and 
rapid  than  the  contractions  of  the  small  intestine.  Indeed,  when  the  abdominal  organs 
are  exposed,  either  in  a  living  animal  or  immediately  after  death,  movements  of  the  large 
intestine  are  generally  not  observed,  except  on  the  application  of  mechanical  or  galvanic 
irritation ;  and  they  are  then  more  circumscribed  and  are  much  less  marked  than  in  any 
other  part  of  the  alimentary  canal.  In  the  rabbit,  in  which  the  colon  is  very  large,  the 
few  spontaneous  movements  which  are  sometimes  seen  on  opening  the  abdomen  immedi- 
ately after  death  are  feeble  and  irregular,  particularly  in  the  caecum.  That  the  fa3ces  re- 
main for  a  considerable  time  in  some  of  the  sacculated  pouches  of  the  colon,  is  evident 
from  the  appearance  which  they  sometimes  present  of  having  been  moulded  to  the  shape 
of  the  canal.  This  appearance  is  frequently  observed  in  the  dejections,  which  are  then 
said  to  be  u  figured." 

In  the  caecum,  the  pressure  of  matters  received  from  the  ileum  forces  the  mass  onward 
into  the  ascending  colon,  and  the  contractions  of  its  muscular  fibres  are  undoubtedly 
slight  and  inefficient.  Once  in  the  colon,  it  is  easy  to  see  how  the  contractions  of  the 
muscular  structure  (the  longitudinal  bands  shortening  the  canal,  and  the  transverse  fibres 
contracting  below  and  relaxing  above)  are  capable  of  passing  the  faecal  mass  slowly 
onward.  Although  the  transverse  fibres  are  thin  and  seemingly  of  little  power,  their  con- 
traction is  undoubtedly  sufficient  to  empty  the  sacculi,  when  assisted  by  the  movements  of 
the  longitudinal  fibres,  especially  as  the  canal  is  never  completely  filled  and  the  fasces  are 
frequently  in  the  form  of  small,  moulded  lumps.  By  these  slow  and  gradual  movements, 
the  contents  of  the  large  intestine  are  passed  toward  the  sigmoid  flexure  of  the  colon, 
where  they  are  arrested  until  the  period  arrives  for  their  final  discharge.  The  time 
occupied  in  the  passage  of  the  fseces  through  the  ascending,  transverse,  and  descending 
colon  is  undoubtedly  variable  in  different  persons,  as  we  find  great  variations  in  the  inter- 
vals between  the  acts  of  defecation.  During  their  passage  along  the  colon,  the  contents 
of  the  canal  assume  more  and  more  of  the  normal  fecal  consistence  and  odor  and  become 
slightly  coated  with  the  mucous  secretion  of  the  parts. 

It  has  been  pretty  conclusively  shown  that  the  accumulation  of  fseces  generally  takes 
place  in  the  sigmoid  flexure  of  the  colon ;  for,  under  normal  conditions,  the  rectum  is  found 
empty  and  contracted.  This  part  of  the  colon  is  much  more  movable  than  other  por- 
tions and  is  better  calculated  as  a  receptacle  for  fseces.  At  certain  tolerably  regular  in- 
tervals, the  faecal  matter  is  passed  into  the  rectum  and  is  then  almost  immediately  dis- 
charged from  the  body. 

Defalcation. 

In  health,  expulsion  of  faecal  matters  takes  place  with  regularity  generally  once  in 
the  twenty-four  hours.  This  rule,  however,  is  by  no  means  invariable,  and  dejections 
may  habitually  occur  twice  in  the  day  or  every  second  or  third  day,  within  the  limits  of 
perfect  health.  It  is  well  known  that  habit  has  a  great  influence  upon  the  regularity  of 
defascation ;  and  sometimes,  in  cases  of  irregularity,  physicians  have  recommended  pa- 
tients to  make  an  effort  to  void  the  fseces  at  a  certain  time  every  day,  this  practice  being 
frequently  followed  by  the  best  results.  At  the  time  when  defecation  ordinarily  takes 
place,  a  peculiar  sensation  is  experienced  calling  for  an  evacuation  of  the  bowels ;  and, 
if  this  be  disregarded,  the  desire  may  pass  away,  after  a  little  time,  the  act  becoming 


DEFECATION. 


297 


impossible.  Under  these  circumstances,  it  is  probable  that  the  faeces  are  passed  out  of 
the  rectum  by  antiperistaltic  action. 

The  condition  which  immediately  precedes  the  desire  for  defecation  is  probably  the 
descent  of  the  contents  of  the  sigmoid  flexure  of  the  colon  into  the  rectum.  It  was  for- 
merly thought  that  the  faeces  constantly  accumulated  in  the  dilated  portion  of  the  rec- 
tum, where  they  remained  until  an  evacuation  took  place  ;  but  the  arguments  of  O'Beirne 
against  such  a  view  are  conclusive.  He  has  demonstrated,  by  numerous  explorations  in 
the  human  subject,  that,  under  ordinary  conditions,  the  rectum  is  contracted  and  con- 
tains neither  fa3ces  nor  gas.  It  is,  indeed,  a  fact  familiar  to  every  surgeon,  ,that  the  rec- 
tum usually  contains  nothing  which  can  be  reached  by  the  finger  in  physical  examina- 
tions, and  that  paralysis  or  section  of  the  muscles  which  close  the  anus  by  no  means  in- 
volves, necessarily,  a  constant  passage  of  faecal  matter.  O'Beirne  not  only  found  the  rectum 
empty  and  presenting  a  certain  amount  of  resistance  to  the  passage  of  injected  fluids,  but, 
on  passing  a  stomach-tube  into  the  bowel,  after  penetrating  from  six  to  eight  inches  it 
passed  into  a  space  in  which  its  extremity  could  be  moved  with  great  freedom,  and  there 
was  instantly  a  rush  of  flatus,  of  fluid  fasces,  or  of  both,  through  the  tube.  In  some  in- 
stances in  which  nothing  escaped  through  the  tube,  the  instrument  conveyed  to  the  hand 
an  impression  of  having  entered  a  solid  mass ;  and  on  being  withdrawn  it  contained  solid 
fseces  in  its  upper  portion.  According  to  this  observer,  the  sensation  which  leads  to  an 
effort  to  discharge  the  faeces  is  due  to  the  accumulation  of  matters  in  the  sigmoid 
flexure,  which  finally  present  at  the  contracted  portion  of  the  rectum  just  at  its  com- 
mencement. This  constriction,  situated  at  the  most  superior  portion  of  the  rectum,  is 
sometimes  spoken  of  as  the  sphincter  of  O'Beirne. 

The  above  is  undoubtedly  the  mechanism  of  the  descent  of  fascal  matter  into  the 
rectum  in  defaecation,  as  the  act  is  usually  performed  ;  but,  under  certain  circumstances, 
faeces  must  accumulate  in  the  dilated  portion  of  the  rectum.  Ordinarily,  the  discharge 
of  faeces  only  takes  place  after  the  efforts  have  been  continued  for  a  certain  time  ;  and 
when  the  evacuation  is  "  figured,"  the  whole  length  discharged  frequently  exceeds  so 
much  the  length  of  the  rectum,  that  it  is  evident  that  a  portion  of  it  must  have  come 
from  the  colon.  O'Beirne  states,  indeed,  that  he  has  frequently  examined  the  rectum  at 
the  moment  when  a  moderate  inclination  to  go  to  stool  is  felt,  and  found  it  empty  and  con- 
tracted. But,  in  cases  in  which  the  faeces  are  very  fluid,  or  when  the  call  for  an  evacua- 
tion has  not  been  regarded  and  has  become  imperative,  the  immediate  discharge  of  mat- 
ters when  the  sphincter  is  relaxed  shows  that  the  rectum  has  been  more  or  less  distended. 
In  many  persons  of  constipated  habit,  and  particularly  in  old  subjects,  the  rectum  may 
become  the  seat  of  large  accumulations  of  hardened  and  impacted  faeces;  but  this  is  a 
pathological  condition. 

The  sensation  which  ordinarily  precedes  and  gives  rise  to  the  evacuation  of  faacal  mat- 
ter is  peculiar  and  very  variable  in  intensity.  When  this  sensation  is  well  marked  but  not 
excessive,  it  is  probably  due  to  the  presence  of  faacal  matter  in  the  rectum,  not  in  suffi- 
cient quantity,  however,  to  press  forcibly  upon  the  sphincter.  Pressure  upon  the  rectum 
from  any  cause,  or  irritation  of  its  mucous  membrane,  is  apt  to  give  rise  to  this  peculiar 
sensation  to  a  very  marked  degree.  In  some  diseases,  the  exaggeration  of  this  sensation, 
then  called  tenesmus,  is  very  distressing. 

In  the  process  of  defaecation,  the  first  act  is  the  passage,  by  peristaltic  contractions, 
of  the  contents  of  the  sigmoid  flexure  of  the  colon  through  the  slightly-constricted  open- 
ing of  the  rectum  into  its  dilated  portion  below.  The  fgecal  matter,  however,  is  not  al- 
lowed to  remain  in  this  situation,  but  it  passes  into  the  lower  portion  of  the  rectum,  in 
obedience  to  the  contractions  of  its  muscular  coat,  assisted  by  the  action  of  the  abdomi- 
nal muscles  and  the  diaphragm.  The  circular  fibres  of  the  rectum  undergo  the  ordinary 
peristaltic  contraction  ;  and  the  action  of  the  longitudinal  fibres  is  to  render  the  rectum 
shorter  and  more  nearly  straight.  The  internal  and  the  external  sphincter  present  a  cer- 
tain amount  of  resistance  to  the  discharge  of  the  faaces,  more  particularly  the  external 


298  DIGESTION. 

sphincter,  which  is  a  striated  muscle  of  considerable  power.  There  is  always,  however, 
a  voluntary  relaxation  of  this  muscle,  or  rather  a  cessation  of  its  semi-voluntary  con- 
traction, which  immediately  precedes  the  expulsive  act.  The  dilatation  of  the  anus  is 
also  facilitated  by  the  action  of  the  levator  ani,  which  arises  from  the  posterior  surface 
of  the  body  and  ramus  of  the  pubis,  the  inner  surface  of  the  spine  of  the  ischium,  and  a 
line  of  fascia  between  these  two  points,  passes  downward,  and  is  inserted  into  the  me- 
dian raphe  of  the  perineum  and  the  sides  of  the  rectum,  the  fibres  uniting  with  those  of 
the  sphincter.  While  this  muscle  forms  a  support  for  the  pelvic  organs  during  the  act 
of  straining,  it  steadies  the  end  of  the  rectum,  and,  by  its  contractions,  favors  the  relaxa- 
tion of  the  sphincter  and  draws  the  anus  forward. 

The  action  of  the  diaphragm  and  the  abdominal  muscles  is  very  simple.  They  merely 
compress  the  abdominal  organs,  and  consequently  those  contained  in  the  pelvis,  and  as- 
sist in  the  expulsion  of  the  contents  of  the  rectum.  The  diaphragm  is  the  most  impor- 
tant of  the  voluntary  muscles  concerned  in  this  process;  and,  during  the  act  of  straining, 
the  lungs  are  moderately  filled  and  respiration  is  interrupted.  The  vigor  of  these  efforts 
depends  greatly  upon  the  consistence  of  the  fascal  mass,  very  violent  contractions  being 
frequently  required  for  the  expulsion  of  hardened  faeces  after  long  constipation.  Al- 
though more  or  less  straining  generally  takes  place,  the  contractions  of  the  muscular 
coats  of  the  rectum  are  frequently  competent  of  themselves  to  expel  the  faeces,  espe- 
cially when  they  are  soft.  This  can  be  shown  by  arresting  all  voluntary  muscular  action 
during  an  easy  act  of  defecation,  when  the  faeces  may  be  passed  by  contractions  of  the 
rectum  alone. 

By  a  combination  of  the  movements  above  described,  the  floor  of  the  perineum  is 
pressed  outward,  the  anus  is  dilated,  the  sharp  bend  in  the  lower  part  of  the  rectum  is 
brought  more  into  line  with  the  rest  of  the  canal,  and  a  portion  of  the  contents  of  the 
rectum  is  expelled.  Very  soon,  however,  the  passage  of  faeces  is  interrupted  by  a  con- 
traction of  the  levator  ani  and  the  sphincter,  by  which  the  anus  is  suddenly  and  rather 
forcibly  retracted.  This  muscular  action  may  be  effected  voluntarily;  but,  after  the 
sphincter  has  been  dilated  for  a  time,  the  evacuation  is  interrupted  in  this  way,  notwith- 
standing all  efforts  to  oppose  it.  After  a  time,  another  portion  of  fasces  is  discharged, 
until  the  matters  have  ceased  to  pass  out  of  the  sigmoid  flexure  and  the  rectum  has 
been  emptied.  The  mucous  membrane  of  the  rectum,  which  is  rather  loosely  held  to 
the  subjacent  tissue,  is  slightly  prolapsed  during  an  evacuation,  but  it  returns  shortly  after 
the  act  has  been  completed. 

Very  little  need  be  said  concerning  the  influence  of  the  nervous  system  on  the  move- 
ments concerned  in  defsecation.  The  non-striated  muscular  fibres  which  form  the  mus- 
cular coat  of  the  rectum  are  supplied  with  nerves  from  the  sympathetic  system ;  and  to 
the  external  sphincter  are  distributed  filaments  from  the  last  sacral  pair  of  the  spinal 
nerves.  These  nerves  bring  the  sphincter  to  a  certain  degree  under  the  control  of  the 
will  and  impart  likewise  the  property  of  tonic  contraction,  by  which  the  anus  is  kept 
constantly  closed. 

Gases  found  in  the  Alimentary  Canal. 

In  the  human  subject,  a  certain  quantity  of  gas  is  generally  found  in  the  stomach  and 
in  the  small  and  large  intestine.  The  most  accurate  analyses  of  these  gases,  as  they  may 
be  supposed  to  exist  in  the  human  subject  in  health,  are  those  of  Magendie  and  Chev- 
reul,  who  had  the  opportunity  of  examining  the  bodies  of  several  criminals  immediately 
after  execution. 

The  gases  in  the  stomach  appear  to  have  no  definite  function.  They  generally  exist 
in  very  small  quantity,  and  they  are  sometimes  absent.  The  oxygen  and  nitrogen  are  de- 
rived from  the  little  bubbles  of  air  which  are  incorporated  with  the  alimentary  bolus  dur- 
ing mastication  and  insalivation.  The  other  gases  are  probably  evolved  from  the  food 
during  digestion ;  at  least,  there  is  no  satisfactory  evidence  that  they  are  produced  in  any 


GASES  CONTAINED  IN  THE   STOMACH,  SMALL  INTESTINE,  ETC.    299 

other  way.  Magendie  and  Chevreul  collected  and  analyzed  a  small  quantity  of  gas  from 
the  stomach  of  an  executed  criminal  a  short  time  after  death  and  ascertained  that  it  had 
the  following  composition : 

Gases  contained  in  the  Stomach. 

Oxygen H-QQ 

Carbonic  acid 14-00 

Pure  hydrogen 3.55 

Nitrogen 71-45 


100-00 

Magendie  and  Chevreul  found  three  different  gases  in  the  small  intestine.  Their  ex- 
aminations were  made  upon  three  criminals  soon  after  execution.  The  first  was  twenty- 
four  years  of  age,  and,  two  hours  before  execution,  had  eaten  bread  and  Gruy£re  cheese 
and  had  drunk  red  wine  and  water.  The  second,  who  was  executed  at  the  same  time,  was 
twenty -three  years  of  age,  and  the  conditions  as  regards  digestion  were  the  same.  The 
third  was  twenty-eight  years  of  age,  and,  four  hours  before  death,  he  ate  bread,  beef,  and 
lentils,  and  drank  red  wine  and  water.  The  following  was  the  result  of  the  analyses  : 


Gases  contained  in  the  Small  Intestine. 


First  Criminal 

Carbonic  acid 24'39 

Pure  hydrogen 55'53. . .  . 

Nitrogen 20'08 


Second  Criminal.  Third  Criminal. 

40'00 25-00 

61-15 8-40 

8-85.  .  .  66-60 


100-00 


100-00 


100-00 


No  oxygen  was  found  in  either  of  the  examinations,  and  the  quantities  of  the  other 
gases  were  so  variable  as  to  lead  to  the  supposition  that  their  proportion  is  not  at  all  defi- 
nite. We  have  already  alluded  to  the  mechanical  function  of  these  gases  in  intestinal 
digestion. 

In  the  large  intestine,  the  constitution  of  the  gases  presented  the  same  variability  as 
in  the  small  intestine.  Carburetted  hydrogen  was  found  in  all  of  the  analyses.  In  the 
large  intestine  of  the  first  criminal  and  in  the  rectum  of  the  third,  were  found  traces  of 
sulphuretted  hydrogen.  The  following  is  the  result  of  the  analyses  in  the  cases  just 
cited.  In  the  third,  the  gaseous  contents  of  the  caecum  and  the  rectum  were  analyzed 
separately  : 

Gases  contained  in  the  Large  Intestine. 


First  Criminal. 

Second  Criminal. 

Third  Criminal. 

Third  Criminal. 

Carbonic  acid  

43-50 

70-00 

Caecum. 
12-50 

Kectum. 
42-86 

Carburetted  hydrogen  and  traces  of  sul- 
phuretted hydrogen 

5'47 

Pure  hydrogen  and  carburetted   hydro- 
eren  . 

11-60 

11-18 

Pure  hydrogen  

7-50 

Carburetted  hydrogen  

12-50 

Nitrogen  

51'03 

18-40 

67-50 

45-96 

100-00 

100-00 

100-00 

100-00 

Origin  of  the  Intestinal  Gases. — With  our  present  information  on  this  subject,  the 
most  reasonable  view  to  take  of  the  origin  of  the  gases  normally  found  in  the  intestines 
is  that  they  are  given  off  from  the  articles  of  food  in  their  various  stages  of  digestion  and 


300  ABSORPTION. 

decomposition.  That  this  is  the  principal  source  of  the  intestinal  gases,  there  can  be  no 
doubt;  and  it  is  well  known  that  certain  articles  of  food,  particularly  vegetables,  gen- 
erate much  more  gas  than  others.  The  principal  gases  found  in  the  intestinal  canal  may 
all  be  obtained  from  the  food.  Some  of  them,  as  hydrogen  and  carburetted  hydrogen, 
do  not  exist  in  the  blood  ;  and  it  is  difficult  to  conceive  how  they  can  be  generated  in  the 
intestine  except  by  decomposition  of  some  of  the  articles  of  food.  Hydrogen  and  its 
compounds  are  always  found  in  quantity  in  the  small  and  the  large  intestine. 

It  is  said  that  gas  is  sometimes  found  in  the  intestines  of  the  foetus,  and  that  it  may 
be  generated  in  a  loop  of  intestine  in  a  living  animal,  after  a  portion  of  the  canal  has  been 
drawn  out,  isolated  by  ligatures,  freed  from  its  liquid  and  gaseous  contents,  and  returned 
to  the  abdomeu.  In  some  diseased  conditions,  also,  it  is  very  common  for  the  abdomen 
to  become  rapidly  tympanitic,  the  gas  being  generated  so  quickly  that  its  presence  is  not 
easily  explained  by  supposing  it  to  be  evolved  by  decomposition  of  the  ingesta.  It  has, 
indeed,  been  supposed  that  the  intestinal  mucous  membrane  is  capable  of  secreting  gases 
as  well  as  liquids ;  but  there  do  not  appear  to  be  any  positive  facts  in  support  of  this 
view.  No  doubt  some  of  the  gases  which  may  be  formed  in  the  intestine  are  capable 
of  absorption.  It  is  impossible  to  say,  however,  that  even  the  gases  normally  held  in 
solution  in  the  blood,  namely,  oxygen,  nitrogen,  and  carbonic  acid,  are  exhaled  from  the 
blood  into  the  intestinal  cavity.  Oxygen  is  never  given  off  in  this  way,  for  this  gas  has 
been  found  only  in  the  stomach  and  is  there  derived  from  air  which  has  been  swallowed. 
With  regard  to  the  origin  of  the  other  gases  found  in  the  intestine  under  the  peculiar 
circumstances  just  mentioned,  in  which  they  are  apparently  generated  with  much  rapidity, 
there  are  not  sufficient  data  to  enable  us  to  form  an  intelligent  opinion. 


CHAPTER   X. 

ABSORPTION— LYMPH  AND  CHYLE. 

General  considerations  of  absorption— Absorption  by  blood-vessels— Absorption  by  lacteal  and  lymphatic  vessels- 
Physiological  anatomy  of  the  lacteal  and  lymphatic  system— Absorption  by  the  lacteals— Absorption  from  parts 
not  connected  with  the  digestive  system— Absorption  of  fats  and  insoluble  substances— Variations  and  modifica- 
tions of  absorption — Imbibition  and  endosmosis — Imbibition  by  animal  tissues — Mechanism  of  the  passage  of 
liquids  through  membranes— Capillary  attraction— Endosmosis  through  porous  septa— Endosmosis  through  ani- 
mal membranes— Endosmosis  through  liquid  septa— Diffusion  of  liquids— Endosmotic  equivalents— Modifications 
of  endosmosis — Application  of  physical  laws  to  the  function  of  absorption — Transudation — Lymph  and  chyle — 
Mode  of  obtaining  lymph— Quantity  of  lymph— Properties  and  composition  of  lymph— Alterations  of  the  lymph 
— Corpuscular  elements  of  the  lymph — Leucocytes — Development  of  leucocytes  in  the  lymph  and  chyle — Glob- 
ulins—Origin and  function  of  the  lymph— General  properties  of  the  chyle— Composition  of  the  chyle— Compara- 
tive analyses  of  the  lymph  and  the  chyle— Microscopical  characters  of  the  chyle— Movement  of  the  lymph  and 
chyle. 

DIGESTION  has  two  great  objects :  one  is  to  liquefy  the  different  alimentary  princi- 
ples ;  and  the  other,  to  commence  the  series  of  transformations  by  which  these  principles 
are  rendered  capable  of  nourishing  the  organism.  The  principles  thus  acted  upon  are 
taken  into  the  blood  as  fast  as  the  requisite  changes  in  their  constitution  are  effected ; 
and,  once  received  into  the  circulation,  they  become  part  of  the  great  nutritive  fluid,  sup- 
plying the  waste  which  the  constant  regeneration  of  the  tissues  from  materials  furnished 
by  the  blood  necessarily  involves.  The  only  group  of  principles  which  possibly  does  not 
obey  this  general  law  is  the  fats.  Although  a  small  portion  of  the  fat  taken  as  food 
passes  directly  into  the  blood-vessels  of  the  intestinal  canal,  by  far  the  greatest  part  finds 
its  way  into  the  circulation  by  means  of  special  absorbent  vessels  which  empty  into  large 
veins.  In  whatever  way  fat  enters  the  blood,  it  is  never  dissolved,  but  is  reduced  to  the 
condition  of  a  fine  emulsion. 


ABSORPTION  BY  BLOOD-VESSELS.  301 

The  process  by  which  digested  materials  are  taken  into  the  blood  is  called  absorption. 
It  is  now  recognized  that  two  sets  of  vessels  are  concerned  in  the  performance  of  this 
function;  namely,  the  blood-vessels  and  the  lacteals.  Those  parts  of  the  food  which 
have  been  rendered  fluid  and  are  capable  of  forming  a  homogeneous  mixture  with  the 
blood-plasma  are  absorbed  chiefly  by  the  blood-vessels,  although  a  small  portion  finds  its 
way  into  the  lacteals.  The  emulsified  fats  are  taken  up  in  greatest  part  by  the  lacteals, 
although  a  small  quantity  is  taken  directly  into  the  blood.  In  treating  of  this  subject,  it 
will  be  convenient  to  consider  separately  the  action  of  these  two  kinds  of  vessels. 

Absorption  by  JBlood-  Vessels. 

That  soluble  substances  can  pass  through  the  delicate  walls  of  the  capillaries  and 
small  veins  and  that  absorption  actually  takes  place  in  great  part  by  blood-vessels,  are 
facts  which  hardly  demand  discussion  at  the  present  day.  Soluble  principles  which 
have  disappeared  from  the  alimentary  canal  have  been  repeatedly  found  in  the  blood 
coming  from  this  part,  even  when  the  lymphatics  have  been  divided  and  communication 
existed  only  through  the  blood-vessels.  The  old  theoretical  view  which  was  entertained 
before  the  lymphatics  and  lacteals  were  discovered  was  that  absorption  took  place  by 
blood-vessels ;  but,  after  special  absorbent  vessels  had  been  described,  it  was  generally 
supposed  that  they  furnished  the  only  avenue  for  the  entrance  of  new  matters  into  the 
economy,  although  the  doctrine  of  vascular  absorption  was  retained  by  a  few.  It  was 
only  after  the  conclusive  experiments  of  Magendie,  in  1809,  that  positive  proof  was  given 
of  the  absorbing  power  of  the  blood-vessels.  These  experiments  settled  the  question  of 
vascular  absorption,  although  they  led  some  to  take  too  exclusive  a  view  of  the  impor- 
tance of  the  venous  radicles  in  this  function  and  to  deny  that  absorption  took  place  to  any 
considerable  extent  through  the  lymphatic  and  the  lacteal  system.  At  the  present  day, 
there  is  no  difference  of  opinion  among  physiologists  concerning  the  direct  absorption  of 
nutritive  matters  by  the  blood-vessels  of  the  alimentary  canal.  It  has  been  repeatedly 
shown,  indeed,  that,  during  absorption,  the  blood  of  the  portal  vein  is  rich  in  albumi- 
noids, sugar,  and  in  other  principles  resulting  from  digestion. 

In  the  mouth  and  oesophagus,  the  sojourn  of  alimentary  principles  is  so  brief  and 
the  changes  which  they  undergo  so  slight,  that  no  absorption  of  any  moment  can  take 
place.  It  is  evident,  however,  that  the  mucous  membrane  of  the  mouth  is  capable  ot 
absorbing  certain  soluble  matters,  from  the  effects  which  are  constantly  observed  when 
the  smoke  or  the  juice  of  tobacco  is  retained  in  the  mouth,  even  for  a  short  time.  In 
the  stomach,  however,  the  absorption  of  certain  materials  takes  place  with  great  activity. 
A  large  proportion  of  the  ingested  liquids  and  of  those  principles  of  food  which  are  dis- 
solved by  the  gastric  juice  and  converted  into  albuminose  is  taken  up  directly  by  the 
blood-vessels  of  the  stomach.  It  may,  indeed,  be  assumed,  as  a  general  law,  that  di- 
gested matters  are  in  great  part  absorbed  as  soon  as  their  transformations  in  the  alimen- 
tary canal  have  been  completed. 

In  the  passage  of  the  food  down  the  intestinal  canal,  as  we  have  already  seen,  there 
is  a  constant  loss  of  material.  As  the  digestion  of  the  albuminoids  is  completed,  these 
principles  are  absorbed,  and  their  passage  into  the  mass  of  blood  is  indicated  chiefly  by 
an  increase  in  its  proportion  of  albuminoid  constituents.  Many  of  the  other  products  of 
digestion,  such  as  glucose  and  fatty  emulsion,  have  also  been  demonstrated  in  quantity 
in  the  blood  of  the  portal  vein  during  absorption.  The  fats,  though  taken  up  in  greatest 
part  by  the  lacteals,  are  always  found  in  greater  or  less  quantity  in  the  portal  blood.  It 
has  frequently  been  observed  that,  after  a  full  meal  consisting  largely  of  fat,  the  blood 
from  the  portal  vein,  as  it  cools  and  coagulates,  leaves  a  white  scum  of  fat  upon  the  sur- 
face. On  one  occasion,  we  observed,  in  the  portal  blood  of  an  animal  killed  in  full  diges- 
tion, a  layer  of  fat  on  cooling  so  thick  that  a  quantity  of  blood,  which  was  spilled  upon 
a  table  and  the  floor,  was  white,  like  milk.  We  have  since  frequently  attempted  to 


302  ABSORPTION. 

demonstrate  this  excessively  chylous  condition  of  the  blood  during  the  absorption  of  fats, 
but  have  found  that  it  is  not  generally  so  well  marked. 

The  greatest  part  of  the  food  is  absorbed  by  the  intestinal  mucous  membrane,  and, 
with  the  alimentary  substances  proper,  a  large  quantity  of  secreted  fluid  is  reabsorbed. 
This  fact  is  particularly  striking  as  regards  the  bile.  The  biliary  salts  disappear  as  the 
alimentary  mass  passes  down  the  intestine  and  are  undoubtedly  absorbed,  although  they 
are  so  changed  that  they  cannot  be  detected  in  the  blood  by  the  ordinary  tests.  In  this 
portion  of  the  alimentary  canal,  it  will  be  remembered  that  an  immense  absorbing  sur- 
face is  provided,  by  the  arrangement  of  the  mucous  membrane  in  folds,  forming  the  val- 
vulse  conniventes,  and  by  the  presence  of  the  innumerable  villi  which  are  found  through- 
out the  small  intestine.  A  certain  portion  of  the  gaseous  contents  of  the  intestines  is  also 
absorbed,  although  it  is  not  easily  ascertained  what  particular  gases  are  thus  taken  up. 

Absorption  by  Lacteal  and  Lymphatic  Vessels. 

The  history  of  the  discovery  of  what  is  ordinarily  termed  the  absorbent  system  ot 
vessels,  from  the  vague  allusions  of  Hippocrates,  Galen,  Aristotle,  and  others,  to  the  de- 
scription of  the  thoracic  duct  in  the  middle  of  the  sixteenth  century,  by  Eustachius,  and 
finally  to  the  discovery  of  the  lacteals  by  Asellius,  in  1622,  is  more  interesting  in  an  ana- 
tomical than  in  a  physiological  point  of  view.  Our  knowledge  of  the  anatomy  of  the 
absorbent  system  dates  from  the  discovery  of  the  thoracic  duct ;  but,  from  the  discovery 
of  the  lacteals  by  Asellius,  dates  the  history  of  these  vessels  as  the  carriers  of  nutritive 
matters  from  the  intestinal  canal  to  the  general  system. 

In  1649,  Pecquet  discovered  the  receptaculum  chyli  and  demonstrated  that  the  lacteals 
did  not  pass  to  the  liver,  but  emptied  the  chyle  into  the  commencement  of  the  thoracic 
duct,  by  which  it  was  finally  conveyed  into  the  venous  system.  In  1650-'51,  the  ana- 
tomical history  of  the  absorbent  vessels  was  completed  by  the  discovery,  by  Eudbeck, 
of  vessels  carrying  a  colorless  fluid,  in  the  liver  and  finally  in  almost  all  parts  of  the 
body.  Rudbeck  demonstrated  the  anatomical  identity  of  these  vessels  with  the  lacteals. 
They  were  afterward  carefully  studied  by  Bartholinus,  who  gave  them  the  name  of  lym- 
phatics. It  is  unnecessary  to  follow  out  the  various  researches  made  into  the  structure 
of  the  lymphatics  in  man  and  the  inferior  animals  by  the  Hunters,  Hewson,  Monro, 
Cruikshank,  and  other  of  the  older  anatomists  and  physiologists. 

The  old  idea,  which  dates  from  the  discoveries  of  Asellius  and  Pecquet,  that  the  lac- 
teals absorb  all  the  products  of  digestion,  was  overthrown  by  the  experiments  of  Magen- 
die  and  of  those  who  experimented  after  him  upon  vascular  absorption.  It  is  now  known 
that  the  fatty  portions  of  the  food,  reduced  to  a  very  fine  emulsion  by  the  pancreatic 
juice,  arc  absorbed  by  this  system  of  vessels,  and  that  these  are  the  only  principles  which 
are  taken  up  in  great  quantity.  The  arguments  which  we  have  already  mentioned  are 
sufficient  to  establish  this  fact.  If  the  abdomen  of  a  living  animal  be  opened  during  full 
digestion,  then,  and  then  only,  will  the  lacteals  and  the  thoracic  duct  be  found  dis- 
tended with  fatty  emulsion.  If  the  organ  which  digests  fat  be  rendered  incapable  of 
performing  its  function,  the  lacteals  cease  to  carry  chyle.  These  vessels  do  not  appear 
in  the  mesentery  until  the  food  has  passed  the  orifice  of  the  pancreatic  duct.  Finally, 
the  observations  of  Bouchardat  and  Sandras  remove  all  doubt  as  to  the  absorption  of  the 
products  of  the  digestion  of  fatty  matters  by  the  lacteals ;  for  these  observers  found  not 
only  that  in  dogs  the  proportion  of  fat  in  the  chyle  was  increased  pari  passu  with  an  in- 
crease in  the  quantity  of  fat  taken  as  food,  but  that  the  particular  kinds  of  fat  adminis- 
tered to  the  animals  could  be  recognized  in  the  chyle.  "We  have  seen  that  a  certain  quan- 
tity of  fat  escapes  the  lacteals  and  is  absorbed  directly  by  the  blood-vessels ;  and  it  be- 
comes an  important  question  to  determine  whether  the  lacteals,  in  addition  to  their  more 
prominent  function,  be  not  concerned  in  the  absorption  of  drinks,  the  albuminoids,  saline 
and  saccharine  matters,  etc.  This  question  will  be  taken  up  after  a  consideration  of 
certain  points  in  the  anatomy  of  the  lymphatic  system. 


ABSOKPTION  BY  LACTEAL  AND  LYMPHATIC  VESSELS. 


303 


Physiological  Anatomy  of  the  Lacteal  and  Lymphatic  System.— One  of  the  most  diffi- 
cult problems  in  anatomy  is  to  determine  the  situation  and  mode  of  origin  of  the  lym- 
phatics in  different  parts  of  the  body.  The  tenuity  of  the  walls  of  these  vessels,  even  in 
their  course,  aiid  the  presence  of  innumerable  valves,  render  it  impossible  to  study  them 
by  the  ordinary  methods  of  injection.  Since  it  lias  been  ascertained,  however,  that  they 
originate  in  many  parts  by  a  rich,  anastomosing  plexus,  their  anatomy  has  been  well 
made  out  in  certain  situations  by  simply  puncturing  with  a  fine-pointed  canula  the  parts 
in  which  the  plexus  is  supposed  to  exist,  and  allowing  a  fluid,  generally  mercury,  to 
gently  diffuse  itself  in  the  vessels  of  origin.  Following  the  course  of  the  vessels,  the 
fluid  passes  into  the  larger  trunks  and  thence  to  the  lymphatic  glands.  The  regularity 
of  the  plexus  through  which  the  fluid  is  first  diffused  and  the  passage  of  the  injection 
through  the  larger  vessels  to  the  glands  are  positive  proof  that  the  lymphatics  have  been 
penetrated  and  that  the  appearances  observed  are  not  the  result  of  mere  infiltration. 

By  the  method  of  investigation  above  indicated,  we  may  recognize  the  superficial 
vessels  of  the  skin,  deeper  vessels  situated  just  beneath  the  skin,  and  vessels  in  the  serous 
membranes,  glandular  organs,  lungs,  tendons,  etc.,  in  addition  to  the  larger  trunks,  such 
as  the  thoracic  duct.  The  lacteal  system  presents  essentially  the  same  characters  as  the 
general  lymphatics,  and  the  vessels  are  filled  with  colorless  lymph  during  the  intervals 
of  digestion.  In  many  situations,  the  lymphatics  present  in  their  course  little,  solid 
structures  called  lymphatic  glands. 

The  mode  of  origin  of  the  finest  vessels,  in  the  lymphatic  radicles,  is  exceedingly  ob- 
scure, notwithstanding  the  numerous  investigations  which  have  been  made  within  the 
last  few  years,  particularly  by  German  anatomists.  We  shall  first  describe,  however, 
the  mode  of  origin  of  what  may  be  called  the  true  vessels,  in  those  parts  in  which 
the  results  of  anatomical  study  seem  positive  and  definite,  before  we  discuss  the -va- 
rious theories  which  have  been  proposed  to  account  for  certain  of  the  phenomena  of 
absorption. 

Lymphatics  have  not  been  actually  injected  and  demonstrated  in  all  the  tissues  of  the 
body  ;  but,  in  some  parts  in  which  it  has  been  thus  far  impossible  to  inject  them,  we  are 
not  justified  in  assuming  positively  that  they  do  not  exist.  For  example,  in  the  intestinal 
villi,  according  to  Sappey,  these  vessels  have  never  been  seen,  although  their  existence  is 
almost  certain.  The  most  generally  received  view  with  regard  to  the  ordinary  mode  of 
origin  of  the  lymphatic  vessels  is  that  they  commence  by  a  capillary  plexus,  which  does 
not  communicate  with  either  the  small  arteries,  veins,  or  the  capillary  blood-vessels,  and 
is  generally  situated  external  to  the  blood-vessels.  It  does  not  appear  that  the  vessels 
composing  this  plexus  vary  much  in.  size.  They  are  very  elastic,  and,  after  distention 
by  injection,  they  return  to  a  very  small  diameter  when  the  fluid  is  allowed  to  escape. 
It  is  probable,  therefore,  that  the  capacity  of  the  vessels  is  much  exaggerated  by  the 
means  which  are  taken  to  render  them  apparent.  In  the  elaborate  observations  by  Dr. 
Belaieff,  of  St.  Petersburg,  into  the  origin  of  the  lymphatics  of  the  penis,  the  walls  of  the 
vessels  were  rendered  apparent  by  the  action  of  nitrate  of  silver  in  solution  in  pure  water, 
and  it  is  probable  that  they  were  very  little  distended.  The  smallest  of  these  vessels  had 
a  diameter  of  about  ^^  of  an  inch.  This  may  be  taken  as  their  average  diameter  in  the 
primitive  plexus.  This  plexus,  when  the  vessels  are  abundant,  as  they  are  in  certain 
parts  of  the  cutaneous  surface,  resembles  an  ordinary  plexus  of  capillary  blood-vessels, 
except  that  the  walls  of  the  vessels  are  thinner  and  their  diameter  is  greater. 

The  smallest  lymphatic  vessels  are  by  far  the  most  numerous.  They  are  arranged  in 
the  form  of  a  fine  plexus,  very  superficially  situated  in  the  skin.  A  second  plexus  exists 
just  beneath  the  skin,  composed  of  vessels  of  much  greater  diameter.  The  skin  is  thus 
enclosed,  as  it  were,  between  two  plexuses  of  capillary  lymphatics.  A  -plexus  analogous 
to  the  most  superficial  plexus  of  the  skin  is  found  just  beneath  the  surface  of  the  mucous 
membranes.  These  may,  indeed,  be  classed  with  the  superficial  lymphatics.  The  deep 
lymphatics  are  much  larger  and  less  numerous,  and  their  origin  is  less  easily  made  out. 


304 


ABSOEPTIO^. 


These  accompany  the  deeper  veins  in  their  course.     They  receive  the  lymph  from  the 
superficial  vessels. 

No  valvular  arrangement  is  found  in  the  smallest  lymphatics ;  but  the  vessels  coming 
from  the  primitive  plexuses,  as  well  as  the  large  vessels,  contain  valves  in  immense  num- 
bers. These  valves,  being  so  closely  set  in  the  vessels,  give  to  them,  when  filled  with 
injection,  a  peculiar  and  characteristic  beaded  appearance. 


FIG.  ^.—Superficial  lym- 
phatics of  the  skin  of  the 
palmar  surface  of  the 
finger.  (Sappey.) 


FIG.  84.— Deep  lymphatics  of  the  skin 
of  the  finger.  (Sappey.) 

1, 1,  deep  net-work  of  cutaneous  lymphat- 
ics; 2,  2,  2,  2,  lymphatic  trunks  con- 
nected with  this  net- work. 


FIG.  85  —Same  finger,  lat- 
eral view,  showing  lym- 
phatic trunks  connected 
with  the  superficial  net- 
work. (Sappey.) 


The  course  of  the  lymphatics  is  generally  tolerably  direct.  As  they  pass  toward  the 
great  trunks  by  which  they  communicate  with  the  venous  system,  they  present  a  peculiar 
anastomosis  with  the  adjacent  vessels,  called  anastomosis  by  bifurcation;  that  is,  as  a 
vessel  passes  along  with  other  vessels  nearly  parallel  with  it,  it  bifurcates,  and  the  two 
branches  pass  into  the  nearest  vessels  on  either  side.  These  anastomoses  are  quite  fre- 
quent, and  they  generally  occur  between  vessels  of  equal  size.  In  their  course,  the  ves- 
sels pass  through  the  lymphatic  glands,  which  will  be  described  farther  on. 

A  notable  peculiarity  in  the  lymphatic  vessels  is  that  they  vary  very  little  in  size, 
being  nearly  as  large  at  the  extremities  as  they  are  near  the  trunk.  In  their  course,  they 
are  always  much  smaller  than  the  veins  and  do  not  progressively  enlarge  as  they  pass  on 
to  the  great  lymphatic  trunks.  The  largest-sized  vessels  as  they  pass  from  the  skin  are 
from  -^5-  to  -£%  of  an  inch  in  diameter,  and  the  larger  vessels,  in  their  course,  have  a  diameter 
of  from  -^  to  ^  of  an  inch.  As  in  the  case  of  the  smallest  lymphatics  in  the  primitive  plexus, 
the  elasticity  of  the  walls  of  the  vessels  renders  their  caliber  greatly  dependent  upon  the 
pressure  of  fluid  in  their  interior.  Many  anatomists  have  noticed  that  vessels,  which  are 


ABSORPTION  BY  LACTEAL  AND  LYMPHATIC   VESSELS. 


305 


hardly  perceptible  while  empty,  are  capable  of  being  dilated  to  the  diameter  of  half  a  line 
or  more,  returning  to  their  original  size  as  soon  as  the  distending  fluid  is  removed. 

The  peculiarities  which  the  lymphatics  present  in  the  different  tissues  and  organs  do 
not  possess  much  physiological  interest,  except  the  arrangement  of  the  vessels  of  origin 
in  the  substance  of  the  brain  and  spinal  cord.  In  the  skin,  the  only  interesting  peculiarity 
which  we  have  not  already  noticed  is  that  the  vessels  appear  to  be  very  unequally  dis- 
tributed in  different  parts  of  the  surface.  According  to  Sappey,  they  are  particularly 


FIG.  86.— Superficial  lymphatics  of  the  arm. 
(Sappey.) 


FIG.  SI.— Superficial  lymphatics  of  the.  leg. 
(Sappey.) 


abundant  in  the  scalp  over  the  biparietal  suture,  the  soles  of  the  feet  and  the  palms  of  the 
hand,  the  fingers  at  the  lateral  portion  of  the  last  phalanges,  and  the  scrotum.  In  the 
median  portion  of  the  scrotum,  they  attain  their  highest  degree  of  development.  They 
are  also  found,  though  in  less  number,  originating  from  around  the  median  line  on  the 
anterior  and  posterior  surface  of  the  trunk,  the  posterior  median  portion  of  the  extremi- 
ties, the  skin  over  the  mammae,  and  around  the  orifices  of  the  mucous  passages.  Sappey 
has  injected  lymphatic  vessels  in  the  anterior  portion  of  the  forearm,  the  thigh,  and  the 
leg,  and  the  middle  portion  of  the  face,  although  they  are  demonstrated  with  difficulty  in 
these  situations.  If  they  exist  at  all  in  other  portions  of  the  cutaneous  surface,  they  are 
not  numerous  and  are  rudimentary. 
20 


306  ABSORPTION. 

In  the  mucous  system  the  lymphatics  are  very  abundant.  Here  are  found,  as  in  the 
skin,  two  distinct  layers  which  enclose  between  them  the  whole  thickness  of  the  mucous 
membrane.  The  more  superficial  of  these  layers  is  composed  of  a  rich  plexus  of  small 
vessels,  and,  beneath  the  mucous  membrane,  is  a  plexus  consisting  of  vessels  of  larger  size 
and  less  numerous.  The  superficial  plexus  is  exceedingly  rich  in  the  mixed  structure 
which  forms  the  lips  and  the  glans  penis,  and  around  the  orifices  of  the  mouth,  the  nares, 
the  vagina,  and  the  anus.  There  are  certain  mucous  membranes  in  which  the  lymphatics 
have  never  been  injected.  In  the  serous  membranes,  the  lymphatics  have  been  demon- 
strated in  great  abundance.  Lymphatics  have  been  demonstrated  taking  their  origin  in 
the  voluntary  muscles,  the  diaphragm,  the  heart,  and  the  non-striated  muscular  coats  of 
the  hollow  viscera,  although  their  investigation  in  these  situations  is  exceedingly  difficult. 

Lymphatics  are  found  coming  from  the  lungs  in  immense  numbers.  These  arise  in 
the  walls  of  the  air-cells  and  surround  each  pulmonary  lobule  with  a  close  plexus.  The 
deep  vessels  follow  the  course  of  the  bronchial  tubes,  passing  through  the  bronchial  glands 
and  the  glands  of  the  bifurcation  of  the  trachea,  to  empty  into  the  thoracic  duct  and  the 
great  lymphatic  duct  of  the  right  side. 

In  the  glandular  system,  including  the  ductless  glands,  and  in  the  ovaries,  the  lym- 
phatic vessels  are,  as  a  rule,  more  abundant  than  in  any  other  parts  of  the  body.  They 
are  especially  numerous  in  the  testicle,  the  ovary,  the  liver,  and  the  kidney. 

In  the  substance  of  the  brain  and  spinal  cord,  Robin  and  His  have  demonstrated  a 
curious  system  of  vessels  which  entirely  surround  the  capillary  blood-vessels  and  are 
connected  with  the  lymphatic  trunks  or  reservoirs  described  by  Fohmann  under  the  pia 
mater.  The  capillary  blood-vessels  thus  float  in  a  fluid  contained  in  these  cylindrical 
sheaths,  which  exceed  them  in  diameter  by  from  y^o  to  4^  of  an  inch.  These  investing 
vessels  follow  the  blood-vessels  in  their  ramifications,  and  contain  a  clear  fluid,  with  bodies 
resembling  the  lymph-corpuscles.  When  Robin  first  described  these  vessels  minutely,  he 
did  not  state  definitely  their  physiological  relations ;  but  he  has  since  published  a  memoir 
in  which  he  describes  them  as  true  lymphatic  vessels,  analogous  to  the  lymphatics  which 
partly  surround  the  small  blood-vessels  in  fishes,  reptiles,  and  batrachians.  In  these  ani- 
mals, the  lymphatics  in  many  parts  nearly  surround  the  blood-vessels,  to  the  walls  of 
which  the  edges  of  their  proper  coat  are  adherent ;  and  that  portion  of  the  wall  of  the 
blood-vessel  which  is  thus  enclosed  forms  at  the  same  time  the  wall  of  the  lymphatic. 
This  disposition  of  the  lymphatics  in  the  brain  and  spinal  cord  would  allow  of  free  inter- 
change, by  endosmosis  and  exosmosis,  of  the  liquid  portions  of  the  blood  and  the  lymph. 

The  lymphatic  vessels  from  the  superficial  and  deep  portions  of  the  head  and  face  on 
the  right  side,  and  those  from  the  superficial  and  deep  portions  of  the  right  arm,  the  right 
half  of  the  chest,  and  the  mammary  gland,  with  a  few  vessels  from  the  lungs,  pass  into 
the  great  lymphatic  duct  (ductus  lymphaticus  dexter),  which  empties  into  the  venous 
system  at  the  junction  of  the  right  subclavian  with  the  internal  jugular.  This  vessel  is 
about  an  inch  in  length  and  from  one-twelfth  to  one-eighth  of  an  inch  in  diameter.  It  is 
provided  with  a  pair  of  semilunar  valves  at  its  opening  into  the  veins,  which  effectually 
prevent  the  ingress  of  blood. 

The  vessels  from  the  inferior  extremities,  and  those  from  the  lower  portions  of  the 
trunk,  the  pelvic  viscera,  and  the  abdominal  organs,  generally  pass  into  the  thoracic  duct. 
In  their  course,  all  of  the  lymphatics  pass  through  the  small,  flattened,  oval  bodies,  called 
the  lymphatic  glands,  which  are  so  abundant  in  the  groin,  the  axilla,  the  pelvis,  and  in  some 
other  parts.  From  two  to  six  vessels,  called  the  vasa  afferentia,  enter  these  bodies,  having 
first  broken  up  into  a  number  of  smaller  vessels  just  before  they  pass  in.  They  pass  out 
by  a  number  of  small  vessels  which  unite  to  form  one,  two,  or  three  trunks,  generally  of 
larger  size  than  the  vasa  afferentia.  The  vessels  which  thus  emerge  from  the  glands  are 
called  vasa  efferentia. 

The  lymphatics  of  the  small  intestine,  called  lacteals,  pass  from  the  intestine  between 
the  folds  of  the  mesentery  to  empty,  sometimes  by  one,  and  sometimes  by  four  or  five 


ABSORPTION  BY   LACTEAL  AND   LYMPHATIC   VESSELS. 


307 


trunks,  into  the  receptaculum  chyli.      In  their  course,  the  lacteals  pass  through  several 
sets  of  lymphatic  glands,  which  are  here  called  mesenteric  glands. 

The  thoracic  duct,  into  which  the  great  majority  of  the  lymphatic  vessels  empty,  is 


Fia.  S8.— Stomach,  intestine,  and  mesentery,  ^oith  the  mesenterie  blood-vessels  and  lacteals.    (Copied  and  slightly 

reduced  from  a  figure  in  the  original  work  of  Asellius,  published  in  1628.) 
A,  A,  A,  A,  A,  mesenteric  arteries  and  veins;   B,  B,  B,  B,  B,  B,  B,  B,  B,  B,  lacteals;   C,  C,  C,  C,  mesentery;   D,  D, 

stomach ;  E,  pyloric  portion  of  the  stomach ;  F,  duodenum ;  G,  G,  G,  jejunum ;  H,  H,  H,  H,  H,  ileum ;  I,  artery 

and  vein  on  the  fundus  of  the  stomach ;  K,  portion  of  the  omentum. 

a  vessel  with  exceedingly  delicate  walls  and  about  the  size  of  a  goose-quill.  It  com- 
mences by  a  dilatation,  more  or  less  marked,  called  the  receptaculum  chyli.  This  is 
situated  upon  the  second  lumbar  vertebra.  The  canal  passes  upward  in  the  median 


308 


ABSORPTION. 


line  for  the  inferior  half  of  its  length.      It  then  inclines  to  the   left  side,  forms  a 
semicircular  curve  something  like  the  arch  of  the  aorta,  and  empties  at  the  junction  of 

the  left  subclavian  with  the  internal 
jugular  vein.  It  diminishes  in  size 
from  the  receptaculum  to  its  middle 
portion  and  becomes  larger  again 
near  its  termination.  It  occasionally 
bifurcates  near  the  middle  of  the 
thorax,  but  the  branches  become  re- 
united a  short  distance  above.  At 
its  opening  into  the  venous  system, 
there  is  generally  a  valvular  fold, 
but,  according  to  Sappey,  this  is  not 
constant.  There  is  always,  however, 
a  pair  of  semilunar  valves  in  the 
duct,  from  three-quarters  of  an  inch 
to  an  inch  from  its  termination,  which 
effectually  prevent  the  entrance  of 
blood  from  the  venous  system. 

It  is  probable  that  the  lymphatic 
and  lacteal  vessels  have  no  direct  con- 
nection with  the  blood-vessels,  except 
by  the  two  openings  by  which  they 
discharge  their  contents  into  the  ven- 
ous system.    The  foregoing  sketch  of 
the  descriptive  anatomy  of  what  has 
been  called  the  absorbent  system  of 
vessels  shows  that  they  may  collect 
fluids,  not  only  from  the  intestinal  ca- 
nal during  digestion,  but  from  nearly 
every  tissue  and  organ  in  the  body, 
and  that  these  fluids  are  received  into 
the  venous  circulation. 
Structure  of  the  Lacteal  and  Lymphatic  Vessels. — The  lymphatic  vessels,  even  those 
of  largest  size,  are  remarkable  for  the  delicacy  and  transparency  of  their  walls.     This  is 
well  illustrated  in  the  case  of  the  lacteals,  which  are  hardly  visible  in  the  transparent 
mesentery,  unless  they  be  filled  with  opaque  chyle. 

From  the  difficulty  in  studying  the  lymphatics  at  their  origin,  except  by  means  of 
injections  or  by  reagents  which  stain  the  vessels,  investigations  into  the  structure  of  the 
smallest  vessels  have  been  very  few  and  are  not  very  satisfactory.  It  is  supposed,  how- 
ever, that  the  vessels  here  consist  of  a  single  amorphous  coat,  resembling,  in  this  regard, 
the  capillary  blood-vessels.  Dr.  Belaieff  describes,  in  the  capillary  lymphatics  of  the 
penis,  a  lining  of  epithelial  cells  arranged  in  a  single  layer.  These  cells  are  oval,  polygo- 
nal, fusiform  or  dentated,  with  their  long  diameter  in  the  direction  of  the  axis  of  the 
vessels. 

In  all  but  the  capillary  lymphatics,  although  the  walls  are  excessively  thin,  three  dis- 
tinct coats  can  be  distinguished.  The  internal  coat  consists  of  an  elastic  membrane  lined 
with  oblong  epithelial  cells.  This  coat  readily  gives  way  when  the  vessels  are  forcibly 
distended.  The  middle  coat  is  composed  of  longitudinal  fibres  of  the  white  fibrous  tissue, 
with  delicate  elastic  fibres  and  unstriped  muscular  fibres  arranged  transversely.  The 
external  coat  is  composed  of  the  same  structures  as  the  middle  coat ;  but  the  fibres  are 
arranged,  for  the  most  part,  longitudinally.  In  this  coat,  the  muscular  fibres  do  not  form 
a  continuous  sheet,  but  are  collected  into  separate  fasciculi,  which  have  a  direction  either 


FIG.  89.—  Thoracic  duct.    (Mascagni.) 

1,  thoracic  duct;  2,  great  lymphatic  duct;  8,  receptaculum  chyli; 
4,  curve  of  the  thoracic  duct  just  before  it  empties  into  the 
venous  system. 


ABSORPTION   BY  LACTEAL  AND   LYMPHATIC   VESSELS.  3Q9 

longitudinal  or  oblique.  The  fibres  of  connective  tissue  are  very  abundant  and  loosely 
unite  the  vessels  to  the  surrounding  parts.  The  internal  and  the  middle  coat  are  closely 
adherent  to  each  other ;  but  the  external  coat  may  readily  be  separated  from  the  others 
Blood-vessels  have  been  found  in  the  walls  of  the  lymphatics,  but,  as  yet,  the  presence 
of  nerves  has  not  been  demonstrated. 

The  walls  of  the  lymphatic  vessels  are  very  closely  adherent  to  the  surrounding  tis- 
sues ;  so  closely,  indeed,  that  even  a  small  portion  of  a  vessel  is  detached  with  great  dif- 
ficulty, and  the  vessels,  even  those  of  large  size,  cannot  be  followed  out  and  isolated  for 
any  considerable  distance. 

In  all  the  lymphatic  vessels,  beginning  a  short  distance  from  their 
plexus  of  origin,  are  found  numerous  sernilunar  valves,  generally  ar- 
ranged in  pairs,  with  their  concavities  looking  toward  the  larger  trunks. 
These  folds  are  formed  of  the  inner  two  coats ;  but  the  fold  formed  of 
the  lining  membrane  is  by  far  the  wider,  so  that  the  free  edges  of  the 
valves  are  considerably  thinner  than  that  portion  which  is  attached  di- 
rectly to  the  vessel.  In  some  of  the  vessels,  at  the  point  where  one  lym- 
phatic communicates  with  another,  there  is  a  valve  formed  of  two  folds, 
one  of  which  is  much  wider  than  the  other  ;  but,  in  the  valves  situated  in 
the  course  of  the  vessels,  the  curtains  are  of  about  equal  size.  The  valves 
are  very  numerous  in  all  of  the  lymphatics,  but  they  are  most  abundant 
in  the  superficial  vessels.  The  distance  between  the  valves  is  from  one- 
twelfth  to  one-eighth  of  an  inch,  near  the  origin  of  the  vessels,  and  from 
one-quarter  to  one-third  of  an  inch,  in  their  course.  In  the  lymphatics 
situated  between  the  muscles,  the  valves  are  less  numerous.  They  are 
always  relatively  few  in  the  vessels  of  the  head  and  neck  and  in  all  that 
have  a  direction  from  above  downward.  Although  there  are  a  number 
of  valves  in  the  thoracic  duct,  they  are  not  so  numerous  here  as  in  the 
smaller  vessels. 

In  their  anatomy  and  general  properties,  the  lymphatics  bear  a  close 
resemblance  to  the  veins.    Although  much  thinner  and  more  transparent, 
their  coats  have  nearly  the  same  arrangement.     The  arrangement  of 
valves  is  entirely  the  same  ;  and,  in  both  systems,  the  folds  prevent  the  FIG.  90.—  Valves  of 
reflux  of  fluids  when  the  vessels  are  subjected  to  pressure.     A  number       (Sappeyo 
of  forces  (which  will  be  considered  hereafter)  combine  to  produce  the 
flow  of  lymph  and  chyle  in  the  absorbent  system.     Among  these  is  intermittent  pressure 
from  surrounding  parts,  which  could  only  operate  favorably  in  vessels  provided  with  nu- 
merous valves. 

We  have  already  referred  to  the  great  elasticity  of  the  lymphatics.  It  is  now  pretty 
generally  admitted  that  the  larger  vessels  and  those  of  medium  size  are  endowed  also 
with  contractility,  although  the  action  of  their  muscular  fibres,  like  that  of  all  fibres  of 
the  involuntary  or  non-striated  variety,  is  slow  and  gradual.  Todd  and  Bowman  have 
demonstrated  this  property  by  mechanically  irritating  the  thoracic  duct  in  an  animal  re- 
cently killed,  but  they  observed  that  the  contraction  was  very  slow.  Milne-Edwards, 
quoting  from  a  manuscript  presented  by  Colin  to  the  Academy  of  Sciences,  in  1858,  states 
that  this  observer  noted  alternate  filling  and  emptying  of  some  of  the  lacteal  vessels  in 
the  mesentery  of  the  ox ;  portions  of  the  vessels  becoming  alternately  enlarged  in  the 
form  of  pouches,  and  contracted  so  that  they  almost  disappeared.  There  can  be  no 
doubt  that  the  lymphatic  vessels  possess  a  certain  degree  of  contractility,  which  is  fully 
as  marked,  perhaps,  as  in  the  venous  system. 

One  of  the  most  important  points  in  connection  with  the  physiological  anatomy  of 
the  lymphatic  vessels,  and  one,  indeed,  upon  which  rest  our  ideas  of  the  mechanism  of 
absorption  by  these  vessels,  is  the  question  of  the  existence  of  orifices  in  their  walls,  which 
might  allow  the  passage  of  solid  particles  or  emulsions.  The  most  recent  observations 


310 


ABSOEPTIOK 


have  indicated  the  probable  existence  of  stomata,  of  variable  size  and  irregular  shape,  in 
the  smallest  vessels ;  but  it  must  be  acknowledged  that  one  of  the  strongest  arguments 
in  favor  of  the  existence  of  these  orifices  is,  not  their  anatomical  demonstration,  but  the 
fact  of  the  actual  passage,  through  the  walls  of  the  vessels,  of  fatty  particles,  the  en- 
trance of  which  cannot  be  explained  by  the  well-known  laws  of  endosmosis.  The  ana- 


FIG.  91.— Lymphatic  plexus,  showing  the  epithelial  lining  of  the  vessels.    (Belaieff.) 

tomical  evidence  of  the  existence  of  openings  is  derived  mainly  from  preparations  stained 
with  nitrate  of  silver.  It  is  assumed  that  nitrate  of  silver  stains  the  solid  parts  of  tis- 
sues and  the  borders  of  the  epithelial  cells,  and  that  areas  which  do  not  present  any 
staining  are  necessarily  open,  If  this  be  true,  and  this  view  is  now  very  generally  ac- 
cepted, we  may  consider  the  existence  of  openings  in  the  lymphatic  vessels  as  demon- 
strated. In  preparations  of  the  lymphatics,  the  solution  of  silver  is  seen  staining  the 
tissues  and  the  borders  of  the  epithelial  cells  lining  the  vessels ;  but  there  are  areas  be- 
tween these  cells  where  no  staining  is  observed  and  in  which  no  nuclei  are  brought  on 
by  staining  with  carmine.  It  is  not  impossible,  however,  that  the  solutions  used  may 
fail  to  attack  all  parts  of  the  tissue,  and  that  these  colorless  areas  may  be  closed  by  an 
amorphous  membrane. 

With  regard  to  the  origin  of  the  lymphatics  in  the  tissues,  it  does  not  seem  that  our 
actual  knowledge  extends  beyond  the  small  vessels,  such  as  are  observed  in  the  superfi- 
cial net-work  of  the  skin.  Within  the  last  few  years,  Kecklinghausen  and  others  have 
assumed  the  existence,  in  the  connective  tissue  (which  is  so  widely  distributed  in  the 
organism),  of  minute  tubes  or  canaliculi,  which  open  into  the  lymphatic  vessels,  and  that 
these  are  the  true  vessels  of  origin  of  a  great  part  of  the  lymphatic  system.  These  lit- 
tle vessels  are  called  serous  canaliculi.  This  view,  however,  is  not  sustained  by  positive 
demonstration  and  must  be  regarded  as  purely  hypothetical ;  and  the  same  may  be  said 
of  the  opinion  advanced  by  some  that  the  lymphatics  originate  in  lacunae  or  spaces  in  the 
connective  tissue  or  in  a  system  of  canals  formed  by  connective-tissue  corpuscles  and 
fibres.  Sappey  asserts  very  emphatically  that  not  one  lymphatic  vessel  has  ever  been 
demonstrated  as  arising  from  the  substance  of  connective  tissue  ;  and  a  careful  study  of 
recent  observations  in  Germany  shows  this  to  be  the  fact. 

Lymphatic  Glands. — In  the  course  of  the  lymphatic  vessels,  are  found  numerous  small, 


ABSORPTION  BY  LACTEAL  AND  LYMPHATIC  VESSELS.  3n 

lenticular  bodies,  called  lymphatic  glands.  The  number  of  these  glands  is  very  great  al 
though  it  is  estimated  with  difficulty,  from  the  fact  that  many  of  them  are  very  small  and 
are  consequently  liable  to  escape  obser- 
vation. It  may  be  stated  as  an  approxi-  ^^EfSJfa^ 
mation  that  there  are  from  six  hundred 
to  seven  hundred  lymphatic  glands  in 
the  body.  Their  size  and  form  are  also 
very  variable  within  the  limits  of  health. 
They  are  generally  flattened  and  len- 
ticular, some  as  large  as  a  bean,  and 
others  as  small  as  a  small  pea  or  even 
a  pin's-head.  They  are  arranged  in 
two  sets ;  one  superficial,  correspond- 
ing with  the  superficial  lymphatic  ves- 
sels, and  a  deep  set,  corresponding  with 
the  deep  vessels.  The  superficial  glands 
are  most  numerous  in  the  folds  at  the 
flexures  of  the  great  joints  and  about 
the  great  vessels  of  the  head  and  neck. 
The  deep-seated  glands  are  most  numer- 
ous around  the  vessels  coming  from  the 
great  glandular  viscera.  A  distinct  set 
of  large  glands  is  found  connected  with 
the  lymphatic  vessels  between  the 
folds  of  the  mesentery.  These  are 
known  as  the  mesenteric  glands.  All 
of  the  lymphatic  vessels  pass  through 
glands  before  they  arrive  at  the  great 
lymphatic  trunks,  and  most  of  them 
pass  through  several  glands  in  their 
course. 

There  is  some  difference  of  opinion 
among  anatomists  concerning  the  inti- 
mate structure  of  the  lymphatic  glands.  Some  regard  them  as  composed  simply  of  a 
plexus  of  lymphatic  vessels,  held  together  by  a  delicate  stroma  of  fibrous  tissue  ;  while 
others  deny  that  there  is  any  direct  communication  between  the  afferent  and  the  efferent 
vessels,  assuming  that  the  vessels  which  penetrate  the  glands  break  up  into  small  branches 
which  open  into  a  parenchyma  filled  with  closed  follicles,  and  that  the  fluids  are  collected 
from  the  glands  by  a  second  set  of  capillaries  connected  with  the  efferent  lymphatics. 
According  to  the  latter  view,  the  mesenteric  glands  are  little  more  than  collections  of 
follicles  like  the  solitary  glands  of  the  intestines,  held  together  by  a  delicate  fibrous 
structure.  This  difference  of  opinion  seems  to  be  due  to  the  different  methods  which 
have  been  employed  in  studying  the  structure  of  the  glands.  Taking,  for  example,  the 
results  arrived  at  by  two  prominent  investigators,  Sappey,  who  has  studied  these  organs 
with  great  success  by  injections,  seems  to  have  clearly  demonstrated  a  lymphatic  plexus 
in  their  interior,  while  Kolliker,  .whose  investigations  have  been  confined  chiefly  to  ex- 
aminations of  the  organs  in  a  recent  state,  has  not  been  able  to  follow  out  the  lymphatic 
vessels,  but  has  accurately  described  the  contents  of  the  alveoli,  or  what  are  regarded  by 
others  as  closed  follicles.  In  attempting  to  represent  what  has  been  actually  demon- 
strated concerning  the  structure  of  these  bodies,  we  shall  first  take  up  the  appearances 
which  are  observed  in  the  fresh  structures,  and  afterward,  those  points  which  have  been 
demonstrated  by  minute  injections. 

The  perfect,  healthy  glands  are  of  a  grayish- white  or  reddish  color,  of  about  the  con- 


.  92. — Lymphatics  and  lymphatic  glands.    (Sappey.) 
1,   upper  extremity  of  the  thoracic  duct,  passing  behind ,  the 
internal  jugular  vein ;  2,  opening  of  the  thoracic  duct  into 
the  internal  jugular  and  left  subclavian  vein.    The  lym- 
phatic glands' are  seen  in  the  course  of  the  vessels. 


312  ABSOEPTION. 

sistence  of  the  liver,  presenting  a  hilum  where  the  larger  blood-vessels  enter  and  the 
efferent  vessels  emerge,  and  covered,  except  at  the  hilum,  with  rather  a  delicate  mem- 
brane, composed  of  inelastic,  with  a  few  elastic  fibres.  Their  exterior  is  somewhat  tu- 
berculated,  from  the  projections  of  the  follicles  just  beneath  the  investing  membrane. 
The  interior  of  the  glands  is  soft  and  pulpy.  It  presents  a  coarsely-granular  cortical 
substance,  of  a  reddish-white  or  gray  color,  which  is  from  one-sixth  to  one-fourth  of  an 
inch  in  thickness  in  the  largest  glands.  The  medullary  portion,  which  comes  to  the  sur- 
face at  the  hilum,  is  lighter  colored  and  coarser  than  the  cortical  substance.  Through- 
out the  gland,  are  found  delicate  fasciculi  of  fibrous  tissue  connected  with  the  investing 
membrane,  which  serve  as  a  fibrous  skeleton  for  the  gland  and  divide  its  substance  into 
little  alveoli.  The  structure  is  far  more  delicate  in  the  cortical  than  in  the  medullary 
portion. 

Within  the  alveoli,  are  irregularly-oval,  closed  follicles,  about  ^-^  of  an  inch  in  di- 
ameter, filled  with  a  fluid  and  with  cells  like  those  contained  in  the  solitary  glands  of  the 
intestines  and  the  patches  of  Peyer.  These  follicles  do  not  seem  to  occupy  the  medul- 
lary portion  of  the  glands,  which,  according  to  Kolliker,  is  composed  chiefly  of  a  net- 
work of  lymphatic  capillaries,  mixed  with  rather  coarse  bands  of  fibrous  tissue.  The 
follicular  structures  in  the  lymphatic  glands  resemble  the  closed  follicles  in  the  mucous 
membrane  of  the  intestinal  canal  and  the  Malpighian  bodies  of  the  spleen. 

The  elaborate  researches  of  Sappey  leave  scarcely  any  doubt  as  to  the  course  and  ar- 
rangement of  the  lymphatic  vessels  in  the  interior  of  the  lymphatic  glands,  although  the 
view  advanced  by  him  that  these  bodies  consist  mainly  of  lymphatics  with  a  little 
fibrous  tissue  cannot  be  sustained.  By  pricking  a  perfectly  healthy  gland  with  the  deli- 
cate point  of  his  apparatus  for  injecting  the  lymphatics,  he  has  seen  the  mercury  succes- 
sively fill  the  different  capillary  vessels  and  pass  into  the  vasa  efferentia.  Sappey  does 
not  appear,  however,  to  have  caused  the  injection  to  pass  from  the  afferent  to  the  effer- 
ent vessels,  entirely  through  this  plexus ;  and,  while  the  fact  of  the  continuity  of  these 
vessels  through  a  capillary  plexus  is  extremely  probable,  it  has  not,  as  yet,  been  posi- 
tively proven. 

As  far  as  has  been  ascertained,  the  following  is  the  course  of  the  lymphatic  vessels 
through  the  glands :  From  two  to  six  vasa  afferentia  approach  the  gland,  and,  when 
within  about  a  quarter  of  an  inch  of  it,  they  break  up  into  numerous  small  branches  which 
penetrate  its  investing  membrane.  In  the  substance  of  the  gland,  these  vessels  are  dis- 
tributed in  the  capillary  plexus  just  described  and  emerge  by  the  vasa  efferentia,  which 
are  always  larger  than  the  afferent  vessels  and  are  from  one  to  three  in  number.  In 
attempting  to  pass  injections  entirely  through  the  glands,  the  fluid  has  frequently  been 
observed  to  pass  into  the  small  veins ;  so  that  some  anatomists  have  assumed  that  there 
is  a  connection  in  the  substance  of  the  glands  between  the  lymphatics  and  the  blood- 
vessels. It  is  altogether  probable  that  the  passage  of  fluids  into  the  veins  under  these 
circumstances  is  due  to  rupture  of  the  vessels ;  and,  at  all  events,  the  direct  connection 
between  them  and  the  lymphatics  has  never  been  satisfactorily  demonstrated. 

The  lymphatic  glands  are  supplied  with  blood  by  sometimes  one,  but  generally  by  sev- 
eral small  arteries,  which  penetrate  at  the  hilum.  These  vessels  pass  directly  to  the  medul- 
lary portion  and  there  break  up  into  several  coarse  branches,  to  be  distributed  to  the 
cortical  substance,  where  they  ramify  in  an  exceedingly  delicate  capillary  net-work,  with 
rather  wide  meshes,  in  the  closed  follicles  found  in  this  portion  of  the  gland.  This  capil- 
lary plexus  also  receives  branches  from  small  arterial  twigs  which  penetrate  the  capsule 
of  the  gland  at  different  points.  Returning  on  themselves  in  loops,  the  vessels  unite  to 
form  one  or  more  large  veins,  which  generally  emerge  at  the  hilum. 

Very  little  is  known  regarding  the  distribution  of  nerves  in  the  lymphatic  glands. 
A  few  filaments  from  the  sympathetic  system  enter  with  the  arteries,  but  they  have 
never  been  traced  to  their  final  distribution.  The  entrance  of  filaments  from  the  cerebro- 
spinal  system  has  never  been  demonstrated. 


ABSORPTION   BY  LACTEAL  AND  LYMPHATIC  VESSELS.  313 

It  is  evident,  from  the  structure  of  the  lymphatic  glands,  that  they  must  materially 
retard  the  passage  of  the  lymph  toward  the  great  trunks;  and  it  is  well  known  in 
pathology  that  morbid  matters  taken 
up  by  the  absorbents  are  frequently 
arrested  and  retained  in  the  nearest 
glands. 

The  function  of  the  lymphatic 
glands-  is  very  obscure.  By  some 
they  are  supposed  to  have  an  im- 
portant office  in  the  elaboration  of 
the  corpuscular  elements  of  the 
lymph  and  chyle;  and  it  has  been 
observed  that  the  lymph  contained 
in  vessels  which  have  passed  through 
no  glands  is  relatively  poor  in  cor- 
puscles, while  the  large  trunks  and 
the  efferent  vessels  contain  them  in 
large  numbers.  This  single  fact  is 
indefinite  enough,  as  regards  the 
mode  of  formation  of  the  lymph- 
corpuscles,  but  it  represents  about 
all  that  is  actually  known  concern- 
ing the  function  of  the  lymphatic 
glands. 

In  endeavoring  to  estimate  the 

Share  which   the   lacteals   and  lym-     Fl(}  w.-Werent  varMi*  of  lymphatic  glands.     tSappey.) 
phatics  have  in  the  function  of  ab- 
sorption, it  becomes  an  important  question  to  determine  what  principles  these  vessels 
are  capable  of  taking  up,  beside  the  fatty  elements  of  the  food,  and  how  far,  if  at  all, 
they  assist  the  blood-vessels  in  the  absorption  of  the  general  products  of  digestion. 

Absorption  of  Albuminoids  J)y  the  Lacteals. — Comparative  analyses  of  the  lymph  and 
chyle  always  show  in  the  latter  fluid  an  excess  of  albuminoid  matters.  As  we  may  rea- 
sonably suppose  that,  during  the  intervals  of  digestion,  the  lacteals  carry  ordinary  lymph — 
for,  at  this  time,  these  vessels  are  filled  with  a  colorless,  transparent  fluid,  having  the  gen- 
eral physical  characters  of  lymph — it  is  natural  to  infer  that  the  excess  of  nitrogenized 
matters  in  the  white  chyle  is  due  to  absorption  of  albuminoids  from  the  intestinal  canal. 
Mr.  Lane  collected  the  chyle  from  the  lacteals  of  a  donkey,  seven  and  a  half  hours  after 
a  full  meal  of  oats  and  beans,  and  compared  its  composition  with  that  of  the  lymph.  The 
analyses  were  made  by  Dr.  Rees,  who  found  that  the  chyle  contained  about  three  times 
as  much  albumen  and  fibrin  as  the  lymph.  While  by  far  the  greater  part  of  the  products 
of  digestion  of  the  albuminoids  is  absorbed  by  the  blood-vessels,  there  can  be  no  doubt 
that  a  small  portion  is  also  taken  up  by  the  lacteals. 

Absorption  of  Glucose  and  Salts  ~by  the  Lacteals. — What  has  just  been  stated  regard- 
ing the  absorption  of  albuminoids  applies  with  equal  force  to  saccharine  niatters  and 
the  inorganic  salts.  Small  quantities  of  sugar  and  sometimes  lactic  acid  have  been 
detected  in  the  chyle  from  the  thoracic  duct  in  the  herbivora  ;  and  the  presence  of  sugar 
in  both  the  lymph  and  the  chyle  has  been  accurately  determined  by  Colin. 

It  is  true  that  the  products  of  the  digestion  of  saccharine  and  amylaceous  matters  are 
taken  up  mainly  by  the  blood-vessels,  but  a  small  quantity  is  also  absorbed  by  the  lac- 
teals. In  the  comparative  analyses  of  the  chyle  and  lymph  by  Dr.  Rees,  the  proportion 
of  inorganic  salts  was  found  to  be  considerably  greater  in  the  chyle.  The  great  excess 


314  ABSORPTION. 

in  the  quantity  of  blood  coming  from  the  intestine  and  the  rapidity  of  its  circulation,  as 
compared  with  the  chyle,  will  explain  the  more  rapid  penetration  by  endosmosis  of  the 
soluble  products  of  digestion. 

Absorption  of  Water  ~by  the  Lacteals. — There  can  be  no  doubt  that  a  small  portion  of 
the  liquids  taken  as  drink  finds  its  way  into  the  circulation  by  the  lacteals,  although  the 
greatest  part  passes  directly  into  the  blood-vessels.  This  has  been  proven  by  experi- 
ments of  a  most  positive  character.  Leuret  and  Lassaigne  state  that,  when  an  animal  is 
fed  with  an  aliment  which  is  very  substantial  and  is  killed  during  digestion,  the  thoracic 
duct  contains  a  very  small  quantity  of  chyle ;  but,  when  the  animal  has  taken  liquids  with 
the  food,  the  thoracic  duct  and  the  lacteals  are  very  much  distended.  In  an  experiment 
by  Ernest  Burdach,  a  dog  was  deprived  of  food  and  drink  for  twenty-four  hours,  after 
which  he  was  allowed  to  drink  water,  and,  in  addition,  half  a  pound  was  injected  into 
the  stomach.  The  animal  was  killed  a  half  an  hour  after,  and  the  thoracic  duct  was 
found  engorged  with  watery  lymph,  which  contained  a  very  small  number  of  lyrnph-cor- 
puscles. 

In  discussing  the  question  of  absorption  by  the  blood-vessels  of  the  intestinal  canal, 
we  alluded  to  experiments  which  showed  that  various  poisonous  substances  introduced 
into  the  intestines  produced  their  characteristic  effects  upon  the  system  with  great 
rapidity  when  the  veins  leading  from  the  part  were  intact,  while  no  such  effects  followed 
when  the  only  avenue  to  the  general  system  was  through  the  lacteals.  Without  again 
discussing  these  observations  in  detail,  it  may  be  stated,  as  the  general  results  of  experi- 
ments on  this  subject,  that  few,  if  any,  of  the  active  poisons  were  found  to  be  absorbed 
from  the  alimentary  canal,  except  by  blood-vessels  ;  and,  when  soluble  coloring  matters, 
or  salts  which  could  be  easily  recognized,  were  found  in  the  lacteals  or  the  thoracic  duct 
after  they  had  been  introduced  into  the  intestine,  they  penetrated  in  small  quantity  and 
very  slowly ;  while  it  has  been  repeatedly  found  that  the  same  substances  were  taken  up 
by  the  veins  with  great  rapidity  and  excreted,  in  many  instances,  by  the  urine. 

Absorption  from  Parts  not  connected  with  the  Digestive  System. — Aside  from  the 
entrance  of  gases  into  the  blood  from  the  pulmonary  surface,  physiological  absorption  is 
almost  entirely  confined  to  the  mucous  membrane  of  the  alimentary  canal.  It  is  true 
that  liquids  may  find  their  way  into  the  circulation  through  the  skin,  the  lining  mem- 
brane of  the  air-passages,  the  reservoirs,  ducts,  and  parenchyma  of  glands,  the  serous  and 
other  closed  cavities,  the  areolar  tissue,  the  conjunctiva,  the  muscular  tissue,  and,  in 
fact,  all  parts  which  are  supplied  with  blood-vessels ;  but  here  the  absorption  of  foreign 
matters  is  an  occasional  or  an  accidental  circumstance  and  is  not  connected  with  the 
general  process  of  nutrition.  It  is  now  well  known  that  all  parts  of  the  body,  except 
the  epidermis  and  its  appendages,  the  epithelium,  and  some  other  structures  which  are 
regularly  desquamated,  are  constantly  undergoing  change,  and  the  effete  matters  which 
result  from  their  decay  are  taken  up  by  what  is  called  interstitial  absorption  and  are  car- 
ried by  the  blood  to  the  proper  organs,  to  be  excreted.  It  seems  probable  that  the  ves- 
sels of  these  parts  would  also  be  capable  of  taking  up  soluble  foreign  substances  when 
presented  to  them ;  and  this  is,  indeed,  the  fact  with  regard  to  all  parts  in  which  the 
nutritive  processes  are  even  moderately  active,  or  where  the  structures  covering  the  vas- 
cular parts%are  permeable. 

Absorption  from  the  Skin. — It  is  now  generally  admitted  that  absorption  can  take 
place  from  the  general  surface,  although,  at  one  time,  this  was  a  question  much  discussed 
by  physiologists  and  practical  physicians.  The  proofs,  however,  of  the  entrance  of  cer- 
tain medicinal  preparations  from  the  surface  of  the  body  are  now  entirely  conclusive ; 
and  the  constitutional  effects  of  medicines  administered  in  this  way  are  frequently  as 
marked  as  when  they  are  taken  into  the  alimentary  canal.  But  the  question  which  is 


ABSORPTION  BY  THE   SKIN.  315 

of  most  interest  to  us  as  physiologists  concerns  the  normal  functions  of  the  skin  as  an 
absorbing  surface.  Looking  at  this  subject  from  a  purely  physiological  point  of  view 
absorption  from  the  skin,  under  ordinary  conditions,  must  be  very  slight,  if,  indeed,  it  take 
place  at  all.  There  are  a  few  observations  by  the  older  physiologists  which  would  at 
first  seem  to  show  that  a  certain  amount  of  water  is  taken  up  by  the  skin  when  the 
atmosphere  is  unusually  moist.  In  all  of  these,  however,  this  conclusion  is  drawn  from  the 
circumstance  that  the  weight  is  occasionally  somewhat  increased  under  these  conditions; 
but  no  account  is  taken  of  the  fact,  that,  when  the  surrounding  atmosphere  is  moist,  the 
amount  of  the  exhalations  is  greatly  decreased.  The  lungs,  also,  present  an  immense 
absorbing  surface,  which  is  not  at  all  considered.  Experiments  on  this  point  are  not  suffi- 
ciently definite  to  warrant  any  positive  conclusions ;  but  it  is  evident  that,  if  any  articles 
enter  in  this  way,  the  quantity  must  be  excessively  minute. 

The  experiments  upon  the  entrance  of  water  and  soluble  substances  through  the  skin, 
when  the  body  has  been  immersed  for  a  long  time  in  a  bath,  are  somewhat  contradictory. 
Most  experimenters  have  noted  an  increase  in  the  weight,  which  they  attribute  to  absorp- 
tion of  water,  but  others  profess  to  have  observed  a  slight  diminution  in  the  weight  of  the 
body.  In  some  experiments  on  this  subject,  by  Madden,  in  which  all  necessary  precau- 
tions were  adopted,  the  air  being  respired  through  a  tube  passed  out  of  the  window  of  the 
room,  so  that  no  unusual  absorption  of  moisture  could  take  place  by  the  lungs,  the  results 
were  very  conclusive.  In  experiments  of  this  kind,  there  are  many  modifying  influences 
to  be  guarded  against.  For  example,  it  has  been  found  to  be  important  to  regulate  care- 
fully the  temperature  of  the  bath ;  for,  when  it  exceeds  that  of  the  body,  there  may  be  a 
loss  of  weight  by  cutaneous  transpiration.  It  is  stated  by  Longet  that,  when  the  tem- 
perature of  the  water  is  lower  than  that  of  the  body,  there  is  a  gain  in  weight ;  but  that 
the  cutaneous  exhalation  and  absorption  are  balanced  when  the  temperature  of  the  bath 
and  the  body  are  the  same.  There  is  another  source  of  complication  in  these  observa- 
tions, which  has  been  brought  forward  very  strongly  by  a  French  writer,  M.  Delore. 
This  observer  has  carefully  noted  the  increase  in  weight  of  the  hair,  nails,  and  epidermis, 
after  immersion  for  half  an  hour  in  distilled  water,  and  has  always  found  it  to  be  v,ery 
considerable.  He  assumes  that  this  is  more  than  sufficient  to  account  for  the  increase  in 
the  weight  of  the  entire  body  after  immersion  in  water  for  half  an  hour,  which  amounts 
to  about  seven  hundred  grains. 

There  are,  nevertheless,  facts  which  render  it  certain  that  water  can  be  absorbed  by 
the  skin.  In  an  elaborate  series  of  experiments  by  Collard  de  Martigny,  it  was  proven 
conclusively  that  water  could  be  absorbed  in  small  quantity  by  the  skin  of  the  palm  of 
the  hand.  In  one  experiment,  a  small  bell-glass  filled  with  water  was  applied  hermeti- 
cally to  the  palm.  This  was  connected  with  a  tube  bent  in  the  form  of  a  siphon,  also 
filled  with  water,  the  long  branch  of  which  was  placed  in  a  vessel  of  mercury.  After 
the  apparatus  had  been  applied  for  an  hour  and  three-quarters,  the  mercury  was  found 
sensibly  elevated  in  the  tube,  showing  that  a  certain  quantity  of  the  water  had  disap- 
peared. More  recently,  a  very  extended  series  of  observations  upon  the  absorption  of 
water  and  soluble  substances  has  been  made  by  Dr.  Willemin,  in  which  it  is  conclusively 
proven  that  water  is  absorbed  in  a  bath,  and  that  various  medicinal  substances  may  be 
taken  up  by  the  skin  in  this  way  and  can  be  detected  afterward  in  the  urine.  In  a  large 
number  of  experiments,  he  found  that  the  weight  of  the  body,  after  remaining  in  a  tepid 
bath  for  from  thirty  to  forty-five  minutes,  was  generally  stationary  ;  but  that  sometimes 
there  was  a  very  slight  diminution  in  weight  and  sometimes  a  very  slight  increase.  By 
comparative  observations,  however,  he  found  that  the  diminution  of  weight  in  the  bath 
was  always  less  than  the  amount  lost  by  the  same  subject  in  the  air.  Dr.  "Willemin 
employed  a  very  delicate  apparatus  for  weighing,  and  his  observations  were  apparently 
conducted  with  great  care.  He  also  confirmed  the  statement  of  W.  F.  Edwards  and 
others,  that  transpiration  from  the  general  surface  goes  on  in  a  bath.  This  he  showed 
by  differences  in  the  composition  of  the  bath  before  and  after  immersion  of  the  body. 


316  ABSORPTION. 

These  observations  do  much  to  reconcile  the  contradictory  experiments  of  others,  in  some 
of  which  a  diminution  in  weight  was  observed,  while  in  some  an  increase  was  noted.  In 
studying  this  subject,  it  must  always  be  remembered  that  there  is  a  constant  loss  of 
weight  by  evaporation  from  the  general  surface  and  from  the  lungs ;  a  fact  which  was 
not  taken  into  account  by  some  of  the  earlier  experimenters. 

It  has  been  frequently  remarked  that  the  sensation  of  thirst  is  always  least  pressing 
in  a  moist  atmosphere,  and  that  it  may  be  appeased  to  a  certain  extent  by  baths.  It  is 
true  that,  in  a  moist  atmosphere,  the  cutaneous  exhalations  are  diminished,  and  this 
might  account  for  the  maintenance  of  the  normal  proportion  of  fluids  in  the  body  with  a 
less  amount  of  drink  than  ordinary  ;  but  we  could  hardly  account  for  an  actual  allevia- 
tion of  thirst  by  immersion  of  the  body  in  water,  unless  we  assumed  that  a  certain 
quantity  of  water  had  been  absorbed.  A  striking  example  of  relief  of  thirst  in  this  way 
is  given  by  Captain  Kennedy,  in  the  narrative  of  his  sufferings  after  shipwreck,  when  lie 
and  his  men  were  exposed  for  a  long  time  without  water,  in  an  open  boat.  With  regard 
to  his  sufferings  from  thirst,  he  says:  "I  cannot  conclude  without  making  mention  of 
the  great  advantage  I  derived  from  soaking  my  clothes  twice  a  day  in  salt-water, 
and  putting  them  on  without  wringing.  .  .  .  There  is  one  very  remarkable  circum- 
stance, and  worthy  of  notice,  which  was,  that  we  daily  made  the  same  quantity  of  urine 
as  if  we  had  drunk  moderately  of  any  liquid,  which  must  be  owing  to  a  body  of  water 
absorbed  through  the  pores  of  the  skin.  ...  So  very  great  advantage  did  we  derive 
from  this  practice,  that  the  violent  drought  went  off,  the  parched  tongue  was  cured  in  a 
few  minutes  after  bathing  and  washing  our  clothes ;  at  the  same  time  we  found  ourselves 
as  much  refreshed  as  if  we  had  received  some  actual  nourishment." 

Absorption  ~by  the  Respiratory  Surface. — In  studying  the  physiological  anatomy  of 
the  respiratory  apparatus,  we  have  seen  how  admirably  the  respiratory  surface  is  calcu- 
lated for  the  introduction  of  gaseous  principles  into  the  blood.  The  great  rapidity  with 
which  the  oxygen  of  the  inspired  air  penetrates  through  the  delicate  covering  of  the  pul- 
monary vessels  has  already  been  fully  considered  under  the  head  of  respiration.  Under 
natural  conditions,  the  gases  of  the  air  are  the  only  principles  absorbed  by  the  lungs ;  but 
examples  of  the  absorption  of  other  gaseous  matters  are  exceedingly  common,  and  this 
process  has  been  the  subject  of  numerous  experiments  by  physiologists.  The  fact  of  the 
absorption  of  foreign  substances  by  the  lungs,  also,  has  long  been  definitely  settled ;  but 
this  belongs  to  pathology  or  to  therapeutics,  rather  than  to  physiology. 

It  is  now  almost  universally  conceded  that  animal  and  vegetable  emanations  may  be 
taken  into  the  blood  by  the  lungs  and  produce  certain  well-marked  pathological  condi- 
tions. It  is  supposed  that  many  contagious  diseases  are  propagated  in  this  way,  as  well 
as  some  fevers  and  other  general  diseases  which  are  not  contagious.  With  regard  to  cer- 
tain poisonous  gases  and  volatile  principles,  the  effects  of  their  absorption  by  the  lungs 
are  even  more  striking.  Carbonic  oxide  and  arseniuretted  hydrogen  produce  death  al- 
most instantly,  even  when  inhaled  in  small  quantity.  The  vapor  of  pure  hydrocyanic  acid 
acts  frequently  with  great  promptness  through  the  lungs.  Turpentine,  iodine,  and  many 
medicinal  substances  may  be  introduced  with  great  rapidity  by  inhalation  of  their  va- 
pors ;  and  we  well  know  the  serious  effects  produced  by  the  emanations  from  lead  or  mer- 
cury in  persons  who  work  in  these  articles.  Among  the  most  striking  proofs  of  the 
absorption  of  vapors  by  the  lungs  are  the  effects  of  the  inhalation  of  ether.  This  passes 
into  the  blood  and  manifests  its  characteristic  anesthetic  influence  almost  immediately. 
Not  only  have  vapors  introduced  in  this  way  been  recognized  in  the  blood,  but  many  of 
the  principles  thus  absorbed  are  excreted  by  the  kidneys  and  may  be  recognized  by  their 
characteristic  reactions  in  the  urine. 

As  would  naturally  be  expected,  water  and  substances  in  solution,  when  injected 
into  the  respiratory  passages,  are  rapidly  absorbed,  and  poisons  administered  in  this  way 
manifest  their  peculiar  effects  with  great  promptness.  Experimenters  on  this  subject 


ABSORPTION   OF  FATS   AND   INSOLUBLE   SUBSTANCES.  317 

have  shown  the  facility  with  which  liquids  may  be  absorbed  from  the  lungs  and  the  air- 
passages,  but  it  must  be  remembered  that  the  natural  conditions  are  never  such  as  to  ad- 
mit of  this  action.  The  normal  function  of  the  lungs  is  to  absorb  oxygen  and  sometimes 
a  little  nitrogen  from  the  air ;  and  the  absorption  of  any  thing  else  by  these  surfaces  is 
unnatural  and  generally  deleterious. 

Absorption  from  Closed  Cavities,  Reservoirs  of  Glands,  etc. — Facts  in  pathology  show- 
ing absorption  from  closed  cavities,  the  areolar  tissue,  the  muscular  and  nervous  tissue, 
the  conjunctiva,  and  other  parts,  are  sufficiently  numerous.  In  all  cases  of  effusion  of 
serum  into  the  pleural,  peritoneal,  pericardial,  or  synovial  cavities,  in  which  recovery 
takes  place,  the  liquid  becomes  absorbed.  It  has  been  shown  by  experiment  that  warm 
water  injected  into  these  cavities  is  disposed  of  in  the  same  way.  Eifusions  into  the 
areolar  tissue  are  generally  removed  by  absorption.  In  cases  of  penetration  of  air  into 
the  pleura  or  the  general  areolar  tissue,  absorption  likewise  takes  place ;  showing  that 
gases  may  be  taken  up  in  this  way  as  well  as  liquids.  Effusions  of  blood  beneath  the 
skin  or  the  conjunctiva  or  in  the  muscular  or  nervous  tissue  may  become  entirely  or  in 
part  absorbed.  It  is  true  that  these  are  pathological  conditions,  but,  in  the  closed  cavi- 
ties, the  processes  of  exhalation  and  absorption  are  constantly  going  on,  although  not 
very  actively.  As  regards  absorption  from  the  areolar  tissue,  the  administration  of 
remedies  by  the  hypodermic  method,  which  is  now  so  common,  is  a  familiar  proof  of  the 
facility  with  which  soluble  principles  are  taken  into  the  blood  when  introduced  beneath 
the  skin. 

Under  some  circumstances,  absorption  takes  place  from  the  reservoirs  of  the  various 
glands,  the  watery  portions  of  the  secretions  being  generally  taken  up,  leaving  the  solid 
and  the  organic  matters.  It  is  supposed  that  the  bile  becomes  somewhat  inspissated 
when  it  has  remained  for  a  time  in  the  gall-bladder,  even  when  the  natural  flow  of  the  se- 
cretion is  not  interrupted.  Certainly,  when  the  duct  is  in  any  way  obstructed,  absorption 
of  a  portion  of  the  bile  takes  place,  as  is  proven  by  coloration  of  the  conjunctiva  and 
even  of  the  general  surface.  The  serum  of  the  blood,  under  these  conditions,  is  always 
strongly  colored  with  bile. 

It  is  probable  that  some  of  the  watery  portions  of  the  urine  are  reabsorbed  by  the 
mucous  membrane  of  the  urinary  bladder,  when  the  urine  has  been  long  confined  in  its 
cavity,  although  this  resorption  is  ordinarily  very  slight.  A  great  many  cases  of  dis- 
charge of  urinary  matters  by  the  stomach  and  intestines,  skin,  etc.,  when  the  urine  has 
been  long  retained,  have  been  reported  by  the  older  physiologists  and  were  supposed  to 
indicate  resorption  of  these  principles  from  the  bladder.  The  mechanism  of  the  excretion 
of  urinary  matters  was  not  understood  before  the  experiments  of  Prevost  and  Dumas, 
who  showed  that  urea  accumulates  in  the  blood  after  the  extirpation  of  both  kidneys 
in  the  inferior  animals.  It  is  now  generally  admitted  that  this  takes  place  when  the 
function  of  excretion  of  urine  is  seriously  interfered  with,  and  that  an  attempt  is  made 
by  Nature  to  remove  these  effete  principles  from  the  system  by  the  stomach,  intestine, 
skin,  and  lungs.  It  is  possible,  therefore,  that  the  vicarious  discharge  of  urinary  matters, 
in  the  cases  reported  before  the  true  process  of  excretion  by  the  kidneys  was  understood, 
was  due  to  accumulation  of  the  constituents  of  the  urine  in  the  blood,  and  not  to  their 
resorption  from  the  urinary  passages. 

Absorption  may  take  place  from  the  ducts  and  the  parenchyma  of  glands,  although 
this  occurs  chiefly  when  foreign  substances  have  been  injected  into  these  parts. 

Absorption  of  Fats  and  Insoluble  Substances. 

The  general  proposition  that  all  substances  capable  of  being  absorbed  are  soluble  in 
water  or  in  the  digestive  fluids  must  be  modified  in  the  case  of  the  fats.  These  are  never 
dissolved  in  any  appreciable  quantity  in  digestion,  the  only  change  which  they  undergo 
being  a  minute  subdivision  in  the  form  of  a  very  fine  emulsion.  In  this  condition,  the 


318 


ABSORPTION. 


fats  are  taken  up  by  the  lacteals  and  may  be  absorbed  in  small  quantity  by  the  blood- 
vessels. Although  it  is  now  pretty  well  understood  how  endosmotic  liquids  pass  through 
the  walls  of  the  blood-vessels  and  absorbents,  the  mechanism  of  the  penetration  of  fatty 
particles,  which  is  no  less  constant,  is  still  somewhat  obscure. 

There  can  be  no  question  with  regard  to  the  actual  penetration  of  the  minute  parti- 
cles of  the  chyle  into  the  lacteals  and  even  into  the  blood-vessels.  In  birds,  indeed,  ac- 
cording to  Bernard,  all  the  fat  which  is  absorbed  is  taken  up  by  the  blood-vessels,  the 
lymphatics  of  the  intestine  never  containing  a  milky  fluid.  Confining  our  discussion  to 
the  mechanism  of  the  absorption  of  fatty  emulsion  in  mammals,  it  must  be  admitted  that 
the  assumption  of  the  existence  of  orifices  in  the  walls  of  the  lacteals,  even  if  we  deny  the 
actual  anatomical  demonstration  of  these  openings,  becomes  almost  necessary  ;  for  the 
experiments  upon  the  passage  of  fatty  particles  through  closed  membranes  are  certainly 
very  unsatisfactory.  Taking  into  consideration  all  of  the  facts  bearing  upon  the  question, 
it  seems  more  probable  that  orifices  exist  in  the  vessels  than  that  the  fatty  particles  pene- 
trate by  endosmosis;  but  it  must  be  remembered  that  this  idea  rests  upon  the  un- 
doubted physiological  fact  of  the  absorption  of  emulsions  rather  than  upon  anatomical 
grounds  ;  and,  if  we  were  not  called  upon  to  explain  the  absorption  of  fatty  particles,  it 
is  doubtful  whether  the  stomata  of  the  vessels  would  be  so  generally  admitted.  It  is  not 
infrequently  the  case  that  we  are  forced  to  assume  the  existence  of  certain  anatomical 
arrangements  as  the  only  reasonable  explanation  of  physiological  phenomena,  when  act- 
ual demonstrations  are  unsatisfactory.  With  regard  to  the  lacteals,  when  we  remember 
the  excessive  tenuity  of  the  vessels  of  origin,  the  close  adhesion  of  their  walls  to  the 
surrounding  tissues,  the  novelty  and  uncertainty  of  the  staining  processes,  and  the  fact 
that  some  anatomists  deny  that  the  finest  so-called  lymphatic  plexuses  of  origin  have  any 
distinct  walls,  it  is  readily  understood  how,  as  physiologists,  we  must  regard  the  exist- 
ence of  stomata  in  the  lymphatics  as  an  idea  based  upon  the  necessity  of  explaining  well- 
established  physiological  phenomena,  rather  than  a  clearly-demonstrable  anatomical  fact. 
In  studying  the  mechanism  of  the  penetration  of  fatty  particles  into  the  intestinal  villi, 

it  has  been  ascertained  that  the  epithelial  cells 
covering  the  villi  play  an  important  part  in  this 
process.  It  was  first  ascertained  by  Goodsir  that, 
during  the  digestion  of  fat,  these  cells  became 
filled  with  fatty  granules.  This  fact  has  been 
confirmed  by  Gruby  and  Delafond,  Kolliker, 
Funke,  and  others.  Funke,  in  his  atlas  of  physi- 
ological chemistry,  figures  the  appearances  of  the 
intestinal  epithelium  during  the  digestion  of  fat, 
as  contrasted  with  the  epithelium  observed  dur- 
ing the  intervals  of  digestion,  showing  the  cells, 
during  absorption,  filled  with  fatty  granules. 

It  is  true,  as  a  general  law,  that  insoluble  sub- 
stances, with  the  exception  of  the  fats,  are  never 
regularly  absorbed,  no  matter  how  finely  they 
may  be  divided.  The  apparent  exceptions  to  this 

^  mercury  ^  &  ^  of  mmute  subdivision  like 

an  emulsion,  and  carbonaceous  particles.   In  the 

case  of  mercury,  it  is  well  known  that  minute  particles  in  the  form  of  unguents  may  be 
introduced  into  the  system  by  prolonged  frictions  ;  but  this  cannot  be  regarded  as  an 
instance  of  physiological  absorption.  The  passage  of  small  carbonaceous  particles 
through  the  pulmonary  membrane  seems  to  be  purely  mechanical.  The  same  thing  may 
possibly  occur  when  fine,  sharp  particles  of  carbon  are  introduced  into  the  alimentary 
canal  ;  but  the  experiments  of  Mialhe  with  pulverized  charcoal,  and  particularly  those 
of  Berard,  Robin,  and  Bernard  with  lamp-black  introduced  into  the  intestinal  canal  of 


intestine  of  the 


VARIATIONS   AND  MODIFICATIONS   OF  ABSORPTION. 


310 


animals,  showed  that,  although  the  intestinal  mucous  membrane  became  of  a  deep  black, 
this  could  easily  be  removed  by  a  stream  of  water,  and  no  carbonaceous  particles  could 
be  discovered  in  the  mesenteric  veins,  the  lacteals,  or  the  mesenteric  glands.  When  the 
carbon  is  used  in  the  form  of  lamp-black,  the  particles  are  very  minute  and  rounded,  and 
they  do  not  present  the  sharp  points  and  edges  which  sometimes  enable  the  grains  of 
pulverized  charcoal  to  penetrate  the  vessels  mechanically. 


FIG.  95.— Epithelium  from  the  duodenum  of  a  rab- 
bit, two  hours  after  having  been  fed  with  melt- 
ed butter.  (Fuhke.) 


FIG.  96.— Villi,  fitted  with  fat.  from  the  small  in- 
testine of  an  executed  criminal,  one  hour  after 
death.  (Funke.) 


Variations  and  Modifications  of  Absorption. 

Very  little  is  known  concerning  the  variations  in  lacteal  or  lymphatic  absorption ; 
but,  in  absorption  by  blood-vessels,  important  modifications  occur,  due,  on  the  one  hand, 
to  different  conditions  of  the  fluids  to  be  absorbed,  and,  on  the  other,  to  differences  in  the 
constitution  of  the  blood  and  in  the  conditions  of  the  vessels. 

The  different  conditions  of  the  fluids  to  be  absorbed  apparently  do  not  always  have 
the  same  influence  in  physiological  absorption  as  in  endosmotic  experiments  made  out  of 
the  body.  Saccharine  solutions  of  different  densities  confined  in  distinct  portions  of  the 
intestinal  canal  of  a  living  animal  do  not  present  any  marked  variations  in  the  rapidity 
of  their  absorption,  and  they  are  taken  up  by  the  blood,  even  when  their  density  is 
greater  than  that  of  the  blood-plasma.  Solutions  of  nitrate  of  potash  and  sulphate  of 
soda  of  greater  density  than  the  serum,  which  would,  therefore,  attract  the  endosmotic 
current  in  an  endosmometer,  are  readily  taken  up  by  the  blood-vessels  in  a  living  animal. 
Indeed,  nearly  all  soluble  substances,  whatever  be  the  density  of  their  solutions,  may  be 
taken  up  by  the  various  absorbing  surfaces  during  life.  The  woorara  poison  and  most  of 
the  venoms  are  remarkable  exceptions  to  this  rule.  In  a  series  of  very  interesting 
experiments  upon  the  absorption  of  woorara,  Bernard  has  shown  that  this  curious  poison, 
which  is  absorbed  so  readily  from  wounds  or  when  introduced  under  the  skin,  generally 
produces  no  effect  when  introduced  into  the  stomach,  the  small  intestine,  or  the  urinary 
bladder.  This  result,  however,  is  not  invariable,  for  poisonous  effects  are  produced  when 
woorara  is  introduced  into  the  stomach  of  a  fasting  animal.  This  peculiarity  in  the 
absorption  of  many  of  the  animal  poisons  has  long  been  observed  ;  and  it  is  well  known 
that  the  flesh  of  animals  poisoned  with  woorara  can  be  eaten  with  impunity.  It  is 
curious,  however,  to  see  an  animal  carrying  in  the  stomach  without  danger  a  fluid  which 
would  produce  death  if  introduced  under  the  skin ;  and  the  explanation  of  this  is  not 
readily  apparent.  The  poison  is  not  neutralized  by  the  digestive  fluids,  for  woorara 
digested  for  a  long  time  in  gastric  juice,  or  taken  from  the  stomach  of  a  dog,  is  found  to 
possess  all  its  toxic  properties,  as  we  have  frequently  shown  (repeating  the  experiment 


320  ABSORPTION. 

of  Bernard)  by  poisoning  a  pigeon  with  woorara  drawn  by  a  fistula  from  the  stomach  of 
a  living  dog.  If  we  recognize  the  absorption  of  this  poison  simply  by  its  effects  upon  the 
system,  it  must  be  assumed  that,  during  digestion,  it  cannot  be  absorbed  by  the  mucous 
membrane  of  the  stomach  and  small  intestine,  notwithstanding  that  it  is  exceedingly 
soluble. 

It  has  also  been  shown  that  liquids  which  immediately  disorganize  the  tissues,  such  as 
concentrated  nitric  or  sulphuric  acid,  cannot  be  absorbed.  Another  important  peculiar- 
ity in  absorption  has  been  demonstrated  by  Mialhe,  who  has  shown  that  solutions  which 
readily  coagulate  the  albumen  of  the  circulating  fluids  are  absorbed  very  slowly.  This 
is  explained  on  the  supposition  that  there  is  a  coagulation  of  the  albuminous  fluids  with 
which  the  absorbing  membrane  is  permeated,  which  interferes  with  the  passage  of 
liquids.  These  substances  are  nevertheless  taken  up  by  the  blood-vessels,  though  rather 
slowly. 

The  modifications  which  are  due  simply  to  the  physical  conditions  of  liquids  to  be 
absorbed  are  chiefly  manifested  out  of  the  body  and  will  be  considered  in  connection  with 
the  subject  of  endosmosis. 

Influence  of  the  Condition  of  the  Blood  and  of  the  Vessels  on  Absorption. — After  loss 
of  blood  or  deterioration  of  the  nutritive  fluid  from  prolonged  abstinence,  absorption  gen- 
erally takes  place  with  great  activity.  This  is  well  known,  both  as  regards  the  entrance 
of  water  and  alimentary  substances  and  the  absorption  of  medicines.  It  was  at  one  time 
quite  a  common  practice  to  bleed  before  administering  certain  remedies,  in  order  to  pro- 
duce their  more  speedy  action  upon  the  system. 

The  rapidity  of  the  circulation  has  an  important  influence  upon  absorption.  "We  have 
already  shown,  in  treating  of  the  action  of  the  blood-vessels  on  absorption,  that  this  pro- 
cess may  be  impeded  or  even  arrested  by  the  ligation  of  important  vessels.  It  has  been 
evident,  also,  that  absorption  is  generally  active  in  proportion  to  the  vascularity  of  differ- 
ent parts.  During  the  process  of  intestinal  absorption,  the  increase  in  the  activity  of  the 
circulation  in  the  mucous  membrane  is  very  marked  and  undoubtedly  has  an  influence 
upon  the  rapidity  with  which  the  products  of  digestion  are  taken  up. 

Influence  of  the  Nervous  System  on  Absorption. — Experiments  upon  the  influence  of 
the  nervous  system  on  absorption  are  still  very  imperfect.  It  is  certain  that  this  process, 
especially  in  the  stomach,  is  subject  to  variations,  which  can  hardly  be  dependent  upon 
any  thing  but  nervous  action.  Water  and  other  liquids,  which  usually  are  readily  ab- 
sorbed from  the  stomach,  are  sometimes  retained  for  a  time,  and  are  afterward  rejected 
in  nearly  the  condition  in  which  they  were  taken.  It  is  probable,  however,  that  the  most 
important  influences  thus  exerted  by  the  nervous  system  are  effected  through  the  circu- 
lation. The  recent  experiments  of  Bernard  and  others  upon  the  sympathetic  system  of 
nerves  and  its  connection  with  the  muscular  coats  of  the  small  arteries,  by  the  action  of 
which  the  supply  of  blood  in  different  parts  is  regulated,  point  out  a  line  of  experimenta- 
tion which  would  probably  throw  much  light  upon  some  of  the  important  variations  in 
absorption.  When  it  is  remembered  that  the  small  arteries  may  become  so  contracted 
under  the  influence  of  the  sympathetic  system  that  their  caliber  is  almost  obliterated, 
of  course  retarding  to  a  corresponding  degree  the  capillary  and  venous  circulation  in  the 
parts,  and,  again,  that,  through  the  sympathetic  nerves,  the  same  vessels  may  be  so 
dilated  as  to  admit  to  a  particular  part  three  or  four  times  as  much  blood  as  it  ordinarily 
receives,  it  becomes  apparent  that  absorption  may  be  profoundly  affected  through  this 
system  of  nerves. 

As  far  as  the  influence  of  the  cerebro-spinal  system  is  concerned,  it  has  been  ascer- 
tained that,  while  section  of  some  of  the  nerves  distributed  to  the  alimentary  canal  will 
slightly  retard  the  absorption  of  poisonous  substances,  it  is  never  entirely  arrested.  Lon- 
get  found  that  the  operation  of  strychnine  injected  into  the  stomach  of  a  dog  in  which 


IMBIBITION  AND  ENDOSMOSIS.  321 

both  pneumogastric  nerves  had  been  divided  was  retarded  about  five  minutes  •  but  that 
the  convulsions,  when  they  occurred,  were  fully  as  severe  as  in  an  animal  which  had 
received  an  equal  dose,  without  section  of  the  nerves. 

Imbibition  and  Endosmosis. 

The  ideas  of  physiologists  concerning  the  mechanism  of  the  absorption  of  soluble  sub- 
stances have  become  radically  changed  since  the  beginning  of  the  present  century;  and 
it  is  now  generally  admitted  that  this  process  takes  place  chiefly  by  blood-vessels,  and 
that  the  absorbents  have  no  such  wonderful  elective  power  as  was  attributed  to  them  by 
the  older  writers.  This  involves  the  passage  of  liquids  through  the  coats  of  the  blood- 
vessels and  lymphatics;  a  process  which  has  been  the  subject  of  numerous  experiments, 
resulting  in  the  development  of  many  important  physical  laws  capable  of  application  to 
physiological  absorption.  At  the  present  day,  therefore,  the  history  of  absorption  is  not 
complete  without  a  consideration  of  the  laws  of  imbibition  and  endosmosis. 

If  liquids  can  pass  through  the  substance  of  an  animal  membrane,  it  is  evident  that 
the  membrane  itself  must  be  capable  of  taking  up  a  certain  portion  of  the  liquid  by 
imbibition;  and  this  must  be  considered  as  the  starting-point  in  absorption.  Imbibi- 
tion is,  indeed,  a  property  common  to  all  animal  structures.  One  of  the  most  strik- 
ing characteristics  of  organic  principles  is  that  they  may  lose  water  by  desiccation  and 
regain  it  by  imbibition.  It  is  also  a  well-known  fact  that  the  tissues  do  not  imbibe  all 
solutions  with  the  same  degree  of  activity.  Distilled  water  is  the  liquid  which  is  al- 
ways taken  up  in  greatest  quantity,  and  saline  solutions  enter  the  substance  of  the  tis- 
sues in  an  inverse  ratio  to  their  density.  This  is  also  the  fact  with  regard  to  mixtures 
of  alcohol  and  water,  imbibition  always  being  in  an  inverse  proportion  to  the  quantity 
of  alcohol  present  in  the  liquid.  Among  the  other  circumstances  which  have  a  marked 
influence  upon  imbibition,  is  temperature.  It  is  a  familiar  fact  that  dried  animal  mem- 
branes may  be  more  rapidly  softened  in  warm  than  in  cold  water ;  and,  with  regard  to 
the  imbibition  of  liquids  by  sand,  the  researches  of  Matteucci  and  Cima  have  shown  an 
immense  increase  at  a  moderately-elevated  temperature.  While  nearly  all  the  structures 
of  the  body,  after  desiccation,  will  imbibe  liquids,  the  membranes  through  which  the  pro- 
cesses of  absorption  are  most  active  are,  as  a  rule,  most  easily  permeated ;  and  we  shall 
see,  when  we  come  to  study  the  mechanism  of  the  passage  of  liquids  through  these  mem- 
branes, that  the  character  of  the  liquid,  the  temperature,  etc.,  have  a  great  influence 
upon  the  activity  of  this  process.  For  example,  all  liquids  which  have  a  tendency  to 
harden  the  tissues,  such  as  saline  solutions,  alcohol,  etc.,  pass  through  with  much  less 
rapidity  than  pure  water.  These  facts  will  be  found  particularly  interesting  in  connec- 
tion with  observations  on  the  passage  of  liquids  through  membranes,  in  experiments  on 
endosmosis  with  artificial  apparatus. 

Mechanism  of  the  Passage  of  Liquids  through  Membranes. — The  attention  of  physi- 
ologists was  first  directed  to  this  subject  by  the  researches  of  Dutrochet,  in  1826.  Al- 
though not  by  any  means  the  first  to  observe  the  phenomena  which  he  described  under 
the  name  of  endosmosis,  to  Dutrochet  is  generally  ascribed  the  honor  of  having  first 
indicated  the  applications  of  the  laws  of  endosmosis  to  the  nutrition  of  plants  and  ani- 
mals. Undoubtedly,  Dutrochet  was  the  first  to  make  experiments  upon  endosmosis  which 
attracted  the  attention  of  scientific  men  in  different  parts  of  the  world  and  which  were 
immediately  repeated  and  extended ;  but  the  experiments  made  upon  living  animals  by 
Lebkuchner,  in  1819,  and  by  Magendie,  in  1820,  had  already  demonstrated  most  conclu- 
sively the  passage  of  liquids  through  the  walls  of  the  blood-vessels ;  and  the  explanation 
offered  by  these  physiologists  was  fully  as  definite  as  that  proposed  by  Dutrochet. 

Dutrochet  constructed  an  instrument  called  the  endosmometer,  which  consists  sim- 
ply of  a  small  bell-glass,  the  lower  opening  of  which  is  closed  by  a  membrane,  the  open- 
ing above  being  connected  with  a  long  glass  tube  by  which  the  force  with  which  liquids 
21 


322  ABSORPTION. 

pass  through  the  membrane  can  be  measured.  The  bell-glass  is  generally  filled  with  a 
liquid  capable  of  attracting  a  current  of  water  from  without,  and  is  immersed  in  pure 
water,  so  that  the  membrane  is  completely  covered.  Under  these  circumstances,  there 
is  a  current  of  water  through  the  membrane,  which  will  cause  the  liquid  to  mount  in  the 
tube,  sometimes  to  the  height  of  several  feet ;  but,  at  the  same  time,  there  is  a  feebler 
current  from  the  interior  of  the  apparatus  to  the  water.  Dutrochet  called  the  stronger, 
the  endosmotic  current,  and  the  feebler,  the  exosmotic  current.  This  nomenclature, 
however,  is  not  strictly  accurate ;  for,  if  the  position  of  the  liquids  be  reversed,  the 
stronger  current  is  exosmotic  and  the  feebler  is  endosmotic.  It  must  be  remembered, 
therefore,  that  the  name  endosmosis  is  always  to  be  understood  as  applied  to  the  princi- 
pal current,  while  the  term  exosmosis  is  applied  to  the  current  in  the  opposite  direction. 
This  possible  inaccuracy  of  expression  has  led  to  the  adoption  by  Graham  and  others  of 
the  term  osmosis,  as  applied  generally  to  the  currents  which  take  place  through  mem- 
branes; but  the  terms  first  proposed  by  Dutrochet  are  most  commonly  used. 

The  phenomena  of  endosmosis,  which,  since  the  publication  of  the  researches  of  Du- 
trochet, have  been  so  closely  studied  by  physicists,  are  chiefly  interesting  to  the  physiolo- 
gist in  their  application  to  absorption.  While  it  is  true,  perhaps,  that  all  the  phenomena 
of  physiological  absorption  cannot  as  yet  be  explained  upon  purely  physical  principles, 
it  is  nevertheless  important  to  ascertain  how  far  physical  laws  are  involved  in  this  pro- 
cess. With  this  end  in  view,  we  shall  study  the  physical  phenomena  of  endosmosis, 
chiefly  with  reference  to  their  physiological  applications. 

It  is  now  definitely  ascertained  that  the  following  conditions  are  necessary  for  the 
operation  of  endosmosis  and  exosmosis : 

1.  That  both  liquids  be  capable  of  "wetting"  the  interposed  membrane,  or,  in  other 
words,  that  the  membrane  be  capable  of  imbibing  both  liquids.    If  but  one  of  the  liquids 
can  wet  the  membrane,  the  current  can  take  place  in  only  one  direction. 

2.  That  the  liquids  be  iniscible  with  each  other  and  be  differently  constituted.     Al- 
though it  is  found  that  the  currents  are  most  active  when  the  liquids  are  of  different  den- 
sities, this  condition  is  not  indispensable  ;  for  currents  will  take  place  between  solutions 
of  different  substances,  such  as  salt,  sugar,  or  albumen,  when  they  have  precisely  the 
same  density. 

The  physiological  applications  of  the  laws  of  endosmosis  can  now  be  more  fully 
appreciated,  as  it  is  evident  that  the  above  conditions  are  fulfilled  whenever  absorption 
takes  place,  with  the  single  exception  of  the  absorption  of  fats,  which  has  been  specially 
considered.  For  example,  all  substances  are  dissolved  or  liquefied  before  they  are  ab- 
sorbed, and,  in  this  condition,  they  are  capable  of  "  wetting  "  the  walls  of  the  blood-vessels 
All  the  liquids  absorbed  are  capable,  also,  of  mixing  with  the  plasma  of  the  blood.  What 
makes  this  application  still  more  complete,  is  the  behavior  of  albumen  in  endosmotic  ex- 
periments. In  physiological  absorption,  there  is  always  a  great  predominance  of  the 
endosmotic  current,  and  there  is  very  little  transudation,  or  exosmosis,  of  the  albuminoid 
constituents  of  the  blood.  On  the  other  hand,  there  is  a  constant  absorption  of  albu- 
minose,  which  is  destined  to  be  converted  into  the  albuminoid  matters  of  the  blood. 

Recognizing  the  fact,  which  was,  indeed,  pointed  out  clearly  by  Dutrochet,  that  albu- 
men is  capable  of  inducing  a  more  powerful  endosmotic  current  than  almost  any  other 
liquid,  it  has  been  shown  that  it  never  itself  passes  through  membranes  in  the  exosmotic 
current ;  but  that  albuminoids,  after  transformation  by  digestion  into  albuminose,  or 
albumen  mixed  with  gastric  juice,  pass  through  animal  membranes  with  great  facility. 
The  experiments  by  which  these  facts  are  demonstrated  are  very  conclusive  and  are 
of  the  highest  physiological  importance.  On  removing  part  of  the  shell  of  an  egg,  so 
as  to  expose  its  membranes,  and  immersing  it  in  pure  water,  the  passage  of  water  into 
the  egg  was  rendered  evident  by  the  projection  of  the  distended  membranes;  but, 
although  the  surrounding  liquid  had  become  alkaline  and  the  appropriate  tests  revealed 
the  presence  of  some  of  the  inorganic  constituents  of  the  egg,  the  presence  of  albumen 


IMBIBITION  AND  ENDOSMOSIS. 


323 


could  never  be  detected.     When  the  contents  of  the  egg  were  replaced  by  the  serum 
of  the  blood,  the  same  result  followed.     "After  six  or  eight  hours  of  immersion  the 
serum  had  yielded  to  the  water  in  the  vessel  all  its  saline  elements,  chlorides,  sulphates, 
phosphates,  which  were  easily  recognized  by  their  peculiar  reactions,  but 
not  an  atom  of  albumen." 

A  very  simple  apparatus  for  illustrating  endosmotic  action  can  be  con- 
structed in  the  following  way :  Remove  carefully  a  circular  portion, 
about  an  inch  in  diameter,  of  the  shell  from  one  end  of  an  egg,  which 
may  be  done  without  injuring  the  membranes,  by  cracking  the  shell  into 
small  pieces,  which  are  picked  off  with  forceps.  A  delicate  glass-tube, 
about  six  inches  in  length,  is  then  introduced  through  a  small  opening  in 
the  shell  and  membranes  of  the  other  end  of  the  egg,  and  is  secured  in  a 
vertical  position  by  wax,  the  tube  penetrating  the  yolk.  The  egg  is  then 
placed  in  a  wine-glass  partly  filled  with  water.  In  the  course  of  half  an 
hour  or  an  hour,  the  water  will  have  penetrated  the  exposed  membrane, 
and  the  yolk  w;ll  rise  in  the  tube. 

Influence  of  Membranes  upon  Osmotic  Currents. — The  force  with 
which  liquids  pass  through  membranes,  called  endosmotic  or  osmotic 
force,  is  to  a  great  degree  dependent  upon  the  influence  of  the  mem- 
branes themselves.  This  influence  is  always  purely  physical,  in  experi- 
ments made  out  of  the  body ;  and  physiological  absorption  can  be  ex- 
plained, to  a  certain  extent,  by  the  same  laws.  It  must  be  remem- 
bered, however,  that  the  properties  of  organic  structures,  which  are 
manifested  only  in  living  bodies,  are  capable  of  modifying  these  physical 
phenomena  to  a  remarkable  degree.  For  example,  all  living  tissues  are 
capable  of  selecting  and  appropriating  from  the  nutritive  fluids  the  ma- 
terials necessary  for  their  regeneration ;  and  the  secreting  structures  of 
glands  also  select  from  the  blood  certain  principles  which  are  used  in 
the  formation  of  their  secretions.  At  the  present  day,  these  phenomena  and  their  modi- 
fications through  the  nervous  system  cannot  be  fully  explained.  This  is  true,  also,  of 
many  of  the  phenomena  of  absorption  and  their  modifications,  which  are  probably  de- 
pendent upon  the  same  kind  of  action.  In  view  of  these  undoubted  facts,  the  influence 
of  the  structures  through  which  liquids  pass  in  physiological  absorption  may  be  divided 
as  follows :  first,  into  physical  influences,  which  may  be  illustrated  by  endosmotic  ex- 
periments with  organic  membranes  out  of  the  body ;  and  second,  modifications  of  these 
phenomena,  which  are  presented  only  in  the  living  organism. 

Numerous  experiments  have  demonstrated  that  both  the  endosmotic  and  the  exos- 
motic  current  may  be  produced  by  using  a  porous  instead  of  a  membranous  septum, 
though  then  they  are  always  comparatively  feeble.  The  phenomena  thus  presented  are 
to  be  explained  entirely  by  the  laws  of  capillary  attraction  and  of  the  diffusion  of  liquids. 
These  laws  would  enter  largely  into  the  explanation  of  the  passage  of  liquids  through 
animal  membranes,  if  it  could  be  demonstrated,  or  even  rendered  probable,  that  these 
membranes  are  invariably  porous,  or  provided  with  capillary  openings.  It  will  be  neces- 
sary, however,  to  study  this  question  very  carefully  and  to  examine  all  the  properties  of 
animal  membranes,  both  within  and  without  the  living  organism. 

In  the  first  place,  is  there  any  proof  that  all  membranes  which  will  admit  the  passage 
of  liquids  are  porous  ?  This  is  a  most  important  question ;  and  it  lies  at  the  foundation 
of  the  explanation  of  the  phenomena  of  endosmosis  by  the  laws  of  capillary  attraction. 

In  all  membranes  which  possess  an  anatomical  structure  discoverable  by  the  micro- 
scope, there  are  undoubtedly  interstices  between  the  fibres,  cells,  etc.,  of  which  the  tis- 
sue is  composed ;  but,  on  the  other  hand,  animal  membranes  generally  have  a  layer,  like 
the  basement-membranes  of  mucous  tissues,  which  is  absolutely  homogeneous  and  struct- 


FIG.  97.— Egg  pre- 
pared so  as  to  il- 
lustrate, wdos- 
motie  action. 


324  ABSORPTION. 

ureless.  In  applying  the  laws  of  endosmosis  to  physiological  absorption,  it  is  found  that 
the  membranes  which  are  most  easily  penetrated  by  fluids  are  excessively  thin  and 
nearly  homogeneous.  Take,  for  example,  the  walls  of  the  capillary  blood-vessels,  through 
which  the  greatest  part  of  physiological  absorption  takes  place.  This  membrane  is 
from  25*00  to  ial 00  of  an  inch  thick,  and  is  entirely  amorphous,  with  the  exception  of 
the  lining  epithelium  with  its  nuclei.  The  assumption  that  invisible  capillary  orifices 
exist  in  these  thin,  amorphous  membranes,  aside  from  the  so-called  stomata,  is  purely 
hypothetical  and  is  unwarrantable.  The  only  circumstance  which  could  lead  to  such  a 
supposition  is  the  fact  that  these  membranes  can  be  penetrated  by  liquids. 

It  is  manifestly  unphilosophical  and  absurd  to  offer,  as  an  explanation  ol  endosmosis 
through  structureless  membranes,  an  hypothesis  which  has  its  only  support  in  the  exist- 
ence of  the  phenomena  which  it  is  intended  to  explain.  This  mode  of  reasoning  is  all 
the  more  unsound,  as  the  phenomena  of  endosmosis  are  very  far  from  being  completely 
understood,  and  as  many  important  properties  of  organic  structures,  which  bear  directly 
upon  the  question  under  consideration,  are  ignored.  For  example,  physiological  absorp- 
tion does  not  always  take  place  in  accordance  with  known  physical  laws.  It  undergoes 
modifications  which  can  at  present  only  be  explained  on  the  supposition  that  the  liquids 
become,  for  the  time,  part  of  the  living  organic  structures  and  partake  of  their  peculiar 
properties ;  one  of  them,  the  property  by  virtue  of  which  they  appropriate  both  the 
organic  and  the  inorganic  principles  necessary  to  their  proper  constitution  and  regenera- 
tion, is  called  by  some,  vital ;  a  word  which  simply  expresses  ignorance  of  its  essen- 
tial character.  It  must  be  understood,  however,  that  this  remark  does  not  apply  to  the 
general  phenomena  of  endosmosis  or  absorption,  but  only  to  certain  of  its  unexplained 
modifications. 

A  most  important  property  of  organic  tissues,  which  is  ignored  by  those  who  explain 
absorption  on  the  principle  of  capillary  attraction,  is  that  of  hygrometricity.  All  the 
organic  nitrogenized  proximate  principles  are  capable  of  losing  their  water  of  composi- 
tion by  desiccation  and  of  regaining  it  by  imbibition.  The  water  which  enters  into  their 
composition  is  not  necessarily  contained  in  interstices  in  the  tissue,  but,  in  the  case  of 
structureless  parts  especially,  is  uniformly  disseminated,  or,  we  may  term  it,  diffused 
throughout  the  organic  substance,  of  which  it  forms  a  constituent  part.  This  action  of 
certain  liquids  upon  the  organic  semisolids  is  something  like  the  diffusion  of  liquids ;  the 
difference  being  that  it  is  the  liquid  only  which  is  diffused  in  the  sernisolid,  the  semisolid 
being  incapable  of  diffusing  in  the  liquid.  As  it  has  been  found  that  all  liquids  are  not 
equally  subject  to  capillary  attraction,  so  animal  tissues  imbibe  different  liquids  with  dif- 
ferent degrees  of  activity ;  a  fact  which  will  account  in  a  measure  for  the  variations  in 
the  endosmotic  currents  with  different  solutions. 

Examples  are  not  wanting  of  endosmosis  by  imbibition  or  diffusion,  when  it  cannot 
be  assumed  that  there  is  any  such  thing  as  porosity  in  the  septum.  The  following 
experiment  of  Lhermite  fully  illustrates  this  point.  A  tube  was  partly  filled  with  a  col- 
umn of  chloroform ;  and  upon  this  was  poured  a  layer  of  water,  and  above  it  a  layer  of 
ether.  The  ether  gradually  penetrated  the  layer  of  water  and  passed  to  the  chloroform, 
mingling  with  it.  After  a  certain  time,  all  the  ether  had  thus  been  diffused  in  the  chlo- 
roform, and  the  layer  of  water  retained  its  original  volume.  We  have  repeated  this 
experiment  with  some  slight  modifications,  using  first  a  layer  of  sulphuric  acid,  then  a 
layer  of  water,  and  finally  a  solution  of  blue  litmus  in  alcohol ;  and,  in  a  very  short 
time,  the  acid  penetrated  the  water  and  reddened  the  litmus  above.  A  liquid  septum  is 
certainly  not  porous,  in  any  sense  of  the  word ;  and  the  explanation  of  the  phenomenon 
of  endosmosis  through  liquids  depends  simply  upon  the  law  of  diffusion  of  liquids,  the 
molecules  of  the  liquids  being  held  together  so  feebly  that  they  will  admit  the  molecules 
of  other  liquids  with  which  they  are  capable  of  mixing. 

With  regard  to  the  passage  of  liquids  through  different  septa,  the  following  seem  to  be 
the  facts  which  can  be  considered  as  definitely  settled  : 


IMBIBITION  AND  ENDOSMOSIS. 


325 


The  cohesive  attraction  of  the  constituent  particles  of  insoluble  solids  is  so  great,  that 
the  entrance  of  fluids  is  impossible,  unless  the  substance  be  porous,  and  this  always 
involves  the  law  of  capillary  attraction ;  but,  in  liquids,  the  cohesive  attraction  is  so 
slight  as  to  admit  of  the  penetration  and  diffusion  of  certain  other  liquids. 

Homogeneous  animal  membranes,  which  are  of  a  semisolid  consistence,  are  capable 
of  imbibing  certain  liquids ;  and  any  liquid  which  can  pass  into  such  membranes  will 
pass  through  them  under  proper  conditions.  The  cohesive  attraction  of  the  particles  of 
the  membrane  is  not  such  as  to  allow  them  to  imbibe  an  indefinite  quantity  of  any  liquid ; 
but  it  is  one  of  the  distinctive  properties  of  organic  tissues,  that  a  limited  quantity  of 
liquid  can  be  taken  up  in  this  way. 

In  view  of  these  facts,  it  is  not  necessary  to  assume  the  existence  of  infinitely  small 
capillary  openings  in  homogeneous  membranes  through  which  osmotic  currents  can  be 
made  to  take  place,  in  order  to  explain  the  mechanism  of  these  currents.  In  the  case  of 
two  liquids  capable  of  diffusing  with  each  other  and  separated  by  an  animal  membrane, 
the  mechanism  of  the  endosmotic  and  exosmotic  currents  is  very  simple.  In  the  first 
place,  the  membrane  imbibes  both  the  liquids,  but  one  is  always  taken  up  in  greater 
quantity  than  the  other.  If  water  and  a  solution  of  common  salt  be  employed,  the  sur- 
face of  the  membrane  exposed  to  the  water  will  imbibe  more  than  the  surface  exposed  to 
the  saline  solution  ;  but  both  liquids  will  meet  in  its  substance.  The  first  step,  therefore, 
in  the  production  of  the  currents  is  imbibition.  Once  in  contact  with  each  other,  the 
liquids  diffuse,  the  water  passing  to  the  saline  solution,  and  vice  versa.  This  takes  place 
by  precisely  the  same  mechanism  as  that  of  the  passage  of  liquids  through  porous  septa. 

The  osmotic  currents  may  be  modified  with  the  same  liquids  by  using  different  mem- 
branes. This  fact  was  well  illustrated  in  some  of  the  experiments  of  Matteucci  and  Cima, 
in  which  comparative  observations  were  made  upon  the  currents  through  the  skin  of  the 
torpedo,  the  skin  of  the  frog,  and  the  skin  of  the  eel.  The  results  obtained  with  these 
different  membranes  showed  marked  and  constant  variations.  The  same  observers, 
using  the  mucous  membrane  of  the  stomach  of  the  lamb,  found  a  marked  difference  in  the 
endosmotic  phenomena  when  the  surface  exposed  to  the  water  was  reversed.  In  two 
experiments,  with  the  epithelial  surface  of  the  membrane  turned  toward  the  interior  of 
the  endosmometer,  the  elevations  of  the  liquid  in  an  hour  and  a  quarter  were  forty- 
four  and  fifty-six  millimeters;  but,  with  the  membrane  reversed,  so  that  the  attached  sur- 
face was  turned  toward  the  interior,  the  elevations  during  the  same  period  were  sixty-six 
and  seventy-two  millimeters.  This  difference  is  readily  explained  by  the  difference  in  the 
constitution  of  the  two  surfaces  of  the  membrane  used.  From  these  facts,  it  is  evident 
that,  while  the  diffusion  of  liquids  as  they  meet  in  the  substance  of  a  membrane  is  the 
actual  cause  of  the  osmotic  currents,  which  are  continued  as  the  liquids  diffuse  with  each 
other  upon  either  side  of  the  membrane,  the  determination  of  a  predominating  or  endos- 
motic current,  the  ordinary  conditions  being  undisturbed,  is  effected  by  the  greater  at- 
tractive force  which  the  membrane  exerts  upon  one  of  the  liquids. 

Influence  of  Different  Liquids  upon  Osmotic  Currents.— The  action  of  the  liquids  be- 
tween which  endosmotic  currents  take  place  is,  as  we  have  seen,  most  intimately  con- 
nected with  the  force  by  which  the  liquids  enter  the  membrane,  be  it  capillary  attraction 
or  imbibition ;  but  the  attractive  force  exerted  by  the  membrane  is  never  capable,  in  itself, 
pf  producing  a  current.  It  is  evident,  therefore,  that  the  properties  of  the  liquids  must 
have  an  important  influence  upon  osmosis,  both  from  differences  in  the  attraction  of  the 
membrane  for  the  liquids  and  their  different  degrees  of  diffusibility.  In  order  to  appre- 
ciate fully  all  the  physical  phenomena  of  osmosis,  it  will  be  necessary  to  study  carefully 
the  laws  of  diffusion  of  liquids  and  the  diffusibility  of  different  solutions ;  but  it  will  be 
sufficient  for  our  present  purpose  to  state  a  few  general  propositions,  which  will  be  found 
more  or  less  applicable  to  physiological  absorption. 

When  two  liquids,  capable  of  mixing  with  each  other,  are  brought  together,  they 
diffuse  with  greater  or  less  rapidity,  until  the  constitution  of  the  mixture  becomes  uniform. 


326  ABSORPTION. 

Different  liquids  possess  widely  different  degrees  of  diffusibility ;  and,  as  a  rule,  in 
saline  solutions,  the  rate  of  diffusion  increases  in  proportion  to  the  strength  of  the  solu- 
tion, at  least  when  the  quantity  of  salt  dissolved  does  not  exceed  four  or  five  per  cent. 
It  follows  from  this  that  the  activity  of  the  endosmotic  current  toward  any  saline  solution 
will  be  greatest  at  the  beginning  of  the  experiment  and  will  progressively  diminish  as  the 
currents  continue  and  the  two  liquids  assume  a  more  nearly  uniform  density. 

The  rate  of  diffusion  of  different  solutions  is  generally  increased  by  a  moderate  eleva- 
tion of  temperature. 

Bearing  in  mind  these  general  laws,  and  remembering  that  they  are  applicable  to 
diffusion  as  it  takes  place  through  animal  membranes,  we  can  easily  understand  how 
different  liquids  and  solutions,  in  an  endosmometer,  will  attract  with  different  degrees  of 
intensity  any  given  liquid,  such  as  pure  water ;  and  how  this  attractive  force,  which  is 
measured  by  the  rapidity  and  extent  of  the  rise  of  liquid  in  an  endosmometer,  may  be 
modified  by  the  concentration  of  the  solution,  differences  in  temperature,  and  other  con- 
ditions. The  influence  which  the  membrane  exerts  upon  the  relative  intensity  of  these 
currents  is  dependent  to  a  certain  extent  upon  the  diffusion  which  takes  place  when  the 
two  liquids  come  together  in  its  substance. 

As  a  rule  to  which  there  are  not  many  exceptions,  pure  water  will  penetrate  ani- 
mal membranes  more  readily  than  any  other  liquid ;  and  it  is  consequently  from  the 
water  to  the  liquid  contained  in  the  endosmometer  that  the  principal  current  generally 
takes  place.  Liquids  like  alcohol,  saline  solutions,  etc.,  which  have  this  property,  are 
said  to  be  positively  osmotic ;  while  those  with  which  the  current  takes  place  in  the 
opposite  direction,  such  as  oxalic  acid,  weak  hydrochloric  acid,  bichloride  of  platinum, 
etc.,  are  said  to  be  negatively  osmotic.  In  a  series  of  experiments  with  different  liquids, 
if  the  endosmometer  be  always  the  same  and  if  all  the  liquids  used  be  exposed  to  the  action 
of  pure  water,  in  a  given  time  a  definite  change  in  the  quantity  of  fluid  in  the  endosmom- 
eter will  be  produced,  which  will  be  indicated  by  a  certain  amount  of  elevation  or  de- 
pression in  its  level. 

Applications  of  Physical  Laws  to  the  Function  of  Absorption. 

In  no  experiments  performed  out  of  the  body,  can  the  conditions  favorable  to  the 
passage  of  liquids  through  membranes  in  accordance  with  purely  physical  laws  be  realized 
as  they  exist  in  the  living  organism.  The  vast  extent  of  the  absorbing  surfaces ;  the  great 
delicacy  and  permeability  of  the  membranes ;  the  rapidity  with  which  principles  are  car- 
ried on  by  the  torrent  of  the  circulation,  as  soon  as  they  pass  through  these  membranes ; 
the  uniformity  of  the  pressure,  notwithstanding  the  penetration  of  liquids ;  all  these  favor 
the  physical  phenomena  of  absorption  in  a  way  which  cannot  be  imitated  in  artificially- 
constructed  apparatus.  It  is  not  necessary  to  invoke  the  vital  properties  of  tissues  to 
explain  the  ordinary  phenomena  of  absorption.  Enough  has  been  learned  of  the  laws 
which  regulated  endosmosis  and  exosmosis  to  enable  us  to  explain  most  of  these  phe- 
nomena upon  physical  principles.  This  fact  has  been  apparent  in  studying  these  princi- 
ples in  their  relation  to  absorption  in  the  living  body ;  but  it  is  an  important  question  to 
determine  whether  this  be  applicable  to  all  the  varied  phenomena  of  physiological  ab- 
sorption. In  other  words,  are  there  any  modifications  in  this  function  which  cannot,  as 
yet,  be  explained  by  physical  laws  ? 

Admitting  the  fact  that  the  general  process  of  absorption  takes  place  in  accordance 
with  the  laws  of  endosmosis,  we  shall  now  consider  some  of  the  phenomena  which  ap- 
pear to  be  in  opposition  to  known  physical  principles,  or  in  which  the  application  of 
these  principles  seems  to  be  imperfectly  understood. 

It  is  not  easy  to  understand  how  particles  of  emulsified  fat  find  their  way  through 
the  walls  of  the  lacteals  and  blood-vessels,  unless  we  admit  the  existence  of  orifices, 
such  as  have  been  described  by  recent  anatomists.  The  experiments  of  Matteucci  with 
alkaline  emulsions  seem  to  show  that  alkalinity  is  a  condition  necessary  to  the  penetra- 


IMBIBITION  AND  ENDOSMOSIS.  337 

tion  of  fatty  particles,  although  they  do  not  offer  an  explanation  of  the  mechanism  by 
which  these  particles  pass  through  membranes.  It  has  been  demonstrated  that  the  epi- 
thelium which  covers  these  membranes  becomes  filled  with  fatty  granules  during  the 
absorption  of  emulsions,  and  some  physiologists  invoke  the  aid  of  "  cell-action," — con- 
cerning which  it  must  be  confessed  that  there  exists  very  little  definite  information — in 
explanation  of  this  phenomenon.  The  penetration  of  fatty  particles  through  membranes 
must  be  regarded  as  one  of  the  points  which  cannot  be  explained  by  the  laws  of  endos- 
mosis. 

There  are  certain  experiments  on  absorption  in  the  living  body,  to  which  a  great  deal 
of  importance  was  attached  by  Longet,  which  are  seemingly  in  opposition  to  physical 
laws.  This  author  states  that,  when  solutions  of  sugar  of  different  densities  are  secured 
in  isolated  portions  of  the  intestine  of  a  living  animal,  the  denser  solutions  are  absorbed 
with  as  much  rapidity  as  those  which  are  less  concentrated.  He  also  shows  that  saline 
solutions  of  greater  density  than  the  blood  are  absorbed  in  the  living  animal,  when, 
according  to  physical  laws,  the  current  should  take  place  in  the  opposite  direction.  The 
view  that  these  facts  are  in  opposition  to  physical  laws  is  very  successfully  controverted 
by  Milne-Edwards.  This  author,  referring  to  some  experiments  by  Von  Becker  in  sup- 
port of  his  position,  asserts  that  there  is  first  an  exosmosis  of  the  watery  portions  of  the 
blood  to  these  dense  solutions,  with  a  feeble  penetration  of  the  solutions  into  the  blood- 
vessels, until,  by  the  laws  of  diffusion,  the  solutions  become  so  diluted  as  to  be  readily  taken 
into  the  circulation.  Such  an  action  as  this  could  not  take  place  between  two  saline 
solutions  in  an  endosmometer,  for  both  the  currents  would  be  equal  when  the  liquids 
became  of  equal  density ;  but  it  has  been  shown  that,  after  endosmosis  in  an  endosmome- 
ter has  ceased,  it  may  be  again  induced  by  simply  agitating  the  liquids.  In  physiological 
absorption,  the  motion  is  constant  and  very  rapid,  and  solutions  in  their  passage  along  the 
alimentary  canal  are  continually  exposed  to  fresh  absorbing  surfaces.  Farthermore,  the 
albuminoid  matters  of  the  blood,  which  are  very  slightly  exosmotic,  will  attract  an  en- 
dosmotic  current  from  liquids  even  when  they  are  of  the  same  density.  The  kind  of 
action  described  by  Milne-Edwards  would  be  by  no  means  an  isolated  example  of  a 
liquid  passing  out  of  the  blood-vessels  to  be  again  absorbed  after  it  has  acted  upon  mat- 
ters contained  in  the  alimentary  canal.  This  takes  place  with  all  the  digestive  fluids ; 
and  the  liquid  is  effused,  not  by  simple  exosmosis,  but  by  an  act  of  secretion  excited  by 
the  impression  made  upon  the  mucous  membrane.  We  are  not  justified,  therefore,  in 
assuming,  with  Longet,  that  the  absorption  of  solutions  of  greater  density  than  the  blood 
is  always  in  opposition  to  the  laws  of  endosmosis. 

The  imbibition  of  the  coloring  matter  of  the  bile  by  the  coats  of  the  gall-bladder 
after  death,  while  nothing  of  the  kind  takes  place  during  life,  is  not  due  to  the  absence 
of  so-called  vital  action.  During  life,  the  circulation  in  the  mucous  membrane  of  this 
reservoir  would  readily  remove  the  few  particles  of  coloring  matter  which  might  pene- 
trate from  the  bile,  and  of  course  there  is  no  time  for  any  coloration  to  take  place. 

In  treating  of  the  variations  and  modifications  of  absorption,  we  noted  an  apparent 
elective  power  in  the  mucous  membrane  of  some  portions  of  the  alimentary  canal.  This 
is  illustrated  in  the  failure  of  the  mucous  membrane  to  absorb  woorara  and  various  of 
the  animal  poisons,  which,  as  a  rule,  produce  their  effects  only  when  introduced  into  a 
wound  or  injected  into  the  areolar  tissue.  The  separation  of  various  soluble  substances  by 
the  process  known  as  dialysis  may  throw  some  light  upon  this  subject,  but  as  yet  we  have 
no  facts  which  offer  a  satisfactory  explanation  of  this  phenomenon.  Certain  of  these  phe- 
nomena which  show  an  apparent  elective  power  in  absorbing  membranes  are  probably 
due  to  a  cell-action  resembling  secretion  ;  for  all  these  surfaces  are  covered  with  epithe- 
lium, which  must  be  penetrated  before  the  fluids  can  get  to  the  blood-vessels.  But,  even 
with  regard  to  the  selection  of  materials  from  the  blood  to  form  secretions,  very  little  of 
a  definite  character  is  known. 

Those  who  believe  that  absorption  is  often  modified  by  so-called  vital  action  offer  this 


328  ABSORPTION. 

in  explanation  of  the  important  influence  of  the  nervous  system  upon  this  function.  Pre- 
cisely how  the  nervous  system  affects  absorption,  in  all  instances,  it  is  impossible,  in  the 
present  state  of  our  knowledge,  to  determine;  but  modifications  are  frequently  effected 
through  the  sympathetic  nerves.  These  nerves,  as  is  well  known,  are  capable  of  pro- 
ducing important  local  changes  in  the  circulation,  and  can  even  temporarily  arrest  the 
capillary  circulation  in  some  parts ;  and  it  is  in  this  way  that  many  of  the  variations  in 
absorption  may  be  produced. 

Lymph  and  Chyle. 

To  complete  the  history  of  physiological  absorption,  it  will  be  necessary  to  treat  of 
the  origin,  composition,  and  properties  of  the  lymph  and  chyle.  It  is  only  within  a  few 
years  that  physiologists  have  been  able  to  appreciate  the  importance  of  the  lymph,  for 
the  experiments  indicating  the  enormous  quantity  of  this  liquid  which  is  continually 
passing  into  the  blood  are  of  recent  date.  The  earlier  experimenters  never  succeeded  in 
obtaining  more  than  a  small  quantity  of  fluid  from  the  lymphatic  system.  On  the  other 
hand,  for  the  long  period  during  which  it  was  supposed  that  all  the  products  of  diges- 
tion entered  the  system  by  the  thoracic  duct,  the  importance  of  the  chyle  was  much 
exaggerated ;  but  the  researches  upon  intestinal  absorption  by  Magendie  and  those  who 
followed  him,  and  the  experiments  of  Colin  on  the  quantity  of  fluid  which  passes  into 
the  blood  by  the  thoracic  duct  during  the  intervals  of  digestion,  have  enabled  physiologists 
to  form  a  better  estimate  of  the  importance  of  the  lymph  and  chyle.  In  studying  the 
properties  of  these  fluids,  the  consideration  of  the  lymph  naturally  precedes  that  of  the 
chyle,  as  the  latter  consists  simply  of  lymph,  to  which  certain  of  the  products  of  diges- 
tion have  been  added  by  absorption  from  the  alimentary  canal. 

Mode  of  obtaining  Lympli. — The  old  methods  of  obtaining  this  fluid  are  no  longer 
employed.  In  the  inferior  animals,  recently  killed,  a  few  drops  may  be  obtained  by 
pricking  the  lymphatic  glands  or  by  exposing  the  right  lymphatic  trunk  or  the  thoracic 
duct  and  collecting  the  small  quantity  of  fluid  which  is  discharged  when  these  vessels  are 
punctured.  Although  a  notable  quantity  of  chyle  can  be  obtained  from  the  thoracic  duct 
of  an  animal  killed  during  intestinal  absorption,  it  is  difficult  to  collect  even  a  small  quan- 
tity of  fluid  during  the  intervals  of  digestion.  Various  occasions  have  presented  them- 
selves for  obtaining  lymph,  possessing  more  or  less  of  its  normal  characters,  from  the 
human  subject  during  life ;  but,  in  many  of  these  instances,  there  existed  some  pathologi- 
cal condition  of  the  lymphatic  system,  and  it  cannot  be  assumed  that  the  liquid  thus 
obtained  was  in  a  perfectly  healthy  condition. 

The  first  successful  experiments  in  which  the  lymph  and  chyle  were  obtained  in  quan- 
tity were  made  by  Colin.  This  observer,  in  operating  upon  large  animals,  particularly 
the  ruminants,  experienced  no  great  difficulty  in  isolating  the  thoracic  duct  near  its  junc- 
tion with  the  subclavian  vein  and  introducing  a  metallic  tube  of  sufficient  size  to  allow 
the  free  discharge  of  fluid.  These  experiments,  made  upon  horses  and  the  larger  rumi- 
nants, were  the  first  to  give  any  clear  idea  of  the  quantity  of  liquids  (lymph  and  chyle) 
which  pass  through  the  thoracic  duct.  In  an  observation  upon  a  cow  of  medium  size,  he 
succeeded  in  collecting,  in  the  course  of  twelve  hours,  the  enormous  quantity  of  105-3  Ibs. 
av.  (47,963  grammes) ;  and  he  farther  states  that  a  very  much  greater  amount  can  be 
obtained  by  operating  upon  ruminants  of  larger  size.  Whether  this  represent  the  actual 
quantity  which  is  normally  discharged  into  the  venous  circulation,  is  a  question  which 
will  be  considered  under  the  head  of  the  probable  quantity  of  lymph  and  chyle ;  but  it 
certainly  shows  that  the  lymph  cannot  but  be  regarded  as  one  of  the  most  important  of 
the  animal  fluids. 

Among  the  observations  upon  the  fluids  discharged  from  the  thoracic  duct,  which 
followed  the  experiments  of  Colin,  the  most  interesting  are  those  made  in  1859,  by  Dai- 
ton,  who  operated  upon  carnivorous  as  well  as  herbivorous  animals.  These  experiments 


LYMPH  AND   CHYLE.  339 

were  performed  upon  young  goats  and  dogs,  and  the  general  results  with  regard  to  the 
quantity  of  fluids  discharged  closely  corresponded  with  those  obtained  by  Colin.  The 
operation  of  making  the  fistula  in  goats  is  not  very  difficult,  all  that  is  necessary  being 
to  cut  down  upon  the  subclavian  vein  at  the  point  where  the  duct  empties  into  it,  and  to 
fix  in  it  a  tube  of  appropriate  size  ;  but,  in  dogs,  the  vessels  are  more  deeply  situated,  and 
the  operative  procedure  is  much  more  tedious.  This,  however,  is  the  only  way  in  which 
lymph  and  chyle  can  be  obtained  from  the  lower  animals  in  any  considerable  quantity. 

Quantity  of  Lymph.—  Although  the  experiments  just  described  might  at  first  seera 
sufficient  to  give  a  pretty  clear  idea  of  the  entire  quantity  of  lymph  discharged  into  the 
venous  system,  it  is  evident  that  the  conditions  of  the  circulation  of  this  fluid  must  be  so 
seriously  modified  by  the  establishment  of  a  fistula,  that  the  results  thus  obtained  are  far 
from  being  entirely  satisfactory.  In  the  first  place,  Colin  found  that  the  canal,  at  its 
junction  with  the  subclavian  vein,  was  seldom  single ;  and,  in  many  of  his  observations 
in  which  a  very  large  quantity  of  liquid  was  obtained,  there  were  several  vessels  of  nearly 
equal  size  emptying  into  the  venous  system.  In  the  experiment  to  which  we  have 
referred,  however,  the  opening  was  single ;  and  the  quantity  of  fluid  obtained  represented 
all  that  passed  up  the  thoracic  duct  during  the  time  that  the  observation  was  continued. 
As  we  should  naturally  expect,  the  discharge  of  liquid  was  subject  to  certain  variations, 
its  maximum  corresponding  with  the  period  of  greatest  activity  in  digestion  and  absorption. 

It  is  not  possible  to  estimate  the  influence  of  the  unobstructed  discharge  of  lymph 
and  chyle  by  a  fistulous  opening  upon  the  absolute  quantity  which  passes  out  of  the 
canal ;  and,  in  the  natural  course  of  the  circulation,  there  is  a  certain  amount  of  obstruc- 
tion to  its  entrance  into  the  vein,  which  might  sensibly  retard  the  current. 

According  to  the  estimates  of  Dalton,  deduced  from  his  own  observations  upon  dogs 
and  the  experiments  of  Colin  upon  horses,  the  total  quantity  of  lymph  and  chyle  pro- 
duced in  the  twenty-four  hours  in  a  man  weighing  one  hundred  and  forty  pounds  is  from 
six  to  six  and  a  half  pounds.  And,  again,  reasoning  from  experiments  made  upon  dogs 
eighteen  hours  after  feeding,  when  the  fluid  which  passes  up  the  thoracic  duct  may  be 
assumed  to  be  pure,  unmixed  lymph,  the  total  quantity  of  lymph  alone,  produced  in  the 
twenty -four  hours  by  a  man  of  ordinary  weight,  would  be  between  three  and  a  half  and 
four  pounds  (3-864  Ibs.).  These  estimates  can  only  be  accepted  as  approximative,  and 
they  do  not  indicate  the  entire  quantity  of  lymph  actually  contained  in  the  organism. 

There  are  no  very  satisfactory  recent  researches  with  regard  to  the  physiological 
variations  in  the  quantity  of  lymph.  Collard  de  Martigny  made  a  series  of  elaborate 
investigations  a  number  of  years  ago,  with  regard  to  the  effects  of  starvation  upon  the 
constitution  and  the  quantity  of  the  lymph.  He  found  the  lymphatics  always  distended 
with  fluid  in  dogs  killed  after  two  days  of  total  deprivation  of  food.  This  condition  con- 
tinued during  the  first  week  of  starvation ;  but,  after  that  time,  the  quantity  in  the  ves- 
sels gradually  diminished,  and,  a  few  hours  before  death,  the  lymphatics  and  the  thoracic 
duct  were  nearly  empty.  In  comparing  the  quantity  of  fluid  in  the  lymphatics  of  the 
neck  during  digestion  and  absorption  with  the  quantity  which  they  contained  soon  after 
digestion  was  completed,  the  same  observer  found  that,  while  digestion  and  absorption 
were  going  on  actively,  the  vessels  of  the  neck  contained  scarcely  any  fluid ;  but  the 
quantity  gradually  increased  after  these  processes  were  completed. 

Properties  and  Composition  of  Lymph.— Lymph  taken  from  the  vessels  in  various 
parts  of  the  system,  or  the  fluid  which  is  discharged  from  the  thoracic  duct  during  the 
intervals  of  digestion,  is  either  perfectly  transparent  and  colorless  or  of  a  slightly  yellow- 
ish or  greenish  hue.  "When  allowed  to  stand  for  a  short  time,  it  becomes  faintly  tinged 
with  red,  and  frequently  it  has  a  pale  rose-color  when  first  discharged.  Miscroscopical 
examination  shows  that  this  reddish  color  is  dependent  upon  the  presence  of  a  few  blood- 
corpuscles,  which  are  entangled  in  the  clot  as  the  lymph  coagulates,  thus  accounting  for 


330  ABSORPTION. 

the  deepening  of  the  color  when  the  fluid  has  been  allowed  to  stand.  The  origin  of  these 
red  corpuscles  has  long  been  a  subject  of  discussion.  Their  constant  presence  in  lymph 
or  chyle  discharged  by  fistulous  openings  has  led  to  the  opinion  that  they  are  normal 
constituents  of  these  fluids ;  and  this  view  has  been  adopted  without  reserve  by  those 
who  assume  that  the  blood-corpuscles  are  formed  from  the  white  corpuscles,  or  leuco- 
cytes. If  this  view  of  the  formation  of  the  corpuscular  elements  of  the  blood  be  adopted, 
there  is  no  good  reason  why  red  corpuscles  should  not  be  formed  from  the  leucocytes  in 
the  lymph  and  chyle  as  well  as  in  the  blood  itself;  particularly  as  the  clear  fluid  of  the 
lymph  and  chyle  contains  nearly  all  the  principles  found  in  the  plasma  of  the  blood.  On 
the  other  hand,  many  physiologists  regard  the  presence  of  red  corpuscles  as  always  acci- 
dental ;  and,  in  support  of  this  view,  Kobin  brings  forward  the  fact  that  red  corpuscles  are 
never  found  in  lymph  taken  from  a  portion  of  a  vessel  included  between  two  ligatures. 
This  is  certainly  a  very  strong  argument  against  the  constant  and  normal  existence  of  red 
corpuscles  in  the  lymph,  particularly  as  the  connection  between  the  lymphatics  and  the 
blood-vessels  is  very  close,  and  all  operations  upon  the  lymphatic  system  involve  dis- 
turbances in  the  circulation.  There  is  no  positive  evidence  of  the  formation  of  red  cor- 
puscles from  the  leucocytes ;  and,  if  it  be  the  fact  that  red  corpuscles  never  exist  in  lymph 
taken  from  a  portion  of  a  lymphatic  vessel  included  between  two  ligatures,  it  is  fair  to 
assume  that  the  presence  of  these  corpuscles  in  lymph  and  chyle  is  accidental,  and  that 
they  are  always  derived  from  the  blood. 

Lymph  has  no  decided  or  characteristic  odor.  It  is  very  slightly  saline  in  taste,  being 
almost  insipid.  Its  specific  gravity  is  much  lower  than  that  of  the  blood.  Magendie 
found  the  specific  gravity  in  the  dog  to  be  about  1022.  Eobin  states  that  the  specific 
gravity  of  the  defibrinated  serum  of  lymph  is  1009.  In  some  recent  analyses,  by 
Dahnhardt,  of  the  lymph  taken  from  dilated  vessels  in  the  leg,  in  the  human  subject,  the 
specific  gravity  was  only  1007".  The  exceedingly  low  specific  gravity  in  the  last  instance 
would  rather  lead  to  the  opinion  that  the  fluid  was  not  entirely  normal.  The  difficulty 
in  obtaining  this  fluid  in  a  perfectly  normal  condition  from  the  human  subject  has  ren- 
dered it  impossible  to  ascertain  its  normal  specific  gravity,  even  approximatively ;  but  it 
evidently  possesses  a  density  much  inferior  to  that  of  the  blood.  The  reaction  of  the 
lymph  is  constantly  alkaline. 

A  few  minutes  after  discharge  from  the  vessels,  both  the  lymph  and  chyle  undergo 
spontaneous  coagulation.  According  to  Colin,  the  fluid  collected  from  the  thoracic  duct 
in  the  large  ruminants  coagulates  at  the  end  of  five,  ten,  or  twelve  minutes,  and  sets  into 
a  mass  having  exactly  the  form  of  the  vessel  in  which  it  is  contained.  Colin  states  that 
the  clot  is  tolerably  consistent,  but  that  there  is  never  any  spontaneous  separation  of 
serum.  This  may  be  the  fact  with  regard  to  the  lymph  and  the  chyle  of  the  large  rumi- 
nants, but,  in  the  observations  of  Dalton,  who  operated  upon  dogs  and  goats,  after  a  few 
hours'  exposure,  the  clot  contracted  to  about  half  its  original  size,  precisely  like  coagu- 
lated blood,  expressing  a  considerable  quantity  of  serum.  In  one  instance,  in  the  dog,  the 
volume  of  serum,  after  twenty-four  hours  of  repose,  was  about  twice  that  of  the  contract- 
ed clot.  Milne-Edwards,  quoting  from  an  unpublished  memoir  presented  by  Colin  to  the 
Academy  of  Sciences,  in  1858,  states  that  the  lymph  does  not  coagulate  in  the  vessels, 
even  when  the  circulation  is  interrupted.  This  may  be  the  case  under  ordinary  condi- 
tions, when  the  vessels  are  simply  tied ;  but  it  was  found  by  Flandrin,  that  coagulation 
obstructed  the  tubes  which  he  introduced  into  the  thoracic  duct  so  completely  that  he 
was  able  to  obtain  but  a  small  quantity  of  fluid;  a  diflficulty  which  is  also  mentioned  by 
Colin,  who  states  that  "the  clearing  of  the  tube  rarely  suffices  to  reestablish  the  flow,  for 
the  coagulum  formed  in  the  tube  is  prolonged  for  a  greater  or  less  distance  into  the  in- 
terior of  the  thoracic  duct."  Coagulation  of  lymph  in  the  vessels  during  life,  if  it  occur 
at  all,  must  be  exceedingly  infrequent,  notwithstanding  that  the  flow  of  lymph  and  chyle 
is  very  slow  and  irregular,  as  compared  with  the  circulation  of  the  blood,  and  is  subject, 
probably,  to  frequent  interruptions. 


COMPOSITION  OF  LYMPH.  331 

Although  numerous  analyses  have  been  made  of  lymph  from  the  human  subject,  the 
conditions  under  which  the  fluid  has  been  obtained  render  it  probable  that,  in  the  ma- 
jority of  instances,  it  was  not  entirely  normal.  It  will  be  necessary,  therefore,  to  com- 
pare these  analyses  with  observations  made  upon  the  lymph  of  the  inferior  animals ;  aa, 
in  the  latter,  this  fluid  has  been  collected  under  conditions  which  leave  no  doubt  as  to  its 
normal  character.  In  the  experiments  of  Colin  especially,  the  fluids  taken  from  the  tho- 
racic duct  during  the  intervals  of  digestion  undoubtedly  represented  the  normal,  mixed 
lymph  collected  from  nearly  all  parts  of  the  body ;  and  the  operative  procedure  in  the 
large  ruminants  is  so  simple  as  to  produce  little  if  any  general  disturbance.  The  follow- 
ing is  an  analysis  by  Lassaigne  of  specimens  of  lymph  collected  by  Colin  from  the  thoracic 
duct  of  a  cow,  under  the  most  favorable  conditions : 

Composition  of  Lymph  from  a  Cow. 

Water 964*0 

Fibrin 0'9 

Albumen 28'0 

Fatty  matter 0'4 

Chloride  of  sodium 5-0 

Carbonate,  phosphate,  and  sulphate  of  soda 1-2 

Phosphate  of  lime 0'5 


1,000-0 

The  proportions  given  in  the  table  are  by  no  means  invariable,  the  differences  in  coag- 
ulability indicating  differences  in  the  proportion  of  fibrin,  and  the  degree  of  lactescence 
showing  great  variations  in  the  amount  of  fatty  matters.  The  table  may  be  taken,  how- 
ever, as  a  pretty  close  approximation  of  the  average  composition  of  the  lymph  of  these 
animals,  during  the  intervals  of  digestion. 

The  analysis  of  human  lymph  which  seems  to  be  the  most  reliable,  and  in  which  the 
fluid  was  apparently  pure  and  normal,  is  that  of  Gubler  and  Qu6venne.  The  lymph, 
in  this  case,  was  collected  by  Desjardins  from  a  female  who  suffered  from  a  varicose  dila- 
tation of  the  lymphatic  vessels  in  the  anterior  and  superior  portion  of  the  left  thigh. 
These  vessels  occasionally  ruptured,  and  the  lymph  could  then  be  obtained  in  consider- 
able quantity.  When  an  opening  existed,  the  discharge  of  fluid  could  be  arrested  at  will 
by  flexing  the  trunk  upon  the  thigh.  Gubler  and  Quevenne  made  elaborate  analyses  of 
two  different  specimens  of  the  fluid,  with  the  following  results : 

Composition  of  Human  Lymph. 

First  analysis.  Second  analysis. 

Water 939-87  934-77 

Fibrin 0'56  0'63 

Caseous  matter  (with  earthy  phosphates  and  traces  of  iron)  42'75  42'80 
Fatty  matter  (in  the  second  analysis,  fusible  at  102'3°  Fahr.)  3'82  9'20 
Hydro-alcoholic   extract   (containing   sugar,    and   leaving, 
after  incineration,  chloride  of  sodium,  with  the  phos- 
phate and  the  carbonate  of  soda) 13*00  12-60 

1,000-00  1,000-00 

The  above  analyses  show  a  much  larger  proportion  of  solid  constituents  than  was 
found  by  Lassaigne  in  the  lymph  of  the  cow.  This  excess  is  pretty  uniformly  distributed 
throughout  all  the  constituents,  with  the  exception  of  the  fatty  matters  and  fibrin;  the 
former  existing  largely  in  excess  in  the  human  lymph,  especially  in  the  second  analysis, 
while  the  latter  is  smaller  in  quantity  than  in  the  lymph  of  the  cow.  It  is  evident,  how- 
ever, from  a  comparison  of  the  two  analyses  by  Gubler  and  Quevenne,  that  the  composi- 


332 


ABSOKPTIOtf. 


tion  of  the  lymph,  even  when  it  is  unmixed  with  chyle,  is  subject  to  great  variations. 
The  caseous  matter  given  by  Gubler  and  Quevenne  is  probably  equivalent  to  the  albu- 
minous matter  of  other  chemists. 

The  distinctive  characters  of  the  different  principles  found  in  the  lymph  do  not  de- 
mand extended  consideration,  inasmuch  as  most  of  them  have  already  been  treated  of  in 
connection  with  the  blood.  In  comparing,  however,  the  composition  of  the  lymph  with 
that  of  the  blood,  we  are  at  once  struck  with  the  great  excess  of  solid  constituents  in  the 
latter  fluid. 

In  all  analyses,  except  those  of  Lheritier,  the  organic  nitrogenized  compounds  have 
been  found  to  be  very  much  less  in  the  lymph  than  in  the  blood.  This  is  generally  most 
marked  with  regard  to  the  elements  of  fibrin  ;  but,  as  before  stated,  the  proportion  of 
all  these  ingredients  is  quite  variable.  On  account  of  this  deficiency,  lymph  is  much  infe- 
rior to  the  blood  in  coagulability,  and  the  coagulum,  when  it  is  formed,  is  soft  and  fria- 
ble. There  does  not  appear,  however,  to  be  any  actual  difference  between  the  coagulat- 
ing principles  of  the  lymph  and  of  the  blood. 

Fatty  matters  have  generally  been  found  more  abundantly  in  the  lymph  than  in  the 
blood  ;  but  their  proportion  is  even  more  variable  than  that  of  the  albuminoid  substances. 
Very  little  remains  to  be  said  concerning  the  ordinary  inorganic  constituents  of  the 
lymph.  The  analyses  of  Dahnhardt  have  shown  that  nearly  if  not  all  of  the  inorganic 
matters  which  have  been  demonstrated  in  the  blood  are  contained  in  the  lymph  ;  and 
even  a  small  proportion  of  iron  is  given  in  the  analyses  by  Gubler  and  Quevenne. 

These  facts  indicate  a  remarkable  correspondence  between  the  composition  of  the 
lymph  and  that  of  the  blood.  All  of  the  constituents  of  the  blood,  except  the  red  cor- 
puscles, exist  in  the  lymph,  the  only  difference  being  in  their  relative  proportions. 

In  addition  to  the  constituents  of  the  lymph  ordinarily  given,  the  presence  of  glucose, 
and,  more  lately,  the  existence  of  a  certain  proportion  of  urea,  have  been  demonstrated 
in  this  fluid.  It  has  not  been  ascertained  how  the  sugar  contained  in  the  lymph  takes  its 
origin,  and  its  function  in  this  situation  is  equally  obscure. 

The  presence  of  urea  in  considerable  quantity  in  both  the  chyle  and  the  lymph  has 
been  determined  by  Wurtz  ;  and  it  is  thought  by  Bernard  that  the  lymph  is  the  principal 
fluid,  if  not  the  only  one,  by  which  this  excrementitious  substance  is  taken  up  from  the 
tissues.  Although  urea  always  exists  in  the  blood,  its  quantity  is  less  than  in  the  lymph. 

Corpuscular  Elements  of  the  Lymph.  —  In 
every  part  of  the  lymphatic  system,  in  addition 
to  a  few  very  minute  fatty  granules,  there  are 
found  certain  corpuscular  elements  known  as 
the  lymph-corpuscles.  These  exist,  not  only  in 
the  clear  lymph,  but  in  the  opaque  fluid  con- 
tained in  the  lacteals  during  absorption.  They 
are  now  regarded  as  identical  with  the  color- 
less, globular  corpuscles  found  in  the  blood, 
known  under  the  name  of  white  blood-corpus- 
cles, or  leucocytes.  Although  these  bodies 
have  been  pretty  fully  described  in  treating  of 
the  corpuscular  elements  of  the  blood,  they 
present  some  peculiarities  in  the  lymphatic  sys- 
tem, particularly  in  their  mode  of  development, 
which  demand  consideration. 

The  leucocytes    found    in  the  lymph    and 

chy}e  are  rather  less 


FIG.  98.— Chyle  taken  from  the  lacteals  and  tho- 
racic duct  of  a  criminal  executed  during 
digestion.  (Funke.) 


ftn 

eral  appearance  than  the  white  corpuscles  of 

the  blood.     Their  average  diameter  is  about  ^5-  of  an  inch  ;  but  some  are  larger,  and 
others  are  as  small  as  -5-5^  of  an  inch.     Some  of  these  corpuscles  are  quite  clear  and 


COMPOSITION  OF  LYMPH.  333 

transparent,  presenting  but  few  granulations  and  an  indistinct  nuclear  appearance  in 
their  centre  ;  but  others  are  granular  and  quite  opaque.  They  present  the  same  adhesive 
character  in  the  lymph  that  we  have  noted  in  the  blood,  and  frequently  they  are  found 
collected  in  masses  in  different  parts  of  the  lymphatic  system.  Treated  with  acetic  acid, 
the  corpuscles  generally  become  swollen  and  are  rendered  very  transparent,  then  pre- 
senting from  one  to  four  or  five  nuclear  concretions  in  their  interior.  In  all  other  re- 
gards, these  bodies  present  the  same  characters  as  the  leucocytes  of  the  blood,  and  they 
need  not,  therefore,  be  farther  described. 

We  have  already  alluded  to  the  fact  that  the  lymph-corpuscles  are  more  abundant  in 
the  larger  than  in  the  smaller  vessels,  and  that  they  have  been  thought  to  be  particu- 
larly numerous  in  the  vessels  coming  from  the  lymphatic  glands.  It  is  nevertheless  true 
that  corpuscles  exist  even  in  the  smallest  vessels,  and  they  are  sometimes  quite  abundant 
in  lymph  which  has  not  passed  through  the  glands.  These  considerations  naturally  lead 
to  the  theory  of  the  development  of  leucocytes  in  the  lymphatics,  as  well  as  in  the  ordi- 
nary vascular  system,  particularly  as  the  constant  discharge  of  lymph  and  chyle  into  the 
blood-vessels  renders  it  more  than  probable  that  most  of  the  leucocytes  found  in  the 
blood  are  derived  from  the  lymph. 

The  researches  of  Robin,  and  of  others,  by  whom  his  observations  have  been  some- 
what extended,  have  conclusively  demonstrated  that  leucocytes  may  be  developed,  under 
proper  conditions,  in  a  clear,  structureless  blastema,  without  the  intervention  of  any 
glandular  organ ;  and,  farthermore,  it  is  not  necessary  that  the  blastema  should  be  en- 
closed in  any  system  of  vessels.  These  facts  refute  completely  the  idea  that  the  lymph- 
corpuscles  are  formed  exclusively  either  by  the  lymphatic  glands  or  by  the  walls  of  the 
lymphatic  vessels.  Observations  have  also  shown  that  leucocytes  exist  in  the  blood  of  the 
embryon  before  any  lymphatic  vessels  can  be  demonstrated ;  a  fact  which  shows  that 
these  bodies  may  be  developed  de  novo  in  the  blood-plasma. 

As  regards  the  lymph,  there  is  no  fluid  in  the  body  which  is  placed  under  conditions 
more  favorable  to  the  development  of  leucocytes.  It  is  enclosed  in  a  system  of  ves- 
sels possessing  extremely  thin  walls  and  undoubtedly  subjected  to  active  osmotic  cur- 
rents. It  contains,  likewise,  a  considerable  quantity  of  coagulating  matters ;  and  the 
proportion  of  these  principles  has  always  been  found  to  influence  the  rapidity  of  the  devel- 
opment of  white  corpuscles.  Its  circulation  is  not  very  rapid,  and  the  obstacles  to  the 
current  which  are  presented  in  the  lymphatic  glands  undoubtedly  give  time  for  the  per- 
fection of  the  structure  of  leucocytes.  It  is  in  this  way  that  the  increase  in  the  number 
of  leucocytes  as  the  lymph  passes  from  the  periphery  to  the  larger  vessels,  and  especially 
as  the  fluid  passes  through  the  glands,  can  be  explained. 

From  the  fact  that  leucocytes  are  developed  before  the  lymphatic  system  makes  its 
appearance,  that  they  are  found  in  lymph  which  has  never  passed  through  lymphatic 
glands,  and  from  observations  showing  their  spontaneous  formation  in  an  amorphous 
blastema,  it  is  the  inevitable  conclusion  that  nearly  if  not  quite  all  of  the  lymph-cor- 
puscles are  developed  by  genesis  in  the  clear  lymph-plasma,  and  that  their  development 
goes  on  as  the  fluid  circulates  toward  the  venous  system.  With  regard  to  the  influence 
of  the  lymphatic  glands  upon  the  generation  of  leucocytes,  there  is  no  evidence  that  the 
corpuscles  which  are  developed  in  the  course  of  the  lymph  through  these  organs  are  not 
here,  as  elsewhere,  formed  simply  from  the  blastema ;  and  it  is  not  necessary  to  invoke 
any  special  formative  action  taking  place  in  the  peculiar  structures  of  the  glands. 

The  function  of  the  lymph-corpuscles  is  obscure.  They  are  discharged  into  the  blood, 
of  which  they  form  a  constant  constituent.  Aside  from  the  hypothesis  that  they  are 
concerned  in  the  formation  of  the  red  blood-disks,  no  definite  and  reasonable  theory  of 
their  physiological  office  has  been  proposed. 

In  addition  to  the  ordinary  leucocytes  and  a  certain  number  of  fatty  granules,  a  few 
small,  clear  globules  or  granules,  about  y^Vfr  of  an  inch  in  diameter,  called  sometimes 
globulins,  are  almost  constantly  present  in  the  lymph.  These  are  insoluble  in  ether  and 


334  ABSORPTION. 

acetic  acid,  but  are  dissolved  by  ammonia.  They  are  regarded  by  Robin  as  a  variety  of 
leucocytes  and  are  described  by  him  as  free  nuclei.  They  make  their  appearance  in  the 
blastema  before  the  larger  leucocytes  are  developed. 

Origin  and  Function  of  the  Lymph. — There  can  hardly  be  any  doubt  concerning  the 
source  of  most  of  the  liquid  portions  of  the  lymph,  for  they  can  be  derived  only  from  the 
blood.  Although  the  exact  relations  between  the  smallest  lymphatics  and  the  blood- 
vessels have  not  been  made  out  in  all  parts  of  the  system,  there  is  manifestly  no  ana- 
tomical reason  why  the  water,  mixed  with  albuminoid  matters  and  holding  salts  in  solu- 
tion, should  not  pass  from  the  blood  into  the  lymphatics ;  and  this  is  rendered  nearly 
certain  if  it  can  be  demonstrated  that  the  lymphatics  partly  or  entirely  surround  many 
of  the  blood-vessels,  for,  under  these  circumstances,  endosmotic  and  exosmotic  currents 
would  inevitably  take  place.  We  have  seen,  in  comparing  the  composition  of  the  lymph 
with  that  of  the  plasma  of  the  blood,  that  the  constituents  of  these  fluids  are  nearly  if 
not  quite  identical ;  the  only  variations  being  in  their  relative  proportions.  This  is  an- 
other strong  argument  in  favor  of  the  passage  of  most  of  the  constituents  of  the  blood 
into  the  lymph. 

One  of  the  most  important  physiological  facts  in  the  chemical  history  of  the  lymph  is 
the  constant  existence  of  a  considerable  proportion  of  urea.  This  cannot  be  derived  from 
the  blood,  for  its  proportion  is  greater  in  the  lymph,  notwithstanding  that  this  fluid  is 
being  constantly  discharged  into  the  blood-vessels.  The  urea  which  exists  in  the  lymph 
is  derived  from  the  tissues ;  it  is  discharged  then  into  the  blood,  and  is  constantly  being 
removed  from  this  fluid  by  the  kidneys. 

The  positive  facts  upon  which  to  base  any  precise  ideas  with  regard  to  the  general 
function  of  the  lymph  are  not  very  numerous.  From  the  composition  of  this  fluid,  its 
mode  of  circulation,  and  the  fact  that  it  is  being  constantly  discharged  into  the  blood,  it 
would  not  seem  to  have  an  important  function  in  the  active  processes  of  nutrition.  The 
experiments  of  Collard  de  Martigny  sustain  this  view,  inasmuch  as  the  quantity  and  the 
proportion  of  solid  constituents  of  the  lymph  were  rather  increased  than  diminished  in 
animals  that  had  been  deprived  of  food  and  drink  for  several  days;  while  it  is  well  known 
that  starvation  always  impoverishes  the  blood  from  the  first.  On  the  other  hand,  urea, 
one  of  the  most  important  of  the  products  of  destructive  metamorphosis  of  the  tissues,  is 
undoubtedly  taken  up  by  the  lymph  and  conveyed  in  this  fluid  to  the  blood.  It  re- 
mains now  for  future  investigations  to  determine  whether  other  excrementitious  princi- 
ples may  not  be  taken  up  from  the  tissues  in  the  same  way — a  question  of  great  importance 
in  its  relations  to  the  mechanism  of  excretion. 

What  is  positively  known  with  regard  to  the  functions  of  the  lymph  may  be  summed 
up  in  a  very  few  words :  A  great  part  of  its  constituents  is  evidently  derived  from  the 
blood,  and  the  relations  of  these  principles  to  nutrition  are  not  understood.  The  same 
may  be  said  of  sugar,  also  a  constant  constituent  of  the  lymph,  the  origin  of  which,  even, 
is  not  known.  Urea  and,  perhaps,  other  excrementitious  matters  are  taken  up  from  the 
tissues  by  the  lymph,  and  are  discharged  into  the  blood,  to  be  removed  by  the  appropriate 
organs  from  the  system. 

While  the  blood  is  evidently  the  great  nutritive  fluid  of  the  body,  being  constantly 
regenerated  and  purified  by  the  absorption  of  nutritive  matters,  by  respiration,  and  by  the 
action  of  excreting  organs,  the  lymph  has  an  important  function  in  removing  from  the 
tissues  some,  at  least,  of  the  products  of  physiological  decay  of  the  organism. 

Chyle. 

During  the  intervals  of  digestion,  the  intestinal  lymphatics  and  the  thoracic  duct  carry 
ordinary  lymph  ;  but,  as  soon  as  absorption  of  alimentary  matters  begins,  certain  nutritive 
principles  are  taken  up  in  quantity  by  these  vessels,  and  their  contents  are  now  known 
tinder  the  name  of  chyle.  But  little  remains  to  be  said  concerning  this  fluid,  as  we  have 


CHYLE.  335 

considered  pretty  fully  the  composition  and  properties  of  the  lymph  as  well  as  the  different 
principles  taken  up  by  the  lacteal  vessels  which,  with  the  lymph,  form  the  chyle.  Some 
general  considerations,  however,  remain  concerning  the  composition  and  properties  of 
the  chyle  as  a  distinct  fluid. 

In  the  human  subject  and  in  carnivorous  animals,  the  chyle,  taken  from  the  lacteals 
near  the  intestine,  where  it  is  nearly  pure,  or  from  the  thoracic  duct,  when  it  is  mixed 
with  lymph,  is  a  white,  opaque,  milky  fluid,  of  a  slightly  saline  taste,  and  an  odor  which 
is  said  to  resemble  that  of  the  semen.  The  odor  is  also  said  to  be  characteristic  of  the 
animal  from  which  the  fluid  is  taken ;  although  this  is  not  very  marked,  except  on  the 
addition  of  a  concentrated  acid,  the  process  employed  by  Barreul  to  develop  the  charac- 
teristic odor  in  the  fluids  from  different  animals.  Bouisson  has  found  that  the  peculiar 
odor  of  the  dog  was  thus  developed  in  fresh  chyle  taken  from  the  thoracic  duct. 

The  chyle  taken  from  a  fistula  into  the  thoracic  duct  is  frequently  of  a  more  or  less 
rosy  tint ;  and  it  has  been  a  question  whether  this  be  due  to  a  peculiar  coloring  matter  or 
to  the  accidental  presence  of  a  few  red  blood-corpuscles.  Colin,  whose  experiments  in 
collecting  chyle  from  living  animals  have  been  very  numerous  and  successful,  assumes  that 
the  red  coloration  is  always  due  to  blood-corpuscles  coming  from  the  subclavian  vein ;  the 
valve  at  the  orifice  of  the  thoracic  duct  not  being  always  sufficient  to  prevent  regurgita- 
tion.  He  has  never  found  blood  in  the  fluid  taken  from  the  mesenteric  vessels  or  the 
receptaculum  chyli,  and  he  states,  farthermore,  that  the  chyle  from  these  vessels  never 
becomes  colored  under  the  influence  of  the  air  or  of  oxygen. 

The  reaction  of  the  chyle  is  either  alkaline  or  neutral.  Dalton  noted  an  alkaline  re- 
action in  the  chyle  of  the  goat  and  of  the  dog ;  and  a  specimen  of  chyle  taken  from  a 
criminal  immediately  after  execution,  examined  by  Rees,  was  neutral.  Leuret  and  Las- 
saigne  obtained  the  fluid  from  the  receptaculum  chyli  in  a  man  that  had  died  of  cerebral 
inflammation,  and  found  its  reaction  to  be  alkaline. 

The  specific  gravity  of  the  chyle  is  always  less  than  that  of  the  blood  ;  but  it  is  very 
variable  and  depends  upon  the  quality  of  the  food  and  particularly  upon  the  quantity  of 
liquids  ingested.  Lassaigne  found  the  specific  gravity  of  a  specimen  of  pure  chyle  taken 
from  the  mesenteric  lacteals  of  a  bull  to  be  1013,  and  the  specific  gravity  of  the  specimen 
of  human  chyle  examined  by  Rees  was  1024. 

The  differences  in  the  appearance  of  the  chyle  in  different  animals  depend  chiefly  upon 
the  diet.  Colin  found  it  excessively  milky  in  the  carnivora,  especially  after  fats  had  been 
taken  in  quantity ;  while,  in  dogs  that  were  nourished  with  articles  containing  but  little 
fat,  its  appearance  was  hardly  lactescent.  Tiedemann  and  Gmelin  found  the  chyle  almost 
transparent  in  herbivora  fed  with  hay  or  straw.  They  also  observed  the  fact  that  the 
chyle  was  nearly  transparent  in  dogs  fed  with  liquid  albumen,  fibrin,  gelatine,  starch,  and 
gluten  ;  while  it  was  white  in  the  same  animals  fed  with  milk,  meat,  bones,  etc. 

It  is  impossible  to  give  even  an  approximative  estimate  of  the  entire  quantity  of  pure 
chyle  taken  up  by  the  lacteal  vessels.  When  it  finds  its  way  into  the  thoracic  duct,  it  is 
mingled  immediately  with  all  the  lymph  from  the  lower  extremities ;  and  the  immense 
quantities  of  fluid  which  have  been  collected  from  this  vessel  by  Colin  and  others  give 
no  idea  of  the  quantity  of  chyle  absorbed  from  the  intestinal  canal.  "We  cannot,  therefore, 
attempt  to  give  even  an  approximate  estimate  of  the  absolute  quantity  of  chyle  ;  but  it  is 
evident  that  this  is  variable,  depending  upon  the  nature  of  the  food  and  the  quantity  of 
liquids  ingested. 

Like  the  lymph,  the  chyle,  when  removed  from  the  vessels,  speedily  undergoes  coagu- 
lation. Different  specimens  of  the  fluid  vary  very  much  as  regards  the  rapidity  with 
which  coagulation  takes  place.  The  contents  of  the  thoracic  duct  taken  from  the  inferior 
animals  generally  coagulate  in  a  few  minutes.  The  first  portion  of  the  fluid  collected 
from  the  human  subject  by  Dr.  Rees  (the  chyle  was  collected  in  this  case  in  two  portions) 
coagulated  in  an  hour.  Received  into  an  ordinary  glass  vessel,  the  chyle  generally  sepa- 
rates more  or  less  completely  after  coagulation  into  clot  and  serum,  the  density  and  size 


336  ABSORPTION. 

of  the  clot  indicating  the  proportion  of  fibrin.  The  serum  which  thus  separates  is  quite 
variable  in  quantity  and  is  never  clear.  Its  milkiness  does  not  depend  entirely  upon  the 
presence  of  particles  of  emulsified  fat,  and  it  is  not  rendered  transparent  by  ether.  It  con- 
tains, in  addition  to  these  particles,  numerous  leucocytes  and  organic  granules. 

Numerous  observations  have  been  made  with  reference  to  the  influence  of  different 
kinds  of  food  upon  the  chyle  ;  but  these  have  not  been  followed  by  any  definite  results 
that  can  be  applied  to  the  human  subject.  It  is  usual  to  find  the  chyle  fluid  in  the  lac- 
teals  and  in  the  thoracic  duct  for  many  hours  after  death  ;  but  it  soon  coagulates  after  ex- 
posure to  the  air.  Although  the  entire  lacteal  system  is  sometimes  found,  in  the  human 
subject  and  in  the  inferior  animals,  filled  with  perfectly  opaque,  coagulated  chyle,  the 
fluid  does  not  often  coagulate  in  the  vessels. 

Composition  of  the  Chyle. — Analyses  of  the  milky  fluid  taken  from  the  thoracic  duct 
during  full  digestion  by  no  means  represent  the  composition  of  pure  chyle  ;  and  it  is  only 
by  collecting  the  fluid  from  the  mesenteric  lacteals,  that  it  can  be  obtained  without  a 
very  large  admixture  of  lymph.  In  the  human  subject,  it  is  rare  even  to  have  an  oppor- 
tunity of  taking  the  fluid  from  the  thoracic  duct  in  cases  of  sudden  death  during  diges- 
tion ;  and,  in  most  of  the  inferior  animals  which  have  been  operated  upon,  it  is  difficult  to 
obtain  fluid  from  the  small  lacteals  in  quantity  sufficient  for  accurate  analysis.  In  oper- 
ating upon  the  ox,  however,  Colin  has  succeeded  in  collecting  pure  chyle  in  considera- 
ble quantity. 

The  most  complete  analysis  of  chyle  from  the  human  subject  is  given  by  Dr.  Rees. 
The  fluid  was  taken  from  the  thoracic  duct  of  a  vigorous  man,  a  little  more  than  an  hour 
after  his  execution  by  hanging.  The  subject  was  apparently  in  perfect  health  up  to  the 
moment  of  his  death.  The  evening  before,  he  ate  two  ounces  of  bread  and  four  ounces 
of  meat.  At  seven  o'clock  A.  M.,  precisely  one  hour  before  death,  he  took  two  cups  of 
tea  and  a  piece  of  toast ;  and  he  drank  a  glass  of  wine  just  before  mounting  the  scaffold. 
When  the  dissection  was  made,  the  body  was  yet  warm,  although  the  weather  was  quite 
cold.  The  thoracic  duct  was  rapidly  exposed  and  divided,  and  about  six  fluidrachms  of 
milky  chyle  were  collected.  The  fluid  was  neutral  and  had  a  specific  gravity  of  1024. 
The  following  was  its  proximate  composition  : 

Composition  of  Human  Chyle  from  the  Thoracic  Duct. 

Water 904-8 

Albumen,  with  traces  of  fibrinous  matter 70'8 

Aqueous  extractive 5*6 

Alcoholic  extractive,  or  osmazome ^ .  5*2 

Alkaline  chlorides,  carbonates,  and  sulphates,  with  traces  of  alkaline  phosphates 

and  oxides  of  iron 4*4 

Fatty  matters 9'2 

1,000-0 

Of  the  constituents  of  the  chyle  not  given  in  the  ordinary  analyses,  the  most  impor- 
tant are  the  urea,  which,  in  all  probability,  is  derived  exclusively  from  the  lymph,  and 
sugar,  coming  from  the  saccharine  and  amylaceous  articles,  of  food  during  the  digestion 
of  these  principles. 

The  difference  in  chemical  composition  between  the  unmixed  lymph  and  the  chyle  is 
very  well  illustrated  in  a  comparative  examination  of  these  two  fluids  taken  from  a  don- 
key. The  fluids  were  collected  by  Mr.  Lane,  the  chyle  being  taken  from  the  lacteals 
before  reaching  the  thoracic  duct.  The  animal  was  killed  seven  hours  after  a  full  meal 
of  oats  and  beans.  The  following  analyses  of  the  fluids  were  made  by  Dr.  Rees : 


MOVEMENTS   OF  THE  LYMPH  AND  CHYLE.  337 

Composition  of  Chyle  and  Lymph  before  reaching  the  Thoracic  Duct. 

Chyle.  Lymph. 

Water 902-37  965-36 

Albuminous  matter 35*16  12-00 

Fibrinous  matter 3.^0  1-20 

Animal  extractive  matter  soluble  in  water  and  alcohol 3-33  ,  2'40 

Animal  extractive  matter  soluble  in  water  only 12'33  13-19 

Fatty  matter S6.0i  a  trace 

g  ,,     (  Alkaline  chlorides,    sulphates,   and   carbonates,   with  ) 

'  (      traces  of  alkaline  phosphates,  oxide  of  iron \  "  ^-11  5'85 

1,000-00          1,000-00 

The  above  analyses  show  a  very  marked  difference  in  the  proportion  of  solid  constitu- 
ents in  the  two  fluids.  The  chyle  contains  about  the  same  proportion  of  albumen 
and  fibrin  as  the  lymph,  with  a  much  larger  proportion  of  salts.  The  proportion  of  fatty 
matters  in  the  chyle  is  very  great,  while  in  the  lymph  there  exists 'only  a  trace.  The 
individual  constituents  of  the  chyle  given  in  the  above  tables  do  not  demand  any 
farther  consideration  than  they  have  already  received  under  the  head  of  lymph.  The 
albuminoid  matters  are  in  part  derived  from  the  food,  and  in  part  from  the  blood,  through 
the  admixture  of  the  chyle  with  lymph.  The  fatty  matters  are  derived  in  greatest  part 
from  the  food.  As  far  as  has  been  ascertained  by  analyses  of  the  chyle  for  salts,  this 
fluid  has  been  found  to  contain  essentially  the  same  inorganic  constituents  as  the 
plasma  of  the  blood.  All  of  these  principles  are  rapidly  poured  into  the  blood,  where 
they  assist  in  supplying  the  material  which  is  being  constantly  consumed  in  the  process 
of  nutrition. 

The  presence  of  sugar  in  the  chyle  was  first  mentioned  by  Brande,  who  described 
it,  however,  rather  indefinitely.  Glucose  was  distinctly  recognized  in  the  chyle  by 
Trommer,  and  its  existence  in  many  of  the  higher  orders  of  animals  has  since  been  fully 
established  by  Colin. 

Microscopical  Characters  of  the  Chyle. — The  milky  appearance  of  the  chyle  as  con- 
trasted with  the  lymph  is  due  to  the  presence  of  an  immense  number  of  excessively 
minute  fatty  granules.  The  liquid  becomes  much  less  opaque  when  treated  with  ether, 
which  dissolves  many  of  the  fatty  particles.  In  fact,  the  chyle  of  the  thoracic  duct  is 
nothing  more  than  lymph  to  which  an  emulsion  of  fat  in  a  liquid  containing  albuminoid 
matters  and  salts  is  temporarily  added  during  the  process  of  intestinal  absorption.  The 
quantity  of  fatty  granules  in  the  chyle  varies  considerably  with  the  diet,  and  it  generally 
diminishes  progressively  from  the  smaller  to  the  larger  vessels,  on  account  of  the  con- 
stant admixture  of  lymph.  The  size  of  the  granules  is  pretty  uniformly  from  &sloo  *° 
TSTTO  °f  an  inch.  They  are  much  smaller  and  more  uniform  in  size  in  the  lacteals  than 
in  the  cavity  of  the  intestine.  Their  constitution  is  not  constant ;  and  they  are  com- 
posed of  the  different  varieties  of  fat  which  are  taken  as  food,  mingled  together  in  varia- 
ble proportions. 

The  ordinary  corpuscular  elements  of  the  lymph  (leucocytes  and  globulins)  are  also 
found  in  variable  quantity  in  the  chyle.  These  have  already  been  fully  considered. 

Movements  of  the  Lymph  and  the  Chyle. 

Compared  with  the  current  of  blood,  the  movements  of  the  lymph  and  chyle  are 
feeble  and  irregular ;  and  the  character  of  these  movements  is  such  that  they  are  evi- 
dently due  to  a  variety  of  causes.  As  regards  those  elements  which  are  derived  directly 
from  the  blood,  the  lymph  may  be  said  to  undergo  a  true  circulation ;  inasmuch  as  there 
is  a  constant  transudation  at  the  peripheral  portion  of  the  vascular  system,  of  fluids  which 
are  returned  to  the  circulating  blood  by  the  communications  of  the  lymphatic  system 
22 


338  ABSORPTION. 

with  the  great  veins.  But  we  have  seen  that  the  lymph  is  not  derived  entirely  from 
the  blood,  a  considerable  portion  resulting  from  interstitial  absorption  in  the  general  lym- 
phatic system  and  from  the  absorption  of  certain  nutritive  matters  by  the  chyliferous 
vessels.  These  are,  physiologically,  the  most  important  constituents  of  the  lymph  and 
chyle ;  and  they  are  taken  up  simply  to  be  carried  to  the  blood  and  do  not  pass  again 
from  the  general  vascular  system  into  the  lymphatics. 

As  far  as  the  mode  of  origin  of  the  lymph  and  chyle  has  any  bearing  upon  the  move- 
ments of  these  fluids  in  the  lymphatic  vessels,  there  is  no  difference  between  the  imbibi- 
tion of  new  materials  from  the  tissues  or  from  the  intestinal  canal,  and  the  transudation 
of  the  liquid  portions  of  the  blood ;  for  the  mechanism  of  the  passage  of  liquids  from  the 
blood-vessels  is  such  that  the  motive  power  of  the  blood  cannot  be  felt.  An  illustration 
of  this  is  in  the  mechanism  of  the  transudation  of  the  liquid  portions  of  the  secretions. 
The  force  with  which  fluids  are  discharged  into  the  ducts  of  the  glands  is  enormous  and 
is  independent  of  the  action  of  the  heart,  being  due  entirely  to  the  force  of  transudation 
and  secretion.  This  is  combined  with  the  force  of  imbibition,  and  with  it  forms  one  of 
the  important  agents  in  the  movements  of  the  lymph  and  chyle.  These  movements  are 
studied  with  great  difficulty.  One  of  the  first  peculiarities  to  be  observed  is,  that,  under 
normal  conditions,  the  vessels  are  seldom  distended,  and  the  quantity  of  fluid  which  they 
contain  is  subject  to  considerable  variation.  As  far  as  the  flow  in  the  vessels  of  medium 
size  is  concerned,  the  movement  is  probably  continuous,  subject  only  to  certain  moment- 
ary obstructions  or  accelerations  from  various  causes.  But,  in  the  large  vessels  situated 
near  the  thorax  and  in  those  within  the  chest,  the  movements  are  in  a  marked  degree 
remittent,  or  they  may  even  be  intermittent.  All  experimenters  who  have  observed  the 
flow  of  lymph  or  chyle  from  a  fistula  into  the  thoracic  duct  have  noted  a  constant 
acceleration  with  each  act  of  expiration,  and  an  impulse  synchronous  with  the  pulsa- 
tions of  the  heart  has  been  frequently  observed. 

The  fact  that  the  lymphatic  system  is  never  distended,  and  the  existence  of  the 
numerous  valves  by  which  different  portions  may  become  isolated,  render  it  impossible 
to  estimate  the  general  pressure  of  fluid  in  these  vessels.  This  is  undoubtedly  subject  to 
great  variations  in  the  same  vessels  at  different  times,  as  well  as  in  different  parts  of  the 
lymphatic  system.  It  is  well  known,  for  example,  that  the  amount  of  distention  of  the 
thoracic  duct  is  exceedingly  variable,  its  capacity  not  infrequently  being  many  times 
increased  during  active  absorption.  At  the  same  time  it  is  difficult  to  attach  a  manometer 
to  any  part  of  the  lymphatic  system  without  seriously  obstructing  the  circulation  and 
consequently  exaggerating  the  normal  pressure  ;  but  the  force  with  which  liquids  pene- 
trate these  vessels  is  very  great.  This  is  illustrated  by  the  experiment  of  ligating  the 
thoracic  duct ;  for,  after  this  operation,  unless  communicating  vessels  exist  by  which  the 
fluids  can  be  discharged  into  the  venous  system,  their  accumulation  is  frequently  suffi- 
cient to  rupture  the  vessel. 

The  general  rapidity  of  the  current  in  the  lymphatic  vessels  has  never  been  accurate- 
ly estimated.  As  a  natural  consequence  of  the  variations  in  the  distention  of  these  ves- 
sels, the  rapidity  of  the  circulation  must  be  subject  to  constant  modifications.  Beclard, 
making  his  calculation  from  the  experiments  of  Colin,  who  noted  the  quantity  of  fluid 
discharged  in  a  given  time  from  fistulous  openings  into  the  thoracic  duct,  estimates  that 
the  rapidity  of  the  flow  in  this  vessel  is  about  one  inch  per  second.  This  estimate,  how- 
ever, can  be  only  approximative  ;  and  it  is  evident  that  the  flow  must  be  much  less  rapid 
in  the  vessels  near  the  periphery  than  in  the  large  trunks,  as  the  liquid  moves  in  a  space 
which  becomes  rapidly  contracted  as  it  approaches  the  openings  into  the  venous  system. 

Causes  of  the  Movements  of  the  Lymph  and  Chyle. 

Various  influences  combine  to  produce  the  movements  of  fluids  in  the  lymphatic  sys- 
tem, some  being  constant  in  their  operation,  and  others,  intermittent  or  occasional. 
These  will  be  considered,  as  nearly  as  possible,  in  the  order  of  their  relative  importance. 


MOVEMENTS  OF  THE  LYMPH  AND  CHYLE.         339 

Influence  of  the  Forces  of  Endosmosis  and  Transudation  (vis  a  tergo^.—The  forces 
of  endosmosis  and  transudation  are  undoubtedly  the  main  causes  of  the  lymphatic  circu- 
lation, more  or  less  modified,  however,  by  influences  which  may  accelerate  or  retard 
the  current ;  but  this  action  is  capable  in  itself  of  producing  the  regular  movement  of 
the  lymph  and  chyle.  It  is  a  force  which  is  in  constant  activity,  as  is  seen  in  cases  of 
ligation  of  the  thoracic  duct,  an  operation  which  must  finally  abolish  all  other  forces 
which  aid  in  producing  the  lymphatic  circulation.  When  the  receptaculum  chyli  is  rup- 
tured as  a  consequence  of  obstruction  of  the  thoracic  duct,  the  vessel  gives  way  as  the 
result  of  the  constant  endosmotic  action,  in  the  same  way  that  the  exposed  membranes 
of  an  egg  may  be  ruptured  by  endosmosis,  when  immersed  in  water. 

"We  have  already  alluded  to  the  influence  of  transudation  from  the  blood-vessels  and 
have  compared  it  to  the  force  with  which  the  secretions  are  discharged  into  the  ducts  of 
the  glands ;  and  in  placing  this,  with  the  force  of  endosmosis,  at  the  head  of  the  list  of  the 
agents  which  effect  the  lymphatic  circulation,  its  importance  is  not  over-estimated.  This 
conclusion  can  hardly  be  avoided  when  we  consider  the  anatomy  of  the  lymphatic  sys- 
tem. The  situations  in  which  the  endosmotic  force  originates  are  at  the  periphery,  where 
the  single,  homogeneous  wall  of  the  plexus  is  excessively  thin,  and  where  the  extent  of 
absorbing  surface  is  enormous.  If  liquids  can  penetrate  with  such  rapidity  and  force 
through  the  walls  of  the  blood-vessels,  where  their  entrance  is  opposed  by  the  pressure 
of  the  fluids  already  in  their  interior,  they  certainly  must  pass  without  difficulty  through 
the  walls  of  the  lymphatics,  where  there  is  no  lateral  pressure  to  oppose  their  entrance, 
except  that  produced  by  the  weight  of  the  column  of  liquid.  This  pressure  is  readily 
overcome ;  and  the  numerous  valves  in  the  lymphatic  system  effectually  prevent  any 
backward  current.  The  liquid  that  passes  into  the  lymphatics  by  endosmosis  or  by 
transudation  produces  movement  by  displacing  an  equal  bulk  of  liquid  contained  in  the 
vessel.  We  observe  with  the  microscope  the  rapid  filling  and  rupture  of  microscopic 
cells  when  immersed  in  water ;  and  the  rough  experiments  by  which  the  operation  of 
endosmosis  is  ordinarily  illustrated,  in  which  the  extent  of  endosmotic  surface  is  infinite- 
ly small  as  compared  with  that  of  the  lymphatic  system,  exhibit  a  current  of  considerable 
force  and  rapidity.  When  we  remember  that  the  infinitely  numerous  lymphatic  radicles 
are  bathed  in  fluids  which  undoubtedly  pass  into  their  interior  with  great  facility,  and 
when  we  compare  the  probable  extent  of  this  endosmotic  surface  with  the  diameter  of  the 
thoracic  duct,  we  can  hardly  be  surprised  that  this  force  should  be  capable  of  producing  a 
movement  in  the  great  trunk  at  the  rate  of  an  inch  per  second.  The  great  elasticity  of 
the  vessels  and  the  fact  that  they  are  never  completely  filled  allow  of  considerable  dis- 
tention  of  isolated  portions  of  the  lymphatic  system  when  there  is  any  obstruction  to  the 
curreiit  that  is  not  readily  overcome.  In  this  way  we  account  for  the  variations  in  the 
flow  of  the  lymph  and  chyle  which  are  of  such  constant  occurrence. 

Influence  of  the  Contractile  Walls  of  the  Vessels. — In  treating  of  the  anatomy  of  the 
lymphatic  system,  it  has  already  been  observed  that  the  large  vessels  and  those  of  me- 
dium size  are  provided  with  unstriped  muscular  fibres  and  are  endowed  with  contractil- 
ity. This  fact  has  been  demonstrated  by  physiological  as  well  as  anatomical  investiga- 
tions. Beclard  states  that  he  has  often  produced  contractions  of  the  thoracic  duct  by 
the  application  of  the  two  poles  of  an  inductive  apparatus.  It  is  not  uncommon  to  see 
the  lacteals  become  reduced  in  size  to  a  mere  thread,  even  while  under  observation. 
Although  experiments  have  generally  failed  to  demonstrate  any  regular  rhythmical  con- 
tractions in  the  lymphatic  system,  it  is  probable  that  the  vessels  contract  upon  their  con- 
tents, when  they  are  unusually  distended,  and  thus  assist  the  circulation,  the  action  of  the 
valves  opposing  a  regurgitating  current.  This  action,  however,  cannot  have  any  consid- 
erable and  regular  influence  upon  the  general  current. 

Influence  of  Pressure  from  Surrounding  Parts. — Contractions  of  the  ordinary  vol- 
untary muscles,  compression  of  the  abdominal  organs  by  contraction  of  the  abdominal 


340  ABSORPTION. 

muscles,  peristaltic  movements  of  the  intestines,  and  pulsations  of  large  arteries  situ- 
ated against  the  lymphatic  trunks,  particularly  the  thoracic  aorta,  are  all  capable  of 
increasing  the  rapidity  of  the  circulation  of  the  lymph  and  chyle. 

The  contractions  of  voluntary  muscles  assist  the  lymphatic  circulation  in  precisely 
the  way  in  which  they  influence  the  flow  of  blood  in  the  venous  system ;  and  we  have 
nothing  to  add  regarding  this  action  to  what  has  already  been  said  on  this  subject  in 
connection  with  the  venous  circulation. 

Increase  in  the  flow  of  chyle  in  the  thoracic  duct,  as  the  result  of  compression  of  the 
abdominal  organs  or  of  kneading  the  abdomen  with  the  hands,  was  observed  by  Magen- 
die,  and  the  fact  has  been  confirmed  in  all  recent  experiments  on  this  subject.  The  same 
effect,  though  probably  less  in  degree,  is  produced  by  the  peristaltic  contractions  of  the 
intestines. 

"When  a  tube  is  introduced  into  the  upper  part  of  the  thoracic  duct,  it  is  frequently 
the  case  that  the  fluid  is  discharged  with  increased  force  at  each  pulsation  of  the  heart. 
This  was  frequently  observed  by  Dalton  in  his  experiments  on  the  thoracic  duct,  and  he 
describes  the  jets  as  being  "  like  blood  coming  from  a  small  artery  when  the  circulation 
is  somewhat  impeded."  This  impulse  is  due  to  compression  of  the  thoracic  duct  as  it 
passes  under  the  arch  of  the  aorta.  Its  influence  upon  the  general  current  of  the  lymph 
and  chyle  is  probably  insignificant,  but  the  fact  attracted  the  attention  of  Haller,  who 
attached  to  it  a  great  deal  more  importance  than  it  is  now  believed  to  possess. 

Influence  of  the  Movements  of  Respiration. — "While  the  vis  a  tergo  must  be  regarded 
as  by  far  the  most  important  agent  in  the  production  of  the  lymphatic  circulation,  the 
movements  of  fluids  in  the  thoracic  duct  receive  constant  and  important  aid  from  the 
respiratory  acts.  This  fact  has  long  been  recognized ;  and  in  the  works  of  Haller  will 
be  found  a  full  discussion  of  the  influence  of  the  diaphragm  and  of  the  movements  of  the 
thorax  upon  the  circulation  of  chyle.  The  observations  of  Colin  on  this  subject  are 
most  valuable,  as  he  was  the  first  to  successfully  establish  a  fistula  into  the  thoracic  duct 
in  large  animals.  He  always  found  a  marked  remittency  in  the  flow  of  chyle  from  a  fis- 
tula into  the  thoracic  duct,  which  was  absolutely  synchronous  with  the  movements  of 
respiration.  "With  each  act  of  expiration,  the  fluid  was  forcibly  ejected,  and,  with  inspira- 
tion, the  flow  was  very  much  diminished  or  even  arrested.  These  impulses  became  much 
more  marked  when  respiration  was  interfered  with  and  the  efforts  became  violent.  The 
intermittency  of  the  current  was  sometimes  so  decided,  that  the  pulsations  were  repeated 
in  a  long  elastic  tube  attached  to  the  canula  for  the  purpose  of  collecting  the  fluid. 

The  amount  of  influence  exerted  by  the  respiratory  movements  upon  the  flow  of  the 
lymph  and  chyle  can  be  best  appreciated  by  examining  carefully  the  mechanism  of  its 
operation. 

With  each  act  of  inspiration,  all  the  liquids,  as  well  as  the  air,  are  drawn  toward  the 
cavity  of  the  thorax.  In  this  way,  the  thoracic  duct  is  dilated  and  then  becomes  most 
distended  with  fluid.  At  the  same  time,  the  flow  of  lymph  from  the  right  lymphatic 
duct  into  the  right  subclavian  vein  is  increased.  After  the  thoracic  duct  has  been  thus 
dilated  in  inspiration,  at  the  moment  of  expiration,  in  common  with  all  the  other  parts 
contained  within  the  thorax,  it  undergoes  compression ;  the  valves  prevent  the  reflux  of 
its  contents,  and,  as  a  necessary  consequence,  the  fluid  is  then  discharged  with  increased 
force  into  the  left  subclavian  vein.  It  can  be  readily  understood  how  the  act  of  inspira- 
tion, while  it  has  a  tendency  to  fill  the  thoracic  duct  from  below,  opposes  the  discharge 
of  fluid  from  a  fistula. 

From  all  these  considerations,  it  is  evident  that,  although  there  are  many  circum- 
stances capable  of  modifying  the  currents  in  the  lymphatic  system,  the  regular  flow  of  the 
lymph  and  chyle  depends  chiefly  upon  the  ms  a  tergo  ;  but  the  vessels  themselves  some- 
times undergo  contraction,  and  they  are  subject  to  occasional  compression  from  sur- 
rounding parts,  which,  from  the  existence  of  numerous  valves  in  the  vessels,  must  favor 


SECRETION  IN  GENERAL.  34! 

the  current  toward  the  venous  system.  The  alternate  dilatation  and  compression  of  the 
thoracic  duct  with  the  acts  of  respiration  likewise  aid  the  circulation,  and  they  are  more 
efficient  than  any  other  force,  except  the  vis  a  tergo.  The  action  of  the  valves  is  pre- 
cisely the  same  in  the  lymphatic  as  hi  the  venous  system. 


CHAPTER    XI. 

SECRETION. 

General  considerations — Differences  between  the  secretions  and  fluids  containing  formed  anatomical  elements— Classi- 
fication of  the  secretions — Mechanism  of  the  production  of  the  true  secretions — Mechanism  of  the  production  of 
the  excretions— General  structure  of  secreting  organs— Anatomical  classification  of  glandular  organs— Classification 
of  the  secreted  fluids— Secretions  proper  (permanent  fluids;  transitory  fluids)— Excretions — Fluids  containing 
formed  anatomical  elements— Physiological  anatomy  of  the  serous  and  synovial  membranes— Pericardial,  peri- 
toneal, and  pleural  secretions — Synovial  fluid — Mucus — Mucous  membranes — Mechanism  of  the  secretion  of  mucus 
— Composition  and  varieties  of  mucus — Microscopical  characters  of  mucus — General  function  of  mucus— Non- 
absorption  of  certain  soluble  substances,  particularly  venoms,  by  mucous  membranes— Sebaceous  fluids— Physio- 
logical anatomy  of  the  sebaceous,  ceruminous,  and  Meibomian  glands — Ordinary  sebaceous  matter — Smegma  of 
the  prepuce  and  of  the  labia  minora — Vernix  caseosa — Cerumen — Meibomian  secretion — Function  of  the  Meibo- 
mian secretion— Mammary  secretion— Physiological  anatomy  of  the  mammary  glands— Condition  of  the  mam- 
mary glands  during  the  intervals  of  lactation — Structure  of  the  mammary  glands  during  lactation — Mechanism 
of  the  secretion  of  milk— Conditions  which  modify  the  lacteal  secretion— Quantity  of  milk— General  characters 
of  milk— Microscopical  characters  of  milk— Composition  of  milk— Variations  in  the  composition  of  milk— Colos- 
trum—Lacteal  secretion  in  the  newly-born. 

Secretion  in   General. 

THE  phenomena  classed  by  physiologists  under  the  head  of  secretion  are  intimately 
connected  with  the  general  process  of  nutrition.  In  the  sense  in  which  the  term  secre- 
tion is  usually  received,  it  embraces  most  of  the  processes  in  which  there  is  a  separation 
of  material  from  the  blood  or  a  formation  of  a  new  fluid  out  of  matters  furnished  by  the 
blood.  The  blood  itself,  the  lymph,  and  the  chyle,  are  no  longer  regarded  as  secre- 
tions. These  fluids,  like  the  tissues,  are  permanent  constituents  of  the  organism,  under- 
going those  changes  only  that  are  necessary  to  their  proper  regeneration.  They  are 
likewise  characterized  by  the  presence  of  certain  formed  anatomical  elements,  which 
themselves  undergo  the  processes  of  molecular  destruction  and  regeneration.  These 
characters  are  not  possessed  by  the  secretions.  As  a  rule,  the  latter  are  homogeneous 
fluids,  without  formed  anatomical  elements,  except  as  accidental  constituents,  such  as  the 
desquamated  epithelium  in  mucus  or  in  sebaceous  matter.  The  secretions  are  not  per- 
manent, self-regenerating  fluids,  except  when  they  perform  simply  a  mechanical  function, 
as  the  humors  of  the  eye,  or  the  liquids  in  serous  and  synovial  cavities.  They  are  either 
discharged  from  the  body,  when  they  are  called  excretions,  or,  after  having  performed 
their  proper  function  as  secretions,  are  taken  up  again  in  a  more  or  less  modified  form 
by  the  blood. 

With  the  exception  of  those  fluids  which  have  a  function  almost  entirely  mechanical, 
the  relations  of  the  secretions  to  nutrition  are  so  close,  that  the  production  of  many  of 
them  forms  almost  a  part  of  this'  great  function.  It  is  difficult,  for  example,  to  con- 
ceive of  nutrition  without  the  formation  of  the  characteristic  constituents  of  the  urine, 
the  bile,  and  the  perspiration ;  and  it  is  impossible,  indeed,  to  study  satisfactorily  the 
phenomena  of  nutrition  without  considering  fully  the  various  excrementitious  principles, 
such  as  urea,  cholesterine,  creatine,  creatinine,  etc.,  for  the  constant  formation  and  dis- 
charge of  these  principles  by  disassimilation  create  the  necessity  for  the  deposition  of 
new  matter  in  nutrition.  Again,  the  most  important  of  the  secretions,  as  contradistin- 
guished from  the  excretions,  are  concerned  in  the  preparation  of  food  by  digestion,  for 
the  regeneration  of  the  great  nutritive  fluid. 


342  SECRETION. 

As  would  naturally  be  supposed,  the  general  mechanism  of  secretion  was  very  im- 
perfectly understood  early  in  the  history  of  physiology,  when  little  was  known  of  the 
circulation,  the  functions  of  the  digestive  fluids,  and  particularly  of  nutrition.  From  its 
etymology,  the  term  should  signify  separation ;  but  it  is  now  known  that  many  of  the 
secreted  fluids  are  formed  in  the  glands  and  are  not  simply  separated  or  filtered  from 
the  blood.  Physiologists  now  regard  secretion  as  the  act  by  which  fluids,  holding  cer- 
tain solid  principles  in  solution,  and  sometimes  containing  liquid  nitrogenized  princi- 
ples, but  not  necessarily  possessing  formed  anatomical  elements,  are  separated  from  the 
blood  or  are  manufactured  by  special  organs  out  of  materials  furnished  by  the  blood. 
These  organs  may  be  membranes,  follicles,  or  collections  of  follicles  or  tubes.  In  the 
latter  instance  they  are  called  glands.  The  liquids  thus  formed  are  called  secretions ; 
and  they  may  be  destined  to  perform  some  function  connected  with  nutrition  or  may  be 
simply  discharged  from  the  organism. 

It  is  not  strictly  correct  to  speak  of  formed  anatomical  elements  as  the  results  of 
secretion,  except,  perhaps,  in  the  case  of  the  fatty  particles  in  the  milk.  The  leucocytes 
found  in  pus,  the  spermatozoids  of  the  seminal  fluid,  and  the  ovum,  which  are  sometimes 
spoken  of  as  products  of  secretion,  are  real,  anatomical  elements  developed  in  the  way  in 
which  these  structures  are  ordinarily  formed.  It  has  been  conclusively  demonstrated, 
for  example,  that  leucocytes,  or  pus-corpuscles,  are  developed  in  a  clear  blastema,  with- 
out the  intervention  of  any  special  secreting  organ,  and  that  spermatozoids  and  ova  are 
generated  by  a  true  development  in  the  testicles  and  the  ovaries,  by  a  process  entirely 
different  from  ordinary  secretion.  It  is  important  to  recognize  these  facts  in  studying 
the  mechanism  by  which  the  secretions  are  produced.  It  is  true  that,  in  some  of  the 
secretions,  as  the  sebaceous  matter,  a  certain  quantity  of  epithelium,  more  or  less  disin- 
tegrated, is  found,  but  this  is  to  be  regarded  as  an  accidental  admixture  of  desquamated 
matter  and  not  as  a  product  of  secretion. 

Classification  of  the  Secretions. — The  secretions  are  capable  of  a  physiological  clas- 
sification, dependent  upon  differences  in  their  functions  and  in  the  mechanism  of  their  pro- 
duction. Investigations  within  the  past  few  years  have  shown  that  these  differences  are 
very  distinct. 

Certain  of  the  fluids  are  formed  by  special  organs,  and  have  important  functions  to 
perform  which  do  not  involve  their  discharge  from  the  organism.  These  may  be  classed 
as  the  true  secretions;  and  the  most  striking  examples  of  such  are  the  digestive  fluids. 
Each  one  of  these  fluids  is  formed  by  a  special  gland  or  set  of  glands,  which  generally 
has  no  other  function ;  and  they  are  never  produced  by  any  other  part.  It  is  the  gland 
which  produces  the  characteristic  element  or  elements  of  the  true  secretions  out  of  mate- 
rials furnished  by  the  blood ;  and  the  principles  thus  formed  never  preexist  in  the  circu- 
lating fluid.  The  function  which  these  fluids  have  to  perform  is  generally  intermittent ; 
and,  when  this  is  the  case,  the  flow  of  the  secretion  is  intermittent,  taking  place  only 
when  its  action  is  required.  "When  the  parts  which  produce  one  of  the  true  secretions 
are  destroyed,  as  maybe  sometimes  done  in  experiments  upon  living  animals,  the  charac- 
teristic elements  of  this  particular  secretion  never  accumulate  in  the  blood,  nor  are  they 
formed  vicariously  by  other  organs.  The  simple  effect  of  such  an  experiment  is  absence 
of  the  secretion  and  disturbances  consequent  upon  the  loss  of  its  function. 

Certain  other  of  the  fluids  are  composed  of  water,  holding  one  or  more  characteristic 
principles  in  solution,  which  result  from  the  physiological  waste  of  the  tissues.  These 
principles  have  no  function  to  perform  in  the  animal  economy  and  are  simply  separated 
from  the  blood  to  be  discharged  from  the  body.  These  may  be  classed  as  excretions, 
the  urine  being  the  type  of  fluids  of  this  kind.  The  characteristic  principles  of  the  excre- 
mentitious  fluids  are  formed  in,  the  tissues,  as  one  of  the  results  of  the  constant  changes 
going  on  in  all  organized,  living  structures.  They  are  not  produced  in  the  glands  by 
which  they  are  eliminated  but  appear  in  the  secretion  as  the  result  of  a  sort  of  elective 


PRODUCTION   OF  THE   TRUE   SECRETIONS.  343 

filtration  from  the  blood.  They  always  preexist  in  the  circulating  fluid  and  may  be  elim- 
inated, either  constantly  or  occasionally,  by  a  number  of  organs.  As  they  are  produced 
continually  in  the  substance  of  the.  tissues  and  are  taken  up  by  the  blood,  they  are  con- 
stantly discharged  into  the  substance  of  the  proper  eliminating  organs.  "When  the  glands 
which  thus  eliminate  these  principles  are  destroyed  or  when  their  functions  are  serious- 
ly impaired,  the  excrementitious  matters  may  accumulate  in  the  blood  and  give  rise  to 
certain  toxic  phenomena.  These  effects,  however,  are  often  retarded  by  the  vicarious 
discharge  of  such  principles  by  other  organs. 

There  are  some  fluids,  as  the  bile,  which  perform  important  functions  as  secretions, 
and  which  nevertheless  contain  certain  excrementitious  matters.  In  these  instances,  it  is 
only  the  excrementitious  matters  that  are  discharged  from  the  organism. 

In  the  sheaths  of  some  tendons  and  of  muscles,  the  substance  of  muscles,  and  in 
some  other  situations,  are  found  fluids  which  simply  moisten  the  parts,  and  which  contain 
very  little  organic  matter,  with  but  a  small  proportion  of  inorganic  salts.  Although 
these  are  frequently  spoken  of  as  secretions,  they  are  produced  generally  by  a  simple, 
mechanical  transudation  of  certain  of  the  constituents  of  the  blood  through  the  walls 
of  the  vessels.  Still,  it  is  difficult  to  draw  a  line  rigorously  between  transudation  and 
some  of  the  phenomena  of  secretion;  particularly  as  late  experiments  upon  dialysis  have 
shown  that  simple,  osmotic  membranes  are  capable  of  separating  complex  solutions,  allow- 
ing certain  constituents  to  pass  much  more  freely  than  others.  This  fact  explains  why 
the  transuded  fluids  do  not  contain  all  the  soluble  principles  of  the  blood  in  the  propor- 
tions in  which  they  exist  in  the  plasma.  All  the  secreted  fluids,  both  the  true  secretions 
and  the  excretions,  contain  many  of  the  inorganic  salts  of  the  blood-plasma. 

Mechanism  of  the  Production  of  the  True  Secretions. — Although  the  characteristic  ele- 
ments of  the  true  secretions  are  not  to  be  found  in  the  blood  or  in  any  other  of  the  animal 
fluids,  they  can  generally  be  extracted  in  quantity  from  the  glands,  particularly  during 
their  intervals  of  repose.  This  fact  has  been  repeatedly  demonstrated  with  regard  to 
many  of  the  digestive  fluids,  as  the  saliva,  the  gastric  juice,  and  the  pancreatic  juice ;  and 
artificial  fluids,  possessing  many  of  the  physiological  properties  of  the  natural  secretions, 
have  been  prepared  by  simply  infusing  the  glandular  tissue  in  water.  There  can  be  no 
doubt, 'therefore,  that,  even  during  the  periods  when  the  secretions  are  not  discharged, 
the  glands  are  taking  from  the  blood  matters  which  are  to  be  transformed  into  principles 
characteristic  of  the  individual  secretions,  and  that  this  process  is  constant.  Extending 
our  inquiries  into  the  nature  of  the  process  by  which  these  peculiar  principles  are  formed, 
it  is  found  to  bear  a  close  resemblance  to  the  general  act  of  nutrition.  There  are  certain 
anatomical  elements  in  the  glands  which  have  the  power  of  selecting  the  proper  material 
from  the  blood  and  causing  them  to  undergo  a  peculiar  transformation ;  in  the  same  way 
that  the  muscular  tissue  takes  from  the  great  nutritive  fluid  albuminoid  matters  and 
transforms  them  into  its  own  substance.  The  exact  nature  of  this  property  is  unex- 
plained. It  belongs  to  the  class  of  phenomena  observed  in  living  structures  only  and  is 
sometimes  called  vital. 

In  all  of  the  secreting  organs,  a  Variety  of  epithelium  is  found,  called  glandular,  which 
seems  to  possess  the  power  of  forming  the  peculiar  elements  of  the  different  secretions. 
Inasmuch  as  the  epithelial  cells  lining  the  tubes  or  follicles  of  the  glands  constitute  the 
only  peculiar  structures  of  these  parts,  the  rest  being  made  up  of  basement-membrane, 
connective  tissue,  blood-vessels,  nerves,  and  other  structures  which  are  distributed  gen- 
erally in  the  economy,  we  should  expect  that  these  alone  would  contain  the  elements  of 
the  secretions.  In  all  probability  this  is  the  fact ;  and,  with  regard  to  some  of  the  glands, 
this  has  been  satisfactorily  demonstrated.  It  has  been  found,  for  example,  that  the  liver- 
cells  contain  the  glycogenic  matter  formed  by  the  liver  ;  and  it  has  been  farther  shown 
that,  when  the  cellular  structures  of  the  pancreas  have  been  destroyed,  the  secretion  is 
no  longer  produced.  There  can  be  hardly  any  doubt  with  regard  to  the  application  of 


344  SECRETION. 

this  principle  to  the  glands  generally,  both  secretory  and  excretory.  Indeed,  it  is  well 
known  to  pathologists,  that,  when  the  tubes  of  the  kidney  have  become  denuded  of  their 
epithelium,  they  are  no  longer  capable  of  separating  from  the  blood  the  peculiar  constitu- 
ents of  the  urine. 

With  regard  to  the  origin  of  the  principles  peculiar  to  the  true  secretions,  it  is  impos- 
sible to  entertain  any  other  view  than  that  they  are  produced  in  the  epithelial  structures 
of  the  glands ;  and  the  old  idea  that  they  exist  ready-formed  in  the  blo'od  cannot  be 
maintained.  While  the  secretions  contain  inorganic  salts  in  solution,  transuded  from  the 
blood,  the  organic  constituents,  such  as  pepsin,  ptyaline,  pancreatine,  etc.,  are  readily 
distinguished  from  all  other  albuminoid  principles  by  their  peculiar  physiological  proper- 
ties; although  some  of  them  are  apparently  identical  with  albumen  in  their  ultimate 
composition  and  in  most  of  their  chemical  reactions. 

It  may  be  stated,  then,  as  a  general  proposition,  that  the  characteristic  elements  of 
the  true  secretions,  as  contradistinguished  from  the  excretions,  are  formed  de  now  by  the 
epithelial  structures  of  the  glands,  out  of  material  furnished  by  the  blood.  Their  forma- 
tion is  by  no  means  confined  to  what  is  usually  termed  the  period  of  functional  activity 
of  the  glands,  or  the  time  when  the  secretions  are  poured  out,  but  it  takes  place  more 
or  less  constantly  when  no  fluid  is  discharged. 

It  is  more  than  probable  that  the  formation  of  the  elements  of  the  secretions  takes  place 
with  fully  as  much  activity  in  the  intervals  of  secretion  as  during  the  discharge  of  fluid  ; 
and  most  of  the  glands  connected  with  the  digestive  system  seem  to  require  certain  inter- 
vals of  repose  and  are  capable  of  discharging  their  secretions  for  a  limited  time  only. 

When  a  secreting  organ  is  called  into  functional  activity — like  the  gastric  mucous 
membrane,  or  the  pancreas,  upon  the  introduction  of  food  into  the  alimentary  canal — a 
marked  change  in  its  condition  takes  place.  The  circulation  in  the  part  is  then  very 
much  increased  in  activity,  thus  furnishing  water  and  the  inorganic  elements  of  the 
secretion.  This  difference  in  the  vascularity  of  the  glands  during  their  activity  is  very 
marked  when  the  organs  are  exposed  in  a  living  animal  and  is  one -of  the  important  facts 
bearing  upon  the  mechanism  of  secretion.  Beaumont  observed  this  in  his  experiments 
on  St.  Martin  and  was  the  first  to  show  conclusively  that  the  gastric  juice  is  secreted  only 
when  food  is  taken  into  the  stomach  or  when  some  stimulus  is  applied  to  its  mucous 
membrane.  Bernard,  in  his  experiments  upon  the  pancreas,  noted  the  pale  appearance 
of  the  gland  during  the  intervals  of  digestion  and  its  reddened  and  congested  condition 
when  the  secretion  flowed  from  the  duct ;  and  these  observations  have  been  confirmed 
by  all  who  have  experimented  upon  the  glands  in  living  animals. 

In  later  experiments  upon  the  circulation  in  the  salivary  glands  and  its  relation  to 
secretion,  Bernard  has  fully  investigated  the  variations  in  the  vascular  supply  to  the 
glands,  with  the  most  definite  and  satisfactory  results.  His  observations  were  made 
chiefly  upon  the  submaxillary  gland  in  dogs ;  and  he  has  shown  that,  during  the  func- 
tional activity  of  this  organ,  if  a  tube  be  introduced  into  the  vein,  the  quantity  of  blood 
which  may  be  collected  in  a  given  time  is  four  or  five  times  that  which  is  discharged  in 
the  intervals  of  secretion.  It  was  ascertained,  also,  that  the  venous  blood  coming  from 
the  gland  contained  much  less  water  than  the  arterial  blood ;  and,  on  comparing  the 
quantity  of  water  lost  by  the  blood  in  its  passage  through  the  gland  in  a  given  time  with 
the  quantity  discharged  in  the  saliva,  they  were  found  to  exactly  correspond. 

The  differences  in  the  quality  and  the  composition  of  the  blood  corning  from  the 
glands  during  their  repose  and  their  activity  have  an  important  bearing  upon  the  mech- 
anism of  secretion.  As  far  as  the  composition  is  concerned,  these  differences  appear  to 
be  dependent  mainly  upon  the  modifications  in  the  circulation.  When  the  gland  is  in 
repose,  the  blood  coming  from  it  has  the  usual  dark,  venous  hue  and  contains  the  ordinary 
proportion  of  carbonic  acid ;  but,  during  secretion,  when  the  quantity  of  blood  passing 
through  the  organ  is  increased,  the  color  is  nearly  as  bright  as  that  of  arterial  blood,  and 
the  proportion  of  carbonic  acid  is  very  small.  At  this  time,  also,  the  blood  is  frequently 


PRODUCTION  OF  THE  TRUE  SECRETIONS.  345 

discharged  from  the  vein  pulsatim  to  the  distance  of  several  inches.  The  cause  of  this 
difference  in  color  is  very  easily  understood.  During  the  intervals  of  secretion,  the  blood 
is  sent  to  the  gland  for  the  purposes  of  nutrition  and  the  manufacture  of  the  elements  of 
the  secretion.  It  then  passes  through  the  part  in  moderate  quantity  and  undergoes  the 
usual  change  from  arterial  to  venous,  in  which  a  great  part  of  the  oxygen  disappears  and 
carbonic  acid  is  formed;  but,  when  secretion  commences,  the  ordinary  nutritive  changes 
are  not  sufficient  to  deoxidize  the  increased  quantity  of  blood,  and  the  venous  charatcer 
of  the  blood  coming  from  the  part  is  very  much  less  marked.  These  facts  enable  us  to 
form  a  pretty  clear  idea  of  the  mechanism  of  secretion ;  although  the  exact  nature  of 
the  forces  which  effect  the  changes  of  the  organic  principles  of  the  blood  into  the  charac- 
teristic elements  of  the  secretions  is  not  understood.  Experiments,  however,  have  shown 
that,  in  the  act  of  secretion,  there  are  two  tolerably  distinct  processes : 

1.  It  may  be  assumed  that,  at  all  times,  the  peculiar  secreting  cells  of  the  glands  are 
forming,  more  or  less  actively,  the  elements  of  the  secretions,  which  may  be  washed  out 
of  the  part  or  extracted  by  maceration  ;  but,  during  the  intervals  of  secretion,  the  quan- 
tity of  blood  received  by  the  glands  is  relatively  small. 

2.  In  obedience  to  the  proper  stimulus,  when  a  gland  takes  on  secretion,  the  quantity 
of  blood  which  it  receives  is  four  or  five  .times  greater  than  it  is  during  repose.     At  that 
time,  water,  with  certain  of  the  salts  of  the  blood  in  solution,  passes  into  the  secreting 
structure,  takes  up  the  characteristic  elements  of  the  secretion,  and  fluid  is  discharged 
by  the  duct. 

In  all  the  secretions  proper,  there  are  intervals,  either  of  complete  repose,  as  is  the 
case  with  the  gastric  juice  or  the  pancreatic  juice,  or  periods  when  the  activity  of  the 
secretion  is  very  greatly  diminished,  as  in  the  saliva.  These  periods  of  repose  seem  to 
be  necessary  to  the  proper  performance  of  the  function  of  the  secreting  glands  ;  forming 
a  marked  contrast  with  the  constant  action  of  the  organs  of  excretion.  It  is  well 
known,  for  example,  that  the  function  of  digestion  is  seriously  disturbed  when  the  act  is 
too  prolonged  from  the  habitual  ingestion  of  an  excessive  quantity  of  food. 

From  the  considerations  already  mentioned,  it  is  evident  that  the  secretions,  as  a 
rule,  are  formed  by  the  epithelial  structures  of  the  glands.  There  has  been  a  great  deal 
of  speculation  with  regard  to  the  mechanism  of  this  action  of  the  cells.  As 'we  before 
remarked,  this  question  cannot  be  considered  as  settled.  It  does  not  seem  probable  that 
the  cells  are  ruptured  during  secretion  and  discharge  their  contents  into  the  ducts,  for, 
under  these  circumstances,  we  should  expect  to  find  some  of  their  structure  in  the 
secreted  fluid  ;  whereas,  aside  from  accidental  constituents,  the  secretions  are  homogene- 
ous and  do  not  contain  any  formed  anatomical  elements.  There  is  no  good  reason  for 
supposing  that  this  action  takes  place  and  that  more  or  less  of  the  glandular  epithelium 
is  destroyed  whenever  secretion  occurs ;  and,  in  the  present  state  of  our  knowledge,  we 
can  only  assume  that  the  secreting  cells  induce  certain  transformations  in  the  organic 
elements  of  the  blood  and  modify  transudation,  without  pretending  to  understand  the 
exact  nature  of  this  process. 

The  theory,  that  the  discharge  of  the  secretions  is  due  simply  to  mechanical  causes  and 
is  attributable  solely  to  the  increase  in  the  pressure  of  blood,  cannot  be  sustained.  Press- 
ure undoubtedly  has  considerable  influence  upon  the  activity  of  secretion ;  but  the  flow 
will  not  always  take  place  in  obedience  to  simple  pressure,  and  secretion  may  be  induced 
for  a  limited  time  without  any  increase  in  the  quantity  of  blood  circulating  in  the  gland. 

The  glands  possess  a  peculiar  irritability,  which  is  manifested  by  their  action  in 
response  to  proper  stimulation.  During  secretion,  they  generally  receive  an  increased 
quantity  of  blood;  but  this  is  not  indispensable,  and  secretion  may  be  excited  without 
any  modification  of  the  circulation.  This  irritability  will  disappear  when  the  artery  sup- 
plying the  part  with  blood  is  ligated  for  a  number  of  hours ;  and  secretion  cannot  then 
be  excited,  even  when  the  blood  is  again  allowed  to  circulate.  If  the  gland  be  not 
deprived  of  blood  for  too  long  a  period,  the  irritability  is  soon  restored;  but  it  may  be 


346  SEORETIOK 

permanently  destroyed  by  depriving  the  part  of  blood  for  a  long  time.  These  facts 
are  very  striking  and  they  show  a  certain  similarity  between  glandular  and  muscular 
irritability,  although  their  properties  are  manifested  in  very  different  ways. 

Mechanism  of  the  Production  of  the  Excretions.— Certain  of  the  glands  have  the  func- 
tion of  separating  from  the  blood  excrementitious  matters,  which  are  of  no  use  in  the 
economy  and  are  simply  to  be  discharged  from  the  system.  These  matters,  which  will 
be  fully  considered,  both  in  connection  with  the  fluids  of  which  they  form  a  part  and 
under  the  head  of  nutrition,  are  entirely  different  in  their  mode  of  production  from  the 
characteristic  elements  of  the  secretions.  The  formation  of  excrementitious  principles 
takes  place  in  the  tissues  and  is  connected  with  the  general  process  of  nutrition ;  and  in 
the  excreting  glands  there  is  simply  a  separation  of  matters  already  formed.  The  action 
of  the  excreting  organs  being  constant,  there  is  not  that  regular,  periodic  increase  in  the 
activity  of  the  circulation  which  is  observed  in  secreting  organs ;  but  it  has  been  observed 
that  the  blood  which  comes  from  the  kidneys  is  nearly  as  red  as  arterial  blood,  showing 
that  the  quantity  of  blood  which  this  organ  receives  is  greater  than  is  required  for  mere 
nutrition,  the  excess,  as  in  the  secreting  organs,  furnishing  the  water  and  inorganic  salts 
that  are  found  in  the  urine.  It  has  also  been  shown  that,  when  the  secretion  of  urine  is 
interrupted,  the  blood  of  the  renal  veins  becomes  dark,  like  the  blood  in  the  general 
venous  system. 

The  function  of  excretion  is  not,  under  all  conditions,  confined  to  the  ordinary  excre- 
tory organs.  When  their  action  is  disturbed,  certain  of  the  secreting  glands,  as  the 
follicles  of  the  stomach  and  intestine,  may  for  a  time  eliminate  excrementitious  matters ; 
but  this  is  abnormal  and  is  analogous  to  the  elimination  of  foreign  matters  from  the 
blood  by  the  glands. 

Influence  of  the  Composition  and  Pressure  of  the  Blood  upon  Secretion. — Under  nor- 
mal conditions,  the  composition  of  the  blood  has  little  to  do  with  the  action  of  the  secret- 
ing organs,  as  it  simply  furnishes  the  material  out  of  which  the  characteristic  principles 
of  the  secretion  are  formed ;  but,  when  certain  foreign  matters  are  taken  into  the  system 
or  are  injected  into  the  blood-vessels,  they  are  eliminated  by  the  different  glandular 
organs,  both  secretory  and  excretory.  These  organs  seem  to  possess  a  power  of  selection 
in  the  elimination  of  different  substances.  Thus,  sugar,  ferrocyanide  of  potassium,  and 
the  salts  of  iron,  are  eliminated  in  greatest  quantity  by  the  kidneys ;  the  salts  of  iron,  by 
the  kidneys  and  the  gastric  tubules ;  and  iodine,  by  the  salivary  glands. 

The  act  of  secretion  is  almost  always  accompanied  with  an  increase  in  the  pressure  of 
blood  in  the  vessels  supplying  the  glands ;  and  it  has  been  shown,  on  the  other  hand, 
that  an  exaggeration  in  the  pressure,  if  the  nerves  of  the  glands  do  not  exert  an  opposing 
influence,  increases  the  activity  of  secretion.  The  experiments  of  Bernard  on  this  point 
show  the  influence  of  pressure  upon  the  salivary  and  the  renal  secretion,  particularly  the 
latter.  After  inserting  a  tube  into  one  of  the  ureters  of  a  living  animal,  so  that  the 
activity  of  the  renal  secretion  could  be  accurately  observed,  the  pressure  in  the  renal  artery 
was  increased  by  tying  the  crural  and  the  brachial.  It  was  then  found  that  the  flow  of 
urine  was  markedly  increased.  The  pressure  was  afterward  diminished  by  the  abstrac- 
tion of  blood,  which  was  followed  by  a  corresponding  diminution  in  the  quantity  of  urine. 
The  same  phenomena  were  observed  in  analogous  experiments  upon  the  submaxillary 
secretion.  These  striking  facts,  as  we  have  already  seen,  do  not  demonstrate  that  secretion 
is  due  simply  to  an  increase  in  the  pressure  of  blood  in  the  glands,  although  this  undoubt- 
edly exerts  an  important  influence.  It  is  necessary  that  every  condition  should  be 
favorable  to  the  act  of  secretion  for  this  influence  to  be  effective.  Experiments  have 
shown  that  pain  is  capable  of  completely  arresting  the  secretion  of  urine,  operating 
undoubtedly  through  the  nervous  system.  If  the  flow  of  urine  be  arrested  by  pain, 
an  increase  in  the  pressure  of  blood  in  the  part  fails  to  influence  the  secretion.  To  illus- 


INFLUENCE   OF  THE  NERVOUS  SYSTEM  UPON  SECRETION.       347 

trate  this  fact  more  fully,  Bernard  divided  the  nerves  on  one  side,  through  which  the 
reflex  nervous  action  was  communicated  to  the  kidney,  leaving  the  other  side  intact.  He 
then  found  that  increase  in  the  arterial  pressure,  accompanied  with  pain,  diminished  the 
flow  of  urine  upon  the  sound  side,  through  which  the  nervous  action  could  operate,  and 
increased  it  upon  the  other. 

The  influence  of  pressure  of  blood  upon  secretion  may,  then,  be  summed  up  in  a  few 
words :  There  is  always  an  increase  in  the  activity  of  secretion  when  the  pressure  of 
blood  in  the  glands  is  increased,  and  a  diminution  when  the  pressure  is  reduced ;  except 
when  there  is  some  modifying  influence  operating  through  the  nervous  system. 

Influence  of  the  Nervous  System  upon  Secretion. — The  fact  that  the  secretions  are  gen- 
erally intermittent  in  their  flow,  being  discharged  in  obedience  to  impressions  which  are 
made  only  when  there  is  a  demand  for  the  exercise  of  their  functions,  would  naturally 
lead  to  the  supposition  that  they  are  regulated,  to  a  great  extent,  through  the  nervous 
system;  particularly  as  it  is  now  well  established  that  the  nerves  are  capable  of  modify- 
ing and  regulating  local  circulations.  The  same  facts  apply,  to  a  certain  extent,  to  the 
excretions,  which  are  also  subject  to  considerable  modifications.  A  few  years  ago, 
indeed,  there  was  considerable  discussion  regarding  a  subdivision  of  the  reflex  system  of 
nerves,  which  was  supposed  to  preside  over  secretion  and  was  called  the  excito-secre- 
tory  system.  The  facts  which  led  to  the  description  of  this  system  of  nerves  had  long 
been  observed,  and  they  simply  illustrated  the  production  of  the  secretions  in  response  to 
irritation. 

Experiments  have  clearly  demonstrated  the  importance  of  the  nervous  influence  in  the 
production  of  the  secretions  ;  but  the  observations  of  Bernard  show  that  the  effects  are 
produced  mainly  by  increasing  the  activity  of  the  circulation  in  the  glands.  This  takes 
place  in,  greatest  part  through  filaments  from  the  sympathetic  system,  which  are  dis- 
tributed to  the  muscular  coats  of  the  arteries  of  supply.  "When  these  filaments  are 
divided,  the  circulation  is  increased  here,  as  in  other  situations,  and  secretion  is  the  result ; 
and,  if  the  extremity  of  the  nerve  connected  with  the  gland  be  galvanized,  contraction 
of  the  vessels  follows,  and  the  secretion  is  arrested. 

With  regard  to  many  of  the  glands,  Bernard  has  shown  that  the  influence  of  the  sym- 
pathetic is  antagonized  by  nerves  derived  from  the  cerebro-spinal  system,  which  latter  he 
calls  the  motor  nerves  of  the  glands.  The  motor  nerve  of  the  submaxillary  is  the  chorda 
tympani;  and,  as  both  this  nerve  and' the  sympathetic,  together  with  the  excretory  duct 
of  the  gland,  can  be  easily  exposed  and  operated  upon  in  a  living  animal,  most  of  the 
experiments  of  Bernard  have  been  performed  upon  this  gland.  "When  all  these  parts  are 
exposed  and  a  tube  is  introduced  into  the  salivary  duct,  division  of  the  sympathetic  induces 
secretion,  with  an  increase  in  the  circulation  in  the  gland,  the  blood  in  the  vein  becoming 
red.  On  the  other  hand,  division  of  the  chorda  tympani,  the  sympathetic  being  intact, 
arrests  secretion,  and  the  venous  blood  coming  from  the  gland  becomes  dark.  If  the 
nerves  be  now  galvanized  alternately,  it  will  be  found  that  galvanization  of  the  sympa- 
thetic produces  contraction  of  the  vessels  of  the  gland  and  arrests  secretion,  while  the 
stimulus  applied  to  the  chorda  tympani  increases  the  circulation  and  excites  secretion. 
Enough  is  known  of  the  nervous  influences  which  modify  secretion,  to  admit  of  the 
inference  that  all  the  glands  are  possessed  of  nerves  through  which  reflex  phenomena, 
affecting  their  secretions,  take  place.  It  is  the  motor,  or  functional  nerve  of  the  gland 
through  which  the  reflex  action  takes  place ;  the  influence  of  the  sympathetic  being  con- 
stant and  the  same  as  in  other  parts  where  it  is  distributed  to  blood-vessels. 

As  reflex  phenomena  involve  the  action  of  a  nervous  centre,  it  becomes  an  interesting 
question  to  determine  whether  any  particular  parts  of  the  central  nervous  system  preside 
over  the  various  secretions.  We  must  refer  again  to  the  experiments  of  Bernard  for  an 
elucidation  of  this  question.  If  a  puncture  be  made  in  the  space  included  between  the 
origin  of  the  pneumogastrics  and  the  auditory  nerves,  in  the  floor  of  the  fourth  ventricle, 


348  SECRETION. 

there  is  an  increase  in  the  discharge  of  urine,  with  an  excretion  of  sugar  due  to  an  exag- 
geration in  the  sugar-producing  function  of  the  liver.  Irritation  applied  a  little  higher, 
toward  the  pons  Varolii  and  just  posterior  to  the  origin  of  the  fifth  pair  of  nerves,  is 
followed  by  a  great  increase  in  the  activity  of  the  salivary  secretion. 

Mental  emotions,  pain,  and  various  circumstances,  the  influence  of  which  upon  secre- 
tion has  long  been  observed,  operate  through  the  nervous  system.  Numerous  familiar 
instances  of  this  kind  are  quoted  in  works  on  physiology:  such  as  the  secretion  of  tears; 
arrest  or  production  of  the  salivary  secretions ;  sudden  arrest  of  the  secretion  of  the 
mammary  glands,  from  violent  emotion ;  increase  in  the  secretion  of  the  kidneys  or  of  the 
intestinal  tract,  from  fear  or  anxiety ;  with  other  examples  which  it  is  unnecessary  to 
enumerate. 

The  effects  of  destruction  of  the  nerves  distributed  to  the  parenchyma  of  some  of  the 
glandular  organs  are  very  curious  and  interesting.  Miiller  and  Peipers  destroyed  the 
nerves  distributed  to  the  kidney  and  found  that,  not  only  was  the  secretion  arrested 
in  the  great  majority  of  instances,  but  the  tissue  of  the  kidneys  became  softened  and 
broken  down.  These  experiments  have  been  repeated  by  Bernard.  He  found  that  ani- 
mals operated  upon  in  this  way  died,  and  that  the  tissue  of  the  kidney  was  broken  down 
into  a  fetid,  semifluid  mass.  After  division  of  the  nerves  of  the  salivary  glands,  the  organs 
became  atrophied,  bat  they  did  not  undergo  the  peculiar  putrefactive  change  which  was 
observed  in  the  kidneys.  The  same  effect  was  produced  when  the  nerve  was  paralyzed  by 
introducing  a  few  drops  of  a  solution  of  woorara  at  the  origin  of  the  little  artery  which 
is  distributed  to  the  submaxillary  gland. 

General  Structure  of  Secreting  Organs. — In  treating  of  the  mechanism  of  secretion 
and  excretion,  it  has  been  evident  that  all  glandular  organs  must  be  supplied  with  blood 
to  furnish  the  materials  for  secretion,  and  be  provided  with  epithelium,  which  changes 
these  matters  into  the  characteristic  elements  of  the  secretions.  We  can  understand  how 
certain  of  the  liquid  and  saline  constituents  of  the  blood  can  escape  by  exosmosis  through 
the  homogeneous  walls  of  the  capillaries,  but  the  more  complex  secreted  fluids  require 
for  their  formation  a  different  kind  of  action ;  although,  in  the  act  of  secretion,  there  is 
considerable  transudation  of  liquid  and  saline  matters,  which  take  up  in  their  course  the 
peculiar  principles  formed  by  the  cells. 

Although  it  is  somewhat  difficult  to  draw  a  line  between  transudation  and  the  simplest 
forms  of  secretion,  it  may  be  assumed,  in  general  terms,  that  fluids  which  are  exhaled 
directly  from  the  blood-vessels,  without  the  intervention  of  glandular  apparatus  or  of  a 
secreting  membrane,  are  transudations ;  while  all  fluids  produced  by  simple  membranes 
or  by  follicles,  or  which  are  discharged  from  the  ducts  of  glands,  are  secretions.  This 
division  places  the  intermuscular  fluid  and  the  fluid  found  in  all  soft  tissues  among  the 
transudations,  and  the  serous  and  synovial  fluids  among  the  secretions. 

The  serous  and  synovial  membranes  present  the  simplest  form  of  a  secreting  apparatus. 
Blood  is  supplied  to  them  in  small  quantity,  and,  on  their  free  surfaces,  are  arranged  one 
or  two  layers  of  epithelial  ceils  which  effect  the  slight  changes  that  take  place  in  the 
transuded  fluids.  In  some  of  the  serous  membranes,  as  the  pleura  and  peritoneum,  the 
amount  of  secretion  is  very  small ;  but  others,  like  the  serous  pericardium  and  the  synovial 
membranes,  secrete  a  considerable  quamtity  of  fluid.  The  action  of  all  of  these  membranes 
may  become  exaggerated,  as  a  pathological  condition,  and  the  amount  of  their  secretions 
is  then  very  large. 

Anatomists  have  now  a  pretty  clear  idea  of  the  structure  of  what  are  called  the 
glandular  organs ;  and  it  will  be  seen  that  they  simply  present  an  arrangement  by  which 
the  secreting  surface  is  increased,  and  at  the  same  time  compressed,  as  it  were,  into  a 
comparatively  small  space.  The  mucous  follicles,  for  example,  are  simple  inversions  of  a 
portion  of  the  mucous  membrane  ;  while  the  ordinary  racemose  glands  are  nothing  more 
than  collections  of  follicles  around  the  extremities  of  excretory  ducts.  These  ideas  con- 


CLASSIFICATION  OF  GLANDULAR  ORGANS.  349 

cerning  the  general  anatomy  of  the  glands  date  from  the  observations  of  Malpighi,  who 
was  the  first  to  correct  the  old  notion  that  the  secretions  were  discharged  into  the  glan- 
dular organs  through  openings  in  the  blood-vessels.  It  is  evident  that  nothing  could  have 
been  known  of  the  mechanism  of  secretion  before  the  connection  between  the  arteries 
and  veins  had  been  ascertained,  which,  it  will  be  remembered,  was  also  discovered  by 
Malpighi.  Although  the  ideas  of  Malpighi  were  not  at  first  generally  received,  more 
recent  observations  with  the  microscope  have  shown  that  they  were  in  the  main  correct ; 
although,  from  the  imperfection  of  his  optical  instruments,  Malpighi  was  unable  to  inves- 
tigate very  thoroughly  the  minute  structure  of  the  glands. 

Anatomical  Classification  of  Glandular  Organs. — The  organs  which  produce  the 
different  secretions  are  susceptible  of  a  classification  according  to  their  anatomical  pecu- 
liarities, which  greatly  facilitates  their  study.  They  may  be  divided  as  follows  : 

1.  Secreting  membranes. — Examples  of  these  are  the  serous  and  synovial  membranes. 

2.  Follicular  glands. — Examples  of  these  are  the  simple  mucous  follicles,  the  follicles 
of  Lieberkuhn,  and  the  uterine  follicles. 

3.  Tubular  glands. — Examples  of  these  are  the  ceruminous  glands,  the  sudoriparous 
glands,  and  the  kidneys. 

4.  Racemose  glands,  simple  and  compound. — Examples  of  the  simple  racemose  glands 
are  the  sebaceous  and  Meibomian  glands,  the  tra'cheal  glands,  and  the  glands  of  Brunner. 
Examples  of  the  compound  racemose  glands  are  the  salivary  glands,  the  pancreas,  the 
lachrymal  glands,  and  the  mammary  glands. 

5.  Ductless,  or  Hood-glands. — Examples  of  these  are  the  thymus,  the  thyroid,  the 
supra-renal  capsules,  and  the  spleen. 

The  liver  is  a  glandular  organ  which  cannot  be  placed  in  any  one  of  the  above  sub- 
divisions, as  we  shall  see  when  we  come  to  treat  specially  of  its  anatomy.  The  lymphatic 
glands  and  other  parts  connected  with  the  lymphatic  and  the  lacteal  system  are  not 
embraced  in  the  above  classification.  These  are  sometimes  called  conglobate  glands. 

The  general  structure  of  secreting  membranes  and  the  follicular  glands  is  very  simple. 
The  secreting  parts  consist  of  a  membrane,  generally  homogeneous,  on  the  secreting  sur- 
face of  which  are  found  epithelial  cells,  either  tesselated  or  of  the  variety  called  glandular. 
Beneath  this  membrane,  ramify  the  blood-vessels  which  furnish  the  elements  of  the  secre- 
tions. The  follicular  glands  are  simply  digital  inversions  of  this  structure,  with  rounded, 
blind  extremities,  the  glandular  epithelium  lining  the  follicles. 

The  tubular  glands  have  essentially  the  same  structure  as  the  follicles,  except  that  the 
tubes  are  long  and  are  more  or  less  convoluted.  The  more  complex  of  these  organs  con- 
tain connective  tissue,  blood-vessels,  nerves,  and  lymphatics. 

The  compound  racemose  glands  are  composed  of  branching  ducts,  around  the  extrem- 
ities of  which  are  arranged  collections  of  rounded  follicles,  like  bunches  of  grapes.  In 
addition  to  the  epithelium,  basement-membrane,  and  blood-vessels,  these  organs  contain 
connective  tissue,  fibro-plastic  elements,  lymphatics,  involuntary  muscular  fibres,  and 
nerves.  In  the  simple  racemose  glands  the  excretory  duct  does  not  branch. 

The  ductless  glands  contain  blood-vessels,  lymphatics,  nerves,  sometimes  involuntary 
muscular  fibres,  fibro-plastic  elements,  and  a  peculiar  structure  called  pulp,  which  is  com- 
posed of  fluid  with  cells  and  occasionally  with  closed  vesicles.  These  are  sometimes  called 
blood-glands,  because  they  are  supposed  to  modify  the  blood  as  it  passes  through  their 
substance. 

The  testicles  and  the  ovaries  are  not  simply  glandular  organs ;  for,  in  addition  to  the 
production  of  mucous  or  watery  secretions,  their  principal  function  is  to  develop  certain 
anatomical  elements,  the  spermatozoids  and  the  ova.  The  physiology  of  these  organs 
will  be  considered  in  connection  with  the  subject  of  generation 

Classification  of  the  Secreted  Fluids.— The  products  of  the  various  glands  may  be 


350 


SECRETION. 


divided,  according  to  their  function,  into  secretions  and  excretions.  The  secreted  fluids 
may  be  subdivided  into  the  permanent  secretions,  which  have  a  more  or  less  mechanical 
function,  and  transitory  secretions;  some  of  the  latter,  like  mucus,  are  thrown  off  in 
small  quantity,  without  being  actually  excrementitious ;  others,  like  most  of  the  digestive 
fluids,  are  produced  intermittently  and  they  rapidly  and  finally  undergo  resorption. 

Tabular   View  of  the  Secreted  Fluids. 
Secretions  Proper. 
Permanent  Fluids. 

Vitreous  humor  of  the  eye. 

Fluid  of  the  labyrinth  of  the  internal  ear. 

Cephalo  rachidian,  or  subarachnoid  fluid. 


Serous  fluids. 

Synovial  fluid. 

Aqueous  humor  of  the  eye. 


Transitory  Fluids. 


Mucus,  in  many  varieties. 

Sebaceous  matter. 

Cerumen,  the  waxy  secretion  of  the  external  me- 

atus. 

Meibomian  fluid. 
Milk  and  colostrum. 
Tears. 


Saliva. 

Gastric  juice. 

Pancreatic  juice. 

Secretion  of  the  glands  of  Brunner. 

Secretion  of  the  follicles  of  Lieberkiihn. 

Secretion  of  the  follicles  of  the  large  intestine. 

Bile  (also  an  excretion). 


Excretions. 


Perspiration  and  the  secretion  of  the  axillary 
glands. 


Urine. 

Bile  (also  a  secretion). 


Fluids  containing  Formed  Anatomical  Elements. 

Seminal  fluid,  containing,  beside  spermatozoids,  the  secretions  of  a  number  of  glandular  structures. 
Fluid  of  the  Graafian  follicles. 


Physiological  Anatomy  of  the  Serous  and  Synovial  Membranes. 

The  serous  and  synovial  membranes,  which  are  frequently  classed  together  by  anato- 
mists, present  several  well-marked  points  of  distinction,  both  as  regards  their  structure 
and  the  products  of  their  secretion.  The  serous  membranes  are  the  arachnoid,  pleura, 
pericardium,  peritoneum,  and  tunica  vaginalis  testis.  The  synovial  membranes  are 
found  around  all  the  movable  articulations.  They  also  form  elongated  sacs  enveloping 
many  of  the  long  tendons,  and  they  exist  in  various  parts  of  the  body  in  the  form  of 
shut  sacs,  when  they  are  called  bursse. 

Serous  Membranes. — The  structure  of  the  serous  membranes  is  very  simple.  They 
consist  of  a  dense  tissue  of  fibres,  which  is  frequently  quite  closely  adherent  to  the  sub- 
jacent parts,  covered  by  a  single  layer  of  pavement,  or  tesselated  epithelium.  The 
fibres  are  mainly  of  the  inelastic  variety,  arranged  in  bundles,  interlacing  each  other  in 
the  form  of  a  close  net-work,  and  mingled  with  small,  wavy  fibres  of  elastic  tissue  and 
numerous  blood-vessels.  It  lias  not  been  satisfactorily  demonstrated  that  the  serous 
membranes  contain  nerves  and  lymphatics,  although  the  latter  are  generally  quite  abun- 
dant in  the  subjacent  parts,  particularly  beneath  the  serous  membranes  covering  the 
viscera.  The  capillary  blood-vessels  are  in  the  form  of  a  close,  polygonal  net-work,  with 
sharp  angles.  The  epithelium  of  the  serous  membranes  is  pale,  regular,  with  rather 
large  nuclei,  and  is  easily  detached  after  death.  These  membranes,  as  a  rule,  form  closed 
sacs,  with  their  opposing  or  free  surfaces  nearly  in  apposition.  The  secretion,  which  is 
generally  very  small  in  quantity,  is  usually  contained  in  their  cavity.  The  exception  to 
this  rule  is  the  arachnoid  membrane,  the  surfaces  of  which  are  exactly  in  apposition, 


PHYSIOLOGICAL  ANATOMY   OF  THE  SYNOVIAL  MEMBRANES.      351 

the  fluid  being  situated  beneath  both  layers.     The  peritoneum  of  the  female  has  an  open- 
ing on  either  side  for  the  Fallopian  tubes. 

Synovial  Membranes. — The  true  synovial  membranes  are  found  in  the  diarthrodial,  or 
movable  articulations ;  but  in  various  parts  of  the  body  are  found  closed  sacs,  sheaths, 
etc.,  which  resemble  synovial  membranes  both  in  structure  and  in  function.  Every  mova- 
ble joint  is  enveloped  in  a  capsule,  which  is  closely  adherent  to  the  edges  of  the  articu- 
lating cartilage  and  is  even  reflected  upon  its  surface  for  a  short  distance.  It  was  for- 
merly thought  that  these  membranes,  like  the  serous  sacs,  were  closed  bags,  with  one 
layer  attached  to  the  cartilage  and  the  other  passing  between  the  bones  so  as  to  enclose 
the  joint ;  but  it  is  now  the  general  opinion  that  the  cartilage  which  incrusts  the  articu- 
lating extremities  of  the  bones,  thougli  bathed  in  synovial  fluid,  is  not  itself  covered  by 
a  membrane. 

The  fibrous  portion  of  the  synovial  membranes  is  more  dense  and  resisting  and  less 
elastic  than  the  serous  membranes.  It  is  composed  of  white  inelastic  fibrous  tissue,  with 
a  few  elastic  fibres  and  blood-vessels.  The  latter  are  generally  not  so  numerous  as  in 
the  serous  membranes.  The  internal  surface  is  lined  with  small  cells  of  flattened  pave- 
ment-epithelium, with  rather  large,  rounded  nuclei.  These  cells  exist  in  from  one  to  two 
or  four  layers. 

In  most  of  the  joints,  especially  those  of  large  size,  as  the  knee  and  the  hip,  the  syno- 
vial membrane  is  thrown  into  folds  which  contain  a  considerable  amount  of  true  adipose 
tissue.  In  nearly  all  the  joints,  the  membrane  presents  fringed,  vascular  processes, 
called  sometimes  synovial  fringes.  These  are  composed  of  looped  vessels  of  considerable 
size;  and  when  injected  they  bear  a  certain  resemblance  to  the  choroid  plexus.  The 
edges  of  these  fringes  present  numerous  leaf-like,  membranous  appendages,  of  a  great 
variety  of  curious  forms.  They  are  generally  situated  near  the  attachment  of  the  mem- 
brane to  the  cartilage.  There  is  no  reason  for  supposing  that  either  the  adipose  folds  or 
the  vascular  fringes  have  any  special  office  in  the  production  of  the  synovial  secretion 
different  from  that  of  other  portions  of  the  membrane,  although  such  a  theory  has  been 
advanced. 

The  arrangement  of  the  synovial  barsse  is  very  simple.  Wherever  a  tendon  plays 
over  a  bony  surface,  we  find  a  delicate  membrane  in  the  form  of  an  irregularly-shaped, 
closed  sac,  one  layer  of  which  is  attached  to  the  tendon,  and  the  other,  to  the  bone. 
These  sacs  are  lined  with  an  epithelium  like  that  found  in  the  synovial  cavities,  and  they 
secrete  a  true  synovial  fluid.  Numerous  bursas  are  also  found  beneath  the  skin,  espe- 
cially in  parts  where  the  integument  moves  over  bony  prominences,  as  the  olecranon, 
the  patella,  and  the  tuberosities  of  the  ischium.  These  sacs,  sometimes  called  bursa3 
mucosa3,  are  much  more  common  in  man  than  in  the  inferior  animals  and  have  essen- 
tially the  same  function  as  the  deep-seated  bursas.  The  form  of  both  the  superficial  and 
deep-seated  bursaa  is  very  irregular,  and  their  interior  is  frequently  traversed  by  small 
bands  of  fibrous  tissue.  The  synovial  sheaths,  or  vaginal  processes,  line  the  canals  in 
which  the  long  tendons  play,  particularly  the  tendons  of  the  flexors  and  extensors  of 
the  fingers  and  toes.  They  have  essentially  the  same  structure  as  the  bursae,  and  present 
two  layers,  one  of  which  linesrthe  canal,  while  the  other  is  reflected  over  the  tendon. 
The  vascular  folds,  described  in  connection  with  the  articular  synovial  membranes,  are 
found  in  many  of  the  bursa3  and  the  synovial  sheaths. 

Pericardia^  Peritoneal,  and  Pleural  Secretions.— In  the  normal  condition  of  the  true 
serous  membranes,  the  amount  of  secretion  is  very  small ;  so  small,  indeed,  that  it  never 
has  been  obtained  in  quantity  sufficient  for  ultimate  analysis.  It  is  not  true  that  these 
membranes  produce  merely  a  vaporous  exhalation.  Their  secretion  is  always  liquid, 
and,  small  as  it  is  in  quantity,  it  can  be  found  in  the  pericardial  sac  and  sometimes  in 
the  lower  part  of  the  abdominal  cavity.  As  the  only  apparent  function  of  these  fluids 


352  SECRETION. 

is  to  moisten  the  membranes  so  that  the  opposing  surfaces  can  move  over  each  other 
without  undue  friction,  only  enough  fluid  is  secreted  to  keep  these  surfaces  in  a  proper 
condition.  The  error  frequently  committed  by  authors,  in  describing  the  serous  exhala- 
tions as  vaporous,  is  due  to  the  fact  that  a  vapor  is  generally  given  off  when  the  serous 
cavities  are  exposed,  either  in  a  living  animal  or  in  one  recently  killed.  This  vaporous 
exhalation  takes  place  after  exposure  of  the  parts ;  but,  if  the  cavities  be  observed  with- 
out exposing  the  serous  surfaces  to  the  air,  a  certain  quantity  of  liquid  can  be  detected. 
Colin  always  found  liquid  in  the  peritoneal,  pericardial,  and  pleural  cavities  of  animals 
recently  killed  or  opened  during  life.  In  these  cavities,  the  opposite  surfaces  of  the 
serous  membrane  were  either  in  contact  or  the  space  between  them  was  filled  with 
liquid.  In  one  of  the  small  ruminants,  he  removed  the  muscles  and  the  elastic  tunic 
from  the  lower  part  of  the  abdomen,  exposing  the  transparent  peritoneum,  and  through 
this  membrane  he  could  see  liquid  collected  in  the  dependent  parts. 

As  far  as  has  been  ascertained,  the  secretions  of  the  different  serous  membranes  bear 
a  close  resemblance  to  each  other.  They  are  either  colorless  or  of  a  slight  amber  tinge, 
alkaline  in  reaction,  and  have  a  specific  gravity  of  from  1012  to  1020.  Their  composi- 
tion resembles  that  of  the  serum  of  the  blood,  except  that  the  proportion  of  water  is 
very  much  greater.  They  contain  albumen,  chlorides,  carbonate  and  phosphate  of  soda, 
and  a  little  glucose.  These  facts  are  the  result  of  observations  upon  the  serous  fluids  of 
some  of  the  inferior  animals ;  and  it  is  exceedingly  difficult  to  obtain  the  normal  fluids 
from  the  human  subject.  The  elaborate  analyses  which  are  sometimes  given  of  the 
fluids  from  the  different  serous  cavities  in  the  human  subject  are  the  results  of  examina- 
tions of  large  morbid  accumulations. 

The  normal  quantity  of  pericardial  fluid  in  the  human  subject  is  generally  estimated 
at  from  one  to  two  fluidrachms.  Colin  found  that  the  pericardial  sac  of  the  horse  con- 
tained from  two  and  a  half  to  three  and  a  half  fluidounces,  the  cavity  being  exposed 
immediately  after  the  death  of  the  animal  from  haemorrhage. 

The  quantity  of  fluid  found  in  the  peritoneal  cavity  in  horses  killed  in  this  way  was 
from  ten  to  thirty-four  fluidounces. 

The  quantity  of  fluid  in  the  pleural  cavity  in  the  same  animal  was  from  three  and  a 
half  to  seven  fluidounces. 

These  estimates  are  simply  approximative;  but  they  give  an  idea  of  the  normal 
quantity  of  liquid  which  may  reasonably  be  supposed  to  exist  in  the  serous  cavities  of 
the  human  subject.  Judging  from  the  weight  of  a  man  of  ordinary  size  as  compared 
with  that  of  a  horse,  it  may  be  stated,  in  general  terms,  that  the  pericardial  sac  contains 
from  two  and  a  half  to  three  and  a  half  fluidrachms ;  the  peritoneal  cavity,  from  one  to 
four  fluidounces;  and  the  pleural  sac,  from  three  and  a  half  to  seven  fluidrachms. 

The  fluid  in  the  cavity  of  the  tunica  vaginalis  is  small  in  quantity  and  resembles  in 
every  respect  the  peritoneal  secretion.  The  cephalo-rachidian,  or  subarachnoid  fluid 
will  be  described  in  connection  with  the  anatomy  of  the  cerebro-spinal  nervous  system. 

Synovial  Fluid. — Although  there  is  a  certain  similarity  between  the  serous  and  the 
synovial  membranes,  their  secretions  differ  very  considerably  in  their  physical  and  chemi- 
cal characters.  Like  the  serosities,  the  synovial  fluid  has  simply  a  mechanical  function ; 
but  it  is  more  viscid  and  contains  a  larger  proportion  of  organic  matter  than  the  serous 
fluids.  The  quantity  of  fluid  in  the  joints  is  sufficient  to  lubricate  freely  the  articulating 
surfaces.  In  a  horse  of  medium  size  and  in  good  condition,  examined  immediately  after 
death,  Colin  found  1-6  fluidrachm  in  the  shoulder-joint;  1-9  drachm  in  the  elbow- 
joint;  1-6  drachm  in  the  coxo-femoral  articulation;  2-2  in  the  femoro-tibial  articula- 
tion ;  and  T9  in  the  tibio-tarsal  articulation. 

When  perfectly  normal,  the  synovial  fluid  is  either  colorless  or  of  a  pale,  yellowish 
tinge.  It  is  so  viscid  that  it  is  with  difficulty  poured  from  one  vessel  into  another.  This 
peculiar  character  is  due  to  the  presence  of  an  organic  substance  called  synovine.  When 


COMPOSITION   OF  THE   SYNOVIAL  FLUID— MUCUS.  353 

this  organic  matter  has  been  extracted  and  mixed  with  water,  it  gives  to  the  fluid  the 
peculiar  viscidity  of  the  synovial  secretion.  The  reaction  of  the  fluid  is  faintly  alkaline, 
on  account  of  the  presence  of  a  small  proportion  of  carbonate  of  soda.  The  fluid,  espe- 
cially when  the  joints  have  been  much  used,  usually  contains  in  suspension  pale  epithe- 
lial cells  and  a  few  leucocytes.  The  following  is  the  composition  of  the  synovial  fluid 
of  the  human  subject : 

Composition  of  the  Synovial  Fluid.     (Robin.) 

Water 928*00 

Synovine  (called  albumen) 64*00 

Principles  of  organic  origin  (belonging  to  the  second  class  of  Robin) not  estimated. 

Fatty  matter 0'60 

Chloride  of  sodium 


Carbonate  of  soda    r 

Phosphate  of  lime 1-50 

Ammonio-magnesian  phosphate.  .  .   traces. 

The  observations  of  Frerichs  indicate  considerable  variations  in  the  composition  and 
general  characters  of  the  synovial  fluid,  dependent  upon  use  of  the  joints.  In  a  stall- 
fed  ox,  the  proportion  of  water  to  solid  matter  was  969-90  to  30-10 ;  and,  in  animals 
that  took  considerable  exercise,  the  proportions  were  948-54  of  water  to  51 '46  of  solid 
matter.  In  the  latter,  the  fluid  was  more  viscid  and  contained  a  larger  proportion  of 
synovine  with  a  smaller  proportion  of  salts.  It  was  also  more  deeply  colored  and  con- 
tained a  larger  number  of  leucocytes. 

Like  the  serous  fluids,  the  synovial  secretion  is  produced  by  the  general  surface  of  the 
membrane  and  not  by  any  special  organs.  The  folds  and  fringes  which  have  been  de- 
scribed were  at  one  time  supposed  to  be  most  active  in  secreting  the  organic  matter,  but 
there  is  no  evidence  that  they  have  any  such  special  office. 

The  aqueous  humor  of  the  eye  and  the  fluid  of  the  labyrinth  of  the  internal  ear  resem- 
ble the  serous  secretions  in  many  regards ;  but  these  fluids,  with  the  vitreous  humor, 
will  be  considered  in  connection  with  the  physiological  anatomy  of  the  eye  and  ear. 

Mucus. 

Mucous  Membranes. — The  mucous  membranes  in  different  situations  present  impor- 
tant peculiarities  in  structure,  many  of  which  have  already  been  considered.  We  have 
described  in  detail  the  mucous  membrane  of  the  air-passages  and  of  the  alimentary  canal, 
in  connection  with  the  subjects  of  respiration  and  digestion ;  and  the  membranes  in  other 
parts  will  necessarily  be  described  in  treating  of  the  physiology  of  the  organs  in  which 
they  are  found.  It  will  be  sufficient  at  present  to  take  a  general  view  of  the  structure 
of  these  membranes  and  the  mechanism  of  the  production  of  the  various  fluids  known 
under  the  name  of  mucus. 

A  distinct  anatomical  division  of  the  mucous  membranes  may  be  made  into  two 
classes,  as  follows  :  First,  those  provided  with  pavement-epithelium  ;  and  second,  those 
provided  with  columnar  or  conoidal  epithelium.  All  of  the  mucous  membranes  line 
cavities  or  tubes  communicating  with  the  exterior  by  the  different  openings  in  the  body. 

The  following  are  the  principal  situations  in  which  the  first  variety  of  mucous  mem- 
branes, covered  with  pavement-epithelium,  are  found :  The  mouth,  the  lower  part  of  the 
pharynx,  the  oesophagus,  the  conjunctiva,  the  female  urethra,  and  the  vagina.  In  these 
situations,  the  membrane  is  composed  of  a  chorion  made  up  of  inelastic  and  elastic 
fibrous  tissue,  a  few  fibro-plastic  elements,  with  capillaries,  lymphatics,  and  nerves.  The 
elastic  fibres  are  small  and  quite  abundant.  The  membrane  itself  is  loosely  united  to 
the  subjacent  parts  by  areolar  tissue.  The  chorion  is  provided  with  vascular  papilla), 
more  or  less  marked  ;  but,  in  all  situations,  except  in  the  pharynx,  the  epithelial  cover- 
23 


354  SECRETION. 

ing  fills  up  the  spaces  between  these  papillaB,  so  that  the  membrane  presents  a  smooth 
surface.  Between  the  chorion  and  the  epithelium,  is  an  amorphous  basement-membrane. 
The  mucous  glands  open  upon  the  surface  of  the  membrane  by  their  ducts,  but  the  glan- 
dular structure  is  situated  in  the  submucous  areolar  tissue.  These  glands  have  many  of 
them  been  described  in  connection  with  the  mucous  membrane  of  the  mouth,  pharynx, 
and  O3sophagus.  They  are  generally  simple  racemose  glands,  presenting  a  collection  of 
follicles  arranged  around  the  extremity  of  a  single  excretory  duct,  lined  or  filled  with 
rounded,  nucleated  epithelium.  The  pavement-epithelium  covering  these  membranes 
exists  generally  in  several  layers,  and  presents  great  variety,  both  in  form  and  size.  The 
most  superficial  layers  are  of  large  size,  flattened,  and  irregularly  polygonal.  The  deeper 
layers  are  smaller  and  more  rounded.  The  size  of  these  cells  is  from  -g^Vo"  to  -^  of  an 
inch.  The  cells  are  pale,  slightly  granular,  and  possess  a  small,  ovoid  nucleus,  with  one 
or  two  nucleoli. 

The  second  variety  of  mucous  membranes,  covered  with  columnar  epithelium,  is  found 
lining  the  alimentary  canal  below  the  cardiac  orifice  of  the  stomach,  the  biliary  passages, 
the  excretory  ducts  of  all  the  glands,  the  nasal  passages,  the  upper  part  of  the  pharynx, 
the  uterus  and  Fallopian  tubes,  the  bronchi,  the  Eustachian  tubes,  and  the  male  urethra. 
In  certain  situations,  this  variety  of  epithelium  is  provided  on  its  free  surface  with  little 
hair-like  processes  called  cilia.  During  life  the  cilia  are  in  constant  motion,  producing  a 
current  generally  in  the  direction  of  the  mucous  orifices.  Ciliated  epithelium  is  found 
throughout  the  nasal  passages,  commencing  about  three-quarters  of  an  inch  within  the 
nose ;  in  the  upper  part  of  the  pharynx  ;  the  posterior  surface  of  the  soft  palate  ;  the  Eu- 
stachian tube  ;  the  tympanic  cavity ;  the  larynx,  trachea,  and  bronchial  tubes,  until  they 
become  less  than  -5^  of  an  inch  in  diameter ;  the  neck  and  body  of  the  uterus  ;  the  Fal- 
lopian tubes ;  the  internal  surface  of  the  eyelids ;  and  the  ventricles  of  the  brain.  This 
variety  of  mucous  membrane  is  formed  of  a  chorion,  a  basement-membrane,  and  epithe- 
lium. The  chorion  is  composed  of  inelastic  and  elastic  fibres,  with  fibro-plastic  ele- 
ments, a  few  unstriped  muscular  fibres,  amorphous  matter,  blood-vessels,  nerves,  and  lym- 
phatics. It  is  less  dense  and  less  elastic  than  the  chorion  of  the  first  variety  and  is  gen- 
erally more  closely  united  to  the  subjacent  tissue.  The  surface  of  these  membranes  is 
generally  smooth,  the  only  exception  being  the  mucous  membrane  of  the  pyloric  portion 
of  the  stomach  and  the  small  intestines.  These  membranes  are  provided  with  follicular 
glands,  extending  through  their  entire  thickness  and  terminating  in  rounded  extremities, 
sometimes  single  and  sometimes  double,  which  rest  upon  the  submucous  structure.  Many 
of  them  are  provided  also  with  simple  racemose  glands,  the  ducts  passing  through  the 
membrane,  the  glandular  structure  being  situated  in  the  submucous  areolar  tissue.  The 
columnar  epithelium  covering  these  membranes  rests  upon  an  amorphous  structure, 
called  basement-membrane.  It  generally  presents  but  few  layers,  and  sometimes,  as 
in  the  intestinal  canal,  there  is  only  a  single  layer.  The  cells  are  prismoidal,  with  a 
large,  free  extremity,  and  a  pointed  end  which  is  attached.  The  lower  strata  of  cells 
are  shorter  and  more  rounded  than  those  in  the  superficial  layer.  The  cells  are  pale, 
very  closely  adherent  to  each  other  by  their  sides,  and  provided  with  a  moderate-sized, 
oval  nucleus  with  one  or  two  nucleoli.  The  length  of  the  cells  is  from  -^  to  ^  of  an 
inch,  and  their  diameter,  from  ^^  to  -g^  of  an  inch.  When  villosities  exist  on  the 
surface  of  the  membranes,  the  cells  follow  the  elevations  and  do  not  fill  up  the  spaces 
between  them,  as  in  most  of  the  membranes  covered  with  pavement-epithelium. 

The  mucous  membrane  of  the  urinary  bladder,  the  ureters,  and  the  pelvis  of  the  kid- 
neys, cannot  be  classed  in  either  of  the  above  divisions.  They  are  covered  with  mixed 
epithelium,  presenting  all  varieties  of  form  between  the  pavement  and  the  columnar,  some 
of  the  cells  being  caudate  and  quite  irregular  in  shape. 

Mechanism  of  the  /Secretion  of  Mucus. — Nearly  every  one  of  the  great  variety  of 
fluids  known  under  the  name  of  mucus  is  composed  of  the  products  of  several  different 


MUCUS.  355 

glandular  structures.  According  to  Robin,  mucus  proper  is  produced  by  the  epithelial 
cells  of  that  portion  of  the  membrane  situated  on  the  surface,  between  the  opening  of 
the  so-called  mucous  follicles  or  glands ;  while  the  secretion  of  these  special  glandular 
organs  always  possesses  peculiar  properties.  It  is  undoubtedly  true  that  certain  mem- 
branes which  do  not  possess  glands,  as  the  mucous  lining  of  the  ureters  and  a  great  por- 
tion of  the  urinary  bladder,  are  capable  of  secreting  mucus.  The  mucous  membrane  of 
the  stomach  produces  an  alkaline,  viscid  secretion,  during  the  intervals  of  digestion 
when  the  gastric  glands  do  not  act ;  and  the  gastric  glands,  during  digestion,  secrete  a 
fluid  of  an  entirely  different  character.  The  fluid  produced  by  the  follicles  of  the  small 
intestine  likewise  has  peculiar  digestive  properties.  These  circumstances,  and  the  fact 
that  the  entire  extent  of  the  mucous  membranes  is  covered  with  more  or  less  secretion, 
show  that  the  general  epithelial  covering  of  these  membranes  is  capable  of  secreting  a 
fluid  which  forms  one  of  the  constituents  of  what  is  ordinarily  recognized  as  mucus.  It 
is  impossible,  however,  to  separate  the  secretion  of  the  superficial  layer  of  cells  from  the 
other  fluids  that  are  found  on  the  mucous  membranes  ;  and  it  will  be  more  convenient  to 
regard  as  mucus,  the  secretion  which  is  found  upon  mucous  membranes,  except  when,  as 
in  the  case  of  the  gastric  or  the  intestinal  juice,  we  can  recognize  a  special  fluid  by  cer- 
tain distinctive  physiological  properties. 

In  the  membranes  covered  with  cylinder-epithelium,  which  are  usually  provided  with 
numerous  simple  follicles,  the  secretion  is  produced  mainly  by  these  follicles,  but  in  part 
by  the  epithelium  covering  the  general  surface.  The  membranes  covered  with  pavement- 
epithelium  usually  contain  but  few  follicles  and  are  provided  with  simple  racemose  glands 
situated  in  the  submucous  structure,  which  are  to  be  regarded  rather  as  appendages  to 
the  membrane.  The  secretion  is  here  produced  by  the  epithelium  on  the  free  surface 
and  is  always  mixed  with  fluids  resulting  from  the  action  of  the  mucous  glands. 

There  is  nothing  to  be  said  with  regard  to  the  mechanism  of  the  secretion  of  mucus 
beyond  what  has  already  been  stated  in  connection  with  the  general  mechanism  of  secre- 
tion. All  the  raucous  membranes  are  quite  vascular,  and  the  cells  covering  the  mem- 
brane and  lining  the  follicles  and  glands  attached  to  it  have  the  property  of  taking  from 
the  blood  the  materials  necessary  for  the  formation  of  the  secretion.  These  principles 
pass  out  of  the  cells  upon  the  surface  of  the  membrane  in  connection  with  water  and 
inorganic  salts  in  variable  proportion.  Many  of  the  cells  themselves  are  desquamated 
and  are  found  in  the  secretion,  together  with  a  few  leucocytes,  which  are  produced  upon 
mucous  surfaces  with  great  facility. 

Composition  and  Varieties  of  Mucus. — In  comparing  the  secretions  of  the  different 
mucous  membranes,  each  one  will  be  found  to  possess  certain  distinctive  peculiarities, 
more  or  less  marked ;  but  there  are  certain  general  characters  which  belong  to  all  varie- 
ties of  mucus.  The  fluid  is  usually  a  mixture  of  the  secretion  from  the  simple  membrane 
and  the  product  of  its  follicles  or  glandular  appendages  and  always  contains  a  certain 
amount  of  desquamated  epithelium ;  and  it  is  frequently  possible,  from  the  microscopical 
characters  of  the  epithelium,  to  indicate  the  part  from  which  any  given  specimen  of  mucus 
has  been  taken.  This  desquamation  of  epithelium  must  not  be  regarded  as  a  necessary 
condition  of  the  secretion  of  mucus,  any  more  than  the  desquamation  of  the  epidermic 
scales  is  to  be  regarded  as  a  condition  necessary  to  the  secretion  of  perspiration  or  seba- 
ceous matter.  It  is  a  property  of  the  epidermis  and  the  epithelial  covering  of  mucous 
membranes  to  be  regenerated  by  the  formation  of  new  cells  from  below,  the  effete  struct- 
ures being  thrown  off,  and  the  admixture  of  these  with  mucus  is  simply  accidental. 
The  leucocytes,  formerly  called  mucus-corpuscles,  are  the  result  of  irritation  of  the  mu- 
cous membrane  and  are  not  constant  constituents  of  normal  mucus. 

All  the  varieties  of  mucus  are  more  or  less  viscid  ;  but  this  character  is  very  variable 
in  the  secretions  from  different  membranes,  in  some  of  them  the  secretion  being  quite 
fluid,  and  in  others,  almost  semisolid.  The  different  kinds  of  mucus  vary  considerably  in 


356  SECRETION. 

general  appearance.  Some  of  them  are  perfectly  clear  and  colorless  ;  but  the  secretion 
is  generally  grayish  and  semitransparent.  Examined  by  the  microscope,  in  addition  to 
the  mixture  of  epithelium  and  the  occasional  leucocytes,  which  give  to  the  fluid  its  semi- 
opaque  character,  the  mass  of  the  secretion  presents  a  very  finely-striated  appearance,  as 
though  it  were  composed  of  thin  layers  of  a  nearly  transparent  substance,  with  many 
folds.  These  delicate  striae  do  not  usually  interlace  with  each  other,  and  they  are  ren- 
dered more  distinct  by  the  action  of  acetic  acid.  This  appearance,  with  the  peculiar 
effect  of  the  acid,  is  characteristic  of  mucus.  Some  varieties  of  mucus  present  very 
fine,  pale  granulations  and  a  few  small  globules  of  oil. 

On  the  addition  of  water,  mucus  is  somewhat  swollen  but  is  not  dissolved.  An 
exception  to  this  is  the  secretion  of  the  conjunctival  mucous  membrane,  which  is  coagu- 
lated on  the  addition  of  water.  As  a  rule,  the  reaction  of  mucus  is  alkaline  ;  the  only 
exception  to  this  being  the  vaginal  mucus,  which  is  very  fluid  and  is  distinctly  acid. 

It  is  exceedingly  diificult  to  get  an  exact  idea  of  the  proximate  composition  of  nor- 
mal mucus,  from  the  fact  that  the  quantity  secreted  by  the  membranes  in  their  natural 
condition  is  very  small,  being  just  sufficient  to  lubricate  their  surface.  All  varieties,  how- 
ever, contain  a  peculiar  organic  principle,  called  mucosine,  which  gives  to  the  fluid  its 
peculiar  viscidity.  They  likewise  present  a  considerable  variety  of  inorganic  salts,  as  the 
chlorides  of  sodium  and  potassium,  alkaline  lactates,  carbonate  of  soda,  phosphate  of 
lime,  a  small  proportion  of  the  sulphates,  and,  in  some  varieties,  traces  of  iron  and  silica. 
Of  all  these  constituents,  mucosine  is  the  most  important,  as  it  gives  to  the  secretion  its 
characteristic  properties.  Like  all  other  organic  nitrogenized  principles,  mucosine  is 
coagulable  by  various  reagents.  It  is  imperfectly  coagulated  by  heat ;  and,  after  desica- 
tion,  it  can  be  made  to  assume  its  peculiar  consistence  by  the  addition  of  a  small  quantity 
of  water.  It  is  coagulated  by  acetic  acid  and  by  a  small  quantity  of  the  strong  mineral 
acids,  being  redissolved  in  an  excess  of  the  latter.  It  is  also  coagulated  by  strong  alco- 
hol, forming  a  fibrinous  clot  soluble  in  hot  and  cold  water.  Mucosine  may  be  readily 
isolated  by  adding  water  to  a  specimen  of  normal  mucus,  filtering,  and  precipitating  with 
an  excess  of  alcohol.  If  this  precipitate,  after  having  been  dried,  be  exposed  to  water, 
it  assumes  the  viscid  consistence  peculiar  to  mncosine.  This  property  serves  to  distin- 
guish it  from  albumen  and  other  organic  nitrogenized  principles. 

Nasal  Mucus. — The  nasal  mucus,  being  subject  to  so  many  changes  from  irritation  of 
the  Schneiderian  membrane,  presents  considerable  variation  in  its  appearance  and  com- 
position. Under  perfectly  normal  conditions,  it  is  very  viscid,  clear  or  slightly  opaque 
and  grayish,  and  strongly  alkaline.  It  always  contains  more  or  less  columnar  epithelium. 
In  its  behavior  in  the  presence  of  various  reagents,  it  presents  the  characteristics  which 
we  have  ascribed  to  the  secretions  of  the  mucous  membranes  generally.  The  following 
is  the  composition  of  the  normal  secretion  : 

Composition  of  JVasal  Mucus.     (Robin.) 

Water 933*00       to  947'00 

Mucosine  (with  a  trace  of  albumen  ?) 63*30       "  54'80 

Lactate  of  soda  (?) : 1-00       "  5'00 

Organic  crystalline  principles 2'00       "  1'05 

Fatty  matters  and  cholesterine not  estimated.  5 '01 

Chlorides  of  sodium  and  potassium 5-60       to  5'09 

Calcareous  and  alkaline  phosphates 3-50       "  2*00 

Sulphate  and  carbonate  of  soda 0'90  not  estimated. 

Bronchial  and  Pulmonary  Mucus. — This  is  the  secretion  of  the  general  mucous  sur- 
face of  the  larynx  and  bronchial  tubes,  mixed  with  the  products  of  the  glands  situated  in 
the  substance  of  these  membranes  and  in  the  submucous  tissue.  In  addition  to  this 
secretion,  there  is  an  exhalation  of  watery  vapor  containing  traces  of  organic  matter,  com- 


MUCUS.  357 

ing  from  the  air-cells  and  the  bronchial  tubes  less  than  -^  of  an  inch  in  diameter,  which 
are  not  provided  with  mucous  glands.  This  variety  of  mucus  is  alkaline  and  is  quite 
similar  to  nasal  mucus  in  its  appearance  and  general  characters. 

Mucus  secreted  by  the  Mucous  Membrane  of  the  Alimentary  Canal. — Throughout  the 
alimentary  canal,  from  the  mouth  to  the  anus,  the  lining  membrane  secretes  a  certain 
quantity  of  mucus,  which  does  not  differ  very  much  from  the  mucus  found  in  other  situa- 
tions. This  secretion  appears  to  take  place  independently  of  the  act  of  digestion,  and 
the  mucus  in  most  parts  of  the  tract  is  not  known  to  possess  any  peculiar  digestive  prop- 
erties. By  ligating  all  of  the  salivary  ducts,  the  buccal  mucus  has  been  procured.  This 
secretion  is  produced  by  the  cells  covering  the  general  surface  of  the  membrane  and  is 
mixed  with  the  secretion  of  the  isolated  follicular  and  racemose  glands  of  the  mouth. 
An  analogous  secretion  is  produced  by  the  mucous  membrane  of  the  pharynx  and  oesoph- 
agus. During  the  intervals  of  digestion,  a  viscid,  alkaline  secretion  covers  the  mucous 
membrane  of  the  stomach.  The  digestive  secretions  of  the  small  intestine  are  so  viscid 
that  it  has  been  found  impossible  to  separate  them  from  the  true  mucous  secretion ;  but 
undoubtedly  a  secretion  of  ordinary  mucus  is  constantly  taking  place  from  the  lining 
membrane  of  both  the  small  and  the  large  intestine.  This  secretion  probably  has  a 
purely  mechanical  function,  serving  to  lubricate  the  membranes  and  facilitate  the  move- 
ments of  the  opposing  surfaces  against  each  other. 

The  mucous  membrane  of  the  gall-bladder  produces  quite  an  abundant  secretion ;  but 
this  is  always  mixed  with  the  bile,  and  it  will  be  considered  in  connection  with  the  com- 
position of  this  fluid,  although  it  is  not  known  to  possess  any  peculiar  properties. 

Mucus  of  the  Urinary  Passages. — A  small  quantity  of  mucus  is  secreted  by  the  uri- 
nary passages.  This  is  present  in  the  normal  urine,  in  the  form  of  a  very  slight,  cloudy 
deposit,  which  forms  after  the  urine  has  been  allowed  to  stand  for  a  few  hours.  A  cer- 
tain amount  of  secretion  takes  place  from  the  mucous  membrane  of  the  bladder,  which, 
as  we  have  seen,  does  not  possess  glands  except  near  the  neck.  This  secretion  is 
produced  in  very  small  quantity,  aud  it  may  be  recognized  in  the  urine  by  the  ordinary 
microscopical  characters  of  mucus. 

Mucus  of  the  Generative  Passages. — The  vagina  secretes  a  small  quantity  of  mucus, 
which  differs  from  the  secretions  of  the  other  mucous  membranes  in  being  distinctly  acid 
and  almost  entirely  wanting  in  viscidity.  The  mucus  of  the  neck  of  the  uterus  is  clear, 
viscid,  and  distinctly  alkaline.  This  is  ordinarily  produced  in  small  quantity,  but  it  is  very 
abundant  during  pregnancy.  It  is  the  result  of  the  action  chiefly  of  the  large,  rounded 
glands  found  in  this  situation.  The  mucus  of  the  body  of  the  uterus  and  of  the  Fallopian 
tubes  is  alkaline,  of  a  grayish  color,  and  slightly  viscid.  The  secretions  of  these  parts 
are  greatly  modified  during  menstruation.  These  considerations,  however,  belong  prop- 
erly to  the  subject  of  generation  and  will  be  taken  up  more  fully  hereafter. 

Conjunctival  Mucus. — A  small  quantity  of  a  viscid  secretion  constantly  covers  the 
conjunctival  mucous  membrane,  and  this  is  a  mixture  of  the  secretion  of  the  membrane 
itself  with  the  fluid  produced  by  the  little  mucous  glands  found  near  the  internal  angle  of 
the  eye.  A  peculiarity  of  this  variety  of  mucus  is  that  it  becomes  white,  like  coagulated 
albumen,  by  the  action  of  pure  water.  A  peculiarity  of  the  mucus  from  the  conjunctiva, 
the  urethra  of  the  male,  and  the  vagina,  is  that  they  readily  become  virulent  when 
secreted  in  abnormal  quantity.  They  then  contain  a  large  number  of  leucocytes  and  have 
a  more  or  less  puriform  character.' 

General  Function  of  Mucus. — The  smooth,  viscid,  and  adhesive  character  of  mucus, 
forming,  as  this  fluid  does,  a  coating  for  the  mucous  membranes,  serves  to  protect  these 
parts,  enables  their  surfaces  to  move  freely  one  upon  the  other,  and  modifies  to  a  certain 
extent  the  process  of  absorption.  This  function  is  entirely  independent  of  the  function 
of  some  of  the  mucous  glands,  as  the  follicles  of  Lieberkuhn,  which  produce  secretions 
only  at  particular  times. 


358  SECRETION. 

Aside  from  the  mechanical  functions  of  mucus,  it  has  been  shown  that  this  fluid,  in 
connection  with  the  epithelial  covering  of  the  mucous  membranes,  is  capable  of  prevent- 
ing the  absorption  of  certain  substances.  It  is  well  known,  for  example,  that  venoms  may 
be  applied  with  impunity  to  certain  mucous  surfaces,  while  they  produce  poisonous 
effects  if  introduced  into  the  circulation.  These  agents  are  not  neutralized  by  the  secre- 
tions of  the  parts,  for  they  will  produce  their  characteristic  effects  upon  the  system  when 
removed  from  the  mucous  surfaces  and  introduced  into  the  circulation ;  and  it  is  reason- 
able to  suppose  that  the  mucous  membranes  are  capable  of  resisting  their  absorption. 
This  fact  is  proven  by  the  following  interesting  experiment,  detailed  by  Robin : 

Let  an  endosmometer  be  constructed,  using  a  fresh  mucous  membrane,  on  the  surface 
of  which  the  epithelium  and  layer  of  mucus  remain  intact,  and  in  the  interior  of  the 
apparatus,  place  a  saccharine  solution,  and  let  the  membrane  be  exposed  to  a  solution  con- 
taining some  venomous  fluid.  The  liquid  will  mount  in  the  interior  of  the  apparatus,  but 
the  poison  will  not  penetrate  the  membrane.  If  the  mucus  and  epithelium  be  now 
removed  with  the  finger-nail  from  even  a  small  portion  of  the  membrane,  the  poison  will 
immediately  pass  through  that  part  of  the  membrane,  and  an  animal  may  be  killed  with 
the  fluid  which  now  penetrates  into  the  interior  of  the  endosmometer. 

These  facts  show  that  mucus  is  an  important  secretion.  It  not  only  has  a  useful  me- 
chanical function,  but  it  is  in  all  probability  closely  connected  with  some  of  the  phenomena 
of  elective  absorption  which  are  so  often  observed,  particularly  in  the  alimentary  canal. 

Sebaceous  Fluids. 

The  general  cutaneous  surface  is  constantly  lubricated  by  a  small  quantity  of  a  pecul- 
iar, oily  secretion,  called  sebum,  or  sebaceous  matter.  This  secretion  is  somewhat  modi- 
fied in  certain  situations,  and  an  analogous  fluid  is  produced  by  special  glands  opening 
into  the  external  meatus  of  the  ear.  Another  fluid,  very  much  like  the  ordinary  seba- 
ceous matter,  is  smeared  upon  the  edges  of  the  eyelids.  These  secretions,  called  respec- 
tively cerumen  and  Meibomian  fluid,  resemble  the  secretion  of  the  ordinary  sebaceous 
glands  sufficiently  to  be  classed  with  it. 

Physiological  Anatomy  of  the  Sebaceous,  Ceruminous,  and  Meibomian  Glands. — The 
true  sebaceous  glands  are  found  in  all  parts  of  the  body  that  are  provided  with  hair ;  and, 
as  nearly  every  part  of  the  general  surface  presents  either  the  long,  the  short,  or  the 
downy  hairs,  these  glands  are  very  generally  distributed.  They  exist,  indeed,  in  greater 
or  less  numbers  in  all  parts  of  the  skin,  except  the  palms  of  the  hands  and  the  soles  of 
the  feet.  In  the  labia  minora  in  the  female,  and  in  portions  of  the  prepuce  and  glans 
penis  of  the  male,  parts  not  provided  with  hair,  small,  racemose  sebaceous  glands  are 
found,  which  produce  secretions  differing  somewhat  from  that  formed  by  the  ordinary 
glands.  The  glands  in  the  areola  of  the  nipple  in  the  female  are  very  large  and  are  con- 
nected with  small,  downy  hairs. 

Nearly  all  of  the  sebaceous  glands  are  either  simple  racemose  glands,  that  is,  present- 
ing a  number  of  follicles  connected  with  a  single  excretory  duct,  or  compound  race- 
mose glands  presenting  several  ducts,  with  their  follicles,  opening  by  a  common  tube. 
Although  there  is  this  variation  in  the  size  and  arrangement  of  the  glands  of  the  general 
surface,  they  secrete  essentially  the  same  fluid,  and  their  anatomical  differences  consist 
simply  in  a  multiplication  of  follicles. 

The  differences  in  the  size  of  the  sebaceous  glands  bear  a  certain  relation  to  the  size 
of  the  hairs  with  which  they  are  connected ;  and,  as  a  rule,  the  largest  glands  are  con- 
nected with  the  small,  downy  hairs.  These  distinctions  in  size  are  so  marked,  that  the 
glands  may  be  divided  into  two  classes;  viz.,  those  connected  with  the  long  hairs  of  the 
head,  face,  chest,  axilla,  and  genital  organs,  and  the  coarse,  short  hairs,  and  those  con- 
nected with  the  fine,  downy  hairs. 


SEBACEOUS  FLUIDS. 


359 


The  glands  connected  with  the  larger  hair-follicles  are  of  the  simple  racemose  variety 
and  are  from  T|^  to  -fa  of  an  inch  in  diameter.  From  two  to  five  of  these  glands  are  gen- 
erally found  arranged  around  each  hair-follicle.  They  discharge  their  secretion  at  about 
the  junction  of  the  upper  third  with  the  lower  two-thirds  of  the  hair-follicle.  The  folli- 
cles of  the  long  hairs  of  the  scalp  are  generally  provided  each  with  a  pair  of  sebaceous 
glands,  measuring  from  T|^¥  to  ^  of  an  inch  in  diameter.  Encircling  the  hairs  of  the 
beard,  the  chest,  axilla,  and  genital  organs,  are  large  glands,  some  of  them  5V  °f  an  inch 
in  diameter,  arranged  in  groups  of  from  four  to  eight. 

The  glands  connected  with  the  follicles  of  the  small,  downy  hairs  are  so  large,  as  com- 
pared with  the  hair-follicles,  that  the  latter  seem  rather  as  appendages  to  the  glandular 
structures.  These  glands  are  of  the  compound  racemose  variety  and  present  sometimes 
as  many  as  fifteen  culs-de-sac.  The  largest  are  found  on  the  nose,  the  ear,  the  caruncula 
lachrymalis,  the  penis,  and  the  areola  of  the  nipple,  where  they  measure  from  /0-  to  T^ 
of  an  inch.  The  glands  connected  with  the  downy  hairs  of  other  parts  are  usually  small- 
er. The  glands  of  Tyson,  situated  upon  the  corona  of  the  glans  penis  and  behind,  upon 
the  cervix,  are  sebaceous  glands  of  the  compound  racemose  variety. 


FIG.  99.  —  Sebaceous  giands.    (Sappey.) 

A,  a  gland  in  its  most  rudimentary  form  :  1,  rudimentary  hair-follicle;  2,  downy  hair;  3,  simple  sebaceous  follicle.  B, 
a  gland  more  developed  :  1,  hair-follicle  ;  2,  simple  sebaceous  follicle.  0,  a  gland  with  two  follicles  :  1  ,  hair-  follicle  ; 
2,  simple  follicle  ;  3,  follicle  imperfectly  divided.  D,  a  compound  gland  :  1,  hair-follicle  ;  2,  lobule  with  three  folli- 
cles; 8,  lobule  with  four  follicles.  E,  a  gland  with  four  lobules:  1,  hair-follicle  ;  2,  2,  first  lobule;  3,  second  lobule; 
4,  4,  third  lobule  ;  5,  fourth  lobule  ;  6,  excretory  duct  with  a  hair  passing  through  it.  F,  a  gland  with  four  lobules  : 
1,  hair-follicle  ;  2,  2,  first  lobule;  3,  second  lobule  ;  4,  third  lobule  ;  5,  fourth  lobule;  6,  excretory  duct. 


The  minute  structure  of  the  sebaceous  glands  is  very  simple.  The  follicles  which 
compose  the  simple  glands  and  the  follicular  terminations  of  the  simple  and  compound 
racemose  glands  are  formed  of  a  delicate,  structureless  or  slightly  granular  membrane, 


360 


SECRETIOK 


with  an  external  layer  of  inelastic  and  small  elastic  fibres,  and  are  lined  by  cells.  Next 
the  membrane,  the  cells  are  polyhedric,  pale,  and  granular,  most  of  them  presenting  a 
nucleus  and  a  nucleolus ;  but  the  follicle  itself  contains  fatty  granules  and  the  other  con- 
stituents of  the  sebaceous  matter,  with  cells  filled  with  fatty  particles.  These  cells 
abound  in  the  sebaceous  matter  as  it  is  discharged  from  the  duct.  The  great  quantity  of 
fatty  granules  and  globules  found  in  the  ducts  and  follicles  of  the  sebaceous  glands  ren- 
ders them  dark  and  opaque  when  examined  with  the  microscope  by  transmitted  light, 
and  their  appearance  is  quite  distinctive.  The  larger  glands  are  surrounded  with  capil- 
lary blood-vessels.  The  glands  which  open  into  the  larger  hair-follicles  will  be  illus- 
trated in  connection  with  the  anatomy  of  the  hairs. 

The  ceruminous  glands  of  the  ear  produce  a  secretion  resembling  the  sebaceous  mat- 
ter in  many  regards,  but  in  their  anatomy  they  are  almost  identical  with  the  sudoripa- 
rous glands.  They  belong  to  the  variety  of  glands  called  tubular,  and  they  consist  of  a 
nearly  straight  tube  which  penetrates  the  skin  and  a  rounded  or  ovoid  coil  situated  in  the 
subcutaneous  structure.  These  glands  are  found  only  in  the  cartilaginous  portion  of  the 
external  meatus,  where  they  exist  in  great  numbers.  They  are  rather  more  numerous  in 
the  inner  than  in  the  outer  half  of  the  meatus. 

The  ducts  of  the  ceruminous  glands  are  short  and  nearly  straight,  simply  penetrating 
the  different  layers  of  the  skin,  and  are  from  -^-Q  to  -5^  of  an  inch  in  diameter.  Their 
openings  are  rounded  and  about  -^  of  an  inch  in  diameter.  They  sometimes  terminate 
in  the  upper  part  of  one  of  the  hair-follicles.  They  present  an  external  coat  of  white 
fibrous  tissue  and  are  lined  with  several  layers  of  small,  pale,  nucleated  epithelial  cells. 


FIG.  100. — Ceruminous  glands.    (Sappey.) 

Vertical  section  of  the  skin  of  the  external  auditory  meatus:  1, 1,  epidermis;  2,  2,  derma:  3,  3,  series  of  hair-follicles 
lodged  in  the  substance  of  the  skin ;  4, 4.  series  of  sebaceous  glands  attached  to  these  follicles ;  5,  5,  subcutaneous 
areolar  layer ;  6,  6,  ceruminous  glands ;  7,  7,  ceruminous  glands  with  the  ducts  divided ;  8,  8,  adipose  vesicles. 

The  glandular  coil  is  an  ovoid  or  rounded,  brownish  mass,  from  T£F  to  -fa  or  iV  of 
an  inch  in  diameter.  It  is  simply  a  convoluted  tube,  continuous  with  the  excretory  duct 
and  terminating  in  a  somewhat  dilated,  rounded  extremity.  It  presents,  occasionally, 
small,  lateral  protrusions.  The  diameter  of  the  tube  is  from  ^  to  ^  of  an  inch.  It 
possesses  a  fibrous  coat,  with  a  longitudinal  layer  of  involuntary  muscular  fibres,  and 
externally  a  few  elastic  fibres.  It  is  lined  by  a  single  layer  of  irregularly  polygonal  cells, 
which  are  from  ^Vcr  to  TFOT  of  an  inch  in  diameter.  These  cells  contain  numerous 


SEBACEOUS  FLUIDS. 


361 


brownish  or  yellowish  pigmentary  granules.     The  tube  forming  the  gland  contains  a  clear 
fluid  mixed  with  a  granular  substance  containing  cells. 

In  addition  to  the  ceruminous  glands  of  the  ear,  numerous  sebaceous  follicles  are  found 
connected  with  the  hair-follicles  here,  as  in  other  parts  provided  with  hair.  The  arrange- 
ment of  the  ordinary  sebaceous  glands  and  the  ceruminous  glands,  which  are  situated  in 
different  planes  in  the  subcutaneous  structure,  is  shown  in  Fig.  100. 

The  Meibomian  glands  of  the  eyelids  have  essentially  the  same  structure  as  the  ordi- 
nary sebaceous  glands.  Their  ducts,  however,  are  longer,  and  the  terminal  follicles  are 
arranged  in  a  peculiar  manner  by  the  sides  of  the  tubes  along  their  entire  length. 
These  glands  are  situated  partly  in  the  substance  of  the  tarsal  cartilages,  between 
their  posterior  surfaces  and  the  conjunctival  mucous  membrane.  They  are  placed  at 
right  angles  to  the  free  border  of  the  eyelids,  opening  upon  the  inner  edge  and  occupy- 
ing the  entire  width  of  the  cartilages.  From  twenty-five  to  thirty  glands  are  found  in  the 
upper,  and  from  twenty  to  twenty-five,  in  the  lower  lid. 

Each  Meibomian  gland  consists  of  a  nearly  straight  excretory  duct,  from  -^^  to  ^-^ 
of  an  inch  in  diameter,  communicating  laterally  with  numerous  compound  racemose 
acini,  or  collections  of  follicles,  measuring  from  -g^  to  T^¥  of  an  inch.  From  fifteen  to 
twenty  of  these  collections  of  follicles  are  found  on  either  side  of  the  duct  in  glands 
of  medium  length.  Most  of  the  excretory  ducts  are  nearly  straight,  but  some  are 
turned  upon  themselves  near  their  upper  extremity.  The  general  arrangement  of  these 
glands  is  shown  in  Fig.  101. 

In  general  structure  there  is  little  if  any 
difference  between  the  terminal  follicles  of  the 
Meibomian  glands  and  the  follicles  of  the  ordi- 
nary sebaceous  glands.  They  are  lined  with 
cells  measuring  from  -g-j1^  to  T^V?  °f  an  mcn  iQ 
diameter.  These  cells  contain  numerous  fatty 
globules,  but  they  do  not  coalesce  into  large 
drops,  such  as  are  often  seen  in  the  ordinary 
sebaceous  cells.  The  follicles  and  ducts  are 
filled  with  the  whitish,  oleaginous  matter  which 
constitutes  the  Meibomian  secretion,  or  the 
sebum  palpebrale. 

In  addition  to  the  Meibomian  secretion,  the 
edges  of  the  palpebral  orifice  receive  a  small 
amount  of  secretion  from  ordinary  sebaceous 
glands  of  the  compound  racemose  variety  (cili- 
ary glands),  which  are  appended  in  pairs  to  each 
of  the  follicles  of  the  eyelashes,  and  from  the 
sebaceous  glands  attached  to  the  small  hairs  of 
the  caruncula  lachrymalis. 


Ordinary   Sebaceous    Matter.  —  Although  it 
may  be  inferred,  from  the  great  number  of 

sebaceous   glands  opening  upon   the   cutaneous     FIG.  101.—  Meibomian  glands  of  the  upper  lid; 

J  magnified  1  diameters.    (Sappey.) 

surface,  that  the  amount  of  sebaceous  matter 

must  be  considerable,  it  has  been  impossible  to 

n.,1  i  .a    -a  •  J.-.L         a*   •      -L  £• 

Collect  the  normal  fluid  in  quantity  Sufficient  for 

nltimafp  analvsjia       Tn    PArtoin   -novfa    aa  fho  sViri 

imate  analysis.      n  certain  paits,  as  tne  skin 

of  the   nose,  where  the  glands  are  particularly 

abundant,  a  certain  amount  of  oily  secretion  is 

sometimes  observed,  giving  to  the  surface  a  greasy,  glistening  aspect.     This  may  be 

absorbed  by  paper,  giving  it  the  well-known  appearance  produced  by  oily  matters,  and  it 


,  free  border  of  the  lid ;  2,  2,  anterior  lip  pene- 
trated by  the  eyelashes ;  3,  3,  posterior  lip,  with 
the  openings  of  the  Meibomian  glands ;  4,  a  gland 
passing  obliquely  at  the  summit ;  5,  another 
gland  bent  upon  itself;  6,  6,  two  glands  in  the 
form  of  racemose  glands  at  their  origin;  7,  a 
very  small  gland ;  8,  a  medium-sized  gland. 


362  SECRETION". 

may  be  collected  in  small  quantity  upon  a  glass  slide  and  examined  microscopically.  It  then 
presents  a  number  of  strongly-refracting  fatty  globules,  with  a  few  epithelial  cells.  The 
cells,  however,  are  not  numerous  in  the  fluid  as  it  is  discharged  upon  the  general  surface ; 
but,  if  the  contents  of  the  ducts  and  follicles  be  examined,  cells  will  here  be  found  in  great 
abundance.  Most  of  the  cells,  indeed,  remain  in  the  glands,  and  the  oily  matter  only  is 
discharged.  The  object  of  this  secretion  is  to  lubricate  the  general  cutaneous  surface 
and  to  give  to  the  hairs  that  softness  which  is  characteristic  of  them  when  in  a  perfectly 
healthy  condition. 

It  is  only  when  the  action  of  the  sebaceous  glands  has  become  more  or  less  modified, 
'  that  the  secretion  can  be  obtained  in  sufficient  quantity  for  chemical  analysis ;  but  we 
cannot  be  certain  that  the  fluid  taken  under  these  conditions  is  perfectly  normal.  The 
analysis  by  Esenbeck,  which  is  often  quoted  in  works  on  physiology,  was  the  result  of  an 
examination  of  the  contents  of  a  largely-distended  hair-follicle ;  and,  as  the  secretion  was 
confined  for  a  long  time,  it  is  evident  that  it  must  have  undergone  material  alteration. 
We  cannot,  indeed,  refer  to  any  ultimate  analysis  of  the  normal  sebaceous  secretion  ;  but, 
of  all  the  examinations  that  have  been  made  of  the  secretion  when  it  has  been  consider- 
ably increased  in  quantity,  those  of  Lutz  give  the  best  idea  of  what  may  be  supposed  to 
be  nearly  its  ordinary  composition.  This  observer  analyzed  the  secretion  in  a  case  of 
general  hypertrophy  of  the  sebaceous  system.  The  fluid  which  he  extracted  from  the 
dilated  glands  was  milky-white,  and  of  about  the  consistence,  when  cold,  of  wax.  The 
mean  of  eight  analyses  of  this  fluid  was  as  follows : 

Composition  of  Sebaceous  Matter. 

Water   357 

Oleine 270 

Margarine 135 

Butyric  acid  and  butyrate  of  soda  3 

Caseine 129 

Albumen 2 

Gelatine 87 

Phosphate  of  soda  and  traces  of  phosphate  of  lime 7 

Chloride  of  sodium 5 

Sulphate  of  soda 5 

1,000 

This  analysis  gives  the  proportions  of  animal  and  solid  matters,  desiccated  in  a  current 
of  dry  air.  Eobin,  who  has  reviewed  at  considerable  length  the  analytical  process  em- 
ployed by  Lutz,  regards  the  matter  supposed  to  be  either  caseine  or  some  analogous 
albuminoid  substance,  as  the  organic  matter  of  the  epithelial  cells  that  exist  in  such  great 
numbers  in  distended  sebaceous  glands.  He  regards  the  weight  of  the  substances  desig- 
nated under  the  names  of  albumen,  caseine,  and  gelatine,  with  a  certain  quantity  of  the 
water  driven  off  by  desiccation,  as  representing  the  proportion  of  epithelium.  This  view 
is  very  reasonable,  as  the  microscope  always  shows  in  these  collections  great  numbers  of 
epithelial  cells.  Cholesterine,  which  is  present  so  frequently  in  the  contents  of  sebaceous 
cysts,  does  not  exist  in  the  normal  secretion,  nor  was  it  found  in  the  analyses  by  Lutz. 

During  the  latter  months  of  pregnancy  and  during  lactation,  the  sebaceous  glands  of 
the  areola  of  the  nipple  become  considerably  distended  with  a  grayish-white,  opaque 
secretion,  containing  numerous  oily  globules  and  granules.  Frequently  the  fluid  contains 
also  a  large  number  of  epithelial  cells.  During  the  periods  above  indicated,  the  secretion 
here  is  always  much  more  abundant  than  in  the  ordinary  sebaceous  glands. 

Smegma  of  the  Prepuce  and  of  the  LaUa,  Minora.—ln  the  folds  of  the  prepuce  of  the 
male  and  on  the  inner  surface  and  folds  of  the  labia  minora  in  the  female,  a  small  quantity 


VERNIX  OASEOSA.  363 

of  a  whitish,  grumous  matter,  of  a  cheesy  consistence,  is  sometimes  found,  particularly 
when  proper  attention  is  not  paid  to  cleanliness.  The  matter  which  thus  collects  in 
the  folds  of  the  prepuce  has  really  little  analogy  with  the  ordinary  sebaceous  secretion. 
Examination  with  the  microscope  shows  that  it  is  composed  almost  entirely  of  irregular 
scales  of  pavement-epithelium,  which  do  not  present  the  fatty  granules  and  globules  usu- 
ally observed  in  the  cells  derived  from  the  sebaceous  glands.  Eobin  regards  the  produc- 
tion of  this  substance  as  entirely  independent  of  the  secretion  of  sebaceous  matter,  as  it 
is  formed  chiefly  in  parts  of  the  prepuce  in  which  the  sebaceous  glands  are  wanting. 

The  smegma  of  the  labia  minora  is  of  the  same  character  as  the  smegma  preputiale ; 
but  it  contains  drops  of  oil  and  the  other  products  of  the  sebaceous  glands  found  in  these 
parts. 

Vernix  Caseosa. — The  surface  of  the  foetus  at  birth  and  near  the  end  of  gestation  is 
generally  covered  with  a  whitish  coating,  or  smegma,  called  the  vernix  caseosa.  This  is 
most  abundant  in  the  folds  of  the  skin ;  but  it  usually  covers  the  entire  surface  with  a 
coating  of  greater  or  less  thickness  and  of  about  the  consistence  of  lard.  There  are 
great  differences  in  foetuses  at  term  as  regards  the  quantity  of  the  vernix  caseosa.  In 
some  the  coating  is  so  slight  that  it  would  not  be  observed  unless  on  close  inspection. 
There  are  few  analyses  giving  an  accurate  view  of  the  ultimate  composition  of  this 
substance ;  and  we  can  form  the  best  idea  of  its  constitution  and  mode  of  formation  from 
microscopical  examinations.  If  a  small  quantity  be  scraped  from  the  surface  and  be  spread 
out  upon  a  glass  slide  with  a  little  glycerine  and  water,  it  will  be  found,  on  microscopical 
examination,  to  consist  of  an  immense  number  of  epithelial  cells,  with  a  very  few  small, 
fatty  granules.  In  the  following  table,  it  is  seen  that  these  cells,  after  desiccation,  con- 
stituted about  ten  per  cent,  of  the  entire  mass.  The  fatty  granulations  are  very  few  and 
do  not  seem  to  be  necessary  constituents  of  the  vernix,  as  they  are  of  the  sebaceous  mat- 
ter. In  fact,  the  vernix  caseosa  must  be  regarded  as  the  residue  of  the  secretion  of  the 
sebaceous  glands,  rather  than  an  accumulation  of  true  sebaceous  matter. 

Composition  of  the  Vernix   Caseosa.     (Robin.) 

Water 769-80  to  778-70 

Nitrogenized  matter,  mucous  or  caseous 4'50 

Desiccated  epithelium 101'30 

Cholesterine,  \ 

Oleine  and  margarine,  V 108'25 

Oleates  and  margarates  of  potassa  and  of  soda,  ) 
Chloride  of  sodium,  ^ 

Hydrochlorate  of  ammonia, 
Phosphate  of  soda  and  of  lime,     f  ' 
Ammonio-magnesian  phosphate,  ) 

The  function  of  the  vernix  caseosa  is  undoubtedly  protective.  If  we  attempt  to  make 
a  microscopical  preparation  of  the  cells  with  water,  it  becomes  evident  that  the  coat- 
ing is  penetrated  by  the  liquid  with  very  great  difficulty,  even  when  mixed  with  it  as 
thoroughly  as  possible.  Indeed,  we  never  observe  at  birth  the  peculiar  effects  of  pro- 
longed contact  of  the  cutaneous  surface  with  water.  The  protecting  coat  of  vernix  caseosa 
allows  the  skin  to  perform  its  functions  in  utero,  and,  at  birth,  when  this  coating  is 
removed,  the  surface  is  found  in  a  condition  perfectly  adapted  to  extra-uterine  existence. 
It  is  not  probable  that  the  vernix  caseosa  is  necessary  to  facilitate  the  passage  of  the  child 
into  the  world,  for  the  parts  of  the  mother  are  always  sufficiently  lubricated  with  mucous 
secretion. 

Cerumen. — A  peculiar  substance  of  a  waxy  consistence  is  secreted  by  the  glands  that 
have  been  described  in  the  external  meatus,  under  the  name  of  ceruminous  glands,  mixed 


364  SECRETIOK. 

with  the  secretion  of  sebaceous  glands  connected  with  the  short  hairs  in  this  situation. 
It  is  difficult  to  ascertain  what  share  these  two  sets  of  glands  have  in  the  formation  of 
the  cerumen.  Robin  is  of  the  opinion  that  the  waxy  portion  of  the  secretion  is  produced 
entirely  by  the  sebaceous  glands,  and  that  the  convoluted  glands,  commonly  known  as  the 
ceruminous  glands,  produce  a  secretion  like  the  perspiration.  He  calls  the  latter,  indeed, 
the  sudoriparous  glands  of  the  meatus.  This  view  is,  to  a  certain  extent,  reasonable ; 
for  the  sebaceous  matter  is  not  removed  from  the  meatus  by  friction,  as  in  other  situa- 
tions, and  would  have  a  natural  tendency  to  accumulate.  But  the  contents  of  the  ducts 
of  the  ceruminous  glands  differ  materially  from  the  fluid  found  in  the  ducts  of  the  ordi- 
nary sudoriparous  glands,  containing  granules  and  fatty  globules,  such  as  exist  in  the 
cerumen.  Although  the  glands  of  the  ear  are  analogous  in  structure,  and,  to  a  certain 
extent,  in  the  character  of  their  secretion,  to  the  sudoriparous  glands,  the  fluid  which  they 
produce  is  peculiar.  We  shall  see,  also,  that  the  perspiratory  glands  of  the  axilla  and  of 
some  other  parts  produce  secretions  differing  somewhat  from  ordinary  perspiration.  As 
far  as  can  be  ascertained,  the  cerumen  is  produced  by  both  sets  of  glands.  The  sebaceous 
glands  attached  to  the  hair-follicles  probably  secrete  most  of  the  oleaginous  and  waxy 
matter,  while  the  so-called  ceruminous  glands  produce  a  secretion  of  much  greater  fluid- 
ity, but  containing  a  certain  amount  of  granular  and  fatty  matter. 

The  consistence  and  general  appearance  of  cerumen  are  quite  variable  within  the  lim- 
its of  health.  When  first  secreted,  it  is  of  a  yellowish  color,  about  the  consistence  of 
honey,  becoming  darker  and  much  more  viscid  upon  exposure  to  the  air.  It  has  a  very 
decided  and  bitter  taste.  It  readily  forms  a  sort  of  emulsive  mixture  with  water. 

Examined  microscopically,  the  cerumen  is  found  to  contain  semisolid,  dark  granula- 
tions of  an  irregularly  polyhedric  shape,  with  epithelium  from  the  sebaceous  glands,  and 
epidermic  scales,  both  isolated  and  in  layers.  Sometimes,  also,  a  few  crystals  of  choles- 
terine  are  found. 

Chemical  examination  shows  that  the  cerumen  is  composed  of  oily  matters  fusible  at 
a  low  temperature,  a  peculiar  organic  matter  resembling  mucosine,  with  salts  of  soda 
and  a  certain  quantity  of  phosphate  of  lime.  The  yellow  coloring  matter  is  soluble  in 
alcohol ;  and  the  residue  after  evaporation  of  the  alcohol  is  very  soluble  in  water  and 
may  be  precipitated  from  its  watery  solution  by  the  neutral  acetate  of  lead  or  the  chloride 
of  tin.  This  extract  has  an  exceedingly  bitter  taste. 

The  cerumen  lubricates  the  external  meatus,  accumulating  in  the  canal  around  the 
hairs.  Its  peculiar  bitter  taste  is  supposed  to  be  efficient  in  preventing  the  entrance  of 
insects.  . 

Meibomian  Secretion. — Very  little  is  known  concerning  any  special  properties  of  the 
Meibomian  fluid,  except  that  it  mixes  with  water  in  the  form  of  an  emulsion  more  readily 
than  the  other  sebaceous  secretions.  It  is  produced  in  small  quantity,  mixed  with  a  cer- 
tain amount  of  mucus  and  the  secretion  from  the  ordinary  sebaceous  glands  attached  to 
the  eyelashes  (ciliary  glands)  and  the  glands  of  the  caruncula  lachrymalis,  and  smears 
the  edges  of  the  palpebral  orifice.  This  oily  coating  on  the  edges  of  the  lids,  unless  the 
tears  be  produced  in  excessive  quantity,  prevents  their  overflow  upon  the  cheeks  and 
directs  the  excess  of  fluid  into  the  nasal  duct. 

Mammary  Secretion. 

The  mammary  glands  are  among  the  most  remarkable  organs  in  the  economy;  not 
only  from  the  peculiar  character  of  their  secretion,  which  is  unlike  the  product  of  any 
other  of  the  glands,  but  from  the  great  changes  which  they  undergo  at  different  periods, 
both  in  size  and  structure.  Rudimentary  in  early  life,  and  in  the  male  at  all  periods  of 
life,  these  organs  are  fully  developed  in  the  adult  female,  only  in  the  latter  months  of 
pregnancy  and  during  lactation.  It  is  true  that,  in  the  female,  after  puberty,  the  mam- 
mary glands  undergo  a  marked  and  rapid  increase  in  size ;  but  even  then  they  are  not 


PHYSIOLOGICAL  ANATOMY   OF  THE   MAMMARY   GLANDS.         365 

fully  developed,  and,  if  examined  with  the  microscope,  they  are  found  to  lack  the  essential 
anatomical  characters  of  secreting  organs.  The  physiological  anatomy  of  the  mammary 
glands  consequently  possesses  peculiar  interest,  aside  from  the  great  importance  of  their 
secretion. 

It  will  be  found  convenient  to  consider  these  organs  in  three  stages  of  development ; 
viz.,  in  their  rudimentary  condition,  as  they  exist  in  the  male  and  in  the  female  before 
puberty ;  in  the  partially-developed  state,  as  they  are  found  in  the  unimpregnated  female 
after  puberty  and  during  the  intervals  of  lactation ;  and,  finally,  in  the  fully-developed 
condition,  when  milk  is  secreted. 

Physiological  Anatomy  of  the  Mammary   Glands. 

The  form,  size,  and  situation  of  the  mammas  in  the  adult  female  are  too  well  known 
to  demand  more  than  a  passing  mention.  These  organs  are  almost  invariably  double 
and  are  situated  on  the  anterior  portion  of  the  thorax,  over  the  great  pectoral  mus- 
cles. In  women  who  have  never  borne  children,  they  are  generally  firm,  nearly  hemi- 
spherical, with  the  nipple  at  the  most  prominent  point.  In  women  who  have  borne 
children,  the  glands,  during  the  intervals  of  lactation,  are  usually  larger,  are  held  more 
loosely  to  the  subjacent  parts,  and  are  apt  to  become  flabby  and  pendulous.  The  areola 
of  the  nipple  is  also  darker. 

In  both  sexes,  the  mammary  glands  are  nearly  as  fully  developed  at  birth  as  at  any 
time  before  puberty.  They  make  their  appearance  at  about  the  fourth  month,  in  the 
form  of  little  elevations  of  the  structure  of  the  true  skin,  which  soon  begin  to  send  off 
processes  beneath  the  skin,  which  are  destined  to  be  developed  into  the  lobes  of  the 
glands.  In  the  foetus  at  term,  the  glands  measure  hardly  more  than  one-third  of  an  inch 
in  diameter.  At  this  time,  there  are  from  twelve  to  fifteen  lobes  in  each  gland,  and 
each  lobe  is  penetrated  by  a  duct,  with  but  few  branches,  composed  of  fibrous  tissue 
and  lined  with  columnar  epithelium.  The  ends  of  these  ducts  are  frequently  somewhat 
dilated;  but  what  have  been  called  the  gland- vesicles  do  not  make  their  appearance 
before  puberty.  In  the  adult  male,  the  glands  are  from  half  an  inch  to  two  inches 
broad,  and  from  T^  to  J  of  an  inch  in  thickness.  In  their  structure,  however,  they  pre- 
sent little  if  any  difference  from  the  rudimentary  glands  of  the  infant. 

As  the  period  of  puberty  approaches  in  the  female,  the  rudimentary  ducts  of  the  differ- 
ent lobes  become  more  and  more  ramified.  Instead  of  each  duct  having  but  two  or  three 
branches,  the  different  lobes,  as  the  gland  enlarges,  are  penetrated  by  innumerable  rami- 
fications, which  have  gradually  been  developed  as  processes  from  the  main  duct.  It  is 
important  to  remember,  however,  that  these  branches  are  never  so  numerous  or  so  long 
during  the  intervals  of  lactation  as  they  are  when  the  organ  is  in  full  activity.  The  ordina- 
ry condition  of  the  gland,  as  compared  with  its  structure  during  activity,  is  one  of  atrophy. 

Condition  of  the  Mammary  Glands  during  tlie  Intervals  of  Lactation. — At  this 
time  the  glands  are  not  secreting  organs.  They  present  the  ducts,  ramifying,  to  a  certain 
extent,  in  the  substance  of  the  lobes  into  which  the  structure  is  divided,  but  their  branches 
are  short  and  possess  but  few  of  the  glandular  acini  that  are  observed  in  every  part  of 
the  organs  during  lactation.  This  difference  in  the  structure  of  the  glands  is  most 
remarkable ;  and,  as  they  pass  from  a  secreting  to  a  non-secreting  condition  at  the  end  of 
lactation,  the  ducts  retract  in  all  their  branches,  and  most  of  the  secreting  culs-de-sac 
disappear.  At  this  time,  the  glandular  tissue  is  of  a  bluish-white  color  and  loses  the 
granular  appearance  which  it  presents  during  functional  activity.  The  ducts  are  then 
lined  with  a  small,  nucleated,  pavement-epithelium,  which  is  not  found  during  the  secre- 
tion of  milk.  These  changes,  pointed  out  by  Robin,  whose  observations  have  been  veri- 
fied and  extended  by  Sappey,  are  confined  almost  exclusively  to  the  secreting  structure  of 
the  glands.  The  interstitial  tissue  remains  about  the  same,  the  blood-vessels,  only,  being 
increased  in  number  during  lactation.  » 


366  SECRETION. 

Structure  of  the  Mammary  Glands  during  Lactation. — Between  the  fourth  and  the 
fifth  month  of  utero-gestation,  the  mammary  glands  begin  to  increase  in  size ;  and,  at 
term,  they  are  very  much  larger  than  during  the  unimpregnated  state.  At  this  time,  the 
breasts  become  quite  hard,  and  the  surface  near  the  areola  is  somewhat  uneven,  from 
the  great  development  of  the  ducts.  The  nipple  itself  is  increased  in  size,  the  papillae 
upon  its  surface  and  upon  the  areola  are  more  largely  developed,  and  the  areola  becomes 
larger,  darker,  and  thicker.  The  glandular  structure  of  the  breasts  during  the  latter  half 
of  pregnancy  becomes  so  far  developed,  that,  if  the  child  be  born  at  the  seventh  month, 
the  lacteal  secretion  may  generally  be  established  at  the  usual  time  after  parturition. 
Even  when  parturition  takes  place  at  term,  a  few  days  elapse  before  secretion  is  fully 
established,  and  the  first  product  of  the  glands,  called  colostrum,  is  very  different  from  the 
fully-formed  milk. 

The  only  parts  of  the  covering  of  the  breasts  that  present  any  peculiarities  are  the 
areola  and  the  nipple.  The  surface  of  the  nipple  is  covered  with  papilla,  which  are 
very  largely  developed  near  the  summit.  It  is  covered  by  epithelium  in  several  layers, 
the  lower  strata  being  filled  with  pigmentary  granules.  The  true  skin  covering  the  nip- 
ples is  composed  of  inelastic  and  elastic  fibres,  containing  a  large  number  of  sebaceous 
glands,  but  no  hair-follicles  or  sudoriparous  glands.  According  to  Sappey,  these  glands, 
which  are  from  eighty  to  one  hundred  and  fifty  in  number,  are  always  of  the  racemose 
variety,  and  they  never  exist  in  the  form  of  simple  follicles,  as  they  are  described  by  most 
anatomists.  The  nipple  contains  the  lactiferous  ducts,  fibres  of  inelastic  and  elastic  tis- 
sue, with  an  immense  number  of  non-striated  muscular  fibres.  The  muscular  fibres  have 
no  definite  direction,  but  are  so  numerous  that,  when  they  are  contracted,  the  nipple 
becomes  very  firm  and  hard.  The  nipple,  although  it  may  thus  become  hard  upon  the 
application  of  cold  or  other  stimulus,  presents  none  of  the  anatomical  characteristics  of 
the  true  erectile  organs,  as  is  erroneously  supposed  by  some  authors ;  and  its  hardening 
is  simply  due  to  contraction  of  its  muscular  fibres. 

The  areola  does  not  lie,  like  the  general  integument  covering  the  gland,  upon  a  bed 
of  adipose  tissue,  but  it  is  closely  adherent  to  the  subjacent  glandular  structure.  The 
skin  here  is  much  thinner  and  more  delicate  than  in  other  parts,  and  the  pigmentary 
granules  are  very  abundant  in  some  of  the  lower  strata  of  epidermic  cells,  particularly 
during  pregnancy.  The  true  skin  of  the  areola  is  composed  of  inelastic  and  elastic  fibres 
and  lies  upon  a  distinct  layer  of  non-striated  muscular  fibres.  The  arrangement  of  the 
muscular  fibres  (sometimes  called  the  subareolar  muscle)  is  quite  regular,  forming  con- 
centric rings  around  the  nipple.  These  fibres  are  supposed  to  be  useful  in  compressing 
the  ducts  during  the  discharge  of  milk.  The  areolar  presents  the  following  structures : 
numerous  papillae,  considerably  smaller  than  those  upon  the  nipple ;  hair-follicles,  con- 
taining small,  rudimentary  hairs ;  sudoriparous  glands  ;  and  sebaceous  glands  connected 
with  the  hair- follicles.  The  sebaceous  glands  in  this  situation  are  very  large,  and  their 
situation  is  indicated  by  little  prominences  on  the  surface  of  the  areola,  which  are  espe- 
cially marked  during  pregnancy. 

The  mammary  gland  itself  is  of  the  compound  racemose  variety.  It  is  covered  in 
front  by  a  subcutaneous  layer  of  fat,  and  posteriorly  it  is  enveloped  in  a  fibrous  membrane 
loosely  attached  to  the  pectoralis  major  muscle.  A  considerable  amount  of  adipose  tissue 
is  also  found  in  the  substance  of  the  gland  between  the  lobes. 

Separated  from  the  adipose  and  fibrous  tissue,  the  mammary  gland  is  found  divided 
into  lobes,  from  fifteen  to  twenty-four  in  number.  These,  in  their  turn,  are  subdivided 
into  lobules  made  up  of  a  greater  or  less  number  of  acini,  or  culs-de-sac.  The  secreting 
structure  is  of  a  reddish-yellow  color  and  is  distinctly  granular,  presenting  a  decided 
contrast  to  the  pale  and  uniformly  fibrous  appearance  of  the  gland  during  the  intervals 
of  lactation.  If  the  ducts  be  injected  from  the  nipple  and  be  followed  into  the  substance 
of  the  gland,  each  one  will  be  found  distributing  its  branches  to  a  distinct  lobe  ;  so  that 
the  organ  is  really  made  up  of  a  number  of  glands,  in  their  structure  identical  with  each 


PHYSIOLOGICAL  ANATOMY   OF  THE  MAMMARY  GLANDS.         367 

other.  It  will  be  most  convenient,  in  studying  the  intimate  structure  of  the  gland  to 
begin  at  the  nipple  and  follow  out  one  of  the  ducts  to  the  termination  of  its  branches  in 
the  secreting  culs-de-sac. 

The  canals  which  discharge  the  milk  at  the  nipple  are  called  lactiferous  or  galac- 
tophorous  ducts.  They  vary  in  number  from  ten  to  fourteen.  The  openings  of  the  ducts 
at  the  nipple  are  very  small,  measuring  only  from  -£-$  to  ^  of  an  inch.  As  each  duct 
passes  downward,  it  enlarges  in  the  nipple  to  ^  or  T^  of  an  inch  in  diameter,  and  beneath 
the  areola  it  presents  an  elongated  dilatation,  from  -*-  to  \  of  an  inch  in  diameter,  called  the 
sinus  of  the  duct.  During  lactation,  a  considerable  quantity  of  milk  collects  in  these  sinuses, 
which  serve  as  reservoirs.  Beyond  the  sinuses,  the  caliber  of  the  ducts  measures  from 
TV  to  £  of  an  inch.  They  penetrate  the  different  lobes,  branching  and  subdividing,  to 
terminate  finally  in  the  collections  of  culs-de-sac  which  form  the  acini.  Most  modern 
observers  are  agreed  that  there  is  no  anastomosis  between  the  different  lactiferous  ducts, 
and  that  each  one  is  distributed  independently  to  one  or  more  lobes. 


FIG.  102.— Mammary  gland  of  the  human  female*    (Lie"geois.) 

a,  nipple,  the  central  portion  of  which  is  retracted ;   &,  areola;  c,  c,  c,  c,  c,  lobules  of  the  gland :  1,  sinus,  or  dilated 
portion  of  one  of  the  lactiferous  ducts;  2,  extremities  of  the  lactiferous  ducts. 

The  intimate  structure  of  the  lactiferous  ducts  is  interesting  and  important.  They 
are  possessed  of  three  distinct  coats.  The  external  coat  is  composed  of  anastomosing 
fibres  of  elastic  tissue,  with  some'  inelastic  fibres.  The  middle  coat  is  composed  of  non 
striated  muscular  fibres,  arranged  longitudinally  and  existing  throughout  the  duct,  from 
its  opening  at  the  nipple  to  the  secreting  culs-de-sac.  The  internal  coat  is  an  amor- 
phous membrane,  lined  with  roundish  or  elongated  cells  during  the  intervals  of  lactation 
and  even  during  pregnancy,  but  deprived  of  epithelium  during  the  period  when  the  lac- 
teal secretion  is  most  active. 

The  acini  of  the  gland,  which  are  very  numerous,  are  visible  to  the  naked  eye,  in  the 
form  of  small,  rounded  granules,  of  a  reddish-yellow  color.  Between  these  acini,  there 
exist  a  certain  quantity  of  the  ordinary  white  fibrous  tissue  and  quite  a  number  of  adi- 


368  SECRETION. 

pose  vesicles.  The  presence  of  adipose  tissue  in  considerable  quantity  in  the  substance 
of  the  glandular  structure  is  peculiar  to  the  mammary  glands.  Each  acinus  is  made  up 
of  from  twenty  to  forty  secreting  vesicles,  or  culs-de-sac.  These  vesicles  are  irregular  in 
form,  often  varicose,  and  sometimes  they  are  enlarged  and  imperfectly  bifurcated  at  their 
terminal  extremities.  During  lactation,  their  diameter  is  from  ¥^  to  ^  of  an  inch.  Dur- 
ing pregnancy,  and  when  the  gland  has  just  arrived  at  its  full  development,  the  secreting 
vesicles  are  formed  of  a  structureless  membrane,  lined  with  small,  nucleated  cells  of 
pavement-epithelium.  The  nuclei  are  relatively  large,  ovoid,  and  are  embedded  in  a  small 
amount  of  amorphous  matter,  so  that  they  almost  touch  each  other.  Sometimes  the  epi- 
thelium is  segmented,  and  sometimes  it  exists  in  the  form  of  a  continuous  nucleated 
sheet.  When  the  secretion  of  milk  becomes  active,  the  epithelium  entirely  disappears, 
and  it  reappears  as  the  secretion  diminishes.  This  observation  is  due  to  Robin  and  has  an 
important  bearing  upon  the  mechanism  of  the  secretion  of  milk. 

During  the  intervals  of  lactation,  as  the  lactiferous  ducts  become  retracted,  the  glan- 
dular culs-de-sac  disappear ;  and,  in  pregnancy,  as  the  gland  takes  on  its  full  develop- 
ment, the  ducts  branch  and  extend  themselves,  and  the  vesicles  are  gradually  developed 
around  their  terminal  extremities.  These  changes  in  the  development  of  the  mammae  at 
different  periods  are  most  remarkable  and  are  not  observed  in  any  other  of  the  glandu- 
lar organs. 

Mechanism  of  the  Secretion  of  Mills. — With  the  exception  of  water  and  inorganic 
principles,  all  the  important  and  characteristic  constituents  of  the  milk  are  formed  in  the 
substance  of  the  mammary  glands.  The  secreting  structures  have  the  property  of  sep- 
arating from  the  blood  a  great  variety  of  inorganic  principles ;  and  we  shall  see,  when 
we  come  to  study  the  composition  of  the  milk  more  minutely,  that  it  furnishes  all  the 
inorganic  matter  necessary  for  the  nutrition  of  the  infant,  containing,  even,  a  small  quan- 
tity of  iron.  Precisely  how  the  secreting  vesicles  separate  the  proper  quantity  of  these 
principles  from  the  circulating  fluid,  we  are  unable,  in  the  present  state  of  our  knowl- 
edge, to  state.  It  is  unsatisfactory  enough  to  say  that  the  membranes  of  the  vesicles 
have  an  elective  action,  but  this  expresses  the  extent  of  our  information  on  the  subject. 

The  lactose,  or  sugar  of  milk,  the  caseine,  and  the  fatty  particles,  are  all  produced 
de  novo  in  the  gland.  The  peculiar  kind  of  sugar  here  found  does  not  exist  anywhere 
else  in  the  organism.  Even  when  the  secretion  of  milk  is  most  active,  different  varieties 
of  sugar,  such  as  glucose  or  cane-sugar,  injected  into  the  blood-vessels  of  a  living  animal, 
are  never  eliminated  by  the  mammary  glands,  as  they  are  by  the  kidneys ;  and  their 
presence  in  the  blood  does  not  influence  the  quantity  of  lactose  found  in  the  milk.  All 
that  can  be  said  with  regard  to  the  formation  of  sugar  of  milk  is  that  it  is  produced  in 
the  mammary  glands.  The  mechanism  of  its  formation  is  not  understood. 

Caseine  is  produced  in  the  mammary  glands,  probably  by  a  peculiar  transformation  of 
the  albuminoid  constituents  of  the  blood.  This  principle  does  not  exist  in  the  blood, 
although  its  presence  here  has  been  mentioned  by  some  observers.  It  is  well  known  that 
the  caseine  of  milk  is  precipitated  by  an  excess  of  sulphate  of  magnesia ;  but  the  so- 
called  caseine  of  the  blood  is  not  affected  by  this  salt  and  passes  through  it  like  albumen. 

The  fatty  particles  of  the  milk  are  likewise  produced  in  the  substance  of  the  gland, 
and  the  peculiar  kind  of  fat  which  exists  in  this  secretion  is  not  found  in  the  blood.  The 
mechanism  of  the  production  of  fat  in  the  mammary  glands  is  obscure.  The  particles 
are  not  produced  in  cells  and  set  free  by  their  rupture,  by  a  process  analogous  to  that 
which  takes  place  in  the  formation  of  the  fatty  particles  found  in  the  sebaceous  matter, 
for,  during  the  time  when  the  secretion  of  milk  is  most  active,  the  epithelium  of  the 
secreting  culs-de-sac  has  entirely  disappeared.  The  butter  is  produced  by  the  action  of 
the  amorphous  walls  of  the  vesicles,  in  the  same  way,  probably,  as  fat  is  produced  by 
the  vesicles  of  the  ordinary  adipose  tissue.  At  least,  this  is  all  that  is  known  regarding 
the  mechanism  of  its  production. 


PHYSIOLOGICAL   ANATOMY   OF  THE  MAMMARY   GLANDS.         369 

As  regards  the  mechanism  of  the  formation  of  the  peculiar  and  characteristic  con- 
stituents of  the  milk,  the  mammary  glands  are  to  be  classed  among  the  organs  of  secre- 
tion and  not  with  those  of  elimination  or  excretion;  for  none  of  these  elements  preexist 
in  the  blood,  and  they  all  appear  first  in  the  substance  of  the  glands. 

During  the  period  of  secretion,  the  glands  receive  a  much  larger  supply  of  blood  than 
at  other  times.  Pregnancy  favors  the  development  of  the  secreting  portions  of  the 
glands  but  does  not  induce  secretion.  On  the  other  hand,  when  pregnancy  occurs  dur- 
ing lactation,  it  diminishes,  modifies,  and  it  may  arrest  the  secretion  of  milk.  The  secre- 
tion is  destined,  however,  for  the  nourishment  of  the  child  and  not  for  use  in  the  economy 
of  the  mother — an  important  point  of  distinction  from  all  other  secretions — and  its  pro- 
duction presents  one  or  two  interesting  peculiarities. 

In  the  first  place,  the  secreting  action  of  the  mammary  glands  is  nearly  continuous. 
When  the  secretion  of  milk  has  become  fully  established,  while  there  may  be  certain 
periods  when  it  is  formed  in  greater  quantity  than  at  others,  there  is  no  absolute  inter- 
mitteucy  in  its  production. 

Again,  in  all  the  other  glandular  organs,  the  epithelial  cells  found  in  their  secreting 
portion  seem  to  be  the  active  agents  in  the  production  of  the  secretions;  but,  in  the  mam- 
mary glands,  as  we  have  already  noted,  the  epithelium  entirely  disappears  from  the  secret- 
ing culs-de-sac  during  the  period  of  greatest  functional  activity  of  the  gland,  and  nothing 
is  left  to  perform  the  work  of  secretion  but  the  amorphous  membrane  of  the  vesicles. 

Conditions  which  modify  the  Lacteal  Secretion. — Very  little  is  known  concerning  the 
physiological  conditions  which  modify  the  secretion  of  milk.  When  lactation  is  fully 
established,  the  quantity  and  quality  of  the  milk  secreted  become  adapted  to  the  require- 
ments of  the  child  at  different  periods  of  its  existence.  In  studying  the  composition  of 
the  milk,  therefore,  it  will  be  found  to  vary  considerably  in  the  different  stages  of  lacta- 
tion. It  is  evident  that,  as  the  development  of  the  child  advances,  a  constant  increase  of 
nourishment  is  demanded ;  and,  as  a  rule,,  the  mother  is  capable  of  supplying  all  the 
nutritive  requirements  of  the  infant  for  from  eight  to  twenty  months. 

During  the  time  when  such  an  amount  of  nutritive  matter  is  furnished  to  the  child, 
the  quantity  of  food  taken  by  the  mother  is  sensibly  increased  ;  but  observations  have 
shown  that  the  secretion  of  milk  is  not  much  influenced  by  the  nature  of  the  food.  It  is 
necessary  that  the  mother  should  be  supplied  with  good,  nutritious  articles ;  but,  as  far  as 
solid  food  is  concerned,  there  seems  to  be  no  great  difference  between  a  coarse  and  a  deli- 
cate alimentation,  and  the  milk  of  females  in  the  lower  walks  of  life,  when  the  general 
condition  is  normal,  is  fully  as  good  as  in  women  who  are  able  to  live  luxuriously.  It 
is,  indeed,  a  fact  generally  recognized  by  physiologists,  that  the  secretion  of  milk  is  little 
influenced  by  any  special  diet,  provided  the  alimentation  be  sufficient  and  of  the  quality 
ordinarily  required  by  the  system  and  that  it  contain  none  of  the  few  articles  of  food 
which  are  known  to  have  a  special  influence  upon  lactation.  So  long  as  the  mother  is 
healthy  and  well-nourished,  the  milk  will  take  care  of  itself;  and  the  appetite  is  the 
surest  guide  to  the  proper  variety,  quality,  and  quantity  of  food.  It  is  very  common, 
however,  for  females  to  become  quite  fat  during  lactation  ;  which  shows  that  the  fatty 
elements  of  the  food  do  not  pass  exclusively  into  the  milk,  but  that  there  is  a  tendency, 
at  the  same  time,  to  a  deposition  of -  adipose  tissue  in  the  ordinary  situations  in  which  it 
is  found.  It  is  a  matter  of  common  experience,  that  certain  articles,  such  as  acids  and 
fermentable  substances,  often  disturb  the  digestive  organs  of  the  child  without  producing 
any  change  in  the  milk,  that  can  be  recognized  by  chemical  analysis.  The  individual 
differences  in  women,  in  this  regard,  are  very  great. 

The  statements  with  regard  to  solid  food  do  not  apply  to  liquids.     During  lactation, 

there  is  always  an  increased  demand  for  water  and  for  liquids  generally ;  and,  if  these  be 

not  supplied  in  sufficient  quantity,  the  secretion  of  milk  is  diminished,  and  its  quality  is 

almost  always  impaired.     It  is  a  curious  fact,  which  has  been  fully  established  by  obser- 

24 


370  SECRETION. 

vations  upon  the  human  subject  and  the  inferior  animals,  that,  while  the  quantity  of 
milk  is  increased  by  taking  a  large  amount  of  simple  water,  the  solid  constituents  are 
also  increased,  and  the  milk  retains  all  of  its  qualities  as  a  nutritive  fluid. 

Alcohol,  especially  when  largely  diluted,  as  in  malt-liquors  and  other  mild  beverages, 
is  well  known  to  exert  an  influence  upon  the  secretion  of  milk.  Drinks  of  this  kind 
almost  always  temporarily  increase  the  activity  of  the  secretion,  and  sometimes  they  pro- 
duce a  certain  amount  of  effect  upon  the  child ;  but  direct  and  accurate  observations  on 
the  actual  passage  of  alcohol  into  the  milk  are  wanting.  During  lactation,  the  moderate 
use  of  drinks  containing  a  small  proportion  of  alcohol  is  frequently  beneficial,  particu- 
larly in  assisting  the  mother  to  sustain  the  unusual  drain  upon  the  system.  There  are. 
however,  few  instances  of  normal  lactation  in  which  their  use  is  absolutely  necessary. 

It  is  well  known  that  the  secretion  of  milk  may  be  profoundly  affected  by  violent 
mental  emotions.  This  is  the  case  in  many  other  secretions,  as  the  saliva  and  the 
gastric  juice.  It  is  hardly  necessary,  however,  to  cite  the  numerous  instances  of  modifi- 
cation or  arrest  of  the  secretion  from  this  cause,  which  are  quoted  in  many  works.  Ver- 
nois  and  Becquerel  mention  a  very  striking  case,  in  which  a  hospital  wet-nurse,  who  had 
lost  her  only  child  from  pneumonia,  became  violently  affected  with  grief  and  presented, 
as  a  consequence,  an  immediate  diminution  in  the  quantity  of  her  milk,  with  a  great 
reduction  in  the  proportion  of  salts,  sugar,  and  butter.  In  this  case  the  proportion  of 
caseine  was  increased.  Sir  Astley  Cooper  mentions  two  cases  in  which  the  secretion  of 
milk  was  instantaneously  and  permanently  arrested  from  terror.  These  cases  are  types 
of  numerous  others,  which  have  been  reported  by  writers,  of  the  effects  of  mental  emo- 
tions upon  secretion. 

In  the  present  state  of  our  knowledge,  we  can  comprehend  the  influence  of  men- 
tal emotions  upon  secretion,  only  by  assuming  that  they  operate  through  the  nervous 
system ;  and,  in  many  of  the  glands,  the  influence  of  the  nerves  has  been  clearly  demon- 
strated by  actual  experiment.  Direct  observations,  however,  upon  the  influence  of  the 
nerves  upon  the  mammary  glands  are  few  and  unsatisfactory.  The  operation  of  dividing 
the  nerves  distributed  to  these  glands,  which  has  occasionally  been  practised  upon  ani- 
mals in  lactation,  has  not  been  observed  to  produce  any  sensible  diminution  in  the  quan- 
tity of  the  secretion.  It  is  difficult,  however,  to  operate  upon  all  the  nerves  distributed 
to  these  organs. 

Quantity  of  Milk.— It  is  very  difficult  to  form  a  reliable  estimate  of  the  average  quan- 
tity of  milk  secreted  by  the  human  female  in  the  twenty-four  hours.  The  amount  un- 
doubtedly varies  very  much  in  different  persons ;  some  women  being  able  to  nourish  two 
children,  while  others,  though  apparently  in  perfect  health,  furnish  hardly  enough  food 
for  one.  Cooper,  as  the  result  of  direct  observation,  states  that  the  quantity  that  can  be 
drawn  from  a  full  breast  is  usually  about  two  fluidounces.  This  may  be  assumed  to  be 
about  the  quantity  contained  in  the  lactiferous  ducts  when  they  are  moderately  distended. 
Lehmann,  taking  for  the  basis  of  his  calculations  the  observations  of  Lampe"rierre,  who 
found,  as  the  result  of  sixty-seven  experiments,  that  from  fifty  to  sixty  grammes  of  milk 
were  secreted  in  two  hours,  estimates  that  the  average  quantity  discharged  in  twenty- 
four  hours  is  1,320  grammes,  or  about  44'5  fluidounces.  Taking  into  consideration  the 
evident  variations  in  the  quantity  of  milk  secreted  by  different  women,  it  may  be 
assumed  that  the  daily  production  is  from  two  to  three  pints. 

Certain  conditions  of  the  female  are  capable  of  materially  influencing  the  quantity  of 
milk  secreted.  It  is  evident  that  the  secretion  is  usually  somewhat  increased  within  the 
first  few  months  of  lactation,  when  the  progressive  development  of  the  child  demands  an 
increase  in  the  quantity  of  nourishment.  If  the  menstrual  function  become  reestablished 
during  lactation,  the  milk  is  usually  diminished  in  quantity  during  the  periods,  but  some- 
times it  is  not  affected,  either  in  its  quantity  or  composition.  Should  the  female  become 
pregnant,  there  is  generally  a  great  diminution  in  the  quantity  of  milk,  and  that  which 


PROPERTIES  AND   COMPOSITION   OF  THE  MILK.  371 

it  secreted  is  ordinarily  regarded  as  possessing  little  nutritive  power.  In  obedience  to  a 
popular  prejudice,  apparently  well-founded,  the  child  is  usually  taken  from  the  breast  as 
soon  as  pregnancy  is  recognized.  Authors  have  not  noted  any  marked  and  constant 
variations  in  the  quantity  of  milk  in  females  of  different  ages. 

Properties  and  Composition  of  the  Milk. 

The  general  appearance  and  characters  of  ordinary  cow's  milk  are  sufficiently  famil- 
iar and  may  serve  as  a  standard  for  comparison  with  the  milk  of  the  human  female. 
Human  milk  is  neither  so  white  nor  so  opaque  as  cow's  milk,  having  ordinarily  a  slightly 
bluish  tinge.  The  milk  of  different  healthy  women  presents  some  variation  in  this 
regard.  After  the  secretion  has  become  fully  established,  the  fluid  possesses  no  visicidty 
and  is  nearly  opaque.  It  is  almost  inodorous,  of  a  peculiar  soft  and  sweetish  taste, 
and,  when  perfectly  fresh,  has  a  decidedly  alkaline  reaction.  The  taste  of  human  milk 
is  sweeter  than  that  of  cow's  milk.  A  short  time  after  its  discharge  from  the  gland,  the 
reaction  of  milk  becomes  faintly  acid ;  but  this  change  takes  place  more  slowly  in 
human  milk  than  in  the  milk  of  most  of  the  inferior  animals. 

The  average  specific  gravity  of  human  milk,  according  to  Vernois  and  Becquerel,  is 
1032 ;  although  this  is  subject  to  considerable  variation,  the  minimum  of  eighty-nine 
observations  being  1025,  and  the  maximum,  1046.  The  observations  of  most  physiological 
chemists  have  shown  that  this  average  is  nearly  correct. 

Milk  is  not  coagulated  by  heat,  even  after  prolonged  boiling ;  but  a  thin  pellicle  then 
forms  on  the  surface,  which  is  probably  due  to  the  combined  action  of  heat  and  the 
atmosphere  upon  the  caseine.  Although  a  small  quantity  of  albumen  exists  in  the  milk, 
this  does  not  coagulate  on  the  surface  by  the  action  of  the  heat,  for  the  scum  does  not 
form  when  the  fluid  is  heated  in  an  atmosphere  of  carbonic  acid  or  of  hydrogen,  or  in  a 
vacuum. 

When  the  milk  is  coagulated  by  any  substance  acting  upon  the  caseine,  or  when  it 
coagulates  spontaneously,  it  separates  into  a  curd,  composed  of  caseine  with  most  of  the 
fatty  particles,  and  a  nearly  clear,  greenish-yellow  serum,  called  whey.  This  separation 
occurs  spontaneously,  at  a  variable  time  after  the  discharge  of  the  milk,  taking  place 
much  more  rapidly  in  warm  than  in  cold  weather.  It  is  a  curious  fact  that  fresh  milk  is 
frequently  coagulated  during  a  thunder-storm,  a  phenomenon  which  has  never  been  sat- 
isfactorily explained. 

On  being  allowed  to  stand  for  a  short  time,  the  milk  separates,  without  coagulating, 
into  two  tolerably  distinct  portions.  A  large  proportion  of  the  globules  rises  to  the  top, 
forming  a  yellowish-white  and  very  opaque  fluid,  called  cream,  leaving  the  lower  portion 
poorer  in  globules  and  of  a  decidedly  bluish  tint.  In  healthy  milk,  the  stratum  of  cream 
forms  from  one-fifth  to  one-third  of  the  entire  mass  of  the  milk.  In  the  human  subject, 
the  skim-milk  is  not  white  and  opaque,  but  it  is  nearly  as  transparent  as  the  whey.  A 
very  good  method  of  testing  the  richness  of  milk  is  by  the  use  of  little  graduated  glasses, 
called  lactometers,  by  which  we  can  measure  the  thickness  of  the  layer  of  cream.  The 
specific  gravity  of  the  cream  from  milk  of  the  average  specific  gravity  of  1032  is  about 
1024.  The  specific  gravity  of  skim-milk  is  about  1034. 

Microscopical  Characters  of  tJfe  Milk. — If  a  drop  of  milk  be  examined  with  a  magni- 
fying power  of  from  three  hundred  to  six  hundred  diameters,  the  cause  of  its  opacity 
will  be  apparent.  It  contains  an  immense  number  of  minute  globules,  of  great  refractive 
power,  held  in  suspension  in  a  clear  fluid.  These  are  known  under  the  name  of  milk- 
globules  and  are  composed  of  margarine,  oleine,  and  a  fatty  matter,  peculiar  to  milk, 
called  butyrine.  In  human  milk  the  particles  are  perfectly  spherical ;  but  in  cow's  milk 
they  are  often  polyhedric  from  mutual  compression.  This  difference  is  due  to  the  softer 
consistence  of  the  butter  in  human  milk,  the  globules  containing  a  much  larger  propor- 
tion of  oleine  ;  and,  if  cow's  milk  be  warmed,  the  particles  also  assume  a  spherical  form. 


372 


SECRETION. 


The  human  milk-globules  measure  from  ^^  to  T?Vir  of  an  inch  in  diameter.   They  are 
usually  distinct  from  each  other,  but  they  may  occasionally  become  collected  into  groups 


without  indicating  any  thing  abnormal. 


FIG.  103. — Human  milk-globules,  from  a  healthy 
n 
.) 


lying-in  woman,  eight  days  after  delivery. 
(Funke.) 


In  a  perfectly  normal  condition  of  the  glands, 
when  the  lacteal  secretion  has  become  fully  es- 
tablished, the  milk  contains  nothing  but  a  clear 
fluid  with  these  globules  in  suspension.  The 
proportion  of  fatty  matter  in  the  milk  is  from 
twenty-five  to  forty-eight  parts  per  thousand, 
and  this  gives  an  idea  of  the  proportion  of 
globules  which  are  seen  on  microscopical  ex- 
amination. 

There  has  been  a  great  deal  of  discussion 
with  regard  to  the  anatomical  constitution  of 
the  milk-globules.  In  many  late  works  it  is 
stated  that  these  are  true  anatomical  elements, 
composed  of  fatty  matters  surrounded  by  an 
albuminoid  membrane ;  but  some  writers  as- 
sume that  the  fat  is  merely  in  the  form  of  an 
emulsion  and  is  simply  divided  into  globules 
and  held  in  suspension,  like  the  fatty  particles 
of  the  chyle.  No  one,  however,  has  assumed 
to  have  seen  the  investing  membrane  of  the  milk-globules,  and  its  existence  is  only 
inferred  from  the  behavior  of  these  little  particles  in  the  presence  of  certain  reagents. 
It  is  unnecessary  to  review  in  detail  the  numerous  opinions  that  have  been  advanced 
on  this  subject.  As  far  as  can  be  ascertained  by  simple  examination,  even  with  the 
highest  magnifying  powers,  the  globules  appear  perfectly  homogeneous ;  and  the  burden 
of  proof  rests  with  those  who  profess  to  be  able  to  demonstrate  the  existence  of  an 
investing  membrane.  Robin,  one  of  the  highest  authorities  on  these  subjects,  argues 
against  the  existence  of  a  membrane  and  opposes  the  observations  of  those  who  assume 
to  have  demonstrated  it,  by  explanations  of  the  phenomena  produced  by  reagents,  which 
do  not  involve,  as  a  necessity,  the  presence  of  such  a  structure.  The  arguments  in  favor 
of  its  existence  are  not  very  satisfactory ;  and  the  experiments  upon  which  they  are 
based  relate  chiefly  to  the  action  of  ether  upon  the  globules  before  and  after  the  action 
of  other  reagents. 

If  a  quantity  of  milk  be  shaken  up  with  an  equal  volume  of  ether,  the  mixture 
remains  opaque ;  but,  if  a  little  potash  be  added,  the  fatty  matters  are  dissolved,  and  the 
mixture  then  becomes  more  or  less  clear.  These  facts  are  all  that  can  be  observed  with- 
out following  out  the  changes  with  the  microscope.  Robin  has  shown  that  the  fatty 
particles  are  acted  upon  when  the  milk  is  thoroughly  agitated  with  ether  alone ;  and 
that  the  opacity  is  then  due  to  the  fact  that  the  ether,  with  the  fat  in  solution,  is  itself 
in  the  form  of  an  emulsion.  If  the  opaque  mixture  of  milk  and  ether  be  examined 
with  the  microscope,  globules  are  seen,  larger  than  the  ordinary  milk-globules,  paler, 
and  possessing  much  less  refractive  power.  These  he  supposes  to  be  composed  of  fat 
and  ether.  If  potash  be  added,  either  before  or  after  the  addition  of  ether,  the  consti- 
tution of  the  whole  mass  of  liquid  is  changed,  and  it  becomes  somewhat  transparent, 
though  by  no  means  perfectly  clear.  It  is  assumed  that,  in  the  first  instance,  the  ether 
does  not  attack  the  globules,  because  it  has  no  effect  upon  the  membrane  which  is  sup- 
posed to  exist,  and  that  the  potash  acts  npon  the  membrane,  allowing  the  ether  then  to 
take  up  the  fat ;  but,  if  the  observations  of  Robin  be  correct,  it  is  evident  that  this  view 
cannot  be  sustained. 

If  dilute  acetic  acid  be  added  to  a  specimen  of  milk  under  the  microscope,  the  glob- 
ules become  deformed,  and  some  of  them  show  a  tendency  to  run  together;  an  appear- 
ance which  is  supposed  by  Henle,  who  was  the  first  to  study  closely  the  action  of  acetic 


COMPOSITION   OF  HUMAN  MILK.  373 

acid  upon  the  milk-globules,  to  indicate  the  existence  of  a  membrane.  This  deduction 
however,  is  not  justifiable.  Acetic  acid  readily  coagulates  the  caseine,  a  principle  which 
is  most  efficient  in  maintaining  the  fat  in  its  peculiar  condition.  The  coagulating  caseine 
then  presses  upon  the  globules,  and  produces,  in  this  way,  all  the  changes  in  form  that 
have  been  observed. 

Most  of  the  other  arguments  in  favor  of  the  existence  of  a  membrane  have  no  support 
from  direct  observation,  and  consequently  they  do  not  demand  special  consideration; 
while  all  the  facts  which  we  have  been  able  to  find  relating  to  this  subject  go  to  show 
that  the  fatty  matters  in  the  milk  are  in  the  condition  of  a  simple  emulsion.  The  precise 
condition,  however,  of  the  fluid  immediately  surrounding  the  globules  is  not  fully  under- 
stood. Certain  of  the  constituents  of  fluids  capable  of  forming  emulsive  mixtures  with 
liquid  fats  may  form  a  coating  of  excessive  tenuity  immediately  around  the  globules,  but 
they  never  constitute  distinct  membranes  capable  of  resisting  the  action  of  solvents  upon 
the  fats;  and,  in  the  case  of  the  milk,  they  do  not  prevent  the  mechanical  union  of  the 
globules  into  masses,,  as  occurs  in  the  process  of  churning.  Milk-globules  less  than  -5-3^  °f 
an  inch  in  diameter  present  under  the  microscope  that  peculiar  oscillating  motion  known 
as  the  Brownian  movement.  This  is  arrested  on  the  addition  of  acetic  acid,  by  coagula- 
tion of  the  caseine.  From  these  facts,  it  is  evident  that  the  milk-globules  are  composed 
simply  of  fat  in  the  form  of  a  fine  emulsion.  They  are  not  true  anatomical  elements, 
originating  by  a  process  of  genesis  in  a  blastema,  undergoing  physiological  decay,  and  ca- 
pable of  self-regeneration  from  materials  furnished  by  the  menstruum  in  which  they  are 
suspended,  like  the  blood-corpuscles  or  leucocytes.  They  are  simply  elements  of  secretion. 

Composition  of  the  Milk. — "We  do  not  propose,  in  treating  of  the  composition  of  the 
milk,  to  consider  the  various  methods  of  analysis  which  have  been  employed  by  different 
chemists.  The  only  constituent  that  has  ever  presented  much  difficulty  in  the  estimation 
of  its  quantity  is  caseine ;  but  the  various  processes  now  employed  for  its  extraction  have 
led  to  nearly  identical  results.  The  following  table,  compiled  by  Robin  from  the  analy- 
ses of  various  chemists,  gives  the  constituents  of  human  milk : 

Composition  of  Human  Milk. 

Water 902*717  to  863-149 

Caseine  (desiccated) 29-000  "  39-000 

Lacto-proteine 1-000  "  2-770 

Albumen traces  u  0'880 

f  Margarine 17'000  "  25'840 

Butter,  25  to  38  -j  Oleine 7'500  "  H'400 

[Butyrine,  caprine,  caprome,  capriline 0-500  "  0'760 

Sugar  of  milk  (lactine,  or  lactose) 37*000  "  49-000 

Lactate  of  soda(?) 0-420  "  0*450 

Chloride  of  sodium 0-240  "  0'340 

Chloride  of  potassium 1*440  "  1-830 

Carbonate  of  soda 0-053  "  0*056 

Carbonate  of  lime 0'069  "  0-070 

Phosphate  of  lime  of  the  bones 2-310  "  3-440 

Phosphate  of  magnesia 0'420  "  0'640 

Phosphate  of  soda 0-225  "  0-230 

Phosphate  of  iron  (?) 0-032  "  0'070 

Sulphate  of  soda 0-074  "  0'075 

Sulphate  of  potassa traces. 

C  Oxygen 1'29  J  1,000*000          1,000-000 

Gases  in  solution  <  Nitrogen 12*17  >  30  parts  per  1,000  in  volume.     (Hoppe.) 

(  Carbonic  acid .    16*54; 


374  SECRETION. 

The  proportion  of  water  in  milk  is  subject  to  a  certain  amount  of  variation,  but  this 
is  not  so  considerable  as  might  be  expected  from  the  great  variations  in  the  entire  quan- 
tity of  the  secretion.  In  treating  of  the  quantity  of  milk  in  the  twenty-four  hours,  we 
have  seen  that  the  influence  of  drinks,  even  when  nothing  but  pure  water  has  been  taken, 
is  very  marked ;  and,  although  the  activity  of  the  secretion  is  much  increased  by  fluid 
ingesta,  the  quality  of  the  milk  is  not  usually  affected,  and  the  proportion  of  water  to  the 
solid  matters  remains  about  the  same. 

Nitrogenized  Constituents  of  Milk.— Very  little  remains  to  be  said  concerning  the 
nitrogenized  constituents  of  human  milk,  after  what  has  been  stated  under  the  head  of 
alimentation.  The  different  principles  of  this  class  undoubtedly  have  the  same  nutritive 
function  and  they  appear  to  be  identical  in  all  varieties  of  milk,  the  only  difference  being 
in  their  relative  proportion.  It  is  a  matter  of  common  experience,  indeed,  that  the  milk 
of  many  of  the  lower  animals  will  take  the  place  of  human  milk,  when  prepared  so  as  to 
make  the  proportions  of  its  different  constituents  approximate  the  composition  of  the  nat- 
ural food  of  the  child.  A  comparison  of  the  composition  of  human  milk  and  cow's  milk 
shows  that  the  former  is  poorer  in  nitrogenized  matters  and  richer  in  butter  and  sugar ; 
and  consequently,  the  upper  strata  of  cow's  milk,  appropriately  sweetened  and  diluted 
with  water,  very  nearly  represent  the  ordinary  breast-milk. 

Caseine  is  by  far  the  most  important  of  the  nitrogenized  principles  of  milk,  and  it  sup- 
plies nearly  all  of  this  kind  of  nutritive  matter  demanded  by  the  child.  Lacto-proteine, 
a  principle  described  by  Millon  and  Commaille,  is  not  so  well  defined,  and  albumen 
exists  in  the  milk  in  very  small  quantity.  That  albumen  always  exists  in  milk,  can  readily 
be  shown  by  the  following  process  described  by  Bernard :  If  milk,  treated  with  an 
excess  of  sulphate  of  magnesia  so  as  to  form  a  thin  paste,  be  thrown  upon  a  filter,  the  case- 
ine  and  fatty  matters  will  be  retained,  and  the  clear  liquid  that  passes  through  shows  a 
marked  opacity  upon  the  application  of  heat  or  the  addition  of  nitric  acid. 

The  coagulation  of  milk  depends  upon  the  reduction  of  caseine  from  a  liquid  to  a 
semisolid  condition.  When  milk  is  allowed  to  coagulate  spontaneously,  or  sour,  the 
change  is  effected  by  the  action  of  the  lactic  acid  which  results  from  a  transformation  of  a 
portion  of  the  sugar  of  milk.  Caseine,  in  fact,  is  coagulated  by  any  of  the  acids,  even 
the  feeble  acids  of  organic  origin.  It  differs  from  albumen  in  this  regard  and  in  the  fact 
that  it  is  not  coagulated  by  heat.  It  has  been  suggested  that,  in  fresh  milk,  the  caseine 
exists  in  combination  with  carbonate  of  soda,  and  that  coagulation  always  takes  place 
from  the  action  of  acids  upon  this  salt,  by  which  the  caseine  is  set  free.  It  is  true  that 
coagulated  caseine  may  be  readily  dissolved  in  a  solution  of  carbonate  of  soda,  but  it  has 
been  shown  that  coagulation  may  be  induced  by  the  agency  of  certain  neutral  principles, 
while  the  milk  retains  its  alkaline  reaction.  If  fresh  milk  be  slightly  raised  in  tempera- 
ture and  be  treated  with  an  infusion  of  the  gastric  mucous  membrane  of  the  calf,  coagu- 
lation will  take  place  in  from  five  to  ten  minutes,  the  clear  liquid  still  retaining  its  alka- 
line reaction.  Simon  has  observed  that  the  mucous  membrane  of  the  stomach  of  an 
infant  a  few  days  old,  that  had  recently  died,  coagulated  woman's  milk  more  readily  than 
the  mucous  membrane  of  the  stomach  of  the  calf. 

Non- Nitrogenized  Constituents  of  Milk. — Non-nitrogenized  matters  exist  in  abun- 
dance in  the  milk.  The  liquid  caseine  and  the  water  hold  the  fats,  as  we  have  seen,  in 
the  condition  of  a  fine  and  permanent  emulsion.  This  fat  has  been  separated  from  the 
milk  and  analyzed  by  chemists  and  is  known  under  the  name  of  butter.  In  human 
milk,  the  butter  is  much  softer  than  in  the  milk  of  many  of  the  inferior  animals,  particu- 
larly the  cow ;  but  it  is  composed  of  essentially  the  same  constituents,  although  in  differ- 
ent proportions.  In  different  animals,  there  are  developed,  even  after  the  discharge  of 
the  milk,  certain  odorous  principles,  which  are  more  or  less  characteristic  of  the  animal 
from  which  the  butter  is  taken. 

The  greatest  part  of  the  butter  consists  of  margarine.  It  contains,  in  addition,  oleine, 
with  a  small  quantity  of  peculiar  fats,  which  have  not  been  very  well  determined,  called 


VARIATIONS  IN  THE   COMPOSITION  OF  THE  MILK.  375 

butyrine,  caprine,  caproine,  and  capriline.  The  margarine  and  oleine  are  principles  found 
in  the  fat  throughout  the  body  ;  but  the  last-named  substances  are  peculiar  to  the  milk. 
These  are  especially  liable  to  acidification,  and  the  acids  resulting  from  their  decomposi- 
tion give  the  peculiar  odor  and  flavor  to  rancid  butter. 

Sugar  of  milk,  sometimes  called  lactine,  or  lactose,  is  the  most  abundant  of  the  solid 
constituents  of  the  mammary  secretion.  It  is  this  principle  that  gives  to  the  milk  its 
peculiar  sweetish  taste,  although  this  variety  of  sugar  is  much  less  sweet  than  cane-sugar. 
The  chief  peculiarities  of  milk-sugar  are  that  it  readily  undergoes  change  into  lactic  acid 
in  the  presence  of  nitrogenized  ferments  and  takes  on  alcoholic  fermentation  slowly  and 
with  difficulty.  At  one  time,  indeed,  it  was  supposed  that  milk-sugar  could  not  be  de- 
composed into  alcohol  and  carbonic  acid  ;  but  it  is  now  well  established  that  this  change 
can  be  induced,  the  only  peculiarity  being  that  it  takes  place  very  slowly.  In  some  parts 
of  the  world,  intoxicating  drinks  are  made  by  the  alcoholic  fermentation  of  milk. 

A  consideration  of  the  nutritive  action  of  the  fatty  and  saccharine  constituents  of  milk 
belongs  properly  to  the  subjects  of  alimentation  and  nutrition.  It  may  be  stated  here, 
however,  that  these  principles  seem  to  be  as  necessary  to  the  nutrition  of  the  child  as  the 
nitrogenized  principles ;  although  the  precise  manner  in  which  they  affect  the  develop- 
ment and  regeneration  of  the  tissues  has  not  been  ascertained. 

Inorganic  Constituents  of  Milk. — It  is  probable  that  many  inorganic  principles  exist 
in  the  milk  which  are  not  given  in  the  table ;  and  the  separation  of  these  principles  from 
their  combinations  with  organic  matters  is  one  of  the  most  difficult  problems  in  physio- 
logical chemistry.  This  must  be  the  case  for,  during  the  first  months  of  extra-uterine 
existence,  the  child  derives  all  the  inorganic,  as  well  as  the  organic  matters  necessary  to 
nutrition  and  development,  from  the  breast  of  the  mother.  The  reaction  of  the  milk 
depends  upon  the  presence  of  the  alkaline  carbonates,  and  these  principles  are  important 
in  preserving  the  fluidity  of  the  caseine.  It  is  not  determined  precisely  in  what  form  iron. 
exists  in  the  milk,  but  its  presence  here  is  undoubted.  A  comparison  of  the  composition 
of  the  milk  with  that  of  the  blood  shows  that  most  of  the  important  inorganic  prin- 
ciples found  in  the  latter  fluid  exist  also  in  the  milk. 

Hoppe  has  indicated  the  presence  of  carbonic  acid,  nitrogen,  and  oxygen,  in  solution 
in  milk.  Of  these  gases,  carbonic  acid  is  the  most  abundant.  It  is  well  known  that 
the  presence  of  gases  in  solution  in  liquids  renders  them  more  agreeable  to  the  taste, 
and  carbonic  acid  increases  very  materially  their  solvent  properties.  Aside  from  these 
considerations,  the  precise  function  of  the  gaseous  constituents  of  the  milk  is  not  ap- 
parent. 

A  study  of  the  composition  of  the  milk  fully  confirms  the  fact,  which  we  have  already 
had  occasion  to  state,  that  this  is  a  typical  alimentary  fluid  and  presents  in  itself  the 
proper  proportion  and  variety  of  material  for  the  nourishment  of  the  body  during  the 
period  when  the  development  of  the  system  is  going  on  with  its  maximum  of  activity. 
The  form  in  which  its  different  nutritive  constituents  exist  is  such  that  they  are  easily 
digested  and  are  assimilated  with  great  rapidity. 

Variations  in  the   Composition  of  the  Milk. 

Vernois  and  Becquerel  have  indicated  a  certain  amount  of  variation  at  different  ages 
and  at  different  periods  in  lactation,  but  they  show,  at  the  same  time,  that  the  fluid  is  not 
subject  to  changes  in  its  composition  sufficiently  great  to  influence  materially  the  nutrition 
of  the  child. 

If  the  composition  of  the  milk  be  compared  at  different  periods  of  lactation,  it  will  be 
found  to  undergo  great  changes  during  the  first  few  days.  In  fact,  the  first  fluid  secreted 
after  parturition  is  so  different  from  ordinary  milk,  that  it  has  been  called  by  another  name. 
It  is  then  known  as  colostrum,  the  peculiar  properties  of  which  will  be  considered  more 
fully  hereafter,  under  a  distinct  head.  As  the  secretion  of  milk  becomes  established,  the 
fluid,  from  the  first  to  the  fifteenth  day,  becomes  gradually  diminished  in  density  and 


376  SECRETION. 

in  its  proportion  of  water  and  of  sugar,  while  there  is  a  progressive  increase  in  the  pro- 
portion of  most  of  the  other  constituents,  viz.,  butter,  caseine,  and  the  inorganic  salts. 
The  milk,  therefore,  as  far  as  we  can  judge  from  its  composition,  as  it  increases  in 
quantity  during  the  first  few  days  of  lactation,  is  constantly  increasing  in  its  nutritive 
properties. 

The  differences  in  the  composition  of  the  milk,  taken  from  month  to  month  during  the 
entire  period  of  lactation,  are  not  so  distinctly  marked.  It  is  difficult,  indeed,  to  indicate 
any  constant  variations  of  sufficient  importance  to  lead  to  the  view  that  the  milk  varies 
much  in  its  nutritive  properties  at  different  times,  during  the  ordinary  period  of  lactation. 
The  differences  noted  between  the  milk  of  primiparas  and  multipart  were  very  slight  and 
unimportant.  As  a  rule,  however,  the  milk  of  primiparse  approaches  more  nearly  the 
normal  standard. 

The  menstrual  periods,  when  they  occur  during  lactation,  have  been  found  by  most 
observers  to  modify  considerably  the  composition  and  properties  of  the  milk ;  and  it  is 
well  known  to  practical  physicians  that  the  secretion  is  then  liable  to  produce  serious 
disturbances  of  the  digestive  system  of  the  child,  although  frequently  these  effects  are  not 
observed.  The  changes  in  the  composition  of  the  milk  which  commonly  occur  during 
menstruation  are,  great  increase  in  the  quantity  of  caseine,  increase  in  the  proportion  of 
butter  and  the  inorganic  salts,  and  a  slight  diminution  in  the  proportion  of  sugar.  The 
common  impression  that  the  milk  is  unfit  for  the  nourishment  of  the  child  if  pregnancy 
occur  during  lactation  is  undoubtedly  well-founded,  although  analyses  of  the  milk  of 
pregnant  women  have  never  been  made  upon  an  extended  scale. 

In  normal  lactation,  there  is  no  marked  and  constant  difference  in  composition  between 
milk  that  has  been  secreted  in  great  abundance  and  milk  which  is  produced  in  compara- 
tively small  quantity ;  nor  do  we  observe  that  difference  between  the  milk  first  drawn 
from  the  breast  and  that  taken  when  the  ducts  are  nearly  empty,  which  is  observed  in 
the  milk  of  the  cow. 

The  influence  of  alimentation  and  the  taking  of  liquids  upon  lactation  relates  chiefly  to 
the  quantity  of  milk  and  has  already  been  considered. 

In  treating  of  the  influences  which  modify  the  secretion  of  milk,  we  have  already 
alluded  to  the  effects  of  violent  mental  emotions  upon  the  production  and  the  composition 
of  this  fluid.  The  very  remarkable  case  of  profound  alteration  of  the  milk  by  violent 
grief,  detailed  by  Vernois  and  Becquerel,  is  the  only  one  in  which  the  secretion  in  this 
condition  has  been  carefully  analyzed.  The  changes  thus  produced  in  its  composition 
have  already  been  referred  to,  the  most  marked  difference  being  observed  in  the  propor- 
tion of  butter,  which  became  reduced  from  23*79  to  5'14  parts  per  1,000. 

Colostrum. 

Near  the  end  of  utero- gestation,  during  a  period  which  varies  considerably  in  different 
women  and  has  not  been  accurately  determined,  a  small  quantity  of  a  thickish,  stringy 
fluid  may  frequently  be  drawn  from  the  mammary  glands.  This  bears  little  resemblance 
to  perfectly-formed  milk.  It  is  small  in  quantity  and  is  usually  more  abundant  in  multi- 
part than  in  primiparso.  This  fluid,  with  that  secreted  for  the  first  few  days  after 
delivery,  is  called  colostrum.  It  is  yellowish,  semiopaque,  of  a  distinctly  alkaline  reaction, 
and  is  somewhat  mucilaginous  in  its  consistence.  Its  specific  gravity  is  considerably  above 
that  of  the  ordinary  milk,  being  from  1040  to  1060.  As  lactation  progresses,  the  charac- 
ter of  the  secretion  rapidly  changes,  until  it  becomes  loaded  with  true  milk-globules  and 
assumes  the  characters  of  ordinary  milk. 

The  opacity  of  the  colostrum  is  due  to  the  presence  of  a  number  of  different  cor- 
puscular elements.  Milk-globules,  very  variable  in  size  and  number,  are  to  be  found  in 
the  secretion  from  the  first.  These,  however,  do  not  exist  in  sufficient  quantity  to  render 
the  fluid  very  opaque,  and  they  are  frequently  aggregated  in  rounded  and  irregular 
masses,  held  together,  apparently,  by  some  glutinous  matter.  Peculiar  corpuscles,  first 


COMPOSITION   OF   COLOSTRUM. 


377 


accurately  described  by  Donne,  under  the  name  of  "  granular  bodies,"  and  supposed  to 

be  characteristic  of  the  colostrum,  always  exist  in  this  fluid.     These  are  now  known  as 

colostrum-corpuscles.    They  are  spherical,  varying  in  size  from  ^Vo  to  -gfa  of  an  inch,  are 

sometimes  pale,  but  more  frequently  quite  gran- 

ular, and  they  contain  very  often  a  large  num- 

ber of  fatty  particles.  They  behave  in  all  respects 

like  leucocytes  and  are  described  by  Robin  as  a 

variety  of  these  bodies.    Many  of  them  are  pre- 

cisely like  the  leucocytes  found  in  the  blood, 

lymph,  or  pus.     We  now  know,  however,  that 

the  so-called  mucus-  corpuscle  does  not  differ 

from  the  pus-corpuscle  or  the  white  corpuscle 

of  the  blood  ;  and  leucocytes  generally,  when 

confined  in  liquids    that   are  not  subject  to 

movements,  are  apt  to  undergo  enlargement, 

to  become  fatty,  and,  in  short,  they  may  pre- 

sent all  the  different  appearances  observed  in 

the  colostrum-corpuscles.     In  addition  to  these 

corpuscular  elements,  a  small  quantity  of  muco- 

sine  may  frequently  be  observed  in  the  colos-   Fl« 

J 
trum  on  microscopical  examination. 

On  the  addition  of  ether  to  a  specimen  of 

Colostrum  under  the  microscope,   most   of   the 
..  ,         ,     ,,         .,  ,  .  ,        .,,  ,, 

fatty  particles,  both  within   and  without  the 

colostrum-corpuscles,  are  dissolved.     Ammonia 

added  to  the  fluid  renders  it  stringy,  and  sometimes  the  entire  mass  assumes  a  gelati- 

nous consistence. 

In  its  proximate  composition,  colostrum  presents  many  points  of  difference  from 
true  milk.  It  is  sweeter  to  the  taste  and  contains  a  greater  proportion  of  sugar  and 
of  the  inorganic  salts.  The  proportion  of  fat  is  at  least  equal  to  the  proportion  in  the 
milk  and  is  generally  greater.  Instead  of  caseine,  pure  colostrum  contains  a  large 
proportion  of  albumen  ;  and,  as  the  character  of  the  secretion  changes  in  the  process  of 
lactation,  the  albumen  becomes  gradually  reduced  in  quantity  and  caseine  takes  its  place. 

The  following,  deduced  from  the  analyses  of  Clemm,  may  be  taken  as  the  ordinary 
composition  of  colostrum  of  the  human  female  : 


Colostrum,  from  a  healthy  lying-in  wo- 
man,  twelve  hours  after  delivery.    (Funke.) 
The  smaller  globules  are  globules  of  milk  ;  the  larger 


lostrum-corpuscles  gradually  disappear,  and  the 
milk-globules  become  more  numerous,  smaller, 

and  more  uniform  in  size. 


Composition  of  Colostrum. 

Water 945-24 

Albumen,  and  salts  insoluble  in  alcohol 29'81 

Butter . 7-07 

Sugar  of  milk,  extractive  matter,  and  salts  soluble  in  alcohol 17'2Y 

Loss 0-61 

1,000-00 

Colostrum  ordinarily  decomposes  much  more  readily  than  milk  and  takes  on  putre- 
factive changes  very  rapidly.  If  it  be  allowed  to  stand  for  from  twelve  to  twenty-four 
hours,  it  separates  into  a  thick,  opaque,  yellowish  cream  and  a  serous  fluid.  In  an 
observation  by  Sir  Astley  Cooper,  nine  measures  of  colostrum,  taken  soon  after  partu- 
rition, after  twenty-four  hours  of  repose,  gave  six  parts  of  cream  to  three  of  milk. 

The  peculiar  constitution  of  the  colostrum,  particularly  the  presence  of  an  excess  of 
sugar  and  inorganic  salts,  renders  it  somewhat  laxative  in  its  effects,  and  it  is  supposed 
to  be  useful,  during  the  first  few  days  after  delivery,  in  assisting  to  relieve  the  infant  of 

the  accumulation  of  meconium. 

V 


378  SECRETION". 

As  the  quantity  of  colostrum  that  may  be  pressed  from  the  mammary  glands  during 
the  latter  periods  of  utero-gestation,  particularly  the  last  month,  is  very  variable,  it 
becomes  an  interesting  and  important  question  to  determine  whether  this  secretion  have 
any  relation  to  the  quantity  of  milk  that  may  be  expected  after  delivery.  This  has  been 
made  the  subject  of  careful  study  by  Donne,  who  arrived  at  the  following  important 
conclusions : 

In  women  in  whom  the  secretion  of  colostrum  is  almost  absent,  the  fluid  being  in 
exceedingly  small  quantity,  viscid,  and  containing  hardly  any  corpuscular  elements,  there 
is  hardly  any  milk  produced  after  delivery. 

In  women  who,  before  delivery,  present  a  moderate  quantity  of  colostrum,  contain- 
ing very  few  milk-globules  and  a  number  of  colostrum-corpuscles,  after  delivery  the  milk 
will  be  scanty  or  it  may  be  abundant,  but  it  is  always  of  poor  quality. 

When  the  quantity  of  colostrum  produced  is  considerable,  the  secretion  being  quite 
fluid  and  rich  in  corpuscular  elements,  particularly  milk-globules,  the  milk  after  delivery 
is  always  abundant  and  of  good  quality. 

From  these  observations,  it  would  seem  that  the  production  of  colostrum  is  an  indi- 
cation of  the  proper  development  of  the  mammary  glands ;  and  the  early  production  of 
fatty  granules,  which  are  first  formed  by  the  cells  lining  the  secreting  vesicles,  indicates 
the  probable  activity  in  the  secretion  of  milk  after  lactation  has  become  fully  estab- 
lished. 

The  secretion  of  the  mammary  glands  preserves  the  characters  of  colostrum  until 
toward  the  end  of  the  milk-fever,  when  the  colostrum-corpuscles  rapidly  disappear,  and 
the  milk-globules  become  more  numerous,  regular,  and  uniform  in  size.  It  may  be  stated, 
in  general  terms,  that  the  secretion  of  milk  becomes  fully  established  and  all  the  charac- 
ters of  the  colostrum  disappear  at  from  the  eighth  to  the  tenth  day  after  delivery.  A  few 
colostrum-corpuscles  and  masses  of  agglutinated  milk-globules  may  sometimes  be  dig- 
covered  after  the  tenth  day,  but  they  are  very  rare.  After  the  fifteenth  day,  the  milk 
does  not  sensibly  change  in  its  microscopical  or  its  chemical  characters. 

Lacteal  Secretion  in  the  Newly-Born. 

It  is  a  curious  fact  that  in  infants  of  both  sexes  there  is  generally  a  certain  amount 
of  secretion  from  the  mammary  glands,  commencing  at  birth  or  from  two  to  three  days 
after,  and  continuing  sometimes  for  two  or  three  weeks.  The  quantity  of  fluid  that  may 
be  pressed  out  at  the  nipples  at  this  time  is  very  variable.  Sometimes  only  .a  few  drops 
can  be  obtained,  but  occasionally  the  fluid  amounts  to  one  or  two  drachms.  Although 
it  is  impossible  to  indicate  the  object  of  this  secretion,  which  takes  place  when  the  glands 
are  in  a  rudimentary  condition,  it  has  been  so  often  observed  and  described  by  physiolo- 
gists, that  there  can  be  no  doubt  with  regard  to  the  nature  of  the  fluid  and  the  fact  that 
the  secretion  is  almost  always  produced  in  greater  or  less  quantity.  The  following  is  an 
analysis  by  Quevenne  of  the  secretion  obtained  by  Gubler.  The  observations  of  GubJer 
were  very  extended  and  were  made  upon  about  twelve  hundred  children.  The  secretion 
rarely  continued  for  more  than  four  weeks,  but  in  four  instances  it  persisted  for  two 
months. 

Composition  of  the  Milk  of  the  Infant. 

Water 4 894.00 

Caseine 26  "40 

Sugar  of  milk 62'20 

But*er '..'.'I!.'.'!!.'.'.'  14-00 

Earthy  phosphates j-2Q 

Soluble  salts  (with  a  small  quantity  of  insoluble  phosphates) 2-20 

1,000-00 


GENERAL  CONSIDERATIONS.  379 

This  fluid  does  not  differ  much  in  its  composition  from  ordinary  milk.  The  propor- 
tion of  butter  is  much  less,  but  the  amount  of  sugar  is  greater,  and  the  quantity  of  case- 
ine  is  nearly  the  same. 

Of  the  other  fluids  which  are  enumerated  in  the  list  of  secretions,  the  saliva,  gastric 
juice,  pancreatic  juice,  and  the  intestinal  fluids  have  already  been  considered  in  connec- 
tion with  digestion.  The  physiology  of  the  lachrymal  secretion  will  be  taken  up  in  con- 
nection with  the  eye,  and  the  bile  will  be  treated  of  fully  under  the  head  of  excretion. 


CHAPTER    XII. 

EXCRETION-  BY  THE  SKIN  AND  KIDNEYS. 

Differences  between  the  secretions  proper  and  the  excretions— Physiological  anatomy  of  the  skin— Physiological 
anatomy  of  the  nails  and  hairs— Sudden  blanching  of  the  hair— Uses  of  the  hairs— Perspiration— Sudoriparous 
glands— Mechanism  of  the  secretion  of  sweat— Properties  and  composition  of  the  sweat— Peculiarities  of  the 
sweat  in  certain  parts— Physiological  anatomy  of  the  kidneys— Distribution  of  blood-vessels  in  the  kidneys 
—Lymphatics  and  nerves  of  the  kidneys— Mechanism  of  the  production  and  discharge  of  urine— Formation 
of  the  excrementitious  constituents  of  the  urine  in  the  tissues,  absorption  of  these  principles  by  the  blood, 
and  separation  of  them  from  the  blood  by  the  kidneys— Effects  of  removal  of  both  kidneys  from  a  living  animal 
—Effects  of  tying  the  ureters  in  a  living  animal— Extirpation  of  one  kidney— Influence  of  blood-pressure,  the 
nervous  system,  etc.,  upon  the  secretion  of  urine— Alternation  in  the  action  of  the  kidneys  upon  the  two  sides- 
Changes  in  the  composition  of  the  blood  in  passing  through  the  kidneys— Physiological  anatomy  of  the  urinary 
passages— Mechanism  of  the  discharge  of  urine— Properties  and  composition  of  the  urine— General  physical  prop- 
erties of  the  urine— Quantity,  specific  gravity,  and  reaction  of  the  urine— Composition  of  the  urine— Gases  of 
the  urine— Variations  in  the  composition  of  the  urine— Variations  produced  by  food— Urina  potus,  urina  cibi, 
and  urina  sanguinis — Influence  of  muscular  exercise  upon  the  urine — Influence  of  mental  exertion. 

IN  entering  upon  the  study  of  the  elimination  of  effete  matters,  it  is  necessary  to 
appreciate  fully  the  broad  distinctions  between  the  secretions  proper  and  the  excretions, 
in  their  composition,  the  mechanism  of  their  production,  and  their  destination.  These 
considerations  are  again  referred  to,  for  the  reason  that  they  have  not  ordinarily  received 
that  attention  in  works  upon  physiology  which  their  importance  seems  to  demand.  The 
mechanism  of  excretion  is  inseparably  connected  with  the  function  of  nutrition,  and  it 
forms  one  of  the  great  starting-points  in  the  study  of  all  the  modifications  of  nutrition  in 
diseased  conditions. 

Taking  the  urine  as  the  type  of  the  excrementitious  fluids,  it  is  found  to  contain  none 
of  those  principles  included  in  the  class  of  non-crystallizable,  organic  nitrogenized  mat- 
ters, but  is  composed  entirely  of  crystallizable  matters,  simply  held  in  solution  in  water. 
The  character  of  these  principles  depends  upon  the  constitution  of  the  blood  and  the  gen- 
eral condition  of  nutrition,  and  not  upon  any  formative  action  in  the  glands.  The  principles 
themselves  represent  the  ultimate  physiological  changes  of  certain  constituent  parts  of  the 
living  organism,  and  they  are  in  such  a  condition  that  they  are  of  no  farther  use  in  the 
economy  and  are  simply  discharged  from  the  body.  Certain  inorganic  matters  are  found 
in  the  excrementitious  fluids,  are  discharged  with  the  products  of  excretion,  and  are  thus 
associated  with  the  organic  principles  of  the  economy  in  their  physiological  destruction, 
as  well  as  in  their  deposition  in  the  tissues.  Coagulable  organic  matters,  or  albuminoid 
principles,  never  exist  in  the  excrementitious  fluids  under  normal  conditions ;  except  as 
the  products  of  other  glands  may  become  accidentally  or  constantly  mixed  with  the 
excrementitious  fluids  proper.  The  same  remark  applies  to  the  non-nitrogenized  matters 
(sugars  and  fats),  which,  whether  formed  in  the  organism  or  taken  as  food,  are  consumed 
as  such  in  the  process  of  nutrition.  The  production  of  the  excretions  is  constant,  being 
subject  only  to  certain  modifications  in  activity,  which  are  dependent  upon  varying  con- 
ditions of  the  system.  All  of  the  elements  of  excretion  preexist  in  the  blood,  either  in 
the  precise  condition  in  which  they  are  discharged  or  in  some  slightly-modified  form. 


380  EXCRETION. 

Under  the  head  of  excretion,  it  is  proposed  to  consider  the  general  properties  and 
composition  of  the  different  excrementitious  fluids ;  but  the  relations  of  the  excremen- 
titious  matters  themselves  to  the  tissues  will  be  more  fully  treated  of  in  connection  with 
nutrition. 

The  urine  is  a  purely  excrementitious  fluid.  The  perspiration  and  the  secretion  of  the 
axillary  glands  are  excrementitious  fluids,  but  they  contain  a  certain  amount  of  the  secre- 
tion of  the  sebaceous  glands.  Certain  excrementitious  matters  are  found  in  the  bile,  but, 
at  the  same  time,  this  fluid  contains  principles  manufactured  in  the  liver  and  has  an  impor- 
tant function  as  a  secretion,  in  connection  with  the  process  of  digestion. 

Physiological  Anatomy  of  the  Skin. 

The  skin  is  one  of  the  most  complex  and  important  structures  in  the  body,  and  it  pos- 
sesses a  variety  of  functions.  In  the  first  place,  it  forms  a  protective  covering  for  the 
general  surface.  It  is  quite  thick  over  the  parts  most  subject  to  pressure  and  friction,  is 
elastic  over  movable  parts  and  those  liable  to  variations  in  size,  and,  in  many  situations, 
is  covered  with  hair,  which  affords  an  additional  protection  to  the  subjacent  structures. 
The  skin  and  its  appendages  are  imperfect  conductors  of  caloric,  are  capable  of  resisting 
very  considerable  variations  in  temperature,  and  they  thus  tend  to  maintain  the  normal 
standard  of  the  animal  heat.  As  an  organ  of  tactile  sensibility,  the  skin  has  an  important 
function,  being  abundantly  supplied  with  sensitive  nerves,  some  of  which  present  an 
arrangement  peculiarly  adapted  to  the  nice  appreciation  of  external  impressions.  The 
skin  assists  in  preserving  the  external  forms  of  the  muscles.  It  also  relieves  the  abrupt 
projections  and  depressions  of  the  general  surface  and  gives  roundness  and  grace  to  the 
contours  of  the  body.  In  some  parts  it  is  very  closely  attached  to  the  subjacent  struct- 
ures, while  in  others  it  is  less  adherent  and  is  provided  with  a  layer  of  adipose  tissue. 

As  an  organ  of  excretion,  the  skin  is  very  important ;  and,  although  the  quantity  of 
excrementitious  matter  exhaled  from  it  is  not  very  great  and  probably  not  subject  to 
much  variation,  the  evaporation  of  water  from  the  general  surface  is  always  considerable 
and  is  subject  to  such  modifications  as  may  become  necessary  from  the  varied  conditions 
of  the  animal  temperature.  Thus,  while  the  skin  protects  the  body  from  external  influ- 
ences, its  function  is  important  in  regulating  the  heat  produced  as  one  of  the  numerous 
phenomena  attendant  upon  the  general  process  of  nutrition. 

As  the  skin  presents  such  a  variety  of  functions,  its  physiological  anatomy  is  most 
conveniently  considered  in  connection  with  different  divisions  of  the  subject  of  physi- 
ology. For  example,  under  the  head  of  secretion,  we  have  already  taken  up  the  struct- 
ure of  the  different  varieties  of  sebaceous  glands ;  and  the  anatomy  of  the  skin  as  an  organ 
of  touch  will  be  most  appropriately  considered  in  connection  with  the  nervous  system. 
In  this  connection,  we  shall  describe  the  excreting  organs  found  in  the  skin ;  and  here  it 
will  be  most  convenient  to  study  briefly  its  general  structure  and  the  most  important 
points  in  the  anatomy  of  the  epidermic  appendages.  A  full  and  connected  description  of 
the  skin  and  its  appendages  belongs  properly  to  works  upon  anatomy. 

Extent  and  Thickness  of  the  Skin. — Sappey  has  made  a  number  of  very  careful 
observations  upon  the  extent  of  the  surface  of  the  skin.  Without  detailing  the  measure- 
ments of  different  parts,  it  may  be  stated,  as  the  general  result  of  his  observations,  that 
the  cutaneous  surface  in  a  good-sized  man  is  equal  to  a  little  more  than  sixteen  square  feet ; 
and,  in  men  of  more  than  ordinary  size,  it  may  extend  to  twenty-one  or  twenty-two 
square  feet.  In  women  of  medium  size,  as  the  mean  result  of  three  observations,  the 
surface  was  found  to  equal  about  twelve  square  feet.  When  we  consider  the  great  extent 
of  the  cutaneous  surface,  it  is  not  surprising  that  the  amount  of  secretion,  under  certain 
conditions,  should  be  enormous.  Indeed,  under  all  circumstances,  the  amount  of  elimina- 
tion is  very  considerable,  and  the  skin  is  really  one  of  the  most  important  of  the  organs 
of  excretion. 


PHYSIOLOGICAL  ANATOMY   OF  THE   SKIN.  381 

The  thickness  of  the  skin  varies  very  much  in  different  parts.  Where  it  is  exposed 
to  constant  pressure  and  friction,  as  on  the  soles  of  the  feet  or  the  palms  of  the 
hands,  the  epidermis  becomes  very  much  thickened,  and  in  this  way  the  more  delicate 
structure  of  the  true  skin  is  protected.  It  is  well  known  that  the  development  of  the 
epidermis,  under  these  conditions,  varies  in  different  persons,  with  the  amount  of  press- 
ure and  friction  to  which  the  surface  is  habitually  subjected.  The  true  skin  is  from  T^ 
to  ^  of  an  inch  in  thickness ;  but  in  certain  parts,  particularly  in  the  external  auditory 
meatus,  the  lips,  and  the  glans  penis,  it  frequently  measures  not  more  than  T^  of 
an  inch. 

Layers  of  the  S~kin. — The  skin  is  naturally  divided  into  two  principal  layers,  which 
may  be  readily  separated  from  each  other  by  maceration.  These  are,  the  true  skin  (cutis 
vera,  derma,  or  corium),  and  the  epidermis,  cuticle,  or  scarf-skin.  The  true  skin  is  at- 
tached to  the  subjacent  structures,  more  or  less  closely,  by  a  fibrous  structure  called  the 
subcutaneous  areolar  tissue,  in  the  meshes  of  which  we  commonly  find  a  certain  quantity 
of  fatty  tissue.  This  layer  is  sometimes  described  under  the  name  of  the  panniculus  adi- 
posus.  The  thickness  of  the  adipose  layer  varies  very  much  in  different  parts  of  the 
general  surface  and  in  different  persons.  There  is  no  fat  beneath  the  skin  of  the  eyelids, 
the  upper  and  outer  part  of  the  ear,  the  penis,  and  the  scrotum.  Beneath  the  skin  of 
the  cranium,  the  nose,  the  neck,  the  dorsum  of  the  hand  and  foot,  the  knee,  and  the 
elbow,  the  fatty  layer  is  about  -£%  of  an  inch  in  thickness.  In  other  parts  it  usually 
measures  from  ^  to  ^  of  an  inch.  In  very  fat  persons  it  may  measure  one  inch  or  more. 
Upon  the  head  and  the  neck,  in  the  human  subject,  are  muscles  attached  more  or  less 
closely  to  the  skin.  These  are  capable  of  moving  the  skin  to  a  slight  extent.  Muscles 
of  this  kind  are  largely  developed  and  quite  extensively  distributed  in  some  of  the  lower 
animals. 

There  is  no  sharply-defined  line  of  demarcation  between  the  cutis  and  the  subcuta- 
neous areolar  tissue ;  and  the  under  surface  of  the  skin  is  always  irregular,  from  the 
presence  of  numerous  fibres  which  are  necessarily  divided  in  detaching  it  from  the  sub- 
jacent structures.  The  fibres  which  enter  into  the  composition  of  the  skin  become  looser 
in  their  arrangement  near  its  under  surface,  the  change  taking  place  rather  abruptly, 
until  they  present  large  aveolse,  which  generally  contain  a  certain  amount  of  adipose 
tissue. 

The  layer  called  the  true  skin  is  subdivided  into  a  deep,  reticulated,  or  fibrous  layer, 
and  a  superficial  portion,  called  the  papillary  layer.  The  epidermis  is  also  divided  into 
two  layers,  as  follows  :  an  external  layer,  called  the  horny  layer ;  and  an  internal  layer, 
called  the  Malpighian,  or  the  mucous  layer,  which  is  in  contact  with  the  papillary  layer 
of  the  corium. 

The  Corium,  or  True  Skin. — The  reticulated  and  the  papillary  layer  of  the  true  skin  are 
quite  distinct.  The  lower  stratum,  the  reticulated  layer,  is  much  thicker  than  the  papil- 
lary layer  and  is  dense,  resisting,  quite  elastic,  and  slightly  contractile.  It  is  composed  of 
numerous  bundles  of  white  fibrous  tissue  interlacing  with  each  other  in  every  direction, 
generally  at  acute  angles.  Distributed  throughout  this  layer,  are  found  numerous  anas- 
tomosing, elastic  fibres  of  the  small  variety,  and  with  them  a  number  of  non-striated 
muscular  fibres.  This  portion  of  the  skin  contains,  in  addition,  a  considerable  quantity 
of  amorphous  matter,  which  serves  to  hold  the  fibres  together.  The  muscular  fibres  are 
particularly  abundant  about  the  hair-follicles  and  the  sebaceous  glands  connected  with 
them,  and  their  arrangement  is  such  that,  when  they  are  excited  to  contraction  by  cold 
or  by  electricity,  the  follicles  are  drawn  up,  projecting  upon  the  general  surface  and 
producing  the  appearance  known  as  "goose-flesh."  Contraction  of  these  fibres  is  par- 
ticularly marked  about  the  nipple,  producing  the  so-called  erection  of  this  organ,  and 
about  the  scrotum  and  penis,  wrinkling  the  skin  of  these  parts.  The  peculiar  arrange- 


382  EXCRETION. 

ment  of  the  little  muscles  around  the  hair-follicles,  forming  little  bands  attached  to  the 
surface  of  the  true  skin  and  the  base  of  the  follicles,  explains  fully  the  manner  in  which 
the  "  goose-flesh  "  is  produced.  (See  Fig.  107,  page  387.)  Contraction  of  the  skin,  in 
obedience  to  the  stimulus  of  electricity,  has  been  repeatedly  demonstrated,  both  in  the 
living  subject  and  in  executed  criminals  immediately  after  death. 

The  papillary  layer  of  the  skin  passes  insensibly  into  the  subjacent  structure  and 
presents  no  well-marked  line  of  division.  It  is  composed  chiefly  of  amorphous  mat- 
ter like  that  which  exists  in  the  reticulated  layer.  The  papilla?  themselves  appear  to 
be  simple  elevations  of  this  amorphous  matter,  although  they  may  contain  a  few  fibres. 
In  this  layer,  we  find  a  number  of  fibro-plastic  nuclei,  with  a  few  little  corpuscular  bodies 
called  by  Robin,  cytoblastions. 

As  regards  their  form,  the  papilla?  may  be  divided  into  two  varieties ;  the  simple  and 
the  compound.  The  simple  papilla?  are  conical,  rounded,  or  club-shaped  elevations  of 
the  amorphous  matter  and  are  irregularly  distributed  on  the  general  surface.  The 
smallest  are  from  ^-^  to  ¥^  of  an  inch  in  length  and  are  found  chiefly  upon  the  face. 
The  largest  are  on  the  palms  of  the  hands,  the  soles  of  the  feet,  and  the  nipple.  These 
measure  from  ^-f^  to  ^¥  °f  an  inch.  Large  papillae,  regularly  arranged  in  a  longitudinal 
direction,  are  found  beneath  the  nails.  The  regular,  curved  lines  observed  upon  the 
palms  of  the  hands  and  the  soles  of  the  feet,  particularly  the  palmar  surfaces  of  the  last 
phalanges,  are  formed  by  double  rows  of  compound  papilla?,  which  present  two,  three, 
or  four  points  attached  to  a  single  base.  In  the  centre  of  each  of  these  double  rows  of 
papilla?,  is  an  excessively  fine  and  shallow  groove,  in  which  are  found  the  orifices  of  the 
sudoriferous  ducts. 

The  papilla?  are  abundantly  supplied  with  blood-vessels,  terminating  in  looped  capil- 
lary plexuses,  and  with  nerves.  The  termination  of  the  nerves  is  peculiar  and  will  be  fully 
described  in  connection  with  the  organs  of  touch.  The  arrangement  of  the  lymphatics, 
which  are  very  numerous  in  the  skin,  has  already  been  indicated  in  the  general  descrip- 
tion of  the  lymphatic  system. 

The  Epidermis  and  its  Appendages. — The  epidermis,  or  external  layer  of  the  skin,  is 
a  membrane  composed  exclusively  of  cells,  containing  neither  blood-vessels,  nerves,  nor 
lymphatics.  Its  external  surface  is  marked  by  exceedingly  shallow  grooves,  which  cor- 
respond to  the  deep  furrows  between  the  papilla?  of  the  derma.  Its  internal  surface  is 
applied  directly  to  the  papillary  layer  of  the  true  skin  and  follows  closely  all  its 
inequalities.  This  portion  of  the  skin  is  subdivided  into  two  tolerably-distinct  layers. 
The  internal  layer  is  called  the  rete  mucosum,  or  the  Malpighian  layer,  and  the  external 
is  called  the  horny  layer.  These  two  layers  present  certain  important  distinctive  char- 
acters. 

The  Malpighian  layer  is  composed  of  a  single  stratum  of  prismoidal,  nucleated  cells, 
containing  a  greater  or  less  amount  of  pigmentary  matter,  which  are  applied  directly  to 
all  the  inequalities  of  the  derma,  and  of  a  number  of  layers  of  rounded  cells  containing  no 
pigment.  The  upper  layers  of  cells,  with  the  scales  of  the  horny  layer,  are  semitransparent 
and  nearly  colorless ;  and  it  is  the  pigmentary  layer  chiefly  which  gives  to  the  skin  its 
characteristic  color  and  the  peculiarities  in  the  complexion  of  different  races  and  of  differ- 
ent individuals.  In  the  negro,  this  layer  is  nearly  black ;  and,  when  the  epidermis  is  re- 
moved, the  true  skin  does  not  present  any  marked  difference  from  the  skin  of  the  white 
race.  All  the  epidermic  cells  are  somewhat  colored  in  the  dark  races,  but  the  upper 
layers  contain  no  pigmentary  granules.  The  cells  of  the  pigmentary  layer  are  from  ^Vo 
to  WTHT  of  an  inch  in  length  and  from  -^-^  to  ^Vfr  of  an  inch  in  their  short  diameter. 
The  rounded  cells  in  the  upper  layers  are  from  :nJVo  to  in>Vo  of  an  inch  in  diameter. 
The  absolute  thickness  of  the  rete  mucosum  is  from  T^  to  TV  of  an  inch. 

The  horny  layer  is  composed  of  numerous  strata  of  hard,  flattened  cells,  irregularly 
polygonal  in  shape,  generally  without  nuclei,  and  measuring  from  -^-^  to  T^  of  an  inch 


PHYSIOLOGICAL  ANATOMY   OF  THE  SKIN.  383 

in  diameter.  The  deeper  cells  are  thicker  and  more  rounded  than  those  of  the  super- 
ficial layers. 

The  epidermis  serves  as  a  protection  to  the  more  delicate  structure  of  the  true  skin, 
and  its  thickness  is  proportionate  to  the  exposure  of  the  different  parts.  It  is  conse- 
quently much  thicker  upon  the  soles  of  the  feet  and  the  palms  of  the  hands  than  in  other 
portions  of  the  general  surface,  and  its  thickness  is  very  much  increased  in  those  who 
are  habitually  engaged  in  manual  labor.  Upon  the  face,  the  eyelids,  and  in  the  exter- 
nal auditory  passages,  the  epidermis  is  most  delicate,  measuring  from  -^  to  ^  of  an 
inch  in  thickness.  Upon  the  palm  it  is  from  ^  to  ^  of  an  inch  thick,  and  upon  the  sole 
of  the  foot  it  measures  from  ^  to  ^  of  an  inch.  These  variations  in  thickness  depend 
entirely  upon  the  development  of  the  horny  layer.  The  thickness  of  the  rete  mucosum,, 
although  it  presents  considerable  variation  in  different  parts,  is  rather  more  uniform. 

There  is  constantly  more  or  less  desquamation  of  the  epidermis,  particularly  of  the 
horny  layer,  and  the  cells  are  regenerated  by  a  blastema  exuded  from  the  subjacent  vas- 
cular parts.  It  is  probable  that  there  is  a  constant  formation  of  cells  in  the  deeper  strata 
of  the  horny  layer,  which  become  flattened  as  they  near  the  surface ;  but  there  is  no  direct 
evidence  that  the  cells  of  the  rete  mucosum  undergo  transformation  into  the  hard,  flat- 
tened scales  of  the  horny  layer. 

Physiological  Anatomy  of  the  Nails  and  Hairs. — It  is  unnecessary,  in  this  connec- 
tion, to  discuss  very  minutely  the  anatomy  of  the  nails  and  hairs.  They  are  ordi- 
narily regarded  as  appendages  of  the  epidermis,  produced  by  certain  peculiar  organs 
belonging  to  the  true  skin ;  and  an  elaborate  study  of  these  parts  belongs  strictly  to 
descriptive  and  general  anatomy.  To  complete,  however,  the  physiological  history  of 
the  skin,  it  will  be  necessary  to  consider  briefly  the  general  arrangement  of  the  cuticular 
appendages. 

The  nails  are  situated  on  the  dorsal  surfaces  of  the  distal  phalanges  of  the  fingers  and 
toes.  They  serve  to  protect  these  parts,  and,  in  the  fingers,  they  are  quite  important  in 
prehension.  The  general  appearance  of  the  nails  is  so  familiar  that  it  requires  no  special 
description.  In  their  study,  anatomists  have  distinguished  a  root,  a  body,  and  a  free 
border. 


FIG.  105.— Anatomy  of  the  nails.    (Sappey.) 

A,  nail  in  situ :  1,  cutaneous  fold  covering  the  root  of  the  nail ;  2,  section  of  this  fold,  turned  back  to  show  the  root 
of  the  nail ;  3,  lunula ;  4,  nail.  B,  concave  or  adherent  surface  of  the  nail:  1,  border  of  the  root  ;  2,  lunula  and 
root;  3,  body  ;  4,  free  border.  G,  longitudinal  section  of  the  nail:  1,  2,  epidermis;  3,  superficial  layer  of  the 
nail ;  4,  epidermis  of  the  pulp  of  the  finger  ;  5,  6,  true  skin  ;  7,  11,  bed  of  the  nail ;  8,  Malpighian  layer  of  the 
pulp  of  the  finger ;  9, 10,  true  skin  on  the  dorsal  surface  of  the  finger ;  12,  true  skin  of  the  pulp  of  the  finger  ; 
1 3,  last  phalanx  of  the  finger. 

The  root  of  the  nail  is  thin  and  soft,  terminating  in  rather  a  jagged  edge,  which  is 
turned  slightly  upward  and  is  received  into  a  fold  of  the  skin  extending  around  the  nail 
to  its  free  edge.  The  length  of  the  root  of  course  varies  with  the  size  of  the  nail,  but  it 
is  generally  from  one-fourth  to  one-third  of  the  length  of  the  body. 

The  body  of  the  nail  extends  from  the  fold  of  skin  which  covers  the  root  to  the  free 
border.  This  portion  of  the  nail,  with  the  root,  is  closely  adherent  by  its  under  surface 
to  the  true  skin.  It  is  marked  by  fine  but  distinct  longitudinal  stria?  and  very  faint 


384 


EXCRETION". 


transverse  lines.  It  is  usually  reddish  in  color,  from  the  great  vascularity  of  the  subja- 
cent structure.  At  the  posterior  part,  is  a  whitish  portion  of  a  semilunar  shape,  called 
the  lunula,  which  has  this  appearance  simply  from  the  fact  that  the  corium  in  this  part  is 
less  vascular  and  the  papillae  are  not  so  regular  as  in  the  rest  of  the  body.  That  portion 
of  the  skin  situated  beneath  the  root  and  the  body  of  the  nail  is  called  the  matrix.  It 
presents  highly  vascular  papillae,  arranged  in  regular,  longitudinal  rows,  and  it  receives 
into  its  grooves  corresponding  ridges  on  the  under  surface  of  the  nail. 

The  free  border  of  the  nail  begins  at  the  point  where  the  nail  becomes  detached  from 
the  skin.  This  is  generally  cut  or  worn  away  and  is  constantly  growing ;  but,  if  left  to 
itself,  it  attains  in  time  a  definite  length,  which  may  be  stated,  in  general  terms,  to  be 
from  an  inch  and  a  half  to  two  inches. 


FIG.  106.— Section  of  the,  nail,  etc.    (Sappey.) 

A,  section  of  the  nail:  1, 1,  superficial  layer  ;  2,  deep  layer  ;  3,  3,  4,  4,  section  of  the  grooves  on  the  attached  sur- 
lace  ;  5,  5  union  of  the  superficial  with  the  deep  layer  ;  6,  6,  dark  line  between  the  two  layers.  B,  cells  of  the 
superficial  layer,  lateral  view.  C,  cells  of  the  superficial  layer,  flat  view.  D,  cells  of  the  deep  layer. 

Examining  the  nail  in  a  longitudinal  section,  the  horny  layer,  which  is  usually 
regarded  as  the  true  nail,  is  found  to  increase  progressively  in  thickness  from  the  root  to 
near  the  free  border.  If  the  nail  be  examined  in  a  transverse  section,  it  will  also  be 
found  much  thicker  in  the  central  portion  than  near  the  edge,  and  that  part  which  is 
received  into  the  lateral  portions  of  the  fold  becomes  excessively  thin  like  the  rest  of  the 
root.  The  thickness  of  the  true  nail  at  the  root  is  from  ^  to  -^  of  an  inch  ;  and,  in 
the  thickest  portion  of  the  body,  it  usually  measures  from  ~V  to  ^  of  an  inch.  The  nail 
becomes  somewhat  thinner  at  and  near  the  free  border. 

Sections  of  the  nails  show  that  they  are  composed  of  two  layers,  which  correspond 
to  the  Malpighian  and  the  horny  layer  of  the  epidermis,  although  they  are  much  more 


PHYSIOLOGICAL  ANATOMY   OF  THE  NAILS.  385 

distinct.  The  Malpighian  layer  is  applied  directly  to  the  ridges  of  the  bed  of  the  nail 
and  presents  upon  its  upper  surface  ridges  much  less  strongly  marked  than  those  of  the 
underlying  true  skin.  This  layer  is  rather  thinner  than  the  horny  layer,  is  whitish  in 
color,  and  is  composed  of  numerous  strata  of  elongated,  prismoidal,  nucleated  cells, 
arranged  perpendicularly  to  the  matrix.  These  cells  are  from  ^Vfr  to  TTTO  °f  an  mch  in 
length. 

The  horny  layer,  which  constitutes  the  true  nail,  is  applied  by  its  under  surface 
directly  to  the  ridges  of  the  Malpighian  layer.  It  is  dense  and  brittle  and  is  composed  of 
numerous  strata  of  flattened  cells,  which  cannot  be  isolated  without  the  use  of  reagents. 
If  the  different  strata  of  this  portion  of  the  nail  be  studied  after  boiling  in  a  dilute  solu- 
tion of  soda  or  potash,  it  becomes  evident  that  here,  as  in  the  horny  layer  of  the  epider- 
mis, the  lower  cells  are  somewhat  rounded,  while  those  nearer  the  surface  are  flattened. 
These  cells  are  nearly  all  nucleated  and  measure  from  ToVo  to  ^fo  of  an  inch  in  diame- 
ter. The  thickness  of  this  layer  varies  in  different  portions  of  the  nail,  while  that  of 
the  Malpighian  layer  is  nearly  uniform.  This  layer  is  constantly  growing,  and  it  consti- 
tutes the  entire  substance  of  the  free  borders  of  the  nails. 

The  connections  of  the  nails  with  the  true  skin  resemble  those  of  the  epidermis ;  but 
the  relations  of  these  structures  to  the  epidermis  itself  are  somewhat  peculiar.  Up  to 
the  fourth  month  of  foetal  life,  the  epidermis  covering  the  dorsal  surfaces  of  the  last 
phalanges  of  the  fingers  and  toes  does  not  present  any  marked  peculiarities ;  but,  at 
about  the  fourth  month,  the  peculiar  hard  cells  of  the  horny  layer  of  the  nails  make 
their  appearance  between  the  Malpighian  and  the  horny  layer  of  the  epidermis,  and  at 
the  same  time  the  Malpighian  layer  beneath  this  plate,  which  is  destined  to  become  the 
Malpighian  layer  of  the  nails,  is  somewhat  thickened,  and  the  cells  assume  more  of  an 
elongated  form.  The  horny  layer  of  the  nails  constantly  thickens  from  this  time  ;  but, 
until  the  end  of  the  fifth  month,  it  is  covered  by  the  horny  layer  of  the  epidermis.  After 
the  fifth  month,  the  epidermis  breaks  away  and  disappears  from  the  surface ;  and,  at  the 
seventh  month,  the  nails  begin  to  increase  in  length.  Thus,  at  one  time,  the  nails  are 
actually  included  between  the  two  layers  of  the  epidermis ;  but,  after  they  have  become 
developed,  they  are  simply  covered  at  their  roots  by  a  narrow  border  of  the  horny 
layer,  the  epidermis  commencing  again  under  the  nail  where  the  free  border  leaves  the 
bed.  The  nails  are  therefore  to  be  regarded  as  modifications  of  the  horny  layer  of 
the  epidermis,  possessing  certain  anatomical  and  chemical  peculiarities.  The  Malpighian 
layer  of  the  nails  is  continuous  with  the  same  layer  of  the  epidermis,  but  the  horny  lay- 
ers are,  as  we  have  seen,  distinct. 

One  of  the  most  striking  peculiarities  of  the  nails  is  in  their  mode  of  growth.  The 
Malpighian  layer  is  stationary,  but  the  horny  layer  is  constantly  growing,  if  the  nails  be 
cut,  from  the  root  and  bed.  It  is  evident  that  the  nails  grow  from  the  bed,  as  their 
thickness  progressively  increases  in  the  body  from  the  root  to  near  the  free  border;  but 
their  longitudinal  growth  is  by  far  the  more  rapid.  Indeed,  the  nails  are  constantly 
pushing  forward,  increasing  in  thickness  as  they  advance.  Near  the  end  of  the  body  of 
the  nail,  as  the  horny  layer  becomes  thinner,  the  growth  from  below  is  diminished. 

Hairs,  varying  greatly  in  size  and  development,  cover  nearly  every  portion  of  the 
cutaneous  surface.  The  only  parts  in  which  they  are  not  found  are  the  palms  of  the 
hands  and  soles  of  the  feet,  the  palmar  surface  of  the  fingers  and  toes,  the  dorsal  surface 
of  the  last  phalanges  of  the  fingers  and  toes,  the  lips,  the  upper  eyelids,  the  lining  of  the 
prepuce,  and  the  glans  penis.  Some  of  the  hairs  are  long,  others  are  short  and  stiff,  and 
others  are  fine  and  downy.  These  differences  have  led  to  a  division  of  the  hairs  into 
three  varieties : 

The  first  variety  includes  the  long,  soft  hairs,  which  are  found  on  the  head,  on  the 
face  in  the  adult  male,  around  the  genital  organs  and  under  the  arms  in  both  the  male 
and  the  female,  and  sometimes  upon  the  breast  and  over  the  general  surface  of  the  body 
and  extremities,  particularly  in  the  male. 
25 


386  EXCRETION. 

The  second  variety,  the  short,  stiff  hairs,  is  found  at  the  entrance  of  the  nostrils, 
upon  the  edges  of  the  eyelids,  and  upon  the  eyebrows. 

The  third  variety,  the  short,  soft,  downy  hairs,  are  found  on  the  general  surface 
not  occupied  by  the  long  hairs,  and  in  the  caruncula  lachryraalis.  In  early  life,  and  ordi- 
narily in  the  female  at  all  ages,  the  trunk  and  extremities  are  covered  with  downy 
hairs  ;  but,  in  the  adult  male,  these  frequently  become  developed  into  long,  soft  hairs. 

The  hairs  are  usually  set  obliquely  in  the  skin  and  take  a  definite  direction  as  they 
lie  upon  the  surface.  Upon  the  head  and  face,  and,  indeed,  the  entire  surface  of  the 
body,  the  general  course  of  the  hairs  may  be  followed  out,  and  they  present  currents 
or  sweeps  that  have  nearly  always  the  same  direction. 

The  diameter  and  length  of  the  hairs  are  exceedingly  variable  in  different  persons, 
especially  in  the  long,  soft  hairs  of  the  head  and  beard.  It  may  be  stated  in  gen- 
eral terms  that  the  long  hairs  attain  the  length  of  from  twenty  inches  to  three  feet, 
in  women,  and  considerably  less  in  men.  There  are  instances,  however,  in  women,  in 
which  the  hairs  of  the  head  measure  considerably  more  than  three  feet,  but  these  are 
quite  unusual.  Like  the  nails,  the  hair,  when  left  to  itself,  attains  in  three  or  four  years 
a  definite  length,  but  when  it  is  habitually  cut  it  grows  constantly.  The  short,  stiff 
hairs  are  from  one  quarter  to  one  half  an  inch  in  length.  The  soft,  downy  hairs 
measure  ordinarily  from  one-twelfth  to  one-half  an  inch.  Hairs  that  have  never  been 
cut  terminate  in  pointed  extremities ;  and  sometimes  in  hairs  that  have  been  cut,  the 
ends  become  somewhat  pointed,  although  they  are  never  so  sharp  as  in  the  new  hairs. 

Of  the  long  hairs,  the  finest  are  upon  the  head,  where  they  average  about  ^^  of 
an  inch  in  diameter,  the  extremes  being  from  15106  to  T^g-  of  an  inch  for  the  finest, 
and  from  ±^$  to  yi-^  of  an  inch  for  the  coarsest.  The  hair  is  ordinarily  coarser  in 
women  than  in  men.  Dark  hair  is  generally  coarser  than  light  hair ;  and,  upon  the 
same  head,  the  extremes  of  variation  are  sometimes  observed.  The  hairs  of  the  beard 
and  the  long  hairs  of  the  body  are  coarser  than  the  hairs  of  the  head.  Wilson  esti- 
mates that  the  average  number  of  hairs  upon  a  square  inch  of  the  scalp  is  about  1,000, 
and  the  number  upon  the  entire  head,  about  120,000. 

The  short,  stiff  hairs  are  from  f^  to  -^  of  an  inch  in  diameter,  and  the  fine,  downy 
hairs,  from  ^^-g-  to  T^OTT  of  an  inch.  The  variations  in  the  color  of  the  hairs  in  different 
races  and  in  different  individuals  of  the  same  race  are  sufficiently  familiar. 

"When  the  hairs  are  in  a  perfectly  normal  condition,  they  are  very  elastic  and  may  be 
stretched  to  from  one-fifth  to  one-third  more  than  their  original  length.  Their  strength 
varies  with  their  thickness,  but  an  ordinary  hair  from  the  head  will  bear  a  weight  of 
six  or  seven  ounces.  A  well-known  property  of  the  hair  is  that  of  becoming  strongly 
electric  by  friction ;  and  this  is  particularly  well-marked  when  the  weather  is  cold  and 
dry.  The  electricity  thus  excited  is  negative.  Sections  of  the  shaft  of  the  hairs  show 
that  they  are  oval,  but  their  shape  is  very  variable,  straight  hairs  being  nearly  round, 
while  curled  hairs  are  quite  flat.  Another  peculiarity  of  the  hairs  is  that  they  are 
strongly  hygrometric.  They  readily  absorb  moisture  and  become  sensibly  elongated,  a 
property  which  has  been  made  use  of  by  physicists  in  the  construction  of  delicate  hy- 
grometers. 

Boots  of  the  Hairs  and  Hair-follicles. — The  roots  of  the  hairs  are  embedded  in  fol- 
licular  openings  in  the  skin,  which  differ  in  the  different  varieties  only  in  the  depth  to 
which  they  penetrate  the  cutaneous  structure.  In  the  downy  hairs,  the  roots  pass  only 
into  the  superficial  layers  of  the  true  skin ;  but,  in  the  thicker  hairs,  the  roots  pass 
through  the  skin  and  penetrate  the  subcutaneous  cellulo- adipose  tissue. 

The  root  of  the  hair  is  softer,  rounder,  and  a  little  larger  than  the  shaft.  It  be- 
comes enlarged  into  a  rounded  bulb  at  the  bottom  of  the  follicle  and  rests  upon  a  fungi- 
form  papilla,  constricted  at  its  base,  to  which  it  is  closely  attached.  In  describing  the 
connection  between  the  hairs  and  the  skin,  anatomists  mention  three  membranes  forming 
the  walls  of  the  hair-follicles,  and  two  membranes  that  envelop  the  roots  of  the  hair  in 


PHYSIOLOGICAL  ANATOMY   OF   THE  HAIRS. 


387 


the  form  of  a  sheath.  The  study  of  these  parts  is  much  simplified  by  keeping  constant- 
ly in  view  the  correspondence  between  the  different  layers  of  the  follicles  and  the  layers 
of  the  true  skin,  and  the  relations  of  the  root -sheaths  with  the  epidermis. 

The  follicles  are  tubular  inversions  of  the  structures  that  compose  the  corium,  and 
their  walls  present  three  membranes.     Their  length  is  from  T^  to  £  of  an  inch.    The 


FIG.  107.— Hair  and  A  air-follicle.    (Sappey.)  Fro.  108.— Root  of  the  Jiair.    (Sappey.) 

:,  root  of  the  hair:  2,  bulb  of  the  hair,  covering  the  papilla  1,  root  of  the  hair;  2,  hair-bulb;  3,  pa- 

of  the  hair-follicle ;   3,  internal  root-sheath ;  4,  external  pilla  of  the  follicle ;    4,  opening  of 

root-sheath;  5,  membrane  of  the  hair-follicle,  composed  the  follicle  ;  5,  5,  internal  root-sheath; 

of  fusiform,  nucleated  fibres  arranged  transversely  (the  6,  external  root-sheath  ;  7,  7,  sebace- 

internal,  amorphous  membrane  of  the  follicle  is  very  deli-  .     ous  glands  ;  8,  8,  excretory  ducts  of 

cate  and  is  not  represented  in  the  figure) ;   6,  external  the  sebaceous  glands, 

membrane  of  the  follicle,  composed  chiefly  of  longitudinal 
fibres :  7,  7,  muscular  bands  attached  to  the  follicle ;  8,  8, 
extremities  of  these  bands  passing  to  the  skin ;  9,  com- 
pound sebaceous  gland,  with  its  duct  (10)  opening  into 
the  upper  third  of  the  follicle  ;  11,  simple  sebaceous  gland  ; 
12,  opening  of  the  hair-follicle. 

membrane  that  forms  the  external  coat  of  the  follicles  is  composed  of  inelastic  fibres, 
arranged  for  the  most  part  longitudinally,  provided  with  blood-vessels  and  a  few  nerves, 
containing  some  fibro-plastic  elements,  but  deprived  entirely  of  elastic  tissue.  This  is 


388 


EXCRETION. 


the  thickest  of  the  three  membranes  and  is  closely  connected  with  the  corium.  Next  to 
this,  is  a  fibrous  membrane  composed  of  fusiform,  nucleated  fibres  arranged  transversely. 
These  resemble  the  non-striated  muscular  fibres.  The  internal  membrane  is  structure- 
less and  corresponds  to  the  amorphous  layer  of  the  true  skin.  The  papilla  at  the  bottom 
of  the  hair-sac  varies  in  size  with  the  size  of  the  hairs  and  is  connected  with  the  fibrous 
layers  of  the  walls  of  the  follicle.  It  is  composed  of  amorphous  matter,  with  a  few 
granules  and  nuclei,  and  it  probably  contains  blood-vessels  and  nerves,  although  these 
are  not  very  distinct. 

Although  the  different  membranes  of  the  hair-follicles  are  sufficiently  recognizable,  it 
is  evident  that  the  hair-sac  is  nothing  more  than  an  inversion  of  the  corium,  with  some 
slight  modifications  in  the  character  and  arrangement  of  its  anatomical  elements.  The 
fibrous  membranes  correspond  to  the  deeper  layers  of  the  true  skin,  without  the  elastic 
elements,  and  they  present  a  peculiar  arrangement  of  its  inelastic  fibres,  the  external 
fibres  being  longitudinal  and  the  internal  fibres  transverse.  The  structureless  membrane 
corresponds  to  the  upper  layers  of  the  true  skin,  which  are  composed  chiefly  of  amorphous 
matter.  The  hair-papilla  corresponds  to  the  papillaB  on  the  general  surface  of  the  corium. 

The  investment  of  the  root  of  the  hair  presents  two  distinct  layers  called  the  external 
and  internal  root-sheaths.  The  external  root-sheath  is  three  or  four  times  as  thick  as 
the  inner  membrane,  and  it  corresponds  exactly  with  the  Malpighian  layer  of  the  epider- 
mis. This  sheath  is  continuous  with  the  bulb  of  the  hair.  The  internal  root -sheath  is  a 
transparent  membrane,  composed  of  flattened  cells,  mostly  without  nuclei.  This  extends 
from  the  bottom  of  the  hair- follicle  and  covers  the  lower  two-thirds  of  the  root. 

Structure  of  the  Hairs. — The  different  varieties  of  hairs  present  certain  peculiarities 
in  their  anatomy,  but  all  of  them  are  composed  of  a  fibrous  structure  forming  the  great- 
er part  of  their  substance,  covered  by  a  thin  layer  of  imbricated  cells.  In  the  short, 
stiff  hairs,  and  in  the  long,  white  hairs,  there  is  a  distinct  medullary  substance  ;  but  this 
is  wanting  in  the  downy  hairs  and  is  indistinct  in  many  of  the  long,  dark  hairs. 


FIG.  109.—  Human  hair  from  the  head  of  a  white 
cliild  ;  magnified  870  diameters.  (From  a  photo- 
graph taken  at  the  United  States  Array  Medical 
Museum.)  This  figure  shows  the  imbricated  ar- 
rangement of  the  epidermis  of  the  hair. 


FIG.  110.—  Transverse  section  of  a  human  hair  from 
the  beard  of  a  white  adult ;  magnified  370  diam- 
eterK.  (From  a  photograph  taken  at  the  United 
States  Army  Medical  Museum.) 


The  fibrous  substance  is  composed  of  hard,  elongated,  longitudinal  fibres,  which  can- 
not be  isolated  without  the  aid  of  reagents.  They  may  be  separated,  however,  by  macer- 
ation in  warm  sulphuric  acid,  when  they  present  themselves  in  the  form  of  dark,  irregu- 
lar, spindle-shaped  plates,  from  ^  to  ^  of  an  inch  long,  and  from  -^Vo  to  ^¥Vo  °f 
an  inch  wide.  These  contain  pigmentary  matter  of  various  shades,  occasional  cavities 


GROWTH  OF  THE  HAIRS.  339 

filled  with  air,  and  a  few  nuclei.  The  pigment  may  be  of  any  color,  from  a  light  yellow 
to  an  intense  black,  and  it  is  this  substance  that  gives  to  the  hair  the  great  variety  in 
color  which  is  observed  in  different  persons.  In  the  lower  part  of  the  root  the  fibres 
are  much  shorter,  and  at  the  bulb  they  become  transformed,  as  it  were,  into  the  soft, 
rounded  cells  found  in  this  situation  covering  the  papilla. 

The  epidermis  of  the  hair  is  excessively  thin  and  is  composed  of  flattened,  quadran- 
gular plates,  overlying  each  other  from  below  upward.  These  scales,  or  plates,  are  with- 
out nuclei,  and  they  exist  in  a  single  layer  over  the  shaft  of  the  hair  and  the  upper  part 
of  its  root ;  but,  in  the  lower  part  of  the  root,  the  cells  are  thicker,  softer,  are  frequent- 
ly nucleated,  and  they  exist  in  two  layers. 

The  medulla  is  found  in  the  short,  stiff  hairs,  and  it  is  often  beautifully  distinct  in 
the  long,  white  hairs  of  the  head.  It  occupies  from  one-fourth  to  one-third  of  the  diam- 
eter of  the  hair.  The  medulla  can  be  traced,  under  favorable  circumstances,  from  just 
above  the  bulb  to  near  the  pointed  extremity  of  the  hair.  It  is  composed  of  small, 
rounded  cells,  from  ^Vfr  to  y^  of  an  inch  in  diameter,  nucleated,  and  frequently  con- 
taining dark  granules  of  pigmentary  matter.  Mixed  with  these  cells  are  numerous  air- 
globules  ;  and  frequently  the  cells  are  interrupted  for  a  short  distance  and  the  space  is 
occupied  with  air.  The  dark  granules  of  the  medullary  cells  are  supposed  by  Kolliker 
to  be  globules  of  air.  The  medulla  likewise  contains  a  glutinous  fluid  between  the  cells 
and  surrounding  the  air-globules. 

Growth  of  the  Hairs. — Although  not  provided  with  blood  and  deprived  of  sensibility, 
the  hairs  are  connected  with  vascular  parts  and  are  nourished  by  imbibition  from  the 
papillae.  Each  hair  is  first  developed  in  a  closed  sac,  and  at  about  the  sixth  month  its 
pointed  extremity  perforates  the  epidermis.  These  first-formed  hairs  are  afterward  shed, 
like  the  milk-teeth,  being  pushed  out,  as  it  were,  by  new  hairs  from  below,  which  arise 
from  a  second  and  a  more  deeply-seated  papilla.  This  shedding  of  the  hairs  usually  takes 
place  from  two  to  six  months  after  birth. 

The  difference  in  the  color  of  the  hair  depends  upon  differences  in  the  quantity  and 
the  tint  of  the  pigmentary  matter ;  and,  in  old  age,  the  hair  becomes  white  or  gray  from 
a  blanching  of  the  cortex  and  medulla. 

Sudden  Blanching  of  the  Hair. — It  is  an  interesting  question,  in  connection  with  the 
nutrition  of  the  hair,  to  examine  the  instances  so  often  quoted  of  sudden  blanching  of  the 
hair  from  violent  emotions  or  other  causes.  Some  physiologists  are  of  the  opinion  that 
the  hair  may  become  almost  white  in  the  course  of  a  few  hours,  and  this,  indeed,  is  a 
popular  impression ;  but  others  assume  that  such  sudden  changes  never  take  place, 
although  it  is  certain  that  the  hair  frequently  turns  gray  in  the  course  of  a  few  weeks. 
In  examining  the  literature  of  this  subject,  it  is  difficult  to  find,  in  the  older  works,  well- 
authenticated  cases  of  these  sudden  changes,  and  most  of  those  that  have  been  quoted  are 
taken  upon  the  loose  authority  of  persons  evidently  not  in  the  habit  of  making  scientific 
observations.  Such  instances,  unsupported  by  analogous  cases  of  a  reliable  character, 
must  necessarily  be  rejected  as  not  fulfilling  the  rigid  requirements  demanded  in  scientific 
inquiries,  in  which  all  possible  sources  of  error  should  be  carefully  excluded.  It  is  not 
necessary,  therefore,  to  quote  the  instances  of  sudden  blanching  of  the  hair  recorded  by 
the  ancient  writers,  or  those  well-known  cases  of  later  date,  so  often  detailed  in  scien- 
tific works,  such  as  that  of  Marie  Antoinette  or  Sir  Thomas  More;  and  it  seems  proper 
to  exclude,  also,  cases  in  which  the  blanching  of  the  hair  has  been  observed  only  by 
friends  or  relatives  ;  for  in  most  of  them  the  statements  with  regard  to  time  are  conflict- 
ing and  unsatisfactory. 

Regarding  the  subject,  however,  from  a  purely  scientific  point  of  view,  there  are  a 
few  instances  of  late  date,  in  which  sudden  blanching  of  the  hair  has  been  observed  and 
the  causes  of  this  remarkable  phenomenon  fully  investigated  by  competent  observers; 
and  it  is  almost  unnecessary  to  say  that  a  single  well-authenticated  case  of  this  kind 
demonstrates  the  possibility  of  its  occurrence  and  is  interesting  in  connection  with  the 


390  EXCRETION. 

reported  instances  which  have  not  been  subjected  to  proper  investigation.  One  of  these 
cases  is  reported  in  Virchow's  Archiv,  for  April,  1866,  by  Dr.  Landois,  as  occurring  under 
the  observation  of  himself  and  Dr.  Lohmer.  In  this  case,  the  blanching  of  the  hair  oc- 
curred in  a  hospital  in  a  single  night,  while  the  patient  was  under  the  daily  observation 
of  the  visiting  physician.  As  this  is  one  of  the  few  well-authenticated  instances  of  sudden 
blanching  of  the  hair,  we  shall  give,  in  a  few  words,  its  essential  particulars  : 

The  patient,  a  compositor,  thirty-four  years  of  age,  with  light  hair  and  blue  eyes,  was 
admitted  into  the  hospital,  July  9,  1865,  suffering  apparently  from  an  acute  attack  of 
delirium  tremens.  A  marked  peculiarity  in  the  disease  was  excessive  terror  when  any 
person  approached  the  patient.  He  slept  for  twelve  hours  on  the  night 'of  the  llth 
of  July,  after  taking  thirty  drops  of  laudanum.  Up  to  this  time  nothing  unusual  had 
been  observed  with  regard  to  the  hair.  On  the  morning  of  July  12th,  it  was  evident  to 
the  medical  attendants  and  all  who  saw  the  patient  that  the  hair  of  the  head  and  beard 
had  become  gray.  This  fact  was  also  remarked  by  the  friends  who  visited  the  patient; 
and  he  himself  called  for  a  mirror  and  remarked  the  change  with  intense  astonishment. 
The  patient  continued  in  the  hospital  until  September  Vtb,  when  he  was  discharged,  the 
hair  remaining  gray.  An  interesting  point  connected  with  this  case  is  the  fact  that  the 
hairs  were  submitted  to  careful  microscopical  examination.  The  white  hairs  were  found 
to  contain  a  great  number  of  air-globules  in  the  medulla  and  in  the  cortical  substance, 
but  the  pigment  was  everywhere  preserved.  The  presence  of  air  gave  the  hairs  a  dark 
appearance  by  transmitted  light  and  a  white  appearance  by  reflected  light.  Dr.  Landois 
quotes,  in  this  connection,  instances  of  blanching  of  the  hair,  in  which  each  hair  pre- 
sented alternate  rings  of  a  white  and  a  brown  color.  Another  very  curious  case  of  this 
kind  was  lately  reported  to  the  Royal  Society  by  Mr.  Erasmus  Wilson.  In  this  case,  the 
white  portions  presented,  on  microscopical  examination,  great  bubbles  of  air ;  but  there 
was  no  diminution  in  the  quantity  of  pigmentary  matter. 

The  microscopical  examinations  by  Dr.  Landois  and  others  leave  no  doubt  as  to  the 
cause  of  the  white  color  of  the  hair  in  cases  of  sudden  blanching  ;  and  the  instances  we 
have  just  quoted  show  that  the  fact  of  the  occurrence  of  this  phenomenon  can  no  longer 
be  called  in  question.  All  are  agreed  that  there  is  no  diminution  in  the  pigment,  but  that 
the  greater  part  of  the  medulla  becomes  filled  with  air,  small  globules  being  also  found 
in  the  cortical  substance.  The  hair  in  these  cases  presents  a  marked  contrast  with  hair 
that  has  become  gray  gradually  from  old  age,  when  there  is  always  a  loss  of  pigment  in 
the  cortex  and  medulla.  How  the  air  finds  its  way  into  the  hair  in  sudden  blanching,  it 
is  difficult  to  imagine ;  and  the  views  that  have  been  expressed  on  this  subject  by  different 
authors  are  entirely  theoretical. 

The  fact  that  the  hair  may  become  white  or  gray  in  the  course  of  a  few  hours  renders 
it  probable  that  many  of  the  cases  reported  upon  unscientific  authority  actually  occurred ; 
and  these  have  all  been  supposed  to  be  connected  with  intense  grief  or  terror.  The  terror 
was  very  marked  in  the  case  reported  by  Dr.  Landois.  In  the  great  majority  of  recorded 
observations,  the  sudden  blanching  of  the  hair  has  been  apparently  connected  with  intense 
mental  emotion;  but  this  is  all  that  can  be  said  on  the  subject  of  causation,  and  the 
mechanism  of  the  change  is  not  understood. 

Uses  of  the  Hairs. — The  hairs  serve  an  important  purpose  in  the  protection  of  the 
general  surface  and  in  guarding  certain  of  the  orifices  of  the  body.  The  hair  upon  the 
head  and  the  face  protects  from  cold  and  shields  the  head  from  the  rays  of  the  sun  during 
exposure  in  hot  climates.  Although  the  amount  of  hair  upon  the  general  surface  is  small, 
as  it  is  a  very  imperfect  conductor  of  caloric,  it  serves  in  a  degree  to  maintain  the  heat 
of  the  body.  It  also  moderates  the  friction  upon  the  surface.  The  eyebrows  prevent  the 
perspiration  from  running  from  the  forehead  upon  the  lids;  the  eyelashes  protect  the 
surface  of  the  conjunctiva  from  dust  and  other  foreign  matters ;  the  mustache  protects 
the  lungs  from  dust,  a  function  very  important  in  persons  exposed  to  dust  in  long  journeys 
or  in  their  daily  work ;  and  the  short,  stiff  hairs  at  the  openings  of  the  ears  and  nose  pro- 


PERSPIRATION. 


391 


tect  these  orifices.     It  is  difficult  to  assign  any  special  office  to  the  hairs  in  some  other 
situations,  but  their  general  uses  are  sufficiently  evident. 

Perspiration. 

.  In  the  fullest  acceptation  of  the  term,  perspiration  embraces  the  entire  function  of  the 
skin  as  an  excreting  organ  and  includes  the  exhalation  of  carbonic  acid  as  well  as  of 
watery  vapor  and  organic  matter.  The  office  of  the  skin  as  an  eliminator  is  undoubtedly 
very  important ;  but  the  quantity  of  excrementitious  matters  with  the  properties  of  which 
we  are  well  acquainted,  such  as  carbonic  acid  and  urea,  thrown  off  from  the  general  sur- 
face is  small  as  compared  with  the  amount  exhaled  by  the  lungs  and  discharged  by  the 
kidneys.  If  the  surface  of  the  body  be  covered  with  an  impermeable  coating,  death 
occurs  in  a  very  short  time ;  but  the  phenomena  which  precede  the  fatal  result  are  diffi- 
cult to  explain.  All  that  we  can  say  upon  this  point  is  that  death  takes  place  when  the 
heat  of  the  body  has  been  reduced  to  about  Y0°  Fahr.,  and  that  suppression  of  the 
function  of  the  skin  in  this  way  is  always  followed  by  a  depression  of  the  animal  tem- 
perature. The  cause  of  death  has  never  been  satisfactorily  explained,  partly  for  the 
reason  that  we  are  unacquainted  with  the  nature  and  properties  of  all  the  excrementitious 
matters  exhaled  from  the  skin  ;  and  it  is  not  easy  to  understand  why  coating  the  surface 
should  be  followed  by  such  a  rapid  diminution  in  the  general  temperature.  The  experi- 
mental facts,  however,  indicate  that  the  skin  probably  possesses  important  functions  with 
.which  we  are  entirely  unacquainted.  Physiological  chemists  have  detected  urea  and  some 
other  effete  matters  in  the  perspiration,  but  it  is  probable  that  some  volatile  principles 
are  eliminated  by  the  general  surface,  which  have  thus  far  escaped  observation. 

Sudoriparous  Glands. — The  most  numerous  and  the  most  important  glands  of  the 
skin  are  those  which  secrete  the  sweat.  The  other  glands,  which  have  been  already 
considered,  have  rather  a  mechanical  function,  serving  to  keep  the  skin  and  its  append- 
ages in  a  proper  condition  for  the  protection  of  the  subjacent  parts ;  but  it  is  the  perspir- 
atory apparatus  chiefly  which  is  concerned  in  the  great  function  of  elimination. 

With  few  exceptions,  every  portion  of  the  skin  is  provided  with  sudoriparous  glands. 
They  are  not  found,  however,  in  the  skin  covering  the  concave  surface  of  the  concha  of 
the  ear,  the  glans  penis,  the  inner  lamella  of  the  prepuce,  and,  unless  the  ceruminous  glands 
be  regarded  as  sudoriparous  organs,  in  the  external  auditory  meatus. 

On  examining  the  surface  of  the  skin  with  a  low 
magnifying  power,  especially  on  the  palms  of  the 
hands  and  the  soles  of  the  feet,  the  orifices  of  the 
sudoriferous  ducts  may  be  seen  in  the  middle  of  the 
papillary  ridges,  forming  a  regular  line  in  the  shal- 
low groove  between  the  two  rows  of  papilla3.  The 
tubes  always  open  upon  the  surface  obliquely.  If 
a  thin  section  of  the  skin  be  carefully  made  and 
examined  microscopically,  the  ducts  are  seen  pass- 
ing through  the  different  layers  and  terminating 
in  rounded,  convoluted  coils  in  the  subcutaneous 
structure.  These  little,  rounded  or  ovoid  bodies, 
which  constitute  the  sudoriparous,  or  sweat-pro- 
ducing apparatus,  may  be  seen  attached  to  the  un- 
der surface  of  the  skin,  when  it  has  been  removed 
from  the  subjacent  parts  by  maceration.  The  per- 
spiratory apparatus  consists,  indeed,  of  a  simple 
tube,  presenting  a  coiled  mass  beneath  the  skin,  the 

sudoriparous  portion,  and  a  tube  of  greater  or  less  length,  in  proportion  to  the  thickness 
of  the  cutaneous  layers,  which  is  the  excretory  duct,  or  the  sudoriferous  portion. 


FIG.  111. — Surface  of  the  palm  of  the  hand : 
a  portion  of  the  skin  about  one-half 
an  inch  square,  magnified  4  diameters. 
(Sappey.) 

1, 1, 1, 1,  openings  of  the  sudoriferous  ducts ;  2, 
2,  2,  2,  grooves  between  the  papillae  of  the 
skin. 


392 


EXCKETIOK 


The  glandular  coils  vary  in  size  from  yfy  to  fa  of  an  inch  ;  the  smallest  coils  being 
found  beneath  the  skin  of  the  penis,  the  scrotum,  the  eyelids,  the  nose,  and  the  convex 
surface  of  the  concha  of  the  ear,  and  the  largest,  on  the  areola  of  the  nipple  and  the  peri- 
neum. Very  large  glands  are  found  mixed  with  smaller  ones  in  the  axilla,  but  these 
produce  a  peculiar  secretion  which  will  be  specially  considered.  The  coiled  portion  of 
the  tube  is  about  -g-f^  of  an  inch  in  diameter  and  forms  from  six  to  twelve  convolutions. 
It  consists  of  a  sharply-defined,  strong,  external  membrane,  from  ^Vo  to  irsVo  of  an  incn 
in  thickness,  very  transparent,  uniformly  granular,  and  sometimes  indistinctly  striated. 
This  is  of  uniform  diameter  throughout  the  coil  and  terminates  in  a  very  slightly  dilated, 
rounded,  blind  extremity.  It  is  filled  with  epithelium  in  the  form  of  finely  granular  mat- 
ter, usually  not  segmented  into  cells,  and  provided  with  small,  oval  nuclei.  The  glandu- 
lar mass  is  surrounded  by  a  plexus  of  capillary  blood-vessels,  which  send  a  few  small 
branches  between  the  convolutions  of  the  coil.  Sometimes  the  coil  is  enclosed  in  a  deli- 
cate fibrous  envelope. 

The  excretory  duct  is  simply  a  continuation  of  the  glandular  coil.  Its  course  through 
the  layers  of  the  true  skin  is  nearly  straight.  It  then  passes  into  the  epidermis  between 
the  papillaa  of  the  corium,  and  presents,  in  this  layer,  a  number  of  spiral  turns.  The 
spirals  vary  in  number  according  to  the  thickness  of  the  epidermis.  Sappey  has 
found  from  six  to  ten  in  the  palms  of  the  hands  and  from  twelve  to  fifteen  in  the  soles 
of  the  feet.  As  it  emerges  from  the  glandular  coil,  the  excretory  duct  is  somewhat  nar- 
rower than  the  tube  in  the  secreting  portion  ;  but,  as  it  passes  through  the  epidermis,  it 

again  becomes  larger.  It  possesses  the  same  external 
membrane  as  the  glandular  coil  and  is  lined  generally 
by  two  layers  of  cells  of  pavement-epithelium. 

In  a  section  of  the  skin  and  the  subcutaneous  tissue, 
involving  several  of  the  sudoriparous  glands  with  their 
ducts,  it  is  seen  that  the  glandular  coils  are  generally 
situated  at  different  planes  beneath  the  skin,  as  is  indi- 
cated in  Fig.  112. 

Kobin  has  described  a  variety  of  sudoriparous  glands 
in  the  axilla,  which  do  not  differ  so  much  from  the 
glands  in  other  parts  in  their  anatomy  as  in  the  charac- 
ter of  their  secretion.  The  coil  in  these  glands  is  much 
larger  than  in  other  parts,  measuring  from  fa  to  fa  of 
an  inch  ;  the  walls  of  the  tube  are  thicker,  and  they 
present  an  investment  of  fibrous  tissue  with  an  internal 
layer  of  longitudinal,  unstriped  muscular  fibres;  and, 
finally,  the  tubes  of  the  coil  itself  are  lined  with  cells 
of  pavement-epithelium.  They  are  very  numerous  in 
the  axilla,  forming  a  continuous  layer  beneath  the  skin. 
Mixed  with  these,  are  a  few  glands  of  the  ordinary  va- 
riety. 

Estimates  have  been  made  by  different  writers  of 
the  absolute  number  of  sudoriparous  glands  in  the  body 
an<*  ^Q  Probal)le  extent  of  the  exhalant  surface  of  the 
skin*  One  of  the  most  carefu^  and  probably  the  most 
reliable  of  these  estimates,  is  that  made  by  Krause; 
^ut,  ^e  all  estimates  of  this  kind,  the  results  are  to 
be  taken  as  merely  approximative.  Krause  found 
great  differences  in  the  number  of  perspiratory  open- 

ings in  different  portions  of  the  skin,  and  he  estimated  the  number  in  a  square  inch  in 
certain  parts  as  follows:  On  the  forehead,  he  found  1,258  glands  to  a  square  inch;  on 
the  cheeks,  548;  on  the  anterior  and  lateral  portions  of  the  neck,  1,303;  on  the  breast 


FlG' 


PERSPIEATIOK  393 

and  abdomen,  1,136 ;  on  the  back  of  the  neck,  the  back,  and  the  nates,  417;  on  the  fore- 
arm, inner  surface,  1,123,  and  the  outer  surface,  1,093;  on  the  hand,  palmar  surface, 
2,736,  and  dorsal  surface.  1,490  ;  on  the  upper  part  of  the  thigh,  inner  surface,  576,  outer 
surface,  554 ;  on  the  lower  part  of  the  thigh,  inner  surface,  576 ;  on  the  foot,  plantar 
surface,  2,685,  and  dorsal  surface,  924.  From  these  figures,  it  is  estimated  that  the 
entire  number  of  perspiratory  glands  is  2,381,248;  and,  assuming  that  each  coil  when 
unravelled  measures  about  -£$  of  an  inch,  the  entire  length  of  the  secreting  tubes  is 
about  2£  miles.  It  must  be  remembered,  however,  that  the  length  of  the  secreting  coil 
only  is  given,  and  that  the  excretory  ducts  are  not  included. 

Mechanism  of  the  Secretion  of  Sweat. — The  action  of  the  skin  as  a  glandular  organ  is 
continuous  and  not  intermittent ;  but,  under  ordinary  conditions,  the  sweat  is  exhaled 
from  the  general  surface  in  the  form  of  vapor.  With  regard^to  the  mechanism  of  its  sepa- 
ration from  the  blood,  nothing  is  to  be  said  in  addition  to  the  general  remarks  upon  the 
subject  of  secretion ;  and  it  is  probable  that  the  epithelium  of  the  secreting  coils  is  the 
active  agent  in  the  selection  of  the  peculiar  matters  which  enter  into  its  composition. 
There  are  no  examples  of  the  separation  by  glandular  organs  of  vapor  from  the  blood, 
and  the  perspiration  is  secreted  as  a  liquid,  and  only  becomes  vaporous  as  it  is  discharged 
upon  the  surface. 

The  influence  of  the  nervous  system  upon  the  secretion  of  sweat  is  remarkable.  It  is 
well  known,  for  example,  that  an  abundant  production  of  perspiration  is  frequently  the 
result  of  mental  emotions.  Bernard  has  shown,  in  a  series  of  interesting  experiments,  that 
the  nervous  influence  may  be  propagated  through  the  sympathetic  system.  In  one  of  these 
observations,  he  divided  the  sympathetic  in  the  neck  of  a  horse,  producing,  as  a  conse- 
quence, an  elevation  in  temperature  and  an  increase  in  the  arterial  pressure  in  the  part 
supplied  with  branches  of  the  nerve.  He  found,  also,  that  the  skin  of  the  part  became 
covered  with  a  copious  perspiration.  Upon  galvanizing  the  divided  extremity  of  the  nerve, 
the  secretion  of  sweat  was  arrested.  When  the  skin  is  in  a  normal  condition,  after  exer- 
cise or  whenever  there  is  a  tendency  to  elevation  of  the  animal  temperature,  there  is  a 
determination  of  blood  to  the  surface,  accompanied  with  an  increase  in  the  secretion  of 
sweat.  This  is  the  case  when  the  body  is  exposed  to  a  high  temperature  ;  and  it  is  by 
an  increase  in  the  transpiration  from  the  surface  that  the  animal  heat  is  maintained  at  the 
normal  standard. 

Quantity  of  Cutaneous  Exhalation. — The  amount  of  cutaneous  exhalation  is  subject 
to  great  variations,  depending  upon  conditions  of  temperature  and  moisture,  exercise,  the 
quantity  and  character  of  the  ingesta,  etc.  Most  of  these  variations  relate  to  the  func- 
tion of  the  skin  in  regulating  the  temperature  of  the  body ;  and  it  is  probable  that  the 
elimination  of  excrementitious  matters  by  the  skin  is  not  subject,  under  normal  condi- 
tions, to  the  same  modifications,  although  positive  experiments  upon  this  point  are  want- 
ing. It  is  not  designed,  in  this  connection,  to  discuss  all  the  experiments  that  have  been 
made  upon  the  quantity  and  the  modifications  of  the  cutaneous  exhalations,  and  we  shall 
consider  only  what  appear  to  be  the  most  reliable  of  the  numerous  recorded  observations 
upon  this  subject.  The  classical  experiments  of  Sanctorius  were  among  the  first  at- 
tempts to  determine  by  the  balance  the  relations  of  the  ingesta  to  the  exhalations ;  but 
these  were  necessarily  imperfect,  on  account  of  the  difficulty  in  constructing  proper  in- 
struments for  the  investigations,  and  the  cutaneous  and  pulmonary  exhalations  were  esti- 
mated together.  When  there  is  such  a  wide  range  of  variation  in  different  individuals 
and  in  the  same  person  under  different  conditions  of  season,  climate,  etc.,  it  is  only  pos- 
sible to  give  approximate  estimates  of  the  quantity  of  sweat  secreted  and  exhaled  in  the 
twenty-four  hours ;  and  more  recent  observations  have  shown  that  the  calculations  of 
Seguin  and  Lavoisier,  made  in  1790,  are  very  nearly  correct.  These  observers  estimated 
the  daily  quantity  of  cutaneous  transpiration  at  about  two  pounds  (one  pound  and  four- 


394  EXCRETION. 

teen  ounces).  The  estimates  of  Krause  and  of  Valentin  are  a  little  less,  but  the  difference 
is  not  considerable. 

Under  violent  and  prolonged  exercise,  the  loss  of  weight  by  exhalation  from  the  skin 
and  lungs  may  become  very  considerable.  It  is  stated  by  Mr.  Maclaren,  the  author  of 
an  excellent  work  on  training,  that,  in  one  hour's  energetic  fencing,  the  loss  by  perspira- 
tion and  respiration,  taking  the  average  of  six  consecutive  days,  was  about  three  pounds, 
or,  accurately,  forty  ounces,  with  a  range  of  variation  of  eight  ounces. 

When  the  body  is  exposed  to  a  very  high  temperature,  the  amount  of  exhalation  from 
the  surface  is  immensely  increased ;  and  it  is  by  this  rapid  evaporation  that  persons  have 
been  able  to  endure  for  several  minutes  a  dry  heat  considerably  exceeding  that  of 
boiling  water.  Dr.  South  wood  Smith  made  some  very  interesting  observations  with 
regard  to  this  point  upon  workmen  employed  about  the  furnaces  of  gas-works  and  exposed 
to  intense  heat ;  and  he  found  that,  in  an  hour,  the  loss  of  weight  amounted  to  from  two 
to  four  pounds,  this  being  chiefly  by  exhalation  of  watery  vapor  from  the  skin.  In  such 
instances,  the  loss  of  water  by  transpiration  is  supplied  constantly  by  the  ingestion  of 
large  quantities  of  liquid. 

Properties  and,  Composition  of  the  Sweat. — A  very  complete  and  satisfactory  analysis 
of  the  sweat  was  made  by  Favre,  in  1853.  After  taking  every  precaution  to  obtain  the 
secretion  in  a  perfectly  pure  state,  he  collected  a  very  large  quantity,  nearly  thirty  pints 
(fourteen  litres),  the  result  of  six  transpirations  from  one  person,  which  he  assumed  to 
represent  about  the  average  in  composition.  The  liquid  was  perfectly  limpid,  colorless, 
and  of  a  feeble  but  characteristic  odor.  Almost  all  observers  have  found  the  reaction  of 
the  sweat  to  be  acid ;  but  it  readily  becomes  alkaline  on  being  subjected  to  evaporation, 
showing  that  it  contains  some  of  the  volatile  acids.  In  the  experiments  of  Favre,  it  was 
found  that  the  fluid  collected  during  the  first  half-hour  of  the  observation  was  acid,  during 
the  second  half-hour  it  was  neutral  or  feebly  alkaline,  and  during  the  third  half-hour,  con- 
stantly alkaline.  The  specific  gravity  of  the  sweat  is  from  1003  to  1004.  The  following 
is  the  composition  of  the  fluid  collected  by  Favre : 

Composition  of  the  Sweat. 

Water 995-573 

Urea 0-043 

Fatty  matters 1 0'014 

Alkaline  lactates 0-317 

Alkaline  sudorates 1'562 

Chloride  of  sodium,       ")    2*230 

Chloride  of  potassium,       0*244 

Alkaline  sulphates,         j*  soluble  in  water 0'012 

Alkaline  phosphates,      j    a  trace. 

Alkaline  albuminates,  J   0'005 

Alkaline  earthy  phosphates  (soluble  in  acidulated  water) a  trace. 

Epidermic  debris  (insoluble) a  trace. 

1,000-000 

We  have  already  alluded  to  the  functions  of  the  skin  as  a  respiratory  organ  and  its 
office  in  regulating  the  temperature  of  the  body  by  the  evaporation  of  what  is  known  as 
the  insensible  perspiration  ;  but  the  composition  of  the  sweat  indicates  clearly  that  the  skin 
is  an  important  organ  of  excretion.  Urea  is  now  known  to  be  a  constant  constituent  of 
the  sweat,  and  the  compounds  of  sudoric  acid  are  probably  excrementitious  in  their  char- 
acter, although  they  have  not  yet  been  detected  in  the  blood  or  in  any  of  the  tissues. 
The  quantity  of  urea,  under  ordinary  conditions,  is  not  large ;  but  it  is  well  known  that  its 
proportion  in  the  sweat  is  very  much  increased  when  there  is  deficient  elimination  by  the 


PHYSIOLOGICAL  ANATOMY  OF  THE  KIDNEYS.  395 

kidneys.  The  sudoric  acid,  obtained  by  decomposition  of  the  sudorates  of  soda  and  of 
potassa,  is  a  nitrogenized  substance,  with  a  formula,  according  to  Favre,  who  first  de- 
scribed it,  of  CioH8Oi3  K  The  nature  of  the  volatile  acid  has  not  yet  been  determined. 
The  fatty  matters  are  probably  produced  by  the  sebaceous  glands,  and  the  ordinary 
nitrogenized  matters  are  derived  from  the  epidermic  scales.  With  regard  to  the  in- 
organic constituents,  there  is  no  great  interest  attached  to  any  but  the  chloride  of  sodium, 
which,  exists  in  a  proportion  many  times  greater  than  that  of  all  the  other  inorganic  mat- 
ters combined. 

Peculiarities  of  the  Sweat  in  Certain  Parts. — In  the  axilla,  the  inguino-scrotal  region 
in  the  male,  and  the  inguino-vulvar  region  in  the  female,  and  between  the  toes,  the  sweat 
always  has  a  peculiar  odor,  more  or  less  marked,  which,  in  some  persons,  is  excessively 
disagreeable.  Donne  has  shown  that  whenever  the  secretion  has  an  odor  of  this  kind 
its  reaction  is  distinctly  alkaline ;  and  he  is  disposed  to  regard  its  peculiar  characters  as 
due  to  a  mixture  of  the  secretion  of  the  other  follicles  found  in  these  situations.  Some- 
times the  sweat  about  the  nose  has  an  alkaline  reaction.  In  the  axillary  region,  the 
secretion  is  rather  less  fluid  than  on  the  general  surface  and  frequently  has  a  yellowish 
color,  so  marked,  sometimes,  as  to  stain  the  clothing.  The  odor  is  probably  due  to  the 
presence  of  volatile,  odorous  compounds  of  the  fatty  acids,  like  the  caproates,  the  vale- 
rates,  or  the  butyrates ;  but  the  presence  of  these  principles  has  never  been  accurately 
determined. 

Physiological  Anatomy  of  the  Kidneys. 

The  -urine  is  generally  regarded  by  physiologists  as  the  type  of  the  excrementitious 
fluids,  it  having  no  function  to  perform  in  the  economy,  but  being  simply  retained  in 
the  bladder  to  be  voided  at  convenient  intervals.  All  the  remarks,  indeed,  that  have 
been  made  concerning  excretion  in  general  may  be  applied  without  reserve  to  the  action 
of  the  kidneys ;  and  there  are  few  subjects  in  physiology  of  greater  interest  than  the 
process  of  urinary  excretion,  with  its  relations  to  nutrition  and  disassimilation.  In 
entering  upon  the  study  of  the  functions  of  the  kidneys,  it  will  be  found  useful  to  con- 
sider certain  points  in  their  anatomy. 

The  kidneys  are  symmetrical  organs,  situated  in  the  lumbar  region  beneath  the  peri- 
toneum, invested  by  a  proper  fibrous  coat,  and  always  surrounded  by  more  or  less  adipose 
tissue.  They  usually  extend  from  the  eleventh  or  twelfth  rib  downward  to  near  the 
crest  of  the  ilium,  and  the  right  is  always  a  little  lower  than  the  left.  In  shape,  the 
kidney  is  very  aptly  compared  to  a  bean ;  and  the  concavity,  the  deep,  central  portion 
of  which  is  called  the  hilum,  looks  inward  toward  the  spinal  column  The  weight  of 
each  kidney  is  from  four  to  six  ounces,  usually  about  half  an  ounce  less  in  the  female 
than  in  the  male.  The  left  kidney  is  nearly  always  a  little  heavier  than  the  right. 

Outside  of  the  proper  coat  of  the  kidney,  is  a  certain  amount  of  fatty  tissue  enclosed 
in  a  loose  fibrous  structure.  This  is  sometimes  called  the  adipose  capsule ;  but  the 
proper  coat  consists  of  a  close  net-work  of  the  ordinary  white  fibrous  tissue,  interlaced 
with  numerous  small  fibres  of  the  elastic  variety.  This  coat  is  thin  and  smooth  and  may 
be  readily  removed  from  the  surface  of  the  organ.  At  the  hilum,  it  is  continued  inward 
to  line  the  pelvis  of  the  kidney,  covering  the  calices  and  blood-vessels.  This  coat,  how- 
ever, is  not  continued  into  the  substance  of  the  kidney. 

On  making  a  vertical  section  of  the  kidney,  it  presents  a  cavity  at  the  hilum,  bounded 
internally  by  the  dilated  origin  of  the  ureter.  This  is  called  the  pelvis.  It  is  lined  by 
a  smooth  membrane,  which  is  simply  a  continuation  of  the  proper  coat  of  the  kidney, 
and  which  forms  little  cylinders,  called  calices,  into  which  the  apices  of  the  pyramids  are 
received.  Some  of  the  calices  receive  the  apex  of  a  single  pyramid;  while  others  are 
larger  and  receive  two  or  three.  The  calices  unite  into  three  short,  funnel-shaped  tubes, 
called  infundibula,  corresponding  respectively  to  the  superior,  middle,  and  inferior  por- 
tions of  the  kidney.  These  finally  open  into  the  common  cavity,  or  pelvis.  The  sub- 


396 


EXCRETION. 


stance  of  the  kidney  is  composed  of  two  distinctly-marked  portions  called  the  cortical 

substance,  and  the  medullary,  or  pyramidal  substance. 

The  cortical  substance  is  reddish  and  gran- 
ular, rather  softer  than  the  pyramidal  sub- 
stance, and  is  about  one-sixth  of  an  inch  in 
thickness.  This  occupies  the  exterior  of  the 
kidney  and  sends  little  prolongations  (col- 
umns of  Bertin)  between  the  pyramids.  The 
surface  of  the  kidney  is  marked  by  little  po- 
lygonal divisions,  giving  it  a  lobulated  appear- 
ance. This,  however,  is  simply  due  to  the 
arrangement  of  the  superficial  blood-vessels. 
The  medullary  substance  is  arranged  in  the 
form  of  pyramids,  sometimes  called  the  pyra- 
mids of  Malpighi,  from  twelve  to  fifteen  or 
eighteen  in  number,  their  bases  presenting 
toward  the  cortical  substance,  and  their  apices 
being  received  into  the  calices  at  the  pelvis. 
Ferrein  subdivided  the  pyramids  of  Malpighi 
into  smaller  pyramids  (the  pyramids  of  Fer- 
rein), each  formed  by  about  one  hundred 
tubes  radiating  from  the  openings  at  the 
summit  of  the  pyramids  toward  their  bases. 
The  tubes  composing  these  pyramids  were 
supposed  to  pass  into  the  cortical  substance, 
forming  corresponding  pyramids  of  convo- 
Fm.  us.—  Vertical  section  of  the  kidney.  (Sappey.)  luted  tubes,  thus  dividing  this  portion  of  the 

1,1,2,2,3,3,3,4,4,4,4,  pyramids  of  MaipigW;  5  5,    kidney  into   lobules,   more   or  less   distinct. 

5,  5,  5,  5,  apices  ot  the  pyramids  surrounded  by 

the  calices ;  6, 6,  columns  of  Bertin  ;  7,  pelvis  of    The  medullary  substance  is  firm,  of  a  dark- 

thekidney;  8,  upper  extremity  of  the  ureter.  ^  ^  ^^  ^  ^   ^.^   ^^^  and 

is  marked  by  tolerably  distinct  striae,  which  take  a  nearly  straight  course  from  the  bases 
to  the  apices  ol  the  pyramids.  As  these  striaa  indicate  the  direction  of  the  little  tubes 
that,  constitute  tne  greatest  part  of  the  medullary  substance,  this  is  sometimes  called  the 
tubular  portion  of  the  kidney. 

From  the  arrangement  of  the  secreting  portion  of  the  kidneys,  they  are  classed 
among  the  tubular  glands,  presenting  a  system  of  tubes,  or  canals,  some  of  which  are 
supposed  simply  to  carry  off  the  urine,  while  others  separate  the  excrementitious  con- 
stituents of  this  fluid  from  the  blood.  It  is  difficult  to  determine  precisely  where  the 
secreting  tubes  merge  into  the  excretory  ducts,  but  it  is  the  common  idea,  which  is 
probably  correct,  that  the  cortical  substance  is  the  active  portion,  while  the  tubes  of 
the  pyramidal  portion  simply  carry  off  the  excretion. 

Pyramidal  Substance. — Each  papilla,  as  it  projects  into  the  pelvis  of  the  kidney,  pre- 
sents from  ten  to  twenty-five  little  openings,  measuring  from  -g-i¥  to  -gV  of  an  inch  in 
diameter.  The  tubes  leading  from  the  pelvis  immediately  divide  at  very  acute  angles, 
generally  dichotomatously,  until  a  bundle  of  tubes  arises,  as  it  were,  from  each  opening. 
These  bundles  constitute  the  pyramids  of  Ferrein.  In  their  course,  the  tubes  are  slightly 
wavy  and  are  nearly  parallel  with  each  other.  These  are  called  the  straight  tubes  of  the 
kidney,  or  the  tubes  of  Bellini.  They  extend  from  the  apices  of  the  pyramids  to  their 
bases  and  pass  then  into  the  cortical  substance.  The  pyramids  contain,  in  addition  to 
the  straight  tubes,  a  delicate  fibrous  matrix  and  numerous  blood-vessels ;  which  latter, 
for  the  most  part,  pass  beyond  the  pyramids,  to  be  finally  distributed  in  the  cortical 
substance.  Kecent  researches  have  shown  that  some  of  the  convoluted  tubes  dip  down 


PHYSIOLOGICAL  ANATOMY   OF  THE  KIDNEYS. 


397 


into  the  pyramids,  returning  to  the  cortical  substance  in  the  form  of  loops.  This  ar- 
rangement will  be  fully  described  in  connection  with  the  cortical  substance. 

The  tubes  of  the  pyramidal  substance  are  composed  of  a  strong,  structureless  base- 
ment-membrane, lined  with  granular,  nucleated  cells.  According  to  the  researches  of 
Bowman,  the  tubes  measure  from  ^-Q-  to  -^-^  of  an  inch  in  diameter  at  the  apices,  and 
near  the  bases  of  the  pyramids  their  diameter  is  about  -^  of  an  inch.  The  membrane 
of  the  tubes  is  dense  and  resisting,  and  portions  of  it  with  the  epithelial  lining  removed 
can  generally  be  seen  in  microscopical  examinations,  when  the  pyramidal  substance  has 
been  simply  lacerated  with  needles.  This  membrane  is  from  -^fo^  to  FFCW  °f  an  inch 
in  thickness. 

The  cells  lining  the  straight  tubes  exist  in  a  single  layer  applied  to  the  basement- 
membrane.  They  are  thick,  irregularly  polygonal  in  shape,  and  contain  numerous  albu- 
minoid granules.  They  present  one,  and  occasionally,  though  rarely,  two  granular  nuclei, 
with  one  or  two  nncleoli.  They  are  very  liable  to  alteration  and  are  only  seen  in  the 


FIG.  114  (A).— Longitudinal  section  of  the^pyram- 
idal  substance  of  the  kidney  of  the  foetus. 
(Sappey.) 

1,  trunk  of  a  lasge  urinifcrous  tube  ;  2,  2,  primary 
branches  of  this  tube  ;  3, 3, 3,  secondary  branches  ; 
4,  4, 5, 5,  6,  6,  7,  7,  7,  7,  branches  becoming  smaller 
and  smaller  ;  8,  8,  8, 8,  loops  of  the  tubes  of  Henle. 

normal  condition  in  a  perfectly  fresh,  healthy  kidney.     Their  diameter  is  about 
an  inch.     The  caliber  of  the  tubes  is  reduced  by  the  thickness  of  their  lining  epithe- 
lium to  TfifK  or  T^rff  of  an  inch. 


FIG.  114  (B).—  Longitudinal  section  of  the  cortical  sub- 
stance of  the  same  kidney.    (Sappey.) 
1, 1,  limit  of  the  cortical  substance  and  base  of  the  pyra- 
mids ;  2,  2,  2,  tubes  passing  toward  the  surface  of  the 
kidney  ;  3,  3,  3,  8,  8,  8,  convoluted  tubes  ;  4,  4,  4,  4,  5, 
Malpighian  bodies ;  (5,  6,  artery,  with  its  branches  (7, 7, 
7) ;  9,  9,  fibrous  covering  of  the  kidney. 


398 


EXCRETION. 


Cortical  Substance. — In  the  cortical  portion  of  the  kidney,  are  found  numerous  tubes, 
differing  somewhat  from  the  tubes  of  the  pyramidal  portion  in  their  size  and  in  the  char- 
acter of  their  epithelial  lining,  but  presenting  the  most  marked  difference  in  their  direc- 
tion. These  tubes  are  somewhat  larger  than  the  tubes  of  pyramidal  substance  and  are  very 
much  convoluted,  interlacing  with  each  other  inextricably  in  every  direction.  Scattered 
pretty  uniformly  throughout  this  portion  of  the  kidney,  are  rounded  or  ovoid  bodies,  about 
four  times  the  diameter  of  the  convoluted  tubes,  known  as  the  Malpighian  bodies.  At 
one  time  there  was  considerable  difference  of  opinion  with  regard  to  the  relation  of 
these  bodies  to  the  tubes ;  but  the  researches  of  Bowman,  Isaacs,  and  later  anatomists, 

have  established,  without  doubt,  the  fact  that 
they  are  simply  flask-like,  terminal  dilatations 
of  the  tubes  themselves. 

As  the  result  of  recent  researches,  the  cor- 
tical portion  of  the  kidney  is  now  regarded  as 
presenting  a  delicate  fibrous  matrix,  which 
forms  a  sort  of  skeleton  for  the  support  of 
the  secreting  portion  with  its  blood-vessels. 
The  tubes  of  this  portion  are  convoluted  and 
somewhat  larger  than  the  straight  tubes,  but 
are  continuous  with  them,  terminating  finally 
in  the  Malpighian  bodies.  The  researches  of 
late  anatomists,  however,  particularly  in  Ger- 
many, have  shown  that  this  simple  view  of 
the  course  and  termination  of  the  tubes  of  the 
cortical  substance  must  be  somewhat  modified ; 
although,  as  far  as  the  anatomy  of  the  organ 
has  any  bearing  upon  our  ideas  concerning  the 
mechanism  of  the  secretion  of  urine,  the  views 
of  physiologists  need  undergo  no  material 
change. 

The  tubes  of  the  cortical  substance  present 
considerable  variations  in  size,  and,  instead  of 
a  single  system  continuous  with  the  straight 
tubes  and  terminating  in  the  Malpighian  bod- 
ies, we  can  distinguish  three  well-defined  varie- 
ties: 

1.  The  ordinary  convoluted  tubes,  directly 
connected  with  the  Malpighian  bodies.  2. 
Small  tubes,  continuous  with  the  convoluted 
tubes,  dipping  down  into  the  pyramids  and 
returning  to  the  cortical  portion  in  the  form  of 
loops.  3.  Large,  communicating  tubes,  form- 
ing a  plexus  connecting  the  different  varieties 

FIG.  n5.-Diagrammatic  vieio  of  the  Malpighian   °f  tubeS  with  6ach  °ther  and  fina11^  with  thc 
bodies  and  tubes  of  the  kidney.   (Sappey.)         straight  tubes  of  the  pyramidal  portion. 

11  \u2befo^!nUtnUtfh?etube;i,3i  •'  l\  t^^TS        The  relation  of  these  tubes  can  be  readily 
E^^^V5' 5' 5'  $  5'  'convofut'ed'  tubes;' 6,  understood  by  reference  to  Fig.  115.     In  trac- 

6,  66,  6,  descending  portions  of  the  looped  tubes    . 

of  Henle ;  7,  7,  7,  7,  7,  ascending,  larger  portions  of    mg  out  the  COUrse   of  the   tubes,  which   recent 

tab^fd^ii^^wi^^BfflS'S'Sl  observations  have  shown  to  be  somewhat  intri- 
corticai  and  of  the  pyramidal  substance.  k  cate,  it  will  be  found  most  convenient  to  com- 

mence with  a  description  of  the  Malpighian 

bodies  and  to  follow  the  course  of  the  tubes  from  these  bodies  to  their  connections  with 

the  straight  tubes  of  the  pyramidal  substance. 


PHYSIOLOGICAL  ANATOMY   OF  THE  KIDNEYS.  399 

Malpighian  Bodies. — These  are  ovoid  or  rounded  terminal  dilatations  of  the  convo- 
luted tubes,  of  somewhat  variable  size,  measuring  from  ^  to  T-i-g-  of  an  inch  in  diam- 
eter. They  are  composed  of  a  membrane  continuous  with  the  external  membrane  of 
the  convoluted  tubes,  of  the  same  homogeneous  character,  but  somewhat  thicker,  meas- 
uring about  ^oio-o  of  an  mcn>  while  the  membrane  of  the  tubes  is  only  about  40^00-  of  an 
inch  in  thickness.  This  sac,  which  is  sometimes  called  the  capsule  of  Muller,  encloses  a 
mass  of  convoluted  blood-vessels  and  is  lined  with  a  layer  of  nucleated  epithelial  cells. 
In  addition  to  these  pale,  delicate  cells  lining  the  capsule,  there  are  other  cells  which  are 
applied  to  the  blood-vessels.  These  latter  cells  are  probably  concerned  in  the  elimina- 
tion of  the  solid  constituents  of  the  urine. 

The  cells  attached  to  the  capsule  of  Muller  are  smaller  and  more  transparent  than 
those  lining  the  convoluted  tubes.  They  are  ovoid,  nucleated,  and  finely  granular.  The 
cells  covering  the  vessels,  however,  are  larger  and  more  opaque,  and  they  resemble  the 
epithelium  lining  the  tubes.  They  measure  from  y^1-^  to  T¥Vo  °f  an  mc^  m  diameter,  by 
about  -g-jVo-  of  an  inch  in  thickness.  • 

Tubes  of  the  Cortical  Substance. — Following  out  the  tubes  in  the  cortical  substance 
from  the  Malpighian  bodies,  we  find  first  a  short,  constricted  portion,  which  is  some- 
times called  the  neck  of  the  capsule.  The  tube  soon  dilates  to  the  diameter  of  about 
TTO  °f  an  inch,  when  its  course  becomes  exceedingly  intricate  and  convoluted.  These 
are  what  are  known  as  the  convoluted  tubes  of  the  kidney.  The  membrane  of  these 
tubes  is  transparent  and  homogeneous,  but  quite  firm  and  resisting.  It  measures  about 
4(^60  of  an  m°h  in  thickness.  It  is  lined  throughout  with  a  single  layer  of  rounded 
or  irregularly  polygonal  epithelial  cells,  from  y^Vfr  to  ygVg-  of  an  inch  in  diameter,  some- 
what larger,  consequently,  than  the  cells  lining  the  straight  tubes.  These  cells  are 
nucleated  and  usually  quite  granular.  It  has  been  found  that,  in  many  of  the  lower  orders 
of  animals,  the  cells  lining  the  neck  of  the  capsule  are  provided  with  vibratile  cilia ;  and 
it  is  possible  that  they  may  exist  in  man,  although  their  presence  has  never  been  actually 
demonstrated. 

The  course  of  the  tubes,  after  they  have  lost  the  characters  which  were  formerly  sup- 
posed to  be  peculiar  to  the  tubes  of  the  cortical  substance,  and  their  anastomoses,  have 
attracted  much  attention  within  the  last  few  years.  It  has-  been  shown  by  Henle,  and 
the  most  important  points  in  his  observations  have  been  confirmed  by  numerous  anato- 
mists, that  the  convoluted  tubes,  instead  of  connecting  directly  with  the  tubes  of  the 
pyramidal  substance,  are  continuous  with  a  system  of  smaller  tubes,  which  pass  into  the 
pyramids  in  the  form  of  loops. 

Narrow  Tubes  of  Henle. — According  to  the  most  recent  observations,  the  convoluted 
tubes  above  described,  after  a  long  and  tortuous  ramification  in  the  cortical  substance, 
invariably  become  continuous,  near  the  pyramids,  with  tubes  of  much  smaller  diameter, 
which  form  loops,  extending  to  a  greater  or  less  depth  into  the  pyramids.  The  loops 
formed  by  these  canals  (the  narrow  tubes  of  Henle)  are  nearly  parallel  with  the  tubes  of 
Bellini  and  are  much  more  numerous  near  the  bases  of  the  pyramids  than  toward  the 
apices.  The  diameter  of  these  tubes  is  very  variable,  and  they  present  enlargements  at 
irregular  intervals  in  their  course.  The  narrow  portions  are  about  yjnnr  °f  an  mc^  m 
diameter,  and  the  wide  portions,  about  twice  this  size.  The  narrow  portion  is  lined  by 
small,  clear  cells  with  very  prominent  nuclei.  The  wider  portions  are  lined  by  larger, 
granular  cells.  Near  the  bases  of  the  pyramids,  the  wide  portion  sometimes  forms  the 
loop  ;  but,  near  the  apices,  the  loop  is  always  narrow.  The  difference  in  the  size  of  the 
epithelium  is  such,  that,  while  the  diameter  of  the  tube  is  variable,  its  caliber  remains 
nearly  uniform.  The  membrane  of  these  tubes  is  quite  thick,  thicker,  even,  than  the 
membrane  of  the  tubes  of  Bellini. 

Intermediate  Tubes. — After  the  narrow  tubes  of  Henle  have  returned  to  the  cortical 
substance,  they  communicate  with  a  system  of  flattened,  ribbon-shaped  canals,  measuring 
from  y^-fr  to  ToYo  °f  an  mch  in  diameter,  with  excessively  thin,  fragile  walls,  lined  by 


400  EXCRETION. 

clear  pavement-epithelium.  These  tubes  take  an  irregular  and  somewhat  angular  course 
between  the  true  convoluted  tubes  and  finally  empty  into  the  branches  of  the  straight 
tubes  of  Bellini,  thus  establishing  a  communication  between  the  tubes  coming  from  the 
Malpighian  bodies  and  the  tubes  of  the  pyramidal  substance.  They  are  called  the  inter- 
mediate tubes,  or  the  canals  of  communication.  Some  observers  have  described  them  as 
forming  an  anastomosing  plexus,  but  this  disposition  is  not  definitely  established. 

The  tubes  into  which  the  intermediate  canals  open  join  with  others,  generally  two  by 
two,  and  then  pass  in  a  nearly  straight  direction  into  the  pyramids,  where  they  continue 
to  unite  with  each  other  in  their  course,  becoming,  consequently,  less  and  less  numerous, 
until  they  open  at  the  apices  of  the  pyramids  into  the  infundibula  and  the  pelvis  of  the 
kidney. 

Distribution  of  Blood-vessels  in  the  Kidney.— The  renal  artery,  which  is  quite  volumi- 
nous in  proportion  to  the  size  of  the  kidney,  enters  at  the  hilum  and  divides  into  four 
branches.  By  numerous  smaller  branches  it  then  penetrates  between  the  pyramids  and 
ramifies  in  the  columns  of  cortical  substance  which  occupy  the  spaces  between  the  pyra- 
mids (columns  of  Bertin).  The  main  vessels,  which  are  generally  two  in  number,  occupy 
the  centre  of  the  columns  of  Bertin,  sending  off  in  their  course,  at  short  intervals,  regular 
branches  on  either  side,  toward  the  pyramids.  When  these  branches  reach  the  boundary 
of  the  cortical  substance,  they  turn  upward  and  follow  the  periphery  of  the  pyramid  to 
its  base.  Here  the  vessels  form  an  arched,  anastomosing  plexus,  situated  exactly  at  the 
boundary  which  separates  the  rounded  base  of  the  pyramid  from  the  cortical  substance. 
This  plexus  presents  a  convexity  looking  toward  the  cortical  substance,  and  a  concavity, 
toward  the  pyramid.  It  is  so  arranged  that  the  interstices  are  just  large  enough  to  admit 
the  collections  of  tubes  that  form  the  so-called  pyramids  of  Ferrein. 

From  the  arterial  arcade,  branches  are  given  off  in  two  opposite  directions.  From 
its  concavity,  numerous  small  branches,  measuring  at  first  from  T^Vo  to  yfo  °f  an  ^nc^  m 
diameter,  pass  downward  toward  the  papillaB,  giving  off  small  ramifications  at  very  acute 
angles  and  becoming  reduced  in  size  to  about  ^Vff  of  an  inch.  These  vessels — called 
sometimes  the  arteriolas  rectaB — surround  the  straight  tubes  and  pass  into  capillaries  in 
the  substance  of  the  pyramids  and  at  their  apices. 

From  the  convex  surface  of  the  arterial  arcade,  numerous  branches  are  given  off  at 
nearly  right  angles.  These  pass  into  the  cortical  substance,  breaking  up  into  a  large  num- 
ber of  little  arterial  twigs,  from  ^-^Vo  to  -g^-g-  of  an  inch  in  diameter,  each  one  of  which 
penetrates  a  Malpighian  body  at  a  point  opposite  to  the  origin  of  the  convoluted  tube. 
Once  within  the  capsule,  the  arteriole  breaks  up  into  from  five  to  eight  branches,  which 
then  divide  dichotomatously  into  vessels  measuring  from  ^Vo  to  TTOTJ-  °f  an  incn  iQ  diame- 
ter, arranged  in  the  form  of  coils  and  loops,  constituting  a  dense,  rounded  mass  (the 
Malpighian  coil),  filling  the  capsule.  These  vessels  break  up  into  capillaries  without 
anastomoses.  Their  coats  are  amorphous  and  are  provided  with  numerous  nuclei  rather 
shorter  than  those  found  in  the  general  capillary  system. 

The  blood  is  collected  from  the  vessels  of  the  Malpighian  bodies  by  veins,  sometimes 
one,  and  frequently  three  or  four,  which  pass  out  of  the  capsule  and  form  a  second  capil- 
lary plexus  surrounding  the  convoluted  tubes.  When  there  is  but  one  vein,  it  generally 
emerges  from  the  capsule  near  the  point  of  penetration  of  the  arteriole.  The  walls  of 
the  vein  are  much  more  fragile  than  those  of  the  arteriole,  and,  consequently,  in  ordinary 
microscopical  preparations  of  the  cortical  substance,  the  arteriole  is  left  attached,  while 
the  veins  are  torn  off. 

The  efferent  vessels,  immediately  after  their  emergence  from  the  capsule,  break  up 
into  a  very  fine  and  delicate  plexus  of  capillaries,  closely  surrounding  the  convoluted 
tubes.  These  form  a  true  plexus,  the  branches  anastomosing  freely  in  every  direction  ; 
and  the  distribution  of  vessels  in  this  part  resembles  essentially  the  vascular  arrangement 
in  most  of  the  glands.  Bowman  has  called  the  branches  which  connect  together  the 


MECHANISM  OF  THE  PRODUCTION   OF  URINE. 


401 


vessels  of  the  Malpighian  tuft  and  the  capillary  plexus  surrounding  the  tubes,  the  portal 
system  of  the  kidney.     These  intermediate  vessels  form  a  coarse  plexus  surrounding  the 
prolongations  of  the  pyramids  of  Ferrein  into 
the  cortical  substance. 

The  renal,  or  emulgent  vein  takes  its  origin 
in  part  from  the  capillary  plexus  surrounding  the 
convoluted  tubes  and  in  part  from  the  vessels 
distributed  in  the  pyramidal  substance.  A  few 
branches  come  from  vessels  in  the  envelopes  of 
the  kidney,  but  these  are  comparatively  unim- 
portant. The  plexus  surrounding  the  convoluted 
tubes  empties  into  venous  radicles,  which  pass 
to  the  surface  of  the  kidney,  and  these  present  a 
number  of  little  radiating  groups,  each  converg- 
ing toward  a  central  vessel.  This  arrangement 
gives  to  the  vessels  of  the  fibrous  envelope  of  the 
kidney  a  peculiar  stellate  appearance.  These  are 
sometimes  called  the  stars  of  Verheyn.  The 
large  trunks  which  form  the  centres  of  these 
stars  then  pass  through  the  cortical  substance  to 
the  rounded  bases  of  the  pyramids,  where  they 
form  a  vaulted,  venous  plexus  corresponding  to 
the  arterial  plexus  already  described.  The  ves- 
sels distributed  upon  the  straight  tubes  of  the 
pyramidal  substance  form  a  loose  plexus  around 
these  tubes,  except  at  the  papillae,  where  the  net- 
work is  much  closer.  They  then  pass  into  the 
plexus  at  the  bases  of  the  pyramids  to  join  with 
the  veins  from  the  cortical  substance.  From  this 
plexus,  a  number  of  larger  trunks  arise  and  pass 
toward  the  hilum  in  the  centre  of  the  inter-py- 
ramidal substance,  enveloped  in  the  same  sheath 
with  the  arteries.  Passing  thus  to  the  pelvis  of 
the  kidney,  the  veins  converge  into  from  three 
to  four  great  branches,  which  unite  to  form  the 
renal,  or  emulgent  vein.  A  preparation  of  all 
the  vessels  of  the  kidneys  shows  that  the  veins 
are  much  more  voluminous  than  the  arteries. 

The  lymphatics  of  the  kidney  are  few,  and, 
according  to  Sappey,  they  only  exist  in  the  sub- 
stance of  the  organ,  converging  toward  the  hilum. 
This  author  does  not  admit  the  existence  of  su- 
perficial lymphatics. 

The  nerves  are  quite  numerous  and  are  de- 
rived from  the  solar  plexus,  their  filaments  following  the  artery  in  its  distribution  in  the 
interior  of  the  organ  and  ramifying-  upon  the  walls  of  the  vessels. 


FIG.  116.— Blood-vessels  of  the  Malpighian  bodies 
and  convoluted  tubes  of  the  kidney.  (Sappey.) 

1, 1,  Malpighian  bodies  surrounded  by  the  capsules 
of  Miiller;  2,  2,  2,  convoluted  tubes  connected 
with  the  Malpighian  body ;  3,  artery  branch- 
ing to  go  to  the  Malpighian  bodies ;  4, 4,  4, 
branches  of  the  artery ;  6,  G,  Malpighian  bodies 
from  which  a  portion  of  the  capsules  has  been 
removed ;  7.  7,  7,  vessels  passing  out  of  the 
Malpighian  bodies ;  8,  vessel,  the  branches  of 
which  (9)  pass  to  the  capillary  plexus  (10). 


Mechanism  of  the  Production  and  Discharge  of  Urine. 

The  striking  peculiarities  which  the  kidney  presents  in  its  structure,  as  compared  with 

the  true  glands,  and  the  fact  of  the  voluntary  discharge  of  its  secretion  at  certain  intervals, 

would  naturally  lead  to  a  closer  study  of  the  mechanism  of  the  production  and  discharge 

of  the  urine  than  we  have  given  under  the  general  head  of  the  mechanism  of  the  formation 

26 


402  EXCRETION. 

of  the  excretions.  The  composition  of  the  urine,  also,  will  be  found  to  be  exceedingly 
complex,  and  its  various  ingredients  bear  the  closest  relation  to  the  processes  of  nutrition 
and  disassimilation ;  all  of  which  considerations  render  it  of  the  greatest  importance  to 
ascertain  the  precise  mode  of  its  formation  and  to  study  all  the  conditions  by  which  this 
process  may  be  modified.  In  the  present  state  of  our  knowledge,  we  must  certainly  re- 
gard the  excrementitious  constituents  of  the  urine  as  formed  essentially  in  the  system  at 
large,  being  merely  separated  from  the  blood  by  the  kidneys ;  and  a  consideration  of  these 
effete  principles  belongs  to  the  subject  of  nutrition.  It  remains  for  us,  then,  in  this  con- 
nection, to  treat,  in  general  terms,  of  the  way  in  which  these  substances  find  their  way 
into  the  urine. 

The  most  important  constituent  of  the  urine  is  urea,  a  crystallizable,  nitrogenized 
substance,  which  is  discharged  by  the  skin  as  well  as  by  the  kidneys.  This  has  long  been 
recognized  as  an  excrementitious  principle ;  but  the  first  observations  that  gave  any  defi- 
nite idea  of  the  mechanism  of  its  production  were  made  by  Prevost  and  Dumas,  in  1821. 
At  the  time  these  experiments  were  made,  chemists  were  not  able  to  detect  urea  in  the 
normal  blood ;  but  Prevost  and  Dumas  extirpated  the  kidneys  from  living  animals  (dogs 
and  cats),  and  found  an  abundance  of  urea  in  the  blood,  after  certain  symptoms  of  blood- 
poisoning  had  been  manifested.  The  first  experiments  were  performed  by  removing  one 
kidney  by  an  incision  in  the  lumbar  region,  and,  at  the  end  of  three  or  four  days,  after 
the  animal  had  recovered  from  the  first  operation,  removing  the  other.  After  the  second 
operation,  the  animals  lived  for  from  five  to  nine  days.  For  the  first  two  or  three  days 
there  were  no  symptoms  of  blood-poisoning.  Watery  discharges  from  the  stomach  and 
intestinal  canal  occurred  after  a  few  days,  and  finally  stupor  and  other  marked  evidences 
of  nervous  disturbance  supervened,  when  the  presence  of  urea  in  the  blood  could  be  easily 
determined.  These  observations  were  confirmed  and  extended  by  Segalas  and  Vauque- 
lin,  in  1822,  who  presented  to  the  French  Academy  of  Medicine  a  specimen  of  nitrate 
of  urea  extracted  from  the  blood  of  a  dog,  taken  sixty  hours  after  extirpation  of  the  kid- 
neys, giving  its  proportion  to  the  weight  of  blood  employed.  Since  that  time,  as  the 
processes  for  the  determination  of  urea  in  the  animal  fluids  have  been  improved,  this 
substance  has  been  detected  in  minute  quantity  in  the  normal  blood.  Picard  carefully 
estimated  and  compared  the  proportions  of  urea  in  the  renal  artery  and  the  renal  vein, 
and  he  found  that  the  quantity  in  the  blood  was  diminished  by  about  one-half  in  its  passage 
through  the  kidneys.  Still  later,  urea  has  been  found  by  Wurtz  to  exist  in  the  lymph 
and  chyle  in  larger  quantity,  even,  than  in  the  blood.  These  facts,  which  have  been 
almost  universally  regarded  as  established,  have  led  physiologists  to  adopt  the  view  that 
the  peculiar  excrementitious  principles  found  in  the  urine  are  not  produced  by  the  kid- 
neys, but  are  formed  in  the  system  by  the  general  process  of  disassimilation,  are  taken  up 
from  the  tissues  by  the  blood,  either  directly  or  through  the  lymph,  and  are  merely 
separated  from  the  blood  in  the  kidneys ;  and  it  has  consequently  been  pretty  generally 
assumed  that  nearly,  if  not  all,  the  constituents  of  the  urine  preexist  in  the  circulating 
fluid.  There  is,  indeed,  no  well-defined  principle  in  the  urine  that  has  not  been  actually 
demonstrated  in  the  blood.  As  an  additional  argument  in  favor  of  this  view  of  the 
mechanism  of  urinary  excretion,  it  has  been  ascertained  that,  when  the  kidneys  are 
interrupted  in  their  function,  there  is  a  tendency  to  the  elimination  of  the  excrementitious 
principles  of  the  urine  by  the  lungs,  skin,  and  alimentary  canal ;  and  that  these  matters 
accumulate  in  the  blood  only  after  this  vicarious  effort  has  failed  to  effect  their  complete 
discharge.  These  ideas  have  seemed  to  be  so  completely  justified  by  facts,  that  they  have 
been  applied  to  the  mechanism  of  excretion  by  other  organs,  such  as  the  skin  and  the  liver ; 
but,  within  a  few  years,  the  older  observations  with  regard  to  nephrotomized  animals 
have  been  discredited.  It  has  been  asserted,  as  the  result  of  experiment,  that  urea  and 
the  urates  do  not  accumulate  in  the  blood  after  removal  of  the  kidneys,  and  that  this 
only  occurs  when  both  ureters  have  been  tied.  The  experiments  upon  which  this  idea 
is  based  have  been  applied  mainly  to  the  pathology  of  uraemic  intoxication,  but  it  is  evi- 


MECHANISM   OF  THE  PRODUCTION   OF  URINE.  403 

dent  that  they  bear  directly  upon  the  mechanism  of  excretion.  It  is  not  assumed,  how- 
ever, that  excrementitious  principles  are  not  formed  by  the  disassimilation  of  the  tissues, 
but  it  is  asserted  that  urea  and  the  nrates  are  produced  in  the  kidneys  by  a  transforma- 
tion of  excrementitious  matters  which  exist  in  the  blood. 

The  original  experiments  of  Prevost  and  Dumas  are  very  strong  arguments  in  favor 
of  the  view  that  has  been  so  long  almost  unquestioned,  viz.,  that  urea  is  simply  separated 
from  the  blood  by  the  kidneys  ;  but  the  more  recent  observations  of  Bernard  and  Barres- 
wil,  Robin,  and  many  others,  while  they  confirm  the  first  experiments  on  this  subject, 
have  added  very  considerably  to  our  knowledge  of  the  mechanism  of  uraemic  poisoning 
after  extirpation  of  the  kidneys.  The  kidneys,  it  has  been  found,  can  readily  be  removed 
from  living  animals  (dogs,  cats,  rabbits,  etc.)  without  any  great  disturbance  immediately 
following  the  operation.  Bernard  and  Barreswil  found  that  animals  from  which  both 
kidneys  had  been  removed  did  not  usually  present  any  distinctive  symptoms  for  a  day  or 
two  after,  except  that  they  vomited  and  passed  an  unusual  quantity  of  liquid  from  the 
intestinal  canal.  During  this  period,  the  blood  never  contained  an  abnormal  quantity 
of  urea ;  but  the  contents  of  the  stomach  and  intestine  were  found  to  be  highly  ammo- 
niacal.  During  this  time,  also,  the  secretions  from  the  stomach  and  intestines,  particu- 
larly the  stomach,  became  continuous,  as  well  as  increased  in  quantity.  Animals  oper- 
ated upon  in  this  way  usually  live  for  four  or  five  days,  and  they  then  die  in  coma  follow- 
ing upon  convulsions.  Toward  the  end  of  life,  the  secretion  of  gastric  and  intestinal  fluids 
becomes  arrested,  probably  from  the  irritating  effects  of  ammoniacal  decomposition  of 
their  contents,  and  then,  and  then  only,  urea  is  found  to  accumulate  enormously  in  the 
blood. 

It  is  thought  by  Bernard  that  the  hypersecretion  by  the  gastric  and  intestinal  mucous 
membrane,  in  nephrotomized  animals,  is  an  effort  on  the  part  of  the  system  to  eliminate 
urea,  which  is  decomposed  by  contact  with  these  membranes  into  carbonate  of  am- 
monia. This  view  is  sustained  by  the  fact  that,  when  urea  is  introduced  into  the  alimen- 
tary canal  in  living  animals,  it  disappears  almost  immediately  and  is  replaced  by  the  am- 
moniacal salts.  Consequently,  after  removal  of  the  kidneys,  we  should  not  expect  to  find 
an  increased  quantity  of  urea  in  the  blood  until  its  elimination  by  the  mucous  membrane 
of  the  alimentary  canal  has  ceased ;  but  the  fact  that  it  then  accumulates  in  large 
quantity  cannot  be  doubted. 

The  results  obtained  by  other  experimenters  generally  correspond  with  those  of  Ber- 
nard and  Barreswil.  It  has  also  been  ascertained,  as  was  shown  by  Segalas  and  Vau- 
quelin,  that  urea  is  an  active  diuretic  when  injected  in  small  quantity  into  the  veins  of  a 
healthy  animal ;  and  that,  in  this  case,  it  does  not  produce  any  poisonous  effects,  but  is 
immediately  eliminated.  But,  when  urea  is  injected  into  the  vascular  system  of  a  ne- 
phrotomized animal,  it  produces  death  in  a  very  short  time,  with  the  characteristic  symp- 
toms of  ura3mic  poisoning.  We  have  frequently  removed  both  kidneys  from  dogs,  and, 
when  the  operation  is  carefully  performed,  the  animals  live  for  from  three  to  five  days. 
In  some  instances,  they  have  been  known  to  live  for  twelve  days  or  even  longer ;  but 
death  always  takes  place  finally  with  symptoms  of  blood-poisoning. 

The  experiments  which  are  supposed  to  show  that  urea  and  the  urates  are  actually 
formed  in  the  kidneys,  to  which  we  have  already  alluded,  were  made  with  the  view  of 
comparing  the  effects  of  removal  of  both  kidneys  with  those  produced  by  tying  the 
ureters.  According  to  these  observations,  the  blood  contains  much  more  urea  after  the 
ureters  are  tied  than  after  removal  of  the  kidneys.  These  experiments,  which  are  di- 
rectly opposed  in  their  results  to  the  well-considered  observations  of  Prevost  and  Du- 
mas, Bernard  and  Barreswil,  Segalas,  and  many  others,  cannot  be  accepted,  unless  it 
be  certain  that  all  the  necessary  physiological  conditions  have  been  fulfilled.  In  the 
first  place,  it  was  positively  demonstrated,  as  early  as  1847,  that  urea  does  not  accumu- 
late in  the  blood  immediately  after  removal  of  the  kidneys,  but  that  this  occurs  only 
toward  the  end  of  life,  and  then  urea  is  found  in  enormous  quantity.  In  the  second 


404  EXCRETION. 

place,  it  is  well  known  that  the  operation  of  tying  the  ureters  is  followed  by  an  immense 
pressure  of  urine  in  the  kidneys,  which  not  only  disturbs  the  eliminative  action  of  these 
organs,  but  affects  most  seriously  the  general  functions.  Since  the  influence  of  the  ner- 
vous system  upon  the  secretions  has  been  closely  studied,  it  is  evident  that  the  pain  and 
disturbance  consequent  upon  the  accumulation  of  urine  above  the  ligated  ureters  must 
have  an  important  reflex  action  upon  the  secretions;  and  this  would  probably  inter- 
fere with  the  vicarious  elimination  of  urea  and  other  excrementitious  principles  by 
the  stomach  and  intestines.  It  is  well  known  to  practical  physicians  that  an  arrest 
of  these  secretions,  in  cases  of  organic  disease  of  the  kidneys,  is  liable  to  be  followed 
immediately  by  evidences  of  uraemia,  and  that  grave  ursemic  symptoms  are  frequently 
relieved  by  the  administration  of  remedies  that  act  promptly  and  powerfully  upon  the 
intestinal  canal.  As  an  additional  evidence  of  the  great  disturbance  of  the  system— aside 
from  the  mere  accumulation  of  excrementitious  principles  in  the  blood — which  must 
result  from  tying  the  ureters,  we  have  the  intense  distress  and  general  prostration, 
always  so  prominent  in  cases  of  nephritic  colic  in  which  there  may  be  merely  temporary 
obstruction  of  one  ureter. 

From  a  careful  review  of  the  important  facts  bearing  upon  the  question  under  con- 
sideration, there  does  not  seem  to  be  any  valid  ground  for  a  change  in  our  ideas  concern- 
ing the  mode  of  elimination  of  urea  and  the  other  important  excrementitious  constituents 
of  the  urine.  There  is  every  reason  to  suppose  that  these  principles  are  produced  in 
the  various  tissues  and  organs  of  the  body  during  the  process  of  disassimilation,  are 
taken  up  by  the  blood,  and  are  simply  separated  from  the  blood  by  the  kidneys.  There 
may  be  unimportant  modifications  of  some  of  these  principles  in  the  kidneys  or  in  the 
urine,  such  as  the  conversion  of  a  certain  amount  of  creatine  into  creatinine,  but  the  great 
mass  of  excrementitious  matter  is  separated  from  the  blood  by  the  kidneys  unchanged. 

Extirpation  of  one  kidney  from  a  living  animal  is  not  necessarily  fatal.  We  have  fre- 
quently performed  this  operation  as  a  class-demonstration,  and  have  kept  the  animal  for 
weeks  and  months,  without  observing  any  indications  of  disturbance  in  the  eliminative 
functions.  If  the  operation  be  carefully  performed,  the  wound  will  generally  heal  with- 
out difficulty,  and  in  most  instances  the  remaining  kidney  seems  sufficient  for  the  elimi- 
nation of  urine  for  an  indefinite  period.  In  all  of  our  experiments,  save  one,  the  ani- 
mals, killed  long  after  the  wound  had  healed,  never  presented  any  marked  symptoms  of 
retention  of  excrementitious  matters  in  the  blood.  It  is  a  noticeable  fact,  however, 
that  in  many  instances  they  showed  a  marked  change  in  disposition,  and  the  appetite 
became  voracious  and  unnatural.  These  animals  would  sometimes  eat  faeces,  the  flesh 
of  dogs,  etc.,  and,  in  short,  presented  certain  of  the  phenomena  so  frequently  observed 
after  extirpation  of  the  spleen.  After  extirpation  of  one  kidney,  it  has  been  observed 
that  the  remaining  kidney  increases  in  weight,  although  recent  investigations  show  that 
this  is  due  mainly  to  an  increase  in  the  amount  of  blood,  lymph,  and  urinary  princi- 
ples, and  not  to  a  new  development  of  renal  tissue.  It  is  reasonable  to  suppose  that 
Nature  has  provided,  in  the  kidneys,  more  working  substance  than  is  ordinarily  required 
for  the  elimination  of  the  excrementitious  constituents  of  the  urine ;  and  that,  even 
when  one  kidney  is  removed,  the  other  is  competent  to  eliminate  the  amount  of  excre- 
mentitious matter  that  is  produced,  under  ordinary  conditions  of  the  system.  The 
exceptional  experiment  in  which  the  animal  died  after  extirpation  of  one  kidney  is  quite 
interesting:  October  6,  1864,  we  removed  one  kidney  from  a  small  cur-dog,  about 
nine  months  old,  by  an  incision  in  the  lumbar  region.  The  animal  did  not  appear 
to  suffer  from  the  operation,  and  the  wound  healed  kindly.  The  only  marked  effects 
were  great  irritability  of  disposition  and  an  exaggerated  and  perverted  appetite.  He 
would  attack  the  other  dogs  in  the  laboratory  without  provocation,  and  would  eat  with 
avidity,  fseces,  putrid  dog's  flesh,  and  articles  which  the  other  animals  would  not  touch, 
and  which  he  did  not  eat  before  the  operation.  On  the  morning  of  November  18th, 
forty-three  days  after  the  operation,  the  dog  appeared  to  be  uneasy,  cried  frequently,  and 


VARIATIONS  IN  THE  SECRETION   OF  URINE.  405 

at  12  o'clock  went  into  convulsions,  which  continued  until  3£  p.  M.,  when  he  died. 
In  one  other  instance,  in  which  a  dog  was  kept  for  more  than  a  year  after  extirpa- 
tion of  one  kidney,  it  was  occasionally  observed  that  the  animal  was  rather  quiet  and 
indisposed  to  move  for  a  day  or  two,  but  this  always  passed  off,  and  when  he  was 
killed  he  was  as  well  as  before  the  operation. 

Influence  of  the  Nervous  System,  Blood-pressure,  etc.,  upon  the  Secretion  of  Urine. — 
There  are  numerous  instances  in  which  very  marked  and  sudden  modifications  in  the 
action  of  the  kidneys  take  place  under  the  influence  of  fear,  anxiety,  hysteria,  etc., 
when  the  impression  must  have  been  transmitted  through  the  nervous  system.  Although 
little  is  known  of  the  final  distribution  of  the  nerves  in  the  kidney,  it  has  been  ascertained 
that  here,  as  elsewhere,  filaments  from  the  sympathetic  system  ramify  upon  the  walls  of 
the  blood-vessels,  and  they  are  undoubtedly  capable  of  modifying  the  quantity  and  the 
pressure  of  blood  in  these  organs. 

It  may  be  stated  as  a  general  proposition,  that  an  increase  in  the  pressure  of  blood  in 
the  kidneys  increases  the  flow  of  urine,  and  that,  when  the  blood-pressure  is  lowered, 
the  flow  of  urine  is  correspondingly  diminished.  This  fact  will  in  a  measure  account  for 
the  increase  in  the  flow  of  urine  during  digestion ;  but  it  cannot  serve  to  explain  all  of 
the  modifications  that  may  take  place  in  the  action  of  the  kidneys.  The  fact  above 
stated,  although  it  has  been  long  recognized  by  physiologists,  has  lately  been  very  fully 
illustrated  by  the  experiments  of  Bernard.  This  observer  measured  the  pressure  of  blood 
in  the  carotid  artery  of  a  dog  and  carefully  noted  the  quantity  of  urine  discharged  in  the 
course  of  a  minute  from  one  of  the  ureters.  Afterward,  by  tying  the  two  crural,  the  two 
brachial,  and  the  two  carotid  arteries,  he  increased  the  blood-pressure  about  one-half,  and 
the  quantity  of  urine  discharged  in  a  minute  was  immediately  increased  by  a  little  more 
than  fifty  per  cent.  In  another  animal,  he  diminished  the  pressure  by  taking  blood  from 
the  jugular  vein,  and  the  quantity  of  urine  was  immediately  reduced  about  one-half. 
His  later  observations  on  this  subject  showed  that  the  increase  in  the  quantity  of  urine 
produced  by  exaggerated  pressure  of  blood  in  the  kidneys  was  capable  of  being  modified 
through  the  nervous  system.  In  these  experiments,  the  nerves  going  to  one  kidney  were 
divided,  which  produced  an  increase  in  the  arterial  pressure  and  a  consequent  exaggera- 
tion in  the  quantity  of  urine  from  the  ureter  on  that  side.  The  pressure  was  then  farther 
increased  by  stopping  the  nostrils  of  the  animal.  The  quantity  of  urine  was  increased  by 
this  on  the  side  on  which  the  nerves  had  been  divided,  but  the  pain  and  distress  from 
want  of  air  arrested  the  secretion  upon  the  sound  side. 

The  precise  influence  which  special  nerves  exert  upon  the  secretion  of  urine  has  not 
yet  been  positively  ascertained.  8ome  important  facts,  however,  bearing  upon  this  sub- 
ject have  been  developed  of  late  years.  In  his  interesting  and  novel  experiments  upon 
artificial  diabetes  in  animals,  Bernard  found  that,  when  irritation  was  applied  to  the  floor 
of  the  fourth  ventricle,  in  the  median  line,  exactly  in  the  middle  of  the  space  comprised 
between  the  origin  of  the  pneumogastrics  and  the  auditory  nerves,  the  urine  was  in- 
creased in  quantity  and  became  strongly  saccharine.  When  the  irritation  was  applied  a 
little  above  this  point,  the  urine  was  simply  increased  in  quantity,  but  it  contained  no 
sugar ;  and,  when  the  puncture  was  made  a  little  below,  sugar  appeared  in  the  urine, 
without  any  increase  in  the  quantity  of  the  secretion.  It  has  also  been  observed  that 
section  of  the  spinal  cord  in  the  upper  part  of  the  dorsal  region  arrests,  for  a  time,  the 
secretion  of  urine. 

The  final  effect  of  division  of  all  the  nerves  going  to  the  kidney  is  very  curious.  The 
immediate  effect  of  destruction  of  these  nerves  is  to  increase  largely  the  amount  of  blood 
sent  to  the  kidney,  the  organ  then  pulsating  like  an  aneurismal  tumor.  In  experiments 
upon  this  subject,  by  Milller  and  Peipers,  the  flow  of  urine  was  sometimes  arrested  by  divi- 
sion of  these  nerves,  but  occasionally  it  continued.  In  these  observations,  the  nerves 
were  destroyed  by  applying  a  ligature  tightly  to  the  vessels  as  they  enter  at  the  hilum, 


406  EXCRETION". 

including  every  thing  but  the  ureter.  The  ligature  was  then  loosened,  so  as  to  admit  the 
blood,  but  the  nerves  had  been  bruised  and  destroyed.  The  secretion  of  urine  continues, 
however,  under  these  circumstances,  for  only  a  few  hours.  It  then  ceases,  and  the  nutri- 
tion of  the  kidney  becomes  profoundly  affected,  its  tissue  breaking  down  into  a  putrid, 
semifluid  mass,  which  probably  enters  the  blood  and  is  the  cause  of  death. 

The  other  physiological  conditions  that  affect  the  urinary  excretion  influence  the  com- 
position of  the  urine  and  the  quantity  of  excrementitious  matters  separated  by  the  kid- 
neys. These  will  be  more  appropriately  considered  under  the  head  of  nutrition  and  dis- 
assimilation.  It  is  sufficient  to  remark,  in  this  connection,  that,  during  digestion,  when 
the  composition  of  the  blood  is  modified  by  the  absorption  of  nutritive  matters,  the  quan- 
tity of  urine  is  usually  increased.  This  is  particularly  marked  when  a  large  amount  of 
liquid  has  been  taken. 

As  the  excrementitious  principles  eliminated  by  the  kidneys  are  being  constantly  pro- 
duced in  the  tissues  by  the  process  of  disassimilation,  the  formation  of  urine  is  constant ; 
presenting,  in  this  regard,  a  marked  contrast  with  the  intermittent  flow  of  most  of  the 
secretions  proper,  as  distinguished  from  the  excretions.  It  was  noted  by  Erichsen,  in  a 
case  of  extroversion  of  the  bladder,  and  it  has  been  farther  shown  by  experiments  upon 
dogs,  that  there  is  an  alternation  in  the  action  of  the  kidneys  upon  the  two  sides.  Ber- 
nard exposed  the  ureters  in  a  living  animal  and  fixed  a  small  silver  tube  in  each,  so  that 
the  secretion  from  each  kidney  could  be  readily  observed ;  and  he  noted  that  a  large 
quantity  of  fluid  was  discharged  from  one  side  for  from  fifteen  to  thirty  minutes,  while 
the  flow  from  the  other  side  was  slight  and  in  some  instances  was  entirely  arrested.  The 
flow  then  commenced  with  activity  upon  the  other  side,  while  the  discharge  from  the 
opposite  ureter  was  diminished  or  arrested.  We  are  already  familiar  with  this  alterna- 
tion of  action  in  the  parotid  glands. 

Changes  in  the  Composition  of  the  Blood  in  passing  through  the  Kidneys. — Some  of 
the  changes  in  the  blood  in  its  passage  through  the  kidneys  have  already  been  noted. 
The  most  important  of  these  consist  in  a  diminution  in  the  proportion  of  urea,  the  urates, 
and  other  of  the  excrementitious  principles  found  in  the  urine.  This  would  be  expected, 
inasmuch  as  these  principles  are  constantly  present  in  the  urine,  and  they  have  been  shown 
to  be  derived  exclusively  from  the  blood.  It  has  been  ascertained,  also,  that  the  blood 
of  the  renal  veins  contains  less  water  than  the  blood  of  any  other  part  of  the  venous  sys- 
tem. The  constant  separation  of  water  from  the  blood  by  the  kidneys,  for  the  purpose 
of  carrying  off  the  soluble  excrementitious  principles,  is  an  explanation  of  this  fact.  It 
was  also  observed  by  Simon,  a  number  of  years  ago,  that  the  blood  of  the  renal  veins 
does  not  coagulate  readily,  and  that  it  is  impossible  to  obtain  fibrin  from  it  in  the  ordinary 
way  by  stirring  with  rods. 

Reference  has  already  been  made  to  the  researches  of  Bernard,  showing  that  the 
blood  coming  from  many  of  the  glands  during  their  functional  activity  is  but  little  dark- 
er than  arterial  blood.  The  action  of  the  kidneys  is  constant,  and  the  quantity  of  blood 
which  they  receive  is  enormous.  Unless  the  function  of  these  organs  be  disturbed,  the 
blood  passing  through  them  cannot  be  deoxygenated,  and  it  is  consequently  red,  contain- 
ing a  large  quantity  of  oxygen  and  a  very  small  proportion  of  carbonic  acid.  This  fact 
we  have  often  noted,  and  it  has  been  observed  by  all  who  have  examined  the  renal  veins 
in  living  animals.  In  comparative  analyses  for  gases  of  the  blood  of  the  renal  artery  and 
vein,  Bernard  found,  in  one  examination,  no  carbonic  acid  in  either  specimen,  the  pro- 
portion of  oxygen  being  12  parts  per  hundred  in  volume  for  the  artery,  and  10  parts 
for  the  vein.  These  observations  were  made  at  a  temperature  of  from  50°  to  53°  Fahr. 
Making  the  analyses  at  about  the  temperature  of  the  body  (104°  to  113°),  the  quantity 
of  carbonic  acid  was  3  parts  for  the  artery  and  3*13  parts  for  the  vein,  and  the  propor- 
tion of  oxygen  was  19-46  parts  for  the  artery  and  17*26  parts  for  the  vein.  When  the 
secretion  of  urine  was  arrested  by  irritation  of  the  kidney,  the  blood  became  black  in 


PHYSIOLOGICAL  ANATOMY   OF  THE   URINARY  PASSAGES.        407 

the  vein,  and  the  quantity  of  oxygen  diminished,  with  a  corresponding  increase  in  the 
proportion  of  carbonic  acid.  These  observations  show  that  during  secretion  most  of  the 
blood  sent  to  the  kidneys  is  for  the  purpose  of  furnishing  water  and  the  excrementitious 
principles  of  the  urine,  and  that  but  little  is  used  for  ordinary  nutrition.  Secretion  ap- 
pears to  have  no  marked  influence  upon  the  consumption  of  oxygen  and  the  production 
of  carbonic  acid. 

Physiological  Anatomy  of  the  Urinary  Passages. — The  chief  physiological  interest 
attached  to  the  anatomy  of  the  urinary  passages  is  connected  with  the  discharge  of  the 
urine  from  the  kidneys  into  the  bladder,  and  with  the  process  of  micturition;  and  it  will 
be  necessary,  consequently,  to  give  but  a  brief  account  of  the  structure  of  these  parts. 

The  excretory  ducts  of  the  kidneys  (the  ureters)  commence  each  by  a  funnel-shaped 
sac,  the  pelvis,  which  is  applied  to  the  kidney  at  the  hilum.  This  sac  presents  little  tu- 
bular processes,  called  calices,  into  which  the  apices  of  the  pyramids  are  received.  The 
ureters  themselves  are  membranous  tubes  of  about  the  diameter  of  a  goose-quill,  becom- 
ing much  reduced  in  caliber  as  they  penetrate  the  coats  of  the  bladder.  They  are  from 
sixteen  to  eighteen  inches  in  length,  passing  from  the  kidneys  to  the  bladder  behind  the 
peritoneum.  They  have  three  distinct  coats :  an  external  coat,  composed  of  fibrous  tis- 
sue, the  ordinary  white  fibres  mixed  with  elastic  fibres  of  the  small  variety ;  a  middle 
coat,  composed  of  different  layers  of  non- striated  muscular  fibres ;  and  a  mucous  coat. 

The  external  coat  requires  no  special  description.  It  is  prolonged  into  the  calices  and 
is  continuous  with  the  fibrous  coat  of  the  kidney  at  the  apices  of  the  pyramids. 

The  fibres  of  the  muscular  coat  present  two  principal  layers ;  an  external  longitudi- 
nal layer,  and  an  internal  transverse,  or  circular  layer,  to  which  is  added  near  the  blad- 
der a  layer  of  longitudinal  fibres,  internal  to  the  circular  fibres. 

The  mucous  lining  is  thin,  smooth,  and  without  any  follicular  glands.  It  is  thrown 
into  slight  longitudinal  folds,  when  the  tube  is  flaccid,  which  are  easily  effaced  by  dis- 
tention.  The  epithelium  exists  in  several  layers  and  is  remarkable  for  the  irregular 
shape  of  the  cells.  They  present,  usually,  numerous  dark  granulations  and  one  or  two 
clear  nuclei  with  distinct  nucleoli.  Some  of  the  cells  are  flattened,  some  are  rounded, 
and  some  are  caudate,  with  one  or  two  prolongations. 

Passing  to  the  base  of  the  bladder,  the  ureters  become  constricted,  penetrate  the  coats 
of  this  organ  obliquely,  their  course  in  its  walls  being  a  little  less  than  an  inch  in 
length.  This  valvular  opening  allows  the  free  passage  of  the  urine  from  the  ureters,  but 
compression  or  distention  of  the  bladder  closes  the  orifices  and  renders  a  return  of 
the  fluid  impossible. 

The  bladder,  which  serves  as  a  reservoir  for  the  urine,  varies  in  its  relations  to  the 
pelvic  and  abdominal  organs  as  it  is  empty  or  more  or  less  distended.  When  perfectly 
empty,  it  lies  deeply  in  the  pelvic  cavity  and  is  then  a  small  sac,  of  an  irregularly  trian- 
gular form.  As  it  becomes  filled,  it  assumes  a  globular  or  ovoid  form,  rises  up  in  the 
pelvic  cavity,  and,  when  excessively  distended,  it  may  project  into  the  abdomen.  When 
the  urine  is  voided  at  normal  intervals,  the  bladder,  when  filled,  contains  about  a  pint 
of  liquid ;  but,  under  pathological  conditions,  it  may  become  distended  so  as  to  con- 
tain ten  or  twelve  pints,  and,  in  some  instances  of  obstruction,  it  has  been  found  to  con- 
tain even  more.  The  bladder  is  usually  more  capacious  in  the  female  than  in  the  male. 
It  is  held  in  place  by  certain  ligaments  and  folds  of  the  peritoneum,  which  it  is  unneces- 
sary to  describe  in  this  connection,  but  which  are  so  arranged  as  to  allow  of  the  various 
changes  in  volume  and  position  which  the  organ  is  liable  to  assume  under  different  de- 
grees of  distention. 

The  anatomy  of  the  coats  of  the  bladder  possesses  a  certain  amount  of  physiological  in- 
terest. These  are  three  in  number.  The  external  coat  is  simply  a  reflection  of  the  peri- 
toneum, covering  the  posterior  portion  completely,  from  the  openings  of  the  ureters  to  the 
summit,  about  one-third  of  the  lateral  portion,  and  a  small  part  of  the  anterior  portion. 


408  EXCRETION. 

The  middle,  or  muscular  coat,  consists  of  fibres  of  the  non-striated  or  involuntary 
variety,  arranged  in  three  tolerably  distinct  layers. 

The  external  muscular  layer  is  composed  of  longitudinal  fibres,  which  arise  from  parts 
adjacent  to  the  neck,  and  pass  anteriorly,  posteriorly,  and  laterally  over  the  organ,  so 
that  when  they  are  contracted  they  diminish  its  capacity  chiefly  by  shortening  its  verti- 
cal diameter.  The  anterior  fibres  of  this  layer  arise  from  the  body  of  the  pubis  and  the 
symphysis,  by  tendinous  bands,  known  to  most  anatomists  as  the  anterior  ligaments. 
These  tendinous  fibres  spread  out  upon  the  prostate  and  are  attached  to  its  anterior  sur- 
face. As  the  fibres  on  the  anterior  surface  pass  over  the  summit  of  the  bladder,  they  in- 
terlace, and  some  of  them  are  continuous  with  the  fibres  coming  from  the  posterior  sur- 
face. The  posterior  fibres  arise  from  the  base  of  the  prostate,  and,  after  forming  a  dis- 
tinct band  an  inch  or  an  inch  and  a  quarter  in  breadth,  spread  out  upon  the  posterior  sur- 
face of  the  bladder.  The  lateral  fibres  arise  from  the  sides  of  the  prostate  and  spread 
out  upon  the  lateral  surfaces  of  the  bladder.  In  the  female,  the  posterior  fibres  arise 
from  the  dense  fibrous  membrane  between  the  neck  of  the  bladder  and  the  vagina,  and 
the  lateral  fibres,  from  the  perineal  aponeurosis,  the  anterior  fibres  arising  from  the  pubisy 
as  in  the  male.  The  fibres  of  the  external  layer  are  of  a  pinkish  hue,  being  much  more 
highly  colored  than  the  other  layers. 

The  middle  muscular  layer  is  formed  of  circular  fibres,  arranged,  on  the  anterior  sur- 
face of  the  bladder,  in  distinct  bands  at  right  angles  to  the  superficial  fibres.  They  are 
thinner  and  less  strongly  marked  on  the  posterior  and  lateral  surfaces. 

The  internal  muscular  layer  is  composed  of  excessively  pale  fibres  arranged  in  longi- 
tudinal fasciculi,  the  anterior  and  lateral  bundles  anastomosing  with  each  other  as  they 
descend  toward  the  neck  of  the  bladder,  by  oblique  bands  of  communication,  and  the 
posterior  bundles  interlacing  in  every  direction,  forming  an  irregular  plexus.  Here  they 
are  not  to  be  distinguished  from  the  fibres  of  the  middle  layer.  This  arrangement  has 
given  to  these  fibres  the  name  of  the  plexiform  layer,  and  it  gives  to  the  interior  of  the 
bladder  its  reticulated  appearance.  This  layer  is  continuous  with  the  muscular  fibres  of 
the  urachus,  the  ureters,  and  the  urethra. 

The  sphincter  vesicee  is  composed  of  a  band  of  smooth  fibres,  about  half  an  inch  in 
breadth  and  one-eighth  of  an  inch  in  thickness,  embracing  the  neck  of  the  bladder  and 
the  posterior  half  of  the  prostatic  portion  of  the  urethra.  The  tonic  contraction  of  these 
fibres  prevents  the  flow  of  urine,  and,  during  the  ejaculation  of  the  seminal  fluid,  it  offers 
an  obstruction  to  its  passage  into  the  bladder. 

It  is  seen,  from  the  arrangement  of  the  muscular  fibres  of  the  bladder,  that  they  are 
capable  by  their  contraction  of  expelling  the  greatest  part  of  the  urine  when  the  sphinc- 
ter is  relaxed. 

The  mucous  membrane  of  the  bladder  is  smooth,  rather  pale,  thick,  and  loosely  ad- 
herent to  the  submucous  tissue,  except  over  the  corpus  trigonum.  The  epithelium  exists 
in  several  layers  and  presents  the  same  diversity  in  form  as  that  observed  in  the  pelvis 
of  the  kidney  and  the  ureters ;  viz.,  the  deeper  cells  are  elongated  and  resemble  the  co- 
lumnar epithelium,  while  the  cells  on  the  surface  are  flattened.  In  the  neck  and  fundus 
of  the  bladder  are  a  few  mucous  glands,  some  in  the  form  of  simple  follicles,  and  others 
collected  to  form  glands  of  the  simple  racemose  variety. 

The  corpus  trigonum  is  a  triangular  body,  lying  just  beneath  the  mucous  membrane 
at  the  base  of  the  bladder  and  extending  from  the  urethra  in  front  to  the  openings  of 
the  ureters.  It  is  composed  of  white  fibrous  tissue,  with  a  few  elastic  and  muscular 
fibres.  At  the  opening  of  the  urethra,  it  presents  a  small  projecting  fold  of  mucous 
membrane,  which  is  sometimes  called  the  uvula  vesicaa.  Over  the  whole  of  the  surface 
of  the  trigone,  the  mucous  membrane  is  very  closely  adherent,  and  it  is  never  thrown  into 
folds,  even  when  the  bladder  is  entirely  empty. 

The  blood-vessels  going  to  the  bladder  are  ultimately  distributed  to  its  mucous  mem- 
brane. They  are  not  very  numerous,  except  at  the  fundus,  where  the  mucous  mem- 


MECHANISM  OF  THE  DISCHARGE   OF   URINE.  409 

brane  is  tolerably  vascular.  Lymphatics  have  been  described  as  existing  in  the  walls  of 
the  bladder,  but  Sappey,  whose  researches  in  the  lymphatic  system  have  been  very  ex- 
tended and  successful,  has  failed  to  demonstrate  them  in  this  situation.  The  nerves  of 
the  bladder  are  derived  from  the  hypogastric  plexus. 

The  urethra  is  provided  with  muscular  fibres,  and  it  is  lined  by  a  mucous  membrane, 
the  anatomy  of  which  will  be  more  fully  considered  in  connection  with  the  function  of 
generation.  In  the  female  the  epithelium  of  the  urethra  is  like  that  of  the  bladder.  In 
the  male  the  epithelial  cells  are  small,  pale,  and  of  the  columnar  variety. 

Mechanism  of  the  Discharge  of  Urine. — In  some  of  the  lower  orders  of  animals  in 
which  the  urine  is  of  a  semisolid  consistence,  the  movement  of  vibratile  cilia  in  the  uri- 
niferous  tubes  probably  aids  in  the  discharge  of  the  excretion ;  but,  in  the  human  subject, 
the  existence,  even,  of  cilia  is  doubtful,  and  the  urine  is  discharged  into  the  pelves  of  the 
kidneys  and  the  ureters  by  pressure  due  to  the  act  of  separation  of  the  fluid  from  the 
blood.  Once  discharged  into  the  ureters,  the  course  of  the  urine  is  determined  in  part  by 
the  vis  a  tergo,  and  in  part,  probably,  by  the  action  of  the  muscular  coats  of  these  canals. 
Mtiller  has  found  that  the  ureters  can  be  made  to  undergo  a  powerful  local  contraction 
upon  the  application  of  a  galvanic  current ;  and  Bernard  has  shown  that  this  may  be 
produced  by  galvanization  of  the  anterior  root  of  the  eleventh  dorsal  nerve.  Notwith- 
standing these  facts,  it  is  difficult  to  estimate  the  amount  of  influence  ordinarily  exerted 
by  peristaltic  contractions  of  the  ureters ;  but,  when  there  is  excessive  accumulation  of 
urine  in  the  bladder,  or  when  there  is  obstruction  from  any  cause,  such  as  the  presence 
of  a  renal  calculus,  these  contractions  are  probably  quite  energetic. 

When  the  urine  has  accumulated  to  a  certain  extent  in  the  bladder,  a  peculiar  sensa- 
tion is  experienced  which  leads  to  the  act  for  its  expulsion.  This  desire  to  discharge  the 
urine  is  probably  due  to  the  impression  produced  by  the  distention  of  the  bladder.  The 
intervals  at  which  it  is  experienced  are  exceedingly  variable.  The  urine  is  usually  voided 
before  retiring  to  rest  and  upon  rising  in  the  morning,  and  generally  two  or  three  times, 
in  addition,  during  the  day.  The  frequency  of  micturition,  however,  depends  very  much 
upon  habit,  upon  the  quantity  of  liquids  ingested,  and  upon  the  degree  of  activity  of  the 
skin ;  the  latter  conditions  modifying  the  quantity  of  urine. 

Evacuation  of  the  bladder  is  accomplished  by  the  muscular  walls  of  the  organ  itself, 
aided  by  contractions  of  the  diaphragm  and  the  abdominal  muscles  with  certain  muscles 
which  operate  upon  the  urethra,  and  it  is  accompanied  by  relaxation  of  the  sphincter 
vesicse.  This  act  is  at  first  voluntary,  but,  once  commenced,  it  may  be  continued  by 
the  involuntary  contraction  of  the  bladder  alone.  During  the  first  part  of  the  process, 
the  distended  bladder  is  compressed  by  contraction  of  the  diaphragm  and  the  abdominal 
muscles ;  and  this,  after  a  time,  excites  the  action  of  the  bladder  itself.  A  certain  period 
usually  elapses  then  before  the  urine  begins  to  flow.  When  the  bladder  contracts,  aided 
by  the  muscles  of  the  abdomen  and  the  diaphragm,  the  resistance  of  the  sphincter  is  over- 
come, and  a  jet  of  urine  flows  with  considerable  force  from  the  urethra.  All  voluntary 
action  may  then  cease  for  a  time,  and  the  bladder  will  nearly  empty  itself;  but  the  force 
of  the  jet  may  at  any  time  be  considerably  increased  by  voluntary  effort. 

It  is  a  question  whether  the  bladder  be  capable  of  entirely  emptying  itself  by  the  ac- 
tion of  its  muscular  walls.  That  almost  all  the  urine  may  be  expelled  in  this  way  in  the 
human  subject,  there  can  be  no  doubt ;  and  it  has  been  shown  by  experiments  upon  some 
of  the  inferior  animals  that  the  bladder  may  be  completely  evacuated  when  it  has  been 
drawn  out  of  the  abdominal  cavity.  In  vivisections,  we  have  frequently  observed  the 
bladder  so  firmly  contracted  that  it  could  contain  hardly  more  than  a  few  drops  of  liquid. 

Toward  the  end  of  the  expulsive  act,  when  the  quantity  of  liquid  remaining  in  the 
bladder  is  slight,  the  diaphragm  and  the  abdominal  muscles  are  again  called  into  action, 
and  there  is  a  convulsive,  interrupted  discharge  of  the  small  quantity  of  urine  that  re- 
mains. At  this  time,  the  impulse  from  the  bladder,  and,  indeed,  the  influence  of  the  ab- 


410  EXCRETION. 

dominal  muscles  and  diaphragm,  are  very  slight,  and  the  flow  of  urine  along  the  urethra 
is  aided  by  the  contractions  of  its  muscular  walls  and  the  action  of  some  of  the  perineal 
muscles,  the  most  efficient  being  the  accelerator  urinaB ;  but  with  all  this  muscular  action 
a  few  drops  of  urine  generally  remain  in  the  male  urethra  after  the  act  of  urination  is 
accomplished.  The  process  of  evacuation  of  urine  in  the  female  is  essentially  the  same 
as  in  the  male,  with  the  exception  of  the  slight  modifications  due  to  differences  in  the  di- 
rection and  length  of  the  urethra. 

The  movements  of  the  bladder  are  under  the  control  of  the  nervous  system.  Accord- 
ing to  the  researches  of  Budge,  the  influence  of  the  nervous  system  operates  through  the 
sympathetic,  and  he  has  described  a  centre  in  the  spinal  cord,  which  presides  over  the  con- 
tractions of  the  lower  part  of  the  intestinal  canal,  the  bladder,  and  the  vasa  deferentia. 
This  he  calls  the  genito-spinal  centre,  and  he  has  located  it,  in  experiments  upon  rabbits, 
in  the  spinal  cord,  at  a  point  opposite  the  fourth  lumbar  vertebra.  From  this  centre,  the 
nervous  filaments  pass  through  the  sympathetic  nerve  communicating  with  the  ganglion 
which  corresponds  to  the  fifth  lumbar  vertebra. 

Properties  and  Composition  of  the  Urine. 

The  importance  of  an  exact  knowledge  of  the  properties  and  composition  of  the  urine 
has  long  been  recognized  by  physiologists ;  and  our  literature  is  full  of  observations,  more 
or  less  valuable,  upon  this  subject,  dating  from  the  discovery  of  urea,  by  Hillaire  Rouelle, 
in  the  latter  part  of  the  last  century,  to  the  present  time.  It  is  impossible,  however,  to 
follow  out  in  detail  even  the  most  important  of  the  chemical  researches  upon  the  differ- 
ent urinary  constituents,  without  exceeding  the  limits  of  pure  human  physiology ;  and 
the  observations  of  the  earlier  authors  have  now  little  more  than  an  historical  interest. 
But  this  can  hardly  be  said  of  the  analysis  of  the  urine  by  Berzelins,  made  early  in  the 
present  century;  for,  even  in  recent  authoritative  works  upon  physiology,  these  are 
quoted  as  the  most  elaborate  and  reliable  of  the  quantitative  examinations  of  the  renal 
excretion.  In  treating  of  this  subject,  we  propose  to  give  simply  the  chemistry  of  the 
urine  as  it  is  understood  at  the  present  day,  dwelling  particularly  upon  its  relations  to  the 
physiology  of  nutrition  and  disassimilation.  In  doing  this  it  will  be  necessary  to  con- 
sider carefully  the  quantity,  specific  gravity,  reaction,  etc.,  of  the  urine,  with  the  varia- 
tions observed  under  different  physiological  conditions. 

General  Physical  Properties  of  the  Urine. — The  color  of  the  urine  is  very  variable 
within  the  limits  of  health,  and  it  depends  to  a  considerable  extent  upon  the  character  of 
the  food,  the  quantity  of  drink,  and  the  activity  of  the  skin.  As  a  rule,  the  color  is  yel- 
lowish or  amber,  with  more  or  less  of  a  reddish  tint.  The  fluid  is  perfectly  transparent, 
free  from  viscidity,  and  exhales,  when  first  passed,  a  peculiar,  aromatic  odor,  which  is  by 
no  means  disagreeable.  Soon  after  the  urine  cools,  it  loses  this  peculiar  odor  and  has  the 
odor  known  as  urinous.  This  odor  remains  until  the  liquid  begins  to  undergo  decomposi- 
tion. The  color  and  odor  of  the  urine  are  usually  modified  by  the  same  physiological 
conditions.  When  the  fluid  contains  a  relatively  large  amount  of  solid  matters,  the  color 
is  more  intense  and  the  urinous  odor  is  more  penetrating ;  and,  when  its  quantity  is 
increased  by  an  excess  of  water,  the  specific  gravity  is  low,  the  color  pale,  and  the  odor 
faint.  The  urine  passed  in  the  morning  is  usually  more  intense  in  color  than  that  passed 
during  the  day. 

It  is  somewhat  difficult  to  measure  the  exact  temperature  of  the  urine  at  the  moment 
of  its  emission.  In  the  observations  on  this  subject,  by  Dr.  Byasson,  in  which  a  very 
delicate  thermometer  was  used  and  extraordinary  care  was  taken  to  prevent  any  change 
in  temperature  before  the  estimate  was  made,  the  temperature,  under  physiological  con- 
ditions, varied  but  a  small  fraction  of  a  degree  from  100°  Fahr.  It  is  important  to  know 
the  normal  temperature  of  the  urine,  as  it  is  liable  to  vary  very  considerably  in  certain 


PKOPERTIES   AND   COMPOSITION   OF  THE  URINE.  411 

Quantity,  Specific  Gravity,  and  Reaction  of  the  Urine. — In  estimating  the  total  quan- 
tity of  urine  discharged  in  the  twenty-four  hours,  it  is  important  to  take  into  considera- 
tion the  specific  gravity,  as  an  indication  of  the  amount  of  solid  matter  excreted  by  the 
kidneys.  We  have  already  alluded  to  some  of  the  variations  in  quantity  constantly  oc- 
curring in  health,  as  depending  upon  the  proportion  of  water ;  but  the  amount  of  solid 
matters  excreted  is  usually  more  nearly  uniform.  It  must  also  be  taken  into  account  that 
differences  in  climate,  habits  of  life,  etc.,  in  different  countries,  have  an  important  influ- 
ence upon  the  daily  quantity  of  urine.  Dr.  Parkes  has  collected  the  results  of  twenty-six 
series  of  observations  made  in  America,  England,  France,  and  Germany,  and  he  finds  the 
average  daily  quantity  of  urine  in  healthy  male  adults,  between  twenty  and  forty  years 
of  age,  to  be  fifty-two  and  a  half  fluidounces,  the  average  quantity  per  hour  being  two 
and  one-tenth  fluidounces.  The  extremes  were  thirty-five  and  eighty-one  ounces. 

In  attempting  to  decide  the  question  whether  a  certain  quantity  of  urine  passed  be 
abnormal  or  within  the  limits  of  health,  it  is  important  to  recognize,  if  possible,  certain 
limits  of  physiological  variation.  Becquerel  states  that  the  variations  in  the  proportion 
of  water  in  the  urine  likely  to  occur  in  health  are  between  twenty-seven  and  fifty  fluid- 
ounces  ;  but  his  average  of  the  total  quantity  in  the  twenty-four  hours  is  only  forty-four 
ounces,  which  is  rather  lower  than  the  one  we  are  disposed  to  adopt.  The  circumstances 
that  lead  to  a  diminution  in  the  proportion  of  water  are  usually  more  efficient  in  their 
operation  than  those  which  tend  to  an  increase ;  and  the  range  below  the  healthy  standard 
is  rather  wider  than  it  is  above.  All  these  estimates,  however,  are  merely  approxima- 
tive. Assuming  that  the  usual  quantity  in  the  male  is  about  fifty  ounces,  it  may  be  stated, 
in  general  terms,  that  the  range  of  normal  variation  is  between  thirty  and  sixty ;  and 
that,  when  the  quantity  varies  much  from  these  figures,  it  is  probably  due  to  some  patho- 
logical condition. 

According  to  the  researches  of  Becquerel,  the  quantity  of  water  discharged  by  the 
kidneys  in  the  twenty-four  hours  is  a  little  greater  in  the  female  than  in  the  male  ;  but 
in  the  female  the  specific  gravity  is  lower,  and  the  amount  of  solid  constituents  is  rela- 
tively and  absolutely  less. 

The  specific  gravity  of  the  urine  should  always  be  estimated  in  connection  with  the 
absolute  quantity  in  the  twenty-four  hours.  Those  who  assume  that  the  daily  quantity 
is  about  fifty  ounces  give  the  ordinary  specific  gravity  of  the  mixed  urine  of  the  twenty- 
four  hours,  at  60°  Fahr.,  as  about  1020.  The  specific  gravity  is  liable  to  the  same  vari- 
ations as  the  proportion  of  water,  and  the  density  is  increased  precisely  as  the  amount  of 
water  is  diminished.  The  ordinary  range  of  variation  in  specific  gravity  is  between  1015 
and  1025  ;  but,  without  positively  indicating  any  pathological  condition,  it  may  be  as  low 
as  1005  or  as  high  as  1030. 

The  reaction  of  the  urine  is  acid  in  the  carnivora  and  alkaline  in  the  herbivora.  In 
the  human  subject,  it  is  usually  acid  at  the  moment  of  its  discharge  from  the  bladder ; 
although  at  certain  periods  of  the  day  it  may  be  neutral  or  feebly  alkaline,  the  reaction 
depending  upon  the  character  of  the  food.  The  acidity  may  be  measured  by  carefully 
neutralizing  the  urine  with  an  alkali,  in  a  solution  that  has  previously  been  graduated 
with  a  solution  of  oxalic  acid  of  known  strength ;  and  the  degree  of  acidity  is  usually 
expressed  by  calling  it  equivalent  to  so  many  grains  of  crystallized  oxalic  acid. 

As  the  result  of  numerous  observations  made  by  Yogel  and  under  his  direction,  the  total 
quantity  of  acid  in  the  urine  of  the  twenty-four  hours  in  a  healthy  adult  male  is  equal  to 
from  two  to  four  grammes,  or,  omitting  fractions,  to  from  thirty  to  sixty  grains  of  oxalic 
acid.  The  hourly  quantity  in  these  observations  was  equal,  in  round  numbers,  to  from 
one  and  a  half  to  three  grains  of  acid.  The  proportion  of  acid  was  found  to  be  very  vari- 
able in  the  same  person  at  different  periods  of  the  day.  In  one  individual,  upon  whom 
the  greatest  number  of  observations  was  made,  the  average  hourly  quantity  of  acid  at 
night  was  2'9  grains;  in  the  forenoon,  2  grains;  and  in  the  afternoon,  2'3  grains.  "In 
a  series  of  experiments  made  upon  four  different  persons,  the  quantity  was  found  to  be 


412  EXCRETION. 

n-reatest  at  night,  least  in  the  forenoon,  and  between  these  extremes  in  the  afternoon." 
In  estimating  the  degree  of  acidity  of  the  urine,  it  is  necessary  to  test  the  fluid  as  soon  as 
possible  after  it  is  discharged  from  the  bladder;  for  its  acidity  rapidly  increases  after 
emission-until  ammoniacal  decomposition  sets  in-by  the  formation  of  organic  acids,  par- 
ticularly the  lactic. 

There  has  been  considerable  discussion  and  difference  of  opinion  among  physiological 
chemists  with  regard  to  the  cause  of  the  acid  reaction  of  the  urine.  At  the  moment  of 
its  discharge  from  the  bladder,  it  is  distinctly  and  even  strongly  acid  ;  but  it  will  not  de- 
compose the  carbonates,  like  most  acid  solutions.  The  weight  of  chemical  authority  upon 
this  point  is  in  favor  of  the  view  that  there  is  no  free  acid  in  the  urine  when  it  is  first 
passed,  although  the  lactic  acid,  the  acid  lactates,  and,  perhaps,  some  other  of  the  organic 
acids  may  be  produced  after  emission,  as  the  result  of  decomposition ;  but  nearly  all 
authors  agree  that  it  contains  the  acid  phosphate  of  soda.  The  phosphates  exist  in  the 
fluids  of  the  body  in  at  least  three  different  conditions.  The  basic  phosphate  of  soda,  for 
example,  possesses  three  atoms  of  the  base  and  has  an  alkaline  reaction.  In  contact 
with  carbonic  acid,  this  salt  may  lose  one  atom  of  the  base,  forming  the  carbonate  of 
soda  and  what  is  called  the  neutral  phosphate,  the  latter,  however,  having  a  feebly  alka- 
line reaction.  In  contact  with  uric  acid,  the  neutral  phosphate  may  lose  still  another 
atom  of  base,  forming  the  urate  of  soda  and  the  acid  phosphate  ;  and,  according  to  most 
authorities,  it  is  in  this  form  that  it  exists  in  the  urine,  and  the  presence  of  this  salt  is  the 
cause  of  its  acidity.  The  acid  phosphate  of  soda  may  or  may  not  be  associated,  in  the 
human  subject,  with  the  acid  phosphate  of  lime,  which  ordinarily  gives  the  intensely  acid 
reaction  to  the  urine  of  the  carnivora. 

Composition  of  the    Urine. 

Regarding  the  excrementitious  constituents  of  the  urine  as  a  measure,  to  a  certain 
extent,  of  the  general  process  of  disassimilation,  it  is  probably  more  important  to  recog- 
nize the  absolute  quantity  of  these  principles  discharged  in  a  definite  time  than  to  learn 
simply  their  proportions  in  the  urine  ;  and,  in  making  out  a  table  of  the  composition  of 
the  urine,  we  shall  give,  as  far  as  possible,  the  absolute  quantity  of  its  different  constitu- 
ents excreted  in  twenty-four  hours.  This  latter  point,  however,  will  be  more  elaborately 
considered  in  connection  with  the  characters  of  the  individual  excrementitious  principles 
and  their  variations  under  physiological  conditions.  In  compiling  this  table,  we  have 
taken  advantage  of  the  elaborate  bibliographical  and  experimental  researches  of  Prof. 
Robin,  contained  in  his  recent  work  upon  the  humors,1  but  we  have  ventured  to  make 
some  changes  and  corrections  in  his  list  of  urinary  constituents : 

1  ROBIN,  Lemons  sur  les  humeurs,  Paris,  1874.  In  the  table  given  by  Eobin  (p.  762),  there  is  evidently  a  very 
serious  error  in  one  of  the  figures  giving  the  proportion  of  water  and  an  error  in  the  proportion  of  oxygen.  We  have 
omitted  some  of  the  constituents  given  by  Robin,  which  are  stated  to  be  doubtful  or  accidental,  or  are  noted  as  present 
under  pathological  conditions. 

Although  the  table  represents,  very  nearly,  the  latest  and  most  reliable  observations  upon  the  relative  and  abso- 
lute quantities  of  the  urinary  constituents,  there  are  a  few  minor  points  that  demand  some  explanation.  For  example, 
Robin  estimates  the  proportion  of  hippurates  at  a  little  less  than  the  proportion  of  urates,  while  many  writers  of  high 
authority  speak  of  the  hippurates  as  excreted  in  rather  larger  quantity ;  but  the  investigations  with  regard  to  the 
daily  excretion  of  hippuric  acid  have  not  been  so  definite  and  satisfactory  as  those  upon  which  the  estimates  of  the  ex- 
cretion of  uric  acid  are  based.  Robin  gives,  also,  the  proportion  of  creatine  as  1-4  to  2'6  parts  per  1,000,  and  of  crea- 
tinine, 0-2  to  0'4  per  1,000 ;  and  most  authors  give  in  the  urine  a  larger  proportion  of  creatinine.  This  difference,  how- 
ever, is  not  important,  for,  as  far  as  the  process  of  excretion  is  concerned,  these  two  substances  may  be  regarded  as  a 
single  principle,  creatine  being  readily  converted  into  creatinine  in  the  urine  by  simple  decomposition.  In  our  endeavor 
to  make  this  table  as  complete  as  possible,  we  have  reduced  the  figures  given  by  many  authors  to  represent  the  amounts 
of  uric  acid,  phosphoric  acid,  sulphuric  acid,  chlorine,  etc.,  to  the  quantity  of  the  salts  as  they  actually  exist.  This  is 
particularly  important  in  a  work  on  physiology,  for  chlorine  and  the  various  acids  just  enumerated  are  not  proximate 
constituents  of  the  urine,  except  when  combined  with  bases.  It  is  simply  a  matter  of  convenience  to  estimate  them 
separately,  and  the  proportions  of  salts  are  readily  calculated  from  the  combining  equivalents  of  the  different  ele- 
ments. 


COMPOSITION   OF   THE   UKINE.  413 

Composition  of  the  Human    Urine. 

Water  (in.  24  hours,  27  to  50  fluidounces — Becquerel) 967*47  to  940*36 

Urea  (in  24  hours,  355  to  463  grains— Robin) 15'00    u     23*00 

Uric  acid,  accidental,  or  traces 

Urate  of  soda,  neutral  and  acid |       (In  24  hours,  6  to  9 

Urate  of  ammonia,  neutral  and  acid  (in  small  quantity)   |   grs.  of  uric  acid — Bec- 

Urate  of  potassa j>  querel— or  9  to  14  grs.         TOO   "       1*60 

Urate  of  lime I   of  urates,  estimated  as 

Urate  of  magnesia J  neut.  urate  of  soda.) 

Hippurate  of  soda )      (In  24  hours,  about  7*5  grs.  of  hippuric 

Hippurate  of  potassa >  acid — Thudichum — equivalent  to  about  8*7  1*00   "       1*40 

Hippurate  of  lime )  grs.  of  hippurate  of  soda.) 

Lactate  of  soda \ 

Lactate  of  potassa \      (Daily  quantity  not  estimated) 1'50   "       2*60 

Lactate  of  lime ) 

Creatine I      (In  24  hours,  about  11  "5  grains  of  both — 

Creatinine \  Thudichum) 1'60   "       3*00 

Oxalate  of  lime  (daily  quantity  not  estimated) traces   "       1*10 

Xanthine not  estimated. 

Margarine,  oleine,  and  other  fatty  matters 0*10  to      0*20 

Chloride  of  sodium  (in  24  hours,  about  154  grains — Robin) 3*00   "       8*00 

Chloride  of  potassium traces. 

Hydrochlorate  of  ammonia T50  to       2*20 

Sulphate  of  soda. .'.  .}       <In  24  hours>  23  to  38  grains  of  sulPhuric  acid 

Sulphate  of  potassa K^^T,  ?»»**"*  *"*  «f  «*&**         3'00   '<       7'00 

Sulphate  of  lime  (traces). . .       of  soda  and  sulPhate  of  POtassa-Robm-equiv- 

J  alent  to  from  22*5  to  37*5  grains  of  each.) 
Phosphate  of  soda,  neutral. .  . .  / 

Phosphate  of  soda,  acid [      &&l1?  W**™*  not  estimated) 2*50 

Phosphate  of  magnesia  (in  24  hours,  7*7  to  11*8  grains — Neubauer) 0*50   "       1*00 

Phosphate  of  lime,  acid ) 

Phosphate  of  lime,  basic f      <In  24  hours' 4'7  to  5'7  grams-Neubauer). .         0«20   '• 

Ammonio-magnesian  phosphate  (daily  quantity  not  estimated) 1'60   "       2*40 

(Daily  excretion  of  phosphoric  acid,  about  56  grains — Thudichum.) 

Silicic  acid 0'03   "       0*04 

Urrosacine . . 


A.I  A      it  (VKft 

Mucus  from  the  bladder f u  iu  u  ou 

1,000-00     1,000*00 
Proportion  of  solid  constituents,  from  32*63  to  59*89  parts  per  1,000. 

Gases  of  the   Urine.     (Parts  per  1,000,  in  volume.) 

Oxygen,  in  solution 0'90  "  1*00 

Nitrogen,  in  solution 7*00  "  10*00 

Carbonic  acid,  in  solution 45  "  50'00 

Urea. — As  regards  quantity,  and  probably  as  a  measure  of  the  activity  of  the  general 
process  of  disassimilation,  urea  is  the  most  important  of  the  urinary  constituents ;  and 
this  substance,  with  the  changes  which  it  undergoes  in  the  urine  and  the  mode  of  its 
production  in  the  system,  has  been  most  carefully  studied  by  physiologists.  Regarding 
the  daily  excretion  of  urea  as  a  measure  of  nutritive  force  and  physiological  waste,  its 
consideration  would  come  properly  under  the  head  of  nutrition,  in  connection  with  all 
other  substances  known  to  be  the  results  of  disassimilation  ;  but  it  is  more  convenient  to 
treat  of  its  general  physiological  properties,  and  some  of  its  variations  in  common  with 
other  excrementitious  principles  separated  by  the  kidneys,  in  connection  with  the  com- 
position of  the  urine. 


414 


EXCRETION. 


The  formula  for  urea,  showing  the  presence  of  a  large  proportion  of  nitrogen,  would 
lead  us  to  suppose  that  this  substance  is  one  of  the  products  of  the  waste  of  the  nitrogen- 
ized  principles  of  the  body.  It  is  found,  under  normal  conditions,  in  the  urine,  the  lymph 
and  chyle,  the  blood,  the  sweat,  and  the  vitreous  humor.  Its  presence  has  lately  been  de- 
monstrated, also,  in  the  substance  of  the  healthy  liver  in  both  carnivorous  and  herbivorous 
animals  ;  and  it  has  farther  been  shown  by  Zalesky  that  it  exists  in  minute  quantity  in 
the  muscular  juice.  Under  pathological  conditions,  as  has  been  already  intimated,  urea 
finds  its  way  into  various  other  fluids,  such  as  the  secretion  from  the  stomach,  the  serous 
fluids,  etc. 

In  connection  with  the  chemical  properties  of  urea,  it  is  interesting  to  note  that  it  i& 
one  of  the  few  organic  proximate  principles  that  can  be  produced  synthetically  in  the 
laboratory  of  the  chemist.  As  early  as  1828,  Wohler  obtained  urea  by  adding  sulphate 
of  ammonia  to  a  solution  of  cyanate  of  potassa.  The  products  of  this  combination  are 
sulphate  of  potassa,  with  cyanic  acid  and  ammonia  in  a  form  to  constitute  urea.  The 
cyanate  of  ammonia  is  isomeric  with  urea,  and  the  change  is  effected  by  a  simple  re- 
arrangement of  its  elements.  It  has  long  been  known  that  urea,  in  contact  with  certain 
animal  substances,  is  readily  convertible  into  carbonate  of  ammonia.  This  transformation 
is  theoretically  accomplished  by  adding  to  urea  four  atoms  of  water.  It  has  recently  been 
stated  by  Kolbe,  that  carbonate  of  ammonia,  when  heated  in  sealed  tubes  to  the  tem- 
perature at  which  urea  commences  to  decompose,  is  converted  into  urea.  The  decom- 
position of  urea  resulting  in  the  carbonate  of  ammonia  may  be  easily  effected  by  various 
chemical  means.  As  this  occurs  in  the  spontaneous  decomposition  of  urea  in  the  urine 
and  elsewhere,  it  has  been  supposed  that  the  symptoms  of  blood-poisoning  following  re- 
tention of  the  urinary  constituents,  in  cases  of  disease  of  the  kidneys,  are  due  to  the 
decomposition  of  the  urea  into  carbonate  of  ammonia,  and  not  to  the  presence  of  the  urea 
itself  in  the  blood.  Many  interesting  experiments  and  observations  have  been  made  upon 
this  subject,  but  it  is  now  pretty  generally  admitted  that  the  weight  of  evidence  is  against 
the  carbonate-of-ammonia  theory  of  uraemia. 

Except  as  regards  the  probable  changes  that  take  place  in  the  process  of  transforma- 
tion of  certain  constituents  of  the  tissues  into  urea,  the  chemical  history  of  this  substance 
does  not  present  much  physiological  interest.  Urea  may  be  readily  extracted  from  the 
urine,  by  processes  fully  described  in  all  the  modern  works  upon  physiological  chemistry  ; 
and  its  proportion  may  now  be  easily  estimated  by  the  new  methods  of  volumetric  anal- 

ysis. It  is  not  so  easy,  however,  to  separate  it 
from  the  blood  or  the  substance  of  any  of  the 
tissues,  on  account  of  the  difficulty  in  getting 
rid  of  the  other  organic  matters  and  the  great 
facility  with  which  it  undergoes  decomposi- 
tion. 

When  perfectly  pure,  urea  crystallizes  in 
the  form  of  long,  four  -  sided,  colorless,  and 
transparent  prisms,  which  are  without  odor, 
neutral,  and  in  taste  resemble  saltpetre.  These 
crystals  are  very  soluble  in  water  and  in  alco- 
hol, but  they  are  entirely  insoluble  in  ether. 
In  its  behavior  to  reagents,  urea  acts  as  a  base, 
combining  readily  with  certain  acids,  particu- 
larly nitric  and  oxalic.  It  also  forms  combi- 
nations with  certain  salts,  such  as  the  oxide 
-  of  mercury,  chloride  of  sodium,  etc.  It  exists 
in  the  economy  in  a  state  of  watery  solution, 
with  perhaps  a  small  portion  of  it  modified  by  the  presence  of  chloride  of  sodium. 

Origin  of  Urea.—  There  are  two  probable  sources  of  urea  in  the  economy,  assuming 


COMPOSITION  OF  THE   URINE.  415 

that  it  always  preexists  in  the  blood  and  is  not  formed  in  the  kidneys.  One  of  these  is  in 
the  disassirailation  of  the  nitrogenized  constituents  of  the  tissues,  and  the  other,  in  a  trans- 
formation in  the  blood  of  an  excess  of  the  nitrogenized  elements  of  food.  Urea,  as  we 
have  already  seen,  exists  in  considerable  quantity  in  the  lymph  and  chyle,  and  it  is  found, 
also,  in  small  proportion,  in  the  blood.  It  has  lately  been  detected  in  still  smaller  quan- 
tity in  the  muscular  tissue ;  but  chemists  have  thus  far  been  unable  to  extract  it  from  any 
other  of  the  solid  tissues,  under  normal  conditions,  except  the  substance  of  the  liver.  The 
fact  that  it  exists  in  considerable  quantity  in  the  liver  has  led  to  the  supposition  that  this 
is  the  organ  chiefly  concerned  in  its  production.  With  the  small  amount  of  positive  infor- 
mation that  we  have  upon  this  point,  the  view  that  the  liver  produces  urea,  while  the  kid- 
neys are  the  organs  chiefly  concerned  in  its  elimination,  must  be  regarded  as  purely  hy- 
pothetical. But,  if  it  be  true  that  urea  is  the  result  of  the  physiological  wear  of  the  nitro- 
genized elements  of  the  body,  the  liver  would  probably  produce  its  share,  in  the  ordinary 
process  of  disassimilation.  The  fact  that  urea  has  not  yet  been  detected  in  normal  mus- 
cular tissue  is  by  no  means  a  conclusive  argument  against  its  formation  in  this  situation. 
We  have  lately  shown  that,  although  the  liver  is  constantly  producing  sugar,  none  can  be 
detected  in  its  substance,  for  the  reason  that  it  is  washed  out  as  fast  as  it  is  formed,  by 
the  current  of  blood.  In  the  case  of  the  muscles,  it  is  by  no  means  improbable  that  the 
lymph,  and  perhaps  the  blood,  wash  out  the  urea  constantly  and  keep  these  parts 
free  from  its  presence  during  normal  conditions.  In  some  late  experiments  by  Meissner,  - 
in  which  the  observations  of  Prevost  and  Dumas  on  the  accumulation  of  urea  in  the 
blood  of  nephrotornized  animals  were  confirmed,  urea  was  found  in  dogs  and  rabbits,  after 
removal  of  the  kidneys,  not  only  in  the  liver  but  in  the  muscles  and  brain. 

Although  our  experimental  knowledge  does  not  warrant  the  unreserved  conclusion 
that  urea  is  produced  primarily  in  the  nitrogenized  parts  of  the  organism,  particularly 
the  muscular  tissue,  this  view  is  exceedingly  probable ;  and  we  must  wait  for  farther 
information  on  this  subject,  until  physiological  chemists  are  able  to  follow  out  more 
closely  the  exact  atomic  changes  that  intervene  between  the  functional  operation  of  or- 
ganized parts  and  the  change  of  their  substance  into  excrementitious  matters. 

When  we  come  to  consider  the  influence  of  food  upon  the  composition  of  the  urine,  it 
will  be  seen  that  an  excess  of  nitrogenized  matter  taken  into  the  alimentary  canal  causes 
a  proportionate  increase  in  the  quantity  of  urea  discharged.  This  fact  has  led  to  the 
supposition  that  a  part  of  the  urea  contained  in  the  urine  is  the  result  of  a  direct  trans- 
formation in  the  blood  of  the  nitrogenized  alimentary  principles.  This  view  must  be 
regarded  as  purely  hypothetical.  We  do  not  even  know  the  nature  of  the  process  by 
which  the  nitrogenized  elements  of  the  tissues  are  transformed  into  excrementitious  mat- 
ter, and  we  are  still  more  ignorant  of  the  essential  characters  of  nutrition  proper.  When 
more  nitrogenized  food  is  taken  than  is  absolutely  necessary,  it  is  evident  that  the  excess 
must  be  discharged  from  the  system.  This  is  never  discharged  in  the  form  in  which 
it  enters,  like  an  excess  of  chloride  of  sodium  or  other  inorganic  matter,  but  it  is  well 
known  that  a  series  of  complicated  changes  are  necessary,  even  before  organic  matters 
can  be  taken  into  the  blood  by  absorption.  There  is  no  evidence  of  the  direct  transfor- 
mation of  these  principles  into  urea  before  they  have  become  part  of  the  organized  struct- 
ures, except  in  a  comparison  of  the  proportions  of  nitrogen  ingested  and  discharged  ;  and 
this  proves  nothing  with  regard  to  the  nature  of  the  intermediate  processes.  At  the 
present  time,  the  most  rational  'supposition  is,  that  the  nitrogenized  elements  of  food 
nourish  the  corresponding  constituents  of  the  body,  which  are  constantly  undergoing 
conversion  into  excrementitious  matters.  Observations  which  have  appeared  to  demon- 
strate the  formation  of  urea  directly  from  albuminoid  substances  have  not  been  confirmed. 

There  are  certain  arguments,  based  upon  comparisons  of  the  atomic  constitution  of 
urea  with  the  elements  of  uric  acid,  creatine,  and  creatinine,  in  favor  of  the  view  that 
urea  is  the  product  of  a  higher  degree  of  oxidation  of  the  other  excrementitious  matters 
above  mentioned.  It  has  been  found,  also,  that  urea  may  be  formed  artificially  from  uric 


416  EXCRETION. 

acid,  creatine,  creatinine,  xanthine,  hypoxanthine,  and  some  other  bodies  of  similar  nature. 
That  certain  bodies  are  mutally  convertible  by  the  addition  or  subtraction  of  a  few  elements 
of  water,  there  can  be  no  doubt.  Examples  of  these  simple  transformations  are,  the 
change  of  starch,  dextrine,  etc.,  into  glucose,  the  change  of  creatine  into  creatinine,  etc., 
but  the  atomic  changes  necessary  for  the  conversion  into  urea  of  the  principles  from 
which  this  substance  has  been  assumed  to  be  produced  are  much  more  complicated. 
There  is  no  positive  proof  that  the  proportion  of  these  various  principles  in  the  muscles, 
blood,  and  urine,  bears  an  inverse  ratio  to  the  proportion  of  urea.  Again,  the  argument 
that  the  excrements  of  reptiles  contain  an  excess  of  uric  acid  because  the  activity  of  oxi- 
dation is  less  than  in  the  mammalia  is  met  by  the  fact  that,  in  birds,  in  which  the  amount 
of  oxygen  consumed  is  greater,  the  proportion  of  urates  is  enormous ;  and  urea  is  not 
generally  found  in  this  class,  but  is  contained  only  in  the  excrements  of  the  rapacious 
birds,  and  here  only  in  small  quantity. 

There  are  no  sufficient  reasons  for  regarding  urea  as  the  final  result  of  oxidation  of  cer- 
tain of  the  tissues  of  the  body,  uric  acid,  creatine,  etc.,  being  substances  in  an  intermediate 
stage  of  transformation ;  and  we  are  forced  to  admit  that  this  principle  is  formed  during 
the  general  process  of  disassimilation,  probably  from  the  nitrogenized  elements  of  the 
body,  by  a  destructive  action,  with  the  exact  nature  of  which  we  are  as  yet  imper- 
fectly acquainted. 

The  daily  amount  of  urea  excreted  is  subject  to  very  great  variations.  It  is  given  in 
the  table  as  ranging  between  355  and  463  grains.  This  is  much  less  than  the  estimates 
frequently  given ;  but,  when  the  quantity  has  been  very  large,  it  has  generally  depended 
upon  an  unusual  amount  of  exercise  or  of  nitrogenized  food,  or  the  weight  of  the  body 
has  been  above  the  average.  Parkes  gives  the  results  of  twenty -five  different  series  of 
observations  upon  this  point.  The  lowest  estimate  is  2861!  grains,  and  the  highest,  688*4 
grains. 

Uric  Acid  and  its  Compounds. — Uric  acid  seldom  if  ever  exists  in  a  free  state  in 
normal  urine.  It  is  exceedingly  insoluble,  requiring  from  fourteen  to  fifteen  thousand 
times  its  volume  of  cold  water,  and  from  eighteen  to  nineteen  hundred  parts  of  boiling 
water  for  its  solution.  It  was  at  one  time  supposed  to  exist  in  the  urine  in  sufficient 
quantity  to  give  it  its  acid  reaction ;  but  it  has  since  been  ascertained  that  its  solution 
does  not  redden  litmus.  Its  presence  in  the  urine  uncombined  must  be  regarded  as  a 
pathological  condition  ;  still,  it  is  often  found  in  urinary  deposits,  where  it  is  interesting 
to  study  the  peculiar  and  varied  forms  of  its  crystals.  Frequently,  in  tables  of  the  com- 
position of  the  urine,  the  proportion  of  uric  acid  is  given,  but  this  is  simply  a  matter  of 
convenience,  and  it  has  precisely  the  same  signification  as  the  estimates  of  the  proportions 
of  sulphuric  or  of  phosphoric  acid.  None  of  these  acids  constitute,  of  themselves,  prox- 
imate principles  of  the  urine,  but  they  are  always  combined  with  bases. 

In  normal  urine,  uric  acid  is  combined  with  soda,  ammonia,  potassa,  lime,  and  mag- 
nesia. Of  these  combinations,  the  urate  of  soda  and  the  urate  of  ammonia  are  by  far  the 
most  important  and  constitute  the  great  proportion  of  the  urates,  the  urates  of  potassa, 
lime,  and  magnesia  existing  only  in  minute  traces.  The  urate  of  soda  is  very  much  more 
abundant  than  the  urate  of  ammonia.  The  union  of  uric  acid  with  the  bases  is  very 
feeble.  If  from  any  cause  the  urine  become  excessively  acid  after  its  emission,  a  deposit 
of  uric  acid  is  liable  to  occur.  The  addition  of  a  very  small  quantity  of  almost  any  acid 
is  sufficient  to  decompose  the  urates,  when  the  uric  acid  appears,  after  a  few  hours,  in  a 
crystalline  form. 

Uric  acid,  probably  in  combination  with  bases,  was  found  in  the  substance  of  the  liver 
in  large  quantity  by  Oloetta,  and  his  observations  have  been  confirmed  by.  recent  Ger- 
man authorities.  It  is  more  than  probable  that  the  urates  also  exist  in  the  blood  and 
pass  ready -formed  into  the  urine ;  but  their  proportion  in  the  blood  is  so  slight,  under 
normal  conditions,  that  their  presence  in  this  fluid  has  not  been  definitely  determined, 


COMPOSITION   OF  THE  URINE. 


417 


except  in  birds,  in  which  Meissner  has  lately  found  it  in  considerable  quantity.  The  fact 
that  the  urates  exist  in  the  liver,  and  in  no  other  part— except,  perhaps,  the  spleen— has 
led  Meissner  to  the  opinion  that  this  organ  is  the  principal  seat  of  the  formation  of  uric 
acid.  However  this  may  be — and  the  facts  do  not  seem  sufficiently  definite  to  lead  to 
such  an  exclusive  opinion — it  is  certainly  not  formed  in  the  kidneys,  but  is  simply  sepa- 


FIG.  118. — Crystals  of  uric  acid  obtained  partly 
by  the  solution  and  subsequent  precipitation 
of  chemically  pure  acid,  and  partly  by  de- 
composition of  the  urates  by  nitric  or  acetic 
acid.  (Funke.) 


FIG.  119.—  Urate  of  soda.   (Funke.) 


rated  by  these  organs  from  the  blood.  Meissner  did  not  succeed  in  finding  uric  acid  in 
the  muscular  tissue,  although  the  specimens  were  taken  from  the  same  animals  in  which 
he  had  found  large  quantities  in  the  liver. 

We  have  already  discussed  the  theory  of  the  change  of  uric  acid  into  urea.  In  the 
present  state  of  our  knowledge,  we  must  regard  the  urates,  particularly  the  urate  of  soda, 
as  among  the  products  of  disassimilation  of  the  nitrogonized  constituents  of  the  body ; 
and  we  should  admit  that  as  yet  we  are  unable  to  designate  the  precise  seat  of  their 
formation  or  to  follow  out  all  the  processes  involved  in  their  production. 

The  daily  excretion  of  uric  acid,  given  in  the  table,  is  from  six  to  nine  grains ;  which 
is  equal  to  from  nine  to  fourteen  grains  of  urates  estimated  as  neutral  urate  of  soda.  Like 
urea,  the  proportion  of  the  urates  in  the  urine  is  subject  to  certain  physiological  varia- 
tions, which  will  be  considered  farther  on. 

Hippuric  Acid,  Hippurates,  and  Lactates. — The  compounds  of  hippuric  acid,  which 
are  so  abundant  in  the  urine  of  the  herbivora,  are  now  known  to  be  constant  constitu- 
ents of  the  human  urine.  Hippuric  acid  is  always  to  be  found  in  the  urine  of  children, 
but  it  is  sometimes  absent  temporarily  in  the  adult.  The  hippurates  have  been  de- 
tected in  the  blood  of  the  ox  by  Verdeil  and  Dolfuss,  and  they  have  since  been  found  in 
the  blood  of  the  human  subject.  There  can  be  scarcely  any  doubt  that  they  pass,  ready- 
formed,  from  the  blood  into  the  urine.  With  regard  to  the  exact  mode  of  origin  of  the 
hippurates,  we  have  even  less  information  than  upon  the  origin  of  the  other  urinary  con- 
stituents already  considered.  Experiments  have  shown  that  the  proportion  of  hippuric 
acid  in  the  urine  is  greatest  after  taking  vegetable  food ;  but  it  is  found  after  a  purely 
animal  diet,  and  probably  it  also  exists  during  fasting.  We  must  be  content  at  present 
simply  to  class  the  hippurates  among  the  products  of  disassimilation,  without  attempting  to 
specify  their  exact  mode  of  origin.  The  daily  excretion  of  hippuric  acid  amounts  to 
about  7'5  grains,  which  is  equivalent  to  about  8'7  grains  of  hippurate  of  soda. 

Hippuric  acid  itself,  unlike  uric  acid,  is  quite  soluble  in  water  and  in  a  mixture  of 
27 


418 


EXCRETION. 


hydrochloric  acid.     It  requires  six  hundred  parts  of  cold  water  for  its  solution,  and  a 
much  smaller  proportion  of  warm  water.     Under  pathological  conditions,  it  is 
found  free  in  solution  in  the  urine. 

The  lactates  of  soda,  potassa,  and  lime,  exist  in  very  considerable  proportion  m  the 
normal  urine.  They  are  undoubtedly  derived  immediately  from  the  blood,  passing 
ready-formed  into  the  urine,  where  they  exist  in  simple  watery  solution.  According  to 
Robin,  the  lactates  are  formed  in  the  muscles,  in  the  substance  of  which  they  can  be 
readily  detected.  We  have  no  positive  information  with  regard  to  the  precise  mode  of 
formation  of  these  salts.  It  is  probable,  however,  that  the  lactic  acid  is  the  result  of 


FIG.  120.— Crystals  ofhippuric  acla.    (Funke.) 


FIG.  Vll.—Lactate  of  lime,  from  chemically  pure 
lactic  acid  and  carbonate  of  lime,  crystal- 
lized from  a  hot,  watery  solution.  (Funke.) 


transformation  of  glucose.  As  a  curious  chemical  fact,  it  is  interesting  to  note  that  the 
lactic  acid  contained  in  the  lactates  extracted  from  the  muscular  substance  is  not  abso- 
lutely identical  with  the  acid  resulting  from  the  transformation  of  the  sugars.  The  for- 
mer have  been  called  sarcolactates,  and  they  contain  one  equivalent  of  water  less  than 
the  ordinary  lactates.  According  to  Robin,  the  compounds  of  lactic  acid  in  the  urine  are 
in  the  form  of  sarcolactates. 

Although  the  inosates  have  never  been  detected  in  the  urine,  Robin  is  of  the  opinion 
that  traces  of  these  salts  are  separated  from  the  blood  by  the  kidneys,  from  the  fact  that 
they  exist  normally  in  the  blood  and  in  the  muscular  tissue. 

"We  have  little  or  no  information  with  regard  to  the  relations  of  the  inosates  to  ex- 
cretion. 

t  Creatine  and  Creatinine. — Oreatine  and  creatinine  are  undoubtedly  identical  in  their 
relations  to  the  general  process  of  disassimilation,  for  one  is  easily  converted  into  the 
other,  out  of  the  body,  by  very  simple  chemical  means ;  and  there  is  every  reason  to 
suppose  that,  in  the  organism,  they  are  the  products  of  physiological  waste  of  the  same 
tissue  or  tissues.  These  principles  have  been  found  in  the  urine,  blood,  muscular  tissue, 
and  brain.  Scherer  has  demonstrated  the  presence  of  creatine  in  the  amniotic  fluid.  By 
certain  chemical  manipulations,  both  creatine  and  creatinine  may  be  converted  into  urea  ; 
and  the  fact  that  these  substances  are  now  known  to  be  constant  constituents  of  the 
urine  leaves  no  doubt  that  they  are  to  be  classed  among  the  excrementitious  principles. 
Ohevreul,  who  first  discovered  creatine  in  the  extract  of  muscular  tissue,  regarded  it  as 
one  of  the  nutritive  principles  of  meat ;  but  the  subsequent  researches  of  Heintz,  Liebig, 
and  others,  who  found  it  in  the  urine,  revealed  its  true  character.  Verdeil  and  Marcet 
have  since  found  both  creatine  and  creatinine  in  the  blood ;  and  these  principles  are  now 


COMPOSITION   OF  THE   URINE. 


419 


generally  regarded  as  excrementitious  matters,  taken  from  the  tissues  by  the  blood,  to  be 
eliminated  by  the  kidneys. 

Creatine  has  a  bitter  taste,  is  quite  soluble  in  cold  water  (one  part  in  seventy-five),  and 
is  much  more  soluble  in  hot  water,  from  which  it  separates  in  a  crystalline  form  on  cool- 
ing. It  is  but  slightly  soluble  in  alcohol  and  is  insoluble  in  ether.  A  watery  solution 
of  creatine  is  neutral.  It  does  not  readily  form  combinations  as  a  base ;  but  it  has  lately 
been  made  to  form  crystalline  compounds  with  some  of  the  strong  mineral  acids,  the 
nitric,  hydrochloric,  and  sulphuric.  When  boiled  for  a  long  time  with  baryta,  it  is  changed 
into  urea  and  sarcosine ;  but  the  recent  researches  of  Voit  have  pretty  conclusively  shown 
that  this  change  does  not  take  place  in  the  living  organism,  and  that  probably  none  of  the 
urea  of  the  urine  is  produced  in  this  way.  When  boiled  with  the  strong  acids,  creatine 
loses  four  atoms  of  water  and  is  converted  into  creatinine.  This  change  takes  place  very 
readily  in  decomposing  urine,  which  contains  neither  urea  nor  creatine  but  a  large  quan- 
tity of  creatinine,  when  far  advanced  in  putrefaction. 


Fi<;.  122. — Creatine,  extracted  from  the,  muscular 
tissue,  and  crystallized  from  a  hot,  watery 
solution.  (Funke.) 


FIG.  128. — Creatinine,  formed  from  creatine  by 
digestion  with  hydrochloric  acid,  and  crystal- 
lised from  a  hot,  watery  solution.  (Funke.) 


Creatinine  is  more  soluble  than  creatine,  and  its  watery  solution  has  a  strongly  alka- 
line reaction.  It  is  dissolved  by  eleven  parts  of  cold  water  and  is  even  more  soluble  in 
boiling  water.  It  is  slightly  soluble  in  ether  and  is  dissolved  by  one  hundred  parts  of 
alcohol.  This  substance  is  regarded  as  one  of  the  most  powerful  of  the  organic  bases, 
readily  forming  crystalline  combinations  with  a  number  of  acids.  According  to  Thudi- 
chum,  who  has  very  closely  studied  the  physiological  relations  of  these  substances,  crea- 
tine is  the  original  excrementitious  principle  produced  in  the  muscular  substance,  and 
creatinine  is  formed  in  the  blood  by  a  transformation  of  a  portion  of  the  creatine,  some- 
where between  the  muscles  and  the  kidneys  ;  "  for,  in  the  muscle,  creatine  has  by  far  the 
preponderance  over  creatinine ;  in  the  urine,  creatinine  over  creatine." 

In  the  present  state  of  our  knowledge,  there  is  very  little  to  be  said  with  regard  to 
the  physiological  relations  of  creatine  and  creatinine,  except  that  they  are  probably  to  be 
classed  among  the  excrementitious  principles  resulting  from  the  disassimilation  of  the 
muscular  tissue.  As  they  exist  in  considerable  quantity  in  the  muscular  substance,  it  be- 
comes a  question  whether,  in  the  urine  of  carnivorous  animals,  they  be  not  derived  from 
the  food  ;  but  they  could  have  no  such  origin  in  the  herbivora  or  in  the  urine  of  starving 
animals. 

It  has  been  assumed  by  many  authors  that,  inasmuch  as  the  muscular  tissue  of  the 
heart  is  in  almost  constant  action,  it  should  contain  more  creatine  than  any  other  portion 
of  the  muscular  system ;  but  late  observations  on  this  point  show  that  the  reverse  of  this 


420 


EXCRETION. 


is  the  case.  In  comparing  the  proportion  of  creatine  in  the  heart  and  in  the  muscles  of 
the  extremities,  in  oxen  and  in  the  human  subject,  the  quantity  has  been  found  to  be 
much  less  in  the  heart ;  still,  the  proportion  of  creatine  has  been  found  to  be  greater  in 
tetanized  muscles  than  in  the  muscular  tissue  after  repose. 

From  the  meagreness  of  our  facts  with  regard  to  the  physiological  relations  of  creatine 
and  creatinine,  it  is  evident  that  there  is  much  to  be  learned  before  we  can  understand 
the  process  of  their  formation  in  the  healthy  organism  and  the  probable  results  of  their 
retention  or  deficient  elimination  in  disease.  At  present  we  can  only  say  that  these  prin- 
ciples are  probably  produced  in  greatest  part  in  the  muscular  tissue.  The  fact  that  cre- 
atine has  lately  been  demonstrated  in  the  brain  would  lead  to  the  supposition  that  it  is 
also  one  of  the  products  of  disassimilation  of  the  nervous  substance. 

The  average  daily  excretion  of  creatine  and  creatinine  is  estimated  by  Thudichum  at 
about  11 '5  grains.  Of  this  he  estimates  that  4*5  grains  consist  of  creatine,  and  7  grains, 
of  creatinine. 

Oxalate  of  Lime. — This  salt  is  not  constantly  present  in  the  normal  human  urine, 
although  it  may  exist  in  considerable  quantity  without  indicating  any  pathological  condi- 
tion. It  is  exceedingly  insoluble,  and  the  appearance  of  its  crystals,  which  are  commonly 
in  the  form  of  small,  regular  octahedra,  is  quite  characteristic.  According  to  Robin,  a 
trace  may  be  retained  in  solution  by  the  chlorides  and  the  alkaline  phosphates  in  the 
urine.  This  salt  may  find  its  way  out  of  the  system  by  the  kidneys,  after  it  has  been 
taken  with  vegetable  food  or  with  certain  medicinal  substances.  The  ordinary  rhubarb, 
or  pie-plant,  contains  a  large  quantity  of  oxalate  of  lime,  which,  when  this  article  is  taken, 
will  pass  into  the  urine.  It  is  probable,  however,  that  a  certain  quantity  of  oxalate  of  lime 
may  be  formed  in  the  organism.  Pathologists  now  recognize  a  condition  called  oxaluria, 
characterized  by  the  appearance  of  oxalate-of-lime  crystals  in  the  urinary  sediments ;  and 
sometimes  the  quantity  in  the  urine  is  so  large,  and  its  presence  is  so  constant,  that  it 
forms  vesical  calculi  of  considerable  size. 


FIG. ,m.-Crystal8  of  oxalate  of  Ume,  deposited 
from  the  normal  human  urine,  on  the  addition 
to  the  urine,  of  oxalate  of  ammonia.  (Funke.) 


FIG  125—  Crystals  of  leucine.     (Funke.) 


Inasmuch  as  pathological  facts  have  shown  pretty  conclusively  that  oxalic  acid  may 
appear  in  the  system  without  being  introduced  with  the  food,  some  physiologists  have 
endeavored  to  show  how  it  may  originate  from  a  change  in  certain  other  of  the  proximate 
principles  from  which  it  can  be  produced  artificially  out  of  the  body.  One  of  the  sub- 
stances from  which  oxalic  acid  can  be  thus  formed  is  uric  acid.  It  remains,  however,  to 
show  that  this  can  take  place  in  the  living  organism.  Woehler  and  Frerichs  injected 


COMPOSITION   OF   THE   URINE. 


421 


into  the  jugular  vein  of  a  dog  a  solution  containing  about  twenty-three  grains  of  urate  of 
ammonia.  In  the  urine,  taken  a  short  time  after,  there  was  no  deposit  of  uric  acid  but 
there  appeared  numerous  crystals  of  oxalate  of  lime.  The  same  result  followed  in  the 
human  subject,  on  the  administration  of  sixty-seven  grains  of  urate  of  ammonia  by  the 
mouth.  These  questions  have  more  of  a  pathological  than  a  physiological  interest ;  for 
the  quantity  of  oxalate  of  lime  in  the  normal  urine  is  insignificant,  and  this  salt  does  not 
seem  to  be  connected  with  any  of  the  well-known  processes  of  disassimilation. 

Xanthine,  Hypoxanthine,  Leucine,  Tyrosine,  and  Taurine. — Traces  of  xanthine  have 
been  found  in  the  normal  human  urine,  but  its  proportion  has  not  been  estimated,  and 
we  are  as  yet  but  imperfectly  acquainted  with  its  physiological  relations.  Under  patho- 


FIG.  126.— Crystals  of  tyros  in  e.    (Funke.) 


FIG.  121.— Crystals  oftaurine.    (Funke.) 


logical  conditions,  it  occasionally  exists  in  sufficient  quantity  to  form  urinary  calculi.  It 
has  been  found  in  the  liver,  spleen,  thymus,  pancreas,  muscles,  and  brain.  It  is  in- 
soluble in  water  but  is  soluble  in  both  acid  and  alkaline  fluids.  Hypoxan thine  has  never 
been  found  in  normal  urine,  although  it  exists  in  the  muscles,  liver,  spleen,  and  thymus. 
Leucine  exists  in  the  pancreas,  salivary  glands,  thyroid,  thymus,  suprarenal  capsules, 
lymphatic  glands,  liver,  lungs,  kidneys,  and  in  the  gray  substance  of  the  brain.  It  has 
never  been  detected  in  the  normal  urine.  The  same  remarks  apply  to  tyrosine  (although 
it  is  not  so  extensively  distributed  in  the  economy),  to  taurine  and  cystine.  The  last  two, 
however,  contain  sulphur,  and  they  may  have  peculiar  physiological  and  pathological 
relations  that  we  do  not  at  present  understand. 

These  various  substances  are  mentioned,  although  some  of  them  have  not  been  demon- 
strated in  the  normal  urine,  for  the  reason  that  there  is  evidently  much  to  be  learned 
with  regard  to  the  various  products  of  disassimilation  as  they  are  represented  by  the 
composition  of  the  urine.  While  some  of  these  may  not  be  actual  proximate  principles, 
but  substances  produced  by  the  processes  employed  for  their  extraction,  some,  which 
have  thus  far  been  discovered  only  under  pathological  conditions,  may  yet  be  found  in 
health,  and  they  represent,  perhaps,  important  physiological  acts. 

Fatty  Matters. — Fat  and  fatty  acids  are  said  to  exist  in  the  normal  urine  in  certain 
quantity.  Their  proportion,  however,  is  small,  and  the  mere  fact  of  their  presence, 
only,  is  of  physiological  interest. 

Inorganic   Constituents  of  the    Urine. 

It  is  by  the  kidneys  that  the  greatest  quantity  and  variety  of  inorganic  principles  are 
discharged  from  the  organism ;  and  it  is  probable  that  even  now  we  are  not  acquainted 


423 


EXCRETION. 


with  the  exact  proportion  and  condition  of  all  the  principles  of  this  class  contained  in 
the  urine.  In  all  the  processes  of  nutrition,  it  is  found  that  the  inorganic  constituents  of 
the  blood  and  tissues  accompany  the  organic  matters  in  their  various  transformations, 
although  they  are  themselves  unchanged.  In  fact,  the  condition  of  union  of  the  inorganic 
with  the  organic  principles  is  so  intimate,  that  they  cannot  be  completely  separated  with- 
out incineration.  In  view  of  these  facts,  it  is  evident  that  a  certain  part,  at  least,  of  the 
inorganic  salts  of  the  urine  is  derived  from  the  tissues,  of  which,  in  combination  with 
organic  matters,  they  have  formed  a  constituent  part.  As  the  kidneys  frequently  elimi- 
nate from  the  blood  foreign  matters  taken  into  the  system  and  are  capable  sometimes  of 
throwing  off  an  excess  of  the  normal  principles  which  may  be  introduced  into  the  cir- 
culation, it  can  be  readily  understood  how  a  large  proportion  of  some  of  the  inorganic 
matters  of  the  urine  may  be  derived  from  the  food. 

From  the  fact  that  the  inorganic  matters  discharged  in  the  urine  are  generally  the 
same  as  those  introduced  with  the  food,  and  that  they  vary  in  proportion  with  the  con- 
stitution of  the  food,  it  is  difficult  to  ascertain  how  far  their  presence  and  quantity  in  the 
urine  represent  the  processes  of  disassimilation.  One  thing,  however,  is  certain :  that 
the  organic  constituents  of  the  food,  the  blood,  the  tissues,  and  the  urine,  are  never  with- 
out inorganic  matter  in  considerable  variety  ;  and  it  is  more  than  probable  that  the  pres- 
ence of  these  salts  in  a  tolerably  definite  proportion  influences  the  processes  of  absorption 
and  secretion  and  has  an  important  bearing  upon  nutrition  ;  but  we  are  as  yet  so  imper- 
fectly acquainted  with  the  processes  of  nutrition  of  the  tissues,  that  we  cannot  follow 
out  all  the  relations  of  the  inorganic  matters,  first  to  nutrition,  and  afterward  to  disas- 
similation. 

Chlorides. — Almost  all  of  the  chlorine  in  the  urine  is  in  the  form  of  chloride  of  so- 
dium, the  amount  of  chloride  of  potassium  being  insignificant  and  not  of  any  special 

physiological  importance.  It  is  unnecessary,  in 
this  connection,  to  describe  the  well-known 
properties  of  common  salt,  and  the  methods  for 
determining  its  presence  and  proportion  in  the 
urine  are  fully  treated  of  in  works  upon  physi- 
ological chemistry.  All  that  we  have  to  con- 
sider is  its  importance  and  significance  as  a  uri- 
nary constituent. 

By  reference  to  the  table  of  the  composition 
of  the  urine,  it  is  seen  that  the  proportion  of 
chloride  of  sodium  is  subject  to  very  great  vari- 
ations, the  range  being  from  three  to  eight  parts 
per  thousand.  This  at  once  suggests  the  idea 
that  the  quantity  excreted  is  dependent  to  a 
considerable  extent  upon  the  amount  taken  in 
with  the  food ;  and,  indeed,  it  has  been  shown 
by  numerous  observations  that  this  is  the  fact. 
The  proportion  of  chloride  of  sodium  in  the  blood 
seems  to  be  tolerably  constant;  and  any  excess  that  maybe  introduced  is  thrown  off 
chiefly  by  the  kidneys.  It  has  been  shown  conclusively  that  deprivation  of  common  salt 
in  the  food  after  a  time  is  followed  by  serious  disturbances  in  the  general  process  of 
nutrition  ;  and  it  is  an  acknowledged  fact  that  this  proximate  principle  is  a  constituent 
of  every  tissue  of  the  body,  except  the  enamel  of  the  teeth.  As  the  chlorides  are  de- 
posited with  the  organic  matter  in  all  the  acts  of  nutrition,  they  are  found  to  be  elimi- 
nated constantly  with  the  products  of  disassimilation  of  the  nitrogenized  parts,  and  their 
absence  from  the  food  does  not  completely  arrest  their  discharge  in  the  urine.  Accord- 
ing to  Robin,  by  suppressing  salt  in  the  food,  its  daily  excretion  may  be  reduced  to  from 


FIG.  128.— Crystals  of  chloride  of  sodium. 
(Funke.) 


INORGANIC   CONSTITUENTS   OF  THE  URINE.  423 

thirty  to  forty-five  grains,  the  normal  quantity  being  from  one  hundred  and  fifty  to  one 
hundred  and  sixty  grains.  This  quantity  is  less  than  the  amount  contained  in  the 
ingesta,  and  under  these  circumstances  there  is  a  gradual  diminution  in  the  nutritive 
activity.  "This  tact  demonstrates  the  necessity  of  adding  chloride  of  sodium  to  the 
food."  It  is  an  interesting  pathological  fact  that,  in  all  acute  febrile  disorders,  the  pro- 
portion of  chlorine  in  the  urine  rapidly  diminishes  and  is  frequently  reduced  to  one  hun- 
dredth of  the  normal  amount.  The  quantity  rapidly  increases  to  the  normal  standard 
during  convalescence.  Most  of  the  chlorides  of  the  urine  are  in  simple  watery  solution ; 
but  a  certain  proportion  of  the  chloride  of  sodium  exists  in  combination  with  urea. 

The  daily  elimination  of  chloride  of  sodium  is  about  one  hundred  and  fifty-four  grains 
(Robin).  The  great  variations  in  its  proportion  in  the  urine,  under  different  conditions 
of  alimentation,  etc.,  will  explain  the  differences  in  the  estimates  given  by  various 
authorities. 

Sulphates. — There  is  very  little  to  be  said  regarding  the  sulphates,  beyond  the  general 
statements  we  have  made  concerning  the  inorganic  principles  of  the  urine.  The  propor- 
tion of  these  salts  in  the  urine  is  very  much  greater  than  in  the  blood,  in  which  there 
exists  only  about  0'28  of  a  part  per  thousand.  Inasmuch  as  the  proportion  in  the  urine  is 
from  three  to  seven  parts  per  thousand,  it  seems  probable  that  the  kidneys  eliminate 
these  principles  as  fast  as  they  find  their  way  into  the  circulating  fluid,  either  from  the 
food  or  from  the  tissues.  Like  other  principles  derived  in  great  part  from  the  food,  the 
normal  variations  in  the  proportion  of  sulphates  in  the  urine  are  very  great.  It  is  unne- 
cessary to  consider  in  detail  the  variations  in  the  amount  of  sulphates  discharged  in  the 
urine,  depending  upon  the  ingestion  of  different  salts  or  upon  diet,  for  all  the  recorded 
observations  have  been  followed  by  the  same  results,  and  they  show  that  the  ingestion  of 
sulphates  in  quantity  is  followed  by  a  corresponding  increase  in  the  proportion  eliminated. 

Thudichum  estimates  the  daily  excretion  of  sulphuric  acid  at  from  23  to  38  grains. 
Assuming,  with  Robin,  that  the  sulphates  consist  of  about  equal  parts  of  sulphate  of 
potassa  and  sulphate  of  soda,  with  traces  of  sulphate  of  lime,  the  quantity  of  salts  would  be 
from  22*5  to  3V'5  grains  of  sulphate  of  potassa  and  an  equal  quantity  of  sulphate  of  soda. 

Phosphates. — The  urine  contains  phosphates  in  a  variety  of  forms;  but,  inasmuch  as 
it  is  not  known  that  any  one  of  the  different  combinations  possesses  peculiar  relations  to 
the  process  of  disassimilation,  as  distinguished  from  the  other  phosphates,  the  phosphatic 
salts  may  be  considered  together. 

The  remarks  which  we  have  just  made  with  regard  to  the  chlorides  and  the  sulphates 
are  applicable,  to  a  certain  extent,  to  the  phosphates.  These  salts  exist  constantly  in  the 
urine,  and  they  are  derived  in  part  from  the  food  and  in  part  from  the  tissues.  Like  other 
inorganic  matters,  they  are  united  with  the  nitrogenized  elements  of  the  organism,  and, 
when  these  are  changed  into  excrementitious  principles  and  are  separated  from  the  blood 
by  the  kidneys,  they  pass  with  them  and  are  discharged  from  the  organism. 

It  becomes  a  question  of  importance,  now,  to  consider  how  far  the  phosphates  are 
derived  from  the  tissues,  and  what  proportion  comes  directly  from  the  food.  This  point 
is  peculiarly  interesting,  from  the  fact  that  phosphorus  has  been  shown  to  exist  in  the 
nerve-tissue,  and  it  has  been  inferred  that  the  excretion  of  phosphates  represents,  to  some 
extent,  the  physiological  wear  of  the  nervous  system. 

All  observers  agree  that  the  quantity  of  phosphates  in  the  urine  is  in  direct  relation 
to  the  proportion  in  the  food,  and  that  an  excess  of  phosphates  taken  into  the  stomach  is 
immediately  thrown  off  by  the  kidneys.  It  is  a  familiar  fact,  indeed,  that  the  phosphates 
are  deficient  and  the  carbonates  predominate  in  the  urine  of  the  herbivora,  while  the 
reverse  obtains  in  the  carnivora,  and  that  variations,  in  this  respect,  in  the  urine,  may  be 
produced  by  feeding  animals  with  different  kinds  of  food.  Verdeil  made  some  very 
interesting  comparative  analyses  of  the  blood  for  the  alkaline  phosphates  in  the  herbivora, 


424  EXCRETION. 

the  carnivora,  and  in  man.  He  found  the  proportion  very  small  in  the  ox,  as  compared 
with  the  dog,  and  intermediate  in  the  human  subject.  The  proportion  of  phosphates  in 
the  blood  of  the  dog  was  greatly  diminished  by  feeding  with  potato.  Deprivation  of  food 
diminishes  the  quantity  of  phosphates  in  the  urine,  but  a  certain  proportion  is  discharged, 
which  is  derived  exclusively  from  the  tissues.  We  have  already  noted  the  fact  that  the 
products  of  disassimilation  of  the  nitrogenized  principles  are  never  discharged  in  health 
without  being  accompanied  with  certain  inorganic  salts,  such  as  the  chlorides,  sulphates, 

and  phosphates. 

In  connection  with  the  fact  that 'phosphorus  exists  (in  precisely  what  condition  it  is 
not  known)  in  the  nervous  matter,  it  has  been  stated  that  mental  exertion  is  always 
attended  with  an  increase  in  the  elimination  of  phosphates ;  and  this  has  been  advanced  to 
support  the  view  that  these  salts  are  specially  derived  from  disassimilation  of  the  brain- 
substance.  Experiments  show  that  it  is  not  alone  the  phosphates  that  are  increased  in 
quantity  under  these  conditions,  but  urea,  the  chlorides,  sulphates,  and  inorganic  matters 
generally ;  and,  in  point  of  fact,  any  physiological  conditions  which  increase  the  pro- 
portion of  nitrogenized  excrementitious  principles  increase  as  well  the  elimination  of 
inorganic  matters.  It  cannot  be  assumed,  therefore,  that  the  discharge  of  phosphates  is 
specially  connected  with  the  activity  of  the  brain.  We  learn  nothing  from  pathology 
upon  this  point,  for,  although  numerous  observations  have  been  made  upon  the  excretion 
of  phosphoric  acid  in  disease — Vogel  having  made  about  one  thousand  diiferent  analyses 
in  various  affections— no  definite  results  have  been  obtained.  From  these  facts  it  is  seen 
that  there  is  no  physiological  reason  why  we  should  connect  the  elimination  of  the  phos- 
phates with  the  disassimilation  of  any  particular  tissue  or  organ,  especially  as  these  salts 
in  some  form  are  universally  distributed  in  the  organism. 

Observations  have  been  made  upon  the  hourly  variations  in  the  discharge  of  phos- 
phoric acid  at  diiferent  periods  of  the  day  ;  but  these  do  not  appear  to  bear  any  absolute 
relation  to  known  physiological  conditions,  not  even  to  the  process  of  digestion. 

Of  the  different  phosphatic  salts  of  the  urine,  the  most  important  are  those  in  which 
the  acid  is  combined  with  soda.  These  exist  in  the  form  of  the  neutral  and  acid  phos- 
phates. The  acid  salt  has  one  equivalent  of  the  base  and  is  supposed  to  be  the  source  of 
the  acidity  of  the  urine  at  the  moment  of  its  emission.  The  so-called  neutral  salt  i& 
slightly  alkaline  and  has  two  equivalents  of  the  base.  The  proportion  of  the  phosphates 
of  soda  in  the  urine  is  larger  than  that  of  any  of  the  other  phosphatic  salts,  but  the  daily 
amount  excreted  has  not  been  estimated.  The  phosphate  of  magnesia  is  a  constant  con- 
stituent of  the  urine,  as  well  as  the  acid  and  the  basic  phosphate  of  lime.  The  daily 
excretion  of  phosphate  of  magnesia  amounts  to  from  V'7  to  11 '8  grains,  and  that  of  the  phos- 
phates of  lime,  from  4*7  to  5'V  grains.  According  to  Robin,  there  always  exists  in  the 
urine  a  small  quantity  of  the  ammonio-magnesian  phosphate,  but  it  never,  in  health, 
exists  in  sufficient  quantity  to  form  a  crystalline  deposit.  The  daily  excretion  of  the  phos- 
phates is,  as  we  have  seen,  subject  to  great  variations,  but  the  average  quantity  of  phos- 
phoric acid  excreted  daily  may  be  estimated  at  about  fifty  grains,  or,  more  accurately, 
fifty-six  grains. 

The  urine  contains,  in  addition  to  the  inorganic  principles  above  described,  a  small 
quantity  of  silicic  acid ;  but,  as  far  as  we  know,  this  has  no  physiological  importance. 

Coloring  Matter  and  Mucus. 

The  peculiar  color  of  the  urine  is  due  to  the  presence  of  a  nitrogenized  principle, 
known  to  physiological  chemists  under  a  variety  of  names.  We  have  mentioned  it  in  the 
table  as  urrosacine.  It  is  also  called  urochroine,  urohaematine,  uroxan thine,  and  purpu- 
rine.  We  have  no  accurate  account  of  its  ultimate  composition,  and  all  that  is  known 
about  its  constituents  is  that  it  contains  carbon,  oxygen,  hydrogen,  and  nitrogen,  and 
probably  iron.  Although  its  exact  ultimate  composition  is  not  absolutely  settled,  its  con- 
stituents are  supposed  to  be  nearly  the  same  as  those  of  the  coloring  matter  of  the  blood, 


GASES   OF  THE   URINE.  425 

the  proportion  of  oxygen  being  very  much  greater.  These  facts  point  to  the  probability 
of  the  formation  of  urrosacine  from  hasmaglobine. 

The  quantity  of  coloring  matter  in  the  normal  urine  is  very  small.  It  is  subject  to 
considerable  variation  in  disease,  and  almost  always  it  is  fixed  by  deposits  and  calculi  of 
uric  acid  or  the  urates,  giving  them  their  peculiar  color.  This  principle  first  makes  its 
appearance  in  the  urine  and  is  probably  formed  in  the  kidneys.  So  little  is  known  of  its 
physiological  or  pathological  relations  to  the  organism,  that  it  does  not  seem  necessary  to 
follow  out  all  of  the  chemical  details  of  its  behavior  in  the  presence  of  different  reagents. 

The  normal  urine  always  contains  a  small  quantity  of  mucus,  with  more  or  less  epi- 
thelium from  the  urinary  passages,  and  a  few  leucocytes.  These  form  a  faint  cloud  in 
the  lower  strata  of  healthy  urine  after  a  few  hours'  repose.  The  properties  of  the  differ- 
ent kinds  of  mucus  have  already  been  considered.  An  important  peculiarity,  however, 
of  the  mucus  contained  in  normal  urine  is  that  it  does  not  seem  to  excite  decomposition 
of  the  urea,  and  that  the  urine  may  remain  for  a  long  time  in  the  bladder  without  under- 
going any  putrefactive  change. 

Gases  of  the   Urine. 

In  the  process  of  separation  of  the  urine  from  the  blood  by  the  kidneys,  a  certain 
proportion  of  the  gases  in  solution  in  the  circulating  fluid  is  also  removed.  For  a  long 
time,  indeed,  it  has  been  known  that  the  normal  human  urine  contained  different  gases, 
but  lately  some  very  interesting  observations  on  this  subject  have  been  made  by  M. 
Morin,  in  which  the  proportions  of  the  free  gases  in  solution  have  been  accurately  esti- 
mated. By  using  the  method  employed  by  Magnus  in  estimating  the  gases  of  the  blood, 
Morin  was  able  to  extract  about  two  and  a  half  volumes  of  gas  from  a  hundred  parts  of 
urine.  By  careful  experiments,  he  ascertained  that  a  certain  quantity  of  gas  remained  in 
the  urine  and  could  not  be  extracted  by  his  ordinary  process.  This  amounted  to  about 
one -fifth  of  the  whole  volume  of  gas.  Adding  this  to  the  quantity  of  gas  extracted,  he 
obtained  the  proportions  to  one  litre  of  urine,  in  cubic  centimetres,  which  are  given  in 
the  table,  viz. : 

Oxygen 0-824 

Nitrogen 9'589 

Carbonic  acid 19*620 

These  proportions  represent  the  average  of  fifteen  observations  upon  the  urine  secreted 
during  the  night. 

The  proportion  of  these  gases  was  found  by  Morin  to  be  subject  to  certain  variations. 
For  example,  after  the  ingestion  of  a  considerable  quantity  of  water  or  any  other  liquid, 
the  proportion  of  oxygen  was  considerably  increased  (from  0'824  to  1'024),  and  the  car- 
bonic acid  was  diminished  more  than  one-half.  The  most  interesting  variations,  how- 
ever, were  in  connection  with  muscular  exercise.  After  walking  a  long  distance,  the 
exercise  being  taken  both  before  and  after -eating,  the  quantity  of  carbonic  acid  was  found 
to  be  double  that  contained  in  the  urine  after  repose.  The  proportion  of  oxygen  was 
very  slightly  diminished,  and  the  nitrogen  was  somewhat  increased.  The  variations  of 
these  gases,  however,  were  insignificant. 

Morin  explains  the  great  increase  in  the  proportion  of  carbonic  acid,  by  the  greater 
respiratory  activity  during  exercise.  It  is  well  known,  indeed,  that  muscular  exercise 
largely  increases  the  proportion  of  carbonic  acid  in  the  blood  and  the  quantity  eliminated 
by  the  lungs ;  and,  as  the  carbonic  acid  of  the  urine  is  undoubtedly  derived  from  the 
blood,  we  should  expect  that  the  same  conditions  would  increase  its  proportion  in  this 
secretion. 

It  is  not  probable  that  the  kidneys  are  very  important  as  eliminators  of  carbonic  acid 
from  the  system,  but  it  is  certain  that  the  presence  of  this  gas  in  the  urine  assists  in  the 
solution  of  some  of  the  saline  constituents  of  this  fluid,  notably  the  phosphates. 


426  EXCRETION. 

Variations  in  the   Composition  of  the    Urine. 

The  urine  represents,  in  its  varied  constituents,  not  only  a  great  part  of  the  physiolo- 
gical disintegration  of  the  organism,  but  it  contains  elements  evidently  derived  from  the 
food.  Its  constitution  is  varying  with  every  different  condition  of  nutrition,  with  exer- 
cise, bodily  and  mental,  with  sleep,  age,  sex,  diet,  respiratory  activity,  the  quantity  of 
cutaneous  exhalation,  and,  indeed,  with  every  condition  that  affects  any  part  of  the  sys- 
tem. There  is  no  fluid  in  the  body  that  contains  such  a  variety  of  principles,  as  a  con- 
stant condition,  but  in  which  the  proportion  of  these  principles  is  so  variable.  It  is  for 
this  reason  that  we  have  given  in  the  table  of  the  composition  of  the  urine  the  ordinary 
limits  of  variation  of  its  different  constituents ;  and  it  has  been  found  necessary,  in  treat- 
ing of  the  individual  excrementitious  principles,  to  refer  to  some  of  the  variations  in  their 
proportion  in  the  urine.  In  treating  more  specially  of  the  physiological  variations  of  the 
urine,  we  shall  only  refer  in  general  terms  to  conditions  that  produce  wide  and  important 
changes  in  the  proportion  of  its  constituents ;  and,  under  the  head  of  nutrition,  we  shall 
consider  how  far  the  absolute  quantities  of  the  urinary  principles  and  other  excrementi- 
tious substances  represent  the  physiological  waste  which  is  always  coincident  with  the 
repair  of  the  parts. 

Variations  with  Age  and  Sex. — There  are  decided  differences  in  the  composition  of 
the  urine  at  different  periods  of  life  and  in  the  sexes.  These  undoubtedly  depend  in 
part  upon  the  different  conditions,  of  nutrition  and  exercise,  and  in  part  upon  differences 
in  the  food.  Although  the  quantities  of  excrementitious  matters  present  great  varia- 
tions, their  relations  to  the  organism  are  not  materially  modified,  except,  perhaps,  at  an 
early  age ;  and  the  influence  of  sex  and  age  operates  merely  as  these  conditions  affect  the 
diet  and  the  general  habits  of  life. 

It  is  stated  by  most  authors  that  the  urine  of  the  foetus  is  highly  albuminous  and  con- 
tains no  urea ;  but  examinations  of  the  urine  in  the  foetus  and  newly  born  have  been  so 
few  that  we  know  very  little  regarding  its  constitution  and  normal  variations.  The  re- 
searches of  the  authorities  on  this  subject,  quoted  by  Parkes,  leave  the  question  of  the 
composition  of  the  urine  in  the  foetus  and  during  the  first  days  of  extra-uterine  life 
still  uncertain.  In  a  specimen  of  urine  taken  from  a  still-born  child  delivered  with  for- 
ceps, examined  by  Drs.  Elliot  and  Isaacs,  the  presence  of  urea  was  determined.  Dr. 
Beale  found  urea  in  a  specimen  taken  at  the  seventh  month. 

With  our  present  imperfect  knowledge  of  the  composition  of  the  urine  at  the  earliest 
periods  of  existence,  it  is  impossible  to  deduce  any  conclusions  regarding  the  production 
of  the  excrementitious  principles  at  this  time  ;  and  it  would  be  unprofitable  to  detail  the 
unsatisfactory  and  conflicting  examinations  to  be  found  in  works  devoted  specially  to  the 
urine.  Observations  upon  children  between  the  ages  of  three  and  seven  are  more  definite. 
At  this  period  of  life,  the  amount  of  urea  excreted  in  proportion  to  the  weight  of  the  body 
is  about  double  that  in  the  adult.  The  amount  of  chlorine  in  children  is  about  three 
times  the  quantity  in  the  adult ;  and  the  proportionate  amount  of  other  solid  matters  is 
also  greater.  The  amount  of  water  excreted  by  the  kidneys  in  children,  in  proportion 
to  the  weight  of  the  body,  is  very  much  greater  than  in  the  adult,  being  more  than 
double.  From  eight  years  of  age  to  eighteen,  the  urinary  excretion  becomes  gradually 
reduced  to  the  adult  standard.  It  has  been  observed  that  crystals  of  oxalate  of  lime 
are  much  more  frequent  in  the  urine  of  children  between  four  and  fourteen  years  of 
age  than  in  the  adult. 

There  are  not  many  definite  observations  on  record  upon  the  composition  of  the  urine 
in  the  later  periods  of  life.  It  has  been  shown,  however,  that  there  is  a  decided  dimi- 
nution, at  this  time,  in  the  excretion  of  urea,  and  that  the  absolute  quantity  of  urine  is 
somewhat  smaller. 

The  absolute  quantity  of  the  urinary  excretion  in  women  is  less  than  in  men,  and  the 


VARIATIONS   IN  THE   COMPOSITION   OF  THE   URINE.  437 

same  is  true  of  the  proportionate  amount  of  these  principles  to  the  weight  of  the  body  ; 
still,  the  differences  in  the  proportionate  excretion  are  not  very  marked,  and  the  amount 
of  all  these  principles  being  subject  to  modifications  from  the  same  causes  as  in  men,  the 
small  deficiency,  in  the  few  direct  observations  upon  record,  may  be  in  part,  if  not 
entirely,  explained  by  the  fact  that  women  usually  perform  less  mental  and  physical  work 
than  men,  and  that  their  digestive  system  is  generally  not  so  active. 

Variations  at  Different  Seasons  and  at  Different  Periods  of  the  Day. — The  changes 
in  the  quantity  and  composition  of  the  urine  which  may  be  directly  referred  to  the  con- 
ditions of  digestion,  temperature,  sleep,  exercise,  etc.,  have  long  been  recognized  by 
physiologists ;  but  it  is  difficult,  if  not  impossible,  so  to  separate  these  influences,  that 
the  true  modifying  value  of  each  can  be  fully  appreciated.  For  example,  there  is  nothing 
which  produces  such  marked  variations  in  the  composition  of  the  urine  as  the  digestion 
of  food.  So  marked,  indeed,  is  its  influence,  that  some  writers  of  authority  incline  to 
the  belief  that  the  greatest  part  of  what  have  been  regarded  as  the  most  important 
excrementitious  matters  is  derived  from  the  food  and  not  from  physiological  disintegration 
of  the  tissues.  Under  strictly  physiological  conditions,  the  modifying  influence  of  diges- 
tion must  always  complicate  observations  upon  the  effects  of  exercise,  sleep,  season, 
period  of  the  day,  etc. ;  and  the  urine  is  continually  varying  in  health,  with  the  physio- 
logical modifications  in  the  other  processes  and  conditions  of  life.  It  will  be  sufficient 
for  our  purpose  to  note  the  most  important  of  these  variations  and  to  endeavor  to  appre- 
ciate the  conditions  which  combine  to  produce  them,  assigning  to  each  one  its  proper 
value. 

At  different  seasons  of  the  year  and  in  different  climates,  the  urine  presents  certain 
variations  in  its  quantity  and  composition.  It  seems  necessary  that  a  tolerably  definite 
quantity  of  water  should  be  discharged  from  the  body  at  all  times  ;  and,  when  the  tem- 
perature or  the  hygrometric  condition  of  the  atmosphere  is  favorable  to  the  action  of  the 
skin,  as  in  a  warm,  dry  climate,  the  quantity  of  water  in  the  urine  is  diminished,  and  its 
proportion  of  solid  matters  is  correspondingly  increased.  On  the  other  hand,  the  reverse 
obtains  when  the  action  of  the  skin  is  diminished  from  any  cause.  This  fact  is  a  matter 
of  common  remark  as  well  as  of  scientific  observation. 

At  different  periods  of  the  day,  the  urine  presents  constant  and  important  variations. 
It  is  evident  that  the  specific  gravity  must  be  constantly  varying  with  the  proportion  of 
water  and  solid  constituents.  According  to  Dalton,  the  urine  first  discharged  in  the 
morning  is  dense  and  highly  colored  ;  that  passed  during  the  forenoon  is  pale  and  of  a 
low  specific  gravity ;  and  in  the  afternoon  and  evening  it  is  again  deeply  colored,  and  its 
specific  gravity  is  increased.  The  acidity  is  also  subject  to  tolerably  definite  diurnal 
variations,  which  have  already  been  noted. 

Variations  produced  by  Food. — An  immense  number  of  observations  have  been  made 
upon  the  influence  of  ordinary  food  and  upon  diet  restricted  to  particular  articles.  These 
facts  have  necessarily  been  considered  more  or  less  fully  in  connection  with  the  origin 
of  the  urinary  constituents ;  but  it  is  important,  in  studying  the  influence  of  muscular 
exercise,  mental  effort,  etc.,  to  constantly  bear  in  mind  the  variations  occurring  under 
the  influence  of  the  ingesta. 

Water  and  liquids  generally  increase  the  proportion  of  water  in  the  urine  and  dimin- 
ish the  specific  gravity.  This  is  so  marked  after  the  ingestion  of  large  quantities  of 
liquids,  that  the  urine  passed  under  these  conditions  is  sometimes  spoken  of  by  phys- 
iologists as  the  urina  potus.  This  must  be  borne  in  mind  in  clinical  examinations  of 
the  urine.  It  is  a  curious  fact,  however,  that,  when  an  excess  of  water  has  been  taken 
for  purposes  of  experiment,  the  diet  being  carefully  regulated,  the  absolute  amount  of 
solid  matters  excreted  is  considerably  increased.  This  is  particularly  marked  in  the 
urea,  but  it  is  noticeable  in  the  sulphates  and  phosphates,  though  not  to  any  great 


4-28  EXCRETION. 

extent  in  the  chlorides.  The  results  of  experiments  upon  this  point  seem  to  show  that 
water  taken  in  excess  increases  the  activity  of  disassimilation. 

The  ordinary  meals  invariably  increase  the  solid  constituents  of  the  urine,  the  most 
constant  and  uniform  increase  being  in  the  proportion  of  urea.  This,  however,  depends 
to  a  great  extent  upon  the  kind  of  food  taken.  The  increase  is  usually  noted  during  the 
first  hour  after  a  meal,  and  it  attains  its  maximum  at  the  third  or  fourth  hour.  The  inor- 
ganic matters  are  increased  as  well  as  the  excrementitious  principles  proper.  The  urine 
passed  after  food  has  been  called  urina  cibi,  under  the  idea  that  it  is  to  be  distinguished 
from  the  urine  supposed  to  be  derived  exclusively  from  disassimilation  of  the  body,  which 
is  called  the  urina  sanguinis. 

It  is  an  interesting  and  important  question  to  determine  the  influence  of  different 
kinds  of  food  upon  the  composition  of  the  urine,  particularly  the  comparative  effects  of  a 
nitrogenized  and  a  non-nitrogenized  diet.  Lehmann  has  made  some  very  striking  obser- 
vations upon  this  point,  and  his  results  have  been  fully  confirmed  by  many  other  physi- 
ologists of  authority.  Without  discussing  elaborately  all  of  these  observations,  it  is 
sufficient  to  state  that  the  ingestion  of  an  excess  of  nitrogenized  principles  always  pro- 
duced a  great  increase  in  the  proportion  of  the  nitrogenized  constituents  of  the  urine, 
particularly  the  urea.  On  a  non-nitrogenized  diet,  the  proportion  of  urea  was  found  to 
be  diminished  more  than  one-half.  The  results  of  the  experiments  of  Lehmann  are  so 
striking  that  we  quote  them  in  full : 

"My  experiments  show  that  the  amount  of  urea  which  is  excreted  is  extremely 
dependent  on  the  nature  of  the  food  which  has  been  previously  taken.  On  a  purely  ani- 
mal diet,  or  on  food  very  rich  in  nitrogen,  there  were  often  two-fifths  more  urea  excreted 
than  on  a  mixed  diet ;  while,  on  a  mixed  diet,  there  was  almost  one-third  more  than  on 
a  purely  vegetable  diet ;  while,  finally,  on  a  non-nitrogenous  diet,  the  amount  of  urea 
was  less  than  half  the  quantity  excreted  during  an  ordinary  mixed  diet. 

"  In  my  experiments  on  the  influencs  of  various  kinds  of  food  on  the  animal  organism, 
and  especially  on  the  urine,  I  arrived  at  the  above  results,  which  in  mean  numbers  may 
be  expressed  as  follows :  On  a  well-regulated  mixed  diet  I  discharged,  in  twenty-four 
hours,  32-5  grammes  of  urea  (I  give  the  mean  of  fifteen  observations) ;  on  a  purely  ani- 
mal diet,  53-2  grammes  (the  mean  of  twelve  observations) ;  on  a  vegetable  diet,  22*5 
grammes  (the  mean  of  twelve  observations) ;  and  on  a  non-nitrogenous  diet,  15*4  grammes 
(the  mean  of  three  observations)." 

With  regard  to  the  influence  of  food  upon  the  inorganic  constituents  ot  the  urine,  it 
may  be  stated  in  general  terms  that  the  ingestion  of  mineral  substances  increases  their 
proportion  in  the  excretions.  We  have  already  alluded  to  this  fact  in  treating  of  the 
different  inorganic  salts. 

There  are  certain  articles  which,  when  taken  into  the  system,  the  diet  being  regular, 
seem  to  retard  the  process  of  disassimilation ;  or,  at  least,  they  diminish,  in  a  marked 
manner,  the  amount  of  matters  excreted,  particularly  urea.  Alcohol  has  a  very  decided 
influence  of  this  kind.  Its  action  may  be  modified  by  the  presence  of  salts  and  other 
matters  in  the  different  alcoholic  beverages,  but,  in  nearly  all  direct  experiments,  alco- 
hol, either  taken  under  normal  conditions  of  diet,  when  the  diet  is  deficient,  or  when  it 
is  in  excess,  diminishes  the  excretion  of  urea.  The  same  may  be  stated  in  general  terms 
of  tea  and  coffee. 

Influence  of  Muscular  Exercise.— There  can  be  no  doubt  that  muscular  exercise,  under 
ordinary  conditions  of  diet,  increases  the  proportion  of  many  of  the  solid  constituents  of 
the  urine,  particularly  the  urea ;  but  it  must  be  remembered,  in  considering  the  effects 
of  exercise  upon  the  elimination  of  excrementitious  matters,  that  the  modifications  in  the 
urine  produced  by  food  are  very  considerable.  We  have  purposely  considered  the  influ- 
ence of  food  before  taking  up  other  modifying  conditions,  so  as  to  make  apparent  an 
important  element  of  error  in  some  recent  observations  which  are  at  variance  with  the 


VARIATIONS  IN  THE   COMPOSITION  OF  THE  UKINE. 

prevailing  ideas  on  this  subject.  When,  for  example,  it  lias  been  shown  that  restriction 
to  a  non-nitrogenous  diet  will  immediately  diminish  the  daily  elimination  of  urea  more 
than  one-half,  it  is  evident  that  the  diet  must  always  be  fully  considered  in  experiments 
upon  the  effects  of  exercise  or  of  other  modifying  circumstances. 

There  is  another  important  point,  also,  which  is  not  always  taken  into  consideration 
in  comparative  observations  upon  the  absolute  quantities  of  urea  eliminated  during  exer- 
cise and  repose ;  and  that  is  the  elimination  of  this  principle  by  the  cutaneous  surface. 
We  have  already  seen  that  urea  is  a  constant  constituent  of  the  sweat.  Speck,  who 
found  that  exercise  usually  increased  the  elimination  of  excrementitious  matters,  noted 
the  fact  that  urea  was  not  increased  in  the  urine  when  the  sweat  was  very  abundant. 

A  very  elaborate  analysis  of  the  principal  observations  on  this  subject  by  Parkes 
shows  the  discrepancies  in  the  experiments  of  different  authors  and  points  out  sereral  of 
the  sources  of  error.  The  weight  of  experimental  evidence  formerly  was  decidedly  in 
favor  of  an  increase  in  the  elimination  of  urea  by  exercise ;  and  the  observations  opposed 
to  this  view  involved  inaccuracies  which  would  explain,  in  part  at  least,  the  contradictory 
results  obtained.  Lately,  however,  new  observations  have  been  made,  which  are  assumed 
by  some  to  show  an  actual  diminution  by  exercise  in  the  quantity  of  urea  excreted.  Tick 
and  Wislicenus,  Frankland,  and  Haughton,  have  attempted  to  show  that  this  is  the  fact, 
and  these  physiologists  have  come  to  the  conclusion  that  muscular  force  involves  chiefly 
the  consumption  of  non-nitrogenous  principles  and  the  production  of  carbonic  acid. 
While  the  experiments  upon  this  subject  have  been  so  meagre,  it  would  be  unprofitable  to 
enter  into  an  elaborate  discussion  of  their  merits,  particularly  as  they  have  not  been 
directed  specially  to  the  influence  of  exercise  upon  the  composition  of  the  urine,  but  to 
the  amount  of  muscular  power  developed  by  different  kinds  of  food.  This  subject  has 
not  been  reduced  to  such  an  absolute  certainty  that  we  are  able  to  calculate  mathemati- 
cally the  heat-units,  the  digestion-coefficients,  and  the  amount  of  "  work  "  produced  by 
any  given  quantity  of  food  ;  and  such  calculations  cannot,  as  yet,  take  the  place  of  actual 
experimental  observations.  What  we  want  to  know  is  the  measurable  influence  of  mus- 
cular exercise  upon  the  proportion  of  certain  of  the  constituents  of  the  urine,  under  nor- 
mal alimentation,  every  other  modifying  condition  being  taken  into  account.  There  can 
be  no  doubt  that,  under  an  ordinary  mixed  diet,  the  elimination  of  urea  is  increased  by 
exercise.  Fick  and  Wislicenus  made  their  observations,  extending  over  a  period  of  between 
one  and  two  days,  under  a  diet  of  non-nitrogenized  matter ;  and  Prof.  Haughton  com- 
pared his  observations,  made  in  July,  with  an  average  of  experiments  made  at  different 
seasons,  taking  no  account  of  the  action  of  the  skin.  It  may  be  true  that,  with  a  purely 
non-nitrogeneous  diet,  exercise  fails  to  increase  the  quantity  of  urea  eliminated  by  the 
kidneys,  as  appears  from  the  observations  of  Fick  and  Wislicenus ;  but  farther  experi- 
ments are  necessary  to  settle  even  this  point,  and  the  recent  observations  by  Parkes  show 
that  this  is  not  always  the  case. 

With  regard  to  the  influence  of  muscular  exercise  upon  the  other  constituents  of  the 
urine,  experiments  are  somewhat  contradictory.  Sometimes  the  water  is  lessened  and 
sometimes  it  is  increased ;  this  difference  probably  depending  upon  the  activity  of  the 
cutaneous  exhalation.  Sometimes  the  uric  acid  is  increased  and  sometimes  it  is  dimin- 
ished. The  sulphates,  phosphates,  and  chlorides,  are  generally  increased. 

The  general  result  of  experimental  observations  on  the  effects  of  exercise  upon  the 
urine  may  be  summed  up  in  the  proposition  that  this  condition  increases  the  activity  of 
the  nutritive  processes,  and  produces  a  corresponding  activity  in  the  function  of  disas- 
similation,  as  indicated  by  the  amount  of  excrementitious  matters  separated  by  the 
kidneys. 

We  have  had  an  opportunity  of  settling  definitely  the  vexed  question  of  the  influence 
of  muscular  exercise  upon  the  elimination  of  nitrogen.1  In  1871,  we  made  an  exceedingly 

1  FLINT,  JR.,  On  the  Physiological  Ejects  of  Severe  and  Protracted  Muscular  Exercise,  with  special  Refer- 
ence to  its  Influence  upon  the  Excretion  of  Nitrogen.— New  York  Medical  Journal,  1871,  vol.  xiii.,  p.  609,  etseq. 


430  EXCRETION. 

elaborate  series  of  observations  upon  Mr.  "VVeston,  the  pedestrian.  Of  these  we  can  only 
give  here  a  brief  summary.  Mr.  Weston  walked  for  five  consecutive  days  as  follows  : 
First  day,  92  miles;  second  day,  80  miles;  third  day,  57  miles;  fourth  day,  48  miles; 
fifth  day,  40|  miles.  The  nitrogen  of  the  food  was  compared  with  the  nitrogen  excreted 
for  three  periods ;  viz.,  five  days  before  the  walk,  five  days  walking,  and  five  days  after 
the  walk.  '  A  trusty  assistant  was  with  Mr.  Weston  day  and  night  for  the  fifteen  days; 
the  food  was  weighed  and  analyzed ;  the  excreta  were  collected  ;  and  other  observations 
were  made  during  the  entire  period.  The  analyses  were  made  independently,  under  the 
direction  of  Prof.  E.  O.  Doremus,  who  had  no  idea  of  the  results  until  we  had  classified 
and  tabulated  them.  The  conclusions  were  most  decided,  and,  as  far  as  possible,  all  the 
physiological  conditions  were  fulfilled.  As  regards  the  proportion  of  nitrogen  eliminated 
to  the  nitrogen  of  the  food,  the  general  results  were  as  follows  : 

For  the  five  days  before  the  walk,  with  an  average  exercise  of  about  eight  miles  daily, 
the  nitrogen  eliminated  was  95*53  parts  for  100  parts  of  nitrogen  ingested.  For  the  five 
days  of  the  walk,  for  every  hundred  parts  of  nitrogen  ingested,  there  were  discharged 
174-81  parts.  For  the  five  days  after  the  walk,  when  there  was  hardly  any  exercise,  for 
every  hundred  parts  of  nitrogen  ingested,  there  were  discharged  91 '93  parts.  During 
the  walk,  the  nitrogen  excreted  was  in  direct  ratio  to  the  amount  of  exercise  ;  and,  what 
was  still  more  striking,  the  excess  of  nitrogen  eliminated  over  the  nitrogen  of  food  almost 
exactly  corresponded  with  a  calculation  of  the  nitrogen  of  the  muscular  tissue  wasted, 
as  estimated  from  the  loss  of  weight  of  the  body.  Full  details  of  the  method  of  investi- 
gation, the  processes  employed,  etc.,  are  given  in  our  original  paper. 

Influence  of  Mental  Exertion. — Although  the  influence  of  mental  exertion  upon  the 
composition  of  the  urine  has  not  been  very  closely  studied,  the  results  of  the  investiga- 
tions which  have  been  made  upon  this  subject  are,  in  many  regards,  quite  satisfactory. 
It  is  a  matter  of  common  remark  that  the  secretion  of  urine  is  often  modified  to  a 
considerable  extent  through  the  nervous  system.  Fear,  anger,  and  various  violent  emo- 
tions, sometimes  produce  a  sudden  and  copious  secretion  of  urine  containing  a  large 
amount  of  water,  and  this  phenomenon  is  often  observed  in  cases  of  hysteria.  Intense 
mental  exertion  will  occasionally  produce  the  same  result.  We  have  often  observed 
a  frequent  desire  to  urinate  during  a  few  hours  of  intense  and  unremitting  mental  labor ; 
and,  on  one  occasion,  being  struck  with  the  amount  of  urine  voided,  it  was  found,  on 
examination,  to  present  scarcely  any  acidity,  and  a  specific  gravity  of  about  1002.  The 
interesting  point  in  this  connection,  however,  is  to  observe  the  influence  of  mental  labor 
upon  the  elimination  of  solid  matters,  as  contrasted  with  the  amount  of  excretion  during 
complete  repose,  the  conditions  of  alimentation  in  the  two  instances  being  identical. 

In  a  very  interesting  work  upon  the  influence  of  cerebral  activity  upon  the  composi- 
tion of  the  urine,  Byasson  found  that  by  mental  exertion  the  quantity  of  urine  was 
increased ;  the  amount  of  urea  was  also  increased ;  the  phosphoric  acid  was  increased 
about  one-third ;  the  sulphuric  acid  was  more  than  doubled ;  and  the  chlorine  was 
nearly  doubled. 

These  facts  have  an  important  bearing  upon  our  knowledge  of  the  effects  of  mental 
exertion  upon  the  process  of  disassimilation  of  the  nervous  tissue.  They  show  that  nearly 
all  of  the  solid  principles  contained  in  the  urine  are  increased  in  quantity  by  prolonged 
intellectual  exertion,  but  they  fail  to  point  to  any  one  excrementitious  principle,  either 
organic  or  inorganic,  which  is  specially  connected  with  the  physiological  wear  of  the 
brain.  It  has  been  assumed  that  elimination  of  the  phosphates,  increased  out  of  propor- 
tion to  the  increase  of  the  other  solid  matters  of  the  urine,  is  one  of  the  constant  effects 
of  intellectual  effort ;  but  this  view  is  not  sustained  by  direct  physiological  experiments 
or  by  facts  in  pathology.  We  have  already  discussed  this  question  somewhat  elaborately, 
under  the  head  of  the  phosphates  of  the  urine. 


PHYSIOLOGICAL  ANATOMY   OF  THE   LIVER.  431 

CHAPTER   XIII. 

FUNCTIONS    OF    THE    LIVER. 

Physiological  anatomy  of  the  liver— Distribution  of  the  portal  vein,  the  hepatic  artery,  and  the  hepatic  duct- 
Origin  and  course  of  the  hepatic  veins— Structure  of  a  lobule  of  the  liver — Arrangement  of  the  bile-ducts  in 
the  lobules— Anatomy  of  the  excretory  biliary  passages — Nerves  and  lymphatics  of  the  liver — Mechanism  of 
the  secretion  and  discharge  of  bile — Quantity  of  bile — Variations  in  the  flow  of  the  bile — Discharge  of  bile  from 
the  gall-bladder— General  properties  of  the  bile— Composition  of  the  bile— Origin  of  the  biliary  salts— Choles- 
terine— Biliverdine — Tests  for  bile — Excretory  function  of  the  liver — Origin  of  cholesterine — Experiments  show- 
ing the  passage  of  cholesterine  into  the  blood  as  it  circulates  through  the  brain— Elimination  of  cholesterine  by 
the  liver — Cholesteragmia  — Production  of  sugar  in  the  liver — Evidences  of  a  glycogenic  function  in  the  liver — 
Does  the  liver  contain  sugar  during  life  ? — Mechanism  of  the  production  of  sugar  by  the  liver— Glycogenic  mat- 
ter— Variations  in  the  glycogenic  function — Production  of  sugar  in  total  life — Influence  of  digestion  and  of  differ- 
ent kinds  of  food  upon  glycogenesis — Influence  of  the  nervous  system,  etc.,  upon  glycogenesis — Artificial  dia- 
betes— Destination  of  sugar — Alleged  production  of  fat  by  the  liver — Changes  in  the  albuminoid  and  the  corpus- 
cular elements  of  the  blood  in  their  passage  through  the  liver. 

Physiological  Anatomy  of  the  Liver. 

THE  liver,  by  far  the  largest  gland  in  the  body,  is  now  known  to  have  several  entirely 
distinct  functions ;  and  one  of  the  most  important  of  these  has  already  been  fully  con- 
sidered, in  connection  with  digestion.  It  is  true  that  we  know  very  little  with  regard  to 
the  exact  office  of  the  bile  in  digestion,  but  that  this  function  is  essential  to  life,  there 
can  be  no  doubt.  We  have,  however,  more  positive  information  with  regard  to  the 
excrementitious  function  of  the  liver  and  the  changes  which  the  blood  undergoes  in  pass- 
ing* through  its  substance  ;  and  the  study  of  these  functions  is  closely  connected  with 
the  anatomy  of  the  liver  and  the  chemical  constitution  of  the  bile. 

It  is  unnecessary,  in  this  connection,  to  dwell  upon  the  ordinary  descriptive  anatomy  of 
the  liver.  It  is  sufficient  to  state  that  it  is  situated  just  below  the  diaphragm,  in  the  right 
hypochondriac  region,  and  is  the  largest  gland  in  the  body,  weighing,  when  moderately 
filled  with  blood,  about  four  and  a  half  pounds.  Its  weight  is  somewhat  variable,  but  it 
is  stated  by  Sappey  that,  in  a  person  of  ordinary  adipose  development,  its  proportion  to 
the  weight  of  the  body  is  about  as  one  to  thirty-two.  In  early  life,  the  liver  is  relatively 
larger,  its  proportion  to  the  weight  of  the  body,  in  the  new-born  child,  being  as  one  to 
eighteen  or  twenty. 

The  liver  is  covered  externally  by  peritoneum,  folds  or  duplicatures  of  this  mem- 
brane being  formed  as  it  passes  from  the  surface  of  the  liver  to  the  adjacent  parts.  These 
constitute  four  of  the  so-called  ligaments  that  hold  the  liver  in  place.  The  proper  coat 
of  the  liver  is  a  very  thin  but  dense  and  resisting  fibrous  membrane,  adherent  to  the  sub- 
stance of  the  organ,  but  detached  without  much  difficulty,  and  very  closely  united  to  the 
peritoneum.  This  membrane  is  of  variable  thickness  at  different  parts  of  the  liver,  being 
especially  thin  in  the  groove  for  the  vena  cava.  At  the  transverse  fissure,  it  surrounds 
the  duct,  blood-vessels,  and  nerves,  and  it  penetrates  the  substance  of  the  organ  in  the 
form  of  a  vagina,  or  sheath,  surrounding  the  vessels  and  branching  with  them.  This 
membrane,  as  it  ramifies  in  the  substance  of  the  liver,  is  called  the  capsule  of  Glis- 
son.  It  will  be  more  fully  described  in  connection  with  the  arrangement  of  the  hepatic 
vessels. 

The  substance  of  the  liver  is  made  up  of  innumerable  lobules,  of  an  irregularly  ovoid 
or  rounded  form,  and  about  ^  of  an  inch  in  diameter.  The  space  which  separates  these 
lobules  is  about  one-quarter  of  the  diameter  of  the  lobule  and  is  occupied  with  the  blood- 
vessels, nerves,  and  ramifications  of  the  hepatic  duct,  all  enclosed  in  the  fibrous  sheath. 
In  a  few  animals,  as,  for  example,  the  pig  and  the  polar  bear,  the  division  of  the  hepatic 
substance  can  be  readily  made  out  with  the  naked  eye;  but,  in  man  and  in  most  of  the 


432  EXCKETION. 

mammalia,  the  lobules  are  not  so  distinct,  although  their  arrangement  is  essentially  the 
same.  Although  the  lobules  are  intimately  connected  with  each  other  from  the  fact  that 
branches  going  to  a  number  of  different  lobules  are  given  off  from  the  same  interlobular 
vessels,  they  are  sufficiently  distinct  to  represent,  each  one,  the  general  anatomy  of  the 
secreting  substance  of  the  liver ;  but,  before  we  study  the  minute  structure  of  the  lobules, 
it  will  be  convenient  to  follow  out  the  course  of  the  vessels  and  the  duct,  after  they  have 
penetrated  at  the  transverse  fissure.  In  this  description  we  shall  follow,  in  the  main, 
the  observations  of  Kiernan,  who  has  given,  probably,  the  most  accurate  account  of  the 
vascular  arrangement  in  the  liver. 

At  the  transverse  fissure,  the  portal  vein,  collecting  the  blood  from  the  abdominal 
organs,  and  the  hepatic  artery,  a  branch  of  the  cceliac  axis,  penetrate  the  substance  of 
the  liver,  with  the  hepatic  duct,  nerves,  and  lymphatics,  all  enveloped  in  the  fibrous 
vagina,  or  sheath,  known  as  the  capsule  of  Glisson.  The  portal  vein  is  by  far  the  larger 
of  the  two  blood-vessels,  and  its  caliber  may  be  roughly  estimated  at  from  eight  to  ten 
times  that  of  the  artery. 

The  vagina,  or  capsule  of  Glisson,  is  composed  of  fibrous  tissue,  in  the  form  of  a  dense 
membrane,  closely  adherent  to  the  adjacent  structure  of  the  liver,  and  enveloping  the 
vessels  and  nerves,  to  which  it  is  attached  by  a  loose  areolar  tissue.  The  attachment  of 
the  blood-vessels  to  the  sheath  is  so  loose,  that  the  branches  of  the  portal  vein  are  col- 
lapsed when  not  filled  with  blood ;  thus  presenting  a  striking  contrast  to  the  hepatic 
veins,  which  are  closely  adherent  to  the  substance  of  the  liver  and  remain  open  when 
they  are  cut  across.  This  sheath  is  prolonged  over  the  vessels  as  they  branch  and  it  fol- 
lows them  in  their  subdivisions.  It  varies  considerably  in  thickness  in  different  animals. 
In  man  and  in  the  mammalia  generally,  it  is  rather  thin,  becoming  more  and  more  delicate 
as  the  vessels  subdivide,  and  it  is  entirely  lost  before  the  vessels  are  distributed  in  the 
interlobular  spaces. 

The  vessels  distributed  in  and  coming  from  the  liver  are  the  following  : 

1.  The  portal  vein,  the  hepatic  artery,  and  the  hepatic  duct,  passing  in  at  the  trans- 
verse fissure,  to  be  distributed  in  the  lobules.     The  blood-vessels  are  continuous  in  the 
lobules  with  the  radicles  of  the  hepatic  veins.    The  duct  is  to  be  followed  to  its  branches 
of  origin  in  the  lobules. 

2.  The  hepatic  veins ;  vessels  that  originate  in  the  lobules,  and  collect  the  blood  dis- 
tributed in  their  substance  by  branches  of  the  portal  vein  and  of  the  hepatic  artery. 

Branches  of  the  Portal  Vein,  the  Hepatic  Artery,  and  the  Hepatic  Duct. — These 
vessels  follow  out  the  branches  of  the  capsule  of  Glisson,  become  smaller  and  smaller,  and 
they  finally  pass  directly  between  the  lobules.  In  their  course,  however,  they  send  off 
lateral  branches  to  the  sheath  ;  and  those  who  follow  exactly  the  description  of  Kiernan 
call  this  the  vaginal  plexus.  The  arrangement  of  the  vessels  in  the  sheath  is  not  in  the 
form  of  a  true,  anastomosing  plexus,  although  branches  pass  from  this  so-called  vaginal 
plexus  between  the  lobules.  These  vessels  do  not  anastomose  or  communicate  with  each 
other  in  the  sheath. 

The  portal  vein  does  not  present  any  important  peculiarity  in  its  course  from  the 
transverse  fissure  to  the  interlobular  spaces.  It  subdivides,  enclosed  in  its  sheath,  until 
its  small  branches  go  directly  between  the  lobules,  and,  in  its  course,  it  sends  branches 
to  the  sheath  (vaginal  vessels),  which  afterward  go  between  the  lobules.  The  distri- 
bution of  the  hepatic  artery,  however,  is  not  so  simple.  This  vessel  has  three  sets  of 
branches.  As  soon  as  it  enters  the  sheath  with  the  other  vessels,  it  sends  off  minute 
branches  (vasa  vasorum),  to  the  walls  of  the  portal  vein,  to  the  larger  branches  of  the  artery 
itself,  to  the  walls  of  the  hepatic  veins,  and  a  very  rich  net-work  of  branches  to  the  hepatic 
duct.  When  the  hepatic  artery  is  completely  injected,  the  walls  of  the  hepatic  duct  are 
seen  almost  covered  with  vessels.  In  its  course,  the  hepatic  artery  also  sends  branches 
to  the  capsule  of  Glisson  (capsular  branches),  which  join  with  the  branches  of  the  portal 


PHYSIOLOGICAL  ANATOMY   OF  THE  LIVER.  433 

vein,  to  form  the  so-called  vaginal  plexus.  From  these  vessels,  a  few  arterial  branches 
are  given  off  which  pass  between  the  lobules.  The  hepatic  artery  cannot  be  followed 
beyond  the  interlobular  spaces.  The  terminal  branches  of  the  hepatic  artery  are  not 
directly  connected  with  the  radicles  of  the  hepatic  veins,  but  they  empty  into  small 
branches  of  the  portal  vein  within  the  capsule  of  Glisson. 


FIG.  12;).— Lobules  of  the  liver,  interlobular  vessels,  and  intralobular  veins.    (Sappey.) 

1, 1, 1  1,  3,  4,  lobules ;  2,  2,  2,  2,  intralobular  veins,  injected  with  white ;  5,  5,  5,  5,  5,  interlobular  vessels,  filled  with  a 

dark  injection. 

The  hepatic  duct  follows  the  general  course  of  the  portal  vein ;  but  its  structure  and 
relations  are  so  important  and  intricate  that  they  will  be  described  separately. 

Interlolular  Vessels. — Branches  of  the  portal  vein,  coming  from  the  terminal  ramifi- 
cations as  the  vessel  branches  within  the  capsule  and  from  the  branches  in  the  walls  of 
the  capsule,  are  distributed  between  the  lobules,  constituting  the  greatest  part  of  the 
so-called  interlobular  plexus.  These  are  situated  between  the  lobules  and  surround  them  ; 
each  vessel,  however,  giving  off  branches  to  two  or  three  lobules,  and  never  to  one  alone. 
They  do  not  anastomose,  and  consequently  they  are  not  in  the  form  of  a  true  plexus.  The 
diameter  of  these  interlobular  vessels  varies  from  y^7  to  -^  of  an  inch.  In  this  distribu- 
tion, the  blood-vessels  are  followed  by  branches  of  the  duct,  which  are  much  less  numer- 
ous and  smaller,  measuring  only  ^Vo  of  an  inch ;  and  some,  even,  have  been  measured 
that  are  not  more  than  ^Vo  of  an  inch  in  diameter. 

Lobular  Vessels.— In  the  interlobular  plexus,  the  ramifications  of  the  hepatic  artery 
are  lost,  and  this  can  no  longer  be  traced  as  a  distinct  vessel.  One  of  the  peculiarities 
of  its  arrangement,  as  we  have  seen,  is  that  the  artery  does  not  empty  into  the  radicles 
of  the  efferent  vein  but  joins  the  portal  vessels  as  they  are  about  to  be  distributed  in  a 
true  capillary  plexus  in  the  substance  of  the  lobules.  In  the  lobules  themselves,  conse- 
quently, we  have  only  to  study  the  arrangement  of  the  portal  plexus,  with  the  mode  of 
origin  of  the  hepatic  veins  and  the  relations  of  the  hepatic  duct. 

The  arrangement  of  the  lobuiar  plexus  of  blood-vessels  is  very  simple.  From  the 
interlobular  veins,  a  number  of  branches  (eight  to  ten)  are  given  off  and  penetrate  the 
lobule.  As  the  interlobular  vessels  are  situated  between  different  lobules,  each  one 
sends  branches  into  two  and  sometimes  three  of  these  lobules ;  so  that,  as  far  as  vascular 
supply  is  concerned,  these  divisions  of  the  liver  are  never  absolutely  distinct. 

After  passing  from  the  interlobular  plexus  ii?to  the  lobules,  the  vessels  immediately 
break  up  into  a  close  net-work  of  capillaries,  from  ^Vfr to  WOTT  of  an  incl1  in  diameter, 
which  occupy  the  lobules  with  a  true  plexus.  These  vessels  are  very  numerous ;  and, 
28 


434 


EXCRETION. 


when  they  are  fully  distended  by  artificial  injection,  their  diameter  is  greater  than  that 
of  the  intervascular  spaces.  It  must  be  remembered,  however,  that,  in  the  study  of  the 
liver  by  minute  injections,  as  in  other  parts,  the  vessels  probably  are  distended  so  that 
they  occupy  more  space  than  they  ever  do  under  the  physiological  conditions  of  the  cir- 
culation The  blood,  having  been  distributed  in  the  lobules  by  this  lobular  plexus,  is  col- 
lected by  venous  radicles  of  considerable  size  into  a  single  central  vessel  situated  m  the 
long  axis  of  the  lobule,  called  the  intralobular  vein.  A  single  lobule,  surrounded  with 
an  interlobular  vessel,  showing  the  lobular  capillary  plexus,  and  the  central  vein  (the 
intralobular  vein*  cut  across,  is  represented  in  Fig.  130. 


FIG.  130. —  Transverse  section  of  a  single  hepatic  lobule.    (Sappey.) 

1,  intralobular  vein,  cut  across ;  2,  2,  2,  2,  afferent  branches  of  the  intralobular  vein ;  3,  3,  3,  3,  3,  3, 3,  3,  3,  interlobular 
branches  of  the  portal  vein,  with  its  capillary  branches,  forming  the  lobular  plexus,  extending-  to  the  radicles  of 
the  intralobular  vein. 

With  regard  to  the  mode  of  origin  of  the  hepatic  duct  in  the  substance  of  the  lobule, 
recent  researches  have  shown  that  it  begins  by  a  very  fine,  anastomosing  plexus  of  ves- 
sels, with  amorphous  walls,  situated  between  the  liver-cells ;  but  there  are  many  differ- 
ent opinions  on  this  subject,  and  we  shall  defer  its  full  consideration  until  we  take  up  the 
anatomy  of  the  secreting  structures  in  the  lobules. 

Origin  and  Course  of  the  Hepatic  Veins. — The  blood  distributed  in  the  lobular  capil- 
lary plexus  furnishes  the  materials  for  the  formation  of  bile  and  undergoes  those  changes 
produced  by  the  action  of  the  liver  as  a  ductless  gland ;  in  other  words,  it  is  in  and 
around  this  plexus  that  all  the  physiological  functions  of  the  liver  are  performed.  It  is 
then  only  necessary  that  the  blood  should  be  carried  from  the  liver  to  go  to  the  right 
side  of  the  heart ;  and  the  .arrangement  of  the  hepatic  veins  is  accordingly  very  simple. 

Intralobular  Veins. — The  innumerable  capillaries  of  the  lobules  converge  into  three, 
or  four  venous  radicles  (represented  in  Fig.  130),  which  empty  into  a  central  vessel,  from 
Tirotf  to  477  of  an  inch  in  diameter.  This  is  the  intralobular  vein.  If  a  liver  be  carefully 
injected  from  the  hepatic  veins,  and  if  sections  be  made  in  various  directions,  it  will  be 
seen  that  the  intralobular  veins  follow  the  long  axis  of  the  lobules,  receiving  vessels  in 
their  course,  until  they  empty  into  a  larger  vessel,  situated  at  what  may  be  termed  the 
base  of  the  lobules.  These  vessels  have  been  called,  by  Kiernan,  the  sublobular  veins. 
They  collect  the  blood  in  the  manner  just  described  from  all  parts  of  the  liver,  unite 
with  others,  becoming  larger  and  larger,  until  finally  they  form  the  three  hepatic  veins, 
which  discharge  the  blood  from  the  liver  into  the  vena  cava  ascendens. 


PHYSIOLOGICAL  ANATOMY   OF  THE   LIVER. 


435 


The  hepatic  veins  differ  somewhat  in  their  structure  from  other  portions  of  the  venous 
system.  Their  walls  are  thinner  than  those  of  the(  portal  veins,  they  are  not  enclosed 
in  a  sheath,  and  they  are  very  closely  adherent  to  the  hepatic  tissue.  It  is  this  provision 
which  makes  the  force  of  aspiration  from  the  thorax  so  efficient  in  the  circulation  in 
the  liver.  Here,  indeed,  a  force  added  to  the  action  of  the  heart  is  specially  necessary; 
for  the  blood  is  passing,  into  the  liver  through  a  second  capillary  plexus,  having  already 
been  distributed  in  the  capillaries  of  the  alimentary  canal  and  other  abdominal  organs, 
before  it  is  received  into  the  portal  vein.  It  lias  also  been  noted  that  the  hepatic  veins 
possess  a  well-marked  muscular  tunic,  very  thin  in  man,  but  well-developed  in  the  pig, 
the  ox,  and  the  horse,  and  composed  of  unstriped  muscular  fibres  interlacing  with  each 
other  in  every  direction. 

In  addition  to  the  blood-vessels  just  described,  the  liver  receives  venous  blood  from 
vessels  which  have  been  called  accessory  portal  veins,  coming  from  the  gastro-hepatic 
omentum,  the  surface  of  the  gall-bladder,  the  diaphragm,  and  from  the  anterior  abdominal 
walls.  These  vessels  penetrate  at  different  portions  of  the  surface  of  the  liver,  and  they 
may  serve  as  derivatives,  when  the  circulation  through  the  portal  vein  is  obstructed. 

Structure  of  a  Lobule  of  the  Liter. — Each  hepatic  lobule,  bounded  and  more  or  less 
distinctly  separated  from  the  others  by  the  interlobular  vessels,  contains  blood-vessels, 
radicles  of  the  hepatic  ducts,  and  the  so-called  hepatic  cells.  The  arrangement  of  the 
blood-vessels  has  just  been  described ;  but,  in  all  preparations  made  by  artificial  injec- 
tion, the  space  occupied  by  the  blood-vessels  is  exaggerated  by  excessive  distention,  and 
the  difficulties  in  the  study  of  the  relations  of  the  ducts  and  the  liver-cells  are  thereby 
much  increased.  As  the  important  problem  in  the  minute  anatomy  of  the  lobules  has 
been  the  relations  of  the  cells  to  the  radicles  of  the  bile-ducts,  we  shall  first  take  up  the 
structure  of  the  cells. 

Hepatic  Cells. — If  a  scraping  from  the  cut  surface  of  a  fresh  liver  be  examined  with  a 
moderately  high  magnifying  power,  the  field 
of  view  will  be  found  filled  with  numerous 
rounded,  ovoid,  or  irregularly  polygonal  cells, 
measuring  from  j-faf  to  WTO  °f  an  ^nc^  *n 
diameter.  In  their  natural  condition,  they  are 
more  frequently  ovoid  than  polygonal ;  and, 
when  they  have  the  latter  form,  the  corners 
are  always  rounded.  These  cells  present  one 
and  sometimes  two  nuclei,  sometimes  with  and 
sometimes  without  nucleoli.  The  presence  of 
numerous  small  pigmentary  granules  gives  to 
the  cells  a  peculiar  and  characteristic  appear- 
ance ;  and,  in  addition,  nearly  all  of  them 
contain  a  few  granules  or  small  globules  of  fat. 
Sometimes  the  fatty  and  pigmentary  matter  is 
so  abundant  as  to  obscure  the  nuclei.  The 
addition  of  acetic  acid  renders  the  cells  pale 
and  the  nuclei  more  distinct.  By  appropriate 

reagents,  animal  starch  (probably  glycogenic  matter)  has  been  demonstrated  in  the  sub- 
stance of  the  cells. 

Arrangement  of  the  Bile-ducts  in  the  Lobules.— In  describing  the  plexus  of  origin  of 
the  biliary  ducts,  we  shall  not  discuss  the  views  of  Kiernan,  Leidy,  Beale,  and  others,  as 
recent  researches  have  conclusively  shown  that  these  were  entirely  erroneous.  Late 
researches  have  shown  that  the  following  is  probably  the  true  relation  of  the  ultimate 
ramifications  of  the  bile-ducts  in  the  lobules  to  the  hepatic  cells : 

In  the  substance  of  the  lobules,  is  an  exceedingly  fine  and  regular  net- work  of  vessels, 


FIG.  131.— Liver- cells,  from  a  human,  fatty  liver. 
(Funke.) 


436  EXCRETION. 

of  uniform  size,  about  T^oo  of  an  inch  in  diameter,  which  surround  the  liver-cells,  each 
cell  lying  in  a  space  bounded  by  inosculating  branches  of  these  canals.  This  plexus  is 
Entirely  independent  of  the  blood-vessels,  and  it  seems  to  enclose  in  its  meshes  each  indi- 
vidual cell,  extending  from  the  periphery  of  the  lobule  (where  it  is  in  communication 

with  the  interlobular  bile-ducts)  to  the  intra- 
lobular  vein  in  the  centre.  The  vessels  prob- 
ably have  excessively  thin,  homogeneous 
walls — although  the  existence  of  their  mem- 
brane has  not  been  positively  demonstrated — 
and  are  without  any  epithelial  lining,  being 
much  smaller,  indeed,  than  any  epithelial 
cells  with  which  we  are  acquainted.  This 
arrangement,  as  far  as  is  known,  has  no  ana- 
logue in  any  other  secreting  organ. 

Although  it  is  within  a  few  years  only 
that  the  reticulated  bile-ducts  of  the  lobules 
have  attracted  much  attention,  they  were  dis- 
covered in  the  substance  of  the  lobules,  near 
the  periphery,  by  Gerlach,  in  1848.  It  is  evi- 
dent, from  an  examination  of  his  figures  and 
description,  that  he  succeeded  in  filling  with 
injection  that  portion  of  the  lobular  net-work 
near  the  borders  of  the  lobules,  and  he  demon- 
ters.  (Koiiiker.)  strated  the  continuity  of  their  vessels  with 

b,  b,  &,  capillary  blood-vessels ;   g,  g,  g,  capillary  bile-      ,       .         •,-,-,        -,  i     .,  -i      j  •  i 

ducts;  l,  I,  I,  liver-ceils  the  interlobular  ducts  ;  but  he  did  not  recog- 

nize the  vessels  nearer  the  centre  of  the  lob- 
ule. It  is  now  demonstrated,  beyond  a  doubt,  that  there  are  either  canals  or  interspaces 
between  the  liver-cells  in  the  lobules,  and  that  these  open  into  the  interlobular  hepatic 
ducts.  It  is  still  a  question  of  discussion,  however,  whether  these  passages  be  simple 
spaces  between  the  cells  or  true  vessels  lined  by  a  membrane  ;  but  this  point  has  no  great 
physiological  importance,  and  we  can  readily  imagine  that  it  would  be  exceedingly  diffi- 
cult to  demonstrate  a  membrane  forming  the  wall  of  a  tube,  the  whole  measuring  but 
•nr^rfr  of  an  inch. 

A  peculiarly  favorable  opportunity  for  observing  the  bile-ducts  in  the  lobules  was 
presented  in  the  livers  of  animals  that  died  of  the  so-called  "  Texas  cattle-disease."  This 
was  taken  advantage  of  by  the  late  Dr.  R.  C.  Stiles,  who  was  able  to  verify,  in  the  most 
satisfactory  manner,  the  facts  which  have  lately  been  established  by  the  German  anato- 
mists. In  these  livers,  the  finest  bile-ducts  were  found  filled  with  bright  yellow  bile, 
and  their  relations  to  the  liver-cells  were  exceedingly  distinct.  In  the  examination  of 
these  specimens,  the  presence  of  what  appeared  to  be  detached  fragments  of  these  little 
canals  is  an  argument  in  favor  of  the  view  that  they  are  lined  by  a  membrane  of  exces- 
sive tenuity.  These  interesting  anatomical  points  were  demonstrated  by  Dr.  Stiles  before 
the  New  York  Academy  of  Medicine,  and  we  have  since  been  able  to  verify  them  in  every 
particular. 

Anatomy  of  the  Excretory  Biliary  Passages. — There  can  be  scarcely  any  doubt  of  the 
connection  between  the  intercellular  biliary  plexus  in  the  substance  of  the  lobules  and 
the  interlobular  ducts.  We  shall  see,  farther  on,  that  the  ducts,  in  their  course  from  the 
lobules  to  the  intestine,  are  provided  with  numerous  small,  racemose  glands,  which  prob- 
ably secrete  a  mucus  that  is  mixed  with  the  bile ;  but,  in  all  probability,  the  peculiar 
elements  of  the  bile  are  formed  in  the  lobules,  and  the  canals  situated  between  the  lobules 
and  leading  from  them  to  the  larger  ducts  are  merely  excretory. 

Between  the  lobules,  the  ducts  are  very  small,  the  smallest  measuring  about  ^^  of 


PHYSIOLOGICAL  ANATOMY   OF  THE  LIVER. 


437 


an  inch  in  diameter.  They  are  composed  of  a  delicate  membrane,  lined  with  small,  flat- 
tened epithelium.  The  ducts  larger  than  T^7  of  an  inch  have  a  fibrous  coat,  formed  of 
inelastic  with  a  few  elastic  elements,  and,  in  the  larger  ducts,  there  are,  in  addition,  a  few 
non-striated  muscular  fibres.  The  epithelium  lining  these  ducts  is  of  the  columnar  variety, 
the  cells  gradually  undergoing  a  transition  from  the  pavement-form  as  the  ducts  increase 
in  size.  In  the  largest  ducts,  there  is  a  distinct  mucous  membrane,  with  mucous  glands. 
Throughout  the  whole  extent  of  the  biliary  passages,  from  the  interlobular  canals  to 
the  ductus  choledochus,  are  little  utricular  or  racemose  glands,  varying  in  size  in  differ- 
ent portions  of  the  liver,  called  by  Robin,  the  biliary  acini.  These  are  situated,  at  short 
intervals,  by  the  sides  of  the  canals.  The  glands  connected  with  the  smallest  ducts  are 
simple  follicles,  from  -g-A^  to  ^7  of  an  inch  long.  The  larger  glands  are  formed  of  groups 
of  these  follicles,  and  they  measure  from  ^-^  to  T^  of  an  inch  in  diameter.  The  glands  are 
only  found  connected  with  the  ducts  ramifying  in  the  substance  of  the  liver,  and  they  do 
not  exist  in  the  hepatic,  cystic,  and  common  ducts.  They  are  composed  of  a  homogeneous 
membrane,  lined  with  small,  pale  cells  of  pavement-epithelium.  If  the  ducts  in  the  sub- 
stance of  the  liver  be  isolated,  they  are  found  covered  with  these  little  groups  of  follicles 
and  have  the  appearance  of  an  ordinary  racemose  gland,  except  that  the  acini  are  rela- 
tively small  and  scattered.  This  appearance  is  represented  in  Fig.  133. 


FIG.  133.  —  Anastomoses,  and  racemose  glands  attached  to  the  MUary  ducts  of  the  pig  ;  magnified  18  diameters. 

(Sappey.) 

1,  1,  branch  of  an  hepatic  duct,  with  the  surface  almost  entirely  covered 

2,  branch  in  which  the  glands  are  smaller  and  less  numerous  ;  3,  3.  3,  branches  of  the  duct 

4,  4,  4,  4,  biliary  ducts  with  simple  follicles  attached  ;  5,  5.  5,  5,  the  same,  with  fewer  follicles  ;  6,  6,  6,  6,  6,  anasto- 

moses in  arches  ;  7,  7,  7,  angular  anastomoses  ;  8,  8,  8,  8,  anastomoses  by  transverse  branches. 


ith  racemose  glands  opening  into  its  cavity; 
ranches  of  the  duct  with  still  simpler  glands; 


The  excretory  biliary  ducts,  from  the  interlobular  vessels  to  the  point  of  emergence 
of  the  hepatic  duct,  present  numerous  anastomoses  with  each  other  in  their  course. 

Vasa  Aberrantia.  —  In  the  livers  of  old  persons,  and  occasionally  in  the  adult,  certain 
vessels  are  found  ramifying  on  the  surface  of  the  liver,  but  always  opening  into  the  bil- 
iary ducts,  which  have  been  called  vasa  aberrantia.  These  are  never  found  in  the  foetus 
or  in  children.  They  are,  undoubtedly,  appendages  of  the  excretory  system  of  the  liver, 
and  are  analogous  in  their  structure  to  the  ducts,  but  are  apparently  hypertrophied,  with 
thickened,  fibrous  walls,  and  present,  in  their  course,  irregular  constrictions,  not  found 
in  the  normal  ducts.  The  racemose  glands  attached  to  them  are  always  very  much  atro- 
phied. Sappey  is  of  the  opinion  that  these  are  ducts  leading  to  lobules  on  the  surface  of 
the  liver,  which  have  become  atrophied. 

Gall-Madder,  Hepatic,  Cystic,  and  Common  Ducts.—  The  hepatic  duc^  is  formed  by 


438 


EXCRETION. 


the  union  of  two  ducts,  one  from  the  right  and  the  other  from  the  left  lobe  of  the  liver. 
It  is  about  an  inch  and  a  half  in  length  and  joins  at  an  acute  angle  with  the  cystic  duct, 
to  form  the  ductus  communis  choledochus.  The  common  duct  is  about  three  inches  in 
length,  of  the  diameter  of  a  goose-quill,  and  it  opens  into  the  descending  portion  of  the 
duodenum.  It  passes  obliquely  through  the  coats  of  the  intestine  and  opens  into  its 
cavity,  in  connection  with  the  principal  pancreatic  duct.  The  cystic  duct  is  about  an 
inch  in  length  and  is  the  smallest  of  the  three  canals. 


•20  12  10 


FIG.  134.— Gall-bladder,  hepatic,  cystic,  and  common  ducts.     (Sappey.) 

1,  2, 3,  duodenum ;  4, 4, 5,  6,  7,  7, 8,  pancreas  and  pancreatic  ducts  ;  9, 10, 11, 12, 13,  liver ;  14,  gall-bladder;  15,  hepatic 
duct;  16,  cystic  duct;  17,  common  duct;  18,  portal  vein;  19,  branch  from  the  coeliac  axis ;  20,  hepatic  artery;  21, 
coronary  artery  of  the  stomach ;  22,  cardiac  portion  of  the  stomach ;  23,  splenic  artery ;  24,  spleen;  25,  left  kidney ; 
26,  right  kidney ;  27,  superior  mesenteric  artery  and  vein ;  28,  inferior  vena  cava. 

The  structure  of  these  ducts  is  essentially  the  same.  They  have  a  proper  coat,  formed 
of  white  fibrous  tissue,  a  few  elastic  fibres,  and  a  few  non-striated  muscular  fibres.  The 
muscular  tissue  is  not  sufficiently  distinct  to  form  a  separate  coat.  The  mucous  mem- 
brane is  always  found  tinged  yellow  with  the  bile,  even  in  living  animals.  It  is  marked 
by  numerous  minute  excavations  and  is  covered  with  cells  of  columnar  epithelium.  This 
membrane  contains  numerous  mucous  glands. 

The  gall-bladder  is  an  ovoid  or  pear-shaped  sac,  about  four  inches  in  length,  one  inch 
in  breadth  at  its  widest  portion,  and  capable  of  holding  from  an  ounce  to  an  ounce  and  a 
half  of  fluid.  Its  fundus  is  covered  entirely  with  peritoneum,  but  this  membrane  passes 
only  over  the  lower  surface  of  its  body. 

The  proper  coat  of  the  gall-bladder  is  composed  of  white  fibrous  tissue  with  a  few 
elastic  fibres.  In  some  of  the  lower  animals  there  is  a  distinct  muscular  coat,  but  a  few 
1  scattered  fibres  only  are  found  in  the  human  subject.  The  mucous  coat  is  of  a  yellowish 
color  and  marked  with  numerous  very  small,  interlacing  folds,  which  are  exceedingly 
vascular.  Like  the  membrane  of  the  ducts,  the  mucous  lining  of  the  gall-bladder  is  cov- 
ered with  columnar  epithelium.  In  the  gall-bladder,  are  found  numerous  small  racemose 
glands,  formed  of  from  four  to  eight  follicles  lodged  in  the  submucous  structure.  These 
are  essentially  the  same  as  the  glands  opening  into  the  ducts  in  the  substance  of  the  liver, 
and  they  secrete  a  mucus  which  is  mixed  with  the  bile. 


MECHANISM   OF   THE   SECRETION   OF  BILE.  439 

Nerves  and  Lymphatics  of  the  Liver. — The  nerves  of  the  liver  are  derived  from  the 
pneumogastric,  the  phrenic,  and  the  solar  plexus  of  the  sympathetic.  The  branches  of 
the  left  pneumogastric  penetrate  with  the  portal  vein,  while  the  branches  from  the  right 
pneumogastric,  the  phrenic,  and  the  sympathetic  surround  the  hepatic  artery  and  the 
hepatic  duct.  All  of  these  nerves  penetrate  at  the  transverse  fissure  and  follow  the 
blood-vessels  in  their  distribution.  They  have  not  been  traced  farther  than  the  terminal 
ramifications  of  the  capsule  of  Glisson,  and  their  exact  mode  of  termination  is  unknown. 

The  lymphatics  of  the  liver  are  very  numerous.  They  are  divided  into  two  layers : 
the  superficial  layer,  situated  just  beneath  the  serous  membrane ;  and  the  deep  layer, 
formed  of  a  plexus  surrounding  the  lobules  and  situated  outside  of  the  blood-vessels. 
The  superficial  lymphatics  from  the  under  surface  of  the  liver,  and  that  portion  of  the  deep 
lymphatics  which  follows  the  hepatic  veins  out  of  the  liver,  pass  through  the  diaphragm 
and  are  connected  with  the  thoracic  glands.  Some  of  the  lymphatics  from  the  superior 
or  convex  surface  join  the  deep  vessels  that  emerge  at  the  transverse  fissure  and  pass 
into  glands  below  the  diaphragm,  while  others  pass  into  the  thoracic  cavity. 

Mechanism  of  the  Secretion  and  Discharge  of  Bile. — The  liver  has  no  analogue  in  the 
glandular  system,  either  in  its  anatomy  or  in  its  physiology.  There  is  no  gland  in  the 
economy  which  we  know  to  have  two  distinct  functions,  such  as  the  secretion  of  bile  and 
the  production  of  certain  elements  destined  to  be  taken  up  by  the  current  of  blood  as  it 
passes  through.  In  other  words,  there  is  no  organ  in  the  body  which  has  at  the  same 
time  the  functions  of  an  ordinary  secreting  gland  and  a  ductless  gland.  If  we  regard  the 
liver-cells  as  the  anatomical  elements  which  produce  the  bile,  it  is  evident  that  their 
number  is  very  much  out  of  proportion  to  the  amount  of  bile  secreted ;  and  the  liver 
itself  is  an  organ  of  much  greater  size  than  it  seems  to  us  would  be  required  for  the  mere 
secretion  of  bile.  We  explain  this  disproportionate  size  by  the  fact  that  the  liver  has 
other  functions,  which  are  those  of  a  ductless  gland. 

There  is  no  gland  in  which  the  arrangement  of  secreting  tubes  is  the  same  as  in  the 
liver.  It  is  hardly  possible  that  the  intercellular  plexus  of  fine  tubes  in  the  lobules  should 
be  any  thing  but  the  plexus  of  origin,  or  the  secreting  portion  of  the  hepatic  duct.  These 
are  certainly  not  blood-vessels,  and  the  only  vessels  that  could  have  the  appearance  we 
have  described,  except  the  bile-ducts,  are  the  lymphatics ;  but  the  communication  be- 
tween these  vessels  and  the  excretory  bile-ducts,  and  the  fact  that  they  have  been  seen 
distended  with  bile  in  icteric  livers,  are  pretty  conclusive  evidence  of  their  nature.  This 
arrangement,  then,  must  be  regarded  as  peculiar  to  the  liver,  as  the  arrangement  of  a 
capillary  plexus  surrounded  with  cells  and  enveloped  in  a  dilated  extremity  of  a  secreting 
tube  is  peculiar  to  the  kidney  and  is  found  in  no  other  glandular  organ. 

Do  the  liver-cells,  situated  outside  of  the  plexus  of  origin  of  the  biliary  duct,  secrete 
the  bile,  which  is  taken  up  by  these  delicate  vessels  and  carried  to  the  excretory  biliary 
passages?  There  are  very  good  reasons  for  answering  this  question  in  the  affirmative; 
although,  if  we  do,  we  must  recognize  the  fact  that  the  same  cells  produce  glycogenic 
matter.  As  far  as  we  are  able  to  understand  the  mechanism  of  secretion  (except  in  the 
production  of  milk),  it  seems  necessary  that  a  formed  anatomical  element,  known  as  a 
secreting  cell,  should  elaborate,  from  materials  furnished  by  the  blood,  the  elements  of 
secretion ;  and  this  cannot  be  accomplished  by  a  structureless  membrane  like  that  which 
forms  the  walls  of  the  bile-duets.  Under  this  view,  assuming  that  bile,  as  bile,  first 
makes  its  appearance  in  these  little  lobular  tubes,  the  liver-cells  are  the  only  anatomical 
elements  capable  of  producing  the  secretion.  With  regard  to  the  mechanism  of  this 
secreting  action,  we  have  nothing  to  say  beyond  our  general  remarks  in  a  previous 
chapter.  With  the  view  we  have  just  expressed,  certain  elements  of  the  bile  are  sep- 
arated from  the  blood,  and  others  are  manufactured  out  of  materials  furnished  by  the 
blood  by  the  liver-cells  and  are  taken  up  by  the  delicate  plexus  of  vessels  situated  between 
the  cells.  The  discharge  of  the  fluid  is  like  the  discharge  of  any  other  of  the  secretions, 


440  EXCRETION. 

except  that  a  portion  is  temporarily  retained  in  a  diverticulum  from  the  main  duct,  the 
gall-bladder. 

The  two  distinct  functions  of  the  liver  now  recognized  by  many  physiologists,  namely, 
the  secretion  of  bile  and  the  formation  of  sugar,  have  led  to  the  question  of  the  existence 
in  the  liver  of  two  anatomically  distinct  portions  or  organs,  corresponding  to  its  double 
physiological  function.  This  view,  indeed,  has  been  advanced  by  several  eminent  anato- 
mists. Robin  recognizes  two  distinct  parts  in  the  liver ;  a  biliary  organ  and  a  glycogenic 
organ.  He  regards  the  lobules,  with  their  liver-cells  and  blood-vessels,  as  the  parts  con- 
cerned in  the  glycogenic  function  of  the  liver,  and  the  little  glands  which  open  into  the 
biliary  ducts  all  along  their  course  (see  Fig.  133)  and  are  arranged  on  the  duct  "  in  the 
form  of  leaves  of  fern,"  as  the  biliary  organ.  The  same  independence  of  the  glycogenic 
and  biliary  portions  of  the  liver  has  been  argued  by  others. 

The  fact  that  bile  is  found  in  the  lobular  canals  and  the  demonstration  of  the  direct 
communication  of  these  canals  with  the  excretory  biliary  ducts  are  powerful  arguments 
in  favor  of  the  view  that  the  bile  is  formed  in  the  lobules,  and  probably  by  the  liver-cells. 
What,  then,  is  the  function  of  the  little  acini  connected  exclusively  with  the  biliary  ducts  ? 
The  similarity  of  their  structure  to  that  of  the  ordinary  mucous  glands,  and  to  the  mucous 
glands  of  the  gall-bladder  especially,  would  lead  to  the  supposition  that  they  secrete  a 
mucous  fluid.  It  is  well  known  that  the  bile  taken  from  the  gall-bladder  contains  more 
mucus  than  that  discharged  directly  from  the  liver  ;  but  the  bile  of  the  hepatic  duct  in 
most  animals  is  somewhat  viscid  and  contains  a  certain  amount  of  mucus.  This  is  the 
view  entertained  by  Sappey,  who  states  that  the  bile  is  viscid  in  different  animals  in  pro- 
portion to  the  development  of  these  little  glands ;  and,  in  the  rabbit,  in  which  the  glands 
do  not  exist,  the  bile  is  remarkably  fluid. 

Inasmuch  as  there  is  no  direct  evidence  that  the  racemose  glands  attached  to  the 
excretory  biliary  passages  have  any  thing  to  do  with  the  secretion  of  the  essential  con- 
stituents of  the  bile,  and  as  they  are  not  even  to  be  found  in  some  animals  that  produce  a 
considerable  quantity  of  bile,  we  must  regard  the  question  of  the  isolation  of  two  organs 
in  the  liver,  one  for  the  secretion  of  bile  and  the  other  for  the  production  of  sugar,  as  still 
unsettled.  There  is  no  evidence,  indeed,  that  the  bile  is  secreted  anywhere  but  in  the 
hepatic  lobules. 

Secretion  of  Bile  from  Venous  or  Arterial  Blood. — Numerous  experiments  have  been 
made  with  the  view  of  determining  whether  the  bile  be  secreted  from  the  blood  brought 
to  the  liver  by  the  portal  vein  or  from  the  blood  of  the  hepatic  artery.  The  immense 
quantity  of  blood  distributed  in  the  liver  by  the  portal  vein  led  first  to  the  opinion  that 
the  impurities  were  separated  from  this  blood  to  form  the  bile,  and  that  the  hepatic 
artery  had  little  or  nothing  to  do  with  the  secretion.  But,  since  Bernard  discovered  the 
glycogenic  function  of  the  liver,  this  subject  has  assumed  additional  importance  ;  and  it 
becomes  a  question  whether  the  materials  for  the  secretion  of  bile  may  not  be  furnished 
by  one  vessel  (the  hepatic  artery),  while  the  other  (the  portal  vein)  is  specially  con- 
cerned in  the  formation  of  glycogenic  matter.  This  theoretical  view,  however,  is  not 
carried  out  by  well-established  anatomical  facts  or  by  physiological  experiments.  It  is 
not  yet  possible  to  separate  the  liver  anatomically  into  two  organs,  one  for  the  secretion 
of  bile  and  the  other  for  the  production  of  sugar.  It  seems  certain,  also,  from  numerous 
experiments,  that  bile  may  be  secreted  from  the  blood  of  the  portal  vein  after  a  ligature 
has  been  applied  to  the  hepatic  artery  ;  and  it  is  equally  certain,  from  the  recent  experi- 
ments of  Ore,  that,  if  the  portal  vein  be  obliterated  so  gradually  that  the  animal  does  not 
die  from  the  operation,  bile  is  secreted  from  the  blood  of  the  hepatic  artery.  In  support 
of  this  view,  several  instances  of  obliteration  of  the  portal  vein  in  the  human  subject  are 
cited  in  works  upon  physiology.  In  a  note  to  the  communication  of  Or6  in  the  Comptes 
rendus,  Andral  reports  the  case  of  a  patient  that  died  of  dropsy,  and  on  post-mortem 
examination  the  portal  vein  was  found  obliterated.  In  this  instance  the  gall-bladder 


MECHANISM  OF  THE   SECRETION   OF  BILE.  441 

was  found  full  of  bile.  In  addition,  instances  in  which  the  portal  vein  emptied  into 
the  vena  cava  have  been  reported,  and  in  none  was  there  any  deficiency  in  the  secretion 
of  bile. 

If  the  experiments  upon  the  effects  of  tying  the  hepatic  artery,  and  the  observations 
of  instances  of  obliteration  of  the  portal  vein  and  of  congenital  malformation,  in  which 
the  portal  vein  does  not  go  to  the  liver,  be  equally  reliable,  there  is  but  one  conclusion 
to  be  drawn  from  them ;  and  that  is,  that  bile  may  be  secreted  from  either  venous  or 
arterial  blood.  This  view  is  not  inconsistent  with  what  we  know  of  the  general  process 
of  secretion  and  its  applications  to  the  production  of  bile.  Regarding  the  bile  as  in  part 
an  excrementitious  fluid,  its  effete  element,  cholesterine,  is  contained  both  in  the  blood 
of  the  portal  vein  and  the  hepatic  artery.  Its  recrementitious  principles,  glycocho- 
lates,  taurocholates,  etc.,  we  suppose  are  produced  de  novo  in  the  liver,  out  of  materials 
furnished  by  the  blood.  The  exact  nature  of  the  production  of  elements  of  secretion  by 
glandular  cells  we  do  not  understand  ;  but  there  is  no  good  reason  to  suppose  that  the 
principles  necessary  for  the  formation  of  bile  may  not  be  furnished  by  the  blood  of  the 
portal  vein,  as  well  as  by  the  hepatic  artery. 

The  view  most  nearly  in  accordance  with  all  the  facts  bearing  on  the  question  is,  that 
bile  is  produced  in  the  liver  from  the  blood  distributed  in  its  substance  by  the  portal  vein 
and  the  hepatic  artery,  and  not  from  either  of  these  vessels  exclusively ;  and  that  the  bile 
may  continue  to  be  secreted,  if  either  one  of  these  vessels  be  obliterated,  provided  the 
supply  of  blood  be  sufficient. 

Quantity  of  Bile. — The  estimates  of  the  daily  quantity  of  bile  in  the  human  subject 
must  be  merely  approximative  ;  and  our  only  ideas  on  this  point  are  derived  from  experi- 
ments upon  the  inferior  animals.  The  most  complete  and  reliable  observations  upon  this 
subject  are  those  of  Bidder  and  Schmidt,  which  were  made  upon  animals  with  a  fistula  into 
the  gall-bladder,  the  ductus  communis  having  been  tied.  These  observers  found  great 
variations  in  the  daily  quantity  in  different  classes  of  animals,  the  quantity  in  the  car- 
nivora  being  the  smallest.  Applying  their  results  to  the  human  subject,  assuming  that 
the  amount  is  about  equal  to  the  quantity  secreted  by  the  carnivora,  the  daily  secretion 
in  a  man  weighing  one  hundred  and  forty  pounds  would  be  about  two  and  a  half  pounds. 

Variations  in  the  Flow  of  the  Bile. — We  have  already  considered,  under  the  head  of 
digestion,  the  variations  in  the  flow  of  bile  and  their  relation  to  the  process  of  intestinal 
digestion.  It  is  sufficient  in  this  connection  to  repeat  that  the  discharge  from  a  biliary  fis- 
tula in  a  dog  increases  immediately  after  eating ;  that  it  is  at  its  maximum  from  the  second 
to  the  eighth  hour,  during  which  time  it  does  not  vary  to  any  great  extent ;  after  the  eighth 
hour  it  begins  to  diminish  ;  and,  from  the  twelfth  hour  to  the  time  of  feeding,  it  is  at  it& 
minimum.  These  facts  show  that,  while  the  bile  is  discharged  much  more  abundantly 
during  intestinal  digestion  than  during  the  intervals  of  digestion,  its  production  and  dis- 
charge are  constant.  This,  as  we  shall  see  farther  on,  is  a  strong  argument  in  favor  of 
the  view  that  the  liver  has  an  excrementitious  function. 

The  bile  is  stored  up  in  the  gall-bladder  to  a  considerable  extent  during  the  intervals 
of  digestion.  If  an  animal  be  killed  at  this  time,  the  gall-bladder  is  always  distended ; 
but  it  is  found  empty,  or  nearly  so,  in  animals  killed  during  digestion. 

The  influence  of  the  nervous-  system  upon  the  secretion  of  bile  has  been  very  little 
studied,  and  the  question  is  one  of  great  difficulty  and  obscurity.  The  liver  is  supplied 
very  abundantly  with  nerves,  both  from  the  cerebro- spinal  and  the  sympathetic  system, 
and  some  observations  have  been  made  upon  the  influence  of  the  nerves  upon  its  glycogenic 
function  ;  but,  with  regard  to  the  secretion  of  bile,  we  can  only  apply  our  general  remarks 
concerning  the  influence  of  the  nervous  system  on  secretion. 

The  bile  is  discharged  through  the  hepatic  ducts  like  the  secretion  of  any  other  gland. 
During  digestion,  the  fluid  accumulated  in  the  gall-bladder  passes  into  the  ductus  com- 


442  EXCRETION. 

munis,  in  part  by  contractions  of  its  walls,  and  in  part,  probably,  by  compression  exerted 
by  the  distended  and  congested  digestive  organs  adjacent  to  it.  It  seems  that  this  fluid, 
which  is  necessarily  produced  by  the  liver  without  intermission,  separating  from  the  blood 
certain  excrementitious  matters,  is  retained  in  the  gall-bladder  for  use  during  digestion. 

Functions  of  the  Bile. 

Although  the  function  of  the  bile  in  intestinal  digestion  is  essential  to  life,  we  know 
very  little  of  its  mode  of  action  ;  and  we  have  thought  proper  to  defer  until  now  a  full 
consideration  of  the  properties  and  composition  of  this  secretion.  For  an  account  of  what 
is  known  of  its  digestive  function,  the  reader  is  referred  to  the  chapters  treating  of  diges- 
tion. We  shall  show,  in  this  connection,  that  the  liver  excretes  one  of  the  most  important 
of  the  effete  principles ;  but,  before  taking  up  the  relations  of  the  bile  as  an  excretion,  it 
will  be  necessary  to  study  its  general  properties  and  composition. 

General  Properties  of  the  Bile. — The  secretion,  as  it  comes  directly  from  the  liver,  is 
somewhat  viscid ;  but,  after  it  has  passed  into  the  gall-bladder,  its  viscidity  is  much 
increased  from  a  farther  admixture  of  mucus. 

The  color  of  the  bile  is  very  variable  within  the  limits  of  health.  It  may  be  of  any 
shade  between  a  dark,  yellowish-green  and  a  reddish -brown.  It  is  semitransparent,  ex- 
cept when  the  color  is  very  dark.  In  different  classes  of  animals,  the  variations  in  color 
are  very  great.  In  the  pig  it  is  bright-yellow  ;  in  the  dog  it  is  dark-brown  ;  and  in  the 
ox  it  is  greenish-yellow.  As  a  rule,  the  bile  is  dark-green  in  the  carnivora  and  greenish- 
yellow  in  the  herbivora. 

The  specific  gravity  of  the  human  bile  is  from  1020  to  1026.  When  the  bile  is  per- 
fectly fresh,  it  is  almost  inodorous,  but  it  readily  undergoes  putrefactive  changes.  It 
has  an  excessively  disagreeable  and  bitter  taste.  It  is  not  coagulated  by  heat.  When 
mixed  with  water  and  shaken,  it  becomes  frothy,  probably  on  account  of  the  tenacious 
mucus  and  its  saponaceous  constituents. 

It  is  generally  stated  that  the  bile  is  invariably  alkaline.  This  is  true  of  the  fluid  dis- 
charged from  the  hepatic  duct,  although  the  alkalinity  is  not  strongly  marked ;  but  the 
reaction  varies  after  it  has  passed  into  the  gall-bladder.  Bernard  found  it  sometimes  acid 
and  sometimes  alkaline  in  the  gall-bladder,  in  animals  (dogs,  and  rabbits)  killed  under 
various  conditions  ;  but  many  of  these  animals  were  suffering  from  the  effects  of  severe 
operations.  In  the  hepatic  ducts  the  reaction  is  always  alkaline  ;  and  there  are  no  obser- 
vations on  human  bile  that  show  that  the  fluid  is  not  alkaline  in  all  of  the  biliary  passages. 

We  have  already  noted  the  fact  that  the  epithelium  of  the  biliary  passages  is  strongly 
tinged  with  yellow,  even  in  living  animals.  This  is  due  to  the  remarkable  facility  with 
which  the  coloring  principle  of  the  bile  stains  the  animal  tissues.  This  is  very  well  illus- 
trated in  icterus,  when  even  a  small  quantity  of  this  coloring  matter  finds  its  way  into  the 
circulation. 

Perfectly  normal  and  fresh  bile,  examined  with  the  microscope,  presents  a  certain 
amount  of  mucus,  the  characters  of  which  we  have  already  described.  There  are  no 
formed  anatomical  elements  characteristic  of  this  fluid.  The  fatty  and  coloring  matters 
are  in  solution  and  not  in  the  form  of  globules  or  granules. 

Composition  of  the  Bile. 

It  is  a  remarkable  fact,  that,  although  the  bile,  in  a  perfectly  fresh  and  normal  con- 
dition, may  be  obtained  from  the  inferior  animals  with  the  greatest  facility,  no  satisfac- 
tory analyses  of  its  characteristic  principles  were  made  before  the  examinations  of  ox- 
gall  by  Strecker,  in  1848.  The  bile  is,  however,  one  of  the  most  important,  but  least 
understood,  of  the  animal  fluids ;  and  our  scanty  information  with  regard  to  its  func- 
tions has  been  in  a  measure  due  to  the  want  of  an  exact  knowledge  of  its  physiological 


COMPOSITION   OF  HUMAN  BILE.  443 

• 
chemistry.     We  shall  study  the  composition  of  the  bile  very  closely,  and  shall  show  that 

it  contains  two  classes  of  constituents  :  one  class — elements  of  secretion which  is  reab- 

sorbed  ;  and  another — an  element  of  excretion — which  is  discharged  in  a  modified  form 
in  the  faeces.  The  latter  involves  a  newly-described  function  of  the  liver,  but  our  infor- 
mation is  much  more  positive  and  definite  concerning  it  than  with  regard  to  the  digestive 
action  of  the  bile.  In  treating  of  the  subject  of  digestion,  we  have  already  indicated 
some  of  the  difficulties,  which  have  been  but  imperfectly  overcome,  in  the  study  of  the 
action  of  the  bile  as  a  true  secretion,  or  a  recrementitious  fluid.  The  reason  why  the 
same  obscurity  has  prevailed  with  regard  to  the  function  of  the  bile  as  an  excretion  is 
that  physiologists  have  regarded  what  are  known  as  the  biliary  salts  as  the  only  really 
important  constituents  ;  and  these  salts  have  eluded  chemical  investigation  after  the  dis- 
charge of  the  bile  into  the  small  intestine.  Our  recent  positive  knowledge  of  the  excre- 
mentitious  function  of  the  liver  is  due  to  the  recognition  of  cholesterine,  an  invariable 
constituent  of  the  bile,  as  one  of  the  most  important  of  the  elements  of  excretion. 

Composition  of  Human  Bile.     (Robin.) 

Water 916-00  to  819-00 

Taurocholate,  or  choleate  of  soda 56*50    "    106'00 

Glycocholate,  or  cholate  of  soda traces. 

Cholesterine 0'62  to       2-66 

Biliverdine 14-00    "      30'00 

Lecithene.  .  .  ) 

3-20    "      31-00 


Margarine,  oleine,  and  traces  of  soap? 

Choline.  .  .  .  traces. 

Chloride  of  sodium 2'77  to  3'50 

Phosphate  of  soda 1*60    "  2'50 

Phosphate  of  potassa 0'75    "  1-50 

Phosphate  of  lime 0'50    "  1-35 

Phosphate  of  magnesia 0'45    "  0'80 

Salts  of  iron 0'15    u  0'30 

Salts  of  manganese traces  "  0*12 

Silicic  acid 0'03   "  0'06 

Mucosine traces. 

Loss..,  3-43  to  1-21 


1,000-00     1,000-00 

There  are  no  peculiarities  in  the  composition  of  the  bile,  as  regards  its  inorganic  con- 
stituents, which  demand  more  than  a  passing  mention.  It  contains  no  coagulable  organic 
principle,  except  mucosine,  and  all  of  its  constituents  are  simply  solids  in  solution.  The 
quantity  of  solid  matter  is  very  large,  and  the  proportion  of  water  is  relatively  small ;  but, 
in  comparing  its  proportion  of  water  with  that  of  other  fluids  in  the  body,  as  the  blood- 
plasma,  lymph  and  chyle,  milk,  etc.,  it  must  be  remembered,  as  is  suggested  by  Kobin, 
that  all  of  these  contain  water  entering  into  the  composition  of  their  coagulable  prin- 
ciples ;  so  that  their  proportion  of  water,  as  it  is  ordinarily  given,  is  really  not  greater 
than  in  the  bile.  Among  the  inorganic  salts,  we  find  chloride  of  sodium  in  considerable 
quantity  and  a  large  proportion  of  phosphates.  We  also  note  the  presence  of  salts  of 
iron,  of  manganese,  and  a  small  proportion  of  silicic  acid. 

The  fatty  and  saponaceous  matters  demand  hardly  any  more  extended  consideration. 
A  small  quantity  of  margarine  and  oleine  are  held  in  solution,  partly  by  the  small  pro- 
portion of  soaps,  but  chiefly  by  the  taurocholate  of  soda.  These  principles  sometimes 
exist  in  larger  quantity,  when  they  may  be  discovered  in  the  form  of  globules.  The  pro- 
portion of  soaps  is  very  small.  Lecithene,  a  phosphorized  fat,  is  mentioned  by  Robin  and 
others,  but  its  constitution  is  not  definitely  settled.  All  that  is  known  of  this  principle 


444  EXCRETION. 

• 

is  that  it  is  a  neutral  fatty  substance  extracted  from  the  bile,  and  is  capable  of  being 
decomposed  into  phosphoric  acid  and  glycerine.  Choline  is  a  peculiar  alkaloid  found  in 
the  bile  in  exceedingly  minute  quantity. 

Biliary  Salts.— The  principles  which  we  have  called  biliary  salts  are  compounds  of 
soda  with  peculiar  organic  acids,  found  nowhere  but  in  the  liver,  and  undoubtedly  pro- 
duced in  this  organ  from  materials  furnished  by  the  blood.  The  fact  that  the  bile  pos- 
sesses peculiar  principles  has  long  been  recognized.  It  is  unnecessary,  however,  to 
follow  out  in  detail  the  earlier  chemical  investigations  into  their  properties;  for  the 
biliary  matter  of  Berzelius  and  the  picromel  and  biliary  resin  of  Thenard  are  now  known 
to  be  composed  of  several  distinct  proximate  principles.  Our  exact  knowledge  of  these 
substances  dates  from  the  analyses  of  ox-bile  by  Strecker.  He  obtained  two  peculiar 
acids,  cholic  and  choleic  acid,  which  he  found  in  the  bile,  in  combination  with  soda.  In 
the  subsequent  researches  of  Lehmann,  these  acids  are  called,  respectively,  glycocholic 
and  taurocholic  acid,  and  the  salts,  glycocholate  and  taurocholate  of  soda. 

In  human  bile,  the  proportion  of  glycocholate  of  soda  is  very  small,  the  biliary  mat- 
ter existing  almost  entirely  in  the  form  of  the  taurocholate.  The  taurocholate  may  be 
precipitated  from  an  alcoholic  extract  of  bile  by  ether,  in  the  form  of  dark,  resinous 
drops.  These  do  not  crystallize,  and  the  amount  of  glycocholate,  which  is  precipitated 
in  the  same  way  and  soon  assumes  a  crystalline  form,  is  very  slight.  Prof.  Dalton,  who 
has  studied  the  biliary  salts  very  closely,  at  first  was  unable  to  obtain  any  crystalline 
matter  from  human  bile,  but  he  has  lately  found  it  in  minute  quantity. 

Taurocholate  of  Soda. — There  is  some  doubt  whether  the  resinous  drops  obtained  by 
the  addition  of  an  excess  of  ether  to  a  strong  alcoholic  extract  of  bile  consist  of  a  proxi- 
mate principle  in  a  perfectly  pure  state.  These  drops  are  not  crystallizable,  and  this  has 
led  to  the  opinion  that  they  are  impure.  In  fact,  even  now,  there  is  a  certain  amount  of 
obscurity  with  regard  to  the  character  of  these  peculiar  biliary  salts.  In  ox-bile,  the 
non-crystallizable  and  the  crystallizable  salts  exist  together ;  but,  in  human  bile,  the 
greatest  part  is  in  the  form  of  what  we  know  as  the  taurocholate  of  soda. 

These  salts  may  be  readily  obtained  from  ox-bile  and  separated  from  each  other  by 
the  following  process :  The  bile  is  first  evaporated  to  dryness  and  pulverized.  The  dry 
residue  is  then  extracted  with  absolute  alcohol  and  filtered.  In  this  part  of  the  process, 
Dr.  Dalton  uses  five  grains  of  the  dry  residue  to  one  fluidrachm  of  alcohol.  The  filtered 
fluid  is  of  a  clear,  yellowish  color,  and  it  contains  fats  and  coloring  matter,  in  addition  to 
the  biliary  salts.  To  precipitate  the  biliary  salts,  a  small  quantity  of  ether  is  added, 
which  produces  a  dense,  white  precipitate  that  redissolves  by  agitation.  Another  small 
quantity  of  ether  is  again  added,  and  the  precipitate  thus  produced  is  dissolved  by  shak- 
ing the  mixture.  This  process  is  repeated  carefully,  adding  the  ether  and  shaking  the 
mixture  after  each  step,  until  the  precipitate  becomes  permanent.  An  excess  of  ether — 
from  eight  to  ten  times  the  bulk  of  the  alcoholic  extract  used— is  then  added,  the  test- 
tube  or  flask  is  carefully  corked,  and  the  mixture  is  set  aside  to  crystallize.  Gradually 
the  dense,  white  precipitate  falls  to  the  bottom  of  the  vessel  or  becomes  attached  in  the 
form  of  resinous  drops  to  the  sides  of  the  glass ;  and  in  from  six  to  twenty -four  hours  it 
begins  to  form  delicate,  acicular  crystals,  arranged  in  rosettes.  These  are  crystals  of  the 
glycocholate  of  soda ;  and  the  non-crystallizable  matter  remaining  is  the  taurocholate  of 
soda. 

To  separate  the  biliary  salts  from  each  other,  the  ether  is  rapidly  poured  off,  and  the 
crystalline  and  resinous  residue  is  dissolved  in  distilled  water.  On  the  addition  to  this 
solution  of  a  little  acetate  of  lead,  the  glycocholate  is  decomposed  and  precipitated  in  the 
form  of  glycocholate  of  lead,  leaving  the  taurocholate  in  solution.  The  glycocholate  of 
lead  is  then  separated  by  filtration,  and  the  subacetate  of  lead  is  added  to  the  filtered 
fluid.  This  decomposes  the  taurocholate,  and  the  taurocholate  of  lead  is  precipitated. 
The  subacetate  of  lead  will  decompose  both  the  glycocholate  and  the  taurocholate,  but 


BILIARY   SALTS. 


445 


the  glycocholate  only  is  acted  upon  by  the  acetate  of  lead.  The  glycocholate  and  the 
taurocholate  of  lead  are  then  carefully  washed  and  treated  separately  with  the  carbonate 
of  soda,  which  gives  the  original  salts  in  nearly  a  pure  state. 

The  taurocholate  of  soda  is  a  proximate  principle  of  the  bile ;  and  it  is  not  necessary 
to  describe  fully  in  detail  the  purely  chemical  processes  by  which  it  is  decomposed. 
With  a  little  care,  the  taurocholic  acid  may  be  obtained  in  a  state  of  tolerable  purity,  and. 
by  prolonged  boiling  with  potash,  it  may  be  decomposed  into  a  new  acid  and  taurine. 
Some  confusion  exists  in  the  books  about  the  name  of  this  new  acid.  Strecker  calls  it 
choleic  acid,  and  he  applies  the  name  of  cholic  acid  to  what  we  have  described  as  glyco- 
cholic  acid.  As  we  have  adopted  the  nomenclature  of  Lehmann,  we  shall  call  it  cholic 
acid.  It  must  be  remembered,  however,  that  these  substances  are  formed  artificially  and 
are  not  true  proximate  principles.  They  have  been  described  in  explanation  of  the  name 
taurocholic  acid,  which  has  been  applied  to  this  acid  on  the  assumption  that  the  different 
biliary  acids  are  formed  of  cholic  acid  united  with  taurine  or  other  basic  substances. 

If  human  bile  be  treated  in  the  manner  just  described,  frequently  no  crystalline  mat- 
ter is  obtained,  and,  when  it  exists,  it  is  in  very  small  quantity.  The  great  mass  of  the 
precipitate  is  composed  of  the  taurocholate  of  soda.  This,  when  it  has  been  thoroughly 


FIG.  135. — Crystals  of  glycocholate  of  soda;  magnified  100  diameters.    (Robin.) 

purified,  is  whitish  and  gummy,  very  soluble  in  water  and  alcohol,  and  insoluble  in  ether. 
It  is  melted  with  slight  heat  and  is  inflammable.  Its  reaction  is  neutral.  It  has  a  pecul- 
iar sweetish -bitter  taste.  The  proportion  of  this  principle  in  the  bile  is  always  very  large, 
although  it  is  subject  to  considerable  variation.  It  has  very  little  in  common  with  the 
salts  of  fatty  origin,  either  in  its  general  properties  or  composition,  inasmuch  as  it  is 
entirely  insoluble  in  ether,  and  its  acid  contains  nitrogen.  Another  peculiarity  in  its 


446  EXCRETION. 

composition,  and  one  which  serves  to  distinguish  it  from  the  glycocholate  of  soda,  is  that 
it  contains  two  atoms  of  sulphur.  One  of  its  important  properties  in  the  bile  is  that  it 
aids  in  the  solution  of  the  fats  contained  in  this  fluid,  and  to  a  certain  extent,  probably, 
in  the  solution  of  cholesterine. 

Glycocholate  of  Soda.—Wz  have  necessarily  described  the  process  for  the  extraction 
of  the  glycocholate  of  soda,  in  connection  with  the  taurocholate.  The  glycocholate  is 
crystallizable  and  is  more  easily  obtained  in  a  condition  of  purity.  The  chemical  points 
of  difference  between  these  salts  are,  that  the  glycocholate  is  precipitated  by  the  acetate 
of  lead  as  well  as  the  subacetate,  the  acetate  having  no  effect  upon  the  taurocholate  of 
soda,  and  that  the  glycocholic  acid  does  not  contain  sulphur.  By  treating  glycocholic 
acid  with  potash  at  a  high  temperature,  it  is  decomposed  into  cholic  acid  and  glycine,  or 
glycocoll.  It  is  this  which  has  given  it  the  name  of  glycocholic  acid.  In  their  physio- 
logical relations,  the  two  biliary  salts  are,  as  far  as  we  know,  identical. 

Origin  of  the  Biliary  Salts.— There  can  be  no  doubt  that  these  principles  are  ele- 
ments of  secretion  and  are  produced  de  novo  in  the  substance  of  the  liver.  In  no 
instance  have  they  ever  been  discovered  in  the  blood  in  health  ;  and,  although  they  pre- 
sent certain  points  of  resemblance  with  some  of  the  constituents  of  the  urine,  they  have 
never  been  found  in  the  excreta.  In  experiments  made  by  Mtiller,  Kunde,  Lehmann,  and 
Moleschott,  on  frogs,  in  which  the  liver  was  removed  and  the  animal  survived  several 
days,  and,  in  the  observations  of  Moleschott,  between  two  and  three  weeks,  it  was  found 
impossible  to  determine  the  accumulation  of  the  biliary  salts  in  the  blood.  There  is  no 
reason,  therefore,  for  supposing  that  these  principles  are  products  of  disassimilation. 
Once  discharged  into  the  intestine,  they  undergo  certain  changes  and  can  no  longer  be 
recognized  by  the  usual  tests ;  but  experiments  have  shown  that,  changed  or  unchanged, 
they  are  absorbed  with  the  elements  of  food.  They  are  probably  the  elements  con- 
cerned in  the  digestive  function  of  the  bile. 

Cholesterine. — Before  the  publication,  in  1862,  of  a  memoir  on  a  new  excretory  func- 
tion of  the  liver,  the  function  and  relations  of  cholesterine  were  not  known,  and  this  sub- 
stance was  hardly  mentioned  in  most  works  on  physiology.  As  we  believe  that  it  must 
now  be  recognized  as  one  of  the  most  important  of  the  products  of  disassimilation,  it 
becomes  interesting  and  important  to  study  its  properties  more  closely. 

Cholesterine  is  now  recognized  as  a  normal  constituent  of  various  of  the  tissues  and 
fluids  of  the  body.  Most  authors  state  that  it  is  found  in  the  bile,  blood,  liver,  nervous 
tissue,  crystalline  lens,  meconium,  and  faecal  matter.  We  have  found  it  in  all  these  situa- 
tions, with  the  exception  of  the  fa3ces,  where  it  does  not  exist  normally,  being  trans- 
formed into  stercorine  in  its  passage  down  the  intestinal  canal. 

In  the  fluids  of  the  body,  cholesterine  exists  in  solution  ;  but  by  virtue  of  what  con- 
stituents it  is  held  in  this  condition,  is  a  question  that  is  not  entirely  settled.  It  is  stated 
that  the  biliary  salts  have  the  power  of  holding  cholesterine  in  solution  in  the  bile,  and 
that  the  small  amount  of  fatty  acids  contained  in  the  blood  holds  it  in  solution  in  that 
fluid  ;  but  direct  experiments  on  this  point  are  wanting.  In  the  nervous  substance  and 
in  the  crystalline  lens,  it  is  united  "molecule  d  molecule  "  to  the  other  elements  which  go 
to  make  up  these  tissues.  After  it  is  discharged  into  the  intestinal  canal,  when  it  is  not 
changed  into  stercorine,  it  is  to  be  found  in  a  crystalline  form,  as  in  the  meconium  and 
in  the  faeces  of  animals  in  a  state  of  hibernation.  In  pathological  fluids  and  in  tumors, 
it  is  found  in  a  crystalline  form  and  may  be  detected  by  microscopical  examination. 

Cholesterine  is  usually  described  as  a  non-nitrogenized  principle,  having  all  the  prop- 
erties of  the  fats,  except  that  of  saponification  with  the  alkalies.  It  is  neutral,  inodor- 
ous, crystallizable,  insoluble  in  water,  soluble  in  ether,  very  soluble  in  hot  alcohol,  though 
sparingly  soluble  in  cold  alcohol.  It  is  inflammable  and  burns  with  a  bright  flame.  It 
is  not  attacked  by  the  alkalies,  even  after  prolonged  boiling.  When  treated  with  strong 


CIIOLE8TERINE. 


447 


FIG.  136.— Cholesterine  extracted  from  the  Ule ; 
objective. 


inch 


sulphuric  acid,  it  strikes  a  peculiar  red  color,  which  is  mentioned  by  some  as  characteristic 
of  cholesterine.  We  have  found  that  it  possesses  this  character  in  common  with  the  so- 
called  seroline. 

Cholesterine  may  easily  and  certainly  be  recognized  by  the  form  of  its  crystals,  the  char- 
acters of  which  can  be  made  out  by  means  of  the  microscope.  They  are  rectangular  or 
rhomboidal,  exceedingly  thin  and  transparent,  of  variable  size,  with  distinct  and  generally 
regular  borders,  and  frequently  are  arranged 
in  layers,  with  the  borders  of  the  lower  stra- 
ta showing  through  those  which  are  super- 
imposed. This  arrangement  of  the  crystals 
takes  place  when  cholesterine  is  present  in 
considerable  quantity.  In  pathological  speci- 
mens, the  crystals  are  generally  few  in  num- 
ber and  isolated.  The  plates  of  cholesterine 
are  frequently  marked  by  a  cleavage  at  one 
corner,  the  lines  running  parallel  to  the  bor- 
ders; and  frequently  they  are  broken,  and 
the  line  of  fracture  is  generally  undulating. 
Frequently  the  plates  are  rectangular,  and 
sometimes  they  are  almost  lozenge-shaped. 
It  is  by  the  transparency  of  the  plates,  the 
parallelism  of  their  borders,  and  their  ten- 
dency to  break  in  parallel  lines,  that  we  rec- 
ognize cholesterine.  Crystals  of  cholesterine 
melt  at  293°  Fahr.,  but  they  are  formed  again 
when  the  temperature  falls  below  that  point.  The  determination  of  the  fusing-point  is 
one  of  the  means  of  distinguishing  cholesterine  from  seroline,  which  latter  fuses  at  90°  8'. 

Without  considering  in  detail  the  processes  which  have  been  employed  by  other 
observers  for  the  extraction  of  cholesterine  from  the  blood,  bile,  and  various  tissues  of  the 
body,  we  shall  simply  describe  the  method  which  has  been  found  most  convenient  in  the 
various  analyses  we  have  made  for  this  substance.  In  analyses  of  gall-stones,  the  process 
is  very  simple ;  all  that  is  necessary  being  to  pulverize  the  mass,  extract  it  with  boiling 
alcohol,  and  filter  the  solution  while  hot,  the  cholesterine  being  deposited  on  cooling. 
If  the  crystals  be  colored,  they  may  be  redissolved  and  filtered  through  animal  charcoal. 
It  is  only  when  tnis  substance  is  mixed  with  fatty  matters,  that  its  isolation  is  a  matter 
of  any  difficulty.  In  extracting  cholesterine  from  the  blood,  we  have  operated  on  both 
the  serum  and  clot,  and,  in  this  way,  we  have  been  able  to  demonstrate  it  in  greater  quan- 
tities in  this  fluid  than  have  been  observed  by  others,  who  have  employed  only  the  serum. 
The  following  is  the  process  for  quantitative  analysis,  which  was  fixed  upon  after  a 
number  of  experiments : 

The  blood,  bile,  or  brain,  as  the  case  maybe,  is  first  carefully  weighed,  then  evaporated 
to  dryness  over  a  water-bath,  and  afterward  pulverized  in  an  agate  mortar.  The  powder 
is  then  treated  with  ether,  in  the  proportion  of  about  a  fluidounce  for  every  hundred  grains 
of  the  original  weight,  for  from  twelve  to  twenty-four  hours,  agitating  the  mixture  occa- 
sionally. The  ether  is  then  separated  by  filtration,  throwing  a  little  fresh  ether  on  the 
filter  so  as  to  wash  through  every  trace  of  the  fat,  and  the  solution  is  set  aside  to  evaporate. 
If  the  fluid,  especially  the  blood,  have  been  carefully  dried  and  pulverized,  when  the  ether 
is  added  it  divides  it  into  a  very  fine  powder  and  penetrates  every  part.  After  the  ether 
has  evaporated,  the  residue  is  extracted  with  boiling  alcohol,  in  the  proportion  of  about 
a  fluidrachm  for  every  hundred  grains  of  the  original  weight  of  the  specimen,  filtered 
while  hot  into  a  watch-glass,  and  allowed  to  evaporate  spontaneously.  To  keep  the  fluid 
hot  while  filtering,  the  whole  apparatus  may  be  placed  in  the  chamber  of  a  large  water- 
bath,  or,  as  the  filtration  is  generally  rapid,  the  funnel  may  be  warmed  by  plunging  it 


448  EXCRETION. 

into  hot  water,  or  steaming  it,  taking  care  that  it  be  carefully  wiped.  We  now  have  the 
cholesterine  mixed  with  a  certain  quantity  of  saponifiable  fat.  After  the  fluid  has  evapo- 
rated, we  can  see  the  cholesterine  crystallized  in  the  watch-glass,  mingled  with  masses 
of  fat.  This  we  remove  by  saponification  with  an  alkali ;  and,  for  this  purpose,  we  add 
a  moderately  strong  solution  of  caustic  potash,  which  we  allow  to  remain  in  contact 
with  the  residue  for  one  or  two  hours.  If  much  fat  be  present,  it  is  best  to  heat  the 
mixture  to  a  temperature  a  little  below  the  boiling-point ;  but  in  analyses  of  the  blood 
this  is  not  necessary.  The  mixture  is  then  to  be  largely  diluted  with  distilled  water, 
thrown  upon  a  small  filter,  and  thoroughly  washed  till  the  fluid  which  passes  through  is 
neutral.  We  then  dry  the  filter  and  fill  it  up  with  ether,  which,  in  passing  through, 
dissolves  out  the  cholesterine.  The  ether  is  then  evaporated,  the  residue  extracted  with 
boiling  alcohol  as  before,  the  alcohol  collected  on  a  watch-glass  previously  weighed,  and 
allowed  to  evaporate.  The  residue  consists  of  pure  cholesterine,  the  quantity  of  which 
may  be  estimated  by  weight. 

The  accuracy  of  this  process  may  be  tested  by  means  of  the  microscope ;  for  the  crys- 
tals have  so  distinctive  a  form  that  it  is  easy  to  determine,  by  examining  the  watch-glass, 
that  the  cholesterine  is  perfectly  pure.  In  making  this  analysis  quantitatively,  it  is 
necessary  to  be  very  careful  in  all  the  manipulations  ;  and,  for  determining  the  weight  of 
such  minute  quantities,  an  accurate  and  delicate  balance,  one,  at  least,  that  will  turn  with 
the  thousandth  of  a  gramme,  carefully  adjusted,  must  be  employed.  With  these  precau- 
tions, the  quantity  of  cholesterine  in  any  fluid  or  solid  may  be  determined  with  perfect 
accuracy ;  and  the  estimate  may  be  made  in  a  quantity  of  blood  not  exceeding  fifteen  or 
twenty  grains.  In  analyzing  the  brain  and  bile,  we  found  it  necessary  to  pass  the  first 
ethereal  solution  through  animal  charcoal,  in  order  to  get  rid  of  the  coloring  matter. 
In  doing  this,  the  charcoal  must  be  washed  with  fresh  ether  until  the  solution  which 
passes  through  is  brought  up  to  the  original  quantity.  The  other  manipulations  are  the 
same  as  in  the  analyses  of  the  blood.  In  examining  the  meconium,  we  found  that  the 
cholesterine  which  crystallized  from  the  first  alcoholic  extract  was  so  pure  that  it  was 
not  necessary  to  subject  it  to  the  action  of  an  alkali. 

The  proportion  of  cholesterine  in  the  bile  is  not  very  large.  In  the  table,  it  is  esti- 
mated at  from  0'62  to  2*66  parts  per  thousand.  In  a  single  examination  of  the  human 
bile,  we  found  the  proportion  0*618  of  a  part  per  thousand. 

The  origin  and  destination  of  this  principle  involve,  as  we  believe,  an  office  of  the 
liver  which  has  not  hitherto  been  recognized  by  physiologists;  and  we  shall  consider 
these  questions  specially,  under  the  head  of  the  excretory  function  of  the  liver. 

Itiliverdine. — The  coloring  matter  of  the  bile  bears  a  certain  resemblance  to  the  color- 
ing matter  of  the  blood  and  is  supposed  to  be  formed  from  it  in  the  liver.  It  gives 
to  the  bile  its  peculiar  tint,  and  has,  as  we  have  remarked,  the  property  of  coloring 
the  tissues  with  which  it  comes  in  contact.  Whenever  the  flow  of  bile  is  seriously 
obstructed,  the  coloring  matter  is  absorbed  by  the  blood,  and  it  can  be  readily  detected 
in  the  serum  and  in  the  urine.  It  also  colors  the  skin  and  the  conjunctiva.  In  the  bile 
it  is  liquid,  but  it  may  be  coagulated  and  extracted  by  various  processes.  It  does  not 
exist  naturally  in  the  form  of  pigmentary  granulations. 

This  principle  is  precipitated  from  the  bile  by  boiling  with  milk  of  lime.  The  filtered 
residue  is  then  decomposed  with  hydrochloric  acid,  which  unites  with  the  lime  and  leaves 
a  fatty  residue,  of  an  intense-green  color.  The  fat  is  then  removed  by  repeated  washings 
with  ether,  which  is  a  very  long  and  difficult  process.  The  precipitate  is  then  redissolved 
in  alcohol  with  ether  added,  which  gives  to  the  liquid  a  bluish-green  color,  and  leaves, 
after  evaporation,  a  dark-green  powder.  This  powder  contains  iron,  but  its  proportion 
has  never  been  accurately  estimated.  The  matter  thus  obtained  is  insoluble  in  water  and 
in  chloroform,  but  it  is  soluble  in  ether,  alcohol,  sulphuric  and  hydrochloric  acid. 

It  is  unnecessary  to  follow  out  in  detail  all  of  the  chemical  investigations  which  have 


TESTS  FOE  BILE.  449 

been  made  into  the  ultimate  composition  and  the  modifications  of  this  and  the  other  col- 
oring matters.  Eecent  researches  have  shown  that,  in  all  probability,  the  coloring  matter 
called  biliverdine  is  a  mixture  of  several  distinct  coloring  principles,  and  that  these  rapidly 
change  in  contact  with  the  oxygen  of  the  air ;  so  that  there  is  considerable  uncertainty 
with  regard  to  the  ultimate  composition  of  these  and  other  substances  of  the  same  class." 

Tests  for  Bile.— It  is  frequently  desired,  particularly  in  pathological  investigations, 
to  ascertain,  by  some  easy  test,  the  fact  of  the  presence  or  absence  of  bile  in  various 
of  the  fluids  and  solids  of  the  body.  It  is,  indeed,  a  most  interesting  physiological  ques- 
tion to  determine  the  course  and  destination  of  the  biliary  salts  after  the  bile  has  passed 
into  the  intestinal  canal ;  and  this  can  be  done  only  by  the  application  of  appropriate 
tests  to  the  contents  of  the  alimentary  tract  and  the  blood  of  the  portal  system.  The 
ingredients  of  the  bile  which  it  is  important  to  detect  are  biliverdine,  the  biliary  salts, 
and  .cholesterine.  The  last-named  substance  can  be  detected  most  readily  by  applying 
the  method  which  we  have  just  described  for  its  extraction ;  but  several  tests  have  been 
proposed  for  the  detection,  on  the  one  hand,  of  the  coloring  matter  of  the  bile,  and,  on 
the  other,  of  the  peculiar  biliary  salts. 

Test  for  Biliverdine. — There  is  one  test  so  simple  and  easy  of  application,  that  it  alone 
will  suffice  for  the  prompt  detection  of  biliverdine.  This  is  peculiarly  applicable  to  the 
urine,  where  the  presence  or  absence  of  bile  frequently  becomes  an  important  question. 

We  are  led  generally  to  suspect  the  presence  of  bile  in  the  fluids  of  the  body  by  their 
peculiar  color.  If  we  spread  out  the  suspected  fluid  in  a  thin  stratum  upon  a  white  sur- 
face, as  a  porcelain  plate,  and  add  a  single  drop  of  nitric  acid,  or,  what  is  better,  nitroso- 
nitric  acid,  if  the  coloring  matter  of  bile  be  present,  a  peculiar  play  of  colors  will  be  ob- 
served at  the  circumference  of  the  drop  of  acid  as  it  diffuses  itself.  The  color  will  rapidly 
change  from  blue  to  red,  orange,  purple,  and  finally  to  yellow.  This  is  due  to  the  action 
of  the  acid  upon  the  biliverdine ;  and  this  test  does  not  indicate  the  presence  of  either  cho- 
lesterine or  the  biliary  salts.  It  is  used,  therefore,  only  when  we  wish  to  determine  the 
presence  of  the  coloring  matter  of  the  bile. 

Test  for  the  Biliary  Salts.— The  best,  and,  indeed,  the  only  reliable  test  for  the  biliary 
salts,  was  proposed  many  years  ago  by  Pettenkofer,  and  this  is  now  generally  known  as 
Pettenkofer's  test.  This  requires  some  care  and  practice  in  its  application,  but  it  is  entirely 
reliable;  and,  although  it  has  been  objected  that  there  are  other  substances,  beside  the 
biliary  salts,  which  produce  similar  reactions,  they  are  not  met  with  in  the  animal  fluids 
and  consequently  are  not  liable  to  produce  confusion.  If  a  considerable  quantity  of  bile 
be  present  in  any  fluid,  and  if  there  be  not  a  large  admixture  of  animal  matters,  the  test 
may  be  employed  without  any  previous  preparation  ;  but,  in  delicate  examinations,  it  is 
best  to  evaporate  the  suspected  liquid,  extract  the  residue  with  absolute  alcohol,  precipi- 
tate with  ether,  and  dissolve  the  ether-precipitate  in  distilled  water.  By  this  means  a 
clear  solution  is  obtained,  which  will  react  distinctly,  even  when  the  biliary  salts  exist 
in  very  small  quantity.  Pettenkofer's  test  is  applicable  to  any  of  the  biliary  salts,  what- 
ever be  their  form,  and  the  reaction  is  dependent  upon  the  presence  of  cholic  acid,  which 
enters  into  the  composition  of  all  the  varieties  of  the  biliary  acids. 

The  following  is  one  of  the  most  common  methods  of  employing  Pettenkofer's  test : 
To  the  suspected  solution  we  add  a  few  drops  of  a  strong  solution  of  cane-sugar  in 
water.  Sulphuric  acid  is  then  slowly  added,  to  the  extent  of  about  two-thirds  of  the 
bulk  of  the  liquid.  It  is  recommended  to  add  the  acid  slowly,  so  that  the  temperature 
shall  be  but  little  raised.  If  a  large  quantity  of  the  biliary  salts  be  present,  a  red  color 
shows  itself  almost  immediately  at  the  bottom  of  the  test-tube,  and  this  soon  extends 
through  tne  entire  liquid,  rapidly  deepening  until  it  becomes  of  a  dark-lake  or  purple. 
If  the  biliary  matters  exist  in  very  small  proportion,  it  may  be  several  minutes  before  any 
red  color  makes  its  appearance,  and  the  change  to  a  purple  is  correspondingly  slow,  the 
whole  process  occupying  from  fifteen  to  twenty  minutes.  Many  organic  matters  may  be 
29 


450  EXCRETION. 

rendered  dark  by  the  action  of  the  acid,  and  the  sugar  itself  will  be  acted  upon,  even  if 
no  bile  be  present,  but  the  color  due  to  the  sugar  alone  is  yellow.  The  peculiar  play  of 
colors  above  described  can  easily  be  recognized  after  a  little  practice,  and  is  observed 
only  in  the  presence  of  the  biliary  salts. 

The  ordinary  modifications  in  the  application  of  this  test  are  unimportant.  Some 
recommend  to  add  the  sulphuric  acid  first,  and  then  to  add  the  solution  of  sugar;  and 
some,  after  adding  to  the  liquid  two-thirds  of  its  volume  of  sulphuric  acid,  drop  into  the 
mixture  one  or  two  lumps  of  cane-sugar.  The  reaction  with  the  biliary  salts  is  essen- 
tially the  same,  whichever  of  these  methods  be  employed. 

Excretory  Function  of  the  Liver. 

In  1862,  in  studying  the  properties  and  physiological  relations  of  cholesterine,  we 
gave  the  first  definite  account  of  an  excretory  function  of  the  liver.  The  experiments  and 
observations  upon  which  we  based  our  conclusions  were  extended  and  laborious,  and,  as 
far  as  we  know,  they  have  not  been  repeated  in  detail  by  other  observers ;  but  the  results 
must  be  taken  as  positive,  if  the  accuracy  of  the  experiments  be  admitted,  and  they  have 
been  adopted,  to  a  greater  or  less  extent,  by  scientific  authorities.  The  details  of  these 
experiments  are  too  elaborate  to  be  given  in  full,  as  contained  in  the  original  memoir.1 

The  few  statements  with  regard  to  the  function  of  cholesterine  to  be  found  in  works 
published  before  1862  are  very  indefinite.  In  most  treatises  on  physiology,  this  substance 
is  hardly  mentioned,  it  being  generally  regarded  as  a  curious  principle,  interesting  only 
to  the  physiological  chemist.  We  have  given,  in  the  memoir  referred  to,  extracts  from 
the  works  of  Carpenter,  Lehmann,  Mialhe,  and  Dalton,  which  contain  all  that  is  said 
with  regard  to  the  probable  function  of  cholesterine  ;  and  these  quotations,  which  embody 
about  all  that  we  could  find  on  the  subject,  show  that  its  office  was  not  in  the  least 
understood.  Inasmuch  as  cholesterine  is  the  only  excrementitious  principle  as  yet  dis- 
covered in  the  bile,  bearing  the  same  relation  to  this  fluid  that  urea  does  to  the  urine,  it  is 
evident  that  the  ideas  of  physiologists,  with  regard  to  any  excretory  function  of  the  liver, 
must  have  been  very  indefinite  before  the  relations  of  cholesterine  had  been  determined. 

The  first  question  which  arises  is  whether  the  liver  has  any  excretory  function.  Some 
authors  have  assumed  that  the  bile  is  purely  excrementitious  and  has  no  function  as  a 
secretion.  This  question  we  have  fully  discussed  in  connection  with  the  subject  of  diges- 
tion. The  confusion  that  has  arisen  with  regard  to  this  point  has  been  due  to  the  fact 
that  those  who  adopted  the  view  that  the  bile  was  simply  an  excretion  denied  to  it  any 
digestive  properties  ;  while,  on  the  other  hand,  those  who  believed  it  to  be  concerned  in 
digestion  would  not  admit  that  it  was  an  excretion.  We  have  shown  conclusively,  in 
treating  of  intestinal  digestion,  that  the  bile  is  so  important  in  this  process  as  to  be  essen- 
tial to  life ;  but  we  have  shown,  at  the  same  time,  that  the  liver  eliminates  from  the 
blood  one  of  the  most  important  of  the  products  of  disassimilation.  It  will  be  found 
important,  as  bearing  upon  the  probable  function  of  the  bile,  to  apply  to  this  fluid  the 
general  law  of  the  distinctions  between  secretions  and  excretions. 

Cells  of  glandular  epithelium  are  constantly  manufacturing,  out  of  materials  furnished 
by  the  blood,  the  elements  of  the  true  secretions ;  but  these  elements  do  not  preexist  in 
the  blood,  they  appear  de  novo  in  the  secreting  organ,  and  they  never  accumulate  in  the 
system  when  the  function  of  the  secreting  organ  is  disturbed.  Again,  the  true  secretions 
are  not  discharged  from  the  body,  but  they  have  a  function  to  perform  in  the  economy, 
and  are  poured  out  by  the  glands  intermittently,  at  the  times  when  this  function  is  called 
into  action.  As  far  as  the  biliary  salts  (the  taurocholate  and  glycocholate  of  soda)  are 
concerned,  the  bile  corresponds  entirely  to  the  true  secretions.  These  principles  are 
manufactured  by  the  liver,  they  do  not  preexist  in  the  blood,  and  they  do  not  accumu- 

1  FLINT,  Jr.,  Experimental  Researches  into  a  New  Excretory  Function  of  the  Liver. —American  Journal  of 
the  Medical  Sciences,  Philadelphia,  1862,  New  Series,  vol.  xliv.,  p.  305,  et  seq. ';  and,  Recherche*  experimental^  vur 
unz  nouvellefonction  dufoie,  Paris,  1868. 


EXCRETORY  FUNCTION   OF  THE  LIVER.  45! 

late  in  the  blood  when  their  formation  in  the  liver  is  disturbed.  The  researches  of 
Bidder  and  Schmidt  and  others  have  shown  that,  although  we  cannot  detect  the  biliary 
salts  in  the  blood  or  chyle  coming  from  the  intestine,  these  principles  are  not  discharged 
in  the  faeces.  All  of  these  facts  point  to  an  important  function  of  the  bile  as  a  secretion. 
It  is  true  that  it  is  discharged  constantly,  but,  during  digestion,  its  flow  is  very  much 
more  abundant  than  at  any  other  time.  It  is  pretty  well  established  that,  during  the 
intervals  of  the  flow  of  the  secretions,  the  glands  are  manufacturing  the  materials  of 
secretion,  which  are  washed  out,  as  it  were,  in  the  great  afflux  of  blood  which  takes 
place  during  what  has  been  called  the  functional  activity  of  the  gland.  Now,  if  the  liver, 
in  addition  to  its  function  as  a  secreting  organ,  be  constantly  forming  bile  for  the  purpose 
of  eliminating  an  excrementitious  matter,  it  is  to  be  expected  that  the  bile  would  al- 
ways contain  a  certain  proportion  of  its  elements  of  secretion. 

The  constant  and  invariable  presence  of  cholesterine  in  the  bile  assimilates  it  in  every 
regard  to  the  excretions,  of  which  the  urine  may  be  taken  as  the  type.  Cholesterine 
always  exists  in  the  blood  and  in  certain  of  the  tissues  of  the  body.  It  is  not  produced 
in  the  substance  of  the  liver,  but  is  merely  separated  from  the  blood  by  this  organ.  It 
is  constantly  passed  into  the  intestine,  and  is  discharged,  although  in  a  modified  form,  in 
the  faeces.  We  know  of  no  function  which  it  has  to  perform  in  the  economy,  any  more 
than  urea  or  any  other  of  the  excrementitious  principles  of  the  urine ;  and  we  have 
shown,  in  the  memoir  already  referred  to,  that  it  accumulates  in  the  blood  in  certain 
cases  of  organic  disease  of  the  liver  and  gives  rise  to  symptoms  of  blood-poisoning. 

Origin  of  Cholesterine. — Cholesterine  exists  in  largest  quantity  in  the  substance  of 
the  brain  and  nerves.  It  is  also  found  in  the  substance  of  the  liver — probably  in  the 
bile  contained  in  this  organ — the  crystalline  lens,  and  the  spleen ;  but,  with  these  excep- 
tions, it  is  found  only  in  the  nervous  system  and  blood.  Two  views  present  themselves 
with  regard  to  its  origin.  It  is  either  deposited  in  the  nervous  matter  from  the  blood,  or 
it  is  formed  in  the  brain  and  taken  up  by  the  blood.  This  is  a  question,  however,  which 
can  be  settled  experimentally,  by  analyzing  the  blood  for  cholesterine  as  it  goes  to  the 
brain  by  the  carotid  and  as  it  comes  from  the  brain  by  the  internal  jugular.  The  cho- 
lesterine being  found  also  in  the  nerves,  and,  of  course,  a  large  quantity  of  nervous  mat- 
ter existing  in  the  extremities,  it  is  desirable  at  the  same  time  to  make  an  analysis  of  the 
venous  blood  from  the  general  system. 

With  a  view  of  determining  this  question,  we  made  the  following  experiments : 

Experiment  I. — In  this  experiment,  specimens  of  blood  were  taken  from  the  carotid, 
the  internal  jugular,  the  vena  cava,  hepatic  veins,  hepatic  artery,  and  portal  vein,  in  a  liv- 
ing animal  (a  dog  about  six  months  old).  In  addition,  we  took  a  specimen  of  bile  from 
the  gall-bladder,  and  some  of  the  substance  of  the  brain.  These  were  all  carefully  ex- 
amined for  cholesterine,  and  the  following  were  the  main  results :  In  the  brain,  choles- 
terine was  found  in  large  quantity.  There  was  no  cholesterine  in  the  extract  of  the 
blood  from  the  carotid,  examined  three  days  after,  and  but  a  few  crystals,  eleven  days 
after.  Cholesterine  was  almost  immediately  discovered  in  the  extract  of  the  blood  from 
the  internal  jugular,  and  the  crystals  were  present  in  large  numbers  on  the  twelfth  day. 
In  this  experiment,  the  animal  was  etherized  when  the  blood  was  taken,  and  the  examina- 
tions for  cholesterine  were  not  quantitative.  In  the  succeeding  experiments,  the  propor- 
tion of  cholesterine  in  the  different  specimens  of  blood  was  accurately  estimated,  and,  in 
most  of  them,  no  anaesthetic  was  used  during  the  operative  procedure. 

Experiment  II.— A  medium-sized  adult  dog  was  put  under  the  influence  of  ether,  and 
the  carotid  artery,  internal  jugular,  and  femoral  vein  exposed.  Specimens  of  blood  were 
drawn,  first  from  the  internal  jugular,  next  from  the  carotid,  and  last  from  the  femoral 
vein.  These  specimens  were  received  into  carefully-weighed  vessels,  and  weighed.  They 
were  then  analyzed  for  cholesterine  by  the  process  already  described,  with  the  follow- 
ing results : 


452  EXCRETION. 

Quantity  of  blood.  Cholesterine.  Cholesterine  per 

grains.  grains.  1,000  pts. 

Carotid 179-462  0'139  0-774 

Internal  jugular 134*780  0-108  0'801 

Femoral  vein 133-886  0-108  0'806 

Percentage  of  increase  in  the  blood  from  the  jugular  over  the  arterial  blood 3 -4 88 

Percentage  of  increase  in  the  blood  from  the  femoral  vein  over  the  arterial  blood 4-134 

This  experiment  shows  an  increase  in  the  quantity  of  cholesterine  in  the  blood  in  its 
passage  through  the  brain,  and  an  increase,  even  a  little  greater,  in  the  blood  passing 
through  the  vessels  of  the  posterior  extremity.  To  facilitate  the  operation,  however, 
the  animal  was  brought  completely  under  the  influence  of  ether,  which,  from  its  action 
upon  the  brain,  would  not  improbably  produce  some  temporary  disturbance  in  the  nutri- 
tion of  that  organ,  and  consequently  might  interfere  with  the  experiment.  For  the  pur- 
pose of  avoiding  this  difficulty,  we  performed  the  following  experiments  without  adminis- 
tering an  anesthetic : 

Experiment  III. — A  small,  young  dog  was  secured  to  the  operating-table,  and  the  inter- 
nal jugular  and  carotid  were  exposed  upon  the  right  side.  Blood  was  taken,  first  from  the 
jugular,  and  afterward  from  the  carotid.  The  femoral  vein  upon  the  same  side  was  then 
exposed,  and  a  specimen  of  blood  was  taken  from  that  vessel.  The  animal  was  very 
quiet  under  the  operation,  although  no  anesthetic  was  used,  so  that  the  blood  was  drawn 
without  any  difficulty  and  without  the  slightest  admixture. 

The  three  specimens  were  analyzed  for  cholesterine,  with  the  following  results : 

Quantity  of  blood.  Cholesterine.  Cholesterine  per 

grains.  grains.  1,000  pts. 

Carotid 143-625  0'679  0'967 

Internal  jugular 29'956  0*046  1-545 

Femoral  vein 45'035  0'046  1-028 

Percentage  of  increase  in  the  blood  from  the  jugular  over  the  arterial  blood 59'772 

Percentage  of  increase  in  the  blood  from  the  femoral  vein  over  the  arterial  blood 6*308 

Experiment  IV. — A  large  and  powerful  dog  was  secured  to  the  operating-table,  and 
the  carotid  and  internal  jugular  were  exposed.  Specimens  of  blood  were  taken  from  these 
vessels,  first  from  the  jugular,  and  were  carefully  weighed  and  analyzed  for  cholesterine 
in  the  usual  way.  The  following  results  were  obtained  : 

Quantity  of  blood.  Cholesterine.  Cholesterine  per 

grains.  grains.  1,000  pts. 

Carotid \ 140-847  0-108  0'768 

Internal  jugular 97-811  0'092  0'947 

Percentage  of  increase  in  the  blood  passing  through  the  brain 23*307 

Experiment  III.  shows  a  very  considerable  increase  in  the  quantity  of  cholesterine  in 
the  blood  passing  through  the  brain,  while  the  increase  is  comparatively  slight  in  tho 
blood  of  the  femoral  vein.  The  proportion  of  cholesterine  is  also  large  in  the  arterial 
blood,  as  compared  with  other  observations. 

Experiment  IV.  shows  but  a  slight  difference  in  the  quantity  of  cholesterine  in  the 
arterial  blood  in  the  two  animals ;  the  proportion  in  the  animal  that  was  etherized  being 
0-774  per  1,000,  and  in  the  animal  that  was  not  etherized,  0'768  per  1,000,  the  difference 
being  but  0-006 ;  but,  as  was  suspected,  the  ether  seemed  to  have  an  influence  upon  the 
quantity  of  cholesterine  absorbed  by  the  blood  in  its  passage  through  the  brain.  In  the 
first  instance  the  increase  was  but  3-488  per  cent.,  while  in  the  latter  it  was  23-307  per 
cent. 

The  natural  conclusions  to  be  drawn  from  these  observations,  with  regard  to  the  ori- 
gin of  cholesterine  in  the  economy,  are  the  following :  It  has  been  ascertained  that  the 
brain  and  nerves  contain  a  large  quantity  of  this  substance,  which  is  found  in  hardly  any 


EXCRETORY  FUNCTION  OF  THE  LIVER.  453 

other  of  the  tissues  of  the  body ;  and  these  experiments,  especially  Experiments  III.  and 
IV.,  show  that  the  blood  that  comes  from  the  brain  contains  a  much  larger  quantity  of 
cholesterine  than  the  blood  supplied  to  this  organ. 

The  conclusion  is,  then,  that  cholesterine  is  produced  in  the  brain  and  is  taken  up  by 
the  blood  as  it  passes  through  this  organ. 

But  the  brain  is  not  the  only  part  where  cholesterine  is  produced.  It  will  be  seen  by 
Experiment  II.  that  there  is  4'134  per  cent.,  and  in  Experiment  III.,  6-308  per  cent,  of 
increase  in  cholesterine  in  the  passage  of  the  blood  through  the  inferior  extremities, 
and  probably  about  the  same  in  other  parts  of  the  muscular  system.  In  examining  these 
tissues  chemically,  we  find  that  the  muscles  contain  no  cholesterine,  but  that  it  is  abun- 
dant in  the  nerves ;  and,  as  we  have  found  that  the  proportion  of  cholesterine  is  immense- 
ly increased  in  the  passage  of  the  blood  through  the  great  centre  of  the  nervous  system, 
taken,  as  the  specimens  were,  from  the  internal  jugular,  which  collects  the  blood  mainly 
from  the  brain  and  very  little  from  the  muscular  system,  it  is  very  probable  that,  in  the 
general  venous  system,  the  cholesterine  which  the  blood  contains  is  produced  in  the 
substance  of  the  nerves. 

If  the  above  conclusion  be  correct,  and  if  cholesterine  be  one  of  the  products  of  the 
disassimilation  of  nervous  tissue,  its  formation  would  be  proportionate  in  activity  to  the 
nutrition  of  the  nerves;  and  any  thing  which  interfered  to  any  great  extent  with  their 
nutrition  would  diminish  the  quantity  of  cholesterine  produced.  In  the  production  of 
urea  by  the  general  system,  which  is  analogous  to  the  formation  of  cholesterine,  mus- 
cular activity  increases  the  quantity,  and  inaction  diminishes  it,  on  account  of  their 
influence  upon  nutrition.  In  cases  of  paralysis,  we  have  a  diminution  of  the  nutritive 
forces  in  the  parts  affected,  especially  of  the  nervous  system,  which,  after  a  time,  becomes 
so  disorganized  that,  although  the  cause  of  the  paralysis  be  removed,  the  nerves  cannot 
resume  their  functions.  It  is  true  that  we  have  this  disorganization  taking  place  to  a 
certain  extent  in  the  muscles,  but  this  is  by  no  means  so  marked  as  it  is  in  the  nerves. 
We  should  be  able,  then,  to  confirm  the  observations  on  animals  by  examining  the 
blood  in  cases  of  paralysis,  when  we  should  expect  to  find  a  very  marked  difference  in 
the  quantity  of  cholesterine,  between  the  venous  blood  coming  from  the  paralyzed  parts 
and  the  blood  from  other  parts  of  the  body.  With  this  point  in  view,  we  made  analyses 
of  the  blood  from  both  arms,  in  three  cases  of  hemiplegia  : 

Case  I. — Sarah  Rumsby,  set.  47,  was  affected  with  hemiplegia  of  the  left  side.  Two 
years  ago  she  was  attacked  with  apoplexy  and  was  insensible  for  three  days.  When  she 
recovered  consciousness,  she  found  herself  paralyzed  on  the  left  side.  She  said  she  had 
epilepsy  four  or  five  years  before  the  attack  of  apoplexy.  Now  she  has  entire  paralysis 
of  motion  of  the  affected  side,  with  the  exception  of  some  slight  power  over  the  fingers, 
but  sensation  is  perfect.  The  speech  is  not  affected.  The  general  health  is  good. 

Case  II. — Anna  Wilson,  set.  23,  Irish,  was  affected  with  hemiplegia  of  the  right  side. 
Four  months  ago  she  was  attacked  with  apoplexy,  from  which  she  recovered  in  one  day, 
with  loss  of  motion  and  sensation  of  the  right  side.  She  is  now  improving  and  can  use 
the  right  arm  slightly.  The  leg  is  not  so  much  improved,  because  she  will  make  no  effort 
to  use  it. 

Case  III. — Honora  Sullivan,  set.  40,  Irish,  was  affected  with  hemiplegia  of  the  right 
side.  About  six  months  ago  she  was  attacked  with  apoplexy  and  recovered  consciousness 
the  next  day,  with  paralysis.  The  leg  was  less  affected  than  the  arm,  from  the  first. 
The  cause  was  supposed  by  Dr.  Austin  Flint,  the  attending  physician,  to  be  due  to  an 
embolus.  Her  condition  is  now  about  the  same  as  regards  the  arm,  but  the  leg  has 
somewhat  improved. 

These  cases  all  occurred  at  the  Blackwell's  Island  Hospital.  The  treatment  in  all 
consisted  of  good  diet,  frictions,  passive  motion,  and  use  of  the  paralyzed  members  as 
much  as  possible. 

A  small  quantity  of  blood  was  drawn  from  both  arms  in  these  three  cases.    It  was 


454 


EXCRETION. 


drawn  from  the  paralyzed  side,  in  each  instance,  with  great  difficulty,  and  but  a  small 
quantity  could  be  obtained. 

The  specimens  were  all  examined  for  cholesterine,  with  the  following  results  : 

Table  of  Quantities  of  Cholesterine  in  Mood  of  Paralyzed  and  Sound  Sides, 
in  Three  Cases  of  Hemiplegia. 


Blood. 

Cholesterine. 

Cholesterine  per  1,000. 

Case  I.  Paralyzed  side. 
Do.  Sound  side.  .  . 

Grains. 

55-458 
128-407 

Grains. 

0-062 

The     watch  -  glass     contained 
0'031  of  a  grain  of  a  granu- 
lar substance,  but  the  most 
careful  examination  failed  to 
reveal  a  single  crystal  of  cho- 
lesterine. 
0-481. 

Case  II.  Paralyzed  side. 
Do.  Sound  side.  .  . 

18-381 
66-396 

6-062 

Same  as  Case  I. 
0-808. 

Case  III.  Paralyzed  side. 
Do.  Sound  side.  .  . 

21-842 
52-261 

b'oti 

Same  as  Case  I. 
0-579. 

The  result  of  these  examinations  is  very  interesting :  not  a  single  crystal  of  choleste- 
rine was  found  in  any  of  the  three  specimens  of  blood  from  the  paralyzed  side,  while 
about  the  normal  quantity  was  found  in  -the  blood  from  the  sound  side.  As  the  nutrition 
of  other  tissues  is  interfered  with  in  paralysis,  it  is  impossible  to  say  positively,  from 
these  observations  alone,  that  cholesterine  is  produced  in  the  nervous  system  only. 
But  the  nutrition  of  the  nerves  is  undoubtedly  most  affected ;  and  these  observations, 
taken  in  connection  with  the  preceding  experiments  on  animals,  point  very  strongly  to 
such  a  conclusion. 

Our  experiments  upon  animals  were  so  marked  and  invariable  in  their  results,  even 
when  performed  under  different  conditions,  that  they  leave  hardly  any  doubt  of  the 
fact  that  the  blood,  in  passing  through  the  brain,  takes  up  cholesterine.  It  is  more  diffi- 
cult to  show,  by  actual  demonstration,  that  the  general  system  of  nerves  also  gives  up 
cholesterine  to  the  blood ;  but  the  fact  that  the  venous  blood  coming  from  the  extremi- 
ties contains  more  cholesterine  than  the  arterial  blood,  taken  in  connection  with  the 
fact  that  none  of  the  tissues  of  the  extremities  contain  cholesterine,  except  the  nerves, 
renders  it  more  than  probable  that  the  nerves,  as  well  as  the  brain,  are  the  seat  of  the 
formation  of  this  principle. 

Elimination  of  Cholesterine  ly  the  Liver. — We  attempted  to  demonstrate  experimen- 
tally the  separation  of  cholesterine  from  the  blood  by  the  liver,  in  the  same  way  that  we 
determined  its  passage  into  the  blood  circulating  through  the  brain.  In  the  first  series 
of  experiments  upon  this  subject,  we  endeavored  to  show,  in  the  same  animal,  the  origin 
of  cholesterine  in  certain  parts,  and  the  mechanism  of  its  elimination.  In  these  experi- 
ments, which  were  only  approximative,  as  we  had  not  then  succeeded  in  extracting  the 
cholesterine  perfectly  pure,  we  commenced  with  the  arterial  blood,  examining  it  as  it 
went  to  the  brain  by  the  carotid,  analyzing  the  substance  of  the  brain,  then  analyzing 
the  blood  as  it  came  from  the  brain  by  the  internal  jugular,  examining  the  blood  as  it 
went  to  the  liver  by  the  hepatic  artery  and  portal  vein,  examining  the  secretion  of  the 
liver,  then  the  blood  as  it  came  from  the  liver  by  the  hepatic  vein,  examining,  also, 
the  blood  of  the  abdominal  vena  cava.  The  analyses  of  the  blood  from  the  carotid,  inter- 
nal jugular,  and  vena  cava,  have  already  been  referred  to  in  treating  of  the  origin  of 


ELIMINATION  OF  CHOLESTERINE  BY  THE  LIVER.  455 

cholesterine.  It  will  be  remembered  that  there  was  a  large  quantity  of  this  substance 
in  the  internal  jugular,  and  but  a  small  quantity  in  the  carotid,  showing  that  it  was 
formed  in  the  brain.  We  now  give  the  conclusion  of  these  observations,  which  bears 
upon  the  separation  of  cholesterine  from  the  blood : 

Experiment  I. — Specimens  of  blood  were  taken  from  the  hepatic  artery,  portal  vein, 
and  hepatic  vein,  and  a  small  quantity  of  bile  was  taken  from  the  gall-bladder.  These 
specimens  were  treated  in  the  manner  already  indicated  ;  viz.,  evaporated  and  pulverized, 
extracted  with  ether,  the  ether  evaporated  and  the  residue  extracted  with  boiling  alco- 
hol, this  evaporated,  a  solution  of  caustic  potash  added,  and  the  specimen  then  subjected 
to  microscopical  examination. 

Microscopical  examination  of  the  extract  from  the  portal  vein  showed  quite  a  number 
of  crystals  of  cholesterine.  These  were  observed  after  the  fluid  had  nearly  evaporated. 

Microscopical  examination  of  the  extract  from  the  hepatic  artery,  made  after  the  fluid 
had  nearly  evaporated,  showed  a  considerable  quantity  of  cholesterine,  more  than  was 
observed  in  the  preceding  specimen.  There  were  also  observed  a  few  crystals  of  ster- 
corine. 

The  first  examination  of  the  extract  from  the  hepatic  vein,  which  was  made  just 
before  the  potash  was  added,  showed  a  number  of  fatty  masses,  with  some  crystals  of 
stercorine.  The  solution  of  potash  was  then  added,  and,  two  days  after,  another  careful 
examination  was  made,  revealing  nothing  but  fatty  globules  and  granules.  The  watch- 
glass  was  then  set  aside  and  was  examined  eleven  days  after,  when  the  fluid  had  entirely 
evaporated.  At  this  examination,  a  few  crystals  of  cholesterine  were  observed  for  the 
first  time.  There  were  also  a  number  of  crystals  of  margaric  and  stearic  acid. 

All  the  examinations  of  the  extract  from  the  bile  showed  cholesterine;  and  the  pre- 
cipitate consisted,  indeed,  of  this  substance  in  a  nearly  pure  state. 

Taking  these  experiments  in  connection  with  the  first  observations  upon  the  carotid  and 
internal  jugular,  while  the  one  series  demonstrates  pretty  conclusively  that  cholesterine 
is  formed  in  the  brain,  the  other  shows  that  it  disappears,  in  a  measure,  from  the  blood 
in  its  passage  through  the  liver,  and  is  passed  into  the  bile.  In  other  words,  it  is  formed 
in  the  nervous  tissue  and  is  prevented  from  accumulating  in  the  blood  by  its  excretion 
by  the  liver.  This  suggests  an  interesting  series  of  inquiries ;  and  this  fact,  fully  sub- 
stantiated, would  be  as  important  to  the  pathologist  as  to  the  physiologist.  But,  in  order 
to  settle  this  question,  it  is  necessary  to  do  something  more  than  make  an  approximative 
estimate  of  the  quantity  of  cholesterine  removed  from  the  blood  by  the  liver.  The  quan- 
tity thus  removed  in  the  passage  of  the  blood  through  this  organ  should  be  estimated,  if 
possible,  as  closely  as  the  quantity  which  the  blood  gains  in  its  passage  through  the  brain. 
This  estimate,  however,  is  more  difficult.  The  operation  for  obtaining  the  specimens  of 
blood,  in  the  first  place,  is  much  more  serious  than  that  for  collecting  blood  from  the  carot- 
id and  internal  jugular.  It  is  very  difficult  to  take  the  unmixed  blood  from  the  hepatic 
vein ;  and  the  exposure  of  the  liver,  if  prolonged,  may  interfere  with  its  eliminative  func- 
tion, in  the  same  way  that  exposure  of  the  kidneys  arrests,  in  a  few  moments,  the  flow 
from  the  ureters.  It  is  probable,  however,  that  the  administration  of  ether  does  not 
interfere  with  the  elimination  of  cholesterine  by  the  liver,  as  it  does,  apparently,  with  its 
formation  in  the  brain.  Anesthetics,  as  we  know,  have  a  peculiar  and  special  action  upon 
the  brain,  but  they  do  not  appear  to  interfere  with  the  functions  of  vegetative  life,  such 
as  secretion  or  excretion ;  and,  we  may  suppose,  they  would  not  interfere  with  the  depu- 
rative  function  of  the  liver.  It  is  fortunate  that  this  is  the  case,  for  the  operation  of 
taking  blood  from  the  abdominal  vessels  is  immensely  increased  in  difficulty  by  the  strug- 
gles of  an  animal  that  is  not  under  the  influence  of  an  anaesthetic. 

With  the  view  of  settling  the  question  of  the  disappearance  of  a  portion  of  the  eholes- 
terine  of  the  blood  in  its  passage  through  the  liver,  by  an  accurate  quantitative  analysis, 
we  repeated  the  operation  for  drawing  blood  from  the  vessels  which  go  into  and  emerge 
from  the  liver.  In  the  first  trial,  the  blood  was  drawn  so  unsatisfactorily,  and  the  oper- 


456  EXCRETION. 

ation  was  so  prolonged,  that  it  was  not  thought  worth  while  to  complete  the  analysis, 
and  the  experiment  was  abandoned.  In  the  following  experiment  we  were  more  suc- 
cessful. 

Experiment  II.— A  good-sized  bitch  (pregnant)  was  brought  completely  under  the 
influence  of  ether,  the  abdomen  was  laid  freely  open,  and  blood  was  drawn,  first  from  the 
hepatic  vein,  and  next  from  the  portal  vein.  The  taking  of  the  blood  was  entirely  satis- 
factory, the  operation  being  done  rapidly,  and  the  blood  collected  without  any  admixture. 
A  specimen  of  blood  was  then  taken  from  the  carotid,  to  represent  the  blood  from  the 
hepatic  artery,  assuming  that  the  arterial  blood  is  of  uniform  composition. 

The  three  specimens  of  blood  were  then  examined  in  the  usual  way  for  cholesterine, 
with  the  following  results 

Quantity  of  blood.  Cholesterine.  Cholesterine  per 

grains.  grains.  1,000  pts. 

Arterial  blood 159-537  0'200  1'257 

Portal  vein 168'257  0'170  1'009 

Hepatic  vein 79-848  0'077  O964 

Percentage  of  loss  in  arterial  blood  in  its  passage  through  the  liver 23-309 

Percentage  of  loss  in  the  blood  of  the  portal  vein 4-460 

This  experiment  proves  positively,  what  there  was  good  ground  for  supposing  from 
Experiment  I.,  that  cholesterine  is  separated  from  the  blood  by  the  liver ;  and  here  we 
may  note,  in  passing,  a  striking  coincidence  between  the  analysis  in  a  previous  experiment, 
in  which  the  blood  was  studied  in  its  passage  through  the  brain,  and  the  one  just  men- 
tioned, where  the  blood  was  examined  after  its  passage  through  the  liver.  The  gain  of 
the  arterial  blood  in  cholesterine  in  passing  through  the  brain  was  23*307  per  cent.,  and 
the  loss  of  this  substance  in  passing  through  the  liver  is  23-309  per  cent.  There  must 
be,  of  course,  the  same  quantity  separated  by  the  liver  as  is  produced  by  the  nervous 
system,  it  being  formed,  indeed,  only  to  be  separated  by  this  organ,  its  formation  being 
continuous,  and  its  removal  necessarily  the  same,  in  order  to  prevent  its  accumulation  in 
the  circulating  fluid.  The  almost  exact  coincidence  between  these  two  quantities,  in 
specimens  taken  from  different  animals,  though  not  at  all  necessary  to  prove  the  fact  just 
mentioned,  is  still  very  striking. 

It  is  shown  by  Experiment  II.  that  the  portal  blood,  as  it  goes  into  the  liver,  contains 
but  a  small  percentage  of  cholesterine  over  the  blood  of  the  hepatic  vein,  while  the  per- 
centage in  the  arterial  blood  is  large.  The  arterial  blood  is  the  mixed  blood  of  the  entire 
system ;  and,  as  it  probably  passes  through  no  organ  which  diminishes  its  cholesterine 
before  it  gets  to  the  liver,  it  contains  a  quantity  of  this  substance  which  must  be  removed. 
The  portal  blood,  coming  from  a  limited  part  of  the  system,  contains  less  cholesterine, 
although  it  gives  up  a  certain  quantity.  In  the  circulation  in  the  liver,  the  portal  system 
largely  predominates  and  is  necessary  to  other  important  functions  of  this  organ,  such  as 
the  production  of  sugar ;  but,  soon  after  the  portal  vein  enters  the  liver,  its  blood  becomes 
mixed  with  that  from  the  hepatic  artery,  and  from  this  mixture  the  cholesterine  is  sep- 
arated. It  is  only  necessary  that  blood,  containing  a  certain  quantity  of  cholesterine, 
should  come  in  contact  with  the  bile- secreting  cells,  in  order  that  this  substance  shall  be 
separated.  The  fact  that  it  is  eliminated  by  the  liver  is  proven  with  much  less  difficulty 
than  that  it  is  formed  in  the  nervous  system.  In  fact,  its  presence  in  the  bile,  and  the 
necessity  of  its  constant  removal  from  the  blood,  consequent  on  its  constant  formation 
and  absorption  by  this  fluid,  are  almost  sufficient  in  themselves  to  warrant  the  conclusion 
that  it  is  eliminated  by  the  liver.  This,  however,  is  put  beyond  a  doubt  by  the  preceding 
analyses  of  the  blood  going  to  and  coming  from  this  organ. 

In  treating  of  the  composition  of  the  fa3ces,  we  have  considered  so  fully  the  changes 
which  the  cholesterine  of  the  bile  undergoes  in  its  passage  down  the  intestinal  canal,  that 
it  is  not  necessary  to  refer  to  this  portion  of  the  subject  again.  We  have  made  but  one 
examination  of  the  quantity  of  stercorine  contained  in  the  daily  fecal  evacuation,  and, 


ELIMINATION  OF  CHOLESTERINE  BY  THE  LIVER.  457 

assuming  that  the  amount  of  cholesterine  excreted  by  the  liver  in  twenty-four  hours  is 
equal  to  the  amount  of  stercorine  found  in  the  evacuations,  the  quantity  is  about  ten  and 
a  half  grains.  This  corresponds  with  the  estimates  of  the  daily  quantity  of  cholesterine 
excreted,  calculated  from  its  proportion  in  the  bile  and  the  estimated  daily  amount  of 
bile  produced  by  the  liver. 

To  complete  the  chain  of  the  evidence  leading  to  the  conclusion  that  cholesterine  is 
an  excrementitious  principle  which  is  formed  in  certain  of  the  tissues  and  eliminated  by 
the  liver,  it  is  only  necessary  to  show  that  it  is  liable  to  accumulate  in  the  blood  when 
the  eliminating  function  of  the  liver  is  interrupted.  It  will  be  remembered  that  it  was 
only  after  extirpation  of  the  kidneys,  followed  by  accumulation  of  urea  in  the  blood,  that 
Prevost  and  Dumas  were  able  to  demonstrate  the  preexistence  of  this  principle  in  the  cir- 
culating fluid  and  to  indicate  the  mechanism  of  its  separation  from  the  blood  by  the  kid- 
neys. This  mode  of  study  has  been  applied  to  certain  of  the  elements  of  the  bile,  though 
without  success ;  for  Miiller,  Kunde,  Lehmann,  and  Moleschott,  who  extirpated  the  livers 
from  frogs,  looked  in  the  blood  only  for  the  biliary  salts.  We  have  not  been  able  to 
repeat  these  experiments  upon  frogs  and  analyze  the  blood  for  cholesterine,  but  we  have 
arrived  at  very  positive  results  in  the  study  of  the  blood  in  diseased  conditions  of  the 
liver,  that  are  interesting  alike  to  the  physiologist  and  the  pathologist. 

It  has  long  been  recognized  that  cases  of  ordinary  icterus  are  not  of  a  grave  character, 
while  there  are  instances  in  which  the  jaundice,  though  less  marked  as  regards  coloration 
of  the  skin,  is  a  very  different  condition.  Chemists  have  analyzed  the  blood,  in  the  hope 
of  explaining  this  difference  by  the  presence,  in  the  grave  cases,  of  the  taurocholate  and 
glycocholate  of  soda ;  but  their  failure  to  detect  these  principles  leaves  the  question  still 
uncertain.  The  real  distinction,  arguing  from  purely  theoretical  considerations,  would  lie 
in  the  proposition  that,  in  cases  of  simple  jaundice,  there  is  merely  a  resorption  from  the 
biliary  passages  of  the  coloring  matter  of  the  bile,  and,  in  grave  cases — which  are  almost 
invariably  fatal — there  is  retention  of  cholesterine  in  the  blood. 

We  have  not  been  able,  on  account  of  the  insolubility  of  cholesterine,  to  observe  the 
effects  of  injecting  it  into  the  blood-vessels,  but  we  have  had  an  opportunity  of  making 
an  examination  of  the  blood  of  a  patient  in  the  last  stages  of  cirrhosis  of  the  liver,  accom- 
panied with  jaundice,  and  we  compared  it  with  an  examination  of  the  blood  of  a  patient 
suffering  from  simple  icterus.  Both  of  these  patients  had  decoloration  of  the  faeces ;  but 
in  the  first  the  icterus  was  a  grave  symptom,  accompanying  the  last  stages  of  disorgani- 
zation of  the  liver,  while  in  the  latter  it  was  simply  dependent  on  duodenitis,  and  the 
prognosis  was  favorable  and  verified  by  the  result.  As  icterus  accompanying  jaundice  is 
of  very  infrequent  occurrence,  we  were  fortunate  in  having  an  opportunity  of  comparing 
the  two  cases. 

Without  giving  in  full  the  details  of  these  cases  and  the  examinations,  which  are  con- 
tained in  our  original  memoir  on  cholesterine,  it  is  sufficient  here  to  state  the  main  results 
of  the  examinations  of  the  blood  and  faeces. 

In  the  case  of  simple  jaundice  from  duodenitis,  in  which  there  was  no  great  disturb- 
ance of  the  system,  a  specimen  of  blood,  taken  from  the  arm,  presented  undoubted  evi- 
dences of  the  coloring  matter  of  the  bile,  but  the  proportion  of  cholesterine  was  not 
increased,  being  only  0*508  of  a  part  per  thousand.  The  faeces  contained  a  large  propor- 
tion of  saponifiable  fat,  but  no  cholesterine  or  stercorine. 

In  the  case  of  cirrhosis  with  jaundice,  there  were  ascites  and  great  general  prostra- 
tion. This  patient  died  a  few  days  after  the  blood  and  fa3ces  had  been  examined,  and 
the  liver  was  found  in  a  condition  of  cirrhosis,  with  the  liver-cells  shrunken,  and  the 
gall-bladder  contracted.  In  this  case  the  blood  contained  1-850  pt.  of  cholesterine  per 
thousand,  more  than  double  the  largest  quantity  we  had  ever  found  in  health.  The  faeces 
contained  a  small  quantity  of  stercorine. 

Inasmuch  as  cases  frequently  present  themselves  in  which  there  are  evidences  of  cir- 
rhosis of  the  liver,  with  little  if  any  constitutional  disturbance,  while  others  are  attended 


458  SECRETION. 

with  grave  nervous  symptoms,  it  seemed  an  interesting  question  to  determine  whether  it 
be  possible  for  cholesterine  to  accumulate  in  the  blood  without  the  ordinary  evidence  of 
jaundice.  We  had  an  opportunity  of  examining  the  blood  in  two  strongly-contrasted 
cases  of  cirrhosis,  in  neither  of  which  was  there  jaundice. 

One  of  these  patients  had  been  tapped  repeatedly  (about  thirty  times),  but  the  ascites 
was  the  only  troublesome  symptom,  and  his  general  health  was  pretty  good.  In  this  case 
the  proportion  of  cholesterine  in  the  blood  was  only  0*246  of  a  part  per  thousand,  con- 
siderably below  the  quantity  that  we  had  found  in  health. 

The  other  patient  had  cirrhosis,  but  he  was  confined  to  the  bed  and  was  very  feeble. 
The  proportion  of  cholesterine  in  the  blood  in  this  case  was  0'922  of  a  part  per  thousand, 
a  little  above  the  largest  proportion  we  had  found  in  health. 

Like  the  examinations  of  the  blood  in  the  three  cases  of  paralysis,  these  pathological 
observations  are  not  sufficient,  in  themselves,  to  establish  the  function  of  cholesterine  ; 
but,  taken  in  connection  with  our  other  experiments,  they  fully  confirm  our  views  with 
regard  to  the  excretory  function  of  the  liver.  It  is  pretty  certain  that  organic  disease  of 
the  liver,  accompanied  with  grave  symptoms  generally  affecting  the  nervous  system,  does 
not  differ  in  its  pathology  from  cases  of  simple  jaundice  in  the  fact  of  retention  of  the 
biliary  salts  in  the  blood ;  but  these  grave  symptoms,  it  is  more  than  probable,  are  due 
to  a  deficiency  in  the  elimination  of  cholesterine — the  true  excrementitious  principle  of 
the  bile — and  its  consequent  accumulation  in  the  system.  Like  the  accumulation  of  urea 
in  structural  disease  of  the  kidney,  this  produces  blood-poisoning ;  and  we  have  charac- 
terized this  condition  by  the  name  Cholestersemia,  a  term  expressing  a  pathological  con- 
dition, but  at  the  same  time  indicating  the  physiological  relations  of  cholesterine. 

Since  the  first  publication  of  the  preceding  observations,  numerous  experiments  have 
been  made  upon  the  relations  of  cholesterine  to  nutrition  and  disassimilation  ;  but  most  of 
those  observations  in  which  attempts  were  made  to  produce  toxic  effects  by  injecting  cho- 
lesterine into  the  blood  have  been  unsuccessful.  In  1873,  Koloman  Muller  (  Ueber  Choles- 
terdmie. — Archivfiir  experimentelle  Pathologic  und  Pharmakologie,  Leipzig,  1873,  Bd.  i., 
S.  213,  et  seq.)  succeeded  in  injecting  cholesterine  without  producing  any  bad  effects  by 
mechanical  obstruction  of  the  blood-vessels.  He  made  a  preparation  by  rubbing  choles- 
terine with  glycerine  and  mixing  the  mass  with  soap  and  water.  He  injected  into  the 
veins  of  dogs,  2'16  fluidounces  of  this  solution,  containing  about  69  grains  of  choles- 
terine. In  five  experiments  of  this  kind,  he  produced  a  complete  representation  of  the 
phenomena  of  "grave  jaundice."  Mtiller's  experiments  are  in  exact  accordance  with 
our  views  concerning  the  physiological  and  pathological  relations  of  cholesterine.  Picot 
(Journal  de  V anatomic,  Paris,  1872,  tome  viii.,  p.  246,  et  seq.)  has  reported  a  fatal  case 
of  "grave  jaundice,"  in  which  he  determined  a  great  increase  in  the  proportion  of  choles- 
terine in  the  blood,  the  quantity  being  1-804  per  1,000. 

In  view  of  all  of  these  facts,  the  missing  link  in  our  own  chain  of  evidence  having 
been  supplied  by  the  experiments  of  Muller,  the  excrementitious  function  of  the  liver, 
consisting  in  the  separation  of  cholesterine  from  the  blood  and  its  discharge  in  the  fasces 
in  the  form  of  stercoriue,  must,  we  think,  be  regarded  as  definitely  established. 

Production  of  Sugar  in  the  Liver, 

It  was  formerly  supposed  that  the  chief  and  the  only  important  office  of  the  liver  was 
to  produce  bile,  and  all  physiological  researches  into  the  functions  of  this  organ  were 
then  directed  to  the  question  of  the  uses  of  the  biliary  secretion;  but,  in  1848,  it  was 
announced  by  Bernard  that  he  had  discovered  in  the  liver  a  new  and  important  function, 
and  he  proceeded  to  show,  by  an  ingeniously-conceived  series  of  experiments,  that  the 
liver  is  constantly  producing  sugar  of  the  variety  that  had  long  been  recognized  in  the 
urine  of  persons  suffering  from  diabetes  mellitus.  The  great  physiological  and  pathologi- 
cal importance  of  the  discovery,  attested,  as  it  was,  by  experiments  which  seemed  to  be 


PRODUCTION  OF  SUGAR  IN  THE  LIVER.  459 

positively  conclusive  in  their  results,  excited  the  most  profound  scientific  interest.  Dur- 
ing the  present  century,  indeed,  there  have  been  few  physiological  questions  that  have 
attracted  so  much  attention ;  and  the  observations  of  Bernard  were  soon  repeated, 
modified,  and  extended  by  experimentalists  in  different  parts  of  the  world.  In  1857,' 
Bernard  discovered  a  sugar-forming  material  in  the  liver,  analogous  in  its  composition 
and  properties  to  starch  ;  and  this  seemed  to  complete  the  history  of  glycogenesis. 

Shortly  after  the  publication  of  the  glycogenic  theory,  it  was  found  that  other  changes 
were  effected  in  the  blood  in  its  passage  through  the  liver ;  and  physiologists  then  under- 
stood, for  the  first  time,  how  glandular  organs  might  produce  secretions  and  yet  not  dis- 
charge them  into  excretory  ducts.  This,  indeed,  pointed  the  way  to  the  explanation 
of  the  function  of  the  ductless  glands.  It  is  perfectly  correct  to  say  that  the  liver 
secretes  sugar ;  but  the  secretion,  in  this  instance,  is  carried  away  by  the  blood,  and,  from 
this  point  of  view,  the  liver  is  to  be  regarded  as  a  ductless  gland.  It  is  evident,  there- 
fore, that,  even  after  having  studied  fully  the  secretion  and  the  physiological  relations  of 
the  bile,  we  have  to  consider  other  glandular  functions  of  the  liver  which  are  hardly  less 
important. 

Evidences  of  a  Glycogenic  Function  in  the  Liver. — The  proof  of  the  glycogenic  func- 
tion of  the  liver  rests  upon  the  fact,  experimentally  demonstrated  by  Bernard,  that,  in 
all  animals,  the  blood  coming  from  the  liver  by  the  hepatic  veins  contains  sugar,  and 
that  the  presence  of  this  principle  here  is  not  dependent  upon  the  starch  or  sugar  of 
the  food.  Bernard  assumes  to  have  proven  that,  in  carnivorous  animals,  never  having 
taken  starch  or  sugar  into  the  alimentary  canal  except  in  the  milk,  there  is  no  sugar  in 
the  blood  of  the  portal  vein  as  it  passes  into  the  liver  ;  but,  under  normal  conditions,  the 
blood  of  the  hepatic  veins  always  contains  sugar.  Having  examined  the  blood  from  vari- 
ous parts  of  the  body  and  made  extracts  of  all  the  other  tissues  and  organs,  Bernard  was 
unable  to  find  sugar  in  any  other  situations  than  in  the  liver  and  the  blood  coming  from 
the  liver.  As  the  blood  from  the  liver  is  mixed  in  the  vena  cava  with  the  blood  from  the 
lower  extremities,  and  in  the  right  side  of  the  heart,  with  the  blood  from  the  descending 
cava,  the  amount  of  sugar  is  proportionately  diminished  in  passing  from  the  liver  to  the 
heart.  It  was  found  that  the  sugar  generally  disappeared  in  the  lungs  and  did  not  exist 
in  the  blood  of  the  arterial  system.  Assuming  that  these  statements  have  been  sustained 
by  experimental  facts,  there  can  be  no  doubt  that  the  liver  produces  or  secretes  sugar, 
that  this  secretion  is  taken  up  by  the  blood,  and  that  the  sugar  is  destroyed  in  its  pas- 
sage through  the  lungs. 

The  question  of  the  production  of  sugar  in  the  economy  has  given  rise  to  a  great  deal 
of  discussion,  and  the  experiments  of  Bernard  have  been  repeated  very  extensively. 
Many  physiologists  of  high  authority  have  been  able  to  verify  these  observations  in  every 
particular ;  but  others  have  published  accounts  of  experiments  which  seem  to  disprove 
the  whole  theory. 

There  can  be  no  doubt  of  the  fact  that  sugar  may,  under  certain  conditions,  be  pro- 
duced de  novo  in  the  organism.  Cases  of  diabetes,  in  which  the  discharge  of  sugar  by  the 
urine  continues,  to  a  certain  extent,  when  no  starch  or  sugar  is  taken  as  food,  are  conclu- 
sive evidence  of  this  proposition.  It  is  a  fact  equally  well  established,  that  the  sugar 
taken  as  food  and  resulting  from  the  digestion  of  starch  is  consumed  in  the  organism 
and  is  never  discharged.  The  fact  with  regard  to  diabetes  shows,  then,  that  it  is  not 
impossible,  when  no  sugar  or  starch  is  taken  as  food,  that  sugar  should  be  produced  in 
the  body ;  and  the  failure  to  find  the  sugar  of  the  food  in  the  blood  or  excreta  shows 
that  this  principle  is  normally  destroyed  or  consumed  in  the  organism.  It  only  remains, 
therefore,  to  determine  whether  the  production  of  sugar  in  diabetes  be  a  new  pathologi- 
cal process  or  merely  the  exaggeration  of  a  physiological  function. 

We  have  so  often  repeated  and  verified  the  observations  of  Bernard,  both  in  experi- 
ments made  for  purposes  of  investigation  and  in  public  demonstrations,  that  we  can 


460  SECRETION. 

entertain  no  doubt  with  regard  to  the  glycogenic  function  of  the  liver.  We  have,  how- 
ever, made  some  late  observations  which  have  modified  our  views  concerning  the 
mechanism  of  glycogenesis ;  but  the  fact  of  the  production  of  sugar  in  the  healthy  organ- 
ism is  not  affected.  Notwithstanding  that  it  seems  so  easy  to  verify  these  experiments, 
there  is,  particularly  in  Great  Britain,  a  pretty  wide-spread  conviction,  that  the  liver 
does  not  produce  sugar  during  life,  and  that  the  sugar  found  by  Bernard  and  others  is 
due  to  post-mortem  action.  This  view  is  based  chiefly  upon  the  observations  of  Dr.  Pavy, 
of  Guy's  Hospital ;  but  it  has  been  adopted  by  some  authorities  in  Germany  and  in 
France.  In  this  state  of  the  question,  it  will  not  be  sufficient  to  detail  merely  the  experi- 
ments that  seem  to  demonstrate  the  glycogenic  function,  but  it  will  be  necessary  to  exam- 
ine these  observations  critically  and  compare  them  with  experiments  which  lead,  appar- 
ently, to  opposite  conclusions ;  for  it  is  but  fair  to  admit  that  the  observations  of  Pavy 
seem  to  be  as  accurate,  and,  at  the  first  blush,  as  conclusive  as  those  of  Bernard. 

In  the  account  of  the  discovery,  given  by  Bernard,  it  appears  that  he  first  sought  for 
the  situation  in  the  body  where  the  sugar  derived  from  alimentary  substances  is  destroyed. 
With  this  end  in  view,  he  fed  a  dog  for  seven  days  with  articles  containing  a  large  pro- 
portion of  sugar  and  starch.  On  analyzing  the  blood  from  the  portal  system,  he  found 
a  large  proportion  of  sugar ;  and  he  also  found  it  in  the  blood  of  the  hepatic  veins.  As  a 
counter-experiment,  he  fed  a  dog  for  seven  days  exclusively  on  meat  and  then  looked  for 
sugar  in  the  blood  of  the  hepatic  veins ;  and,  to  his  surprise,  he  found  it  in  abundance. 
This  experiment  he  repeated  frequently  with  the  greatest  care  and  always  with  the  same 
result ;  and  he  concluded  that  sugar  was  formed  in  the  liver  and  was  contained  in  the 
blood  coming  from  this  organ  independently  of  the  diet  of  the  animal.  He  afterward 
made  extracts  of  the  substance  of  the  liver  and  of  the  other  tissues,  and  he  found  that  this 
organ  always  contained  sugar;  while  it  was  not  to  be  detected  in  any  other  organ  or  tis- 
sue in  the  economy.  In  subsequent  experiments,  it  was  demonstrated  that  the  livers  of 
nearly  all  classes  of  animals  contained  sugar,  and  that  it  existed  also  in  the  human  sub- 
ject. He  made  observations,  also,  upon  the  mechanism  of  its  production,  its  disappear- 
ance in  the  blood  circulating  through  the  lungs,  and  the  various  influences  which  modify 
the  glycogenic  function.  These  points  will  be  considered  in  their  appropriate  place ; 
and  we  shall  now  proceed,  after  examining  the  processes  for  the  determination  of  sugar, 
to  take  up,  seriatim,  the  following  questions : 

1.  The  absence  of  sugar  from  the  blood  of  the  portal  system  in  animals  that  have 
taken  neither  starch  nor  sugar  into  the  alimentary  canal. 

2.  The  presence  of  sugar  in  the  blood  as  it  comes  directly  from  the  liver  by  the 
hepatic  veins,  independently  of  saccharine  or  amylaceous  food. 

3.  The  mechanism  of  the  production  of  sugar  by  the  liver. 

Processes  for  the  Determination  of  /Sugar. — In  Bernard's  first  observations  upon  the 
liver,  he  applied  the  fermentation-test  to  a  simple  decoction  of  the  hepatic  substance  and 
obtained  unmistakable  evidences  of  sugar.  In  operating  upon  perfectly  fresh  and  normal 
blood,  the  addition  of  water  and  subsequent  filtration  frequently  sufficed  to  procure  a  clear 
solution,  to  which  the  ordinary  copper-tests  could  be  applied ;  but  the  most  satisfactory 
method  of  making  a  clear  extract  was  to  boil  the  blood  with  water  and  an  excess  of  sul- 
phate of  soda.  By  this  means  a  clear  extract  can  be  obtained,  containing,  it  is  true,  a 
large  quantity  of  sulphate  of  soda,  but  this  salt,  fortunately,  does  not  interfere  with 
the  tests.  Later,  Bernard  decolorized  his  solutions  and  extracts  by  making  the  liquid 
into  a  paste  with  animal  charcoal  and  filtering.  We  have  long  been  in  the  habit  of 
employing  both  of  these  methods;  but,  when  we  have  simply  desired  to  determine  the 
presence  or  absence  of  sugar,  the  process  with  the  sulphate  of  soda  has  proved  the  more 
convenient.  In  delicate  examinations,  however,  we  have  generally  used  animal  char- 
coal. We  have  used  both  methods  in  decolorizing  the  decoction  of  the  liver-substance, 
as  well  as  in  operating  upon  the  blood. 


PRODUCTION  OF  SUGAK  IN  THE  LIVER.  461 

In  ordinary  examinations,  Trommer's  test  is  sufficiently  delicate  ;  but  it  is  not  so  sen- 
sitive or  so  convenient  as  some  of  the  standard  test-solutions.  "We  have  been  in  the 
habit  of  using,  for  the  determination  of  sugar  in  the  urine,  a  modification  of  Fehling's 
test,  which  is  also  very  convenient  for  examinations  of  the  blood  and  liver-extract.  This 
may  be  used  as  well  for  quantitative  examinations ;  but,  like  all  of  the  standard  solutions,  it 
presents  the  inconvenience  of  undergoing  alteration  by  keeping,  so  that  it  is  desirable  to 
use  it  freshly  made  for  each  series  of  examinations.  We  have  succeeded  in  obviating 
this  difficulty,  however,  by  the  following  modification  in  its  preparation ;  and,  made  in 
this  way,  it  is  probably  the  most  convenient  test  that  can  be  used  in  the  examination  of 
any  of  the  animal  fluids  for  sugar. 

Fehling's  Test  for  Sugar. — The  modification  in  this  test  consists  simply  in  preparing 
three  separate  solutions,  which  are  to  be  mixed  just  before  using,  as  follows : 

Solution  of  crystallized  sulphate  of  copper,  94'73  grains  in  an  ounce  of  distilled  water. 

Solution  of  neutral  tartrate  of  potash,  378-91  grains  in  an  ounce  of  distilled  water. 

Solution  of  caustic  soda,  specific  gravity  1'12. 

These  solutions  are  to  be  kept  in  separate  bottles  and  used  as  follows : 

Take  half  of  a  fluidrachm  of  the  copper-solution,  add  half  a  fluidrachm  of  the  tar- 
trate of  potash,  and  add  the  caustic  soda,  to  make  three  fluidrachms.  It  is  important  to 
measure  the  copper-solution  with  accuracy,  in  quantitative  analyses,  as  the  quantity  of 
copper  decomposed  indicates  the  amount  of  sugar. 

To  apply  Fehling's  test  in  ordinary  qualitative  analyses,  heat  a  small  portion  of  the 
test-liquid  to  the  boiling-point  in  a  test-tube,  and  add  the  suspected  fluid,  drop  by  drop. 
If  sugar  be  present  in  even  a  moderate  quantity,  a  dense,  yellowish  precipitate  of  the  sub- 
oxide  of  copper  will  be  produced  after  adding  a  few  drops ;  and,  if  the  liquid  be  added  to 
about  the  same  volume  as  the  test,  and  the  mixture  be  again  raised  to  the  boiling-point 
without  producing  any  deposit,  it  is  certain  that  no  sugar  is  present.  The  estimation  of 
the  quantity  of  sugar  in  any  liquid  depends  upon  the  fact  that  two  hundred  grains  of  the 
test-liquid  is  decolorized  by  exactly  one  grain  of  glucose.  To  apply  this  test,  measure  off, 
in  a  glass  specially  graduated  for  the  purpose,  two  hundred  grains  of  the  solution  ;  put 
this  into  a  flask,  with  about  twice  its  volume  of  distilled  water,  and  boil ;  when  boiling, 
add  the  suspected  solution,  little  by  little,  from  a  burette  graduated  in  grains  (raising  the 
mixture  to  the  boiling-point  each  time  and  afterward  allowing  the  precipitate  to  subside), 
until  the  blue  color  is  completely  discharged ;  by  then  reading  off  the  number  of  grains 
of  the  saccharine  solution  that  has  been  added,  the  proportion  of  sugar  may  be  readily 
calculated.  If  the  solution  be  suspected  to  contain  a  considerable  quantity  of  sugar,  the 
estimate  may  be  more  accurately  made  by  diluting  it  to  a  known  degree,  say  with  nine 
parts  of  water,  and  adding  this  diluted  mixture  to  the  test-liquid. 

Examination  of  the  Blood  of  the  Portal  System  for  Sugar. — If  starch  or  sugar  be 
taken  into  the  alimentary  canal,  it  is  well  known  that  sugar  is  always  to  be  found,  during 
absorption,  in  the  blood  of  the  portal  system ;  but,  in  carnivorous  animals,  that  have  been 
fed  entirely  upon  meat,  no  sugar  can  be  discovered  in  the  portal  blood.  The  statements  of 
Bernard  are  very  definite  upon  this  point,  and  he  indicates  a  liability  to  error  when  the 
operation  of  tying  the  portal  vein  has  not  been  skilfully  performed,  and  when  blood,  con- 
taining sugar,  is  allowed  to  regurgitate  from  the  substance  of  the  liver.  In  taking  the 
blood  just  before  it  enters  the  liver^it  is  necessary  to  apply  a  ligature  to  the  vessels  as 
they  penetrate  at  the  transverse  fissure.  This  should  be  done  quickly,  and  the  opening 
into  the  abdominal  cavity  should  be  small.  Otherwise,  as  the  vessels  have  no  valves,  we 
are  liable  to  have  reflux  of  blood  from  the  liver.  We  have  frequently  performed  the 
experiment,  after  the  method  described  by  Bernard,  making  a  small  opening  in  the  linea 
alba  a  little  below  the  ensiform  cartilage,  just  large  enough  to  admit  the  forefinger  of  the 
left  hand  ;  introducing  the  finger,  and  feeling  along  the  concave  surface  of  the  liver  until 
we  are  able  to  seize  the  vessels;  then  passing  in  an  aneurism-needle,  and  constricting 
the  vessels  before  the  abdomen  is  widely  opened,  when  a  firm  ligature  is  applied.  When 


462  SECRETION. 

this  step  of  the  operation  has  been  satisfactorily  performed,  we  have  never  found  a  trace 
of  sugar  in  the  extract  from  the  blood  of  the  portal  system,  in  animals  that  have  been 
fed  upon  nitrogenized  matter  alone. 

There  can  be  no  doubt  that  the  blood  carried  to  the  liver  by  the  portal  vein  does  not 
contain  sugar,  in  animals  fed  solely  upon  nitrogenized  matters.  The  quantity  of  blood 
carried  to  the  liver  by  the  hepatic  artery  is  insignificant ;  and.  although  the  arterial 
blood  may  temporarily  contain  a  trace  of  sugar,  as  we  shall  see  farther  on,  this  need  not 
complicate  the  question  under  consideration,  as  the  presence  of  sugar  in  the  blood  of  the 
hepatic  artery  is  exceptional,  and  its  proportion,  when  it  exists,  is  very  minute. 

Examination  of  the  Blood  of  the  Hepatic  Veins  for  Sugar.— It  is  upon  this  question 
that  the  whole  doctrine  of  the  sugar-producing  function  of  the  liver  must  rest.  If  it  can 
be  proven  that  the  blood,  taken  from  the  hepatic  veins  during  life  or  immediately  after 
death,  normally  contains  sugar,  while  the  blood  distributed  to  the  liver  contains  neither 
sugar  nor  any  substance  that  can  be  immediately  converted  into  sugar,  the  inevitable 
conclusion  is  that  the  liver  is  a  sugar-producing  organ.  We  shall,  consequently,  examine 
this  part  of  the  question  with  the  care  which  its  importance  demands. 

The  proposition  that  the  blood  from  the  hepatic  veins  does  not  contain  sugar  during 
life  and  health  cannot  be  sustained  by  actual  experiment.  Observers  may  say  that  the 
quantity  is  very  slight,  but  its  existence  in  this  situation,  independently  of  the  kind  of 
food  taken,  cannot  be  denied.  Dr.  Pavy,  who  is  the  originator  of  the  theory  that  the 
sugar  found  in  the  liver  and  in  the  blood  coming  from  the  liver  is  due  to  a  post-mortem 
change,  nowhere  states  that  he  has  taken  the  blood  from  the  hepatic  veins  and  failed  to 
find  sugar.  He  says  that  he  has  found  the  blood  taken  from  the  right  side  of  the  heart 
by  catheterization,  in  a  living  animal,  u  scarcely  at  all  impregnated  with  saccharine  mat- 
ter," but  he  does  not  deny  ite  presence  in  small  quantity.  In  twelve  examinations  made 
by  Dr.  M'DonneU,  of  Dublin,  traces  of  sugar  were  found  in  five  specimens  of  blood  taken 
from  the  right  auricle  by  catheterization,  in  the  living  animal,  and  no  sugar  was  detected 
in  seven.  It  must  be  remembered,  in  considering  these  experiments,  that  the  blood  of 
the  right  side  of  the  heart  is  the  mixed  blood  from  the  entire  body  ;  and,  assuming  that 
the  hepatic  blood  is  constantly  saccharine,  the  quantity  in  the  blood  of  the  right  heart 
would  riot  be  very  great.  In  opposition  to  these  experiments,  which  are  only  partially 
negative,  we  have  the  following  results  of  examinations  of  the  blood  of  the  hepatic  veins 
and  of  the  right  side  of  the  heart,  taken  as  nearly  as  possible  under  normal  conditions. 

To  demonstrate  the  absence  of  sugar  in  the  portal  vein  and  its  constant  presence  in 
the  hepatic  veins  in  dogs  fed  exclusively  upon  meat,  Bernard  employed  the  following  pro- 
cess :  The  animal  was  killed  instantly  by  section  of  the  medulla  oblongata.  A  small 
opening  was  then  made  into  the  abdomen,  just  large  enough  to  admit  the  finger  and  to 
enable  him  to  seize  the  portal  vein  as  it  enters  at  the  transverse  fissure  and  to  apply  a  liga- 
ture. The  abdomen  was  then  freely  opened  and  a  ligature  was  applied  to  the  vena  cava 
just  above  the  renal  veins,  to  shut  oif  the  blood  from  the  posterior  extremities.  The  chest 
was  then  opened,  and  a  ligature  was  applied  to  the  vena  cava  just  above  the  opening  of  the 
hepatic  veins.  Operating  in  this  way,  blood  may  be  taken  from  the  portal  system  before 
it  enters  the  liver,  and  from  the  hepatic  veins  as  it  passes  out.  In  the  blood  from  the 
portal  system  no  sugar  is  to  be  found,  but  its  presence  is  unmistakable  in  the  blood  from 
the  hepatic  veins.  To  avoid  disturbing  the  circulation  in  the  liver,  and  in  order  to  col- 
lect from  the  hepatic  veins  as  large  a  quantity  of  blood  as  possible,  Bernard  modified  the 
experiment,  in  some  instances,  by  introducing  into  the  vena  cava  in  the  abdomen  a 
double  sound,  the  extremity  of  which  is  provided  with  a  bulb  of  India-rubber.  This 
was  pushed  into  the  vein  above  the  diaphragm  ;  and,  by  inflating  the  bulb,  the  vein  was 
obstructed  above  the  liver,  and  the  blood  could  be  collected  through  one  of  the  canulse, 
as  it  came  directly  from  the  hepatic  vessels.  Bernard  never  failed  to  determine  the 
presence  of  sugar  in  these  specimens  of  blood,  employing  a  number  of  different  pro- 
cesses, including  the  fermentation-test  and  even  collecting  the  alcohol.  To  complete 


PRODUCTION   OF  SUGAR  IN  THE  LIVER. 


463 


FIG.  151.—Cat?ieter  for  the 
right  side  of  the  heart. 
(Bernard.) 


E,  extremity  of  the  tube; 

E,  stop-cock,  e,  extrem- 

ity to  be  introduced  into 

the  right  auricle. 
The     tube     is     introduced 

through  a  small  opening 


ugh 

into  the  external  jugular 
vein,  the  concavity  of  the 
tube  turned  toward  the 
sternum,  and  the  stop- 
cock closed.  When  the 
tube  reaches  the  heart, 
we  feel  the  pulsations, 
and  the  jet  of  blood, 
when  the  stop-cock  is 
opened,  is  intermittent. 


0'-. 


the  proof  of  the  existence  of  sugar  in  the  blood  coming  from  the  liver,  Bernard  demon- 
strated its  presence  in  blood  taken  from  the  right  auricle  in  a  living  animal,  which  can 
be  readily  done  by  introducing  a  catheter  into  the  right  side  of  the  heart  through 
an  opening  in  the  external  jugular 
vein.  He  also  showed  that,  during 
digestion,  the  whole  mass  of  blood 
contained  sugar,  but  that  the  quantity 

was  greater  in  the  right  side  of  the  ^  lilllliililillililiiP''-  V 

heart  than  in  the  arterial  system. 

It  is  unnecessary  to  cite  all  the 
authorities  that  have  confirmed  the 
observations  of  Bernard.  Shortly 
after  these  experiments  were  pub- 
lished, Lehmann,  Frerichs,  and  many 
others  verified  their  accuracy.  Ber- 
nard gives  in  full  the  experiments  of 
Poggiale  and  of  Leconte,  the  results 
of  which  were  identical  with  his 
own.  He  gives,  also,  in  one  of  his 
later  works,  the  proportions  of  sugar 
in  the  blood  of  the  hepatic  veins,  ob- 
tained by  Lehmann,  Schmidt,  Pog- 
giale, and  Leconte,  no  sugar  being 
found  in  the  blood  of  the  portal  sys- 
tem. We  have  ourselves  made  a 
number  of  experiments  with  a  view 
of  harmonizing,  if  possible,  the  dis- 
cordant observations  of  Bernard  and 
Pavy,  and  have  examined  the  blood 
from  the  hepatic  veins  for  sugar,  tak- 
ing the  specimens  under  what  seemed 
to  be  strictly  physiological  condi- 
tions. In  one  of  these  published  ex- 
periments, blood  was  taken  from  the 
hepatic  veins  of  a  large  dog,  fully- 
grown  and  fed  regularly  every  day 
but  not  in  digestion  at  the  time  of 
the  experiment,  and  the  operation 
lasted  only  seventy  seconds.  No 
anesthetic  was  employed.  The  ex- 


T- 


tract  of  this  specimen  of  blood,  treat- 
ed  with    Fehling's    test-liquid,   pre- 
sented a  well-marked  deposit  of  the 
oxide  of  copper,  revealing  unequivo- 
cally the  presence  of  a  small  quan- 
tity of  sugar.1    This  has  been  the  in- 
variable result  in  numerous  experi- 
ments and  class-demonstrations  made  since  1858 ;    and,  since 
the  experiments  just  referred  to  were  published,  we  have  veri- 
fied the  observation  with  regard  to  the  hepatic  blood,  keeping 
the  animal  perfectly  quiet  before  the  operation,  avoiding  the 
administration  of  an  anaesthetic,  and  taking  the  blood  so  rap- 

1  FLINT,  Jr.,  Experiments  undertaken  for  the  Purpose  of  reconciling  some  of  the  Discordant  Observations 
upon  the  Glycogenic  Function  of  the  Liver. — New  York  Medical  Journal,  1869,  vol.  viii.,  p.  381.    These  experi- 


FIG.  138.— Double  sound,  used 
for  collecting  blood  from  the 
hepatic  veins.  (Bernard.) 

0,  t,  o',  tube,  with  a  stop-cock  (r), 
used  to  innate  the  rubber 
bulb  (G,  b') ;  O,  T,  tube,  with 
an  opening  (o'},  which  re- 
ceives the  blood  from  the 
hepatic  veins,  and  is  provided 
with  a  stop-cock  (K). 


464  SECRETION. 

idly  that  no  sugar  could  be  formed  by  the  liver  post  mortem.  These  experiments  leave 
no  doubt  of  the  fact  that,  during  life  and  in  health,  the  blood,  as  it  passes  through  the 
liver  and  is  discharged  by  the  hepatic  veins  into  the  vena  cava,  contains  sugar,  which  is 
formed  by  the  liver,  independently  of  the  sugar  and  starch  taken  as  food. 

Does  the  Liver  contain  Sugar  normally  during  Life?— This  is  the  only  question  upon 
which  the  results  of  reliable  experiments  have  been  entirely  opposite.  Bernard  made 
the  greater  part  of  his  observations  by  analyzing  the  substance  of  the  liver;  and  he 
arrived  at  most  of  his  conclusions  with  regard  to  the  variations  in  the  glycogenic  function, 
from  estimates  of  the  proportion  of  sugar  in  the  liver  under  different  conditions.  For 
many  years  we  have  been  in  the  habit  of  repeating  these  experiments,  with  like  results, 
and  we  have  never  failed  to  find  sugar  under  normal  conditions  of  the  system.  We  were 
formerly  in  the  habit  of  making  the  demonstrations  of  the  formation  of  sugar  in  the  liver 
upon  animals  that  had  been  etherized ;  and  then  we  always  obtained  a  brilliant  precipitate 
from  the  clear  extract  of  the  substance  of  the  liver  boiled  with  the  test-liquid.  The 
experiment  was  performed  in  this  way  before  we  had  acquired  sufficient  dexterity  to  seize 
the  portal  vein  readily  and  to  go  through  with  the  necessary  manipulations  with  rapidity. 
We  subsequently  made  the  operation  by  first  suddenly  breaking  up  the  medulla  oblon- 
gata,  then  making  a  small  incision  into  the  abdominal  cavity,  seizing  the  portal  vein 
instantly,  and  following  out  the  remaining  steps  of  the  experiment  without  delay.  In  this 
way,  although  sugar  was  always  found  in  the  blood  of  the  hepatic  veins,  we  frequently 
failed  to  obtain  a  distinct  reaction  in  the  extract  of  the  liver ;  and  it  appeared,  indeed,  that 
the  more  accurately  and  rapidly  the  operation  was  performed,  the  more  difficult  was  it 
to  detect  sugar  in  the  hepatic  substance.  It  seems  probable,  in  reflecting  upon  these 
facts,  that,  inasmuch  as  no  one  has  assumed  that  the  actual  quantity  of  sugar  produced 
by  the  liver  is  very  considerable,  and  as  a  large  quantity  of  blood  (in  which  the  sugar 
is  very  soluble)  is  constantly  passing  through  the  liver,  precisely  as  we  pass  water  through 
its  vessels  to  remove  the  sugar,  the  sugar  might  be  washed  out  by  the  blood  as  fast 
as  it  is  formed ;  and  that  really  the  liver  might  never  contain  sugar  in  its  substance,  as 
a  physiological  condition,  although  it  is  constantly  engaged  in  its  production.  We  know 
that  the  characteristic  elements  of  the  various  secretions  proper  are  produced  in  the 
substance  of  the  glands  and  are  washed  out  at  the  proper  time  by  liquid  derived  from 
the  blood,  which  circulates  in  their  substance  during  their  functional  activity  in  very 
much  greater  quantity  than  during  the  intervals  of  secretion.  Now,  the  liver-sugar  may 
certainly  be  regarded  as  an  element  of  secretion ;  and,  possibly,  it  may  be  completely 
washed  out  of  the  liver,  as  fast  as  it  is  formed,  by  the  current  of  blood,  the  hepatic 
vein,  in  this  regard,  serving  as  an  excretory  duct.  To  put  this  hypothesis  to  the  test 
of  experiment,  it  was  necessary  to  obtain  and  analyze  a  specimen  of  the  liver  in  a  condi- 
tion as  near  as  possible  to  that  under  which  it  exists  in  the  living  organism ;  and,  in 
carrying  out  this  idea,  we  instituted  the  following  experiments : 

Experiment  I. — A  medium-sized  dog,  full-grown,  in  good  condition,  and  not  in  digestion, 
was  held  upon  the  operating-table  by  two  assistants,  and  the  abdomen  was  widely  opened 
by  a  single  sweep  of  the  knife.  A  portion  of  the  liver,  weighing  about  two  ounces,  was 
then  excised  and  immediately  cut  into  small  pieces,  which  were  allowed  to  fall  into  boil- 
ing water.  The  time  from  the  first  incision  until  the  liver  was  in  the  boiling  water  was 
twenty-eight  seconds.  An  excess  of  crystallized  sulphate  of  soda  was  then  added,  and 
the  mixture  was  boiled  for  about  five  minutes.  It  was  then  thrown  upon  a  filter,  and  the 
clear  fluid  that  passed  through  was  tested  for  sugar  by  Trommer's  test.  The  reaction 
was  doubtful  and  afforded  no  marked  evidence  of  sugar. 

Experiment  II.— A  medium-sized  dog,  in  the  same  condition  as  the  animal  in  the  first 
experiment,  was  held  upon  the  table,  and  a  portion  of  the  liver  was  excised,  as  above 

ments  are  the  first  on  record,  made  with  the  view  above  indicated.    The  experiments  by  Dr.  Lusk  and  by  Dr.  Dai- 
ton  were  made  later,  with  the  view  of  confirming  our  original  observations. 


PRODUCTION  OF  SUGAR  IN  THE  LIVER.  465 

described.  The  whole  operation  occupied  twenty-two  seconds.  Only  ten  seconds  elapsed 
from  the  time  the  portion  of  the  liver  was  cut  off  until  it  was  in  the  boiling  water.  It 
was  boiled  for  about  fifteen  minutes,  made  into  a  paste  with  animal  charcoal,  and  thrown 
upon  a  filter.  The  clear  fluid  that  passed  through  was  tested  for  sugar  by  Trommer's 
test.  There  was  no  marked  evidence  of  sugar. 

Experiment  III. — A  large  dog,  full-grown  and  fed  regularly  every  day,  but  not  in  diges- 
tion at  the  time  of  the  experiment,  was  held  firmly  upon  the  table.  This  dog  had  been 
in  the  laboratory  about  a  week  and  was  in  a  perfectly  normal  condition.  The  abdominal 
cavity  was  opened,  and  a  piece  of  the  liver  was  cut  off  and  thrown  into  boiling  water, 
the  time  occupied  in  the  process  being  ten  seconds.  Before  the  liver  was  cut  up  into  the 
boiling  water,  the  blood  was  rinsed  off  in  cold  water.  The  liver  was  boiled  for  about 
seventeen  minutes,  mixed  with  animal  charcoal,  and  the  whole  was  thrown  upon  a  filter. 

Immediately  after  cutting  off  a  portion  of  the  liver  and  throwing  it  into  boiling  water, 
the  medulla  oblongata  was  broken  up,  a  ligature  was  applied  to  the  ascending  vena  cava 
just  above  the  renal  veins,  the  chest  was  opened,  and  a  ligature  was  applied  to  the  vena 
cava  just  above  the  opening  of  the  hepatic  veins.  A  specimen  of  blood  was  then  taken 
from  the  hepatic  veins.  This  portion  of  the  operation  occupied  not  more  than  one  minute. 
A  little  water  was  added  to  the  blood,  which  was  boiled  briskly,  mixed  with  animal  char- 
coal, and  thrown  upon  a  filter.  The  liquid  that  passed  through  from  both  specimens  was 
perfectly  clear. 

While  the  filtration  was  going  on,  Fehling's  test-liquid  was  made  up,  so  as  to  be 
perfectly  fresh.  The  two  liquids  were  then  carefully  tested  for  sugar.  The  extract  of 
the  liver  presented  not  the  slightest  trace  of  sugar.  The  extract  from  the  blood  of  the 
hepatic  veins  presented  a  well-marked  deposit  of  the  oxide  of  copper,  revealing  unequivo- 
cally the  presence  of  a  small  quantity  of  sugar. 

Experiment  IV. — This  experiment  was  made  upon  a  medium-sized  dog,  in  full  diges- 
tion of  meat.  The  medulla  oblongata  was  broken  up ;  the  portal  vein  was  tied  through 
a  small  opening  in  the  abdomen ;  and  the  abdomen  was  then  widely  opened,  and  a  por- 
tion of  the  liver  excised,  rapidly  rinsed,  and  cut  up  into  boiling  water.  The  length  of 
time  that  elapsed  between  breaking  up  the  medulla  and  cutting  up  the  specimen  of  liver 
into  the  boiling  water  was  one  minute. 

The  vena  cava  was  then  tied  above  the  renal  veins,  the  chest  opened,  and  the  cava 
again  tied  above  the  hepatic  veins.  Blood  was  then  taken  from  the  hepatic  veins,  about 
an  equal  bulk  of  water  was  added,  with  an  excess  of  the  crystallized  sulphate  of  soda,  and 
the  mixture  was  boiled.  A  portion  of  the  portal  blood  and  the  decoction  of  the  liver 
were  then  treated  in  the  same  way,  and  the  three  specimens  were  filtered. 

The  clear  extracts  were  then  tested  with  Fehling's  liquid,  with  the  following  result : 

There  was  no  sugar  in  the  portal  blood. 

There  was  no  sugar  in  the  extract  of  the  liver. 

There  was  a  marked  reaction  in  the  extract  of  the  blood  from  the  hepatic  veins,  the 
precipitate  rendering  the  whole  solution  bright  yellow  and  entirely  opaque. 

This  experiment  was  made  in  the  presence  of  the  class  at  the  Bellevue  Hospital  Med- 
ical College,  January  4,  1869. 

The  importance  of  the  question  under  consideration  and  its  present  unsettled  condi- 
tion are,  we  hope,  sufficient  to  justify  the  introduction  of  the  details  of  the  preceding 
experiments.  They  were  undertaken  with  the  view  of  harmonizing,  if  possible,  the  facts 
brought  forward  by  different  experimentalists. 

It  is  difficult  to  imagine  how  any  observer,  so  well  known  and  accurate  as  Dr.  Pavy, 
could  assert  positively,  as  the  result  of  personal  examination,  that  the  liver  does  not 
contain  sugar  when  examined  immediately  after  its  removal  from  the  living  body,  when 
Bernard  and  so  many  others  have  demonstrated  its  presence  in  this  organ  in  large  quantity. 
Yet,  such  was  the  result  of  all  the  experiments  of  Pavy,  and  the  same  conclusion  was  ar- 
rived at  by  M'Donnell,  and  afterward  by  Meissner  and  Jaeger,  and  by  Schiff.  The  ingenious 
30 


466  SECRETION. 

experiment  of  Bernard,  showing  that  sugar  is  formed  in  a  liver  removed  from  the  body 
and  washed  sugar-free  by  a  stream  of  water  passed  through  its  vessels,  demonstrated  the 
possibility  of  the  production  of  sugar  post  mortem,  so  strongly  claimed  by  Pavy  as  the 
only  condition  under  which  it  is  ever  formed  ;  still,  it  does  not  seem  possible  to  deny  the 
sugar-producing  function  of  the  liver,  in  view  of  the  conclusive  experimental  proof  of  the 
constant  presence  of  glucose  in  the  blood  of  the  hepatic  veins. 

From  our  own  experiments,  we  have  come  to  the  conclusion  that  Dr.  Pavy  and  those 
who  adopt  his  views  cannot  consistently  deny  that  sugar  is  constantly  formed  in  the  liver 
and  discharged  into  the  blood  of  the  hepatic  veins ;  nor  can  Bernard  and  his  followers 
ignore  the  fact  that  the  liver  does  not  contain  sugar  during  life ;  although,  as  has  been 
shown  by  Pavy,  and  more  specifically  by  M'Donnell,  sugar  appears  in  the  liver  in  great 
abundance  soon  after  death. 

In  the  experiments  that  we  have  just  detailed,  which  are  simply  typical  examples  of 
numerous  unrecorded  observations,  we  attempted  to  verify  the  observations  of  Pavy 
without  losing  sight  of  the  facts  observed  by  Bernard,  and  to  verify  the  experiments  of 
Bernard  in  the  face  of  the  apparently  contradictory  statements  of  Pavy.  "When  an  ani- 
mal is  in  perfect  health,  has  been  kept  quiet  before  the  experiment,  and  a  piece  of  the 
liver  is  taken  from  him  by  two  sweeps  of  the  knife,  the  blood  rinsed  from  it  and  the  tis- 
sue cut  up  into  water  already  boiling,  the  whole  operation  occupying  only  ten  seconds 
(as  was  the  case  in  Experiment  III.),  the  liver  is  as  nearly  as  possible  in  the  condition  in 
which  it  exists  in  the  living  organism.  As  this  was  done  repeatedly  in  animals  during 
digestion  and  in  the  intervals  of  digestion,  and  an  extract  was  thoroughly  made  without 
finding  any  sugar,  we  regarded  the  experiments  of  Pavy  as  entirely  confirmed  and  the  fact 
demonstrated  that  the  liver  does  not  contain  sugar  during  life.  On  the  other  hand,  when 
we  made  the  experiment  upon  the  liver  as  above  described,  and,  in  addition,  took  specimens 
of  the  portal  blood  and  the  blood  from  the  hepatic  veins,  under  strictly  physiological 
conditions  (as  was  done  in  Experiment  IV.),  and  found  no  sugar  in  the  portal  blood  or 
in  the  substance  of  the  liver,  but  an  abundance  in  the  blood  of  the  hepatic  veins,  it  was 
impossible  to  avoid  the  conclusion  that  the  sugar  was  formed  in  the  liver  and  was  washed 
out  in  the  blood  as  it  passed  through. 

In  treating  of  the  mechanism  of  the  formation  of  sugar  in  the  liver,  we  shall  describe 
more  fully  the  glycogenic  matter ;  but,  taking  into  consideration  the  demonstration  of 
the  presence  of  sugar  in  the  blood  of  the  hepatic  veins  by  Bernard ;  his  discovery  of  the 
post-mortem  production  of  sugar  in  a  liver  washed  sugar-free,  probably  from  a  substance 
remaining  in  the  liver  and  capable  of  being  transformed  into  sugar ;  the  negative  results 
of  the  examinations  of  the  liver  for  sugar  by  Pavy ;  and,  adding  to  this  our  own  experi- 
ments upon  all  of  these  points,  we  are  justified  in  adopting  the  following  conclusions : 

1.  A  substance  exists  in  the  healthy  liver,  which  is  capable  of  being  converted  into 
sugar ;  and,  inasmuch  as  this  is  formed  into  sugar  during  life,  the  sugar  being  washed 
away  by  the  blood  passing  through  the  liver,  it  is  perfectly  proper  to  call  it  glycogenic, 
or  sugar-forming  matter. 

2.  The  liver  has  a  glycogenic  function,  which  consists  in  the  constant  formation  of 
sugar  out  of  the  glycogenic  matter,  this  being  carried  away  by  the  blood  of  the  hepatic 
veins,  which  always  contains  sugar  in  a  certain  proportion.     This  production  of  sugar 
takes  place  in  the  carnivora,  as  well  as  in  those  animals  that  take  sugar  and  starch  as 
food ;  and  it  is,  essentially,  independent  of  the  kind  of  food  taken. 

3.  During  life,  the  liver  contains  the  glycogenic  matter  only  and  no  sugar,  because 
ie  great  mass  of  blood  which  is  constantly  passing  through  this  organ  washes  out  the 

sugar  as  fast  as  it  is  formed ;  but,  after  death  or  when  the  circulation  is  interfered  with, 
the  transformation  of  glycogenic  matter  into  sugar  goes  on ;  the  sugar  is  not  removed 
under  these  conditions,  and  can  then  be  detected  in  the  substance  of  the  liver. 

Characters  of  the  Liver- Sugar. —Very  little  is  to  be  said  regarding  the  chemical  pe- 


PRODUCTION  OF  SUGAR  IN  THE  LIVER.  467 

culiarities  of  liver-sugar.  It  resembles  glucose,  or  the  sugar  resulting  from  the  digestion 
of  starch,  in  its  composition.  This  sugar,  like  glucose,  responds  promptly  to  all  of  the 
copper-tests,  and  it  undergoes  transformation  into  melassic  acid  on  being  boiled  with  an 
alkali.  One  of  its  most  marked  peculiarities  is  that  it  ferments  more  readily  than  any 
other  variety  of  sugar ;  and  another  is  that  it  is  destroyed  in  the  economy  with  extraor- 
dinary facility.  This  fact  has  been  illustrated  by  the  following  ingenious  experiment : 
Bernard  injected  under  the  skin  of  a  rabbit  a  little  more  than  seven  grains  of  cane- 
sugar  dissolved  in  about  an  ounce  of  water,  and  he  found  sugar  in  the  urine.  Under 
the  same  conditions,  he  found  he  could  inject  seven  grains  of  milk-sugar,  fourteen  and 
a  half  grains  of  glucose,  twenty-one  and  a  half  grains  of  diabetic  sugar,  and  nearly 
thirty  grains  of  liver-sugar,  without  finding  any  sugar  in  the  urine ;  showing  that  the 
liver-sugar  is  consumed  in  the  organism  more  rapidly  and  completely  than  any  other  sac- 
charine principle. 

Mechanism  of  ike  Production  of  Sugar  in  the  Liver. — When  Bernard  first  described 
the  glycogenic  function  of  the  liver,  he  thought  that  the  sugar  was  produced  from  nitro- 
genized  principles,  in  some  manner  which  he  did  not  attempt  to  explain.  Subsequent 
discoveries,  however,  have  led  to  conclusions  entirely  different. 

In  1855,  Bernard  first  published  an  account  of  his  remarkable  experiment  showing 
the  post-mortem  production  of  sugar.  After  washing  out  the  liver  with  water  passed 
through  the  vessels  until  it  no  longer  contained  a  vestige  of  sugar,  it  was  allowed  to 
remain  at  about  the  temperature  of  the  body  for  a  few  hours  and  was  then  found  to  con- 
tain sugar  in  abundance.  This  experiment  we  have  already  referred  to,  and  it  is  one 
that  we  have  frequently  verified.  Bernard  explained  the  phenomenon  by  the  supposition, 
subsequently  shown  to  be  correct,  that  the  liver  contains  a  peculiar  principle,  slightly 
soluble  in  water  and  capable  of  transformation  into  sugar. 

Glycogenic  Matter. — In  its  composition,  reactions,  and  particularly  in  the  facility  with 
which  it  undergoes  transformation  into  sugar,  glycogenic  matter  bears  a  very  close 
resemblance  to  starch.  It  is  described  by  Pavy  under  the  name  of  amyloid  matter,  a 
name  which  is  applied  to  it,  also,  by  Rouget.  It  is  insoluble  in  water,  and,  by  virtue 
of  this  property,  it  may  be  extracted  from  the  liver  after  the  sugar  has  been  washed 
out.  The  following  is  the  method  for  its  extraction  proposed  by  Bernard : 

The  liver  of  a  small  and  young  animal,  like  the  rabbit,  in  full  digestion,  presents  the 
most  favorable  conditions  for  the  extraction  of  the  glycogenic  matter.  The  liver  is 
taken  from  the  animal  immediately  after  it  is  killed,  is  cut  into  thin  slices,  and  thrown 
into  boiling  water.  When  the  tissue  is  hardened,  it  is  removed  and  ground  into  a  pulp 
in  a  mortar.  It  is  then  boiled  a  second  time  in  the  water  of  the  first  decoction,  strained 
through  a  cloth,  and  the  opaline  liquid  which  passes  through  is  made  into  a  thin 
paste  with  animal  charcoal.  The  paste  is  then  put  into  a  displacement-apparatus,  the 
end  of  which  is  loosely  filled  with  shreds  of  moistened  cotton.  By  successive  wash- 
ings, the  paste  is  exhausted  of  its  glycogenic  matter,  leaving  behind  the  albuminoid 
and  coloring  matters.  The  whitish  liquid,  as  it  flows,  is  received  into  a  vessel  of  abso- 
lute alcohol,  when,  as  each  drop  falls,  the  glycogenic  matter  is  precipitated  in  white 
flakes.  This  is  filtered  and  dried  rapidly  in  a  current  of  air.  If  the  alcohol  be  not 
allowed  to  become  too  dilute,  the  matter  when  dried  is  white  and  easily  pulverized. 
The  substance  thus  obtained  may  be  held  in  suspension  in  water,  giving  to  the  liquid  a 
strongly  opaline  appearance.  It  is  neutral,  without  odor  or  taste,  and  presents  nothing 
characteristic  under  the  microscope.  It  reacts  strongly  with  iodine,  which  produces 
a  dark-violet  or  chestnut-brown  color,  but  rarely  a  well-marked  blue.  It  presents  none 
of  the  reactions  of  sugar  and  is  entirely  insoluble  in  alcohol.  It  is  changed  into  sugar 
by  boiling  for  a  long  time  with  dilute  acids,  and  this  conversion  is  rapidly  effected 
by  the  saliva,  the  pancreatic  juice,  and  a  peculiar  ferment  found  in  the  substance  of 


468 


SECRETION. 


the  liver.     Prepared  in  the  way  above  indicated,  and  pulverized,  it  may  be  preserved 

for  an  indefinite  period. 

The  peculiar  reaction  of  the  glycogenic  matter  with 

iodine  has  led  to  its  recognition  in  the  substance  of  the 
liver-cells  and  in  some  other  situations.  Schiff  found  in 
the  liver-cells  minute  granulations,  which  presented  the 
peculiar  color  on  the  addition  of  iodine,  characteristic  of 
glycogenic  matter.  Bernard,  a  few  years  after  his  dis- 
covery of  this  principle  in  the  liver,  recognized  it  in  cells 
attached  to  the  placenta.  He  believes  that  these  cells 
produce  sugar  during  the  early  period  of  foetal  life,  before 
the  liver  takes  on  this  function,  and  that  they  disappear 
during  the  later  months,  as  the  liver  becomes  fully  devel- 
oped. 

Since  the  discovery  of  the  glycogenic  function  of  the 
liver,  anatomists  have  found  amyloid  corpuscles  in  various 
of  the  tissues  of  the  body.  We  do  not  propose,  how- 
ever, to  discuss  this  question  in  all  its  bearings,  but  only 
to  consider  the  known  relations  of  the  amyloid  substances 
found  in  the  body  to  the  formation  of  sugar. 

In  the  first  place,  there  can  be  no  doubt  of  the  fact, 
that  the  liver  of  a  carnivorous  animal  that  has  been  fed 
exclusively  on  meat  contains  an  amyloid  substance  readily 
convertible  into  sugar.  The  question  of  the  existence  of 
the  same  amyloid  matter  in  other  tissues  and  organs  is 
only  pertinent  in  so  far  as  it  bears  upon  the  production 
of  sugar  or  upon  the  formation  of  the  glycogenic  matter 
in  the  liver.  In  no  tissue  or  organ  in  the  adult  has  it 
been  demonstrated  that  there  is  any  formation  of  sugar, 
except  the  ordinary  transformation  of  starch  into  sugar 
in  the  process  of  digestion. 

If  the  liver  taken  from  an  animal  recently  killed  be 
simply  kept  at  about  the  temperature  of  the  body,  after 
it  has  been  drained  of  blood  or  even  after  it  has  been 
washed  through  the  vessels,  sugar  will  be  rapidly  formed 
in  its  substance.  This  must  be  due  to  some  ferment  re- 
maining in  the  tissue ;  and  Bernard  has,  indeed,  been  able 
to  isolate  a  principle  which  exerts  this  influence  in  a 
marked  degree.  If  an  opaline  decoction  of  the  liver  be 
allowed  to  stand  until  it  has  become  entirely  clear,  show- 
ing that  all  the  glycogenic  matter  has  been  transformed 
into  sugar,  and  alcohol  be  added  to  the  liquid,  the  hepatic 
ferment  will  be  precipitated.  This  may  be  redissolved 
in  water,  and  it  effects  the  transformation  of  starch  into 
sugar  with  great  rapidity.  From  these  facts,  it  is  pretty 
Conclusively  shown  that  the  following  is  the  mechanism 
nard.)  of  the  production  of  sugar  in  the  liver  : 

^edfi£rntk:fpTS;8i%±Cah1         The  liver  first  Produces  a  Peculiar  principle  (analo- 
charcoai  mixed  with  the  decoction  gous  to  starch  in  its  composition  and  in  many  of  its  prop- 

ot   the  liver;    E,   glycogenic  solu-          .  .  . 

tion;  M,  lamp-wicking,  attached  to   erties,  though  it  contains  two  atoms  more  of  water)  out 
r  of  which  tne  sugar  is  to  be  formed.    The  name  glycogenic 
matter  ma7  P™Perly  *>e  applied  to  this  substance.     It  is, 
precipitated;  v,  alcohol.  as  far  as  is  known,  produced  in  all  classes  of  animals, 


VAKIATIONS  IN  THE   GLYCOGENIC  FUNCTION".  469 

carnivora  and  herbivora ;  and,  although  its  quantity  may  be  modified  by  the  kind  of  food, 
its  formation  is  essentially  independent  of  the  alimentary  principles  absorbed. 

The  glycogenic  matter  is  not  taken  up  by  the  blood  as  it  passes  through  the  liver,  but 
is  gradually  transformed,  in  the  substance  of  the  liver,  into  sugar,  which  is  washed  out 
of  the  organ  as  fast  as  it  is  produced.  Thus  the  blood  of  the  hepatic  veins  always  con- 
tains sugar,  although  sugar  is  not  contained  in  the  substance  of  the  liver  during  life. 

Variations  in  the  Gtycogenic  Function. 

In  following  out  the  relations  of  the  glycogenic  process  to  the  various  animal  func- 
tions, Bernard  studied  very  closely  its  variations  at  different  periods  of  life,  with  diges- 
tion, the  influence  of  the  nervous  system,  and  other  modifying  conditions.  He  made 
some  of  his  observations  by  examining  the  blood  in  living  animals,  and  others,  by  esti- 
mating the  proportion  of  sugar  in  the  liver.  The  latter  method  is  to  be  considered,  with 
an  appreciation  of  the  fact  that  the  liver  does  not  normally  contain  sugar  during  life ; 
but  it  represents,  to  a  certain  extent,  the  activity  of  the  glycogenic  function.  Still,  the 
facts  arrived  at  in  this  way  must  be  taken  with  a  certain  degree  of  caution. 

Glycogenesis  in  the  Fcetus. — In  the  early  months  of  fcetal  life,  many  of  the  tissues 
and  fluids  of  the  body  were  found  by  Bernard  to  be  strongly  saccharine ;  but  at  this 
time  no  sugar  is  to  be  found  in  the  liver.  Taking  the  observations  upon  foetal  calves  as 
a  criterion,  sugar  does  not  appear  in  the  liver  until  toward  the  fourth  or  fifth  month  of 
intra-uterine  life.  Before  this  period,  however,  epithelial  cells  filled  with  glycogenic 
matter  are  found  in  the  placenta,  and  these  produce  sugar  until  the  liver  takes  on  its 
functions.  As  the  result  of  numerous  observations  by  Bernard  upon  foetal  calves,  this 
function  of  the  placenta  appears  very  early  in  foetal  life,  and,  at  the  third  or  fourth 
month,  it  has  attained  its  maximum.  At  about  this  time,  when  glycogenic  matter  begins 
to  appear  in  the  liver,  the  glycogenic  organs  of  the  placenta  become  atrophied,  and  they 
disappear  some  time  before  birth. 

Influence  of  Digestion  and  of  Different  Kinds  of  Food. — Activity  of  the  digestive 
organs  has  a  marked  influence  upon  the  production  of  sugar  in  the  liver.  In  a  fasting 
animal,  sugar  is  always  found  in  the  blood  of  the  hepatic  veins  and  in  the  vessels  between 
the  liver  and  the  heart,  but  it  never  passes  the  lungs  and  does  not  exist  in  the  arterial 
system.  During  digestion,  however,  even  when  the  diet  is  entirely  nitrogenized,  the 
production  of  sugar  is  so  much  increased  that  a  small  quantity  frequently  escapes  decom- 
position in  the  lungs  and  passes  into  the  arterial  blood.  Under  these  conditions,  the 
quantity  in  the  arterial  blood  is  sometimes  so  large  that  a  trace  may  appear  in  the  urine, 
as  a  temporary  and  exceptional,  but  not  an  abnormal  condition.  This  physiological  fact 
is  well  illustrated  in  certain  cases  of  diabetes.  There  are  instances,  indeed,  in  which  the 
sugar  appears  in  the  urine  only  during  digestion ;  and,  in  almost  all  cases,  the  quantity 
of  sugar  eliminated  is  largely  increased  after  eating. 

The  influence  of  the  kind  of  food  upon  the  glycogenic  function  is  a  question  of  great 
pathological  as  well  as  physiological  importance.  It  is  well  known  to  pathologists  that 
certain  cases  of  diabetes  are  relieved  when  the  patient  is  confined  strictly  to  a  diet  con- 
taining neither  saccharine  nor  amylaceous  principles,  and  that,  almost  always,  the  quan- 
tity of  sugar  discharged  is  very  much  diminished  by  such  a  course  of  treatment ;  but 
there  are  instances  in  which  the  discharge  of  sugar  continues,  in  spite  of  the  most  care- 
fully-regulated diet.  Bernard  does  not  recognize  fully  the  influence  of  different  kinds  of 
food  upon  glycogenesis,  and  his  experiments  on  this  point  are  wanting  in  accuracy,  from 
the  fact  that  the  proportion  of  sugar  in  the  liver  is  given,  without  indicating  at  what 
period  after  death  the  examinations  were  made.  In  the  observations  upon  this  point  by 
Pavy,  the  examinations  of  the  liver  were  made  immediately  after  death,  and  the  propor- 
tion of  glycogenic  matter — not  sugar — was  estimated.  His  results  are,  consequently,  much 


470  SECRETION". 

more  reliable  and  satisfactory.  In  a  number  of  analyses  of  the  livers  of  dogs  confined 
to  different  articles  of  diet,  Pavy  found  a  little  over  seven  per  cent,  of  glycogenic  matter, 
upon  a  diet  of  animal  food ;  over  seventeen  per  cent.,  upon  a  diet  of  vegetable  food  ;  and 
fourteen  and  a  half  per  cent.,  upon  a  diet  of  animal  food  and  sugar.  These  results  have 
been  confirmed  by  M'Donnell,  who,  in  addition,  found  that  hardly  a  trace  of  amyloid 
substance  could  be  detected  in  the  liver  upon  a  diet  of  fat,  and  none  whatever  upon  a  diet 
of  gelatine.  Bernard  had  already  observed  that  the  amount  of  sugar  produced  by  the 
liver  upon  a  diet  of  fat  was  the  same  as  during  total  abstinence  from  food.  These  facts  are 
entirely  in  accordance  with  observations  upon  the  effects  of  different  kinds  of  food  in 
diabetes,  and  they  have  an  important  bearing  upon  the  dietetic  measures  to  be  employed 
in  this  disease. 

The  effect  of  entire  deprivation  of  food  is  to  arrest  the  production  of  sugar  in  the 
liver,  three  or  four  days  before  death.  This  arrest  of  the  glycogenic  function  has  gener- 
ally been  observed  in  cases  of  disease,  except  when  death  has  occurred  suddenly. 

Influence  of  the  Nervous  System,  etc.—  Bernard  has  studied  the  influence  of  the  ner- 
vous system  upon  the  production  of  sugar  more  satisfactorily  than  any  other  of  the  vari- 
ations of  the  glycogenic  function,  for  the  reason  that  he  has  noted  these 
modifications  by  determining  the  sugar  in  the  blood  and  in  the  nrine. 
Some  of  the  points  with  regard  to  the  nervous  system  we  shall  consider 
again,  and  it  is  sufficient,  in  this  connection,  to  mention  the  main  results 
of  some  of  the  most  striking  of  the  experiments  upon  this  subject. 

The  most  remarkable  experiment  upon  the  influence  of  the  ner- 
vous system  on  the  liver  is  the  one  in  which  artificial  diabetes  is 
produced  by  irritation  of  the  floor  of  the  fourth  ventricle.  This 
operation  is  not  difficult,  and  it  is  one  that  we  have  often  repeated. 
The  instrument  used  is  a  delicate  stilet,  with  a  flat,  cutting  extremity, 
and  a  small,  projecting  point  about  ^  of  an  inch  long.  In  perform- 
ing the  operation  upon  a  rabbit,  the  head  of  the  animal  is  firmly 
held  in  the  left  hand,  and  the  skull  is  penetrated  in  the  median 
line,  just  behind  the  superior  occipital  protuberance.  This  can  easily 
be  done  by  a  few  lateral  movements  of  the  instrument.  Once  with- 
in the  cranium,  the  instrument  is  passed  obliquely  downward  and  for- 
ward, so  as  to  cross  an  imaginary  line  drawn  between  the  two  auditory 
canals,  until  its  point  reaches  the  basilar  process  of  the  occipital  bone. 
The  point-then  penetrates  the  medulla  oblongata,  between  the  roots  of 
the  auditory  nerves  and  the  pneumogastrics,  and,  by  its  projection, 
serves  to  protect  the  nervous  centre  from  more  serious  injury  from  the 
cutting  edge.  The  instrument  is  then  carefully  withdrawn,  and  the 
operation  is  completed.  This  experiment  is  almost  painless,  and  it  is 
not  desirable  to  administer  an  anaesthetic,  as  this,  in  itself,  would  dis- 
turb the  glycogenic  process.  The  urine  may  be  drawn  before  the  oper- 
ation, by  pressing  the  lower  part  of  the  abdomen,  taking  care  not  to 
allow  the  bladder  to  pass  up  above  the  point  of  pressure,  and  it  will  be 
found  turbid,  alkaline,  and  without  sugar.  In  one  or  two  hours  after 
the  operation,  the  urine  will  have  become  clear  and  acid,  and  it  will  react 
FIG.  140.— instru-  readily  with  any  of  the  copper-tests.  When  this  operation  is  performed 
without  injuring  the  adjacent  organs,  the  presence  of  sugar  in  the  urine 
™  O10i}y  temP°raiT>  and  the  next  day  the  secretion  will  have  returned 
to  its  normal  condition.  It  is  best,  in  performing  this  experiment,  to 
operate  upon  an  animal  in  full  digestion,  when  the  production  of  sugar  is  at  its  maximum. 
The  production  of  diabetes  in  this  way,  in  animals,  is  exceedingly  interesting  in  its 
relations  to  certain  cases  of  the  disease  in  the  human  subject,  in  which  the  affection  is 


V  ABLATIONS  IN  THE   GLYCOGENIO  FUNCTION. 


471 


traumatic  and  directly  attributable  to  injury  near  the  medulla.  Its  mechanism  is  dif- 
ficult to  explain.  The  irritation  is  not  propagated  through  the  pneumogastric  nerves, 
for  the  experiment  succeeds  after  both  of  these  nerves  have  been  divided;  but  the 
influence  of  the  pneumogastrics  upon  glycogenesis  is  curious  and  interesting.  If  both 
of  these  nerves  be  divided  in  the  neck,  in  a  few  hours  or  days,  depending  upon  the 
length  of  time  that  the  animal  survives  the  operation,  no  sugar  is  to  be  found  in  the  liver, 
and  there  is  reason  to  believe  that  the  glycogenic  function  has  been  arrested.  After  divi- 
sion of  the  nerves  in  this  situation,  galvanization  of  their  peripheral  ends  does  not  affect 
the  production  of  sugar ;  but,  by  galvanization  of  the  central  ends,  an  impression  is  con- 
veyed to  the  nervous  centre,  which  is  reflected  to  the  liver  and  produces  a  hypersecretion 
of  sugar.  These  questions  will  be  referred  to  again,  in  connection  with  the  physiology 
of  the  nervous  system. 


FIG.  141. — Section  of  the  head  of  a  rabbit,  showing  the  operation  of  puncturing  the  floor  of  the  fourth  ventricle, 

(Bernard.) 

a,  cerebellum ;  &,  origin  of  the  seventh  pair  of  nerves ;  c,  spinal  cord ;  d,  origin  of  the  pneumogastric;  e,  opening  of 
entrance  of  the  instrument  into  the  cranial  cavity ;  /,  instrument ;  g,  fifth  pair  of  nerves ;  A,  auditory  canal :  «', 
extremity  of  the  instrument  upon  the  spinal  cord  after  having  penetrated  the  cerebellum ;  k,  occipital  venous 
sinus ;  Z,  tubercula  quadrigemiua ;  m,  cerebrum ;  n}  section  of  the  atlas. 


With  regard  to  the  influence  of  the  sympathetic  system  upon  the  glycogenic  function, 
there  have  been  few  if  any  experiments  which  lead  to  conclusions  of  any  great  value. 

It  has  been  observed  that  the  inhalation  of  anaesthetics  and  irritating  vapors  produces 
temporary  diabetes ;  and  this  has  been  attributed  to  an  irritation  conveyed  by  the  pneu- 
mogastrics to  the  nerve-centre,  and  reflected,  in  the  form  of  a  stimulus,  to  the  liver.  It 
is  for  this  reason  that  we  should  avoid  the  administration  of  anaesthetics  in  all  accurate 
experiments  on  the  glycogenic  function. 

Destination  of  Sugar. — Although  sugar  is  constantly  produced  by  the  liver  and  taken 
up  by  the  circulation,  it  is  exceptional  to  find  it  in  the  blood  after  it  has  passed  through 
the  lungs.  It  is  difficult  to  ascertain  the  precise  mode  of  its  destruction  in  the  lungs,  and, 
indeed,  the  nutritive  function  of  sugar  in  the  economy  is  not  thoroughly  understood.  All 
that  we  can  say  of  the  destination  of  liver-sugar  is,  that  it  probably  has  the  same  office 
in  nutrition  as  the  sugar  taken  as  food  and  that  resulting  from  the  digestion  of  amylaceous 
matters.  The  facts  bearing  upon  this  question  will  be  reviewed  under  the  head  of  nutri- 
tion. 


472  SECKETIOK 

Alleged  Production  of  Fat  ly  the  Liver.— It  is  stated  by  Bernard  that,  in  animals  fed 
largely  with  saccharine  and  amylaceous  principles,  the  blood  of  the  hepatic  veins  contains 
an  emulsive  matter,  which  seems  to  be  fat  combined  with  a  proteine  substance.  In  sup- 
port of  the  opinion  that  fat  is  thus  produced  in  the  liver,  he  brings  forward  the  well- 
known  fact,  that  a  diet  of  starch  and  sugar  is  particularly  favorable  to  the  development 
of  adipose  tissue.  But  the  examinations  of  the  matter  supposed  to  be  fatty  have  not  been 
sufficiently  minute  to  lead  to  any  positive  conclusions  with  regard  to  its  character  or 
composition.  While  there  can  be  no  doubt  of  the  formation  of  fat  in  the  organism  inde- 
pendently of  the  fat  taken  as  food,  there  is  not  sufficient  ground  for  regarding  the  liver  as 
one  of  the  organs  specially  concerned  in  its  production. 

Changes  in  the  Albuminoid  and  the  Corpuscular  Elements  of  the  Blood  in  passing 
through  the  Liver. — In  verifying  the  observations  of  Bernard  upon  the  presence  of  sugar 
in  the  blood  of  the  hepatic  veins,  Lehmann  was  led  to  observe  other  differences  in  the 
composition  of  the  blood  from  these  vessels,  as  compared  with  the  portal  blood  and  the 
blood  of  the  arterial  system.  One  of  the  most  important  of  these  was  the  absence  of 
coagulating  principles.  While  the  portal  blood  coagulates  strongly,  like  blood  from  any 
other  part  of  the  body,  the  blood  of  the  hepatic  veins  does  not  coagulate,  and  "  the  fibrin 
is  either  entirely  absent,  or  is  present  in  mere  traces." 

Some  very  curious  observations  were  also  made  by  Lehmann  upon  the  blood-corpuscles 
in  the  hepatic  vessels.  He  estimated  that  the  proportion  of  white  corpuscles  in  the  blood 
of  the  hepatic  veins  was  at  least  fivefold  the  proportion  in  the  portal  blood.  He  also 
noted  certain  differences  in  the  appearance  of  the  red  corpuscles,  which  he  explained  by 
the  supposition  that  the  liver  was  the  seat  of  development  of  these  elements,  which  were 
formed  from  the  white  corpuscles,  and  that  the  blood  of  the  hepatic  veins  contained  a 
greater  number  of  "  newly-formed  or  rejuvenescent  blood-corpuscles." 

It  is  not  our  purpose,  in  this  connection,  to  discuss  the  development  of  the  corpuscular 
.  elements  of  the  blood ;  but  it  is  interesting  to  note  the  above-mentioned  changes  in  the 
blood  as  it  passes  through  the  liver.  The  physiological  significance  of  the  destruction  of 
albuminoids  is  not  understood,  although  the  fact  is  undoubted. 


CHAPTER  XIY. 

THE  DUCTLESS   GLANDS 

Probable  office  of  the  ductless  glands— Anatomy  of  the  spleen— Fibrous  structure  of  the  spleen  (trabeculse)— Malpi- 
ghian  bodies— Spleen-pulp— Vessels  and  nerves  of  the  spleen— Some  points  in  the  chemical  constitution  of  the 
spleen— State  of  our  knowledge  concerning  the  functions  of  the  spleen— Variations  in  the  volume  of  the  spleen 
—Extirpation  of  the  spleen— Anatomy  of  the  suprarenal  capsules— Cortical  substance— Medullary  substance 
—Vessels  and  nerves— Chemical  reactions  of  the  suprarenal  capsules— State  of  our  knowledge  concerning 
the  functions  of  the  suprarenal  capsules— Extirpation  of  the  suprarenal  capsules— Addison's  disease— Anatomy 
of  the  thyroid  gland— State  of  our  knowledge  concerning  the  functions  of  the  thyroid  gland— Anatomy  of  the 
thymus— Pituitary  body  and  pineal  gland. 

CERTAIN  organs  in  the  body,  with  a  structure  resembling,  in  some  regards,  the  true 
glands,  but  without  excretory  ducts,  have  long  been  the  subject  of  physiological  specula- 
tion; and  the  most  extravagant  notions  concerning  their  functions  have  prevailed  in  the 
early  history  of  the  science.  The  discovery  of  those  functions  of  the  liver  which  consist 
in  modifications  in  the  composition  of  the  blood  passing  through  its  substance  dimly  fore- 
shadowed the  probable  office  of  the  ductless  glands ;  for,  as  far  as  the  production  of  sugar 
is  concerned,  the  liver  belongs  to  this  class.  Indeed,  the  supposition  that  the  ductless 
glands  effect  some  change  in  the  blood  is  now  regarded  by  physiologists  as  the  most 


ANATOMY   OF   THE   SPLEEN".  473 

reasonable  of  the  many  theories  that  have  been  entertained  concerning  their  office  in 
the  economy.  Under  this  idea,  these  organs  have  been  called  blood-glands  or  vascular 
glands;  but,  inasmuch  as  the  supposition  that  these  parts  effect  changes  in  the  blood 
or  lymph  is  merely  to  supply  the  want  of  any  definite  idea  of  their  function  and  rests 
mainly  upon  analogy  with  certain  of  the  functions  of  the  liver,  we  shall  retain  the  name 
ductless  glands,  as  indicating  the  most  striking  of  their  anatomical  peculiarities. 

As  far  as  presenting  any  definite  and  important  physiological  information  is  concerned, 
we  might  terminate  here  the  history  of  the  ductless  glands.  It  is  true  that  the  largest 
of  them,  the  spleen,  was  extensively  experimented  upon  by  the  earlier  physiologists; 
but,  in  point  of  fact,  investigations  have  done  little  more  than  exhibit  a  want  of  knowl- 
edge of  the  functions  of  these  remarkable  organs;  and  the  literature  of  the  subject  is 
mainly  a  collection  of  speculations  and  fruitless  experiments.  There  are,  however,  some 
interesting  experimental  facts  with  relation  to  the  spleen  and  the  suprarenal  capsules, 
although  they  are  not  very  instructive,  except  that  they  indicate  the  extremely  narrow 
limits  of  our  positive  knowledge.  These  few  facts,  with  a  sketch  of  the  anatomy  of  the 
parts,  will  embrace  all  that  we  shall  have  to  say  concerning  the  ductless  glands.  Under 
this  head  are  classed,  the  spleen,  the  suprarenal  capsules,  the  thyroid  gland,  the  thymus, 
and  sometimes  the  pituitary  body  and  the  pineal  gland.  These  parts  have  certain 
anatomical  points  in  common  with  each  other,  but,  on  account  of  our  want  of  knowl- 
edge of  their  functions,  it  is  difficult  to  distinguish,  as  we  have  done  in  other  organs, 
their  physiological  anatomy. 

Anatomy  of  the  Spleen. 

The  spleen  is  situated  in  the  left  hypochondriac  region,  next  the  cardiac  extremity  of 
the  stomach.  Its  color  is  of  a  dark  bluish-red,  and  its  consistence  is  rather  soft  and  fri- 
able. It  is  shaped  somewhat  like  the  tongue  of  a  dog,  presenting  above,  a  rather  thick- 
ened extremity,  which  is  in  relation  with  the  diaphragm,  and  below,  a  pointed  extremity, 
in  relation  with  the  transverse  colon.  Its  external  surface  is  convex,  and  its  internal 
surface,  concave,  presenting  a  vertical  fissure,  the  hilum,  which  gives  passage  to  the  ves- 
sels and  nerves.  It  is  connected  with  the  stomach  by  the  gastro-splenic  omentum  and  is 
still  farther  fixed  by  a  fold  of  the  peritoneum  passing  to  the  diaphragm.  It  is  about  five 
inches  in  length,  three  or  four  inches  in  breadth,  and  a  little  more  than  an  inch  in  thick- 
ness. Its  weight  is  between  six  and  seven  ounces.  In  the  adult  it  attains  its  maximum 
of  development,  and  it  diminishes  slightly  in  size  and  weight  in  old  age.  In  early  life  it 
bears  about  the  same  relation  to  the  weight  of  the  body  as  in  the  adult. 

The  external  coat  of  the  spleen  is  the  peritoneum,  which  is  very  closely  adherent  to 
the  subjacent  fibrous  structure.  The  proper  coat  is  dense  and  resisting;  but,  in  the 
human  subject,  it  is  quite  thin  and  somewhat  translucent.  It  is  composed  of  inelastic 
fibrous  tissue,  mixed  with  numerous  small  fibres  of  elastic  tissue  and  a  few  unstriped  mus- 
cular fibres. 

At  the  hilum,  the  fibrous  coat  penetrates  the  substance  of  the  spleen  in  the  form  of 
sheaths  for  the  vessels  and  nerves ;  an  arrangement  analogous  to  the  fibrous  sheath  of 
the  analogous  structures  in  the  liver.  The  number  of  the  sheaths  in  the  spleen  is  equal 
to  the  number  of  arteries  that  penetrate  the  organ.  This  membrane  is  sometimes  called 
the  capsule  of  Malpighi.  The  fibrous  sheaths  are  closely  adherent  to  the  surrounding 
substance,  but  they  are  united  to  the  vessels  by  a  loose  fibrous  net-work.  They  follow 
the  vessels  in  their  ramifications  to  the  smallest  branches  and  are  lost  in  the  spleen-pulp. 
Between  the  sheath  and  the  outer  coat,  are  numerous  bands,  or  trabeculas,  presenting  the 
same  structure  as  the  fibrous  coat.  The  presence  of  elastic  fibres  in  these  structures  can 
be  easily  demonstrated,  and  this  kind  of  tissue  is  very  abundant  in  the  herbivora.  In 
the  carnivora  the  muscular  tissue  is  particularly  abundant  and  can  be  readily  demon- 
strated ;  but  in  man  this  is  not  so  easy,  and  the  fibres  are  less  numerous,  some  anatomists 
denying  the  existence  of  any  muscular  structure.  These  peculiarities  in  the  fibrous  struct- 


474 


SECRETION. 


ure  are  important  in  their  relation  to  certain  physiological  changes  in  the  size  of  the 
spleen.  Its  contractility  may  be  easily  demonstrated  in  the  dog  by  the  application  of  a 
galvanic  current  to  the  nerves  as  they  enter  at  the  hilum.  This  is  followed  by  a  prompt 
and  energetic  contraction  of  the  organ.  Contractions  may  be  produced,  though  they 
are  much  more  feeble,  by  applying  the  current  directly  to  the  spleen. 

The  substance  of  the  spleen  is  soft  and  friable;  and  a  portion  of  it,  the  spleen-pulp, 
may  be  easily  pressed  out,  or  even  washed  away  by  a  current  of  water.  Aside  from  the 
vessels  and  nerves,  it  presents  for  study:  1.  An  arrangement  of  fibrous  bands,  or  tra- 
beculse,  by  which  it  is  divided  into  innumerable  communicating  cellular  interspaces.  2. 
Closed  vesicles  (Malpighian  bodies),  attached  to  the  walls  of  the  blood-vessels.  3.  A  soft, 
reddish  substance,  containing  numerous  cells  and  free  nuclei,  called  the  spleen-pulp. 

Fibrous  Structure  of  the  Spleen  (Trdbeculce). — From  the  internal  face  of  the  investing 
membrane  of  the  spleen  and  from  the  fibrous  sheath  of  the  vessels  (capsule  of  Malpighi). 
are  numerous  bands,  or  trabeculse,  which,  by  their  interlacement,  divide  the  substance 
of  the  organ  into  irregularly-shaped,  communicating  cavities.  These  bands  are  from  ^ 
to  y^  of  an  inch  broad,  and  are  composed,  like  the  proper  coat,  of  ordinary  fibrous  tissue 
with  elastic  fibres  and  probably  a  few  smooth  muscular  fibres.  They  pass  off'  from  the 
capsule  of  Malpighi  and  the  fibrous  coat  at  right  angles,  very  soon  branch,  interlace,  and 
unite  with  each  other,  becoming  smaller  and  smaller,  until  they  measure  from  ^-^  to  -fa 
of  an  inch.  As  we  should  expect  from  the  very  variable  size  of  the  trabeculas,  the  dimen- 
sions as  well  as  the  form  of  the  cavities  are  exceedingly  irregular.  This  fibrous  net- work 
serves  as  a  skeleton  or  a  support  for  the  softer  and  more  delicate  parts. 

Malpighian  Bodies. — In  the  very  elabo- 
rate work  on  the  spleen,  by  Malpighi,  is  a  full 
account  of  the  closed  follicles,  which  have 
since  been  called  the  Malpighian  bodies. 
They  are  sometimes  called  the  splenic  cor- 
puscles or  glands.  They  are  in  the  form  of 
rounded  or  slightly  ovoid  corpuscles,  about 
•jV  of  an  inch  in  diameter,  consisting  of  a  deli- 
cate membrane,  generally  homogeneous,  but 
sometimes  faintly  striated,  with  semifluid  con- 
tents. In  their  form,  size,  and  structure, 
they  bear  a  close  resemblance  to  the  closed 
follicles  of  the  small  intestine.  The  investing 
membrane  has  no  epithelial  lining,  and  the 
contents  consist  of  an  albuminoid  liquid,  with 
numerous  small,  nucleated  cells  and  a  few 
free  nuclei.  The  cells  measure  from  ^^  to 
2-gVfr  of  an  incn  in  diameter.  Both  the  cells 
and  the  free  nuclei  of  the  splenic  corpuscles 

bear  a  close  resemblance  to  cells  and  nuclei 
rn.-Malpi.kian  ^softke  spleen  of  the  pig.    found  in  the  spleen_pulp.     The  corpuscles  are 

a,  an  artery,  with  its  branches  (6,  &) ;  c,  c,  c,  Malpighian    Surrounded    by     blood- vessels,    which     send 

branches  into  the  interior,  to  form  a  delicate 

capillary  plexus. 

The  number  of  the  Malpighian  corpuscles  in  a  spleen  of  ordinary  size  has  been  esti- 
mated by  Sappey  at  about  ten  thousand.  They  are  readily  made  out  in  the  ox  and 
sheep  but  are  frequently  not  to  be  discovered  in  the  human  subject.  In  about  forty 
examinations,  in  man,  Sappey  found  them  in  only  four ;  but  in  these  they  presented  the 
same  characters  as  in  the  ox  and  the  sheep,  and  resisted  decomposition  for  twelve  days, 


ANATOMY  OF  THE   SPLEEN".  475 

showing  that  it  is  not  necessary  to  have  recourse  to  perfectly  fresh  specimens  to  discover 
them  if  they  exist.  Kolliker  notes  the  fact  that  they  are  often  absent  in  the  human  sub- 
ject when  death  has  taken  place  from  disease  or  after  long  abstinence.  He  believes  that 
they  are  nearly  always  to  be  found  in  perfectly  healthy  persons.  The  occasional  absence 
of  these  bodies  constitutes  another  point  of  resemblance  to  the  solitary  glands  of  the 
small  intestine. 

The  relations  of  the  Malpighian  bodies  to  the  arterial  branches  distributed  throughout 
the  spleen  are  peculiar.  In  specimens  in  which  these  corpuscles  are  easily  made  out,  if  a 
thin  section  be  made  and  the  spleen-pulp  be  washed  away  by  a  stream  of  water,  the  cor- 
puscles may  be  seen  attached  in  some  parts  to  the  sides  of  the  vessels,  in  others  lying  in 
the  notch  formed  by  the  branching  of  a  vessel,  and  in  others  attached  to  an  extremity  of 
an  arterial  twig,  the  vessel  then  breaking  up  into  plexuses  surrounding  each  corpuscle. 
According  to  Sappey,  the  corpuscles  are  attached  to  arteries  measuring  from  -fa  to  -fa  of 
an  inch  or  less  in  diameter.  When  the  artery  is  enclosed  in  its  fibrous  sheath,  the  cor- 
puscles are  applied  to  the  sheath,  but,  in  the  smallest  arteries,  they  are  attached  to  the 
walls  of  the  vessels.  The  attachment  of  the  Malpighian  bodies  to  the  vessels  is  very  firm, 
and  they  cannot  be  separated  without  laceration  of  the  membranes. 

Spleen-pulp. — "With  regard  to  the  constitution  of  the  spleen-pulp,  there  is  consider- 
able diversity  of  opinion.  While  anatomists  and  physiologists  are  pretty  generally  agreed 
concerning  the  structure  and  relations  of  the  Malpighian  bodies,  some  minutely  describe 
cells  in  the  pulp,  the  existence  of  which  is  denied  by  others  of  equal  authority.  The 
pulp,  however,  contains  the  essential  elements  of  the  spleen,  and  an  accurate  knowledge 
of  all  the  structures  contained  in  it  could  hardly  fail  to  throw  some  light  on  its  function ; 
but  there  is  so  little  that  is  definitely  known  of  either  the  anatomy  or  the  physiology  of 
the  spleen,  that  we  shall  refrain  from  discussing  the  views  of  different  authors,  referring 
the  reader  for  full  information  upon  these  points  to  elaborate  works  upon  general  anatomy. 

The  spleen-pulp  is  a  dark,  reddish,  semifluid  substance,  its  color  varying  in  intensity  in 
different  specimens.  It  is  so  soft  that  it  may  be  washed  by  a  stream  of  water  from  a  thin 
section,  and  it  readily  decomposes,  becoming  then  nearly  fluid.  It  is  contained  in  the 
cavities  bounded  by  the  fibrous  trabecula3,  and  it  contains  itself  numerous  microscopic 
bands  of  fibres  arranged  in  the  same  way.  It  surrounds  the  Malpighian  bodies,  contains 
the  terminal  branches  of  the  blood-vessels,  and  probably  the  nerves  and  lymphatics. 
Upon  microscopical  examination,  it  presents  numerous  free  nuclei  and  cells  like  those 
described  in  the  Malpighian  bodies ;  but  the  nuclei  are  here  relatively  much  more  abun- 
dant. In  addition  are  found,  blood-corpuscles  (white  and  red)  some  natural  in  form  and 
size  and  others  more  or  less  altered,  with  pigmentary  granules,  both  free  and  enclosed  in 
cells.  Anatomists  have  attached  a  great  deal  of  importance  to  large  vesicles  enclosing 
what  have  been  supposed  by  some  to  be  blood-corpuscles,  and  by  others  to  be  pigmentary 
corpuscles.  The  state  of  our  knowledge  upon  these  points,  however,  is  very  unsatisfac- 
tory. Some  authorities  deny  the  existence  of  the  so-called  blood-corpuscle-containing 
cells.  We  shall  abstain  from  a  discussion  of  these  disputed  questions,  which  are  at  present 
of  a  character  purely  anatomical.  All  that  we  can  say  of  the  spleen-pulp  is,  that  it  con- 
tains cells,  nuclei,  blood-corpuscles,  and  pigmentary  granules,  with  a  yellowish-red  fluid, 
and  that  it  is  intersected  with  microscopic  trabeculae  of  fibrous  and  muscular  tissue  and  a 
delicate  net-work  of  blood-vessels.  It  is  difficult  to  determine  whether  the  blood-cor- 
puscles come  from  vessels  that  have  been  divided  in  making  our  preparations  or  are  really 
free  in  the  pulp ;  or  whether  the  free  nuclei  are  normal  or  come  from  cells  that  have 
been  artificially  ruptured. 

Vessels  and  Nerves  of  the  Spleen. — The  quantity  of  blood  which  the  spleen  receives 
is  very  large  in  proportion  to  the  size  of  the  organ.  The  splenic  artery  is  the  larg- 
est branch  of  the  coeliac  axis.  It  is  a  vessel  of  considerable  length  and  is  remarkable 


476  SECKETIOK 

for  its  excessively-  tortuous  course.  In  a  man  between  forty  and  fifty  years  of  age, 
the  vessel  measured  about  five  inches,  without  taking  account  of  its  deflections ;  and  a 
thread  placed  on  the  vessel,  so  as  to  follow  exactly  all  its  windings,  measured  a  little  more 
than  eight  inches.  The  large  caliber  of  this  vessel  and  its  tortuous  course  are  interesting 
points  in  connection  with  the  great  variations  in  size  and  situation  which  the  spleen  is 
liable  to  undergo  in  health  and  disease.  The  artery  gives  off  several  branches  to  the 
adjacent  viscera  in  its  course,  and,  as  it  passes  to  the  hilum,  it  divides  into  three  or  four 
branches,  which  again  divide  so  as  to  form  from  six  to  ten  vessels.  These  penetrate  the 
substance  of  the  spleen,  with  the  veins,  nerves,  and  lymphatics,  enveloped  in  the  fibrous 
sheath,  the  capsule  of  Malpighi.  In  the  substance  of  the  spleen,  the  arteries  branch 
rather  peculiarly,  giving  off  many  small  ramifications  in  their  course,  generally  at  right 
angles  to  the  parent  trunk.  These  are  accompanied  by  the  veins  until  they  are  reduced 
to  from  ?V  to  tV  °f  an  mch  in  diameter.  The  two  classes  of  vessels  then  separate,  and 
the  arteries  have  attached  to  them  the  corpuscles  of  Malpighi.  It  is  also  a  noticeable 
fact  that  the  distinct  trunks  passing  in  at  the  hilum  have  but  few  inosculations  with  each 
other  in  the  substance  of  the  spleen,  so  that  the  organ  is  divided  up  into  from  six  to  ten 
vascular  compartments. 

The  veins  join  the  fine  branches  of  the  arteries  in  the  spleen-pulp  and  pass  out  of  the 
spleen  in  the  same  sheath.  They  anastomose  quite  freely  in  their  larger  as  well  as  their 
smaller  branches.  Their  caliber  is  estimated  by  Sappey  as  about  twice  that  of  the  arte- 
ries. This  author  regards  the  estimates,  which  have  put  the  caliber  of  the  veins  at  four  or 
five  times  that  of  the  arteries,  as  much  exaggerated.  The  number  of  veins  emerging 
from  the  spleen  is  equal  to  the  number  of  arteries  of  supply. 

The  lymphatics  of  the  spleen  are  not  numerous.  By  most  anatomists,  two  sets  of 
vessels  have  been  recognized,  the  superficial  and  the  deep;  but  those  who  have  studied 
the  subject  practically  have  found  it  very  difficult  to  demonstrate  the  superficial  layer. 
The  deep  lymphatics  have  been  demonstrated  in  the  capsule  of  Malpighi,  attached  to  the 
veins  and  emerging  with  them  at  the  hilum.  At  the  hilum,  the  deep  vessels  are  joined 
by  a  few  from  the  surface  of  the  spleen.  The  vessels,  numbering  five  or  six,  then  pass 
into  small  lymphatic  glands  and  empty  into  the  thoracic  duct  opposite  the  eleventh  or 
twelfth  dorsal  vertebra.  It  was  an  old  idea  that  the  lymphatics  were  the  excretory  ducts 
of  the  spleen ;  but  this  is  a  speculation  which  does  not  demand  discussion  at  the  pres- 
ent day. 

The  nerves  of  the  spleen  are  derived  from  the  solar  plexus.  They  follow  the  vessels 
in  their  distribution  and  are  enclosed  with  them  in  the  capsule  of  Malpighi.  They  are 
distributed  ultimately  in  the  spleen-pulp,  but  nothing  definite  is  known  of  their  mode  of 
termination.  "We  have  already  referred  to  the  fact  that,  when  these  nerves  are  galvanized, 
the  non- striated  muscles  in  the  substance  of  the  spleen  are  thrown  into  contraction. 

Some  Points  in  the  Chemical  Constitution  of  the  Spleen. — Very  little  has  been  learned 
with  regard  to  the  probable  function  of  the  spleen,  from  the  numerous  chemical  analyses 
that  have  been  made  of  its  substance.  It  will  therefore  be  out  of  place  to  discuss  its 
chemical  constitution  very  fully,  and  we  shall  only  refer  to  certain  principles,  the  exist- 
ence of  which,  in  the  spleen-substance,  may  be  considered  as  pretty  well  determined. 
In  the  first  place,  cholesterine  has  been  found  to  exist  in  the  spleen  constantly  and  in 
considerable  quantity,  and  the  same  may  be  said  of  uric  acid.  In  addition,  chemists 
have  extracted  from  the  substance  of  the  spleen,  hypoxanthine,  leucine,  tyrosine,  a 
peculiar  crystallizable  substance  called,  by  Scherer,  lienine,  crystals  of  hsematoidine,  lac- 
tic acid,  acetic  acid,  butyric  acid,  inosite,  amyloid  matter,  and  some  indefinite  fatty  prin- 
cjples.  It  is  difficult,  however,  to  say  how  far  some  of  these  principles  are  formed  by 
the  processes  employed  for  their  extraction  or  are  due  to  morbid  action ;  certainly,  physi- 
ologists have  thus  far  been  unable  to  connect  them  with  any  definite  views  with  regard 
to  the  probable  function  of  the  spleen. 


FUNCTIONS  OF  THE   SPLEEN.  477 

State  of  our  Knowledge  concerning  the  Functions  of  the  Spleen.— -The  spleen  is  al- 
most universal  in  vertebrate  animals ;  it  is  an  organ  of  considerable  size,  and  is  very 
abundantly  supplied  with  vessels  and  nerves ;  it  has  a  complex  structure,  unlike  that  of 
any  of  the  true  glands ;  its  tissue  presents  a  variety  of  proximate  principles  ;  but  it  has 
no  excretory  duct,  and  no  opportunity  is  afforded  for  the  study  of  its  secretion,  except 
as  it  may  be  taken  up  by  the  current  of  blood.  It  must  be  admitted,  also,  that,  up  to 
the  present  time,  no  definite  physiological  ideas  have  followed  the  elaborate  microscopi- 
cal and  chemical  examinations  of  the  spleen.  There  have  been  only  two  methods  of 
inquiry,  indeed,  which  have  promised  any  such  results :  First,  a  comparison  of  the  blood 
and  lymph  going  into  and  coming  from  the  spleen,  and  an  examination  of  the  variations 
in  the  volume  of  the  organ  during  life  ;  and  second,  a  study  of  the  phenomena  which  fol- 
low its  extirpation  in  living  animals.  A  review  of  the  literature  of  the  subject  will  show 
that  we  have  gained  but  little  positive  information  from  either  of  these  methods  of  study. 

The  condition  of  the  question  of  the  influence  of  the  spleen  upon  the  composition  of 
the  blood  is  well  illustrated  in  the  last  edition  of  Longet's  elaborate  work  upon  physiology. 
This  author  quotes  opinions  of  the  highest  authorities,  based  chiefly  upon  microscopical/ 
investigations,  some  in  favor  of  the  view  that  the  blood-corpuscles  are  destroyed,  and 
others  arguing  that  they  are  formed  in  the  spleen,  while  he  himself  offers  no  opinion 
upon  the  subject.  Still,  there  are  certain  established  points  of  difference  between  the 
blood  of  the  splenic  artery  and  of  the  splenic  vein.  There  can  be  little  doubt  of  the  fact 
that  the  blood  coming  from  the  spleen  contains  a  large  excess  of  white  corpuscles ;  but 
it  can  by  no  means  be  considered  as  settled  that  the  function  of  the  spleen  is  to  form 
white  blood-corpuscles.  In  pathology,  although  great  increase  in  the  leucocytes  of  the 
blood  frequently  attends  hypertrophy  of  the  spleen,  this  condition  is  also  observed  when 
the  spleen  is  perfectly  healthy. 

Diminution  in  the  proportion  of  red  corpuscles  in  the  blood  in  passing  through  the 
spleen,  in  a  very  marked  degree,  has  been  noted,  and  this  gives  color  to  the  supposition 
that  the  spleen  is  an  organ  for  the  destruction  of  the  blood-corpuscles ;  but  we  know 
nothing  of  the  importance  or  significance  of  this  process,  and  it  is  not  shown  that  the 
corpuscles  exist  in  undue  quantity  in  animals  after  the  spleen  has  been  removed.  We 
learn  nothing  more  definite  from  the  fact  that  the  blood  of  the  splenic  vein  seems  to  contain 
an  unusual  quantity  of  pigmentary  matter.  In  connection  with  the  marked  diminution 
in  the  proportion  of  blood-corpuscles,  physiologists  have  observed  a  marked  increase  in 
albuminoid  matters  in  the  blood  of  the  splenic  vein. 

The  significance  of  the  facts  just  stated  is  so  little  understood,  that  it  would  seem 
hardly  necessary  even  to  mention  them,  except  as  an  illustration  of  the  small  amount  of 
definite  information  regarding  the  functions  of  the  spleen  that  has  resulted  from  an 
examination  of  the  blood  coming  from  this  organ.  We  know  nothing  of  any  changes 
effected  by  the  spleen  in  the  constitution  of  the  lymph. 

Variations  in  the  Volume  of  the  Spleen. — One  of  the  theories  with  regard  to  the 
function  of  the  spleen,  which  merits  a  certain  amount  of  consideration,  is  that  it  serves 
as  a  diverticulum  for  the  blood,  when  there  is  a  tendency  to  congestion  of  the  other 
abdominal  viscera. 

It  has  been  shown  that  the  spleen  is  greatly  enlarged  in  dogs,  from  four  to  five  hours 
after  feeding,  that  its  enlargement  is  at  its  maximum  at  about  the  fifth  hour,  and  that  it 
gradually  diminishes  to  its  original  size  during  the  succeeding  twelve  hours ;  but  it  is  not 
apparent  how  far  these  changes  are  important  or  essential  to  the  proper  performance  of  the 
functions  of  digestion  and  absorption.  Experiments  have  shown  that  animals  may  live, 
digest,  and  absorb  alimentary  principles  perfectly  well  after  the  spleen  has  been  re- 
moved, and  this  has  even  been  observed  in  the  human  subject ;  and,  in  view  of  these  facts, 
it  is  impossible  to  assume  that  the  presence  of  the  spleen,  as  a  diverticulum  for  the  blood, 
is  essential  to  the  proper  action  of  the  other  abdominal  organs. 


478  SECRETION. 

Extirpation  of  the  Spleen. — There  is  one  experimental  fact  that  has  presented  itself 
in  opposition  to  nearly  every  theory  advanced  with  regard  to  the  function  of  the  spleen ; 
which  is,  that  the  organ  may  be  removed  from  a  living  animal,  and  yet  all  the  functions 
of  life  go  on  apparently  as  before.  The  spleen  is  certainly  not  necessary  to  life,  nor,  as 
far  as  we  know,  is  it  essential  to  any  of  the  important  general  functions.  It  has  been 
removed  over  and  over  again  from  dogs,  cats,  and  even  from  the  human  subject,  and 
its  absence  is  attended  with  no  constant  and  definite  changes  in  the  phenomena  of  life. 
If  it  act  as  a  diverticulum,  this  function  is  not  essential  to  the  proper  operation  of 
the  organs  of  digestion  and  absorption ;  and,  if  its  office  be  the  destruction  or  the  forma- 
tion of  the  blood-corpuscles,  the  formation  of  leucocytes,  of  uric  acid,  of  cholesterine,  or 
of  any  excrementitious  matter,  there  are  other  organs  which  may  perform  these  functions. 
What  renders  this  question  even  more  obscure  is  the  fact  that  we  have  no  knowledge  of 
any  constant  modifications  in  the  size  or  the  functions  of  other  organs  as  a  consequence 
of  removal  of  the  spleen.  This  is  not  surprising,  however,  when  we  reflect  that  one 
kidney  may  accomplish  the  function  of  urinary  excretion  after  the  other  has  been  removed, 
and  that  the  single  organ  which  remains  does  not  present  enlargement  of  the  Malphigian 
bodies  and  the  convoluted  tubes. 

There  are  certain  phenomena  that  sometimes  follow  removal  of  the  spleen  from  the 
lower  animals,  which  are  curious  and  interesting,  even  if  they  do  not  afford  much  posi- 
tive information.  Extirpation  of  this  organ  is  an  old  and  a  very  common  experiment. 
In  the  works  of  Malpighi,  published  in  1687,  we  find  an  account  of  an  experiment  on  a 
dog,  in  which  the  spleen  was  destroyed,  and  the  operation  was  followed  by  no  serious 
results.  Since  then  it  has  been  removed  so  often,  and  the  experiments  have  been  so 
universally  negative  in  their  results,  that  it  is  hardly  necessary  to  cite  authorities  upon  the 
subject.  There  are  numerous  instances,  also,  in  which  it  has  been  in  part  or  entirely 
removed  from  the  human  subject,  which  it  is  unnecessary  to  refer  to  in  detail ;  but,  in 
nearly  every  case,  when  there  was  no  diseased  condition  to  complicate  the  observation, 
the  results  have  been  the  same  as  in  experiments  on  the  inferior  animals. 

One  of  the  phenomena  following  extirpation  of  the  spleen,  to  which  we  desire  to 
call  attention,  is  a  modification  of  the  appetite.  Great  voracity  in  animals  after  removal 
of  the  spleen  was  noted  by  the  earlier  experimenters,  and  this  formed  the  basis  of  some 
of  their  extravagant  theories.  Later  experimenters  have  observed  this  change  in  the 
appetite  and  have  noted  that  digestion  and  assimilation  do  not  appear  to  be  disturbed, 
the  animals  becoming  unusually  fat.  Prof.  Dalton  has  also  observed  that  the  animals, 
particularly  dogs,  sometimes  present  a  remarkable  change  in  their  disposition,  becoming 
unnaturally  ferocious  and  aggressive.  "We  have  frequently  observed  these  phenomena 
after  removal  of  the  spleen ;  and,  in  the  following  experiment,  performed  in  1861,  they 
were  particularly  marked : 

The  spleen  was  removed  from  a  young  dog  weighing  twenty-two  pounds,  by  tho 
ordinary  method  ;  viz.,  making  an  incision  into  the  abdominal  cavity  in  the  linea  alba, 
drawing  out  the  spleen,  and  exsecting  it  after  tying  the  vessels.  Before  the  operation 
the  dog  presented  nothing  unusual,  either  in  his  appetite  or  disposition.  The  wound 
healed  rapidly,  and,  after  recovery  had  taken  place,  the  animal  was  fed  moderately  once 
a  day.  It  was  noticed,  however,  that  the  appetite  was  excessively  voracious ;  and  the 
dog  became  so  irritable  and  ferocious  that  it  was  dangerous  to  approach  him,  and  it 
became  necessary  to  separate  him  from  the  other  animals  in  the  laboratory.  He  would 
eat  refuse  from  the  dissecting-room,  the  flesh  of  dogs,  fa?ces,  etc.  On  February  11,  1861, 
about  six  weeks  after  the  operation,  having  been  well  fed  twenty-four  hours  before,  the  dog 
was  brought  before  the  class  at  the  New  Orleans  School  of  Medicine,  and  he  ate  a  little 
more  than  four  pounds  of  beef-heart,  nearly  one  fifth  of  his  weight.  This  he  digested 
perfectly  well,  and  the  appetite  was  the  same  upon  the  following  day.  This  dog  had  a 
remarkably  sleek  and  well-nourished  appearance. 

The  above  is  a  striking  example  of  the  change  in  the  appetite  and  disposition  of  ani- 


SUPRARENAL   CAPSULES.  479 

mals  after  extirpation  of  the  spleen  ;  but  these  results  are  hy  no  means  invariable.  We 
have  often  removed  the  spleen  from  dogs  and  kept  the  animals  for  months  without 
observing  any  thing  unusual ;  and,  on  the  other  hand,  we  have  observed  the  change  in 
disposition  and  the  development  of  an  unnatural  appetite,  in  animals  after  removal  of 
one  kidney.  These  effects  were  also  very  well  marked  in  an  animal  with  biliary  fistula, 
that  lived  for  thirty-eight  days.  In  the  latter  instance,  the  voracity  could  be  explained 
by  the  disturbance  in  digestion  and  assimilation  produced  by  shutting  off  the  bile  from 
the  intestine ;  but  these  phenomena  occurring  after  removal  of  one  kidney,  which  ap- 
peared to  have  no  effect  upon  the  ordinary  functions,  are  not  so  readily  understood.  We 
have  observed  both  increase  in  the  appetite  and  the  development  of  extraordinary  ferocity 
after  extirpation  of  one  kidney  almost  invariably,  since  our  attention  has  been  directed 
to  this  point ;  and,  in  the  experiments  of  which  records  were  preserved,  these  effects 
were  very  marked.  In  one,  a  dog  lived  for  nearly  two  years  with  one  kidney  and  was 
finally  killed.  The  appetite  was  voracious  and  depraved.  He  would  eat  dogs'  flesh 
greedily.  In  another,  death  took  place  in  convulsions,  forty-three  days  after  removal  of 
one  kidney,  the  animal  having  apparently  recovered  from  the  operation.  This  dog  was 
very  ferocious,  had  an  extraordinary  appetite,  and  would  eat  faeces,  putrid  dogs'  flesh,  etc., 
which  the  other  dogs  in  the  laboratory  would  not  touch.  The  other  dog  entirely  recov- 
ered from  the  operation  of  removing  one  kidney  and  presented  the  same  phenomena. 

In  view  of  the  above  facts,  it  must  be  admitted  that  removal  of  the  spleen  in  the 
lower  animals  and  the  human  subject  has  thus  far  demonstrated  nothing,  except  that  this 
part  is  not  essential  to  the  proper  performance  of  the  vital  functions.  The  voracity 
which  occasionally  follows  the  operation  in  animals  is  one  of  the  phenomena,  like  the 
increase  in  the  size  of  animals  after  castration,  for  which  physiologists  can  offer  no  satis- 
factory explanation. 

It  is  evident  from  the  foregoing  considerations  that,  notwithstanding  the  great  amount 
of  literature  upon  the  anatomy  and  functions  of  the  spleen,  physiologists  have  no  definite 
knowledge  of  any  important  office  performed  by  this  organ.  With  this  conclusion,  we 
pass  to  a  consideration  of  the  other  ductless  glands,  the  physiology  of  which  is,  unfortu- 
nately, even  more  unsatisfactory. 

Suprarenal  Capsules. 

The  theories  that  have  been  advanced  with  regard  to  the  function  of  the  suprarenal 
capsules  have  not,  as  a  rule,  been  based  upon  anatomical  investigations,  but  have  taken 
their  origin  from  pathological  observations  and  experiments  upon  living  animals.  This  fact 
detracts  from  the  physiological  interest  attached  to  the  structure  of  these  bodies,  and  we 
shall  consequently  treat  of  their  anatomy  very  briefly. 

The  suprarenal  capsules,  as  their  name  implies,  are  situated  above  the  kidneys.  They 
are  small,  triangular,  flattened  bodies,  situated  behind  the  peritoneum,  and  capping  the 
kidneys  at  the  anterior  portion  of  their  superior  ends.  The  left  capsule  is  a  little  larger 
than  the  right,  and  is  rather  semilunar  in  form,  the  right  being  more  nearly  triangular. 
Their  size  and  weight  are  very  variable  in  different  individuals.  Of  the  different  esti- 
mates given  by  anatomists,  we  may  state,  as  an  average,  that  each  capsule  weighs  about 
one  hundred  grains.  They  are  about  an  inch  and  a  half  in  length,  a  little  less  in  width, 
and  a  little  less  than  one-fourth  of  an  inch  in  thickness. 

The  weight  of  the  capsules,  in  proportion  to  that  of  the  kidneys,  presents  great  vari- 
ations at  different  periods  of  life ;  and  they  are  so  much  larger  in  the  foetus  than  after 
birth,  that  some  physiologists,  in  the  absence  of  any  reasonable  theory  of  their  function  in 
the  adult,  have  assumed  that  their  office  is  chiefly  important  in  intra-uterine  life.  Meckel 
states  that  they  are  easily  distinguished  in  the  foetus  of  two  months ;  at  the  end  of  the 
third  month,  they  are  a  little  larger  and  heavier  than  the  kidneys ;  they  are  equal  in  size 
to  the  kidneys  (though  a  little  lighter)  at  four  months  ;  and,  at  the  beginning  of  the  sixth 
month,  they  are  to  the  kidneys  as  two  to  five.  In  the  foetus  at  term,  the  proportion  is  as 


480  SECRETION. 

one  to  three,  and  in  the  adult,  as  one  to  twenty-three.  It  was  asserted  by  some  of  the 
older  writers,  that  the  capsules  are  larger  in  the  negro  than  in  the  white  races,  but 
Meckel  states  that,  although  he  had  observed  this  in  a  negress,  he  saw  nothing  of  it  in 
dissecting  a  negro.  This  observation  did  not  have  much  significance  at  that  time  ;  but 
since  it  has  been  supposed  that  the  suprarenal  capsules  have  some  function  in  connection 
with  the  formation  of  pigment,  authors  have  quoted  it  as  important. 

The  color  of  the  capsules  is  whitish-yellow.  They  are  completely  covered  by  a  thin, 
fibrous  coat,  which  penetrates  their  interior,  in  the  form  of  trabeculaB.  Upon  section, 
they  present  a  cortical  and  a  medullary  substance.  The  cortex  is  yellowish,  from  ^  to 
T^  of  an  inch  in  thickness,  surrounding  the  capsule  entirely,  and  constituting  about  two- 
thirds  of  its  substance.  The  medullary  substance  is  whitish,  very  vascular,  and  is 
remarkably  prone  to  decomposition,  so  that  it  is  desirable  to  study  the  anatomy  of  these 
bodies  in  specimens  that  are  perfectly  fresh. 

Structure  of  the  Suprarenal  Capsules. 

Cortical  Substance. — The  cortical  substance  is  divided  into  two  layers.  The  external 
is  pale-yellow,  and  is  composed  of  closed  vesicles,  rounded  or  ovoid  in  form,  containing 
an  albuminoid  fluid,  cells,  nuclei,  and  fatty  globules.  This  layer  is  very  thin.  The  greater 
part  of  the  cortical  substance  is  of  a  reddish-brown  color  and  is  composed  of  closed  tubes. 
On  making  thin  sections  through  the  cortical  substance  previously  hardened  in  chromic 
acid  and  rendered  clear  by  means  of  glycerine,  numerous  rows  of  cells  are  seen,  arranged 
with  great  regularity,  and  extending,  apparently,  from  the  investing  membrane  to  the 
medullary  substance.  On  studying  these  sections  with  a  high  magnify  ing-power,  it  is 
evident  that  the  cells  are  enclosed  in  tubes  measuring  from  ToVfr  to  ^ir  °f  an  *ncn  m 
diameter.  The  cells  are  granular,  with  a  distinct  nucleus  and  nucleolus,  and  a  variable 
number  of  oil-globules.  They  measure  from  yy1^  to  T^7  of  an  inch  in  diameter.  Be- 
tween the  tubes  of  the  cortical  substance,  are  bands  of  fibrous  tissue,  connected  with  the 
covering  of  the  capsule. 

Medullary  Substance. — The  medullary  substance  is  much  paler  and  more  transparent 
than  the  cortex.  In  its  centre  are  numerous  openings,  marking  the  passage  of  its  venous 
sinuses.  It  is  penetrated  in  every  direction  by  excessively  delicate  bands  of  fibrous  tis- 
sue, which  enclose  blood-vessels,  nerves,  and  numerous  elongated,  closed  vesicles,  contain- 
ing cells,  nuclei,  and  granular  matter.  These  vesicles,  -^  of  an  inch  long  and  about  ^^ 
of  an  inch  broad,  have  been  demonstrated  in  the  ox  and  in  the  human  subject.  The  cells 
in  the  human  subject  are  from  T1^nr.to  isW  °f  an  men  *n  diameter.  They  are  isolated 
with  difficulty  and  are  very  irregular  in  their  form.  The  nuclei  measure  about  ygV*  °f 
an  inch.  The  medullary  substance  is  peculiarly  rich  in  vessels  and  nerves. 

Vessels  and  Nerves. — The  blood-vessels  going  to  the  suprarenal  capsules  are  very 
numerous  and  are  derived  from  the  aorta,  the  phrenic  artery,  the  coeliac  axis,  and  the  renal 
artery.  Sometimes  as  many  as  twenty  distinct  vessels  penetrate  each  capsule.  In  the 
cortical  substance,  the  capillaries  are  arranged  in  elongated  meshes,  anastomosing  freely, 
and  surrounding  the  tubes,  but  never  penetrating  them.  In  the  medullary  substance,  the 
meshes  are  more  rounded,  and  here  the  vessels  form  a  very  rich  capillary  plexus.  Two 
large  veins  pass  out,  to  empty,  on  the  right  side,  into  the  vena  cava,  and  on  the  left, 
into  the  renal  vein.  Other  smaller  veins  empty  into  the  vena  cava,  the  renal,  and  the 
phrenic  veins. 

The  nerves  are  very  numerous  and  are  derived  from  the  semilunar  ganglia,  the  renal 
plexus,  the  pneumogastric,  and  the  phrenic.  Kolliker  mentions  that  he  has  counted,  in 
the  human  subject,  thirty -three  nervous  trunks  entering  the  right  suprarenal  capsule. 
The  nerves  probably  pass  directly  to  the  medullary  substance,  but  here  their  mode  of  dis- 
tribution is  unknown.  In  the  medullary  matter,  however,  are  two  ganglia,  characterized 
by  nerve-cells  of  the  ordinary  form,  and  situated  close  to  the  central  vein. 


FUNCTIONS   OF  THE  SUPRARENAL  CAPSULES.  481 

Nothing  whatever  is  known  of  the  lymphatics  of  the  suprarenal  capsules,  and  the 
existence  of  these  vessels,  even,  is  doubtful. 

Chemical  Reactions  of  the  Suprarenal  Capsules. — A  few  years  ago,  M.  Vulpian 
discovered  in  the  medullary  portion  of  the  suprarenal  capsules  a  peculiar  substance, 
soluble  in  water  and  in  alcohol,  which  gave  a  greenish  reaction  with  the  salts  of  iron  and 
a  peculiar  rose-tint  on  the  addition  of  iodine.  He  could  not  determine  the  same  reaction 
with  extracts  from  any  other  parts.  Later,  in  conjunction  with  M.  Cloez,  he  discovered 
hippuric  and  taurocholic  acid  in  the  capsules  of  some  of  the  herbivora.  Other  researches 
have  been  made  into  the  chemistry  of  these  bodies,  but  without  results  of  any  great  physi- 
ological importance. 

State   of  our  Knowledge  concerning  the  Functions  of  the   Suprarenal 

Capsules. 

In  1855,  the  late  Dr.  Addison,  of  Guy's  Hospital,  published  a  remarkable  memoir  upon 
a  peculiar  disease  which  he  had  found  connected  with  disorganization  of  the  suprarenal 
capsules.  This  disease,  sometimes  called  Addison's  disease,  is  characterized  by  bronzing 
of  the  skin  and  is  accompanied  by  serious  disorders  in  nutrition.  It  was  supposed  to  be 
invariably  fatal.  The  peculiar  discoloration  of  the  surface,  attended  with  disorganization 
of  the  suprarenal  capsules,  led  physiologists  to  suppose  that,  perhaps,  these  bodies  had 
some  function  connected  with  the  formation  of  pigment ;  and,  following  the  publication 
of  Dr.  Addison's  memoir,  we  find  quite  a  number  of  experiments  upon  animals,  consisting 
chiefly  in  extirpation  of  the  capsules.  Before  this  time,  there  had  been  no  reasonable 
theory,  even,  of  the  probable  function  of  these  bodies.  As  our  first  ideas  of  the  rela- 
tions of  the  suprarenal  capsules  to  the  formation  of  pigment  were  derived  from  cases  of 
disease,  it  may  not  be  out  of  place  to  consider  briefly  whether  there  be  any  invariable 
and  positive  connection  between  structural  change  in  these  organs  and  the  affection 
known  under  the  name  of  bronzed  skin. 

In  the  memoir  by  Dr.  Addison,  are  reported  eleven  cases  of  anaemia,  accompanied 
with  bronzing  of  the  skin,  terminating  fatally,  and  found,  after  death,  to  be  attended 
with  extensive  disorganization  of  the  suprarenal  capsules.  The  reports  of  these  cases 
attracted  a  great  deal  of  attention  among  physiologists  as  well  as  pathologists.  A  year 
later,  Prof.  I.  E.  Taylor,  of  Bellevue  Hospital,  reported  seven  cases  of  bronzed  skin,  in 
two  of  which  the  diagnosis  of  disease  of  the  suprarenal  capsules  was  verified  by  post- 
mortem examination.  Attention  now  being  directed  to  this  peculiar  condition  of  the 
system,  accompanied  with  discoloration  of  the  skin,  numerous  cases  were  reported  from 
time  to  time,  but  some  of  them  did  not  fully  carry  out  the  views  of  Dr.  Addison.  Per- 
haps the  most  extensive  collection  of  cases  taken  from  a  great  number  of  authorities  is 
given  by  Dr.  Greenhow,  in  his  work  upon  Addison's  disease.  Dr.  Greenhow  is  appar- 
ently convinced  that  the  connection  between  the  constitutional  symptoms  and  discolora- 
tion of  the  skin,  described  by  Addison,  and  disorganization  of  the  suprarenal  capsules  is 
well  established.  He  reports  one  hundred  and  ninety-six  cases ;  and,  out  of  these,  he 
selects  one  hundred  and  twenty-eight,  as  fair  representatives  of  Addison's  disease.  There 
are  several  cases  (ten)  in  which-there  was  bronzing  of  the  skin,  the  suprarenal  capsules 
being  perfectly  healthy ;  but  in  only  one  of  these  were  there  any  of  the  characteristic 
constitutional  symptoms.  There  are  twenty-two  cases  cited  of  cancer  of  the  suprarenal 
capsules,  not  one  of  which  presented  the  characteristic  constitutional  symptoms,  only 
seven  presenting  some  slight  discoloration  Of  the  skin.  Without  discussing  this  subject 
more  fully,  it  seems  justifiable  to  adopt  the  opinion,  entertained  by  many  pathologists, 
that  there  is  a  connection  between  bronzed  skin  accompanied  with  certain  grave  consti- 
tutional symptoms,  and  disorganization  of  the  suprarenal  capsules,  which  is  frequent  but 
not  invariable  ;  but  it  is  not  established  that  the  destruction  of  the  capsules  stands  in  a 
31 


482  SECRETION. 

causative  relation  to  the  discoloration  or  to  the  constitutional  disturbance.  It  is  more 
interesting  to  us,  however,  to  know  that  the  investigations  into  these  diseased  conditions 
have  developed  little  or  nothing  of  importance  concerning  the  physiology  of  the  supra- 
renal capsules. 

Extirpation  of  the  Suprarenal  Capsules.— There  are  two  important  questions  to  be 
settled  by  the  removal  of  the  suprarenal  capsules  from  living  animals.  The  first  is, 
whether  or  not  these  organs  are  essential  to  life ;  and  the  second,  to  determine  the  con- 
sequences of  their  removal,  as  exhibited  in  modifications  of  the  animal  functions. 

Are  the  suprarenal  capsules  essential  to  life  ?  This  question  can  be  answered  in  a  very 
few  words.  Dr.  Brown-Sequard,  in  his  first  experiments,  removed  sometimes  one  and 
sometimes  both  capsules  in  rabbits,  Guinea-pigs,  dogs,  and  cats,  and  the  animals  died  in 
the  course  of  two  or  three  days.  He  also  noted  several  peculiar  results,  such  as  turning, 
and  contraction  of  the  pupil,  when  one  capsule  had  been  extirpated,  and  the  development 
of  peculiar  crystals  in  the  blood.  M.  Gratiolet  repeated  these  experiments  and  ascertained 
that  the  left  capsule  could  be  removed  with  impunity,  while  extirpation  of  the  right  was 
always  fatal.  M.  Philipeaux  added  a  number  of  observations,  experimenting  chiefly  upon 
rats  and  taking  great  care  to  disturb  the  adjacent  organs  as  little  as  possible.  As  the  result 
of  these  experiments,  he  concluded  that  the  capsules  are  not  essential  to  life.  Of  four  rats 
operated  upon  in  this  way,  three  died,  as  Philipeaux  supposed,  of  cold,  the  first  in  nine 
days,  the  second  in  twenty-three  days,  and  the  third  in  thirty-four  days.  One  was  alive 
and  well  when  the  report  was  made,  although  the  capsules  had  been  removed  for  forty- 
nine  days.  In  such  a  question  as  this,  negative  experiments  are  of  little  account ;  and  the 
instances  in  which  animals  have  recovered  and  lived  perfectly  well  after  removal  of  both 
suprarenal  capsules  show  conclusively  that  they  are  not  essential  to  life.  Death  has  prob- 
ably been  due,  in  most  of  the  experiments,  to  injury  of  the  semilunar  ganglia,  and  it  is 
probably  on  account  of  the  greater  injury,  from  the  situation  of  the  capsule,  produced 
by  operating  on  the  right  side,  that  the  removal  of  the  capsule  of  that  side  has  been  more 
generally  fatal.  It  is  not  necessary  to  take  account,  in  this  connection,  of  the  contraction 
of  the  pupil,  "turning"  and  other  symptoms  referable  to  the  nervous  system,  which  have 
sometimes  followed  these  operations.  These  phenomena  are  undoubtedly  due  to  injury 
of  adjacent  parts,  and  not  to  extirpation  of  the  capsules.  The  only  remaining  question  to 
determine  is  whether  the  capsules  have  any  thing  to  do  with  the  formation  or  change  of 
pigment.  Notwithstanding  the  assertion  of  Dr.  Brown-Sequard,  that  flakes  of  pigment 
and  blood-crystals  differing  from  those  developed  in  normal  blood  are  found  in  animals 
deprived  of  the  suprarenal  capsules,  this  view  is  adopted  by  a  few  physiological  authori- 
ties. In  view  of  these  facts,  and  in  the  absence  of  comparative  examinations  of  the  blood 
going  to  the  suprarenal  capsules  by  the  arteries  and  returned  from  them  by  the  veins,  it 
is  impossible  to  assign  any  definite  function  to  these  bodies,  and  it  is  certain  that  they 
are  not  essential  to  life.  Their  greater  relative  size  before  birth  has  led  to  the  supposi- 
tion that  they  might  have  an  important  office  in  intra-uterine  life,  but  this  is  a  pure 
hypothesis,  based  upon  no  positive  knowledge. 

Thyroid  Gland. 

The  history  of  this  gland  belongs  almost  exclusively  to  descriptive  anatomy,  and  its 
only  physiological  interest  is  in  the  similarity  of  its  structure  to  that  of  the  other  ductless 
glands.  It  has  no  excretory  duct.  It  is  attached  to  the  lower  part  of  the  larynx,  follow- 
ing it  in  its  various  movements.  Its  color  is  brownish-red.  The  anterior  face  is  convex 
and  is  covered  by  certain  of  the  muscles  of  the  neck.  The  posterior  surface  is  concave 
and  is  applied  to  the  larynx  and  trachea.  It  is  formed  of  two  lateral  lobes,  with  a 
rounded,  thickened  base  below,  and  a  long,  pointed  extremity  extending  upward,  con- 
nected by  an  isthmus.  Each  of  these  lobes  is  about  two  inches  in  length,  three-quarters 
of  an  inch  in  breadth,  and  about  the  same  in  thickness  at  its  thickest  portion.  The  isth- 


THYMUS  GLAND.  483 

mus  connects  the  lower  portion  of  the  lateral  lobes.  It  covers  the  second  and  third 
tracheal  rings  and  is  about  half  an  inch  wide  and  one-third  of  an  inch  thick.  From  the 
left  side  of  the  isthmus,  and  sometimes  from  the  left  lobe,  is  a  portion  projecting  upward, 
called  the  pyramid.  The  weight  of  the  thyroid  gland,  according  to  Sappey,  is  from  three 
hundred  and  fifty  to  three  hundred  and  eighty  grains.  It  is  usually  stated  by  anatomical 
writers  that  it  is  relatively  larger  in  the  foetus  and  in  early  life  than  in  the  adult ;  but 
Sappey,  from  his  own  researches,  is  disposed  to  believe  that  its  weight,  in  proportion  to 
the  weight  of  the  adjacent  organs,  does  not  vary  with  age.  It  is  a  little  larger  and  more 
prominent  in  the  female  than  in  the  male. 

Structure  of  the  Thyroid  Gland. — The  thyroid  gland  is  covered  with  a  thin  but  resisting 
coat  of  ordinary  fibrous  tissue,  which  is  loosely  connected  with  the  surrounding  parts.  From 
the  internal  surface  of  this  membrane,  are  numerous  fibrous  bands,  or  trabeculae,  giving 
off,  as  they  pass  through  the  gland,  secondary  trabeculae,  and  then  subdividing  until  they 
become  of  microscopic  size.  By  this  arrangement,  the  gland  is  divided  up  into  communi- 
cating cells,  like  a  sponge.  These  bands  are  mingled  with  numerous  small  elastic  fibres. 
Throughout  the  substance  of  the  gland,  lodged  in  the  meshes  of  the  trabeculee,  are  numer- 
ous rounded  or  ovoid  closed  vesicles,  measuring  from  -fa  to  -fa  of  an  inch.  These  are 
formed  of  a  structureless  membrane,  and  they  are  lined  by  a  single  layer  of  pale,  granular, 
nucleated  cells,  from  ^-^  to  ^Vfr  °f  an  incn  in  diameter.  The  layer  of  cells  sometimes 
lines  the  vesicle  completely,  sometimes  it  is  incomplete,  and  sometimes  it  is  wanting. 
The  contents  of  the  vesicles  are  a  clear,  yellowish,  slightly  viscid,  albuminoid  fluid,  with 
a  few  granules,  pale  cells,  and  nuclei.  Robin  has  described  in  these  vesicles  curiously- 
shaped,  translucent,  feebly-retracting,  colorless  bodies  which  he  has  called  sympexions; 
but  there  is  little  known  of  their  constitution  or  properties.  The  vesicles  are  arranged 
in  little  collections  or  lobes,  with  the  great  veins  passing  between  them. 

Vessels  and  Nerves. — The  blood-vessels  of  the  thyroid  gland  are  very  numerous,  this 
organ  being  supplied  by  the  superior  and  inferior  thyroid  arteries  and  sometimes  by  a 
branch  of  the  innominata.  The  arteries  break  up  into  a  close  capillary  plexus,  surround- 
ing the  vesicles  with  a  rich  net-work,  but  never  penetrating  their  interior.  The  veins 
are  large,  and,  like  the  hepatic  veins,  they  are  so  closely  adherent  to  the  surrounding 
tissue  that  they  do  not  collapse  when  cut  across.  The  veins  emerging  from  the  gland 
form  a  plexus  over  its  surface  and  the  surface  of  the  trachea,  and  they  then  go  to  form 
the  superior,  middle,  and  inferior  thyroid  veins.  The  nerves  are  derived  from  the  pneu- 
mogastric  and  the  cervical  sympathetic  ganglia.  The  lymphatics  are  numerous  but  are 
difficult  to  inject.  The  exact  distribution  of  the  nerves  and  the  origin  of  the  lymphatics 
are  not  well  understood. 

State  of  our  Knowledge  concerning  the  Functions  of  the  Thyroid  Gland. — It  is  gen- 
erally admitted  that  the  thyroid  gland  may  be  removed  from  animals  without  interfering 
with  any  of  the  vital  functions ;  and  this,  taken  in  connection  with  the  fact  that  it  is  so 
often  diseased  in  the  human  subject  without  producing  any  general  disturbance,  shows 
that  its  function  cannot  be  very  important.  Nothing  of  importance  has  been  learned 
from  a  chemical  analysis  of  its  substance.  The  blood  of  the  thyroid  veins  has  been  ana- 
lyzed, but  the  changes  in  its  composition  in  passing  through  the  gland  are  slight  and 
indefinite.  An  instance  is  quoted  by  Longet  of  periodical  enlargement  of  the  gland  in  a 
female  during  menstruation,  but  there  is  no  evidence  that  this  is  of  constant  occurrence. 

Thymus   Gland. 

The  anatomy  of  the  thymus  assimilates  it  to  the  ductless  glands,  but  its  function, 
whatever  it  may  be,  is  confined  to  early  life.  In  the  adult  the  organ  is  wanting,  traces, 
only,  of  fibrous  tissue,  with  a  little  fat,  existing  after  puberty  in  the  situation  previously 
occupied  by  this  gland.  As  there  never  has  been  a  plausible  theory,  even,  of  the  func- 


484 


SECRETION". 


tion  of  this  organ,  the  existence  of  which  is  confined  to  the  first  two  or  three  years  of 
life,  we  shall  abstain  from  all  discussions  with  regard  to  minute  points  in  its  anatomy, 
and  give  a  simple  sketch  of  its  structure,  as  compared  with  the  ductless  glands  already 
considered. 

The  thymus  appears  at  about  the  third  month  of  foetal  life,  and  it  gradually  increases  in 
size  until  about  the  end  of  the  second  year.  It  then  undergoes  atrophy,  and  it  disappears 
almost  entirely  at  the  age  of  puberty.  It  is  situated  partly  in  the  thorax  and  partly  in 
the  neck.  The  thoracic  portion  is  in  the  anterior  mediastinum,  resting  upon  the  pericar- 
dium, extending  as  low  as  the  fourth  costal  cartilage.  The  cervical  portion  extends 
upward  as  far  as  the  lower  border  of  the  thyroid  gland.  The  whole  gland  is  about  two 
inches  in  length,  one  and  a  half  inch  broad  at  its  lower  portion,  and  about  one-quarter 
of  an  inch  thick.  Its  color  is  grayish,  with  a  slightly  rosy  tint.  It  is  usually  in  the  form  of 
two  lateral  lobes  lying  in  apposition  in  the  median  line,  although  sometimes  there  exists 
but  a  single  lobe.  It  is  composed  of  numerous  lobules  held  together  by  fibrous  tissue. 

The  proper  coat  of  the  thymus  is  a  delicate  fibrous 
membrane,  sending  processes  into  the  interior  of  the 
organ.  Its  fibrous  structure,  however,  is  loose,  so  that 
the  lobules  can  be  separated  with  little  difficulty.  Por- 
tions of  the  gland  may  be,  as  it  were,  unravelled,  by 
loosening  the  interstitial  fibrous  tissue.  In  this  way  it 
will  be  found  to  be  composed  of  numerous  little  lobular 
masses  attached  to  a  continuous  cord.  This  arrange- 
ment is  more  distinct  in  the  inferior  animals  of  large 


FIG.  143.—  Unravelled  thymus  from  the  calf; 

natural  size.    (Koll'iker.) 
a,  a,  cord  of  the  thymus ;  &,  ft,  &,  lobules :  c, 
small  nodules  attached  to  the  cord. 


FIG.  144. 


-Half  of  the  human  thymus,  laid  open  in 
its  lower  portion.    (Koiliker  ) 


size  than  in  man.  The  lobules  are  composed  of  rounded  vesicles,  from  ten  to  fifteen  in  num- 
ber, and  from  ^  to  ^  of  an  inch  in  diameter.  The  walls  of  these  vesicles  are  thin, 
finely  granular,  and  excessively  fragile.  The  vesicles  contain  a  small  quantity  of  an 
albuminoid  fluid,  with  cells  and  free  nuclei.  The  cells  are  small  and  transparent,  and  the 
nuclei,  spherical,  relatively  large,  and  containing  from  one  to  three  nucleoli.  The  free 
nuclei  are  also  rounded  and  contain  several  distinct  nucleoli.  These  vesicles  are  easily 


PITUITARY  BODY  AND  PINEAL  GLAND.  485 

ruptured,  when  their  contents  exude  in  the  form  of  an  opalescent  fluid,  sometimes  called 
the  thymic  juice. 

Anatomists  are  somewhat  divided  in  their  opinions  with  regard  to  the  structure 
of  the  central  cord  and  the  lobules.  Some  adopt  the  view  advanced  by  Sir  Astley 
Cooper,  that  the  cord  has  a  central  canal  connected  with  cavities  in  the  lobules ;  while 
others  believe  that  the  cavities  thus  described  are  produced  artificially,  by  the  processes 
employed  in  anatomical  investigation.  The  latter  opinion  is  the  latest  and  is  probably 
correct. 

The  blood-vessels  of  the  thymus  are  numerous,  but  their  caliber  is  small,  and  the  gland 
is  not  very  vascular.  They  are  derived  chiefly  from  the  internal  mammary  artery,  a  few 
coming  from  the  inferior  thyroid,  the  superior  diaphragmatic,  or  the  pericardial.  They 
pass  between  the  lobules,  surround  and  penetrate  the  vesicles,  and  form  a  capillary  plexus 
in  their  interior.  The  vesicles,  in  this  respect,  bear  a  certain  resemblance  to  the  closed 
follicles  of  the  intestine.  The  veins  are  also  numerous,  but  they  do  not  follow  the  course 
of  the  arteries.  The  principal  vein  emerges  at  about  the  centre  of  the  gland  posteriorly, 
and  it  empties  into  the  left  brachio-cephalic.  Other  small  veins  empty  into  the  internal 
mammary,  the  superior  diaphragmatic,  and  the  pericardial.  A  few  nervous  filaments 
from  the  sympathetic  system  surround  the  principal  thymic  artery  and  penetrate  the 
gland.  Their  ultimate  distribution  is  uncertain.  The  lymphatics  are  very  numerous. 

Inasmuch  as  the  thymus  is  peculiar  to  early  life,  one  of  the  most  interesting  points  in 
its  anatomical  history  relates  to  its  mode  of  development.  This,  however,  does  not  pre- 
sent any  great  physiological  importance  and  is  fully  treated  of  in  works  upon  anatomy. 

Pituitary  Body  and  Pineal  Gland. 

These  little  bodies,  situated  at  the  base  of  the  brain,  are  quite  vascular,  contain  closed 
vesicles  and  but  few  nervous  elements,  and  are  sometimes  classed  with  the  ductless  glands. 
Physiologists  have  no  idea  of  their  function. 

The  pituitary  body  is  of  an  ovoid  form,  a  reddish-gray  color,  weighs  from  five  to  ten 
grains,  and  is  situated  on  the  sella  turcica  of  the  sphenoid  bone.  It  is  said  to  be  larger  in 
the  foetus  than  in  the  adult,  and  in  foetal  life  it  has  a  cavity  communicating  with  the  third 
ventricle.  This  little  body  has  been  studied  by  M.  Grandry,  in  connection  with  the 
suprarenal  capsules.  He  regards  it  as  essentially  composed  of  closed  vesicles,  with  fibres 
of  connective  tissue  and  blood-vessels.  The  vesicles  measure  from  7f^  to  -^  of  an  inch 
in  diameter.  They  are  formed  of  a  transparent  membrane,  containing  irregularly  po- 
lygonal, nucleated  cells,  and  free  nuclei.  The  cells  are  from  ^V^  to  yyV^  of  an  inch  in 
diameter.  The  nuclei  are  distinct,  with  a  well-marked  nucleolus,  and  measure  about 
-^•Q- o-  of  an  inoh.  Capillary  vessels  surround  these  vesicles  without  penetrating  them. 
M.  Grandry  did  not  observe  either  nerve-cells  or  fibres  between  the  vesicles.  In  old 
subjects  he  found  the  peculiar  concretions  (sympexions)  already  described  as  existing  in 
the  thyroid  gland. 

The  pineal  gland  is  situated  just  behind  the  posterior  commissure  of  the  brain,  between 
the  nates,  and  is  enclosed  in  the  velum  interpositum.  It  is  of  a  conical  shape,  one-third 
of  an  inch  in  length,  and  of  nearly  the  color  of  the  pituitary  body.  It  is  connected  with 
the  base  of  the  brain  by  several  delicate  commissural  peduncles.  It  presents  a  small 
cavity  at  its  base,  and  frequently  it  contains  in  its  substance  little  calcareous  masses,  com- 
posed of  phosphate  and  carbonate  of  lime,  phosphate  of  magnesia  and  ammonia,  and  a 
small  quantity  of  organic  matter.  It  is  covered  with  a  fibrous  envelope,  which  sends 
processes  into  its  interior.  As  the  result  of  the  researches  of  M.  Grandry,  it  has  been 
found  to  present  a  cortical  substance,  entirely  analogous  in  its  structure  to  the  pituitary 
body,  and  a  central  portion,  composed  of  the  ordinary  nervous  elements  found  in  the  gray 
matter  of  the  brain.  Its  structure  is  regarded  by  Grandry  as  very  like  that  of  the  medul- 
lary portion  of  the  suprarenal  capsules. 


486  NUTRITION. 

It  is  difficult  to  classify  organs,  of  the  function  of  which  we  are  entirely  ignorant ;  but 
the  structure  of  the  little  bodies  just  described  certainly  resembles  that  of  the  ductless 
glands.     We  have  indicated  their  anatomy  merely  to  show  that  their  function  is  probably 
\        analogous  to  that  of  other  organs  of  the  same  class. 


CHAPTER    XV. 

NUTRITION— ANIMAL  HEAT. 

Nature  of  the  forces  involved  in  nutrition— Definition  of  vital  properties— Life,  as  represented  in  development  and 
nutrition— Principles  which  pass  through  the  organism— Principles  consumed  in  the  organism— Development  of 
power  and  endurance  by  exercise  (training)— Formation  and  deposition  of  fat— Conditions  under  which  fat  exists 
in  the  organism — Physiological  anatomy  of  adipose  tissue — Conditions  which  influence  nutrition — Products  of 
disassimilation— Animal  heat — Limits  of  variation  in  the  normal  temperature  in  man — Variations  with  external 
temperature — Variations  in  different  parts  of  the  body — Variations  at  different  periods  of  life — Diurnal  variations 
— Relations  of  animal  heat  to  digestion — Influence  of  defective  nutrition  and  inanition — Influence  of  exercise, 
mental  exertion,  and  the  nervous  system,  upon  the  heat  of  the  body— Sources  of  animal  heat— Connection  of  the 
production  of  heat  with  nutrition — Seat  of  the  production  of  animal  heat — Eelations  of  animal  heat  to  the  different 
processes  of  nutrition — Eelations  of  animal  heat  to  respiration — Exaggeration  of  the  animal  temperature  in  par- 
ticular parts  after  division  of  the  sympathetic  nerve  and  in  inflammation — Intimate  nature  of  the  calorific  pro- 
cesses—Equalization of  the  animal  temperature. 

NUTRITION  proper,  in  the  light  in  which  we  propose  to  consider  it  in  this  chapter, 
is  the  process  by  which  the  physiological  decay  of  the  tissues  and  fluids  of  the  body  is 
compensated  by  the  appropriation  of  new  matter.  All  of  the  physiological  processes 
that  we  have  thus  far  studied,  including  circulation,  respiration,  alimentation,  digestion, 
absorption,  and  secretion,  are  to  be  regarded  as  means  directed  to  a  single  end ;  and 
the  great  function,  to  which  all  the  others  are  subservient,  is  the  general  process  of 
nutrition. 

The  nature  of  the  main  forces  involved  in  nutrition,  be  it  in  a  highly-organized  part, 
like  the  brain  or  muscles,  or  in  a  tissue  called  extra- vascular,  like  the  cartilages  or  nails,  is 
unknown.  The  phenomena  attending  the  general  process,  however,  have  been  studied 
most  carefully,  and  certain  important  positive  results  have  been  attained ;  but  we  really 
find  no  more  satisfactory  explanation  of  the  nature  of  the  causative  force  of  nutrition  in 
the  doctrines  of  to-day  than  in  the  speculative  theories  of  the  ancients. 

We  can  hardly  realize  the  vast  extent  of  the  problem  of  nutrition  from  a  review  of  the 
functions  which  we  have  already  considered.  We  have  seen  that  the  blood  contains  all 
the  elements  that  enter  into  the  composition  of  the  tissues  and  secretions,  either  identical 
with  them  in  form  and  composition,  as  is  the  case  with  the  inorganic  principles,  or  in  a 
condition  which  allows  of  their  transformation  into  the  characteristic  principles  of  the 
tissues,  as  we  see  in  the  organic  substances  proper.  These  materials  are  supplied  to 
the  tissues,  in  the  required  quantity,  through  the  circulatory  apparatus;  and  oxygen, 
which  is  immediately  indispensable  to  all  the  operations  of  life,  is  introduced  by  respira- 
tion. The  great  nutritive  fluid,  being  constantly  drawn  upon  by  the  tissues  for  materials 
for  their  regeneration,  is  kept  at  the  proper  standard  by  the  introduction  of  new  matter 
into  the  system  in  alimentation,  its  elaborate  preparation  by  digestion,  and  its  appropria- 
tion by  the  fluids  by  absorption.  Many  of  these  processes  require  the  action  of  cer- 
tain secretions.  The  introduction  of  new  matter,  so  essential  to  the  continuance  of  the 
phenomena  of  life,  is  demanded,  on  account  of  the  change  of  the  substance  of  the  tissues 
into  what  we  call  effete  matter ;  and  this  is  discharged  from  the  animal  organism,  to  be 
appropriated  by  vegetables,  and  thus  maintain  the  equilibrium  between  these  two  great 
kingdoms  in  Nature. 

What  is  it  that  causes  the  parts  of  a  living  animal  organism  to  undergo  change  into 


GENERAL  CONSIDERATIONS.  487 

effete  matter,  incapable  of  any  further  animal  functions ;  and  what  is  it  that  gives  to 
these  parts  the  power  of  self-regeneration,  when  new  matter  is  presented  under  proper 
conditions  ? 

These  questions  are  the  physiological  ignis  fatuus,  which,  it  is  to  he  feared,  will  forever 
elude  the  grasp  of  scientific  inquiry.  They  constitute  one  of  the  great  mysteries  ever 
present  in  the  mind  of  the  student  of  Nature,  and  one,  the  grandeur  of  which  is  so 
immense  that  it  is  a  problem  with  which  our  intelligence  can  scarcely  grapple.  Its 
greatness  is  commensurate  with  that  of  the  question  of  the  soul,  and  its  relations  to  the 
finite  and  the  infinite ;  a  question  which  philosophers  have  been  constrained  either  to 
admit  upon  the  faith  of  revelation  or  to  hopelessly  abandon.  Little  if  any  real  progress 
is  to  be  made  by  endeavoring  to  cover  the  inscrutable  problem  of  life  with  a  simplicity 
entirely  artificial.  This  will  always  be  attractive,  and,  to  a  certain  extent,  satisfactory  to 
the  minds  of  those  unacquainted  with  the  details  of  natural  laws  or  willing  to  admit 
speculative  theories  upon  subjects  concerning  which  it  is  impossible,  in  the  present  con- 
dition of  science,  to  have  any  positive  information  ;  and,  if  generally  admitted  by  biologi- 
cal students,  it  would  carry  our  science  back  to  the  dark  periods  in  its  history,  when  the 
study  of  Nature  was  confined  to  speculation,  and  there  existed  no  knowledge  based  upon 
the  direct  observation  of  phenomena.  A  new  name,  arbitrarily  applied  to  organic  matter, 
without  any  addition  to  its  physiological  history,  does  not  advance  our  definite  knowledge. 
For  example,  it  has  long  been  known  that  certain  nitrogenized  constituents  of  the  organ- 
ism, classed  collectively  as  organic  principles,  seem  to  give  to  the  tissues  their  property 
of  self-regeneration  and  development.  It  may  seem  to  those  not  engaged  in  scientific 
inquiry  that  a  recital  of  the  wonderful  properties  of  "  protoplasm  "  affords  some  additional 
information  concerning  the  phenomena  observed  in  organized  bodies ;  but  the  true  defi- 
nition of  the  term  leads  us  back  to  our  former  ideas  of  the  so-called  vital  properties  of 
organic  matters. 

It  is  a  well-established  fact  that,  while  nearly  all  of  the  tissues  undergo  disassimila- 
tion,  or  conversion  into  effete  matter,  during  their  physiological  decay  in  the  living  or- 
ganism, others,  like  the  epidermis  and  its  appendages,  are  gradually  desquamated,  and, 
when  once  formed,  do  not  pass  through  any  farther  changes.  The  whole  question  of  the 
essence  and  nature  of  the  nutritive  property  or  force  resolves  itself  into  vitality.  Life  is 
always  attended  with  what  we  know  as  the  phenomena  of  nutrition,  and  nutrition  does 
not  exist  except  in  living  organisms.  "When  we  can  state  positively  what  is  life,  we  shall 
know  something  of  nutrition.  At  present,  physiologists  have  been  able  to  define  life 
only  by  a  recital  of  certain  of  its  invariable  and  characteristic  attendant  conditions ;  and 
yet  there  are  few,  if  any,  definitions  of  life — regarding  it  as  the  sum  of  the  phenomena 
peculiar  to  living  organisms — that  are  not  open  to  grave  objections. 

If  we  regard  life  as  a  principle,  it  stands  in  the  relation  of  a  cause  to  the  vital  phe- 
nomena ;  if  we  regard  it  as  the  totality  of  these  phenomena,  it  is  an  effect. 

If  we  study  the  development  of  a  fecundated  ovum,  life  seems  to  be  a  principle,  giv- 
ing the  wonderful  property  of  appropriating  matter  from  without,  until  the  germ 
becomes  changed,  from  a  globule  of  microscopic  size  and  an  apparently  simple  structure, 
into  a  complete  organism  with  highly-elaborated  parts.  This  organism  has  a  definite 
form  and  size,  a  definite  period  of  existence,  and  it  produces,  at  a  certain  time,  generative 
elements,  capable  of  perpetuating  its  life  in  new  beings.  We  may  say  that  an  organism 
dies  physiologically  because  the  vital  principle,  if  we  admit  the  existence  of  such  a  prin- 
ciple, has  a  limited  term  of  existence.  But,  on  the  other  hand,  the  fully -developed  living 
organism,  which  we  call  an  animal,  presents  numerous  distinct  parts,  each  endowed  with 
an  independent  property  called  vital,  that  property  recognized  by  Haller  in  various  tis- 
sues, under  the  name  of  irritability ;  and  it  is  the  coordinated  sum  of  these  vitalities  that 
constitutes  the  perfect  being.  These  are  more  or  less  distinct ;  and  we  do  not  commonly 
observe  a  sudden  and  simultaneous  arrest  of  the  vital  properties  in  all  the  tissues,  in 
what  we  call  death.  For  example,  the  nerves  may  die  before  the  muscles,  or  the  inus- 


488 


NUTRITION. 


cles  before  the  nerves.  It  is  also  found  that  vital  properties,  apparently  lost  or  destroyed, 
may  be  made  to  return;  as  in  resuscitation  after  asphyxia,  or  in  the  restoration  of  mus- 
cular or  nervous  irritability  by  injection  of  blood. 

The  life  of  a  fecundated  ovum  is  the  property  which  enables  it  to  undergo  a  certain 
development  when  placed  under  favorable  conditions ;  and,  by  the  surrounding  condi- 
tions, its  development  may  be  arrested,  suspended,  or  modified.  The  life  of  a  non-fecun- 
dated ovum  is  like  that  of  any  ordinary  anatomical  element. 

The  life  of  an  anatomical  element  or  tissue  in  process  of  development  is  the  property 
by  virtue  of  which  it  arrives  at  its  perfection  of  organization  and  performs  certain 
defined  functions,  as  far  as  its  organization  will  permit.  This  can  also  be  destroyed, 
suspended,  or  modified  by  surrounding  conditions. 

The  life  of  a  perfect  anatomical  element  or  tissue  is  the  property  which  enables  it  to 
regenerate  itself  and  perform  its  functions,  subject,  also,  to  modifications  from  surround- 
ing conditions. 

The  life  of  a  perfect  animal  organism  is  the  sum  of  the  vitalities  of  its  constituent 
parts;  but  a  being  may  live  with  the  vitality  of  certain  parts  abolished  or  seriously 
modified,  as  a  man  exists  and  preserves  his  identity  with  a  limb  amputated.  Life  may 
continue  for  a  long  time  without  consciousness,  or  with  organs  paralyzed  or  their  func- 
tion destroyed ;  but  certain  functions,  such  as  respiration  and  circulation,  are  indispensa- 
ble to  the  nutrition  of  all  parts,  and  the  vitality  of  the  different  tissues  is  speedily  lost 
when  these  processes  are  arrested,  and  the  being  then  ceases  to  exist. 

These  considerations  make  it  evident  that  it  is  difficult,  if  not  impossible,  to  give  a 
single,  comprehensive  definition  of  life,  a  study  of  the  varied  phenomena  of  which  con- 
stitutes the  science  of  physiology. 

The  general  process  of  nutrition  begins  with  the  introduction  of  matter  from  with- 
out, called  food.  It  is  carried  on  by  the  appropriation  of  this  matter  by  the  organ- 
ism. It  is  attended  with  the  production  of  excrementitious  principles  and  the  develop- 
ment of  certain  phenomena  that  we  have  not  yet  studied,  the  most  important  of  which  is 
the  production  of  heat.  We  shall  have  little  to  say  about  food,  beyond  what  we  have 
already  considered  under  the  head  of  alimentation,  except  to  classify  the  alimentary 
principles  with  reference  to  their  relations  to  the  general  process  of  nutrition. 

Principles  which  pass  through  the   Organism. 

All  of  the  inorganic  principles  taken  in  with  the  food  pass  out  of  the  organism,  gen- 
erally in  the  form  in  which  they  enter,  in  the  fasces,  urine,  and  perspiration ;  but  it  must 
not  be  inferred  from  this  fact  that  they  are  not  useful  as  constituent  parts  of  the  body. 
Some  of  these  principles,  such  as  water  and  the  chlorides,  have  very  important  functions 
of  a  purely  physical  nature.  It  is  necessary,  for  example,  that  the  blood  should  contain 
a  certain  proportion  of  the  chloride  of  sodium,  this  substance  modifying  and  regulating 
the  processes  of  absorption  and  probably  of  assimilation.  In  addition,  however,  we  find 
the  chlorides  as  constituent  parts  of  every  tissue  and  organ  of  the  body,  and  they  are  so 
closely  united  with  the  nitrogenized  principles  that  they  cannot  be  completely  separated 
without  incineration.  Those  inorganic  matters,  the  function  of  which  is  so  marked  in  their 
passage  through  the  body,  are  found  largely  as  constituents  of  the  fluids  and  are  less 
abundant  in  the  solids.  They  are  contained  in  quantity,  also,  in  the  liquid  excretions ; 
and  any  excess  over  the  amount  actually  required  by  the  system  is  thrown  off  in  this 
way.  Other  inorganic  matters  are  especially  important  as  constituent  parts  of  the  tissues, 
and  they  are  more  abundant  in  the  solids  than  in  the  fluids.  Examples  of  principles  of 
this  class  are  the  salts  of  lime,  particularly  the  phosphates.  These  are  also  in  a  condition 
of  intimate  union  with  organic  matter,  and  they  accompany  these  principles  in  all  of  their 
so-called  vital  acts. 

If  we  except  certain  simple  chemical  changes,  such  as  the  decomposition  of  the  bicar- 


INORGANIC  PRINCIPLES. 


489 


bonates,  the  inorganic  elements  of  food  do  not  necessarily  undergo  any  modification  in 
the  process  of  digestion.  They  are  generally  introduced  already  in  combination  with 
organic  matter,  and  they  accompany  it  in  the  changes  which  it  passes  through  in  digestion, 
assimilation  by  the  blood,  deposition  in  the  tissues,  and  the  final  transformations  that 
result  in  the  various  excrementitious  matters ;  so  that  we  find  the  inorganic  principles 
united  with  the  organic  matter  of  the  food  as  it  enters  the  body,  and  what  seem  to  be 
the  same  principles  in  connection  with  the  organic  excrementitious  matters.  Between 
these  two  extremes,  however,  are  the  various  operations  of  assimilation  and  disassimila- 
tion,  from  which  inorganic  matter  is  never  absent.  As  we  have  not  yet  taken  up  fully 
the  connection  of  the  various  inorganic  matters  with  nutrition,  it  will  be  convenient  here 
to  give  a  brief  review  of  the  different  individual  principles  of  this  class. 

Inorganic  Principles. 

The  number  of  these  principles  now  well  established  as  existing  in  the  human  body 
is  about  twenty-one.  All  substances  which  at  any  time  exist  in  the  body  are  proximate 
principles ;  but  some  are  found  in  small  quantities,  are  not  always  present,  and  apparent- 
ly have  no  very  important  function.  These  will  be  passed  over  rapidly,  as  well  as 
those  which  are  so  intimately  connected  with  some  important  function  as  to  render  their 
full  consideration  in  connection  with  that  function  indispensable.  The  following  is  a 
list  of  the  most  important  inorganic  principles,  excluding  those  which  are  excrementi- 
tious and  one  or  two  which  are  not  yet  well  established : 


Proximate  Principle. 
C  Oxygen. 
„•      Hydrogen. 
|  •{  Nitrogen. 

O      Carburetted  hydrogen. 
[_  Sulphuretted  hydrogen. 
Water. 

Chloride  of  sodium. 
Chloride  of  potassium. 

Phosphate  of  lime  (basic). 
Carbonate  of  lime. 

Carbonate  of  soda. 

Carbonate  of  potassa. 
Phosphate  of  magnesia. 
Phosphate  of  soda  (neutral). 
Phosphate  of  potassa. 
Sulphate  of  soda. 
Sulphate  of  potassa. 
Sulphate  of  lime. 
Hydrochlorate  of  ammonia. 
Carbonate  of  magnesia. 
Bicarbonate  of  soda. 


Table  of  Inorganic  Principles. 

Where  fov/nd. 

Lungs  and  blood. 

Gases  of  stomach  and  colon,  and  blood. 

Lungs,  intestinal  gases,  and  blood. 

Lungs  (expired  air),  intestines. 

Lungs  (expired  air),  intestines. 

Universal. 

Universal,  except  the  enamel. 

Muscles,  liver,  milk,  chyle,  blood,  mucus,  saliva,  bile,  gas- 
tric juice,  cephalo-rachidian  fluid,  and  urine. 

Universal. 

Bones,  teeth,  cartilage,  internal  ear,  blood,  sebaceous  mat- 
ter, and  sometimes  the  urine. 

Blood,  bone,  saliva,  lymph,  cephalo-rachidian  fluid,  and 
urine. 

Blood,  bone,  lymph,  and  urine. 

Universal. 

Universal. 

Universal. 

Universal,  except  milk,  bile,  and  gastric  juice. 

Same  as  sulphate  of  soda. 

Blood  and  faeces. 

Gastric  juice,  saliva,  tears,  and  urine. 

A  trace  in  the  blood  and  sebaceous  matter. 

Blood  (Liebig). 


Gases. — The  gases  (oxygen,  hydrogen,  nitrogen,  carburetted  hydrogen,  and  sulphuretted 
hydrogen)  exist  both  in  a  gaseous  state  and  in  solution  in  some  of  the  fluids  of  the  body. 
Oxygen  plays  a  most  important  part  in  the  function  of  respiration ;  but  the  office  of  the 


490  NUTRITION. 

other  gases  is  by  no  means  so  essential.  Nitrogen  seems  to  be  formed  by  the  system  in 
small  quantity  and  is  taken  up  by  the  blood  and  exhaled  by  the  lungs,  except  during  inani- 
tion, when  the  blood  absorbs  a  little  from  the  inspired  air.  It  exists  in  greatest  quantity 
in  the  intestinal  canal.  Carburetted  and  sulphuretted  hydrogen,  with  pure  hydrogen, 
are  found  in  minute  quantities  in  the  expired  air  and  are  also  found  in  a  gaseous  state  in 
the  alimentary  canal.  From  the  offensive  nature  of  the  contents  of  the  large  intestine, 
we  should  suspect  the  presence  of  sulphuretted  hydrogen  in  considerable  quantity ;  but 
actual  analysis  has  shown  that  the  gas  contained  in  the  stomach  and  intestines,  large  as 
well  as  small,  is  composed  chiefly  of  nitrogen,  with  hydrogen  and  carburetted  hydrogen 
in  about  equal  proportions  (five  to  eleven  parts  per  hundred),  and  but  a  trace  of  sulphu- 
retted hydrogen.  With  the  exception,  then,  of  oxygen  and  carbonic  acid,  the  latter  being* 
an  excretion,  the  gases  do  not  hold  an  important  place  among  the  proximate  principles. 
At  all  events,  their  function,  whether  it  be  important  or  not,  is  but  little  understood. 

Water. — This  principle  exists  in  all  parts  of  the  body  ;  in  the  fluids,  some  of  which, 
as  the  lachrymal  fluid  and  perspiration,  contain  little  else,  and  in  the  hardest  structures, 
as  the  bones  and  the  enamel  of  the  teeth.  In  the  solids  and  semisolids  it  does  not  exist  as 
water,  but  it  enters  into  their  structure,  assuming  the  consistence  by  which  the  tissues  are 
characterized.  For  example,  we  have  water  in  the  bones,  teeth,  and  even  in  the  enamel, 
not  contained  in  the  interstices  of  their  structure  as  in  a  sponge,  but  incorporated  into 
the  substance  of  the  tissue.  In  these  situations,  it  is  essentially  water  of  composition. 
During  the  process  of  nutrition,  water  is  deposited  in  the  tissues  with  the  other  nutritive 
principles,  as  we  have  it  incorporated  in  the  substance  of  certain  inorganic  compounds  in 
the  process  of  crystallization,  when  it  is  known  in  chemistry  as  water  of  crystallization. 
In  the  interior  of  the  body,  water  is  thus  incorporated  in  the  substance  of  organic  mat- 
ters, which  are  of  indefinite  chemical  composition  and  non-cry  stallizable,  and  the  water 
enters  into  their  composition,  within  certain  limits,  in  indefinite  proportions,  assuming 
the  consistence  of  the  organic  substance.  As  physiologists,  studying  the  organism  not 
from  a  purely  chemical  point  of  view,  w.e  must  consider  water  as  an  integral  constituent 
of  the  tissues  and  not  as  merely  absorbed  by  them. 

All  the  organized  structures  contain  a  certain  proportion  of  water,  and  this  is  neces- 
sary to  the  performance  of  all  or  any  of  their  functions.  If  a  normal  muscle  be  consid- 
ered as  a  contracting  organ,  and  a  nerve,  as  a  conducting  organ,  or  albumen,  as  a  nutri- 
tious element,  we  must  consider  water  as  one  of  their  constituents.  It  is  necessary  to 
the  proper  form,  consistence,  and  function  of  these  and  of  all  organized  structures.  In 
analyses  of  organic  matters,  when  water  is  lost  or  driven  off  in  our  manipulations,  the 
principle  is  not  brought  near  a  state  of  chemical  purity,  but  it  is  essentially  and  radically 
changed. 

The  quantity  of  water  which  each  organic  substance  contains  is  important ;  and  it  is 
provided  that  this  quantity,  though  indefinite,  shall  not  exceed  or  fall  below  certain  lim- 
its. The  truth  of  this  proposition  is  made  evident  from  the  following  facts :  In  the  first 
place,  all  organs  and  tissues  must  contain  a  tolerably  definite  quantity  of  water  to  give 
them  proper  consistence.  The  evils  of  too  great  a  proportion  of  water  in  the  system, 
and  consequently  a  diminution  of  solid  elements,  are  well  known  to  the  practical  physi- 
cian. General  muscular  debility,  loss  of  appetite,  dropsies,  and  various  other  indications 
of  imperfect  nutrition,  are  among  the  results  of  such  a  condition  ;  while  a  deficiency  of 
water  is  immediately  made  known  by  the  sensation  of  thirst,  which  leads  to  its  introduc- 
tion from  without. 

^  The  fact  that  water  never  exists  in  any  of  the  fluids,  semisolids,  or  solids,  without 
being  combined  with  inorganic  salts,  and  especially  chloride  of  sodium,  is  one  reason  why 
its  proportion  in  various  situations  is  to  a  Certain  extent  constant.  The  presence  of  these 
salts  influences,  in  the  semisolids  at  least,  the  quantity  of  water  entering  into  their  com- 
position, and  consequently  it  regulates  their  consistence.  A  very  simple  experiment  shows 


INORGANIC  PRINCIPLES. 


491 


this  with  reference  to  the  chloride  of  sodium.  If  a  piece  of  muscle  be  placed  in  a  strong 
solution  of  common  salt,  as  in  salting  meat,  it  becomes  harder  and  loses  a  portion  of  its 
water  of  composition ;  but,  if  it  be  exposed  to  the  action  of  pure  water,  it  absorbs  a  cer- 
tain quantity  and  becomes  softer.  The  nutrient  fluid  of  the  muscles  during  life  contains 
water  with  just  enough  saline  matter  to  preserve  the  normal  consistence  of  the  parts. 
This  action  of  saline  matters  is  even  more  apparent  in  the  case  of  the  blood-corpuscles. 
If  pure  water  be  added  to  the  blood,  these  bodies  swell  up  and  are  finally  dissolved ; 
while,  if  we  add  a  strong  solution  of  salt,  they  lose  water  and  become  shrunken  and  cor- 
rugated. Their  natural  form  and  consistence  can  be  restored,  however,  even  after  they 
have  been  completely  dried,  by  adding  water  containing  about  the  proportion  of  salt 
which  exists  in  the  blood-plasma.  It  seems  clear,  then,  that  water  is  a  necessary  ele- 
ment of  all  tissues  and  is  especially  important  to  the  proper  constitution  of  organic  nitro- 
genized  substances  ;  that  it  enters  into  the  constitution  of  these  substances,  not  as  pure 
water,  but  always  in  connection  with  certain  inorganic  salts ;  that  its  proportion  is  con- 
fined within  certain  limits ;  and  that  the  quantity  in  which  it  exists,  in  organic  nitrogen- 
ized  substances  particularly,  is  regulated  by  the  quantity  of  salts  which  enter,  with  it, 
into  the  constitution  of  these  substances. 

The  quantities  of  water  which  can  be  driven  off  by  a  moderate  temperature  (212° 
Fahr.)  from  the  different  fluids  and  tissues  of  the  body  vary  of  course  very  consider- 
ably, according  to  the  consistence  of  the  parts.  The  following  is  a  list  of  the  quantities 
in  the  most  important  fluids  and  solids : 

Table  of  Quantities  of  Water. 

Parts  per  1,000. 

In  Enamel  of  the  teeth 2 

"  Epithelial  desquamation 37 

"  Teeth 100 

"Bones 130 

"  Tendons  (Burdach) 500 

"  Articular  cartilages 550 

"  Skin  (Weinholt) 575 

"  Liver  (Frommherz  and  Gugert) 618 

"  Muscles  of  man  (Bibra) 725 

"  Ligaments  (Chevreul) 768 

"  Mean  of  blood  of  man  (Becquerel  and  Rodier) 780 

"  Milk  of  human  female  (Simon) 887 

"  Chyle  of  man  (Rees) 904 

"  Bile 905 

"  Urine 933 

g,  -j      "  Human  lymph  (Tiedemann  and  Gmelin) 960 

"  Human  saliva  (Mitscherlich) '. 983 

"  Gastric  juice 984 

"  Perspiration 986 

"  Tears 990 

"  Pulmonary  vapor 997 

Function  of  Water. — After  what  has  been  stated  respecting  the  condition  in  which 
water  exists  in  the  body,  there  remains  but  little  to  say  concerning  its  function.  As  a 
constituent  of  organized  tissues,  it  gives  to  cartilage  its  elasticity,  to  tendons  their  plia- 
bility and  toughness ;  it  is  necessary  to  the  peculiar  power  of  resistance  of  the  bones ; 
and,  as  we  have  already  seen,  it  is  essential  to  the  proper  consistence  of  all  parts  of  the 
body.  It  has  other  important  functions  as  a  solvent.  Soluble  articles  of  food  are  intro- 
duced in  solution  in  water.  The  excrementitious  matters,  which  are  generally  soluble  in 
water,  are  dissolved  by  it  in  the  blood,  are  carried  to  the  organs  of  excretion,  and  are  dis- 
charged in  a  watery  solution  from  the  body. 


492  NUTRITION. 

Origin  and  Discharge  of  Water.— It  is  evident  that  a  great  proportion  of  the  water  in 
the  organism  is  introduced  from  without,  in  the  fluids  and  in  the  watery  constituents  of  all 
kinds  of  food ;  but  the  theoretical' views  of  some  physiologists  with  regard  to  the  hydro- 
carbons and  their  combustion  have  led  to  the  supposition  that  water  is  also  formed  in  the 
body  by  a  direct  union  of  oxygen  and  hydrogen.  The  true  way  of  determining  this  point 
is  to  estimate  all  the  water  introduced  into  the  organism,  and  then  to  compare  this  quan- 
tity with  that  which  is  discharged.  The  latter  estimate,  however,  presents  very  great 
difficulties.  As  water  is  continually  given  off  in  the  form  of  vapor  from  the  skin  and  in 
the  expired  air,  the  quantities  thus  discharged  are  subject  to  great  variations,  dependent 
upon  exercise,  temperature,  the  state  of  the  atmosphere,  etc.,  and  even  if  constant  they 
could  be  estimated  with  great  difficulty.  Experiments  upon  this  point  have  been  under- 
taken by  Sanctorius,  Barral,  Boussingault,  and  others,  but  they  are  not  sufficiently  com- 
plete to  settle  the  question. 

In  the  present  state  of  our  knowledge,  we  can  only  say  that  water  is  introduced  with 
the  fluid  and  solid  elements  of  food  by  the  stomach,  and  that  it  escapes  by  the  urine, 
faeces,  lungs,  and  skin.  There  is  no  direct  evidence  that  water  is  produced  de  now  in  the 
interior  of  the  body.  In  the  issue  of  water  by  the  kidneys  and  skin,  it  has  long  been 
observed  that,  in  point  of  activity,  these  two  emunctories  bear  a  certain  relation  to  each 
other.  When  the  skin  is  inactive,  as  in  cold  weather,  the  kidneys  discharge  a  large  quan- 
tity of  water ;  and,  when  the  skin  is  active,  the  quantity  of  water  discharged  by  the  kid- 
neys is  diminished.  Certain  therapeutical  agents,  also,  can  be  made  to  act  as  diapho- 
retics, by  combining  other  measures  which  favor  cutaneous  action,  or  as  diuretics,  by 
employing  measures  to  diminish  the  action  of  the  skin. 

Chloride  of  Sodium. — Chloride  of  sodium  is  next  in  importance,  as  an  inorganic 
proximate  principle,  to  water.  It  is  found  in  the  body  at  all  periods  of  life,  existing,  like 
water,  in  the  ovum.  It  exists  in  all  the  fluids  and  solids  of  the  body,  with  the  single 
exception  of  the  enamel  of  the  teeth.  In  the  fluids,  it  seems  to  be  simply  in  a  state  of 
solution,  and  it  can  be  recognized  by  the  ordinary  tests.  In  this  respect  we  may  class 
together  the  chlorides  of  sodium  and  potassium. 

The  quantity  of  chloride  of  sodium  in  the  entire  body  has  never  been  estimated ;  nor, 
indeed,  has  any  accurate  estimate  been  made  of  the  quantity  contained  in  the  various 
tissues,  for  all  the  chlorides  are  generally  estimated  together.  It  exists  in  greatest  pro- 
portion in  the  fluids,  giving  to  some  of  them,  as  the  tears  and  perspiration,  a  distinctly 
saline  taste.  The  following  table  gives  an  idea  of  the  quantities  which  have  been  found 
in  some  of  the  most  important  of  the  fluids  and  solids : 

Table  of  Quantities  of  Chloride  of  Sodium. 

Parts  per  1,000. 

In  Blood,  human  (Lehmann) 4*210 

"  Chyle  (Lehmann) 5*310 

"  Lymph  (Nasse) 4-120 

"  Milk,  human  (Lehmann) 0-870 

"  Saliva,  human  (Lehmann) 1-530 

"  Perspiration,  human  (mean  of  three  analyses,  Piutti) 3 '433 

"  Urine  (maximum)  }  C 7-280 

"     (mean)         >  Valentin.  < 4'610 

"     (minimum)  )  ( 2'400 

"  Faecal  matters  (Berzelius) 3-010 

Function  of  Chloride  of  Sodium. — The  function  of  this  principle  is  undoubtedly  im- 
portant, but  it  is  not  yet  fully  understood.  It  does  not  seem  to  enter  into  the  substance 
of  the  organized  solids  and  semisolids  as  an  important  and  essential  element,  but  apparent- 


INORGANIC  PRINCIPLES.  493 

ly  it  exercises  its  chief  function  in  the  fluids.  It  certainly  determines,  to  a  great  extent, 
the  quantities  of  exudations,  regulates  absorption,  and  serves  to  maintain  the  albuminoids, 
especially  those  contained  in  the  blood,  in  a  state  of  fluidity.  Albumen  is  coagulated  by 
heat  with  much  greater  difficulty  in  a  solution  of  chloride  of  sodium  than  when  mixed 
with  pure  water.  A  strong  solution  of  common  salt  is  capable  of  dissolving  caseine  or 
of  preventing  the  formation  of  fibrin.  We  have  already  alluded  to  the  fact  that  it  is 
the  chloride  of  sodium  particularly  which  regulates  the  quantity  of  water  entering  into 
the  composition  of  the  blood-corpuscles,  thereby  preserving  their  form  and  consistence ; 
and  that  it  seems  to  perform  an  analogous  function  with  regard  to  the  other  semi- 
solids  of  the  body.  As  to  the  general  function  of  this  substance,  the  following  proposi- 
tion of  Liebig  is  adopted  by  Robin  and  Verdeil,  and  a  little  reflection  will  show  that  it 
is  sustained,  as  far  as  we  know,  by  the  facts : 

"  Common  salt  is  intermediate  in  certain  general  processes,  and  does  not  participate 
by  its  elements  in  the  formation  of  organs." 

In  the  first  place,  the  fluids  of  the  body  are  generally  intermediate  in  their  functions, 
containing  nutritious  elements,  which  are  destined  to  be  appropriated  by  the  tissues  and 
organs,  and  worn-out  elements,  which  are  to  be  separated  from  the  body.  In  the  blood 
and  chyle,  chloride  of  sodium  is  found  in  greatest  abundance.  As  the  nutrition  of  organs 
occurs,  which  consists  in  the  fixation  of  new  proximate  principles,  chloride  of  sodium  is 
not  deposited  in  any  considerably  quantity,  but  it  seems  to  regulate  the  general  process,  at 
least  to  a  certain  extent.  In  all  civilized  countries,  salt  is  used  extensively  as  a  condi- 
ment, and  it  undoubtedly  facilitates  digestion  by  rendering  the  food  more  savory  and 
increasing  the  flow  of  the  digestive  fluids ;  here,  likewise,  acting  simply  as  an  interme- 
diate agent.  There  is  nothing  more  general  among  men  and  animals  than  this  desire  for 
common  salt.  The  carnivora  crave  it  and  obtain  it  in  the  blood  of  animals ;  the  her- 
bivora  frequent  "  salt  licks  "  and  places  where  it  is  found,  and  relish  it  when  mixed  with 
their  food;  and  by  man  its  use  is  almost  universal.  In  the  domestic  herbivora,  the 
effect  of  a  deprivation  of  this  article  is  very  marked  and  has  been  made  the  subject  of 
some  very  interesting  experiments,  by  Boussingault.  This  observer  experimented  upon 
two  lots  of  bullocks,  of  three  each,  all  of  them,  at  the  time  the  observations  were  com- 
menced, being  perfectly  healthy  and  in  fine  condition.  One  of  these  lots  he  deprived 
entirely  of  salt,  except  what  was  contained  in  their  fodder,  while  the  other  was  sup- 
plied with  the  usual  quantity.  No  marked  difference  in  the  two  lots  was  noticed  until 
between  five  and  six  months,  when  the  difference  in  general  appearance  was  very  distinct. 
The  animals  receiving  salt  retained  their  fine  appearance,  while  the  others,  though  not 
diminished  in  flesh,  were  not  so  sleek  and  fine.  At  the  end  of  a  year  the  difference  was 
very  marked.  The  hides  of  those  which  had  been  deprived  of  salt  were  rough  and  ragged, 
and  their  appearance,  listless  and  inanimate,  contrasting  strongly  with  the  sleek  appearance 
and  vivacious  disposition  of  the  others.  The  experiments  of  Boussingault  are  the  most 
conclusive  that  have  ever  been  instituted  with  regard  to  the  influence  of  chloride  of  sodium 
upon  nutrition.  They  indicate  a  certain  deficiency  in  the  nutrition  of  animals  deprived 
of  it,  but  not  any  considerable  loss  of  weight.  Before  these  observations  were  made, 
Dailly  made  analogous  experiments  upon  twenty  sheep,  which  were  continued  for  three 
months.  At  the  end  of  that  time,  the  lot  which  received  salt  presented  a  considerable 
excess  of  weight  (about  22|  Ibs.)  over  the  others. 

It  is  a  significant  fact  that  the  quantity  of  chloride  of  sodium  existing  in  the 
blood  is  not  subject  to  variation,  but  that  an  excess  introduced  with  the  food  is  thrown 
off  by  the  kidneys.  The  quantity  in  the  urine,  then,  bears  a  relation  to  the  amount 
introduced  as  food,  but  the  proportion  in  the  blood  is  constant.  This  is  another 
fact  in  favor  of  the  view  that  the  presence  of  a  definite  quantity  of  common  salt  in 
the  circulating  fluid  is  essential  to  the  proper  performance  of  the  general  function  of 
nutrition. 

Origin  and  Discharge  of  Chloride  of  Sodium. — This  substance  is  always  introduced 


494  NUTRITION. 

with  food  in  the  condition  in  which  it  is  found  in  the  body.  It  is  contained  in  the  sub- 
stance of  all  kinds  of  food,  animal  and  vegetable  ;  but,  in  the  herbivora  and  in  man,  this 
source  is  not  sufficient  to  supply  the  wants  of  the  system,  and  it  is  introduced,  therefore, 
as  salt.  The  quantity  which  is  discharged  from  the  body  has  been  estimated  by  Barral 
to  be  somewhat  less  than  the  quantity  introduced,  about  one-fifth  disappearing ;  but 
these  estimates  are  not  exactly  accurate,  for  the  amount  thrown  off  in  the  perspiration  has 
never  been  directly  ascertained.  It  exists  in  the  blood  in  connection  with  the  phosphate 
of  potassa,  and  a  certain  amount  is  lost  in  a  double  decomposition  which  takes  place 
between  these  two  salts,  resulting  in  the  formation  of  chloride  of  potassium  and  phos- 
phate of  soda.  It  also  is  supposed  to  furnish  the  soda  to  all  the  salts  which  have  a  soda 
base,  and  a  certain  quantity,  therefore,  disappears  in  this  way. 

Existing,  as  it  does,  in  all  the  solids  and  fluids  of  the  body,  chloride  of  sodium  is 
discharged  in  all  the  excretions,  being  thrown  off  in  the  urine,  faeces,  perspiration, 
and  mucus. 

Chloride  of  Potassium. — Chloride  of  potassium,  although  neither  so  important  a  proxi- 
mate principle  as  the  chloride  of  sodium  nor  so  generally  distributed  in  the  economy, 
seems  to  have  an  analogous  function.  It  is  found  in  the  muscles,  liver,  milk,  chyle,  blood, 
mucus,  saliva,  bile,  gastric  juice,  cephalo-rachidian  fluid,  and  urine.  It  is  exceedingly 
soluble,  and  in  these  situations  it  exists  in  solution  in  the  fluids.  Its  quantity  in  these 
situations  has  not  been  accurately  ascertained,  as  it  has  generally  been  estimated  in 
connection  with  the  chloride  of  sodium.  In  the  muscles,  it  exists,  however,  in  a  larger 
proportion  than  common  salt.  In  cow's  milk,  Berzelius  has  found  1'7  part  per  1,000; 
Pfaff  and  Schwartz,  1-35  per  1,000  in  cow's  milk,  and  0*3  per  1,000  in  human  milk. 
Of  the  function  of  this  principle,  little  remains  to  be  said  after  what  has  been  stated 
with  regard  to  the  chloride  of  sodium.  The  functions  of  these  two  principles  are  prob- 
ably identical,  although  the  latter,  from  its  greater  quantity  in  the  fluids  and  its  univer- 
sal distribution,  is  by  far  the  more  important. 

Origin  and  Discharge  of  Chloride  of  Potassium. — This  substance  has  two  sources ; 
one  in  the  food,  existing,  as  it  does,  in  muscular  tissue,  milk,  etc.,  and  the  other  in  a 
chemical  reaction  between  the  phosphate  of  potassa  and  the  chloride  of  sodium,  forming 
the  chloride  of  potassium  and  the  phosphate  of  soda.  That  this  decomposition  takes 
place  in  the  body,  is  evident  from  the  fact  that  the  ingestion  of  a  considerable  quantity 
of  common  salt  has  been  found,  in  the  sheep,  to  increase  the  quantity  of  chloride 
of  potassium  in  the  urine,  without  having  any  influence  upon  the  amount  of  chloride 
of  sodium.  The  chloride  of  potassium  is  discharged  from  the  body  in  the  urine  and 
mucus. 

Phosphate  of  Lime.— This  salt  is  found  in  all  the  solids  and  fluids  of  the  body.  As  it 
is  always  united,  in  the  solids,  with  organic  substances  as  an  important  element  of  consti- 
tution, it  is  hardly  second  in  importance  to  water.  It  differs  in  its  functions  so  essen- 
tially from  the  chlorides  of  sodium  and  potassium,  that  they  are  hardly  to  be  compared. 
It  is  insoluble  in  water,  but  is  held  in  solution  in  the  fluids  of  the  body  by  virtue  of  free 
carbonic  acid,  the  bicarbonates,  and  the  chloride  of  sodium.  In  the  solids  and  semi- 
solids,  the  condition  of  its  existence  is  the  same  as  that  of  water ;  i.  e.  it  is  incorporated, 
particle  to  particle,  with  the  organic  substance  characteristic  of  the  tissue  and  is  one 
of  its  essential  elements  of  composition,  and  cannot  be  completely  separated  without 
incineration.  Nothing  need  be  added  here  with  regard  to  this  mode  of  union  in  the 
body  of  organic  and  inorganic  substances,  after  what  has  been  said  under  the  head  of 
water. 

The  following  table  gives  the  relative  quantities  of  phosphate  of  lime  in  various  situa- 
tions : 


INOKGANIC  PKINCIPLES.  495 

Table  of  Quantities  of  Phosphate  of  Lime. 

Parts  per  1,000. 

In  Arterial  blood,  )pialeandMarcha]< 0*79 

"  Venous  blood,   f  \ 0*76 

"  Milk,  human  (Pfaff  and  Schwartz) 2*50 

"  Saliva  (Wright) 0*60 

"  Urine,  proportion  to  weight  of  ash  (Fleitmann) 25*70 

"  Excrements  (Berzeiius) 40*00 

"  Bone  (Lassaigne) 400'00 

"  Vertebra  of  a  rachitic  patient  (Bostock) 136*00 

"  Teeth  of  an  infant  one  day  old  ^  ( 510-00 

"  Teeth  of  adult I  .         I    610-00 

<-  Teeth,  at  eighty-one  years. .    |  1    660*00 

"  Enamel  of  the  teeth J  I 885*00 

By  this  table  it  is  seen  that  the  phosphate  of  lime  exists  in  very  small  quantity  in  the 
fluids  but  is  abundant  in  the  solids.  In  the  latter,  the  quantity  is  in  proportion  to  the 
hardness  of  the  structure,  the  quantity  in  enamel  being,  for  example,  more  than  twice 
that  in  bone.  The  variations  in  quantity  with  age  are  very  considerable.  In  the  teeth 
of  an  infant  one  day  old,  Lassaigne  found  510  parts  per  1,000 ;  in  the  teeth  of  an  adult, 
610  parts ;  and  in  the  teeth  of  an  old  man  of  eighty-one  years,  660  parts.  This  increase 
in  the  calcareous  elements  of  the  bones,  teeth,  etc.,  in  old  age  is  very  marked;  and  in 
extreme  old  age  they  are  deposited  in  considerable  quantity  in  situations  where  there 
existed  but  a  small  proportion  in  adult  life.  The  system  seems  to  gradually  lose  the 
property  of  appropriating  to  itself  organic  matters ;  and,  although  articles  of  food  are 
digested  as  well  as  ever,  the  power  of  assimilation  by  the  tissues  is  diminished.  The  bones 
become  brittle,  and  fractures,  therefore,  are  common  at  this  period  of  life,  when  disloca- 
tions are  almost  unknown.  Inasmuch  as  the  real  efficiency  of  organs  depends  upon  organic 
matters,  the  system  actually  wears  out,  and  this  progressive  change  finally  unfits  the 
various  parts  for  the  performance  of  their  functions.  An  individual,  if  he  escape  acci- 
dents and  die,  as  we  term  it,  of  old  age,  passes  away  thus  by  a  simple  wearing  out  of  his 
organism. 

Function  of  Phosphate  of  Lime. — This  substance,  as  before  remarked,  enters  largely 
into  the  constitution  of  the  solids  of  the  body.  In  the  bones  its  function  is  most  appar- 
ent. Its  existence,  in  suitable  proportion,  is  necessary  to  the  mechanical  office  of  these 
parts,  giving  them  their  power  of  resistance,  without  rendering  them  too  brittle.  It  is 
more  abundant  in  the  bones  of  the  lower  extremities,  which  have  to  sustain  the  weight 
of  the  body,  than  in  those  of  the  upper  extremities ;  and  in  the  ribs,  which  are  elastic 
rather  than  resisting,  it  exists  in  less  quantity  than  in  the  bones  of  the  arm. 

The  necessity  of  a  proper  proportion  of  phosphate  of  lime  in  the  bones  is  made  evi- 
dent by  cases  of  disease.  In  rachitis,  where,  as  is  seen  by  the  table,  its  quantity  is  very 
much  diminished,  the  bones  are  unable  to  sustain  the  weight  of  the  body,  and  they  become 
deformed ;  and  finally,  when  the  phosphate  of  lime  is  deposited,  they  retain  their  distorted 
shape.  The  phosphate  of  lime  may  be  extracted  from  the  bones  by  maceration  in  dilute 
hydrochloric  acid,  which  dissolves  it,  leaving  only  the  organic  substance.  Bones  treated 
in  this  way,  although  they  retain  their  form,  become  very  pliable ;  and  a  long  slender 
bone,  like  the  fibula,  may  be  actually  tied  into  a  knot. 

Origin  and  Discharge  of  Phosphate  of  Lime. — The  origin  of  this  principle  is  exclu- 
sively from  the  external  world.  It  enters  into  the  constitution  of  our  food  and  is  dis- 
charged in  the  faeces,  urine,  and  other  matters  thrown  off  by  the  body.  Its  quantity 
in  the  urine  is  exceedingly  variable.  Lecanu  found  from  0'437  to  29*250  grains  thrown 
off  by  the  kidneys  during  the  twenty-four  hours. 

Carbonate  of  Lime. — This  principle  exists  in  the  bones,  teeth,  cartilage,  internal  ear, 


496  NUTRITION. 

blood,  sebaceous  matter,  and  sometimes  in  the  urine.  It  exists  as  a  normal  constituent  in 
the  urine  of  some  herbivora,  but  not  in  the  carnivora  or  in  man.  It  is  most  appro- 
priately considered  immediately  after  the  phosphate  of  lime,  because  it  is  the  salt  next 
in  importance  in  the  constitution  of  the  bones  and  teeth.  In  these  structures  it  exists 
intimately  combined  with  the  organic  matter,  under  the  same  conditions  as  the  phos- 
phates, and  it  has  analogous  functions.  In  the  fluids  it  exists  in  small  quantity  and  is  held 
in  solution  by  virtue  of  free  carbonic  acid  and  the  chloride  of  potassium. 

The  carbonate  of  lime  is  the  only  example  of  an  inorganic  proximate  principle  exist- 
ing uncombined  and  in  a  crystalline  form  in  the  body.  In  the  internal  ear  it  is  found  in 
this  form  and  has  some  function  connected  with  audition. 

Table  of  Quantities  of  Carbonate  of  Lime. 

Parts  per  1,000. 

In  Bone,  human  (Berzelius) 1 1 3'00 

"      "  «        (Marchand) 102-00 

"      "  "        (Lassaigne) 76'00 

"  Teeth  of  an  infant  one  day  old \  ( 140'00 

"  Teeth  of  an  adult V  Lassaigne  < 100-00 

"  Teeth  of  an  old  man,  eighty-one  years  1  ( 10*00 

"  Urine  of  the  horse  (Boussingault) 10'82 

Origin  and  Discharge  of  Carbonate  of  Lime. — Carbonate  of  lime  is  introduced  into 
the  body  with  our  food,  held  in  solution  in  water  by  the  carbonic  acid  which  is  always 
present  in  small  quantity.  It  is  also  formed  in  the  body,  particularly  in  the  herbivora, 
by  a  decomposition  of  the  tartrates,  malates,  citrates,  and  acetates  of  lime  contained  in 
the  food.  These  salts,  meeting  with  carbonic  acid,  are  decomposed,  and  the  carbonate 
of  lime  is  formed.  It  is  probable  that,  in  the  human  subject,  some  of  it  is  changed  into 
the  phosphate  of  lime,  and  in  this  form  is  discharged  in  the  urine  ;  but  when  and  how 
this  change  takes  place  has  not  been  definitely  ascertained. 

Carbonate  of  Soda. — This  salt  is  found  in  the  blood  and  saliva,  giving  to  these  fluids 
their  alkalinity ;  in  the  urine  of  the  human  subject,  when  it  is  alkaline  without  being 
ammoniacal ;  in  the  urine  of  the  herbivora ;  and  in  the  lymph,  cephalo-rachidian  fluid,  and 
in  bone.  The  analyses  of  chemists  with  regard  to  this  substance  are  very  contradictory,  on 
account  of  its  formation  during  the  process  of  incineration;  but  there  is  no  doubt  that  it 
is  found  in  the  above  situations.  The  following  table  gives  the  quantities  which  have 
been  found  in  some  of  the  fluids  and  solids  : 

Table  of  Quantities  of  Carbonate  of  Soda. 

Parts  per  1,000. 

In  Blood  of  the  ox  (Marcet) 1'62 

"  Lymph  (Nasse) 0'56 

"  Cephalo-rachidian  fluid  (Lassaigne) 0'60 

"  Compact  tissue  of  the  tibia  in  a  male  of  38  years  (Valentin) 2*00 

"  Spongy  tissue  of  the  same  (Valentin) 0'70 

Function  of  Carbonate  of  Soda. — This  substance  has  a  tendency  to  maintain  the 
fluidity  of  the  albuminoid  constituents  of  the  blood,  and  it  assists  in  preserving  the  form 
and  consistence  of  the  blood-corpuscles.  Its  function  in  nutrition  is  rather  accessory, 
like  that  of  chloride  of  sodium,  than  essential,  like  the  phosphate  of  lime,  in  the  con- 
stitution of  certain  structures. 

Origin  and  Discharge  of  Carbonate  of  Soda.— This  substance  is  not  introduced  into 
the  body  as  carbonate  of  soda,  but  it  is  formed,  as  is  the  carbonate  of  lime  in  part,  by  a 
decomposition  of  the  malates,  tartrates,  etc.,  which  exist  in  fruits.  It  is  discharged  occa- 
sionally in  the  urine  of  the  human  subject,  and  a  great  part  of  it  is  decomposed  in  the 


INORGANIC  PRINCIPLES.  497 

lungs  by  the  action  of  pneumic  acid,  setting  free  carbonic  acid,  which  is  discharged  in 
the  expired  air. 

Carbonate  of  Potassa. — This  salt  exists  particularly  in  herbivorous  animals.  It  is 
found  in  the  human  subject  when  subjected  to  a  vegetable  diet.  Under  the  heads  of  func- 
tion, origin,  and  discharge,  what  has  been  said  with  regard  to  the  carbonate  of  soda  will 
apply  to  the  carbonate  of  potassa. 

Carbonate  of  Magnesia  and  Bicarbonate  of  Soda. — It  is  most  convenient  to  take  up 
these  two  salts  in  connection  with  the  other  carbonates,  though  they  are  put  at  the  end 
of  the  list  of  inorganic  substances  as  the  least  important.  "We  know  very  little  about 
them,  chemically  or  physiologically.  Traces  of  carbonate  of  magnesia  have  been  found 
in  the  blood  of  man,  and  it  exists  normally  in  considerable  quantity  in  the  urine  of 
herbivora.  In  the  human  subject  it  is  discharged  in  the  sebaceous  matter. 

Liebig  has  merely  indicated  the  presence  of  bicarbonate  of  soda  in  the  blood. 

Phosphate  of  Magnesia,  Phosphate  of  Soda  (neutral),  and  Phosphate  of  Potassa. — These 
salts  are  found  in  all  the  fluids  and  solidg  of  the  body,  though  not  existing  in  a  very  large 
proportion,  as  compared  with  the  phosphate  of  lime,  which  we  have  already  considered. 
In  their  relations  to  organized  structures,  they  are  analogous  to  the  phosphate  of  lime, 
entering  into  the  composition  of  the  tissues,  and  existing  there  in  a  state  of  intimate 
combination.  They  are  all  taken  into  the  body  with  food,  especially  by  the  carnivora,  in 
the  fluids  of  which  they  are  found  in  much  greater  abundance  than  the  carbonates ; 
which  latter,  as  we  have  already  seen,  are  in  great  part  the  result  of  the  decomposition 
by  carbonic  acid  of  the  malates,  tartrates,  oxalates,  etc.  With  respect  to  their  functions, 
we  can  only  say  that,  with  the  phosphate  of  lime,  they  go  to  form  the  organized  struct- 
ures of  which  they  are  necessary  constituents.  They  are  discharged  from  the  body  in 
the  urine  and  faeces. 

Sulphate  of  Soda,  Sulphate  of  Potassa,  and  Sulphate  of  Lime.— The  sulphate  of  soda 
and  the  sulphate  of  potassa  are  identical  in  their  situation,  and  apparently  in  their  func- 
tions. They  are  found  in  all  the  fluids  and  solids  of  the  body,  except  in  the  milk,  bile,  and 
gastric  juice.  Their  origin  in  the  body  is  from  the  food,  in  which  they  are  contained  in 
small  quantity,  and  they  are  discharged  in  the  urine.  Their  chief  function  appears  to  be 
in  the  blood,  where  they  tend  to  preserve  the  fluidity  of  the  albuminoid  matters  and  the 
form  and  consistence  of  the  blood-corpuscles.  The  sulphate  of  lime  is  found  in  the  blood 
and  faeces.  It  is  introduced  into  the  body  in  solution  in  the  water  which  is  used  as  drink, 
and  it  is  discharged  in  the  faeces.  Its  function  is  not  understood  and  is  probably  not  very 
important. 

Hydrochlorate  of  Ammonia. — This  substance  has  simply  been  indicated  by  chemists 
as  existing  in  the  gastric  juice  of  ruminants,  the  saliva,  tears,  and  urine.  Some  chemists 
make  a  rearrangement  of  its  atoms,  calling  it  chloride  of  ammonium.  It  is  discharged  in 
the  urine,  in  which  it  exists,  according  to  Simon,  in  the  proportion  of  0'41  part  per  1,000. 
Its  origin  and  function  are  unknown.  Various  combinations  of  bases  with  organic  acids 
taken  as  food,  as  the  acetates,  tartrates,  etc.,  found  in  fruits,  undergo  decomposition  in 
the  body  and  are  transformed  into  carbonates.  In  this  form  they  behave  precisely  like 
the  other  inorganic  salts. 

Principles  consumed  by  the   Organism. 

All  of  the  assimilable  organic  matter  taken  as  food  is  consumed  in  the  organism,  and 
none  is  ever  discharged  from  the  body,  in  health,  in  the  form  under  which  it  was  intro- 
duced.    The  principles  thus  consumed  in  nutrition  have  been  divided  into  nitrogenized 
32 


498  NUTRITION. 

and  non-nitrogenized;  and,  although  they  both  disappear  in  the  organism,  they  possess 
certain  marked  differences  in  their  properties,  and  probably,  also,  in  their  relations  to 
nutrition. 

Nitrogenized  Principles.- -The  nitrogenized  principles,  having  for  their  basis,  carbon, 
hydrogen,  nitrogen,  and  oxygen,  undergo,  in  the  process  of  digestion  and  absorp- 
tion, remarkable  changes ;  but  these  are  more  marked  as  regards  their  properties  than 
their  ultimate  chemical  composition.  They  are  all  converted  into  the  nitrogenized  ele- 
ments of  the  blood,  which,  in  their  turn,  are  transformed  into  the  characteristic  nitro- 
genized principles  of  the  different  tissues,  and  are  appropriated  by  these  tissues,  to  sup- 
ply the  place  of  worn-out  matter.  With  the  intimate  nature  of  this  series  of  transfor- 
mations, we  are  entirely  unacquainted;  but  we  know  that  the  deposition  of  new 
nitrogenized  matter  in  the  tissues,  constituting  one  of  the  most  important  of  the  acts  of 
nutrition,  is  attended  with  a  corresponding  loss  of  matter  that  has  become  changed  into 
the  nitrogenized  elements  of  excretion.  It  is  the  intermediate  series  of  phenomena  that 
is  so  obscure. 

The  nutrition  of  the  nitrogenized  elements  of  the  tissues  may  be  greatly  modified  by 
the  supply  of  new  matter.  For  example,  a  diet  composed  of  nitrogenized  matter  in  a 
readily  assimilable  form  will  undoubtedly  affect  favorably  the  development  of  the  corre- 
sponding tissues  of  the  body ;  and,  on  the  other  hand,  a  deficiency  in  the  supply  will  pro- 
duce a  corresponding  diminution  in  power  and  development.  The  modifications  in  nutri- 
tion due  to  supply  have,  however,  certain  well-defined  limits.  An  excess  taken  as  food 
is  not  discharged  in  the  faeces,  nor  does  it  pass  out  in  the  form  in  which  it  entered,  in 
the  urine ;  but  it  apparently  undergoes  digestion,  becomes  absorbed  by  the  blood,  and 
increases  the  quantity  of  uitrogenized  excrementitious  matter  discharged,  particularly 
the  urea.  This  fact  is  shown  by  the  great  increase  in  the  elimination  of  urea  produced 
by  an  excess  of  nitrogenized  food.  Whether  the  nitrogenized  matter  that  is  not  actually 
needed  in  nutrition  be  changed  into  urea  in  the  blood,  or  whether  it  be  appropriated  by 
the  tissues,  increasing  the  activity  of  their  disassimilation,  is  a  question  difficult  to  deter- 
mine experimentally.  Certain  it  is,  however,  that  an  excess  of  nitrogenized  food  is 
thrown  off  in  nearly  the  same  way  as  an  excess  of  inorganic  matter ;  the  difference  being 
that  the  latter  passes  out  in  the  form  in  which  it  has  entered,  and  the  former  is  discharged 
in  the  form  of  nitrogenized  excrementitious  matter. 

Development  of  Power  and  Endurance  ly  Exercise  and  Diet  (Training). — The  nutrition 
of  the  nitrogenized  elements  of  the  body  is  greatly  influenced  by  functional  exercise. 
This  is  partly  local  and  partly  general  in  its  effects.  For  example,  by  the  persistent 
exercise  of  particular  muscles,  their  development  can  be  carried  to  a  high  degree  of  per- 
fection, the  rest  of  the  muscular  system  undergoing  no  change ;  or  the  entire  muscular 
system  may,  by  appropriate  general  exercise,  be  made  to  increase  considerably  in  volume, 
and  a  person  may  become  capable  of  great  endurance,  under  an  ordinary  diet.  It  is  sur- 
prising, sometimes,  to  see  how  small  an  amount  of  well-regulated  exercise  will  accomplish 
this  end.  But,  if  it  be  desired  to  attain  the  maximum  of  strength  and  endurance,  it  is 
necessary  to  carefully  regulate  the  diet  as  well  as  the  exercise.  Those  who  are  in  the 
habit  of  "  training "  men,  particularly  for  pugilistic  encounters,  have  long-since  demon- 
strated practically  certain  facts  which  physiologists  have  been  rather  slow  to  appreciate. 
By  carefully  regulating  the  diet,  confining  it  chiefly  to  nitrogenized  articles,  eliminating 
fat  entirely,  and  reducing  the  starchy  elements  to  the  minimum  ;  by  regulating  the  exer- 
cise so  as  to  increase  the  nutritive  activity  of  all  the  muscles  to  the  greatest  possible 
extent ;  by  increasing  the  respiratory  activity  by  running,  etc.,  and  removing  from  the 
body  all  the  unnecessary  adipose  tissue  ;  by  all  these  means,  which  favor  nutritive  assimi- 
lation by  the  nitrogenized  elements  of  the  organism,  a  man  may  be  "  trained  "  so  as  to  be 
capable  of  immense  muscular  effort  and  endurance. 


PRINCIPLES   CONSUMED  BY  THE  ORGANISM.  499 

The  process  of  training,  skilfully  carried  out,  is  in  accordance,  with  what  are  now 
admitted  as  physiological  laws;  although  it  has  been  practised  for  years  by  ignorant 
persons,  and  its  rules  are  entirely  empirical.  It  is  stated  that  the  athletes  of  ancient 
times,  while  vigorously  exercising  the  muscles,  favored  by  their  diet  the  development  of 
fat,  so  as  to  be  better  able  to  resist  the  blows  of  their  antagonists.  However  this  may 
be,  since  the  English  prize-ring  has  been  regularly  organized,  or  since  about  the  middle 
of  the  last  century,  the  system  of  training  has  been  entirely  different,  and  fat  has  been, 
as  far  as  possible,  removed  from  every  part  of  the  body.  Fat  is  regarded  by  trainers  as 
inert  matter;  and  they  recognize,  practically  at  least,  the  fact  that  the  characteristic 
functions  of  parts  depend  for  their  activity  upon  their  nitrogenized  constituents.  The 
contraction  of  a  muscle,  for  example,  is  powerful  in  proportion  to  the  amount  and  condi- 
tion of  its  musculine ;  and  it  has  been  ascertained  by  experience  that  the  muscular  sys- 
tem can  be  most  thoroughly  developed  by  carefully-graduated  exercise  and  a  diet  com- 
posed largely  of  nitrogenized  matter.  In  the  regular  system  of  training,  starch,  sugar,  fat, 
and  liquids  are  avoided  ;  and  the  diet  is  confined  almost  entirely  to  rare  meats,  eggs,  and 
stale  bread  or  toast,  with  oatmeal-gruel.  The  oatmeal  has  been  used  from  time  immemo- 
rial, and  it  is  supposed  to  be  useful  in  keeping  the  bowels  in  good  condition.  A  very 
small  amount  of  alcohol  and  of  other  nervous  stimulants,  chiefly  in  the  form  of  home- 
brewed ale,  sherry  win£,  and  tea,  is  allowed.  Sexual  intercourse  and  all  unusual  nervous 
excitement  are  interdicted. 

Those  who  adopt  absolutely  the  classification  of  food  into  plastic,  or  tissue-forming, 
and  calorific,  or  respiratory,  would  regard  this  course  of  diet  as  eminently  plastic ;  but, 
during  the  severe  habitual  exercise,  which  is  most  rigid  after  the  man  has  been  "  trained 
down"  so  that  his  fat  is  reduced  to  the  minimum,  the  respiratory  power  and  the  exhala- 
tion of  carbonic  acid  are  immensely  increased,  while  the  proportion  of  hydro-carbons  in 
the  food  is  very  small. 

We  do  not  propose  to  discuss  from  a  scientific  point  of  view  all  of  the  minutiae 
of  training.  Many  of  its  traditional  rules  are  trivial  and  unimportant ;  but  it  is  certainly 
a  question  of  great  physiological  interest  to  study  the  processes  by  which  the  muscular 
strength  and  endurance  of  a  man  may  be  brought  to  the  highest  possible  point  of 
development. 

One  of  the  most  remarkable  of  the  results  of  thorough  training  is  the  development  of 
immense  endurance  and  "  wind."  This  is  accomplished  by  running  and  prolonged  exer- 
cise, not  so  violent  as  to  be  exhausting,  and  always  followed  by  ablutions  and  frictions, 
so  as  to  secure  a  full  reaction.  The  surprising  faculty  of  endurance  thus  developed  must 
be  due  in  a  great  measure  to  nervous  power  as  well  as  to  a  gradual,  careful,  and  perfectly 
physiological  development  of  the  muscular  system.  A  man  may  be  brought  into  the  ring 
in  what  would  appear  to  be  perfect  condition ;  but,  if  he  be  trained  down  too  much  or 
too  rapidly,  he  is  liable  to  give  out  after  comparatively  slight  exertion.  A  man  who  does 
not  possess  the  required  constitutional  stamina  and  nervous  power  is  likely  to  break  down 
in  training,  and  he  cannot  be  brought  to  proper  condition.  On  the  other  hand,  a  man  in 
perfect  condition  is  capable  of  the  maximum  of  muscular  exertion  for  an  hour,  or  can 
easily  walk  a  hundred  miles  in  a  day. 

It  is  a  question  of  great  importance,  in  connection  with  the  subject  of  nutrition,  to 
determine  whether  the  extraordinary  muscular  power  developed  by  severe  training  be, 
in  the  end,  beneficial  or  deleterious.  This  can  be  answered  very  easily  upon  practical  as 
well  as  theoretical  grounds.  A  fully-grown,  well-developed  man,  in  perfect  health,  may 
be  trained  so  as  to  be  brought  to  what  is  technically  called  fine  condition,  and  he  will 
present  at  that  time  all  the  animal- functions  in  their  perfection.  He  is  then  a  model  of  a 
physical  man ;  and  the  only  consequences  that  can  result  from  such  a  course  are  beneficial. 
The  argument  that  professional  pugilists  are  short-lived  is  fallacious ;  for  it  is  well  known 
that  almost  all  of  them,  after  training  for  and  passing  through  an  encounter,  immediately 
relapse  into  a  course  of  life  in  which  all  physiological  laws  are  habitually  violated. 


500  NUTRITION. 

During  training,  even  of  the  most  severe  character,  not  only  is  great  attention  paid  to 
diet  and  exercise,  but  all  of  the  functions  are  scrupulously  watched.  Tranquillity  of 
mind,  avoidance  of  exhaustion,  of  artificial  excitement,  stimulants,  tobacco,  etc.,  are 
strictly  enjoined;  and  the  process  is  always  very  gradual,  especially  at  its  commencement, 
and  is  continued  for  several  months.  The  cases  in  which  training  has  been  followed  by 
bad  effects  are  entirely  different.  Undeveloped  boys  are  frequently  trained  for  boating, 
in  the  most  reckless  manner,  until  they  break  down.  An  attempt  is  made  to  accomplish 
in  a  few  weeks  what  can  only  be  done  physiologically  in  several  months ;  and  the  result 
is,  that  some  of  the  vital  organs,  particularly  the  heart,  are  liable  to  become  permanently 
injured.  To  improve  the  "  wind  "  and  endurance,  a  person  undergoes  the  most  violent 
exercise,  which  is  followed  by  great  exhaustion,  intense  respiratory  distress,  and  disturb- 
ance of  the  action  of  the  heart,  these  parts  being  suddenly  forced  far  beyond  their  func- 
tional capacity.  This  cannot  be  done  without  danger  of  permanent  disturbances  of  the 
system,  such  as  have  been  frequently  observed;  and  it  is  all  the  more  liable  to  be  followed 
by  bad  results,  from  the  fact  that  amateurs  are  trained  together,  five  or  six  under  one 
man,  and  are  more  or  less  independent,  while  the  professional  athlete  is  never  out  of  the 
sight  of  his  trainer  for  months,  and  during  that  time  is  under  complete  control.  There 
is,  it  seems,  every  physiological  reason  to  believe  that  it  is  beneficial  to  the  general  sys- 
tem to  bring  it  to  the  highest  point  of  functional  activity  by  training ;  but,  if  this  be  not 
done  with  great  caution  and  judgment,  it  is  liable  to  be  followed  by  serious  results. 

Non-Nitrogenized  Principles.— The  non-nitrogenized  principles  present  a  marked 
contrast  to  the  alimentary  substances  we  have  just  considered.  In  the  first  place,  they 
are  not  indispensable  to  the  nutrition  of  all  animals.  The  carnivora,  for  example,  may  be 
well  nourished  upon  a  diet  composed  exclusively  of  nitrogenized  matter ;  and  the  remarks 
we  have  just  made  upon  training  show  that  the  human  subject  may  be  brought  to  a  high 
condition  of  physical  development,  when  starch,  sugar,  and  fat  are  almost  entirely  elimi- 
nated from  the  food.  This  shows  conclusively  that  the  division  of  the  food  into  plastic 
and  calorific  elements  is  not  absolute,  and  that  the  animal  temperature  may  be  maintained 
without  the  hydro-carbons.  The  nitrogenized  principles  are  probably  the  only  class  of 
alimentary  substances  capable  of  forming  muscular  tissue ;  but,  by  certain  transformations, 
with  the  exact  nature  of  which  we  are  imperfectly  acquainted,  this  class  of  substances  is 
capable  of  producing  heat  and  of  furnishing  the  carbonic  acid  eliminated  in  respiration. 
The  non-nitrogenized  principles  are  incapable  in  themselves  of  meeting  the  nutritive 
demands  of  the  system,  and  they  are  either  consumed  without  forming  part  of  the  tis- 
sues or  are  deposited  in  the  form  of  fat.  These  questions  we  have  already  considered 
under  the  head  of  alimentation ;  and  it  will  be  remembered  that,  with  a  few  exceptions, 
fat  always  exists  in  the  body  uncombined,  either  in  the  form  of  adipose  tissue  or  of  fatty 
granulations  in  the  substance  of  other  tissues. 

The  non-nitrogenized  elements  taken  up  by  the  blood  may  be  divided  into  two  varie- 
ties :  one,  the  sugars,  composed  of  carbon  with  hydrogen  and  oxygen  in  the  proportions 
to  form  water,  constituting  the  true  hydro-carbons ;  and  the  other,  the  fats,  in  which  the 
hydrogen  and  oxygen  do  not  exist  in  the  proportion  to  form  water.  "We  speak  of  the  sugars 
only,  because  starch  and  all  varieties  of  sugar  taken  as  food  are  transformed  into  glucose. 

In  connection  with  the  study  of  alimentation  and  glycogenesis,  -we  have  already 
referred  to  the  destination  of  the  true  hydro-carbons  in  the  organism.  They  are  taken 
as  food  to  a  considerable  extent,  particularly  in  the  form  of  starch,  and  are  formed  con- 
stantly by  the  liver  in  all  classes  of  animals.  Sugar  is  never  discharged  from  the  body 
m  health,  nor  is  it  deposited  in  any  part  of  the  organism,  even  as  a  temporary  condition. 
It  generally  disappears  in  the  passage  of  the  blood  through  the  lungs.  In  studying  the 
changes  which  sugar  is  capable  of  undergoing,  it  has  been  found  that  it  may  be  converted 
into  lactic  acid  or  be  changed  into  carbonic  acid  and  water ;  but  precisely  to  what  extent 
the  sugars  undergo  these  changes,  or  how  they  are  acted  upon  by  the  inspired  oxygen,  it 


PRINCIPLES   CONSUMED  BY  THE   OPvGANISM.  501 

has  been  impossible  thus  far  to  determine.  We  must  be  content  to  say  that  the  exact 
changes  which  the  sugars  undergo  in  nutrition  are  unknown.  They  seem  to  be  very 
important  in  development,  being  abundant  in  the  food  and  formed  largely  in  the  system 
in  early  life.  They  certainly  do  not  enter  into  the  composition  of  the  tissues;  and  it 
would  seem  that  they  must  be  important  in  the  two  remaining  phenomena  of  nutrition, 
namely,  the  formation  of  fat  and  the  development  of  animal  heat.  The  relations  of  sugar 
to  these  two  processes  will  be  taken  up  under  their  appropriate  heads. 

The  fats  taken  as  food  are  either  consumed  in  the  organism  or  are  deposited  in  the 
form  of  adipose  tissue.  That  the  fats  are  consumed,  there  can  be  no  doubt;  for,  in  the 
normal  alimentation  of  man,  fat  is  a  constant  article,  and  it  is  never  discharged  from  the 
body.  We  are  forced  to  admit,  however,  that  the  changes  which  fat  undergoes  in  its 
process  of  destruction  are  not  thoroughly  understood.  All  that  we  positively  know  is, 
that  the  fatty  principles  of  the  food  are  formed  into  a  fine  emulsion  in  the  small  intestine, 
and  are  taken  up,  chiefly  by  the  lacteals,  and  discharged  into  the  venous  system.  For  a 
time,  during  absorption,  fat  may  exist  in  certain  quantity  in  the  blood ;  but  it  soon  disap- 
pears and  is  either  destroyed  directly  in  the  circulatory  system  or  is  deposited  in  the 
form  of  adipose  tissue  to  supply  a  certain  amount  of  this  substance  consumed.  That  it 
may  be  destroyed  directly  is  proven  by  the  consumption  of  fat  in  instances  where  the 
amount  of  adipose  matter  is  insignificant ;  and  that  the  adipose  tissue  of  the  organism 
may  be  consumed  is  shown  by  its  rapid  disappearance  in  starvation. 

The  question  of  the  relations  of  fat  to  nutrition  is  important  but  somewhat  obscure. 
It  does  not  take  part  in  the  nutrition  of  the  parts  that  are  endowed  to  an  eminent 
degree  with  the  so-called  vital  functions ;  and,  when  these  tissues  are  brought  to  their 
highest  point  of  development,  the  fat  is  entirely  removed  from  their  substance.  If 
fat  be  not  a  plastic  material,  it  would  seem  to  have  no  function  remaining  but  that  of 
keeping  up,  by  its  oxidation,  the  animal  temperature.  But  it  is  not  proven  that  the  fats,  or 
fats  and  sugar,  are  the  sole  principles  concerned  in  the  production  of  carbonic  acid  and 
the  generation  of  heat;  for  both  of  these  phenomena  occur  in  the  carnivora,  and  in  man, 
when  fat  and  sugar  are  eliminated  from  the  food  and  the  fat  in  the  body  has  been 
reduced  to  the  minimum.  Fat  is  undoubtedly  destroyed  in  the  organism,  and  probably 
it  assists  in  the  formation  of  the  carbonic  acid  eliminated ;  it  is  also  taken  in  much  larger 
proportion  in  cold  than  in  temperate  or  warm  climates;  but  we  cannot,  with  our  present 
information,  say  without  reserve  that  fats  and  sugar  are  oxidized  directly,  by  a  process 
with  which  we  are  familiar  under  the  name  of  combustion,  and  that  their  exclusive  func- 
tion is  the  production  of  animal  heat. 

It  is  a  curious  fact  that  fat  is  generally  deposited  in  tissues  during  their  retrograde 
processes.  The  muscular  fibres  of  the  uterus,  during  the  involution  of  this  organ  after 
parturition,  become  the  seat  of  a  deposit  of  fatty  granulations.  Long  disuse  of  any  part 
will  produce  such  changes  in  its  power  of  appropriating  nitrogenized  matter  for  its  regen- 
eration, that  it  soon  becomes  atrophied  and  altered.  Instead  of  the  normal  nitrogenized 
elements  of  the  tissue,  we  have,  under  these  circumstances,  a  deposition  of  fatty  matter. 
The  fat  is  here  inert,  and  it  takes  the  place  of  the  substance  that  gives  to  the  part  its  char- 
acteristic functions.  These  phenomena  are  strikingly  apparent  in  muscles  that  have  been 
long  disused  or  paralyzed  and  in  nerves  that  have  lost  their  functional  activity.  If  the 
change  be  not  too  extensive,  the  fat  may  be  made  to  disappear,  and  the  part  will  return 
to  its  normal  constitution,  with  appropriate  exercise ;  but  frequently  the  alteration  has 
proceeded  so  far  as  to  be  irremediable  and  permanent. 

Accurate  observations  have  shown  that,  in  young  animals  rapidly  fattened,  all  the 
adipose  matter  in  the  body  cannot  be  accounted  for  by  what  is  taken  in  as  food ;  and  it 
is  certain  that  fat  may  be  produced  de  novo  in  the  organism. 

Formation  and  Deposition  of  Fat. — The  question  of  the  generation  of  fat  in  the  econo- 
my is  one  of  great  importance.  Whatever  the  exact  nature  of  the  changes  accompanying 


502  NUTRITION. 

the  destruction  of  non-nitrogenized  matters  may  be,  it  is  certain  that  the  fat  stored  up  in 
the  body  is  consumed,  when  there  is  a  deficiency  in  any  of  the  elements  of  food,  as  well 
as  that  which  is  taken  into  the  alimentary  canal.  It  is  rendered  probable,  indeed,  by  the 
few  experiments  that  have  been  made  upon  the  subject,  that  obesity  increases  the  power 
of  resistance  to  inanition.  At  all  events,  in  starvation,  the  fatty  constituents  of  the  body 
are  the  first  to  be  consumed,  and  they  almost  entirely  disappear  before  death.  As  we 
have  already  seen,  sugar  is  never  deposited  in  any  part  of  the  organism,  and  it  is  merely  a 
temporary  constituent  of  the  blood.  If  the  sugars  and  fats  have,  in  certain  regards,  simi- 
lar functions  in  nutrition,  and  if,  in  addition  to  the  mechanical  functions  of  fat,  it  may 
be  retained  in  the  organism  for  use  under  extraordinary  conditions,  it  becomes  very 
important  to  ascertain  the  mechanism  of  its  production  and  deposition. 

The  production  of  fatty  matter  by  certain  insects,  in  excess  of  the  fat  supplied  with 
the  food,  was  established  long  ago  by  the  researches  of  Huber ;  and  analogous  observa- 
tions have  been  made  upon  birds  and  mammals  by  Boussingault.  Some  of  the  experi- 
ments of  Boussingault  are  peculiarly  interesting,  as  they  were  made  upon  pigs,  in  which 
the  digestive  apparatus  closely  resembles  that  of  the  human  subject.  They  showed  con- 
clusively that,  under  certain  circumstances,  more  fat  exists  in  the  bodies  of  animals  than 
can  be  accounted  for  by  the  total  amount  of  fat  taken  as  food  added  to  the  fat  existing 
at  birth.  In  some  very  interesting  experiments  with  reference  to  the  influence  of  different 
kinds  of  food  upon  the  development  of  fat,  it  was  ascertained  that  fat  could  be  produced 
in  animals  upon  a  regimen,  sufficiently  nitrogenized,  but  deprived  of  fatty  matters ;  but 
the  fact  should  be  recognized  that  "  the  nutriment  which  produces  the  most  rapid  and 
pronounced  fattening  is  precisely  that  which  joins  to  the  proper  proportion  of  albuminoid 
substances  the  greatest  proportion  of  fatty  principles." 

Animals  cannot  be  fattened  without  a  certain  variety  in  the  regimen.  We  have 
already  discussed  the  necessity  of  a  varied  diet  and  have  shown  that  an  animal  will  die 
of  starvation  when  confined  exclusively  to  one  class  of  principles,  even  if  this  be  of  the 
most  nutritious  character ;  and  it  is  not  necessary  to  refer  again  to  the  experiments  which 
have  demonstrated  that  a  diet  confined  exclusively  to  starch,  sugar,  or  fat,  or  even  pure 
albumen  or  fibrin,  cannot  sustain  life,  much  less  fatten  an  animal.  We  are  prepared, 
then,  to  understand  why,  in  the  pigs  experimented  upon  by  Boussingault,  a  regimen  con- 
fined to  potatoes  did  not  prove  to  be  fattening,  notwithstanding  the  large  proportion  of 
starch,  and  that  fat  was  produced  in  abundance  only  when  the  food  presented  the  proper 
variety  of  principles. 

Very  little  is  known  concerning  the  precise  mechanism  of  the  production  of  fat.  The 
experiments  of  Boussingault  seem  to  leave  no  doubt  that  it  may  be  formed  from  any  kind 
of  food,  even  when  the  alimentation  is  exclusively  nitrogenized ;  but  it  is,  nevertheless,  a 
matter  of  common  observation  that  certain  articles  of  diet  are  more  favorable  to  its 
deposition  than  others ;  and  it  is  also  true  that  the  herbivora  are  fattened  much  more 
readily,  as  a  rule,  than  the  carnivora. 

Theoretical  considerations  would  immediately  point  to  starch  and  sugar  as  the  ele- 
ments of  food  most  easily  convertible  into  fat,  as  they  contain  the  same  elements,  though 
in  different  proportions ;  and  it  is  more  than  probable  that  this  view  is  correct.  It  is  said 
that,  in  sugar-growing  sections,  during  the  period  of  grinding  the  cane,  the  laborers  be- 
come excessively  fat,  from  eating  large  quantities  of  the  saccharine  matter.  We  cannot 
refer  to  any  exact  scientific  observations  upon  this  point,  but  the  fact  is  pretty  generally 
admitted  by  physiologists.  Again,  it  has  been  frequently  a  matter  of  individual  experience 
that  sugar  and  starch  are  favorable  to  the  deposition  of  fat,  especially  when  there  is  a 
constitutional  tendency  to  obesity.  A  most  remarkable  example  of  this,  and  one  which 
has  met  with  considerable  notoriety,  is  worthy  of  mention,  though  not  reported  by  a 
scientific  observer.  We  refer  to  the  letter  on  corpulence,  by  Mr.  Banting.  The  writer 
of  this  curious  pamphlet,  in  1862,  was  sixty-six  years  old,  five  feet  and  five  inches  in 
height,  and  weighed  two  hundred  and  two  pounds.  Under  the  advice  of  Mr.  William 


PRINCIPLES   CONSUMED  BY  THE  ORGANISM.  503 

Harvey,  F.  R.  C.  8.,  of  London,  he  confined  himself  to  a  diet  containing  no  sugar  and  as 
little  starch  and  fat  as  possible.  Continuing  this  regimen  for  one  year,  he  gradually  lost 
weight,  at  the  rate  of  about  one  pound  each  week,  until  he  was  reduced  to  one  hundred 
and  fifty-six  pounds.  At  the  time  the  last  edition  of  the  pamphlet  was  published,  in 
1864,  he  enjoyed  perfect  health  and  weighed  one  hundred  and  fifty  pounds,  his  weight 
varying  only  to  the  extent  of  one  pound,  more  or  less,  in  the  course  of  a  month.  This 
little  tract  is  very  interesting,  both  from  the  importance  of  its  physiological  deductions  and 
its  quaint  literary  style.  It  has  had  an  immense  circulation,  and  many  persons  suffering 
from  excessive  adipose  development  have  adopted  the  system  here  advised,  with  results 
more  or  less  favorable.  A  study  of  the  course  of  diet  here  prescribed  shows  it  to  be  a 
pretty  rigid  training  system,  with  the  exception  of  succulent  vegetables  and  liquids, 
which  are  allowed  without  restriction.  It  is  proper  to  remark,  however,  that  some 
enthusiastic  advocates  of  the  plan  have  exceeded  the  limits  prescribed  and  have  neglected 
the  caution  of  the  author  always  to  employ  it  under  the  advice  of  a  physician  ;  and  its  too 
rigid  enforcement  has  been  followed  by  serious  disturbances  in  general  nutrition.  Others, 
however,  have  verified  the  favorable  results  obtained  by  Mr.  Banting. 

It  is  difficult  to  explain  the  remarkable  constitutional  tendency  to  obesity  observed  in 
some  individuals,  which  is  very  often  hereditary.  Such  persons  will  become  very  fat 
upon  a  comparatively  low  diet,  while  others  deposit  but  little  adipose  matter,  even  when 
the  regimen  is  abundant.  It  is  to  be  noted,  however,  that  the  former  are  generally 
addicted  to  the  use  of  starchy,  saccharine,  and  fatty  elements  of  food,  while  the  latter  con- 
sume a  greater  proportion  of  nitrogenized  matter. 

It  is  not  an  uncommon  remark  that  the  habit  of  taking  large  quantities  of  liquids 
favors  the  formation  of  fat ;  but  it  is  not  easy  to  find  any  scientific  basis  for  such  an 
opinion.  As  to  the  formation  of  fat  by  any  particular  organ  or  organs  in  the  body,  no 
positive  scientific  view  has  been  advanced,  except  the  proposition  by  Bernard,  that  the 
liver  had  this  function,  in  addition  to  its  glycogenic  office.  This  we  have  already  dis- 
cussed and  have  shown  that  such  a  function  is  far  from  being  positively  established. 

Condition  under  which  Fat  exists  in  the  Organism. — It  is  said  that  fat  combined  with 
phosphorus  is  united  with  nitrogenized  matter  in  the  substance  of  the  nervous  tissue  ;  but 
its  condition  here  is  not  well  understood,  as  we  shall  see  when  we  come  to  treat  of  the 
nervous  system.  A  small  quantity  of  fat  is  contained  in  the  blood-corpuscles,  and  a  little 
is  held  in  solution  in  the  bile;  but,  with  these  exceptions,  fat  always  exists  in  the  body 
isolated  and  uncombined  with  nitrogenized  matter,  in  the  form  of  granules  or  globules 
and  of  adipose  tissue.  The  three  varieties  of  fat  are  here  combined  in  variable  propor- 
tions, which  is  the  cause  of  the  differences  in  its  consistence  in  different  situations.  The 
ultimate  elements  of  fat  are,  carbon,  hydrogen,  and 
oxygen,  the  two  latter  in  unequal  proportions. 


Physiological  Anatomy  of  Adipose  7%sw0.— Adipose 
tissue  is  found  in  abundance  in  the  interstices  of  the 
subcutaneous  areolar  tissue,  where  it  is  sometimes 
known  as  the  panniculus  adiposus.  It  is  not,  how- 
ever, to  be  confounded  with  the  so-called  cellular  or  ^  u^_Adipose  vMes .  ^ 
areolar  tissue,  and  is  simply  associated  with  it  without  850  diameters.  (Koiiiker.) 

being  one  of  its  essential  parts;  for  the  areolar  tissue    a'  ^J™*1 &a ^2Jfes ^Sd ^tTetber6 
is  abundant  in  certain  situations,  as  the  eyelids  and        by  which  the  fat  is  dissolved,  the 
scrotum,  where  there  is  no  adipose  matter,  and  adipose 
tissue  exists  sometimes,  as  in  the  marrow  of  the  bones,  without  any  areolar  tissue. 

Adipose  tissue  is  widely  distributed  in  the  body  and  has  important  mechanical  func- 
tions. Its  anatomical  element  is  a  vesicle,  from  -g-^-g-  to  -g-^-g-  of  an  inch  in  diameter,  com- 
posed of  a  delicate,  structureless  membrane,  25^66  of  an  inch  thick,  enclosing  fluid  con- 


504  NUTRITION. 

tents.  The  form  of  the  vesicles  is  naturally  rounded  or  ovoid ;  but  in  microscopical 
preparations  they  are  generally  compressed  so  as  to  become  irregularly  polyhedrical. 
The  membrane  sometimes  presents  a  small  nucleus  attached  to  its  inner  surface.  The 
contents  are,  a  minute  quantity  of  an  albuminoid  fluid  moistening  the  internal  surface 
of  the  membrane,  and  a  mixture  of  oleine,  margarine,  and  stearine,  liquid  at  the  temper- 
ature of  the  body,  but  becoming  harder  on  cooling.  Little  rosettes  formed  of  acicular 
crystals  of  margarine  are  frequently  observed  in  the  fat-vesicles,  when  the  temperature 
is  rather  low. 

The  adipose  vesicles  are  collected  into  little  lobules,  from  ^7  to  i  °f  an  incn  in  diame- 
ter, which  are  surrounded  by  a  rather  wide  net-work  of  capillary  blood-vessels.  Close 
examination  of  these  vessels  shows  that  they  frequently  surround  individual  fat-cells,  in 
the  form  of  single  loops.  There  is  no  distribution  of  nerves  or  lymphatics  to  the  ele- 
ments of  adipose  tissue.  It  is  seen  by  this  sketch  of  the  structure  of  adipose  tissue,  that 
there  is  no  anatomical  reason  for  classing  these  vesicles  with  the  ductless  glands,  as 
is  done  by  some  physiologists.  They  undoubtedly,  under  certain  conditions,  have  the 
power  of  filling  themselves  with  fat ;  but  it  would  be  no  more  appropriate  to  call  fat 
a  secretion  than  to  apply  this  term  to  the  development  and  nutrition  of  the  muscular 
substance  within  the  sarcolemma. 

Conditions  which  influence  Nutrition. — We  know  more  concerning  the  conditions 
that  influence  the  general  process  of  nutrition  than  about  the  nature  of  the  process  itself. 
It  will  be  seen,  for  example,  when  we  come  to  study  the  nervous  system,  that  there  are 
nerves  which  regulate,  to  a  certain  extent,  the  nutritive  forces.  We  do  not  mean  to 
imply  that  nutrition  is  effected  through  the  influence  of  the  nerves,  but  it  is  the  fact  that 
certain  nerves,  by  regulating  the  supply  of  blood,  and  perhaps  by  other  influences,  are 
capable  of  modifying  the  nutrition  of  parts  to  a  very  considerable  extent. 

In  discussing  the  influence  of  exercise  upon  the  development  of  parts,  we  have  shown 
that  this  is  not  only  desirable  but  indispensable ;  and  the  proper  performance  of  the  func- 
tions of  nearly  all  parts  involves  the  action  of  the  nervous  system.  It  is  true  that  the  sep- 
arate parts  of  the  organism  and  the  organism  as  a  whole  have  a  limited  existence  ;  but  it  is 
not  true  that  the  change  of  nitrogenized,  living  substance  into  effete  matter,  a  process  that 
is  increased  in  activity  by  physiological  exercise,  consumes,  so  to  speak,  a  definite  amount 
of  the  limited  life  of  the  parts.  Physiological  exercise  increases  disassimilation,  but  it  also 
increases  the  activity  of  nutrition  and  favors  development.  It  is  a  favorite  sophism  to 
assert  that  bodily  or  mental  effort  is  made  always  at  the  expense  of  a  definite  amount  of 
vitality  and  matter  consumed.  This  is  partly  true,  but  mainly  false.  Work  involves 
change  into  effete  matter  ;  but,  when  restricted  within  physiological  limits,  it  engenders 
a  corresponding  activity  of  nutrition,  assuming,  of  course,  that  the  supply  from  without 
be  sufficient.  Other  things  being  equal,  a  man  will  live  longer  under  a  system  of  physio- 
logical exercise  of  every  part,  than  if  he  made  the  least  effort  possible.  It  is,  indeed, 
only  by  such  use  of  parts  that  they  can  undergo  proper  development  and  become  the  seat 
of  normal  nutrition.  But,  notwithstanding  all  these  facts,  life  is  self-limited.  Unless 
subjected  to  some  process  which  arrests  all  changes,  such  as  cold,  the  action  of  preserva- 
tive fluids,  etc.,  organic  substances  are  constantly  undergoing  transformation.  In  the 
living  body,  their  disassimilation  and  nutrition  are  unceasing ;  and,  after  they  are  re- 
moved from  what  are  termed  vital  conditions,  they  change,  first  losing  irritability,  or 
becoming  incapable  of  performing  their  functions,  and  afterward  decomposing  into  mat- 
ters which,  like  the  results  of  their  disassimilation,  are  destined  to  be  appropriated  by 
the  vegetable  kingdom.  Nutrition  sufficient  to  supply  the  physiological  decay  of  parts 
cannot  continue  indefinitely.  The  wonderful  forces  in  the  fecundated  ovum  lead  it 
through  a  process  of  development  that  requires,  in  the  human  subject,  more  than  twenty 
years  for  its  completion  ;  and,  when  development  ceases,  no  one  can  say  why  it  becomes 
arrested,  nor  can  we  give  any  sufficient  reason  why,  with  a  sufficient  and  appropriate 


PRINCIPLES   CONSUMED  BY  THE  ORGANISM.  505 

supply  of  material,  a  man  should  not  grow  indefinitely.  After  the  being  is  fully  devel- 
oped, and  during  what  is  known  as  the  adult  period,  the  supply  seems  to  be  about  equal 
to  the  waste.  But,  after  this,  nutrition  gradually  becomes  deficient,  and  the  deposition  of 
new  matter  in  progressive  old  age  becomes  more  and  more  inadequate  to  supply  the  place 
of  the  living  nitrogenized  substance.  We  may  at  this  time,  as  an  exception,  have  a  con- 
siderable deposition  of  fat,  but  the  nitrogenized  matter  is  always  deficient,  and  the  pro- 
portion of  inert,  inorganic  matter  combined  with  it  is  increased. 

There  can  be  little  if  any  doubt  that  the  forces  which  induce  the  regeneration  or 
nutrition  of  parts  reside  in  the  organic  nitrogenized  substance,  and  that  these  give  to  the 
parts  their  characteristic  functions,  which  we  call  vital;  the  inorganic  matter  being 
passive,  or  having,  at  the  most,  purely  physical  functions.  If,  therefore,  as  age  advances, 
the  organic  matter  be  gradually  losing  the  power  of  completely  regenerating  its  sub- 
stance, and  if  its  proportion  be  progressively  diminishing  while  the  inorganic  matter  is 
increasing  in  quantity,  a  time  will  come  when  some  of  the  organs  necessary  to  life  will 
be  unable  to  perform  their  office.  When  this  occurs  we  have  death  from  old  age,  or 
physiological  dissolution.  This  may  be  a  gradual  failure  of  the  general  process  of  nutri- 
tion, or  it  may  attack  some  one  organ  or  system.  Why  death  is  thus  certain  to  occur, 
we  do  not  know,  any  more  than  we  can  explain  why  and  how  animals  live. 

The  modifications  in  nutrition  due  to  the  very  varied  influences  that  may  be  brought 
to  bear  upon  it  present  a  most  extended  subject  for  discussion  ;  but  we  shall  not  touch 
upon  any  of  these  influences  that  are  not  purely  physiological.  Among  the  most  inter- 
esting of  these  modifications,  are  those  due  to  age,  constituting,  as  they  do,  in  early  life, 
the  process  of  development.  These  will  be  treated  of  fully  in  connection  with  the  subject 
of  generation.  It  is  evident,  also,  from  what  we  have  already  said,  that  each  tissue  and 
organ  has  its  own  conditions  of  nutrition  and  development ;  and  this  constitutes  another 
important  division  of  the  subject,  the  more  interesting,  because  the  nutrition  and  develop- 
ment of  the  individual  tissues  are  closely  connected  with  the  processes  of  regeneration 
and  repair  after  injury.  We  have  stated,  as  far  as  possible,  all  that  is  positively  known  of 
the  nutrition  of  the  fully-formed  tissues  of  the  body  ;  but  the  history  of  their  develop- 
ment belongs  to  embryology.  If  we  were  to  attempt  to  follow  the  processes  of  regenera- 
tion after  injury,  in  nerves,  muscles,  bone,  etc.,  we  should  be  compelled  to  pass  almost 
immediately  into  the  domain  of  pathology.  The  influences  of  climate,  respiratory  activity, 
food,  etc.,  have  already  been  considered  under  the  heads  of  respiration,  alimentation,  and 
excretion,  and  will  be  touched  upon  again  in  connection  with  animal  heat. 

Products  of  Disassimilation. — It  only  remains  now  to  recapitulate  briefly  tlie  mode 
of  production  of  the  excretions.  The  process  of  disassimilation,  we  are  aware,  always 
accompanies  nutrition,  and  the  substances  thus  formed  are  the  result  of  the  final  changes 
of  the  organic  constituents  of  the  tissues.  As  we  have  seen  in  studying  the  urine,  the 
excrementitious  principles  proper  are  always  associated  with  inorganic  matter  which  has 
passed  through  the  organism ;  and,  while  there  are  many  effete  substances  that  we  have 
been  able  to  recognize,  the  physiological  and  pathological  relations  of  which  have  been 
more  or  less  successfully  studied,  there  are  probably  others  which  have  thus  far  escaped 
observation.  It  is  almost  futile  to  speculate  upon  the  probable  bearing  which  the  discovery 
of  new  excrementitious  principles  will  have  upon  pathological  conditions,  while  there  are 
so  many  which  we  now  know  only  by  name,  their  relations  to  the  different  tissues  being 
still  obscure ;  but,  if  we  reason  from  the  light  thrown  upon  certain  diseased  conditions  by 
the  fact  that  urea,  the  urates,  and  cholesterine  are  liable  to  be  retained  in  the  blood  and 
produce  certain  symptoms,  we  may  safely  infer  that  the  description  of  new  effete  prin- 
ciples will  have  an  important  influence  upon  our  pathological  knowledge  as  well  as  our 
comprehension  of  physiological  processes.  The  following  are  the  most  important  excre- 
mentitious matters,  the  relations  of  which  to  nutrition  and  disassimilation  are  more  or 
less  fully  understood : 


506       ,  NUTRITION. 

Products  of  Disassimilation. 

Excrementitious  Principles. 

f  Principally  by  the 

lungs;   but  also 

Carbonic  acid ]       by  the  skin,  and 

in  solution  in  the 
(^      excreted  fluids. 

Alkaline  sudorates Perspiration. 

f  Principally  in  the 

urine ;  but  a  cer- 
Urea j       tain  quantity  in 

the  perspiration. 

Urate  of  soda Urine- 

Urate  of  ammonia 

Urate  of  potassa 

Urate  of  lime 

Urate  of  magnesia 

Hippurate  of  soda 

Hippurate  of  potassa 

Hippurate  of  lime " 

Creatine " 

Creatinine 

Oxalate  of  lime " 

Xanthine " 

Stercorine  (changed  from  cholesterine) Faeces. 

Excretine " 

In  the  above  list  we  have  omitted  all  doubtful  excrementitious  principles,  as  well 
as  the  inorganic  compounds  found  in  the  excreted  fluids;  and  we  may  assume  that 
the  substances  therein  enumerated  represent,  as  far  as  we  are  now  able  to  determine, 
the  physiological  wear  of  the  organism.  We  shall  not  again  discuss  the  fact  that  the  life 
of  tissues  involves  physiological  waste  or  decay,  and  that  the  excrementitious  principles 
proper  represent  the  final  changes  of  organic  substances.  "We  know  that  this  process 
goes  on  without  necessarily  involving  exercise  of  the  peculiar  functions  of  the  parts ;  but 
it  is  no  less  true  that  exercise,  or  work,  increases  the  activity  both  of  nutrition  and  wear. 
This  is  one  of  the  great  principles  underlying  all  our  ideas  of  the  process  of  nutrition. 
"We  shall  not  discuss  here  the  influence  of  work  upon  the  elimination  of  some  of  the 
nitrogenized  compounds,  particularly  urea,  for  we  have  already  examined  that  subject 
most  carefully  in  another  place ;  but  we  have  no  hesitation  in  stating,  as  a  general  law 
that  has  yet  to  meet  with  exceptions,  that  physiological  work  increases  excretion. 

Animal  Heat. 

The  process  of  nutrition  in  animals  is  always  attended  with  the  development  of  heat, 
and  it  produces  a  temperature  more  or  less  independent  of  external  conditions.  This  is 
true  in  the  lowest  as  well  as  the  highest  animal  organizations ;  and  analogous  phenomena 
have  even  been  observed  in  plants.  In  cold-blooded  animals,  nutrition  may  be  suspended 
by  a  diminished  external  temperature,  and  certain  of  the  functions  become  temporarily 
arrested,  to  be  resumed  when  the  animal  is  exposed  to  a  greater  heat.  This  is  true,  to 
some  extent,  in  certain  warm-blooded  animals  that  periodically  pass  into  a  condition  of 
stupor,  called  hibernation ;  but  in  man,  and  in  nearly  all  the  warm-blooded  animals,  the 
general  temperature  of  the  body  can  undergo  but  slight  variations.  The  animal  heat  is 
essentially  the  same  in  the  intense  cold  of  the  frigid  zones  and  under  the  burning  sun  of 
the  tropics ;  and  if.  from  any  cause,  the  body  become  incapable  of  keeping  up  its  temper- 


ANIMAL  HEAT.  507 

ature  when  exposed  to  cold,  or  of  moderating  it  when  exposed  to  heat,  death  is  the  invari- 
able result. 

The  production  of  animal  heat  is  so  closely  connected  with  nutrition,  that,  in  serious 
pathological  modifications  of  this  process,  as  in  the  essential  fevers  or  extensive  inflam- 
mations, the  temperature  of  the  body  becomes  an  Important  guide,  particularly  in 
prognosis. 

The  study  of  the  temperature  in  different  classes  of  animals  presents  very  great  inter- 
est, but  the  limits  of  a  work  on  pure  human  physiology  restrict  us  to  the  phenomena  as 
observed  in  man,  and  in  animals  in  which  the  processes  of  nutrition  are  similar,  if  not 
identical.  We  shall  therefore  treat  of  the  subject  from  one  point  of  view  and  consider 
it  as  follows : 

1.  The  normal  temperature  in  the  human  subject,  with  its  variations  in  different  parts 
of  the  body  and  at  different  periods  of  life. 

2.  The  diurnal  variations  in  the  animal  temperature,  and  the  relations  of  alimenta- 
tion, digestion,  respiration,  nutrition,  exercise,  and  the  nervous  system. 

3.  The  means  by  which  the  temperature  of  the  body  is  kept  within  the  limits  neces- 
sary to  the  preservation  of  life  and  health. 

Limits  of  Variation  in  the  Normal  Temperature  in  Man. — A  great  number  of  obser- 
vations have  been  made  upon  the  normal  temperature  in  the  human  subject  under  differ- 
ent conditions ;  but  we  shall  cite  those  only  in  which  all  sources  of  error  in  thermometry 
seem  to  have  been  avoided,  and  in  which  the  results  present  noticeable  peculiarities. 
One  of  'the  most  common  methods  of  taking  the  general  temperature  has  been  to  intro- 
duce a  delicate  thermometer,  carefully  protected  from  all  disturbing  conditions,  into  the 
axilla,  reading  off  the  degrees  after  the  mercury  has  become  absolutely  stationary. 
Nearly  all  observations  made  in  this  way  agree  with  the  results  obtained  by  Gavarret, 
who  estimated  that  the  temperature  in  the  axilla,  in  a  perfectly  healthy  adult  man.  in  a 
temperate  climate,  ranges  between  97*7°  and  99*5°  Fahr.  Dr.  Davy,  from  a  large  num- 
ber of  observations  upon  the  temperature  under  the  tongue,  fixes  the  standard,  in  a 
temperate  climate,  at  98°.  When  we  examine  the  temperature  of  the  blood  in  the  deeper 
vessels  and  the  variations  in  different  parts,  we  shall  see  that  the  axilla  and  the  tongue, 
being  more  or  less  exposed  to  external  influences,  do  not  exactly  represent  the  general 
heat  of  the  organism ;  but  these  are  the  situations,  particularly  the  axilla,  in  which  the 
temperature  is  most  frequently  taken,  both  in  physiological  and  pathological  examina- 
tions. As  a  standard  for  comparison,  we  may  assume  that  the  most  common  temperature 
in  these  situations  is  98°,  subject  to  variations,  within  the  limits  of  health,  of  about  0'5° 
below  and  1-5°  above. 

Variations  with  External  Temperature. — There  can  be  no  doubt  that  the  general  tem- 
perature of  the  body  varies,  though  within  very  restricted  limits,  with  extreme  changes 
in  climate.  The  results  obtained  by  Davy,  in  a  large  number  of  observations  in  temper- 
ate and  hot  climates,  show  an  elevation  in  the  tropics  of  from  0'5°  to  3°.  It  is  well 
known,  also,  that  the  human  body,  the  surface  being  properly  protected,  is  capable  of 
enduring  for  some  minutes  a  heat  much  greater  than  that  of  boiling  water.  Under  these 
conditions,  the  general  temperature  is  raised  but  very  slightly,  as  compared  with  the 
intense  heat  of  the  surrounding  atmosphere.  According  to  the  observations  of  Dr.  Dob- 
son,  the  temperature  was  only  raised  to  99'5°  in  one  instance,  101'5°  in  another,  and  102° 
in  a  third,  when  the  body  was  exposed  to  a  heat  of  more  than  212°.  MM.  Delaroche 
and  Berger,  however,  found  that  the  temperature  in  the  mouth  could  be  increased  by 
from  3°  to  9°,  after  sixteen  minutes'  exposure  to  intense  heat.  This  was  for  the  external 
parts  only ;  but  it  is  not  at  all  probable  that  the  temperature  of  the  internal  organs  ever 
undergoes  such  extensive  variations. 

It  is  very  difficult  to  estimate  the  temperature  in  persons  exposed  to  intense  cold,  as 


508  NUTRITION. 

in  Arctic  explorations,  because  the  greatest  care  is  always  taken  to  protect  the  surface 
of  the  body  as  completely  as  possible ;  but  experiments  have  shown  that  the  animal  heat 
may  be  considerably  reduced,  as  a  temporary  condition,  without  producing  death.  In  the 
latter  part  of  the  last  century,  Dr.  Ourrie  caused  the  temperature  in  a  man  to  fall  15° 
by  immersion  in  a  cold  bath ;  but  he  could  not  bring  it  below  83°.  This  extreme 
depression,  however,  lasted  only  two  or  three  minutes,  and  the  temperature  afterward 
returned  to  within  a  few  degrees  of  the  normal  standard.  Nearly  the  same  results  were 
obtained  by  Hunter,  in  a  series  of  experiments  on  a  mouse.  With  an  external  tempera- 
ture of  60°,  he  found  the  temperature  in  the  upper  part  of  the  abdomen  99°,  and  in  the 
pelvis,  96°.  The  animal  was  then  exposed  for  an  hour  to  a  cold  atmosphere  of  13°,  and 
there  was  a  diminution  of  the  temperature  at  the  diaphragm  of  16°,  and  at  the  pelvis,  of 
18°.  These  results  show  that,  while  the  normal  variations  in  the  temperature  in  the  human 
subject,  even  when  exposed  to  great  climatic  changes,  are  very  slight,  generally  not  rang- 
ing beyond  two  degrees,  the  body  may  be  exposed  for  a  time  to  excessive  heat  or  cold, 
and  the  extreme  limits,  consistent  with  the  preservation  of  life,  may  be  reached.  As  far 
as  has  been  ascertained  by  direct  experiment,  these  limits  are  83°  and  107°;  giving  a 
range  of  about  15°  below  and  9°  above  the  average  standard  under  normal  conditions. 

Variations  in  Different  Parts  of  the  Body. — It  is  to  be  expected  that  the  temperature 
of  the  internal  organs  should  be  higher  and  more  constant  than  that  of  parts,  like  the 
axilla  or  mouth,  more  or  less  exposed  to  loss  of  heat  by  evaporation  and  contact  with 
the  cool  air ;  and  the  differences  observed  in  the  blood  in  certain  parts,  as  in  the  two 
sides  of  the  heart,  have  important  bearings,  as  we  shall  hereafter  show,  upon  the  various 
theories  of  animal  heat.  We  shall  here  simply  note  the  variations  observed  in  the  blood 
in  different  situations  and  confine  ourselves  chiefly  to  late  observations,  which  have  gen- 
erally been  made  with  apparatus  much  more  reliable  and  delicate  than  that  which  was 
formerly  employed. 

A  great  number  of  experiments  have  been  made  upon  modifications  in  temperature 
accompanying  the  general  change  of  the  blood  from  arterial  to  venous  ;  but  perhaps  the 
most  exact  and  elaborate  are  those  by  M.  Claude  Bernard.  For  measuring  the  tempera- 
ture in  different  parts  of  the  vascular  system,  he  used  the  exceedingly  delicate  "  metastatic  " 
thermometers  of  M.  Walferdin ;  and  in  all  comparative  observations  he  employed  the 
same  instrument,  introduced  successively  into  different  parts,  frequently  reversing  the 
order  and  employing  every  precaution  so  as  to  insure  perfectly  physiological  conditions. 
The  preeminent  skill  of  this  distinguished  observer  in  experimenting  upon  living  animals 
is  almost  in  itself  a  sufficient  guarantee  of  the  accuracy  of  his  results. 

It  is  universally  admitted  that  the  blood  becomes  slightly  lowered  in  its  temperature 
in  passing  through  the  general  capillary  circulation ;  but  the  amount  of  difference  is  ordi- 
narily not  more  than  a  fraction  of  a  degree,  and  it  is  dependent,  in  all  probability,  upon 
external  conditions  and  the  evaporation  constantly  going  on  from  the  surface  of  the  body. 
This  fact  is  not  at  all  opposed  to  the  proposition  that  the  animal  heat  is  generated  in 
greatest  part  in  the  general  capillary  system,  as  one  of  the  results  of  nutritive  action ;  for 
the  blood  circulates  with  such  rapidity  that  the  heat  acquired  in  the  capillaries  of  the 
internal  organs,  where  little  or  none  is  lost,  is  but  slightly  diminished  before  the  fluid 
passes  into  the  arteries,  even  in  circulating  through  the  lungs  ;  and  the  evaporation  from 
the  surface  simply  moderates  the  heat  acquired  in  the  tissues  and  keeps  it  at  the  proper 
standard.  We  know  that  the  heat  of  the  body  is  equalized  by  means  of  the  circulation 
and  by  cutaneous  transpiration;  and  all  comparative  observations  upon  the  temperature 
in  different  parts  show  that,  where  it  is  not  subjected  to  refrigerating  influences,  the 
blood  is  warmer  in  the  veins  than  in  the  arteries. 

The  elaborate  investigations  of  Bernard  have  demonstrated  that  the  blood  is,  as  the 
rule,  from  0'36°  to  1-8°  warmer  in  the  hepatic  veins  than  in  the  aorta.  The  tempera- 
ture in  the  hepatic  veins  is  from  0-18°  to  1'44°  higher  than  in  the  portal  veins.  These 


ANIMAL  HEAT.  509 

figures  are  the  result  of  numerous  experiments  made  upon  dogs.  The  maximum  of  thirty- 
three  observations  upon  the  temperature  in  the  aorta  was  105'8°,  and  the  minimum,  98-78°; 
the  maximum  of  thirty-two  observations  upon  the  portal  vein  was  106'34°,  and  the  mini- 
mum, 100'04°  ;  the  maximum  of  thirty -five  observations  upon  the  hepatic  veins  was  107°, 
and  the  minimum,  99'86°.  Compared  with  the  aorta,  the  temperature  of  the  portal  vein 
was  generally  found  to  be  higher  (maximum  of  difference,  0'9°)  ;  but,  in  a  few  instances 
(five  out  of  fifteen),  it  was  a  very  little  lower,  which  is  explained  by  Bernard  upon  the  sup- 
position that  the  intestinal  canal  is  not  entirely  removed  from  external  modifying  influ- 
ences. These  results  show  that  the  blood  coming  from  the  liver  is  warmer  than  in  any 
other  part  of  the  body. 

The  general  fact  that  the  superficial  parts  are  cooler  than  those  less  exposed  to  loss 
of  heat  by  evaporation  does  not  demand  extended  discussion ;  but,  in  a  series  of  experi- 
ments by  Breschet  and  Becquerel,  who  were  among  the  first  to  employ  thermo-electric 
apparatus  in  the  study  of  animal  heat,  it  was  found  that  the  cellular  tissue  was  from  2'5° 
to  3-3°  cooler  than  the  muscles.  This  difference  will  be  readily  understood  when  we 
consider  the  production  of  heat  in  the  general  system,  and  more  especially  in  the  highly- 
organized  parts. 

A  most  interesting  question,  in  this  connection,  relates  to  the  comparative  tempera- 
ture of  the  blood  in  the  two  sides  of  the  heart.  I}pon  this  point  there  have  been  several 
conflicting  observations,  the  results  favoring  two  opposite  theories  of  calorification.  By 
some  it  has  been  thought  that  the  blood  gains  heat  in  passing  through  the  lungs,  and  this 
is  explained  by  the  theory  of  the  direct  union,  in  these  organs,  of  oxygen  with  the 
hydro-carbons.  Others  suppose  that  the  blood  is  slightly  refrigerated  in  the  air-cells. 
The  questions  here  involved  will  be  fully  discussed  in  connection  with  the  theories  of 
animal  heat ;  and  we  shall  confine  ourselves  at  present  to  a  study  of  the  experimental 
facts. 

It  is  evident  that,  when  the  chest  is  opened,  the  external  refrigerating  influences 
might  act  differently  upon  the  two  sides  of  the  heart,  particularly  as  the  right  ventricle 
is  much  thinner  than  the  left.  It  would  not  be  improper,  indeed,  to  exclude  all  observa- 
tions made  in  this  way,  and  to  depend  entirely  upon  experiments  in  which  the  physiological 
conditions  are  not  so  palpably  violated.  Magendie  and  Bernard  introduced  delicate  ther- 
mometers into  the  two  sides  of  the  heart,  through  the  vessels  in  the  neck,  without  opening 
the  chest.  These  experiments  were  made  upon  a  horse,  and  the  right  heart  was  always 
found  considerably  warmer  than  the  left.  Hering  introduced  a  thermometer  into  the  cavi- 
ties of  the  heart  in  a  living  calf  affected  with  cardiac  ectopia.  The  temperature  of  the 
right  side  was  102'74°,  and  the  left  side,  101 '79°.  Georg  von  Liebig  illustrated  one  of 
the  sources  of  error  in  all  examinations  made  after  opening  the  chest,  by  filling  the  cavi- 
ties of  the  heart  of  a  dog  with  warm  water,  placing  the  organ  in  a  water-bath,  and  bring- 
ing the  two  sides  to  precisely  the  same  temperature.  After  five  minutes'  exposure  to  the 
air,  the  temperature  in  the  right  ventricle  was  sensibly  lower  than  in  the  left,  which 
was  undoubtedly  due  to  the  difference  in  the  thickness  of  the  ventricular  walls.  The 
observations  by  Bernard  himself  upon  dogs  and  sheep  are  very  conclusive,  as  far  as 
these  animals  are  concerned.  In  dogs  he  found  a  difference  of  from  0'1°  to  0*2°, 
always  in  favor  of  the  right  side ;  and  the  results  in  sheep  were  nearly  the  same. 
These  experiments  are  only  indirectly  applicable  to  the  human  subject;  and  if  it  be 
proven  that,  in  animals,  the  conditions  vary  with  "the  state  of  the  skin,  the  digestive 
apparatus,  and  the  muscular  system  "  (Colin),  it  is  impossible,  in  the  absence  of  positive 
demonstration,  to  say  what  change  in  temperature,  if  any,  takes  place  in  the  blood  in  its 
passage  through  the  lungs.  The  only  reliable  observations  upon  this  point  in  man  are 
those  made  by  Prof.  Lombard,  of  Boston.  Prof.  Lombard  used  in  his  experiments  a  very 
ingenious  and  delicate  thermo-electric  apparatus,  capable  of  indicating  a  difference  of 
?oVo  °f  a  degree  cent.  With  this  instrument,  he  was  able  to  determine  very  slight  varia- 
tions in  the  temperature  of  the  blood  in  the  arterial  system,  by  simply  placing  the  con- 


510  NUTRITION. 

ductors  over  any  of  the  superficial  vessels,  like  the  radial.  Of  course  it  is  impossible  to 
note  the  actual  temperature  in  the  two  sides  of  the  heart  in  the  human  subject  during 
life ;  but  Prof.  Lombard  endeavored  to  arrive  at  the  same  end,  by  calculating  that,  if  all 
the  sources  of  refrigeration  in  the  lungs  were  artificially  removed,  the  blood  in  the  arte- 
ries should  gain  about  the  same  amount  of  heat  that  would  be  lost  under  ordinary  condi- 
tions. To  effect  this  object,  he  breathed  air  saturated  with  moisture  and  of  the  same 
temperature  as  the  circulating  blood.  "If,  then,  when  respiration  takes  place  under 
ordinary  circumstances,  the  blood  is  cooled  one-third  of  a  degree  (cent.)  in  passing  through 
the  luDgs,  the  temperature  should  be  raised  so  much ;  that  is  to  say,  one-third  of  a  degree, 
when  we  respire  air  at  the  temperature  of  the  blood  and  saturated  with  the  vapor  of 
water,  all  loss  of  heat  then  being  impossible."  In  numerous  experiments  performed  upon 
this  principle,  Prof.  Lombard  failed  to  observe  a  sufficiently  marked  elevation  of  tempera- 
ture to  justify  the  conclusion  that  the  blood  is  ordinarily  cooled  in  passing  through  the 
lungs.  These  experiments  cannot  be  so  positive  as  those  made  by  introducing  thermome- 
ters into  the  heart  in  living  animals  without  opening  the  chest  or  disturbing  the  circula- 
tion ;  but  they  are  important,  in  connection  with  such  observations,  as  failing  to  prove 
that  the  blood  is  either  cooled  or  heated  in  the  lungs.  From  these  facts  it  appears  that 
there  is  no  positive  evidence  of  any  change  in  the  temperature  in  the  blood  in  passing 
through  the  lungs  in  the  human  subject.  In  animals  there  probably  exist  no  constant 
differences  in  temperature  in  the  two  sides  of  the  heart.  When  the  loss  of  heat  by  the 
general  surface  is  active,  as  in  animals  with  a  slight  covering  of  hair,  the  blood  is  gener- 
ally cooler  in  the  right  cavities ;  but,  in  animals  with  a  thick  covering,  that  probably  lose  a 
great  deal  of  heat  by  the  pulmonary  surface,  the  blood  is  cooler  upon  the  left  side.  There 
can  be  no  doubt  that  there  are  refrigerating  influences  in  the  lungs,  both  from  the  low 
temperature  of  the  inspired  air  and  from  evaporation ;  but  these  are  equalized  and  some- 
times overcome  by  processes  in  the  blood  itself,  although,  as  we  shall  see  hereafter,  the 
lungs  are  by  no  means  the  most  important  organs  of  calorification. 

Variations  at  Different  Periods  of  Life, — The  most  important  variations  in  the  tem- 
perature of  the  body  at  different  periods  of  life  are  observed  in  infants  just  after  birih. 
Aside  from  one  or  two  observations,  which  are  admitted  to  be  exceptional,  the  body  of 
the  infant  and  of  young  mammalia  and  birds,  removed  from  the  mother,  presents  a  dimi- 
nution in  temperature  of  from  one  to  nearly  four  degrees.  In  infancy  the  ability  to  resist 
cold  is  less  than  in  later  years ;  but  after  a  few  days  the  temperature  of  the  child  nearly 
reaches  the  standard  in  the  adult,  and  the  variations  produced  by  external  conditions  are 
not  so -great. 

The  experiments  of  "W.  F.  Edwards  have  an  important  bearing  upon  our  ideas  of  nutri- 
tion during  the  first  periods  of  extra-uterine  life.  He  found  that,  in  certain  animals, 
particularly  dogs  and  cats,  that  are  born  with  the  eyes  closed  and  in  which  the  foramen 
ovale  remains  open  for  a  few  days,  the  temperature  rapidly  diminished  when  they  were 
removed  from  the  body  of  the  mother,  and  that  they  then  become  reduced  to  a  condition 
approximating  that  of  cold-blooded  animals;  but,  after  about  fifteen  days,  this  change  in 
temperature  could  not  be  effected.  In  dogs  just  born,  the  temperature  fell  after  three  or 
four  hours'  separation  from  the  mother  to  a  point  but  a  few  degrees  above  that  of  the 
surrounding  atmosphere.  The  views  advanced  by  Edwards  are  fully  illustrated  in  in- 
stances of  premature  birth,  when  the  animal  heat  is  much  more  variable  than  in  infants 
at  term,  and  in  cases  of  persistence  of  the  foramen  ovale.  In  certain  instances  in  which 
life  has  been  prolonged  under  this  abnormal  condition,  the  individual  is  nearly  in  the 
condition  of  a  cold-blooded  animal.  We  can  also  understand  the  remarkable  power  of 
resistance  to  asphyxia  in  newly-born  animals,  for  it  is  well  known  that  cold-blooded  ani- 
mals will  bear  deprivation  of  oxygen  much  better  than  the  higher  classes. 

In  adult  life  there  does  not  appear  to  be  any  marked  and  constant  variation  in  the 
normal  temperature ;  but,  in  old  age,  according  to  the  observations  of  Davy,  while  the 


ANIMAL  HEAT.  511 

actual  temperature  of  the  body  is  not  notably  reduced,  the  power  of  resisting  refrigerat- 
ing influences  is  diminished  very  considerably. 

There  are  no  positive  observations  showing  any  constant  differences  in  the  tempera- 
ture of  the  body  in  the  sexes ;  and  it  may  be  assumed  that,  in  the  female,  the  animal 
heat  is  modified  by  the  same  influences  and  in  the  same  way  as  in  the  male. 

Diurnal  Variations  in  the  Temperature  of  the  Body. — Although  the  limits  of  variation 
in  the  animal  temperature  are  not  very  extended,  certain  fluctuations  are  observed, 
depending  upon  repose  or  activity,  digestion,  sleep,  etc.,  which  it  is  necessary  to  take 
into  account.  These  conditions,  which  are  of  a  perfectly  normal  character,  may  in- 
duce changes  in  the  temperature  amounting  to  from  one  to  three  degrees.  It  has  been 
ascertained  that  there  are  two  well-marked  periods  in  the  day  when  the  heat  is  at  its 
maximum.  These,  according  to  the  most  recent  observations  in  Germany,  are  at  eleven 
A.  M.  and  four  p.  M.  ;  and  it  is  a  curious  fact,  that,  while  all  observations  agree  upon  this 
point,  the  very  elaborate  experiments  of  Lichtenfels  and  Frohlich  show  that  these  periods 
are  well  marked,  even  when  no  food  is  taken.  Biirensprung  and  Ladame  farther  show 
that  the  fall  in  temperature  during  the  night  takes  place  sleeping  or  waking ;  and  that 
when  sleep  is  taken  during  the  day  it  does  not  disturb  the  period  of  the  maximum,  which 
occurs  at  about  four  p.  M.  According  to  these  experiments,  at  eleven  in  the  morning, 
the  animal  heat  is  at  one  of  its  periods  of  maximum  ;  it  gradually  diminishes  for  two  or 
three  hours  and  is  raised  again  to  the  maximum  at  about  four  in  the  afternoon,  when  it 
again  undergoes  diminution  until  the  next  morning.  The  variations  amount  to  from  about 
1°  to  2'16.°  The  minimum  is  always  during  the  night. 

The  relations  of  the  animal  temperature  to  digestion  are  still  somewhat  indefinite.  It 
is  well  known  that  activity  of  the  digestive  organs  increases  the  consumption  of  oxygen, 
and,  to  a  corresponding  degree,  the  exhalation  of  carbonic  acid ;  but  we  have  to  assume 
that  the  production  of  heat  is  in  direct  ratio  to  the  respiratory  action  in  order  to  estab- 
lish any  relation  between  calorification  and  the  digestion  of  ordinary  food.  It  is  easy  to 
calculate  that  a  given  amount  of  oxygen  will  produce  a  definite  quantity  of  carbonic  acid, 
and  will,  by  its  union  with  carbon  and  hydrogen,  generate  a  certain  number  of  "units 
of  caloric  ;  "  but  the  mechanism  of  the  production  of  animal  heat  is  too  complex  and  not 
well  enough  understood  to  admit  of  such  positive  reasoning.  There  is,  indeed,  no  experi- 
mental evidence  of  any  marked  and  constant  change  in  the  general  temperature  of  the 
body  during  the  ordinary  process  of  digestion ;  but  it  is  none  the  less  true  that  the  quan- 
tity and  quality  of  food  bear  a  certain  relation  to  calorification.  This  is  inevitable  from 
the  connection  of  animal  heat  with  the  general  process  of  nutrition  ;  but  this  relation  is 
expressed  in  the  connection  of  calorification  with  nutrition  of  the  tissues,  and  not  in  the 
process  of  the  digestion  or  absorption  of  food.  We  shall  see  that,  when  nutrition  is  modi- 
fied by  alimentation,  the  general  temperature  is  always  more  or  less  affected ;  and  when 
the  requirements  of  the  system,  as  far  as  the  generation  of  heat  is  concerned,  are 
changed,  by  climate  or  otherwise,  alimentation  is  modified.  One  of  the  objects  of  ali- 
mentation and  nutrition  is  to  maintain  the  body  at  a  nearly  constant  temperature. 

The  influence  of  defective  nutrition  or  inanition  upon  the  heat  of  the  body  is  very 
marked.  John  Hunter,  in  his  experiments  upon  animal  heat,  made  a  few  observations 
upon  this  point  and  noted  a  decided  fall  in  temperature  in  a  mouse  kept  fasting.  The 
same  phenomena  were  also  observed  by  Collard  de  Martigny ;  and  Chossat  noted  the 
effects  of  deprivation  of  food  upon  the  power  of  maintaining  the  animal  temperature,  in 
the  most  exact  and  satisfactory  manner.  In  pigeons,  the  extreme  diurnal  variation  in 
temperature,  under  normal  conditions,  was  found  by  Chossat  to  be  1'3.°  During  the 
progress  of  inanition,  the  daily  variation  was  increased  to  5 -9,°  with  a  slight  but  well- 
marked  diminution  in  the  absolute  temperature  ;  and  the  periods  of  minimum  tempera- 
ture were  unusually  prolonged.  Immediately  preceding  death  from  starvation,  the  dimi- 
nution in  temperature  became  very  rapid,  the  rate,  in  the  observations  on  turtle-doves, 


512  NUTRITION. 

being  from  V°  to  11°  per  hour.  Death  usually  occurred  when  the  diminution  had 
amounted  to  about  30°. 

When  the  surrounding  conditions  call  for  the  development  of  an  unusual  amount  of 
heat,  the  diet  is  always  modified,  both  as  regards  the  quantity  and  kind  of  food ;  but 
when  food  is  taken  in  sufficient  quantity  and  is  of  a  kind  capable 'of  maintaining  proper 
nutrition,  its  composition  does  not  affect  the  general  temperature.  If  we  were  to  adopt 
without  reserve  the  view  that  the  non-nitrogenized  alimentary  principles  are  the  sole 
agents  in  the  production  of  heat,  we  should  certainly  be  able  to  determine  either  an 
increase  in  the  animal  heat  or  a  greater  loss  of  heat  from  the  surface,  in  persons  partak- 
ing largely  of  this  kind  of  food.  This,  however,  has  not  been  shown  to  be  true  ;  and  the 
temperature  of  the  body  seems  to  be  uniform  in  the  same  climate,  even  in  persons  living 
upon  entirely  different  kinds  of  food.  The  elaborate  observations  of  Dr.  Davy  are  very 
conclusive  upon  this  point :  "  The  similarity  of  temperature  in  different  races  of  men  is  the 
more  remarkable,  since  between  several  of  them  whose  temperatures  agreed,  there  was 
nothing  in  common  but  the  air  they  breathed — some  feeding  on  animal  food  almost 
entirely,  as  the  Vaida — others  chiefly  on  vegetable  diet,  as  the  priests  of  Boodho — and 
others,  as  Europeans  and  Africans,  on  neither  exclusively,  but  on  a  mixture  of  both." 
Nevertheless,  the  conditions  of  external  temperature  have  a  remarkable  influence  upon  the 
diet.  It  is  well  known,  for  example,  that,  in  the  heat  of  summer,  the  amount  of  meats 
and  fat  taken  is  relatively  small,  and  the  succulent,  fresh  vegetables  and  fruits,  large,  as 
compared  with  the  diet  in  the  winter.  But  although  the  proportion  of  starchy  matters  in 
many  of  the  fresh  vegetables  used  during  a  short  season  of  the  year  is  not  large,  these 
articles  are  equally  deficient  in  nitrogenized  matter.  During  the  winter,  the  ordinary 
diet,  composed  of  meat,  fat,  bread,  potatoes,  etc.,  contains  a  large  amount  of  nitrogenized 
substance,  as  well  as  a  considerable  proportion  of  the  hydro-carbons ;  and,  in  the  sum- 
mer, we  instinctively  reduce  the  proportion  of  both  of  these  varieties  of  principles,  the 
more  succulent  articles  taking  their  place.  This  is  even  more  strikingly  illustrated  by  a 
comparison  of  the  diet  in  the  torrid  or  temperate  and  in  the  frigid  zone.  Under  the  head 
of  alimentation,  we  have  already  noted  the  prodigious  quantities  of  food  consumed  in  the 
Arctic  regions  and  the  effect  of  the  continued  cold  upon  the  habits  of  diet  of  persons 
accustomed  to  a  temperate  climate.  It  is  stated,  upon  undoubted  authority,  that  the  daily 
ration  of  the  Esquimaux  is  from  twelve  to  fifteen  pounds  of  meat,  about  one-third  of 
which  is  fat.  Dr.  Hayes,  the  Arctic  explorer,  noted  that,  with  a  temperature  ranging 
from  —60°  to  —70,°  there  was  a  continual  craving  for  a  strong,  animal  diet,  particularly 
fatty  substances.  Some  of  the  members  of  the  party  were  in  the  habit  of  drinking  the 
contents  of  the  oil-kettle  with  evident  relish. 

Under  such  conditions  as  those  which  surround  inhabitants  of  temperate  regions,  in 
passing  into  the  frigid  zones  a  change  in  diet  is  imperatively  demanded,  in  order  to  keep 
the  animal  temperature  at  the  proper  standard ;  but,  when  the  climate  is  changed  from 
the  temperate  to  the  torrid,  the  habits  of  life  frequently  remain  the  same.  It  is  a  pretty 
general  opinion  among  physicians  who  have  studied  the  subject  specially,  that  many  of 
the  peculiar  disorders  that  affect  those  who  have  changed  their  residence  from  a  temper- 
ate to  a  very  warm  climate  are  due,  in  a  great  measure,  to  the  fact  that  the  diet  and  hab- 
its of  life  are  unchanged. 

The  influence  of  alcoholic  beverages  upon  the  animal  temperature  has  been  studied 
chiefly  with  reference  to  the  question  of  their  use  in  enabling  the  system  to  resist  exces- 
sive cold.  We  have  already  discussed  somewhat  fully  the  physiological  effects  of  alcohol, 
and  we  have  seen  that  its  use  does  not  enable  men  to  endure  a  very  low  temperature  for 
a  great  length  of  time.  This  is  the  universal  testimony  of  scientific  Arctic  explorers ;  and 
Dr.  Hayes  particularly  states,  that,  "  in  almost  any  shape,  it  is  not  only  completely 
useless,  but  positively  injurious." 

The  relations  of  animal  heat  to  respiration  and  nutrition  constitute  a  most  interesting 
and  important  division  of  the  subject,  which  will  be  more  fully  considered  in  discussing 


ANIMAL  HEAT.  5^3 

the  various  theories  of  calorification.  As  a  rule,  when  the  respiratory  activity  is  physio- 
logically increased,  as  it  is  by  exercise,  bodily  or  mental,  ingestion  of  food,  or  by  dimin- 
ished external  temperature,  the  generation  of  heat  in  the  body  is  correspondingly  aug- 
mented ;  and,  on  the  other  hand,  it  is  diminished  by  conditions  which  physiologically 
decrease  the  absorption  of  oxygen  and  the  exhalation  of  carbonic  acid. 

The  relations  of  animal  heat  to  the  general  process  of  nutrition  are  most  intimate. 
Any  condition  that  increases  the  activity  of  nutrition  and  of  disassimilation,  or  even  any 
thing  that  increases  disassimilation  alone,  will  increase  the  production  of  heat.  The 
reverse  of  this  proposition  is  equally  true.  In  pathology,  the  heat  of  the  body  may  be 
increased  by  a  deficient  action  of  the  skin  in  keeping  down  the  temperature,  without  any 
increase  in  the  activity  of  calorification. 

Influence  of  Exercise,  etc.,  upon  the  Heat  of  the  Body. — The  influence  of  muscular 
activity  upon  animal  heat  is  peculiarly  interesting  in  connection  with  the  theories  of  calori- 
fication, from  the  fact  that  the  muscular  system  constitutes  the  greatest  part  of  the  organ- 
ism ;  and,  as  has  repeatedly  been  shown  by  experiment,  a  muscle  taken  from  a  living 
animal  is  not  only  capable  of  contraction  upon  the  application  of  a  stimulus,  but  it  will 
perform  for  a  time  certain  of  the  acts  of  nutrition  and  disassimilation,  such  as  the  appro- 
priation of  oxygen  and  the  generation  and  exhalation  of  carbonic  acid. 

The  most  complete  repose  of  the  muscular  system  is  observed  during  sleep,  when 
hardly  any  of  the  muscles  are  brought  into  action,  except  those  concerned  in  tranquil 
respiration.  There  is  always  a  notable  diminution  in  the  general  temperature  at  this 
time.  This  fact  has  been  observed  by  all  who  have  studied  the  question  experimentally. 
In  the  diurnal  variations  in  the  temperature  of  the  body,  the  minimum  is  always  during 
the  night ;  and,  as  we  have  already  seen,  this  is  not  entirely  dependent  upon  sleep,  for  a 
depression  in  temperature  is  constantly  observed  at  that  time,  even  when  sleep  is  avoided. 

It  is  a  matter  of  common  observation,  that  one  of  the  most  efficient  methods  of 
resisting  the  depressing  influence  of  cold  is  to  constantly  exercise  the  muscles ;  and  it 
is  well  known  that,  after  long  exposure  to  intense  cold,  the  tendency  to  sleep,  which 
becomes  almost  irresistible,  if  indulged  in,  is  followed  by  a  very  rapid  loss  of  heat  and 
almost  certain  death.  It  is  not  necessary  to  cite  the  accounts  of  travellers  and  others  in 
support  of  these  facts.  In  some  animals,  the  amount  of  increase  in  the  temperature 
during  muscular  activity  is  very  great,  and  this  is  notably  marked  in  the  class  of  insects. 
In  the  experiments  of  Newport,  upon  bees  and  other  insects,  a  difference  of  about  27°  was 
noted  between  the  conditions  of  complete  repose  and  great  muscular  activity.  These 
facts  are  interesting,  as  showing  the  very  great  elevation  of  temperature  that  can  be 
produced  in  the  lower  order  of  beings  during  violent  excitement ;  but,  in  man,  the  differ- 
ences, although  distinct,  are  never  very  considerable,  for  the  reason  that  violent  muscular 
exertion  is  generally  attended  with  greatly-increased  action  of  the  skin,  which  keeps  the 
heat  of  the  body  within  very  restricted  limits.  In  the  experiments  of  Newport,  the  loss 
of  heat  from  the  surface  was  arrested  by  confining  the  insects  in  small  glass  bottles. 

The  effects  of  active  exercise,  as  in  fast  walking  or  riding,  were  very  well  observed 
by  Dr.  Davy.  He  found  a  constant  elevation  in  the  general  temperature  (taken  under 
the  tongue),  amounting  to  between  one  and  two  degrees ;  but  the  most  marked  effects 
were  observed  in  the  extremities,  especially  when  they  were  cold  before  taking  the 
exercise. 

The  elevation  in  temperature  that  attends  muscular  action  is  produced  directly  in  the 
substance  of  the  muscle.  This  important  fact  was  settled  by  the  very  interesting  and 
ingenious  experiments  of  Becquerel  and  Breschet.  Introducing  a  thermo-electric  needle 
into  the  biceps  of  a  man  who  used  the  arm  in  sawing  wood  for  five  minutes,  these  physi- 
ologists noted  an  elevation  of  temperature  of  one  degree  centigrade  (nearly  two  degrees 
Fahr.).  The  production  of  heat  in  the  muscular  tissue  was  even  more  strikingly  illus- 
trated by  Matteucci,  in  experiments  with  portions  of  muscle  from  the  frog.  Not  only 
33 


514  NUTRITION. 

did  he  observe  absorption  of  oxygen  and  exhalation  of  carbonic  acid  after  the  muscle  had 
been  removed  from  the  body  of  the  animal,  but  he  noted  an  elevation  in  tempera- 
ture of  about  one  degree  Fahr.,  following  contractions  artificially  excited. 

It  is  useless  to  multiply  citations  of  experiments  illustrating  the  facts  above  noted  or 
to  discuss  elaborately  the  theoretical  transformation  of  a  given  quantity  of  caloric  into 
a  definite  and  an  invariable  amount  of  work.  The  conditions  in  the  animal  economy  are 
siich  that  we  cannot  exactly  appreciate  the  loss  of  heat  by  the  cutaneous  and  respiratory 
surfaces ;  nor  can  we  follow  the  processes  in  the  body  which  involve  the  disappearance 
of  oxygen  and  the  evolution  of  carbonic  acid ;  the  exact  changes  undergone  by  the 
hydro-carbonaceous  elements  of  food  and  constituents  of  the  body ;  the  amount  of  heat 
involved  in  the  changes  of  the  nitrogenized  elements ;  and,  in  short,  we  cannot  make 
the  corrections  that  are  absolutely  necessary  before  we  can  hope  to  reduce  the  question 
of  the  oxidation  of  certain  principles  in  the  body,  the  development  of  heat,  and  the 
generation  of  mechanical  force,  to  exact  mathematical  calculation. 

Observations  upon  the  influence  of  mental  exertion  on  the  temperature  of  the  body 
have  not  been  so  numerous,  but  they  are,  apparently,  no  less  exact  in  their  results.  Dr. 
Davy  was  the  first  to  make  any  extended  experiments  upon  this  point  and  has  noted  a 
slight  but  constant  elevation  during  "excited  and  sustained  attention."  The  same  line 
of  observation  has  been  followed  by  Prof.  Lombard,  who  employed  much  more  exact 
methods  of  investigation.  Prof.  Lombard  noted  an  elevation  of  temperature  in  the  head 
during  mental  exertion  of  various  kinds,  but  it  was  slight,  the  highest  rise  not  exceeding 
the  twentieth  of  a  degree.  It  is  stated,  also,  that  the  temperature  of  the  body  is  increased 
by  the  emotions  of  hope,  joy,  anger,  and  all  exciting  passions,  while  it  is  diminished 
by  fear,  fright,  and  mental  distress.  Burdach,  from  whom  the  foregoing  statement  is 
taken,  cites  an  example  of  an  elevation  of  temperature  from  96°  to  99 '5°  in  a  violent 
access  of  anger,  and  a  descent  to  92-75°  under  the  influence  of  fear,  but  the- temperature 
soon  returned  to  97*25°. 

The  nervous  system  exerts  a  most  important  influence  over  the  animal  temperature, 
as  it  modifies  the  circulation  and  the  nutritive  processes  in  particular  parts.  The  most 
interesting  of  these  influences  are  transmitted  through  the  sympathetic  system.  These 
will  be  discussed,  to  a  certain  extent,  in  connection  with  the  theories  of  calorification  ; 
but  they  cannot  be  taken  up  fully  until  we  come  to  consider  the  functions  of  the  sympa- 
thetic system  and  its  relations  to  nutrition.  In  this  connection,  we  shall  simply  allude 
to  certain  phenomena  manifested  through  the  nervous  system,  without  attempting  to 
fully  explain  their  mechanism. 

It  is  well  known  that,  when  the  sympathetic  nerves  going  to  a  particular  part  are 
divided,  the  arterial  coats  are  paralyzed  and  dilated,  the  supply  of  blood  is  increased, 
nutrition  is  locally  exaggerated  and  more  or  less  modified,  and  the  temperature  of  the 
part  is  increased  by  from  five  to  ten  degrees.  An  illustration  of  these  facts  in  the  ear 
of  the  rabbit,  after  division  of  the  sympathetic  in  the  neck,  is  a  very  common  observa- 
tion, which  we  have  often  verified  in  public  demonstrations.  All  of  these  unnatural 
phenomena  disappear  upon  galvanization  of  the  divided  extremity  of  the  nerve.  These 
local  modifications  in  the  temperature  have  been  frequently  observed  pathologically  in 
the  human  subject.  A  number  of  curious  local  variations  of  temperature  can  be  explained 
by  direct  or  reflex  action  through  the  sympathetic  nerves. 

It  is  evident  that,  if  animal  heat  be  one  of  the  necessary  attendant  phenomena  of 
nutrition,  it  must  be  greatly  influenced  by  conditions  of  the  circulation.  It  has  been  a 
question,  indeed,  whether  the  modifications  in  temperature  produced  by  operating  upon 
the  sympathetic  system  of  nerves  be  not  due  entirely  to  changes  in  the  supply  of  blood, 
t  is  certain  that  whatever  determines  an  increased  supply  of  blood  to  any  part  raises 
the  temperature ;  and,  whenever  the  quantity  of  blood  in  any  organ  or  part  is  consid- 
erably diminished,  the  temperature  is  reduced.  This  fact  is  constantly  illustrated  in 
operations  for  the  deligation  of  large  arteries.  It  is  well  known  that,  after  tying  a 


SOUKCES   OF  ANIMAL  HEAT.  515 

large  vessel,  the  utmost  care  is  necessary  to  keep  up  the  temperature  of  the  part  to 
which  its  branches  are  distributed,  until  the  anastomosing  vessels  become  enlarged 
sufficiently  to  supply  the  amount  of  blood  necessary  for  healthy  nutrition. 

Sources  of  Animal  Heat. 

The  most  interesting  question  connected  with  calorification  relates  to  the  sources 
of  heat  in  the  living  organism ;  and  a  careful  estimate  of  the  physiological  value  of 
all  the  facts  that  have  been  positively  established  with  reference  to  this  point  places 
the  following  proposition  beyond  any  reasonable  doubt : 

The  generation  of  heat  in  the  living  animal  organism  is  connected,  more  or  less 
intimately,  with  all  of  the  processes  of  nutrition  and  disassimilation,  including,  of  course, 
the  consumption  of  oxygen  and  the  production  of  carbonic  acid ;  and  this  function  is 
modified,  to  a  greater  or  less  degree,  by  all  conditions  that  influence  the  general  process 
of  nutrition  or  the  operation  of  the  nutritive  forces  in  particular  parts. 

This  proposition  is  not  contradicted  by  any  well-settled  physiological  facts  or  princi- 
ples. Every  one  of  the  functions  of  the  body  bears  more  or  less  closely  upon  nutrition ; 
and  all  the  physiological  modifications  of  the  various  functions,  without  exception, 
affect  the  process  of  calorification.  We  must  bear  in  mind  the  fact  that,  in  man  and  in 
the  warm-blooded  animals  generally,  the  maintenance  of  the  temperature  of  the  organism 
at  a  nearly  fixed  standard  is  a  necessity  of  life  and  of  the  physiological  action  of  the 
different  parts  ;  and  that,  while  heat  is  generated  in  the  organism  with  an  activity  that 
is  constantly  varying,  it  is  as  constantly  counterbalanced  by  physiological  loss  of  heat  from 
the  cutaneous  and  the  respiratory  surfaces.  Variations  in  the  activity  of  calorification 
are  not  to  be  measured  by  corresponding  changes  in  the  temperature  of  the  body,  but 
are  to  be  estimated  by  calculating  the  amount  of  heat  lost.  The  ability  of  the  human 
race  to  live  in  all  climates  is  explained  by  the  adaptability  of  man  to  different  conditions 
of  diet  and  exercise,  and  to  the  power  of  regulating  loss  of  heat  from  the  surface  by 
appropriate  clothing. 

Our  proposition  regarding  the  production  of  animal  heat  is  in  no  wise  opposed  to  the 
so-called  combustion-theory,  as  it  is  received  by  most  physiologists  of  the  present  day ; 
but  it  must  be  admitted  that  it  is  an  unfortunate  use  of  terms  to  apply  the  name  com- 
bustion to  the  general  process  of  nutrition,  as  is  done  by  those  who  attempt  to  preserve, 
not  only  the  ideas  of  the  great  author  of  this  theory,  but  certain  modes  of  expression, 
which  were  in  accordance  only  with  his  limited  knowledge  of  the  phenomena  of  nutri- 
tion. If  we  speak  of  animal  heat  as  the  result  of  combustion  of  certain  elements,  it 
will  be  necessary  either  to  refer  constantly  to  the  difference  between  combustion  as  it 
occurs  in  the  organism  and  mere  oxidation  out  of  the  body,  or  to  start  with  a  full 
definition  of  what  is  to  be  understood  by  the  term  physiological  combustion,  which 
reduces  itself  simply  to  a  definition  of  nutrition.  Regarding  calorification,  then,  as  con- 
nected with  all  of  the  varied  processes  of  nutrition,  it  remains  for  us  to  determine  the 
following  questions : 

1.  In  what  part  or  parts  of  the  organism  is  heat  generated  ? 

2.  What  is  the  relative  importance  in  calorification,  as  regards  the  amount  of  heat 
generated,  of  the  processes  of  nutrition,  as  we  can  study  them  separately  ? 

3.  What  are  the  principles  invariably  and  of  necessity  consumed  and  produced  in  the 
organism  in  calorification ;  and  what  is  the  relative  importance  of  the  principles  thus 
consumed  and  the  products  thus  generated  and  thrown  off? 

4.  How  far  have  we  been  able  to  follow  those  material  transformations  in  the  organ- 
ism which  involve  the  consumption  of  certain  principles,  the  production  of  new  com- 
pounds, and  the  generation  of  heat  ? 

Seat  of  the  Production  of  Animal  Neat. — Few  if  any  physiologists  at  the  present 
day  hold  to  the  opinion  that  there  is  any  part  or  organ  in  the  body  specially  and 


516  NUTRITION. 

exclusively  concerned  in  the  production  of  heat.  In  the  early  history  of  the  oxidation- 
theory  of  Lavoisier,  it  was  thought  by  some  that  the  inspired  oxygen  combined  with 
the  hydro-carbons  of  the  blood  in  the  lungs,  and  that  the  heat  of  the  body  was  gener- 
ated almost  exclusively  in  these  organs;  but  this  idea  has  long  since  been  abandoned. 
We  have  already  fully  considered  the  question  of  the  loss  or  gain  in  the  temperature  of  the 
blood  in  its  passage  through  the  lungs,  and  we  have  seen  that  there  is,  to  say  the  least, 
no  constant  elevation  showing  a  generation  of  heat  in  these  organs,  sufficient  to  warm 
the  blood,  and  through  it  the  different  parts  of  the  body.  If  we  find  that  the  blood  in 
coming  from  the  lungs  has  about  the  same  temperature  as  when  it  entered  these  organs, 
it  must  be  admitted  that  there  is  a  certain  generation  of  heat  to  compensate  the  loss  by 
evaporation  from  the  pulmonary  surface.  As  far  as  we  know,  the  heat  that  results  from 
the  mere  physical  solution  of  oxygen  in  the  blood  is  all  that  is  produced  in  the  lungs.  There 
is  no  sufficient  evidence  to  show  that  the  lungs  are  special  organs  of  calorification  ;  and 
any  generation  of  heat  that  takes  place  here  is  due,  probably,  to  purely  physical  phe- 
nomena in  the  blood. 

It  is  only  necessary  to  refer  back  to  the  pages  treating  of  the  variations  in  the  tem- 
perature of  the  blood  in  different  parts,  to  show  that  heat  is  produced  in  the  general  sys- 
tem and  not  in  any  particular  organ  or  in  the  blood  as  it  circulates.  The  experiments 
of  Matteucci,  showing  an  elevation  of  temperature  in  a  muscle  excited  to  contraction 
after  it  had  been  removed  from  the  body,  and  the  observations  of  Becquerel  and  Bre- 
schet,  showing  increased  development  of  heat  by  muscular  contraction,  are  sufficient 
evidence  of  the  production  of  heat  in  the  muscular  system;  and,  inasmuch  as  the  muscles 
constitute  by  far  the  greatest  part  of  the  weight  of  the  body,  they  are  a  most  important 
source  of  animal  heat. 

It  has  been  demonstrated,  by  the  experiments  of  Bernard,  that  the  blood  becomes 
notably  warmer  in  passing  through  the  abdominal  viscera.  This  is  particularly  marked 
in  the  liver,  and  it  shows  that  the  large  and  highly-organized  viscera  are  also  important 
sources  of  caloric. 

As  far  as  it  is  possible  to  determine  by  experimental  demonstration,  not  only  is  there 
no  particular  part  or  organ  in  the  body  endowed  with  the  special  function  of  calorifica- 
tion, but  every  part  in  which  the  nutritive  forces  are  in  operation  produces  a  certain 
amount  of  heat ;  and  this  is  probably  true  of  the  blood-corpuscles  and  other  anatomical 
elements  of  this  class.  The  production  of  heat  in  the  body  is  general  and  is  one  of  the 
necessary  consequences  of  the  process  of  nutrition ;  but,  with  nutrition,  it  is  subject  to 
local  variations,  as  is  strikingly  illustrated  in  the  effects  of  operations  upon  the  sympa- 
thetic system  of  nerves  and  in  the  phenomena  of  inflammation. 

Relations  of  Animal  Heat  to  Nutrition. — Nutrition  involves  the  appropriation  of 
matters  taken  into  the  body  and  the  production  and  elimination  of  effete  substances.  In 
its  widest  signification,  this  includes  the  consumption  of  oxygen  and  the  elimination  of 
carbonic  acid ;  and,  consequently,  we  may  strictly  regard  respiration  as  a  nutritive  act. 
All  of  the  nutritive  processes  go  on  together,  and  they  all  involve,  in  most  warm-blooded 
animals  at  least,  a  nearly  uniform  temperature.  During  the  first  periods  of  embryonic 
life,  the  heat  derived  from  the  mother  is  undoubtedly  necessary  to  the  development  of 
tissue  by  a  change  of  substance,  analogous  to  nutrition  and  even  superior  to  it  in  activity. 
During  adult  life,  animal  heat  and  the  nutritive  force  are  coexistent.  It  now  becomes  a 
question  to  determine  whether  there  be  any  class  of  nutritive  principles  specially  con- 
cerned in  calorification,  or  any  of  the  nutritive  acts,  that  we  have  been  able  to  study  by 
themselves,  which  are  exclusively  or  specially  directed  to  the  maintenance  of  the  temper- 
ature of  the  body.  These  questions  simply  involve  a  review  of  considerations  with  regard 
to  the  relations  of  various  of  the  functions  to  the  production  of  heat. 

The  supply  of  the  waste  of  tissue  being  effected  by  metamorphosis  of  alimentary  matter 
— a  process,  the  exact  nature  of  which  we  have  not  been  able  to  determine — it  has  thus 


SOUKCES   OF  ANIMAL  HEAT.  517 

far  been  possible,  only,  to  divide  the  food  into  different  classes.  Of  these,  leaving  out 
oxygen,  we  shall  consider,  in  this  connection,  the  organic  matters,  divided  into  nitrogen- 
ized-and  non-nitrogenized.  The  inorganic  salts  are  always  combined  with  nitrogenized 
matter,  and  they  seem  to  pass  through  the  organism  without  undergoing  any  considerable 
change ;  and  there  is  no  evidence  that  they  have  any  connection,  of  themselves,  with  the 
production  of  heat. 

What  is  the  relation  to  calorification  of  those  processes  of  nutrition  which  involve  the 
consumption  of  nitrogenized  matter  and  the  production  of  the  nitrogenized  excrementi- 
tious  principles  ? 

We  cannot  study  the  phenomena  of  calorification  alone,  isolated  from  the  other  acts 
of  nutrition.  We  may  confine  an  animal  to  a  purely  nitrogenized  diet,  and  the  heat  of  the 
body  will  be  maintained  at  the  proper  standard ;  but  at  all  times  there  is  a  certain  quan- 
tity of  non-nitrogenized  matter  (sugar  and  perhaps  fat)  produced  in  the  system,  which  is 
formed  only  to  be  consumed.  We  may  starve  an  animal,  and  the  temperature  will  not  fall 
to  any  very  great  extent  until  a  short  time  before  death.  Here  we  may  suppose  that  the 
process  of  deposition  of  nutritive  matter  in  the  tissues  from  the  blood  is  inconsiderable, 
as  compared  with  the  transformation  of  the  substance  of  these  tissues  into  effete  matter ; 
and  it  is  almost  certain  that  non-nitrogenized  matter  is  not  produced  in  the  organism  in 
quantity  sufficient  to  account,  by  its  destruction  in  the  lungs,  for  the  carbonic  acid  exhaled. 
It  seems  beyond  question  that  there  must  be  heat  evolved  in  the  body  by  oxidation  of 
nitrogenized  matter.  When  the  daily  amount  of  food  is  largely  increased  for  the  purpose 
of  generating  the  immense  amount  of  heat  required  in  excessively  cold  climates,  the  nitro- 
genized matters  are  taken  in  greater  quantity,  as  well  as  the  fats,  although  their  increase 
is  not  in  the  same  proportion.  When,  however,  we  endeavor  to  assign  to  the  nitrogenized 
matters  a  definite  proportion  of  heat-producing  power,  we  are  arrested  by  a  want  of 
positive  knowledge  with  regard  to  the  metamorphoses  which  these  principles  undergo ; 
and  it  is  equally  impossible  to  fix  the  relative  calorific  value  of  the  deposition  of  new 
material  in  repair  of  the  tissues  and  the  change  of  their  substance  into  effete  matter  in 
disassimilation.  From  these  facts,  and  from  other  considerations  that  have  already  been 
fully  discussed  under  different  heads,  it  is  evident  that  the  physiological  metamorphoses 
of  nitrogenized  matter  bear  a  certain  share  in  the  production  of  animal  heat ;  although, 
in  connection  with  inorganic  matter,  their  chief  function  seems  to  be  the  repair  of  the 
tissues  endowed  with  so-called  vital  properties. 

What  is  the  relation  of  the  consumption  of  non-nitrogenized  matter  to  the  production 
of  animal  heat  ? 

It  has  been  impossible  to  treat  of  the  relations  of  the  non-nitrogenized  elements  to 
nutrition  without  considering  more  or  less  fully  the  part  which  these  principles  bear  in 
the  production  of  heat ;  and  we  must  refer  the  reader  to  the  previous  pages  for  a  discus- 
sion of  certain  of  these  points.  In  this  connection,  we  shall  simply  state  the  relations 
that  this  class  of  principles  is  known  to  bear  to  calorification,  and  the  facts  upon  which 
our  statements  are  based. 

It  has  been  pretty  clearly  shown  that  both  sugar  and  fat  are  actually  produced  in  the 
organism,  even  when  the  diet  is  strictly  nitrogenized  in  its  character ;  but  we  shall  con- 
sider only  the  relations  of  the  non-nitrogenized  elements  introduced  into  the  body,  assuming 
that  the  principles  of  this  class  appearing  de  now  in  the  organism  are  the  result  of  a  trans- 
formation of  nitrogenized  substances. 

As  far  as  the  destination  of  the  amylaceous,  saccharine,  and  fatty  elements  of  food 
is  concerned,  we  only  know  that  they  are  incapable,  of  themselves,  of  repairing  muscu- 
lar tissue,  and  that  they  cannot  sustain  life.  They  are  never  discharged  from  the  body  in 
health  in  the  form  under  which  they  enter ;  but  they  are  in  part  or  completely  destroyed 
in  nutrition.  They  are  completely  destroyed  in  persons  who,  from  habitual  muscular  exer- 
cise, have  very  little  adipose  tissue.  When  their  quantity  in  the  food  is  large,  they  are  not 
of  necessity  entirely  consumed,  but  they  may  be  deposited  in  the  form  of  adipose  tissue. 


518  NUTRITION. 

This,  however,  may  be  made  to  disappear  by  violent  exercise  or  under  an  insufficient 

diet. 

There  can  be  no  doubt  that  the  non-nitrogenized  class  of  alimentary  principles  is 
craved  by  the  system  in  long-continued  exposure  to  extreme  cold.  This  is  particularly 
marked  with  regard  to  the  fats.  In  all  cold  climates,  fat  is  a  most  important  element  of 
food ;  and,  in  excessively  cold  regions,  while  the  nitrogenized  elements  are  largely  in- 
creased, there  is  a  very  much  larger  proportional  increase  in  the  quantity  of  fat.  These 
facts  are  very  significant.  If  the  non-nitrogenized  elements  of  food — which  are  not  always 
indispensable,  though  often  very  necessary  articles— do  not  form  tissue,  are  not  discharged 
from  the  body,  and  are  consumed  in  some  of  the  processes  of  nutrition,  it  would  seem 
that  their  change  must  involve  the  production  of  carbonic  acid,  perhaps  also  of  water, 
and  the  evolution  of  heat.  It  is  so  difficult  to  ascertain  the  exact  quantities  of  carbonic 
acid,  watery  vapor,  etc.,  thrown  off  by  the  lungs,  skin,  and  other  emunctories,  and  to  esti- 
mate the  exact  amount  of  heat  produced  and  lost,  that  it  is  not  surprising  that  calculations 
of  the  calorific  power  of  different  articles  of  food  should  be  frequently  erroneous;  par- 
ticularly as  we  have  no  means  of  knowing  the  exact  calorific  value  of  the  nitrogenized 
principles. 

Although  we  may  assume  that  the  non-nitrogenized  elements  of  food  are  particularly 
important  in  the  production  of  animal  heat,  and  that  they  are  not  concerned  in  the  repair 
of  tissue,  it  must  be  remembered  that  the  animal  temperature  may  be  kept  at  the  proper 
standard  upon  an  exclusively  nitrogenized  diet ;  and  we  cannot,  indeed,  connect  calorifi- 
cation exclusively  with  the  consumption  of  any  single  class  of  principles  or  with  any 
single  one  of  the  acts  of  nutrition. 

Relations  of  Calorification  to  Respiration. — Respiration  is  one  of  the  nutritive  pro- 
cesses that  can  be  closely  studied  by  itself,  as  it  involves  the  appropriation  by  the  system 
of  a  single  principle  (oxygen),  and  that  simply  in  solution  in  the  blood.  There  can  be 
no  doubt  that,  of  all  the  nutritive  acts,  respiration  is,  far  more  than  any  other,  intimately 
connected  with  calorification.  As  far  as  the  general  process  is  concerned,  the  production 
of  heat  is  usually  in  direct  ratio  to  the  consumption  of  oxygen  and  the  exhalation  of  car- 
bonic acid.  In  the  animal  scale,  wherever  we  have  the  largest  amount  of  heat  produced, 
we  observe  the  greatest  respiratory  activity.  In  man,  whatever  increases  the  generation 
of  heat  increases  as  well  the  consumption  of  oxygen  and  the  elimination  of  carbonic  acid. 
The  production  of  heat  in  warm-blooded  animals  is  constant,  and  it  cannot  be  interrupted, 
even  for  a  few  minutes.  The  same  is  true  of  respiration.  The  tissues  may  waste  for 
want  of  nourishment,  but  the  heat  of  the  body  must  be  kept  near  a  certain  standard, 
which  is  almost  always  much  higher  than  the  surrounding  temperature  ;  and  there  is  no 
other  nutritive  act  so  constant  and  so  immediately  necessary  to  existence  as  the  appro- 
priation of  oxygen.  It  is  not  surprising,  then,  that,  early  in  the  history  of  the  physiology 
of  nutrition,  before  we  knew  even  the  exact  condition  and  proportion  of  the  gases  in 
the  blood,  it  should  have  been  thought  that  animal  heat  was  the  result  of  slow  combustion 
of  the  hydro-carbons. 

The  physiological  history  of  respiration  and  of  animal  heat  dates  from  the  same  series 
of  discoveries.  In  the  latter  part  of  the  last  century,  the  great  chemist,  Lavoisier,  discov- 
ered the  intimate  nature  of  the  respiratory  process  and  applied  the  theory  of  the  con- 
sumption of  oxygen  and  the  evolution  of  carbonic  acid  to  calorification.  Like  nearly  all 
of  the  great  advances  in  physiological  science,  the  distinctly-enunciated  idea  was  fore- 
shadowed by  earlier  writers.  It  will  not  be  necessary  to  treat,  from  a  purely  historical 
point  of  view,  of  the  discoveries  made  by  Lavoisier.  He  undoubtedly  went  as  far  in  his 
explanations  of  the  phenomena  of  animal  heat  as  was  possible  in  the  condition  of  the 
science  at  the  time  his  investigations  were  made ;  and,  although  he  inevitably  fell  into 
some  errors  in  his  calculations  and  deductions,  he  must  forever  be  regarded  as  the  author 
of  the  first  reasonable  theory  of  the  generation  of  heat  by  animals. 


SOURCES   OF  ANIMAL  HEAT.  519 

The  Consumption  of  Oxygen  and  Production  of  Carbonic  Acid  in  Connection  with 
the  Evolution  of  Heat. — As  far  as  it  has  been  possible  to  determine  by  actual  experi- 
ment, all  animals,  even  those  lowest  in  the  scale,  appropriate  oxygen  and  eliminate  car- 
bonic acid.  This  is  equally  true  of  all  living  tissues  ;  and,  since  it  has  been  ascertained 
that  oxygen  is  dissolved,  as  oxygen,  in  the  arterial  blood,  that  it  disappears  in  part  or 
entirely  in  the  capillary  circulation,  that  carbonic  acid  is  taken  up  by  the  venous  blood, 
both  in  solution  and  in  feeble  combination  in  the  bicarbonates,  to  be  discharged  in  the 
lungs  by  displacement  and  the  action  of  the  pneumic  acid,  and  that  the  tissues  them- 
selves have  the  property  of  appropriating  oxygen  and  exhaling  carbonic  acid,  those  who 
adopt  the  theory  of  Lavoisier  have  simply  changed  the  seat  of  oxidation  from  the  lungs 
to  the  general  system. 

It  has  been  proven  beyond  question  that  oxygen,  of  all  the  principles  introduced  from 
without,  is  the  one  most  immediately  necessary  to  nutrition  ;  and  it  differs  from  the  class 
of  substances  ordinarily  known  as  alimentary,  only  in  the  fact  that  it  is  consumed  more 
promptly  and  constantly.  In  the  same  way.  carbonic  acid  is  to  be  regarded  as  an  ele- 
ment of  excretion,  like  urea,  creatine,  etc.,  differing  from  them  only  in  the  immediate 
necessity  for  its  elimination.  As  the  comparatively  slow  excretion  of  urea  and  other 
nitrogenized  matters  is  connected  with  the  ingestion  of  ordinary  alimentary  substances 
that  are  slowly  appropriated  by  the  tissues,  so  the  rapid  elimination  of  carbonic  acid  is 
connected  with  the  equally  rapid  appropriation  of  oxygen.  There  is  no  reason  why  we 
should  not  regard  carbonic  acid,  like  other  effete  substances,  as  an  excretion,  the  result 
of  disassimilation  of  the  tissues  generally ;  but,  more  closely  than  any,  it  is  connected 
with  the  rapid  and  constant  evolution  of  heat. 

Experiments  on  the  influence  of  the  sympathetic  nerves  upon  the  temperature  of  par- 
ticular parts  have  completed  the  chain  of  evidence  in  favor  of  the  localization  of  the 
heat-producing  function  in  the  tissues.  It  is  not  our  purpose  to  discuss  the  relations  of 
the  sympathetic  system  to  nutrition,  deferring  this  subject  until  we  come  to  treat  spe- 
cially of  the  nervous  system ;  but  the  facts  bearing  on  calorification  are  briefly  as  follows : 

If  the  sympathetic  nerve  be  divided  in  the  neck  of  a  rabbit  or  any  other  warm- 
blooded animal,  the  side  of  the  head  supplied  by  this  nerve  will  become  from  five  to 
eight  or  ten  degrees  warmer  than  the  opposite  side,  or  than  the  rest  of  the  body.  This 
observation  we  have  repeatedly  verified.  The  conditions  under  which  this  local  exag- 
geration of  the  animal  heat  is  manifested  are,  dilatation  of  the  arteries  of  supply  of  the 
part,  so  that  it  receives  very  much  more  blood  than  before,  and  increased  activity  in  the 
general  process  of  nutrition.  It  also  has  been  observed,  in  experiments  upon  the  horse, 
that  the  blood  coming  from  the  part  is  red  and  contains  very  much  more  oxygen  than 
ordinary  venous  blood. 

The  observations  of  MM.  Estor  and  Saint-Pierre  show  that  the  blood  coming  from 
inflamed  parts,  in  which  there  is  a  considerable  elevation  above  the  normal  temperature, 
is  red,  and  that  it  contains  from  fifty  to  two  hundred  and  fifty  per  cent,  more  oxygen  than 
ordinary  venous  blood.  These  facts  are  regarded  as  inconsistent  with  the  view  that  the 
temperature  of  parts  is  due  chiefly  to  oxidation ;  but,  when  we  consider  the  fact  that,  in 
the  conditions  above  mentioned,  the  actual  quantity  of  blood  circulating  in  these  parts  is 
increased  many  times,  the  error  in  the  deduction  is  palpable  enough.  It  is  not  sufficient 
to  show  that  the  blood  coming  from  an  inflamed  tissue,  with  an  abnormally  high  temper- 
ature, contains  more  oxygen  than  under  ordinary  conditions,  but  it  is  indispensable  to 
demonstrate  that  the  absolute  quantity  of  oxygen  consumed  is  diminished.  For  exam- 
ple, if  the  venous  blood  should  contain  double  the  normal  proportion  of  oxygen,  but  the 
quantity  coming  from  the  part  should  be  increased  threefold,  it  is  evident  that  the  actual 
consumption  of  oxygen  would  be  doubled.  As  an  illustration,  let  us  assume  that,  in  one 
minute,  100  parts  of  blood,  containing  10  parts  of  oxygen,  circulate  through  a  member, 
losing  in  its  passage  7*5  parts  of  oxygen,  thus  leaving  a  proportion  of  2*5  of  oxygen  for 
the  venous  blood ;  if  the  part  become  inflamed,  let  us  suppose  that,  during  the  same 


520  NUTRITION. 

period,  300  parts  of  blood,  with  30  parts  of  oxygen,  pass  through,  but  that  the  venous  blood 
contains  five  per  cent,  of  oxygen,  or  15  parts.  That  would  show  an  actual  consumption 
of  15  parts  of  oxygen  in  inflammation,  against  7'5  under  normal  nutritive  conditions. 
Estor  and  Saint-Pierre  do  not  state  the  amount  of  increase  in  the  quantity  of  blood  cir- 
culating through  inflamed  tissues,  but  they  admit  that,  "  in  inflammation,  the  vessels  are 
dilated,  and  the  current  of  blood  is  more  rapid."  An  increase  in  the  absolute  quantity 
of  blood  passing  through  parts  after  division  of  the  sympathetic  nerves  distributed  to  the 
coats  of  the  blood-vessels  has  been  observed  by  all  who  have  experimented  upon  the  sub- 
ject ;  and  the  increase  is  probably  greater  than  that  which  we  have  assumed  in  our  argu- 
ment. An  additional  argument  in  favor  of  our  interpretation  of  the  experiments  of 
Estor  and  Saint-Pierre  is  the  fact,  noted  by  them,  that  the  blood  from  inflamed  parts 
contains  more  carbonic  acid  than  ordinary  venous  blood. 

Taking  into  account  all  the  facts  bearing  upon  the  question,  there  can  be  little  doubt, 
that,  while  the  processes  of  nutrition  and  disassimilation,  involving  changes  in  the  nitro- 
genized  constituents  of  the  blood  and  the  tissues,  are  not  disconnected  with  calorifica- 
tion, the  production  of  heat  by  animals  is  most  closely  related  to  the  appropriation  of 
oxygen  and  the  formation  of  carbonic  acid. 

Intimate  Nature  of  the  Calorific  Processes. — A  comprehension  of  the  intimate  nature 
of  the  calorific  processes  involves  simply  an  answer  to  the  question,  how  far  we  can  fol- 
low the  material  transformations  in  the  organism,  which  involve  the  consumption  of  cer- 
tain principles,  the  production  of  new  compounds,  and  the  evolution  of  heat.  As  regards 
the  nature  of  the  intermediate  processes  connecting  the  disappearance  of  oxygen  with 
the  production  of  carbonic  acid,  we  can  only  explain  it  by  reciting  the  simple  facts. 
Oxygen  disappears,  carbonic  acid  is  formed,  and  the  carbon  is  furnished,  perhaps  by  the 
tissues,  perhaps  by  the  blood,  probably  by  both.  It  is  probable  that  the  intermediate 
changes  are  more  simple  and  rapid  than  those  which  intervene  between  the  appropria- 
tion of  nitrogenized  nutritive  matter  and  the  formation  of  the  nitrogenized  excretions  ; 
but  we  have  never  been  able  to  follow  either  of  these  processes  through  all  of  its  dif- 
ferent phases.  We  must  be  content,  in  the  present  condition  of  our  positive  knowledge, 
to  regard  calorification  as  one  of  the  attendant  phenomena  of  nutrition ;  and  we  have 
only  to  study  as  closely  as  possible  the  facts  with  regard  to  the  disappearance  of  certain 
principles  and  the  formation  of  effete  matters,  that  are  always  and  of  necessity  associated 
with  the  development  of  heat. 

Equalization  of  the  Animal  Temperature. — A  study  of  the  phenomena  of  calorification 
in  the  human  subject  has  shown  that  under  all  conditions  of  climate  the  general  heat  of 
the  body  is  equalized.  Nearly  always,  the  surrounding  temperature  is  below  the  standard 
of  heat  of  the  body,  and  there  is,  of  necessity,  an  active  production  of  caloric.  Under 
all  conditions,  there  is  more  or  less  loss  of  heat  by  evaporation  from  the  general  surface ; 
and,  when  the  surrounding  atmosphere  is  very  cold,  it  becomes  desirable  to  reduce  this 
loss  to  the  minimum.  This  is  done  by  appropriate  clothing,  which  must  certainly  be 
regarded  as  a  physiological  necessity.  The  proper  kind  of  clothing,  the  conducting 
power  of  different  materials,  their  porosity,  etc.,  form  important  questions  in  practical 
hygiene,  and  their  full  discussion  belongs  to  special  treatises.  Clothing  protects  from 
excessive  heat  as  well  as  from  cold.  Thin,  porous  articles  moderate  the  heat  of  the  sun, 
equalize  evaporation,  and  afford  great  protection  in  hot  climates.  In  excessive  cold, 
clothing  is  of  the  greatest  importance  in  preventing  the  escape  of  heat  from  the  body. 
When  the  body  is  not  exposed  to  currents  of  air,  the  garments  are  useful  chiefly  as  non- 
conductors, imprisoning  many  layers  of  air,  which  are  warmed  by  contact  with  the  person. 
It  is  farther  very  important  to  protect  the  body  from  the  wind,  which  increases  so  greatly 
the  loss  of  heat  by  evaporation.  It  is  wonderful,  however,  how  intense  a  cold  may  be 
resisted  by  healthy  men  under  proper  conditions  of  alimentation  and  exercise  and  with 


EQUALIZATION   OF  THE  ANIMAL  TEMPERATURE.  521 

the  protection  of  appropriate  clothing,  as  in  Arctic  explorations,  when  the  thermometer 
has  for  days  ranged  from  —60°  to  —70°  Falir. 

When  from  any  cause  there  is  a  tendency  to  undue  elevation  of  the  heat  of  the  body, 
cutaneous  transpiration  is  increased,  and  the  temperature  is  kept  at  the  proper  standard. 
We  have  already  considered  this  question  in  treating  of  the  action  of  the  skin,  and  we  have 
noted  facts  showing  that  men  can  work  when  exposed  to  a  heat  much  higher  than  that 
of  the  body  itself.  The  amount  of  vapor  that  is  lost  under  these  conditions  is  sometimes 
enormous,  amounting  to  from  two  to  four  pounds  in  an  hour.  We  have  ourselves  often 
noted  a  loss  of  between  two  and  three  pounds  after  exposure  for  less  than  an  hour  to  a 
steam-bath  of  from  110°  to  116° ;  and  a  much  greater  elevation  of  temperature,  in  dry 
air,  can  be  tolerated  with  impunity.  We  have  alluded  to  some  of  the  observations  upon 
the  temperatures  that  could  be  borne  without  bad  results,  in  connection  with  the  ques- 
tion of  variations  in  the  heat  of  the  body.  In  the  experiments  of  Delaroche  and  Berger, 
the  temperature  was  considerably  under  200°.  Tillet  recorded  an  instance  of  a  young 
girl  who  remained  in  an  oven  for  ten  minutes  without  inconvenience,  at  a  temperature 
of  130°  Reaumur,  or  324'5°  Fahr.  Dr.  Blagden,  in  his  noted  experiments  in  a  heated 
room,  made  in  connection  with  Drs.  Banks,  Solander,  Fordyce,  and  others,  found,  in  one 
series  of  observations,  that  a  temperature  of  211°  could  be  easily  borne  ;  and,  at  another 
time,  the  heat  was  raised  to  260°.  Chabert,  who  exhibited  in  this  country  and  in  Eu- 
rope under  the  name  of  the  u  fire-king,"  is  said  to  have  entered  ovens  at  from  400°  to 
600°.  Under  these  extraordinary  temperatures,  the  body  is  protected  from  the  radiated 
heat  by  clothing,  the  air  is  perfectly  dry,  and  the  animal  temperature  is  kept  down  by 
excessive  exhalation  from  the  surface. 

It  is  a  curious  fact,  that,  after  exposure  of  the  body  to  an  intense  dry  heat  or  to  a 
heated  vapor,  as  in  the  Turkish  or  Russian  baths,  when  the  general  temperature  is 
somewhat  raised  and  the  surface  is  bathed  in  perspiration,  a  cold  plunge,  which  checks 
the  action  of  the  skin  almost  immediately,  is  not  injurious  and  is  decidedly  agreeable. 
This  presents  a  striking  contrast  to  the  effects  of  sudden  cold  upon  a  system  heated  and 
exhausted  by  long-continued  exertion.  In  the  latter  instance,  when  the  perspiration  is 
suddenly  checked,  serious  disorders  of  nutrition,  inflammations,  etc.,  are  very  liable  to 
occur.  The  explanation  of  this,  as  far  as  we  can  present  any,  seems  to  be  the  following: 
When  the  skin  acts  to  keep  down  the  temperature  of  the  body  in  simple  exposure  to 
external  heat,  there  is  no  modification  in  nutrition,  and  the  tendency  to  an  elevation  of 
the  animal  temperature  comes  from  causes  entirely  external.  It  is  a  practical  observa- 
tion that  no  bad  effects  are  produced,  under  these  circumstances,  by  suddenly  changing 
the  external  conditions ;  but,  when  the  animal  temperature  is  raised  by  a  modification 
of  the  internal  nutritive  processes,  as  in  prolonged  muscular  effort,  these  changes  cannot 
be  suddenly  arrested  ;  and  a  suppression  of  the  compensative  action  of  the  skin  is  apt  to 
produce  disturbances  in  nutrition,  very  often  resulting  in  inflammations. 


522  MOVEMENTS. 

CHAPTEK    XVI. 

MOVEMENTS— VOICE  AND  SPEECH. 

Amorphous  contractile  substance— Ciliary  movements— Movements  due  to  elasticity— Varieties  of  clastic  tissue- 
Muscular  movements— Physiological  anatomy  of  the  involuntary  muscles— Mode  of  contraction  of  the  invol- 
untary muscular  tissue— Physiological  anatomy  of  the  voluntary  muscles— Fibrous  and  adipose  tissue  in  the 
voluntary  muscles— Connective  tissue— Blood-vessels  and  lymphatics  of  the  muscular  tissue— Connection  of 
the  muscles  with  the  tendons— Chemical  composition  of  the  muscles— Physiological  properties  of  the  mus- 
cles—Muscular contractility,  or  irritability— Muscular  contraction— Changes  in  the  form  of  the  muscular 
fibres  during  contraction— Secousse,  Ziickung,  or  spasm— Mechanism  of  prolonged  muscular  contraction- 
Tetanus— Electric  phenomena  in  the  muscles— Muscular  effort— Passive  organs  of  locomotion— Physiological 
anatomy  of  the  bones— Marrow  of  the  bones— Medullocells— Myeloplaxe-s— Periosteum— Physiological  anatomy 
of  cartilage— Fibro-cartilage— Voice  and  speech— Sketch  of  the  physiological  anatomy  of  the  vucal  organs- 
Vocal  chords— Muscles  of  the  larynx— Mechanism  of  the  production  of  the  voice— Appearance  of  the  glottis 
during  ordinary  respiration— Movements  of  the  glottis  during  phonation— Variations  in  the  quality  of  the 
voice,  depending  upon  differences  in  the  size  and  form  of  the  larynx  and  the  vocal  chords— Action  of  the 
intrinsic  muscles  of  the  larynx  in  phonation— Action  of  the  accessory  vocal  organs— Mechanism  of  the  differ- 
ent vocal  registers— Mechanism  of  speech. 

THE  organic,  or  vegetative  functions  of  animals  involve  certain  movements;  and 
almost  all  animals  possess,  in  addition,  the  power  of  locomotion.  Very  many  of  these 
movements  have,  of  necessity,  been  considered  in  connection  with  the  different  functions ; 
as  the  action  of  the  heart  and  vessels  in  the  circulation,  the  uses  of  the  muscles  in  respi- 
ration, the  ciliary  movements  in  the  air-passages,  the  muscular  acts  in  deglutition,  the 
peristaltic  movements,  and  the  mechanism  of  defalcation  and  urination.  There  remain, 
however,  certain  general  facts  with  regard  to  various  kinds  of  movement  and  the  mode 
of  action  of  the.  different  varieties  of  muscular  tissue,  that  will  demand  more  or  less 
extended  consideration.  As  regards  the  exceedingly  varied  and  complex  acts  concerned 
in  locomotion,  it  is  difficult  to  fix  the  limits  between  anatomy  and  physiology.  A  full 
comprehension  of  such  movements  must  be  preceded  by  a  complete  descriptive  anatomi- 
cal account  of  the  passive  and  active  organs  of  locomotion ;  and  special  treatises  on 
anatomy  almost  invariably  give  the  uses  and  actions,  as  well  as  the  structure  and  rela- 
tions of  these  parts. 

Amorphous  Contractile  Substance  and  Amoeboid  Movements. — In  some  of  the  very' 
lowest  orders  of  beings,  in  which  hardly  any  thing  but  amorphous  matter  and  a  few  gran- 
ules can  be  recognized  by  the  microscope,  certain  movements  of  elongation  and  retrac- 
tion of  their  amorphous  substance  have  been 
observed.      In   the  higher    animals,   similar 
movements  have  been  noticed  in  certain  of 
their  structures,  such  as  the  leucocytes,  the 
contents  of  the  ovum,   epithelial  cells,  and 
connective-tissue   cells.       These   movements 
are  generally  simple   changes  in   the   form 
of  the  cell,  nucleus,  or  whatever  it  may  be. 
FIG.  •UR.-Amaiba  diffluens,  changing  in  form  ^d  The?  are  supposed  to  depend  upon  an  organic 
^ng^ntte  direction  indicated  ly  the  arrow,   principle  called  sarcode  or  protoplasm;  but 

it  is  not  known  that  such  movements  are 

characteristic  of  any  one  definite  proximate  principle,  nor  is  it  easy  to  determine  their 
cause  and  their  physiological  importance.  In  the  anatomical  elements  of  adult  animals 
of  the  higher  classes,  the  sarcodic  movements  usually  appear  slow  and  gradual,  even 
when  viewed  with  high  magnifying  powers ;  but,  in  some  of  the  very  lowest  orders  of 
beings,  these  movements  serve  as  the  means  of  progression  and  are  more  rapid.  Such 
movements  are  sometimes  called  amoeboid. 

It  does  not  seem  possible,  in  the  present  condition  of  our  knowledge,  to  explain  the 


CILIARY  MOVEMENTS.  523 

nature  and  cause  of  the  movements  of  homogeneous  contractile  substance ;  and  it  must 
be  .excessively  difficult,  if  not  impossible,  to  observe  directly  the  effects  of  different  stim- 
uli, in  the  manner  in  which  we  study  the  movements  of  muscles.  As  far  as  we  can 
judge,  they  are  analogous  to  the  ciliary  movements,  the  cause  of  which  is  equally  obscure. 

Ciliary  Movements. — The  epithelium  covering  certain  of  the  mucous  membranes  is  pro- 
vided with  little  hair-like  processes  upon  the  free  portion  of  the  cells,  called  cilia.  These 
are  in  constant  motion,  from  the  beginning  to  the  end  of  life,  arid  they  produce  currents 
upon  the  surfaces  of  the  membranes  to  which  they  are  attached,  the  direction  being  gener- 
ally from  within  outward.  In  many  of  the  infusoria,  the  ciliary  motion  serves  as  a  means 
of  progression,  effects  the  introduction  of  nutriment  into  the  alimentary  canal,  and,  indeed, 
is  almost  the  sole  agent  in  the  performance  of  the  functions  involving  movement.  Even 
in  higher  classes,  as  the  mollusca,  the  movements  of  the  cilia  are  of  great  importance. 
In  man  and  in  the  warm-blooded  animals  generally,  the  ciliated  or  vibratile  epithelium  is 
of  the  variety  called  columnar,  conoidal,  or  prismoidal.  The  cilia  are  attached  to  the 
thick  ends  of  the  cells,  and  they  form  on  the  surface  of  the  membrane  a  continuous  sheet 
of  vibrating  processes. 

It  is  unnecessary  to  describe  in  detail  the  size  and  form  of  the  cells  provided  with 
cilia,  as  their  variations  in  different  situations  have  been  and  will  be  considered  in  con- 
nection with  the  physiological  anatomy  of  different  parts.  In  general  structure,  the  ciliary 
processes  are  entirely  homogeneous,  and  they  gradually  taper  from  their  attachment  to 
the  cell  to  an  extremity  of  excessive  tenuity.  Although  anatomists,  from  time  to  time, 
have  described  striae  at  the  bases  of  the  cilia  and  have  attempted  to  explain  their  mo- 
tion by  a  kind  of  muscular  action,  no  well-defined  structure  has  ever  been  actually 
demonstrated  in  their  substance. 

The  presence  of  cilia  has  been  demonstrated  upon  the  following  surfaces :  The  respira- 
tory passages,  including  the  nasal  fossae,  the  pituitary  membrane,  the  summit  of  the 
larynx,  the  bronchial  tubes,  the  superior  surface  of  the  velum  palati,  and  the  Eustachian 
tubes ;  the  sinuses  about  the  head ;  the  lachrymal  sac  and  the  internal  surface  of  the 
eyelids ;  the  genital  passages  of  the  female,  from  the  middle  of  the  neck  of  the  uterus 
to  the  extremities  of  the  Fallopian  tubes ;  and  the  ventricles  of  the  brain.  They  prob- 
ably exist,  also,  at  the  neck  of  the'  capsule  of  Mtiller,  in  the  cortical  substance  of  the  kid- 
ney. In  these  situations,  to  each  cell  of 
conoidal  epithelium  are  attached  from  six  to 
twelve  prolongations,  about  ^y^nnr  of  an  inch 
in  thickness  at  their  base,  and  from  -^-^  to 
•zfas  of  an  inch  in  length.  The  appearance 
of  the  cilia  in  detached  cells  is  represented 
in  Fig.  147.  When  seen  in  situ,  they  ap- 
pear regularly  disposed  upon  the  surface,  are 
of  nearly  equal  length,  and  are  generally 
slightly  inclined  in  the  direction  of  the  open- 
ing of  the  cavity  lined  by  the  membrane. 

The  ciliary  motion  is  one  of  the  most 
beautiful  physiological  demonstrations  that 
can  be  made  with  the  microscope.  By  scrap- 
ing the  roof  of  the  mouth  of  a  living  frog, 
the  mucous  membranes  of  the  respiratory 
passages  in  a  warm  -  blooded  animal  just 

killed,  the  beard  of  the  oyster  or  clam,  and  FlG"  14T'"*OW<  ^  *"*""* 

placing  the  preparation,  moistened  with  a 
little  serum,  under  a  magnifying  power  of  about  two  hundred  and  fifty  diameters,  the 
currents  produced  in  the  liquid  will  be  strikingly  exhibited.    The  movements  may  be 


524  MOVEMENTS. 

studied  in  detached  cells,  in  the  human  subject,  by  introducing  a  feather  into  the  nose,  by 
which  a  few  cells  may  be  removed  with  the  mucus  and  can  be  observed  in  the  same  way. 
This  demonstration  serves  to  show  the  similarity  between  the  movements  in  man  and  in 
the  lower  orders  of  animals.  When  the  movements  are  seen  in  a  large  number  of  cells 
in  situ,  the  appearance  is  very  graphically  illustrated  by  the  apt  comparison  of  Henle  to 
the  undulations  of  a  field  of  wheat  agitated  by  the  wind.  In  watching  this  movement, 
it  is  usually  seen  to  gradually  diminish  in  rapidity,  until  what  at  first  appeared  simply  as 
a  current,  produced  by  movements  too  rapid  to  be  studied  in  detail,  becomes  revealed  as 
distinct  undulations,  in  which  the  action  of  individual  cilia  can  be  readily  studied.  Sev- 
eral kinds  of  movement  have  been  described,  but  the  most  common  is  a  bending  of  the 
cilia,  simultaneously  or  in  regular  succession,  in  one  direction,  followed  by  an  undulating 
return  to  the  perpendicular.  The  other  movements,  such  as  the  infundibuliform,  in 
which  the  point  describes  a  circle  around  the  base,  the  pendulum-movement,  etc.,  are 
not  common  and  are  unimportant. 

The  combined  action  of  the  cilia  upon  the  surface  of  a  mucous  membrane,  moving  as 
they  do  in  one  direction,  is  to  produce  currents  of  considerable  power.  This  may  be 
illustrated  under  the  microscope  by  covering  the  surface  with  a  liquid  holding  little  solid 
particles  in  suspension.  In  this  case,  the  granules  are  tossed  from  one  portion  of  the 
field  to  another,  with  considerable  force.  It  is  not  difficult,  indeed,  to  measure  in  this 
way  the  rapidity  of  the  ciliary  currents.  In  the  frog  it  has  been  estimated  at  from  -gfa 
to  y^  of  an  inch  per  second,  the  number  of  vibratile  movements  being  from  seventy-five 
to  one  hundred  and  fifty  per  minute.  In  the  fresh- water  polyp  the  movements  are  more 
rapid,  being  from  two  hundred  and  fifty  to  three  hundred  per  minute.  There  is  no  reli- 
able estimate  of  the  rapidity  of  the  ciliary  currents  in  man,  but  they  are  probably  more 
active  than  in  animals  low  in  the  scale. 

The  movements  of  cilia,  like  those  observed  in  fully-developed  spermatozoids,  seem 
to  be  entirely  independent  of  nervous  influence,  and  they  are  affected  only  by  purely  local 
conditions.  They  will  continue,  under  favorable  circumstances,  for  more  than  twenty- 
four  hours  after  death  and  can  be  seen  in  cells  entirely  detached  from  the  body  when 
they  are  moistened  with  proper  fluids.  When  the  cells  are  moistened  with  pure  water, 
the  activity  of  the  movement  is  at  first  increased ;  but  it  soon  disappears  as  the  cells 
become  swollen.  Acids  arrest  the  movement,  but  it  may  be  excited  by  feeble  alkaline 
solutions.  All  abnormal  conditions  have  a  tendency  either  to  retard  or  to  abridge  the 
duration  of  the  ciliary  motion.  It  is  true  that,  when  the  movement  is  becoming  feeble, 
it  may  be  temporarily  restored  by  very  dilute  alkaline  solutions,  but  the  ordinary  stimuli, 
such  as  are  capable  of  exciting  muscular  contraction,  are  without  effect.  Purkinje  and 
Valentin,  Sharpey,  and  others,  have  attempted  to  excite  the  movements  of  cilia  by  gal- 
vanic stimulus,  but  without  success.  Anesthetics  and  narcotics,  which  have  such  a 
decided  effect  upon  muscular  action,  have  no  influence  upon  the  cilia. 

It  is  useless  to  follow  the  speculations  that  have  been  advanced  to  account  for  the  move- 
ment of  cilia.  There  is  no  muscular  structure  in  the  cilia,  no  connection  with  the  nervous 
system,  and  there  seems  to  be  no  possibility  of  explaining  the  movement  except  by  a  bare 
statement  of  the  fact  that  the  cilia  have  the  property  of  moving  in  a  certain  way  so  long 
as  they  are  under  normal  conditions.  As  regards  the  physiological  uses  of  these  move- 
ments, it  is  sufficient  to  refer  to  the  physiology  of  the  parts  in  which  cilia  are  found, 
where  the  peculiarities  of  their  action  are  considered  more  in  detail.  In  the  lungs  and 
the  air-passages  generally  and  in  the  genital  passages  of  the  female,  the  currents  are  of 
considerable  importance ;  but  it  is  difficult  to  imagine  the  use  of  these  movements  in 
certain  other  situations,  as  the  ventricles  of  the  brain. 

Movements  due  to  Elasticity.— There  are  certain  important  movements  in  the  body 
that  are  due  simply  to  the  action  of  elastic  ligaments  or  membranes.  These  are  entirely 
distinct  from  muscular  movements,  and  are  not  even  to  be  classed  with  the  movements 


MOVEMENTS  DUE  TO  ELASTICITY. 


525 


produced  by  the  resiliency  of  muscular  tissue,  in  which  that  curious  property,  called 
muscular  tonicity,  is  more  or  less  involved.  Movements  of  this  kind  are  never  excited 
by  nervous,  galvanic,  or  other  stimulus,  but  they  consist  simply  in  the  return  of  movable 
parts  to  a  certain  position  after  they  have  been  displaced  by  muscular  action,  and  the 
reaction  of  tubes  after  forcible  distention,  as  in  the  walls  of  the  large  arteries. 

Elastic  Tissue. — Most  writers  of  the  present  day  adopt  the  division  of  the  elements  of 
elastic  tissue  into  three  varieties.  This  division  relates  to  the  size  of  the  fibres ;  and  all 
varieties  are  found  to  possess  essentially  the  same  chemical  composition  and  general 
properties,  including  the  elasticity  for  which  they  are  so  remarkable.  On  account  of  the 
yellow  color  of  this  tissue,  presenting,  as  it  does,  a  strong  contrast  to  the  white,  glisten- 
ing appearance  of  the  inelastic  fibres,  it  is  frequently  called  the  yellow  elastic  tissue. 

The  first  variety  of  elastic  tissue  is  composed  of  small  fibres,  generally  intermingled 


FIG.  148.— Small  elastic  fibres,  from  the  peritoneum ; 
magnified  350  diameters.    (Kolliker.) 


FIG.  149.— Larger  elastic  fibres.    (Eobin.) 


with  fibres  of  the  ordinary  inelastic  tissue.  These  are  sometimes  called,  by  the  French, 
dartoic  fibres.  They  possess  all  the  chemical  and  physical  characters  of  the  larger  fibres, 
but  are  excessively  minute,  measuring  from  25^00  to  -^-g-  or  ^Vo  of  an  inch  in  diameter. 
If  we  add  acetic  acid  to  a  preparation  of  ordinary  connective  tissue,  the  inelastic  fibres 
are  rendered  semitransparent,  but  the  elastic  fibres  are  unaffected  and  become  very  dis- 
tinct. They  are  then  seen  isolated,  that  is,  never  arranged  in  bundles,  generally  with  a 
dark,  double  contour,  branching,  brittle,  and  when  broken,  their  extremities  curled  and 
presenting  a  sharp  fracture,  like  a  piece  of  India-rubber.  These  fibres  pursue  a  wavy 
course  between  the  bundles  of  inelastic  fibres  in  the  areolar  tissue  and  in  most  of  the  ordi- 
nary fibrous  membranes,  and  here  they  exist  as  an  accessory  anatomical  element.  They 
are  found  in  greater  or  less  abundance  in  the  situations  just  mentioned ;  also,  in  the  liga- 
ments (but  not  the  tendons)  ;  in  the  layers  of  involuntary  muscular  tissue  ;  the  true  skin ; 
the  true  vocal  cords ;  the  trachea,  bronchial  tubes,  and  largely  in  the  parenchyma  of  the 
lungs  ;  the  external  layer  of  the  large  arteries ;  and,  in  brief,  in  nearly  all  situations  in 
which  the  ordinary  connective  tissue  exists. 

The  second  variety  of  elastic  tissue  is  composed  of  fibres,  larger  than  the  first,  ribbon- 
shaped,  with  well-defined  outlines,  anastomosing,  undulating  or  curved  in  the  form  of  the 
letter  S,  presenting  the  same  curled  ends  and  sharp  fracture  as  the  smaller  fibres.  These 
measure  from  -^-^  to  ^Vfr  of  an  inch  in  diameter.  Their  type  is  found  in  the  ligamenta 
subflava  and  the  ligamentum  nucha3.  They  are  also  found  in  some  of  the  ligaments  of 
the  larynx,  the  stylo-hyoid  ligament,  and  the  suspensory  ligament  of  the  penis.  The 
form  and  arrangement  of  these  fibres  may  be  very  strikingly  demonstrated  by  tearing 
off  a  portion  of  the  ligamentum  nuchse  and  lacerating  it  with  needles  in  a  drop  of  acetic 


526  MOVEMENTS. 

acid.  The  action  of  the  acetic  acid  renders  the  accessory  structures  of  the  ligament 
transparent,  and  the  elastic  fibres  become  very  distinct.  The  same  may  be  accomplished 
by  boiling  the  tissue  for  a  short  time  in  caustic  soda. 

The  third  variety  of  elastic  tissue  can  hardly  be  said  to  consist  of  fibres,  as  their  branches 
are  so  short  and  their  anastomoses  so  frequent.     This  kind  of  structure  is  found  forming 
the  middle  coat  of  the  large  arteries,  and  it  has  already  been  de- 
scribed  in  connection  with  the  vascular  system.     The  fibres  are 
very  large,  flat,  with  numerous  short  branches,  "  which  unite 
again  with  the  trunk  from  which  they  originate  or  with  adja- 
cent fibres.     In  certain  situations,  the  interstices  are  considera- 
ble, in  proportion  to  the  diameter  of  the  fibres,  and  the  anasto- 
mosing branches  are  given  off  at  acute  angles,  so  that  they 
follow  pretty  closely  the  direction  of  the  trunks,  and  the  anas- 
tomoses do  not  disturb  the  longitudinal  direction  and  parallelism 
of  the  fibres.    Indeed,  the  anastomoses  are  so  numerous,  and  the 
intervals  so  small,  proportionally  to  the  fibres,  that  we  should 
believe  we  had  under  observation  a  reticulated  membrane,  pre- 
diameters,    senting  openings,  rounded  and   oval,  some  large  and  others 
small."     (Henle.)     These  anastomosing  fibres,  forming  the  so- 
called  fenestrated  membranes,  are  arranged  in  layers,  and  the  structure  is  sometimes 
called  the  lamellar  elastic  tissue. 

The  great  resistance  which  the  elastic  tissue  presents  to  chemical  action  serves  to 
distinguish  it  from  nearly  every  other  structure  in  the  body.  We  have  already  seen  that 
it  is  not  affected  by  acetic  acid  or  by  boiling  with  caustic  soda.  It  is  not  softened 
by  prolonged  boiling  in  water,  but  it  is  slowly  dissolved,  without  decomposition,  by 
sulphuric,  nitric,  or  hydrochloric  acid,  the  solution  not  being  precipitable  by  potash.  Its 
organic  base  is  a  nitrogenized  substance  called  elasticine,  containing  carbon,  hydrogen, 
.oxygen,  and  nitrogen,  without  sulphur.  This  is  supposed  to  be  identical  with  the  sarco- 
lemma  of  the  muscular  tissue. 

The  purely  physical  property  of  elasticity  plays  an  important  part  in  many  of  the 
animal  functions.  We  have  already  had  an  example  of  this  in  the  action  of  the  large 
arteries  in  the  circulation  and  in  the  resiliency  of  the  parenchyma  of  the  lungs ;  and  we 
shall  have  occasion,  in  treating  of  the  functions  of  other  parts,  to  refer  again  to  the  uses 
of  elastic  membranes  and  ligaments.  The  ligamenta  subflava  and  the  ligamentum  nucha) 
are  important  in  aiding  to  maintain  the  erect  position  of  the  body  and  head,  and  to  restore 
this  position  when  flexion  has  been  produced  by  muscular  action.  Still,  the  contraction 
of  muscles  is  also  necessary  to  keep  the  body  in  a  vertical  position. 

Muscular  Movements. 

Muscular  movements  are  observed  only  in  the  higher  classes  of  animals.  Low  in  the 
scale  of  animal  life,  we  have  the  contractions  of  amorphous  substance  and  ciliary  motion ; 
and,  in  some  vegetables,  movements,  even  attended  with  locomotion,  have  been  observed. 
These  facts  make  the  absolute  distinction  between  the  two  kingdoms  a  question  of  some 
difficulty;  but  in  animals  only,  do  we  have  a  distinct  muscular  system. 

The  muscular  movements  capable  of  being  excited  by  stimulus  of  various  kinds  are 
divided  into  voluntary  and  involuntary  ;  and  generally  there  is  a  corresponding  division 
of  the  muscles  as  regards  their  minute  anatomy.  The  latter,  however,  is  not  absolute  ; 
for  there  are  certain  involuntary  functions,  like  the  action  of  the  heart  or  the  movements 
of  deglutition,  that  require  the  rapid,  vigorous  contraction  characteristic  of  the  voluntary 
muscular  tissue,  and  here  we  do  not  find  the  structure  characteristic  of  the  involuntary 
muscles.  With  a  few  exceptions,  however,  the  anatomical  division  of  the  muscular  tissue 
into  voluntary  and  involuntary  is  sufficiently  distinct. 


STRUCTURE   OF  THE  INVOLUNTARY  MUSCLES. 


527 


Physiological  Anatomy  of  the  Involuntary  Muscles. — We  have  so  often  described  this 
tissue,  as  it  is  found  in  the  vascular  system,  the  digestive  organs,  the  skin,  and  in  other 
situations,  that  it  will  not  be  necessary,  in  this  connection,  to  give  more  than  a  sketch 
of  its  structure  and  mode  of  action. 

The  involuntary  muscular  system  presents  a  striking  contrast  to  the  voluntary  mus- 
cles, not  only  in  its  minute  anatomy  and  mode  of  action,  but  in  the  arrangement  of  its 
fibres.  While  the  voluntary  muscles  are  almost  invariably  attached  by  their  two  extrem- 
ities to  movable  parts,  the  involuntary  muscles  form  sheets  or  membranes  in  the  walls  of 
hollow  organs,  and,  by  their  contraction,  they  simply  modify  the  capacity  of  the  cavities 
which  they  enclose.  Various  names  have  been  given  to  this  tissue  to  denote  its  distribu- 
tion, mode  of  action,  or  structure.  The  name  involuntary  muscle  indicates  that  its  contrac- 
tion is  not  under  the  control  of  the  will ;  and  this  is  the  fact,  these  muscles  being  chiefly 
animated  by  the  sympathetic  system  of  nerves,  while  the  voluntary  muscles  are  supplied 
mainly  from  the  cerebro-spinal  system.  On  account  of  the  peculiar  structure  of  these 
fibres,  they  have  been  called  muscular  fibre-cells,  smooth  muscular  fibres,  pale  fibres, 
non-striated  fibres,  fusiform  fibres,  and  contractile  cells.  The  distribution  of  these  fibres 
to  parts  concerned  in  the  organic  or  vegetative  functions,  as  the  alimentary  canal,  has 
given  them  the  name  of  organic  muscular  fibres,  or  fibres  of  organic,  or  vegetative  life. 
It  is  difficult  to  isolate  the  individual  fibres  of  this  tissue  in  microscopical  preparations; 
and,  when  seen  in  situ,  their  borders  are  faint,  and  we  can  make  out  their  arrangement 


FIG.  151. — Muscular  fibres  from 
the  urinary  bladder  of  the 
hitman  subject;  magnified 
•200  diameters.  (Sappey.) 

1, 1, 1,  nuclei ;  2,  2,.  2,  borders  of 
some  of  the  fibres ;  3,  3,  iso- 
lated fibres;  4,  4,  two  fibres 
joined  together  at  (5). 


FIG.  152.— Muscular  fibres  from 
the  aorta  of  the  calf;  magni- 
fied 200  diameters.  (Sappey.) 

1. 1.  fibres  joined  with  each  other ; 
2,  2,  2,  isolated  fibres. 


FIG.  153.—  Muscular  fibres  from  the  uterus 
of  a  woman  who  died  at  the  ninth 
month  of  utero-gestation  ;  magnified 
350  diameters.  (Sappey.) 

1, 1,  2,  short,  wide  fibres ;  3,  4,  5,  5,  longer 
and  narrower  fibres;  6,  6,  two  fibres 
united  at  (7) ;  8,  small  fibres  in  process 
of  development. 


best  by  the  appearance  of  their  nuclei.  Robin  recommends  soaking  of  the  tissue  for  a  few 
days  in  a  mixture  of  one  part  of  ordinary  nitric  acid  to  ten  of  water.  This  renders  the 
fibres  dark  and  granular,  makes  their  borders  very  distinct,  and  frequently  some  of  them 
become  entirely  isolated.  The  nuclei,  however,  are  obscured.  In  their  natural  condi- 
tion, the  fibres  are  excessively  pale,  very  finely  granular,  flattened,  and  of  an  elongated 
spindle-shape,  with  a  very  long,  narrow,  almost  linear  nucleus  in  the  centre.  The  nu- 
cleus generally  has  no  nucleolus,  and  it  is  sometimes  curved  or  shaped  like  the  letter  S. 


528  MOVEMENTS. 

The  ordinary  length  of  these  fibres  is  about  ^fo,  and  their  breadth  about  ^fa  of  an  inch. 
In  the  gravid  uterus  they  undergo  remarkable  hypertrophy,  measuring  here  from  ^ 
to  ^  of  an  inch  in  length,  and  ^Vo-  of  an  inch  in  breadth.  The  peculiarities  of  their 
structure  in  the  uterus  will  be  fully  considered  under  the  head  of  generation. 

In  the  contractile  sheets  formed  of  involuntary  muscular  tissue,  the  fibres  are  arranged 
side  by  side,  are  closely  adherent,  and  their  extremities  are,  as  it  were,  dove-tailed  into  each 
other.  Generally  the  borders  of  the  fibres  are  regular  and  their  extremities  are  simple ; 
but  sometimes  the  ends  are  forked,  and  the  borders  present  one  or  more  little  projections. 
It  is  very  seldom  that  we  see  the  fibres  in  a  single  layer,  except  in  the  very  smallest  arte- 
rioles.  Usually  the  layers  are  multiple,  being  superimposed  in  regular  order.  The  action 
of  acetic  acid  is  to  render  the  fibres  pale,  so  that  their  outlines  become  almost  indistin- 
guishable, and  to  bring  out  the  nuclei  more  strongly.  If  we  have  an  indistinct  sheet  of 
this  tissue  in  the  field  of  view,  the  addition  of  acetic  acid,  by  bringing  out  the  long,  nar- 
row, and  curved  nuclei  arranged  in  regular  order,  and  by  rendering  the  fibrous  and  other 
structures  more  transparent,  will  often  enable  us  to  recognize  its  character. 

Contraction  of  the  Involuntary  Muscular  Tissue. — The  mode  of  contraction  of  the 
involuntary  muscles  is  peculiar.  It  does  not  take  place  immediately  upon  the  reception 
of  a  stimulus,  applied  either  directly  or  through  the  nerves,  but  it  is  gradual,  enduring  for 
a  time  and  then  followed  by  slow  and  gradual  relaxation.  A  description  of  the  peristaltic 
movements 'of  the  intestines  gives  a  perfect  idea  of  the  mode  of  contraction  of  these 
fibres,  with  the  gradual  propagation  of  the  stimulus  along  the  alimentary  canal,  as  the 
food  makes  its  impression  upon  the  mucous  membrane.  An  equally  striking  illustration 
is  afforded  by  labor-pains.  These  are  due  to  the  muscular  contractions  of  the  uterus, 
and  they  last  from  a  few  seconds  to  one  or  two  minutes.  Their  gradual  access,  continua- 
tion for  a  certain  period,  and  gradual  disappearance  coincide  exactly  with  the  history  of 
the  contractions  of  the  involuntary  muscular  fibres. 

The  contraction  of  the  involuntary  muscular  tissue  is  slow,  and  the  fibres  return 
slowly  to  a  condition  of  repose.  The  movements  are  always  involuntary.  Peristaltic 
action  is  the  rule,  and  the  contraction  takes  place  progressively  and  without  oscillations. 
Contractility  persists  for  a  long  time  after  death.  Arrest  of  function  is  followed  by  little 
or  no  atrophy,  and  hypertrophy  is  very  marked  as  the  result  of  exaggerated  action.  Ex- 
citation of  the  nerves  has  less  influence  upon  contraction  of  these  fibres  than  direct  exci- 
tation of  the  muscles.  The  involuntary  muscular  tissue  is  regenerated  very  rapidly,  while 
the  structure  of  the  voluntary  muscles  is  restored  with  great  difficulty  after  destruction 
or  division.  (Legros  and  Onimus.) 

Physiological  Anatomy  of  the  Voluntary  Muscles. — A  voluntary  muscle  is  the  most 
highly  organized  and  is  possessed  of  the  most  varied  endowments  of  all  living  structures. 
It  contains,  in  addition  to  its  own  peculiar  contractile  substance,  fibres  of  inelastic  and 
elastic  tissue,  adipose  tissue,  numerous  blood-vessels,  nerves,  and  lymphatics,  with  certain 
nuclear  and  cellular  anatomical  elements.  The  muscular  system  constitutes  by  far  the 
greatest  part  of  the  organism,  and  its  nutrition  consumes  a  large  proportion  of  the  repara- 
tive  material  of  the  blood,  while  its  disassimilation  furnishes  a  corresponding  quantity  of 
excrementitious  matter.  The  condition  of  the  muscular  system,  indeed,  is 'an  almost  un- 
failing evidence  of  the  general  state  of  the  body,  allowing,  of  course,  for  peculiarities  in 
different  individuals.  Among  the  characteristic  properties  of  the  muscles  are,  elasticity, 
a  constant  and  insensible  tendency  to  contraction,  called  tonicity,  the  power  of  contract- 
ing forcibly  on  the  reception  of  a  proper  stimulus,  called  irritability,  a  peculiar  kind  of 
sensibility,  and  the  faculty  of  generating  galvanic  currents.  The  relations  of  particular 
muscles,  as  taught  by  descriptive  anatomy,  involve  special  functions  ;  but  the  most  inter- 
esting physiological  points  connected  with  this  system  relate  to  the  general  properties 
and  functions  of  the  muscles,  and  must  necessarily  be  prefaced  with  a  sketch  of  their 
general  anatomy. 


STRUCTURE   OF  THE  VOLUNTARY  MUSCLES. 


529 


It  has  been  demonstrated  by  minute  dissection  that  all  of  the  red,  or  voluntary  mus- 
cles are  made  up  of  a  great  number  of  microscopic  fibres,  known  as  the  primitive  muscular 
fasciculi.  These  are  called  red,  striated,  or  voluntary  fibres,  or  the  fibres  of  animal  life. 
Their  structure  is  complex,  and  they  may  be  subdivided  longitudinally  into  fibrillae,  and 
transversely  into  disks,  so  that  it  is  somewhat  doubtful  as  to  what  is,  strictly  speaking, 
the  ultimate  anatomical  element  of  the  muscular  tissue. 

A  primitive  muscular  fasciculus  runs  the  entire  length  of  the  muscle,  and  is  enclosed 
in  its  own  sheath,  without  branching  or  inosculation.  This  sheath  contains  the  true 
muscular  substance  only,  and  it  is  not  penetrated  by  blood-vessels,  nerves,  or  lymphatics. 
If  we  examine  with  the  microscope  a  thin,  transverse  section  of  a  muscle,  the  divided  ends 
of  the  fibres  will  present  an  irregularly  polygonal  form,  with  rounded  corners.  They 
seem  to  be  cylindrical,  however,  when  viewed  in  their  length  and  isolated.  Their  color 
by  transmitted  light  is  a  delicate  amber,  resembling  somewhat  the  color  of  the  blood- 
corpuscles. 


FIG.  154. — Striated  muscular  fibres,  from  the  mouse ;  magnified  500  diameters.    (From  a  photograph  taken  at 

the  United  States  Army  Medical  Museum.) 
The  injected  capillaries  are  seen,  somewhat  out  of  focus. 

The  primitive  fasciculi  vary  very  much  in  size  in  different  individuals,  in  the  same 
individual  under  different  conditions,  and  in  different  muscles.  As  a  rule,  they  are  smaller 
in  young  persons  and  in  females  than  in  adult  males.  They  are  comparatively  small  in 
persons  of  slight  muscular  development.  In  persons  of  great  muscular  vigor,  or  when 
the  general  muscular  system  or  particular  muscles  have  been  increased  in  size  and  power 
by  exercise,  the  fasciculi  are  relatively  larger.  It  is  probable  that  the  physiological 
increase  in  the  size  of  a  muscle  from  exercise  is  due  to  an  increase  in  the  size  of  the  pre- 
existing fasciculi,  and  not  to  the  formation  of  any  new  elements.  In  young  persons,  the 
34 


530 


MOVEMENTS. 


fasciculi  are  from  ^Vs  to  rsW  of  an  mcn  in  diameter.     In  the  adult,  they  measure  from 

TTTF  to  yfa  of  an  incn- 

The  appearance  of  the  primitive  muscular  fasciculi  under  the  microscope  is  character- 
tic  and  unmistakable.  They  present  regular,  transverse  striaa,  formed  of  alternating  dark 
and  clear  bands  about  ^^  of  an  inch  wide.  These  are  generally  very  distinct  in  healthy 
muscles.  In  addition,  we  frequently  observe  longitudinal  strias,  not  so  distinct,  and  quite 
difficult  to  follow  to  any  extent  in  the  length  of  the  fasciculus,  but  tolerably  well  marked, 
particularly  in  muscles  that  are  habitually  exercised.  The  muscular  substance,  present- 
ing this  peculiar  striated  appearance,  is  enclosed  in  an  excessively  thin  but  elastic  and 
resisting  tubular  membrane,  called  the  sarcolemma  or  myolemma,  which  is  probably 
composed  of  the  same  substance  as  the  elastic  tissue.  This  envelope  cannot  be  seen  in 
ordinary  preparations  of  the  muscular  tissue ;  but  it  frequently  happens  that  the  con- 
tractile muscular  substance  is  broken,  leaving  the  sarcolemma  intact,  which  gives  a  good 
view  of  the  membrane  and  conveys  an  idea  of  its  strength  and  elasticity.  Attached  to 
the  inner  surface  of  the  sarcolemma,  are  numerous  small,  elongated  nuclei  with  their 
long  diameter  in  the  direction  of  the  fasciculi.  These  are  usually  not  well  seen  in  the 
unaltered  muscle,  but  the  addition  of  acetic  acid  renders  the  muscular  substance  pale  and 
destroys  the  stria3,  when  the  nuclei  become  very  distinct. 

Water,  after  a  time,  acts  upon  the  muscular  tissue,  rendering  the  fasciculi  somewhat 
paler  and  larger.  Acetic  acid  and  alkaline  solutions  efface  the  striae,  and  the  fibres 
become  semitransparent.  'In  fasciculi  that  are  slightly  decomposed,  there  is  frequently  a 
separation  at  the  extremity  into  numerous  smaller  fibres,  called  fibrillas.  These,  when 
isolated,  present  the  same  striated  appearance  as  the  primitive  fasciculus ;  viz.,  alternate 
dark  and  light  portions.  They  measure  about  -^^-Q-Q  of  an  inch  in  diameter,  and  their 
number,  in  the  largest  primitive  fibres,  is  estimated  by  Kolliker  at  about  two  thousand. 
The  structure  of  the  fibrillae  is  probably  uniform,  the  appearance  of  alternate  dark  and 
light  segments  being  due  to  dhTerences  in  thickness.  In  fact,  it  is  well  known  that  water, 
by  its  simple  mechanical  action,  swells  the  fibrillaa  and  causes  the  striss  to  disappear. 

Late  researches  have  shown  that  the  interior  of  each  primitive  fasciculus  is  pene- 
trated by  an  excessively  delicate  membrane,  closely  surrounding  the  fibrillae.  This 

arrangement  may  be  distinctly  seen  in  a 
thin  section  of  a  fibre  treated  with  a  solu- 
tion of  salt  in  water  in  the  proportion  of 
five  parts  per  thousand.  The  arrangement 
of  this  membrane,  which  is  nothing  more 
nor  less  than  a  series  of  tubular  sheaths 
for  the  fibrillaa,  is  a  strong  argument  in 
favor  of  the  view  that  the  fibrilla  is  the  ana- 
tomical element  of  the  muscular  tissue. 

When  we  come  to  the  question  of  the 
real  anatomical  element  of  the  muscular  tis- 
sue, there  are  only  two  reasonable  views 
that  present  themselves.  One  is  that  any 
subdivision  of  the  primitive  fasciculus  is  arti- 
ficial, and  that  it,  with  its  investing  mem- 
brane, the  sarcolemma,  is  the  true  element. 
An  argument  in  favor  of  this  opinion  is  that 
the  tissue  is  most  readily  separated  into  fas- 
ciculi, each  enclosed  in  its  own  membrane 
and  not  penetrated  by  vessels,  nerves,  or 
lymphatics;  while  the  fibrillse  are  situated 
in  a  reticulum  of  canals,  from  which  they  cannot  readily  be  isolated.  The  other  opinion, 
that  the  fibrillas  are  the  ultimate  elements,  is  based  upon  the  fact  that  these  little  fibres 


inagn  ijied 


FIG.   165.—  Voluntary   muscular  fibre, 
250  diameters.    (Sappey.) 

A,  transverse  strife  and  nuclei  of  a  primitive  fasciculus; 
B,  longitudinal  striae  and  fibrillae  of  a  primitive  fas- 
ciculus in  which  the  sarcolemma  has  been  lacerated 
at  one  point  by  pressure. 


STRUCTURE  OF  THE  VOLUNTARY  MU8CLES. 


531 


present  the  striae  and  all  the  anatomical  characteristics  of  the  primitive  fasciculi,  and  that 
by  far  the  most  natural  and  easy  mode  of  separation  of  these  fasciculi  is  in  a  longi- 
tudinal direction.  The  question  of  adopting  one  or  the  other  of  these  views  is  not  of 
very  great  physiological  importance. 

Fibrous  and  Adipose  Tissue  in  the  Voluntary  Muscles. — The  structure  of  the  mus- 
cles strikingly  illustrates  the  relations  between  the  principal  and  the  accessory  anatomi- 
cal elements  of  tissues.  The  characteristic,  or  principal  element  is,  of  course,  the  mus- 
cular fibre  or  fibrilla ;  but  we  also  find  in  the  substance  of  the  muscles  certain  anatomi- 
cal elements,  not  peculiar  to  the  muscles,  and  merely  accessory  in  their  function,  but 
none  the  less  necessary  to  their  proper  constitution.  For  example,  every  muscle  is  com- 
posed of  a  number  of  primitive  fasciculi ;  but  these  are  gathered  into  secondary  bundles, 
which  in  turn  are  collected  into  bundles  of  greater  and  greater  size,  until,  finally,  the 
whole  muscle  is  enveloped  in  its  sheath  and  is  penetrated  by  a  fibrous  connective  sub- 
stance. We  find,  probably,  in  the  muscles,  the  best  illustration  of  the  structure  of  what 
is  known  as  the  connective  tissue. 

Connective  Tissue. — We  have  already  had  occasion  to  refer  to  certain  of  the  elements 
of  connective  tissue,  more  especially  the  inelastic  and  elastic  fibres.  In  this  connection, 
we  shall  treat  specially  of  the  connective  tissue  of  the  muscles  ;  but  our  description  will 
answer  for  almost  all  situations  in  which  fibrous  tissue  exists  merely  for  the  purpose  of 
holding  parts  together.  In  the  muscles,  we  have  a  membrane  holding  a  number  of  the 
primitive  fasciculi  into  secondary  bundles.  This  is  known  as  the  perimysium.  The 
fibrous  membranes  that  connect  together  these  secondary  bundles  with  their  contents 
are  enclosed  in  a  sheath  enveloping  the  whole  muscle,  sometimes  called  the  external 
perimysium.  The  peculiarity  of  these  membranes,  and  their  distinction  from  the  sar- 
colemma,  are  that  they  have  a  fibrous  structure  and  are  connected  together  throughout  the 
muscle,  while  the  tubes  forming  the  sarcolemma  are  structureless,  and  each  one  is  dis- 
tinct. 


FIG.  156.— Fibres  of  tendon  of  the  human  subject.    (Eollett.) 

The  name  now  most  generally  adopted  for  the  tissue  under  consideration  is  connec- 
tive tissue.  It  has  been  called  cellular,  areolar,  or  fibrous,  but  most  of  these  names  were 
given  to  it  without  a  clear  idea  of  its  structure.  Its  principal  anatomical  element  is  a 
fibre  of  excessive,  almost  immeasurable,  tenuity,  wavy,  and  with  a  single  contour.  These 
fibres  are  connected  into  bundles  of  very  variable  size  and  are  held  together  by  an 
adhesive  amorphous  substance.  The  wavy  lines  that  mark  the  bundles  of  fibres  give 
them  a  very  characteristic  appearance. 

Tbe  direction  and  arrangement  of  the  fibres  in  the  various  tissues  present  marked 


532 


MOVEMENTS. 


differences.  In  the  loose  areolar  tissue  beneath  the  skin  and  between  the  muscles,  and 
in  the  loose  structure  surrounding  some  of  the  glands  and  connecting  the  sheaths  of 
blood-vessels  and  nerves  to  the  adjacent  parts,  the  bundles  of  fibres  form  a  large  net- 
work and  are  very  wavy  in  their  course.  In  the  strong,  dense  membranes,  as  the 
aponeuroses,  the  proper  coats  of  many  glands,  the  periosteum  and  perichondrium,  and 
the  serous  membranes,  the  waves  of  the  fibres  are  shorter,  and  the  fibres  themselves 
interlace  much  more  closely.  In  the  ligaments  and  tendons,  the  fibres  are  more  nearly 
straight  and  are  all  arranged  longitudinally. 

On  the  addition  of  acetic  acid,  the  bundles  of  inelastic  fibres  swell  up,  become  semi- 
transparent,  and  the  nuclei  and  elastic  fibres  are  brought  out.  The  proportion  of  elastic 
fibres  differs  very  much  in  different  situations,  but  they  are  all  of  the  smallest  variety,  and 
they  present  a  striking  contrast  to  the  inelastic  fibres  in  their  form  and  size.  Although 
they  are  still  very  small,  they  always  present  a  double  contour. 


FIG.  157.—  Loose  net-wwlc  of  connective  tissue  from  the  Jiuman  subject,  showing  the  fibres  and  cells.    (Eollett.) 

a,  a,  a  capillary  blood-vessel. 

Certain  cellular  and  nuclear  elements  are  always  found  in  the  connective  tissue.  The 
cells  have  been  described  under  the  name  of  connective-tissue  cells.  They  are  very 
irregular  in  size  and  form,  some  of  them  being  spindle-shaped  or  caudate,  and  others, 
star-shaped.  They  possess  one,  and  sometimes  two  or  three  clear,  ovoid  nuclei,  with 
distinct  nucleoli.  On  the  addition  of  acetic  acid  the  cells  disappear,  but  the  nuclei  are 
unaffected.  These  are  the  fibro-plastic  elements  of  Lebert,  and  the  embryo-plastic  ele- 
ments of  Robin.  It  is  impossible  to  give  any  accurate  measurements  of  the  cells,  on 
account  of  their  great  variations  in  size.  The  length  of  the  nuclei  is  from  ^V<r  to  ^Vo 
of  an  inch,  and  their  diameter,  from  y^  to  ^-5-  of  an  inch.  The  appearance  of  the 
connective  tissue,  with  a  few  cells  and  nuclei,  is  represented  in  Fig.  157. 

Between  the  muscles,  and  in  the  substance  of  the  muscles  between  the  bundles  of 
fibres,  there  always  exists  a  greater  or  less  quantity  of  adipose  tissue  in  the  meshes  of 
the  fibrous  structure. 


Blood-vessels  and  Lymphatics.  —  The  muscles  are  abundantly  supplied  with  blood-ves- 
sels, generally  by  a  number  of  small  arteries  with  two  satellite  veins.     The  capillary 


PHYSIOLOGICAL  PKOPEKTIES   OF  THE  MUSCLES.  533 

arrangement  in  this  tissue  is  peculiar.  From  the  smallest  arterioles,  capillary  vessels  are 
given  off,  arranged  in  a  net-work  with  tolerably  regular,  oblong,  rectangular  meshes, 
their  long  diameter  following  the  direction  of  the  fibres.  These  envelop  each  primitive 
fasciculus,  enclosing  it  completely,  the  artery  and  vein  being  upon  the  same  side.  The 
capillaries  are  smaller  than  in  any  other  part  of  the  vascular  system.  When  distended 
Avith  blood  they  are  from  T71Tr7  to  ^y^  of  an  inch  in  diameter;  and  when  empty  their 
diameter  is  from  7-^  to  TTFS  °f  an  inch. 

The  arrangement  of  the  lymphatics  in  the  muscles  has  never  been  definitely  ascer- 
tained. There  are  numerous  lymphatics  surrounding  the  large  vascular  trunks  of  the 
extremities  and  of  the  abdominal  and  thoracic  walls,  which,  it  would  appear,  must  come 
from  the  substance  of  the  muscles ;  but  they  have  never  been  traced  to  their  origin. 
Sappey  has  succeeded  in  injecting  lymphatics  upon  the  surface  of  some  of  the  larger 
muscles,  but  he  has  not  been  able  to  follow  them  into  the  muscular  substance. 

Connection  of  the  Muscles  with  the  Tendons. — It  is  now  generally  admitted  that  the 
primitive  muscular  fasciculi  terminate  in  little  conical  extremities,  which  are  received 
into  corresponding  depressions  in  the  bundles  of  fibres  composing  the  tendons;  but  this 
union  is  so  close,  that  the  muscle  or  the  tendon  may  be  ruptured  without  a  separation  at 
the  point  of  union.  In  the  penniform  muscles  this  arrangement  is  quite  uniform  and 
elegant.  In  other  muscles  it  is  essentially  the  same,  but  the  perimysium  seems  to  be  con- 
tinuous with  the  loose  areolar  tissue  enveloping  the  corresponding  tendinous  bundles. 

Chemical  Composition  of  the  Muscles. — We  are  as  yet  so  little  acquainted  with  the 
exact  constitution  of  the  nitrogenized  constituents  of  the  body,  that  we  cannot  appreciate 
the  nature  of  all  the  proximate  principles  that  exist  in  the  muscular  substance.  The 
most  important  of  these  is  musculine.  This  resembles  fibrin,  but  it  presents  certain  points 
of  difference  in  its  behavior  to  reagents,  by  which  it  may  be  readily  distinguished.  One 
of  its  peculiar  properties  is  that  it  is  dissolved  at  an  ordinary  temperature  by  a  mixture 
of  one  part  of  hydrochloric  acid  and  ten  of  water. 

The  muscular  substance  is  permeated  by  a  fluid,  called  the  muscular  juice,  which  con- 
tains a  peculiar  coagulable  principle  called  myosine. 

Combined  with  the  organic  principles,  we  find  a  great  variety  of  mineral  salts  in  the 
muscular  substance,  that  cannot  be  separated  without  incineration.  Certain  excremen- 
titious  matters  have  also  been  found  in  the  muscles;  and  probably  nearly  all  of  those 
eliminated  by  the  kidneys  exist  here,  although  they  are  taken  up  by  the  blood  as  fast  as 
they  are  produced  and  are  consequently  detected  with  difficulty.  The  muscles  also  con- 
tain inosite,  inosic  acid,  lactic  acid,  and  certain  other  acids  of  fatty  origin.  During  life, 
the  muscular  fluid  is  slightly  alkaline,  but  it  becomes  acid  soon  after  death.  The  muscle 
itself,  during  contraction,  has  an  acid  reaction.  The  muscular  juice  is  alkaline  or  neutral 
after  moderate  exercise,  as  well  as  during  complete  repose  ;  but,  when  a  muscle  is  made 
to  undergo  excessive  exercise,  the  lactic  acid  exists  in  greater  quantity,  and  the  reaction 
becomes  acid. 

Physiological  Properties  of  the  Muscles. 

The  general  properties  of  the  striated  muscles,  as  distinguished  from  all  other  tissues 
except  the  involuntary  muscles,  are  as  follows:  1.  Elasticity;  2.  Tonicity;  3.  Sensi- 
bility of  a  peculiar  kind ;  4.  Contractility,  or  irritability.  These  are  all  necessary  to  the 
physiological  action  of  the  muscles.  Their  elasticity  is  brought  into  play  in  opposing 
muscles  or  sets  of  muscles ;  one  set  acting  to  move  a  part  and  to  extend  the  antagonistic 
muscles,  which,  by  virtue  of  their  elasticity,  retract  when  the  extending  force  is  removed. 
Their  tonicity  is  an  insensible  and  a  more  or  less  constant  contraction,  by  which  the 
action  of  opposing  muscles  is  balanced  when  both  are  in  the  condition  of  what  we  call 
repose.  Their  sensibility  is  peculiar  and  is  expressed  chiefly  in  the  sense  of  fatigue  and 


534:  MOVEMENTS. 

in  the  appreciation  of  weight  and  of  resistance  to  contraction.  Their  contractility  or 
irritability  is  the  property  which  enables  them  to  contract  and  exert  a  certain  amount  of 
mechanical  force  under  the  proper  stimulus.  All  of  these  general  properties  strictly 
belong  to  physiology,  as  do  some  special  acts  that  are  not  necessarily  involved  in  the 
study  of  ordinary  descriptive  anatomy. 

Elasticity  of  Muscles. — The  true  muscular  substance  contained  in  the  sarcolemma  is 
eminently  contractile ;  and,  although  it  may  possess  a  certain  degree  of  elasticity,  this 
property  is  most  strongly  marked  in  the  accessory  anatomical  elements.  The  interstitial 
fibrous  tissue  is  loose  and  possesses  a  certain  number  of  elastic  fibres,  and,  as  we  have 
seen,  the  sarcolemma  is  very  elastic.  It  is  probably  the  sarcolemma  that  gives  to  the 
muscles  their  retractile  power  after  simple  extension. 

It  is  unnecessary  to  follow  out  in  detail  all  of  the  numerous  experiments  that  have 
been  made  upon  the  elasticity  of  muscles.  There  is  a  certain  limit,  of  course,  to  their 
perfect  elasticity  (understanding  by  this  the  degree  of  extension  that  is  followed  by  com- 
plete retraction),  and  this  cannot  be  exceeded  in  the  human  subject  without  dislocation 
of  parts.  It  has  been  found  by  Marey,  that  the  gastrocnemius  muscle  of  a  frog,  detached 
from  the  body,  can  be  extended  about  one-fiftieth  of  an  inch  by  a  weight  of  a  little  more 
than  three  hundred  grains.  This  weight,  however,  did  not  extend  the  muscle  beyond 
the  limit  of  perfect  elasticity.  The  muscle  of  a  frog  of  ordinary  size  was  extended  beyond 
the  possibility  of  complete  restoration,  by  a  weight  of  about  seven  hundred  and  fifty 
grains.  Marey  also  showed  that  fatigue  of  the  muscles  increased  their  extensibility  and 
diminished  their  power  of  subsequent  retraction.  This  fact  has  an  application  to  the 
physiological  action  of  muscles ;  for  it  is  well  known  that  they  are  unusually  relaxed 
during  fatigue  after  excessive  exertion,  and,  as  we  should  expect,  they  are  at  that  time 
more  than  ordinarily  extensible. 

Muscular  Tonicity. — The  muscles,  under  normal  conditions,  have  an  insensible  and 
a  constant  tendency  to  contract,  which  is  more  or  less  dependent  upon  the  action  of  the 
motor  nerves.  If,  for  example,  a  muscle  be  cut  across  in  a  surgical  operation,  the  divided 
extremities  become  permanently  retracted ;  or,  if  the  muscles  of  one  side  of  the  face  be 
paralyzed,  the  muscles  upon  the  opposite  side  insensibly  distort  the  features.  It  is  diffi- 
cult to  explain  these  phenomena  by  assuming  that  tonicity  is  due  to  reflex  action,  for 
there  is  no  evidence  that  the  contraction  takes  place  as  the  consequence  of  a  stimulus. 
All  that  we  can  say  is,  that  a  muscle,  not  excessively  fatigued,  and  with  its  nervous 
connections  intact,  is  constantly  in  a  state  of  insensible  contraction,  more  or  less  marked, 
and  that  this  is  an  inherent  property  of  all  of  the  contractile  tissues. 

Sensibility  of  the  Muscles. — The  muscles  possess  to  an  eminent  degree  that  kind  of 
sensibility  which  enables  us  to  appreciate  the  power  of  resistance,  immobility,  and  elas- 
ticity of  substances  that  are  grasped,  on  which  we  tread,  or  which,  by  their  weight,  are 
opposed  to  the  exertion  of  muscular  power.  It  is  by  the  appreciation  of  weight  and 
resistance  that  we  regulate  the  amount  of  force  required  to  accomplish  muscular  acts. 
These  properties  refer  chiefly  to  simple  muscular  efforts.  After  long-continued  exertion 
we  appreciate  a  sense  of  fatigue  that  is  peculiar  to  the  muscles.  It  is  difficult  to  separate 
this  entirely  from  the  sense  of  nervous  exhaustion,  but  it  seems  to  be,  to  a  certain  extent, 
distinct;  for,  when  suffering  from  the  fatigue  that  follows  over-exertion,  it  seems  as 
though  we  could  send  a  nervous  stimulus  to  the  muscles,  to  which  they  are,  for  the  time, 
unable  to  respond.  When  we  come  to  consider  fully  the  subjects  of  muscular  and  ner- 
vous irritability,  we  shall  see  that  these  two  properties  are  entirely  distinct,  and  that  we 
may  exhaust  or  destroy  the  one  without  necessarily  affecting  the  other. 
^  When  the  muscles  are  thrown  into  spasm  or  tetanic  contraction,  a  peculiar  sensation 
is  produced,  entirely  different  from  painful  impressions  made  upon  the  ordinary  sensitive 


PHYSIOLOGICAL  PROPERTIES   OF  THE   MUSCLES.  535 

nerves.  In  the  cramps  of  cholera,  tetanus,  or  the  convulsions  from  strychnine,  these 
distressing  sensations  are  very  marked.  The  so-called  recurrent  sensibility  of  the  anterior 
roots  of  the  spinal  nerves  is  probably  due  in  part  to  the  tetanic  contractions  produced  by 
galvanizing  these  filaments.  This  question,  however,  will  be  taken  up  again  in  connection 
with  the  nervous  system. 

If  the  muscles  possess  any  general  sensibility,  it  is  very  faint.  A  muscle  may  be 
lacerated  or  irritated  in  any  way  without  producing  actual  pain,  although  we  always  can 
appreciate  the  contraction  produced  by  irritants  and  the  sense  of  tension  when  the  mus- 
cles are  drawn  upon. 

Muscular  Contractility,  or  Irritability. — Physiologists  now  regard  muscular  irrita- 
bility as  synonymous  with  contractility;  and,  perhaps,  the  latter  term  more  nearly 
expresses  the  fact,  although  the  term  irritability,  applied  to  the  nerves,  and  even  of  late 
years  to  the  glands,  is  one  very  generally  used. 

By  irritability  we  understand  a  property  belonging  to  highly-organized  parts,  which 
enables  them  to  perform  certain  peculiar  and  characteristic  functions  in  obedience  to  a 
proper  stimulus.  In  the  sense  in  which  the  term  is  generally  received,  it  is  proper  to  apply 
it  to  any  tissue  or  organ  that  performs  its  vital  function,  so  called,  under  a  natural  or  an 
artificial  stimulus.  The  nerves  receive  impressions  and  carry  a  stimulus  to  the  muscles, 
causing  them  to  contract.  This  property,  which  is  always  present  during  life,  under  normal 
conditions,  and  which  persists  for  a  certain  period  after  death,  is  called  nervous  irritability. 
It  has  lately  been  shown  that  the  application  of  a  proper  stimulus  will  induce  secretion  by 
the  glands ;  and  Bernard  has  called  this  glandular  irritability.  The  application  of  a  stim- 
ulus to  the  muscular  tissue  causes  the  fibres  to  contract ;  and  this  is  muscular  irritability. 
As  it  always  involves  contraction  and  is  extinct  only  when  the  muscles  can  no  longer  act, 
it  is  equally  proper  to  call  this  property  contractility.  No  property,  such  as  we  under- 
stand by  this  definition  of  irritability,  is  manifested  by  tissues  or  organs  that  have  purely 
passive  or  mechanical  functions,  such  as  bones,  cartilages,  and  fibrous  or  elastic  mem- 
branes. The  term  irritability  can  only  be  applied  properly  to  nerves  or  nerve-centres, 
to  contractile  structures,  and  to  glands. 

During  life  and  under  normal  conditions,  the  muscles  will  always  contract  in  obe- 
dience to  a  proper  stimulus  applied  either  directly  or  through  the  nerves.  In  the  natural 
action  of  the  organism,  this  contraction  is  induced  by  nervous  influence  through  reflex 
action  or  volition.  Still,  a  muscle  may  be  living  and  yet  have  lost  its  contractility. 
For  example,  after  a  muscle  has  been  for  a  long  time  paralyzed  and  disused,  the  applica- 
tion of  the  most  powerful  galvanic  excitation  will  fail  to  induce  contraction.  But,  when 
we  examine  such  a  muscle  with  the  microscope,  it  is  found  that  the  nutrition  has  become 
profoundly  affected,  and  that  the  contractile  substance  has  disappeared,  giving  place  to 
inert  fatty  matter.  Muscular  contractility  persists  for  a  certain  time  after  death  and  in 
muscles  separated  from  the  body;  and  this  fact  has  been  taken  advantage  of  by  physiolo- 
gists in  the  study  of  the  so-called  vital  properties  of  the  muscular  tissue.  We  have 
already  seen  that  a  muscle  detached  from  the  living  body  continues  for  a  time  to  respire, 
and  probably  it  undergoes  some  of  the  changes  of  disassimilation  observed  in  the  organ- 
ism. So  long  as  these  changes  are  restricted  to  the  limits  of  physical  and  chemical  integ- 
rity of  the  fibre,  contractility  remains.  As  these  processes  are  very  slow  in  the  cold- 
blooded animals,  the  irritability  of  all  the  parts  persists  for  a  considerable  time  after 
death.  We  have  repeatedly  demonstrated  muscular  contractility,  several  days  after 
death,  in  alligators  and  turtles. 

In  the  human  subject  and  the  warm-blooded  animals,  the  muscles  cease  to  respond  to 
excitation  a  few  hours  after  death,  although  the  time  of  disappearance  of  irritability  is 
very  variable.  ISTysten,  in  a  number  of  experiments  upon  the  disappearance  of  contrac- 
tility in  the  human  subject  after  decapitation,  found  that  different  parts  lost  their  con- 
tractility at  different  periods,  but  that  generally  this  depended  upon  exposure  to  the  air. 


536 


MOVEMENTS. 


With  the  exception  of  the  right  auricle  of  the  heart,  the  muscles  of  the  voluntary  sys- 
tem were  the  last  to  lose  their  irritability.  In  one  instance,  certain  of  the  voluntary 
muscles  that  had  not  been  exposed  retained  their  contractility  seven  hours  and  fifty  min- 
utes after  death.  The  observations  of  Longet  and  Masson  show  that  a  galvanic  shock, 
sufficiently  powerful  to  produce  death,  instantly  destroys  the  irritability  of  the  muscular 
tissue  and  of  the  motor  nerves. 

One  of  the  most  important  questions  to  determine  with  regard  to  muscular  irritability 
is  whether  it  be  a  property  inherent  in  the  muscular  tissue  or  derived  from  the  nervous 
system.  The  fact  that  muscles  can  be  excited  to  more  powerful  and  regular  contractions 
by  stimulating  the  motor  nerves  than  by  operating  directly  upon  their  substance,  and  the 
great  difficulty  in  tracing  the  nerves  to  their  termination  in  the  muscles,  have  led  to  the 
view  that  muscular  contractility  is  dependent  upon  nervous  influence,  and  consequently 
that  the  muscles  have  no  irritability  or  contractility,  as  a  property  inherent  in  their  own 
substance.  This  doctrine,  however,  cannot  be  sustained. 

The  experiments  of  Longet,  published  in  1841,  presented  almost  conclusive  proof 
of  the  independence  of  muscular  irritability.  He  resected  the  facial  nerve  and  found 
that  it  ceased  to  respond  to  mechanical  and  galvanic  stimulus,  or,  in  other  words,  lost 
its  irritability,  after  the  fourth  day.  Operating,  however,  upon  the  muscles  supplied 
exclusively  with  filaments  from  this  nerve,  he  found  that  they  responded  promptly  to 
mechanical  and  galvanic  irritation,  and  that  they  continued  to  contract,  under  stimu- 
lation, for  more  than  twelve  weeks.  In  some  farther  experiments  it  was  shown  that, 
while  the  contractility  of  the  muscles  could  be  seriously  influenced  through  the  ner- 
vous system,  this  was  effected  only  by  modifications  in  their  nutrition.  When  the 
mixed  nerves  were  divided,  the  nutrition  of  the  muscles  was  generally  disturbed ;  and, 

although  muscular  irritability  persisted  for  some  time 
after  the  nervous  irritability  had  disappeared,  it  be- 
came very  much  diminished  at  the  end  of  six  weeks. 
These  experiments  are  very  striking  and  satisfactory; 
but  the  whole  question  was  definitively  settled  by  the 
observations  of  Bernard  upon  the  peculiar  influence  of 
the  woorara-peison  and  the  sulphocyanide  of  potas- 
sium. As  the  result  of  these  experiments,  it  was 
ascertained  that  some  varieties  of  woorara  destroy 
the  irritability  of  the  motor  nerves,  leaving  the  sen- 
sitive filaments  intact.  If  a  frog  be  poisoned  by  intro- 
ducing a  little  of  this  agent  under  the  skin,  irritation, 
galvanic  or  mechanical,  applied  to  an  exposed  nerve, 
fails  to  produce  the  slightest  muscular  contraction ;  but, 
if  the  stimulus  be  applied  directly  to  the  muscles,  they 
will  contract  vigorously.  In  this  way  the  nerves  are, 
as  it  were,  dissected  out  from  the  muscles ;  and  the  dis- 
covery of  an  agent  that  will  paralyze  the  nerves  with- 
out affecting  the  muscles  affords  conclusive  proof  that 
the  irritability  of  these  two  systems  is  entirely  distinct. 
If  a  frog  be  poisoned  with  sulphocyanide  of  potassium, 
precisely  the  contrary  effect  will  be  observed  ;  that  is, 
the  muscles  will  become  insensible  to  excitation,  while 
^the  nerves  \n  this  animal,  the  nervous  system  is  unaffected.  This  fact  may  be 
demonstrated  by  applying  a  tight  ligature  around  the 
lines)  body  in  the  lumbar  region,  involving  all  the  parts  ex- 
cept the  lumbar  nerves.  If  the  poison  be  now  intro- 
duced beneath  the  skin  .of  the  parts  above  the  ligature,  the  anterior  parts  only  are  affect- 
ed, because  the  vascular  communication  with  the  posterior  extremities  is  cut  off.  If  the 


has  no 


PHYSIOLOGICAL  PROPERTIES   OF  THE  MUSCLES.  537 

exposed  nerves  be  now  galvanized,  the  muscles  of  the  legs  are  thrown  into  contraction, 
showing  that  the  nervous  irritability  remains.  Reflex  movements  in  the  posterior 
extremities  may  also  be  produced  by  irritation  of  the  parts  above  the  ligature.  These 
experiments,  most  of  which  we  have  frequently  repeated,  taken  in  connection  with  the 
observations  of  Longet,  leave  no  doubt  of  the  existence  of  an  inherent  and  independent 
irritability  in  the  muscular  tissue.  Contractions  of  muscles,  it  is  true,  are  normally 
excited  through  the  nervous  system,  and  artificial  stimulation  of  a  motor  or  mixed  nerve 
is  the  most  efficient  method  of  producing  the  simultaneous  action  of  all  the  fibres  of  a 
muscle  or  of  a  set  of  muscles ;  but  galvanic,  mechanical,  or  chemical  irritation  of  the 
muscles  themselves  will  produce  contraction,  after  the  nervous  irritability  has  been 
abolished. 

The  conditions  under  which  muscular  irritability  exists  are  simply  those  of  normal 
nutrition  of  the  muscular  tissue.  When  the  muscles  have  become  profoundly  affected 
in  their  nutrition,  as  the  result  of  section  of  the  mixed  nerves  or  after  prolonged  paraly- 
sis, the  irritability  disappears  and  cannot  be  restored.  The  determination  of  the  pres- 
ence or  absence  of  muscular  contractility,  in  cases  of  paralysis,  is  one  of  the  methods  of 
ascertaining  whether  treatment  directed  to  the  restoration  of  the  nervous  power  will  be 
likely  to  be  followed  by  favorable  results.  If  the  muscular  irritability  have  entirely  dis- 
appeared, it  is  almost  useless  to  attempt  to  restore  the  functions  of  the  part. 

A  great  many  experiments  have  been  made  with  regard  to  the  influence  of  the  circu- 
lation upon  muscular  irritability,  chiefly  with  reference  to  the  effects  of  tying  large  vessels. 
Among  the  most  recent  are  those  of  Longet.  He  tied  the  abdominal  aorta  in  five  dogs  and 
found  that  voluntary  motion  ceased  in  about  a  quarter  of  an  hour,  and  that  the  muscular 
irritability  was  extinct  in  two  hours  and  a  quarter.  When  the  blood  was  restored,  after 
three  or  four  hours,  by  removing  the  ligature,  the  irritability  and  finally  voluntary  move- 
ment returned.  These  experiments  show  that  the  circulation  of  the  blood  is  necessary 
to  the  contractility  of  the  muscles.  Tying  the  vena  cava  did  not  affect  the  irritability  of 
the  muscles.  In  dogs  in  which  this  experiment  was  performed,  the  lower  extremities 
preserved  their  contractility,  and  the  voluntary  movements  were  unaffected  up  to  the 
time  of  death,  which  took  place  in  twenty-six  hours. 

The  relations  of  muscular  irritability  to  the  circulation  have  been  farther  illustrated, 
in  some  very  curious  and  interesting  experiments,  by  Dr.  Brown-Sequard.  The  first 
observations  were  made  upon  two  men  executed  by  decapitation.  Thirteen  hours  and 
ten  minutes  after  death,  when  the  muscular  irritability  had  entirely  disappeared  and  was 
succeeded  by  cadaveric  rigidity,  a  quantity  of  fresh,  defibrinated  venous  blood,  from  the 
human  subject,  was  injected  into  the  arteries  of  one  hand  and  was  returned  by  the  veins. 
It  was  afterward  reinjected  several  times  during  a  period  of  thirty- five  minutes.  The 
whole  time  occupied  in  the  different  injections  was  from  ten  to  fifteen  minutes.  Ten 
minutes  after  the  last  injection,  and  about  fourteen  hours  after  death,  the  irritability  was 
found  to  have  returned,  in  a  marked  degree,  in  twelve  muscles  of  the  hand.  There  were 
only  two  muscles  out  of  the  nineteen,  in  which  the  irritability  could  not  be  demonstrated. 
Three  hours  after,  the  irritability  still  existed,  but  it  disappeared  a  quarter  of  an  hour 
later.  The  second  observation  was  essentially  the  same,  except  that  defibrinated  blood 
from  the  dog  was  used,  and  the  experiments  were  made  upon  the  muscles  of  the  arm. 
The  irritability  was  restored  in  ail  of  the  muscles,  and  it  persisted,  the  cadaveric  rigidity 
having  disappeared,  twenty  hours  after  decapitation.  These  experiments  are  exceedingly 
interesting,  as  showing  the  dependence  of  irritability  upon  certain  of  the  processes 
of  nutrition,  which  are  probably  restored,  though  temporarily  and  imperfectly,  by  the 
injection  of  fresh  blood.  They  are  also  important  in  connection  with  the  study  of 
cadaveric  rigidity  of  muscles,  a  condition  which  follows  the  loss  of  their  so-called  vital 
properties.  The  subject  of  cadaveric  rigidity  will  be  fully  discussed  as  one  of  the  phe- 
nomena of  death. 


538 


MOVEMENTS. 


Muscular   Contraction. 

The  stimulus  of  the  will,  conveyed  through  the  conductors  of  motor  influences  from 
the  brain  to  a  muscle  or  set  of  muscles,  produces  an  impression  upon  the  muscular  fibres 
and  causes  them  to  contract.  In  parts  where  the  muscles  have  been  exercised  and  edu- 
cated, this  action  is  regulated  with  exquisite  nicety,  so  that  the  most  delicate  and  rapid, 
as  well  as  powerful  contractions  may  be  produced.  Certain  movements,  not  under  the 
control  of  the  will,  are  produced  as  the  result  of  unconscious  reflection  from  a  nervous 
centre,  along  the  motor  conductors,  of  an  impression  made  upon  sensitive  nerves.  During 
this  action,  certain  important  phenomena  are  observed  in  the  muscles  themselves.  They 
change  in  form,  consistence,  and,  to  a  certain  extent,  in  their  constitution  ;  the  different 
periods  of  their  stimulation,  contraction,  and  relaxation  are  positive  and  well-marked ; 
their  nutrition  is  for  the  time  modified  ;  they  develop  galvanic  currents ;  and,  in  short, 
they  present  a  number  of  general  phenomena,  distinct  from  the  results  of  their  action, 
that  are  more  or  less  interesting  and  important  to  the  physiologist. 

The  most  striking  of  the  phenomena  accompanying  muscular  action  is  shortening  and 
hardening  of  the  fibres.  It  is  only  necessary  to  observe  the  action  of  any  well-developed 
muscle  to  appreciate  these  changes.  The  active  shortening  is  shown  by  the  approxima- 
tion of  the  points  of  attachment,  and  the  hardening  is  sufficiently  palpable.  The  latter 

phenomenon  is  marked  in  proportion  to 
the  development  of  the  true  muscular 
tissue  and  its  freedom  from  inert  mat- 
ter, such  as  fat.  We  have  already  seen 
that  it  is  the  muscular  substance  alone 
which  has  the  property  of  contraction  ; 
and  we  have  shown  that  this  action  in- 
creases the  consumption  of  oxygen  and 
probably  of  other  matters,  the  produc- 
tion of  carbonic  acid  and  some  other 
excrernentitious  principles,  and  that  it 
develops  heat. 

Notwithstanding  the  marked  and 
constant  changes  in  the  form  and  con- 
sistence of  the  muscles  during  contrac- 
tion, their  actual  volume  is  unchanged, 
or  it  undergoes  modifications  so  slight 
that  they  may  practically  be  disre- 
garded. Experiments  upon  this  point 
have  been  so  uniform  in  their  results, 
that  it  is  hardly  necessary  to  refer  to 
them  in  detail.  All  modern  observers 
accept  the  results  of  the  older  experi- 
ments, in  which  muscles  have  been  made 
to  contract  in  a  vessel  of  water  con- 
nected with  a  small  upright  tube,  show- 
ing that,  when  the  muscles  are  in  active 

FIG.  159.— Apparatus  to  show  that  mmcles  do  not  increase    contraction   as  the   result  of  a  galvanic 

in  volume  during  contraction.   (Marey.)  stimulus,  the  elevation  of  the  liquid  in 

A,  vessel  of  water,  provided  with  a  tube  (0) :  B  galvanic  ai>     ^ 

paratiis ;  D,  nerve,  to  which  the  stimulus  is  applied.  tne  ™be   1S   unchanged.      It   IS   evident, 

therefore,  that  a  muscle,  while  it  hard- 
ens and  changes  in  form  during  contraction,  does  not  sensibly  change  in  its  actual  volume. 

Changes  in  the  Form  of  the  Muscular  Fibres  during  Contraction.— It  has  been  found 
exceedingly  difficult  to  determine  a  question  apparently  so  simple  as  that  of  the  change 


MUSCULAR   CONTRACTION.  539 

in  form  which  the  muscular  fibres  undergo  during  contraction ;  and  it  is  only  of  late 
years  that  this  single  point  has  been  definitively  settled.  The  idea  that  the  fibres 
do  not  shorten,  but  that  they  assume  a  zigzag  arrangement  during  contraction,  is  not 
adopted  by  any  modern  writers.  All  are  now  agreed  that  in  muscular  contraction 
there  is  an  increase  in  the  thickness  of  the  fibre,  exactly  compensating  its  diminution  in 
length.  This  has  been  repeatedly  observed  in  microscopical  examinations,  and  the  only 
points  now  to  determine  are  the  exact  mechanism  of  this  transverse  enlargement,  its 
duration,  the  means  by  which  it  may  be  excited,  and  its  physiological  modifications. 
These  questions,  within  the  last  few  years,  have  been  made  the  subjects  of  elaborate 
investigations  by  Helmholtz,  Du  Bois-Reymond,  Aeby,  Marey,  and  others ;  and,  although 
it  is  hardly  necessary  to  follow  these  experimenters  through  all  of  their  investigations, 
many  points  have  been  developed,  particularly  by  the  system  of  registering  the  muscular 
movements,  that  possess  considerable  physiological  importance. 

One  essential  condition  in  the  study  of  the  mechanism  of  muscular  contraction  is  to 
imitate,  in  a  muscle  or  a  part  of  a  muscle  that  can  be  subjected  to  direct  observation,  the 
force  that  naturally  excites  it  to  contraction.  The  application  of  electricity  to  the  nerve 
is  beyond  all  question  the  most  perfect  method  that  can  be  employed  for  this  purpose. 
We  can  in  this  way  excite  a  single  contraction,  or,  by  employing  a  rapid  succession  of 
currents,  we  can  excite  either  continuous  or  tetanic  action.  While  the  electric  current  is 
not  identical  with  the  nervous  force,  it  is  the  best  substitute  we  can  employ  in  experi- 
ments upon  muscular  contractility,  and  it  has  the  advantage  of  not  affecting  the  physical 
and  chemical  integrity  of  the  nervous  and  muscular  tissue.  In  studying  this  subject,  we 
shall  first  follow  some  of  the  experiments  upon  muscular  contraction  excited  artificially, 
and  then  apply  them,  as  far  as  possible,  to  the  strictly  physiological  actions  of  muscles. 

There  are  two  classes  of  phenomena  that  may  be  produced  by  electrical  excitation  of 
motor  nerves  :  1.  When  the  stimulus  is  applied  in  the  form  of  a  single  discharge,  it  is  fol- 
lowed by  a  single  muscular  contraction.  2.  Under  a  rapid  succession  of  discharges,  the 
muscle  is  thrown  into  a  state  of  permanent,  or  tetanic  contraction.  It  will  greatly  facilitate 
our  comprehension  of  the  subject  to  study  these  phenomena  separately  and  successively. 

The  muscular  contraction  produced  by  a  single  stimulus  applied  to  the  nerve  is  called 
by  the  French,  secousse  (shock),  and  by  the  Germans,  Zuckung  (convulsion).  It  will  be 
convenient  for  us  to  employ  some  term  that  will  express  this  sudden  action  of  the  mus- 
cular fibres,  as  distinguished  from  the  contraction  that  takes  place  on  repeated  stimula- 
tion or  in  continued  muscular  effort ;  and  we  shall  designate  a  single  muscular  contraction, 
then,  as  spasm,  applying  the  term  tetanus,  to  continued  action. 

Spasm  produced  ~by  Artificial  Excitation. — If  an  electric  discharge,  even  very  feeble, 
be  applied  to  a  motor  nerve  connected  with  a  fresh  muscle,  it  is  followed  by  a  sudden 
contraction,  which  is  succeeded  by  a  rapid  relaxation.  Under  this  stimulation,  the  muscle 
shortens  by  about  three-tenths  of  its  entire  length.  The  form  of  the  contraction,  as 
registered  by  the  apparatus  of  Helmholtz,  Marey,  and  others  who  have  applied  the 
so-called  graphic  method  to  the  study  of  muscular  action,  presents  certain  interesting 
peculiarities.  We  shall  give,  however,  only  the  general  characters  of  this  action,  with- 
out discussing  in  detail  the  complicated  apparatus  employed. 

According  to  Helmholtz,  the  -whole  period  of  a  single  contraction  and  relaxation  of 
the  gastrocnemius  muscle  of  a  frog  is  a  little  less  then  one-third  of  a  second.  The  mus- 
cles of  mammals  and  birds  contract  more  rapidly,  but,  with  this  exception,  the  essential 
characters  of  the  contraction  are  the  same.  The  following  are  the  periods  occupied  by 
these  different  phenomena : 

Interval  between  stimulation  and  contraction : 0"'020 

Contraction 0"'180 

Relaxation .  0"'105 


0"-305 


540  MOVEMENTS. 

The  duration  of  the  electric  current  applied  to  the  nerve  is  only  0"'0008.  Contrac- 
tion, however,  does  not  follow  immediately,  there  being  an  interval,  called  pose,  of  about 
one-fiftieth  of  a  second.  The  contraction  then  follows,  which  is  succeeded  by  gradual 
relaxation,  the  former  being  a  little  longer  than  the  latter.  This  description  represents 
the  contraction  of  an  entire  muscle,  but  it  does  not  indicate  the  changes  in  form  of  the 
individual  fibres,  a  point  much  more  difficult  to  determine  satisfactorily.  It  is  pretty 
well  established,  however,  that  a  single  fibre,  with  its  irritability  unimpaired,  becomes 
contracted  and  swollen  at  the  point  where  the  stimulation  is  applied.  Now,  the  question 
is  whether,  in  normal  contraction  of  the  fibres  in  obedience  to  the  natural  nervous  stimu- 
lus, there  be  a  uniform  shortening  of  the  whole  fibre,  a  shortening  of  those  portions  only 
that  are  the  seat  of  the  terminations  of  the  motor  nerves,  or  a  peristaltic  shortening  and 
swelling,  rapidly  running  the  length  of  the  fibre. 

The  recent  experiments  of  Aeby,  which  have  been  repeated  and  extended  by  Marey, 
demonstrate  beyond  a  doubt  that,  when  one  extremity  of  a  muscle  is  excited,  a  contrac- 
tion occurs  at  that  point  and  is  propagated  along  the  muscle  in  the  form  of  a  wave,  ex- 
actly like  the  peristaltic  action  of  the  intestines,  except  that  it  is  more  rapid.  Both  Aeby 
and  Marey  have  succeeded  in  measuring  the  rapidity  of  the  wave,  and  they  find  it  to  be 
about  forty  inches  per  second.  Applying  this  principle  to  the  physiological  action  of 
muscles,  Aeby  advances  the  theory  that  shortening  of  the  fibres  takes  place  wherever  a 

stimulus  is  received,  and  that 
this  is  propagated  in  the  form  of 
a  wave,  which  meets  in  its  course 
another  wave  starting  from  a  dif- 
ferent point  of  stimulation.  As 
we  know  that  the  motor  nerves 
terminate  at  different  points  by 
becoming  fused,  as  it  were,  with 
the  sarcolemma,  we  can  readily 
comprehend,  under  this  theory, 
how  the  simultaneous  contrac- 
tion of  all  the  fibres  of  a  muscle 
is  produced  by  stimulation  of  its 
motor  nerve.  This  idea  is  ex- 
pressed in  the  accompanying  dia- 

FTG.  160.— Diagram  of  the  muscular  icave.    (Aeby.)  gram.     Although  this  view  of  the 

physiological  action  of  the  mus- 
cular fibres  is  extremely  probable,  it  cannot  be  assumed  that  it  has  been  absolutely 
demonstrated ;  but  it  is  certainly  more  satisfactory  and  better  sustained  by  experimental 
facts  than  any  theory  that  has  hitherto  been  advanced. 

Mechanism  of  prolonged  Muscular  Contraction. — By  a  voluntary  effort  we  are  able 
to  produce  a  muscular  contraction  of  a  certain  duration,  and  of  a  power,  within  certain 
limits,  proportionate  to  the  amount  of  force  we  may  desire  to  produce  ;  but,  after  a  cer- 
tain time,  the  muscle  becomes  fatigued,  and  it  may  become  exhausted  to  the  extent  that 
it  will  not  respond  to  the  normal  stimulus.  This  is  the  kind  of  muscular  action  most 
interesting  to  us  as  physiologists. 

The  experiments  of  Marey  seem  to  show  precisely  how  far  the  nervous  action  that 
gives  rise  to  a  powerful  and  continuous  muscular  contraction  can  be  imitated  by  elec- 

nty.  Calling  the  movement  produced  by  a  single  electric  discharge,  secousse,  which 
we  have  translated  by  the  word  spasm,  he  calls  the  persistent  contraction,  tetanus.  We 
shall  adopt  this  name  to  distinguish  persistent  muscular  action  from  the  single  contrac- 
tion that  we  have  just  described. 

It  is  a  curious  fact  that  a  continued  current  of  galvanic  electricity  passed  through  a 


MUSCULAR   CONTRACTION.  541 

nerve  or  a  muscle  does  not  induce  muscular  contraction ;  and  it  is  only  when  the  cur- 
rent is  closed  or  broken,  that  any  action  is  observed.  But  if  we  employ  statical  elec- 
tricity, a  muscular  spasm  occurs  at  every  discharge,  proportionate,  in  some  degree,  to 
the  power  of  the  excitation.  If  the  discharges  be  very  frequently  repeated,  or  if  a  gal- 
vanic current  be  applied,  broken  by  an  interrupting  apparatus,  the  spasms  follow  each 
other  in  quick  succession.  In  experimenting  upon  the  muscles  of  the  frog,  with  a  regis- 
tering apparatus,  Marey  has  found  that,  with  a  gradual  increase  in  the  rapidity  of  the 
electric  shocks,  the  individual  muscular  spasms  become  less  and  less  distinct,  and  that 
finally  the  contraction  is  permanent.  His  diagrams  show  well-marked  spasms  under 
ten  excitations  per  second,  a  more  complete  fusion  of  the  different  acts  with  twenty 
per  second,  and  a  complete  fusion,  or  tetanus,  with  twenty-seven  per  second.  When 
the  contraction  had  become  continuous,  there  was  an  elevation  in  the  line,  showing 
increased  power,  as  the  excitations  became  more  and  more  frequent.  This  is  precisely 
the  kind  of  contraction  that  occurs  in  the  physiological  action  of  muscles.  Although 
the  nervous  force  is  not  by  any  means  identical  with  electricity,  either  the  interrupted 
galvanic  current  or  a  succession  of  statical  discharges  is  capable  of  producing  a  muscular 
action  very  like  that  which  is  involved  in  voluntary  movements.  The  observations 
of  Marey,  showing  that  the  intensity  of  what  he  terms  artificial  tetanic  contraction 
is  in  proportion  to  the  rapidity  with  which  the  electric  discharges  succeed  each  other, 
are  exceedingly  interesting  in  their  practical  applications ;  and  an  important  question  at 
once  arises  regarding  the  nervous  force  that  excites  voluntary  motion.  Is  this  a  series  of 
discharges,  as  it  were,  producing  a  power  of  muscular  contraction  in  exact  proportion  to 
their  rapidity  ?  In  view  of  the  experiments  just  cited,  this  theory  is  very  probable  ;  and 
it  is  certain  that  the  effect  of  a  rapid  succession  of  electric  discharges  almost  exactly  simu- 
lates the  normal  action  of  muscles.  That  vibrations,  more  or  less  regular,  actually  occur 
in  muscular  contraction,  has  been  settled  beyond  a  doubt  by  the  researches  of  Wollaston, 
Ilaughton,  and  more  lately  by  Helmholtz,  the  latter  having  recognized  a  musical  tone  in 
contracting  muscles,  exactly  corresponding  with  the  number  of  impressions  per  second 
made  upon  the  nerve.  He  farther  devised  an  ingenious  method  of  recognizing  the  tone, 
by  filling  the  ears  with  wax  and  contracting  the  temporal  and  masseter  muscles.  Marey 
has  found,  in  repeating  this  experiment,  that  the  tone  may  be  changed  by  modifying  the 
intensity  of  the  muscular  action.  With  the  jaws  feebly  contracted,  a  grave  sound  is 
produced,  and  this  can  be  raised  one-fifth,  by  contracting  the  muscles  as  forcibly  as 
possible. 

The  nerves  are  not  capable  of  conducting  an  artificial  stimulus  for  an  indefinite  period, 
nor  are  the  muscles  able  to  contract  for  more  than  a  limited  time  upon  the  reception  of 
such  an  excitation.  The  electric  current  may  be  made  to  destroy  for  a  time  both  the 
nervous  and  muscular  irritability ;  and  these  properties  become  gradually  extinguished,  the 
parts  becoming  fatigued  before  they  are  completely  exhausted.  Precisely  the  same  phe- 
nomena are  observed  in  the  physiological  action  of  muscles.  When  a  muscle  is  fatigued 
artificially,  a  tetanic  condition  is  excited  more  and  more  easily,  but  the  intensity  of  the 
contraction  proportionally  diminishes.  Muscles  contracting  in  obedience  to  an  effort  of 
the  will  pass  through  the  same  stages  of  action.  It  is  probable  that  constant  contraction 
is  excited  more  and  more  easily  as  the  muscles  become  fatigued,  because  the  nervous 
force  gradually  diminishes  in  intensity.  It  is  certain  that  the  vigor  of  contraction  at  the 
same  time  progressively  diminishes. 

Electric  Phenomena  in  the  Muscles. — It  was  ascertained  a  number  of  years  ago,  by 
Matteucci,  that  all  living  muscles  are  the  seat  of  electric  currents,  which  are  not  very 
powerful,  it  is  true,  but  still  are  sufficiently  marked  to  be  detected  by  ordinary  galvanome- 
ters. It  is  difficult,  in  the  present  state  of  our  knowledge,  to  appreciate  the  physiological 
significance  of  this  fact,  and  we  shall  therefore  merely  allude  to  the  chief  electric  phe- 
nomena that  are  ordinarily  observed,  without  attempting  to  follow  out  the  elaborate  and 


542 


MOVEMENTS. 


nerve 


curious  experiments  since  made  by  Du  Bois-Keyinond  and  others.  One  of  the  most  sim- 
ple methods  of  demonstrating  this  current  is  to  prepare  the  leg  of  a  frog  with  the  crural 
attached,  and  to  apply  one  portion  of  the  nerve  to  the  deep  parts  of  an  incised 

muscle  and  the  other  to  the 
surface.  As  soon  as  the  con- 
nection  is  made,  a  contraction 

of  the  leg  takes  place>  The 

same  fact  may  be  demonstrated 
with  an  ordinary  galvanometer  ; 
but  the  evidence  obtained  by 
the  frog's  leg,  when  the  experi- 
ment is  properly  performed,  is 
sufficiently  conclusive. 

Matteucci  constructed  out  of 
the  fresh  muscles  from  the  thigh 
of  the  frog,  what  is  sometimes 
called  a  frog-battery  ;  which  ex- 
hibits these  currents  in  the  most 
striking  manner,  their  intensity 
being  in  direct  ratio  to  the  num- 
ber of  elements  in  the  pile.  To 
do  this,  he  takes  the  muscles 
of  the  lower  half  of  the  thigh 
from  several  frogs,  removing 
the  bones,  and  arranges  them  in 
a  series,  each  with  its  conical 
extremity  inserted  into  the  cen- 
tral cavity  of  the  one  below. 
In  this  way  the  external  sur- 
face of  each  thigh  except  the 
last  is  in  contact  with  the  in- 
ternal surface  of  the  one  below. 
If  the  two  extremities  of  the 
pile  be  now  connected  with  a  galvanometer,  quite  a  powerful  current  from  the  internal 
to  the  external  surface  of  the  muscle  may  be  demonstrated.  In  a  pile  formed  of  ten  ele- 
ments, the  needle  of  a  galvanometer  was  deviated  to  from  30°  to  40°. 

Electric  currents  are  observed  in  all  living  muscles,  but  they  are  most  marked  in  the 
mammalia  and  warm-blooded  animals.  They  exist,  also,  for  a  certain  time  after  death. 
Artificial  tetanus  of  the  muscles,  however,  instead  of  intensifying  the  current,  causes  the 
galvanometer  to  recede.  If,  for  example,  the  needle  of  the  instrument  show  a  deviation 
of  30°  during  repose,  when  the  muscle  is  excited  to  tetanic  contraction,  it  will  return  so 
as  to  mark  only  10°  or  15°.  This  phenomenon  is  observed  only  during  a  continued  mus- 
cular contraction,  and  it  does  not  attend  a  single  spasm. 

Muscular  Effort.  —  The  mere  voluntary  movement  of  parts  of  the  body,  when  there 
is  no  obstacle  to  be  overcome  or  no  great  amount  of  force  is  required,  is  very  different 
from  a  muscular  effort.  For  example,  in  ordinary  progression  there  is  simply  a  move- 
ment produced  by  the  action  of  the  proper  muscles,  almost  without  our  consciousness, 
and  this  is  unattended  with  any  modification  in  the  circulation  or  respiration  ;  but,  if  we 
attempt  to  lift  a  heavy  weight,  to  jump,  to  strike  a  powerful  blow,  or  to  make  any  vigor- 
ous effort,  the  action  is  very  different.  In  the  latter  instance,  we  prepare  for  the  mus- 
cular action  by  inflating  the  lungs,  closing  the  glottis,  and  contracting  more  or  less  forci- 
bly the  expiratory  muscles,  so  as  to  render  the  thorax  rigid  and  unyielding  ;  and,  by 


FIG.  161.— Muscular  current  in  the  frog.    (Bernard.) 

Fig.  1,  portion  of  the  thigh,  with  the  skin  removed;  «,  surface  of  the 
muscles ;  &,  section ;  the  direction  of  the  current  is  indicated  by  the 
arrow. 

Fig.  2,  the  nerve  of  a  frog's  leg  (the  leg  enclosed  in  a  glass  tube)  is  ap- 
plied to  the  section  and  the  surface  of  the  muscle.  There  is  no  contrac- 
tion, because  it  is  necessary  that  a  portion  of  the  nerve  should  be 
raised  up. 

Fig.  8,  a  portion  of  the  nerve  is  raised  with  a  glass  rod.  The  contraction 
of  the  galvanoscopic  leg  occurs  at  the  making  of  the  circuit,  because 
the  current  follows  the  course  of  the  nerve,  or  is  direct. 

Fig.  4,  the  contraction  here  occurs  at  the  breaking  of  the  circuit,  because 
the  direction  of  the  current  is  opposite  the  course  of  the  nerve,  or  is 
inverse. 


PASSIVE   ORGANS   OF  LOCOMOTION.  543 

a  concentrated  effort  of  the  will,  the  proper  muscles  are  then  brought  into  action. 
This  remarkable  action  of  the  muscles  of  the  thorax  and  abdomen,  due  to  simple 
effort  and  independent  of  the  particular  muscular  act  that  is  to  be  accomplished,  com- 
presses the  contents  of  the  rectum  and  bladder  and  obstructs  very  materially  the  venous 
circulation  in  the  large  vessels.  It  is  well  known  that  hernia  is  frequently  produced  in 
this  way ;  the  veins  of  the  face  and  neck  become  turgid  ;  the  conjunctiva  may  become 
ecchymosed;  and  sometimes  aneurismal  sacs  are  ruptured.  An  effort  of  this  kind  is 
generally  of  short  duration,  and  it  cannot,  indeed,  be  prolonged  beyond  the  time  during 
which  respiration  can  be  conveniently  arrested.  At  its  conclusion  there  is  commonly  a 
prolonged  expiration,  which  is  audible  and  somewhat  violent  at  its  commencement. 

There  are  degrees  of  effort  which  are  not  attended  with  this  powerful  action  of  the 
muscles  of  the  chest  and  abdomen,  and  in  which  the  glottis  is  not  completely  closed ; 
and  an  opening  into  the  trachea  or  larynx,  rendering  immobility  of  the  thorax  impossi- 
ble, does  not  interfere  with  certain  acts  that  require  considerable  muscular  power.  If 
we  examine  a  dog  with  the  glottis  exposed,  when  he  makes  violent  efforts  to  escape,  we 
can  see  that  the  opening  is  firmly  closed.  This  fact  we  have  often  observed  in  vivisec- 
tions ;  but  Longet  has  shown  that  dogs  with  an  opening  into  the  trachea  are  frequently 
able  to  run  and  leap  with  "  astonishing  agility."  He  also  saw  a  horse,  with  a  large 
canula  in  the  trachea,  that  performed  severe  labor  and  drew  heavily -loaded  wagons  in 
the  streets  of  Paris. 

Passive   Organs  of  Locomotion. 

It  would  be  out  of  place  to  describe  fully  and  in  detail  all  of  the  varied  and  complex 
movements  produced  by  muscular  action.  Many  of  these,  such  as  the  movements  of 
deglutition  and  of  respiration,  are  necessarily  considered  in  connection  with  the  func- 
tions of  which  they  form  a  part ;  but  others  are  purely  anatomical  questions.  Associ- 
ated and  antagonistic  movements,  automatic  and  reflex  movements,  etc.,  belong  to  the 
history  of  the  motor  nerves  and  will  be  fully  considered  under  the  head  of  the  nervous 
system. 

The  study  of  locomotion  involves  a  knowledge  of  the  physiological  anatomy  of  cer- 
tain passive  organs,  the  bones,  cartilages,  and  ligaments.  Although  a  complete  history 
of  the  structure  of  these  parts  trenches  somewhat  upon  the  domain  of  anatomy,  we  are 
tempted  to  give  a  brief  description  of  their  histology,  as  it  will  complete  our  account  of 
the  tissues  of  the  body,  with  the  exception  of  the  nervous  system  and  the  organs  of 
generation,  which  will  be  taken  up  hereafter. 

Locomotion  is  effected  by  the  muscles  acting  upon  certain  passive,  movable  parts. 
These  are  the  bones,  cartilages,  ligaments,  aponeuroses,  and  tendons.  We  have  already 
described  the  fibrous  structures,  and  it  only  remains  for  us  to  study  the  bones  and  car- 
tilages. 

Physiological  Anatomy  of  the  Bones. — The  number,  classification,  and  relations  of  the 
bones  are  questions  belonging  to  descriptive  anatomy  ;  and  the  only  points  we  propose  to 
consider  refer  to  their  general,  or  microscopical  structure. 

Every  bone,  be  it  long  or  short,  is  composed  of  what  is  called  the  fundamental  sub- 
stance, marked  by  microscopic  cavities  and  canals  of  peculiar  form.  The  cavities  con- 
tain corpuscular  bodies,  called  bone-corpuscles.  The  canals  of  larger  size  serve  for  the 
passage  of  blood-vessels,  while  the  smaller  canals  (canaliculi)  connect  the  cavities  with 
each  other  and  finally  with  the  vascular  tubes.  Many  of  the  bones  present  a  medullary 
cavity,  filled  with  a  peculiar  structure,  called  marrow.  \In  almost  all  bones  there  are  two 
distinct  portions ;  one,  which  is  exceedingly  compact,  and  the  other,  more  or  less  spongy 
or  cancellated.  The  bones  are  also  invested  with  a  membrane,  containing  vessels  and 
nerves,  called  the  periosteum. 

The  method  usually  employed  in  the  study  of  the  bones  is  by  thin  sections  made  in 


544 


MOVEMENTS. 


various  directions  and  examined  either  in  their  natural  condition  or  with  the  calcareous 
matter  removed  by  maceration  in  weak  acid  solutions.  By  the  first  method,  we  can 
make  out  the  relations  of  the  fundamental  substance,  the  direction  and  relations  of  the 
vascular  canals,  and  the  form,  size,  relations,  and  connections  of  the  bone-cavities  and 
small  canals.  By  the  latter  method,  we  can  isolate  and  study  the  organic  and  corpuscular 

elements. 

Fundamental  Substance.— This  constitutes  the  true  bony  substance,  the  medullary 
contents,  vessels,  nerves,  etc.,  being  simply  accessory.  It  is  composed  of  a  peculiar 
organic  matter,  called  osteine,  combined  with  various  inorganic  salts,  in  which  the  phos- 
phate of  lime  largely  predominates.  In  addition  to  the  phosphate  of  lime,  the  bones 
contain  carbonate  of  lime,  fluoride  of  calcium,  phosphate  of  magnesia  and  of  soda,  and 
chloride  of  sodium.  The  relative  proportions  of  the  organic  and  inorganic  matters  are 
somewhat  variable ;  but  the  average  is  about  one-third  of  the  former  to  two-thirds  of 
salts.  This  proportion  is  necessary  to  the  proper  consistence  and  toughness  of  the  bones. 


FIG.  162. —  Vascular  canals  and  lacunae,  seen  in  a  lon- 
gitudinal section  of  the  humerus ;  magnified  200 
diameters.  (Sappey.) 

a,  a,  a,  vascular  canals ;  &,  6,  &,  lacunae  and  canaliculi  in 
the  fundamental  substance. 


FIG.  1C3. — Longitudinal  section  of  bone,  from  the 
ahaft  of  the  human  femur;  magnified  180  di- 
ameters. (From  a  photograph  taken  at  the  United 
States  Army  Medical  Museum.) 

This  figure  is  introduced  for  the  reason  that  it  is  a  copy 
of  a  photograph  of  the  actual  structure. 


Anatomically,  the  fundamental  substance  of  the  bones  is  arranged  in  the  form  of  regu- 
lar, concentric  lamellae,  about  s-^  of  an  inch  in  thickness.  This  matter  is  of  an  indefinite- 
ly and  faintly  striated  appearance,  but  it  cannot  be  reduced  to  distinct  fibres.  In  the  long 
bones,  the  arrangement  of  the  lamellae  is  quite  regular,  surrounding  the  Haversian  canals, 
and  forming  what  are  sometimes  called  the  Haversian  rods,  following  in  their  direction 
the  length  of  the  bone.  In  the  short,  thick  bones  the  lamellae  are  more  irregular,  fre- 
quently radiating  from  the  central  portion  to  the  periphery.  These  peculiarities  in  the 
disposition  of  the  fundamental  substance  will  be  more  readily  understood  after  a  descrip- 
tion of  the  Haversian  canals. 

The  Haversian  canals  exist  in  the  compact  bony  structure.  They  are  either  absent  or 
very  rare  in  the  spongy  and  reticulated  portions.  Their  form  is  rounded  or  ovoid,  the  larger 


PASSIVE   ORGANS   OF  LOCOMOTION. 


545 


canals  being  sometimes  quite  irregular.  In  the  long  bones  their  direction  is  generally  lon- 
gitudinal, although  they  anastomose  by  lateral  branches.  Each  one  of  these  canals  con- 
tains a  blood-vessel,  and  their  disposition  constitutes  the  vascular  arrangement  of  the  bones. 
They  are  all  connected  with  the  openings  on  the  surface  of  the  bones,  by<  which  the  arte- 
ries penetrate  and  the  veins  emerge.  Their  size,  of  course,  is  variable.  According  to 
Sappey,  the  largest  are  about  -^5-  and  the  smallest,  -g^  of  an  inch  in  diameter.  Their 
average  size  is  from  -^  to  ^^  of  an  inch.  In  a  transverse  section  of  a  long  bone,  the 
Haversian  canals  may  be  seen  cut  across  and  surrounded  by  from  twelve  to  fifteen 
lamella.  In  a  longitudinal  section  the  course  and  anastomoses  may  be  studied. 

Lacunae. — The  fundamental  substance  is  everywhere  marked  by  irregular,  micro- 
scopic excavations,  of  a  peculiar  form,  called  lacunas  or  osteoplasts.  These  were  at  one 
time  supposed  to  be  corpuscles  of  calcareous  matter  and  were  known  as  the  bone-cor- 
puscles ;  but  it  has  since  been  ascertained  that  this  appearance  is  due  to  the  imperfect 
methods  of  preparation  of  the  thin  sections  of  bone.  They  are  connected  with  numer- 
ous little  canals,  giving  them  a  stellate  appearance.  These  are  most  numerous  at  the 
sides.  The  lacunae  measure  from  ^^  to  -^^  of  an  inch  in  their  long  diameter,  by  about 
s-^Vo  of  an  inch  in  width.  They  contain  the  true  bone-corpuscles,  which  we  shall  pres- 
ently describe. 

Canaliculi. — These  are  little  wavy  canals,  connecting  the  lacunae  with  each  other 
and  presenting  a  communication  between  the  first  series  of  lacunae  and  the  Haversian 


FIG.  161—  Vascular  canals  and  lacuna,  seen  in  a  transverse  section  of  the  humer-us;  magnified  200  diameters. 

(Sappey.) 

1, 1, 1,  section  of  the  Haversian  canals ;  2,  section  of  a  longitudinal  canal  divided  at  the  point  of  its  anastomosis  with 
a  transverse  canal.  Around  the  canals,  cut  across  perpendicularly,  are  Been  the  lacunas  (with  their  canaliculi), 
forming  concentric  rings. 


canals.  Each  osteoplast  presents  from  eighteen  to  twenty  canaliculi  radiating  from  its 
borders.  Their  length  is  from  -^  to  ^  of  an  inch,  and  their  diameter,  about  25£00  of 
an  inch.  The  arrangement  of  the  Haversian  canals,  lacuna?,  and  canaliculi  is  shown  in 
Fig.  164. 

Bone-cells  or  Corpuscles. — By  treating  perfectly  fresh  specimens  of  bone  with  weak 
acid  solutions,  Virchow  has  demonstrated  the  presence  of  stellate  cells  or  corpuscles, 
exactly  filling  up  the  lacunae  and  sending  prolongations  into  the  canaliculi.  These 
structures  have  since  been  studied  by  Kouget,  who  has  succeeded  in  demonstrating  them 
in  fresh  bones  from  the  foetus,  without  using  any  reagent.  They  are  stellate,  granular, 
with  a  large  nucleus  and  several  nucleoli,  and  are  of  exactly  the  size  and  form  of  the 
35 


546 


MOVEMENTS. 


lacuna.     They  send  out  prolongations  into  the  canaliculi,  but  it  has  been  impossible  to 

ascertain  positively  whether  or  not  they  form  membranes  lining  the  canaliculi  through- 
out their  entire  length. 

Marrow  of  the  Bones.— I\\Q  peculiar 
structure  called  marrow  is  found  in  the  me- 
dullary cavities  of  the  long  bones,  filling 
them  completely  and  moulded  to  all  the 
irregularities  of  their  surface.  It  is  also 
found  filling  the  cells  of  the  spongy  portion. 
In  other  words,  with  the  exception  of  the 
vascular  canals,  lacunse,  and  canaliculi,  the 
marrow  fills  all  the  spaces  in  the  fundament- 
al substance.  We  know  very  little  of  the 
functions  of  the  marrow,  and  we  shall  there- 
fore pass  it  over  with  a  brief  description. 

It  is  now  settled  that  the  cavities  of  the 
bones  are  not  lined  with  a  membrane  corre- 
sponding to  the  periosteum,  and  that  the 
marrow  is  applied  directly  to  the  bony  sub- 
stance. In  the  foetus  and  in  very  young 
children,  the  marrow  is  red  and  very  vascu- 
lar. In  the  adult  it  is  yellow  in  some  bones 
and  gray  or  gelatiniform  in  others.  It  con- 
tains certain  peculiar  cells  and  nuclei,  with 

amorphous  matter,  adipose  vesicles,  connective  tissue,  blood-vessels,  and  nerves. 

Medullocells. — Robin  has  described  little  bodies,  existing  both  in  the  form  of  cells 

and  free  nuclei,  called  medullocells.     These  are  found  in  greater  or  less  number  in  the 


FIG.  165. — Transverse  section  of  bone,  from  the  shaft 
of  the  human  humerus  ;  magnified  180  diameters. 
(From  a  photograph  taken  at  the  United  States  Army 
Medical  Museum.) 

This  figure  is  introduced  for  the  reason  that  it  is  a  copy 
of  a  photograph  of  the  actual  structure. 


FIG.  ~L66.—£one-corp'iwcles,  with  their  prolongations.    (Rollett.) 

bones  at  all  ages,  but  they  are  more  abundant  in  proportion  as  the  amorphous  matter  and 
fat-cells  are  deficient.  The  nuclei  are  spherical,  with  borders  sometimes  irregular,  gen- 
erally without  nucleoli,  finely  granular,  and  from  ^  to  ^Vo  of  an  inch  in  diameter. 


PASSIVE   ORGANS   OF  LOCOMOTION.  547 

They  are  insoluble  in  acetic  acid.  The  cells  are  less  numerous  than  the  free  nuclei.  They 
are  spherical  or  slightly  polyhedric,  contain  a  few  pale  granulations,  are  rendered  pale 
but  are  not  dissolved  by  acetic  acid,  and  they  measure  about  ^^  of  an  inch  in  diameter. 

Myeloplaxes. — These  are  irregular,  nucleated  patches,  also  described  by  Kobin,  more 
abundant  in  the  spongy  portions  of  the  bones  than  in  the  medullary  canals,  and  are 
applied  to  the  internal  surfaces  of  the  bones.  They  are  exceedingly  irregular  in  size  and 
form  (measuring  from  Y^O-  to  -^  of  an  inch  in  diameter),  are  finely  granular,  and  present 
from  two  to  twenty  or  thirty  nuclei.  The  nuclei  are  clear,  ovoid,  generally  with  a  nucle- 
olus,  and  are  from  ^^  to  ^^  of  an  inch  lcmg>  bv  innro  or  TTiW  of  an  incn  broad.  The 
myeloplaxes  are  rendered  pale  by  acetic  acid,  and  the  nuclei  are  then  brought  out  more 
distinctly. 

In  addition  to  the  anatomical  elements  just  described,  the  marrow  contains  a  few  very 
delicate  bundles  of  connective  tissue,  most  of  which  accompany  the  blood-vessels.  In 
the  fostus,  the  adipose  vesicles  are  few  or  may  be  absent ;  but  in  the  adult  they  are  quite 
numerous,  and  in  some  bones  they  seem  to  constitute  the  whole  mass  of  the  marrow. 
They  do  not  differ  materially  from  the  fat-cells  in  other  situations.  Holding  these  different 
structures  together,  is  a  variable  quantity  of  semitransparent,  amorphous,  or  slightly 
granular  matter. 

The  nutrient  artery  of  the  bones  sends  branches  to  the  marrow,  generally  two  in 
number  for  the  long  bones,  which  are  distributed  between  the  various  anatomical  elements 
and  finally  surround  the  fatty  lobules  and  the  fat- vesicles  with  a  delicate  capillary  plexus. 
The  veins  correspond  to  the  arteries  in  their  distribution.  The  nerves  follow  the  arteries 
and  are  lost  when  these  vessels  no  longer  present  a  muscular  coat.  Nothing  is  known 
of  the  presence  of  lymphatics  in  any  part  of  the  bones  or  in  the  periosteum. 

The  only  point  of  physiological  interest  connected  with  the  marrow  is,  that  it  has 
been  found  to  possess,  in  common  with  the  periosteum  but  in  a  less  degree,  the  property 
of  generating  true  bony  substances.  We  shall  see  farther  on,  that  the  periosteum  is  not 
only  very  important  to  the  nutrition  of  the  bones,  but  that  it  will  generate  bone  when 
transplanted  into  vascular  parts.  M.  Oilier,  who  has  made  a  very  extended  series  of 
experiments  upon  the  physiological  properties  of  the  periosteum,  endeavored  to  produce 
bone  by  transplanting  portions  of  marrow,  but  was  unsuccessful.  M.  Goujon,  however, 
has  lately  been  more  fortunate.  He  has  found  that  frequently,  but  not  always,  marrow 
transplanted  into  the  muscular  tissue  will  generate  bone,  particularly  the  marrow  taken 
from  young  bones,  but  the  bony  tissue  thus  formed  is  soon  absorbed. 

Periosteum. — In  most  of  the  bones  the  periosteum  presents  a  single  layer  of  fibrous 
tissue,  but  in  some  of  the  long  bones  two  or  three  layers  may  be  demonstrated.  This 
membrane  adheres  to  the  bone  but  can  generally  be  separated  without  much  difficulty. 
It  covers  the  bones  completely,  except  at  the  articular  surfaces,  where  its  place  is  supplied 
by  cartilaginous  incrustation.  It  is  composed  mainly  of  fibres  of  the  white  inelastic  variety, 
with  numerous  small  elastic  fibres,  blood-vessels,  nerves,  and  a  few  adipose  vesicles. 

The  arterial  branches  ramifying  in  the  periosteum  are  quite  numerous,  forming  a  close, 
anastomosing  plexus,  which  sends  numerous  small  branches  into  the  bony  substance. 
There  is  nothing  peculiar  in  the  arrangement  of  the  veins.  The  distribution  of  the  veins 
in  the  bony  substance  has  been  very  little  studied. 

The  nerves  of  the  periosteum  are  very  abundant  and  form  in  its  substance  quite  a 
close  plexus. 

The  adipose  tissue  is  very  variable  in  quantity.  In  some  parts  it  forms  a  continuous 
sheet,  and  in  others  the  vesicles  are  scattered  here  and  there  in  the  substance  of  the 
membrane. 

The  importance  of  the  periosteum  to  the  nutrition  of  the  bones  is  very  great.  Instances 
are  on  record  where  bones  have  been  removed,  leaving  the  periosteum,  and  in  which  the 
entire  bone  has  been  regenerated.  The  importance  of  the  periosteum  has  been  still 


548 


MOVEMENTS. 


farther  illustrated  by  the  remarkable  experiments  of  M.  Oilier,  upon  transplantation  of 
this  membrane  in  the  different  tissues  of  living  animals. 

Physiological  Anatomy  of  Cartilage.-lu  this  connection,  the  structure  of  the  articu- 
lar cartilages  presents  the  chief  physiological  interest.  The  articular  surfaces  of  all  the 
bones  are  encrusted  with  a  layer  of  cartilage,  varying  in  thickness  from  -^  to  ^  of  an 
inch.  The  cartilaginous  substance  is  white,  opaline,  and  semitransparent  when  examined 
in  thin  sections.  It  is  not  covered  with  a  membrane,  but  in  the  non-articular  carti- 
lages it  has  an  investment  analogous  to  the  periosteum. 

Examined  in  thin  sections,  cartilage  is  found  to  consist  of  a  homogeneous  fundamental 
substance,  marked  with  numerous  excavations,  called  cartilage-cavities,  or  chondroplasts. 
The  intervening  substance  has  a  peculiar 
organic  base,  called  cartilagine.  By  pro- 
longed boiling  this  is  changed  into  a  new 
substance,  called  chondrine.  The  organic 
matter  is  united  with  a  certain  proportion 
of  inorganic  salts.  This  fundamental  sub- 
stance is  elastic  and  resisting.  The  car- 
tilages are  closely  united  to  the  subjacent 
bony  tissue.  The  free  articular  surface 
has  already  been  described  in  connection 
with  the  synovial  membranes. 

Cartilage-  Cavities. — These  cavities  are 


FIG.  167.— Section  of  cartilage  from  the  rib  of  the  ox, 
shmcing  the  homogeneous  fundamental  substance, 
cartilage-cavities,  and  cartilage-cells;  magnified 
370  diameters.  (From  a  photograph  taken  at  the 
United  States  Army  Medical  Museum.) 


FIG.  168.— Perpendicular  section  of  a  diarthrodial 
cartilage.  (Sappey.) 

1,1,  osseous  tissue;  2,2,  superficial  layer  of  osseous 
tissue  treated  with  hydrochloric  acid ;  3,  3,  cavities 
and  cells  of  the  deep  layer  of  cartilage ;  4,  4,  cavities 
and  cells  of  the  middle  layer;  5,  5,  cavities  and  ceils 
of  the  superficial  layer. 


rounded  or  ovoid,  measuring  from  y^y  to  ¥^  °f  an  mcn  iQ  diameter.  They  are  gener- 
ally smaller  in  the  articular  cartilages  than  in  other  situations,  as  in  the  costal  cartilages. 
They  are  simple  excavations  in  the  .fundamental  substance,  have  no  lining  membrane, 
and  contain  a  small  quantity  of  a  viscid  liquid,  with  one  or  more  cells.  They  are  entirely 
analogous  to  the  lacuna  of  the  bones. 

Cartilage- Cells. — Near  the  surface  of  the  articular  cartilages,  the  cavities  contain  each 
a  single  cell ;  but  in  the  deeper  portions  the  cavities  are  long  and  contain  from  two  to 
twenty  cells  arranged  longitudinally.  The  cells  are  of  about  the  size  of  the  smallest 
cavities.  They  are  ovoid,  with  a  large,  granular  nucleus.  They  often  contain  a  few 
small  globules  of  oil.  In  the  costal  cartilages  the  cavities  are  not  numerous  but  are 


PASSIVE   ORGANS   OF  LOCOMOTION. 


549 


rounded  and  quite  large.  The  cells  contain  generally  a  certain  amount  of  fatty  matter. 
The  appearance  of  the  ordinary  articular  cartilage  is  represented  in  Fig.  168. 

The  ordinary  cartilages  have  neither  blood-vessels,  lymphatics,  nor  nerves,  and  are 
nourished  exclusively  by  imbibition  from  the  surrounding  parts.  Their  function  has 
already  been  sufficiently  considered  in  treating  of  the  synovial  membranes.  In  the  devel- 
opment of  the  body,  the  anatomy  of  the  cartilaginous  tissue  possesses  peculiar  interest, 
from  the  fact  that  the  deposition  of  cartilage  precedes  the  formation  of  bone ;  but  we 
have  here  only  to  do  with  the  permanent  cartilages. 

Fibro-  Cartilage. — This  variety  of  cartilage  presents  certain  important  peculiarities 
in  the  structure  of  its  fundamental  substance.  It  exists  in  the  synchondroses,  the  car- 
tilages of  the  ear,  of  the  Eustachian  tubes,  the  interarticular  disks,  the  intervertebral 
cartilages,  the  cartilages  of  Santorini  and  of  Wrisberg,  and  the  epiglottis.  Its  structure 
has  been  very  closely  and  successfully  studied  by  Sappey,  who  has  arrived  at  results  dif- 
fering considerably  from  those  obtained  by  other  observers. 

According  to  Sappey,  fibro-cartilage  is  composed  of  true  fibrous  tissue,  with  a  great 
predominance  of  elastic  fibres,  fusiform,  nucleated  fibres,  a  certain  number  of  adipose 


I  ( 


FIG.  169.— Section  of  the  cartilage  of  the  ear  of  the  human  subject*   (Rollett.) 
a,  fibro-cartUage ;  &,  connective  tissue.    In  this  preparation,  the  cartilage  had  been  boiled  and  dried. 

vesicles,  cartilage-cells,  and  numerous  blood-vessels  and  nerves.  The  presence  of  cartilage- 
cells  assimilates  this  tissue  to  the  ordinary  cartilage,  although  its  structure  is  very  much 
more  complex.  The  fibrous  elements  above  mentioned  take  the  place  of  the  homogeneous 
fundamental  substance  of  the  true  cartilage.  The  most  important  peculiarity  in  the 
structure  of  this  tissue  is  that  it  is  abundantly  supplied  with  blood-vessels  and  nerves. 

The  reader  is  referred  to  works  upon  anatomy  for  a  history  of  the  action  of  the  muscles. 
In  some  works  upon  physiology,  will  be  found  descriptions  of  the  acts  of  walking,  running, 
leaping,  swimming,  etc. ;  but  we  have  thought  it  better  to  omit  these  subjects,  rather  than 
to  enter  as  minutely  as  would  be  necessary  into  anatomical  details  and  to  give  elaborate 
descriptions  of  movements  which  are  simple  and  familiar. 

Voice  and  Speech. 

There  are  few  subjects  connected  with  human  physiology  of  greater  interest  than  the 
mechanism  of  voice  and  speech.  In  common  with  most  of  the  higher  classes  of  animals, 
man  is  endowed  with  voice ;  but,  in  addition,  he  is  able  to  express  by  speech  the  ideas 
that  are  the  result  of  the  working  of  the  brain.  In  this  regard  there  is  a  difference  be- 
tween man  and  all  other  animals.  It  is  the  remarkable  development  and  the  peculiar 


550 


VOICE   AND  SPEECH. 


properties  of  the  brain  that  enable  him  to  acquire  the  series  of  movements  that  constitute 
articulate  language  ;  and  this  faculty  is  nearly  always  impaired  pari passu  with  deficiency 
in  the  intellectual  endowment.  Language  is  one  of  the  chief  expressions  of  intelligence ; 
and  its  study,  in  itself,  constitutes  almost  a  distinct  science,  inseparably  connected  with 
psychology.  In  connection  with  the  study  of  movements,  therefore,  it  is  not  necessary 
to  discuss  the  origin  and  construction  of  language,  but  simply  to  indicate  the  mechanism, 
first,  of  the  formation  of  the  voice,  and  afterward,  the  manner  in  which  the  voice  is 
modified  in  the  production  of  articulate  sounds. 

The  voice  in  the  human  subject,  presenting,  as  it  does,  a  variety  of  characters  as 
regards  intensity,  pitch,  and  quality,  and  being  susceptible  of  great  modifications  by  habit 
and  cultivation,  affords  a  very  extended  field  for  physiological  study.  Of  late  years,  this 
has  been  the  subject  of  careful  investigation  by  the  most  eminent  physicists  and  physiolo- 
gists of  the  day ;  but  to  follow  it  out  to  its  extreme 
limits  requires  a  knowledge  of  the  physics  of  sound 
and  the  theory  of  music,  a  full  consideration  of  which 
would  be  inconsistent  with  the  scope  and  objects  of 
this  work.  "We  shall  content  ourselves,  therefore,  with 
a  sketch  of  the  physiological  anatomy  of  the  parts  con- 
cerned in  the  formation  of  the  voice,  and  the  mechanism 
by  which  sounds  are  produced  in  the  larynx,  without 
treating  fully  of  their  varied  modifications  in  quality. 
It  will  not  be  necessary  to  treat  of  the  different  the- 
ories of  the  voice  that  have  been  presented  from  time 
to  time,  except  in  so  far  as  they  have  been  confirmed 
by  recent  and  complete  observations,  particularly 
those  in  which  the  vocal  organs  have  been  studied  in 
action  by  means  of  the  laryngoscope. 


Sketch,  of  the  Physiological  Anatomy  of  the  Vocal 
Organs. — The  principal  organ  concerned  in  the  pro- 
duction of  the  voice  is  the  larynx.  The  accessory  or- 
gans are  the  lungs,  trachea,  and  expiratory  muscles, 
and  the  mouth  and  resonant  cavities  about  the  face. 
The  lungs  furnish  the  air  by  which  the  vocal  chords 
are  thrown  into  vibration,  and  the  mechanism  of  this 
action  is  merely  a  modification  of  the  process  of  expira- 
tion. By  the  action  of  the  expiratory  muscles  the 
intensity  of  vocal  sounds  is  regulated.  The  trachea 
not  only  conducts  the  air  to  the  larynx,  but,  by  cer- 
tain variations  in  its  length  and  caliber,  it  may  assist 
in  modifying  the  pitch  of  the  voice.  Most  of  the  varia- 


19. 


FIG.  no.— Longitudinal  section  of  the  hu- 
man larynx,  showing  the  vocal  chords. 
(Sappey.) 

1,  ventricle  of  the  larynx ;  2,  superior  vocal 
chord ;  8,  inferior  vocal  chord ;  4,  aryte- 

noid  cartilage;  5,  section  of  the  arytenoid   tions  in  the  tone  and  quality,  however,  are  effected  by 

muscle;  6,  6,  inferior  portion  of  the  cav-    ,, 

ity  of  the  larynx;  7,  section  of  the  pos-   the  action  of  the  larynx  itself  and  of  the  parts  situated 

terior  portion  of  the  cricoid  cartilage  ;  8,    f,V,nva  \+ 
section  of  the  anterior  portion  of  the  cri-    ' 

Start? ™Sge9;  iopesec°tioS  the0^!         Tt  is  iraPossible  to  Sive  *  complete  account  of  the 
roid  cartilage ;  ii,  ii,  superior  portion  of    structure  of  the  larynx,  without  going  more  fully  than 

the  cavity  of  the  larynx;  12,13.  arytenoid    •      -,      •      tl     .    ,  -,  .      -i    -i    ,    «i          n 

gland;  14,16,  epiglottis:  is,  17,  adipose   1S  desirable  into  purely  anatomical  details.     Some  an- 
I99,8i9e;20,8tra^hei°n  °f  the  "^  bone;   atomical  points  have  already  been  referred  to  under 

the  head  of  respiration,  in  connection  with  the  respi- 
ratory movements  of  the  glottis ;  and  we  propose  here  only  to  refer  to  the  situation  of 
the  vocal  chords,  and  to  indicate  the  modifications  that  they  can  be  made  to  undergo  in 
their  relations  anfftension  by  the  action  of  certain  muscles. 

The  vocal  chords  are  stretched  across  the  superior  opening  of  the  larynx  from  before 


ANATOMY  OF  THE  VOCAL  ORGANS.  551 

backward.  They  consist  of  two  pairs.  The  superior,  called  the  false  vocal  chords,  are 
not  concerned  in  the  production  of  the  voice.  They  are  less  prominent  than  the  inferior 
chords,  although  they  have  nearly  the  same  direction.  They  are  covered  by  an  excessively 
thin  mucous  membrane,  which  is  closely  adherent  to  the  subjacent  tissue.  The  chords 
themselves  are  composed  of  fibres  of  the  white  inelastic  variety,  mixed  with  a  few 
elastic  fibres. 

The  true  vocal  chords  are  situated  just  below  the  superior  chords.  Their  anterior 
attachments  are  near  together,  at  the  middle  of  the  thyroid  cartilage,  and  are  immovable. 
Posteriorly  they  are  attached  to  the  movable  arytenoid  cartilages ;  and,  by  the  action  of 
certain  muscles,  their  tension  may  be  modified,  and  the  chink  of  the  glottis  may  be  opened 
or  closed.  These  ligaments  are  much  larger  than  the  false  vocal  chords,  and  they  con- 
tain a  very  great  number  of  elastic  fibres.  Like  the  superior  ligaments,  they  are  covered 
with  an  excessively  thin  and  closely  adherent  mucous  membrane.  The  mucous  mem- 
brane over  the  borders  of  the  chords  is  covered  with  pavement-epithelium  without 
cilia.  There  are  no  mucous  glands  in  the  membrane  covering  either  the  superior  or 
the  inferior  chords. 

It  has  been  conclusively  shown  that  the  inferior  vocal  chords  alone  are  concerned 
in  the  production  of  the  voice.  Longet,  who  has  made  numerous  experiments  upon 
phonation,  has  demonstrated,  by  operations  upon  dogs,  that  the  epiglottis,  the  superior 
vocal  chords,  and  the  ventricles  of  the  larynx,  may  be  injured,  without  producing  any 
serious  alteration  in  the  voice,  but  that  phonation  becomes  impossible  after  serious 
lesion  of  the  inferior  chords.  This  being  the  fact,  as  far  as  the  mere  production  of  the 
voice  in  the  larynx  is  concerned,  we  have  only  to  study  the  mechanism  of  the  action  of 
the  inferior  ligaments  and  the  muscles  by  which  their  tension  and  relations  are  modified. 

Muscles  of  the  Larynx. — Anatomists  usually  divide  the  muscles  of  the  larynx  into 
extrinsic  and  intrinsic.  The  extrinsic  muscles  are  attached  to  the  outer  surface  of  the 
larynx  and  to  adjacent  organs,  such  as  the  hyoid  bone  and  the  sternum.  They  are  con- 
cerned chiefly  in  the  movements  of  elevation  and  depression  of  the  larynx.  The  intrinsic 
muscles  are  attached  to  the  different  parts  of  the  larynx  itself,  and,  by  their  action  upon 
the  articulating  cartilages,  are  capable  of  modifying  the  condition  of  the  vocal  chords. 
The  number  of  the  intrinsic  muscles  is  nine,  consisting  of  four  pairs  and  a  single  muscle. 
In  studying  the  situation  and  attachments  of  these  muscles,  it  will  be  useful  at  the  same 
time  to  note  their  mode  of  action. 

Bearing  in  mind  the  relations  and  attachments  of  the  vocal  chords,  we  can  understand 
precisely  how  they  can  be  rendered  tense  or  loose  by  muscular  action.  Their  fixed  point 
is  in  front,  where  their  extremities,  attached  to  the  thyroid  cartilage,  are  nearly  or  quite 
in  contact  with  each  other.  The  arytenoid  cartilages,  to  which  they  are  attached  poste- 
riorly, present  a  movable  articulation  with  the  cricoid  cartilage  ;  and  the  cricoid,  which  is 
narrow  in  front,  and  is  wide  behind,  where  the  arytenoid  cartilages  are  attached,  presents  a 
movable  articulation  with  the  thyroid  cartilage.  It  is  evident,  therefore,  that  muscles  act- 
ing upon  the  cricoid  cartilage  can  cause  it  to  swing  upon  its  two  points  of  articulation  with 
the  inferior  cornuaof  the  thyroid,  raising  the  anterior  portion  and  approximating  it  to  the 
lower  edge  of  the  thyroid ;  and,  as  a  consequence,  the  posterior  portion,  which  carries 
the  arytenoid  cartilages  and  the  posterior  attachments  of  the  vocal  chords,  is  depressed. 
This  action  would,  of  course,  increase  the  distance  between  the  arytenoid  cartilages  and 
the  anterior  portion  of  the  thyroid,  elongate  the  vocal  chords,  and  subject  them  to  a  cer- 
tain degree  of  tension.  Experiments  have  shown  that  such  an  effect  is  produced  by  the 
contraction  of  the  crico-thyroid  muscles. 

The  articulations  of  the  different  parts  of  the  larynx  are  such  that  the  arytenoid  car- 
tilages may  be  approximated  to  each  other  posteriorly,  though  perhaps  only  to  a  slight 
extent,  thus  diminishing  the  interval  between  the  posterior  attachments  of  the  vocal 
chords.  This  action  can  be  effected  by  contraction  of  the  single  muscle  of  the  larynx 
(the  arytenoid)  and  also  by  the  lateral  crico-arytenoid  muscles.  The  thyro-arytenoid  mus- 


552 


VOICE  AND  SPEECH. 


cles  the  most  complicated  of  all  the  intrinsic  muscles  in  their  attachments  and  the  direc- 
tion of  their  fibres,  give  rigidity  and  increased  capacity  of  vibration  to  the  vocal  chords. 

The  posterior  crico-arytenoid  muscles,  arising  from  each  lateral  half  of  the  posterior 
surface  of  the  cricoid  cartilage  and  passing  upward  and  outward  to  be  inserted  into  the 
outer  angle  of  the  inferior  portion  of  the  arytenoid  cartilages,  rotate  these  cartilages 
outward,  separate  them,  and  act  as  dilators  of  the  chink  of  the  glottis.  These  muscles 
are  chiefly  concerned  in  the  respiratory  movements  during  inspiration. 

The  muscles  mainly  concerned  in  the  modifications  of  the  voice,  by  their  action  upon 


FIG.  111.— Posterior  view  of  the  muscles  of  the  larynx.       FIG.  172.— Lateral  view  of  the  muscles  of  the  larynx. 

(Sappey.)  (Sappey.) 

1,  posterior  crico-arytenoid  muscle ;  2.  8,  4,  different  fas-        1,  body  of  the  hyoid  bone ;  2,  vertical  section  of  the  thy- 
ciculi  of  the  arytenoid  muscle;   5,  aryteno-epiglot-  roid   cartilage;  3,  horizontal  section  of  the  thyroid 

tidean  muscle.  cartilage  turned  downward  to  show  the  deep  attach- 

ment of  the  crico-thyroid  muscle ;  4,  facet  of  articu- 
lation of  the  small  cornu  of  the  thyroid  cartilage  with 
the  cricoid  cartilage ;  5,  facet  on  the  cricoid  cartilage ; 

6,  superior  attachment  of  the  crico-thyroid  muscle ; 

7,  posterior  crico-arytenoid  muscle;  8, 10,  arytenoid 
muscle ;  9,  thyro-arytenoid  muscle ;  11,  aryteno-epi- 
glottidean  muscle;  12,  middle  thyro-hyoid  ligament; 
13,  lateral  thyro-hyoid  ligament. 

the  vocal  chords,  are  the  crico-thyroids,  the  arytenoid,  the  lateral  crico-arytenoids, 
and  the  thyro-arytenoids.  The  following  is  a  sketch  of  their  attachments  and  mode  of 
action : 

Crico-thyroid  Muscles. — These  muscles  are  situated  on  the  outside  of  the  larynx  at 
the  anterior  and  lateral  portions  of  the  cricoid  cartilage.  Each  muscle  is  of  a  triangular 
form,  the  base  of  the  triangle  looking  posteriorly.  It  arises  from  the  anterior  and  lateral 
portions  of  the  cricoid  cartilage,  and  its  fibres  diverge  to  be  inserted  into  the  inferior 
border  of  the  thyroid  cartilage,  extending  from  the  middle  of  this  border  posteriorly,  as 
far  back  as  the  inferior  cornua.  Longet,  after  dividing  the  nervous  filaments  distributed 
to  these  muscles,  noted  hoarseness  of  the  voice  due  to  relaxation  of  the  vocal  chords; 
and,  by  imitating  their  action  mechanically,  he  approximated  the  cricoid  and  thyroid  car- 
tilages in  front,  carried  back  the  arytenoid  cartilages,  and  rendered  the  chords  tense. 

Arytenoid  Muscle. — This  single  muscle  fills  up  the  space  between  the  two  arytenoid 
cartilages  and  is  attached  to  their  posterior  surface  and  borders.  Its  action  evidently  is  to 
approximate  the  posterior  extremities  of  the  chords  and  to  constrict  the  glottis,  as  far  as 


MECHANISM  OF  THE  PRODUCTION  OF  THE  VOICE.  553 

the  articulations  of  the  arytenoid  cartilages  with  the  cricoid  will  permit.  In  any  event 
this  muscle  is  important  in  phonation,  as  it  serves  to  fix  the  posterior  attachments  of  the 
vocal  chords  and  to  increase  the  efficiency  of  certain  of  the  other  intrinsic  muscles. 

Lateral  Crico-arytenoid  Muscles. — These  muscles  are  situated  in  the"  interior  of  the 
larynx.  They  arise  from  the  sides  and  superior  borders  of  the  cricoid  cartilage,  pass 
upward  and  backward,  and  are  attached  to  the  base  of  the  arytenoid  cartilages.  By 
dividing  all  of  the  filaments  of  the  recurrent  laryngeal  nerves,  except  those  distributed  to 
these  muscles,  and  then  galvanizing  the  nerves,  Longet  has  shown  that  they  act  to  ap- 
proximate the  vocal  chords,  and  to  constrict  the  glottis,  particularly  in  its  interligamentous 
portion.  These  muscles,  with  the  arytenoid,  act  as  constrictors  of  the  larynx. 

Thyro-arytenoid  Muscles. — It  is  sufficiently  easy  to  indicate  the  relations  and  attach- 
ments of  these  muscles,  but  their  mode  of  action  is  more  complex  and  difficult  of  compre- 
hension. When  we  come  to  study  the  conditions  of  the  vocal  chords  involved  in  certain 
modifications  of  the  voice,  we  shall  refer  more  in  detail  to  the  action  of  different  fasciculi 
of  these  muscles.  In  this  connection,  we  shall  only  describe  very  briefly  their  situation 
and  attachments  and  the  general  results  of  their  contraction. 

The  thyro-arytenoid  muscles  are  situated  within  the  larynx.  They  are  broad  and  flat, 
and  they  arise  in  front  from  the  upper  part  of  the  crico-thyroid  membrane  and  the  lower 
half  of  the  thyroid  cartilage.  From  this  line  of  origin,  each  muscle  passes  backward  in  two 
fasciculi,  both  of  which  are  attached  to  the  anterior  surface  and  the  outer  borders  of  the 
arytenoid  cartilages.  The  application  of  galvanism  to  the  nervous  filaments  distributed  to 
these  muscles  has  the  effect  of  rendering  the  vocal  chords  rigid,  increasing  the  inten- 
sity of  their  vibrations.  The  great  variations  that  may  be  produced  in  the  pitch  and 
quality  of  the  voice  by  the  action  of  muscles  operating  directly  or  indirectly  upon  the  vocal 
chords  render  the  problem  of  determining  the  precise  mode  of  action  of  the  intrinsic 
muscles  of  the  larynx  exceedingly  complicated  and  difficult.  It  is  certain,  however,  that, 
in  these  muscular  acts,  the  (thyro-arytenoids  play  an  important  part.  Their  contraction 
regulates  the  thickness  and  rigidity  of  the  vocal  chords,  while  at  the  same  time  it  modi- 
fies their  tension.  The  swelling  of  the  chords,  which  may  be  rendered  regular  and  pro- 
gressive under  the  influence  of  the  will,  is  one  of  the  most  important  agents  in  the  forma- 
tion of  the  timbre  of  the  voice. 

Mechanism  of  the  Production  of  the  Voice. 

It  will  save  much  unprofitable  discussion  to  dismiss  quite  briefly  most  of  the  theories 
that  have  been  advanced  to  explain  the  production  of  the  voice,  and  to  avoid  compari- 
sons of  the  larynx  with  different  kinds  of  musical  instruments.  Before  the  larynx  had 
been  studied  in  action  by  means  of  the  laryngoscope,  physiologists,  having  the  anatomical 
structure  of  the  parts  for  their  only  guide,  presented  various  speculations  with  regard  to 
the  mechanism  of  phonation,  which  were  frequently  entirely  opposed  to  each  other  in 
principle.  The  vocal  apparatus  was  compared  to  wind  or  brass  instruments,  to  reed- 
instruments,  to  string-instruments,  to  the  flute,  etc.,  and  some  even  refused  to  the  vocal 
chords  any  share  in  the  sonorous  vibrations.  An  apparatus  was  devised  to  imitate  the 
vocal  organs,  experiments  were  made  with  the  larynx  removed  from  the  body,  and  every 
thing  seemed  to  be  done,  indeed,  except  to  observe  the  organs  in  actual  function.  A  short 
time,  however,  after  the  laryngoscope  came  into  use,  the  larynx  was  examined  during  the 
production  of  vocal  sounds.  The  true  value  of  previous  theories  was  then  positively 
demonstrated ;  and,  while  it  has  not  been  possible  to  settle  all  disputed  points  with  regard 
to  the  precise  mode  of  action  of  certain  muscles,  the  appearances  of  the  larynx  itself  dur- 
ing phonation  and  the  results  of  the  action  of  certain  of  the  intrinsic  muscles  have  been 
quite  accurately  described. 

Appearance  of  the  Glottis  during  Ordinary  Respiration. — If  the  glottis  be  examined 
with  the  laryngoscope  during  ordinary  respiration,  the  wide  opening  of  the  chink  during 


554  VOICE  AND  SPEECH. 

inspiration,  due  to  the  action  of  the  crico-arytenoid  muscles,  can  be  observed  without 
difficulty.  This  action  is  effected  by  a  separation  of  the  posterior  points  of  attachment 
of  the  vocal  chords  to  the  arytenoid  cartilages.  During  ordinary  expiration,  none  of  the 
intrinsic  muscles  seem  to  act,  and  the  larynx  is  entirely  passive,  while  the  air  is  gently 
forced  out  by  the  elasticity  of  the  lungs  and  of  the  thoracic  walls.  But,  as  soon  as  an 
effort  is  made  to  produce  a  vocal  sound,  the  appearance  of  the  glottis  undergoes  a  re- 
markable change,  and  it  becomes  modified  in  the  most  varied  and  interesting  manner  with 
the  different  changes  in  pitch  and  intensity  that  the  voice  can  be  made  to  assume.  Al- 
though it  is  sufficiently  evident  that  a  sound  may  be  produced,  and  even  that  words  may 
be  articulated,  with  the  act  of  inspiration,  true  and  normal  phonation  is  effected  during 
expiration  only.  It  is  evident,  also,  that  the  inferior  vocal  chords  alone  are  concerned 
in  this  act.  The  changes  in  the  position  and  tension  of  the  chords  we  shall  study,  first 
with  reference  to  the  general  act  of  phonation,  and  afterward,  as  the  chords  act  in  the 
varied  modifications  of  the  voice  as  regards  intensity,  pitch,  and  quality. 

Movements  of  the  Glottis  during  Phonation. — It  is  somewhat  difficult  to  observe  with 
the  laryngoscope  all  of  the  vocal  phenomena,  on  account  of  the  epiglottis,  which  hides  a 
considerable  portion  of  the  vocal  chords  anteriorly,  especially  during  the  production  of 
certain  tones;  but  the  patience  and  skill  of  Garcia  enabled  him  to  overcome  most  of 
these  difficulties,  and  to  settle,  by  antolaryngoscopy,  the  most  important  questions  with 
regard  to  the  movements  of  the  larynx  in  singing.  It  is  fortunate  that  these  observa- 
tions, which  are  models  of  scientific  accuracy  and  the  result  of  most  persevering  study, 
were  made  by  one  profoundly  versed,  theoretically  and  practically,  in  the  knowledge  of 
music,  and  possessed  of  great  control  over  the  vocal  organs.1 

Garcia,  after  having  observed  the  respiratory  movements  of  the  larynx,  as  we  have 
briefly  described  them,  noted  that,  as  soon  as  any  vocal  effort  was  made,  the  arytenoid 
cartilages  were  approximated,  so  that  the  glottis  appeared  as  a  narrow  slit  formed  by 
two  chords  of  equal  length,  firmly  attached  posteriorly  as  well  as  anteriorly.  The  glottis 
thus  undergoes  a  marked  change.  A  nearly  passive  organ,  opening  widely  for  the  pas- 
sage of  air  into  the  lungs  (because  the  inspiratory  act  has  a  tendency  to  draw  its  edges 
/  together)  and  entirely  passive  in  expiration,  has  now  be- 

.  y^J!^pi|J  come  a  sort  of  musical  instrument,  presenting  a  slit  with 

borders  capable  of  accurate  vibration. 

The  approximation  of  the  posterior  extremities  of  the 
vocal  chords  and  their  tension  by  the  action  of  certain  of 
the  intrinsic  muscles  are  accomplished  jnst  before  the  vocal 
effort  is  actually  made.     The  glottis  being  thus  prepared 
for  the  emission  of  a  particular  sound,  the  expiratory  mus- 
cles force  air  through  the  larynx  with  the  required  power. 
It  seems  wonderful  how  a  carefully-trained  voice  can  be 
FIG.  m-tftowT^  'with  the  la-  modulated  and  varied  in  all  its  qualities,  including  the  in- 
ryngoscope  during  the  emission  tensity  of  vibration,  which  is  so  completely  under  control : 

of  high-pitched  sounds.  (LeBon.)    v    .        ,  . ,        ,,         , 

1,2,  base  of  the  tongue;  3, 4,  epiglottis;   "^  wlien  we  consider  the  changes  in  its  quality,  we  must 
«in^flpha»ynx ;  7<'a7teno*d  carl  remember,  in  explanation,  the  varying  conditions  of  ten- 

tilages;    8,  opening  between  the      .  .       .,  J 

true  vocal  chords;  9,  aryteno-epi-  sion  and  length  oi  the  vocal  chords,  the  differences  in  the 

glottidean  folds:   10   cartilaee  of      •         e  j.^      t  ^  •>  it 

Santorini;  ii,  cuneiform  cartilage-  size  of  *°e  larynx,  trachea,  and  vocal  passages  generally, 

StaJvS?€SS.<i(0rta;  18'  ID:   and  the  different  relations  that  the  accessory  vocal  organs 

can  be  made  to  assume.     The  power  of  the  voice  is  simply 

due  to  the  force  of  the  expiratory  act,  which  is  regulated  chiefly  by  the  antagonistic  rela- 

|  Manuel  Garcia,  the  author  of  these  observations,  is  the  son  of  Garcia,  the  great  composer  and  singer,  and  the 

of  Mme.  Malibran.    He  now  enjoys  a  great  reputation  in  London,  as  a  singing-master;  and  his  experiments 

i  a  view,  if  possible,  of  reducing  the  art  of  singing,  which  had  always  been  taught  according  to  purely 

al  methods,  to  scientific  accuracy.    It  is  evident  that  this  could  be  accomplished  only  through  an  exact 

knowledge  of  the  mechanism  of  the  production  of  vocal  sounds. 


MECHANISM  OF  THE   PRODUCTION   OF  THE   VOICE.  555 

tions  of  the  diaphragm  and  the  abdominal  muscles.  From  the  fact  that  the  diaphragm, 
as  an  active  inspiratory  muscle,  is  exactly  opposed  to  the  muscles  which  have  a  tendency 
to  push  the  abdominal  organs,  with  the  diaphragm  over  them,  into  the  thoracic  cavity, 
and  thus  to  diminish  the  pulmonary  capacity,  the  expiratory  and  inspiratory  acts  may 
be  balanced  so  nicely  that  the  most  delicate  vocal  vibrations  can  be  produced.  The 
glottis,  thus  closed  as  a  preparation  to  a  vocal  act,  presents  a  certain  amount  of  resist- 
ance to  the  egress  of  air.  This  is  overcome  by  the  action  of  the  expiratory  muscles, 
and,  with  the  passage  of  air  through  the  chink,  the  edges  of  the  opening,  which  are  formed 
by  the  true  vocal  chords,  are  thrown  into  vibration.  Many  of  the  different  qualities 
that  are  recognized  in  the  human  voice  are  due  to  differences  in  the  length,  breadth,  and 
thickness  of  the  vibrating  ribbons ;  but,  aside  from  what  is  technically  known  as  quality, 
the  pitch  is  dependent  chiefly  upon  the  length  of  the  opening  through  which  the  air  is 
made  to  pass  and  the  degree  of  tension  of  the  chords.  The  mechanism  of  these  changes 
in  the  pitch  of  vocal  sounds  is  well  illustrated  by  Garcia  in  the  following  passage,  which 
relates  to  what  is  known  as  the  chest-voice  : 

"  If  we  emit  veiled  and  feeble  sounds,  the  larynx  opens  at  the  notes  I 
and  we  see  the  glottis  agitated  by  large  and  loose  vibrations  through-  f^~^    ** 
out  its  entire  extent.     Its  lips  comprehended  in  their  length  the  do   re> 

anterior  apophyses  of  the  arytenoid  cartilages  and  the  vocal  chords ;  but,  I  repeat  it, 
there  remains  no  triangular  space. 

"  As  the  sounds  ascend,  the  apophyses,  which  are  slightly  rounded  on  their  internal 
side,  by  a  gradual  apposition  commencing  at  the  back,  encroach  on  the  length  of  the  glottis  ; 
and  as  soon  as  we  reach  the  sounds  pr^~  j,  they  finish  by  touching  each  other 

throughout  their  whole  extent  ;  Hff)-^1— |— ^f^H  but  their  summits  are  only  solidly 
fixed  one  against  the  other  at  t/  -&-  -*-  the  notes  r  0  ~  ~i.  In  some 

organs  these  summits  are  a  little  va-  «i,    do.         dilating  |-(n) 1—-  I— ^j  when  they 

form  the  posterior  end  of  the  glottis,  and  two  or  three  half-tones  «T  i*1-  "^  which  are 
formed  show  a  certain  want  of  purity  and  strength,  which  is  do,  re.  very  well 

known  to   singers.     From  r--fi-  i  the  vibrations,  having  become  rounder  and 

purer,  are  accomplished  by  F^y—'-^z] — [  the  vocal  ligaments  alone,  up  to  the  end  of 
the  register.  ^y~~4gjgr~& 

"  The    glottis    at    this  do,    re.       moment  presents  the  aspect  of  a  line  swelled 

toward  its  middle,  the  length  of  which  diminishes  still  more  as  the  voice  ascends.  We 
shall  also  see  that  the  cavity  of  the  larynx  has  become  very  small,  and  that  the  superior 
ligaments  have  contracted  the  extent  of  the  ellipse  to  less  than  one-half." 

These  observations  have  been  in  the  main  confirmed  by  Battaille,  Emma  Seiler,  and 
all  who  have  applied  the  laryngoscope  to  the  study  of  the  voice  in  singing.  A  few  years 
ago  we  had  an  opportunity  of  observing  the  changes  in  the  form  of  the  glottis  during 
the  production  of  vocal  sounds  of  different  degrees  of  pitch,  through  the  kindness  of  Dr. 
Ephraim  Cutter,  of  Boston.  In  these  experiments,  the  various  points  to  which  we  have 
alluded  were  illustrated  by  autolaryngoscopy  in  the  most  marked  manner ;  and  nothing 
could  be  more  striking  than  the  changes  in  the  form  of  the  glottis  in  the  transition  from 
low  to  high  notes.  We  have  also  frequently  observed  the  general  appearance  of  the 
glottis  in  phonation  in  experiments  upon  animals  in  which  the  glottis  has  been  exposed 
to  view. 

Variations  in  the  Quality  of  the  Voice,  depending  upon  Differences  in  the  Size  and 
Form  of  the  Larynx  and  the  Vocal  Chords. — We  are  all  sufficiently  familiar  with  the  char- 
acters of  the  male  as  distinguished  from  the  female  voice,  and  with  what  are  known  as  the 
different  vocal  registers.  In  childhood,  the  general  characters  of  the  voice  are  essentially 
the  same  in  both  sexes.  The  larynx  is  smaller  than  in  the  adult,  and  the  vocal  muscles 
are  evidently  more  feeble ;  but  the  quality  of  the  vocal  sounds  at  this  period  of  life  is 
peculiarly  pure  and  penetrating.  While  there  are  certain  characters  that  distinguish  the 
voices  of  boys  before  the  age  of  puberty,  they  present,  as  in  the  female,  the  different  qualities 


556  VOICE  AND  SPEECH. 

of  the  soprano  and  contralto.  At  this  age  the  voices  of  boys  are  capable  of  considerable 
cultivation,  and  their  peculiar  quality  is  sometimes  highly  prized  in  church-music.  After 
the  age  of  puberty,  the  female  voice  does  not  commonly  undergo  any  very  marked 
change,  except  in  the  development  of  additional  strength  and  increased  compass,  the 
quality  remaining  the  same ;  but  in  the  male  there  is  a  rapid  change  at  this  time  in  the 
development  of  the  larynx,  and  the  voice  assumes  an  entirely  different  quality  of  tone. 
This  change  does  not  usually  take  place  if  castration  be  performed  in  early  life ;  and  this 
operation  was  frequently  resorted  to  in  the  seventeenth  century,  for  the  purpose  of  pre- 
serving the  qualities  of  the  soprano  and  contralto,  particularly  for  church-music.  It 
is  only  of  late  years,  indeed,  that  this  practice  has  fallen  into  disuse  in  Italy. 

The  ordinary  range  of  all  varieties  of  the  human  voice  is  given  by  Mtiller  as  equal  to 
nearly  four  octaves ;  but  it  is  rare  that  any  single  voice  has  a  compass  of  more  than  two 
and  a  half  octaves.  There  are  examples,  however,  in  which  singers  have  acquired  a 
compass  of  three  octaves  and  even  more.  The  celebrated  singer,  Mme.  Parepa-Rosa, 
had  a  compass  of  voice  that  touches  three  full  octaves,  from  so!2  to  sols.  In  music,  the 
notes  are  written  the  same  for  the  male  as  for  the  female  voice,  but  the  actual  value  of 
the  female  notes,  as  reckoned  by  the  number  of  vibrations  in  a  second,  is  always  an 
octave  higher  than  the  male. 

In  both  sexes  there  are  differences,  both  in  the  range  and  the  quality  of  the  voice, 
which  it  is  impossible  for  a  cultivated  musical  ear  to  mistake.  In  the  male,  we  have  the 
bass  and  the  tenor,  with  an  intermediate  voice,  called  the  barytone.  In  the  female,  we 
have  the  contralto  and  the  soprano,  with  the  intermediate,  or  mezzo-soprano.  In  the 
bass  and  barytone,  the  lower  and  middle  notes  are  the  most  natural  and  perfect ;  and, 
while  the  higher  notes  may  be  acquired  by  cultivation,  they  are  not  easy  and  do  not  pos- 
sess the  same  quality  as  the  corresponding  notes  of  the  tenor.  The  same  remarks  apply 
to  the  contralto  and  soprano.  The  mezzo-soprano  is  regarded  by  many  as  an  artificial 
division. 

The  following  scale,  proposed  by  Miiller,  gives  the  ordinary  ranges  of  the  different 
kinds  of  voice ;  but  it  must  be  remembered  that  there  are  individual  instances  in  which 
these  limits  are  vejy  much  exceeded : 


r  i 

mi  fa  sol  la  si  do  re  mi  fa  sol  la  si  do  re  mi  fa  sol  la  si  do  re  mi  fa  sol   la  si  do 

1111122      22      2223383  333      44      44      4445 

I 


There  is  really  no  great  difference  in  the  mechanism  of  the  different  kinds  of  voice, 
and  the  differences  in  pitch  are  due  chiefly  to  the  greater  length  of  the  vocal  chords  in 
the  low-pitched  voices  and  to  their  shortness  in  the  higher  voices.  The  differences  in 
quality  are  due  to  peculiarities  in  the  conformation  of  the  larynx,  to  differences  in  its 
size,  and  to  variations  in  the  size  and  form  of  the  auxiliary  resonant  cavities.  Great 
changes  in  the  quality  of  the  voice  may  be  effected  by  practice.  A  cultivated  note,  for 
example,  has  an  entirely  different  sound  from  a  harsh,  irregular  vibration  ;  and,  by  prac- 
tice, a  tenor  may  imitate  the  quality  of  the  bass,  and  vice  versa,  although  the  effort  is 
unnatural.  It  is  not  at  all  unusual  to  hear  male  singers  imitate  very  closely  the  notes  of 
the  female,  and  the  contralto  will  sometimes  imitate  the  voice  of  the  tenor  in  a  sur- 
prisingly natural  manner.  These  facts  have  a  somewhat  important  bearing  upon  certain 
disputed  points  with  regard  to  the  mechanism  of  the  different  vocal  registers,  which  will 
be  considered  farther  on. 

Action  of  the  Intrinsic  Muscles  of  the  Larynx  in  Phonation.—It  is  much  more  diffi- 


MECHANISM  OF  THE   PRODUCTION  OF  THE  VOICE.  557 

cult  to  find  an  entirely  satisfactory  explanation  of  the  different  tones  produced  by 'the 
human  larynx  in  the  action  of  the  intrinsic  muscles  than  to  describe  the  changes  in  the 
tension  and  relations  of  the  vocal  chords.  These  muscles  are  concealed  from  view,  and 
the  only  idea  that  we  can  have  of  their  action  is  by  reasoning  from  a  knowledge  of  their 
points  of  attachment,  and  by  operations  upon  the  dead  larynx,  either  imitating  the  con- 
traction of  special  muscles  or  galvanizing  the  nerves  in  animals  recently  killed.  In  this 
way,  as  we  have  seen,  some  of  the  muscular  acts  have  been  studied  very  satisfactorily ; 
but  the  precise  effect  of  the  contraction  of  certain  of  the  muscles,  particularly  the  thyro- 
arytenoids,  is  still  a  matter  of  discussion. 

In  the  production  of  low  chest-tones,  in  which  the  vocal  chords  are  elongated  and  are  at 
the  mininum  of  tension  that  will  allow  of  regular  vibrations,  the  crico-thyroid  muscles  are 
undoubtedly  brought  into  action,  and  these  are  assisted  by  the  arytenoid  and  the  lateral 
crico-arytenoids,  which  combine  to  fix  the  posterior  attachments  of  the  vibrating  liga- 
ments. It  will  be  remembered  that  the  crico-thyroids,  by  approximating  the  cricoid  and 
thyroid  cartilages  in  front,  have  a  tendency  to  remove  the  arytenoid  cartilages  from  the 
anterior  attachment- of  the  chords. 

As  the  tones  produced  by  the  larynx  become  higher  in  pitch,  the  posterior  attach- 
ments of  the  chords  are  approximated  more  firmly,  and  at  this  time  the  lateral  crico- 
arytenoids  are  probably  brought  into  vigorous  action. 

The  function  of  the  thyro-arytenoids  is  more  complex ;  and  it  is  probably  in  great 
part  by  the  action  of  these  muscles  that  the  varied  and  delicate  modifications  in  the 
rigidity  of  the  vocal  chords  are  produced. 

The  remarkable  differences  in  singers  as  regards  the  purity  of  their  tones  are  undoubt- 
edly due  in  greatest  part  to  the  unswerving  accuracy  with  which  some  put  the  vocal  chords 
upon  the  stretch ;  while,  in  those  in  whom  the  tones  are  of  inferior  quality,  the  action  of 
the  muscles  is  more  or  less  vacillating,  and  the  tension  is  frequently  incorrect.  The  fact 
that  some  celebrated  singers  can  make  the  voice  heard  above  the  combined  sounds  from  a 
large  chorus  and  orchestra  is  not  due  entirely  to  the  intensity  of  the  sound,  but  in  a  great 
measure  to  the  absolute  mathematical  equality  of  the  sonorous  vibrations  and  the  com- 
parative absence  of  discordant  waves.  Musicians  who  have  heard  the  voice  of  the  cele- 
brated basso,  Lablache,  all  bear  testimony  to  the  remarkable  quality  of  his  voice,  which 
could  be  heard  at  times  above  a  powerful  chorus  and  orchestra.  A  grand  illustration  of 
this  occurred  at  the  musical  festival  at  Boston,  in  1869.  In  some  of  the  solos  by  Mme. 
Parepa-Rosa,  accompanied  by  a  chorus  of  nearly  twelve  thousand,  with  an  orchestra  of 
more  than  a  thousand  and  largely  composed  of  brass  instruments,  we  distinctly  heard  the 
pure  and  just  notes  of  this  remarkable  soprano,  standing  alone,  as  it  were,  against  the 
entire  choral  and  instrumental  force ;  and  this  in  an  immense  building  containing  an 
audience  of  forty  thousand  persons.  The  absolute  accuracy  of  the  tone  was  undoubtedly 
an  important  element  in  its  remarkably  penetrating  quality.  In  the  same  way  we  explain 
the  fact  that  the  flute,  clarinet,  or  the  sound  from  a  Cremona  violin,  may  be  heard  soaring 
above  the  chords  of  a  full  orchestra. 

Action  of  Accessory  Vocal  Organs. — A  correct  use  of  the  accessory  organs  of  the 
voice  is  of  the  greatest  importance  in  singing ;  but  the  manner  in  which  these  parts  per- 
form their  function  is  exceedingly  simple  and  does  not  require  a  very  extended  descrip- 
tion. The  human  vocal  organs,' indeed,  consist  of  a  vibrating  instrument,  the  larynx, 
and  of  certain  tubes  and  cavities  by  which  the  sound  is  reenforced  and  modified. 

The  trachea  serves,  not  only  to  conduct  air  to  the  larynx,  but  to  reenforce  the  sound 
to  a  certain  extent  by  the  vibrations  of  the  column  of  air  in  its  interior.  When  a  power- 
ful vocal  effort  is  made,  it  is  easy  to  feel,  with  the  finger  upon  the  trachea,  that  the  air 
contained  in  it  is  thrown  into  vibration.  The  structure  of  this  tube  is  such  that  it  may 
be  elongated  and  shortened  at  will.  In  the  production  of  low  notes,  the  trachea  is 
shortened  and  its  caliber  is  increased,  the  reverse  obtaining  in  the  higher  notes  of  the 


558  VOICE  AND  SPEECH. 

Coming  to  the  larynx  itself,  we  find  that  the  capacity  of  its  cavity  is  capable  of  certain 
variations.  In  fact,  both  the  vertical  and  the  bilateral  diameters  are  diminished  in  high 
notes  and  are  increased  in  low  notes.  The  vertical  diameter  may  be  modified  slightly 
by  ascent  and  descent  of  the  true  vocal  chords,  and  the  lateral  diameter  may  be  reduced 
by  the  inferior  constrictors  of  the  pharynx,  acting  upon  the  sides  of  the  thyroid  cartilage. 

The  epiglottis,  the  superior  vocal  chords,  and  the  ventricles,  are  by  no  means  indis- 
pensable to  the  production  of  vocal  sounds.  In  the  formation  of  higli  notes,  the  epiglottis 
is  somewhat  depressed,  and  the  superior  chords  are  brought  nearer  together ;  but  this 
only  affects  the  character  of  the  resonant  cavity  above  the  glottis.  In  low  notes .  the 
superior  chords  are  separated.  It  was  before  the  use  of  the  laryngoscope  in  the  study  of 
vocal  phenomena  that  the  epiglottis  and  the  ventricles  were  thought  to  be  so  important 
in  phonation.  Undoubtedly  the  epiglottis  has  something  to  do  with  the  character  of  the 
voice ;  but  its  function  in  this  regard  is  not  absolutely  necessary,  or  even  very  important, 
as  has  been  clearly  shown  in  experiments  of  excising  the  part  in  living  animals. 

The  most  important  modifications  of  the  laryngeal  sounds  are  produced  by  the  reso- 
nance of  air  in  the  pharynx,  mouth,  and  nasal  fo^sse.  This  resonance  is  indispensable  to 
the  production  of  the  natural  human  voice.  Under  ordinary  conditions,  in  the  production 
of  low  notes  the  velum  palati  is  fixed  by  the  action  of  its  muscular  fibres,  so  that  there  is 
a  reverberation  of  the  bucco-pharyngeal  and  naso-pharyngeal  cavities;  that  is,  the  velum  is 
in  such  a  position  that  neither  the  opening  into  the  nose  nor  into  the  mouth  is  closed,  and 
all  of  the  cavities  resound.  As  the  notes  are  raised,  the  isthmus  contracts,  the  part  imme- 
diately above  the  glottis  is  also  constricted,  the  resonant  cavity  of  the  pharynx  and  mouth 
is  reduced  in  size,  until  finally,  in  the  highest  notes  of  the  chest-register,  the  communica- 
tion between  the  pharynx  and  the  nasal  fossae  is  closed,  and  the  sound  is  reenforced 
entirely  by  the  pharynx  and  mouth.  At  the  same  time  the  tongue,  a  very  important 
organ  to  singers,  particularly  in  the  production  of  high  notes,  is  drawn  back  into  the 
mouth.  The  point  being  curved  downward,  its  base  projects  upward  posteriorly  and 
assists  in  diminishing  the  capacity  of  the  cavity.  In  the  changes  which  the  pharynx  thus 
undergoes  in  the  production  of  different  notes,  the  uvula  acts  with  the  velum  and  assists 
in  the  closure  of  the  different  openings.  In  singing  up  the  scale,  this  is  the  mechanism, 
as  far  as  the  chest-notes  extend.  When,  however,  we  pass  into  what  is  known  as  the 
head-voice,  the  velum  palati  is  drawn  forward  instead  of  backward,  and  the  resonance 
takes  place  chiefly  in  the  naso-pharyngeal  cavity. 

Mechanism  of  the  different  Vocal  Registers. — There  has  been  a  great  deal  of  discus- 
sion, even  among  those  who  have  studied  the  voice  with  the  laryngoscope,  with  regard 
to  the  exact  mechanism  of  the  different  vocal  registers.  It  is  now  pretty  well  settled 
how  the  ordinary  notes  of  what  is  known  as  the  chest-register  are  produced  ;  but,  with 
regard  to  the  falsetto,  the  difficulties  in  the  way  of  direct  observation  are  so  great,  that 
the  question  of  its  mechanism  cannot  be  said  to  be  definitively  established. 

The  following  are  the  vocal  registers  now  recognized  by  most  physiologists : 

1.  The  chest-register,  most  powerful  in  male  voices  and  in  contraltos,  and,  indeed, 
almost  characteristic  of  the  male. 

2.  The  falsetto  register,  which  is  the  most  natural  voice  of  the  soprano  ;  though  this 
voice  is  capable  of  chest-notes,  not  so  full,  however,  as  in  the  contralto  or  in  the  male. 
In  the  female  this  is  known  as  the  middle  register. 

3.  The  head-register,  produced  by  a  peculiar  action  of  the  glottis  and  the  resonant 
cavities  above  the  larynx.     This  is  cultivated  particularly  in  tenors  and  in  the  female. 

Aside  from  the  three  registers,  which  belong  to  every  voice,  a  practised  ear  can  find 
no  difficulty  in  distinguishing  the  different  voices  in  nearly  any  part  of  the  scale,  both  in 
the  male  and  the  female,  by  the  following  peculiarities :  In  the  bass,  the  low  notes  are 
full,  natural,  and  powerful,  and  the  higher  notes  nearly  always  seem  more  or  less  artifi- 
cial. In  singing,  the  passage  from  the  natural  to  the  artificial  notes  in  the  scale  is  gen- 
erally more  or  less  apparent.  In  the  tenor  the  full,  natural  notes  are  higher  in  the  scale, 


VOCAL  REGISTERS.  559 

the  lower  notes  being  almost  always  feeble  and  wanting  in  roundness.  Corresponding 
peculiarities  enable  us  to  distinguish  between  the  contralto  and  the  soprano. 

Chest- Register. — We  shall  simply  recapitulate  briefly  the  mechanism  of  the  chest- 
notes,  to  enable  us  to  study  more  easily  the  transitions  to  the  different  upper  registers. 
This  is  the  voice  commonly  used  in  speaking,  and  it  is  the  most  natural,  the  vocal  liga- 
ments vibrating  according  to  their  tension,  as  the  air  is  forced  through  the  larynx  from 
the  chest,  and  the  air  in  the  pharynx,  mouth,  and  nasal  fossro  producing  a  resonance 
without  any  artificial  division  of  the  different  cavities.  As  the  notes  are  elevated,  the 
vocal  chords  are  simply  rendered  more  tense,  and  the  parts  above  the  larynx  are  more 
or  less  constricted,  without  any  other  change  in  the  mechanism  of  the  sound.  But  the 
chest-voice  in  the  male  cannot  pass  certain  well-defined  limits ;  and  in  the  very  highest 
notes  it  must  be  merged  either  into  the  head-voice  or  the  falsetto.  The  falsetto,  how- 
ever, is  now  but  little  cultivated,  although  some  tenor  singers,  after  long  practice,  succeed 
in  making  the  change  from  one  register  to  the  other  so  nicely  that  it  is  hardly  perceptible, 
even  to  a  cultivated  ear.  The  head-voice  has  essentially  the  same  mechanism  in  the 
male  as  in  the  female,  and  this  will  be  considered  after  we  have  discussed  the  falsetto, 
which  is  the  natural  voice  of  soprano  singers. 

Falsetto  Register.— The  difference  of  opinion  among  laryngoscopists  with  regard  to 
the  mechanism  of  the  falsetto  is  probably  in  great  part  due  to  the  fact  that,  when  these 
notes  are  produced,  the  isthmus  of  the  fauces  is  so  powerfully  contracted  that  it  becomes 
exceedingly  difficult  to  study  the  action  of  the  vocal  chords.  There  is  no  reason  for  sup- 
posing that  the  mechanism  of  this  register  does  not  involve  vibration  of  the  true  vocal 
chords,  as  in  the  chest-voice,  the  difference  being  in  the  tension  and  in  the  extent  of  the 
vibrating  portion.  According  to  the  observations  of  Fourni6,  in  the  falsetto  the  tongue 
is  pressed  strongly  backward  and  the  epiglottis  is  forced  over  the  larynx.  Mrs.  Emma 
Seiler,  from  an  extended  series  of  autolaryngoscopic  observations,  has  arrived  at  the  con- 
clusion that  this  voice  involves  vibrations  of  the  fine,  thin  edges  of  the  chords  only,  a 
greater  width  vibrating  in  the  production  of  the  chest-voice.  She  is  particularly  careful 
to  insist  upon  the  distinction  between  the  falsetto  and  the  head-register,  the  latter  being 
produced  by  an  entirely  different  mechanism.  '  On  the  whole,  this  explanation  seems  to 
be  the  most  satisfactory. 

It  must  be  remembered  that  the  distinction  between  the  chest-register  or  the  head- 
register  and  the  falsetto,  as  far  as  pitch  is  concerned,  is  not  absolute.  Certain  of  the  high 
notes  of  the  chest  or  the  head-voice,  for  example,  may  be  produced  in  the  falsetto.  In 
the  cultivation  of  the  female  voice,  Mrs.  Seiler  considers  that  it  is  exceedingly  important 
not  to  strain  the  chest-voice  to  its  highest  point,  but  to  use  each  register  in  its  normal 
place  in  the  scale,  taking  care,  by  practice,  to  render  the  transition  from  one  to  the  other 
natural  and  agreeable.  "We  have  heard  male  singers,  probably  endowed  with  peculiar 
vocal  powers,  who  were  able,  by  the  use  of  the  falsetto,  to  imitate  almost  exactly  the 
soprano  voice,  though  without  the  sweetness  and  purity  of  tone  characteristic  of  the  per- 
fect female  organ.  In  the  same  way,  by  straining  the  chest-voice  beyond  its  normal 
limits,  some  females,  particularly  contraltos,  are  able  to  produce  a  very  good  imitation 
of  the  tenor  quality. 

Head- Register. — This  voice  is  highly  cultivated,  particularly  in  tenors  and  in  the  best 
female  singers.  It  is  not  to  be  confounded,  however,  with  the  falsetto,  as  was  done  by 
some  physiologists  before  the  invention  of  the  laryngoscope.  Head-notes  may  be  pro- 
duced by  cultivated  male  singers,  bass  and  barytone,  as  well  as  tenor ;  but  the  former 
seldom  have  occasion  for  any  but  the  chest-notes.  Still,  there  are  musical  passages  in 
which  the  sotto-voce  head-notes  of  the  bass  have  an  exquisite  softness  and  are  used  with 
great  effect.  We  have  already  stated  that,  in  the  transition  to  the  head-voice,  the  velum 
palati  is  applied  to  the  base  of  the  tongue,  and  the  sound  is  reenforced  by  resonance 
from  the  naso-pharyngeal  cavity.  If  this  be  its  mechanism,  its  study  with  the  laryngo- 
scope must  be  exceedingly  difficult. 


560  VOICE  AND  SPEECH. 

The  most  important  theory  of  the  mechanism  of  the  head-voice  has  been  proposed  by 
Mrs.  Seiler.  After  long  and  patient  effort,  she  was  able  to  expose  the  glottis  during  the 
production  of  these  notes,  when  it  was  found  that  the  vocal  chords  were  firmly  approxi- 
mated posteriorly,  leaving  an  oval  opening,  with  vibrating  edges,  involving  only  one-half 
or  one-third  of  the  vocal  ligaments.  This  orifice  contracted  progressively  with  the  higher 
notes.  This  peculiar  division  of  the  vocal  ligaments  is  due,  according  to  Mrs.  Seiler,  to 
the  action  of  a  muscular  bundle,  called  the  internal  thyro-arytenoid,  upon  little  cartilages 
(the  cuneiform)  extending  forward  from  the  arytenoid  cartilage,  in  the  substance  of  the 
vocal  ligaments,  as  far  as  the  middle  of  the  glottis. 

With  proper  cultivation,  the  transition  from  the  middle  register  to  the  head-voice  in 
the  female  may  be  effected  almost  imperceptibly,  thereby  increasing  the  compass  from 
three  to  six  notes,  and  even  more ;  and  in  the  male  the  same  may  be  accomplished  with- 
out difficulty,  particularly  in  tenors.  There  can  be  hardly  any  doubt  of  the  fact  that  the 
naso-pharyngeal  space  is  chiefly  concerned  in  the  resonance  that  takes  place  in  head- 
notes,  though  its  actual  demonstration  is  very  difficult.  The  distinction  between  the 
head  and  the  chest  notes  is  fully  as  marked  in  the  male  as  in  the  female ;  but  it  must  be 
remembered  that  one  of  the  great  ends  to  be  accomplished  in  the  cultivation  of  the  human 
voice  is  to  make  the  three  registers  pass  into  each  other  so  that  they  shall  appear  as  one. 

Mechanism  of  Speech. 

Articulate  language  consists  in  a  conventional  series  of  sounds  made  for  the  purpose 
of  conveying  certain  ideas.  There  being  no  universal  language,  we  must  confine  our 
description  of  the  faculty  of  speech  to  the  mode  of  production  of  the  language  in  which 
this  work  is  written.  Language,  as  it  is  naturally  acquired,  is  purely  imitative  and  does 
not  involve  of  necessity  the  construction  of  an  alphabet,  with  its  combinations  into 
syllables,  words,  and  sentences ;  but,  as  civilization  has  advanced,  we  have  been  taught 
to  associate  certain  differences  in  the  accuracy  and  elegance  with  which  ideas  are 
expressed,  with  the  degree  of  development  and  cultivation  of  the  intellectual  faculties. 
Philologists  have  long  since  established  a  certain  standard — varying,  to  some  extent,  it  is 
true,  with  usage  and  the  advance  of  knowledge,  but  still  sufficiently  definite — by  which 
the  correctness  of  modes  of  expression  is  measured.  We  do  not  propose  to  discuss  the 
science  of  language,  or  to  consider,  in  this  connection,  at  least,  the  peculiar  mental  opera- 
tions concerned  in  the  expression  of  ideas,  but  to  take  our  own  tongue  as  we  find  it,  and 
describe  briefly  the  mechanism  of  the  production  of  the  most  important  articulate  sounds. 

Almost  every  language  is  imperfect,  as  far  as  an  exact  correspondence  between  its 
sounds  and  written  characters  is  concerned.  Our  own  language  is  full  of  incongruities 
in  spelling,  such  as  silent  letters  and  arbitrary  and  unmeaning  variations  in  pronuncia- 
tion ;  but  these  do  not  belong  to  the  subject  of  physiology.  There  are,  however,  certain 
natural  divisions  of  the  sounds  as  expressed  by  the  letters  of  the  alphabet. 

Vowels. — Certain  articulate  sounds  are  called  vowel,  or  vocal,  from  the  fact  that  they 
are  produced  by  the  vocal  chords  and  are  but  slightly  modified  as  they  pass  out  of  the 
mouth.  The  true  vowels,  #,  e,  *,  0,  w,  can  all  be  sounded  alone  and  may  be  prolonged 
in  expiration.  These  are  the  sounds  chiefly  employed  in  singing.  The  differences  in 
their  characters  are  produced  by  changes  in  the  position  of  the  tongue,  mouth,  and  lips. 
The  vowel-sounds  are  necessary  to  the  formation  of  a  syllable,  and,  although  they  are 
generally  modified  in  speech  by  consonants,  each  one  may,  of  itself,  form  a  syllable  or  a 
word.  In  the  construction  of  syllables  and  words,  the  vowels  have  many  different  quali- 
ties, the  chief  differences  being  as  they  are  made  long  or  short.  In  addition  to  the  modi- 
fications in  the  vowel-sounds  by  consonants,  two  or  three  may  be  combined  so  as  to  be 
pronounced  by  a  single  vocal  effort,  when  they  are  called  respectively,  diphthongs  and 
triphthongs.  In  the  proper  diphthongs,  as  oi,  in  voice,  the  two  vowels  are  sounded.  In 


MECHANISM  OF  SPEECH.  561 

the  improper  diphthongs,  as  ea,  in  heat,  and  in  the  Latin  diphthongs,  as  <E,  in  Csesar,  one 
of  the  vowels  is  silent.  In  triphthongs,  as  eau,  in  beauty,  only  one  vowel  is  sounded. 
I",  at  the  beginning  of  words,  is  usually  pronounced  as  a  consonant ;  but  in  other  situa- 
tions it  is  pronounced  as  e  or  i. 

A  very  curious  and  interesting  inquiry  relates  to  the  differences,  with  which  we  are 
all  familiar,  in  the  quality  of  the  different  vowel-sounds  when  pronounced  with  equal 
pitch  and  intensity.  The  cause  of  these  differences  was  studied  very  closely  in  the  latter 
part  of  the  last  century,  but  it  has  lately  been  rendered  very  clear  by  the  elaborate  and 
convincing  researches  of  Helmholtz.  In  this  connection,  it  will  be  sufficient  to  indi- 
cate the  results  of  modern  investigations  very  briefly.  When  we  come  to  study  the 
physics  of  sound  in  connection  with  the  sense  of  hearing,  we  shall  see  that  nearly  all 
sounds,  even  when  produced  by  a  single  vibrating  body,  are  compound.  Helmholtz,  by 
means  of  his  resonators,  has  succeeded  in  analyzing  the  apparently  simple  sounds  into  dif- 
ferent component  parts,  and  he  has  shown  that  the  quality  of  such  sounds  may  be  modified 
by  reenforcing  certain  of  the  overtones,  as  they  are  called,  such  as  the  third,  fifth,  or 
octave.  For  those  who  are  familiar  with  the  physics  of  sound,  the  explanation  which  we 
shall  give  of  the  mechanism  of  the  production  of  vowel-sounds  will  be  readily  compre- 
hensible. The  reader  is  referred,  however,  to  our  remarks  upon  overtones  in  another  part 
of  this  work,  under  the  head  of  audition,  for  a  more  thorough  exposition  of  this  subject. 
This  should  be  read  in  connection  with  what  we  shall  say  here  of  vowel-sounds,  when 
the  whole  subject  will  be  sufficiently  clear.  We  may  pronounce  the  different  vowel- 
sounds  with  the  same  pitch  and  intensity,  but  the  sound  in  each  is  different,  on  account 
of  variations  in  the  resonant  cavities  of  the  accessory  vocal  organs,  especially  the  mouth. 
It  has  been  ascertained  experimentally  that  the  overtones  in  each  instance  are  different, 
as  they  are  reenforced  by  the  vibrations  of  air  in  the  accessory  vocal  organs,  in  some 
instances  the  third,  in  others,  the  fifth,  etc.,  being  increased  in  intensity.  We  cannot 
illustrate  this  better  than  by  the  following  quotation  from  Tyndall,  in  which  modern 
researches  have  been  applied  to  the  vowel-sounds  of  our  own  language : 

"  For  the  production  of  the  sound  U  (o  o  in  hoop),  I  must  push  my  lips  forward  so  as 
to  make  the  cavity  of  the  mouth  as  deep  as  possible,  at  the  same  time  making  the  orifice 
of  the  mouth  small.  This  arrangement  corresponds  to  the  deepest  resonance  of  which 
the  mouth  is  capable.  The  fundamental  tone  of  the  vocal  chords  is  here  reenforced,  while 
the  higher  tones  are  thrown  into  the  shade.  The  £7"  is  rendered  a  little  more  perfect 
when  a  feeble  third  tone  is  added  to  the  fundamental. 

"The  vowel  0  is  pronounced  when  the  mouth  is  so  far  opened  that  the  fundamental 
tone  is  accompanied  by  its  strong  higher  octave.  A  very  feeble  accompaniment  of  the 
third  and  fourth  is  advantageous,  but  not  necessary. 

"  The  vowel  A  derives  its  character  from  the  third  tone,  to  strengthen  which  by 
resonance  the  orifice  of  the  mouth  must  be  wider,  and  the  volume  of  air  within  it  smaller 
than  in  the  last  instance.  The  second  tone  ought  to  be  added  in  moderate  strength,  whilst 
weak  fourth  and  fifth  tones  may  also  be  included  with  advantage. 

"  To  produce  E  the  fundamental  tone  must  be  weak,  the  second  tone  comparatively 
strong,  the  third  very  feeble,  but  the  fourth,  which  is  characteristic  of  this  vowel,  must 
be  intense.  A  moderate  fifth  tone  may  be  added.  No  essential  change,  however,  occurs 
in  the  character  of  the  sound  when  the  third  and  fifth  tones  are  omitted.  In  order  to 
exalt  the  higher  tones  which  characterize  the  vowel-sound  E,  the  resonant  cavity  of  the 
mouth  must  be  small. 

"  In  the  production  of  the  sound  ah  !  the  higher  overtones  come  principally  into 
play;  the  second  tone  may  be  entirely  neglected  ;  the  third  rendered  feebly  ;  the  higher 
tones,  particularly  the  fifth  and  seventh,  being  added  strongly. 

"These  examples  sufficiently  illustrate  the  subject  of  vowel-sounds.     We  may  blend 
in  various  ways  the  elementary  tints  of  the  solar  spectrum,  producing  innumerable  com- 
posite colors  by  their  admixture.     Out  of  violet  and  red  we  produce  purple,  and  out  of 
36 


562  VOICE  AND  SPEECH. 

yellow  and  blue  we  produce  white.  Thus  also  may  elementary  sounds  be  blended  so  as 
to  produce  all  possible  varieties  of  clang-tint.  After  having  resolved  the  human  voice 
into  its  constituent  tones,  Helmholtz  was  able  to  imitate  these  tones  by  tuning-forks,  and, 
by  combining  them  appropriately  together,  to  produce  the  clang-tints  of  all  the  vowels." 

Consonants.— Some  of  the  consonants  have  no  sound  in  themselves  and  serve  merely  to 
modify  vowel-sounds.  These  are  called  mutes.  They  are  &,  <?,  &,  p,  t,  and  c  and  g  hard. 
Their  office  in  the  formation  of  syllables  is  sufficiently  apparent. 

The  consonants  known  as  semivowels  are,  /,  I,  m,  n,  r,  *,  and  c  and  g  soft.  These 
have  an  imperfect  sound  of  themselves,  approaching  in  character  the  true  vowel-sounds. 
Some  of  these,  I,  m,  n,  and  r,  from  the  facility  with  which  they  flow  into  other  sounds, 
are  called  liquids.  Orthoepists  have  farther  divided  the  consonants  with  reference  to  the 
mechanism  of  their  pronunciation :  d,  j,  s,  t,  z,  and  g  soft,  being  pronounced  with  the 
tongue  against  the  teeth,  are  called  dentals ;  d,  g,  j,  k,  I,  72,  and  q  are  called  palatals ;  6, 
j9,/,  u,  and  m  are  called  labials ;  m,  n,  and  ng  are  called  nasals;  and  &,  g,  and  c  and  g 
hard  are  called  gutturals.  After  the  description  we  have  given  of  the  voice,  it  is  not 
necessary  to  discuss  farther  the  mechanism  of  these  simple  acts  of  articulation. 

For  the  easy  and  proper  production  of  articulate  sounds,  absolute  integrity  of  the 
mouth,  teeth,  lips,  tongue,  and  palate  is  required.  We  are  all  acquainted  with  the  modi- 
fications in  articulation,  in  persons  in  whom  the  nasal  cavities  resound  unnaturally,  from 
imperfection  of  the  palate ;  and  the  slight  peculiarities  observed  after  loss  of  the  teeth 
and  in  hare-lip  are  sufficiently  familiar.  The  tongue  is  generally  regarded,  also,  as  an 
important  organ  of  speech,  and  this,  is  the  fact  in  tho  great  majority  of  cases ;  but 
instances  are  on  record  in  which  distinct  articulation  has  been  preserved  after  complete 
destruction  of  this  organ.  These  cases,  however,  are  unusual,  and  they  do  not  invalidate 
the  great  importance  of  the  tongue  in  ordinary  speech. 

It  is  thus  seen  that  speech  consists  essentially  in  a  modification  of  the  vocal  sounds 
by  the  accessory  organs,  or  by  parts  situated  above  the  larynx ;  the  latter  being  the  true 
vocal  instrument.  While  the  peculiarities  of  pronunciation  in  different  persons  and  the 
difficulty  of  acquiring  foreign  languages  after  the  habits  of  speech  have  been  formed  show 
that  the  organs  of  articulation  must  perform  their  function  with  great  accuracy,  their 
movements  are  simple,  and  they  vary  with  the  peculiarities  of  different  languages.  The 
most  interesting  question,  in  its  general  physiological  relations,  is  that  to  which  a  great 
part  of  this  chapter  has  been  devoted ;  and  that  is  the  mechanism  of  the  production  of 
the  voice. 


GENERAL  CONSIDERATIONS.  563 


CHAPTER   XVII. 

PHYSIOLOGICAL  DIVISIONS,  STRUCTURE,  AND  GENERAL  PROPERTIES  OF  THE 

NERVOUS  SYSTEM. 

General  considerations— Divisions  of  the  nervous  system— Physiological  anatomy  of  the  nervous  tissue — Anatomical 
divisions  of  the  nervous  tissue— Medullated  nerve-fibres— Simple,  or  non-medullated  nerve-fibres— Gelatinous 
nerve-fibres  (fibres  of  Eemak)— Accessory  anatomical  elements  of  the  nerves — Branching  and  course  of  the  nerves 
— Termination  of  the  nerves  in  the  muscular  tissue — Termination  of  the  nerves  in  glands — Terminations  of  the 
sensory  nerves—Corpuscles  of  Pacini,  or  of  Vater— Tactile  corpuscles— Terminal  bulbs— Structure  of  the  nerve- 
centres— Nerve-cells — Connection  of  the  cells  with  the  fibres  and  with  each  other — Accessory  anatomical  elements 
of  the  nerve-centres— Composition  of  the  nervous  substance— Eegeneration  of  the  nervous  tissue — Eeunion  of 
nerve-fibres — Motor  and  sensory  nerves — Distinct  seat  of  the  motor  and  sensory  properties  of  the  spinal  nerves- 
Experiments  of  Magendie  upon  the  roots  of  the  spinal  nerves — Properties  of  the  posterior  roots  of  the  spinal  nerves 
—Properties  of  the  anterior  roots  of  the  spinal  nerves— Recurrent  sensibility— Mode  of  action  of  the  motor  nerves 
— Associated  movements— Mode  of  action  of  the  sensory  nerves — Sensation  in  amputated  members — General  prop- 
erties of  the  nerves— Nervous  irritability— Different  means  employed  for  exciting  the  nerves— Disappearance  of 
the  irritability  of  the  motor  and  sensory  nerves  after  exsection — Nerve-force — Rapidity  of  nervous  conduction — 
— Estimation  of  the  duration  of  acts  involving  the  nerve-centres — Action  of  electricity  upon  the  nerves — Induced 
muscular  contraction — Galvanic  current  from  the  exterior  to  the  cut  surface  of  a  nerve — Effects  of  a  constant  gal- 
vanic current  upon  the  nervous  irritability— Electrotonus,  anelectrotonus,  and  catelectrotonus— Neutral  point- 
Negative  variation. 

I 

THE  nervous  system  is  anatomically  distinct  in  all  animals  except  those  lowest  in  the 
scale  of  being.  It  is  useless  to  speculate  upon  the  question  of  the  existence  of  matter 
endowed  with  properties  analogous  to  those  observed  in  the  nervous  system  of  the  higher 
animals,  in  beings  so  low  in  their  organization  as  to  present  no  divisions  into  anatomical 
elements ;  for  the  present  condition  of  physiological  science  does  not  admit  of  the  recog- 
nition of  functions  without  organs.  All  animals  that  present  any  thing  like  nervous 
functions  present  also  an  anatomically  distinct  nervous  system.  Within  certain  limits, 
the  perfection  of  the  animal  organization  depends  upon  the  general  development  of  the 
nervous  system. 

High  in  the  animal  scale,  as  in  the  warm-blooded  animals,  the  general  development  of 
the  nervous  system  presents  little  if  any  variation ;  but  special  attributes  are  coexistent 
with  the  development  of  special  organs.  The  development  in  this  way  of  particular  por- 
tions of  the  nervous  system  is  in  accordance  with  the  peculiar  conditions  of  existence  of 
different  animals ;  it  is  a  necessary  part  of  their  organization,  and  is  not  dependent  upon 
education  or  intelligence.  Examples  of  this  are  in  the  extraordinary  development  of  the 
sense  of  sight,  hearing,  or  smell,  in  different  animals.  There  are  animals  in  which  these 
special  senses  possess  a  delicacy  of  perception  to  which  man,  even  with  the  greatest 
amount  of  intelligent  education,  can  never  attain  ;  but  man,  possessing  a  nervous  organi- 
zation not  superior  to  that  of  other  warm-blooded  animals  in  its  general  development, 
and  inferior  to  many  in  the  development  of  special  organs,  stands  immeasurably  above 
all  other  beings,  by  virtue  of  the  immense  preponderance  of  what  is  known  as  the 
encephalic  portion  of  the  nervous  system. 

These  brief  general  considerations  will  convey  some  idea  of  the  physiological  impor- 
tance of  the  nervous  system  ;  of  tHe  care  which  should  be  exercised  in  its  study ;  and  of 
the  great  interest  attached  to  it,  from  the  fact  that  the  most  complex  and  important  of 
its  functions  belong  to  human  physiology,  and  to  human  physiology  alone. 

We  can  best  define  what  is  to  be  included  under  the  head  of  the  nervous  system,  by 
citing  certain  of  its  prominent  and  well-established  properties  and  functions  : 

1.  The  nervous  system  is  anatomically  and  physiologically  distinct  from  all  other  sys- 
tems and  organs  in  the  body.  It  receives  impressions  made  upon  the  terminal  branches  of 
its  sensory  portion  and  it  conveys  stimulus  to  parts,  determining  and  regulating  the  opera- 
tion of  their  functions;  but  its  physiological  properties  are  inherent,  and  it  gives  to  no 


564  NERVOUS  SYSTEM. 

tissue  or  organ  its  special  "irritability"  or  the  power  of  performing  its  particular  func- 

tion. 

2.  The  nervous  system  connects  into  a  coordinated  organism  all  parts  and  organs  of 
the  body.  It  is  the  medium  through  which  all  impressions  are  received.  It  animates 
or  regulates  all  movements,  voluntary  and  involuntary.  It  regulates  the  functions  of 
secretion,  nutrition,  calorification,  and  all  the  processes  of  organic  life. 

In  addition  to  its  functions  as  a  medium  of  conduction  and  communication,  the  ner- 
vous system,  in  certain  of  its  parts,  is  capable  of  receiving  impressions  and  of  generating 
a  stimulating  influence,  or  force,  peculiar  to  itself.  As  there  can  be  no  physiological 
connection  or  coordination  of  different  parts  of  the  organism,  having  an  active  function, 
without  nerves,  there  can  be  no  unconscious  reception  of  impressions  giving  rise  to  invol- 
untary movements,  no  appreciation  of  impressions,  general,  as  in  ordinary  sensation,  or 
special,  as  in  sight,  smell,  taste,  or  hearing,  no  instinct,  volition,  thought,  or  even  knowl- 
edge of  existence,  without  nerve-centres. 

Possessing,  as  it  does,  these  varied  properties  and  functions,  it  is  evidently  of  the 
greatest  physiological  importance  that  the  anatomical  characters  of  the  nervous  sys- 
tem should  be  most  carefully  studied,  with  a  view  of  connecting,  if  possible,  certain  of 
the  nervous  properties  with  peculiarities  in  structure.  It  is  also  important  to  subdivide 
the  system,  as  regards  general  properties  and  functions,  as  well  as  with  reference  to  the 
special  office  of  particular  parts.  With  this  end  in  view,  we  shall  point  out  first,  the 
great  anatomico-physiological  divisions  common  to  nervous  matter  wherever  it  exists, 
and  afterward,  the  subdivisions  of  the  system  as  regards  special  functions. 

.Divisions  of  the  Nervous  System. 

Nervous  matter,  whatever  may  be  its  special  function,  presents  two  great  divisions, 
each  with  distinct  anatomical  as  well  as  physiological  differences.  One  of  these  divisions 
presents  the  form  of  fibres  or  tubes.  This  kind  of  nervous  matter  is  incapable  of  gener- 
ating a  force  or  stimulus,  and  it  serves  only  as  a  conductor.  The  other  division  is  in  the 
form  of  cells,  and  this  kind  of  nervous  matter  alone  is  capable  of  generating  the  so-called 
nervous  force. 

The  nervous  matter  is  divided  into  two  great  systems,  as  follows : 

1.  The  cerebro-spinal  system,  composed  of  the  brain  and  spinal  cord  with  the  nerves 
directly  connected  with  these  centres,     This  system  is  specially  connected  with  the  func- 
tions of  relation,  or  of  animal  life.     The  centres  preside  over  general  sensation,  the  spe- 
cial senses,  voluntary  and  some  involuntary  movements,  intellection,  and,  in  short,  all 
of  the  functions  that  characterize  the  animal.     The  nerves  serve  as  the  conductors  of 
impressions  known  as  general  or  special  sensations,  and  of  the  stimulus  that  gives  rise  to 
voluntary  and  certain  involuntary  movements,  the  latter  being  the  automatic  movements 
connected  with  animal  life. 

2.  The  sympathetic,  or  organic  system.     This  system  is  specially  connected  with  the 
functions  relating  to  nutrition,  operations  which  have  their  analogue  in  the  vegetable 
kingdom  and  are  sometimes  called  the  functions  of  vegetative  life.     Although  this  sys- 
tem presides  over  functions  entirely  distinct  from  those  characteristic  of  and  peculiar  to 
animals,  the  centres  of  this  system  all  have  an  anatomical  and  physiological  connection 
with  the  cerebro-spinal  nerves. 

The  cerebro-spinal  system  is  subdivided  into  centres  presiding  over  movements  and 
ordinary  sensation,  and  centres  capable  of  receiving  impressions  connected  with  the  special 
senses,  such  as  sight,  audition,  olfaction,  and  gustation.  The  nerves  which  receive  these 
special  impressions  and  convey  them  to  the  appropriate  centres  are  more  or  less  insen- 
sible to  ordinary  impressions.  The  organs  to  which  these  special  nerves  are  distributed 
are  generally  of  a  complex  and  peculiar  structure,  and  they  present  numerous  accessory 
parts  which  are  important  and  essential  in  the  transmission  of  the  special  impressions  to 
the  terminal  branches  of  the  nerves. 


PHYSIOLOGICAL  ANATOMY   OF  THE  NERVOUS   TISSUE.  565 

In  treating  of  the  nervous  system,  we  shall  consider  first  the  physiological  anatomy 
of  the  nervous  tissue ;  next,  the  general  properties  of  the  cerebro-spinal  system  ;  next, 
the  functions  of  different  portions  of  this  system  connected  with  motion,  ordinary  sensi- 
bility, intellection,  etc.  ;  next,  the  functions  of  the  sympathetic,  or  organic  system  of 
nerves ;  and  finally,  the  special  senses,  with  the  physiological  anatomy  and  mechanism 
of  the  accessory  parts. 

Physiological  Anatomy  of  the  Nervous  Tissue. 

The  physiological  anatomy  of  the  nervous  system  naturally  divides  itself  into  two 
sections ;  one  embracing  what  is  called  the  general  anatomy  of  the  nervous  tissue,  and 
the  other,  the  arrangement  of  this  tissue  in  special  organs,  as  far  as  this  is  connected 
with  their  functions. 

The  intimate  structure  of  the  different  portions  of  the  nervous  system  may  now  be 
regarded  as  tolerably  well  understood,  at  least  so  far  as  those  anatomical  points  bearing 
upon  physiology  are  concerned.  The  connection  between  the  nerve-cells  and  the  fibres 
and  the  modes  of  termination  of  the  motor  filaments  in  the  muscles  are  points  nearly  if 
not  quite  settled  ;  and  the  terminations  of  sensory  filaments  in  integument  and  mucous 
membranes  have  lately  been  investigated  very  thoroughly  and  with  quite  positive  and 
satisfactory  results.  These  anatomical  points  are  specially  connected  with  the  general 
properties  of  the  nervous  system,  both  as  a  generator  of  the  so-called  nerve-force  and  as 
a  conductor. 

The  arrangement  of  the  nervous  elements  in  special  organs,  as  in  the  brain  and  spinal 
cord,  has  not  been  so  successfully  investigated  and  presents  immense  difficulties  in  its 
study  ;  and  we  can  hardly  hope  to  acquire  any  thing  like  a  definite  and  thorough  knowl- 
edge of  the  functions  of  these  parts,  until  we  have  much  more  positive  information  con- 
cerning their  anatomical  characters. 

Anatomical  Divisions  of  the  Nervous  Tissue, — The  physiological  division  of  the 
nervous  system  into  nerves  and  nerve-centres  is  pretty  well  carried  out  as  regards  the 
anatomical  structure  of  these  parts.  The  two  great  divisions  of  the  system,  anatomically 
considered,  are  into  nerve-cells  and  nerve-fibres. 

The  nerve-cells,  as  far  as  we  know,  are  the  only  parts  capable,  under  any  circum- 
stances, of  generating  the  nerve-force ;  and,  as  a  rule,  they  cannot  receive  impressions 
in  any  other  way  than  through  the  nerve-fibres.  There  are,  however,  some  exceptions, 
either  apparent  or  real,  to  this  rule,  as  in  the  case  of  direct  irritation  of  the  ganglion  of 
the  tuber  annulare,  portions  of  the  cerebrum,  and  the  sympathetic  ganglia,  which  seem 
sensible  to  direct  irritation ;  but  the  cells  of  most  of  the  ganglia  belonging  to  the  great 
cerebro-spinal  axis  are  insensible  to  direct  stimulation  and  can  only  receive  impressions 
conducted  to  them  by  the  nerves. 

The  nerve-fibres  act  only  as  conductors  and  are  incapable  of  generating  nerve-force. 
There  is  no  exception  to  this  rule,  but  there  are  differences  in  the  properties  of  certain 
fibres.  The  nerves  generally,  for  example,  receive  direct  impressions,  the  motor  fila- 
ments conducting  these  to  the  muscles  and  the  sensory  filaments  conveying  the  impres- 
sions to  the  centres.  These  fibres  also  conduct  the  force  generated  by  the  nerve-centres. 
But  there  are  many  fibres,  such  as  those  composing  the  white  matter  of  the  encephalon 
and  the  spinal  cord,  that  are  insensible  to  direct  irritation,  while  they  convey  to  the 
centres  impressions  made  by  the  sensitive  nerves  and  conduct  to  the  motor  nerves  the 
stimulus  generated  by  nerve-cells. 

Structure  of  the  Nerves. — There  are  few  anatomical  elements  that  present  greater 
variations  in  size  and  appearance  than  the  nerve-fibres.  Certain  fibres  found  in  the 
course  of  the  nerves  between  the  muscles  are  as  large  as  -j-^^  of  an  inch,  have  dark 
borders,  and  possess  three  well-marked  structures,  viz.,  a  tubular  membrane,  medullary 
contents,  and  an  axial  band  ;  others,  with  the  same  structure,  are  only  -^-^  of  an  inch 


566  NERVOUS  SYSTEM. 

in  diameter ;  others  have  only  the  medullary  covering  and  the  axial  band ;  and  others 
present  the  axial  band  alone.  Most  of  these  anatomical  elements  have  essentially  the 
same  physiological  conducting  properties ;  the  variations  in  their  structure  depending 
upon  differences  in  their  anatomical  relations.  In  view  of  these  facts,  it  will  be  con- 
venient to  adopt  some  anatomical  classification  of  the  fibres. 

In  the  most  simple  classification  of  the  nerve-fibres,  they  are  divided  into  two  groups ; 
one  embracing  those  fibres  which  have  the  conducting  element  alone,  and  the  other  pre- 
senting this  element  surrounded  by  certain  accessory  structures.  In  the  course  of  the 
nerves,  the  simple  fibres  are  the  exception,  and  the  other  variety  is  the  rule  ;  but,  as  the 
nerves  are  followed  to  their  terminations  in  muscles  or  sensitive  parts,  or  are  traced  to 
their  origin  in  the  nerve-centres,  we  find  that  they  lose  one  or  another  of  their  adven- 
titious elements.  These  two  varieties  we  shall  term :  1.  The  medullated  fibres,  and  2. 
The  simple,  or  non-medullated  fibres. 

Medullated  Nerve-fibres—  These  fibres  are  so  called  by  French  and  German  writers 
because,  in  addition  to  the  axis-cylinder,  or  conducting  element,  they  contain,  enclosed 
in  a  tubular  sheath,  a  soft  substance  called  the  medulla.  This  substance  is  strongly 
refractive  and  gives  the  nerves  a  peculiar  appearance  under  the  microscope,  from  which 
they  are  sometimes  called  the  dark-bordered  nerve-fibres.  As  the  whole  substance  of 
the  fibre  is  enclosed  in  a  tubular  membrane,  these  are  frequently  spoken  of  as  nerve- 
tubes. 

If  the  nerves  be  examined  while  perfectly  fresh  and  unchanged,  their  anatomical  ele- 
ments appear  in  the  form  of  simple  fibres  with  strongly-accentuated  borders.  The  diame- 
ter of  these  fibres  is  from  -^^  to  yyV^-  of  an  inch.  To  observe  the  fibres  in  this  way,  it  is 
necessary  to  take  a  nerve  from  an  animal  just  killed  and  examine  it  without  delay.  In  a 
very  short  time,  the  borders  become  darker  and  the  fibre  assumes  an  entirely  different 
appearance.  By  the  use  of  certain  reagents,  it  can  be  demonstrated  that  a  medullated 
nerve-fibre  is  composed  of  three  distinct  portions ;  viz.,  a  homogeneous  sheath,  a  semi- 
fluid matter  contained  in  the  sheath,  and  a  delicate  central  band. 

The  tubular  sheath  of  the  nerve-fibres  is  a  somewhat  elastic,  homogeneous  membrane, 
never  striated  or  fibrillated,  and  presenting  generally  oval  nuclei,  with  their  long  diame- 
ter in  the  direction  of  the  tube.  This  is  sometimes  called  the  neurilemma,  a  name,  how- 
ever, which  is  more  generally  applied  to  another  membrane.  It  is  sometimes  spoken  of, 
also,  as  the  "  limiting  membrane  of  Valentin,"  or  "  the  sheath  of  Schwann."  In  its 
chemical  and  general  properties,  this  membrane  resembles  the  sarcolemma,  although  it  is 
less  elastic  and  resisting.  It  exists  in  all  the  medullated  nerve-fibres,  large  and  small, 
except  those  in  the  white  portions  of  the  encephalon  and  spinal  cord.  It  is  not  certain 
that  it  does  not  exist  in  the  small,  non-medullated  fibres,  although  its  presence  here  has 
never  been  satisfactorily  demonstrated.  As  we  before  remarked,  the  tubular  membrane 
cannot  be  seen  in  the  perfectly  fresh  nerves ;  and,  even  after  they  have  become  changed 
by  desiccation,  its  demonstration  requires  the  use  of  reagents.  In  the  ordinary  medul- 
lated fibres,  however,  it  may  be  isolated  by  boiling  the  nerve  in  absolute  alcohol  and  then 
in  acetic  acid,  or  by  treating  it  with  cold  caustic  soda.  By  then  boiling  the  nerve  for  an 
instant  in  the  caustic  soda,  fragments  of  the  tube  may  be  isolated,  when  they  resemble 
the  membrane  forming  the  canals  of  the  kidney.  Another  method  is  to  treat  the  nerve 
with  fuming  nitric  acid,  afterward  adding  a  solution  of  caustic  potash.  The  fatty  sub- 
stance is  then  discharged  in  small  drops,  the  central  band  is  dissolved,  and  the  empty 
sheath  is  seen,  swollen  and  tinged  with  yellow. 

The  medullary  substance  fills  the  tube  and  surrounds  the  central  band.  This  is  called 
by  various  names,  as  myeline,  white  substance  of  Schwann,  medullary  sheath,  nervous 
medulla,  etc.  It  does  not  exist  either  at  the  origin  of  the  nerves  in  the  gray  substance 
of  the  nerve-centres  or  at  the  peripheral  termination  of  the  nerves,  and  it  is  probably  not 
an  essential  conducting  element.  "When  the  nerves  are  perfectly  fresh,  this  substance  is 
transparent,  homogeneous,  and  strongly  refracting,  like  oil ;  but,  as  the  nerves  become 


PHYSIOLOGICAL  ANATOMY  OF  THE  NERVOUS  TISSUE.          567 

altered  by  desiccation,  the  action  of  water,  acetic  acid,  and  various  other  reagents,  it 
coagulates  into  an  opaque,  granular  mass.  The  consistence  of  this  substance  gives  to  the 
medullated  fibres  a  very  peculiar  appearance.  The  tubular  membrane  being  very  thin 
and  not  elastic,  the  white  substance,  by  very  slight  pressure,  is  made  to  fill  the  tubes 
irregularly,  giving  them  a  varicose  appearance,  which  is  entirely  characteristic.  In 
examining  a  preparation  of  the  nervous  tissue,  large  drops,  coagulated  in  irregular  shapes, 
are  seen  scattered  over  the  field  and  frequently  fringing  the  divided  ends  of  the  tubes. 
In  the  white  substance  of  the  encephalon  and  spinal  cord,  where  the  tubular  membrane 
is  wanting,  the  varicose  appearance  of  the  fibres  is  more  remarkable  than  in  any  other 
situation. 

The  axis-cylinder  is,  in  all  probability,  the  essential  anatomical  element  of  the  nerves. 
It  exists  in  all  the  nerves  except  in  those  termed  gelatinous  fibres,  or  fibres  of  Remak, 
which  will  be  described  hereafter.  In  the  ordinary  medullated  fibres,  the  axis-cylinder 
cannot  be  seen  in  the  natural  condition  of  the  tissue,  because  it  refracts  in  the  same 
manner  as  the  medullary  substance,  and  it  cannot  be  demonstrated  afterward,  on  account 
of  the  opacity  of  the  coagulated  matter.  If  a  fresh  nerve,  however,  be  treated  with 
strong  acetic  acid,  the  divided  ends  of  the  fibres  will  retract,  leaving  the  axis-cylinder, 
which  is  but  slightly  affected  by  reagents.  It  then  presents  itself  in  the  form  of  a  pale, 
slightly-flattened  band,  with  outlines  tolerably  regular,  though  slightly  varicose  at  inter- 
vals, somewhat  granular,  and  sometimes  very  finely  striated  in  a  longitudinal  direction. 
This  band  is  elastic  but  not  very  resisting.  Its  granules  are  excessively  pale.  What 
serves  to  distinguish  it  from  all  other  portions  of  the  nerve-fibre  is  its  insolubility  in  most 
of  the  reagents  employed  in  anatomical  investigations.  It  is  slightly  swollen  by  acetic 
acid  but  is  dissolved  after  prolonged  boiling.  If  a  solution  of  carmine  be  applied  to  the 
nervous  tissue,  the  axis-cylinder  only  is  colored.  It  has  been  remarked  that  the  nerve- 
fibres  treated  with  nitrate  of  silver  present  in  the  axis-cylinder  well-marked  transverse 
striations  ;  and  some  observers  are  disposed  to  regard  both  the  nerve-cells  and  the  axes 
of  the  fibres  as  composed  of  two  substances,  the  limits  of  which  are  marked  by  the  regu- 
lar striaa  developed  by  the  nitrate  of  silver.  This,  however,  is  a  point  of  purely  anatomi- 
cal interest.  The  presence  of  regular  and  well-marked  striae  in  the  axis-cylinder  after 
the  addition  of  a  solution  of  nitrate  of  silver  and  the  action  of  light  cannot  be  doubted ; 
but  it  has  not  yet  been  determined  beyond  question  whether  these  markings  be  entirely 
artificial,  or  whether  the  axis-cylinder  be  really  composed  of  two  kinds  of  substance. 

A  still  more  important  question  with  regard  to  the  intimate  structure  of  the  axis- 
cylinder  refers  to  the  longitudinal  striations.  These  are  observed  in  many  fibres,  but 
they  are  not  constant.  Some  authors  have  adopted  the  view  that  the  markings  are  pro- 
duced by  fibrillse,  analogous  to  the  fibrilta  of  the  muscular  fibres,  in  all  the  fibres,  as  well 
as  in  those  of  the  retina,  the  olfactory,  and  some  of  the  sympathetic  nerves.  In  the  organs 
of  special  sense,  there  can  be  no  doubt  of  the  existence  of  fibrillse ;  but  this  is  by  no 
means  so  clearly  demonstrable  in  the  general  system  of  nerves.  Still,  it  is  necessary  to 
take  into  consideration,  in  this  connection,  certain  facts  with  regard  to  the  origin  of  the 
nerve-fibres  in  the  cells  and  their  ultimate  distribution  in  sensitive  parts.  In  the  final 
distribution  of  sensitive  nerves,  we  shall  see  that  the  fibres  break  up  into  filaments 
resembling  fibrillas ;  and,  although  the  fibrillated  character  of  the  poles  of  the  nerve-cells 
is  not  unreservedly  accepted  by  anatomists,  many  observers  positively  state  that  such  is 
their  structure.  In  the  present  condition  of  the  science,  we  cannot  do  more  than  state 
that,  while  a  fibrillated  structure  has  perhaps  been  shown  in  the  nerves  of  some  of  the 
lower  orders  of  animals,  its  existence  in  man  and  in  the  mammalia  is  somewhat  doubtful. 

The  diameter  of  the  axis-cylinder  is  about  one-half  or  one-third  that  of  the  tube  in 
which  it  is  contained.  The  various  appearances  which  the  nerve-fibres  present  under 
different  conditions  are  represented  in  Fig.  174. 

Simple,  or  Non -medullated  Nerve- Fibres. — These  fibres  are  found  very  largely  dis- 
tributed in  the  nervous  system.  When  we  come  to  study  the  structure  and  relations  of 


568 


NERVOUS   SYSTEM. 


FIG.  174.— Nerve-fibres  from  the  human  subject; 
magnified  850  diameters.  (Kolliker.) 

Four  small  fibres,  of  which  two  are  varicose,  one 
medium-sized  fibre  with  borders  of  single  con- 
tour, and  four  large  fibres ;  of  the  latter,  two 
have  a  double  contour,  and  two  contain  granu- 
lar matter. 


these  small  fibres,  which  seem  in  many  instances  to  be  simple  prolongations,  without 
alteration,  of  the  axis-cylinder  of  the  inedullated  fibres,  it  will  be  seen  that  they  are 
chiefly  found  in  the  peripheral  terminations  of  the  nerves  and  in  the  filaments  of  connec- 
tion of  the  fibres  with  the  cells.  The  study  ot 
the  fibres  in  these  relations  constitutes  the  most 
important  part,  physiologically,  of  the  anatomy 
of  the  nerves  and  presents  the  greatest  difficul- 
ties in  the  way  of  direct  observation ;  and,  for 
these  reasons,  we  shall  treat  of  these  questions  sep- 
arately, and  defer,  for  the  present,  the  full  con- 
sideration of  the  non-medullated  fibres. 

Gelatinous  Nerve-Fibres  (Fibres  of  Remalc}.— 
These  fibres  are  entirely  different  in  their  anat- 
omy from  either  of  the  varieties  of  fibres  just 
considered.  They  are  found  chiefly  in  the  sym- 
pathetic system  and  in  that  particular  portion  of 
this  system  connected  with  involuntary  move- 
ments. For  instance,  these  fibres  are  very  abun- 
dant in  the  gray  filaments  sent  to  parts  provided 
with  non-striated  muscular  fibres  and  endowed 
with  undoubted  motor  properties ;  but  they  are 
not  found  in  the  white  filaments  of  the  sympa- 
thetic, which  seem  to  be  incapable  of  exciting 
movements. 

There  is  considerable  difference  of  opinion 
among  physiologists  with  regard  to  the  gelatinous 
filaments.  Some  are  disposed  to  regard  them  as  elements  of  connective  tissue,  not 
endowed  with  properties  characteristic  of  nerves,  while  others  consider  that  they  are 
nerve-fibres,  probably  possessing  functions  distinct  from  those  of  the  fibres  of  different 
structure.  The  latter  is  the  view  now  adopted  by  the  best  anatomists.  While  it  is 
certain  that  elements  of  connective  tissue  exist  in  the  nerves,  and  that  these  have  been 
mistaken  for  true  nerve-fibres,  there  are  in  the  nerves,  particularly  in  those  belonging  to 
the  great  sympathetic  system,  fibres  exactly  resembling  the  nerve-fibres  of  the  embryon. 
These  are  the  true  gelatinous  nerve-fibres,  or  fibres  of  liemak.  It  is  stated  that  the 
nerves  generally  have  this  structure  up  to  the  fifth  month  of  intra-uterine  life,  and  that, 
m  the  regeneration  of  nerves  after  division  or  injury,  the  new  elements  assume  this 
form  before  they  arrive  at  their  full  development. 

The  true  gelatinous  nerve-fibres  present  the  following  characters  :  They  are  flattened, 
with  regular  and  sharp  borders,  grayish  and  pale,  presenting  numerous  very  fine  granu- 
lations, and  a  number  of  oval,  longitudinal  nuclei,  a  characteristic  which  has  given  them 
the  name  of  nucleated  nerve-fibres.  The  diameter  of  the  fibres  is  about  ^^  of  an  inch. 
The  nuclei  have  nearly  the  same  diameter  as  the  fibres  and  are  about  T^Vo-  of  an  inch 
in  length.  They  are  finely  granular  and  present  no  nucleoli.  The  fibres  are  rendered 
pale  by  the  action  of  acetic  acid,  but  they  are  slightly  swollen  only,  and  present,  in  this 
regard,  a  marked  contrast  with  the  elements  of  a  connective  tissue.  The  microscopical 
appearances  of  these  fibres,  which  are  strongly  characteristic,  are  represented  in  Fig.  1V5. 
Accessory  Anatomical  Elements  of  the  Nerves. — The  nerves  present,  in  addition  to  the 
different  varieties  of  true  nerve-fibres  just  described,  certain  accessory  anatomical  ele- 
ments common  to  nearly  all  of  the  tissues  of  the  organism,  such  as  connective  tissue, 
blood-vessels,  and  perhaps  lymphatics,  although  these  have  never  been  demonstrated, 
except  in  the  nerve-centres. 

Like  the  muscular  tissue,  the  nerves  are  made  up  of  their  true  anatomical  elements— 
the  nerve-fibres— held  together  into  primitive,  secondary,  and  tertiary  bundles,  and  so 


PHYSIOLOGICAL  ANATOMY  OF  THE   NERVOUS   TISSUE. 


569 


on,  in  proportion  to  the  size  of  the  nerve.  The  primitive  fasciculi  are  surrounded  by  a 
delicate  membrane,  described  by  Robin  under  the  name  ofperinevre,  but  which  had  been 
already  noted  by  other  anatomists  under  different  names.  This  membrane  is  homogeneous 
or  very  finely  granular,  sometimes  marked  with  longitudinal  striae,  and  possessing  elon- 
gated nuclei,  finely  granular,  from  ^^  to  -^^  of  an  inch  in 
length  by  from  -g-^7  to  3~oVo  °f  an  mcn  wide.  The  thickness  of 
the  membrane  is  from  1 2 1 0  6  to  8  ^  0  of  an  inch.  It  commences  at 
the  point  where  the  nerve-fibres  emerge  from  the  white  portion  of 
the  nervous  centres,  and  it  extends  to  their  terminal  extremities, 
being  interrupted  by  the  ganglia  in  the  course  of  the  nerves.  This 
membrane  generally  envelops  a  primitive  fasciculus  of  fibres,  branch- 
ing as  the  bundles  divide  and  pass  from  one  trunk  to  another ;  but 
it  is  sometimes  found  surrounding  single  fibres.  It  is  not  usually 
penetrated  by  blood-vessels,  the  smallest  capillaries  of  the  nerves 
ramifying  in  its  substance  but  seldom  passing  through  to  the  indi- 
vidual nerve-fibres.  Within  the  perinerve,  are  sometimes  found 
elements  of  connective  tissue,  with  very  rarely  a  few  capillary 
blood-vessels  in  the  largest  fasciculi. 

The  amount  of  fibrous  tissue  in  the  different  nerves  is  very 
variable  and  depends  upon  the  conditions  to  which  they  are  sub- 
jected. In  the  nerves  within  the  bony  cavities,  where  they  are 
entirely  protected,  the  fibrous  tissue  is  very  scanty ;  but,  in  the 
nerves  between  muscles,  we  find  a  tolerably  strong  investing  mem- 
brane or  sheath  surrounding  the  whole  nerve  and  sending  pro- 
cesses into  its  interior,  which  envelop  smaller  bundles  of  fibres. 
This  sheath  is  formed  of  inelastic  fibres,  with  small  elastic  fibres 
and  nucleated  connective-tissue  fibres.  These  latter  may  be  distin- 
guished from  the  gelatinous  nerve-fibres  by  the  action  of  acetic 
acid,  which  swells  and  finally  dissolves  them,  while  the  nerve- 
fibres  are  but  slightly  affected. 

The  late  researches  of  Sappey  have  shown  that  the  structure 
of  the  fibrous  sheath  of  the  nerves  possesses  certain  important 
anatomical  peculiarities.  The  greatest  part  of  this  membrane  is  composed  of  bundles 
of  white  inelastic  tissue,  interlacing  in  every  direction ;  but  it  contains  also  numerous 
elastic  fibres,  adipose  tissue,  a  net-work  of  arteries  and  veins,  and  "nervi-nervorum," 
which  are  to  these  structures  what  the  vasa-vasorum  are  to  the  blood-vessels.  The 
adipose  tissue  is  constant,  being  found  even  in  extremely  emaciated  persons. 

The  vascular  supply  to  most  of  the  nerves  is  rather  scanty.  The  arteries  break  up  into 
a  plexus  of  very  fine  capillaries,  arranged  in  oblong,  longitudinal  meshes  surrounding  the 
fasciculi  of  fibres ;  but  they  rarely  penetrate  the  perinerve,  and  they  do  not  usually  come  in 
contact  with  the  ultimate  nervous  elements.  The  veins  are  rather  more  voluminous  and 
follow  the  arrangement  of  the  arteries.  It  is  not  certain  that  the  nerves  in  their  course 
contain  lymphatics ;  at  least  these  vessels  have  never  been  demonstrated  in  their  substance. 

Branching  and  Course  of  the  Nerves. — The  ultimate  nerve-fibres  in  the  course  of  the 
nerves  have  no  connection  with  each  other  by  branching  or  inosculation.  A  bundle  of 
fibres  frequently  sends  branches  to  other  nerves  and  receives  branches  in  the  same  way ; 
but  this  is  simply  tbe  passage  of  fibres  from  one  sheath  to  another,  the  ultimate  fibres  them- 
selves maintaining  throughout  their  course  their  integrity  and  their  individual  physiologi- 
cal properties.  This  view  with  regard  to  the  course  of  the  fibres  in  the  nerves  is  held  by 
nearly  all  anatomists.  The  nerve-fibres  do  not  branch  or  inosculate  except  at  the  point 
where  they  change  their  character  just  before  their  termination.  The  branching  and  inos- 
culation of  the  ultimate  nerve-fibres  will  be  considered  in  connection  with  the  very  inter- 
esting and  important  question  of  their  ultimate  distribution  to  muscles  and  sensitive  parts. 


Fm.  175.— Fibres  of  Re- 
mak;  magnified  800 
diameters.  (Robin.) 

With  the  gelatinous  fibres, 
are  seen  two  of  the  or- 
dinary, dark-bordered 
nerve-fibres. 


570  NERVOUS  SYSTEM. 

Mode  of  Termination  of  the  Nerves  in  the  Voluntary  Muscles.— For  a  long  time,  the 
mode  of  termination  of  the  nerve-fibres  in  the  muscles  was  a  question  of  great  uncer- 
tainty;  but,  within  the  last  few  years,  thanks  to  the  elaborate  researches  of  French  and 
German  anatomists,  the  peripheral  extremities  of  the  nerves  have  been  so  accurately 
described  and  figured,  that  the  great  question  of  the  mode  of  connection  between  the 
anatomical  element  conducting  the  stimulus  to  the  muscles  and  the  contractile  elements 
of  the  muscles  themselves  may  be  considered  as  definitively  settled.  In  1840,  Doyere  gave 
an  account  of  the  peripheral  termination  of  the  motor  nerves,  probably  as  accurate  as 
was  possible  with  his  imperfect  means  of  investigation ;  but  this  observation,  though 
confirmed  a  few  years  later  by  Quatrefages,  seems  to  have  been  lost  sight  of  by  most 
physiological  writers.  Without  underestimating  the  value  of  other  researches,  we  may 
state  that  those  of  Rouget  represent,  perhaps,  the  present  condition  of  the  question  as 
well  as  any.  The  differences,  however,  between  the  most  reliable  observations  of  recent 
writers  are  nearly  all  unimportant ;  and,  while  future  investigations  may  enable  us  to  go 
farther  in  following  out  some  of  the  elements  of  the  nerve-fibres,  they  will,  in  all  probabil- 
ity, simply  extend  our  knowledge,  without  invalidating  the  information  already  acquired. 
The  observations  of  Rouget  were  published  in  1862  and  were  made  upon  lizards, 
frogs,  Guinea-pigs,  rats,  and  other  animals,  and  have  been  confirmed  in  the  human  subject. 
The  tissues  were  taken  either  from  the  living  animal  or  from  an  animal  just  killed,  and 
they  were  examined,  in  some  instances,  without  the  addition  of  reagents ;  but  the  most 
satisfactory  results  were  obtained  by  macerating  the  muscles  for  from  six  to  twenty-four 
hours  in  a  liquid  containing  T¥Vir  of  hydrochloric  acid,  and  adding  to  the  preparation  on 
the  glass  slide  a  drop  of  a  solution  of  sugar  in  water.  In  preparations  made  in  this  way, 
it  is  easy  to  trace  the  course  of  the  nerves  to  their  termination.  The  following  is  the 
description  given  by  Rouget : 

"  The  nervous  trunks  and  the  branches  of  distribution  generally  cross  the  course  of 
the  muscular  fibres.  As  regards  the  terminal  ramifications,  sometimes  they  meet  the 
muscular  fibres  at  nearly  a  right  angle,  and  sometimes  they  are  placed  nearly  parallel  to 
the  axis  of  the  primitive  fasciculi.  Branches  of  distribution  are  detached  sometimes 
from  branches  containing  two  or  three  fibres,  and  sometimes  from  isolated  fibres.  After 
a  very  short  course  these  tubes  divide,  and  may  present  as  many  as  seven  or  eight  suc- 
cessive divisions.  Most  commonly,  the  termination  takes  place  either  by  divisions  of  the 
second  or  third  order,  or  the  same  tube  gives  off,  successively,  divisions  which  pass  to  the 
adjacent  primitive  fasciculi  and  terminate  here  without  new  divisions  and  after  a  very 
short  course.  They  have  a  less  diameter  than  the  primitive  nerve-tubes,  but  they  pre- 
serve even  to  the  terminal  extremity  their  double  contour,  and  there  can  be  demonstrated, 
very  easily,  a  sheath  provided  with  nuclei,  a  medullary  layer,  and  the  axis-cylinder. 
Never  do  we  observe  at  the  termination  of  the  motor  nerves  the  pale  and  non-medullated 
fibres  described  by  Ktihne  and  Kolliker.  At  the  point  where  the  tube  terminates,  we 
remark  constantly  a  special  arrangement  which  has  no  analogy  with  that  which  has  been 
described  in  the  batrachia  by  these  two  observers,  and  which  Kuhne  believed  could  be 
extended  to  the  higher  vertebrata,  to  the  mammalia,  and  to  the  human  subject.  The 
nerve-tube,  with  a  double  contour,  preserving  still  a  diameter  of  from  ^Vff  to  ^Vfr  of  an 
inch  at  the  point  where  it  touches  the  primitive  fasciculus  to  become  arrested  at  its  sur- 
face, terminates  by  an  expansion  of  the  central  nerve-substance,  the  axis-cylinder,  which 
is  in  immediate  contact  with  the  contractile  fibres  (fibrillse)  of  the  primitive  fasciculus. 
The  layer  of  medullary  substance  ceases  abruptly  at  this  point,  the  sheath  of  the  tube  is 
spread  out  and  blended  with  the  sarcolemma ;  but  in  immediate  continuity  with  the  axis- 
cylinder,  a  layer,  a  plate  of  granular  substance,  from  -^Vc-  to  ^Vo  of  an  incn  in  thick- 
ness, is  spread  out  beneath  the  sarcolemma,  on  the  surface  of  the  fibrillse,  in  a  space 
generally  oval  and  about  ^^  of  an  inch  wide  in  its  short  diameter,  and  ^  of  an  inch 
in  its  long  diameter.  This  granular  substance  masks  more  or  less  completely,  in  the 
space  which  corresponds  to  it,  the  transverse  striae  of  the  muscular  fasciculus.  The  disk 


PHYSIOLOGICAL  ANATOMY   OF  THE  NERVOUS  TISSUE. 


571 


itself  has  exactly  the  granular  appearance  of  the  substance  of  the  axis-cylinder  in  the 
vertebrata,  and  of  that  of  the  nerve-tubes  in  most  of  the  invertebrata,  especially  after 
being  treated  by  diluted  acids.  But  that  which  essentially  characterizes  the  terminal 
plates  of  the  motor  nerves  is  an  agglomeration  of  nuclei  observed  at  their  site.  With  a 
low  magnifying  power,  even,  we  can  distinguish  the  point  where  a  nerve-tube  touches 
the  primitive  fasciculus  to  which  it  belongs,  and  ends  abruptly  at  its  surface,  by  a  collec- 
tion of  from  six  to  twelve  or  even  sixteen  nuclei  which  occupy  the  site  of  the  terminal 
plate.  These  nuclei  are  distinguished  by  their  size  as  well  as  by  their  form,  which  is  less 
elongated  than  the  nuclei  of  the  muscular  tissue  (connective- tissue  nuclei  of  the  primitive 
fasciculi).  They  present,  however,  the  most  complete  analogy  with  the  nuclei  of  the 
nerve-sheath  (connective-tissue  nuclei  of  the  nerves).  They  are,  without  any  doubt,  nothing 
else  than  the  nuclei  which,  scattered  throughout  the  entire  length  of  the  sheath,  are  col- 
lected in  a  mass  at  the  point  where  the  covering  of  the  nerve-fibre  is  spread  out  and  fuses 
with  the  sarcolemma  of  the  primitive  fasciculus." 

There  can  be  little  if  any  doubt  that  the  description  just  given  represents  the  mode 
of  termination  of  the  nerves  in  the  voluntary  muscles  in  man  and  in  the  mammalia.  The 
observations  of  Kolliker,  who  describes  a  plexus  of  pale  fibres  with  nuclei  instead  of  a 
well-defined  terminal  plate,  were  made  upon  frogs,  and  are  probably  correct ;  and  Kolli- 
ker admits  the  accuracy  of  the  observations  of  Rouget  as  regards  reptiles,  birds,  and  the 
mammalia. 

Although  the  sensibility  of  the  muscles  is  slight  as  compared  with  that  of  the  tegu- 
mentary  tissues,  they  undoubtedly  possess  nerve-fibres  other  than  those  exclusively 
devoted  to  motion.  In  addition  to  the  fibres  just  described,  Kolliker  and  some  others 
have  noted  fibres  with  a  different  mode 
of  termination.  These  Kolliker  believes 
to  be  sensitive  nerves,  and  their  mode  of 
termination  has  not  been  so  definitely  de- 
scribed as  that  of  the  fibres  with  terminal 
motor  plates.  We  refrain  from  giving  a 
very  full  description  even  of  what  has 
been  observed  with  regard  to  the  termi- 
nation of  these  fibres,  for  future  and 
more  successful  researches  will  probably 
modify  the  views  now  held  with  regard 
to  this  point.  Kolliker  states  that  the 
fibres  in  question  are  very  fine,  dark-bor- 
dered tubes,  with  a  medullated  sheath, 
which,  when  studied  in  muscular  tissue 
rendered  pale  by  acetic  acid,  may  be  seen 


FIG. 


176. — Mode  of  termination  of  the  motor  nerves. 
(Eouget.) 

A,  primitive  fasciculus  of  the  thyro-hyoid  muscle  of  the  human 

subject,  and  its  nerve-tube  :  1,1,  primitive  muscular  fas- 
ciculus; 2,  nerve-tube;  3,  medullary  substance  of  the 
tube,  which  is  seen  extending  to  the  terminal  plate,  where 
it  disappears ;  4,  terminal  plate  situated  beneath  the  sar- 
colemma, that  is  to  say,  between  it  and  the  elementary 
fibrillse;  5,  5,  sarcolemma. 

B,  primitive  fasciculus  of  the  intercostal  muscle  of  the  lizard, 

in  which  a  nerve-tube  terminates :  1,  1,  sheath  of  the 
nerve-tube ,  2,  nucleus  of  the  sheath ;  3,  8,  sarcolemma 
becoming  continuous  with  the  sheath :  4,  medullary  sub- 
stance of  the  nerve-tube  ceasing  abruptly  at  the  site  of  the 
terminal  plate ;  5,  5,  terminal  plate ;  6,  6,  nuclei  of  the 
plate ;  7, 7,  granular  substance  which  forms  the  principal 
element  of  the  terminal  plate,  and  which  is  continuous 
with  the  axis-cylinder ;  8,  8,  undulations  of  the  sarcolem- 
ma reproducing  those  of  the  fibrillae;  9,  9,  nuclei  of  the 
sarcolemma. 


to  give  off  exceedingly  fine,  non-medul- 
lated  fibres,  which  terminate  in  fibres  of 
the  same  appearance,  but  provided  with 
nuclei.  It  does  not  appear  to  be  certain 
how  these  fibres  end.  Kolliker  is  not 
satisfied  that  the  free  extremities,  as 
they  appear  to  be,  are  the  actual  termi- 
nations; but  he  asserts  that  in  some  rare 
instances  they  communicate  with  each 
other.  For  the  present  this  point  must 
be  considered  as  unsettled. 

Mode  of  Termination  of  the  Nerves  in  the  Involuntary  Muscular  Tissue. — The  nerves 
have  not  been  followed  out  so  satisfactorily  in  the  involuntary  as  in  the  striated  mus- 
cular system ;  and,  as  most  if  not  all  of  the  fibres  are  derived  from  the  sympathetic 


572 


NERVOUS  SYSTEM. 


system,  which  contains  numerous  fibres  of  Remak  the  terminations  of  which  have  not 
been  described,  it  is  evident  that  our  information  concerning  this  part  of  the  peripheral 
nervous  system  must  be  incomplete.  Perhaps  the  most  remarkable  of  the  late  observa- 
tions upon  this  point  are  those  of  Dr.  Frankenhaeuser,  upon  the  nerves  of  the  uterus. 
These  researches  were  very  elaborate ;  but  the  point  most  interesting  in  this  connection 
is  that  the  nerves,  having  formed  a  plexus  in  the  connective  tissue,  send  exceedingly 
small  fibres  into  the  sheets  or  layers  of  muscular-fibre  cells,  which  branch  and  finally  go 
into  the  nucleoli  of  these  structures.  Arnold  has  confirmed  these  observations  and  has 
shown  farther  that,  in  many  instances,  the  tine  terminal  nerve-fibres  branch  and  go  into 
the  nuclei  of  the  muscular  fibres  and  then  pass  out  to  join  with  other  fibres  and  form 
a  plexus. 

Termination  of  the  Nerves  in  Glands. — The  great  influence  which  the  nervous  system 
exerts  upon  secretion  attaches  considerable  interest  to  recent  researches  into  the  ultimate 
distribution  of  the  nerves  in  the  glands.  It  must  be  remembered,  however,  in  these,  as 
in  all  observations  upon  the  destination  of  the  smallest  nerve-fibres,  that  the  problem  is 
one  of  the  most  difficult  in  the  whole  range  of  minute  anatomy ;  and  the  results  arrived 
at  must  be  received  with  a  certain  amount  of  caution,  until  they  shall  have  been  amply 
confirmed. 


FIG.  Ill —Termination  of  the  nerves  in  the  salivary  glands.    (Pfliiger.) 
I,  II,  branching  of  the  nerves  between  the  glandular  cells ;  III,  terminations  of  the  nerves  in  the  nuclei  of  the  cells  ; 

IV,  multipolar  nerve-cell. 

The  researches  of  Pfluger  upon  the  salivary  glands  leave  no  doubt  as  to  the  fact  that 
medullated  nerve-fibres  pass  to  the  cells  of  Jhese  organs  and  there  abruptly  terminate,  at 
least  as  dark -bordered  fibres.  This  author  believes,  however,  that,  having  formed  a  more 
or  less  branching  plexus,  non-medullated  fibres  pass  directly  into  the  glandular  cells,  and 
he  gives  figures  which  seem  to  illustrate  this  arrangement  pretty  clearly.  The  same 
observer  describes  and  figures  multipolar  cells,  mixed  with  the  glandular  cells,  in  which 
some  of  the  nerve-fibres  terminate. 

Modes  of  Termination  of  the  Sensory  Nerves.— There  are  undoubtedly  several  modes 

f  termination  of  the  sensitive  nerves  in  integument  and  in  mucous  membranes,  some  of 

which  have  been  accurately  enough  described,  while  others  are  still  somewhat  uncertain. 

"the  first  place'  anatom«sts  now  recognize  three  varieties  of  corpuscular  terminations, 

ring  m  their  structure,  probably,  according  to  the  different  functions  connected  with 

ation,  with  which  the  parts  are  endowed.     In  addition,  it  is  probable  that  many 

sensitive  nerves  are  connected  with  the  hair- follicles,  which  are  so  largely  distributed 


PHYSIOLOGICAL  ANATOMY   OF  THE  NERVOUS   TISSUE. 


573 


throughout  the  cutaneous  surface.  There  are,  also,  terminal  filaments  not  connected 
with  any  special  organs,  some  of  them,  perhaps,  ending  simply  in  free  extremities,  and 
some  connected  with  epithelium.  There  is  still  considerable  difference  of  opinion 
among  anatomists  concerning  all  of  these  various  points,  but,  with  regard  to  the  terminal 
corpuscles,  these  differences  are  purely  anatomical,  and  they  do  not  materially  affect  our 
ideas  of  the  physiology  of  sensation.  We  do  not  propose,  therefore,  to  enter  fully  into  the 
discussions  upon  these  questions,  and  we  shall  simply  present  what  seem  to  be  the  most 
reasonable  views  of  the  latest  and  most  reliable  observers. 

Corpuscles  of  Pacini,  or  of  Vater. — These  corpuscles,  which  were  the  first  discovered 
and  described  in  connection  with  the  sensitive  nerves,  were  called  corpuscles  of  Pacini, 
until  it  was  shown  that  they  had  been  seen  about  a  century  and  a  half  ago  by  Vater. 
Their  actual  mode  of  connection  with  the  nerves,  however,  has  only  been  ascertained 
within  the  last  few  years.  The  following  are  the  measurements  of  these  bodies  and  the 
situations  in  which  they  are  found,  taken  from  Kolliker : 

In  man,  these  corpuscles  are  oval  or  egg-shaped  and  measure  from  -£-$  to  -|-  of  an  inch 
in  length.  They  are  always  found  in  the  subcutaneous  layer  on  the  palms  of  the  hands 
and  the  soles  of  the  feet,  and  are  most  numerous  on  the  palmar  surfaces  of  the  fingers 
and  toes,  particularly  the  third  phalanges.  In  the  entire  hand  there  are  about  six  hun- 
dred, and  about  the  same  number  on  the  feet.  They  are  sometimes,  but  not  constantly, 
found  in  the  following  situations:  The  dorsal  surfaces  of  the  hands  and  feet,  on  the 
cutaneous  nerves  of  the  arm,  the  forearm  and  the  neck,  the  internal  pudic  nerve,  the 
intercostal  nerves,  all  of  the  articular  nerves  of  the  extremities,  the  nerves  beneath  the 
mammary  glands,  the  nerves  of  the  nipples,  and  in  the  substance  of 
the  muscles  of  the  hands  and  feet.  They  are  found  without  excep- 
tion on  all  of  the  great  plexuses  of  the  sympathetic  system,  in  front 
of  and  by  the  sides  of  the  abdominal  aorta,  and  behind  the  peri- 
toneum, particularly  in  the  vicinity  of  the  pancreas.  They  some- 
times exist  in  the  mesentery  and  have  been  observed  near  the 
coccygeal  gland. 

The  structure  of  the  corpuscles  consists  simply  of  several  layers 
of  connective  tissue  enclosing  a  central  bulb  in  which  is  found 
the  terminal  extremity  of  the  nerve.  This  bulb  is  finely  granu- 
lar, nucleated,  and  is  regarded  by  most  anatomists  as  composed 
of  connective  tissue.  At  the  base  of  the  corpuscle,  is  a  pedicle 
formed  of  connective  tissue  surrounding  a  medullated  nerve-fibre 
which  penetrates  the  corpuscle  and  terminates  in  the  central  bulb. 

The  only  really  important  point  of  discussion  with  reference  to 
the  structure  of  the  nerve-fibre  in  the  central  bulb,  and  this  is 
purely  anatomical,  is  whether  or  not  the  medullary  substance  ex- 
tend into  the  corpuscle  itself.  Probably  the  fibre  is  here  reduced 
simply  to  the  axis- cylinder.  All  anatomists  agree  that  a  single 
thin,  flat  fibre  penetrates  the  corpuscle  and  terminates  near  its 
summit  by  a  slightly  -  enlarged  and  granular  extremity.  The 
arrangement  of  the  different  anatomical  elements  is  shown  in 
Fig.  178. 

The  situation  of  these  corpuscles  beneath,  instead  of  in  the 
substance  of  the  true  skin,  shows  that  they  cannot  be  properly 
considered  as  tactile  corpuscles,  a  name  which  is  applied  to  other 
structures  situated  in  the  papillaa  of  the  corium  ;  and  it  is  impos- 
sible to  assign  to  them  any  special  function  connected  with  sen- 
sation, such  as  the  sense  of  temperature,  or  the  appreciation  of 
pressure  or  weight.  All  that  we  can^say  with  regard  to  them  is  that  they  constitute 
one  of  the  several  modes  of  termination  of  the  nerves  of  general  sensibility. 


FIG.  .—acnan  cor- 
puscles. (Sappey.) 

1,  base  of  the  corpuscle ;  2, 
apex ;  3,  3,  3,  substance 
of  the  corpuscle,  in  lay- 
ers ;  4,  4,  nerve  pene- 
trating the  corpuscle ; 
5,  cavity  of  the  corpus- 
cle ;  6,  nerve ;  7,  nerve, 
which  has  lost  its  rr>e- 
dullary  substance  and 
sheath  ;  8,  termination 
of  the  nerve  ;  9.  pranu- 
lar  substance  continuous 
with  the  nerve. 


574  NERVOUS  SYSTEM. 

Tactile  Corpuscles.— The  name  tactile  corpuscles  implies  that  these  bodies  are  con- 
nected with  the  sense  of  touch ;  and  this  view  is  sustained  by  the  fact  that  they  are 
found  almost  exclusively  in  parts  endowed  to  a  marked  degree  with  tactile  sensibility. 
They  are  sometimes  called  the  corpuscles  of  Meissner  and  Wagner,  after  the  anatomists 
by  whom  they  were  first  described.  The  true  tactile  corpuscles  are  found  in  greatest 
number  on  the  palmar  surfaces  of  the  hands  and  fingers  and  the  plantar  surfaces  of  the 
feet  and  toes.  They  exist,  also,  in  the  skin  on  the  backs  of  the  hands  and  feet,  the  nip- 
ples, and  a  few  on  the  anterior  surface  of  the  forearm.  As  we  shall  see  when  we  come 
to  describe  them  fully,  they  are  situated  in  the  substance  of  the  papillae  of  the  skin,  and 
they  cannot  fail  to  have  an  important  function  in  connection  with  the  sense  of  touch. 

We  have  already  treated  of  the  general  structure  of  the  skin  and  have  seen  that  the 
largest  papillae,  measuring  from  ^  to  -fa  of  an  inch  in  length,  are  found  on  the  hands, 
feet,  and  nipples,  precisely  where  the  tactile  corpuscles  are  most  abundant.  Corpuscles  do 
not  exist  in  all  papilla3,  and  they  are  found  chiefly  in  those  called  compound.  In  a  space 
of  about  7V  of  an  inch  square  on  the  third  phalanx  of  the  index-finger,  Meissner  counted 
four  hundred  papilla?,  in  one  hundred  and  eight  of  which  he  found  tactile  corpuscles,  or 


FIG.  179. — Papillce  of  the  skin  of  the  palm  of  the  hand.     (Sappey.) 

1,  papilla  with  two  vascular  loops ;  2,  papilla  with  a  tactile  corpuscle ;  3,  papilla  with  three  vascular  loops ;  4,  5,  large 
compound  papillae ;  6,  6,  vascular  net-work  beneath  the  papilhe ;  7,  7,  7,  7,  vascular  loops  in  the  papilla? ;  8,  8,  8,  8, 
nerves  beneath  the  papilte ;  9,  9, 10, 11,  tactile  corpuscles. 

about  one  in  four.  In  the  same  space  on  the  second  phalanx,  he  found  forty  corpuscles ; 
on  the  first  phalanx,  fifteen  ;  eight  on  the  skin  of  the  hypothenar  eminence  ;  thirty-four 
on  the  plantar  surface  of  the  ungual  phalanx  of  the  great-toe ;  and  seven  or  eight  in  the 
skin  on  the  middle  of  the  sole  of  the  foot.  In  the  skin  of  the  forearm,  the  corpuscles  are 
very  rare.  Kolliker  states,  also,  that  the  tactile  corpuscles  usually  occupy  special  papillae, 
which  are  not  provided  with  blood-vessels ;  so  that  the  papilla  of  the  hand  may  be 
properly  divided  into  vascular  and  nervous. 

The  form  of  the  tactile  corpuscles  is  oblong,  with  their  long  diameter  in  the  direction 
of  the  papillae.  Their  length  is  from  ^  to  ^  of  an  inch.  In  the  palm  of  the  hand, 
they  are  from  -^  to  -j-i^  of  an  inch  long,  and  from  -^  to  -^  of  an  inch  in  thickness. 
They  are  generally  situated  at  the  summits  of  the  secondary  eminences  of  the  compound 
papillae.  According  to  Kolliker,  the  tactile  corpuscles  consist  of  a  central  bulb  of  homo- 
geneous or  slightly-granular  connective-tissue  substance,  analogous  to  the  central  bulb 
of  the  Pacinian  corpuscles,  and  a  covering.  Treated  with  acetic  acid,  the  covering  pre- 
sents numerous  elongated  nuclei  arranged  in  a  circular  manner,  which  he  believes  to  be 
nuclei  of  connective  tissue,  and  a  few  fine  elastic  fibres.  One,  two,  and  sometimes  three 
or  four  dark-bordered  nerve-fibres  pass  from  the  subcutaneous  nervous  plexus  to  the 
base  of  each  corpuscle.  These  surround  the  corpuscle  with  two  or  three  spiral  turns, 
and  they  terminate  by  pale  extremities  at  the  surface  of  the  central  bulb.  This  arrange- 
ment is  shown  in  Fig.  180. 


PHYSIOLOGICAL  ANATOMY   OF  THE  NERVOUS   TISSUE. 


575 


Terminal  Bulls. — Under  this  name,  a  variety  of  corpuscles  has  lately  been  described 
by  Krause,  as  existing  in  the  conjunctiva  covering  the  eye  and  in  the  semilunar  fold,  in 
the  floor  of  the  buccal  cavity,  the  tongue,  the  glans  penis,  and  the  clitoris.  They  bear 
some  analogy  to  the  tactile  corpuscles,  but  they  are  much  smaller  and  more  simple  in 
their  structure.  They  form  simply  a  rounded  or  oblong  enlargement  at  the  ends  of  the 
nerves,  which  is  composed  of  homogeneous  matter,  with  an  exceedingly  delicate  invest- 
ment of  connective  tissue.  They  measure  from  y^-^  to  -^-Q  of  an  inch  in  diameter.  In  the 
parts  provided  with  papillaa,  they  are  situated  at  the  summits  of  the  secondary  elevations. 


FIG.  ISO.— Cutaneous  papilla  and  tactile  corpuscle. 
(Kolliker.) 

«,  cortical  layer  with  plasmatic  cells  and  fine  elastic  fibres ;  &, 
tactile  corpuscle,  with  transverse  nuclei;  c,  afferent  ner- 
vous branch,  with  its  nucleated  neurilemma  ;  c?,  d,  nerve- 
fibres  encircling  the  corpuscle  ;  e,  the  apparent  termination 
of  one  of  these  fibres. 

The  arrangement  of  the  nerve-fibres  in  these 
corpuscles  is  very  simple.  One,  two,  or  three 
medullated  fibres  pass  from  the  submucous 
plexus  to  the  corpuscles.  The  investing  sheath 
of  the  fibres  is  here  continuous  with  the  connec- 
tive-tissue covering  of  the  corpuscle,  and  the 
nerve-fibres  pass  into  the  corpuscle,  break  up 
into  two  or  three  divisions,  and  terminate  in 
convoluted  or  knotted  coils.  The  nerve-fibres 
are  medullated  for  a  certain  distance,  but  their 
terminations  are  generally  pale.  The  above  is 
one  form  of  these  corpuscles.  Sometimes,  how- 
ever, the  terminal  bulbs  are  oblong,  and  some- 
times but  a  single  nerve-fibre  penetrates  the 
bulb  and  terminates  in  a  simple  pale  filament. 
The  principal  forms  of  the  terminal  bulbs  are 
shown  in  Fig.  181. 

General  Mode  of  Termination  of  the  Sen- 
sory Nerves. — The  actual  termination  of  the  sen- 
sitive nerves  upon  the  general  surface  and  in 
mucous  membranes  is  still  a  question  of  great 
obscurity.  Although  we  have  arrived  at  a 

pretty  definite  knowledge  of  the  sensitive  corpuscles,  it  must  be  remembered  that  there 
is  an  immense  cutaneous  and  mucous  surface  in  which  no  corpuscles  have  as  yet  been 
demonstrated;  and  it  is  in  these  parts,  endowed  with  what  we  may  call  general  sensi- 


Fio.181.—  Corpuscles  of  Krause.     (Ludden.) 

A,  three  corpuscles  of  Krause  from  the  conjunctiva 

of  man,  treated  with  acetic  acid ;  magnified  300 
diameters :  1,  spherical  corpuscle,  with  two 
nerve-fibres  which  form  a  knot  in  its  interior. 
Portions  of  two  pale  nerve-fibres  are  also  seen. 
2,  a  rounded  corpuscle  presenting  a  nerve-fibre 
and  fatty  granulations  in  the  internal  bulb;  3, 
an  elongated  corpuscle  with  a  distinct  terminal 
fibre.  In  these  three  corpuscles,  the  covering, 
nucleated  in  1  and  2,  is  distinguished. 

B,  terminal  bulbs  from  the  conjunctiva  of  the  calf, 

treated  with  acetic  acid ;  magnified  300  diame- 
ters :  1,  extremity  of  a  nerve-fibre  with  its 
bulb ;  2,  double  bifurcation  of  a  nerve-fibre,  with 
two  terminal  bulbs;  a,  covering  of  the  terminal 
bulbs ;  &,  internal  bulb ;  c, 


576  NERVOUS  SYSTEM. 

bility,  as  distinguished  from  the  sense  of  touch,  that  we  have  to  study  the  mode  of  ter- 
mination of  the  nerves. 

Kolliker  is  of  the  opinion  that,  in  the  immense  majority  of  instances,  the  sensitive 
nerves  terminate  in  some  way  in  the  hair-follicles.  If  this  be  true,  it  will  account  for 
the  termination  of  the  nerves  in  by  far  the  greatest  portion  of  the  skin,  as  there  are  few 
parts  in  which  hair-follicles  do  not  exist;  but,  unfortunately,  the  exact  mode  of  connec- 
tion of  the  nerves  with  these  follicles  is  not  apparent.  The  following  is  all  we  know 
positively  of  the  terminations  of  the  nerves  on  the  general  surface  : 

Medullated  nerve-fibres  form  a  plexus  in  the  deeper  layers  of  the  true  skin,  from 
which  fibres,  some  pale  and  nucleated  and  others  medullated,  pass  to  the  hair-follicles, 
divide  into  branches,  penetrate  into  their  interior,  and  are  there  lost.  A  certain  number 
of  fibres  pass  to  the  non-striated  muscular  fibres  of  the  skin.  A  certain  number  pass  to 
papilla  and  terminate  in  tactile  corpuscles,  and  others  pass  to  papilla  that  have  no  tac- 
tile corpuscles. 

In  the  mucous  membranes,  as  far  as  we  know,  the  mode  of  termination  is,  in  general 
terms,  by  a  delicate  plexus  just  beneath  the  epithelium,  coming  from  a  submucous  plexus 
analogous  to  the  deep  cutaneous  plexus.  In  certain  membranes,  we  have  already  noted 
the  termination  in  bulbs  (corpuscles  of  Krause).  In  the  cornea,  the  fibres  have  been 
followed  more  minutely  than  in  any  other  situation,  and  the  results  of  recent  researches 
upon  this  subject  are  very  remarkable.  These  results  are  so  recent  and  unexpected,  that 
we  are  hardly  prepared  to  admit  them  unreservedly  without  full  confirmation.  At 
present  we  can  only  state  that  the  observations  of  Hover,  Lipmann,  and  others,  con- 
firmed in  part  by  Kolliker,  seem  to  show  that  branching  nerve-fibres  pass  to  the  nucleoli 
of  the  corpuscles  of  the  cornea  and  to  the  nucleoli  of  the  cells  of  the  posterior  layer  of 
epithelium. 

Structure  of  the  Nerve-centres. 

A  peculiar  pigmentary  matter  in  the  nerve-cells  and  the  surrounding  granular  sub- 
stance gives  to  the  nerve-centres  a  grayish  color,  by  which  they  are  readily  distinguished 
from  the  white,  or  fibrous  division  of  the  nervous  system.  Wherever  this  gray  matter  is 
found,  the  anatomical  elements  of  the  tissue  are  cellular,  except  in  the  nerves  formed  of 
gray,  or  gelatinous  fibres.  Under  the  general  division  of  nerve-centres,  we  include,  ana- 
tomically at  least,  the  gray  matter  of  the  cerebro-sfinal  centres,  the  ganglia  of  the  roots 
of  the  spinal  and  certain  of  the  cranial  nerves,  and  the  numerous  ganglia  of  the  sympa- 
thetic system.  In  these  parts  are  found  cells,  which  constitute  the  essential  anatomical 
element  of  the  tissue,  granular  matter  resembling  the  contents  of  the  cells,  pale  fibres 
originating  in  prolongations  of  the  cells,  elements  of  connective  tissue,  delicate  mem- 
branes enveloping  some  of  the  cells,  and  blood-vessels.  The  most  interesting  and  im- 
portant of  these  structures,  in  their  physiological  relations,  are  the  cells  and  the  prolon- 
gations by  which  they  are  connected  with  the  nerves. 

Nerve- cells. — Anatomists  are  now  pretty  well  agreed  that  the  following  varieties  of 
cells  exist  in  the  nerve-centres  and  constitute  their  essential  anatomical  elements ;  viz., 
apolar,  unipolar,  bipolar,  and  multipolar  cells.  Although  some  have  denied  the  existence 
of  apolar  cells,  there  can  be  little  doubt  of  their  presence  in  the  centres  in  small  numbers, 
and,  as  is  suggested  by  Kolliker,  they  may  be  nerve-cells  in  an  imperfect  state  of  devel- 
opment. The  nerve-cells  present  great  differences  in  their  size  and  general  appearance, 
and  some  distinct  rarieties  are  found  in  particular  portions  of  the  nervous  system  and 
are  probably  connected  with  special  functions. 

The  apolar  cells  are  simply  rounded  bodies,  with  granular  contents,  a  nucleus  and 
nucleolus  like  other  cells,  but  without  any  prolongations  connecting  them  with  the  nerve- 
fibres.  They  have  been  observed  in  the  cerebro-spinal  centres,  and  they  always  exist  in 
the  sympathetic  ganglia.  Thoss  who  deny  their  existence  believe  that  the  poles  have 


STKUCTUKE   OF  THE   NERVE-CENTRES. 


577 


been  detached  in  preparing  specimens  for  examination.  Unipolar  cells  exist  in  some  of 
the  lower  orders  of  animals,  but  their  presence  in  the  human  subject  is  doubtful.  Bipo- 
lar cells  are  found  in  the  ganglia  of  the  posterior  roots  of  the  spinal  nerves,  where  they 
are  of  considerable  size.  Smaller  bipolar  cells  are  found  in  the  sympathetic  ganglia. 
Multipolar  cells  present  three  or  more  prolongations. 

Small  cells,  with  three,  and  rarely  four  prolongations,  are  found  in  the  posterior  cor- 
nua  of  the  gray  matter  of  the  spinal  cord.  From  their  situation  they  have  been  called 
sensory  cells.  They  are  undoubtedly  found  in  greatest  number  in  parts  known  to  be 
endowed  exclusively  with  sensory  properties. 

Large,  irregularly-shaped  multipolar  cells,  with  numerous  prolongations,  are  found 
chiefly  in  the  anterior  cornua  of  the  gray  matter  of  the  spinal  cord,  and  these  have  been 
called  motor  cells.  They  sometimes  present  as  many  as  ten  or  twelve  poles. 

With  all  these  differences  in  the  size  and  form  of  the  nerve-cells,  they  present  toler- 
ably uniform  general  characters  as  regards  their  structure  and  contents.  Leaving  out  the 
apolar  and  unipolar  cells,  the  perfectly-developed  cells  are  of  an  exceedingly  irregular 
shape,  with  strongly-refracting,  granular  contents,  frequently  a  considerable  number  of  pig- 
mentary granules,  and  with  a  distinct  nucleus  and  nucleolus.  The  nucleus  in  the  adult  is 


FIG.  182. — Nerve-cell  from  the  ferruginous  substance  which  forms  the  floor  of  the  rhornboidal  sinus,  in  man; 

magnified  350  diameters.    (Kolliker.) 

almost  invariably  single,  although,  in  very  rare  instances,  two  have  been  observed.  Cells 
with  multiple  nuclei  are  often  observed  in  young  animals.  The  nucleoli  are  usually  single 
but  there  may  be  as  many  as  four  or  five.  The  strongly-refracting  contents,  the  peculiar 
shape,  and  the  poles  or  prolongations,  give  to  the  nerve-cells  an  exceedingly  characteristic 
appearance,  which  is  represented  in  Fig.  182. 

The  diameter  of  the  cells  is  as  variable  as  their  form.  They  usually  measure  from 
T^Vo  to  TffT  °f  an  incn »  but  there  are  many  of  larger  size,  and  some  are  smaller.  The 
nuclei  measure  from  ^-J^  to  -j^Vo  °*  an  inch. 

The  nerve-cells  are  so  delicate  and  so  prone  to  alteration,  that  their  study  is  exceed- 
37 


578 


NEKVOUS  SYSTEM. 


ingly  difficult.  Sections  of  the  nerve-centres  must  be  prepared  with  great  care,  and 
they  are  not  easily  made  and  preserved.  In  the  numerous  anatomical  investigations  that 
have  been  made  within  the  last  few  years,  the  centres  have  generally  been  hardened 
artificially;  and  almost  every  investigator  has  used  different  processes  and  reagents, 
which  may  account  in  a  measure  for  the  differences  of  opinion  that  now  exist  upon  all 
points  connected  with  the  minute  anatomy  of  these  parts. 

There  is,  at  the  present  time,  considerable  discussion  with  regard  to  the  intimate 
structure  of 'the  substance  of  the  nerve-cells,  their  nuclei  and  nucleoli,  and  the  points 
involved  have  a  certain  amount  of  physiological  interest.  In  the  first  place,  the  transverse 
striae  in  the  axis-cylinder  treated  with  nitrate  of  silver,  noted  by  Frommann  and  confirmed 
by  Grandry  and  others,  have  been  observed  by  Grandry  in  the  substance  of  the  nerve- 
cells.  While  this  fact,  perhaps,  shows  that  the  substance  contained  in  the  cells  and  their 
prolongations  is  the  same  as  the  substance  of  the  axis-cylinder,  as  we  stated  with  regard 
to  the  axis-cylinder,  it  is  possible  that  the  markings  may  be  entirely  artificial,  and  that 
they  do  not  demonstrate  the  existence  of  two  distinct  substances  in  the  tissue. 


FIG.  183.—  Trawvertsc  section  of  the  gray  substance  of  the  anterior  cornua  of  the  spinal  ccrd  of  the  oa\  treated 

with  nitrate  of  silver.    (Grandry.) 

The  most  interesting  question  with  regard  to  the  structure  of  the  nerve-cells  relates 
to  the  mode  of  origin  of  their  fibres  or  poles.  Until  quite  recently,  these  have  been 
regarded  as  simple  prolongations  of  the  substance  of  the  cells ;  but  lately  the  view  has 
been  advanced  that  the  nerve-cells,  in  the  human  subject,  are  composed  of  regular  fibrils 
continuous  with  the  poles  and  starting,  as  it  were,  from  the  nucleoli.  The  fibrillation  of 
the  nerve-cells  and  their  prolongations  is  figured  by  Schultze  in  an  article  in  one  of  the 
most  authoritative  of  the  recent  works  on  histology  (Strieker) ;  but  some  other  eminent 
observers  have  failed  to  note  the  appearances  here  described,  at  least  in  the  human  sub- 
ject and  in  the  mammalia.  With  our  present  knowledge  of  the  physiology  of  the  nerve- 
cells,  the  question  whether  or  not  their  substance  be  fibrillated  has  little  more  than  .an 
anatomical  interest ;  but  there  can  be  no  doubt  that  the  cells  in  some  of  the  lower  orders 


STRUCTURE   OF   THE   NERVE-CENTRES. 


579 


of  animals  possess  striations  more 
or  less  regular.  These,  indeed, 
were  described  soon  after  the  cells 
were  discovered.  While  there  is 
no  anatomist  who  denies  the  fact 
that  the  substance  of  the  cells  is 
marked  by  striae  in  many  animals, 
the  existence  of  an  analogous  ar- 
rangement in  the  human  subject 
is  still  doubtful.  Some  anatomists, 
with  Schultze,  admit  the  striations 
but  have  failed  to  connect  them 
with  the  nuclei  and  nucleoli.  All 
admit  that  they  are  demonstrated 
with  great  difficulty;  and,  while 
this  question  is  so  important  that 
it  can  hardly  be  neglected  in  study- 
ing the  physiological  anatomy  of 
the  nerve-centres,  it  is  one  con- 
cerning which  it  seems  impossible 
to  express  a  positive  and  definite 
opinion. 

Connection  of  the  Nerve-cells 
with  the  Fibres  and  with  each  other. 
— Although  the  mode  of  connec- 
tion of  the  nerve-cells  with  the 
fibres  and  with  each  other  is  one 
of  the  most  important,  in  its  physi- 
ological bearings,  of  all  the  points 
connected  with  the  minute  anat- 
omy of  the  nerve-centres,  it  is  im- 
possible, in  the  present  state  of  our 
anatomical  knowledge,  to  answer 
the  questions  involved  in  a  manner 
entirely  satisfactory.  A  full  dis- 
cussion of  the  different  opinions 
and  the  methods  of  investigation 
that  have  been  employed  would 
be  out  of  place  in  this  work.  The 
difficulties  in  the  way  of  arriving 
at  positive  information  upon  these 
questions  are  the  following : 

1.  The  nerve-cells   and   their 
prolongations  are  so  delicate  and 
easily  torn   that  they  cannot  be 
isolated  and  followed  for  any  con- 
siderable distance,  and  theoretical 
considerations   are   constantly  re- 
quired to  fill  up  the  deficiencies 
in  actual  observation. 

2.  In  the  study  of  sections  of 

the  nerve-centres,  the  parts  must  be  hardened  and  afterward  rendered  transparent  by 


FIG.  184. — Nerve- cell  from  the  anterior  cornua  of  the  spinal  cord 
of  the  calf,  maeeratedfor  a  short  time  in  iodised  serum  ;  mag- 
nified 600  diameters.    (Schultze.) 
a,  a,  axis-cylinder  prolongation;  b,  b,  5,  5,  branching  prolongations. 


580  NERVOUS  SYSTEM. 

reagents,  which  must  produce  more  or  less  change  in  the  structures;  and  it  seems  an 
anatomical  impossibility  to  make  these  sections  so  as  to  follow  out  the  prolongations  of 
the  cells  far  enough  to  establish  beyond  doubt  their  exact  relations. 

These  two  considerations  alone  are  sufficient  to  account  for  the  uncertainty  so  appar- 
ent even  in  the  most  successful  investigations  into  the  anatomy  of  the  central  nervous 
system ;  and  we  shall  content  ourselves,  in  view  of  these  facts,  with  giving  a  summary 
Of  what  seems  to  be  the  probable  relation  of  the  cells  to  the  fibres  of  origin  of  the  nerves 
and  to  each  other. 

Apolar  cells,  if  they  exist  at  all  and  be  not  cells  from  which  the  poles  have  become 
separated,  are  simple,  rounded  bodies,  lying  between  the  fibres,  with  which  they  have  no 
other  relation  than  that  of  mere  contiguity.  Unipolar  cells  have  but  one  prolongation, 
which  is  continuous  with  a  nerve-fibre.  It  is  not  certain  that  these  exist  in  the  human 

subject. 

Bipolar  cells  are  found  in  the  ganglia  of  the  posterior  roots  of  the  spinal  nerves  and  in 
some  of  the  sympathetic  ganglia.  In  many  of  the  lower  animals,  particularly  in  fishes, 
the  cells  of  the  ganglia  of  the  spinal  nerves  are  simple,  nucleated  enlargements  in  the 
course  of  the  sensitive  nerve-fibres,  and  many  anatomists  have  inferred  that  the  same 
arrangement  exists  in  man  and  in  the  mammalia  ;  but  the  constitution  of  these  ganglia  in 
the  higher  classes  of  animals  seems  to  be  entirely  different.  In  the  first  place,  the  roots 
of  the  spinal  nerves  at  the  ganglia  are  undoubtedly  reenforced  by  the  addition  of  new 
fibres,  as  Kolliker  has  shown  by  actual  measurement,  the  roots  being  sensibly  larger 
beyond  the  ganglia,  while  the  filaments  of  entrance  and  exit  have  the  same  diameter. 
Direct  observation  upon  the  ganglia  in  man  also  fails  to  show  the  arrangement  which  is 
so  clearly  demonstrable  in  fishes.  The  cells  in  the  posterior  roots  are  not  continuous  with 
the  fibres  passing  from  the  periphery  to  the  cord,  but  they  give  origin  to  new  fibres, 
generally  two  in  number,  which  sometimes  are  single,  and  sometimes  bifurcated,  and 
which  pass,  in  by  far  the  greatest  number  of  instances,  if  not  in  all,  to  the  periphery. 

The  multipolar  cells,  with  three  or  more  prolongations,  are  found  in  all  of  the  ganglia, 
but  they  predominate  largely  in  the  gray  matter  of  the  cerebro-spinal  centres.  It  is  the 
question  of  the  exact  mode  of  connection  between  these  cells  and  the  fibres  of  origin  of 
the  cerebro-spinal  nerves  and  the  union  of  the  cells  with  each  other  by  commissural  pro- 
longations, that  presents  the  greatest  difficulty  and  uncertainty.  One  point,  which  has 
been  raised  within  a  few  years,  is  with  regard  to  the  character  of  the  different  poles 
connected  with  the  same  cell.  In  ordinary  preparations  of  the  central  nervous  system, 
it  is  impossible,  even  with  the  highest  available  magnifying  powers,  to  distinguish  any 
one  pole  which,  in  its  general  characters  and  connections,  is  different  from  the  others ; 
yet,  some  anatomists  describe  a  single  pole,  more  distinct  in  its  outlines  than  the 
others,  which  does  not  branch  and  is  to  be  regarded  as  an  axis-cylinder.  The  other  poles 
are  supposed  to  be  of  a  different  character,  not  connected  with  the  nerve-fibres,  and 
always  presenting  a  greater  or  less  number  of  branches.  These  views  are  accepted  by 
Schultze,  who  gives  a  figure,  after  Deiters,  in  which  the  contrast  between  the  poles  is 
represented  as  very  marked ;  but,  although  this  opinion  is  accepted  by  other  high  authori- 
ties, it  is  not  easy  to  understand  how  it  can  be  received  without  reserve,  when  it  is  so 
difficult,  if  not  impossible,  to  follow  out  the  poles,  except  for  a  very  short  distance. 

With  our  present  means  of  investigation,  there  seems  to  be  no  doubt  with  regard  to 
the  following  facts :  Tracing  the  nerve-fibres  toward  their  origin,  they  are  seen  to  lose 
their  investing  membrane  as  soon  as  they  pass  into  the  white  portion  of  the  centres,  being 
here  composed  only  of  the  medullary  substance  surrounding  the  axis-cylinder.  They 
then  penetrate  the  gray  substance,  in  the  form  of  axis-cylinders,  losing  here  the  medul- 
lary substance.  In  the  gray  substance,  it  is  impossible  to  make  out  all  of  their  rela- 
tions distinctly,  and  we  cannot  assume,  as  a  matter  of  positive  demonstration,  that  all 
of  them  are  connected  with  the  poles  of  the  nerve-cells.  Still,  it  has  been  shown, 
in  the  gray  matter  of  the  spinal  cord,  that  many  of  the  fibres  are  actual  prolongations 


STRUCTURE   OF  THE   NERVE-CENTRES. 


581 


FIG.  1^—MiUUpolar  nerve-cell  from  the  anterior  cornu  of  the  spinal  cord  oftlie  ov;  magnified  200  diameters. 

(Betters.) 
a.  axis-cylinder  prolongation  ;  5,  &,  &,  6,  b,  &,  branching  prolongations. 


582 


NERVOUS   SYSTEM. 


of  the  cells,  the  others  probably  passing  upward  to  be  connected  with  cells  in  the 
encephalon. 

Tracing  the  prolongations  from  the  cells,  we  find  that  one  or  more  of  the  poles  branch 
and  subdivide  in  the  gray  substance  and  give  origin  to  fibres,  but  that  these  fibres  do 
not  branch  after  they  pass  into  the  white  substance.  Other  poles  connect  the  nerve-cells 
with  each  other  by  commissural  fibres  of  greater  or  less  length  ;  but  it  has  never  been 
positively  demonstrated  that  the  cells  are  thus  connected  into  separate  and  distinct- 
groups,  although  this  is  possible. 

The  accompanying  figure,  taken  from  the  excellent  monograph  on  the  lumbar  enlarge- 


riorootS 

in  every  direction. 


a  transverse  section,  from  «. 

l!       co™ected  ty;  long,  slender  processes  with  the  ante- 
of  cell-connection  may  be  seen,  with  bundles  of  fibres  crossing 


COMPOSITION  OF  THE   NERVOUS  SUBSTANCE.  583 

ment  of  the  spinal  cord,  by  Dean,  shows  the  mode  of  connection  between  certain  of  the 
cellular  prolongations  and  the  fibres  of  the  anterior  roots,  and  the  commissaral  fibres  by 
which  the  cells  are  connected  with  each  other. 

Accessory  Anatomical  Elements  of  the  Nerve-centres. — While  we  must  regard  the  cells 
of  the  gray  matter  and  the  axis-cylinder  of  the  nerves  as  probably  the  only  anatomical 
elements  concerned  in  innervation,  there  are  other  structures  in  the  nervous  system 
which  it  is  important  for  us  to  study.  These  are  the  following  :  1,  Outer  coverings  sur- 
rounding some  of  the  cells ;  2,  intercellular,  granular  matter ;  3,  peculiar  corpuscles, 
called  myelocytes ;  4,  connective-tissue  elements  ;  5,  blood-vessels  and  lymphatics. 

Certain  of  the  cells  in  the  spinal  ganglia  and  in  the  ganglia  of  the  sympathetic  system 
are  surrounded  with  a  nucleated  covering,  removed  a  certain  distance  from  the  cell  itself, 
so  as  to  be  nearly  twice  the  diameter  of  the  cell,  which  is  continuous  with  the  sheath  of  the 
dark-bordered  fibres.  This  membrane  is  always  nucleated,  and  Kolliker  has  lately  shown 
that  it  is  not  homogeneous,  as  was  at  one  time  supposed,  but  is  composed  of  a  layer  of 
very  delicate  epithelium.  The  physiological  significance  of  this  covering  is  not  apparent. 

In  the  gray  matter  of  the  nerve-centres,  there  is  a  finely  granular  substance  between 
the  cells,  which  closely  resembles  the  granular  contents  of  the  cells  themselves.  In  addi- 
tion to  this  granular  matter,  Robin  has  described  new  anatomical  elements  which-  he  has 
called  myelocytes.  These  are  found  in  the  cerebro-spinal  centres,  forming  a  layer  near  the 
boundary  of  the  white  substance,  and  they  are  particularly  abundant  in  the  cerebellum. 
They  exist  in  the  form  of  free  nuclei  and  nucleated  cells,  the  free  nuclei  being  by  far  the 
more  numerous.  The  nuclei  are  rounded  or  ovoid,  with  strongly-accentuated  borders, 
are  unaffected  by  acetic  acid,  finely  granular,  and  generally  without  nucleoli.  The  cells 
are  rounded  or  slightly  polyhedric,  pale,  clear,  or  very  slightly  granular,  and  contain 
bodies  similar  to  the  free  nuclei.  The  free  nuclei  are  from  ^Vs  to  ¥innr  °f  an  mcn  m 
diameter,  and  the  cells  measure  from  ^-gVo  *°  Wiro>  an(^  sometimes  -j^Vo"  °f  an  mcn- 
These  elements  also  exist  in  the  second  layer  of  the  retina. 

There  has  been  a  great  deal  of  discussion  with  regard  to  the  presence  or  absence  of 
connective-tissue  elements  in  the  cerebro-spiual  centres.  In  the  other  ganglia,  there  has 
never  been  any  doubt  with  regard  to  the  presence  of  connective  tissue  in  greater  or  less 
amount,  and  in  the  cerebro-spinal  centres  there  can  be  hardly  any  question  of  the  exist- 
ence of  an  exceedingly  delicate  stroma,  chiefly  in  the  form  of  stellate,  branching  cells, 
serving,  in  a  measure,  to  support  the  nervous  elements. 

The  blood-vessels  of  the  nerve-centres  form  an  exceedingly  graceful  capillary  net-work 
with  very  large  meshes.  The  gray  substance  is  much  richer  in  capillaries  than  the  white. 

A  remarkable  peculiarity  of  the  vascular  arrangement  in  the  cerebro-spinal  centres 
has  already  been  described  in  connection  with  the  lymphatic  system.  The  blood-vessels 
here  are  surrounded  by  what  have  been  called  perivascular  canals,  first  described  by 
Robin,  and  afterward  shown  by  His  and  Robin  to  be  radicles  of  the  lymphatic  system. 

Composition  of  the  Nervous  Substance. 

Our  knowledge  of  the  chemical  constitution  of  the  nervous  system  is,  in  many  regards, 
quite  unsatisfactory ;  but  these  tissues  contain  certain  elements  that  have  been  very  satis- 
factorily determined.  The  chemical  characters  of  cholesterine,  for  example,  have  long  been 
known  to  physiologists,  as  well  as  the  fact  that  this  principle  is  a  constant  constituent  of 
the  nervous  substance,  united  in  some  way  with  the  other  proximate  principles,  so  that 
it  does  not  appear  in  a  crystalline  form.  Since  we  demonstrated,  in  1862,  the  relations 
of  cholesterine  to  the  processes  of  disassimilation,  this  principle  has  assumed  its  proper 
place  as  one  of  the  most  important  of  the  products  of  physiological  waste  of  the  organ- 
ism. The  origin  and  function  of  cholesterine,  with  the  processes  for  its  extraction  from 
the  fluids  and  tissues  of  the  body,  have  been  fully  considered  under  the  head  of  excretion. 


584  NERVOUS   SYSTEM. 

Regarding  cholesteriiie  as  an  excrementitious  product,  to  be  classed  with  principles 
destined  simply  to  be  eliminated  from  the  organism,  the  nerve-substance  proper  has  been 
found  to  contain  the  following  proximate  principles,  the  chemical  properties  of  which 
have  been  more  or  less  accurately  determined ;  viz.,  protagon,  neurine,  fatty  matters 
combined  with  phosphorus,  and  bases  combined  with  peculiar  fatty  acids. 

Protagon.— This  principle  was  discovered  by  Liebreich  and  was  first  described  in  1865. 
Its  formula  is  CnaHauOaaiNUP.  It  may  be  extracted  by  the  following  process :  The  cere- 
bral substance  is  bruised  in  a  mortar  and  afterward  shaken  with  water  and  ether  in  a 
closed  vessel.  The  mixture  is  then  exposed  to  a  temperature  of  32°  Fahr.,  and  the 
ethereal  layer,  containing  cholesterine,  is  removed.  The  insoluble  mass  is  then  extracted 
with  alcohol  (85  per  cent.)  at  113°,  is  again  filtered,  and  is  exposed  to  a  temperature  of 
32°.  An  abundant  precipitate  then  separates,  which  is  washed  with  ether  and  desiccated 
in  vaciw.  The  protagon  is  thus  obtained  in  the  form  of  a  white  powder.  Since  this 
principle  has  been  described  in  the  brain-substance,  a  compound  analogous  to  if  not 
identical  with  protagon  has  been  discovered  by  Hermann  in  the  blood-corpuscles.  In 
its  general  and  chemical  characters,  protagon  resembles  the  albuminoid  proximate  prin- 
ciples ;  but  it  presents  the  remarkable  difference,  that  the  sulphur,  which  exists  in  many 
of  the  principles  of  this  class,  is  replaced  by  phosphorus.  It  is  stated  by  Robin  that  pro- 
tagon is  not  a  true  proximate  principle  but  is  simply  impure  or  imperfectly-prepared 
lecithene. 

Neurine. — This  name  has  been  applied  to  a  rather  indefinite  principle  supposed  to 
represent  the  albuminoid  element  of  the  nervous  tissue  ;  but  its  characters  as  a  proximate 
constituent  of  the  nerve-substance  have  never  been  well  determined.  Robin  and  Verdeil 
place  neurine  among  the  proximate  principles  of  probable  existence.  According  to  these 
authors,  this  is  the  organic  substance  of  the  brain,  not  soluble  in  alcohol.  When  inciner- 
ated it  does  not  leave  a  residue  impregnated  with  phosphoric  acid,  like  the  cerebral  fatty 
matter.  According  to  more  recent  investigations,  particularly  those  of  Liebreich,  neurine 
is  a  derivative  of  protagon.  The  neurine  of  Liebreich  is  obtained  by  boiling  protagon 
for  twenty-four  hours  in  baryta-water,  when  there  are  formed  the  phospho-glycerate  of 
baryta,  and  a  new  base,  neurine.  It  is  evident  that  this  substance  cannot  properly  be 
regarded  as  a  well-determined  proximate  principle. 

The  observations  of  Wurtz  upon  the  synthesis  of  neurine  are  important  as  a  step  tow- 
ard the  synthesis  of  organic  nitrogenized  principles,  but  they  do  not  afford  an  example 
of  the  actual  formation  of  a  characteristic  nitrogenized  constituent  of  the  nerve-tissue. 
They  simply  show  that  the  chlorohydrate  of  an  artificial  organic  compound  presents  crys- 
tals identical  with  the  chlorohydrate  of  neurine  extracted  from  the  brain. 

Cerebral  Fatty  Principles. — Researches  into  the  composition  of  the  fatty  principles 
found  in  the  nervous  substance  have  been  so  indefinite  and  unsatisfactory  in  their  results, 
that,  even  now,  they  possess  but  little  physiological  interest.  In  the  earlier  observations, 
the  fats  extracted  from  the  nerve-tissue  were  generally  combined  with  cholesterine. 
This  substance  has  now  been  isolated,  and  the  residue  contains  a  variety  of  principles, 
which  seem,  under  physiological  conditions,  to  be  intimately  united  with  the  nitrogen- 
ized substance,  presenting  one  of  the  exceptions  to  the  general  law  that  fats  exist  in  the 
body  uncombined  except  with  each  other.  In  this  mass  of  fatty  matter,  we  can  deter- 
mine the  presence  of  oleine,  margarine,  and  stearine ;  but  these  are  combined  with  other 
fats,  fatty  acids,  etc.,  the  remarkable  peculiarity  of  most  of  which  is,  that  they  contain 
a  certain  proportion  of  phosphorus.  These  peculiar  principles  have  received  a  variety 
of  names,  as  they  have  been  described  more  or  less  minutely  by  different  observers,  such 
as  cerebrine,  white  and  red  phosphorized  fat,  lecithene,  cerebric  acid,  and  cerebrate  of 
soda.  The  application  of  most  of  these  names  is  very  indefinite,  and  when  we  say  that 


REGENERATION   OF  THE   NERVOUS   TISSUE. 


585 


.  1ST. — Corpora  amylace<t.    (Funke.) 


the  substances  are,  in  greatest  part,  peculiar  to  the  nervous  tissue,  and  that  they  contain 
phosphorus,  we  have  stated  about  all  that  is  physiologically  important.  Lecithene  is  a 
neutral  phosphorized  fat,  probably  composed  of  a  number  of  different  fatty  principles, 
which  exists,  not  only  in  the  nervous  substance,  but  in  the  blood,  bile,  and  the  yolk  of 
egg.  Its  chemical  history  has  no  physiological  interest.  It  is  said  to  be  identical  with 
protagon  (Robin).  The  same  may  be  said  of  cerebric  acid,  the  cerebrate  of  soda,  of  oleo- 
phosphoric  acid  and  its  compounds  with  soda  and  lime. 

Corpora  Amylacea. — Little  rounded  or  ovoid 
bodies,  about  -j-ro^  of  an  inch  in  diameter,  have 
been  described  by  Virchow  and  others  as  exist- 
ing normally  in  the  corpora  striata,  the  medulla 
oblongata,  and  in  some  other  parts  of  the  cere- 
bro-spinal  system.  With  regard  to  the  actual 
composition  of  these  bodies,  there  is  considera- 
ble difference  of  opinion.  Virchow  and  many 
others  regard  them  as  identical  with  starch,  the 
granules  of  which  they  certainly  resemble  very 
closely,  being  of  the  same  shape,  with  borders 
well  defined,  frequently  presenting  concentric 
laminae  and  a  hilum.  When  carefully  treated, 
first  with  a  solution  of  iodine  and  then  with  a 
little  sulphuric  acid,  they  assume  a  blue  color. 
Some  observers  consider  them  as  analogous  to 
cellulose,  others  have  supposed  that  they  are  formed  of  cholesterine,  and  others  regard 
them  as  nitrogenized  bodies.  These  points  are  of  purely  anatomical  interest,  and  the 
physiological  relations  of  these  bodies  are  not  known. 

Regeneration  of  the  Nervous  Tissue. 

We  do  not  propose  to  discuss  fully  the  question  of  the  regeneration  of  nerves  after 
section  or  even  excision  of  a  portion  of  their  substance,  although  it  is  one  of  great  patho- 
logical interest;  but,  in  this  connection,  we  shall  refer  to  some  experiments  recently 
made,  in  which  it  appears  that  it  is  possible  for  certain  of  the  most  important  of  the 
nerve-centres  to  be  regenerated  and  their  function  restored  after  extirpation. 

With  regard  to  the  simple  reunion  of  nerves  after  division  or  excision,  it  has  long 
been  known  that  this  takes  place  in  the  human  subject  and  in  the  inferior  animals,  with 
restoration  of  function.  The  new  tissue  connecting  the  divided  extremities  of  the  nerve 
seems  to  pass  through  the  regular  stages  of  development  observed  in  the  nerve-tissue  of 
the  embryon,  the  gelatinous  fibres,  or  the  fibres  of  Remak,  first  appearing,  and  these 
being  subsequently  developed  into  true  nerve-tubes.  In  this  process  there  is  not  a  cica- 
trix,  as  in  the  skin  or  muscular  tissue,  but  a  development  of  new  elements  possessing  the 
anatomical  and  physiological  characters  of  the  original  structure. 

A  point  of  considerable  physiological  interest  connected  with  the  regeneration  of  the 
nervous  tissue  is  involved  in  the  recent  observations  of  Voit  upon  the  regeneration  of 
the  cerebral  lobes  after  removal  in  a  pigeon,  and  in  those  of  Masius  and  Vanlair  upon  the 
anatomical  and  functional  regeneration  of  the  spinal  cord  in  frogs. 

The  experiments  recorded  by  Voit,  and  his  deductions,  are  very  curious  and  have 
given  rise  to  a  great  deal  of  comment  and  criticism.  In  one  observation,  the  cerebral 
lobes  were  removed  from  a  young  pigeon  in  the  usual  way,  an  operation  very  easily  per- 
formed, and  one  which  we  practise  yearly  as  a  class-demonstration.  It  is  particularly 
stated  that  the  operation  was  complete,  and  that  the  entire  posterior  lobes  were  removed. 
Immediately  after  the  operation,  the  pigeon  presented  the  condition  of  stupor  ordinarily 
observed.  As  he  gradually  recovered  from  this  condition,  he  began  to  execute  a  number 


586  NERVOUS  SYSTEM. 

of  mechanical  movements,  which  it  is  unnecessary  to  detail  fully,  in  the  most  extraor- 
dinary manner.  The  animal  continued  to  improve,  ceased  the  mechanical  movements, 
and  began  to  fly  about,  exhibiting  timidity  when  approached,  and,  in  short,  seemed,  after 
a  time,  to  have  nearly  or  quite  returned  to  the  normal  condition.  One  thing,  however, 
was  remarked  :  the  animal  never  took  food  (it  was  probably  kept  aiive  by  stuffing,  as  is 
frequently  done  in  such  experiments).  After  five  months,  the  pigeon  was  killed.  The 
cranial  cavity  was  found  to  be  filled  with  a  white  mass,  occupying  the  place  from  which 
the  cerebrum  had  been  removed.  This  mass  had  the  consistence  of  the  white  substance 
of  the  brain  and  presented  a  perfect  continuity  with  the  cerebral  peduncles,  which  had 
not  been  removed.  It  had  the  form  of  the  two  hemispheres,  presenting  a  cavity  filled 
with  liquid,  and  a  septum.  The  whole  mass  consisted  of  perfect  primitive  fibres  of  double 
contour,  and,  in  their  meshes,  ganglionic  cells.  This  observation  is  certainly  one  of  the 
most  remarkable  on  record,  and,  from  the  extraordinary  character  of  its  results,  it  would 
hardly  be  accepted  for  a  moment,  but  for  the  established  reputation  of  Prof.  Voit.  As 
it  is,  such  an  observation  demands  full  confirmation.  It  is  well  known,  to  all  who  have 
been  in  the  habit  of  extirpating  the  cerebral  lobes,  that  it  is  absolutely  necessary  to 
remove  every  portion  of  their  substance,  in  order  to  obtain  uniform  results,  and  that 
this  is  accomplished  sometimes  with  considerable  difficulty,  In  demonstrations  to  a 
medical  class,  we  have  frequently  verified  this  fact,  and  have  observed  recovery,  more 
or  less  complete,  when  but  a  small  portion  of  the  posterior  lobes  escaped.  This  criticism 
upon  the  remarkable  observation  just  detailed  is  made  by  Vulpian,  and  its  pertinence 
will  be  recognized  by  every  practical  physiologist.  We  have  only  to  study  the  experi- 
ments first  made  by  Flourens,  to  learn  how,  in  the  lower  animals,  a  part  of  one  of  the 
great  central  ganglia  may  gradually  assume  the  function  of  the  -whole,  after  this  function 
has  been  interrupted  by  the  first  mutilation.  "We  have  cited  the  essential  points  in  this 
observation  because  it  has  been  so  extensively  commented  upon  by  physiologists,  but  it 
is  far  from  establishing  the  principle  that  a  great  nervous  centre,  ^ike  the  cerebrum,  may 
be  anatomically  and  functionally  regenerated  after  complete  extirpation. 

The  general  results  of  the  experiments  of  Masius  and  Vanlair  upon  the  regeneration 
of  parts  of  the  spinal  cord  in  frogs,  after  loss  of  a  small  portion  of  its  substance,  show 
that  such  reparation  may  take  place  and  be  attended  with  restoration  of  function.  The 
formation  of  cells  precedes  the  development  of  fibres,  and  voluntary  motion  appears  in 
the  parts  situated  below  the  lesion,  before  sensation.  There  are  no  instances  on  record 
of  such  regeneration  in  the  human  subject  or  in  the  warm-blooded  animals. 

Motor  and  Sensory  Nerves. 

The  physiological  property  of  nerves  which  enables  them  to  conduct  to  and  from  the 
centres  the  impressions,  stimulus,  force,  or  whatever  the  imponderable  nervous  agent 
may  be,  is  one  inherent  in  the  tissue  itself,  belonging  to  no  other  structure,  and  is 
dependent  for  its  continuance  upon  proper  conditions  of  nutrition.  So  long  as  the  nerves 
maintain  these  conditions,  they  retain  this  characteristic  physiological  property,  which 
is  generally  known  under  the  name  of  irritability. 

Aside  from  the  special  senses,  the  sense  of  temperature,  and  the  appreciation  of 
weight,  it  is  known  to  every  one  that,  through  the  nerves,  we  appreciate  what  are 
called  ordinary  sensations  and  are  enabled  to  execute  voluntary  movements.  If  a  nerve 
distributed  to  a  part  endowed  with  sensation  and  the  power  of  motion  be  divided,  both 
of  these  properties  are  lost  and  can  only  be  regained  through  a  reunion  of  the  divided 
nerve.  Again,  it  is  equally  well  known  that,  if  such  a  nerve  be  exposed  in  its  course 
and  irritated,  violent  movements  take  place  in  the  muscles  to  which  it  is  distributed, 
and  pain  is  appreciated,  referred  to  parts  supplied  from  the  same  source.  These  facts, 
which  were  fully  appreciated  by  the  ancients,  show  that  the  general  system  of  nerves  is 
endowed  with  motor  and  sensory  properties,  the  question  being  simply  whether  these  be 


MOTOR  AND   SENSORY   NERVES.  537 

inherent  in  the  same  fibres  or  belong  to  fibres  physiologically  distinct  and  derived  from 
different  parts  of  the  central  system.  This  question,  which  was  solved  only  about  half  a 
century  ago,  will  be  the  first  to  engage  our  attention. 

Distinct  Seat  of  the  Motor  and  Sensory  Properties  of  the  Spinal  Nerves. — All  of  the 
nerves  that  take  their  origin  from  the  spinal  cord  are  endowed  with  motor  and  sensory 
properties.  These  nerves  supply  the  whole  body,  except  the  head  and  other  parts 
receiving  branches  from  the  cranial  nerves.  They  arise  by  thirty-one  pairs  from  the 
sides  of  the  spinal  cord,  and  each  nerve  has  an  anterior  and  a  posterior  root.  The  ana- 
tomical differences  between  the  two  roots  are  that  the  anterior  is  the  smaller  and  has  no 
ganglion.  The  larger,  posterior  root  presents  a  ganglionic  enlargement  in  the  interver- 
tebral  foramen.  Just  beyond  the  ganglion,  the  two  roots  coalesce  and  form  a  single 
trunk.  The  nerve-fibres  in  the  two  roots  are  not  of  the  same  size,  the  anterior  fibres 
measuring  on  an  average  about  one-fourth  more  than  the  posterior  fibres.  The  structure 
of  the  ganglia  of  the  posterior  roots  has  already  been  considered  sufficiently  in  detail. 

It  wonld  be  unprofitable  to  discuss  the  vague  ideas  of  the  older  anatomists  and  physi- 
ologists with  regard  to  the  properties  of  the  roots  of  the  spinal  nerves,  and  we  can 
date  our  information  upon  this  point  from  the  suggestion  of  Alexander  Walker,  in  1809, 
that  one  of  these  roots  was  for  sensation  alone  and  the  other  for  motion.  It  is  most 
remarkable,  however,  that  Walker,  from  purely  theoretical  considerations,  should  have 
stated  that  the  posterior  roots  were  motor  and  the  anterior  roots  sensory,  precisely  the 
reverse  of  the  truth,  and  should  have  advanced  this  view  in  a  publication  as  late  as 
1844.  In  the  work  alluded  to,  which  contains  some  of  the  most  extraordinary  pseudo- 
scientific  vagaries  ever  published,  it  is  curious  to  see  how  near  Walker  came  to  the  great- 
est discovery  in  physiology  since  the  description  of  the  circulation  of  the  blood. 

It  is  unnecessary  to  enlarge  upon  the  importance  of  the  discovery  that  the  anterior 
roots  of  the  spinal  nerves  are  motor,  and  the  posterior,  sensory,  and  that  the  union  of 
these  two  roots  in  the  mixed  nerves  gives  them  their  double  properties,  for  we  can  hard- 
ly imagine  a  physiology  of  the  cerebro-spinal  nervous  system  without  this  fact  as  the 
starting-point.  In  an  article  published  in  English,  in  October,  1868,1  and  in  French, 
during  the  same  year,2  we  have  given  an  elaborate  review  of  the  whole  subject,  being 
prompted  to  do  so  by  the  perusal  of  what  purported  to  be  an  exact  reprint  of  the  origi- 
nal pamphlet  by  Charles  Bell.  This  pamphlet  was  printed  for  private  circulation,  in 
1811,  and  was  never  published.  It  has  been  entirely  inaccessible,  and  its  contents  were 
only  to  be  divined  by  references  and  quotations  in  the  subsequent  writings  of  Sir  Charles 
Bell  and  of  his  brother-in-law,  Mr.  Shaw. 

Physiological  literature  d^es  not  present  another  instance  of  the  merit  of  a  great  dis- 
covery resting  upon  references  to  an  unpublished  pamphlet,  which  no  student  could  pos- 
sibly consult  in  the  original,  none  of  these  references,  upon  close  analysis,  proving  to  be 
entirely  distinct  and  satisfactory.  It  is  not  to  be  wondered  at,  therefore,  that,  in  our 
study  of  the  origin  of  one  of  the  greatest  discoveries  of  all  ages,  a  reprint  of  the  original 
memoir  should  be  examined  with  the  most  critical  care.  That  this  reprint  was  correct, 
seemed  probable  from  a  comparison  of  its  text  with  the  quotations  from  the  original  to 
be  found  in  the  writings  of  Sir  Charles  Bell  and  Mr.  Shaw,  and  from  the  testimony  of 
reviewers  who  claimed  to  have  compared  it  with  the  original.  Within  a  short  time, 
however,  an  authorized  reprint  in  full,  from  a  manuscript  in  the  hands  of  the  widow  of 
the  author,  has  appeared  in  the  Journal  of  Anatomy. 

When  the  only  reprint  of  the  celebrated  pamphlet  of  Sir  Charles  Bell  was  itself  exces- 
sively rare,  we  thought  it  desirable  to  make  long  quotations  to  indicate  the  ideas  enter- 
tained by  Bell  regarding  the  properties  of  the  two  roots  of  the  spinal  nerves ;  but,  now 

1  FLINT,  JR.,  Historical  Considerations  concerning  the  Properties  of  the  Roots  of  the  Spinal  Nerved— Quar- 
terly Journal  of  Psychological  Medicine,  New  York,  1868,  vol.  ii.,  p.  025,  et  seq. 

2  Journal  de  Fanatomie,  Paris,  1868,  tome  v.,  p.  520,  etseq.,  and  p.  575,  et  seq. 


588  NERVOUS  SYSTEM. 

that  an  authorized  reprint  can  be  so  readily  consulted,  it  is  only  necessary  to  refer  to 
this  to  show  that  Bell  did  not  at  that  time  regard  the  anterior  roots  as  motor  and  the 
posterior  roots  as  sensory,  hut  that  he  thought  that  the  anterior  roots  were  for  both 
motion  and  sensation  and  the  posterior  roots  presided  over  "  the  secret  operations  of 
the  bodily  frame,  or  the  connections  which  unite  the  parts  of  the  body  into  a  system." 

In  August,  1822,  Magendie  published  his  first  experiments  upon  the  functions  of  the 
roots  of  the  nerves.  Unlike  any  of  the  observations  made  by  Charles  Bell  upon  the 
spinal  nerves,  these  were  made  upon  living  animals.  The  spinal  canal  was  opened,  and 
the  cord,  with  the  roots  of  the  nerves,  was  exposed.  The  posterior  roots  of  the  lumbar 
and  sacral  nerves  were  then  divided  upon  one  side  and  the  wound  was  united  with 
sutures.  The  result  of  this  observation  was  as  follows : 

u  I  thought  at  first  that  the  limb  corresponding  to  the  divided  nerves  was  entirely 
paralyzed  ;  it  was  insensible  to  pricking  and  to  the  most  severe  pinching,  it  also  appeared 
to  me  to  be  motionless ;  but  soon,  to  my  great  surprise,  I  saw  it  move  in  a  very  marked 
manner,  although  the  sensibility  was  still  entirely  extinct.  A  second,  a  third  experi- 
ment, gave  me  exactly  the  same  result ;  I  commenced  to  regard  it  as  probable  that  the 
posterior  roots  of  the  spinal  nerves  might  have  functions  different  from  the  anterior  roots, 
and  that  they  were  more  particularly  devoted  to  sensibility." 

The  experiments  in  which  the  anterior  roots  were  divided  were  no  less  striking : 

"  As  in  the  preceding  experiments,  I  only  made  the  division  upon  one  side,  in  order 
to  have  a  term  of  comparison.  One  can  conceive  with  what  curiosity  I  followed  the 
effects  of  this  division  ;  they  were  not  at  all  doubtful,  the  limb  was  completely  motion- 
less and  flaccid,  while  it  preserved  a  marked  sensibility.  Finally,  that  nothing  should  be 
neglected,  I  divided  at  the  same  time  the  anterior  and  the  posterior  roots ;  then  followed 
absolute  loss  of  sensation  and  of  motion." 

From  these  experiments  Magendie  drew  the  following  conclusions : 

"  I  am  following  out  my  researches,  and  shall  give  a  more  detailed  account  of  them  in 
the  following  number ;  it  is  sufficient  for  me  to  be  able  to  announce  at  present  as  positive, 
that  the  anterior  and  the  posterior  roots  of  the  nerves  which  arise  from  the  spinal  cord 
have  different  functions,  that  the  posterior  seem  more  particularly  devoted  to  sensibility, 
while  the  anterior  seem  more  especially  connected  with  motion." 

In  the  second  note,  published  in  the  same  volume  of  the  Journal  de  physiologic 
(1822),  Magendie  exposed  and  irritated  the  two  roots  of  the  nerves,  with  the  following 
results : 

"  I  commenced  by  examining  in  this  regard  the  posterior  roots,  or  the. nerves  of  sen- 
sation. The  following  is  the  result  which  I  observed :  on  pinching,  pulling,  or  pricking 
these  roots,  the  animal  manifested  pain ;  but  this  was  not  to  be  compared  as  regards 
intensity  with  that  which  was  developed  if  the  spinal  cord  were  touched,  even  lightly, 
at  the  point  of  origin  of  the  roots.  Nearly  every  time  that  the  posterior  roots  were  thus 
stimulated,  contractions  were  produced  in  the  muscles  to  which  the  nerves  were  distrib- 
uted ;  these  contractions,  however,  are  not  well  marked,  and  are  infinitely  more  feeble 
than  when  the  cord  itself  is  touched.  When,  at  the  same  time,  a  bundle  of  the  posterior 
root  is  cut,  there  is  produced  a  movement  in  totality  in  the  limb  to  which  the  bundle  is 
distributed. 

"  I  repeated  the  same  experiments  on  the  anterior  roots,  and  I  obtained  analogous 
results,  but  in  an  opposite  sense  ;  for  the  contractions  excited  by  the  contusion,  the  prick- 
ing, etc.,  are  very  forcible,  and  even  convulsive,  while  the  signs  of  sensibility  are  hardly 
visible.  These  facts  are,  then,  confirmatory  of  those  which  I  have  announced ;  only  they 
seem  to  establish  that  sensation  is  not  exclusively  in  the  posterior  roots,  any  more  than 
motion  in  the  anterior  roots.  Nevertheless,  a  difficulty  may  arise.  When,  in  the  pre- 
ceding experiments,  the  roots  had  been  cut,  they  were  attached  to  the  spinal  cord.  Might 
not  the  disturbance  communicated  to  the  cord  be  the  real  cause  either  of  the  contrac- 
tions or  of  the  pain  which  the  animals  experienced  ?  To  remove  this  doubt,  I  repeated 


MOTOR   AND   SENSORY  NERVES.  589 

the  experiments  after  having  separated  the  roots  from  the  cord ;  and  I  must  say  that, 
except  in  two  animals,  in  which  I  saw  contractions  when  I  pinched  or  pulled  the  anterior 
and  posterior  roots,  in  all  the  other  instances  I  did  not  observe  any  sensible  effect  of  irrita- 
tion of  the  anterior  or  posterior  roots  thus  separated  from  the  cord." 

Magendie  then  goes  on  to  say  that,  when  he  published  the  note  in  the  preceding  num- 
ber of  the  journal,  he  supposed  that  he  was  the  first  who  had  thought  of  cutting  the  roots 
of  the  spinal  nerves ;  but  he  was  soon  undeceived  by  a  letter  from  Mr.  Shaw,  who  stated 
that  Bell  had  divided  the  roots  thirteen  years  before.  Magendie  afterward  received  from 
Mr.  Shaw  a  copy  of  BeU's  essay  ("Idea  of  a  New  Anatomy  of  the  Brain"),  and,  as  will 
be  seen  by  the  following  extract,  gave  Bell  full  credit  for  all  his  observations : 

"  It  is  seen  by  this  quotation  from  a  work  which  I  could  not  be  acquainted  with,  inas- 
much as  it  had  not  been  published,  that  Mr.  Bell,  led  by  his  ingenious  ideas  concerning 
the  nervous  system,  was  very  near  discovering  the  functions  of  the  spinal  roots ;  still  the 
fact  that  the  anterior  are  devoted  to  movement,  while  the  posterior  belong  more  particu- 
larly to  sensation,  seems  to  have  escaped  him ;  it  is,  then,  to  having  established  this  fact 
in  a  positive  manner  that  I  must  limit  my  pretensions." 

Such  are  the  experiments  by  which  the  properties  of  the  roots  of  the  spinal  nerves 
were  discovered.  From  that  time,  the  fact  took  its  place  in  science,  that  the  posterior 
roots  are  for  sensation  and  the  anterior  are  for  motion.  Some  discussion  has  arisen  as  to 
whether  the  anterior  roots  do  not  possess  a  certain  amount  of  sensibility,  called  recur- 
rent sensibility,  and  this  question  has  engaged  the  attention  of  physiologists  within  a  few 
years  ;  but  the  distinct  functions  of  the  two  roots  have  never  been  doubted.  Before  the 
days  of  anaesthetics,  exposing  the  roots  of  the  nerves  in  the  dog  was  very  laborious,  and 
painful  to  the  animal,  and  the  disturbances  produced  by  so  serious  an  operation  interfered 
somewhat  with  the  effects  of  irritation  of  the  different  roots.  But,  now  that  the  canal 
may  be  opened  without  pain  to  the  animal,  the  experiments  are  much  more  satisfactory 
and  have  often  been  repeated  by  physiologists.  We  have  frequently,  indeed,  demon- 
strated the  properties  of  the  roots  of  the  nerves  in  public  teaching. 

Properties  of  the  Posterior  Roots  of  the  Spinal  Nerves. — It  is  unnecessary  to  follow 
out,  from  the  date  of  the  first  experiments  by  Magendie  to  the  present  day,  the  observa- 
tions that  have  been  made  from  time  to  time  upon  the  properties  of  the  roots  of  the 
spinal  nerves.  For  many  years,  the  difficulties  in  operating  upon  animals  high  in  the 
scale  rendered  confirmatory  experiments  somewhat  unsatisfactory.  The  great  German 
physiologist,  J.  Miiller,  showed,  in  experiments  made  upon  frogs,  in  1831,  that  irritation 
of  the  posterior  roots  produced  no  convulsive  movements ;  but  he  despaired  of  operating 
satisfactorily  upon  warm-blooded  animals.  Magendie,  in  his  later  experiments,  and 
Longet,  in  experiments  performed  upon  dogs,  published  in  1841,  showed  very  satisfactorily 
that  the  posterior  roots  were  exclusively  sensory,  and  this  fact  has  been  abundantly  con- 
firmed by  more  recent  observations  upon  the  higher  classes  of  animals.  We  have  our- 
selves frequently  exposed  and  irritated  the  roots  of  the  nerves  in  dogs  in  public  demon- 
strations, in  experiments  upon  the  recurrent  sensibility  of  the  anterior  roots,  and  in 
another  series  of  observations  upon  the  properties  of  the  spinal  cord,  which  will  be 
referred  to  hereafter. 

The  remarkable  anatomical  peculiarity  of  the  posterior  roots,  which  they  have  in 
common  with  all  of  the  exclusively, sensitive  nerves,  is  the  presence  of  a  ganglion.  "While 
Ave  have  no  distinct  idea  of  the  function  of  these  ganglia  in  connection  with  the  trans- 
mission of  impressions  from  the  periphery  to  the  centres,  it  has  been  shown  that  they 
have  a  remarkable  influence  upon  the  nutrition  of  the  nerves  after  their  division.  Oper- 
ating upon  the  second  cervical  nerves,  in  which  the  ganglia  can  be  reached  without 
exposing  the  spinal  cord,  Waller  has  demonstrated  the  following  interesting  facts  : 

When  the  roots  are  divided  between  the  ganglion  and  the  cord,  the  central  end  of  the 
anterior  root,  attached  to  the  cord,  preserves  its  normal  structure,  while  the  peripheral 
end  in  a  few  days  becomes  degenerated,  the  tubes  are  filled  with  granular  matter,  etc.,  and 


« 


590  NERVOUS   SYSTEM. 

in  short,  it  undergoes  those  changes  observed  in  all  nerves  separated  from  their  centres. 
On  the  other  hand,  in  the  posterior  roots,  the  end  attached  to  the  cord  undergoes  degen- 
eration, and  the  peripheral  end,  the  one  to  which  the  ganglion  is  attached,  preserves  its 
normal  histological  characters.  From  these  experiments,  which  have  been  confirmed  and 
somewhat  extended  by  Bernard,  it  is  concluded  that  the  ganglia  of  the  posterior  roots 
have  an  influence  over  the  nutrition  of  the  sensitive  nerves,  in  the  same  way  as  the  cen- 
tres influence  the  nutrition  of  the  motor  nerves  with  which  they  are  connected.  These 
points  are  interesting,  as  showing  the  existence  of  centres  attached  to  the  sensory  system 
of  nerves,  which  have,  as  far  as  we  know,  a  purely  trophic  influence  over  the  nerves, 
while  the  centres  to  which  the  motor  nerves  are  attached  regulate,  to  a  certain  extent, 
the  nutrition  of  the  nerves,  and  also  are  capable  of  generating  nerve-force.  We  do  not 
know  that  the  ganglia  of  the  roots  of  sensitive  nerves  have  any  function  except  that 
which  has  just  been  indicated. 

Properties  of  the  Anterior  Roots  of  the  Spinal  Nerves. — The  same  experiments  that 
demonstrated  that  the  posterior  roots 'of  the  spinal  nerves  are  sensitive  showed  that  the 
anterior  roots  are  motor.  If  the  two  roots  be  exposed  in  an  animal  just  killed,  no  con- 
vulsive movements  are  produced  by  stimulating  the  posterior  roots ;  but,  if  the  anterior 
roots  be  irritated,  movements  of  the  most  violent  character  occur,  confined  to  those 
muscles  to  which  the  filaments  of  the  roots  are  distributed.  There  has  never  been  any 
doubt  upon  this  point  since  the  experiments  of  Magendie ;  and  it  is  now  universally 
admitted  by  physiologists,  that  the  motor  properties  of  the  mixed  nerves  are  derived 
exclusively  from  their  anterior  roots  of  origin  from  the  spinal  cord.  The  question  has 
arisen,  however,  whether  the  anterior  roots  be  not  also  endowed  with  sensibility,  nota- 
bly less  in  degree  than  the  posterior  roots,  but  still  marked  and  invariable.  The  sensi- 
bility observed  in  the  anterior  roots  is  abolished  by  section  of  the  posterior  roots ;  and 
this  property,  which  is  thought  to  be  derived  from  the  posterior  roots,  has  been  called 
recurrent  sensibility. 

Recurrent  Sensibility. — The  experimental  facts  with  regard  to  the  recurrent  sensi- 
bility of  the  anterior  roots  of  the  spinal  nerves  are  very  simple.  If  the  two  roots  of  a 
spinal  nerve  be  exposed,  and  if  the  animal  be  allowed  to  recover,  by  a  few  hours'  repose, 
from  the  shock  of  the  operation,  irritation  of  the  posterior  root  will  produce  pain  and 
the  general  movements  incident  to  it,  but  no  localized  contractions  of  muscles ;  and  irri- 
tation of  the  anterior  root  will  produce  contraction  of  certain  muscles  and  a  certain 
amount  of  pain,  always  less,  however,  than  the  pain  resulting  from  stimulation  of  the 
posterior  roots.  If  the  anterior  root  be  divided,  the  end  attached  to  the  cord  will  be 
found  completely  insensible,  but  the  peripheral  end  will  manifest  the  same  sensibility  as 
the  undivided  root ;  showing  that  the  sensory  properties  of  the  anterior  roots  are  not 
derived  from  the  cord.  If  the  posterior  root  be  divided,  the  sensibility  of  the  anterior 
root  is  instantly  abolished;  showing  that  the  sensibility  of  the  anterior  root  is  recurrent, 
being  derived  from  the  posterior  root  through  the  periphery.  With  regard  to  these 
facts,  which  were  first  noted  by  Magendie,  there  can  be  no  doubt,  and  we  ourselves  veri- 
fied them  in  a  series  of  experiments  published  in  1861.  Experiments  have  simply 
demonstrated  the  fact  that  the  recurrent  sensibility  comes  through  the  periphery,  with- 
out actually  showing  any  recurrent  fibres ;  and  division  of  the  mixed  nerve  beyond  the 
point  of  union  of  the  two  roots  deprives  the  anterior  root  of  its  sensibility,  showing 
that  the  recurrent  fibres,  if  they  exist,  must  turn  back  near  the  periphery. 

The  question  now  arises  with  regard  to  the  exact  mechanism  of  recurrent  sensibility. 
The  explanation  offered  by  Magendie  and  Bernard  is,  that  there  are  actually  fibres  return- 
ing from  the  posterior  to  the  anterior  roots ;  that  these  fibres  are,  of  course,  sensitive ; 
and  that  irritation  of  the  anterior  roots  is  propagated  toward  the  periphery  and  returns 
to  the  centres  through  the  posterior  roots.  This  explanation  satisfies  all  of  the  experi- 
mental conditions,  and  it  is  farther  sustained  by  the  microscopical  examinations  of  Schiff 
and  of  Philipeaux  and  Vulpian.  It  will  be  remembered  that  the  ganglia  of  the  posterior 


MOTOR  AND    SENSORY  NERVES.  591 

nerves,  after  division  of  these  roots,  have  the  remarkable  power  of  preserving  the  ana- 
tomical integrity  of  the  fibres  to  which  they  are  attached.  Now,  it  has  been  shown  by 
Schiff  that,  after  division  of  the  posterior  roots  beyond  the  ganglia,  the  anterior  roots 
contain  altered  fibres,  which  he  believes  come  from  the  posterior  roots  and  give  to  these 
roots  their  sensibility. 

Dr.  Brown-Sequard  offers  a  different  explanation  of  the  pain  developed  upon  irrita- 
tion of  the  anterior  roots.  He  believes  this  to  be  due  entirely  to  cramp  or  convulsive 
contractions  of  the  muscles.  This  may  be  accepted,  perhaps,  as  a  partial  explanation, 
for  there  can  be  no  doubt  of  the  fact  that  violent  muscular  action,  produced  indepen- 
dently of  volition,  is  more  or  less  painful ;  but  it  does  not  explain  the  great  sensibility 
sometimes  observed  when  the  muscular  contraction  is  comparatively  feeble.  There  can 
be  hardly  any  doubt  that  the  explanation  offered  by  Magendie,  and  sustained  by  the 
ingenious  histological  observations  cited  above,  is  in  the  main  correct. 

Mode  of  Action  of  the  Motor  Nerves. — Having  established  the  anatomical  distinction 
between  the  motor  and  sensory  nerves,  it  becomes  necessary  to  study  the  differences  in 
the  mode  of  action  of  these  two  kinds  of  nervous  conductors.  In  the  first  place,  it  is 
evident,  taking  the  nerves  and  their  roots  as  we  find  them  in  the  organism  in  a  normal 
condition,  that  certain  fibres  act  from  the  centres  to  the  periphery,  conducting  motor 
stimulus,  while  others  act  from  the  periphery  to  the  centres,  conducting  sensory  impres- 
sions. 

As  regards  the  motor  nerves,  the  force,  whatever  it  may  be,  generated  in  the  centres, 
is  conducted  from  the  centres  to  the  peripheral  distribution  of  the  nerves  in  the  muscles, 
and  is  here  manifested  by  contraction.  Their  mode  of  action,  therefore,  is  centrifugal. 
When  these  motor  filaments  are  divided,  the  connection  between  the  parts  animated  by 
them  and  the  centre  is  interrupted,  and  motion  in  these  parts,  in  obedience  to  the  natural 
stimulus,  becomes  impossible.  But,  while  we  cannot  always  induce  generation  of  nerve- 
force  in  the  centres  by  the  direct  application  of  any  agent  to  them,  this  force  may  be 
imitated  by  stimulation  applied  to  the  nerve  itself.  A  nerve  that  will  respond  to  direct 
stimulation  is  said  to  be  excitable ;  but  this  property  does  not  extend  throughout  the 
entire  conducting  motor  system.  For  example,  we  shall  see,  when  we  come  to  study 
the  properties  of  the  encephalon,  that  certain  fasciculi  capable  of  conducting  the  motor 
stimulus  from  the  centres  to  the  muscles  are  not  affected  by  direct  stimulation  and  seem 
to  be  inexcitable. 

If  a  motor  nerve  be  divided,  galvanic,  mechanical,  or  other  stimulation  applied  to  the 
extremity  connected  with  the  centres  produces  no  effect ;  but  the  same  stimulation  applied 
to  the  extremity  connected  with  the  muscles  is  followed  by  contraction.  The  phenomena 
indicating  that  a  nerve  retains  its  physiological  properties  are  always  manifested  at  its 
peripheral  distribution,  and  these  do  not  essentially  vary  when  the  nerve  is  stimulated  at 
different  points  in  its  course.  For  example,  stimulation  of  the  anterior  roots  near  the 
cord  produces  contraction  in  those  muscles  to  which  the  fibres  of  these  roots  are  dis- 
tributed ;  but  the  same  effect  follows  stimulation  of  the  nerve  going  to  these  muscles  in 
any  part  of  its  course. 

As  far  as  their  physiological  action  is  concerned,  the  different  nerve-fibres  are  entirely 
independent,  and  the  relations  which  they  bear  to  each  other  in  the  nervous  fasciculi  and 
in  the  so-called  anastomoses  of  nerves  involve  simple  contiguity.  If  we  compare  the 
nerve-force  to  galvanism,  each  individual  fibre  seems  completely  insulated ;  and  a  stimulus 
conducted  by  it  to  muscles  never  extends  to  the  adjacent  fibres.  That  it  is  the  axis- 
cylinder  which  conducts  and  the  medullary  tube  which  insulates,  it  is  impossible  to  say 
with  positiveness ;  but,  as  we  have  already  seen,  it  is  more  than  probable  that  the  central 
band  is  the  only  conducting  element. 

We  have  incidentally  noted  the  fact  that  direct  stimulation  applied  to  the  centres, 
even  when  the  connection  between  these  and  the  muscles  is  perfect,  is  generally  inca- 


592  NERVOUS   SYSTEM. 

puble  of  inducing  the  generation  of  nerve-force ;  but  the  generation  of  a  motor  stimulus 
may  be  induced  by  an  impression  made  upon  sensitive  nerves  and  conveyed  by  them  to 
the  centres.  If,  for  example,  we  isolate  a  certain  portion  of  the  central  nervous  system, 
as  the  spinal  cord,  and  leave  its  connections  with  the  motor  and  sensitive  nerves  intact, 
these  phenomena  may  be  readily  observed.  An  impression  made  upon  the  sensitive  nerves 
will  be  conveyed  to  the  gray  matter  of  the  cord  and  will  induce  the  generation  of  a  motor 
stimulus  by  the  cells  of  this  part,  which  will  be  conducted  to  the  muscles  and  gives  rise  to 
contraction.  As  the  stimulus,  in  such  observations,  seems  to  be  reflected  from  the  cord 
through  the  motor  nerves  to  the  muscles,  this  action  has  been  called  reflex.  These  phe- 
nomena constitute  an  important  division  of  the  physiology  of  the  nervous  system  and  will 
be  fully  considered  by  themselves. 

Associated  Movements. — It  is  well  known  that  the  action  of  certain  muscles  is  with 
difficulty  isolated  by  an  effort  of  the  will.  This  applies  to  sets  of  muscles  upon  one  side 
of  the  body  and  to  corresponding  muscles  upon  the  two  sides.  For  example,  it  is  almost 
impossible,  without  great  practice,  to  move  some  of  the  fingers,  at  the  same  time  restrain- 
ing the  movements  of  the  others ;  and  the  action  of  certain  sets  of  muscles  of  the  extrem- 
ities is  always  simultaneous.  The  toes,  which  are  but  little  used  as  the  foot  is  confined 
in  the  ordinary  dress,  are  capable  of  very  little  independent  action.  It  is  difficult  to 
move  one  eye  without  the  other,  or  to  make  rapid  rotary  movements  of  one  hand  while 
an  entirely  different  order  of  movements  is  executed  by  the  other ;  and  instances  of  this 
kind  might  be  multiplied.  In  studying  these  associated  movements,  the  question  arises 
as  to  how  far  they  are  due  to  the  anatomical  relations  of  the  nerves  to  the  centres  and 
their  connections  with  muscles,  and  how  far  they  depend  upon  habit  and  exercise.  We 
can  imagine  that  there  may  be  certain  sets  of  nerve-cells,  connected  with  each  other  by 
commissural  fibres  and  giving  origin  to  motor  nerves  distributed  to  sets  of  muscles ;  an 
anatomical  arrangement  that  might  render  a  separate  action  of  these  cells  impossible. 
The  anatomy  of  the  nerve-centres  and  their  connection  with  fibres  are  so  difficult  of 
investigation,  that  demonstrative  proof  of  the  existence  of  such  systems  is  impracticable ; 
but  this  affords  a  ready  explanation  of  the  fact  that  we  cannot,  as  a  rule,  by  an  effort  of 
the  will,  cause  only  a  portion  of  a  single  muscle  to  contract ;  yet  some  of  the  larger  mus- 
cles receive  an  immense  number  of  motor  nerve-fibres  which  are  probably  connected 
with  gray  matter  composed  of  numerous  anastomosing  cells. 

Many  of  the  associated  movements  are  capable  of  being  influenced  to  a  surprising 
degree  by  education,  of  which  no  better  example  can  be  found  than  in  the  case  of  skilful 
performers  upon  certain  musical  instruments,  such  as  the  piano,  harp,  violin,  and  other 
stringed  instruments.  In  the  technical  study  of  such  instruments,  not  only  does  one  hand 
become  almost  independent  of  the  other,  but  very  complex  associated  movements  may  be 
acquired.  An  accomplished  pianist  or  violinist  executes  the  different  scales  automatically 
by  a  single  effort  of  the  will,  and  frequently  pianists  execute  at  the  same  time  scales  with 
both  hands,  the  action  being  entirely  opposed  to  the  natural  association  of  movements. 
Feats  of  sleight  of  hand  also  show  how  wonderfully  the  muscles  may  be  educated,  and  to 
what  an  extent  the  power  of  association  and  disassociation  of  movements  may  be  acquired 
by  long  practice. 

Looking  at  the  associated  movements  in  their  relations  to  the  mode  of  action  of  the 
motor  nerves,  it  seems  probable  that,  as  a  rule,  the  anatomical  relations  of  the  nerves  are 
such  that  a  motor  stimulus,  or  an  effort  of  the  will,  cannot  be  conducted  to  a  portion  only 
of  a  muscle,  but  must  act  upon  the  whole  muscle,  and  the  same  is  true,  probably,  of  cer- 
tain restricted  sets  of  muscles ;  but  the  association  of  movements  of  corresponding  muscles 
upon  the  two  sides  of  the  body,  with  the  exception,  perhaps,  of  the  muscles  of  the  eyes, 
is  due  mainly  to  habit  and  may  be  greatly  modified  by  education. 

Mode  of  Action  of  the  Sensory  Nerve*. — The  sensory  nerve-fibres,  like  the  fibres  of  the 
motor  system,  are  entirely  independent  of  each  other  in  their  action ;  and,  in  the  so-called 


MOTOR  AND   SENSORY  NERVES.  593 

anastomoses  that  take  place  between  sensory  nerves,  the  fibres  assume  no  new  relations, 
except  as  regards  contiguity. 

As  motor  fibres  convey  to  their  peripheral  distribution  the  stimulus  engendered  by  an 
irritation  applied  in  any  portion  of  their  course,  so  an  impression  made  upon  a  sensitive 
nerve  is  always  referred  to  the  periphery.  A  familiar  example  of  this  is  afforded  by  the 
very  common  accident  of  contusion  of  the  ulnar  nerve  as  it  passes  between  the  olecranon 
and  the  condyle  of  the  humerus.  This  is  attended  with  painful  tingling  of  the  ring  and 
little  finger  and  other  parts  to  which  the  filaments  of  this  nerve  are  distributed,  without, 
necessarily,  any  pain  at  the  point  of  injury.  More  striking  examples  are  afforded  in  neu- 
ralgic affections  dependent  upon  disease  of  or  pressure  upon  the  trunk  of  a  sensitive  nerve. 
In  such  cases,  excision  of  the  nerve  is  often  practised,  but  no  permanent  relief  follows 
unless  the  section  be  made  between  the  affected  portion  of  the  nerve  and  the  nerve- 
centres  ;  and  the  pain  produced  by  the  disease  is  always  referred  to  the  termination  of 
the  nerve,  even  after  it  has  been  divided  between  the  seat  of  the  disease  and  the  periphery, 
leaving  the  parts  supplied  by  the  nerve  insensible  to  direct  irritation.  In  cases  of  disease 
it  is  not  unusual  to  note  great  pain  in  parts  of  the  skin  that  are  insensible  to  direct  im- 
pressions. The  explanation  of  this  is,  that  the  nerves  are  paralyzed  near  their  terminal 
distribution,  so  that  an  impression  made  upon  the  skin  cannot  be  conveyed  to  the  senso- 
rium ;  but  that  the  trunks  of  the  nerves  still  retain  their  conducting  power  and  are  the 
seat  of  diseased  action,  producing  pain,  which  is  referred  by  the  patient  to  the  periphery. 

In  multiplying  examples  showing  the  mode  of  action  of  the  sensory  nerves,  we  may 
refer  to  the  sensations  experienced  after  certain  plastic  operations.  In  the  very  common 
operation  of  restoring  the  nose  by  transplanting  skin  from  the  forehead,  after  the  opera- 
tion has  been  completed,  the  skin  having  been  entirely  separated  and  cicatrized  in  its 
new  relations,  the  patient  feels  that  the  forehead  is  touched  when  the  finger  is  applied  to 
the  artificial  nose.  After  a  time,  however,  the  sensorimn  becomes  accustomed  to  the 
new  arrangement  of  the  parts,  and  this  deceptive  feeling  disappears. 

There  are  certain  curious  nervous  phenomena,  that  are  not  without  physiological 
interest,  presented  in  persons  who  have  suffered  amputations.  It  has  been  long  observed 
that  after  loss  of  a  limb  the  sensation  of  the  part  remains,  and  pain  is  frequently  experi- 
enced, which  is  referred  to  the  amputated  member.  Thus  a  patient  will  feel  distinctly 
the  fingers  or  toes  after  an  arm  or  a  leg  has  been  removed,  and  irritation  of  the  ends  of 
the  nerves  at  the  stump  produces  sensations  referred  to  the  missing  member.  A  few 
years  since,  we  observed  a  very  striking  example  of  this  in  a  soldier  who  had  suffered 
amputation  of  the  leg.  While  this  patient  was  walking  about  on  crutches,  before  the 
stump  had  entirely  healed,  upon  getting  up  suddenly  from  his  seat,  in  attempting  to 
walk  he  put  the  stump  to  the  ground,  producing  considerable  injury.  His  explanation 
was,  that  he  felt  the  foot  perfectly,  and  it  was  necessary  for  him  to  be  constantly  on  his 
guard  to  prevent  such  an  accident. 

A  very  curious  fact  has  been  observed  with  regard  to  the  imaginary  presence  of  limbs 
after  amputation,  which  we  have  had  ample  opportunities  of  verifying.  After  a  time  the 
sense  of  possession  of  the  lost  limb  becomes  blunted,  and  it  may,  in  some  cases,  entirely 
disappear.  This  may  take  place  a  few  months  after  the  amputation,  or  the  sensations 
may  remain  in  their  full  intensity  for  years.  Examples  are  reported  by  Muller  where 
the  sense  was  undiminished  thirteen,  and,  in  one  case,  twenty  years  after  amputation. 
In  a  certain  number  of  cases,  however,  the  sense  of  the  intermediate  part  is  lost,  the 
feeling  in  the  hand  or  foot,  as  the  case  may  be,  remaining  as  distinct  as  ever,  the  impres- 
sion being  that  the  limb  is  gradually  becoming  shorter.  These  curious  facts,  noted  by  M. 
Gueniot,  show  that  the  sense  of  the  limb  becoming  shorter  is  observed  in  about  half  of 
the  cases  of  amputation  in  which  cicatrization  goes  on  regularly ;  and,  in  these  cases, 
the  patient  finally  experiences  a  feeling  as  though  the  hand  or  foot  were  in  direct  contact 
with  the  stump.  By  careful  inquiries  among  a  large  number  of  patients  in  military  hos- 
pitals, we  have  been  enabled  to  verify  these  observations  in  the  most  satisfactory  manner. 
38 


594  NERVOUS  SYSTEM. 

General  Properties  of  the  Nerves. 

Numerous  experiments  have  been  made,  especially  upon  the  cerebro-spinal  nerves, 
with  regard  to  their  action  under  different  kinds  of  stimulation,  the  probable  nature  of 
the  nervous  agent  or  nerve-force,  the  extent  and  duration  of  their  excitability  and  sensi- 
bility, etc.,  which  have  developed  facts  of  more  or  less  physiological  interest  and  impor- 
tance. As  far  as  the  nerves  of  general  sensibility  are  concerned,  the  phenomena  of  con- 
duction of  impressions  are  essentially  the  same  in  all,  if  we  except  certain  variations  in 
different  nerves  as  regards  the  degree  of  sensibility.  The  motor  nerves  all  respond  in 
the  same  manner  to  stimulation ;  and  it  is  upon  this  portion  of  the  nervous  system  that 
the  most  important  observations  have  been  made.  This  being  the  case,  it  is  evident  that 
the  cerebro-spinal  nerves,  in  their  behavior  under  the  experimental  conditions  above 
mentioned,  possess  certain  general  properties,  and  that  the  functions  of  special  nerves 
are  to  be  studied,  after  a  full  consideration  of  these  general  properties,  in  connection 
with  their  anatomical  distribution  to  the  different  organs  in  the  economy. 

The  points  to  be  considered,  aside  from  the  simple  division  of  the  nerves  into  motor 
and  sensory,  are  as  follows : 

1.  The  conditions  of  excitability  and  sensibility  of  the  nerves,  or  what  is  known  as 
nervous  irritability. 

2.  The  nature  of  the  nervous  agent,  or  the  so-called  nerve-force. 

3.  Certain  phenomena  following  the  application  of  electricity  to  the  nerves. 

Nervous  Irritability. — "We  have  already  alluded  in  a  general  way  to  what  is  known 
as  nervous  irritability.  The  term  is  used  by  physiologists  to  express  the  condition  of 
nerves  which  enables  them  to  respond  to  artificial  stimulation,  or  to  conduct  the  natural 
stimulus  or  external  impressions.  So  long  as  a  nerve  retains  this  property  it  is  said  to 
be  irritable.  Of  course,  while  in  a  normal  condition  and  during  life,  irritability,  as 
applied  to  nerves,  simply  means  that  these  parts  are  capable  of  performing  their  peculiar 
functions ;  but,  after  death,  for  a  certain  time  the  nerves  will  respond  to  artificial  stimu- 
lation ;  and  it  is  to  this  property  that  the  term  "  irritability  "  seems  to  be  most  applicable. 
At  a  certain  time  after  death,  varying  in  different  classes  of  animals  with  the  activity  of 
their  nutrition,  the  irritability  of  the  nerves  disappears.  This  occurs  very  soon  in  warm- 
blooded animals,  but  it  is  later  in  animals  lower  in  the  scale,  so  that  the  latter  present 
the  most  favorable  conditions  for  experimentation.  Most  observations  upon  nervous  irri- 
tability, indeed,  have  been  made  upon  frogs  and  other  cold-blooded  animals.  Analogous 
facts  have  already  been  noted  with  regard  to  the  muscular  system,  although,  as  we  have 
seen,  the  irritability  of  the  muscular  tissue  is  entirely  distinct  from  that  of  the  nerves. 

Immediately  or  soon  after  death,  when  the  irritability  of  the  nerves  is  at  its  maxi- 
mum, they  may  be  excited  by  mechanical,  chemical,  or  galvanic  stimulus,  all  of  these 
agents  producing  contraction  of  the  muscles  to  which  the  motor  filaments  are  distributed. 
Mechanical  irritation,  simply  pinching  a  portion  of  the  nerve,  for  example,  produces  a 
single  muscular  contraction  ;  but,  if  the  injury  to  the  nerve  be  such  as  to  disorganize  its 
fibres,  that  portion  of  the  nerve  will  no  longer  conduct  a  stimulus.  Among  the  irritants 
of  this  kind,  we  may  cite  the  extremes  of  heat  and  cold.  If  an  exposed  nerve  be  cau- 
terized, a  vigorous  muscular  contraction  follows.  The  same  effect,  though  less  marked, 
may  be  produced  by  the  sudden  application  of  intense  cold.  Among  chemical  reagents, 
there  are  some  which  excite  the  nerves  and  others  which  produce  no  effect ;  but  these 
are  not  important  from  a  physiological  point  of  view.  Suffice  it  to  say,  that  mechanical 
irritation  and  the  action  of  certain  chemicals  are  capable  of  exciting  the  nerves ;  but 
that,  when  their  action  goes  so  far  as  to  disorganize  the  fibres,  the  conducting  power  of 
these  fibres  is  lost.  "While,  however,  irritation  of  the  nerve  above  the  point  of  injury  has 
no  effect,  stimulation  between  this  point  and  the  muscles  is  still  followed  by  contraction. 

The  most  convenient  method  of  exciting  the  nerves  in  physiological  experiments  is 


GENERAL  PROPERTIES  OF  THE  NERVES. 


595 


by  means  of  electricity,  a  stimulus  more  closely  resembling  the  nerve-force  than  any 
other,  and  one  which  may  be  employed  without  disorganizing  the  nerve-tissue,  and  which 
consequently  admits  of  extended  and  repeated  application.  The  action  of  electricity, 
however,  with  the  methods  of  preparing  the  nerves  and  muscles  for  experimentation, 
will  be  fully  considered  under  a  separate  head. 

The  irritability  of  the  motor  system  is  entirely  distinct  from  that  of  the  sensory 
nerves,  and  one  may  be  destroyed,  leaving  the  other  intact.  This  follows  almost  as  a 
matter  of  course  upon  the  fact  of  the  anatomical  distinction  between  motor  and  sensory 
nerves  ;  but  it  is  interesting  to  note  the  limits  of  the  irritability  after  death  in  nerves  of 
different  properties  and  the  differences  in  the  manner  of  its  disappearance.  The  woorara- 
poison,  a  very  curious  agent  prepared  by  the  South- American  Indians,  has  the  remarkable 
property  of  paralyzing  the  motor  nerves,  leaving  the  nerves  of  sensation  intact.  This 
fact  has  been  demonstrated  by  Bernard  and  others  by  very  curious  and  ingenious  experi- 
ments. The  poison,  like  those  of  animal  origin,  acts  most  vigorously  after  introduction 
under  the  skin  or  absorption  from  wounds,  and  it  produces  no  toxic  effects  when  taken 
into  the  stomach,  except  when  introduced  in  large  quantity  in  fasting  animals.  Under 
the  influence  of  this  agent,  an  animal 
dies  with  complete  paralysis  of  the 
motor  system,  presenting,  among  other 
phenomena,  arrest  of  respiration.  Most 
of  the  varieties  of  the  poison  affect  only 
the  motor  nerves  and  do  not  influence 
the  action  of  the  heart ;  and,  in  animals 
brought  completely  under  its  influence, 
artificial  respiration  will  enable  the 
heart  to  continue  its  action,  and,  in 
some  instances,  if  this  be  persisted  in, 
recovery  will  take  place. 

The  fact  that  the  woorara-poison 
affects  the  motor  nerves  only  has  been 
experimentally  illustrated  by  Bernard, 
taking  advantage  of  the  reflex  func- 
tions of  the  spinal  cord  to  show  the 
persistence  of  the  irritability  of  the 
sensory  nerves.  The  most  striking  of 
these  experiments  is  the  following :  A 
frog  is  prepared  by  exposing  the  nerves 
in  the  lumbar  region,  and  then  isolating 
the  posterior  extremities  by  applying  a 
strong  ligature,  including  the  aorta  and 
all  the  parts  except  the  nerves ;  so  that, 
practically,  the  only  communication  be- 
tween the  posterior  extremities  and  the 
body  is  by  the  nerves.  It  is  evident, 
therefore,  that,  if  the  poison  be  intro- 
duced under  the  skin  of  the  body,  act- 
ing, as  it  does,  through  the  blood,  it 

will  affect  all  parts  except  the  posterior    FlG.  m.-Frog  prepared  so  as  to  show  that  woorara  d 
extremities;    for  the   poison  acts  from  stroys  the  properties  of  the  motor  nerves.    (Bernard.) 

the  periphery  to  the  centres  and  must  lbar  nerves;  B' aorta' 

circulate  in  the  parts  to  which  the  motor  nerves  are  distributed.  If  the  posterior 
extremities  be  now  irritated,  the  impression  is  conveyed  to  the  spinal  cord  through  the 
sensory  filaments  of  the  lumbar  nerves,  which  are  intact;  this  gives  rise  to  a  stimulus, 


596  NERVOUS  SYSTEM. 

which  is  reflected  back  through  the  motor  filaments  of  the  same  nerve,  and  the  ordinary 
reflex  movements  are  observed  in  the  posterior  extremities.  This  is  to  be  expected,  inas- 
much as  the  posterior  extremities  have  been  removed  from  the  influence  of  the  poison. 
If  the  anterior  extremities,  which  are  completely  under  the  influence  of  the  poison,  be  now 
irritated,  no  movements  are  observed  in  these  parts,  but  they  take  place,  as  before,  in 
the  posterior  extremities.  The  mechanism  of  this  action  is  easily  understood.  Reflex 
phenomena,  consisting  in  the  movements  of  muscles,  may  be  manifested  throughout  the 
entire  system,  following  irritation  of  a  single  part.  An  impression  made  upon  the  surface 
is  conveyed  to  the  spinal  cord,  and,  if  this  be  sufficiently  powerful,  motor  stimulus  may 
be  sent  through  all  of  the  anterior  roots  coming  from  the  cord.  The  impression  made 
upon  the  anterior,  or  poisoned  extremities,  is  conveyed  by  the  sensory  filaments  to  the 
cord  and  is  transmitted  to  the  posterior  extremities  through  their  motor  nerves,  which 
are  intact.  The  fact  of  the  transmission  of  the  impression  from  the  anterior  extremities 
to  the  cord  shows  that  the  poison  does  not  affect  the  sensory  system. 

In  the  same  way  that  the  woorara-poison  paralyzes  the  motor  nerves,  leaving  the 
sensory  system  intact,  other  agents,  as  anesthetics,  will  abolish  the  sensibility  of  the 
nerves  without  affecting  the  motor  filaments. 

As  we  have  already  intimated  in  another  connection,  the  nerves  soon  lose  their  irrita- 
bility after  they  have  been  separated  from  the  centres.  This  loss  of  conducting  power 
is  attended  with  important  structural  changes  in  the  nerve  fibres.  The  tubes  lose  their 
normal  appearance,  and  the  medullary  matter  becomes  opaque  and  coagulates  in  large 
drops.  The  axis-cylinder  is  not  so  much  modified  in  structure,  but  it  certainly  loses 
its  characteristic  physiological  properties. 

The  excitability  of  the  motor  nerves  disappears  in  about  four  days  after  resection. 
Of  course,  in  experiments  upon  this  point,  it  is  necessary  to  excise  a  portion  of  the 
nerve  to  prevent  reunion  of  the  divided  extremities;  but,  when  this  is  done,  after  the 
fourth  day,  galvanization  of  the  nerve  will  produce  no  contraction  in  the  muscles, 
although  the  latter  retain  their  contractility,  as  may  be  shown  by  the  application  of  direct 
irritation.  This  loss  of  irritability  is  gradual,  and  it  continues,  whether  the  nerve  be 
exposed  and  stimulated  from  time  to  time  or  be  left  to  itself;  and  the  loss  of  excitability 
progresses  from  the  centres  to  the  periphery.  In  the  researches  of  Longet  upon  this  sub- 
ject, it  was  found  that  the  lower  portion  of  the  peduncles  of  the  brain  lost  their  irrita- 
bility first,  then  the  anterior  columns  of  the  cord,  then  the  motor  roots  of  the  nerves, 
and,  last  of  all,  the  branches  of  the  nerves  near  their  termination  in  the  muscles. 

The  sensibility  of  the  sensory  nerves  disappears  from  the  periphery  to  the  centres,  as 
is  shown  in  dying  animals  and  in  experiments  with  anesthetics.  The  sensibility  is  lost, 
first  in  the  terminal  branches  of  the  nerves,  next  in  the  trunks  and  in  the  posterior  roots 
of  the  spinal  nerves,  and  so  on  to  the  centres.  "We  have  often  illustrated  this  fact  in 
experiments  upon  the  roots  of  the  spinal  nerves  and  in  section  of  the  large  root  of  the 
fifth  pair  within  the  cranial  cavity.  When  an  animal  is  brought  so  completely  under 
the  influence  of  ether  that  the  operation  of  opening  the  spinal  canal  may  be  performed 
without  inflicting  the  slightest  pain,  the  posterior  roots  will  be  found  to  be  distinctly 
sensible.  We  have  lately  been  in  the  habit,  in  class-demonstrations,  of  dividing  the  fifth 
pair  in  the  cranium  without  using  an  anaesthetic,  as  the  operation  is  instantaneous  and 
the  effects  are  much  more  striking  than  when  the  animal  has  been  rendered  insensible 
and  is  allowed  to  recover ;  but,  when  we  have  used  an  anaesthetic,  we  could  never  push 
the  effects  sufficiently  to  abolish  the  sensibility  of  the  root  of  the  nerve.  In  an  animal 
brought  so  fully  under  the  influence  of  ether  that  the  conjunctiva,  supplied  with  branches 
of  the  fifth,  had  become  absolutely  insensible,  the  instant  the  instrument  touched  the 
root  of  the  nerve  in  the  cranium,  there  were  evidences  of  acute  pain.  Nothing  could 
more  strikingly  illustrate  the  mode  of  disappearance  of  the  sensibility  of  the  nerves 
from  the  periphery  to  the  centres. 

The  nervous  irritability  may  be  momentarily  destroyed  by  severe  shock  in  killing  an 


GENERAL  PEOPERTIES  OF  THE  NERVES.          597 

animal.  This  is  sometimes  illustrated  in  preparing  frogs  for  experiments  upon  the 
nerves;  as  the  shock  of  killing  the  frog  by  decapitation,  tearing  off  the  skin,  etc., 
abolishes  the  irritability  of  the  nerves  for  the  moment.  It  has  been  observed,  also, 
that  a  galvanic  shock  sufficiently  powerful  to  destroy  life  instantly  destroys  the  excita- 
bility of  the  motor  nerves. 

Nerve-Force. — The  so-called  nervous  irritability,  artificially  manifested  by  the  applica- 
tion of  a  stimulus  directly  to  the  nerve-tissue,  enables  the  nerves  to  conduct  from  the 
centres  to  the  periphery  a  force  which  is  generated  in  the  gray  substance.  Tbis  we  may 
call  the  nerve-force.  Its  production  is  one  of  the  most  remarkable  of  the  phenomena  of 
life ;  and  its  essence,  or  the  exact  mechanism  of  its  generation,  is  one  of  the  problems 
that  has  thus  far  eluded  the  investigations  of  physiologists.  We  know,  however,  that, 
in  the  operations  of  the  nervous  system,  the  nerves  serve  simply  as  conductors  and  the 
nerve-cells  generate  the  nerve-force.  It  is  evident,  also,  that  nearly  all  of  the  so-called 
vital  phenomena  are  more  or  less  influenced  and  controlled  through  this  wonderful  agent ; 
and,  throughout  our  study  of  the  nervous  system,  we  shall  be  constantly  investigating  the 
phenomena  attending  the  operation  of  nerve-force,  while  we  are  compelled  to  admit  our 
ignorance  of  its  essential  nature. 

Non-identity  of  Nerve-Force  with  Electricity. — When  we  come  to  study  fully  the 
action  of  electricity  upon  the  nerves,  we  shall  see  that  this  is  by  far  the  most  convenient 
stimulus  for  exciting  the  nervous  action  and  one  by  which  we  closely  imitate  the  true 
nerve-force.  So  great  is  the  similarity,  indeed,  between  certain  of  the  phenomena  pro- 
duced by  the  application  of  electricity  and  those  attending  the  physiological  action  of 
nerves,  that  some  physiologists  have  regarded  the  nerve-cells  as  generators  of  an  electric 
current.  This  hypothesis  explains  the  nature  of  nerve-force,  in  so  far  as  it  assimilates  it 
to  a  force,  with  the  action  of  which,  as  artificially  generated,  we  are  more  or  less  familiar. 
No  one  at  the  present  day,  however,  pretends  that  the  nerve-force  has  been  demonstrated 
to  be  identical  with  any  form  of  electricity ;  and  the  question  does  not  now  demand 
extended  discussion. 

A  series  of  experiments  made  by  Pre"  vost  and  Dumas,  in  1823,  are  worthy  of  note  as 
showing  the  absence  of  a  true  electric  current  in  nerves  in  action ;  but  these  have  been 
confirmed  in  later  years  with  apparatus  sufficiently  delicate  to  settle  the  question  beyond 
a  doubt.  The  most  conclusive  experiments  upon  this  subject  are  those  of  Matteucci  and 
Longet,  made  upon  horses,  at  the  veterinary  school  at  Alfort.  These  physiologists 
exposed  the  sciatic  nerves  in  the  living  animal,  and,  when  there  was  evidently  a  conduc- 
tion in  both  directions,  as  evinced  by  pain  and  muscular  action,  they  failed  to  detect  the 
slightest  evidence  of  an  electric  current  with  the  most  delicate  galvanometer  that  could 
be  constructed.  The  fact  of  the  absence  of  a  galvanic  current  in  nerves  during  their 
physiological  action  was  even  more  strikingly  illustrated  by  Matteucci,  who  demonstrated, 
in  the  electric  eel,  that,  although  the  electric  discharges  from  the  peculiar  organs  of  this 
animal  were  under  the  control  of  the  nervous  system  and  could  be  excited  by  galvanic 
stimulation  of  the  proper  nerves  immediately  after  death,  no  galvanic  current  existed  in 
these  nerves  during  their  physiological  action. 

When  we  abandon  the  hypothesis  of  the  identity  of  nerve-force  with  electricity,  we 
are  compelled  to  admit  that  the- agent  generated  by  the  nerve-centres  is  sui  generis 
and  not  to  be  compared  with  any  force  known  outside  of  living  organisms  or  artificially 
produced  by  direct  stimulation  of  the  nerves ;  but  we  admit,  nevertheless,  the  fact  that 
electricity  may  be  generated  by  animals,  as  the  electric  fishes,  and  that  electric  currents 
exist  in  different  anatomical  structures  in  the  living  body,  including  the  nerves,  under 
certain  conditions.  Our  study  of  the  nerve-force,  then,  leaving  its  essential  nature  unex- 
plained, is  mainly  confined  to  a  description  of  its  characteristic  phenomena. 

Rapidity  of  Nervous  Conduction. — The  first  rigorous  estimates  of  the  velocity  of  the 
nerve-current  were  made  in  1850,  by  Helmholtz,  and  were  applied  to  the  motor  nerves. 


598  -NERVOUS  SYSTEM. 

The  important  and  interesting  results  of  these  experiments  were  arrived  at  by  an  inge- 
nious application  of  the  graphic  method,  which  has  since  been  so  largely  improved  and 
extended  by  Marey,  and  their  accuracy  was  rendered  possible  by  the  exceedingly  delicate 
chronometric  apparatus  which  has  been  devised  within  the  last  few  years. 

It  is  unnecessary  to  describe  fully  the  exact  methods  employed  by  Helmholtz  and 
by  those  who  immediately  followed  in  his  investigations.  Suffice  it  to  say,  that  this  dis- 
tinguished physiologist  and  physicist  constructed  apparatus  which,  though  somewhat 
complex,  was  so  accurate  as  to  leave  no  doubt  as  to  the  reliability  of  his  results.  Taking 
into  account  all  of  the  disturbing  conditions,  and  allowing  for  the  interval  of  pose,  or  the 
length  of  time  between  the  excitation  of  a  muscle  and  the  commencement  of  its  con- 
traction, he  estimated  the  rapidity  of  conduction  in  the  motor  nerves  of  the  frog  at  about 
eighty-five  feet  per  second.  The  results  obtained  by  Marey  upon  frogs  give  a  much 
slower  rate  of  nervous  conduction.  These  were  followed,  however,  by  the  observations 
of  Helmholtz  and  Baxt  upon  the  human  subject,  which  are,  of  course,  the  most  interest- 
ing of  all. 

The  process  devised  by  Marey  is  admirably  simple.  He  employed,  to  estimate  small 
fractions  of  a  second,  a  cylinder  graduated  in  the  following  manner :  An  ordinary  tun- 
ing-fork, vibrating,  say,  five  hundred  times  per  second,  is  so  arranged  that  a  point  con- 
nected with  one  of  its  arms  is  made  to  play  against  a  strip  of  blackened  paper.  As  the 
paper  remains  stationary,  the  point  makes  but  a  single  mark ;  but  when  the  paper 
moves,  as  the  point  vibrates,  a  line  is  produced  with  regular  curves,  every  curve  repre- 
senting yi^  of  a  second.  Now,  if  a  lever  be  attached  to  a  muscle  and  be  so  arranged  as 
to  mark  upon  the  paper,  moving  at  the  same  rate,  the  instant  when  contraction  takes 
place,  it  is  evident  that  the  interval  between  two  contractions  produced  by  stimulating 
the  nerve  at  different  points  in  its  course  will  be  most  accurately  indicated  ;  and,  if  the 
length  of  the  nerve  between  the  two  points  of  stimulation  be  known,  the  difference  in 
time  will  represent  the  rate  of  nervous  conduction. 

In  experiments  upon  frogs,  the  leg  is  prepared  by  cutting  away  the  muscles  and  bone 
of  the  thigh,  leaving  the  nerve  attached.  The  lever  is  then  applied  to  the  muscles  of 
the  leg,  and  the  stimulation  is  applied  successively  to  two  points  in  the  nerve,  the  distance 
between  them  being  carefully  measured.  The  results  obtained  in  this  way  showed  a 
rate  of  conduction  of  from  thirty-six  to  forty-six  feet  per  second ;  but  these  are  not 
regarded  by  Marey  as  invalidating  the  estimates  by  Helmholtz,  in  view  of  the  various 
conditions  by  which  the  rapidity  of  conduction'is  modified. 

Employing  the  myograph  of  Marey,  Baxt,  in  the  laboratory  of  Helmholtz,  has  suc- 
ceeded in  measuring  the  rate  of  nervous  conduction  in  the  human  subject.  In  these 
experiments,  the  swelling  of  the  muscle  during  contraction  was  limited  by  enclosing  the 
arm  in  a  plaster-mould  and  noting  the  contraction  through  a  small  opening.  By  then 
exciting  the  contraction  by  stimulating  the  radial  nerve  successively  at  different  distances 
from  the  muscle,  the  estimate  was  made.  The  rate  in  the  human  subject  was  thus  esti- 
mated at  one  hundred  arid  eleven  feet  per  second.  The  latest  experiments  upon  this  sub- 
ject by  Helmholtz  and  Baxt,  in  which  great  care  was  taken  in  the  adjustment  of  the 
apparatus,  showed  a  mean  of  rapidity  for  the  motor  nerves,  in  man,  of  about  two  hun- 
dred and  fifty-four  feet  per  second.  These  observations  were  made  in  the  summer  of 
1869  ;  and  the  difference  in  the  results  is  in  part  explained  by  the  fact,  which  was  ascer- 
tained experimentally  at  that  time,  that  a  high  temperature  increases,  and  a  diminished 
temperature  retards  the  velocity  of  nervous  conduction.  It  has  been  farther  shown  by 
Munk,  that  the  rate  of  conduction  is  different  in  different  portions  of  the  nervous  trunk ; 
the  rapidity  progressively  increasing  as  the  nerve  approaches  its  termination. 

Helmholtz,  Du  Bois-Reymond,  Marey,  and  others,  have  noted  certain  conditions 
which  modify  the  rate  of  nervous  conduction.  One  of  the  most  prominent  of  these, 
first  observed  by  Helmholtz,  is  due  to  modifications  in  temperature.  By  a  reduction  of 
temperature,  in  the  frog  at  least,  the  rate  is  very  much  reduced ;  and  at  32°  it  is  not 


GENERAL  PROPERTIES  OF  THE  NERVES.          599 

more  than  one-tenth  as  rapid  as  at  60°  or  70°.  Marey  has  also  noted  that  the  rate  is 
sensibly  reduced  by  fatigue  of  the  muscles. 

The  same  principle  which  has  led  to  the  determination  of  the  rate  of  conduction  in 
motor  nerves,  viz.,  an  estimation  of  the  difference  in  time  of  the  passage  of  a  stimulus 
applied  to  a  nerve  at  two  points  situated  at  a  known  distance  from  each  other,  has  been 
applied  to  the  conduction  of  sensations.  Hirsch  is  quoted  as  having  made  the  first 
attempt  to  resolve  this  question,  in  1851.  He  employed  the  delicate  chronometric  instru- 
ments used  in  astronomy,  and  noted  the  difference  in  time  between  the  appreciation  of 
an  impression  made  upon  a  part  of  the  body  far  removed  from  the  brain,  as  the  toe,  and 
an  impression  made  upon  the  cheek.  This  process  admitted  of  a  rough  estimate  of 
about  one  hundred  and  eleven  feet  per  second.  The  later  and  more  elaborate  researches 
of  Schelske  showed  a  rapidity  of  conduction  by  the  sensory  nerves  of  about  ninety-seven 
feet  per  second. 

Attempts  have  been  made  to  estimate  the  duration  of  acts  involving  the  central  ner- 
vous system,  such  as  the  reflex  phenomena  of  the  spinal  cord  or  the  operations  of  the 
cerebral  hemispheres.  These  have  been  partially  successful,  or,  at  least,  they  have 
shown  that  the  reflex  and  the  cerebral  acts  require  a  distinctly  appreciable  period  of 
time.  This,  in  itself,  is  an  important  fact ;  although  the  duration  of  these  acts  has  not 
yet  been  measured  with  all  the  accuracy  that  could  be  desired.  As  the  general  result 
of  experiments  upon  these  points,  it  is  found  that  the  reflex  action  of  the  spinal  cord 
occupies  more  than  twelve  times  the  period  required  for  the  transmission  of  stimulus 
or  impressions  through  the  nerves.  Bonders  found,  in  experiments  upon  his  own  person, 
that  an  act  of  volition  required  one-twenty-eighth  of  a  second,  and  one  of  simple  dis- 
tinction or  recognition  of  an  impression,  one-twenty-fifth  of  a  second.  These  estimates, 
however,  are  merely  approximative  ;  and,  until  they  attain  greater  certainty,  it  is  unne- 
cessary to  describe  in  detail  the  apparatus  employed. 

The  general  result  of  the  various  observations  we  have  detailed  upon  the  rate  of  ner- 
vous conduction  as  applied  to  the  human  subject  is,  in  the  first  place,  that  this  can  be 
measured  with  tolerable  accuracy ;  second,  that  it  is  in  no  wise  to  be  compared  with  the 
rate  of  conduction  of  light  or  electricity  ;  and,  finally,  that  the  rate  in  the  human  subject 
is  essentially  the  same  in  the  motor  and  sensory  nerves,  being,  according  to  the  most 
reliable  estimates,  about  one  hundred  and  eleven  feet  per  second. 

Action  of  Electricity  upon  the  Nerves. — A  great  deal  has  been  written  with  regard  to 
the  effects  of  electricity  upon  the  nervous  system,  and  facts  elicited  by  experiments  upon 
this  subject  are  highly  important  in  their  bearing  upon  physiology  and  pathology.  Still, 
there  are  numerous  observations  upon  this  subject  which  have  but  little  importance,  in  a 
purely  physiological  sense,  except  that  they  are  curious  and  interesting.  These  we  do 
not  propose  to  discuss  elaborately ;  and  we  shall  confine  ourselves  chiefly  to  those  points 
which  bear  directly  upon  our  knowledge  of  the  properties  and  functions  of  the  nerves. 

The  first  important  fact — to  which  we  have  already  alluded — is,  that  electricity  is  the 
best  means  that  we  have  of  artificially  exciting  the  nerves.  Using  electricity,  we  can 
regulate  with  exquisite  nicety  the  degree  of  stimulation  ;  we  can  excite  the  nerves  long 
after  they  have  ceased  to  respond  to  mechanical  or  chemical  irritation ;  the  effects  of 
different  currents  can  be  noted  ;  and,  finally,  this  mode  of  stimulation  produces  a  peculiar 
and  interesting  condition  of  the  parts  of  the  nerve  not  included  between  the  poles  of  the 
battery.  For  these  reasons,  it  seems  proper  to  devote  some  consideration,  in  this  con- 
nection, to  the  effects  of  the  application  of  this  agent  to  the  nerves. 

So  long  as  the  nerves  retain  their  irritability,  they  will  respond  to  an  electrical  stimu- 
lus. Experiments  may  be  made  upon  the  exposed  nerves  in  living  animals  or  in  ani- 
mals just  killed;  and,  of  all  classes,  the  cold-blooded  animals  present  the  most  favorable 
conditions,  on  account  of  the  persistence  of  nervous  and  muscular  irritability  for  a  con- 
siderable time  after  death.  Experimenters  most  commonly  use  frogs,  on  account  of  the 


600 


NERVOUS   SYSTEM. 


long  persistence  of  the  irritability  of  their  tissues  and  the  facility  with  which  certain  por- 
tions of  the  nervous  system  can  be  exposed.  For  ordinary  experiments  upon  the  nervous 
conduction,  the  parts  are  prepared  by  detaching  the  posterior  extremities,  removing  the 
skin,  and  cutting  away  the  bone  and  muscles  of  the  thigh,  so  as  to  leave  the  leg  with  the 
sciatic  nerve  attached.  A  frog's  leg  thus  isolated  presents  a  nervous  trunk  one  or  two 
inches  in  length,  attached  to  the  muscles,  which  will  respond  to  the  slightest  stimulus. 
It  is  by  experiments  made  upon  frogs  prepared  in  this  way  that  most  of  the  important 
facts  relative  to  the  action  of  electricity  upon  the  nervous  system  have  been  developed. 
A  form  of  galvanic  apparatus  which  we  have  long  used  and  found  very  convenient  for 
these  experiments  is  essentially  the  one  described  by  Bernard.  It  consists  simply  of 
alternate  copper  and  zinc  wires  wound  around  a  piece  of  wood  bent  in  the  form  of  a 
horseshoe  and  terminating  in  two  platinum  points  representing  the  positive  and  negative 
poles.  This  forms  a  sort  of  electric  forceps,  about  eight  inches  long,  which,  when  moist- 
ened with  water  slightly  acidulated  with  acetic  acid,  will  give  a  current  of  about  the 
strength  required  for  most  experiments. 

It  is  evident  that  the  galvanic  current  may  be  applied  to  a  nerve  so  that  the  direction 

may,  in  the  one  case,  follow  the  course  of  the 
nerve,  that  is,  from  the  centre  to  the  periphery, 
and,  in  the  other,  be  opposite  to  the  course  of  the 
nerve.  These  currents  have  been  called  respect- 
ively the  direct,  or  descending,  and  the  inverse,  or 
ascending.  When  the  positive  pole  (the  copper)  is 
placed  nearer  the  origin  of  the  nerve,  and  the 
negative  pole  (the  zinc),  below  this  point  in  the 
course  of  the  nerve,  the  galvanic  current  follows 
the  normal  direction  of  the  motor  conduction,  and 
this  is  called  the  direct  current.  When  the  poles 
are  reversed,  and  the  direction  of  the  galvanic  cur- 
rent is  from  the  periphery  toward  the  centre,  it  is 
called  the  inverse  current.  It  will  be  convenient 
to  speak  of  these  two  currents  respectively  as  di- 
rect and  inverse,  in  detailing  experiments  upon 
the  action  of  electricity  upon  the  nerves. 

The  points  to  be  noted  with  regard  to  the  effects 
of  the  application  of  electricity  to  an  exposed  nerve 
are  the  action  of  constant  currents  of  different  de- 
grees of  intensity,  the  phenomena  observed  on 
making  and  breaking  the  circuit,  and  the  effects 
of  an  interrupted  current. 

During  the  passage  of  a  feeble  constant  current 
through  an  exposed  nerve,  whatever  be  its  direc- 
tion, there  are  no  convulsive  movements  and  no 
evidences  of  pain.  This  fact  has  long  been  recog- 
nized by  physiologists,  who  at  first  limited  the 
effects  of  electricity  upon  the  nerves  to  two  pe- 
riods, one  at  the  making  of  the  circuit  and  the 
other  at  its  interruption.  We  si i all  see,  however, 
that  the  passage  of  electricity  through  a  portion 
of  a  nervous  trunk  produces  a  peculiar  condition 
in  parts  of  the  nerve  in  the  neighborhood  of  the 
poles  of  the  battery,  described  under  the  name  of 
Jtrotonus ;  but  the  fact  that  neither  motion  nor  sensation  is  excited  in  a  mixed  nerve 
during  the  actual  passage  of  a  feeble  constant  current  is  not  invalidated. 


FIG.  189.— Electric  forceps.    (Liegeois.) 

C,  copper;  Z,  zinc;  P,  P,  positive  poles;  N  N 

negative  poles. 


GENERAL  PROPERTIES  OF  THE  NERVES. 


601 


If  a  sufficiently  powerful  constant  current  be  passed  through  a  nerve,  disorganization 
of  its  tissue  takes  place,  and  the  nerve  finally  loses  its  excitability,  as  it  does  when 
bruised,  ligatured,  or  when  its  structure  is  destroyed  in  any  other  way.  It  was  thought 
by  Galvani,  and  the  idea  has  been  adopted  by  Matteucci,  Gu6rard,  and  Longet,  that  a 
current  directed  exactly  across  a  nerve,  so  as  to  pass  at  right  angles  to  its  fibres,  does 
not  give  rise  to  muscular  contraction.  This  view  is  now  accepted  by  most  modern 
experimenters. 

All  who  have  experimented  upon  the  action  of  galvanism  upon  the  mixed  nerves 
have  noted  the  fact  alluded  to  above,  that  the  phenomena  of  contraction  are  manifest- 
ed only  on  closing  or  on  breaking  the  circuit.  Take,  for  example,  a  frog's  leg  prepared 
with  the  nerve  attached  ;  place  one  pole  of  a  feeble  galvanic  apparatus  on  the  nerve  and 
then  make  the  connection,  including  a  portion  of  the  nerve  in  the  circuit ;  with  the 
mildest  currents,  contraction  occurs  only  on  closing  the  circuit,  independently  of  the 
direction  of  the  current ;  with  currents  of  medium  strength  (Pfluger),  contractions 
occur  both  at  closing  and  opening  the  circuit,  for  currents  of  either  direction ;  with 
strong  currents,  contraction  occurs  only  at  the  closing  of  the  direct  current  and  the 
opening  of  the  inverse  current.  After  a  time,  however,  the  nervous  irritability  becomes 
somewhat  enfeebled  by  exposure  of  the  parts.  The  phenomena  then  observed  belong  to 
the  conditions  involved  in  the  process  of  "  dying  "  of  the  nerve.  In  the  later  stages  of 
this  condition,  the  phenomena  may  be  formularized  as  follows : 

If  the  sciatic  nerve  attached  to  the  leg  of  a  frog,  prepared  in  the  usual  way  for  such 
experiments,  be  subjected  to  a  feeble  galvanic  current,  there  is  a  time  when  muscular 
contraction  takes  place  only  at  the  instant  when  the  circuit  is  made,  no  contraction 
occurring  when  the  circuit  is  broken  ;  and  this  occurs  only  with  the  direct  current ;  viz., 
when  the  current  flows  toward  the  periphery,  the  positive  pole  being  above,  and  the 
negative  below.  If  the  poles  be  reversed,  so  that  the  galvanic  current  flows  from  the 
periphery  toward  the  centres  (the  inverse  current),  contraction  of  the  muscles  occurs 
only  when  the  circuit  is  broken  and  none  takes  place  when  the  circuit  is  closed.  These 
phenomena  are  distinct  after  the  irritability  of  the  parts  has  become  somewhat  dimin- 
ished by  exposure  or  by  electric  stimulation  of  the  nerve,  but  they  may  occur  in  per- 
fectly fresh  parts,  when  the  galvanic  current  is  very  strong.  Usually,  when  the  ner- 
vous irritability  is  at  its  height,  contractions  occur  both  on  closing  and  breaking  the  cir- 
cuit ;  but  they  are  more  powerful  on  closing  the  circuit,  for  the  direct  current,  and  on 
breaking  the  circuit,  for  the  inverse  current.  This  fact  has  been  noted  by  all  modern 
experimenters. 


FIG.  190.— Frog's  legs  prepared  so 


to  show  the  contrasted  action  of  the  direct  and  the  inverse  cut  rent. 
(Matteucci.) 


A  very  simple  experiment  made  by  Matteucci  strikingly  illustrates  the  contrasted 
action  of  the  direct  and  the  inverse  current.  The  posterior  extremities  of  a  frog  are  pre- 
pared so  as  to  leave  the  nerves  of  the  two  sides  connected  together  by  a  portion  of  the 


602  NERVOUS  SYSTEM. 

spinal  column.  The  legs  are  then  placed  each  one  in  a  vessel  of  water,  and  a  feeble  gal- 
vanic current  is  passed  from  one  glass  to  the  other.  It  is  evident  that,  with  this  arrange- 
ment, the  current  will  pass  through  both  nerves,  being  direct  for  the  one  and  inverse  for 
the  other.  In  this  case,  if  the  irritability  of  the  nerves  be  not  too  great,  there  will  be 
a  contraction  in  the  leg  in  which  the  current  is  direct  at  the  time  of  making  the  circuit, 
and  the  other  leg  will  contract  when  the  circuit  is  broken.  This  experiment  has  been 
modified  by  Ohauveau  and  applied  to  the  two  facial  nerves  in  a  living  horse.  A  Leyden 
jar  is  very  feebly  charged  with  electricity,  and  the  two  facials  are  exposed.  The  current 
is  then  passed  instantaneously  through  both  the  nerves,  which  gives  but  a  single  stimulus 
and  that  corresponds  to  the  time  of  making  the  circuit  with  the  constant  current.  In  this 
experiment,  the  current  is  direct  for  one  nerve  and  inverse  for  the  other,  and  contraction 
takes  place  only  in  those  muscles  supplied  with  the  nerve  for  which  the  current  is  direct. 
The  muscular  contraction  produced  by  galvanic  stimulation  of  a  nerve  is  more  vig- 
orous the  greater  the  extent  of  the  nerve  included  between  the  poles  of  the  battery. 
This  fact  has  long  been  observed,  and  its  accuracy  is  easily  verified.  It  would  naturally 
be  expected  that,  the  greater  the  amount  of  stimulation,  the  more  marked  would  be  the 
muscular  action;  and  the  stimulation  seems  to  be  increased  in  proportion  to  the  extent 
of  nerve  through  which  the  galvanic  current  is  made  to  pass. 

The  irritability  of  a  nerve,  it  is  well  known,  may  be  exhausted  by  the  repeated  appli- 
cation of  electricity,  whatever  be  the  direction  of  the  current,  and  it  is  more  or  less  com- 
pletely restored  by  repose.  It  is  a  curious  fact,  in  this  connection,  that,  when  the  irrita- 
bility of  a  nerve  has  been  exhausted  for  the  direct  current,  it  will  respond  to  the  inverse 
current,  and  vice  versa;  and  it  is  even  more  remarkable  that,  after  the  irritability  has 
been  exhausted  by  the  direct  current,  it  is  restored  more  promptly  by  stimulation  with 
the  inverse  current  than  by  absolute  repose,  and  vice  versa.  This  phenomenon,  observed 
by  Volta,  is  sometimes  known  as  "  voltaic  alternation."  It  is  very  strikingly  illustrated 
in  frogs  prepared  as  above  described,  with  the  two  posterior  extremities,  the  nerves 
attached  through  a  portion  of  the  spinal  cord,  placed  in  vessels  of  water  so  that  a  current 
may  be  simultaneously  passed  through  both  nerves,  being  direct  for  the  one  and  inverse 
for  the  other.  As  we  have  already  seen,  after  a  time,  contraction  occurs  only  in  one  leg, 
for  which  the  current  is  direct,  on  making  the  circuit,  and  in  the  other,  only  on  breaking 
the  circuit.  By  repeatedly  passing  the  current  in  this  way,  after  a  time  there  will  be  no 
contraction  in  either  leg,  the  irritability  of  the  nerves  having  become  exhausted.  If  the 

poles  of  the  battery  be  now  reversed,  so  as 
to  make  the  inverse  current  take  the  place 
of  the  direct,  contractions  with  making  and 
breaking  the  circuit  will  again  occur.  The 
irritability  may  again  be  exhausted  and  re- 
stored by  changing  the  poles,  and  this  may 
be  repeated  several  times  with  the  same 
preparation. 


Induced  Muscular  Contraction.  —  A  cu- 
rious phenomenon  was  discovered  by  Mat- 
teucci,  in  experimenting  upon  nervous  and 
muscular  irritability,  which  has  been  called 
"induced  muscular  contraction."     It  was 
found  that,  if  the  nerve  of  a  galvanoscopic 
frog's  leg  (the  leg  prepared  with  the  nerve 
in  the  way  already  described)  be  placed  in  contact  with  the  muscles  of  another 
leg  prepared  in  the  same  way,  galvanization  of  the  nerve  giving  rise  to  contraction  of 
scles  with  which  the  nerve  of  the  first  leg  is  in  contact  will  induce  contraction  in 
the  muscles  of  both.     This  experiment  may  be  extended,  and  contractions  may  thus  be 


GENERAL  PROPERTIES  OF  THE  NERVES.  603 

induced  in  a  series  of  legs,  the  nerve  of  one  being  in  contact  with  the  muscles  of  another. 
This  illustrates  the  great  delicacy  of  the  galvanoscopic  frog's  leg,  as  it  will  indicate  a 
current  due  to  a  single  muscular  contraction,  which  does  not  affect  an  ordinary  galva- 
nometer. It  is  conclusively  proven  that  the  "induced  contraction,"  as  just  described,  is 
not  due  to  an  actual  propagation  of  the  galvanic  current,  but  to  a  stimulus  attending  the 
muscular  contraction  itself,  by  the  fact  that  the  same  phenomena  occur  when  the  first 
muscular  contraction  is  induced  by  mechanical  or  chemical  excitation  of  the  nerve. 

Galvanic  Current  from  the  Exterior  to  the  Cut  Surface  of  a  Nerve. — Before  we  study 
certain  phenomena  presented  in  nerves  of  which  a  portion  is  subjected  to  the  action  of 
a  constant  galvanic  current,  it  is  important  to  note  the  fact  that  there  exists  in  the 
nerves,  as  in  the  muscles,  a  galvanic  current  from  the  exterior  to  their  cut  surface.  This 
fact  has  been  noted  by  all  who  have  investigated  the  subject  of  electro-physiology.  It 
has  been  roughly  estimated  by  Matteucci  that  the  nerve-current  has  from  one-eighth 
to  one-tenth  the  intensity  of  the  muscular  current.  The  existence  of  the  nerve-current 
has,  as  far  as  we  know,  no  more  physiological  significance  than  the  analogous  fact  ob- 
served in  the  muscular  tissue.  It  is  presented  in  nerves  removed  from  the  body  and  has 
no  relation  to  their  functional  activity,  whether  in  normal  action  or  excited  by  artificial 
stimulation. 

Effects  of  a  Constant  Galvanic  Current  upon  the  Nervous  Irritability. — Aside  from 
the  disorganizing  effect  upon  the  nerves  of  a  powerful  constant  current,  which  is  due 
solely  to  decomposition  of  their  substance,  a  feeble  current  has  been  found  to  exert  an 
important  influence  upon  the  nervous  irritability,  according  to  the  direction  in  which  the 
current  is  passed.  The  law  in  accordance  with  which  this  influence  is  exerted  is  stated 
by  Matteucci  as  follows : 

"A  continued  electric  current  passed  through  a  mixed  nerve,  the  crural  or  the  lum- 
bar, for  example,  modifies  the  excitability  of  the  nerve  in  a  very  different  manner,  accord- 
ing to  its  direction.  The  excitability  is  enfeebled  by  the  passage  of  the  direct  current, 
and,  on  the  contrary,  it  is  preserved  and  augmented,  at  least  within  certain  limits,  by  the 
inverse  current.  The  time  necessary  in  order  that  the  current  shall  produce  this  modifi- 
cation is  proportionate  to  the  degree  of  excitability  of  the  nerve  and  in  inverse  ratio  to 
the  intensity  of  the  current.  After  the  breaking  of  the  circuit,  the  modification  of  the 
nerve  tends  to  cease  at  a  period  that  is  short  in  proportion  as  the  excitability  of  the  nerve 
is  great  and  the  intensity  of  the  current  is  feeble.  This  proposition  explains  the  differ- 
ence in  the  electro-physiological  effects  of  the  continued  current  according  to  its  direc- 
tion, and  the  well-known  phenomenon  of  voltaic  alternations." 

This  law  has  been  carefully  studied  and  formularized,  as  above,  by  Matteucci,  but  its 
discovery  is  attributed  by  physiological  writers  to  Pfaff.  After  a  time,  varying  with  the 
excitability  of  the  nerve  and  the  intensity  of  the  current,  the  direct  current  will  destroy 
the  nervous  irritability,  but  this  may  be  restored  by  repose,  or  more  quickly  by  the  pas- 
sage of  an  inverse  current.  If  the  inverse  current  be  passed  first  for  a  few  seconds,  a 
contraction  follows  the  breaking  of  the  circuit;  and  this  contraction,  within  certain 
limits,  is  more  vigorous  the  longer  the  current  is  passed.  At  the  same  time,  the  pro- 
longed passage  of  the  inverse  current  increases  the  excitability  of  the  nerve  for  any  kind 
of  stimulus.  When  the  inverse  current  has  been  passed  through  the  nerves  for  several 
hours,  breaking  of  the  circuit  is  followed  by  very  violent  contraction  and  a  tetanic  con- 
dition of  the  muscles,  enduring  for  several  seconds. 

Electrotonus,  Anelectrotonus,  and  Catelectrotonus. 

Many  years  ago,  Du  Bois-Reymond  discovered  the  curious  and  interesting  fact  that, 
when  a  constant  galvanic  current  is  passed  through  a  portion  of  a  freshly-prepared  nerve, 
those  parts  of  the  nerve  not  included  between  the  poles  are  brought  into  a  peculiar  con- 


604  NERVOUS  SYSTEM. 

dition.  While  in  this  state,  the  nerve  will  deflect  the  needle  of  a  delicate  galvanometer, 
and  its  excitability  is  modified.  The  deflection  of  the  needle,  in  this  instance,  is  not  due 
to  the  normal  nerve-current,  for  it  occurs  when  the  galvanometer  is  applied  to  the  surface 
of  the  nerve  only.  It  is  due  to  an  electric  tension  of  the  entire  nerve,  induced  by  the 
passage  of  a  current  through  a  portion  of  its  extent.  This  condition  is  called  electrotonus. 
The  phenomena  thus  produced  have  been  most  elaborately  studied  by  Pfliiger,  who 
farther  recognized  a  peculiar  condition  of  that  portion  of  the  nerve  near  the  anode,  or 
positive  pole,  differing  from  the  condition  of  the  nerve  near  the  cathode,  or  negative  pole. 
Near  the  anode,  the  excitability  of  the  nerve  is  diminished,  and  this  condition  has  been 
called  anelectrotonus.  Near  the  cathode,  the  excitability  is  increased,  and  this  condition 
has  been  called  catelectrotonus. 

These  varied  phenomena  have  been  the  subject  of  extended  investigation  by  electro- 
physiologists  ;  and,  although  they  are  not  to  be  ranked  among  the  physiological  properties 
of  the  nerves,  they  have  considerable  pathological  and  therapeutical  importance.  It  is 
well  known,  for  example,  that  electricity  is  one  of  the  most  efficient  agents  at  our  com- 
mand for  the  restoration  of  the  functions  of  nerves  affected  with  disease ;  and  the  con- 
stant current  has,  particularly  of  late,  been  extensively  and  successfully  used  as  a  thera- 
peutical agent.  The  constant  current,  in  restoring  the  normal  condition  of  nerves,  must 
influence,  not  only  that  portion  included  between  the  poles  of  the  battery,  but  the  entire 
nerve;  and  the  electrotonic  condition,  with  its  modifications,  explains  how  this  result 
may  be  obtained.  Undoubtedly  the  sensory  nerves  are  affected  as  well  as  the  motor, 
although  we  have  as  yet  but  little  positive  information  upon  this  point.  A  knowledge  of 
the  fact  that  the  constant  current  diminishes  the  excitability  of  the  nerve  near  the  anode 
(anelectrotonus)  and  increases  it  near  the  cathode  (catelectrotonus)  may  become  important 
in  determining  the  direction  of  the  current  to  be  employed  in  different  cases  of  disease. 

In  the  present  condition  of  the  subject  of  electro-physiology,  it  will  be  unnecessary  to 
do  more  than  to  indicate,  as  clearly  and  simply  as  possible,  the  laws  of  the  phenomena 
attending  the  passage  of  a  constant  current  through  nerves,  as  far  as  they  have  been 
definitively  ascertained. 

The  phenomena  of  electrotonus  are  very  simple ;  and  it  is  only  when  we  attempt  to 
construct  a  theory  to  account  for  these  phenomena  that  the  subject  becomes  obscure. 
Suppose,  for  example,  that  a  nerve  be  exposed  in  a  living  animal  or  in  one  just  killed, 
and  a  galvanic  current  be  applied  from  a  Grove's  battery,  in  which  about  twelve  square 
inches  of  zinc  are  exposed  to  the  action  of  a  liquid  containing  one  part  of  ordinary  sul- 
phuric acid  to  eight  of  water.  A  delicate  galvanometer  applied  to  the  nerve  either  above 
or  below  the  poles  will  indicate  a  decided  current,  much  more  intense  than  the  tranquil 
nerve-current  between  the  exterior  and  the  cut  surface.  This  electrotonic  condition  exists 
so  long  as  the  galvanic  current  is  continued ;  and,  as  has  been  shown  by  Matteucci  in 
operating  upon  the  higher  animals— rabbits,  dogs,  fowls,  and  sheep — when  the  galvanic 
current  has  been  sufficiently  powerful  and  prolonged,  the  electrotonic  condition  persists 
for  a  certain  time  after  the  stimulus  has  ceased.  As  we  have  seen  that  the  muscular 
contraction  following  galvanic  stimulation  of  a  nerve  is  powerful  in  proportion  to  the 
extent  of  nerve  included  between  the  poles  of  the  battery,  so  the  electrotonic  condition 
increases  in  intensity  with  the  length  of  the  nerve  subjected  to  the  constant  current ; 
provided,  always,  that  the  strength  of  the  current  be  slightly  increased  to  compensate  the 
enfeebling  action  due  to  the  resistance  in  the  increased  length  of  the  circuit. 

We  do  not  propose  to  discuss  fully  the  various  theories  that  have  been  advanced  in 
explanation  of  the  phenomena  of  electrotonus.  Matteucci  has  made  a  series  of  interesting 
observations  upon  conductors  formed  of  very  fine  wires,  one  of  platinum  and  the  other 
of  amalgamated  zinc,  covered  with  cotton  thread  soaked  in  a  neutral  solution  of  sulphate 
of  zinc.  The  experiments  were  then  arranged  so  as  to  operate  first  with  the  platinum 
wire  and  afterward  with  the  zinc,  by  passing  a  galvanic  current  through  a  small  portion 
of  the  conductor,  in  the  same  way  as  it  is  passed  through  a  portion  of  a  nerve.  He  found 


GENERAL  PROPERTIES  OF  THE  NERVES.          605 

that  in  this  way  he  could  produce  a  strong  electrotonic  current  in  the  platinum  wire,  even 
at  a  distance  of  more  than  three  feet  from  the  electrodes,  while  no  such  current  was 
observed  in  the  zinc.  He  remarks  that  in  the  platinum  wire  "  secondary  polarities"  are 
produced  very  powerfully  and  rapidly,  while  these  are  not  developed  in  the  zinc.  From 
these  experiments  alone,  it  might  seem  that  the  phenomena  of  electrotonus  are  to  be 
explained  entirely  by  the  physical  properties  of  the  nerves  as  conductors  of  electricity ; 
but  various  observations  on  the  nerves  under  different  conditions  have  conclusively  proven 
the  contrary.  All  observers  are  agreed  that  the  electrotonic  condition  is  marked  in  pro- 
portion to  the  excitability  of  the  nerve,  and  it  is  either  entirely  absent  or  extremely  feeble 
in  nerves  that  are  dead  or  have  lost  their  irritability.  If  a  strong  ligature  be  applied 
to  the  extra-polar  portion  of  the  nerve,  or  if  the  nerve  be  divided  and  the  cut  ends  be 
brought  in  contact  with  each  other,  the  electrotonic  condition  is  either  not  observed  or 
is  very  feeble.  These  facts  show  conclusively  that  the  phenomena  of  electrotonus 
depend  upon  the  physiological  integrity  of  nerves.  A  dead  nerve,  or  one  that  has  been 
divided  or  strongly  ligatured,  may  present  these  phenomena  under  the  stimulation  of  a 
very  powerful  current  (and  then  only  to  a  slight  degree),  when  the  condition  depends 
upon  the  purely  physical  properties  of  the  nerve  as  a  conductor ;  but  there  is  no  com- 
parison between  these  phenomena  and  those  observed  in  nerves  that  retain  their  physi- 
ological properties.  Were  it  otherwise,  how  could  the  physiological  properties  of  a  dis- 
eased nerve  be  restored  throughout  its  whole  extent  by  a  constant  current  passed  through 
a  restricted  portion,  when  the  excitability  of  the  nerve  is  only  manifested  at  the  clos- 
ing or  opening  of  the  circuit? 

Anelectrotonus  and  Cat  electrotonus. — It  is  interesting  to  note  that,  when  a  portion  of 
a  nerve  is  subjected  to  a  moderately  powerful  constant  current,  the  conditions  of  the 
extra-polar  portions  corresponding  to  the  two  poles  of  the  battery  are  entirely  different. 
Near  the  positive  pole,  or  anode,  the  excitability  of  the  nerve  and  the  rate  of  nervous 
conduction  are  diminished.  If,  however,  we  have  a  galvanometer  applied  to  this  portion 
of  the  nerve,  its  electromotive  power,  measured  by  the  deflection  of  the  galvanometric 
needle,  is  increased.  On  the  other  hand,  near  the  negative  pole,  or  cathode,  the  excita- 
bility of  the  nerve  is  increased,  as  well  as  the  rate  of  nervous  conduction  ;  but  the  elec- 
tromotive power  is  diminished.  These  facts,  at  least  so  far  as  they  relate  to  the  increase 
of  the  excitability  of  the  nerve  near  the  cathode  and  its  diminution  near  the  anode, 
are  partially  explained  by  Matteucci  upon  purely  physical  principles,  depending  upon 
the  electrolytic  action  of  the  current,  as  is  shown  by  the  following  experiment : 

Two  cups  are  filled,  the  one  with  a  very  feebly  alkaline  solution,  and  the  other  with 
an  equally  weak  acid  fluid.  A  number  of  galvanoscopic  frogs'  legs  are  then  rapidly  pre- 
pared, of  which  one-half  the  number  is  plunged  in  the  alkaline  and  one-half,  in  the  acid 
fluid,  for  from  thirty  seconds  to  one  or  two  minutes.  The  parts  are  then  removed  from 
the  liquids  and  are  carefully  washed  and  dried  in  bibulous  paper.  By  touching  the 
nerves  with  a  strong  solution  of  common  salt,  which  is  a  powerful  excitant  for  the  ner- 
vous irritability,  the  nerves  that  had  been  exposed  to  the  alkaline  solution  produced 
more  powerful  and  prompt  contractions  than  those  exposed  to  the  acid.  Now,  the  elec- 
trolytic action  of  a  constant  current  tends  to  the  accumulation  of  hydrogen  and  an  alkali 
near  the  cathode,  and  of  oxygen  and  an  acid  near  the  anode  ;  and  by  this  fact,  Matteucci 
explains  the  increase  of  excitability  in  catelectrotouus  and  the  diminished  excitability  in 
anelectrotonus.  As  regards  this  question,  we  have  only  to  say,  as  in  the  case  of  gen- 
eral electrotonus,  that  the  conditions  are  susceptible  of  a  partial  explanation  upon  purely 
physical  grounds  ;  but  precisely  how  far  the  unexplained  physiological  properties  of  the 
nerves  are  involved,  it  is  impossible  to  say. 

Neutral  Point. — The  anelectrotonic  condition,  on  the  one  hand,  and  the  catelectro- 
tonic  condition  at  the  other  pole  of  the  battery,  are  marked  in  extra-polar  portions  of 


606  NERVOUS  SYSTEM. 

the  nerve  and  are  to  be  recognized,  as  well,  in  that  portion  through  which  the  current 
is  passing;  but,  between  the  poles,  is  a  point  where  these  conditions  meet,  as  it  were, 
and  where  the  excitability  is  unchanged.  This  has  been  called  the  neutral  point.  When 
the  galvanic  current  is  of  moderate  strength,  the  neutral  point  is  about  half-way  between 
the  poles.  "  When  a  weak  current  is  used,  the  neutral  point  approaches  the  positive 
pole,  while  in  a  strong  current,  it  approaches  the  negative  pole.  In  other  words,  in  a 
weak  current  the  negative  pole  rules  over  a  wider  territory  than  the  positive  pole, 
whereas  in  a  strong  current  the  positive  pole  prevails."  (Rutherford.) 

Negative  Variation.— There  remains  to  be  considered  one  curious  phenomenon,  dis- 
covered by  Du  Bois-Reymond,  which  depends  upon  the  action  of  a  rapidly-interrupted 
current  applied  to  an  excitable  nerve.  If  a  galvanometer  be  applied  to  a  living  nerve  so 
as  to  indicate  by  its  deviation  the  normal,  or  tranquil  nerve-current,  a  rapidly -interrupted 
current  of  electricity  passed  through  a  portion  of  the  nerve,  it  is  well  known,  produces  a 
tetanic  condition  of  the  muscles.  If  we  now  watch  the  needle  of  the  galvanometer,  it 
will  be  observed  to  retrograde  and  will  finally  return  to  zero,  indicating  that  the  proper 
nerve-current  has  been  overcome.  This  will  be  observed  to  a  slight  degree  under  the 
influence  of  mechanical  or  chemical  stimulation  of  the  nerve,  the  proper  nerve-current 
being  diminished,  but  generally  not  abolished.  This  variation  of  the  needle  under  the 
influence  of  the  tetanic  condition  has  been  called  negative  variation.  We  do  not  yet 
know  that  it  has  any  important  physiological  or  pathological  significance. 


CHAPTER  XVIII. 

SPINAL  NERVES-MOTOR  CRANIAL  NERVES. 

Special  nerves  coming  from  the  spinal  cord — Cranial  nerves — Anatomical  classification — Physiological  classification — 
Motor  oculi  communis  (third  nerve)— Physiological  anatomy— Properties  and  functions— Influence  upon  the 
movements  of  the  iris — Patheticus,  or  trochlearis  (fourth  nerve)— Physiological  anatomy — Properties  and  func- 
tions—Motor oculi  externus,  or  abducens  (sixth  nerve)— Physiological  anatomy— Properties  and  functions- 
Motor  nerves  of  the  face— Nerve  of  mastication  (the  small,  or  motor  root  of  the  fifth)— Physiological  anatomy 
— Deep  origin — Distribution — Properties  and  functions  of  the  nerve  of  mastication — Facial  nerve,  or  nerve  of 
expression  (the  portio  dura  of  the  seventh)— Physiological  anatomy— Intermediary  nerve  of  Wrisberg— Decus- 
sation  of  the  fibres  of  origin  of  the  facial — Alternate  paralysis — Course  and  distribution  of  the  facial— Anasto- 
moses with  sensitive  nerves— Properties  and  functions  of  the  facial— Functions  of  the  branches  of  the  facial 
within  the  aqueduct  of  Fallopius — Functions  of  the  chorda  tympani — Influence  of  various  branches  of  the  facial 
upon  the  movements  of  the  palate  and  uvula— Functions  of  the  external  branches  of  the  facial— Spinal  accessory 
nerve  (third  division  of  the  eighth)— Physiological  anatomy— Properties  and  functions  of  the  spinal  accessory- 
Functions  of  the  internal  branch  from  the  spinal  accessory  to  the  pneumogastric — Influence  of  the  spinal  acces- 
sory upon  the  heart— Functions  of  the  external,  or  muscular  branch  of  the  spinal  accessory— Sublingual,  or 
hypoglossal  nerve  (ninth)— Physiological  anatomy— Properties  and  functions  of  the  sublingual— Glosso-labial 
paralysis. 

Spinal  Nerves. 

WITH  a  thorough  knowledge  of  the  general  properties  of  the  nerves  belonging  to  the 
cerebro-spinal  system,  the  functions  of  most  of  the  special  nerves  are  apparent  simply 
from  their  anatomical  relations.  This  is  especially  true  of  the  spinal  nerves.  These,  in 
general  terms,  are  distributed  to  the  muscles  of  the  trunk  and  extremities,  to  the  sphinc- 
ters and  the  integument  covering  these  parts,  the  posterior  segment  of  the  head,  and 
a  portion  of  the  mucous  membranes.  It  is  evident,  therefore,  that  an  account  of  the 
exact  function  of  each  nervous  branch  would  necessitate  a  full  description,  not  only  of 
the  nerves,  but  of  the  muscles  of  the  body,  which  is  manifestly  within  the  scope  only  of 
elaborate  treatises  on  descriptive  anatomy.  It  is  sufficient  to  indicate,  in  this  connec- 
tion, that  there  are  thirty-one  pairs  of  spinal  nerves ;  eight  cervical,  twelve  dorsal,  five 


SPINAL  NERVES. 


607 


lumbar,  five  sacral,  and  one  coccygeal.  Each  nerve  arises  from  the  spinal  cord  by  an 
anterior  (motor)  and  a  posterior  (sensory)  root ;  the  posterior  roots  being  the  larger,  and 
each  having  a  ganglion.  Immediately  beyond  the  ganglion,  the  two  roots  unite  into  a 
single  mixed  nerve,  which  passes  out  of  the  spinal  canal  by  the  intervertebral  foramen. 
The  nerve  thus  constituted  is  endowed  with  both  motor  and  sensory  properties.  It 
divides  outside  of  the  spinal  canal  into  two  branches,  anterior  and  posterior,  both  con- 
taining motor  and  sensory  filaments,  which  are  distributed  respectively  to  the  anterior 
and  the  posterior  parts  of  the  body.  The  anterior  branches  are  the  larger,  and  they  sup- 
ply the  limbs  and  all  parts  in  front  of  the  spinal  column. 


FIG.  192.— Cervical  portion  of  FIG.  193.— Dorsal  portion  of          FIG.   194.— Inferior  portion  of 

the  spinal  cord.    (Hirsch-  the  spinal  cord.    (Hirsch-  tJie  spinal  cord,  and  cau- 

feld.)  feld).  da  equina."   (Hirschfeld.) 

1,  antero-inferior  wall  of  the  fourth  ventricle;  2,  superior  peduncle  of  the  cerebellum;  8,  middle  peduncle  of  the 
cerebellum ;  4,  inferior  peduncle  of  the  cerebellum ;  5,  inferior  portion  of  the  posterior  median  columns  of  the 
cord;  6,  glosso-pharyngeal  nerve;  7,  pneumogastric ;  8,  spinal  accessory  nerve;  9,  9,  9,  9,  dentated  ligament;  10, 
10, 10,  10,  posterior  roots  of  tJie  spinal  nerves;  11,  11,  11, 11,  posterior  lateral  groove;  12,  12, 12,  12,  ganglia 
of  the  posterior  roots  of  the  nerves;  18, 13,  anterior  roots  of  the  nerves  ;  14,  division  of  the  nerves  into  two 
branches;  15,  lower  extremity  of  the  cord;  16,  16,  coccygeal  ligament;  IT,  17,  cauda  equina;  I— VIII,  cervical 
nerves;  I,  II,  III,  IV— XII,  dorsal  nerves ;  I,  II— V,  lumbar  nerves ;  I— V,  sacral  nerves. 


The  anterior  branches  of  the  four  upper  cervical  nerves  form  the  cervical  plexus,  and 
the  four  inferior  cervical  nerves;  with  the  first  dorsal,  form  the  brachial  plexus.  The 
anterior  branches  of  the  dorsal  nerves,  with  the  exception  of  the  first,  supply  the  walls 
of  the  chest  and  abdomen.  These  nerves  go  directly  to  their  distribution,  and  do  not 
first  form  a  plexus,  like  most  of  the  other  spinal  nerves.  The  anterior  branches  of  the 
four  upper  lumbar  nerves  form  the  lumbar  plexus.  The  anterior  branch  of  the  fifth 
lumbar  nerve  and  a  branch  from  the  fourth  unite  with  the  anterior  branch  of  the  first 
sacral,  forming  the  lumbo-sacral  nerve,  and  enter  into  the  sacral  plexus.  The  three 
upper  anterior  sacral  nerves  with  a  branch  from  the  fourth  form  the  sacral  plexus.  The 
greatest  portion  of  the  fourth  anterior  sacral  is  distributed  to  the  pelvic  viscera  and  the 


608 


NEKVOCS  SYSTEM. 


muscles  of  the  anus.  The  fifth  anterior  sacral  and  the  coccygeal  are  distributed  about 
the  coccyx. 

The  posterior  branches  of  the  spinal  nerves  are  very  simple  in  their  distribution. 
With  one  or  two  exceptions,  which  have  no  great  physiological  importance,  these  nerves 
pass  backward  from  the  main  trunk,  divide  into  two  branches,  external  and  internal,  and 
their  filaments  of  distribution  go  to  the  muscles  and  integument  behind  the  spinal  column. 

It  is  farther  important  to  note,  as  we  shall  have  occasion  to  do  more  particularly  in 
connection  with  the  great  sympathetic  nerve,  that  all  of  the  cerebro- spinal  nerves  anas- 
tomose with  the  sympathetic.  This  anatomical  connection  between  the  two  systems  of 
nerves  has  great  physiological  interest. 

Cranial  Nerves. 

The  nerves  which  pass  out  from  the  cranial  cavity  present  certain  differences,  in  their 
arrangement  and  general  properties,  from  the  ordinary  spinal  nerves.  As  we  have  seen, 
the  spinal  nerves  are  exceedingly  simple,  each  one  being  formed  by  the  union  of  a  motor 

and  a  sensory  root.  The  function  of 
most  of  them  follows  as  a  matter  of 
course  when  we  understand  their  gen- 
eral properties  and  anatomical  distri- 
bution. Many  of  the  cranial  nerves, 
however,  are  peculiar,  either  as  regards 
their  general  properties  or  in  their  dis- 
tribution to  parts  concerned  in  special 
functions.  In  some  of  these  nerves,  the 
most  important  facts  concerning  their 
distribution  have  been  ascertained  only 
by  physiological  experimentation,  and 
their  anatomy  is  inseparably  connected 
with  their  physiology.  It  would  be  de- 
sirable, if  it  were  possible,  to  classify 
these  nerves  with  reference  strictly  to 
their  properties  and  functions ;  but  this 
can  be  done  only  to  a  certain  extent, 
and  we  must  adopt  as  a  basis  those 
divisions  recognized  in  the  best  works 
upon  anatomy. 

The  two  classifications  of  the  cranial 
nerves  adopted  by  most  anatomists  are 
the  arrangements  of  Willis  and  of  Som- 
merring.  The  first  of  these  is  the  more 
common,  and  in  it  the  nerves  are  num- 
bered from  before  backward,  in  the  or- 
der in  which  they  pass  out  of  the  skull, 
making  nine  pairs. 


FIG.  195.— Boots  of  the  cranial  nerves.    (Hirschfeld.) 
I.  First  pair;  olfactory. 
II.  Second  pair;  optic. 

III.  Third  pair  ;  motor  oculi  communis. 

IV.  Fourth  pair;  patheticus. 

V.  Fifth  pair;  nerve  of  mastication  and  trifacial. 
VI.  Sixth  pair;  motor  oculi  externus. 

Vril    Iud?tory.iSeventhP^. 
IX.  Glosso-pharyngeal.  ) 
X.  Pneumogastric.        V  Eighth  pair. 
XI.  Spinal  accessory.     \ 
XII.  Ninth  pair  ;  sublingual. 

The  numbers  1  to  15  refer  to  branches  which  will  be  described 
hereafter. 


of  the 


Anatomical   Classification 

Cranial  Nerves. 
First  Pair. — Olfactory ;  the  special 
nerve  of  smell. 

Second  Pair.— Optic  ;   the  special  nerve  of  sight. 

Third  Pair.— Motor  oculi  communis ;  a  motor  nerve  distributed  to  all  of  the  muscles 
of  the  eyeball,  except  the  external  rectus  and  the  superior  oblique,  to  the  iris,  and  to  the 
levator  palpebrse. 


PHYSIOLOGICAL  CLASSIFICATION  OF  THE  CRANIAL  NERVES.     609 

Fourth  Pair. — Patheticus,  or  trocblearis  ;  a  motor  nerve  sent  to  the  superior  oblique 
muscle  of  the  eye. 

Fifth  Pair. — A  small  motor  root  (nerve  of  mastication),  distributed  to  the  muscles  of 
mastication,  and  a  large  root  (trifacial),  the  nerve  of  general  sensibility  of  the  face. 

Sixth  Pair. — Motor  oculi  externus,  or  abducens ;  a  motor  nerve  passing  to  the  exter- 
nal rectus  muscle  of  the  eye. 

Seventh  Pair. — Portio  mollis,  or  auditory,  a  special  nerve  of  hearing;  and  the  portio 
dura,  or  facial,  a  motor  nerve  distributed  to  the  superficial  muscles  of  the  face. 

Eighth  Pair. — Glosso-pharyngeal  ;  pneumogastric,  or  par  vagum ;  and  spinal  acces- 
sory. Three  mixed  nerves,  with  quite  extensive  distributions. 

Ninth  Pair. — Sublingual,  or  hypoglossal ;  a  motor  nerve  distributed  to  the  tongue. 

Physiological  Classification  of  the   Cranial  Nerves. 

(a)  Nerves  of  Special  Sense. 
Olfactory. 
Optic. 
Auditory. 

Gustatory,  comprising  a  part  of  the  glosso-pharyngeal  and  a  small  filament  from  the 
facial  to  the  lingual  branch  of  the  fifth. 

(b)  Nerves  of  Motion. 

Nerves  of  motion  of  the  eyeball,  comprising  the  motor  oculi  communis,  the  patheti- 
ous,  and  the  motor  oculi  externus. 

Nerve  of  mastication,  or  motor  root  of  the  fifth. 
Facial,  sometimes  called  the  nerve  of  expression. 
Spinal  accessory. 
Sublingual. 

(c)  Nerves  of  General  Sensibility. 

Trifacial,  or  large  root  of  the  fifth. 
A  portion  of  the  glosso-pharyngeal. 
Pneumogastric. 

In  the  above  arrangement,  the  nerves  are  classified  according  to  their  properties  at 
their  roots.  In  their  course,  some  of  these  nerves  become  mixed  and  their  branches  are 
both  motor  and  sensory,  such  as  the  pneumogastric  and  the  inferior  maxillary  branch  of 
the  trifacial. 

The  nerves  of  special  sense  are  but  slightly  if  at  all  endowed  with  general  sensi- 
bility; and,  with  the  exception  of  the  gustatory  nerves,  they  do  not  present  a  ganglion 
on  their  roots,  in  this,  also,  differing  from  the  ordinary  sensory  nerves.  They  are  capa- 
ble, therefore,  of  conveying  to  the  nerve-centres  only  certain  peculiar  impressions;  such 
as  odors,  for  the  olfactory  nerves ;  light,  for  the  optic  nerves ;  and  sound,  for  the  auditory 
nerves.  The  proper  transmission  of  these  impressions,  however,  involves  the  action  of 
accessory  organs,  more  or  less  complex ;  and  we  shall  pass  over  the  properties  of  these 
nerves  until  we  come  to  treat  in  fuH  of  the  special  senses. 

Motor   Oculi   Communis  (Third  JVerve). 

The  third  cranial  nerve  is  the  most  important  of  the  motor  nerves  distributed  to  the 
muscles  of  the  eyeball.  Its  physiology  is  readily  understood  in  connection  with  its  dis- 
tribution, the  only  point  at  all  obscure  being  its  relations  to  the  movements  of  the  iris, 
upon  which  the  results  of  experiments  are  somewhat  contradictory.  As  an  introduction 
to  the  study  of  the  functions  of  this  nerve,  it  will  be  necessary  to  describe  its  anatomical 
relations. 

39 


610 


NERVOUS   SYSTEM. 


Physiological  Anatomy.-!***  all  of  the  cranial  nerves,  this  has  an  apparent  origin, 
where  it  separates  from  the  encephalon,  and  a  deep  origin,  which  is  the  last  point  to- 
which  its  fibres  can  be  traced  in  the  substance  of  the  brain  ;  but  the  origin  has  not  the 
physiological  importance  attached  to  its  ultimate  distribution. 

The  apparent  origin  of  the  third  nerve  is  from  the  inner  edge  of  the  crus  cerebn,  direct- 
ly in  front  of  the  pons  Varolii,  midway  between  the  pons  and  the  corpora  albicantia.  It 
presents  here  from  eight  to  ten  filaments,  of  nearly  equal  size,  which  soon  unite  into  a 
single,  rounded  trunk. 

The  deep  origin  of  the  nerve  has  been  studied  by  dissections  of  the  encephalon  fresh 
and  hardened  by  different  liquids.  From  the  groove  by  which  they  emerge  from  the 
encephalon,  the  fibres  spread  out  in  a  fan-shape,  the  middle  filaments  passing  inward,  the 

anterior,  inward  and  forward,  and  the  posterior, 
inward  and  backward.  It  is  probable  that  the 
middle  filaments  pass  to  the  median  line  and  de- 
cussate with  corresponding  fibres  from  the  oppo- 
site side.  The  anterior  filaments  pass  forward 
and  are  lost  in  the  optic  thalamus.  The  poste- 
rior filaments  on  either  side  pass  backward  and 
decussate  beneath  the  aqueduct  of  Sylvius.  This 
apparent  decussation  of  the  fibres  of  origin  of  the 
third  nerves  is  important  in  connection  with  the 
harmony  of  action  of  the  muscles  of  the  eyes  and 
the  iris  upon  the  two  sides. 

The  distribution  of  the  third  nerve  is  very 
simple.  As  it  passes  into  the  orbit  by  the  sphe- 
noidal  fissure,  it  divides  into  two  branches.  The 
superior,  which  is  the  smaller,  passes  to  the  su- 
perior rectus  muscle  of  the  eye,  and  certain  of 
FIG.  196.—  Distribution  o  the  motor  oculi  com-  its  filaments  are  continued  to  the  levator  palpe- 

b™  s«peri°ris-  The  inferior  division  breaks  UP 

into  three  branches.     The  internal  branch  pass- 

,  ,        .    ,,     . 

es  to  the  internal  rectus  muscle  ;    the  interior 

branch,   to  the    inferior    rectus;    the    external 

branch>  the  iarfst  of  the  three>  is  d:stributed  to 

H  extemus  anastomosing  with  the  sympathet-   the  inferior  oblique  muscle,  and,  in  its  course,  it 

sends  a  short  and  thick  filament  to  the  lenticular, 

or  ophthalmic  ganglion  of  the  sympathetic.  It  is  this  branch  which  is  supposed,  through 
the  short  ciliary  nerves  passing  from  the  lenticular  ganglion,  to  furnish  the  motor  influ- 
ence to  the  iris.  In  its  course,  this  nerve  receives  a  few  very  delicate  filaments  from  the 
cavernous  plexus  of  the  sympathetic  and  a  branch  from  the  ophthalmic  division  of 
the  trifacial. 

Properties  and  Functions  of  the  Motor  Oculi  Communis.  —  Irritation  applied  to  the 
root  of  the  third  nerve  in  a  living  animal  produces  contraction  of  the  muscles  to  which 
it  is  distributed,  but  no  pain.  If  the  irritation,  however,  be  applied  a  little  farther  on, 
in  the  course  of  the  nerve,  there  are  evidences  of  sensibility,  which  is  readily  explained 
by  its  communications  with  the  ophthalmic  branch  of  the  trifacial.  At  its  root,  there- 
fore, this  nerve  is  exclusively  motor,  and  its  functions  are  connected  entirely  with  the 
action  of  muscles. 

Most  of  the  important  facts  bearing  upon  the  functions  of  the  motor  oculi  are  clearly 
demonstrable  by  dividing  the  nerve  in  a  living  animal  and  are  illustrated  by  cases  of  its 
paralysis  in  the  human  subject.  All  physiologists  who  have  divided  the  nerve  in  living 
animals  are  agreed  with  regard  to  the  phenomena  following  its  section,  which  depend 
upon  paralysis  of  the  voluntary  muscles.  These  phenomena  are  as  follows  : 


.  rior  branch  ;  ^jUaments  which  this  branch 
sends  to  the  superior  rectus  and  the  levator 
paipebri  superioris  ;  4,  branch  to  the  inter- 


MOTOR  OCULI   COMMUNIS  (THIRD  NERVE).  611 

1.  Falling  of  the  upper  eyelid,  or  blepharoptosis. 

2.  External  strabismus,  immobility  of  the  eye  (except  in  an  outward  direction),  ina- 
bility to  rotate  the  eye  on  its  antero-posterior  axis  in  certain  directions,  with  slight  pro- 
trusion of  the  eye-ball. 

3.  Dilatation  of  the  pupil,  with  a  certain  amount  of  interference  with  the  movements 
of  the  iris. 

The  falling  of  the  upper  eyelid  is  constantly  observed  after  division  of  the  third  nerve 
in  living  animals  and  always  follows  its  complete  paralysis  in  the  human  subject.  An  ani- 
mal in  which  the  nerve  has  been  divided  cannot  raise  the  lid,  but  can  approximate 
the  lids  more  closely,  by  a  voluntary  effort.  In  the  human  subject,  the  falling  of  the  lid 
gives  to  the  face  a  very  peculiar  and  characteristic  expression.  The  complete  loss  of 
power  shows  that  the  levator  palpebrss  superioris  muscle  depends  upon  the  third  nerve 
entirely  for  its  motor  filaments.  In  pathology,  external  strabismus  is  very  frequently 
observed  without  falling  of  the  lid,  the  filament  distributed  to  the  levator  muscle  not 
being  affected. 

The  external  strabismus  and  the  immobility  of  the  eyeball  except  in  an  outward  direc- 
tion are  due  to  paralysis  of  the  internal,  superior,  and  inferior  recti  muscles,  the  external 
rectus  acting  without  its  antagonist.  This  condition  requires  no  farther  explanation. 
These  points  are  well  illustrated  by  the  experiment  of  dividing  the  nerve  in  rabbits. 
If  the  head  of  the  animal  be  turned  inward,  exposing  the  eye  to  a  bright  light,  the  globe 
will  turn  outward,  by  the  action  of  the  external  rectus ;  but,  if  the  head  be  turned  out- 
ward, the  globe  remains  motionless. 

It  is  somewhat  difficult  to  note  the  effects  of  paralysis  of  the  inferior  oblique  muscle, 
which  is  also  supplied  by  the  third  nerve.  This  muscle,  acting  from  its  origin  at  the 
inferior  and  internal  part  of  the  circumference  of  the  base  of  the  orbit  to  its  attachment 
at  the  inferior  and  external  part  of  the  posterior  hemisphere  of  the  eyeball,  gives  to  the 
globe  a  movement  of  rotation  on  an  oblique,  horizontal  axis,  downward  and  backward, 
directing  the  pupil  upward  and  outward.  When  this  muscle  is  paralyzed,  the  superior 
oblique,  having  no  antagonist,  rotates  the  globe  upward  and  inward,  directing  the  pupil 
downward  and  outward.  The  action  of  the  oblique  muscles  is  observed  when  we  move 
the  head  alternately  toward  one  shoulder  and  the  other.  In  the  human  subject,  when 
the  inferior  oblique  muscle  on  one  side  is  paralyzed,  the  eye  cannot  move  in  a  direction 
opposite  to  the  movements  of  the  head,  as  it  does  upon  the  sound  side,  so  as  to  keep  the 
pupil  fixed,  and  the  patient  has  double  vision. 

When  all  the  muscles  of  the  eyeball,  except  the  external  rectus  and  superior  oblique, 
are  paralyzed,  as  they  are  by  section  of  the  third  nerve,  the  globe  is  slightly  protruded, 
simply  by  the  relaxation  of  most  of  its  muscles.  An  opposite  action  is  easily  observed 
in  a  cat  with  the  facial  nerve  divided,  so  that  it  cannot  close  the  lids.  When  the  cornea 
is  touched,  all  of  the  muscles,  particularly  the  four  recti,  act  to  draw  the  globe  into  the 
orbit,  which  allows  the  lid  to  fall  slightly,  and  projects  the  little  membrane  which  serves 
as  a  third  eyelid  in  these  animals. 

Observations  with  regard  to  the  influence  of  the  third  nerve  upon  the  movements  of 
the  iris  have  not  been  so  satisfactory  in  their  results  as  those  relating  to  the  muscles  of  the 
eyeball.  It  will  be  remembered  that  this  nerve  sends  a  filament  to  the  ophthalmic  gan- 
glion of  the  sympathetic,  and  that,  from  this  ganglion,  the  short  ciliary  nerves  take  their 
origin  and  pass  to  the  iris.  The  ganglia  of  the  sympathetic  system  receive  branches  both 
from  motor  and  sensory  nerves  belonging  to  the  cerebro-spinal  system,  and  the  ophthal- 
mic ganglion  is  no  exception  to  this  rule.  While  it  is  undoubtedly  true  that  division  of 
the  third  nerve  affects  the  movements  of  the  iris,  it  becomes  a  question  whether  this  be 
a  direct  influence,  or  an  influence  exerted  primarily  upon  the  ganglion,  not,  perhaps, 
differing  from  the  general  effects  upon  the  sympathetic  ganglia  that  follow  destruction  of 
their  branches  of  communication  with  the  motor  nerves. 

The  most  important  experimental  observations  with  regard  to  the  influence  of  the 


Q12  NERVOUS  SYSTEM. 

third  nerve  upon  the  iris  are  the  following :  Herbert  Mayo  made  experiments  on  thirty 
pigeons,  living  or  just  killed,  upon  the  action  of  the  optic,  the  third,  and  the  fifth  nerves 
on  the  iris.  He  states  that,  when  the  third  nerves  are  divided  in  the  cranial  cavity  in  a  liv- 
ing pigeon,  the  pupils  become  fully  dilated  and  do  not  contract  on  the  admission  of  intense 
light ;  and,  when  the  same  nerves  are  pinched  in  the  living  or  dead  bird,  the  pupils  are 
contracted  for  an  instant  on  each  stimulation  of  the  nerves.  The  same  results  follow 
division  or  irritation  of  the  optic  nerves  under  similar  conditions ;  but,  when  the  third 
nerves  have  been  divided,  no  change  in  the  pupil  ensues  upon  irritating  the  entire  or 
divided  optic  nerves. 

The  above  experiments  are  accepted  by  nearly  all  physiological  writers ;  and  the 
assumption  is  that  the  third  nerves  animate  the  muscular  fibres  that  contract  the  pupil, 
the  contraction  produced  by  irritation  of  the  optic  nerves  being  reflex  in  its  character. 
Later  observers,  however,  have  carried  their  experiments  somewhat  farther.  Longet 
divided  the  motor  oculi  and  the  optic  nerve  upon  the  right  side.  He  found  that  irrita- 
tion of  the  central  end  of  the  divided  optic  nerve  produced  no  movement  of  the  pupil 
of  the  side  upon  which  the  motor  oculi  had  been  divided,  but  caused  contraction  of  the 
iris  upon  the  opposite  side.  This,  taken  in  connection  with  the  fact  that,  in  amaurosis 
affecting  one  eye,  the  iris  upon  the  affected  side  will  not  contract  under  the  stimulus  of 
light  applied  to  the  same  eye,  but  will  act  when  the  uninjured  eye  is  exposed  to  the 
light,  farther  illustrates  the  reflex  action  which  takes  place  through  these  nerves. 

The  reflex  action  by  which  the  iris  is  contracted  is  not  instantaneous,  like  most  of  the 
analogous  phenomena  observed  in  the  cerebro-spinal  system,  and  its  operations  are  rather 
characteristic  of  the  sympathetic  system  and  the  non-striated  muscular  tissue.  It  has 
been  found,  also,  by  Bernard,  in  experiments  upon  rabbits,  that  the  pupil  is  not  immedi- 
ately dilated  after  division  of  the  third  nerve.  The  method  employed  by  Bernard,  intro- 
ducing a  hook  into  the  middle  temporal  fossa  through  the  orbit  and  tearing  the-  nerve, 
can  hardly  be  accomplished  without  touching  the  ophthalmic  branch  of  the  fifth,  which 
produces  intense  pain  and  is  always  followed  by  a  more  or  less  persistent  contraction  of 
the  pupil.  Several  hours  after  the  operation,  however,  the  pupil  is  generally  found 
dilated,  and  it  may  slowly  contract  when  the  eye  is  exposed  to  the  light.  In  one  experi- 
ment, this  occurred  after  the  eye  had  been  exposed  for  an  hour.  But  farther  experi- 
ments by  Bernard  show  that,  although  the  pupil  contracts  feebly  and  slowly  under  the 
stimulus  of  light  after  division  of  the  motor  oculi,  it  will  dilate  under  the  influence  of 
belladonna  and  can  be  made  to  contract  by  operating  upon  other  nerves.  It  is  well 
known,  for  example,  that  division  or  irritation  of  the  fifth  nerve  produces  contraction  of 
the  pupil.  This  takes  place  after  as  well  as  before  division  of  the  third  nerve.  Section 
of  the  sympathetic  in  the  cervical  region  also  contracts  the  pupil,  and  this  occurs  after 
paralysis  of  the  motor  oculi.  These  facts  show  that  the  third  nerve  is  not  the  only  one 
capable  of  acting  upon  the  iris,  and  that  it  is  not  the  sole  avenue  for  the  transmission 
of  reflex  influences. 

Bernard  also  found  that  galvanization  of  the  motor  oculi  itself  did  not  produce  con- 
traction of  the  pupil,  but  this  result  followed  when  he  galvanized  the  ciliary  nerves 
coming  from  the  ophthalmic  ganglion.  Chauveau  states  that,  in  experiments  upon 
horses,  he  has  not  'observed  contraction  of  the  pupil  following  galvanization  of  the  motor 
oculi,  although  he  has  sometimes  seen  it  in  rabbits.  At  all  events,  contraction  is  by  no 
means  constant ;  and,  when  it  occurs,  it  probably  depends  upon  stimulation  of  the  ciliary 
nerves  themselves  or  irritation  of  the  ophthalmic  branch  of  the  fifth,  and  not  upon  stimu- 
lation of  the  trunks  of  the  third  pair. 

The  movements  of  the  iris  will  be  treated  of  again,  in  connection  with  the  physiology 
of  vision ;  but  we  may  here  allude  to  an  interesting  fact  observed  by  Miiller,  which  relates 
to  the  action  of  the  motores  oculorum.  When  the  eye  is  turned  inward  by  a  voluntary 
effort,  the  pupil  is  always  contracted ;  and  when  the  axes  of  the  two  eyes  are  made  to 
converge  strongly,  as  in  looking  at  near  objects,  the  contraction  is  very  great. 


PATHETIOUS,    OR  TROCHLEARIS   (FOURTH  NERVE).  613 

The  following  case,  kindly  sent  for  examination  by  Dr.  Althof,  of  the  New  York  Eye 
Infirmary,  illustrates,  in  the  human  subject,  nearly  all  of  the  phenomena  following  paraly- 
sis of  the  motor  oculi  communis  in  experiments  upon  the  lower  animals : 

The  patient  was  a  girl,  nineteen  years  of  age,  with  complete  paralysis  of  the  nerve 
upon  the  left  side.  There  was  slight  protrusion  of  the  eyeball,  complete  ptosis,  with  the 
pupil  moderately  dilated  and  insensible  to  ordinary  impressions  of  light.  The  sight  was 
not  affected,  but  there  was  double  vision,  except  when  objects  were  placed  before  the 
eyes  so  that  the  axes  were  parallel,  or  when  an  object  was  seen  with  but  one  eye.  The 
axis  of  the  left  eye  was  turned  outward,  but  it  was  not  possible  to  detect  any  deviation 
upward  or  downward.  Upon  causing  the  patient  to  incline  the  head  alternately  to  one 
shoulder  and  the  other,  it  was  evident  that  the  affected  eye  did  not  rotate  in  the  orbit 
but  moved  with  the  head.  This  seemed  to  be  a  case  of  complete  and  uncomplicated 
paralysis  of  the  third  nerve. 

Patheticus,  or  Trochlearis  (Fourth  Nerve). 

Except  as  regards  the  influence  of  the  motor  oculi  communis  upon  the  iris,  the  pa- 
theticus  is  to  be  classed  with  the  other  motor  nerves  of  the  eyeball.  Its  physiology 
is  extremely  simple  and  resolves  itself  into  the  action  of  a  single  muscle,  the  superior 
oblique.  It  will  be  necessary,  therefore,  only  to  describe  its  origin,  distribution,  and 
connections. 

Physiological  Anatomy. — The  apparent  origin  of  the  patheticus  is  from  the  superior 
peduncles  of  the  cerebellum ;  but  it  may  be  easily  traced  to  the  valve  of  Vieussens.  The 
deep  roots,  which  are  covered  by  an  extremely  thin  layer  of  nerve-substance,  can  be 
traced,  passing  from  without  inward,  to  the  following  parts  :  One  filament  is  lost  in  the 
substance  of  the  peduncles ;  other  filaments  pass  from  before  backward  into  the  valve 
of  Vieussens  and  are  lost,  and  a  few  pass  into  the  frenulum ;  a  few  filaments  pass  back- 
ward and  are  lost  in  the  corpora  quadrigemina ;  bnt  the  greatest  number  pass  to  the 
median  line  and  decussate  with  corresponding  filaments  from  the  opposite  side.  The 
decussation  of  the  fibres  of  origin  of  the  fourth  nerves  has  the  same  physiological  signifi- 
cance as  the  decussation  of  the  roots  of  the  third.  From  this  origin,  the  patheticus  passes 
into  the  orbit  by  the  sphenoidal  fissure  and  is  distributed  to  the  superior  oblique  muscle 
of  the  eyeball.  In  the  cavernous  sinus,  it  receives  branches  of  communication  from  the 
ophthalmic  branch  of  the  fifth,  but  these  are  not  closely  united  with  the  nerve.  A  small 
branch  passes  into  the  tentorium,  and  one  joins  the  lachrymal  nerve,  these,  however, 
being  exclusively  sensitive  and  coming  from  the  ophthalmic  branch  of  the  fifth.  It  also 
receives  a  few  filaments  from  the  sympathetic. 

Properties  and  Functions  of  the  Patheticus. — Direct  observations  upon  the  patheticus 
in  living  animals  have  shown  that  it  is  motor,  and  its  galvanization  excites  contraction 
of  the  superior  oblique  muscle  only.  The  question  of  the  function  of  the  nerve,  there- 
fore, resolves  itself  simply  into  the  mode  of  action  of  the  superior  oblique  muscle.  This 
muscle  arises  just  above  the  inner  margin  of  the  optic  foramen,  passes  forward,  along  the 
upper  wall  of  the  orbit  at  its  inner  fingle,  to  a  little  cartilaginous  ring  which  serves  as  a 
pulley.  From  its  origin  to  this  point  it  is  muscular.  Its  tendon  becomes  rounded  just 
before  it  passes  through  the  pulley,  where  it  makes  a  sharp  curve,  passes  outward  and 
slightly  backward,  and  becomes  spread  out  to  be  attached  to  the  globe  at  the  superior 
and  external  part  of  its  posterior  hemisphere.  It  acts  upon  the  eyeball  from  the  pulley 
at  the  upper  and  inner  portion  of  the  orbit  as  the  fixed  point  and  rotates  the  eye  upon 
an  oblique,  horizontal  axis,  from  below  upward,  from  without  inward,  and  from  behind 
forward.  By  its  action,  the  pupil  is  directed  downward  and  outward.  It  is  the  direct 
antagonist  of  the  inferior  oblique,  the  action  of  which  has  been  described  in  connection 


614 


NERVOUS  SYSTEM. 


with  the  motor  oculi  communis.  When  the  patheticus  is  paralyzed,  the  eyeball  is  im- 
movable, as  far  as  rotation  is  concerned ;  and,  when  the  head  is  moved  toward  the  shoul- 
der, the  eye  does  not  rotate  to  maintain  the  globe  in  the  same  relative  position,  and  we 
have  double  vision. 


FIG.  197.— Distribution  of  the  patheticus.  (Hirschfeld.) 
I,  olfactory  nerve ;  II,  optic  nerves  ;  III,  motor  oculi  com- 
munis; IV,  patheticus,  ~by  the  xide  of  the  ophthal- 
mic branch  of  the  fifth,  and  passing  to  the  superior 
oblique  muscle  ;  VI,  motor  oculi  externus ;  1,  gan- 
glion of  Gasser ;  2,  3,  4,  5,  6,  7,  8.  9.  10,  opththalmic 
division  of  the  fifth  nerve,  with  its  branches. 


FIG.  198.— Distribution  of  the  motor  oculi  externus. 
(Hirschfeld.) 

1,  trunk  of  the  motor  oculi  communis,  with  its  branches 
(2,  3,  4,  5,  6,  7) ;  8,  motor  oculi  externus,  passing 
to  the  external  rectus  muscle;  9,  filaments  of 'the 
motor  oculi  externus  anastomosing  with,  the  sym- 
pathetic; 10,  ciliary  nerves. 


Motor  Oculi  Externus^  or  Abducens  (Sixth  Nerve). 

Like  the  patheticus,  the  motor  oculi  externus  is  distributed  to  but  a  single  muscle,  the 
external  rectus.  Its  uses,  therefore,  are  apparent  from  a  study  of  its  distribution  and 
properties. 

Physiological  Anatomy.— The  apparent  origin  of  the  sixth  nerve  is  from  the  groove 
which  separates  the  anterior  corpus  pyramidale  of  the  medulla  oblongata  from  the  pons 
Varolii,  and  from  the  upper  portion  of  the  medulla  and  the  lower  portion  of  the  pons 
next  the  groove.  Its  origin  at  this  point  is  by  two  roots  :  an  inferior,  which  rs  the  larger, 
and  comes  from  the  corpus  pyramidale ;  and  a  superior  root,  sometimes  wanting,  which 
seems  to  come  from  the  lower  portion  of  the  pons.  All  anatomists  are  agreed  that  the 
deep  fibres  of  origin  of  this  nerve  pass  to  the  gray  matter  in  the  floor  of  the  fourth  ven- 
tricle. Vulpian  has  followed  these  fibres  to  within  about  two-fifths  of  an  inch  of  the 
median  line,  but  they  could  not  be  traced  beyond  this  point.  It  is  not  known  that  the 
fibres  of  the  two  sides  decussate.  From  this  origin,  the  nerve  passes  into  the  orbit  by  the 
sphenoidal  fissure  and  is  distributed  exclusively  to  the  external  rectus  muscle  of  the  eye- 
ball. In  the  cavernous  sinus,  it  anastomoses  with  the  sympathetic  through  the  carotid 
plexus  and  Meckel's  ganglion.  It  also  receives  sensitive  filaments  from  the  ophthalmic 
branch  of  the  fifth.  It  is  stated  by  some  anatomists  that  this  nerve  occasionally  sends  a 
small  filament  to  the  ophthalmic  ganglion  ;  and  it  is  supposed  by  Longet  that  this  branch, 
which  is  exceptional,  exists  in  those  cases  in  which  paralysis  of  the  motor  oculi  com- 
munis, which  usually  furnishes  all  the  motor  filaments  to  this  ganglion,  is  not  attended 
with  immobility  of  the  iris. 


Properties  and  Functions  of  the  Motor  Oculi  Externus. — Direct  experiments  have 
shown  that  the  motor  oculi  externus  is  entirely  insensible  at  its  origin,  its  stimulation 


MOTOR  NERVES  OF  THE  FACE.  615 

producing  contraction  of  the  external  rectus  muscle  and  no  pain.  The  same  experiments 
illustrate  the  function  of  the  nerve,  inasmuch  as  its  irritation  is  followed  by  powerful 
contraction  of  the  muscle  and  deviation  of  the  eye  outward.  Division  of  the  nerve  in  the 
lower  animals  or  its  paralysis  in  the  human  subject  is  attended  with  internal,  or  con- 
verging strabismus,  due  to  the  unopposed  action  of  the  internal  rectus  muscle. 

"With  regard  to  the  associated  movements  of  the  eyeball,  it  is  a  curious  fact  that  all 
of  the  muscles  of  the  eye  that  have  a  tendency  to  direct  the  pupil  inward  or  to  produce 
the  simple  movements  upward  and  downward,  viz.,  the  internal,  inferior,  and  superior 
recti,  are  animated  by  a  single  nerve,  the  motor  oculi  communis,  this  nerve  also  supplying 
the  inferior  oblique  ;  and  that  each  muscle  that  has  a  tendency  to  move  the  globe  so  as 
to  direct  the  pupil  outward,  except  the  inferior  oblique,  viz.,  the  superior  oblique  and 
the  external  rectus,  is  supplied  by  a  special  nerve.  The  various  movements  of  the  eyeball 
will  be  studied  more  minutely  in  connection  with  the  physiology  of  vision. 

Motor  Nerves  of  the  Face. 

The  motor  nerves  of  the  face  are,  the  small,  or  motor  root  of  the  fifth,  and  the  portio 
dura  of  the  seventh,  or  the  facial.  The  first  of  these  nerves  is  distributed  to  the  deep 
muscles,  those  concerned  in  the  act  of  mastication ;  and  the  second,  the  facial,  supplies 
the  superficial  muscles  of  the  face  and  is  sometimes  called  the  nerve  of  expression. 
These  nerves  are  not  so  simple  in  their  anatomy  and  physiology  as  the  motor  nerves  ot 
the  eyeball.  The  nerve  of  mastication,  at  its  origin,  is  deeply  situated  at  the  base  of  the 
brain  and  is  exposed  and  operated  upon  with  difficulty.  It  passes  out  of  the  cranium, 
closely  united  with  one  of  the  great  sensitive  branches  of  the  fifth,  and  its  distribution 
has  been  most  successfully  studied  by  experiments  in  which  it  is  divided  in  the  cranial 
cavity.  The  origin  of  the  facial  is  also  reached  with  great  difficulty.  It  communicates 
with  other  nerves,  and  its  physiology  has  been  most  satisfactorily  studied  by  dividing  it 
at  its  origin  or  in  different  portions  of  its  course.  In  treating  of  these  nerves,  we  shall 
first,  as  in  the  case  of  the  motor  nerves  of  the  eye,  study  their  properties  at  their  roots, 
noting  the  phenomena  following  their  galvanization  and  section.  It  will  be  neces- 
sary, also,  to  describe  their  origin  and  distribution,  as  far  as  has  been  ascertained  by 
dissection. 

Nerve  of  Mastication  (the  Small,  or  Motor  Root  of  the  Fifth  Nerve). 

The  motor  root  of  the  fifth  nerve  is  entirely  distinct  from  its  sensitive  portion,  until 
it  emerges  from  the  cranial  cavity  by  the  foramen  ovale.  It  is  then  closely  united  with 
the  inferior  maxillary  branch  of  the  large  root ;  but  at  its  origin  it  has  been  shown  to  be 
motor,  and  its  section  in  the  cranial  cavity  has  demonstrated  its  distribution  to  a  par- 
ticular set  of  muscles. 

Physiological  Anatomy  of  the  Nerve  of  Mastication. — The  .apparent  origin  of  the  fifth 
nerve  is  from  the  lateral  portion  of  the  pons  Varolii.  The  small,  or  motor  root  arises 
from  a  point  a  little  higher  and  nearer  the  median  line  than  the  large  root,  from  which 
it  is  separated  by  a  few  fibres  of  the  white  substance  of  the  pons.  At  the  point  of 
apparent  origin,  the  small  root  presents  from  six  to  eight  rounded  filaments.  If  a  thin 
layer  of  the  pons  covering  these  filaments  be  removed,  the  roots  will  be  found  pene- 
trating its  substance,  becoming  flattened,  passing  under  the  superior  peduncles  of  the 
cerebellum,  and  going  to  the  anterior  wall  of  the  fourth  ventricle.  At  this  point,  they 
change  their  direction,  passing  now  from  without  inward  and  from  behind  forward  toward 
the  median  line,  the  fibres  diverging  rapidly.  The  posterior  fibres  pass  to  the  median  line, 
and  certain  of  them  decussate  with  the  fibres  from  the  opposite  side.  The  anterior 
fibres  pass  toward  the  aqueduct  of  Sylvius  and  are  lost.  The  fibres  become  changed 
in  their  character  when  they  are  followed  inward  beyond  the  anterior  wall  of  the  fourth 


616 


NERVOUS   SYSTEM. 


ventricle.  Here  they  lose  their  white  color,  become  gray,  and  present  numerous  globules 
of  gray  substance  between  their  filaments. 

From  the  origin  above  described,  the  small  root  passes  beneath  the  ganglion  of  Gasser 
-from  which  it  sometimes,  though  not  constantly,  receives  a  filament  of  communication- 
lies  behind  the  inferior  maxillary  branch  of  the  large  root,  and  passes  out  of  the  cranial 
cavity  by  the  foramen  ovale.  Within  the  cranium,  the  two  roots  are  distinct ;  but,  after 
the  small  root  passes  through  the  foramen,  it  is  united  by  a  mutual  interlacement  of 
fibres  with  the  sensitive  branch. 

The  course  of  the  motor  root  of  the  fifth  possesses  little  physiological  interest.  It  is 
sufficient  in  this  connection  to  note  that  the  inferior  maxillary  nerve,  made  up  of  the 
motor  root  and  the  inferior  maxillary  branch  of  the  sensitive  root,  just  after  it  passes  out 


PIG.  199.— Distribution  of  the  small  root  of  the  fifth  nerve.    (Hirschfeld.) 

1,  branch  to  the  maxseter  muscle;  2,  filament  of  this  branch  to  the  temporal  muscle;  $,  buccal  branch;  4, 
branches  anastomosing  with  the  facial  nerve ;  5,  filament  from  the  buccal  branch  to  tJie  temporal  muscle; 
6,  branches  to  the  external  pterygoid  muscle ;  7,  middle  deep  temporal  branch ;  8,  auriculo-temporal  nerve ; 
9,  temporal  branches;  10,  auricular  branches;  11,  anastomoses  with  the  facial  nerve;  12,  lingual  branch; 
13,  branch  of  the  small  root  to  the  mylo-hyoid  muscle ;  14,  inferior  denta!  nerve,  with  its  branches  (15, 15);  16, 
mental  branch ;  17,  anastomosis  of  this  branch  with  the  facial  nerve. 

by  the  foramen  ovale,  divides  into  two  branches,  anterior  and  posterior.  The  anterior 
branch,  which  is  the  smaller,  is  composed  almost  entirely  of  motor  filaments  and  is  distrib- 
uted to  the  muscles  of  mastication.  It  gives  off  five  branches.  The  first  of  these  passes 
to  be  distributed  to  the  masseter  muscle,  in  its  course  occasionally  giving  oif  a  small 
branch  to  the  temporal  muscle  and  a  filament  to  the  articulation  of  the  inferior  maxilla 
with  the  temporal  bone.  The  two  deep  temporal  branches  are  distributed  to  the  tem- 
poral muscle.  The  buccal  branch  sends  filaments  to  the  external  pterygoid  and  to  the  tem- 
poral muscle,  and  a  small  branch  is  distributed  to  the  internal  pterygoid  muscle.  From  the 
posterior  branch,  which  is  chiefly  sensitive  but  contains  some  motor  filaments,  branches 


NERVE  OF  MASTICATION.  617 

are  sent  to  the  mylo-hyoid  muscle  and  to  the  anterior  belly  of  the  digastric.  In  addition, 
the  motor  branch  of  the  fifth  sends  filaments  to  the  tensor  muscles  of  the  velum  palati. 

The  above  description  shows,  in  general  terms,  the  distribution  of  the  nerve  of  masti- 
cation, without  taking  into  consideration  its  various  anastomoses,  the  most  important  of 
which  are  with  the  facial.  Physiological  experiments  have  shown  that  the  buccinator 
muscle  receives  no  motor  filaments  from  the  fifth  but  is  supplied  entirely  by  the  facial. 
The  buccal  branch  of  the  fifth  sends  motor  filaments  only,  to  the  external  pterygoid  and 
the  temporal,  its  final  branches  of  distribution  being  sensitive  and  going  to  integument 
and  to  mucous  membrane. 

In  treating  of  the  function  of  digestion,  we  have  given  a  table  of  the  muscles  of  mas- 
tication, with  a  description  of  their  action.  It  will  be  seen  by  reference  to  this  table  that 
the  following  muscles  depress  the  lower  jaw  ;  viz.,  the  anterior  belly  of  the  digastric,  the 
mylo-hyoid,  the  genio-hyoid,  and  the  platysma  inyoides.  Of  these,  the  digastric  and  the 
mylo-hyoid  are  animated  by  the  motor  root  of  the  fifth  ;  the  genio-hyoid  is  supplied  by 
filaments  from  the  sublingual ;  and  the  platysma  myoides,  by  branches  from  the  facial 
and  from  the  cervical  plexus.  All  of  the  muscles  which  elevate  the  lower  ja\v  and  move 
it  laterally  and  antero-posteriorly,  viz.,  the  temporal,  masseter,  and  the  internal  and 
external  pterygoids  (the  muscles  most  actively  concerned  in  mastication)  are  animated 
by  the  motor  root  of  the  fifth. 

Properties  and  Functions  of  the  Nerve  of  Mastication. — The  anatomical  distribution 
of  the  small  root  of  the  fifth  nerve  points  at  once  to  its  function.  Charles  Bell,  whose 
ideas  of  the  nerves  were  derived  almost  entirely  from  their  anatomy,  called  it  the  nerve 
of  mastication,  in  1821,  although  he  does  not  state  that  any  experiments  were  made  with 
regard  to  its  function.  All  anatomical  and  physiological  writers  since  that  time  have 
adopted  this  view.  It  would  be  difficult,  if  not  impossible,  to  galvanize  the  root  in  the 
cranial  cavity  in  a  living  animal ;  but  its  galvanization  in  animals  just  killed  determines 
very  marked  movements  of  the  lower  jaw.  Experiments  have  clearly  demonstrated  the 
physiological  properties  of  the  small  root,  which  is  without  doubt  solely  a  nerve  of  motion. 

The  observations  upon  the  division  of  the  fifth  pair  in  the  cranial  cavity  are  most 
interesting  in  connection  with  the  functions  of  its  sensitive  branches,  and  will  be 
referred  to  in  detail  in  treating  of  the  properties  of  the  large  root.  In  addition  to 
the  loss  of  sensibility  following  section  of  the  en- 
tire nerve,  Bernard  has  carefully  noted  the  effects 
of  division  of  the  small  root,  which  cannot  be 
avoided  in  the  operation.  In  rabbits,  the  paraly- 
sis of  the  muscles  of  mastication  upon  one  side, 
and  the  consequent  action  of  the  muscles  upon  the 
unaffected  side  only,  produce,  a  few  days  after 
the  operation,  a  remarkable  change  in  the  appear- 
ance of  the  incisor  teeth.  As  the  teeth  in  these 
animals  are  gradually  worn  away  in  mastication 
and  reproduced,  the  lower  jaw  being  deviated  by 
the  action  of  the  muscles  of  the  SOlind  side,  the  ^\G.  200.— Incisors  of  the,  rabbit,  before  and 
upper  incisor  of  one  side  and  the  lower  incisor  of  n^milf/™  °f  ***  ne™6  °f  mastication' 
the  other  touch  each  other  but  slightly  and  the  A,  incisors,  normal  condition, 
teeth  are  worn  unevenly.  This  makes  the  line  B,  indsors^  se^ven  days  after  section  of  the  nerve 

of  contact  between  the  four  incisors,  when  the 

jaws  are  closed,  oblique  instead  of  horizontal.  We  have  often  divided  the  fifth  pair  in 
the  cranial  cavity  in  rabbits,  by  the  method  employed  by  Magendie  and  Bernard,  and 
have  repeatedly  verified  these  observations. 

There  is  little  left  to  say  with  regard  to  the  functions  of  the  motor  root  of  the  fifth 
nerve,  in  addition  to  our  description  of  the  action  of  the  muscles  of  mastication,  contained 


NERVOUS  SYSTEM. 

in  the  chapters  on  digestion,  except  as  regards  the  action  of  the  filaments  sent  to  the 
muscles  of  the  velum  palati.  In  deglutition,  the  muscles  of  mastication  are  indirectly 
involved.  This  act  cannot  be  well  performed  unless  the  mouth  be  closed  by  these  muscles. 
When  the  food  is  brought  in  contact  with  the  velum  palati,  muscles  are  brought  into 
action  which  render  this  membrane  tense,  so  that  the  opening  is  adapted  to  the  size  of 
the  alimentary  bolus.  These  muscles  are  animated  by  the  motor  root  of  the  fifth.  This 
nerve,  then,  is  not  only  the  nerve  of  mastication,  animating  all  of  the  muscles  concerned 
in  this  act,  except  two  of  the  most  unimportant  depressors  of  the  lower  jaw  (the  genio- 
hyoid  and  the  platysma  myoides),  but  it  is  concerned  indirectly  in  deglutition. 

Facial  Nerve,  or  Nerve  of  Expression  (the  Portio  Dura  of  the  Seventh 

Nerve). 

The  facial,  the  portio  dura  of  the  seventh  according  to  the  arrangement  of  Willis,  is 
one  of  the  most  interesting  of  the  cranial  nerves.  Its  anatomical  relations  are  quite  intri- 
cate, and  its  communications  with  other  nerves,  very  numerous.  As  far  as  can  be  deter- 
mined by  experiments  upon  living  animals,  this  nerve  is  exclusively  motor  at  its  origin ; 
but  in  its  course  it  presents  anastomoses  with  the  sympathetic,  with  branches  of  the  fifth, 
and  with  the  cervical  nerves,  undoubtedly  receiving  sensory  filaments.  While  the  chief 
physiological  interest  attached  to  this  nerve  depends  upon  its  action  upon  muscles,  it  is 
important  to  study  its  origin,  distribution,  and  communications. 

Physiological  Anatomy  of  the  Facial  Nerve. — The  portio  dura  of  the  seventh  has  its 
apparent  origin  from  the  lateral  portion  of  the  medulla  oblongata,  in  the  groove  between 
the  olivary  and  the  restiform  body,  just  below  the  border  of  the  pons  Varolii,  its  trunk 
being  internal  to  the  trunk  of  the  portio  mollis,  or  auditory  nerve.  It  is  separated  from 
the  auditory  by  the  two  filaments  constituting  what  is  known  as  the  intermediary  nerve 
of  Wrisberg,  or  the  portio  inter  duram  et  mollem.  As  this  little  nerve  joins  the  facial, 
it  must  be  included  in  its  root. 

There  are  certain  pathological  considerations  which  render  the  deep,  or  real  origin  of 
the  facial  a  question  of  the  greatest  interest  and  importance.  In  hemiplegia  due  to  injury 
of  the  substance  of  the  encephalon,  particularly  from  haemorrhage,  there  is  almost  always 
more  or  less  paralysis  of  the  superficial  muscles  of  the  face.  It  has  been  observed  that, 
in  certain  cases,  the  facial  paralysis  exists  upon  the  same  side  as  the  hemiplegia  (the  side 
opposite  to  the  cerebral  lesion),  while  in  others,  the  palsy  of  the  face  is  upon  the  same  side 
as  the  lesion,  the  general  hemiplegia  being,  as  usual,  upon  the  opposite  side.  To  explain 
these  phenomena  theoretically,  we  must  assume  that,  in  some  cases,  the  brain-lesion  is  to 
be  located  at  a  point  where  it  involves  the  filaments  of  origin  of  the  facial  (following 
them  from  without  inward)  before  they  decussate,  which  would  produce  facial  paralysis 
upon  the  same  side  as  the  lesion  and  none  upon  the  side  affected  with  general  hemiplegia ; 
while,  in  other  cases,  the  injury  to  the  brain  involves  the  roots  of  the  facial  after  they 
have  decussated,  when  the  paralysis  of  the  face  would  be  upon  the  same  side  as  the  paraly- 
sis of  the  rest  of  the  body.  It  would  be  interesting  to  see  how  far  these  pathological 
facts,  with  their  theoretical  explanation,  correspond  with  anatomical  researches  into  the 
real  origin  of  the  nerves. 

Many  anatomists  have  endeavored  to  trace  the  fibres  of  the  facial  from  their  point  of 
emergence  from  the  encephalon  to  their  true  origin,  but  with  results  not  entirely  satis- 
factory. At  the  present  day,  it  is  pretty  generally  agreed  that  the  fibres  pass  inward, 
with  one  or  two  deviations  from  a  straight  course,  to  the  floor  of  the  fourth  ventricle, 
where  they  spread  out  and  become  fan-shaped.  In  the  floor  of  the  fourth  ventricle,  cer- 
tain of  the  fibres  have  been  thought  to  terminate  in  the  cells  of  the  gray  substance,  and 
others  have  been  traced  to  the  median  line,  where  they  decussate  ;  the  course  of  most  of 
the  fibres,  however,  has  never  been  satisfactorily  established. 


FACIAL  NERVE,  OR  NERVE  OF  EXPRESSION. 


619 


It  is  evident,  from  physiological  experiments,  that  the  decussation  of  the  fibres  in  the 
floor  of  the  fourth  ventricle  itself  is  not  very  important.  Vulpian  has  made,  in  dogs  and 
rabbits,  a  longitudinal  section  in  the  middle  line  of  the  ventricle,  which  would  necessarily 
have  divided  the  fibres  passing  from  one  side  to  the  other,  without  producing  notable 
paralysis  of  the  facial  nerves  upon  either  side.  This  single  fact  is  sufficient  to  show  that 
the  main  decnssation  of  the  fibres  animating  the  muscles  of  the  face  takes  place,  if  at  all, 
at  some  other  point. 

The  pathological  facts  bearing  upon  the  question  of  decussation  of  the  filaments  of 
origin  of  the  facial  have  long  been  recognized.  They  are,  in  brief,  as  follows:  When 
there  is  a  lesion  of  the  brain-substance  anterior  to  the  pons  Varolii,  the  phenomena  due 
to  paralysis  of  the  facial  are  observed  upon  the  same  side  as  the  hemiplegia,  opposite  the 
side  of  injury  to  the  brain.  When  the  lesion  is  either  in  the  pons  or  below  it,  the  face  is 


FIG.  201.— Superficial  branches  of  the  facial  and  the  fifth.    (Hirschfeld.) 

1,  trunk  of  the  facial ;  2,  posterior  auricular  nerve;  3,  branch  which  it  receives  from  the  cervical  plexus ;  4, 
occipital  branch;  5,  6,  branches  to  the  muscles  of  the  ear;  7,  digastric  branches;  8,  branch  to  the  stylo- 
hyoid  muscle;  9,  superior  terminal  branch;  10,  temporal  brandies;  11,  frontal  branches ;  12,  branches  to 


branches  of  the  cervical  nerves. 


affected  upon  the  same  side,  and  not  upon  the  side  of  the  hemiplegia.  In  view  of  these 
facts,  the  remarkable  phenomenon  of  hemiplegia  upon  one  side  and  facial  paralysis  upon 
the  other  is  regarded  as  indicating,  with  tolerable  certainty,  that  the  injury  to  the  brain  has 
occurred  upon  the  same  side  as  the  facial  paralysis,  either  within  or  posterior  to  the  pons 
Varolii.  It  is  unnecessary  to  enter  into  a  farther  discussion  of  these  facts,  which  are 


NERVOUS   SYSTEM. 

accepted  by  nearly  all  writers  upon  diseases  of  the  nervous  system  and  may  be  regarded 
as  settled ;  and  the  only  question  is,  how  far  they  can  be  explained  by  the  anatomy  of 
the  parts. 

As  we  have  just  seen,  the  fibres  of  origin  of  the  facial  have  been  traced  to  the  floor 
of  the  fourth  ventricle,  where  a  few  decussate,  but  the  rest  are  lost.  The  question  now 
is,  whether  or  not  the  fibres  pass  up  through  the  pons  and  decussate  above,  as  the  patho- 
logical facts  just  noted  would  seem  to  indicate.  Anatomical  researches  upon  this  point 
are  entirely  unsatisfactory ;  and  the  existence  of  such  a  decussation  has  never  been  clearly 
demonstrated.  The  pathological  observations,  nevertheless,  remain ;  and,  however  indefi- 
nite anatomical  researches  may  have  been,  there  can  be  no  doubt  that  lesions  in  one-half 
of  the  pons  affect  the  facial  upon  the  same  side,  while  lesions  above  have  a  crossed 
action.  The  most  that  we  can  say  upon  this  point  is,  that  it  is  a  reasonable  inference 
from  pathological  facts  that  the  nerves  decussate  anterior  to  the  pons. 

It  will  be  only  necessary  to  describe  in  a  general  way  the  course  of  the  fibres  of  dis- 
tribution of  the  facial.  The  main  root  of  the  facial,  the  auditory  nerve,  and  the  delicate 
intermediary  nerve  of  Wrisberg  pass  together  into  the  internal  auditory  meatus.  At  the 
bottom  of  the  meatus,  the  facial  and  the  nerve  of  Wrisberg  enter  the  aquaaductus  Fallopii, 
following  its  course  through  the  petrous  portion  of  the  temporal  bone.  In  the  aqueduct, 
the  nerve  of  Wrisberg  presents  a  little  ganglioform  enlargement,  of  a  reddish  color,  which 
has  been  shown  to  contain  nerve-cells.  The  main  root  and  the  intermediary  nerve  then 
unite  and  form  the  common  trunk  of  the  facial,  which  emerges  from  the  cranial  cavity 
by  the  stylo-mastoid  foramen. 

In  the  aquseductus  Fallopii,  the  facial  gives  off  numerous  branches,  as  follows : 

1.  The  large  petrosal  branch  is  given  off  at  the  ganglioform  enlargement  and  goes 
to  Meckel's  ganglion. 

2.  The  small  petrosal  branch  is  given  off  at  the  ganglioform  enlargement  or  a  very 
short  distance  beyond  it,  and  passes  to  the  otic  ganglion. 

3.  A  small  branch,  the  tympanic,  is  distributed  to  the  stapedius  muscle. 

4.  The  chorda  tympani,  a  branch  of  great  physiological  interest,  passes  through  the 
cavity  of  the  tympanum  and  joins  the  lingual  branch  of  the  inferior  maxillary  division 
of  the  fifth  as  it  passes  between  the  two  pterygoid  muscles,  with  which  nerve  it  becomes 
closely  united. 

5.  Opposite  to  the  point  of  origin  of  the  chorda  tympani,  a  communicating  branch 
passes  between  the  facial  and  the  pneumogastric,  connecting  these  nerves  by  a  double 
inosculation. 

The  five  branches  above  described  are  given  of  in  the  aquseductus  Fallopii.  The  fol- 
lowing branches  are  given  off  after  the  nerve  has  emerged  from  the  cranial  cavity  : 

1.  Just  after  the  facial  has  passed  out  at  the  stylo-mastoid  foramen,  it  sends  a  small 
communicating  branch  to  the  glosso-pharyngeal  nerve.     According  to   Sappey,  this 
branch  is  sometimes  wanting. 

2.  The  posterior  auricular  nerve  is  given  off  by  the  facial  a  little  below  the  stylo- 
mastoid  foramen.     Its  superior  branch  is  distributed  to  the  retrahens  aurem  and  the 
attollens  aurem.     In  its  course,  this  nerve  receives  a  communicating  branch  of  consider- 
able size  from  the  cervical  plexus,  by  the  auricularis  magnus.     It  sends  some  filaments 
to  the  integument.      The  inferior,  or  occipital  branch,  the  larger  of  the  two,  is  dis- 
tributed to  the  occipital  portion  of  the  occipito-frontalis  muscle  and  to  the  integument. 

3.  The  digastric  branch  is  given  off  near  the  root  of  the  posterior  auricular.     It  is 
distributed  to  the  posterior  belly  of  the  digastric  muscle.     In  its  course,  it  anastomoses 
with  filaments  from  the  glosso-pharyngeal  nerve.     From  the  plexus  formed  by  this  anas- 
tomosis, filaments  are  given  off  to  the  digastric  and  to  the  stylo-hyoid  muscle. 

4.  Near  the  stylo-mastoid  foramen,  a  small  branch  is  given  off,  which  is  distributed 
exclusively  to  the  stylo-hyoid  muscle. 

5.  Near  the  stylo-mastoid  foramen,  or  sometimes  a  little  above  it,  a  long  and  exceed- 


FACIAL  NERVE,  OR  NERVE   OF  EXPRESSION.  621 

ingly  delicate  branch  is  given  off,  which  is  not  noticed  in  most  works  on  anatomy.  It  is 
described,  however,  by  Hirschfeld,  under  the  name  of  the  lingual  branch.  It  passes 
behind  the  stylo-pharyngeal  muscle,  and  then  by  the  sides  of  the  pharynx  to  the  base 
of  the  tongue.  In  its  course,  it  receives  one  or  two  branches  from  the  glosso-pharyngeal 
nerve,  which  are  nearly  as  large  as  the  original  branch  from  the  facial.  As  it  passes  to 
the  base  of  the  tongue,  it  anastomoses  again  by  numerous  filaments  with  the  glosso- 
pharyngeal.  It  then  sends  filaments  of  distribution  to  the  mucous  membrane,  and  finally 
passes  to  the  stylo-glossus  and  the  palato-glossus  muscle. 

Having  given  off  these  branches,  the  trunk  of  the  facial  passes  through  the  parotid 
gland,  dividing  into  its  two  great  terminal  branches : 

1.  The  temp oro -facial  branch,  the  larger,  passes  upward  and  forward  to  be  distrib- 
uted to  the  superficial  muscles  of  the  upper  part  of  the  face ;  viz.,  the  attrahens  aurem, 
the  frontal  portion  of  the  occipito-frontalis,  the  obicularis  palpebrarum,  corrugator  super- 
cilii,  pyramidalis  nasi,  levator  labii  superioris,  levator  labii  superioris  alseque  nasi,  the 
dilators  and  compressors  of  the  nose,  part  of  the  buccinator,  the  levator  anguli  oris,  and 
the  zygomatic  muscles.     In  its  course,  it  receives  branches  of  communication  from  the 
auriculo-temporal  branch  of  the  inferior  maxillary  nerve.    It  joins  also  with  the  temporal 
branch  of  the  superior  maxillary  and  with  branches  of  the  ophthalmic.     In  its  course,  it 
thus  becomes  a  mixed  nerve  and  is  distributed  in  part  to  integument. 

2.  The  cervico-facial  nerve  passes  downward  and  forward  to  supply  the  buccinator, 
orbicularis  oris,  risorius,  levator  labii  inferioris,  depressor  labii  inferioris,  depressor  anguli 
oris,  and  platysma. 

Summary  of  the  Anastomoses  and  Distribution  of  the  Facial. — In  the  aquseductus 
Fallopii,  filaments  of  communication  go  to  Meckel's  ganglion  and  the  otic  ganglion  of 
the  sympathetic.  The  chorda  tympani  joins  the  lingual  branch  of  the  inferior  maxil- 
lary division  of  the  fifth.  A  branch  is  also  sent  to  the  pneumogastric.  After  the  nerve 
has  passed  out  by  the  stylo-mastoid  foramen,  it  sends  a  communicating  branch  to  the 
glosso-pharyngeal,  and  receives  a  branch  from  the  auricularis  inagnus.  It  anastomoses, 
also,  outside  of  the  cranium,  with  the  glosso-pharyngeal.  In  the  course  of  the  nerve,  it 
receives  anastomosing  filaments  from  the  three  great  divisions  of  the  fifth. 

It  is  thus  seen  that  the  facial,  in  its  course,  receives  numerous  filaments  from  the  great 
sensitive  nerve  of  the  face.  Certain  of  its  fibres  of  distribution  go  to  integument. 

The  muscles  supplied  by  the  facial  are  the  stapedius,  and  probably  the  tensor  tym- 
pani, of  the  internal  ear,  the  muscles  of  the  external  ear,  the  occipito-frontalis,  the  pos- 
terior belly  of  the  digastric,  the  stylo-hyoid,  the  stylo-glossus,  and  the  palato-glossus. 
The  two  great  branches  of  distribution,  the  teinporo-facial  and  the  cervico-facial,  are 
distributed  to  all  of  the  superficial  muscles  of  the  face,  leaving  the  deep  muscles,  or  the 
muscles  of  mastication,  to  be  supplied  by  the  motor  root  of  the  fifth.  In  addition,  it 
supplies  in  part  the  platysma  myoides. 

Properties  and  Functions  of  the  Facial  Nerve. — It  has  long  been  recognized  that  the 
facial  is  the  motor  nerve  of  the  superficial  muscles  of  the  face,  and  that  its  division  pro- 
duces paralysis  of  motion  and  no  marked  effects  upon  sensation.  It  is  evident,  also, 
from  the  numerous  communications  of  the  facial  with  the  fifth,  that  it  probably  contains 
in  its  course  sensitive  fibres.  Indeed,  all  who  have  operated  upon  this  nerve  have  found 
that  it  is  slightly  sensitive  after  it  has  emerged  from  the  cranial  cavity.  It  is  a  question, 
however,  of  great  importance  to  determine  whether  or  not  the  facial  be  endowed  with 
sensibility  by  virtue  of  its  own  fibres  of  origin.  The  main  root  is  evidently  from  the 
motor  tract,  resembles  the  anterior  roots  of  the  spinal  nerves,  and  is  distributed  to  mus- 
cles ;  but  this  is  joined  by  the  intermediary  nerve  of  Wrisberg,  which  presents  a  small 
enlargement,  undoubtedly  containing  nerve-cells,  somewhat  analogous  to  the  ganglia 
upon  the  posterior  roots  of  the  spinal  nerves. 

Direct  observations  upon  the  properties  of  the  facial  as  it  penetrates  the  auditory 


Q22  NERVOUS  SYSTEM. 

canal,  and  before  it  has  received  any  anastomosing  branches  from  sensitive  nerves,  must 
be  to  a  certain  extent  unsatisfactory.  All  who  have  experimented  upon  the  nerves  know 
that  the  pain  and  depression  which  attend  so  serious  an  operation  as  that  of  exposing 
the  roots  of  a  nerve  in  the  cranial  cavity  are  sufficient  to  render  it  doubtful  whether  the 
parts  be  in  a  condition  to  exhibit  a  slight  degree  of  sensibility,  which  the  nerves  may 
possess  when  perfectly  normal.  Magendie  and  Bernard,  who  have  exposed  the  roots  of 
origin  of  the  facial,  state  unreservedly  that  they  are  absolutely  insensible ;  but  Longet 
very  justly  remarks  that  the  conditions  under  which  such  observations  are  made  have 
not  been,  in  his  hands,  sufficiently  favorable  to  admit  of  a  rigorous  conclusion  upon  this 
point.  The  testimony  of  direct  experimentation  is  in  favor  of  the  insensibility  of  the 
facial  at  its  origin.  It  is  true  that  the  intermediary  nerve  of  Wrisberg  has  a  certain  ana- 
tomical resemblance  to  the  sensitive  nerves,  chiefly  by  virtue  of  its  ganglioform  enlarge- 
ment ;  but  direct  experiments  are  wanting  to  show  that  it  is  actually  sensitive.  In  view 
of  this  fact,  it  is  impossible  to  reason  conclusively  from  its  anatomical  characters  alone. 

The  most  convenient  way  to  consider  the  functions  of  the  facial  will  be  to  take  up 
seriatim  the  properties  and  distribution  of  its  different  branches. 

Functions  oftJie  Branches  of  the  Facial  within  the  Aqueduct  of  Fallopius. — The  first 
branch,  the  large  petrosal,  is  the  motor  root  of  Meckel's  ganglion.  This  will  be  referred 
to  again  in  connection  with  the  sympathetic  system.  The  second  branch,  the  small  petro- 
sal, is  one  of  the  motor  roots  of  the  otic  ganglion  of  the  sympathetic.  The  third  branch, 
the  tympanic,  is  distributed  exclusively  to  the  stapedius  muscle.  The  second  and  third 
branches  will  be  again  considered  in  connection  with  the  physiology  of  the  internal  ear. 
The  fourth  branch,  the  chorda  tympani,  is  so  important  that  it  demands  special  consid- 
eration. The  fifth  branch  is  given  off  opposite  the  origin  of  the  chorda  tympani  and 
passes  to  the  pneumogastric,  to  which  nerve  it  probably  supplies  motor  filaments.  We 
have  already  seen,  in  studying  the  properties  of  the  roots  of  the  facial,  that,  in  this 
branch,  sensory  filaments  pass  from  the  pneumogastric  and  constitute  a  part  of  the  sen- 
sory connections  of  the  facial. 

Functions  of  the  Chorda  Tympani. — This  branch  passes  between  the  bones  of  the  ear 
and  through  the  tympanic  cavity  to  the  lingual  branch  of  the  inferior  maxillary  division 

of  the  fifth,  which  it  joins  at  an  acute  angle, 
between  the  pterygoid  muscles.  It  has 
been  a  question  whether  this  nerve  be 
simply  enclosed  in  the  sheath  of  the  lingual 
branch  of  the  fifth  or  be  so  closely  con- 
nected with  it  that  it  cannot  be  traced  to 
a  distinct  distribution.  Upon  this  point 
we  are  disposed  to  adopt  the  opinion  of 
Sappey,  who,  as  the  result  of  minute  dis- 
sections, regards  the  union  as  complete, 
"  fibril  to  fibril."  As  regards  the  portion 
of  the  facial  which  furnishes  the  filaments 
of  the  chorda  tympani,  it  is  impossible  to 
determine  anatomically  whether  these 
come  from  the  main  root  or  from  the  in- 
i  2  34  feet -Chorda-tymva™  ne™-  (Hirschfeid.)  termediary  nerve  of  Wrisberg,  as  the  fibres 

1,  2, 3,  4,  facial  nerve  passing  through  the  aquaiductus  Fal-       f  . ,  /? 

;  5,  ganghoform  enlargement;  6,  great  petrosal   °*  these  roots  are  closely  united  before  the 


--._,  .,  --^'^u,.  vyinpuHVj   IVF,  11,  ne    is,  various 
branche;  acial;   14,  14,  15,  glosso-pharyngeal  The  Only  questions  that  we  propose  to 

consider  in  this  connection  relate  to  the 

functions  of  the  chorda  tympani  as  a  nerve  of  gustation,  and  as  it  influences  the  secretion 
of  the  submaxillary  gland. 

There  can  be  no  doubt  with  regard  to  the  influence  of  the  chorda  tympani  upon  the 


FACIAL  NERVE,  OR  NERVE   OF  EXPRESSION.  623 

sense  of  taste  in  the  anterior  portion  of  the  tongue.  Without  citing  all  of  the  experi- 
Tiients  and  pathological  observations  bearing  upon  this  question,  it  is  sufficient  to  state 
that,  in  cases  of  disease  or  injury  in  which  the  root  of  the  facial  is  involved  so  that  the 
chorda  tympani  is  paralyzed,  in  addition  to  the  ordinary  phenomena  of  paralysis  of  the 
superficial  muscles  of  the  face,  there  is  loss  of  taste  in  the  anterior  portion  of  the  tongue 
upon  the  side  corresponding  to  the  lesion.  Numerous  cases  of  this  kind  are  quoted  in. 
works  on  physiology,  which  will  be  referred  to  more  fully  in  connection  with  the  subject 
of  gustation. 

In  1863,  we  had  under  observation,  for  several  months,  a  soldier  who  received  a  gun- 
shot-wound, the  ball  passing  through  the  head,  entering  just  above  the  ala  of  the  nose  upon 
the  left  side  and  emerging  behind  the  mastoid  process  of  the  right  temporal  bone.  The 
wound  was  nearly  healed  while  he  was  under  observation,  and  the  usual  symptoms  of 
complete  facial  paralysis  were  manifested  upon  the  right  side.  The  buccinator  and  the 
orbicularis  oculi  were  completely  paralyzed.  Vision  in  the  right  eye  was  slightly  im- 
paired, but  was  improving.  The  hearing  was  perfect,  and  there  were  no  abnormal  phe- 
nomena except  those  apparently  due  to  injury  of  the  facial.  The  sense  of  taste  was 
entirely  abolished  in  the  anterior  portion  of  the  tongue  upon  the  right  side.  Experiments 
upon  this  point  were  repeatedly  made  with  salt,  pepper,  and  other  sapid  substances.  This 
patient  was  exhibited  in  two  successive  years  to  the  class  at  the  Bellevue  Hospital  Medi- 
cal College,  when  the  above-mentioned  facts  were  demonstrated. 

Physiologists  have  observed  loss  of  taste  in  the  anterior  portion  of  the  tongue,  in 
dogs,  cats,  and  other  animals,  following  section  of  the  root  of  the  facial  or  of  the  chorda 
tympani.  Some  observers,  it  is  true,  have  failed  to  note  the  phenomena  satisfactorily, 
and  there  is  some  difference  of  opinion  with  regard  to  the  real  origin  of  the  gustatory 
filaments ;  but  the  fact  that  the  chorda  tympani  influences  the  taste  can  hardly  be  doubted. 
Adopting  this  view,  we  shall  defer  the  full  consideration  of  the  functions  of  the  chorda 
tympani  until  we  come  to  treat  of  the  special  sense  of  taste. 

Schiff,  in  1851,  was  the  first  to  note  the  influence  of  the  chorda  tympani  upon  the 
secretion  of  the  submaxillary  gland.  In  his  experiments,  the  chorda  tympani  was 
exposed  and  the  flow  of  the  submaxillary  saliva  noted.  Upon  division  of  the  chorda 
tympani,  the  flow  of  saliva  was  momentarily  increased,  but  was  soon  arrested  ;  and  sub- 
sequently, stimulation  of  the  gustatory  sense  failed  to  induce  secretion,  as  it  does  when 
the  nerve  is  intact.  Similar  experiments,  upon  a  much  more  extended  scale,  were  made 
by  Bernard,  in  the  following  way : 

The  duct  of  the  submaxillary  gland  was  exposed  in  a  dog,  and  into  it  was  fixed  a 
silver  canula.  The  nervous  filaments  going  to  the  gland  from  the  lingual  branch  of  the 
fifth  were  then  isolated.  A  little  vinegar  introduce4  into  the  mouth  caused  an  abundant 
flow  of  saliva  from  the  tube.  The  chorda  tympani  was  then  divided,  by  introducing  a 
sharp  instrument  through  the  membrane  into  the  tympanic  cavity.  After  division  of  the 
nerve,  the  introduction  of  vinegar  into  the  mouth  failed  to  excite  the  salivary  secretion. 
From  this  and  similar  experiments,  Bernard  concludes  that  the  chorda  tympani  is  the 
motor  nerve  of  the  submaxillary  gland.  After  having  arrested  the  secretion  by  section 
of  the  chorda  tympani,  the  action  of  the  gland  was  excited  by  galvanization  of  the  pe- 
ripheral end  of  the  nerve.  Section  of  the  facial  after  its  passage  out  of  the  stylo-mastoid 
foramen  did  not  arrest  the  action  of  the  parotid  ;  but  section  of  the  nerve  within  the  cra- 
nium arrested  the  secretion,  both  of  the  parotid  and  submaxillary. 

These  observations  show  conclusively  that  the  facial,  either  through  branches  from 
its  proper  roots  or  its  filaments  of  communication  with  other  nerves,  regulates  the  secre- 
tion of  at  least  two  of  the  salivary  glands. 

Influence  of  Various  Branches  of  the  Facial  upon  the  Movements  of  the  Palate  and 
Uvula. — There  can  be  little  doubt  that  filaments  from  the  facial  animate  certain  of  the 
movements  of  the  velum  palati  and  uvula.  It  has  been  observed  that,  in  certain  cases 
of  facial  paralysis,  the  palate  upon  one  side  is  perfectly  flaccid  and  the  uvula  is  drawn  to 


624  NERVOUS  SYSTEM. 

the  opposite  side ;  but  these  phenomena  do  not  occur  unless  the  nerve  be  affected  at  its 
root  or  within  the  aquseductus  Fallopii.  It  is  true  that  the  uvula  is  frequently  drawn  to 
one  side  or  the  other  in  persons  unaffected  with  facial  paralysis,  but  it  is  none  the  less 
certain  that  it  is  deviated  as  a  consequence  of  paralysis  of  the  facial  in  some  instances. 

Direct  experiments  upon  the  roots  of  the  facial  have  not  been  followed  by  uniform 
results.  Debrou  mentions  one  experiment  in  which  galvanization  of  the  facial  within 
the  cranial  cavity  produced  decided  contraction  of  the  muscles  of  the  palate ;  but,  in 
four  others,  the  results  were  negative.  Nuhn,  however,  produced  contractions  of  these 
muscles  by  galvanization  of  the  nerve  in  the  cranium  in  a  man  immediately  after  decapi- 
tation. The  experiments  of  Bernard  upon  this  point  are  the  most  conclusive  ;  but  while 
they  show,  beyond  a  doubt,  that  the  facial  animates  the  movements  of  the  soft  palate, 
they  do  not  indicate  the  course  of  the  filaments  from  the  nerve  to  the  muscles.  In  these 
experiments,  made  in  connection  with  M.  Davaine,  the  whole  of  the  velum  palati  was 
exposed  in  a  large-sized  dog,  by  cutting  through  the  hyoid  bone.  The  trunk  of  the 
glosso-pharyngeal  nerve  was  then  exposed  in  the  neck,  near  its  point  of  emergence  at 
the  posterior  foramen  lacerum,  and  the  animal  was  killed  by  section  of  the  spinal  cord 
just  below  the  origin  of  the  cranial  nerves.  This  being  done,  the  glosso-pharyngeal  was 
galvanized,  which  produced  violent  contractions  of  the  velum,  the  pillars  of  the  fauces, 
and  a  part  of  the  pharynx,  upon  one  side.  The  nerve  was  then  divided,  and  galvanization 
was  applied  to  its  peripheral  end  without  producing  any  movement  in  the  velum.  The 
central  end  was  then  galvanized,  when  the  contractions  were  as  vigorous  as  when  the 
nerve  was  intact.  This  result  would  lead  to  the  supposition  that  contractions  of  the 
muscles  of  the  palate  following  galvanization  of  the  glosso-pharyngeal  are  reflex  and  not 
due  to  the  direct  action  of  filaments  of  distribution  from  this  nerve.  In  a  second  experi- 
ment, the  parts  were  exposed  in  the  same  way,  and,  in  addition,  the  facial  was  divided 
upon  the  right  side  at  its  entrance  into  the  internal  auditory  canal.  The  glosso-pharyn- 
geal nerve  was  then  galvanized  upon  the  side  on  which  the  facial  had  been  divided,  with 
the  effect  of  producing  movements  of  the  pillars  of  the  fauces,  but  not  of  the  velum 
palati  itself.  The  glosso-pharyngeal  was  then  galvanized  upon  the  side  on  which  the 
facial  was  intact,  which  produced  movements  of  the  velum  the  same  as  in  the  first  ex- 
periment. Galvanization  of  the  pneumogastric,  the  sublingual,  and  the  lingual  branch 
of  the  fifth,  failed  to  produce  movements  of  the  velum. 

"  The  first  experiment  proves  that  the  glosso-pharyngeal  nerve  is  not  the  motor  nerve 
of  the  velum  palati,  but  that  it  induces  reflex  movements  by  the  excitation  which  it 
transmits  to  the  nervous  centre,  an  excitation  which  is  carried  to  the  parts  by  another 
nerve. 

"  The  second  experiment  proves  that  the  reflex  movements  of  the  velum  palati,  in- 
duced by  the  excitation  of  the  glosso-pharyngeal,  are  in  part  transmitted  by  the  facial 
nerve,  the  movements  of  the  pillars  not  being  produced  by  filaments  belonging  to  this 
nerve." 

Bernard  also  noted  a  fact,  which  has  sometimes  been  observed  in  cases  of  facial 
paralysis,  that  the  point  of  the  tongue  is  deviated  after  section  of  the  facial ;  which  is 
explained  by  the  presence  of  a  filament  described  by  Hirschfeld,  going  from  the  facial  to 
the  tongue. 

As  we  before  remarked,  the  experiments  of  Bernard  do  not  indicate  the  mode  of 
communication  between  the  facial  and  the  muscles  of  the  palate.  Longet  regards  the 
filaments  of  the  facial  which  influence  the  levator  palati  and  azygos  uvulae  muscles  as 
derived  from  the  large  petrosal  branch  of  the  nerve,  passing  to  the  muscles  through 
Meckel's  ganglion,  the  filaments  to  the  palato-glossus  and  the  palato-pharyngeus  being 
given  off  from  the  glosso-pharyngeal,  but  originally  coming  from  an  anastomosing  branch 
of  the  facial.  As  regards  the  branches  of  communication  from  the  glosso-pharyngeal, 
Longet  mentions  a  preparation  by  Richet,  in  the  museum  of  the  Ecole  de  medecine,  of 
Paris,  in  which  branches  of  the  facial  upon  one  side  passed  directly  to  the  palato-glossus 


FACIAL  NERVE,  OR  NERVE  OF  EXPRESSION.  625 

and  the  palato-pharyngeus,  without  any  connection  with  the  glosso-pharyngeal  nerve. 
In  our  anatomical  description  of  the  branches  of  the  facial,  we  have  already  noted  a 
filament,  described  by  Hirschfeld,  which  passes  to  the  stylo-glossus  and  palato-glossus 
muscles.  This  is  the  filament  affected  in  deviation  of  the  point  of  the  tongue. 

In  view  of  the  pathological  examples  of  paralysis  of  the  palate  and  uvula  in  certain 
cases  of  facial  palsy,  the  frequent  occurrence  of  contractions  of  the  muscles  of  these 
parts  upon  galvanization  of  the  facial,  and  the  reflex  action  through  the  glosso-pharyn- 
geal and  the  facial,  there  can  be  little  doubt  that  the  muscles  of  the  palate  and  uvula  are 
animated  by  filaments  derived  from  the  seventh  nerve.  The  effects  of  paralysis  of  these 
muscles  are  manifested  by  more  or  less  difficulty  in  deglutition  and  in  the  pronunciation 
of  certain  words,  with  great  difficulty  in  the  expulsion  of  mucus  collected  in  the  back 
part  of  the  mouth  and  the  pharynx. 

Functions  of  the  External  Branches  of  the  Facial. — The  general  function  of  the 
branches  of  the  facial  going  to  the  superficial  muscles  of  the  face  is  sufficiently  evident, 
in  view  of  our  present  knowledge  of  the  distribution  of  these  branches  and  the  general 
properties  of  the  nerve.  Throughout  the  writings  of  Sir  Charles  Bell,  the  facial  is 
spoken  of  as  the  "  respiratory  nerve  of  the  face."  It  is  now  recognized  as  the  nerve 
which  presides  over  the  movements  of  the  superficial  muscles  of  the  face,  not  including 
those  directly  concerned  in  the  act  of  mastication.  This  being  its  general  function,  it  is 
easy  to  assign  to  each  of  what  may  be  termed  the  external  branches  of  the  facial  its 
particular  office. 

Just  after  the  facial  nerve  has  passed  out  at  the  stylo-mastoid  foramen,  it  sends  to  the 
glosso-pharyngeal  the  communicating  branch,  the  functions  of  which  we  have  just  con- 
sidered in  connection  with  the  movements  of  the  palate. 

The  posterior  auricular  branch,  becoming  sensitive  by  the  addition  of  filaments  from 
the  cervical  plexus,  gives  sensibility  to  the  integunfent  on  the  back  part  of  the  ear  and 
over  the  occipital  portion  of  the  occipito-frontalis  muscle.  It  animates  the  retrahens 
and  the  attollens  aurem,  muscles  but  little  developed  in  man,  but  very  important  in  cer- 
tain of  the  inferior  animals.  It  also  animates  the  posterior  portion  of  the  occipito-fron- 
talis muscle. 

The  branches  distributed  to  the  posterior  belly  of  the  digastric  and  to  the  stylo-hyoid 
muscle  simply  animate  these  muscles,  one  of  the  uses  of  which  is  to  assist  in  deglutition. 
The  same  may  be  said  of  the  filaments  that  go  to  the  stylo-glossus. 

The  two  great  branches  distributed  upon  the  face  after  the  trunk  of  the  nerve  has 
passed  through  the  parotid  gland  have  the  most  prominent  function.  Both  of  these 
branches  are  somewhat  sensitive,  from  their  connections  with  other  nerves,  and  are  dis- 
tributed in  small  part  to  integument. 

The  temporo-facial  branch  animates  all  of  the  muscles  of  the  upper  part  of  the  face. 
In  complete  paralysis  of  this  branch,  the  eye  is  constantly  open,  even  during  sleep,  from 
paralysis  of  the  orbicularis  muscle.  In  cases  of  long  standing,  the  globe  of  the  eye  may 
become  inflamed  from  constant  exposure,  from  abolition  of  the  movements  of  winking  by 
which  the  tears  are  distributed  over  its  surface  and  little  foreign  particles  are  removed, 
and,  in  short,  from  absence  of  the  protective  action  of  the  lids.  In  these  cases,  the 
lower  lid  may  become  slightly  everted.  The  frontal  portion  of  the  occipito-frontalis, 
the  attrahens  aurem,  and  the  corrugator  supercilii  muscles,  are  also  paralyzed.  The 
most  prominent  symptom  of  paralysis  of  these  muscles  is  inability  to  corrugate  the  brow 
upon  one  side,  as  in  frowning. 

Paralysis  of  the  muscles  that  dilate  the  nostrils  has  been  shown  to  have  an  important 
influence  upon  respiration  through  the  nose.  It  was  the  synchronism  between  the  acts 
of  dilatation  of  the  nostrils  and  the  movements  of  inspiration  which  first  led  Sir  Charles 
Bell  to  regard  the  facial  as  a  respiratory  nerve.  In  instances  of  complete  paralysis  of 
the  nostril  of  one  side,  there  is  frequently  some  difficulty  in  inspiration.  Sir  Charles 
Bell  refers  to  a  case  in  which,  when  "the  patient  lay  with  the  sound  side  against  the 
40 


626 


NERVOUS  SYSTEM. 


pillow,  he  was  under  the  necessity  of  holding  the  paralytic  nostril  open  with  the  fingers, 
in  order  to  breathe  freely."  In  the  horse,  the  movements  of  the  nostrils  are  essential  to 
respiration,  the  animal  being  unable  to  breathe  through  the  mouth.  When  both  facial 
nerves  are  divided  in  this  animal,  the  nostrils  collapse  and  are  occluded  with  each  effort 
at  inspiration,  and  death  takes  place  from  suffocation. 

Sir  Charles  Bell  and  others  have  also  noted  an  interference  with  olfaction,  due  to  the 
inability  to  inhale  with  one  nostril,  in  cases  of  facial  paralysis.  The  influence  of  the  nerve 
in  the  act  of  conveying  odorous  emanations  to  the  olfactory  membrane  is  sufficiently  evi- 
dent after  what  we  have  remarked  concerning  the  action  of  the  facial  in  respiration. 

The  effects  of  paralysis  of  the  other  superficial  muscles  of  the  face  are  manifested  in 
the  distortion  of  the  features,  from  the  unopposed  action  of  the  muscles  upon  the  sound 
side ;  a  phenomenon  which  is  sufficiently  familiar  to  the  practical  physician.  When 
facial  palsy  affects  one  side  and  is  complete,  the  angle  of  the  mouth  is  drawn  to  the 
opposite  side,  the  eye  upon  the  affected  side  is  widely  and  permanently  opened  even, 
during  sleep,  and  the  face  has  upon  that  side  a  peculiarly  expressionless  appearance. 
When  a  patient  affected  in  this  way  smiles  or  attempts  to  grimace,  the  distortion  is 
much  increased.  The  lips  are  paralyzed  upon  one  side,  which  sometimes  causes  a  flow 
of  saliva  from  the  corner  of  the  mouth.  In  the  lower  animals  that  use  the  lips  in  pre- 
hension, paralysis  of  these  parts  interferes  considerably  with  the  taking  of  food.  The 
flaccidity  of  the  paralyzed  lips  and  cheek  in  the  human  subject  sometimes  causes  a  puff- 
ing movement  with  each  act  of  expiration,  as  if  the  patient  were  smoking  a  pipe.  • 


FIG.  206. 


FIG    207. 


FIG.  208. 


Expressions  of  the  face  produced  by  contraction  of  t7ie  muscles  under  electrical  excitation-    (Le  Bon,  after 

Duchenne.) 

Fig.  203,  front  view  of  the  face  in  repose. 
Fig.  204,  profile  view. 

Fig.  205,  expression  of  langhter  upon  one  side,  produced  by  contraction  of  the  zygomaticns  major. 
Fig.  206,  expression  of  fear,  produced  by  contraction  of  the  frontal  muscle  and  the  depressors  of  the  lower  jaw. 
Fig.  20T,  expression  of  fear,  profile  view. 

Fig.  208,  expression  of  fear  and  great  pain,  produced  by  contraction  of  the  corrugator  supercilii  and  the  depressors 
of  the  lower  jaw. 

We  have  already  seen  that  the  buccinator  is  not  supplied  by  filaments  from  the  nerve 
of  mastication,  but  is  animated  solely  by  the  facial.  Paralysis  of  this  muscle  interferes 
materially  with  mastication,  from  a  tendency  to  accumulation  of  the  food  between  the 
teeth  and  the  cheek.  Patients  complain  of  this  difficulty,  and  they  sometimes  keep  the 


SPINAL  AOCESSOKY  NERVE.  627 

food  between  the  teeth  by  pressure  with  the  hand.  In  the  rare  instances  in  which  both 
facial  nerves  are  paralyzed,  there  is  very  great  difficulty  in  mastication,  from  the  cause 
just  mentioned. 

The  functions  of  the  external  branches  of  the  facial  are  thus  sufficiently  simple ;  and 
it  is  only  as  its  deep  branches  affect  the  taste,  the  movements  of  deglutition,  etc.,  that  it 
is  difficult  to  ascertain  their  exact  office.  As  this  is  the  nerve  of  expression  of  the  face, 
it  is  in  the  human  subject  that  the  phenomena  attending  its  paralysis  are  most  prominent. 
When  both  sides  are  affected,  the  appearance  is  most  remarkable,  the  face  being  abso- 
lutely expressionless  and  looking  as  if  it  had  been  covered  with  a  mask. 

/Spinal  Accessory  and  Sublingual  JVerves. 

A  description  of  the  properties  and  functions  of  the  spinal  accessory  and  the  sublin- 
gual  completes  the  physiological  history  of  the  motor  nerves  emerging  from  the  cranial 
cavity.  The  functions  of  these  nerves  are  important,  and,  in  the  case  of  the  spinal 
accessory,  they  possess  considerable  interest,  from  the  fact  that  physiological  investigations 
have,  only  within  a  few  years,  determined  the  significance  of  certain  of  its  anatomical 
relations.  As  we  have  done  in  studying  the  other  motor  nerves,  we  shall  treat  succes- 
sively of  their  anatomical  relations,  general  properties  and  functions. 

Spinal  Accessory  JSTerve.     (Third  Division  of  the  Eighth  Nerve.) 

The  spinal  accessory  nerve,  from  the  remarkable  extent  of  its  origin,  its  important 
anastomoses  with  other  nerves,  and  its  curious  course  and  distribution,  has  long  engaged 
the  attention  of  anatomists  and  physiologists,  who  have  advanced  many  theories  with 
regard  to  its  office.  We  shall  content  ourselves,  however,  with  a  simple  description  of 
its  anatomy  as  it  appears  from  late  researches,  and  shall  begin  its  physiological  history 
with  comparatively  recent  experiments,  which  alone  have  advanced  our  positive  knowl- 
edge of  its  properties. 

Physiological  Anatomy  of  the  Spinal  Accessory . — The  origin  of  this  nerve  is  very  exten- 
sive. A  certain  portion  arises  from  the  lower  half  of  the  medulla  oblongata,  and  the  rest 
takes  its  origin  below,  from  the  upper  two-thirds  of  the  cervical  portion  of  the  spinal 
cord.  That  portion  of  the  root  which  arises  from  the  medulla  oblongata  is  called,  by 
the  French,  the  bulbar  portion,  the  roots  from  the  cord  constituting  the  spinal  portion. 
Inasmuch  as  there  is  a  marked  difference  between  the  functions  of  these  two  portions, 
the  anatomical  distinction  just  mentioned  is  important. 

The  superior  roots  arise  by  four  or  five  filaments  from  the  lower  half  of  the  medulla 
oblongata,  below  the  origin  of  the  pneumogastrics.  These  filaments  of  origin,  in  prepara- 
tions hardened  by  prolonged  immersion  in  alcohol,  are  shown  to  be  connected  with  the 
lateral  portion  of  the  medulla,  and  not  with  the  posterior  columns.  Their  origin  seems, 
therefore,  to  be  from  the  motor  tract. 

The  spinal  portion  of  the  nerve  arises  from  the  upper  part  of  the  cervical  division 
of  the  spinal  cord,  between  the  anterior  and  posterior  roots  of  the  upper  four  or  five 
cervical  nerves.  The  filaments  of  origin  are  from  six  to  eight  in  number.  The  most 
inferior  of  these  is  generally  single,  the  other  filaments  being  frequently  arranged  in 
pairs.  These  take  their  origin  from  the  lateral  portion  of  the  cord,  rather  nearer  the 
posterior  median  line  than  the  roots  from  the  medulla  oblongata. 

Following  the  nerve  from  its  most  inferior  filament  of  origin  upward,  it  gradually 
increases  in  size  by  union  with  its  other  roots,  enters  the  cranial  cavity  by  the  foramen 
magnum,  and  passes  to  the  jugular  foramen,  by  which  it  emerges,  in  connection  with  the 
glosso-pharyngeal,  the  pneumogastric,  and  the  internal  jugular  vein. 

In  its  course,  the  spinal  accessory  anastomoses  with  several  nerves.  Just  as  it  enters 
the  cranial  cavity,  it  receives  filaments  of  communication  from  the  posterior  roots  of  the 


628 


NERVOUS   SYSTEM. 


upper  two  cervical  nerves.  These  filaments,  however,  are  not  constant.  It  frequently, 
though  not  constantly,  sends  a  few  filaments  to  the  superior  ganglion,  or  the  ganglion  of 
the  root  of  the  pneumogastric.  After  it  has  emerged  by  the  jugular  foramen,  it  sends  a 
branch  of  considerable  size  to  the  pneumogastric,  from  which  nerve  it  also  receives  a  few 
filaments  of  communication.  This  branch  will  be  again  referred  to  in  connection  with 
the  distribution  of  the  nerve.  In  its  course,  it  also  receives  filaments  of  communication 
from  the  anterior  branches  of  the  second,  third,  and  fourth  cervical  nerves. 

In  its  distribution,  the  spinal  accessory  presents  two  branches.  The  first,  or  anasto- 
motic  branch,  passes  to  the  pneumogastric  just  below  the  plexiform  enlargement  which 
is  sometimes  called  the  ganglion  of  the  trunk  of  the  pneumogastric. 

The  internal,  or  anastomotic  branch,  is  composed  principally,  if  not  entirely,  of  the 
filaments  that  take  their  origin  from  the  medulla  oblongata.  As  it  joins  the  pneumogas- 
tric, it  subdivides  into  two  smaller  branches.  The  first  of  these  forms  a  portion  of  the 

pharyngeal  branch  of  the  pneumogastric.  The 
second  becomes  intimately  united  with  the 
pneumogastric,  lying  at  its  posterior  portion, 
and  furnishes  filaments  to  the  inferior,  or  re- 
current laryngeal  branch,  which  is  distributed 
to  all  of  the  muscles  of  the  larynx  except  the 
crico-thyroid.  The  passage  of  the  filaments 
from  the  spinal  accessory  to  the  pharyngeal 
branch  of  the  pneumogastric  is  easily  observed ; 
but  the  fact  that  filaments  from  this  nerve  pass 
to  the  larynx  by  the  recurrent  laryngeal  has 
been  ascertained  only  by  physiological  experi- 
ments. 

The  external,  or  large  branch  of  the  spinal 
accessory,  called  the  muscular  branch,  pene- 
trates and  passes  through  the  posterior  portion 
of  the  upper  third  of  the  sterno-cleido-mastoid 
muscle,  goes  to  the  anterior  surface  of  the  trape- 
zius,  which  muscle  receives  its  ultimate  branches 
of  distribution.  In  its  passage  through  the 
sterno-cleido-mastoid,  it  joins  with  branches 
from  the  second  and  third  cervical  nerves  and 
sends  filaments  of  distribution  to  the  muscle. 
Alth'ough  the  two  muscles  just  mentioned  re- 
ceive numerous  motor  filaments  from  the  spinal 
accessory,  they  are  also  supplied  from  the  cer- 
vical nerves ;  and,  consequently,  they  are  not 
entirely  paralyzed  when  the  spinal  accessory  is 
divided. 


FIG.  209.— Spinal  accessory  nerve.  (Hirschfeld.) 
1,  trunk  of  the  facial  nerve ;  2,  2,  glosso-pharyngeal 
nerve;  3,  3,  pneumogastric;  4,  4,  4,  trunk  of 
the  spinal  accessory ;  5,  sublingual  nerve ;  6, 
superior  cervical  ganglion  ;  7,  7,  anastomosis  of 
the  first  two  cervical  nerves ;  8,  carotid  branch  of 
the  sympathetic;  9, 10, 11, 12,  13,  branches  of  the 
glosso-pharyngeal ;  14,  15,  branches  of  the  fa- 
cial; 16,  otic  ganglion;  17,  auricular  branch  of 
the  pneumogastric;  IS,  anastomosing  branch 
Jrom  the  spinal  accessory  to  the  pneumogas- 
tric; 19,  anastomosis  of  the  first  pair  of  cervical 
nerves  with  the  sublingual ;  20,  anastomosis  of 
me  spinal  accessory  with  the  second  pair  of 
cervical  nerves;  21,  pharyngeal  plexus ;  22 
superior  laryngeal  nerve  ;  23,  external  larvneeal 
nerve  ;  24,  middle  cervical  ganglion. 


Properties  and  Functions  of  the  Spinal  Ac- 
cessory.— Notwithstanding  the  great  difficulty  in 
exposing  and  in  operating  upon  the  roots  of  the 
spinal  accessory,  it  has  been  demonstrated  that 
their  galvanization  produces  convulsive  move- 
ments in  certain  muscles.  The  most  satisfactory 
experiments  with  relation  to  the  general  proper- 
ties of  the  roots  were  made  by  Bernard.  This  physiologist  cut  through  the  occipito- 
atloid  membranes  and  galvanized  the  filaments  within  the  spinal  canal.  By  galvanizing 
the  filaments  arising  from  the  medulla  oblongata,  he  produced  contractions  of  the  mus- 


SPINAL  ACCESSORY   NERVE.  629 

cles  of  the  pharynx  and  larynx  and  no  movements  of  the  sterno-mastoid  and  trapezius. 
Galvanization  of  the  roots  arising  from  the  spinal  cord  produced  movements  of  the  two 
muscles  just  mentioned  and  absolutely  no  movements  in  the  larynx.  In  view  of  these 
experiments,  it  is  evident  that  the  true  filaments  of  origin  of  the  spinal  accessory  are 
motor ;  and  it  is  farther  evident  that  the  filaments  from  the  medulla  oblongata  are  dis- 
tributed to  the  muscles  of  the  pharynx  and  larynx,  while  the  filaments  from  the  spinal 
cord  go  to  the  sterno-cleido-mastoid  and  trapezius. 

The  trunk  of  the  spinal  accessory,  after  the  nerve  has  passed  out  of  the  cranial  cavity, 
is  endowed  with  a  certain  degree  of  sensibility.  If  the  nerve  be  divided,  the  peripheral 
extremity  manifests  recurrent  sensibility,  but  the  central  end  is  also  sensible,  proba- 
bly from  direct  filaments  of  communication  from  the  cervical  nerves  and  the  pneumo- 
gastric.  As  we  have  remarked,  however,  in  treating  of  the  properties  of  some  other  of 
the  cranial  nerves,  it  is  exceedingly  difficult  to  note  satisfactorily  a  slight  degree  of  sensi- 
bility in  nerves  that  can  be  exposed  only  by  a  tedious  and  painful  operation. 

The  functions  of  the  external,  or  muscular  branch  of  the  spinal  accessory  are  suffi- 
ciently evident ;  and  the  effects  of  the  destruction  of  the  nerves  on  both  sides,  as  far  as 
this  branch  is  concerned,  simply  resolve  themselves  into  the  phenomena  due  to  partial 
paralysis  of  the  sterno-mastoid  and  trapezius ;  but  the  functions  of  the  branch  which 
joins  the  pneumogastric  are  much  more  complex. 

Functions  of  the  Internal  Branch  from  the  Spinal  Accessory  to  the  Pneumogastric. — 
Bischoff  attempted  to  ascertain  the  functions  of  this  branch  by  dividing  the  roots  of  the 
spinal  accessory  upon  both  sides  in  a  living  animal.  The  results  of  his  experiments  may  be 
stated  in  a  very  few  words :  He  attempted  to  divide  all  of  the  roots  of  the  nerves  upon 
both  sides  by  dissecting  down  to  the  occipito-atloid  space  and  penetrating  into  the  cavity 
of  the  spinal  canal.  In  the  first  three  experiments  upon  dogs,  the  animals  died  so  soon 
after  section  of  the  nerves,  that  no  satisfactory  results  were  obtained.  In  two  succeed- 
ing experiments  upon  dogs,  the  animals  recovered.  After  division  of  the  nerves,  the  voice 
became  hoarse,  but  a  few  weeks  later,  it  became  normal.  On  killing  the  animals,  an 
examination  of  the  parts  showed  that  some  of  the  filaments  of  origin  had  not  been 
divided.  An  experiment  was  then  made  upon  a  goat,  but  this  was  unsatisfactory,  as  the 
roots  were  not  completely  divided.  Finally,  another  experiment  was  made  upon  a  goat. 
In  this  the  results  were  more  satisfactory.  After  division  of  the  nerve  upon  one  side, 
the  voice  became  hoarse.  As  the  filaments  were  divided  upon  the  opposite  side,  the 
voice  was  enfeebled,  until  finally  it  became  extinct.  The  sound  emitted  afterward  was 
one  which  could  in  nowise  be  called  voice  ("  qui  neutiquam  vox  appellari  potuit ").  This 
experiment  was  made  in  the  presence  of  Tiedemann  and  Seubertus  and  was  not  re- 
peated. 

Bernard,  whose  ingenious  experiments  determined  exactly  the  influence  of  the  spinal 
accessory  over  the  vocal  movements  of  the  larynx,  first  repeated  the  experiments  of  Bis- 
choff; but  the  animals  operated  upon  died  so  soon,  from  haemorrhage  or  other  causes, 
that  his  observations  were  not  satisfactory.  After  many  unsuccessful  trials,  he  succeeded 
in  overcoming  all  difficulties,  by  following  the  trunk  of  the  nerve  back  to  the  jugular 
foramen,  seizing  it  here  with  a  strong  pair  of  forceps,  and  drawing  it  out  by  the  roots. 
This  operation  is  difficult,  but  we  have  several  times  performed  it  with  entire  success, 
and  have  verified,  in  every  regard,- the  facts  observed  by  Bernard.  Within  the  last  year, 
the  excellent  assistant  to  the  chair  of  Physiology  at  the  Bellevue  Hospital  Medical  Col- 
lege, Dr.  0.  F.  Roberts,  has  succeeded  in  extirpating  these  nerves  for  class-demon- 
strations. The  operation  is  generally  most  successful  in  cats,  although  Bernard  has 
succeeded  frequently  in  other  animals. 

The  operative  procedure  employed  by  Bernard  is  the  following :  The  trunk  of  the 
nerve  is  exposed  as  it  passes  through  the  sterno-cleido-mastoid  muscle.  It  is  then  fol- 
lowed up  by  careful  dissection,  avoiding  blood-vessels  as  much  as  possible,  to  the  poste- 
rior foramen  lacerum.  when  the  sublingual  is  seen  crossing  the  course  of  the  pneumo- 


63o  NERVOUS  SYSTEM. 

gastric.  It  is  here  that  the  anastomotic  branch  leaves  the  spinal  accessory  to  go  to  the 
pneumogastric.  At  this  point,  the  external  branch,  with  the  anastomosing  branch,  is 
seized  with  a  pair  of  rather  broad-billed  forceps,  and  gentle  but  firm  traction  is  applied 
to  the  entire  nerve.  Soon  there  is  a  cracking  sensation  conveyed  to  the  hand  as  the 
roots  give  way,  and  the  nerve  may  then  be  drawn  out  entire.  With  care,  either  the  fila- 
ments of  origin  from  the  medulla  or  those  from  the  cord  may  be  extirpated  alone. 

When  one  spinal  accessory  is  extirpated,  the  vocal  sounds  are  hoarse  and  unnatural. 
When  both  nerves  are  torn  out,  in  addition  to  the  disturbance  of  deglutition  and  the  par- 
tial paralysis  of  the  sterno-mastoid  and  trapezius  muscles,  the  voice  becomes  extinct. 
Animals  operated  upon  in  this  way  move  the  jaws  and  make  evident  efforts  to  cry,  but 
no  vocal  sound  is  emitted.  This  condition  is  very  striking ;  and,  inasmuch  as  Bernard 
has  kept  animals,  with  both  nerves  extirpated,  for  months,  the  question  of  the  function 
of  these  nerves  in  phonation  may  now  be  regarded  as  definitively  settled. 

It  remains  now  to  consider  the  experimental  facts  with  regard  to  the  influence  of  the 
different  filaments  of  origin  of  the  spinal  accessory  upon  the  voice.  These  are  simple  and 
entirely  conclusive ;  and  they  are  due  exclusively  to  the  researches  of  Bernard.  This 
experimenter  found  that  division  of  the  roots  of  origin  from  the  spinal  cord  not  only  did 
not  affect  the  voice,  but  sometimes  it  seemed  to  render  it  clearer ;  but  that  division  of  the 
roots  of  origin  from  the  medulla  oblongata  abolished  the  voice,  although  the  inferior  roots 
were  intact. 

It  is  not  necessary  to  discuss  the  action  of  the  muscles  of  the  larynx  in  phonation,  as 
this  subject  has  already  been  considered  in  connection  with  the  voice.  The  experiments 
that  have  demonstrated  the  influence  of  the  spinal  accessory  nerve  over  these  muscles 
have  pointed  out  the  destination  of  the  fibres  that  join  the  pneumogastric,  which  could 
never  have  been  done  so  satisfactorily  by  dissection.  They  have  shown  farther  that 
the  movements  involved  in  phonation  are  more  or  less  independent  of  the  respiratory 
movements  of  the  larynx. 

If  the  larynx  be  exposed  in  a  living  animal,  with  all  its  nervous  connections  intact, 
it  will  be  seen  to  open  widely  during  inspiration,  being  passive  in  expiration.  The  wide 
opening  of  the  glottis  at  this  time  is  due  to  the  fact  that,  after  the  operation,  respiration 
is  .usually  more  or  less  labored ;  but,  if  we  carefully  observe  the  parts  when  the  respira- 
tory acts  are  perfectly  tranquil,  the  movements  of  the  glottis  seem  to  be  very  slight. 
The  larynx  is  then  permanently  opened  to  a  moderate  degree,  but  the  chink  of  the  glottis 
is  slightly  dilated  with  each  expiration.  If  the  recurrent  laryngeal  nerves,  which  are 
distributed  to  all  of  the  muscles  of  the  larynx  except  the  crico-thyroid,  be  now  divided 
upon  both  sides,  the  larynx  is  entirely  paralyzed,  and  in  cats  and  young  animals,  in  which 
the  cartilages  are  soft  and  flexible,  the  parts  are  occluded  by  the  effort  of  inspiration,  and 
death  takes  place  from  suffocation.  Of  course  the  division  of  the  recurrent  laryngeal 
nerves  abolishes  the  voice,  but  it  arrests  the  other  movements  of  the  larynx  as  well. 
The  distinction  thus  established  between  the  action  of  the  spinal  accessory  and  of  the 
recurrent  laryngeal  nerves  was  fully  illustrated  by  Bernard,  in  the  following  experiments : 

In  a  cat,  in  which  the  voice  had  been  completely  destroyed  by  extirpation  of  both 
spinal  accessory  nerves,  the  larynx  was  exposed.  The  glottis  was  seen  dilated  so  as  to 
permit  the  free  passage  of  air  in  respiration.  The  mucous  membrane  retained  its  sensi- 
bility, and,  when  the  interior  of  the  larynx  was  irritated,  a  very  slight  but  ineffectual 
effort  was  made  to  close  the  glottis.  It  was  impossible  for  the  animal  to  approximate 
the  posterior  points  of  attachment  of  the  vocal  cords  or  to  put  the  cords  upon  the  stretch. 
If  such  irritation  be  applied  to  the  larynx  of  an  animal  with  the  spinal  accessory  nerves 
intact,  the  glottis  is  instantly  and  firmly  closed. 

^  In  a  cat  about  five  weeks  old,  both  spinal  accessory  nerves  were  extirpated,  and  the 
voice  was  thus  destroyed.  Two  days  after,  both  recurrent  laryngeal  nerves  were  divided, 
and  the  animal  died  almost  immediately  of  suffocation. 

These  experiments  show  conclusively  that  the  internal,  or  communicating  branch  of 


SPINAL  ACCESSORY  NERVE.  631 

the  spinal  accessory  is  the  nerve  which  presides  over  the  movements  of  the  larynx  in 
phonation.  The  filaments  undoubtedly  pass  to  the  larynx  in  greatest  part  through  the 
recurrent  laryngeal  branches  of  the  pneumogastric ;  but  the  recurrent  laryngeals  also 
contain  motor  filaments  from  other  sources,  which  latter  are  chiefly  concerned  in  the 
respiratory  movements  of  the  glottis. 

Influence  of  the  Internal  Branch  of  the  Spinal  Accessory  upon  Deglutition.— There 
are  two  ways  in  which  deglutition  is  affected  through  this  nerve :  1.  When  the  larynx  is 
paralyzed  as  a  consequence  of  extirpation  of  both  nerves,  the  glottis  cannot  be  completely 
closed  to  prevent  the  entrance  of  foreign  bodies  into  the  air-passages.  In  rabbits  par- 
ticularly, it  has  been  noted  that  particles  of  food  penetrate  the  trachea  and  find  their 
way  into  the  lungs.  2.  The  spinal  accessory  furnishes  numerous  filaments  to  the  pharyn- 
geal  branch  of  the  pneumogastric,  and,  through  this  nerve,  it  directly  affects  the  muscles 
of  deglutition ;  but  the  muscles  animated  in  this  way  by  the  spinal  accessory  have  a  ten- 
dency to  draw  the  lips  of  the  glottis  together,  while  they  assist  in  passing  the  alimentary 
bolus  into  the  oesophagus.  When  these  important  acts  are  wanting,  there  is  some  diffi- 
culty in  the  process  of  deglutition  itself  as  well  as  danger  of  the  passage  of  foreign 
particles  into  the  larynx. 

Influence  of  the  Spinal  Accessory  upon  the  Heart.— When  we  come  to  study  the  varied 
functions  of  the  pneumogastrics,  we  shall  discuss  fully  the  mechanism  by  which  the  con- 
tractions of  the  heart  are  arrested  by  galvanization  of  both  of  these  nerves  in  the  neck. 
A  very  curious  and  interesting  observation  by  Waller  has  demonstrated  that  this  influ- 
ence, whatever  be  its  mechanism,  is  derived  from  the  spinal  accessory  and  necessarily 
comes  through  its  communicating  branch.  It  has  been  found  that  a  powerful  current  of 
galvanism  passed  through  the  pneumogastric  upon  one  side  will  arrest  the  action  of  the 
heart.  Waller  found  that,  if  he  extirpated  the  spinal  accessory  upon  one  side,  the  action 
of  the  heart  could  not  be  arrested  by  galvanizing  the  pneumogastric  upon  the  same  side ; 
but  this  result  followed  galvanization  of  the  pneumogastric  upon  the  opposite  side,  on 
which  the  connections  with  the  spinal  accessory  were  intact.  These  phenomena,  how- 
ever, could  not  be  observed  until  from  ten  to  twelve  days  had  elapsed  after  the  extirpa- 
tion of  the  spinal  accessory.  We  have  already  seen,  in  treating  of  the  general  properties 
of  the  nerves,  that  the  irritability  of  the  motor  nerves  disappears  in  about  four  days  after 
their  separation  from  the  nerve-centres.  In  the  observation  just  referred  to,  it  seemed 
necessary  that  a  sufficient  time  should  elapse  after  extirpation  of  the  spinal  accessory  for 
the  irritability  of  the  filaments  that  join  the  pneumogastric  to  become  extinct ;  but  the 
experiment  is  sufficient  to  show  the  direct  inhibitory  influence  of  the  spinal  accessory 
upon  the  heart.  This  subject  will  be  more  fully  considered,  however,  in  connection  with 
the  functions  of  the  pneumogastrics. 

Functions  of  the  External,  or  Muscular  Branch  of  the  Spinal  Accessory. — The  most 
interesting  feature  in  the  recent  researches  into  the  functions  of  the  spinal  accessory  is, 
that  experimentalists  have  been  able  to  separate  physiologically  the  internal  from  the 
external  branch.  Observations  have  conclusively  demonstrated  that  the  internal  branch, 
and  the  internal  branch  only,  is  directly  concerned  in  the  vocal  movements  of  the  larynx, 
and,  to  a  great  extent,  in  the  closure  of  the  glottis  during  deglutition.  It  has  been  noted, 
in  addition,  that  animals  in  which  both  branches  have  been  extirpated  present  irregu- 
larity of  the  movements  of  the  anterior  extremities  and  suffer  from  shortness  of  breath 
after  violent  muscular  exertion.  The  use  of  the  corresponding  extremities  in  the  human 
subject  is  so  different,  that  it  is  not  easy  to  make  a  direct  application  of  these  experi- 
ments ;  still,  we  can  draw  from  them  certain  inferences  with  regard  to  the  functions  of 
the  external  branch  in  man. 

In  prolonged  vocal  efforts,  the  vocal  cords  are  put  upon  the  stretch,  and  the  act  of 
expiration  is  very  different  from  that  in  tranquil  breathing.  In  singing,  for  example,  the 
shoulders  are  frequently  fixed;  and  this  is  done  to  some  extent  by  the  action  of  the 
sterno-cleido-mastoid  and  the  trapezius.  We  may  suppose,  then,  that  the  action  of  the 


NERVOUS   SYSTEM. 

branch  of  the  spinal  accessory  which  goes  to  these  muscles  has  a  certain  synchronism 
with  the  action  of  the  branch  going  to  the  larynx  and  the  pharynx  ;  the  one  fixing  the 
upper  part  of  the  chest  so  that  the  expulsion  of  the  air  through  the  glottis  may  be  more 
nicely  regulated  by  the  expiratory  muscles,  and  the  other  acting  upon  the  vocal  cords. 

In  what  is  known  to  physiologists  as  muscular  effort,  the  glottis  is  closed,  the  thorax 
is  fixed  after  a  full  inspiration,  and  respiration  is  arrested  so  long  as  the  effort,  if  it  be 
not  too  prolonged,  is  continued.  The  same  synchronism,  therefore,  obtains  in  this  as  in 
prolonged  vocal  efforts.  In  experiments  in  which  the  muscular  branch  only  has  been 
divided,  shortness  of  breath,  after  violent  muscular  effort,  is  observed  ;  and  this  is  proba- 
bly due  to  the  want  of  synchronous  action  of  the  sterno-cleido-mastoid  and  trapezius, 
The  irregularity  in  the  movements  of  progression  in  animals,  in  which  either  both  branch- 
es or  the  muscular  branches  alone  have  been  divided,  is  due  to  anatomical  peculiarities. 
Bernard  has  observed  these  irregularities  in  the  dog  and  the  horse,  but  they  are  not  so- 
well  marked  in  the  cat.  There  have  been  no  opportunities  for  illustrating  these  points 
in  the  human  subject. 

Sublingual,  or  Hypoglossal  JVerve.     (Ninth  Nerve.) 

The  last  of  the  motor  cranial  nerves  is  the  sublingual';  and  its  functions  are  inti- 
mately connected  with  the  physiology  of  the  tongue  in  deglutition  and  articulation, 
although  it  is  also  distributed  to  certain  of  the  muscles  of  the  neck. 

Physiological  Anatomy  of  the  Sublingual  Nerve. — The  apparent  origin  of  the  sublin- 
gual  is  from  the  medulla  oblongata,  in  the  groove  between  the  olivary  body  and  the 
anterior  pyramid,  on  the  line  of  the  anterior  roots  of  the  spinal  nerves.  At  this  point, 
its  root  is  formed  of  from  ten  to  twelve  filaments,  which  extend  from  the  inferior  por- 
tion of  the  olivary  body  to  about  the  junction  of  the  upper  with  the  middle  third. 
These  filaments  of  origin  are  separated  into  two  groups,  superior  and  inferior.  From 
this  apparent  origin,  the  filaments  have  been  traced  into  the  gray  matter  of  the  floor 
of  the  fourth  ventricle,  between  the  deep  origin  of  the  pneumogastric  and  the  glosso- 
pharyngeal.  Although  there  is  much  difference  of  opinion  upon  this  point,  it  is  probable 
that  some  of  the  filaments  of  origin  of  these  nerves  decussate  in  the  floor  of  the  fourth 
ventricle.  The  superior  and  inferior  filaments  of  origin  of  the  nerve  unite  to  form  two 
bundles,  which  pass  through  distinct  perforations  in  the  dura  mater.  These  two  bundles 
then  pass  into  the  anterior  condyloid  foramen  and  unite  into  a  single  trunk  as  they 
emerge  from  the  cranial  cavity. 

After  the  sublingual  has  passed  out  of  the  cranial  cavity,  it  anastomoses  with  several 
nerves.  It  sends  a  filament  of  communication  to  the  sympathetic  as  it  branches  from 
the  superior  cervical  ganglion.  Soon  after  it  has  passed  through  the  foramen,  it  sends  a 
branch  to  the  pneumogastric.  It  anastomoses  by  two  or  three  branches  with  the  upper 
two  cervical  nerves,  the  filaments  passing  in  both  directions  between  the  nerves.  It 
anastomoses  with  the  lingual  branch  of  the  fifth,  by  two  or  three  filaments  passing  in 
both  directions. 
•  In  its  distribution,  the  sublingual  presents  several  remarkable  peculiarities  : 

Its  first  branch,  the  descendens  noni,  passes  down  the  neck  to  the  sterno-hyoid,  ster- 
no-thyroid,  and  omo-hyoid  muscles.  From  its  relations  with  important  vessels  and 
nerves,  this  branch  possesses  considerable  surgical  interest. 

The  thyro-hyoid  branch  is  distributed  to  the  thyro-hyoid  muscle. 

The  other  branches  are  distributed  to  the  stylo-glossus,  hyo-glossus,  genio-hyoid,  and 
genio-hyo-glossus  muscles,  their  terminal  filaments  going  to  the  intrinsic  muscles  of  the 
tongue. 

It  is  thus  seen  that  the  sublingual  nerve  is  distributed  to  all  of  the  muscles  in  the 
infra-hyoid  region,  the  action  of  which  is  to  depress  the  larynx  and  the  hyoid  bone  after 


SUBLINGUAL,  OR  HYPOGLOSSAL  NERVE. 


633 


the  passage  of  the  alimentary  bolus  through  the  pharynx  ;  to  one  of  the  muscles  in  the 
supra-hyoid  region,  the  genio-hyoid ;  to  most  of  the  muscles  which  move  the  tongue ; 
and  to  the  muscular  fibres  of  the  tongue  itself.  The  action  of  these  muscles  and  of  the 
tongue  itself  in  deglutition  has  already  been  fully  discussed. 


• 


FIG.  210. — Distribution  of  the  sublingual  nerve.    (Sappey.) 

1,  root  of  the  fifth  nerve ;  2,  ganglion  of  Gasser ;  3,  4,  5,  6,  7,  9, 10,  12,  branches  and  anastomoses  of  the  fifth  nerve  ; 
11,  submaxillary  ganglion ;  13,  anterior  belly  of  the  digastric  muscle ;  14,  section  of  the  mylo-hyoid  muscle ;  15, 
glosso-pharyngeal  nerve;  16,  ganglion  of  Andersch;  17,  18,  branches  of  the  glosso-pharyngeal  nerve;  19,  19, 
pneumogastric ;  20,  21,  ganglia  of  the  pneumogastric  ;  22,  22,  superior  laryngeal  branch  of  the  pneumogastric  ; 
23,  spinal  accessory  nerve ;  24,  sublingual  nerve  ;  25,  descendens  noni ;  2(5,  thyro-hyoid  branch ;  27,  terminal 
branches ;  28,  two  branches,  one  to  the  genio-hyo-glossuft  and  the  other  to  the  genio-hyoid  muscle. 

Properties  and  Functions  of  the  Sublingual. — There  is  every  reason  to  believe  that 
the  sublingual  nerve  is  entirely  insensible  at  its  origin  from  the  medulla  oblongata.  The 
fact  that  it  arises  from  a  continuation  of  the  motor  tract  of  the  spinal  cord  and  has  na 
ganglion  upon  its  main  root  would  lead  to  the  supposition  that  it  is  an  exclusively  motor 
nerve.  In  operating  upon  the  roots  of  the  spinal  accessory,  when  the  origin  of  the  sub- 
lingual  is  necessarily  exposed,  Longet  has  irritated  the  roots  in  the  dog,  without  any  evi- 
dence of  pain  on  the  part  of  the  animal.  Such  experiments,  taken  in  connection  with 
the  anatomical  characters  of  the  nerve,  render  it  almost  certain  that  its  root  is  devoid 
of  sensibility  at  its  origin.  All  modern  experimenters  have  confirmed  the  observations 
of  Mayo  and  of  Magendie,  with  regard  to  the  sensibility  of  the  sublingual  after  it  has 
passed  out  of  the  cranial  cavity.  The  anastomoses  of  this  nerve  with  the  upper  two 
cervical  nerves,  with  the  pneumogastric,  and  with  the  lingual  branch  of  the  fifth,  afford 
a  ready  explanation  of  this  fact. 

The  functions  of  the  sublingual  have  already  been  so  fully  considered  under  the  head 
of  deglutition,  that  they  need  not  be  discussed  elaborately  in  this  connection.  We  shall 
here  simply  state  the  phenomena  which  follow  stimulation  of  the  nerve  and  the  division 
of  both  nerves  in  living  animals. 


634  NERVOUS  SYSTEM. 

The  sublingual  may  be  easily  exposed  in  the  dog  by  making  an  incision  just  below 
the  border  of  the  lower  jaw,  dissecting  down  to  the  carotid  artery  and  following  the 
vessel  upward  until  we  see  the  nerve  as  it  crosses  its  course.  On  applying  a  feeble 
current  of  galvanism  at  this  point,  there  are  evidences  of  sensibility,  and  the  tongue  is 
moved  convulsively  at  each  stimulation. 

The  phenomena  following  section  of  both  sublingual  nerves  point  directly  to  their 
function.  The  most  notable  fact  observed  after  this  operation  is,  that  the  movements  of 
the  tongue  are  entirely  lost,  while  general  sensibility  and  the  sense  of  taste  are  not  affected. 
The  phenomena  which  follow  division  of  these  nerves  consist  simply  in  loss  of  power 
over  the  tongue,  with  considerable  difficulty  in  deglutition.  We  have  repeatedly  noted 
all  of  these  points  and  have  demonstrated  them  to  medical  classes. 

In  the  human  subject,  the  sublingual  is  usually  more  or  less  affected  in  hemiplegia. 
In  these  cases,  as  the  patient  protrudes  the  tongue  the  point  is  deviated.  This  is  due  to 
the  unopposed  action  of  the  genio-hyo-glossus  upon  the  sound  side,  which,  as  it  pro- 
trudes the  tongue,  directs  the  point  toward  the  side  affected  with  paralysis. 

A  disease  of  rather  rare  occurrence  has  lately  been  described  under  the  name  of 
glosso-labial  paralysis,  which  is  characterized  by  paralysis  of  the  sublinguals,  affecting 
also  the  orbicularis  oris  and  frequently  the  intrinsic  muscles  of  the  larynx.  The  phe- 
nomena referable  to  the  loss  of  power  over  the  tongue  correspond  to  those  observed  in 
animals  after  section  of  the  sublingual  nerves.  Patients  affected  in  this  way  experience 
difficulty  in  deglutition,  and,  in  addition,  we  note  an  interference  with  articulation,  which 
cannot  be  observed  in  experiments  upon  animals.  We  lately  had  a  case  of  this  disease 
under  observation  in  the  Belle vue  Hospital,  the  phenomena  of  which  were  peculiarly 
interesting  from  a  physiological  point  of  view.  This  patient  presented  complete  paraly- 
sis of  the  tongue,  with  considerable  difficulty  in  deglutition,  probably  from  the  tongue- 
affection.  The  orbicularis  oris  was  also  paralyzed.  The  paralysis  probably  extended 
to  the  intrinsic  muscles  of  the  larynx,  as  little  or  no  vocal  sound  could  be  made.  The 
patient  was  incapable  of  articulate  language  and  communicated  entirely  by  signs. 


CHAPTER    XIX. 

SENSORY  CRANIAL  NERVES. 

Trifacial,  or  trigeminal  nerve— Physiological  anatomy  of  the  trifacial— Properties  and  functions  of  the  trifacial— Divi- 
sion of  the  trifacial  within  the  cranal  cavity^-Immediate  effects  of  division  of  the  trifacial— Eemote  effects  of 
division  of  the  trifacial —Division  of  the  trifacial  before  and  behind  the  ganglion  of  Gasser— Communication  with 
the  sympathetic  at  the  ganglion  of  Gasser— Explanation  of  the  phenomena  of  disordered  nutrition  after  division 
of  the  trifacial— Cases  of  paralysis  of  the  trifacial  in  the  human  subject— Pneumogas  trie  nerve  (second  division  of 
the  eighth)— Physiological  anatomy— Properties  and  functions  of  the  pneumogastric— General  properties  of  the 
roots— Properties  and  functions  of  the  auricular  nerves— Properties  and  functions  of  the  pharyngeal  nerves- 
Properties  and  functions  of  the  superior  laryngeal  nerves— Properties  and  functions  of  the  inferior,  or  recurrent 
laryngeal  nerves— Properties  and  functions  of  the  cardiac  nerves,  and  influence  of  the  pneumogastrics  upon  the 
circulation— Depressor-nerve  of  the  circulation— Properties  and  functions  of  the  pulmonary  branches,  and  influ- 
ence of  the  pneumogastrics  upon  respiration— Properties  and  functions  of  the  cesophageal  nerves— Properties  and 
functions  of  the  abdominal  branches. 

Trifacial,  or  Trigeminal  Nerve.    (Large  Root  of  the  Fifth  Nerve.) 

A  SINGLE  nerve,  the  large  root  of  the  fifth  pair,  called  the  trifacial  or  the  trigeminal, 
gives  general  sensibility  to  the  face  and  to  the  head  as  far  back  as  the  vertex.  This  is  one 
of  the  most  interesting  of  the  cranial  nerves  and  is  one  of  the  first  that  was  experimented 
upon  by  physiologists.  It  is  interesting,  not  only  as  the  great  sensitive  nerve  of  the  face, 
"but  from  its  connections  with  other  nerves  and  its  relations  to  the  organs  of  special  sense. 
In  studying  the  physiology  of  this  nerve,  we  must  necessarily  begin  with  its  physiological 
anatomy. 


TRIFAOIAL.  OR   TRIGEMINAL  NERVE. 


635 


Physiological  Anatomy  of  the  Trifacial  Nerve. — The  apparent  origin  of  the  large  root 
of  the  fifth  is  from  the  lateral  portion  of  the  pons  Varolii,  posterior  and  inferior  to  the 
origin  of  the  small  root,  from  which  it  is  separated  by  a  few  transverse  fibres  of  white 
substance.  The  deep  origin  is  far  removed  from  its  point  of  emergence  from  the  encepha- 
lon.  The  roots  pass  entirely  through  the  substance  of  the  pons,  from  without  inward 
and  from  before  backward,  without  any  connection  with  the  fibres  of  the  pons  itself.  By 
this  course,  it  reaches  the  medulla  oblongata,  where  the  roots  divide  into  three  bundles. 
The  anterior  bundle  passes  from  behind  forward,  between  the  anterior  fibres  of  the  pons 
and  the  cerebellar  portion  of  the  restiform  bodies,  to  anastomose  with  the  auditory  nerve. 
The  other  bundles,  which  are  posterior,  pass,  the  one  in  the  anterior  wall  of  the  fourth 
ventricle  to  the  lateral  tract  of  the  medulla  oblongata,  and  the  other,  becoming  grayish 
in  color,  to  the  restiform  bodies,  from  which  they  may  be  followed  as  far  as  the  point 
of  the  calamus  scriptorius.  A  few  fibres  from  the  two  sides  decussate  at  the  median  line 
in  the  anterior  wall  of  the  fourth  ventricle.  From  this  origin,  the  large  root  of  the  fifth 
passes  obliquely  upward  and  forward  to  the  ganglion  of  Gasser,  which  is  situated  in  a 
depression  in  the  petrous  portion  of  the  temporal  bone  on  the  internal  portion  of  its  ante- 
rior face. 


FIG.  211. — Principal  branches  of  the  large  root  of  the 
fifth  nerve.  (Eobin.) 

a,  ganglion  of  Gasser  ;  a-u\  ophthalmic  division  of 
the  fifth :  b,  ophthalmic  ganglion;  c.branch  from 
the  ophthalmic  division  of  the  fifth  to  the  ophthal- 
mic ganglion;  d,  motor  ocuii  communis;  e,  ca- 
rotid ;  /,  ciliary  nerves ;  g,  cornea  and  iris ;  a-h, 
superior  maxillary  division  of  the  fifth ;  i,  two 
branches  from  the  superior  maxillary  division 
of  the  fifth  to  the  xpheno-palatine  ganglion  ;  j, 
deep  petrosal  nerve ;  &,  filaments  from  the  motor 
root  of  the  fifth  to  the  internal  muscle  of  the  mal- 
leus; I,  mvso-palatine  ganglion;  m,  otic  ganglion; 
n,  small  superficial  petrosal  nerve  ;  o,  branches 
of  the  fifth  to  the  submaxiUary  ganglion;  p, 
branches  to  the  sublingital  aanglion;  q.  facial 
nerve ;  r,  sympathetic  ganglion  ;  s.  nerve  of  mas- 
tication ;  £,'  chorda  tympani.. joining  the  lingual 
branch  of  the  fifth ;  u,  Yidian  nerve  ;  v,  branch 
from  the  motor  root  to  the  internal  pterygoid  mus- 
cle ;  w,  branch  of  the  fifth  to  the  lachrymal  gland ; 
CB,  bend  of  the  facial  nerve ;  y,  middle  meningeal  ar- 
tery ;  z,  filament  from  the  carotid  plexus  to  the 
ophthalmic  ganglion  ;  (1  and  2  are  not  in  the  figure) 
3,  external  spheno-palatine  filaments ;  4,  sptieno- 
palatine  ganglion  ;  5.  naso-palatine  nerve  ;  6,  ante- 
rior palatine  nerve  ;  7,  inferior  maxillary  division 
of  the  fifth  ;  8,  nerve  of  Jacobson. 


FIG.  212.— Ophthalmic  division  of  the  fifth.    (Hirschfeld.) 

1,  ganglion  of  Gasser ;  2,  ophthalmic  division  of  the 
fifth;  3,  lachrymal  branch;  4,  frontal  branch;  5, 
external  frontal ;  6,  internal  frontal ;  7,  supra- 
trochlear';  B,  nasal  branch;  9,  external  nasal;  10, 
internal  nasal;  11.  anterior  deep  temporal  nerve; 
12,  middle  deep  temporal  nerve  ;  13,  posterior  deep 
temporal  nerve  ;  14,  origin  of  the  superficial  temporal 
nerve  ;  15,  great  superficial  petrous  nerve. 

I  to  XII,  roots  of  the  cranial  nerves. 


The  Gasserian  ganglion  is  semilunar  in  form  (sometimes  it  is  called  the  semilunar 
ganglion),  with  its  concavity  looking  upward  and  inward.  At  the  ganglion,  the  nerve 
receives  filaments  of  communication  from  the  carotid  plexus  of  the  sympathetic.  This 


636  NERVOUS  SYSTEM. 

anatomical  point  is  of  importance  in  view  of  some  of  the  remote  effects  which  follow 
division  of  the  fifth  nerve  through  the  ganglion  in  living  animals. 

It  will  be  necessary  only  to  describe  in  a  general  way  the  numerous  branches  of  dis- 
tribution of  the  fifth  nerve,  remembering  that  it  is  the  great  sensitive  nerve  of  the  face. 

At  the  ganglion  of  Gasser,  from  its  anterior  and  external  portion,  are  given  off  a  few 
small  and  unimportant  branches  to  the  dura  mater  and  the  tentorium. 

From  the  convex  border  of  the  ganglion,  the  three  great  branches  arise,  which  have 
given  to  the  nerve  the  name  of  trifacial  or  trigeminal.  These  are :  1,  the  ophthalmic  ; 
2,  the  superior  maxillary ;  3,  the  inferior  maxillary.  The  ophthalmic  and  the  superior 
maxillary  branch  are  derived  entirely  from  the  sensory  root.  The  inferior  maxillary 
branch  joins  with  the  motor  root  and  forms  a  mixed  nerve. 

The  ophthalmic  branch,  the  first  division  of  the  fifth,  is  the  smallest  of  the  three. 
Before  it  enters  the  orbit,  it  receives  filaments  of  communication  from  the  sympathetic, 
sends  small  branches  to  all  of  the  motor  nerves  of  the  eyeball,  and  gives  off  a  small  recur- 
rent branch  which  passes  between  the  layers  of  the  tentorium. 

Just  before  the  ophthalmic  branch  enters  the  orbit  by  the  sphenoidal  fissure,  it  divides 
into  three  branches  ;  the  lachrymal,  frontal,  and  nasal. 

The  lachrymal,  the  smallest  of  the  three,  sends  a  branch  to  the  orbital  branch  of  the 
superior  maxillary  nerve,  passes  through  the  lachrymal  gland,  to  which  certain  of  its  fila- 
ments are  distributed,  and  its  terminal  filaments  go  to  the  conjunctiva  and  to  the  integu- 
ment of  the  upper  eyelid. 


FIG.  213.— Superior  maxillary  division  of  the  fifth.    (Hirschfeld.) 

!•  ganglion  of  Gasser ;  2,  lachrymal  branch  of  the  ophthalmic  division ;  3.  superior  maxillary  division  of  the  fifth; 
4,  orbital  branch;  5,  lachrymo-palpebral  filament;  6,  malar  branch;  7,  temporal  branch;  8,  spheno- 
palatine  ganglion ;  9,  Vidian  nerve;  10.  great  superficial  petrosal  nerve;  11,  facial  nerve;  12,  branch  of  the 
Vidian  nerve;  13,  anterior  and  two  posterior  dental  branches ;  14,  branch  to  the  mucous  membrane  of  the 
alveolar  processes ;  15,  terminal  branches  of  the  superior  maxillary  division;  16,  branch  of  the  facial. 

The  frontal  branch,  the  largest  of  the  three,  divides  into  the  supra-trochlear  and  supra- 
orbital  nerves.  The  supra-trochlear  passes  out  of  the  orbit  between  the  supra-orbital 
foramen  and  the  pulley  of  the  superior  oblique  muscle.  It  sends  in  its  course  a  long, 
delicate  filament  to  the  nasal  branch  and  is  finally  lost  in  the  integument  of  the  forehead. 
The  supra-orbital  passes  through  the  supra-orbital  foramen,  sends  a  few  filaments  to  the 
upper  eyelid,  and  supplies  the  forehead,  the  anterior  and  median  portions  of  the  scalp, 
the  mucous  membrane  of  the  frontal  sinus,  and  the  pericranium  covering  the  frontal  and 
parietal  bones. 

The  nasal  branch,  before  it  penetrates  the  orbit,  gives  off  a  long,  delicate  filament  to 
the  ophthalmic  ganglion,  constituting  its  sensory  root.  It  then  gives  off  the  long  ciliary 


TRIFACIAL,   OR   TRIGEMINAL   NERVE.  637 

nerves,  which  pass  to  the  ciliary  muscle  and  iris.  Its  trunk  finally  divides  into  the  external 
nasal,  or  infra-trochlearis,  and  the  internal  nasal,  or  ethmoidal.  The  infra-trochlearis  is 
distributed  to  the  integument  of  the  forehead  and  nose,  to  the  internal  surface  of  the 
lower  eyelid,  the  lachrymal  sac,  and  the  caruncula.  The  internal  nasal  is  distributed  to 
the  mucous  membrane,  and  also  in  part  to  the  integument  of  the  nose. 

The  superior  maxillary  branch  of  the  fifth  passes  out  of  the  cranial  cavity  by  the 
foramen  rotundum,  traverses  the  infra-orbital  canal,  and  emerges  upon  the  face  by  the 
infra-orbital  foramen.  Branches  from  this  nerve  are  given  off  in  the  spheno-maxillary 
fossa  and  the  infra-orbital  canal,  before  it  emerges  upon  the  face.  In  the  spheno-maxil- 
lary fossa,  the  first  branch  is  the  orbital,  which  passes  into  the  orbit,  giving  off  one 
branch,  the  temporal,  which  passes  through  the  temporal  fossa  by  a  foramen  in  the  malar 
bone  and  is  distributed  to  the  integument  on  the  temple  and  the  side  of  the  forehead. 
Another  branch,  the  malar,  which  likewise  emerges  by  a  foramen  in  the  malar  bone,  is 
distributed  to  the  integument  over  this  bone.  In  the  spheno-maxillary  fossa,  are  also 
given  off  two  branches,  which  pass  to  the  spheno-palatine,  or  Meckel?s  ganglion.  From 
this  portion  of  the  nerve,  branches  are  given  off,  the  two  posterior  dental  nerves,  which 
are  distributed  to  the  molar  and  bicuspid  teeth,  the  mucous  membrane  of  the  correspond- 
ing alveolar  processes,  and  to  the  antrum. 


FIG.  214.— Inferior  maxillary  division  of  the  fifth.    (Hirschfeld.) 

1,  branch  from  the  motor  root  to  the  masseter  muscle ;  £,  filaments  from  this  branch  to  the  temporal  muscle ;  3,  buccal 
branch;  5,  6,  7,  branches  to  the  muscles;  8,  auriculo-temporal  nerve;  9,  temporal  branches;  10,  auricular 
branches;  11,  anastomosis  with  the  facial  nerve;  12,  lingual  branch;  13,  branch  of  the  motor  root  to  the 
mylo-hyoid  muscle ;  14, 15, 15,  inferior  dental  nerve,  with  its  branches;  16,  mental  branch;  17,  anastomosis 
of  this  branch  with  the  facial 


In  the  infra-orbital  canal,  a  large  branch,  the  anterior  dental,  is  given  off  to  the  teeth 
and  mucous  membrane  of  the  alveolar  processes  not  supplied  by  the  posterior  dental 
nerves.  This  nerve  anastomoses  with  the  posterior  dental. 


638 


NERVOUS   SYSTEM. 


The  terminal  branches  upon  the  face  are  distributed  to  the  lower  eyelid  (the  palpebral 
branches) ;  to  the  side  of  the  nose  (the  nasal  branches),  anastomosing  with  the  nasal 
branch  of  the  ophthalmic  ;  and  to  the  integument  and  mucous  membrane  of  the  upper 
lip  (the  labial  branches). 

The  inferior  maxillary  is  a  mixed  nerve,  composed  of  the  inferior  division  of  the  large 
root  and  the  entire  small  root.  The  distribution  of  the  motor  filaments  has  already  been 
described  under  the  head  of  the  nerve  of  mastication.  This  nerve  passes  out  of  the  cranial 
cavity  by  the  foramen  ovale,  and  then  separates  into  the  anterior  division,  containing 
nearly  all  of  the  motor  filaments,  and  the  posterior  division,  which  is  chiefly  sensory. 
The  sensory  portion  breaks  up  into  numerous  branches : 

1.  The  auriculo-temporal  nerve  supplies  the  integument  in  the  temporal  region,  the 
auditory  meatus  and  the  integument  of  the  ear,  the  temporo-maxillary  articulation,  and 
the  parotid  gland.  It  also  sends  important  branches  of  communication  to  the  facial. 

2.  The  lingual  branch  is  distributed  to  the  mucous 
membrane  of  the  tongue  as  far  as  the  point,  the  mucous 
membrane  of  the  mouth,  the  gums,  and  to  the  sublingual 
gland.     This  nerve  receives  an  important  branch  from 
the  facial  (the  chorda  tympani)  which  has  already  been 
described.     From  this  nerve,  also,  are  given  off  two  or 
three  branches  which  pass  to  the  submaxillary  ganglion, 
constituting  its  sensory  roots. 

3.  The  inferior  dental  nerve,  the  largest  of  the  three, 
passes  in  the  substance  of  the  inferior  maxillary  bone, 
beneath  the  teeth,  to    the  mental  foramen,  where   it 
emerges  upon  the  face.     The  most  important  sensory 
branches  are  those  which  supply  the  pulps  of  the  teeth, 
and  the  branches  upon  the  face.     The  nerve,  emerging- 
upon  the  face  by  the  mental  foramen,  called  the  mental 
nerve,  supplies  the  integument  of  the  chin  and  the  lower 
part  of  the  face,  the  lower  lip,  and  sends  certain  filaments 
to  the  mucous  membrane  of  the  mouth. 


FIG.  215.—  Limits  of  cutaneous  distri- 
bution of  sensory  nerves  to  the  face, 
head,  and  neck.  (Beclard.) 

1,  cutaneous  distribution  of  the  ophthal- 
mic division  of  the  fifth ;  2,  distribu- 
tion of  the  superior  maxillary  divi- 
sion ;  3,  8,  distribution  of  the  inferior 
maxillary  division  ;  4,  distribution  of 
the  anterior  branches  of  the  cervical 
nerves ;  5,  5,  distribution  of  the  pos- 
terior branches  of  the  cervical  nerves. 


Properties  and  Functions  of  the  Trifacial. — In  1822, 
Herbert  Mayo  published  an  account  of  "  experiments  to 
determine  the  influence  of  the  portio  dura  of  the  sev- 
enth, and  of  the  facial  branches  of  the  fifth  pair  of 
nerves."  These  experiments  consisted  in  dividing  the  infra-orbital,  inferior  maxillary 
and  frontal  branches  of  the  fifth,  and  the  branch  from  the  fifth  to  the  seventh,  in  asses, 
by  which  it  was  demonstrated  that  these  were  exclusively  sensory  nerves.  In  a  second 
publication,  the  following  year,  it  is  stated  that  the  root  of  the  fifth  was  divided  in  the 
cranial  cavity  in  pigeons ;  but  this  was  with  reference  chiefly  to  the  movements  of  the 
iris,  although  Mayo  notes  that  after  division  of  the  nerve  "  the  surface  of  the  eyeball  ap- 
pears to  have  lost  its  feeling." 

In  1823,  Fodera  published  an  account  of  experiments  in  which  he  had  divided  the 
roots  of  the  fifth  in  living  animals  (rabbits)  by  introducing  a  small  knife  through  an 
opening  in  the  parietal  bone,  along  the  base  of  the  skull,  and  cutting  through  the  roots 
near  the  Gasserian  ganglion.  The  operation  was  followed  by  complete  loss  of  sensibil- 
ity upon  the  side  on  which  the  nerve  had  been  divided.  In  this  and  other  experiments, 
however,  the  animals  died  a  short  time  after  the  operation.  The  paper  in  which  these 
experiments  were  detailed  was  presented  to  the  Academy  of  Sciences,  December  31, 1822, 
and  was  published  at  about  the  same  time  as  the  experiments  of  Mayo. 

In  1824,  Magendie  published  an  account  of  his  experiments  upon  the  fifth  pair.  He 
divided  the  nerve  at  its  root,  by  introducing  a  small  stylet  through  the  skull,  and  noted 


TRIFACIAL,  OR   TRIGEMINAL  NERVE. 


639 


immediate  loss  of  sensibility  upon  the  corresponding  side  of  the  face.  Magendie  was  the 
first  to  succeed  in  keeping  the  animals  alive,  observing  certain  interesting  remote  effects 
following  division  of  the  nerve. 

The  operative  procedure  employed  by  Magendie  has  been  followed,  with  great  suc- 
cess, by  other  physiologists,  particularly  Bernard,  to  whose  researches  we  are  indebted 
for  many  additional  facts  of  interest  concerning  the  functions  of  the  fifth  nerve.  As 
this  is  an  operation  which  we  have  frequently  performed  with  success,  following  the 
minute  directions  laid  down  by  Bernard,  we  shall  quote  from  him  in  brief  the  different 
steps : 

The  nerve  may  be  divided  in  the  cranial  cavity  with  tolerable  certainty  in  rabbits, 
cats,  dogs,  and  Guinea-pigs,  but  it  is  most  easily  done  in  rabbits.     The  operation  is  diffi- 
cult from  the  fact  that  one  is  working  in  the  dark,  and  it  requires  a 
certain  amount  of  dexterity,  to  be  acquired  only  by  practice.      The 
instrument  used  is  represented  in  Fig.  216.     The  operative  procedure 
is  as  follows : 

1.  "  The  head  of  the  rabbit  is  firmly  held  in  the  left  hand.     The 
operator  feels  with  the  finger  of  the  right  hand  the  tubercle  situated  in 
front  of  the  ear,  formed  by  the  condyle  of  the  lower  jaw.     Behind  this 
tubercle,  is  a  hard,  osseous  portion,  the  origin  of  the  auditory  canal. 

2.  "The  operator  penetrates  just  behind  the  superior  border  of  the 
condyle,  directing  the  point  of  the  instrument  slightly  forward  to  avoid 
passing  into  the  substance  of  the  petrous  portion  of  the  temporal  bone, 
and  thus  passes  more  easily  into  the  middle  temporal  fossa ;  at  the  same 
time  the  instrument  is  directed  a  little  upward  to  avoid  slipping  into  the 
zygomatic  fossa  and  thus  failing  to  enter  the  cranial  cavity. 

3.  "As  soon  as  the  instrument  has  penetrated 'the  cranium,  which 
is  recognized  by  the  point  becoming  free,  the  pressure  is  arrested  and 
the  instrument  is  directed  downward  and  backward,  its  back  sliding 
along  the  anterior  face  of  the  bone,  which  should  serve  as  a  guide  in  the 
operation. 

4.  "This  point  of  departure — that  is  to  say,  the  anterior  face  of  the 
bone — being  found,  the  instrument  is  pushed  along,  following  its  inferior 
border  and  proceeding  gradually,  as  the  instrument  penetrates,  pressing 
on  the  bone,  the  resistance  of  which  can  be  easily  recognized.     Soon, 
however,  the  operator  feels,  at  a  certain  depth,  that  the  bony  resistance 
ceases :  he  is  then  on  the  fifth  pair,  and  the  cries  of  the  animal  give 
evidence  that  the  nerve  is  pressed  upon. 

5.  "  It  is  at  this  moment  that  it  is  necessary  to  hold  firmly  the  instru- 
ment and  the  head  of  the  animal ;  then  the  cutting  edge  is  turned  so  as 
to  be  directed  downward  and  backward,  at  the  same  time  pressing  in 

this  direction  so  as  to  divide  the  nerve  on  the  extremity  of  the  petrous  portion,  behind 
the  ganglion  of  Gasser,  if  possible,  or  at  least  on  the  ganglion  itself. 

6.  "  The  instrument  is  then  drawn  back,  pressing  upon  the  bone  so  as  to  accomplish 
completely  the  section  of  the  trunk  of  the  fifth  pair ;  then  it  is  withdrawn  by  passing 
over  the  same  course  on  the  anterior  face  of  the  petrous  portion  so  as  not  to  lacerate  the 
cerebral  substance. 

"  The  accident  to  be  feared  in  the  operation  is  section  of  the  carotid  when  the  instru- 
ment has  penetrated  too  far,  or  lesion  of  the  cavernous  sinus  when  it  is  pressed  too  far 
forward." 

When  this  operation  has  been  performed  without  accident,  its  immediate  effects  are 
very  striking.  The  cornea  and  the  integument  and  mucous  membrane  upon  that  side  of 
the  head  are  instantaneously  deprived  of  sensibility  and  may  be  pricked,  lacerated,  or 
burned,  without  the  slightest  evidence  of  pain  on  the  part  of  the  animal.  Almost  always 


FIG.  216.  —  Instru- 
ment for  di- 
viding the  fifth 
nerve.  (Bernard.) 


640  NERVOUS   SYSTEM. 

the  small  root  of  the  fifth  is  divided  as  well  as  the  large  root,  and  the  muscles  of  masti- 
cation are  paralyzed  upon  one  side;  but,  with  this  exception,  there  is  no  paralysis  of 
motion,  sensation  alone  being  destroyed  upon  one  side. 


FIG.  217.— Operation  for  division  of  the  ji/th  nerve.    (Bernard.) 

The  calvarium  and  the  cerebrum  are  removed  in  order  to  show  the  roots  of  the  nerves  and  the  direction  of  the  instru- 
ment used  in  section  of  the  fifth.  A,  olfactory  nerves ;  B,  optic  nerves ;  0,  motores  oculorum  communes ;  D, 
pathetici;  E,  fifth  nerve ;  H.  blade  of  the  instrument  in  the  cranial  cavity ;  G,  G'  1. 1',  seventh  pair  of  nerves ; 
K,  section  of  the  spinal  cord. 

i 

Immediate  Effects  of  Division  of  the  Trifacial. — It  is  hardly  necessary  to  discuss  the 
functions  of  the  trifacial,  after  the  statement  of  the  effects  which  instantly  follow  upon 
its  division,  taken  in  connection  with  its  physiological  anatomy.  The  nerve  has  never 
been  exposed  in  the  cranial  cavity  in  living  animals ;  but  its  branches  upon  the  face  and 
the  lingual  branch  of  the  inferior  maxillary  division  have  been  operated  upon  and  found 


TRIFACIAL,  OR  TRIGEMINAL  NERVE.  641 

to  be  exquisitely  sensitive.  Longet  and  others  have  exposed  the  roots  in  animals  imme- 
diately after  death,  and  have  found  that  galvanization  of  the  large  root  carefully  insu- 
lated produces  no  muscular  contraction.  All  who  have  divided  this  root  in  living  animals 
must  have  recognized,  not  only  that  it  is  sensitive,  but  that  its  sensibility  is  far  more  acute 
than  that  of  any  other  nervous  trunk  in  the  body.  It  is  much  more  satisfactory  to  divide 
the  nerve  without  etherizing  the  animal,  as  the  evidence  of  pain  is  an  important  guide  in 
this  delicate  operation ;  but,  in  using  anesthetics,  we  have  never  been  able  to  bring  an 
animal  under  their  influence  so  completely  as  to  abolish  the  sensibility  of  the  root  itself. 
For  example,  in  cats  that  appear  to  be  thoroughly  etherized,  as  soon  as  the  instrument 
touches  the  nerve,  there  is  more  or  less  struggling.  The  large  root  of  the  fifth,  then,  is 
an  exclusively  sensory  nerve,  and  its  sensibility  is  more  acute  than  that  of  any  other  of 
the  cerebro-spinal  nerves. 

As  far  as  audition  and  olfaction  are  concerned,  there  are  no  special  effects  immedi- 
ately following  section  of  the  trifacial ;  but  there  are  interesting  phenomena  observed  in 
connection  with  the  eye  and  the  organs  of  taste. 

At  the  instant  of  division  of  the  fifth,  by  the  method  just  described,  the  eyeball  is  pro- 
truded and  the  pupil  becomes  strongly  contracted.  This  occurs  in  rabbits,  and  the  con- 
traction of  the  pupil  was  observed  in  the  first  operations  of  Magendie.  The  pupil,  how- 
ever, is  usually  restored  to  the  normal  condition  in  a  few  hours.  Longet  states  that  the 
pupil  is  dilated  by  division  of  the  fifth  in  dogs  and  cats.  After  division  of  the  nerve,  the 
lachrymal  secretion  becomes  very  much  less  in  quantity  ;  but  this  is  not  the  cause  of  the 
subsequent  inflammation,  for  the  eyes  are  not  inflamed,  as  was  shown  by  Magendie,  even 
after  extirpation  of  both  lachrymal  glands.  The  movements  of  the  eyeball  are  not 
affected  by  division  of  the  fifth. 

Another  of  the  immediate  effects  of  complete  division  of  the  fifth  nerve-is  loss  of  general 
sensibility  in  the  tongue.  Most  experiments  upon  the  influence  of  this  nerve  over  the  gen- 
eral sensibility  and  the  sense  of  taste  in  the  tongue  have  been  made  by  dividing  the  lin- 
gual branch  of  the  inferior  maxillary  division.  When  this  branch  is  irritated,  there  are 
evidences  of  intense  pain.  When  it  is  divided,  the  general  sensibility  and  the  sense  of 
taste  are  destroyed  in  the  anterior  third  or  half  of  the  tongue.  It  will  be  remembered, 
however,  that  the  chorda  tympani  joins  the  lingual  branch  of  the  fifth  as  it  passes  be- 
tween the  pterygoid  muscles,  and  that  section  of  this  branch  of  the  facial  abolishes  the 
sense  of  taste  in  the  anterior  third  or  half  of  the  tongue.  If  the  gustatory  properties  of 
the  lingual  branch  of  the  fifth  be  derived  from  the  chorda  tympani,  lesions  of  the  fifth 
not  involving  this  nerve  would  be  followed  by  loss  of  general  sensibility,  but  the  taste 
would  be  unaffected.  This  has  been  shown  to  be  the  fact,  by  cases  of  paralysis  of  general 
sensibility  of  the  tongue  without  loss  of  taste  in  the  human  subject,  which  will  be  dis- 
cussed more  fully  in  connection  with  gustation. 

Among  the  immediate  effects  of  section  of  the  fifth,  is  an  interference  with  the  reflex 
phenomena  of  deglutition.  In  some  recent  researches  upon  the  action  of  the  sensitive 
nerves  in  deglutition,  by  Waller  and  Prevost,  it  was  found  that,  after  section  of  the  fifth 
upon  both  sides,  it  was  impossible  to  excite  movements  of  deglutition  by  stimulating  the 
mucous  membrane  of  the  velum  palati.  After  sestion  of  the  superior  laryngeal  branches 
of  the  pneumogastrics,  no  movements  of  deglutition  followed  stimulation  of  the  mucous 
membrane  of  the  top  of  the  larynx.  In  these  experiments,  when  the  fifth  was  divided 
upon  one  side,  stimulation  of  the  velum  upon  the  corresponding  side  had  no  effect,  while 
movements  of  deglutition  were  produced  by  irritating  the  velum  upon  the  sound  side. 
These  experiments  show  that  the  fifth  nerve  is  important  in  the  reflex  phenomena  of 
deglutition,  as  a  sensory  nerve,  conveying  the  impression  from  the  velum  palati  to  the 
nerve-centres.  This  action  probably  takes  place  through  filaments  which  pass  from  the 
fifth  to  the  mucous  membrane  through  Meckel's  ganglion. 

Remote  Effects  of  Division  of  the  Trifacial. — After  the  ordinary  operation  of  divid- 
ing the  fifth  nerve  in  the  cranial  cavity,  the  immediate  loss  of  sensibility  of  the  integu- 
41 


642  NERVOUS   SYSTEM. 

ment  and  mucous  membranes  of  the  face  and  head  is  usually  supplemented  by  serious 
disturbances  in  the  nutrition  of  the  eye,  the  ear,  and  the  mucous  membranes  of  the  nose 
and  mouth.  At  a  period  varying  from  a  few  hours  to  one  or  two  days  after  the  opera- 
tion, the  eye  upon  the  affected  side  becomes  the  seat  of  purulent  inflammation,  the  cor- 
nea becomes  opaque  and  ulcerates,  the  humors  are  discharged,  and  the  organ  is  destroyed. 
Congestion  of  the  parts  is  usually  very  prominent  a  few  hours  after  division  of  the  nerve. 
At  the  same  time,  there  is  an  increased  discharge  from  the  mucous  membranes  of  the 
nose  and  mouth  upon  the  affected  side,  and  ulcers  appear  upon  the  tongue  and  lips.  It 
is  probable,  also,  that  disorders  in  the  nutrition  of  the  auditory  apparatus  follow  the  oper- 
ation, although  these  are  not  so  prominent.  Animals  affected  in  this  way  usually  die  in 
from  fifteen  to  twenty  days. 

One  of  the  most  interesting  facts,  particularly  in  view  of  the  information  derived  from 
later  observations,  in  connection  with  the  early  experiments  of  Magendie,  is,  that  he 
noted  that  "  the  alterations  in  nutrition  are  much  less  marked  "  when  the  division  is 
effected  behind  the  ganglion  of  Gasser,  than  when  it  is  done  in  the  ordinary  way  through 
the  ganglion.  It  is  difficult  enough  to  divide  the  nerve  completely  within  the  cranium, 
and  is  almost  impossible  to  make  the  operation  at  will  through  or  behind  the  ganglion  ; 
and  the  phenomena  of  inflammation  are  absent  only  in  exceptional  and  accidental  in- 
stances. Magendie  offers  no  satisfactory  explanation  of  the  differences  in  the  consecu- 
tive phenomena  coincident  with  the  locality  of  section  of  the  nerve.  The  facts,  how- 
ever, have  been  abundantly  verified.  In  the  numerous  experiments  that  we  have  made 
upon  the  fifth  pair,  we  have  generally  noted  the  consecutive  inflammatory  phenomena  in 
the  order  above  described ;  but,  in  exceptional  instances,  these  phenomena  have  been 
wanting.  The  following  experiment  illustrates  these  exceptional  operations : 

February  6,  1868,  the  fifth  pair  of  nerves  was  divided  upon  the  left  side  in  a  full- 
grown  rabbit  in  the  ordinary  way,  before  the  class  at  the  Bellevue  Hospital  Medical  Col- 
lege. There  followed  instant  and  complete  loss  of  sensibility  upon  the  left  side  of  the 
face.  Four  days  after,  the  animal  having  been  fed  ad  libitum  with  cabbage,  the  loss  of 
sensibility  was  still  complete.  There  was  very  little  redness  of  the  conjunctiva  of  the 
left  eye,  and  a  very  slight  streak  of  opacity,  so  slight  that  it  was  distinguished  with  diffi- 
culty. Twelve  days  after  the  operation,  the  sensibility  of  the  left  eye  was  distinct  but 
slight.  There  was  no  redness  of  the  conjunctiva,  and  the  opacity  of  the  cornea  had  dis- 
appeared. The  animal  was  in  good  condition,  and  the  line  of  contact  of  the  upper  with  the 
lower  incisors,  when  the  jaws  were  closed,  was  very  oblique.  The  animal  was  kept  alive 
by  careful  feeding  with  bread  and  milk  for  one  hundred  and  seven  days  after  the  opera- 
tion, there  never  being  any  inflammation  of  the  organs  of  special  sense.  It  died  at  that 
time  of  inanition,  having  become  very  much  emaciated.  The  animal  never  recovered 
power  over  the  muscles  of  mastication  of  the  left  side,  and  the  incisors  grew  to  a  great 
length,  interfering  very  much  with  mastication,  which  seemed  to  be  the  cause  of  death. 

Longet,  in  1842,  furnished  a  satisfactory  explanation  of  the  absence  of  inflammation 
in  certain  cases  of  division  of  the  fifth.  He  attributed  the  consecutive  inflammation  in 
most  experiments  to  lesion  of  the  ganglion  of  Gasser  and  of  the  sympathetic  connections, 
which  are  very  numerous  at  this  point.  These  sympathetic  filaments  are  avoided  when 
the  section  is  made  behind  the  ganglion. 

The  explanation  of  the  phenomena  of  disordered  nutrition  in  the  organs  of  special 
sense,  particularly  the  eye,  following  division  of  the  fifth,  is  not  afforded  by  the  section 
of  this  nerve  alone ;  for,  as  we  have  seen,  when  the  loss  of  sensibility  is  complete  after 
division  of  the  nerve  behind  the  Gasserian  ganglion,  these  results  may  not  follow.  Nor 
are  they  explained  by  deficiency  in  the  lachrymal  secretion,  for  they  are  not  observed 
when  both  lachrymal  glands  have  been  extirpated.  They  are  not  due  to  exposure  of  the 
eyeball,  for  they  do  not  follow  upon  section  of  the  facial.  Nor  are  they  due  simply  to  an 
enfeebled  general  condition,  for,  in  the  experiment  we  have  detailed,  the  animal  died  of 
inanition  after  section  of  the  nerve,  without  any  evidences  of  inflammation.  In  view  of 


TRIFACIAL,  OR  TRIGEMINAL  NERVE.  643 

the  fact  that  section  of  the  sympathetic  filaments  is  well  known  to  modify  the  nutrition 
of  parts  to  which  they  are  distributed,  producing  congestion,  increase  in  temperature,  and 
other  phenomena,  it  is  rational  to  infer  that  the  modifications  in  nutrition  which  follow 
section  of  the  fifth  after  it  receives  filaments  from  the  sympathetic  system,  not  occurring 
when  these  sympathetic  filaments  escape  division,  are  to  he  attributed  to  lesion  of  the 
sympathetic,  and  not  to  the  division  of  the  sensory  nerve  itself. 

A  farther  explanation  is  demanded  for  the  inflammatory  results  which  follow  division 
of  the  sympathetic  filaments  joining  the  fifth,  inasmuch  as  division  of  the  sympathetic 
alone  in  the  neck  produces  simply  exaggeration  of  the  nutritive  processes,  as  evidenced 
chiefly  by  local  increase  in  the  animal  temperature,  and  not  the  well-known  phenomena 
of  inflammation. 

It  has  been  remarked  by  Bernard,  that  the  "  alterations  in  nutrition  appear  more 
promptly  in  animals  that  are  enfeebled."  Section  of  the  small  root  of  the  fifth,  which 
is  unavoidable  when  the  nerve  is  divided  within  the  cranial  cavity,  generally  interferes  so 
much  with  mastication  as  to  influence  seriously  the  general  nutrition;  and  this  might 
modify  the  nutritive  processes  in  delicate  organs,  like  the  eye,  so  as  to  induce  those 
changes  which  are  called  inflammatory.  The  following  observation,  communicated  by 
Dr.  W.  H.  Mason,  Professor  of  Physiology  in  the  Medical  Department  of  the  University 
of  Buffalo,  is  very  striking  in  this  connection : 

The  fifth  pair  of  nerves  was  divided  in  a  cat  in  the  ordinary  way.  By  feeding  the 
animal  carefully  with  milk  and  finely-chopped  meat,  the  nutrition  was  maintained  at  a' 
high  standard,  and  no  inflammation  of  the  eye  occurred  for  about  four  weeks.  The  sup- 
ply of  food  was  then  diminished  to  about  the  quantity  it  would  be  able  to  take  without 
any  special  care,  when  the  eye  became  inflamed,  and  perforation  of  the  cornea  and 
destruction  of  the  organ  followed.  The  animal  was  kept  for  about  five  months;  at  the 
end  of  which  time,  sensation  upon  the  affected  side,  which  had  been  gradually  improving, 
was  completely  restored. 

The  explanation  we  have  to  offer  of  the  consecutive  inflammatory  effects  of  section 
of  the  fifth  with  its  communicating  sympathetic  filaments  is  the  following :  By  dividing 
the  sympathetic,  the  eye  and  the  mucous  membranes  of  the  nose,  mouth,  and- ear  are 
rendered  hyperasmic,  the  temperature  is  probably  raised,  and  the  processes  of  nutrition 
are  exaggerated.  This  condition  of  the  parts  would  seem  to  require  a  full  supply  of 
nutritive  material  from  the  blood,  in  order  to  maintain  the  condition  of  exaggerated 
nutrition  ;  but,  when  the  blood  is  impoverished^ — probably  as  the  result  of  deficiency  in 
the  introduction  of  nutritive  matter,  from  paralysis  of  the  muscles  of  mastication  upon 
one  side — the  nutritive  processes  in  these  delicate  parts  are  seriously  modified,  so  as  to 
constitute  inflammation.  The  observation  just  detailed  is  an  argument  in  favor  of  this 
view ;  for  here  the  inflammatory  action  seemed  to  he  arrested  when  the  action  of  the 
paralyzed  muscles  was  supplied  by  careful  feeding.  With  this  view,  the  disorders  of 
nutrition  observed  after  division  of  the  fifth  may  properly  be  referred  to  the  sympathetic 
system. 

Pathological  facts  in  confirmation  of  experiments  upon  the  fifth  pair  in  the  lower 
animals  are  not  wanting;  but  it  must  be  remembered  that,  in  cases  of  paralysis  of  the 
nerve  in  the  human  subject,  it  is  not  always  possible  to  locate  exactly  the  seat  of  the 
lesion  and  to  appreciate  fully  its  extent,  as  can  be  done  when  the  nerve  is  divided  by 
an  operation.  In  studying  these  cases,  it  sometimes  occurs  that  the  phenomena,  par- 
ticularly those  of  modified  nutrition,  are  more  or  less  contradictory. 

In  nearly  all  works  upon  physiology,  we  find  references  to  cases  of  paralysis  of 
the  fifth  in  the  human  subject.  In  a  recent  article  by  Dr.  H.  D.  Noyes,  Professor  of 
Ophthalmology  in  the  Bellevue  Hospital  Medical  College,  two-  interesting  cases  are  re- 
ported, which  we  had  an  opportunity  of  examining  during  the  progress  of  treatment.  . 
In  both  of  these  cases  there  was  inflammation  of  the  eye.  In  one  case,  the  tongue  was 
entirely  insensible  upon  one  side,  but  there  was  no  impairment  of  the  sense  of  taste.  An 


644  NERVOUS   SYSTEM. 

interesting  feature  in  one  of  the  cases  was  the  fact  that  an  operation  upon  the  eyelid  of 
the  affected  side  was  performed  without  the  slightest  evidence  of  pain  on  the  part  of  the 
patient. 

Oases  of  paralysis  of  the  fifth  in  the  human  subject  in  the  main  confirm  the 
results  of  experiments  upon  the  inferior  animals.  In  all  the  cases  in  which  the  fifth 
nerve  alone  was  involved  in  the  disease,  without  the  portio  dura  of  the  seventh,  there 
was  simply  loss  of  sensibility  upon  one  side,  the  movements  of  the  superficial  muscles 
of  the  face  being  unaffected.  When  the  small  root  was  involved,  the  muscles  of  masti- 
cation upon  one  side  were  paralyzed  ;  but,  in  certain  cases  in  which  this  root  escaped, 
there  was  no  muscular  paralysis.  The  senses  of  sight,  hearing,  and  smell,  except  as  they 
were  affected  by  consecutive  inflammation,  were  little  if  at  all  disturbed  in  uncompli- 
cated cases.  The  sense  of  taste  in  the  anterior  portion  of  the  tongue  was  perfect, 
except  in  those  cases  in  which  the  seventh,  the  chorda  tympani,  or  the  lingual  branch 
of  the  fifth  after  it  had  been  joined  by  the  chorda  tympani,  was  involved  in  the  disease. 
In  some  cases,  there  was  no  alteration  in  the  nutrition  of  the  organs  of  special  sense ; 
but  in  this  respect  the  facts  with  regard  to  the  seat  of  the  lesion  are  not  so  satisfactory 
as  in  experiments  upon  the  lower  animals,  it  being  difficult,  in  most  of  them,  to  limit 
the  exact  boundaries  of  the  lesion. 

Pneumogastric,  or  Par  Vagum  Nerve.     (Second  Division  of  the  Eighth 

Nerve.) 

Of  all  the  nerves  emerging  from  the  cranial  cavity,  the  pneumogastric,  the  second 
division  of  the  eighth  pair,  presents  the  greatest  number  of  anastomoses,  the  most 
remarkable  course,  and  the  most  varied  and  interesting  functions.  Arising  from  the 
medulla  oblongata  by  a  purely  sensory  root,  it  communicates  with  at  least  five  motor 
nerves  in  its  course,  and  it  is  distributed  largely  to  muscular  tissue,  both  of  the  voluntary 
and  the  involuntary  variety.  Finally,  there  is  no  nerve  that  has  been  the  subject  of 
such  extended  and  elaborate  anatomical  and  physiological  investigations,  and  none, 
concerning  the  properties  and  exact  functions  of  which  there  has  been  so  much  differ- 
ence of  opinion. 

We  shall  have  to  treat  of  the  influence  of  the  pneumogastric  upon  the  act  of  degluti- 
tion, the  heart  and  circulatory  system,  the  respiratory  system,  the  stomach,  the  intestines, 
and  various  glandular  organs.  An  indispensable  introduction  to  this  study  is  a  descrip- 
tion of  its  physiological  anatomy. 

Physiological  Anatomy  of.  the  Pneumogastric  Nerve. — The  apparent  origin  of  the 
pneumogastric  is  from  the  lateral  portion  of  the  medulla  oblongata,  just  behind  the 
olivary  body,  between  the  roots  of  the  glosso-pharyngeal  and  of  the  spinal  accessory. 
The  deep  origin  is  mainly  from  what  is  sometimes  called  the  nucleus  of  the  pneumogas- 
tric, in  the  inferior  portion  of  the  gray  substance  in  the  floor  of  the  fourth  ventricle. 
The  course  of  the  fibres,  traced  from  without  inward,  is  somewhat  intricate. 

The  deep  origins  of  the  pneumogastric  and  glosso-pharyngeal  nerves  appear  to  be,  in 
the  main,  identical.  Tracing  the  filaments  from  without  inward,  they  may  be  followed 
in  four  directions.  The  anterior  filaments  pass  from  without  inward,  first  very  superfi- 
cially and  directed  toward  the  olivary  body,  but,  turning  before  they  reach  the  olivary 
body,  they  pass  deeply  into  the  substance  of  the  restiform  body,  in  which  they  are  lost. 
The  posterior  filaments  are  superficial,  and  they  pass,  with  the  fibres  of  the  restiform 
body,  toward  the  cerebellum.  Of  the  intermediate  filaments,  the  anterior  pass  through 
the  restiform  body,  the  greatest  number  extending  to  the  median  line  in  the  floor  of  the 
fourth  ventricle.  A  few  fibres  are  lost  in  the  middle  fasciculi  of  the  medulla,  and  a  few 
pass  toward  the  brain.  The  posterior  intermediate  filaments  traverse  the  restiform 
body  to  the  floor  of  the  fourth  ventricle,  when  some  pass  to  the  median  line,  and  others 


PNEUMOGASTRIO,  OR   PAR   VAGUM  NERVE. 


645 


descend  in  the  substance  of  the  medulla.  It  is  difficult  to  follow  the  fibres  of  origin  of 
the  pneumogastrics  beyond  the  median  line  ;  but  recent  observations  leave  no  doubt  oi 
the  fact  that  many  of  these  fibres  decussate  in  the  floor  of  the  fourth  ventricle. 

There  are  two  ganglionic  enlargements  belonging  to  the  pneumogastric.  In  the 
jugular  foramen,  is  a  well-marked,  grayish,  ovoid  enlargement,  from  one-sixth  to  oner 
fourth  of  an  inch  in  length,  called  the  jugular  ganglion,  or  the  ganglion  of  the  root. 
This  is  united  by  two  or  three  filaments  with  the  ganglion  of  the  glosso-pharyngeal. 
It  is  a  true  ganglion,  containing  nerve-cells.  After  the  nerve  has  emerged  from  the  cra- 
nial cavity,  it  presents  on  its  trunk  another 
grayish  enlargement,  from  half  an  inch  to  an 
inch  in  length,  called  the  ganglion  of  the  trunk. 
This  is  of  rather  a  plexiform  structure,  the 
white  fibres  being  mixed  with  grayish  fibres 
and  nerve-cells.  The  exit  of  the  nerve  from 
the  cranial  cavity  is  by  the  jugular  foramen,  or 
posterior  foramen  lacerum,  in  company  with 
the  spinal  accessory,  the  glosso-pharyngeal,  and 
the  internal  jugular  vein. 

Anastomoses, — The  filaments  of  communi- 
cation which  the  pneumogastric  receives  from 
other  nerves  are  interesting  from  their  great 
importance  and  their  varied  sources.  The 
most  important  of  these  is  the  branch  from 
the  spinal  accessory.  There  are  occasional 
filaments  of  communication  which  pass  from 
the  spinal  accessory  to  the  ganglion  of  the  root, 
but  these  are  not  constant.  After  both  nerves 
have  emerged  from  the  cranial  cavity,  an  im- 
portant branch  of  considerable  size  passes 
from  the  spinal  accessory  to  the  pneumogas- 
tric, with  which  it  becomes  closely  united. 
Experiments  have  shown  that  these  filaments 
from  the  spinal  accessory  pass  in  great  part  to 
the  larynx  by  the  inferior  laryngeal  nerves. 

In  the  aquseductus  Fallopii,  the  facial  nerve 
gives  off  a  filament  of  communication  to  the 
pneumogastric  at  the  ganglion  of  the  root. 
This  filament,  joined  at  the  ganglion  by  sen- 
sory filaments  from  the  pneumogastric  and 
some  filaments  from  the  glosso-pharyngeal,  is 
called  the  auricular  branch  of  Arnold.  By 
some  anatomists  it  is  regarded  as  a  branch 
from  the  facial,  and  by  others  it  is  described  with  the  pneumogastric. 

Two  or  three  small  filaments  of  communication  pass  from  the  sublingual  to  the  gan- 
glion of  the  trunk  of  the  pneumogastric. 

At  the  ganglion  of  the  trunk,  the  pneumogastric  generally  receives  filaments  of  com- 
munication from  the  arcade  formed  by  the  anterior  branches  of  the  first  two  cervical 
nerves.  These,  however,  are  not  constant. 

The  pneumogastric  is  connected  with  the  sympathetic  system  by  numerous  delicate 
filaments  of  communication  received  from  the  superior  cervical  ganglion,  passing  in  part 
upward  toward  the  ganglion  of  the  root  of  the  pneumogastric,  and  in  part  transversely 
and  downward.  These  filaments  are  frequently  short,  and  they  bind,  as  it  were,  the 
sympathetic  ganglion  to  the  trunk  of  the  nerve.  The  main  trunk  of  the  pneumogastric 


FIG  218.— Anastomoses  of  the  pneumogastric, 
(Hirschfeld.) 

1,  facial  nerve :  2,  glosso-pharyngeal  nerve  ;  2',  anas- 
tomoses of  the  glosso-pharyngeal  with  the  facial ; 
8,  8,  pneumogastric^  with  its  two  ganglia;  4,  4, 
spinal  accessory ;  5.  sublingual  nerve ;  C,  superior 
cervical  ganglion  of  the  sympathetic;  7,  anasto- 
mosic  arcade  of  the  first  two  cervical  nerves ;  8, 
carotid  branch  of  the  superior  cervical  ganglion 
of  the  sympathetic;  9,  nerve  of  Jacobson;  10, 
branches  of  this  nerve  to  the  sympathetic;  11, 
branch  to  the  Eustachian  tube  ;  12,  branch  to  the 
fenestra  ovaiis;  13,  branch  to  the  fenestra  rotunda  ; 
14,  external  deep  petrous  nerve ;  15,  internal  deep 
petrous  nerve ;  1(5,  otic  ganglion ;  17,  auricular 
branch  of  tlie  pneumogastric;  IS.  anastomosis 
of  tJie  pneumogastric  with  the  spinal  accessory  ; 
19.  anastomosis  of  the  pneumogastric  with  the 
sublingual ;  20,  anastomosis  of  the  spinal  acces- 
sory with  the  second  pair  of  cervical  nerves  ;  21, 
pharyngeal  plexus  ;  22,  superior  Jaryngeal  nerve. 


646 


NERVOUS   SYSTEM. 


and  its  branches  receive  a  few  delicate  filaments  of  communication  from  the  middle  and 
inferior  cervical  and  the  upper  dorsal  ganglia  of  the  sympathetic. 

The  pneumogastric  frequently  sends  a  very  delicate  filament  to  the  glosso-pharyngeal 
nerve,  at  or  -near  the  ganglion  of  Andersch.  Branches  from  the  pneumogastric  join 
branches  from  the  glosso-pharyngeal,  the  spinal  accessory,  and  the  sympathetic,  to  form 
the  pharyngeal  plexus. 

Distribution. — In  describing  the  very  extensive  distribution  of  the  pneumogastrics, 
while  the  nerves  upon  the  two  sides  do  not  present  any  important  differences  in  the 
destination  of  their  filaments  as  far  down  as  the  diaphragm,  it  will  be  seen  that  the 
abdominal  branches  are  not  the  same.  The  most  important  branches  are  the  following  : 


1.  Auricular. 

2.  Pharyngeal. 

3.  Superior  laryngeal. 

4.  Inferior,  or  recurrent  laryngeal. 


5.  Cardiac,  cervical  and  thoracic. 

6.  Pulmonary,  anterior  and  posterior. 

7.  (Esophageal. 

8.  Abdominal. 


s 

superior  taryn^br^^  ^SSSX 
branch  :  10,  cerrical  car%ac  brantl™n 
branch  of  the  fifth;  15  lowe 
spina,  nen,s;  «,  phre»,c  S 


FIG.  219.—  Distribution  of  the  pneumogastric.    (Hirschfeld.) 

S!1  trunk;  3.  anastomo*is  with  the  spinal  accessory  ;  4,  anas- 
branch  (the  auricular  branch  is  not  shown  in  the  figure)  ;  6, 
'?/  ^        '    9'  9'  ^ferior  laryngeal 

;  14,  lingual 


PNEUMOGASTRIC,  OR  PAR  VAGUM  NERVE.         647 

The  auricular  nerves  are  sometimes  described  in  connection  with  the  facial.  They 
are  given  off  from  the  ganglion  of  the  trunk  of  the  pneumogastric,  and  are  composed  of 
filaments  of  communication  from  the  facial  and  from  the  glosso-pharyngeal,  as  well  as 
of  filaments  from  the  pneumogastric  itself.  The  nerves  thus  constituted  are  distributed  to 
the  integument  of  the  upper  portion  of  the  external  auditory  meatus,  and  a  small  filament 
is  sent  to  the  membrana  tympani. 

The  pharyngeal  nerves  are  very  remarkable  in  their  course.  They  are  given  off  from 
the  superior  portion  of  the  ganglion  of  the  trunk  and  contain  a  large  number  of  the  fila- 
ments of  communication  which  the  pneumogastric  receives  from  the  spinal  accessory. 
In  their  course  by  the  sides  of  the  superior  constrictor  muscles  of  the  pharynx,  these 
nerves  anastomose  with  numerous  filaments  from  the  glosso-pharyngeal  and  the  superior 
cervical  ganglion  of  the  sympathetic,  to  form  what  is  known  as  the  pharyngeal  plexus. 
The  ultimate  filaments  of  distribution  pass  to  the  muscles  and  the  mucous  membrane  of 
the  pharynx.  Physiological  experiments  have  shown  that  the  motor  influence  transmitted 
to  the  pharyngeal  muscles  through  the  pharyngeal  branches  of  the  pneumogastric  is 
derived  from  the  spinal  accessory. 

The  superior  laryngeal  nerves  are  given  off  from  the  lower  part  of  the  ganglion  of  the 
trunk.  Their  filaments  come  from  the  side  opposite  to  the  point  of  junction  of  the  pneu- 
mogastric with  the  communicating  branch  from  the  spinal  accessory,  so  that  probably 
the  superior  laryngeals  contain  few  if  any  motor  fibres  from  this  nerve.  The  superior 
laryngeal  gives  off  the  external  laryngeal,  a  long,  delicate  branch,  which  sends  a  few  fila- 
ments to  the  inferior  constrictor  of  the  pharynx  and  is  distributed  to  the  crico-thyroid 
muscle  and  the  mucous  membrane  of  the  ventricle  of  the  larynx.  The  external  laryngeal 
anastomoses  with  the  inferior  laryngeal  and  with  the  sympathetic.  The  internal  branch 
is  distributed  to  the  mucous  membrane  of  the  epiglottis,  the  base  of  the  tongue,  the  aryt- 
eno-epiglottidean  fold,  and  the  mucous  membrane  of  the  larynx  as  far  down  as  the  true 
vocal  cords.  A  branch  from  this  nerve,  in  its  course  to  the  larynx,  penetrates  the  aryte- 
noid  muscle,  to  which  it  sends  a  few  filaments,  but  these  are  all  sensory.  This  branch 
also  supplies  the  crico-thyroid  muscle.  It  anastomoses  with  the  inferior  laryngeal  nerve. 
An  important  branch,  described  by  Cyon  and  Ludwig,  in  the  rabbit,  under  the  name  of 
the  depressor-nerve,  arises  by  two  roots,  one  from  the  superior  laryngeal  and  the  other 
from  the  trunk  of  the  pneumogastric,  passes  down  the  neck  by  the  side  of  the  sympa- 
thetic, and,  in  the  chest,  joins  filaments  from  the  thoracic  sympathetic,  to  penetrate  the 
heart  between  the  aorta  and  the  pulmonary  artery.  This  nerve  will  be  referred  to  more 
particularly  in  connection  with  the  influence  of  the  pneumogastrics  upon  the  circulation. 

It  is  important,  from  a  physiological  point  of  view,  to  note  that  the  superior  laryngeal 
nerve  is  the  nerve  of  sensibility  of  the  upper  part  of  the  larynx,  as  well  as  of  the  supra- 
laryngeal  mucous  membranes,  and  that  it  animates  a  single  muscle  of  the  larynx  (the 
crico-thyroid)  and  the  inferior  constrictor  of  the  pharynx. 

The  inferior,  or  recurrent  laryngeal  nerves  present  some  slight  differences  in  their 
anatomy  upon  the  two  sides.  Upon  the  left  side,  the  nerve  is  the  larger  and  is  given  off 
at  the  arch  of  the  aorta.  Passing  beneath  this  vessel,  it  ascends  in  the  groove  between 
the  trachea  and  the  oesophagus.  In  its  upward  course,  it  gives  off  certain  filaments 
which  join  the  cardiac  branches,  filaments  to  the  muscular  tissue  and  mucous  membrane 
of  the  upper  part  of  the  oesophagus,  filaments  to  the  mucous  membrane  and  the  inter- 
cartilaginous  muscular  tissue  of  the  trachea,  one  or  two  filaments  to  the  inferior  con- 
strictor of  the  pharynx,  and  a  branch  which  joins  the  superior  laryngeal.  Its  terminal 
branches  penetrate  the  larynx,  behind  the  posterior  articulation  of  the  thyroid  with  the 
cricoid  cartilage,  and  are  distributed  to  all  of  the  intrinsic  muscles  of  the  larynx,  except 
the  crico-thyroids,  which  are  supplied  by  the  superior  laryngeal.  Upon  the  right  side, 
the  nerve  winds  from  before  backward  around  the  subclavian  artery,  and  it  has  essen- 
tially the  same  course  and  distribution  as  upon  the  left  side,  except  that  it  is  smaller  and 
its  filaments  of  distribution  are  not  so  numerous. 


648  NERVOUS   SYSTEM. 

The  important  physiological  point  connected  with  the  anatomy  of  the  recurrent  laryn- 
geals  is  that  they  animate  all  of  the  intrinsic  muscles  of  the  larynx,  except  the  crico-thy- 
roid.  Experiments  have  shown  that  these  nerves  contain  numerous  filaments  from  the 
spinal  accessory. 

The  cervical  cardiac  branches,  two  or  three  in  number,  arise  from  the  pneumogastrics 
at  different  points  in  the  cervical  portion  and  pass  to  the  cardiac  plexus,  which  is  formed 
in  great  part  of  filaments  from  the  sympathetic.  The  thoracic  cardiac  branches  are 
given  off  from  the  pneumogastrics  below  the  origin  of  the  inferior  laryngeals  and  join 
the  cardiac  plexus. 

The  anterior  pulmonary  branches  are  few  and  delicate  as  compared  with  the  posterior 
branches.  They  are  given  oft'  below  the  origin  of  the  thoracic  cardiac  branches,  send  a 
few  filaments  to  the  trachea,  and  then  form  a  plexus  which  surrounds  the  bronchial  tubes 
and  follows  the  bronchial  tree  to  its  terminations  in  the  air-cells.  The  posterior  pulmonary 
branches  are  larger  and  more  numerous  than  the  anterior.  They  communicate  freely 
with  sympathetic  filaments  from  the  upper  three  or  four  thoracic  ganglia  and  then  form 
the  great  posterior  pulmonary  plexus.  From  this  plexus,  a  few  filaments  go  to  the  infe- 
rior and  posterior  portion  of  the  trachea,  a  few  pass  to  the  muscular  tissue  and  mucous 
membrane  of  the  middle  portion  of  the  oesophagus,  and  a  few  are  sent  to  the  posterior 
and  superior  portion  of  the  pericardium.  The  plexus  then  surrounds  the  bronchial  tree 
and  passes  with  its  ramifications  to  the  pulmonary  tissue,  like  the  corresponding  fila- 
ments of  the  anterior  branches.  The  pulmonary  branches  are  distributed  to  the  mucous 
membrane,  and  not  to  the  walls  of  the  blood-vessels. 

The  oesophageal  branches  take  their  origin  from  the  pneumogastrics  above  and  below 
the  pulmonary  branches.  These  branches  from  the  two  sides  join  to  form  the  cesopha- 
geal  plexus,  their  filaments  of  distribution  going  to  the  muscular  tissue  and  the  mucous 
membrane  of  the  lower  third  of  the  oesophagus. 

The  abdominal  branches  are  quite  different  in  their  distribution  upon  the  two  sides. 

Upon  the  left  side,  the  nerve,  which  is  situated  anterior  to  the  cardiac  opening  of  the 
stomach,  immediately  after  its  passage  by  the  side  of  the  oesophagus  into  the  abdomen, 
divides  into  numerous  branches,  which  are  distributed  to  the  muscular  walls  and  the 
mucous  membrane  of  the  stomach.  As  the  branches  pass  from  the  lesser  curvature,  they 
take  a  downward  direction  and  go  to  the  liver,  and,  with  another  branch  running  between 
the  folds  of  the  gastro-hepatic  omentum,  they  follow  the  course  of  the  portal  vein  in  the- 
hepatic  substance.  The  branches  of  this  nerve  anastomose  with  the  nerve  of  the  right 
side  and  with  the  sympathetic. 

The  right  pneumogastric,  situated  posteriorly,  at  the  cesophageal  opening  of  the  dia- 
phragm, sends  a  few  filaments  to  the  muscular  coat  and  the  mucous  membrane  of  the 
stomach,  passes  backward,  and  is  distributed  to  the  liver,  spleen,  kidneys,  suprarenal 
capsules,  and  finally  to  the  whole  of  the  small  intestine.  The  branches  to  the  small  intes- 
tine are  very  important.  These  were  accurately  described  in  1860,  by  Kollmann,  in  an 
elaborate  and  beautifully-illustrated  prize-essay.  In  the  plate  showing  the  distribution 
of  this  nerve,  it  is  seen  that  the  branches  to  the  intestine  are  very  numerous.  Accord- 
ing to  these  researches,  the  branches  described  belong  to  the  pneumogastric  itself  and 
are  not  derived  from  the  sympathetic.  When  we  come  to  treat  of  the  action  of  the  pneu- 
mogastric upon  the  small  intestine,  it  will  be  seen  that  the  anatomical  researches  by  Koll- 
mann have  been  fully  confirmed  by  physiological  experiments.  Before  the  nerves  pass 
to  the  intestines,  there  is  a  free  anastomosis  and  interchange  of  filaments  between  the 
right  and  the  left  pneumogastric. 

Properties  and  Functions  of  the  Pneumogastric  Nerves. 
There  is  no^nerve  in  the  body  that  has  been  the  subject  of  so  many  experiments,  and 
concerning  which  so  much  has  been  written,  as  the  pneumogastric.     Its  accessible  posi- 
tion in  many  parts  of  its  course,  its  extensive  connections  with  the  digestive,  the  respira- 


PNEUMOGASTRIC,   OR  PAR  VAGUM  NERVE.  649 

tory,  and  the  circulatory  system,  and  the  evident  importance  of  its  relations,  have  ren- 
dered the  literature  connected  with  its  physiology  somewhat  redundant.  We  do  not 
propose  to  discuss  in  full  all  of  the  views  entertained  from  time  to  time  with  regard  to 
its  functions,  but  shall  state  merely  what  seem  to  be  well-ascertained  facts,  and  the  most 
reasonable  inferences,  where  the  facts  are  difficult  of  demonstration.  In  treating  of  the 
functions  of  this  nerve,  we  shall  be  compelled  to  make  constant  reference  to  its  anatomy, 
and  for  that  reason  we  have  described  pretty  fully  in  detail  most  of  the  important  points 
in  its  connections  and  distribution. 

Although  the  extensive  distribution  of  the  pneumogastrics  and  their  importance  will 
necessitate  a  long  discussion  of  their  physiology,  we  shall  endeavor  to  separate  the  points 
to  be  considered  distinctly,  and  to  simplify  the  subject  as  much  as  possible. 

We  shall  first  treat  of  the  general  properties  of  those  filaments  derived  from  the  true 
roots  of  the  nerves,  and,  following  them  in  their  course,  shall  note  the  properties  derived 
from  their  connections  with  other  nerves. 

We  shall  then  treat  of  the  properties  of  the  different  branches  of  the  nerves,  under 
distinct  heads,  taking  up  these  branches  as  they  are  given  off,  from  above  downward.  In 
this,  we  shall  consider  first  the  properties  and  functions  of  the  auricular  branches ;  next, 
the  pharyngeal  branches,  with  their  influence  upon  the  action  of  the  pharynx  in  deglu- 
tition; next,  the  superior  and  inferior  laryngeal  branches,  with  their  relations  to  the 
physiology  of  the  larynx ;  next,  the  cardiac  branches,  with  their  influence  on  the  move- 
ments of  the  heart  and  the  circulation ;  next,  the  pulmonary  branches,  with  the  function 
of  the  nerves  in  connection  with  respiration ;  next,  the  oesophageal  branches,  in  connec- 
tion with  the  influence  of  the  nerves  upon  the  action  of  the  O3sophagus,  in  deglutition ; 
and  finally,  the  abdominal  branches,  with  the  influence  of  the  nerves  upon  digestion  and 
the  functions  of  the  abdominal  viscera.  By  dividing  up,  in  this  way,  the  action  of  the 
pneumogastrics,  it  is  hoped  that  their  physiology  may  be  relieved  of  much  of  the  com- 
plexity in  which  it  is  apparently  involved. 

General  Properties  of  the  Roots  of  Origin  of  tJie  Pneumogastrics. — All  who  have  oper- 
ated upon  the  pneumogastrics  in  the  cervical  region  in  living  animals  have  noted  their 
exceedingly  dull  sensibility  as  compared  with  the  ordinary  sensory  nerves.  Bernard, 
indeed,  states  that  in  this  region  they  are  generally  insensible ;  but  we  have  usually  found, 
in  dogs  at  least,  that  their  division  is  attended  with  slight  evidences  of  pain.  Without 
citing  in  detail  all  the  experiments  upon  this  point,  it  is  sufficient  to  state  that  some 
physiologists,  on  galvanizing  or  otherwise  irritating  the  roots  of  the  nerves  in  animals  just 
killed,  have  noted  movements  of  the  muscles  of  deglutition,  of  the  oesophagus,  and  of  the 
muscular  coats  of  the  stomach.  These  experiments  have  led  to  the  opinion  that  the 
proper  roots  of  the  nerves  are  motor  as  well  as  sensory.  It  becomes,  therefore,  a  difficult 
as  well  as  an  important  point  'to  determine  whether  or  not  the  roots  be  of  themselves 
exclusively  sensory  or  mixed.  In  discussing  the  properties  of  the  roots,  we  shall  rely 
almost  entirely  upon  direct  experiments ;  although  the  arguments  drawn  from  their 
anatomical  characters,  in  the  presence  of  ganglia  and  the  deep  origin  of  their  fibres, 
point  strongly  to  their  sensory  character.  It  is  impossible  to  stimulate  the  roots,  before 
they  have  received  motor  filaments  from  other  nerves,  in  living  animals,  and  the  experi- 
ments are  therefore  made  upon  animals  just  killed,  before  the  nervous  irritability  has  dis- 
appeared. If  the  true  roots  of  the  nerves  be  exclusively  sensory,  their  galvanization  in 
animals  just  killed  should  produce,  by  direct  action,  no  muscular  contraction.  If  the 
roots  contain  any  motor  filaments,  contraction  of  muscles  should  follow  their  stimula- 
tion. The  proper  physiological  conditions  in  such  experiments  are  the  following : 

1.  It  is  necessary  to  stimulate  the  roots  so  that  the  filaments  from  the  spinal  accessory 
and  from  other  motor  nerves  are  not  involved. 

2.  It  is  important  to  ascertain,  provided  movements  follow  such  irritation,  whether  or 
not  they  be  due  to  reflex  action. 


650  NERVOUS   SYSTEM. 

The  first  of  these  conditions  is  easily  fulfilled.  All  that  is  necessary  is  to  stimulate 
the  roots  before  the  nerves  have  received  any  anastomosing  filaments.  To  avoid  contrac- 
tions of  muscles  due  to  reflex  action,  it  is  hest  to  divide  the  roots  and  to  stimulate  their 
distal  portion.  If  it  he  true  that  stimulation  of  the  distal  extremities  of  the  roots— the 
irritation  so  applied  as  not  to  involve  communicating  filaments  from  motor  nerves,  and 
not  to  be  conveyed  to  the  centres,  producing  reflex  movements  through  other  nerves — 
does  not  produce  any  movements,  it  is  fair  to  assume  that  the  true  filaments  of  origin  are 
exclusively  sensory.  The  facts  upon  this  point  demand  careful  and  critical  study ;  and  it 
will  be  proper  to  discard  the  earlier  experiments,  made  before  the  mechanism  of  reflex 
action  had  been  satisfactorily  established. 

If  the  experiments  of  Longet  be  accepted  without  reserve,  they  prove — as  conclusively 
as  is  possible  without  exposing  the  roots  in  living  animals,  an  operation  which  is  imprac- 
ticable—that the  true  filaments  of  origin  of  the  pneumogastrics  are*  exclusively  sensory, 
or,  at  least,  that  the  nerve  contains  no  motor  filaments  except  those  derived  from  other 
nerves.  The  following  quotation  gives  the  essential  points  in  these  experiments : 

"  In  dogs  of  large  size  and  in  horses,  I  have  isolated  in  the  cranium,  with  the  most 
minute  care,  the  pneumogastric  of  the  medulla  oblongata  and  the  superior  filaments  of 
the  spinal  accessory  (internal  branch),  in  order  to  avoid  all  reflex  movement  and  any 
derivative  current  upon  the  last-named  nerve ;  I  then  immediately  caused  the  current  to 
act  exclusively  upon  the  filaments  of  origin  of  the  pneumogastric,  without  having  ever 
seen  the'slightest  contraction  supervene,  either  in  the  muscles  of  the  larynx  or  pharynx, 
or  in  the  muscular  tunic  of  the  oesophagus,  or  elsewhere. 

"But  also  I  have  never  failed  to  demonstrate  to  all  those  who  witnessed  my  experi- 
ments, how  it  is  easy  to  obtain  opposite  results  in  neglecting  only  one  precaution :  it 
suffices,  for  example,  to  slightly  moisten  the  slip  of  glass  or  oiled  silk  which  serves  to 
isolate  the  two  nerves,  in  order  that  the  current  should  act  immediately  upon  the  superior 
filaments  of  the  spinal  accessory,  from  which  we  have  marked  contractions  in  the  organs 
just  mentioned." 

These  experiments  seem  entirely  conclusive.  In  treating  of  the  reflex  phenomena  of 
deglutition  and  their  relations  to  the  superior  branches  of  the  pneumogastric,  the  pharyn- 
geal,  and  the  superior  laryngeal,  it  will  be  seen  that  irritation,  either  of  these  nerves  or 
of  the  mucous  membranes  to  which  they  are  distributed,  will  produce  contractions  in  the 
muscles.  All  who  are  practically  familiar  with  the  application  of  electricity  to  the  nerves 
know  how  difficult  it  is  to  insulate  the  nervous  trunks  so  as  to  avoid  the  influence  of 
"derived"  currents.  In  carefully  studying  the  experiments  of  Longet,  it  seems  that  all 
the  physiological  conditions  were  fulfilled ;  and  that,  when  the  nerve  is  divided  at  the 
root  and  the  stimulation  is  applied  to  the  peripheral  end,  so  as  to  cut  off  all  reflex  action 
from  the  nervous  centres,  and  when  sufficient  care  is  exercised  to  prevent  the  propagation 
of  the  current  to  the  motor  connections  of  the  pneumogastric,  the  nerve,  from  its  origin 
at  the  medulla  oblongata  to  the  ganglion  of  the  root,  contains  no  motor  filaments  and  is 
exclusively  sensory.  We  shall  therefore  adopt,  without  reserve,  the  conclusions  of  Longet, 
that  the  true  filaments  of  origin  of  the  pneumogastrics  are  exclusively  sensory,  or,  at  least, 
that  they  have  no  motor  properties. 

Properties  and  Functions  of  the  Auricular  Nerves. — There  is  very  little  to  be  said 
with  regard  to  the  auricular  nerves,  after  the  description  we  have  given  of  their  anatomy. 
They  are  sometimes  described  with  the  facial  and  sometimes  with  the  pneumogastric. 
1  hey  contain  filaments  from  the  facial,  the  pneumogastric,  and  the  glosso-pharyngeal. 
The  sensory  filaments  of  these  nerves  give  sensibility  to  the  upper  part  of  the  external 
auditory  meatus  and  the  membrana  tympani. 

Properties  and  Functions  of  the  Pharyngeal  Nerves.— The  pharyngeal  branches  of 
the  pneumogastric  are  mixed  nerves,  their  motor  filaments  being  derived  from  the  spinal 


PNEUMOGASTRIC,   OR   PAR   VAGUM  NERVE.  651 

accessory.  Their  direct  action  upon  the  muscles  of  deglutition  belongs  to  the  physiologi- 
cal history  of  the  last-named  nerve.  We  have  already  stated,  in  treating  of  the  spinal 
accessory,  that  the  filaments  of  communication  that  go  to  the  pharyngeal  branches  of  the 
pneumogastric  are  distributed  to  the  pharyngeal  muscles. 

It  is  impossible  to  divide  all  of  the  pharyngeal  filaments  in  living  animals  and  observe 
directly  how  far  the  general  sensibility  of  the  pharynx  and  the  reflex  phenomena  of 
deglutition  are  influenced  by  this  section.  As  far  as  we  can  judge  from  the  distribution 
of  the  filaments  to  the  mucous  membrane,  it  would  seem  that  they  combine  with  the 
pharyngeal  filaments  of  the  fifth,  and  possibly  with  sensory  filaments  from  the  glosso- 
pharyngeal,  in  giving  general  sensibility  to  these  parts. 

In  some  recent  experiments  by  Waller  and  Prevost,  upon  the  reflex  phenomena  of 
deglutition,  it  is  shown  that  the  action  of  the  pharyngeal  muscles  cannot  be  excited  by 
stimulation  of  the  mucous  membrane  of  the  supra-laryngeal  region  and  the  pharynx,  after 
section  of  the  fifth  and  of  the  superior  laryrigeal  branch  of  the  pneumogastric.  This 
would  seem  to  show  that  the  pharyngeal  branches  of  the  pneumogastrics  are  of  little  or 
no  importance  in  these  reflex  phenomena. 

Properties  and  Functions  of  the  Superior  Laryngeal  Nerves. — The  distribution  of 
these  nerves  points  to  a  double  function ;  viz.,  an  action  upon  the  crico-thyroid  muscles, 
and  the  important  office  of  supplying  general  sensibility  to  the  upper  part  of  the  larynx 
and  a  portion  of  the  surrounding  mucous  membrane.  The  stimulation  of  these  nerves 
produces  intense  pain  and  contraction  of  the  crico-thyroids ;  but  it  has  been  shown 
by  experiment  that  the  arytenoid  muscles,  through  which  the  nerves  pass,  receive  no 
motor  filaments.  The  action  of  the  nerves  upon  the  muscles  is  very  simple,  and  resolves 
itself  into  the  function  of  the  crico-thyroids,  which  has  been  treated  of  fully  under  the 
head  of  phonation.  When  these  muscles  are  paralyzed,  the  voice  becomes  hoarse.  The 
filaments  to  the  inferior  muscles  of  the  pharynx  are  few  and  comparatively  unimportant. 
It  is  important  in  this  connection  to  note  that  the  superior  laryngeals  do  not  receive  their 
motor  filaments  from  the  spinal  accessory. 

The  sensory  filaments  of  the  superior  laryngeals  have  important  functions  connected 
with  the  protection  of  the  air-passages  from  the  entrance  of  foreign  matters,  particularly 
in  deglutition,  and  are  farther  concerned,  as  we  shall  see,  in  the  reflex  action  of  the  con- 
strictors of  the  pharynx.  In  treating  of  deglutition,  we  have  fully  discussed  the  impor- 
tance of  the  exquisite  sensibility  of  the  top  of  the  larynx  in  the  protection  of  the  air- 
passages.  When  both  superior  laryngeals  have  been  divided  in  living  animals,  liquids 
often  pass  into  the  larynx  in  small  quantity,  owing  to  the  absence  of  the  reflex  closure 
of  the  glottis  when  foreign  matters  are  brought  in  contact  with  its  superior  surface,  and 
the  occasional  occurrence  of  inspiration  during  deglutition. 

Aside  from  the  protection  of  the  air-passages,  the  superior  laryngeal  is  one  of  the 
sensory  nerves  through  which  the  reflex  acts  in  deglutition  operate.  There  are  certain 
parts  which  depend  for  their  sensibility  entirely  upon  this  nerve  ;  viz.,  the  mucous  mem- 
brane of  the  epiglottis,  the  aryteno-epiglottidean  fold,  and  the  larynx  as  far  down  as 
the  true  vocal  cords.  When  an  impression  is  made  upon  these  parts,  as  when  they 
are  touched  with  a  piece  of  meat,  regular  and  natural  movements  of  deglutition  ensue. 

The  experiments  made  by  galvanizing  the  trunks  of  the  superior  laryngeal  nerves  are 
extremely  interesting.  If  the  nerves  be  divided  and  galvanization  be  applied  to  their 
central  ends,  movements  of  deglutition  are  observed,  and  there  is  also  arrest  of  the 
action  of  the  diaphragm.  From  these  experiments,  it  would  seem  that  the  impression 
which  gives  rise  to  the  movements  of  deglutition  aids  in  protecting  the  air-passages 
from  the  entrance  of  foreign  matters,  by  temporarily  arresting  the  inspiratory  act. 

An  important  point  for  our  consideration,  in  this  connection,  is  the  action  of  the 
superior  laryngeal  nerves  in  the  ordinary  phenomena  of  deglutition  ;  and,  in  experiments 
with  galvanism,  a  feeble  current  simulates  most  nearly  the  natural  processes.  In  such 


NERVOUS   SYSTEM. 

experiments  the  results  have  been  quite  satisfactory.  The  experiments  in  which  a  pow- 
erful current  of  galvanism  has  been  applied  to  the  nerves  also  show  an  arrest  of  respi- 
ration ;  but  it  is  argued  that  there  is  nothing  special  in  the  action  of  the  superior  laryn- 
geals  under  these  conditions,  inasmuch  as  other  sensitive  nerves  have  been  found  to  act 
in  the  same  way.  This  is  undoubtedly  true ;  but  it  is  well  known  that,  in  living  animals, 
strong  impressions  made  upon  any  of  the  acutely  sensitive  nerves  arrest  respiration,  and 
that  this  is  one  of  the  phenomena  commonly  observed  in  animals  struggling  under  painful 
operations.  In  view  of  these  facts,  it  seems  unnecessary  to  discuss  more  fully  the  numer- 
ous experiments  with  regard  to  the  effects  upon  respiration  of  stimulation  of  the  superior 
laryngeals ;  and  we  can  assume  that  it  has  been  demonstrated  that  an  impression  made 
upon  the  terminal  filaments  of  these  nerves,  such  as  occurs  in  the  ordinary  process  of 
deglutition,  excites,  by  reflex  action,  contraction  of  the  constrictors  of  the  pharynx,  and, 
at  the  same  time,  momentarily  suspends  the  movements  of  the  diaphragm. 

Important  experiments  have  been  made  within  the  past  few  years,  upon  the  action  of 
the  pneumogastrics  on  the  circulation,  in  which  it  is  claimed  that  nervous  filaments,  aris- 
ing, in  the  rabbit,  in  part  from  the  trunk  of  the  pneumogastric  and  in  part  from  the 
superior  laryngeal  branch,  act  as  reflex  depressors  of  the  vascular  tension.  These  experi- 
ments will  be  fully  discussed  in  connection  with  the  cardiac  branches. 

Properties  and  Functions  of  the  Inferior,  or  Recurrent  Laryngeal  Nerves. — The 
anatomical  distribution  of  these  nerves  shows  that  their  most  important  function  is  con- 
nected with  the  muscles  of  the  larynx.  The  few  filaments  which  are  given  off  in  the 
neck  to  join  the  cardiac  branches  are  probably  not  very  important.  It  is  proper  to  note, 
however,  that  the  inferior  laryngeal  nerves  supply  the  muscular  tissue  and  mucous  mem- 
brane of  the  upper  part  of  the  oesophagus  and  the  trachea,  and  one  or  two  branches  are 
sent  to  the  inferior  constrictor  of  the  pharynx.  The  function  of  these  filaments  is  suffi- 
ciently evident. 

The  inferior  laryngeals  contain  chiefly  motor  filaments,  judging  from  their  distribu- 
tion as  well  as  from  the  effects  of  direct  irritation.  AH  who  have  experimented  upon 
these  nerves  have  noted  little  or  no  evidence  of  pain  when  they  are  stimulated  or  divided. 

One  of  the  most  important  functions  of  the  recurrents  is  connected  with  the  produc- 
tion of  vocal  sounds.  We  have  already  fully  treated  of  the  mechanism  of  the  voice  and 
the  action  of  the  intrinsic  muscles  of  the  larynx  ;  and,  in  our  account  of  the  physiology 
of  the  internal,  or  communicating  branch  from  the  spinal  accessory  to  the  pneumogas- 
tric, it  has  been  shown  that  this  is  the  true  nerve  of  phonation.  In  the  older  works 
upon  physiology,  before  the  functions  of  the  spinal  accessory  were  fully  understood,  the 
experiments  upon  the  inferior  laryngeals  led  to  the  opinion  that  these  were  the  nerves  of 
phonation,  as  they  showed  loss  of  voice  following  their  division  in  living  animals.  It  is 
true  that  these  nerves  contain  the  filaments  which  preside  over  the  vocal  movements  of 
the  larynx  ;  but  it  is  also  the  fact  that  these  vocal  filaments  are  derived  exclusively  from 
the  spinal  accessory,  and  that  the  recurrents  contain  as  well  motor  filaments  which  pre- 
side over  movements  of  the  larynx  not  concerned  in  the  production  of  vocal  sounds. 

The  muscles  of  the  larynx  concerned  in  phonation  are,  the  crico-thyroids,  animated 
by  the  superior  laryngeals,  and  the  arytenoid,  the  lateral  crico-arytenoids,  and  the  thyro- 
arytenoids,  animated  by  the  inferior  laryngeals.  The  posterior  crico-arytenoids  are  re- 
spiratory muscles  ;  and  it  is  curious  that  these  are  not  affected  by  extirpation  of  the  spinal 
accessories,  but  that  the  glottis  is  still  capable  of  dilatation,  so  that  inspiration  is  not 
impeded.  If,  however,  the  spinal  accessories  be  extirpated,  and  the  larynx  be  then 
exposed  in  a  living  animal,  the  glottis  still  remains  dilated,  but  will  not  close  when  irri- 
tated. If  the  inferior  laryngeals  be  then  divided,  the  glottis  is  mechanically  closed  with 
the^inspiratory  act,  and  the  animals  often  die  of  suffocation.  When  we  call  to  mind  the 
varied  sources  from  which  the  pneumogastrics  receive  their  motor  filaments,  it  is  easy  to 
understand  how  certain  of  these  may  preside  over  the  vocal  movements,  and  others, 
from  a  different  source,  may  animate  the  respiratory  movements. 


PNEUMOGASTRIC,  OR  PAR  VAGUM  NERVE.         653 

As  we  should  naturally  expect  from  what  has  already  been  said,  section  of  the  infe- 
rior laryngeal  nerves  paralyzes  both  the  vocal  and  the  respiratory  movements  of  the 
larynx.  It  is  not  necessary  to  refer  in  detail  to  the  ancient  and  modern  experiments 
illustrating  this  point,  the  former  dating  from  the  time  of  Galen.  In  adult  animals,  the 
cartilages  of  the  larynx  are  sufficiently  rigid  to  allow  of  inspiration  after  the  organ  has 
been  completely  paralyzed ;  but,  in  young  animals,  the  glottis  is  closed,  and  suffocation 
ensues.  We  have  generally  observed  in  cats,  that  suffocation  follows  immediately  upon 
section  of  the  recurrents  or  of  the  pneumogastrics  in  the  neck. 

The  impediment  to  the  entrance  of  air  into  the  lungs  is  a  sufficient  explanation  of  the 
increase  in  the  number  of  the  respiratory  acts  after  division  of  both  recurrents.  The 
acceleration  of  respiration  is  much  greater  in  young  than  in  adult  animals.  This  does 
not  apply  to  very  young  animals,  in  which  section  of  the  recurrents  produces  almost  in- 
stant death. 

Feeble  galvanization  of  the  central  ends  of  the  inferior  laryngeals,  after  their  division, 
produces  rhythmical  movements  of  deglutition,  generally  coincident  with  arrest  of  the 
action  of  the  diaphragm.  These  phenomena  are  generally  observed  in  rabbits,  but  they 
are  not  constant.  The  reflex  action  of  these  nerves  in  deglutition  is  probably  dependent 
upon  the  communicating  filaments  which  they  send  to  the  superior  laryngeal  nerves. 

Properties  and  Functions  of  the  Cardiac  Nerves,  and  Influence  of  the  Pneumogastrics 
upon  the  Circulation. — One  of  the  most  interesting  questions  connected  with  the  physi- 
ology of  the  pneumogastric  nerves  is  their  action  upon  the  heart ;  and  the  results  of 
experiments,  which  will  be  fully  detailed  hereafter,  are  precisely  the  opposite  of  what 
would  be  expected  in  the  case  of  a  nerve  containing  motor  filaments  and  distributed  to 
a  muscular  organ.  Section  of  the  pneumogastrics  in  the  neck,  far  from  arresting  the 
action  of  the  heart,  increases  the  rapidity  of  its  pulsations  ;  and  galvanization  of  the 
nerves  arrests  the  heart's  action  in  diastole. 

"Within  the  past  few  years,  some  very  remarkable  experiments  have  been  made  upon 
the  influence  of  certain  nerves  given  off  near  the  superior  laryngeals,  which  have  been 
called  the  depressors  of  the  circulation ;  but  most  observations  have  been  made  upon 
the  trunks  of  the  pneumogastrics  in  the  cervical  region,  as  it  is  exceedingly  difficult  to 
isolate  the  thoracic  cardiac  branches  and  to  operate  upon  them  without  involving  other 
nervous  filaments.  In  galvanizing  the  nerves  in  the  neck,  we  have  to  consider  both  the 
direct  influence  of  the  current  and  the  phenomena  due  to  reflex  action. 

Effects  of  Section  of  the  Pneumogastrics  upon  the  Circulation. — It  is  not  necessary 
to  cite  in  detail  the  various  experiments  upon  the  effects  of  section  of  the  pneumogastrics 
in  the  neck  upon  the  action  of  the  heart.  The  division  of  these  nerves  in  living  animals 
is  sufficiently  easy,  and  all  who  have  performed  this  operation  have  noted  the  same  re- 
sults. By  section  of  these  nerves,  the  heart  is  at  once  separated  from  one  of  the  most 
important  of  its  nervous  connections ;  and  the  effects  show  that,  as  far  as  this  organ  is. 
concerned,  the  motor  filaments  present  great  differences  from  the  ordinary  motor  nerves 
of  the  cerebro-spinal  system.  Most  of  the  observations  made  by  dividing  the  nerves 
have  been  upon  dogs,  and  the  differences  in  the  effects  upon  other  animals  are  slight  and 
unimportant.  The  following  are  the  important  phenomena  presented  in  typical  experi- 
ments : 

Section  of  one  of  the  pneumogastrics  in  the  neck  does  not  produce  any  very  marked 
effect  upon  the  action  of  the  heart,  after  the  slight  disturbance  which  usually  follows  the 
operation  has  passed  away.  The  number  of  pulsations  is  slightly  increased,  and  the  car- 
diac pressure,  as  shown  by  a  cardiometer  fixed  in  the  carotid  artery,  is  slightly  dimin- 
ished ;  but  this  is  insignificant  as  compared  with  the  effects  of  dividing  both  nerves. 

Section  of  both  pneumogastrics  usually  produces  immediate  and  serious  disturbance 
in  the  respirations,  which  are  momentarily  accelerated.  The  animal  usually  becomes 
agitated  and  suffers  from  want  of  air;  and,  when  it  is  desired  especially  to  note  the  car- 


654 


NERVOUS   SYSTEM. 


diac  disturbance,  it  is  often  necessary  to  relieve  the  respiration  by  introducing  a  tube 
into  the  trachea.  In  full-grown  dogs,  however,  the  respirations  soon  become  calm,  but 
they  are  diminished  in  frequency  and  become  unusually  profound.  When  the  animal  is 
in  this  condition,  the  beats  of  the  heart  are  very  much  increased  in  frequency,  at  least 
doubled ;  but  they  are  inefficient  and  tremulous. 

An  interesting  point  in  this  connection  is  the  want  of  influence  of  certain  medicinal 
substances  over  the  action  of  the  heart  in  animals  after  division  of  the  pneumogastrics. 
Traube  has  shown  that,  while  digitalis  injected  into  the  veins  of  a  dog  was  capable  in 
an  hour  of  reducing  the  pulse  to  about  one-fourth  of  the  normal  number  of  beats  per 
minute,  there  was  no  appreciable  effect  upon  the  circulation  when  the  injection  was 
made  in  animals  with  both  pneumogastrics  divided. 

The  influence  of  the  pneumogastrics  upon  the  heart  is  one  of  the  most  interesting 
points  in  the  physiology  of  the  circulation ;  but  we  can  discuss  the  mechanism  of  the 
phenomena  following  section  of  the  nerves  more  satisfactorily  after  we  have  considered 
the  effects  of  their  galvanization. 

Effects  of  Galvanizing  the  Pneumogastrics  or  their  Branches  upon  the  Circulation. — 
The  experiments  upon  the  effects  of  galvanization  of  the  pneumogastrics  in  the  neck  on 
the  action  of  the  heart  are  almost  innumerable ;  and,  although  the  explanations  of  the 
phenomena  observed  present  the  widest  differences,  the  facts  themselves  are  sufficiently 

simple.  These  facts  will  be  discussed  under  the 
following  heads  :  1.  The  direct  influence  of  galvan- 
ization of  the  nerves  in  the  neck,  undivided,  or  of 
galvanization  of  the  peripheral  extremities  of  the 
trunks  after  division.  2.  Reflex  phenomena  follow- 
ing galvanization  of  the  central  ends  of  the  pneu- 
mogastrics, after  their  division. 

Direct  Influence  of  tfie  Pneumogastrics  upon 
the  Heart.— In  1846,  the  brothers  Weber  noted 
the  important  fact,  that  galvanization  of  the  pneu- 
mogastrics in  the  neck  rendered  the  action  of 
the  heart  slow,  and,  if  the  galvanization  were  suffi- 
ciently powerful,  arrested  the  heart,  which  remained 
flaccid  and  in  diastole  for  a  certain  time  while  the 
galvanization  was  continued.  This  fact  has  since 
been  confirmed  by  numerous  experimenters. 

While  there  is  no  difference  of  opinion  among 
physiologists  with  regard  to  the  stoppage  of  the 
heart  by  powerful  galvanization,  it  is  stated  by 
some  that  a  very  feeble  current  passed  through  the 
peripheral  ends  of  the  divided  nerves  quickens  the 
heart's  action ;  but  it  is  admitted  by  all  that  it  is 
very  difficult  to  regulate  the  intensity  of  the  current 
so  as  to  produce  this  effect.     After  section  of  the 
nerves,  the  action  of  the  heart  is  very  readily  modi- 
fied by  struggles,  etc.,  on  the  part  of  the  animal 
under  observation ;  and,  in  view  of  the  exceeding 
FIG.  220.— Branches  of  the  pneumogastric  to   nicety  of  the  reported  experiments,  it  cannot  be 
C,  heart ;  a,  carofld  artw^Sng  to  the  brain ;    admitted  taat  tne  heart  is  capable  of  being  excited 
&<?hSrt  es  °f  the  pncumo^stric  £°ins  t{>   to  increased  rapidity  of  action,  without  observations 

of  the  most  positive   character.      Such  facts  are 

wanting ;  and,  farthermore,  it  has  been  shown  by  Dr.  Rutherford,  in  a  series  of  exceed- 
ingly exact  and  satisfactory  experiments,  that  whenever  a  galvanic  current  passed 
through  the  pneumogastrics  has  any  appreciable  effect  upon  the  action  of  the  heart, 


PNEUMOGASTRIC,  OR  PAR  VAGUM  NERVE.         655 

it  is  to  dimmish  the  frequency  of  its  pulsations.  Inasmuch  as  our  object  is  simply  to 
show  that,  imitating  the  nervous  force  by  galvanism,  the  action  of  the  pneumogastrics 
is  inhibitory,  we  shall  not  discuss  the  effects  of  different  currents,  and  other  experi- 
ments, which  have  little  relation  to  the  natural  action  of  the  nerves,  and  possess  slight 
interest  from  a  purely  physiological  point  of  view. 

The  direct  action  of  the  pneumogastrics  upon  the  heart  is  undoubtedly  through  their 
motor  filaments.  All  the  facts  developed  by  experiments  are  in  accordance  with  this  view. 
If  the  nerves  be  divided  in  the  neck,  galvanization  of  the  central  ends  has  no  effect 
upon  the  heart,  the  pulsations  being  arrested  only  when  the  peripheral  ends  are  stimu- 
lated. This  shows  that,  at  least  as  far  as  the  fibres  passing  down  the  neck  are  con- 
cerned, the  action  is  centrifugal  and  direct,  not  reflex.  Another  curious  fact  illustrates 
the  same  point  very  forcibly.  It  is  well  known  that  the  woorara-poison  completely  par- 
alyzes the  motor  nerves,  leaving  the  muscular  irritability  and  the  sensory  nerves  intact. 
It  has  been  found  that,  in  animals  poisoned  with  woorara,  the  action  of  the  heart  being 
maintained  by  artificial  respiration,  galvanization  of  both  pneumogastrics  has  no  effect 
upon  its  pulsations.  This  fact  we  have  repeatedly  verified  in  public  demonstrations. 
Still  another  curious  fact  remains  bearing  upon  the  question  under  consideration.  If  pow- 
erful galvanization,  which  immediately  arrests  the  cardiac  pulsations,  be  continued  for  a 
certain  time,  so  that  the  motor  filaments  become  temporarily  exhausted  and  lose  their 
irritability,  the  heart  resumes  its  contractions,  notwithstanding  that  the  galvanization  is 
continued;  the  nerves  being  for  the  time  incapable  of  transmitting  the  inhibitory  influence. 

The  source  of  the  motor  filaments  in  the  pneumogastrics  which  exert  a  direct  inhibi- 
tory action  upon  the  heart  becomes  an  important  point  to  determine.  In  the  original 
experiments  by  the  brothers  Weber,  it  was  shown  that,  when  the  galvanic  stimulus  was 
applied  to  that  portion  of  the  centres  from  which  the  nerves  take  their  origin,  the  action 
of  the  heart  was  arrested  in  the  same  way  as  when  the  nerves  themselves  are  galvan- 
ized ;  and  it  has  been  shown  by  subsequent  observations  that,  when  the  heart  is  thus 
arrested  by  galvanization  of  the  medulla  oblongata,  if  both  pneumogastrics  be  divided  in 
the  neck,  its  action  is  resumed.  This  would  at  first  lead  to  the  supposition  that  the 
inhibitory  filaments  are  derived  from  the  roots  themselves  of  the  pneumogastrics;  but  it 
has  been  conclusively  demonstrated  that  they  are  really  derived  from  the  spinal  acces- 
sories, the  upper  filaments  of  origin  of  which  are  situated  just  below  the  roots  of  the 
pneumogastrics. 

It  has  been  shown  that  powerful  galvanization  of  one  pneumogastric  will  arrest  the 
heart's  action,  and  also  that  this  inhibitory  action  is  much  more  marked  in  the  right 
than  in  the  left  nerve.  Waller,  after  extirpating  the  spinal  accessory  nerve  upon  one 
side,  found  that  galvanization  of  the  pneumogastric  upon  that  side  had  no  effect  upon 
the  heart,  provided  that  from  ten  to  twelve  days  had  elapsed  after  extirpation  of  the 
spinal  accessory,  a  sufficient  time  to  secure  disorganization  and  loss  of  irritability  of  its 
fibres.  These  experiments  show  conclusively  that  the  motor  filaments  contained  in  the 
pneumogastric,  which  act  directly  upon  the  heart,  are  derived  exclusively  from  the  com- 
municating branch  of  the  spinal  accessory. 

Reflex  Influence,  through  the  Pneumogastrics,  upon  the  Circulation. — Galvanization 
of  the  central  ends  of  the  pneumogastrics,  after  their  division  in  the  neck,  does  not  influ- 
ence the  action  of  the  heart,  except  as  the  pulsations  are  affected  by  the  modifications  in 
respiration.  When  the  central  ends  are  stimulated,  the  pupils  become  dilated,  the  eyes 
protrude,  sometimes  vomiting  occurs,  and  always  the  number  of  respiratory  acts  is 
diminished,  and,  with  a  powerful  current,  are  arrested  in  inspiration  ;  but  the  pulsations 
of  the  heart  are  not  affected. 

Depressor -Nerve. — An  important  reflex  action  operating  upon  the  circulation  through 
branches  of  the  pneumogastrics  has  lately  been  described  by  Cyon  and  Ludwig,  in  a 
memoir  which  received  the  prize  for  Experimental  Physiology  from  the  French  Academy 
of  Sciences,  in  1867.  The  experiments  upon  which  this  memoir  is  based  are  exceedingly 


656 


NERVOUS  SYSTEM. 


FIG.  221.—Depi'e8Sor-nerves.    (Cyon  and  Ludwig.) 

A,  A,  A,  sympathetic  nerves;  B,  sublingual;  C,  descending  branch  of  the  sublingual;  D,  branch  from  the  cervical 
:us ,  K,  K,  &,  pneumogastrics ;  F,  superior  laryngeal  nerves ;  G,  G,  G,  G,  depressor-nerves. 


PNEUMOGASTRIC,  OR  PAR  VAGUM  NERVE.         65? 

clear  and  satisfactory,  and  they  afford,  perhaps,  the  only  positive  explanation  we  have  of 
reflex  action  upon  the  heart.     The  substance  of  these  observations  is  briefly  as  follows : 

In  the  rabbit,  is  a  nerve,  arising  by  two  roots,  one  coming  from  the  trunk  of  the 
pneumogastric  and  the  other  from  its  superior  laryngeal  branch,  passing  then  toward  the 
carotid  artery  and  taking  its  course  down  the  neck  by  the  side  of  the  sympathetic  as  far 
as  the  thorax.  In  the  chest,  it  joins  with  sympathetic  filaments  to  pass  with  them  to  the 
heart,  by  little  branches  between  the  origin  of  the  aorta  and  the  pulmonary  artery. 
This  nerve  can  be  completely  isolated  in  the  neck  from  the  sympathetic  and  the  trunk 
of  the  pneumogastric.  If  it  be  divided  in  this  situation,  after  the  irritation  produced  by 
the  operation  has  subsided,  very  distinct  and  important  modifications  in  the  circulation 
may  be  produced  by  its  galvanization. 

In  the  first  place,  it  was  noted  in  all  the  experiments,  that  galvanization  of  the  periph- 
eral extremities  produced  no  change,  either  in  the  number  of  the  pulsations  of  the 
heart  or  in  the  pressure  of  blood  in  the  vascular  system ;  which  points  to  the  fact  that 
its  action  is  not  direct,  but  reflex,  and  that  it  is  due  to  an  impression  conveyed  to  the 
nerve-centres. 

If  the  central  ends  of  the  nerves  be  galvanized,  the  pressure  in  the  arteries  dimin- 
ishes little  by  little,  until  it  may  be  reduced  to  one-half  or  two-thirds  of  the  pressure 
before  the  irritation  was  applied.  This  low  pressure  continues  so  long  as  the  interrupted 
current  is  applied  ;  but,  when  the  galvanization  is  arrested,  it  gradually  returns  to  the 
normal  standard.  These  phenomena  are  observed  in  all  the  large  arterial  trunks.  The 
length  of  time  required  to  produce  the  greatest  diminution  in  the  pressure  is  somewhat 
variable,  but  the  experimenters  have  never  seen  it  reach  its  minimum  before  fifteen  pul- 
sations of  the  heart. 

"  The  diminution  in  the  pressure  is  attended  with  a  reduction  of  the  pulse  in  the 
instances  in  which  the  depressor-nerve  only  has  been  divided.  The  irritated  nerve  is 
isolated  in  a  manner  so  complete  that  we  cannot  fear  the  passage  of  the  exciting  current 
in  the  trunk  of  the  pneumogastric.  The  changes  in  the  number  of  pulsations  persist 
even  when  the  pneumogastric  has  been  excited  by  the  side  where  the  irritation  has  been 
.applied,  from  the  point  where  the  superior  laryngeal  is  given  off  to  the  point  where  the 
pneumogastric  enters  the  thoracic  cavity. 

"  From  the  foregoing  it  is  evident  that  the  changes  taking  place  in  the  number  of 
pulsations  are  due  to  excitation  of  the  depressor-nerve.  If  we  study  attentively  the 
progress  of  the  cardiac  pulsations  during  the  excitation,  we  observe  always  that  the  most 
considerable  reduction  takes  place  at  the  beginning  of  the  experiment ;  that  is  to  say,  at 
the  moment  when  the  blood-pressure  descends  from  its  normal  standard  to  the  lowest 
point.  When  the  pressure  is  completely  depressed,  the  pulse  is  accelerated  again  and 
even  reaches  almost  completely  the  numbers  presented  before  the  oscillations.  When 
the  irritation  ceases,  after  a  shorter  or  longer  period,  the  heart  generally  beats  more 
rapidly  than  before  the  irritation,  and  this  during  all  the  time  that  is  occupied  in  the 
return  of  the  pressure  to  the  normal  standard.  This  observation  in  itself  refutes  the 
idea  that  the  diminution  in  the  pressure  may  depend  upon  the  diminished  number  of  pul- 
sations. If  the  reduction  in  the  rate  of  the  pulse  produced  a  diminished  pressure,  it 
should  be  increased  when  the  pulsations  of  the  heart  become  accelerated. 

"  The  manner  in  which  the  pulse  is  reduced  leads  to  the  supposition  that  it  is  due  to 
a  reflex  action  of  the  pneumogastric. 

"  It  was  easy  to  verify  this  last  opinion,  and  we  have  been  able  to  confirm  it  by  first 
cutting  the  pneumogastrics  on  both  sides,  and  afterward  irritating  the  central  end  of  the 
depressor-nerve.  In  this  case,  the  pressure  fell  to  0'62,  0'55,  etc.,  while  the  number  of 
pulsations  remained  the  same,  or  at  least  oscillated  very  slightly  above  and  below  the 
number  observed  before  the  irritation." 

The  above  extract  from  the  observations  of  Cyon  shows  two  important  points  : 

First,  galvanic  stimulation  of  the  central  extremities  of  the  divided  depressor-nerves 
42 


658  NERVOUS   SYSTEM. 

reduces  the  number  of  pulsations  of  the  heart  by  a  reflex  action ;  the  impression  being 
conveyed  to  the  nerve-centres  by  the  depressor-nerves,  and  the  force  operating  directly 
upon  the  heart  being  transmitted  through  efferent  filaments  in  the  trunk  of  the  pneumo- 

gastric. 

Second,  the  reduction  in  the  pressure  of  blood  in  the  larger  arteries  is  independent 
of  the  efferent  filaments  of  the  pneumogastric  and  bears  no  relation  to  the  reduction  in 
the  number  of  cardiac  pulsations. 

It  now  remains  to  explain,  if  possible,  the  mechanism  of  the  reduction  in  the  arte- 
rial pressure.  This  question  is  treated  by  Cyon  by  the  method  of  exclusion.  The  dimi- 
nution in  the  pressure  followed  galvanization  of  the  central  extremities  of  the  depressor- 
nerves  even  when  the  heart  was  removed  from  its  influence  by  section  of  both  pneumo- 
gastrics in  the  neck,  and  when  all  the  voluntary  movements  and  the  movements  of 
respiration  were  abolished  by  poisoning  with  woorara.  In  the  latter  case,  the  circula- 
tion was  kept  up  by  artificial  respiration.  Without  following  out  the  various  observa- 
tions which  go  to  show  that  the  influence  of  the  depressor-nerve  upon  the  arterial  pressure 
is  independent  of  the  force  or  frequency  of  the  heart's  action  and  is  due  to  some  cause 
which  operates  upon  the  vessels  themselves,  we  shall  simply  give  the  results  of  the 
experiments  upon  the  splanchnic  nerves.  If  the  abdomen  be  opened,  and  one  or  more 
of  these  nerves  be  divided,  the  arterial  pressure  is  immediately  diminished.  After  this, 
if  the  peripheral  extremities  of  the  divided  nerves  be  galvanized,  the  pressure  rapidly 
returns  to  the  normal  standard.  These  experiments  "  demonstrate  that  the  splanchnic 
nerves  constitute  the  most  important  vaso-motor  nerves  in  the  entire  organism."  This 
point  being  settled,  the  depressor-nerves  were  galvanized  after  section  of  the  splanch- 
nic nerves,  in  some  cases  exaggerating  the  general  arterial  pressure  by  compressing 
the  aorta,  and  in  others,  leaving  the  aorta  free.  "  The  irritation  of  the  depressor-nerve 
after  section  of  the  splanchnic  nerve  produced  still  a  diminution  in  the  blood-pressure, 
but  the  absolute  value  of  this  diminution  is  much  less  than  it  was  during  the  irritation  of 
the  depressor-nerve  before  the  section  of  the  splanchnic."  These  experiments  show 
pretty  conclusively  that  the  diminished  pressure  in  the  arterial  system  following  stimula- 
tion of  the  central  ends  of  the  depressor-nerves  after  division  is  due  to  a  reflex  action  on 
"the  blood-vessels  of  the  abdominal  organs,  taking  place  through  the  splanchnic  nerves. 
We  are  sufficiently  familiar  with  reflex  paralyzing  action  upon  the  blood- vessels  through 
the  sympathetic  system ;  and,  when  we  call  to  mind  the  immense  extent  of  the  abdominal 
vascular  system,  we  can  readily  understand  how,  if  the  resistance  to  the  flow  of  blood  be 
diminished  by  paralysis  of  the  muscular  coats  of  the  small  arteries,  the  pressure  in  the 
larger  arteries  would  be  reduced. 

Mechanism  of  the  Influence  of  the  Pneumogastrics  upon  the  Action  of  the  Heart. — It 
is  useless  to  speculate  upon  the  exact  mechanism  of  the  action  of  the  pneumogastrics  upon 
the  heart.  Although  various  explanations  have  been  presented  of  the  effects  following 
division  of  the  nerves  in  the  neck,  and  of  the  opposite  phenomena  which  attend  the  gal- 
vanization of  their  peripheral  ends,  they  are  all  more  or  less  unsatisfactory.  All  that  can 
be  said,  in  the  present  state  of  our  knowledge,  is,  that  the  pneumogastrics,  by  virtue  of 
the  communicating  branches  from  the  spinal  accessories,  have  a  direct  inhibitory  influence 
upon  the  heart.  When  they  are  divided  and  the  heart  is  removed  from  their  influence,  the 
pulsations  become  more  rapid.  When  the  peripheral  ends  of  the  divided  nerves  are 
galvanized,  the  .heart  beats  more  slowly,  or  its  action  may  be  arrested  by  a  current  of 
sufficient  power.  This  action  may  also  be  reflex,  due  to  an  impression  conveyed  to  the 
centres  by  the  depressor-nerves. 

Properties  and  Functions  of  the  Pulmonary  Branches,  and  Influence  of  the  Pneumo- 
trics^ upon  Respiration.— The  trachea,  bronchi,  and  the  pulmonary  structure  are  sup- 
plied with  motor  and  sensory  filaments  by  branches  of  the  pneumogastrics.  The  recurrent 
laryngeals  supply  the  upper,  and  the  pulmonary  branches,  the  lower  part  of  the  trachea, 


PNEUMOGASTRIO,   OR  PAR   VAGUM  NERVE.  659 

the  lungs  themselves  being  supplied  by  the  pulmonary  branches  alone.  The  sensibility 
of  the  mucous  membrane  of  the  trachea  and  bronchi  is  due  to  the  pneumogastrics,  for 
these  parts  are  insensible  to  irritation  when  the  nerves  have  been  divided  in  the  neck. 
Longet  has  shown  that,  while  an  animal  coughed  and  showed  signs  of  pain  when  the 
mucous  membrane  of  the  respiratory  passages  was  irritated,  after  division  of  the  pneumo- 
gastrics there  was  no  evidence  of  sensibility,  even  when  the  tracheal  mucous  membrane 
was  treated  with  strong  acid,  or  even  cauterized.  He  also  saw  the  muscular  fibres  of  the 
small  bronchial  tubes  contract  when  a  galvanic  stimulus  was  applied  to  the  branches  of 
the  pneumogastrics. 

The  main  interest,  in  this  connection,  is  attached  to  the  pulmonary  branches  and  their 
relations  to  the  respiratory  acts.  These  are  undoubtedly  connected  with  important  reflex 
phenomena,  acting  as  centripetal  nerves ;  and  their  direct  action  in  respiration  is  probably 
much  less  important.  They  are  exposed  and  operated  upon  in  living  animals  with  so 
much  difficulty,  that  we  know  little  of  the  direct  effects  of  their  irritation  and  must  judge 
of  their  general  properties  chiefly  by  experiments  showing  their  action  upon  respiration. 
Wa  shall  have  to  study,  in  connection  with  the  functions  of  these  nerves,  the  effects  of 
their  division,  upon  the  lungs  and  the  respiratory  acts,  and  the  phenomena,  referable  to 
the  respiratory  organs,  which  follow  their  galvanization.  We  shall  also  consider  certain 
theoretical  views  with  regard  to  their  action  in  the  automatic  processes  of  respiration,  and 
with  the  sense  of  want  of  air  (besoin  de  respirer),  which  gives  rise  to  the  reflex  respira- 
tory acts. 

Effects  of  Division  of  the  Pneumogastrics  upon  Respiration. — Section  of  both  pneumo- 
gastrics in  the  neck,  in  mammals  and  birds,  is  usually  followed  by  dsath,  in  from  two  to 
five  days.  In  young  animals,  death  may  occur  almost  instantly,  from  paralysis  of  the 
respiratory  movements  of  the  glottis,  a  fact  which  we  have  already  noted  in  connection 
with  the  recurrent  laryngeal  nerves. 

Very  little  of  importance,  with  regard  to  the  functions  of  the  pneumogastrics  in  con- 
nection with  respiration,  has  been  ascertained  by  the  numerous  experiments  on  record  of 
section  of  one  or  both  of  these  nerves  in  the  cervical  region.  It  has  been  found  by  all 
experimenters,  that  animals  survived  and  presented  no  very  distinct  abnormal  phenomena 
after  section  of  one  nerve.  Longet  states  that  animals  operated  upon  in  this  way  present 
hoarseness  of  the  voice  and  a  slight  increase  in  the  number  of  respiratory  acts.  Some 
observers  have  found  the  corresponding  lung  partly  emphysematous  and  partly  engorged 
with  blood,  and  others  have  not  noted  any  change  in  the  pulmonary  structure. 

When  both  nerves  are  divided  in  full-grown  dogs,  an  experiment  which  we  have  often 
repeated,  the  effect  upon  the  respiratory  movements  is  very  marked.  For  a  few  seconds, 
the  number  of  respiratory  acts  may  be  increased ;  but,  as  soon  as  the  animal  becomes 
tranquil,  the  number  is  very  much  diminished,  and  the  movements  change  their  character. 
The  inspiratory  acts  become  unusually  profound  and  are  attended  with  excessive  dilata- 
tion of  the  thorax.  The  animal  is  generally  quiet  and  indisposed  to  move.  We  have 
seen,  under  these  conditions,  the  number  of  respirations  fall  from  sixteen  or  eighteen  to 
four  per  minute. 

In  most  animals  that  die  from  section  of  both  pneumogastrics,  the  lungs  are  found 
engorged  with  blood,  and,  as  it  were,  carnified,  so  that  they  sink  in  water.  This  curious 
fact,  although  its  physiological  significance  is  not  apparent,  has  been  the  subject  of  much 
speculation  and  experimental  research.  Bernard  found  that  the  pulmonary  lesion  did  not 
exist  in  birds,  although  section  of  both  nerves  was  fatal.  It  had  previously  been  ascer- 
tained that,  in  some  animals,  death  takes  place  with  no  alteration  of  the  lungs.  When 
the  entrance  of  the  secretions  into  the  air-passages  was  prevented  by  the  introduction  of 
a  canula  into  the  trachea,  the  carnification  of  the  lungs  was  nevertheless  observed. 
Without  detailing  all  of  the  experiments  upon  which  the  explanation  offered  by  Bernard 
is  based,  it  is  sufficient  to  state  that  he  observed  a  traumatic  emphysema  as  a  consequence 
of  the  excessively  labored  and  profound  inspirations.  Indeed,  this  can  be  actually 


660  NERVOUS  SYSTEM. 

when  the  pleura  is  exposed  in  living  animals.  As  a  result  of  this  distention  of  the  air- 
cells,  the  pulmonary  capillaries  are  ruptured  in  different  parts,  the  blood  becomes  coagu- 
lated, and  the  lungs  are  finally  carnified.  This  cannot  occur  in  birds,  because  the  lungs 
are  fixed,  and  their  relations  are  such  that  they  are  not  exposed  to  excessive  distention  in 
inspiration. 

There  is  no  satisfactory  explanation  of  the  remarkable  changes  in  the  respiratory 
movements  that  follow  section  of  the  pneumogastrics. 

In  this  connection  we  may  note  a  curious  fact,  observed  by  Prof.  Dalton  and  others, 
that  the  pneumogastrics  sometimes  reunite  after  division.  In  January,  1874,  we  divided 
both  pneumogastrics  in  a  medium-sized  dog.  The  pulse  was  immediately  increased  from 
one  hundred  and  twenty  to  two  hundred  and  forty  in  the  minute,  and  the  number  of 
respirations  fell  from  twenty-four  to  four  or  six.  In  ten  days,  the  pulse  and  respirations 
had  become  normal.  The  dog  was  then  killed  by  section  of  the  medulla  oblongata,  and 
the  reunion  of  the  divided  ends  of  the  nerves  was  found  to  be  nearly  complete. 

Sense  of  Want  of  Air. — The  pneumogastrics  may  regulate  the  respiratory  acts,  but 
they  are  not  the  medium  through  which  the  sense  of  want  of  air  (besoin  de  respirer), 
which  gives  rise  to  the  reflex  movements  of  respiration,  is  conveyed  to  the  nerve-centres. 
If  it  be  true,  as  it  undoubtedly  is,  that  section  of  both  pneumogastrics  in  the  neck  modifies 
the  number  and  the  character  of  the  respirations,  and  that,  after  division  of  the  nerves, 
galvanization  of  their  central  ends  arrests  respiration,  it  is  more  than  probable  that  this 
function  is  normally  influenced  through  these  nerves,  by  impressions  conveyed  to  the 
centres ;  but  precisely  what  this  influence  is  or  what  is  the  mechanism  of  its  action,  we 
do  not  know. 

The  positive  statement  that  the  sense  of  want  of  air  is  not  conveyed  to  the  nerve- 
centres  through  the  pneumogastrics  is  based,  to  a  great  extent,  upon  our  own  experi- 
ments, which  have  been  fully  detailed  under  the  head  of  respiration ;  and  we  shall  here 
give  simply  their  results  and  the  conclusions  to  which  they  lead. 

The  acts  of  respiration  are  involuntary,  although  they  may  be  modified,  within  cer- 
tain limits,  through  the  will ;  and  they  are  reflex,  due  to  an  impression  conveyed  to  the 
respiratory  nervous  centre,  the  medulla  oblongata,  which  gives  rise  to  the  stimulus  that 
excites  the  action  of  the  inspiratory  muscles.  It  has  been  conclusively  shown  by  experi- 
ments that,  if  artificial  respiration  be  efficiently  carried  on  in  a  living  animal,  so  as  to 
supply  air  fully  to  the  system,  the  sense  of  want  of  air  is  not  appreciated,  and  the  animal 
makes  no  effort  to  breathe ;  but,  if  respiration  be  imperfectly  performed,  the  animal 
almost  immediately  feels  the  want  of  air,  and,  in  our  experiments,  the  exposed  respiratory 
muscles  were  thrown  into  violent  but  ineffectual  contraction. 

The  principal  points  with  reference  to  the  location  of  the  sense  of  want  of  air  and  its 
transmission  to  the  nerve-centres,  developed  by  our  own  experiments,  are  the  following : 

A  dog  was  etherized,  the  chest  was  opened,  exposing  the  heart  and  lungs,  and  arti- 
ficial respiration  was  carried  on  by  means  of  a  bellows  secured  in  the  trachea.  So  long 
as  the  supply  of  air  was  sufficient,  the  animal  made  no  effort  to  breathe,  even  when 
allowed  to  come  from  under  the  influence  of  the  ansesthetic. 

An  artery  was  then  exposed  and  the  color  of  the  blood  noted.  When  the  artificial 
respiration  was  arrested,  the  animal  made  efforts  to  breathe  as  soon  as  the  blood  became 
dark  in  the  arterial  system.  We  concluded  from  this,  that  the  impression  conveyed  to 
the  respiratory  nervous  centre,  giving  rise  to  the  movements  of  respiration,  was  due  to 
the  action  of  non-oxygenated  blood. 

To  ascertain  whether  the  impression  were  made  upon  the  nerves  distributed  to  the 
lungs  or  upon  other  nerves,  a  large  vessel  was  divided  and  the  system  was  drained  of 
blood,  the  lungs  being  continually  supplied  with  fresh  air.  In  this  case,  respiratory 
efforts  of  the  most  violent  character  were  invariably  noted  following  the  hemorrhage. 
This  portion  of  the  experiment  demonstrated  that  the  sense  of  want  of  air  was  not 
dependent  upon  the  accumulation  of  carbonic  acid  in  the  lungs,  but  was  due  to  a  deficient 


PNEUMOGASTRIC,  OR  PAR  VAGUM  NERVE.         661 

supply  of  the  oxygen-carrying  fluid  to  the  general  system.  It  farther  demonstrated  that 
the  impression  in  the  general  system  was  not  due  to  the  presence  of  carbonic  acid 
but  to  the  absence  of  oxygen ;  for  no  blood  containing  carbonic  acid  circulated  in  the 
system. 

These  phenomena  were  observed  without  any  modification,  after  division  of  both 
pneumogastric  nerves  in  the  neck,  and  they  seem  to  prove  conclusively  that  the  sense  of 
want  of  air  is  not  transmitted  to  the  respiratory  nervous  centre  through  the  medium  of 
these  nerves.1 

Effects  of  Galvanization  of  the  Pneumogastrics  upon  Respiration. — The  phenomena 
which  follow  galvanization  of  the  pneumogastrics,  although  they  are  curious  and  inter- 
esting, do  not  throw  much  light  upon  the  relations  of  these  nerves  to  respiration.  We 
have  already  mentioned  the  arrest  of  the  respiratory  movements  by  galvanization  of  the 
superior  laryngeal  branches  and  of  the  central  ends  of  the  pneumogastrics  after  their  divi- 
sion in  the  neck.  The  main  point  of  interest  in  this  connection  is  the  fact  that  the  effects 
observed  are  entirely  reflex,  galvanization  of  the  peripheral  ends  of  the  divided  nerves 
having  no  direct  action  on  the  movements  of  the  thorax. 

In  view  of  the  very  indefinite  physiological  applications  of  the  experiments  made  by 
galvanizing  the  nerves,  we  shall  not  give  in  detail  the  numerous  observations  upon  this 
subject,  but  shall  simply  state  the  results,  as  given  in  a  recent  and  very  elaborate  work 
upon  respiration,  by  M.  Bert : 

"  1.  Respiration  may  be  arrested  by  excitation  of  the  pneumogastrics  (Traube),  of  the 
larynx  (Cl.  Bernard),  of  the  nostrils  (M.  Schiff),  of  most  of  the  sensory  nerves  (M.  Schiff, 
an  assertion  that  I  have  not  been  able  to  verify). 

"  2.  This  arrest  may  take  place  either  in  inspiration  or  in  expiration,  through  any  one 
of  these  nerves,  without  attributing  it  to  the  action  of  derived  currents. 

"  3.  A  feeble  excitation  accelerates  the  respiration ;  a  more  powerful  excitation 
retards  it ;  a  very  powerful  excitation  arrests  it.  These  words  '  feeble  '  and  '  powerful  ' 
having,  it  is  understood,  only  a  relative  sense  for  any  one  animal  and  under  certain  con- 
ditions :  what  is  feeble  for  one  would  be  powerful  for  another,  etc. 

"  I  believe,  in  opposition  to  the  opinion  of  Rosenthal,  that  section  of  the  pneumogas- 
trics does  not  increase  the  difficulty  of  arresting  respiration  ;  at  least,  death  by  excitation 
occurs  much  more  easily  in  this  case. 

"  4.  When  the  respiratory  movements  are  completely  arrested,  it  is  always  the  same 
for  the  general  movements  of  the  animal,  which  remains  motionless. 

"  5.  Respiration  returns  even  during  excitation,  and  when  this  is  arrested,  it  almost 
always  becomes  accelerated. 

"6.  Arrest  in  expiration  is  more  easily  obtained  than  arrest  in  inspiration  ;  there  are 
animals,  indeed,  in  which  it  is  impossible  to  effect  the  latter. 

"7.  If  an  excitation  be  employed  sufficiently  powerful  to  arrest  respiration  in  inspi- 
ration, all  respiratory  movements  may  be  made  to  cease  at  the  very  moment  when  the 
excitation  is  applied  (inspiration,  half-inspiration,  expiration),  either  by  operating  upon 
the  pneumogastric,  or  operating  upon  the  laryngeal.  .  .  . 

"  Any  feeble  excitation  of  centripetal  nerves  increases  the  number  of  the  respiratory 
movements ;  any  powerful  excitation  diminishes  them.  A  powerful  excitation  of  the 
pneumogastrics,  of  the  superior  laryngeal,  of  the  nasal  branch  of  the  infra- orbital,  may 
arrest  them  completely  ;  if  the  excitation  be  sufficiently  energetic,  the  arrest  takes  place 
at  the  very  moment  it  is  applied.  Finally,  sudden  death  of  the  animal  may  follow  a  too 
powerful  impression,  thus  transmitted  to  the  respiratory  centre  r  all  this  being  true  for 
certain  mammalia,  birds,  and  reptiles." 

1  For  a  full  account  of  these  experiments,  with  their  bearing  upon  certain  respiratory  phenomena  before  birth,  the 
reader  is  referred  to  the  original  article,  entitled  Experimental  Researches  on  Points  connected  with  the  Action  of 
the  Heart  and  with  Respiration,  published  in  the  American  Journal  of  the  Medical  Sciences,  Philadelphia,  Octo- 
ber, 1861.  Since  this  publication,  the  experiments  have  been  frequently  repeated  in  public  demonstrations,  and  the 
conclusions  verified. 


662  NERVOUS   SYSTEM. 

The  above  formulated  statements  express  the  experimental  facts  at  present  known 
with  regard  to  the  influence  of  the  pneumogastrics  upon  respiration.  The  pulmonary 
branches  themselves  are  so  deeply  situated  that  they  have  not  as  yet  been  made  the  sub- 
ject of  direct  experiment,  with  any  positive  and  satisfactory  results. 

Properties  and  Functions  of  the  (Esophageal  Nerves. — The  muscular  walls  and  the 
mucous  membrane  of  the  oesophagus  are  supplied  entirely  by  branches  from  the  pneumo- 
gastrics. The  upper  portion  is  supplied  by  filaments  from  the  inferior  laryngeal  branches, 
the  middle  portion,  by  filaments  from  the  posterior  pulmonary  branches,  and  the  inferior 
portion  receives  the  cesophageal  branches.  These  branches  are  both  sensory  and  motor; 
but  probably  the  motor  filaments  largely  predominate,  for  the  mucous  membrane,  although 
it  is  sensible  to  the  extremes  of  heat  and  cold,  the  feeling  of  distention,  and  a  burning 
sensation  upon  the  application  of  strong  irritants,  is  by  no  means  acutely  sensitive. 

That  the  movements  of  the  oesophagus  are  animated  by  branches  from  the  pneumo- 
gastrics, has  been  clearly  shown  by  experiments.  In  the  first  place,  except  in  animals  in 
which  the  anatomical  distribution  of  the  nerves  is  different  from  the  arrangement  in  the 
human  subject,  the  entire  oesophagus  is  paralyzed  by  dividing  the  nerves  in  the  neck. 
When  the  pneumogastrics  are  divided  in  the  cervical  region,  in  dogs,  if  the  animals 
attempt  to  swallow  a  considerable  quantity  of  food,  the  upper  part  of  the  oesophagus  is 
found  enormously  distended.  Bernard  noted  in  a  dog  in  which  a  gastric  fistula  had  been 
established,  that  articles  of  food  given  to  the  animal  did  not  pass  into  the  stomach,  although 
he  made  great  efforts  to  swallow.  An  instant  after  the  attempt,  the  matters  were 
regurgitated,  mixed  with  mucus,  but  of  course  did  not  come  from  the  stomach. 

Direct  experiments  upon  the  roots  of  the  pneumogastrics  have  shown  that  these 
nerves  influence  the  movements  of  the  oesophagus,  and  that  the  motor  filaments  involved 
do  not  come  from  the  spinal  accessory ;  but  it  is  not  known  from  what  nerves  these 
motor  filaments  are  derived. 

Properties  and  Functions  of  the  Abdominal  Branches. — In  view  of  the  very  extensive 
distribution  of  the  terminal  branches  of  the  pneumogastrics  to  the  abdominal  organs,  it 
is  evident  that  the  functions  of  these  nerves  must  be  very  important,  particularly  since 
it  has  been  shown  that  the  right  nerve  is  distributed  to  the  whole  of  the  small  intestine. 
We  shall  consider  the  functions  of  these  branches  in  their  relations  to  the  liver,  the 
stomach,  and  the  intestines.  We  have  no  positive  information  with  regard  to  their  action 
upon  the  spleen,  kidneys,  and  suprarenal  capsules. 

Influence  of  the  Pneumogastrics  upon  the  Liver. — There  is  very  little  known  with  regard 
to  the  influence  of  the  pneumogastrics  upon  the  secretion  of  bile ;  and  the  most  important 
experiments  upon  the  innervation  of  the  liver  relate  to  its  glycogenic  function.  We 
shall  have  little  to  say  upon  this  subject,  however,  in  addition  to  what  we  have  already 
stated  in  treating  of  the  liver  as  a  sugar-producing  organ.  The  view  which  we  have 
advanced  with  regard  to  the  glycogenic  function  is  that  the  liver  is  constantly  producing 
sugar  during  life,  which  is  completely  washed  out  by  the  blood  in  its  passage  through 
this  organ,  the  liver  itself  containing  little  or  no  sugar,  under  normal  conditions.  With 
this  view,  we  are  to  look  for  sugar  in  the  blood  in  certain  situations,  and  not  in  the  liver 
itself ;  although,  after  death,  a  change  of  the  glycogenic  matter  in  the  liver  into  sugar 
takes  place  with  great  rapidity,  and  sugar  may  then  be  found  in  its  substance.  Normally, 
sugar  disappears  in  the  lungs  and  is  not  found  in  the  blood  of  the  arterial  system.  The 
presence  of  sugar  in  the  urine  is  abnormal.  If  both  pneumogastrics  be  divided  in  the 
neck,  and  the  animal  be  killed  at  a  period  varying  from  a  few  hours  to  one  or  two  days 
after,  the  liver  contains  no  sugar,  under  the  conditions  in  which  it  is  generally  found, 
viz.,  a  certain  time  after  death.  From  experiments  of  this  kind,  Bernard  concludes  that 
the  glycogenic  function  is  suspended  when  the  nerves  are  divided.  The  experiments, 
however,  made  by  irritating  the  pneumogastrics,  were  more  satisfactory,  as  in  these  he 


PNEUMOGASTRIC,  OB  PAR  VAGUM  NERVE.         663 

looked  for  sugar  in  the  blood  and  in  the  urine  and  did  not  confine  his  examinations  to 
the  substance  of  the  liver. 

After  division  of  the  pneumogastrics  in  the  neck,  if  the  peripheral  ends  be  galvanized, 
there  is  no  effect  upon  the  liver  ;  but,  if  galvanization  be  applied  to  the  central  ends,  the 
glycogenic  function  becomes  exaggerated,  and  sugar  makes  its  appearance  in  the  blood 
and  in  the  urine.  Bernard  has  made  a  number  of  experiments  illustrating  this  point, 
upon  dogs  and  rabbits.  The  galvanic  current  employed  was  generally  feeble,  and  it  was 
continued  for  from  five  to  ten  minutes,  two  or  three  times  in  an  hour.  In  some  instances 
the  irritation  was  kept  up  for  thirty  minutes.  From  these  experiments,  it  is  assumed  that 
the  physiological  production  of  sugar  by  the  liver  is  reflex  and  is  due  to  an  impression 
conveyed  to  the  nerve-centres  through  the  pneumogastrics.  A  very  interesting  and 
adroit  experiment  by  the  same  observer  shows  that  section  of  the  pneumogastrics  be- 
tween the  lungs  and  the  liver  does  not  affect  the  production  of  sugar.  This  delicate 
operation  is  performed  by  making  a  valvular  opening  in  the  chest,  preventing  the  ingress 
of  air  by  suddenly  forcing  the  finger  into  the  wound,  and  then  introducing  a  long,  deli- 
cate hook  with  a  cutting  edge,  and  dividing  the  nerves,  which  may  be  reached  by  the 
finger  in  small  dogs,  and  feel  like  tense  cords  by  the  side  of  the  O3sophagus.  We  have 
already  noted  that  the  inhalation  of  irritating  vapors  and  of  anaesthetics  produces  a 
hypersecretion  of  sugar  by  the  liver. 

The  remarkable  effects  of  irritating  the  floor  of  the  fourth  ventricle,  by  which  we 
can  produce  temporary  diabetes,  have  been  considered  fully  in  connection  with  the  gly- 
cogenic function  of  the  liver.  This  effect  is  not  due  to  a  direct  transmission  of  the  irri- 
tation to  the  liver  through  the  pneumogastrics,  for  the  phenomena  of  hypersecretion  are 
observed  in  animals  upon  which  this  operation  has  been  performed  after  section  of  both 
pneumogastrics  in  the  neck.  It  is  probable,  indeed,  that  the  impression  is  conveyed  to 
the  liver  through  the  sympathetic  system,  for  it  has  been  shown  that  animals  do  not 
become  diabetic  after  irritation  of  the  floor  of  the  fourth  ventricle,  when  the  branches 
of  the  sympathetic  going  to  the  solar  plexus  have  been  divided.  The  operation,  how- 
ever, of  dividing  the  sympathetic  nerves  in  this  situation  is  so  serious,  that  it  may  inter- 
fere with  the  experiment  in  some  other  way  than  by  the  direct  influence  of  the  nerves 
upon  the  liver. 

Influence  of  the  Pneumogastrics  upon  the  Stomach  and  Intestines. — The  number  of 
observations  that  have  been  made  upon  the  influence  of  the  pneumogastric  nerves  on 
digestion  in  the  stomach  is  immense,  and  many  of  the  earlier  experiments  were  quite 
contradictory.  We  do  not  propose,  however,  to  treat  of  this  subject  from  a  purely  his- 
torical point  of  view,  for  the  reason  that,  before  1842  and  1843,  when  gastric  fistulsB 
were  first  established  in  living  animals,  little  was  known  of  the  normal  movements  of  the 
stomach  and  of  the  mechanism  of  the  secretion  of  the  gastric  juice ;  and,  farthermore, 
before  the  observations  of  Bouchardat  and  Sandras,  in  1847,  the  effects  of  section  of  the 
nerves  in  the  neck  upon  the  action  of  the  oesophagus  in  deglutition  were  not  understood. 
If  we  study  the  literature  of  the  subject  anterior  to  1842,  we  find  a  great  deal  of  confu- 
sion, due  to  the  facts  just  stated.  Leaving  out  of  the  question  most  of  the  earlier  ex- 
periments, we  shall  treat  of  the  influence  of  the  pneumogastrics  upon  the  stomach  and 
intestines,  under  the  following  heads  : 

1.  The  effects  of  galvanization  of  the  nerves. 

2.  The  effects  of  section  of  the  nerves  upon  the  movements  of  the  stomach  in  digestion. 

3.  The  effects  of  section  of  the  nerves  upon  the  secretion  of  the  gastric  juice  and  the 
•chemical  processes  of  digestion. 

4.  The  influence  of  the  nerves  upon  the  small  intestine. 

Effects  of  Galvanization. — As  the  result  of  recent  experiments,  the  effects  of  galvan- 
ization of  the  pneumogastrics  upon  the  movements  of  the  stomach  are  unquestionable. 
Longet  has  shown  that  the  stomach  contracts  as  a  consequence  of  irritation  of  the  nerves, 
not  instantly,  but  after  the  lapse  of  five  or  six  seconds.  He  explains  some  of  the  contra- 


664  NERVOUS   SYSTEM. 

dictory  results  obtained  by  other  observers  by  the  fact  that  these  contractions  are  very 
marked  during  stomach- digestion,  while  they  are  wanting  "when  the  stomach  is  entirely 
empty,  retracted  on  itself  and  in  a  measure  in  repose."  According  to  the  same  author, 
irritation  of  the  splanchnic  nerves,  while  it  produces  movements  of  the  intestines,  does 
not  affect  the  stomach.  Judging  from  the  tardy  contraction  of  the  stomach  and  the 
analogy  between  the  action  of  the  pneumogastrics  upon  this  organ  and  the  action  of  the 
sympathetic  nerves  upon  the  non-striated  muscular  tissue,  Longet  assumes  that  the  motor 
action  of  the  pneumogastrics  is  due,  not  to  the  proper  filaments  of  these  nerves,  but  to 
filaments  derived  from  the  sympathetic  system.  "  This  interpretation  removes  the  sin- 
gular physiological  anomaly  that  an  organ,  the  action  of  which  is  entirely  removed  from 
the  control  of  the  will,  should  depend  upon  a  voluntary,  or  cerebro-spinal  nerve."  This 
explanation  of  the  contradictory  results  of  experiments  and  of  the  mechanism  of  the 
action  of  the  pneumogastrics  upon  the  stomach  seems  entirely  satisfactory  and  may  be 
accepted  without  reserve. 

Effects  of  Section  of  the  Pneumogastrics  upon  the  Movements  of  the  Stomach. — If  the 
pneumogastrics  be  divided  in  the  neck  in  a  dog  in  full  digestion,  in  which  a  gastric  fistula 
has  been  established  so  that  the  interior  of  the  organ  can  be  explored,  the  following 
phenomena  are  observed : 

In  the  first  place,  before  division  of  the  nerves,  the  mucous  membrane  of  the  stomach 
is  turgid,  its  reaction  is  intensely  acid,  and,  if  the  finger  be  introduced  through  the  fis- 
tula, it  will  be  firmly  grasped  by  the  contractions  of  the  muscular  walls.  When  the 
pneumogastrics  are  divided,  under  these  conditions,  the  contractions  of  the  muscular  walls 
instantly  cease,  the  mucous  membrane  becomes  pale,  the  secretion  of  gastric  juice  is 
apparently  arrested,  and  the  sensibility  of  the  organ  is  abolished.  Paralysis  of  the 
stomach,  etc.,  had  been  noted,  long  before  the  observations  of  Bernard ;  but  his  experi- 
ments upon  animals  with  a  fistulous  opening  into  the  stomach  are  the  most  striking. 

Notwithstanding  the  apparent  arrest  of  the  movements  of  the  stomach  in  digestion  by 
section  of  the  pneumogastrics,  experiments  carefully  performed  show  that  substances  may 
be  very  slowly  passed  to  the  pylorus,  and  that  the  movements,  although  they  are  greatly 
diminished  in  activity,  are  not  entirely  abolished.  This  fact  has  been  established  beyond 
question  by  the  experiments  of  Schiff,  who  attributes  the  movements  occurring  after  sec- 
tion of  the  nerves  to  local  irritation  of  the  intramuscular  terminal  nervous  filaments. 

Effects  of  Section  of  the  Pneumogastrics  upon  Digestion,  etc. — When  both  nerves 
are  divided,  in  an  animal  in  full  digestion,  the  mucous  membrane  becomes  pale  and 
flaccid,  and  the  secretion  of  gastric  juice  is  apparently  arrested  at  once ;  but,  if  the  ani- 
mal survive  the  operation  for  a  day  or  two,  a  certain  quantity  of  juice  may  be  secreted  as 
the  result  of  local  stimulation,  and  digestion  of  a  very  small  quantity  of  food,  finely  divided 
and  introduced  into  the  stomach  by  a  fistulous  opening,  may  take  place.  A  serious 
difficulty  in  the  digestion  of  large  masses  of  food  after  division  of  the  nerves  is  due  to  the 
cessation  of  the  movements  of  the  stomach.  It  is  stated  that  digestion  may  be  to  a  cer- 
tain extent  reestablished,  under  these  conditions,  by  galvanizing  the  peripheral  extremi- 
ties of  the  divided  nerves. 

There  is  very  little  to  be  said  with  regard  to  the  relations  of  the  pneumogastrics  to 
the  sensations  of  hunger  and  thirst.  It  would  be  very  natural  to  infer,  from  the  distribu- 
tion of  these  nerves  to  the  mucous  membrane  of  the  stomach,  that  they  should  be  involved 
in  these  sensations;  but,  in  treating  of  this  subject  elaborately,  in  connection  with  ali- 
mentation, we  have  shown  that  hunger  and  thirst  really  have  their  origin  in  the  general 
system,  although  the  sensations  are  referred  subjectively  to  the  stomach  and  fauces,  and 
that,  in  all  probability,  the  sensations  persist  after  division  of  both  pneumogastrics. 

With  regard  to  the  influence  of  the  pneumogastrics  upon  absorption  from  the  stomach, 
we  have  also  mentioned  the  fact  that  the  passage  of  poisons  from  the  stomach  into  the 
blood-vessels  may  be  retarded  by  section  of  the  nerves,  but  is  not  prevented. 

Physiologists  have  given  but  little  attention  to  the  influence  of  the  pneumogastrics 


PNEUMOGASTRIC,   OR  PAR   VAGUM  NERVE.  665 

upon  the  intestinal  canal,  for  the  reason  that  the  distribution  of  the  abdominal  branches 
to  the  small  intestine,  notwithstanding  the  researches  of  Kollmann,  in  1860,  does  not 
appear  to  have  been  generally  recognized.  The  right,  or  posterior  abdominal  branch  was 
formerly  supposed  to  be  lost  in  the  semilunar  ganglion  and  the  solar  plexus,  after  sending  a 
few  filaments  to  the  stomach  ;  but,  since  it  has  been  shown  that  this  nerve  is  supplied  to 
the  whole  of  the  small  intestine,  its  physiology,  in  connection  with  intestinal  secretion, 
has  assumed  considerable  importance. 

In  a  series  of  experiments,  by  Prof.  Horatio  C.  Wood,  Jr.,  of  Philadelphia,  the  impor- 
tance of  the  abdominal  branches  of  the  right  nerve  is  fully  illustrated.  These  experi- 
ments show,  in  the  most  conclusive  and  satisfactory  manner,  that  the  pneumogastrics 
influence  intestinal  as  well  as  gastric  secretion.  One  of  the  most  interesting  and  curious 
points  in  connection  with  their  function  is  that,  after  section  of  the  nerves  in  the  cervical 
region,  the  most  powerful  cathartics,  croton-oil,  calomel,  podophyllin,  jalap,  arsenic,  etc., 
fail  to  produce  purgation,  even  in  doses  sufficient  to  cause  death.  The  articles  used  were 
either  given  by  the  mouth,  just  before  dividing  the  nerves,  or  were  injected  under  the 
skin. 

Although  the  observations  of  Dr.  Wood  are  not  entirely  new,  they  are  by  far  the  most 
extended  and  satisfactory,  and  were  made  with  a  knowledge  of  the  fact  of  the  distribu- 
tion of  the  nerves  to  the  small  intestine.  Dr.  Wood  quotes  freely  from  the  experiments 
made  by  Sir  Benjamin  Brodie  and  by  Dr.  John  Reid.  Brodie  failed  to  produce  purging 
in  dogs,  when  both  pneumogastrics  had  been  divided  in  the  neck,  after  the  administration 
of  arsenic  by  the  mouth  and  after  injecting  it  under  the  skin.  Dr.  Reid  made  five  experi- 
ments, and,  in  all  but  one,  it  is  stated  that  diarrhoea  existed  after  division  of  the  nerves.  In 
twenty  experiments  by  Dr.  Wood,  there  was  no  purgation  after  division  of  the  nerves,  in 
one  there  was  free  purgation,  and  in  one  there  was  "  some  slight  muco-fecal  discharge." 
From  these,  Dr.  Wood  concludes  that,  while  section  of  the  cervical  pneumogastrics,  in 
the  great  majority  of  instances,  arrests  gastro-intestinal  secretion  and  prevents  the  action 
of  purgatives  upon  the  intestinal  canal,  a  few  exceptional  cases  occur  in  which  these 
effects  are  not  observed. 

The  facts  just  mentioned  are  exceedingly  interesting  in  connection  with  the  experi- 
ments of  Traube  upon  the  action  of  digitalis  after  section  of  the  pneumogastrics.  It  will 
be  remembered  that,  in  these  experiments,  digitalis  failed  to  diminish  the  number  of  beats 
of  the  heart  when  the  nerves  had  been  divided  in  the  neck,  showing  that  the  separation 
of  the  heart  from  its  connections  with  the  cerebro-spinal  system  removed  the  organ  from 
the  peculiar  and  characteristic  effects  of  the  poison. 

It  would  be  interesting  to  determine  whether  the  pneumogastrics  influence  the  intes- 
tinal secretions  through  their  own  fibres  or  through  filaments  received  from  the  sympa- 
thetic system  ;  but  there  are  no  experimental  facts  sufficiently  definite  to  admit  of  a  posi- 
tive answer  to  this  question.  If  the  action  take  place  through  the  sympathetic  system, 
as  in  the  case  of  the  stomach,  the  filaments  of  communication  join  the  pneumogastrics 
high  up  in  the  neck. 


666  NERVOUS  SYSTEM. 

CHAPTER   XX. 

FUNCTIONS  OF   THE  SPINAL  CORD. 

General  arrangement  of  the  cerebro-spinal  axis— Membranes  of  the  encephalon  and  spinal  cord— Cephalo-rachidian 
fluid— Physiological  anatomy  of  the  spinal  cord— Direction  of  the  fibres  after  they  have  penetrated  the  cord  by  the 
roots  of  the  spinal  nerves— General  properties  of  the  spinal  cord— Action  of  the  spinal  cord  as  a  conductor— Trans- 
mission of  motor  stimulus  in  the  cord— Decussation  of  the  motor  conductors  of  the  cord— Transmission  of  sen- 
sory impressions  in  the  cord— The  white  substance  of  the  posterior  columns  does  not  conduct  sensory  impres- 
sions—Action of  the  gray  matter  as  a  conductor— Probable  function  of  the  cord  in  connection  with  muscular  co- 
ordination—Decussation  of  the  sensory  conductors  of  the  cord— Summary  of  the  action  of  the  cord  as  a  conductor 
—Action  of  the  spinal  cord  as  a  nerve-centre— Movements  in  decapitated  animals— Definition  and  applications 
of  the  term  u  reflex  "— Reflex  action  of  the  spinal  cord— Question  of  sensation  and  volition  in  frogs  after  decapita- 
tion  Character  of  movements  following  irritation  of  the  surface  in  decapitated  animals — Dispersion  of  impres- 
sions in  the  cord— Conditions  essential  to  the  manifestation  of  reflex  phenomena— Exaggeration  of  reflex  excita- 
bility by  decapitation,  poisoning  with  strychnine,  etc.— Eeflex  phenomena  observed  in  the  human  subject. 

UNDER  the  head  of  special  senses,  we  shall  consider,  in  succeeding  chapters,  the  prop- 
erties and  functions  of  the  first  and  second  nerves,  the  portio  mollis  of  the  seventh,  or 
auditory,  and  the  gustatory  nerves,  comprising  a  part  of  the  glosso-pharyngeal  and  a 
small  filament  from  the  facial  (the  chorda  tympani)  going  to  the  lingual  branch  of  the 
fifth.  This  will  include  a  full  account  of  the  organs  of  smell,  taste,  sight,  and  hearing, 
with  a  description  of  the  general  sensory  nerves,  as  far  as  they  are  concerned  in  the  sense 
of  touch.  We  shall  here  begin  our  history  of  the  cerebro-spinal  axis,  which  will  include 
the  physiological  anatomy,  properties,  and  functions  of  the  encephalon  and  the  spinal  cord. 

General  Arrangement  of  tlte  Cerebro-spinal  Axis. — The  nervous  matter  contained  in 
the  cavity  of  the  cranium  and  in  the  spinal  canal,  exclusive  of  the  roots  of  the  cranial 
and  spinal  nerves,  is  known  as  the  cerebro-spinal  axis.  This  portion  of  the  nervous  sys- 
tem is  composed  of  white  and  gray  nervous  matter.  The  fibres  of  the  white  matter  act 
as  conductors.  The  gray  matter  constitutes  a  chain  of  ganglia,  which  act  as  nerve- 
centres,  receiving  impressions  and  generating  the  so-called  nerve-force.  The  gray  matter 
of  the  spinal  cord  also  serves,  to  a  greater  or  less  extent,  as  a  conductor. 

The  cerebro-spinal  axis  is  enveloped  in  membranes,  which  are  for  its  protection  and 
for  the  support  of  its  nutrient  vessels.  It  is  surrounded,  to  a  certain  extent,  with  liquid, 
and  it  presents  cavities,  as  the  ventricles  of  the  brain  and  the  central  canal  of  the  chord, 
which  contain  liquid.  The  gray  matter  is  distinct  from  the  white,  even  to  the  naked 
eye.  In  the  spinal  cord,  the  white  substance  is  external  and  the  gray  is  internal.  The 
surface  of  the  brain  presents  an  external  layer  of  gray  matter,  the  white  substance  being 
internal.  In  the  white  substance  of  the  brain,  also,  we  find  collections  of  gray  matter. 
As  we  should  expect,  from  the  similarity  in  function  between  the  white  matter  and  the 
nerves,  this  portion  of  the  cebro-spinal  axis  is  composed  largely  of  fibres.  The  gray 
substance  is  composed  chiefly  of  cells. 

The  encephalon  is  contained  in  the  cranial  cavity.  In  the  human  subject  and  in 
many  of  the  higher  animals,  its  surface  is  marked  by  numerous  convolutions,  by  which 
the  extent  of  its  gray  substance  is  very  much  increased.  The  cerebrum,  the  cerebellum, 
and  all  of  the  encephalic  ganglia  are  connected  with  the  white  substance  of  the  encepha- 
lon and  with  the  spinal  cord.  With  the  encephalon  and  the  cord,  all  of  the  cerebro- 
spinal  nerves  are  connected.  The  cerebro-spinal  axis  acts  as  a  conductor,  and  its  diifer- 
ent  collections  of  gray  matter,  or  ganglia,  receive  impressions  conveyed  by  the  sensory 
conducting  fibres,  and  generate  nerve-force,  which  is  transmitted  to  the  proper  organs 
by  the  motor  fibres. 

Membranes  of  the  EmepJialon  and  Spinal  Cord.— The  membranes  of  the  brain  and 
spinal  cord  are,  the  dura  mater,  the  arachnoid,  and  the  pia  mater. 


ARRANGEMENT  OF  THE   CEREBRO-SPINAL  AXIS.  667 

The  dura  mater  of  the  encephalon  is  a  dense,  fibrous  membrane,  in  two  layers,  com- 
posed chiefly  of  inelastic  tissue,  which  lines  the  cranial  cavity  and  is  adherent  to  the 
bones.  In  certain  situations,  its  two  layers  become  separated  and  form  what  are  known 
as  the  venous  sinuses.  The  dura  mater  also  sends  off  folds  or  processes  of  its  internal 
layer.  One  of  these  passes  into  the  longitudinal  fissure  and  is  called  the  falx  cerebri ; 
another  lies  between  the  cerebrum  and  the  cerebellum  and  is  called  the  tentorium ; 
another  is  situated  between  the  lateral  halves  of  the  cerebellum  and  is  called  the  falx 
cerebelli.  The  dura  mater  is  closely  attached  to  the  bone  at  the  border  of  the  foramen 
magnum.  From  this  point  it  passes  into  the  spinal  canal  and  forms  a  loose  covering  for 
the  cord.  In  the  spinal  canal,  this  membrane  is  not  adherent  to  the  bones,  which  have, 
like  most  other  bones  in  the  body,  a  special  periosteum.  At  the  foramina  of  exit  of  the 
cranial  and  the  spinal  nerves,  the  dura  mater  sends  out  processes  which  envelop  the 
nerves,  with  the  fibrous  sheaths  of  which  they  soon  become  continuous. 

The  arachnoid  is  an  excessively  delicate  serous  membrane,  in  two  layers,  the  surfaces 
of  which  are  nearly  in  contact.  The  external  layer  lines  the  internal  surface  of  the  dura 
mater.  Like  the  other  serous  membranes,  the  arachnoid  is  covered  with  a  layer  of  tes- 
selated  epithelium.  There  is  a  small  amount  of  liquid  between  the  two  layers  of  the 
arachnoid  ;  but  by  far  the  greatest  quantity  of  liquid  surrounding  the  cerebro-spinal 
axis  lies  beneath  both  layers,  in  what  is  called  the  subaraclmoid  space.  This  is  called 
the  cerebro-spinal,  or  cephalo-rachidian  fluid.  The  arachnoid  does  not  follow  the  con- 
volutions and  fissures  of  the  encephalon  or  the  sulci  of  the  cord,  but  it  simply  covers  their 
surfaces.  Magendie  pointed  out  a  longitudinal,  incomplete,  cribriform,  fibrous  septum  in 
the  cord,  passing  from  the  inner  layer  of  the  arachnoid  to  the  pia  mater.  A  similar 
arrangement  is  found  in  certain  situations  at  the  base  of  the  skull. 

The  pia  mater  of  the  encephalon  is  a  delicate,  fibrous  structure,  exceedingly  vascular, 
seeming  to  present,  indeed,  only  a  skeleton  net-work  of  fibres  for  the  support  of  the  ves 
sels  going  to  the  nervous  substance.  This  membrane  covers  the  surface  of  the  encephalon 
immediately,  follows  the  sulci  and  fissures,  and  is  prolonged  into  the  ventricles,  where  it 
forms  the  choroid  plexus  and  the  velum  interpositum.  From  its  internal  surface,  small 
vessels  are  given  off  which  pass  into  the  nervous  substance. 

The  pia  mater  of  the  encephalon  is  continuous  with  the  corresponding  membrane  of 
the  cord ;  but,  in  the  spinal  canal,  it  is  thicker,  stronger,  more  closely  adherent  to  the 
subjacent  parts,  and  its  blood-vessels  are  by  no  means  so  numerous.  In  this  situation, 
many  of  the  fibres  are  arranged  in  longitudinal  bands.  This  membrane  lines  the  anterior 
sulcus  and  a  portion  of  the  posterior  sulcus  of  the  cord.  It  is  sometimes  spoken  of  as  the 
neurilemma  of  the  cord.  At  the  foramina  of  exit  of  the  cranial  and  the  spinal  nerves, 
the  fibrous  structure  of  the  pia  mater  becomes  continuous  with  the  nerve-sheaths. 

Between  the  anterior  and  posterior  roots  of  the  spinal  nerves,  on  either  side  of  the 
cord,  is  a  narrow,  ligamentous  band,  the  ligamentum  denticulatum,  which  assists  in  hold- 
ing the  cord  in  place.  This  extends  from  the  foramen  magnum  to  the  terminal  filament 
of  the  cord,  and  is  attached,  internally,  to  the  pia  mater,  and  externally,  to  the  dura 
mater. 

It  is  not  necessary  to  enter  into  a  detailed  description  of  the  arrangement  of  the  blood- 
vessels, nerves,  and  lymphatics  of  the  membranes  of  the  brain  and  spinal  cord,  or  of  the 
vascular  arrangement  in  the  substance  of  the  cerebro-spinal  axis,  as  these  points  are 
chiefly  of  anatomical  interest.  The  circulation  in  these  parts  presents  certain  pecu- 
liarities. In  the  first  place,  the  encephalon  being  contained  in  an  air-tight  case  of  inva- 
riable capacity,  it  has  been  a  question  whether  or  not  the  vessels  be  capable  of  contrac- 
tion and  dilatation,  or  whether  the  quantity  of  blood  in  the  brain  be  subject  to  modifi- 
cations in  health  or  disease.  These  questions  may  certainly  be  answered  in  the  affirmative. 
In  infancy  and  in  the  adult,  when  an  opening  has  been  made  in  the  skull,  the  volume  of 
the  encephalon  is  evidently  increased  during  expiration  and  is  diminished  in  inspiration. 
Under  normal  conditions,  in  the  adult,  it  is  probable  that  the  amount  of  blood  is  increased 


66g  NERVOUS   SYSTEM. 

in  expiration  and  diminished  in  inspiration  ;  but  it  is  not  probable  that  the  cerebro-spinal 
axis  undergoes  any  considerable  movements.  The  important  peculiarities  in  the  cerebral 
circulation"  have  already  been  fully  considered  in  connection  with  the  circulation.  It 
has  been  shown  that  the  encephalic  capillaries  are  surrounded  or  nearly  surrounded  by 
canals  (perivascular  canal-system),  which  exceed  the  blood-vessels  in  diameter  by  from 
T1^FT  to  ¥|-o  °f  an  incn?  an^  are  connected  with  lymphatic  trunks  or  reservoirs  situated 
under  the  pia  mater.  The  system  of  canals  may,  by  variations  in  its  contents,  serve  to 
equalize  the  amount  of  liquid  in  the  brain  as  the  blood-vessels  are  distended  or  contracted. 

Cephalo-rachidian  Fluid. — The  greatest  part  of  the  fluid  in  the  cranium  and  in  the 
spinal  canal  is  contained  in  what  is  known  as  the  subarachnoid  space  ;  that  is,  between 
the  inner  layer  of  the  arachnoid  and  the  pia  mater,  and  not  between  the  two  layers  of 
the  arachnoid.  The  ventricles  of  the  encephalon  are  in  communication  with  the  central 
canal  of  the  cord,  and  are  also  connected  with  the  general  subarachnoid  space,  by  a  nar- 
row, triangular  orifice,  situated  at  the  inferior  angle  of  the  fourth  ventricle.  By  this 
arrangement,  the  liquid  in  the  ventricles  of  the  encephalon  and  in  the  central  canal  of  the 
cord  communicates  with  the  liquid  surrounding  the  cerebro-spinal  axis,  and  the  pressure 
upon  these  delicate  parts  is  equalized. 

As  far  as  we  know,  the  function  of  the  cephalo-rachidian  fluid  is  simply  mechanical, 
and  its  properties  and  composition  have  no  very  definite  physiological  significance.  Its 
quantity  was  estimated  by  Magendie,  in  the  human  subject,  at  about  two  fluidounces ; 
but  this  was  the  smallest  amount  obtained  by  placing  the  subject  upright,  making  an 
opening  in  the  lumbar  region  and  a  counter-opening  in  the  head  to  admit  the  pressure 
of  the  atmosphere.  The  exact  quantity  in  the  living  subject  could  hardly  be  estimated  in 
this  way;  and  it  is  difficult,  indeed,  to  see  how  any  thing  more  than  a  roughly  approx- 
imative idea  could  be  obtained.  The  quantity  obtained  by  Magendie  probably  does  not 
represent  the  entire  amount  of  liquid  contained  in  the  ventricles  and  in  the  subarachnoid 
space,  but  it  is  the  most  definite  estimate  that  has  been  given. 

The  discharge  of  a  certain  quantity  of  the  cephalo-rachidian  fluid  does  not  produce 
any  marked  derangement  in  the  action  of  the  nervous  system.  When  the  liquid  is 
allowed  to  flow  spontaneously  through  a  small  trocar  introduced  without  division  of  the 
muscles  of  the  neck,  there  follows  no  serious  nervous  disturbance ;  but,  when  the  liquid 
is  drawn  out  forcibly  with  a  syringe,  the  animal  first  becomes  enfeebled  and  afterward 
seems  affected  with  general  paralysis.  These  phenomena  are  probably  due,  not  so  much 
to  removal  of  the  fluid,  as  to  congestion  of  blood-vessels  and  even  eifusion  of  blood, 
which  follow  sudden  diminution  in  the  pressure.  Sudden  increase  in  the  quantity  of 
liquid  surrounding  the  cerebro-spinal  axis  produces  coma,  probably  from  compression  of 
the  centres.  This  fact  was  demonstrated  by  Magendie,  by  injecting  water  in  animals, 
and  also  by  compressing  the  tumor,  in  cases  of  spina  bifida  in  the  human  subject,  by 
which  the  fluid  was  pressed  back  into  the  spinal  canal.  In  the  cases  of  spina  bifida,  the 
subject,  during  the  compression,  fell  into  coma,  which  was  instantly  relieved  by  remov- 
ing the  pressure.  The  cephalo-rachidian  fluid  is  speedily  reproduced  after  its  evacuation. 
In  all  probability  it  is  secreted  by  the  pia  mater. 

The  general  properties  and  composition  of  the  fluid  under  consideration  are,  in  brief, 
the  following:  It  is  perfectly  transparent  and  colorless,  free  from  viscidity,  of  a  distinctly 
saline  taste,  alkaline  reaction,  and  it  resists  putrefaction  for  a  long  time.  It  is  not  affected 
by  heat  or  acids.  As  we  should  expect  from  its  low  specific  gravity  and  purely  mechani- 
cal function,  it  contains  a  large  proportion  of  water  (981  to  985  parts  per  thousand).  It 
contains  a  considerable  quantity  of  chloride  of  sodium,  a  trace  of  chloride  of  potassium, 
sulphates,  carbonates,  and  alkaline  and  earthy  phosphates.  In  addition,  it  contains 
traces  of  urea,  glucose,  lactate  of  soda,  fatty  matter,  cholesterine,  and  albumen. 

As  a  summary  of  the  function  of  the  cephalo-rachidian  fluid,  it  may  be  stated,  in  gen- 
eral terms,  that  it  serves  to  protect  the  cerebro-spinal  axis,  chiefly  by  equalization  of  the 


,         PHYSIOLOGICAL   ANATOMY   OF  THE   SPINAL   CORD.  669 

pressure  in  the  varying  condition  of  the  blood-vessels,  accurately  filling  the  space  be- 
tween the  centres  and  the  bony  cavities  in  which  they  are  contained.  That  the  blood- 
vessels of  the  cerebro-spinal  axis  are  subject  to  variations  in  tension,  is  readily  shown  by 
introducing  a  canula  into  the  subarachnoid  space,  when  the  jet  of  fluid  discharged  will 
be  increased  with  every  violent  muscular  effort.  The  pressure  of  the  fluid,  in  this  in- 
stance, could  only  be  affected  through  the  blood-vessels. 

Physiological  Anatomy  of  the  Spinal  Cord. 

The  spinal  cord,  with  its  membranes,  the  roots  of  the  spinal  nerves,  and  the  sur- 
rounding liquid,  occupies  the  spinal  canal  and  is  continuous  with  the  encephalon.  Its 
length  is  from  fifteen  to  eighteen  inches,  and  its  weight  is  about  an  ounce  and  a  half. 
Its  form  is  cylindrical,  being  slightly  flattened  in  certain  portions.  It  extends  from  the 
foramen  magnum  to  the  first  lumbar  vertebra.  It  presents,  at  the  origin  of  the  brachial 
nerves,  an  elongated  enlargement,  and  a  corresponding  enlargement  at  the  origin  of  the 
nerves  which  supply  the  lower  extremities.  It  terminates  below  in  a  slender,  gray  fila- 
ment, called  the  filum  termiuale.  The  sacral  and  coccygeal  nerves,  after  their  origin 
from  the  lower  portion  of  the  cord,  pass  downward  to  emerge  by  the  sacral  foramina, 
and  they  form  what  is  known  as  the  cauda  equina. 

The  substance  of  the  cord  is  formed  of  white  and  gray  matter,  the  white  matter 
being  external.  The  proportion  of  white  matter  to  the  gray  is  greatest  in  the  cervical 
region.  This  fact  is  important  in  studying  the  course  of  the  fibres  and  in  view  of  the 
functions  of  the  cord  as  a  conductor.  The  inferior,  pointed  termination  of  the  cord  con- 
sists entirely  of  gray  matter. 

The  cord  is  marked  by  an  anterior  and  a  posterior  medium  fissure,  and  by  imperfect 
and  somewhat  indistinct  anterior  and  posterior  lateral  grooves,  from  which  latter  arise  the 
anterior  and  the  posterior  roots  of  the  spinal  nerves.  The  posterior  lateral  groove  is 
tolerably  well  marked,  but  there  is  no  distinct  line  at  the  origin  of  the  anterior  roots. 
The  anterior  median  fissure,  or  sulcus,  is  perfectly  distinct.  It  penetrates  the  anterior 
portion  of  the  cord  in  the  median  line  for  about  one-third  of  its  thickness  and  receives  a 
highly  vascular  fold  of  the  pia  mater.  It  extends  to  the  anterior  white  commissure.  The 
posterior  fissure  is  not  so  distinct  as  the  anterior,  and  it  is  not  lined  throughout  by  a  fold 
of  the  pia  mater,  but  is  filled  with  connective  tissue  and  blood-vessels,  which  form  a  sep- 
tum posteriorly,  between  the  lateral  halves  of  the  cord.  The  posterior  median  fissure,  so 
called,  extends  nearly  to  the  centre  of  the  cord,  as  far  as  the  posterior  gray  commissure. 

Physiologically  and  anatomically,  the  cord  is  divided  into  two  lateral  halves ;  but  the 
division  of  each  half  into  columns  is  not  so  distinct.  Anatomists  generally  regard  a  half 
of  the  cord  as  consisting  of  three  columns :  The  anterior  column  is  bounded  by  the 
anterior  fissure  and  the  origin  of  the  anterior  roots  of  the  spinal  nerves ;  the  lateral  col- 
umn is  included  between  the  anterior  and  the  posterior  roots  of  the  nerves ;  the  poste- 
rior column  is  bounded  by  the  line  of  origin  of  the  posterior  roots  and  by  the  posterior 
fissure.  Some  anatomists  include  the  lateral  with  the  anterior  column,  under  the  name  of 
the  antero-lateral  column,  taking  in  about  two-thirds  of  the  cord.  Next  the  posterior 
median  fissure,  is  a  narrow  band,  marked  by  a  faint  line,  which  is  sometimes  called  the 
posterior  median  column. 

The  arrangement  of  the  white  and  the  gray  matter  in  the  cord  is  seen  in  a  transverse 
section.  The  gray  substance  is  in  the  form  of  a  letter  H,  presenting  two  anterior  and 
two  posterior  cornua  connected  by  what  is  called  the  gray  commissure.  The  anterior 
cornua  are  the  shorter  and  broader,  and  they  do  not  reach  to  the  surface  of  the  cord. 
The  posterior  cornua  are  larger  and  narrow,  and  they  extend  nearly  to  the  surface,  at 
the  point  of  origin  of  the  posterior  roots  of  the  spinal  nerves.  In  the  centre  of  the  gray 
commissure,  is  a  very  narrow  canal,  lined  by  cells  of  ciliated  epithelium,  called  the 
central  canal.  This  is  in  communication  above  with  the  fourth  ventricle,  and  it  extends 


670  NERVOUS   SYSTEM. 

below  to  the  filum  terminate.  That  portion  of  the  gray  commissure  situated  in  front 
of  this  canal  is  sometimes  called  the  anterior  gray  commissure,  the  posterior  portion 
being  known  as  the  posterior  gray  commissure.  The  central  canal  is  immediately  sur- 
rounded by  connective  tissue.  In  front  of  the  gray  commissure,  is  a  mass  of  white 
substance  known  as  the  anterior  white  commissure. 


13 


12 


u  13.  n 

FIG.  222.—  Transverse  section  of  the  spinal  cord  at  the  origin  of  the  ffth  pair  of  cervical  nerves.    (Stilling.) 

In  this  figure,  the  white  substance  of  tne  cord  is  represented  in  black,  to  show  more  clearly  the  limits  of  the  grny 
matter:  1,  1,  antero-lateral  columns;  2,  2,  posterior  white  columns;  8,  anterior  median  fissure;  4,  posterior 
median  fissure;  5,  white  commissure  ;  6,  gray  commissure:  7,  central  canal;  8,  9,  anterior  cornua  of  gray  mat- 
ter; 10,  10,  group  of  large  multipolar  cells  :  11,  11, 11,  anterior  roots  of  the  spinal  nerves;  12,  posterior  cornua 
of  gray  matter ;  13,  posterior  roots  of  the  spinal  nerves. 

The  proportion  of  the  white  to  the  gray  substance  is  variable  in  different  portions  of 
the  cord.  In  the  cervical  region,  the  white  substance  is  most  abundant,  and,  in  fact,  it 
progressively  increases  in  quantity  from  below  upward  throughout  the  whole  extent  of 
the  cord.  In  the  dorsal  region,  the  gray  matter  is  least  abundant,  and  it  exists  in  great- 
est quantity  in  the  lumbar  enlargement. 

The  white  substance  of  the  cord  is  composed  of  nerve-fibres,  connective-tissue  ele- 
ments, and  blood-vessels,  the  latter  arranged  in  a  very  wide  and  delicate  plexus.  The 
nerve-fibres  are  variable  in  their  size  and  are  composed  of  the  axis-cylinder  surrounded 
by  the  medullary  substance,  without,  however,  the  investing  membrane.  We  shall  speak 
farther  on  of  the  direction  of  the  fibres  in  the  cord. 

The  anterior  cornua  of  gray  matter  contain  blood-vessels,  connective-tissue  elements, 
very  fine  nerve-fibres,  and  large  multipolar  nerve-cells,  which  are  sometimes  called  motor 
cells.  The  posterior  cornua  are  composed  of  the  same  elements,  the  cells  being  much 
smaller,  and  the  fibres  exceedingly  small,  presenting  very  fine  plexuses.  The  cells  in  this 
situation  are  sometimes  called  sensory  cells.  Near  the  posterior  portion  of  each  poste- 
rior cornu,  is  an  enlargement,  of  a  gelatiniform  appearance,  containing  numerous  small 
cells  and  fibres,  called  the  substantia  gelatinosa. 

The  foregoing  description  of  the  different  structures  and  parts  of  the  cord  is  neces- 
sary to  a  comprehension  of  the  direction  of  the  fibres  in  the  spinal  axis  and  their  con- 
nections with  the  nerve-cells,  which  is  the  anatomical  basis  of  our  knowledge  of  its 
physiology.  The  connections  between  the  cells  and  the  fibres  have  already  been  de- 
scribed in  the  chapter  upon  the  general  structure  of  the  nervous  system.  The  multipolar 
nerve-cells  are  supposed  to  present  certain  prolongations  which  do  not  branch  and  are 
directly  connected  with  the  medullated  nerve-fibres.  These  are  called  nerve-prolonga- 


PHYSIOLOGICAL  ANATOMY   OF  THE   SPINAL  CORD. 


671 


tions.  In  addition,  fine,  branching  poles  are  described  under  the  name  of  protoplasmic 
prolongations. 

The  direction  of  the  fibres  in  the  cord  is  one  of  the  most  difficult  and  complicated 
problems  in  physiological  anatomy  ;  and,  especially  as  regards  the  posterior  roots  of  the 
nerves,  it  is  one  which  cannot  as  yet  be  elucidated  by  purely  anatomical  investigations, 
but  requires  the  aid  of  experimental  and  pathological  observations.  In  order  to  under- 
stand fully  the  importance  of  this  question,  it  is  necessary  to  bear  in  mind  the  following 
physiological  facts,  which  it  is  desirable,  if  possible,  to  explain  by  the  anatomical  rela- 
tions and  connections  of  the  fibres  and  cells : 

1.  The  cord  serves  as  a  conductor  of  impressions  to  the  brain,  conveyed  to  it  through 
the  posterior  roots,  and  of  stimulus  generated  by  the  brain  and  passing  from  the  cord 
by  the  anterior  roots  of  the  spinal  nerves.  This  action  is  crossed,  the  decussation  taking 
place  mainly  at  the  medulla  oblongata,  for  the  anterior  portions,  and  throughout  the 
whole  extent  of  the  cord,  for  the  posterior  portions. 


ITio.  223.—  Transverse  section  of  the  spinal  cord  of  a  cMld  six  months  old,  at  the  middle  of  the  lumbar  enlarge- 
ment, treated  with  potassio-chloride  of  gold  and  nitrate  of  uranium;  magnified  20  diameters.  By 
means  of  t/iese  reagents,  the  direction  of  'the  fibres  in  the  gray  substance  is  rendered  unusually  distinct. 
(Gerlach. ) 

a,  anterior  columns;  &,  posterior  columns ;  c,  lateral  columns ;  d,  anterior  roots ;  e,  posterior  roots ;  /.  anterior  white 
commissure,  in  communication  with  the  fasciculi  of  the  anterior  cornua  and  the  anterior  columns ;  g,  central 
canal  with  its  epithelium ;  h,  surrounding  connective  substance  of  the  central  canal ;  *,  transverse  fasciculi  of 
the  gray  commissure  in  front  of  the  central  canal ;  k,  transverse  fasciculi  of  the  gray  commissure  behind  the 
central  canal;  I,  transverse  section  of  the  two  central  veins;  m.  anterior  cornua ;  n,  great,  lateral  cellular  layer 
of  the  anterior  cornua;  o.  lesser,  anterior  cellular  layer;  p,  smallest,  median  cellular  layer;  q,  posterior  cornua; 
r,  ascending  fasciculi  in  the  posterior  cornua ;  s,  substantia  gelatinosa. 


2.  Independently  of  its  action  as  a  conductor,  the  cord,  disconnected  from  the  rest  of 
the  cerebro-spinal  axis,  acts  as  a  nerve-centre,  by  virtue  of  its  gray  matter  and  the  fibres 
connected  with  the  cellular  elements  of  this  substance. 

Bearing  in  mind  these  points,  which  are  matters  of  positive  demonstration,  we  are 
prepared  to  study  the  anatomical  relations  of  the  fibres  and  cells.  In  this,  we  shall  con- 


672 


NERVOUS   SYSTEM. 


tent  ourselves  with  the  following  very  recent  description,  quoted  in  full  from  Gerlach, 
which  embodies  about  all  of  our  positive  knowledge  upon  the  subject,  presented  in  the 
clearest  manner  possible.  This  extract,  the  translation  of  which  is  almost  literal,  should 
be  carefully  studied  by  those  who  desire  to  learn  what  is  known  at  the  present  clay 
with  regard  to  the  physiological  anatomy  of  the  cord.  As  a  preparation  for  this  study, 
it  would  be  well  to  closely  examine  Fig.  223,  which  gives  a  general  view  of  the  different 
parts  of  the  cord,  shown  in  a  transverse  section  : 

"  With  the  present  methods  and  means  of  investigation  at  our  command,  we  can 
scarcely  give  an  exact,  detailed  description  of  the  course  of  the  fibres  in  the  spinal  cord, 
the  groundwork  of  the  physiology  of  this  organ.  Investigations  up  to  this  time  afford 
at  least  the  outlines  of  a  sketch  which,  as  regards  the  course  of  the  fasciculi  of  the  ante- 
rior roots,  has  a  tolerably  definite  basis  ;  and,  on  the  other  hand,  with  regard  to  the  fas- 
ciculi going  to  the  spinal  cord  through  the  posterior  roots,  is  quite  incomplete  and  un- 
certain. 

"  The  fasciculi  of  the  anterior  roots,  after  their  entrance  into  the  cord,  pass  diagonally 
through  the  white  substance,  and,  as  such,  are  not  at  all  concerned  in  its  formation.  On 
the  contrary,  they  pass  immediately  to  the  gray  substance  of  the  anterior  cornua,  and,  by 
their  prolongations,  are  in  direct  connection  with  the  nerve-cells  in  this  situation,  which, 
accordingly,  are  to  be  regarded  as  the  elements  of  origin  of  the  anterior  roots  in  the 
cord.  The  protoplasmic  processes  of  these  nerve-cells  form  parts  of  the  fine  plexuses  of 
nerve-fibres  in  the  gray  substance,  from  which  larger  nerve-fibres  take  their  origin. 
These,  extending  in  two  directions,  leave  the  gray  substance,  to  pass  up  in  the  white  sub- 
stance to  the  brain.  In  consequence  of  the  entrance  of  additional  nerve-fibres,  the 
white  substance  is  necessarily  increased  in  quantity  in  the  cord  from  below  upward. 
With  regard  to  the  course  of  the  fasciculi  which  pass  out  of  the  gray  substance  of  the 
anterior  cornua,  these  are  to  be  divided  into  median  and  lateral.  The  median  fasciculi 
pass  immediately  into  the  anterior  white  commissure,  where  they  decussate  with  corre- 
sponding fasciculi  from  the  opposite  side,  to  pass  upward  again  in  the  anterior  column  of 
the  other  half  of  the  cord.  The  lateral  fasciculi  go  to  the  lateral  columns  of  the  same 
side,  in  which  they  pass  to  the  brain,  having  first  undergone  decussation  in  the  anterior 
pyramids  of  the  medulla  oblongata. 

"  The  posterior  nerve-roots  enter  horizontally,  running  in  the  white  substance  of  the 
spinal  cord,  in  a  direction  from  without  inward  toward  the  median  line,  and  here  divide 
into  two  portions.  The  lateral  portion,  the  smaller,  retains  the  horizontal  direction  and 
passes  through  the  substantia  gelatinosa,  dividing  into  fine  and  the  finest  bundles,  in  the 
manner  mentioned  above,  to  take  part  in  the  formation  of  the  vertical  bundle  of  fibres, 
which  lies  immediately  in  front.  Here  the  fibres  pass  onward,  a  portion  of  them  ascend- 
ing and  a  portion  descending.  The  fibres  of  the  lateral  portion  of  the  posterior  roots  do 
not  remain  very  long  in  the  vertical  bundle,  but  curve  forward  in  a  horizontal  plane, 
and  in  this  way  reach  the  portion  of  the  posterior  cornua  containing  a  fine  plexus  of 
nerve-fibres. 

"  The  median  (larger)  portion  of  the  posterior  root-fibres  passes  to  that  portion  of  the 
posterior  column  which  bounds  the  substantia  gelatinosa  internally  and  posteriorly ;  and 
curving,  takes  here  a  vertical  course  to  pass  into  the  posterior  columns,  extending  chiefly 
upward,  but  perhaps  downward  as  well.  The  median  posterior  root-fibres  then  under- 
go another  deflection,  by  which  they  again  take  a  horizontal  direction,  and  pass  to  the 
gray  substance  of  the  posterior  cornua,  in  part  through  the  median  portion  and  in  part 
by  the  inner  border  of  the  substantia  gelatinosa.  With  regard  to  the  farther  course  of 
the  posterior  root-fibres,  it  is  impossible  to  present  positive  explanations,  for  the  reason 
that  the  present  methods  of  investigation  do  not  afford  any  means  of  distinguishing  the 
posterior  fibres  from  the  nerve-tubes  in  the  vertical  fasciculi  of  the  posterior  cornua,  or 
those  passing  from  the  gray  substance  into  the  posterior  columns  to  ascend  to  the  brain. 
The  numerous  divisions  which  the  posterior  root-fibres  penetrating  the  posterior  cornua 


GENERAL  PROPERTIES   OF  THE   SPINAL  CORD.  673 

immediately  undergo  indicate,  however,  that  a  portion  of  them  is  lost  directly  in  the  fine 
nerve-plexus  of  the  gray  substance.  But  at  the  same  time  there  are  numerous  fibres 
which  extend  forward,  and  others  which  take  a  more  or  less  wavy  course  toward  the 
median  line.  The  first,  perhaps,  can  be  regarded  as  posterior  root-fibres,  which  pass  in 
a  forward  direction  in  the  nervous  plexus ;  the  latter,  on  the  other  hand,  belong  to  the 
commissural  fibres,  which  cross  the  median  line  in  the  gray  substance  in  front  of  and 
behind  the  central  canal.  In  my  opinion,  the  fibres  which  penetrate  the  posterior  com- 
missure are  not  to  be  regarded  as  belonging  directly  to  the  posterior  roots,  but  are  to  be 
considered  as  fibres  which  pass  backward  to  go  either  to  the  vertical  fasciculi  of  the  gray 
substance  or  to  pass  to  the  brain  in  the  posterior  columns.  If  this  idea  be  correct,  and 
it  is  sustained  by  analogous  conditions  in  the  anterior  cornua,  the  following  view  may  be 
given  of  the  course  of  the  fibres  of  the  posterior  roots  which  penetrate  the  gray  sub- 
stance :  '  A  portion  of  the  posterior  root-fibres,  immediately  after  their  entrance  into 
that  portion  of  the  gray  substance  which  contains  a  nerve-plexus,  is  lost  in  this  plexus ; 
another  portion  extends  farther  forward,  and,  in  proportion  as  the  fibres  pass  forward, 
they  likewise  take  part,  by  constant  divisions,  in  the  formation  of  the  nerve-plexus.  This 
plexus,  in  which  larger  and  smaller  nerve-cells  are  interspersed  as  it  were  as  knotted 
points  (Knotenpunkte),  is  in  direct  connection  with  the  plexus  of  the  anterior  cornua. 
From  these  cells  nerve-fibres  arise,  which  cross  the  median  line  in  the  gray  commissure 
in  front  of  and  behind  the  central  canal,  then  curve  backward  to  pass  up  to  the  brain,  in 
part  in  the  vertical  fasciculi  of  the  posterior  cornua,  in  part  in  the  posterior  columns, 
between  both  of  which  numerous  connections  may  exist  which  are  as  yet  inextricable.' 
This  view  involves  a  complete  decussation  in  the  spinal  cord,  through  the  fibrous  elements 
of  the  posterior  roots  passing  into  this  part.  Whether  this  be  in  reality  a  complete  or  a 
partial  decussation  in  this  situation,  a  part  of  the  fibres  arising  from  the  nerve-plexus 
passing  simply  backward  without  crossing  the  median  line,  cannot  be  determined  by 
definite  anatomical  investigations ;  but  pathological  researches,  as  well  as  the  experi- 
mental results  of  that  most  competent  observer,  Brown-Sequard,  are  decidedly  in  favor 
of  a  complete  decussation. 

"  Finally,  it  must  be  admitted  that  two  points  especially  are  evident : 
"1.  In  the  direction  of  the  nerve-fibres  which  enter  through  the  posterior  roots,  the 
gray  substance  has  more  numerous  connections  than  in  those  which  pass  to  the  spinal 
cord  through  the  anterior  roots. 

"  2.  The  morphological  distinction  determinate  between  the  anterior  and  the  pos- 
terior roots  is,  that  the  former  take  their  origin  directly  from  the  nerve-cells  by  means 
of  the  nerve-prolongations,  while,  in  the  latter,  it  is  only  indirect  through  the  nerve-plexus 
with  the  protoplasmic  prolongations,  and  in  this  wise  they  are  in  communication  with 
the  nerve-cells." 

General  Properties  of  the  Spinal  Cord. 

In  treating  of  the  functions  of  the  spinal  cord,  we  shall  consider,  first,  its  general 
properties,  as  shown  by  direct  stimulation  of  its  substance  in  different  situations ;  next, 
its  functions  as  a  conductor ;  and,  finally,  its  action  as  a  nerve-centre. 

The  first  indication  that  the  different  columns  of  the  cord  were  possessed  of  different 
properties  is  to  be  found  in  the  experiments  of  Magendie.  This  observer,  however,  was 
somewhat  indefinite  in  his  conclusions,  particularly  with  regard  to  the  anterior  columns; 
but  he  stated  distinctly  that  the  posterior  columns  are  sensitive :  "  If  we  lay  bare  the 
cord  in  any  portion  of  its  extent,  and  if  we  touch,  or  prick  slightly  posteriorly,  the  two 
fasciculi  situated  between  the  posterior  roots,  the  animal  gives  signs  of  exquisite  sensi- 
bility ;  if,  on  the  other  hand,  we  make  the  same  trials  upon  the  anterior  portion,  the 
evidences  of  sensibility  are  scarcely  apparent."  Since  this  time,  numerous  observers 
have  experimented  upon  the  different  columns,  both  on  the  surface  and  in  the  deep  por- 
tions of  the  cord,  with  varying  results.  These  observations  we  do  not  propose  to  discuss 
43 


NERVOUS  SYSTEM. 

fully  in  detail,  but  shall  refer  simply  to  certain  of  them,  made  within  a  few  years  with 
the  advantage  of  a  knowledge  of  the  reflex  phenomena  following  irritation  of  the  cord, 
which  must  always  be  taken  into  consideration  in  such  experiments. 

In  1861,  Chauveau,  as  the  result  of  numerous  experiments  performed  upon  horses, 
cows,  sheep,  goats,  rabbits,  pigs,  dogs,  and  cats,  stated  that  the  antero-lateral  columns 
of  the  cord  were  inexcitable,  both  on  the  surface  and  in  the  deep  portions.  The  facts 
upon  which  this  assertion  was  based  were,  that  direct  stimulation  of  these  portions  of  the 
cord  in  living  animals,  whether  by  mechanical  means  or  by  feeble  galvanic  shocks,  pro- 
duced no  contraction  of  muscles  and  no  pain.  Upon  irritating  the  posterior  columns, 
either  by  mechanical  or  galvanic  stimulus,  Chauveau  noted  pain  and  reflex  movements 
when  the  irritation  was  applied  to  the  surface,  but  the  results  were  negative  when  the 
deep  portions  of  the  columns  were  operated  upon.  The  surface  of  the  posterior  columns 
seemed  to  possess  the  same  general  properties  as  the  posterior  roots  of  the  nerves,  espe- 
cially near  the  roots,  where  the  sensibility  was  most  marked,  gradually  diminishing  in 
intensity  toward  the  median  line ;  but  the  deep  portions  of  the  cord  were  everywhere 
found  completely  insensible  and  inexcitable. 

The  experiments  and  conclusions  of  Chauveau  have  a  most  important  bearing  upon 
the  physiology  of  the  cord,  and  they  are  opposed  to  the  views  of  the  majority  of  physio- 
logical writers,  although  they  have  been  admitted  by  some  experimenters.  We  shall  dis- 
cuss first  the  experiments  upon  the  antero-lateral  columns,  which  are  most  remarkable 
in  their  negative  results.  We  shall  use  the  term  excitability  as  signifying  the  property  of 
the  cord  which  enables  it  to  conduct  a  stimulus  applied  directly  to  it  to  certain  muscles, 
producing  convulsive  movements  confined  to  these  muscles,  and  not  of  a  reflex  character. 
We  shall  apply  the  term  sensibility  to  the  property  by  virtue  of  which  an  irritation  directly 
applied  is  conveyed  to  the  brain  and  produces  a  painful  impression. 

The  experiments  of  Chauveau  and  some  others  upon  the  antero-lateral  columns  are 
simply  negative ;  but  their  results  are  directly  opposed  to  those  of  numerous  experimenters, 
who  have  produced  local  and  restricted  convulsive  movements  by  direct  irritation  of  both 
the  superficial  and  the  deep  portions  of  these  columns. 

With  regard  to  the  posterior  columns,  the  views  of  Chauveau  are  in  advance  of  those 
of  previous  observers,  only  in  so  far  as  he  has  shown  that,  although  the  surface  of  this 
portion  of  the  cord  is  endowed  with  sensibility,  its  deeper  portions  are  entirely  insensible, 
except  in  the  immediate  proximity  of  the  posterior  roots  of  the  nerves. 

In  view  of  the  importance  of  the  question  under  consideration,  and  of  the  contradic- 
tory results  of  experiments,  we  repeated,  in  1863,  the  experiments  of  Chauveau,  under 
conditions  as  nearly  physiological  as  possible.  We  had  often  had  occasion  to  note  the 
diminished  sensibility  of  the  roots  of  the  spinal  nerves  immediately  following  the  very 
severe  operation  of  opening  the  spinal  canal,  and  had  also  noted  that  the  sensibility 
increased,  probably  approaching  the  normal  standard,  after  the  animal  had  been  allowed 
a  few  hours  of  repose.  For  this  reason,  we  made  our  observations  about  two  hours  after 
the  first  operation.  To  avoid  the  suspicion  of  an  extension  of  the  galvanic  current  beyond 
the  portion  of  the  cord  which  we  desired  to  stimulate,  the  irritation  was  first  made  by 
simply  scratching  the  parts  with  the  point  of  a  needle.  The  following  experiment  is  the 
type  of  several,  in  all  of  which  the  results  were  identical : 

May  28,  1863,  at  1  p.  M.,  the  laminae  and  the  spinous  processes  of  the  three  lower 
lumbar  vertebrae  were  removed  from  a  medium-sized  dog.  There  was  no  very  great 
haemorrhage.  The  spinal  cord  and  the  roots  of  three  of  the  nerves  were  exposed,  and  the 
wound  was  then  closed.  The  operation  was  performed  with  the  animal  tinder  the  influ- 
ence of  ether,  and  it  lasted  about  three-quarters  of  an  hour. 

About  two  hours  after  the  first  operation,  the  animal  was  brought  before  the  class  at 
the  Long  Island  College  Hospital.  The  wound  was  opened,  and  the  properties  of  the 
anterior  and  posterior  roots  were  demonstrated.  The  following  observations  were  then 
made  upon  the  spinal  cord: 


GENERAL  PROPERTIES  OF  THE  SPINAL  CORD.  675 

The  external  surface  of  the  posterior  columns  was  irritated  by  scratching  with  the 
point  of  a  needle.  This  produced  pain,  the  more  marked  the  nearer  the  irritation  was 
brought  to  the  origin  of  the  posterior  roots.  The  surface  of  the  cord  was  almost  insen- 
sible at  the  median  line.  A  feeble  galvanic  stimulus  was  then  applied  by  means  of  a 
pince  electrique,  with  the  same  results.  The  deep  portions  of  the  posterior  columns 
were  then  irritated,  but  without  effect. 

The  cord  was  then  divided  transversely,  and  mechanical  and  galvanic  stimulus  were 
applied  to  the  cut  surfaces. 

The  surface  of  the  upper  end  of  the  cord  was  irritated  with  the  needle,  and  the  needle 
was  plunged  deeply  into  its  substance,  without  effect.  The  same  negative  results  followed 
application  of  the  galvanic  stimulus. 

The  lower  end  of  the  cord  was  then  elevated  with  a  hook,  and  the  surface  of  the 
anterior  columns  was  irritated  by  the  needle  and  by  galvanism.  The  invariable  effect 
was  convulsive  movements  in  the  lower  extremities,  without  pain.  The  same  irritation 
was  applied  to  the  deep  portions  of  the  anterior  columns  with  like  results ;  viz.,  con- 
vulsive movements  in  the  lower  extremities,  following  the  irritation  immediately. 

The  above-mentioned  phenomena  were  fully  verified  by  repeated  experiments,  and 
the  animal  was  then  killed  by  section  of  the  medulla  oblongata. 

The  general  movements  accompanied-  by  evidences  of  pain  were  readily  distinguish- 
able from  the  local  convulsive  movements  with  no  pain. 

This  experiment  fully  confirms  the  observations  of  Chauveau  with  regard  to  the  pos- 
terior columns,  but  it  shows,  in  opposition  to  Chauveau,  that  the  anterior  columns  are 
excitable,  both  at  the  surface  and  in  the  deep  portions.  The  recent  observations  of 
Vulpian  are  also  opposed  to  the  results  obtained  by  Chauveau  with  regard  to  the  antero- 
lateral  columns.  From  a  number  of  carefully-executed  experiments,  Vulpian  draws  the 
following  conclusions : 

"  1.  The  gray  substance  is  absolutely  inexcitable. 

"  2.  The  anterior  fasciculi  possess  a  certain  degree  of  motor  excitability. 

"3.  There  is  no  doubt  that  the  posterior  fasciculi  are  very  excitable.  They  are 
sensitive  and  excito-motor  if  the  cord  be  left  intact,  and  simply  excito-rnotor  if  the 
cord  be  divided  transversely  and  separated  from  the  encephalon.  It  is  the  same,  but 
to  a  less  degree,  in  that  portion  of  the  lateral  fasciculi  contiguous  to  the  posterior 
fasciculi."  * 

In  the  face  of  definite  and  positive  experiments  showing  the  excitability  of  certain 
portions  of  the  cord,  it  is  impossible  to  accept  the  purely  negative  results  obtained  by 
Chauveau  and  others. 

As  the  result  of  the  most  definite  and  reliable  experiments  of  others,  bearing  upon  the 
question  of  the  properties  of  the  cord,  and  of  our  own  observations,  we  have  arrived  at 
the  following  conclusions : 

The  gray  substance  is  probably  inexcitable  and  insensible  under  direct  stimulation. 

The  antero-lateral  columns  are  insensible,  but  are  excitable  both  on  the  surface  and 
in  their  substance ;  and  direct  stimulation  of  these  columns  produces  convulsive  move- 
ments in  certain  muscles,  which  movements  are  not  reflex  and  are  not  attended  with 
pain.  The  lateral  columns  are  less  excitable  than  the  anterior  columns. 

The  surface,  at  least,  of  the  posterior  columns  is  very  sensitive,  especially  near  the 
posterior  roots  of  the  nerves.  The  deep  portions  of  the  posterior  columns  are  probably 
insensible,  except  very  near  the  origin  of  the  nerves. 

The  above  conclusions  refer  only  to  the  general  properties  of  different  portions  of  the 
cord,  as  shown  by  direct  stimulation,  in  the  same  way  that  we  demonstrate  the  general 
properties  of  the  nerves  in  their  course.  In  all  probability,  the  fibres  in  the  white  and 
gray  substance  of  the  central  nervous  system  conduct  motor  stimulus  from  the  brain  and 
sensory  impressions  to  the  brain,  while  they  themselves  may  be  insensible  and  inexcit- 
able under  direct  stimulation. 


676  NERVOUS  SYSTEM. 

Transmission  of  Motcr  Stimulus  in  the  Cord.— The  antero-lateral  columns  of  the  cord, 
in  both  the  white  and  the  gray  substance,  are  entirely  insensible  to  direct  irritation,  and 
they  conduct  the  motor  stimulus  from  the  centres  to  the  periphery.  This  statement  may 
be  accepted,  as  the  result  of  positive  demonstration,  with  very  little  qualification.  If  the 
posterior  columns  of  the  cord  be  divided  or  even  removed  for  a  certain  length,  the  animal 
retains  the  power  of  voluntary  motion  intact.  On  the  other  hand,  if  the  antero-lateral 
columns  of  the  cord  be  divided  on  both  sides,  the  power  of  voluntary  motion  is  lost  abso- 
lutely in  all  parts  supplied  with  nerves  coming  from  the  cord  below  the  section.  It 
would  be  an  interesting  point  to  determine  positively  the  relative  importance  of  the  white 
and  the  gray  substance  of  the  anterior  columns  in  the  transmission  of  motor  stimulus  ; 
but  this  has  thus  far  been  impossible.  We  cannot  with  certainty  divide  the  gray  matter 
of  the  anterior  columns  completely  and  leave  the  white  substance  intact,  nor  can  we 
divide  the  white  substance  without  injuring  the  gray.  As  far  as  experiments  go,  however, 
they  seem  to  show  that  transmission  is  not  effected  exclusively  by  the  white  substance, 
but  that  the  gray  matter  plays  an  important  part  in  this  function.  We  shall  refer  far- 
ther on  to  the  action  of  the  gray  substance  in  the  transmission  of  sensory  impressions. 

It  is  evident,  from  anatomical  facts  as  well  as  from  the  results  of  direct  experimenta- 
tion, that  the  fibres  of  conduction  of  the  motor  stimulus  pass  from  the  brain  to  the  anterior 
roots  of  the  nerves,  through  the  spinal  cord,  from  above  downward,  and  that  there  is  no 
other  medium  for  the  transmission  of  the  will  to  the  muscles.  Wherever  the  cord  be 
divided,  all  the  muscles  supplied  by  nerves  given  off  below  the  section  are  paralyzed. 
From  the  brachial  enlargement  of  the  cord,  nerves  of  motion  pass  to  the  superior  extremi- 
ties, and  the  inferior  extremities  are  supplied  mainly  by  nerves  coming  from  the  lumbar 
enlargement.  The  direction  of  these  motor  fibres  in  the  cord  itself  has  been  elucidated 
only  by  experiments  upon  living  animals.  If  the  anterior  columns  alone  be  divided  in 
the  dorsal  region,  there  is  almost  complete  paralysis  of  the  lower  extremities.  If  the 
lateral  columns  be  divided  in  this  situation,  without  injuring  the  anterior  columns,  volun- 
tary movements  of  the  lower  extremities  are  diminished  but  are  not  abolished.  If  the 
anterior  columns  be  divided  high  up  in  the  cervical  region,  there  is  a  diminution  in  the 
voluntary  movements,  but  this  is  by  no  means  so  marked  as  when  the  section  is  made  in 
the  dorsal  region ;  but,  if  the  lateral  columns  be  divided  in  the  upper  cervical  region,  the 
paralysis  is  almost  or  quite  complete.  These  facts  clearly  show  that  the  situation  of  the 
chief  motor  conductors  of  the  cord  is  different  in  the  dorsal  and  in  the  cervical  region. 
In  the  dorsal  region,  while  conduction  of  the  motor  stimulus  takes  place  through  fibres 
contained  both  in  the  anterior  and  in  the  lateral  columns,  the  transmission  is  mainly 
through  the  anterior  columns,  the  lateral  columns  being  much  less  important.  In  the 
cervical  region,  the  conditions  are  reversed,  and  the  conduction  takes  place  chiefly  by 
means  of  the  lateral  columns.  Passing  from  above  downward,  therefore,  the  motor 
fibres  are  situated,  in  the  cervical  region,  mainly  in  the  lateral  columns;  but  progres- 
sively, as  they  pass  through  the  dorsal  and  the  lumbar  portions  of  the  cord,  these  fibres 
change  their  location  and  are  found  chiefly  in  the  anterior  columns. 

Recent  observations  have  not  sustained  the  old  idea  that  the  lateral  columns  of  the 
cord  contain  fibres  which  preside  specially  over  the  movements  of  the  thorax.  The 
experiments  of  Vulpian  upon  this  point  are  conclusive.  If  the  lateral  column  be  divided 
upon  one  side  at  about  the  third  or  fourth  cervical  vertebra,  there  is  considerable  enfee- 
blement  of  the  muscles  of  the  thorax  upon  the  corresponding  side,  but  there  is  also  partial 
loss  of  power  in  the  limbs,  which  is  more  marked  in  the  anterior  extremity.  This 
diminution  in  power  in  the  thoracic  muscles  is  such  that,  in  ordinary  tranquil  respiration, 
the  side  corresponding  to  the  section  does  not  move ;  but,  in  difficult  respiration  or  in 
crying,  the  movements  are  very  marked. 

Decussation  of  the  Motor  Conductors  of  the  Cord.— Well-established  anatomical  and 
pathological  facts  show  conclusively  that  there  is  a  complete  decussation  of  the  motor 


FUNCTIONS   OF  THE   SPINAL  CORD  AS  A  CONDUCTOR.  677 

conductors  of  the  cord  ;  so  that  the  stimulus  of  volition  generated  in  one  lateral  half  of 
the  brain  always  passes  to  the  opposite  half  of  the  body.  If  a  lesion  occur  in  the  brain 
upon  one  side,  so  as  to  produce  total  paralysis  of  motion,  the  opposite  side  of  the  body  is 
paralyzed,  while  voluntary  motion  is  absolutely  intact  on  the  side  corresponding  to  the 
injury.  In  the  anterior  pyramids  of  the  medulla  oblongata,  the  decussation  of  the  fibres 
is  easily  demonstrated  anatomically.  In  view  of  these  facts,  concerning  which  there  is 
no  difference  of  opinion,  it  only  remains  to  show  by  physiological  experiments  that  decus- 
sation actually  takes  place  at  the  medulla  oblongata,  and  to  submit  to  the  same  method 
of  inquiry  the  following  important  question :  Assuming  that  crossing  of  motor  fibres  takes 
place  at  the  medulla,  is  this  the  sole  seat  of  decussation  of  these  fibres,  or  does  it  also 
take  place  in  certain  portions  of  the  cord  below  ? 

The  question  of  decussation  at  the  medulla  oblongata  is  easily  answered.  In  the  first 
place,  we  have  the  crossed  action  in  hemiplegia  and  the  easy  anatomical  demonstration 
of  the  decussating  fibres.  The  experimental  confirmation  of  these  facts  is  not  so  simple, 
for  the  reason  that  animals  survive  operations  upon  the  medulla  oblongata  for  a  very 
short  time.  As  far  as  can  be  learned,  however,  from  the  latter  mode  of  inquiry,  the  con- 
clusions drawn  from  anatomy  and  pathology  are  fully  sustained.  If  the  medulla  be 
exposed  in  a  living  animal,  and  "  if  a  section  is  made  longitudinally  just  at  the  place  of 
the  decussation  of  the  anterior  pyramids,  so  as  to  divide  completely  all  of  the  decussating 
elements,  we  find  that,  although  the  animal  lives  some  time  after  the  operation,  it  has  no 
voluntary  movement  at  all  in  any  of  the  limbs,  which  are  almost  always  the  seat  of  con- 
vulsions." (Brown-Sequard.) 

The  question  of  decussation  of  motor  fibres  in  the  cord  itself  is  one  which  can  be 
settled  only  by  physiological  experiments,  as  the  course  of  the  decussating  fibres,  if  they 
exist,  cannot  be  demonstrated  anatomically.  It  is  remarkable  that  Galen  submitted  this 
point  to  experimental  investigation,  by  dividing  the  cord  longitudinally  in  the  median 
line  in  the  lumbar  region.  This  operation  was  not  followed  by  loss  of  voluntary  power 
in  the  lower  extremities,  showing  that  the  motor  fibres  do  not  cross  the  median  line,  at 
least  in  this  portion  of  the  cord.  Recent  experiments  upon  the  cervical  portions  of  the 
cord  show  that  there  is  a  very  slight  decussation  of  motor  fibres  in  this  situation.  The 
first  observations  pointing  to  this  conclusion  are  those  of  Brown-Sequard.  "There  is 
always,  even  in  mammals,  after  a  transversal  section  of  the  whole  or  a  lateral  half  of  the 
spinal  cord,  at  least  some  appearance  of  voluntary  movements  in  the  side  of  the  injury, 
and  always  also  a  diminution  of  voluntary  movements  in  the  opposite  side ;  so  that,  in 
animals,  there  seems  to  be  in  the  spinal  cord  a  decussation  of  a  few  of  the  voluntary 
motor  conductors.  As  there  seems  to  be  no  such  decussation  in  man,  at  least  according 
to  several  pathological  facts,  we  shall  not  insist  upon  its  existence  in  animals." 

Van  Kempen  has  repeated  and  extended  the  very  remarkable  experiment  of  Galen, 
with  the  most  satisfactory  results.  This  observer  made  a  median,  longitudinal  section 
of  the  cord  in  dogs  and  rabbits,  at  the  site  of  the  fifth,  sixth,  and  seventh  cervical  ver- 
tebrae. "  This  experiment  was  followed  by  partial  paralysis  of  voluntary  movements  in 
the  posterior  extremities,  so  that  the  animal  thus  operated  upon  moved  the  posterior 
limbs  and  was  able  to  change  his  position,  without,  however,  being  able  to  raise 
himself." 

As  there  is  some  difference  in  the  results  of  observations  upon  different  animals,  and 
as  decussating  motor  fibres  have  never  been  demonstrated  in  man,  it  is  impossible  to 
apply  the  above  experiments  without  reserve  to  the  human  subject ;  but  they  show, 
nevertheless,  that,  in  mammals,  the  motor  columns  of  the  cord  probably  do  not  decussate 
in  the  dorso-lumbar  region ;  that  partial  decussation  occurs  in  the  cervical  region ;  and 
that  the  decussation  is  completed  in  the  anterior  pyramids  of  the  medulla  oblongata. 

Transmission  of  Sensory  Impressions  in  the  Cord. — Early  in  the  physiological  his- 
tory of  this  portion  of  the  nervous  system,  Longet  made  a  number  of  experiments,  which 


678  NERVOUS  SYSTEM. 

seemed  to  show  that  the  posterior  columns  of  the  cord  were  the  conductors  of  sensory 
impressions  to  the  brain,  and  that  the  antero-lateral  columns  transmitted  the  motor  stim- 
ulus. These  were  made  by  applying  a  stimulus  directly  to  the  cord  itself.  Longet  dis- 
credited observations  made  by  dividing  different  portions  of  the  cord,  for  the  reason  that 
he  supposed  that  the  mere  operation  of  exposing  the  cord  and  of  removing  the  dura 
mater  was  followed  by  a  depression  of  the  nervous  action  sufficient  to  render  the  evidences 
of  sensibility  in  the  lower  extremities  scarcely  appreciable.  The  conclusions  drawn  from 
these  experiments  were  at  first  accepted  by  nearly  all  physiological  writers,  and  it  was 
generally  admitted  that  the  transmission  of  sensory  impressions  was  effected  solely  by 
the  posterior  columns.  It  was  found  that  the  gray  matter  of  the  cord  was  both  insen- 
sible and  inexcitable,  and  the  conduction  was  supposed  to  take  place  exclusively  through 
the  white  substance.  The  views  of  Longet,  however,  were  in  direct  opposition  to  those 
of  Bellingeri,  who  claimed,  in  1823,  to  have  demonstrated  by  experiment,  that  sensory 
impressions  were  conveyed  to  the  brain  exclusively  by  the  gray  substance  of  the  cord, 
and  that  sensibility  persisted  in  the  lower  extremities  after  complete  section  of  the  pos- 
terior white  columns. 

At  the  time  the  above-mentioned  experiments  were  made,  our  knowledge  of  the  prop- 
erties of  the  cord  was  very  incomplete,  and  it  was  difficult  to  understand  how  any  of  its 
fibres  could  conduct  sensory  impressions  and  yet  be  insensible  to  direct  stimulation  ;  but 
now  we  know  that  the  gray  matter  does  act  as  a  conductor,  and  yet  it  is  certainly  insen- 
sible. The  simple  questions  now  to  be  determined  are  the  following : 

1.  Does  or  does  not  the  white  substance  of  the  posterior  columns  of  the  cord  conduct 
sensory  impressions  to  the  brain  ? 

2.  Does  the  entire  gray  substance  of  the  cord  act  as  a  conductor  of  sensation  ? 

3.  Do  both  the  gray  matter  of  the  cord  and  the  white  substance  of  the  posterior  col- 
umns act  as  conductors,  or  does  either  one  act  to  the  exclusion  of  the  other? 

These  questions  may  now  be  considered  as  definitively  answered  by  the  most  positive 
and  unmistakable  results  of  experiments  upon  living  animals,  which,  while  they  render 
the  precise  function  of  the  white  substance  of  the  posterior  columns  to  a  certain  extent 
a  matter  of  conjecture,  leave  no  doubt  with  regard  to  the  parts  of  the  cord  which  act  as 
conductors  of  sensory  impressions. 

The  experimental  answer  to  the  first  question  is  capable  of  but  one  construction.  If 
the  white  substance  of  both  posterior  columns  be  divided,  the  sensibility  of  the  posterior 
extremities  is  not  diminished,  at  least  as  far  as  can  be  shown  by  experiments  upon  ani- 
mals, in  which  these  points  are  always  difficult  of  determination.  On  the  other  hand,  if 
every  portion  of  the  cord  be  divided  except  the  posterior  white  columns,  sensibility  is 
completely  lost  in  the  parts  below  the  section.  The  accuracy  of  these  results  cannot  be 
called  in  question,  especially  when  controlled  by  experiments  showing  the  conducting- 
properties  of  the  gray  substance  of  the  cord  ;  and  they  show  that,  whatever  may  be  the 
functions  of  the  posterior  white  columns,  they  do  not  serve  as  conductors  of  sensory 
impressions. 

The  second  question  admits  of  an  equally  positive  answer  from  the  results  of  experi- 
mental inquiry.  If  the  entire  substance  of  the  cord,  except  the  posterior  columns  of 
white  matter,  be  divided  transversely,  as  we  have  just  seen,  sensibility  is  abolished  in  all 
parts  below  the  section ;  but,  as  we  have  stated  in  treating  of  the  transmission  of  motor 
stimulus  by  the  cord,  voluntary  motion  is  also  destroyed.  Experiments  show,  farther- 
more,  that  sensory  impressions  are  conveyed  exclusively  by  the  gray  substance.  "If  the 
anterior,  the  lateral,  and  the  posterior  columns  of  the  spinal  cord  are  divided  transversely, 
at  the  dorsal  region,  one  set  at  one  place,  another  at  a  distance  of  one  or  two  inches,  and 
the  third  also  at  the  same  distance  from  the  second,  so  that  the  only  channel  of  commu- 
nication between  the  posterior  limbs  and  the  sensorium  is  the  gray  matter,  of  which, 
however,  several  parts  have,  unavoidably,  been  divided  (such  as  the  anterior  and  the 
posterior  gray  cornua,  and  also  more  or  less  of  the  central  gray  matter),  we  find  that  the 


FUNCTIONS   OF  THE   SPINAL  CORD  AS  A  CONDUCTOR.  679 

posterior  limbs  are  still  sensitive,  though  evidently  less  than  in  the  normal  condition." 
(Brown-Sequard.) 

It  is  impossible  to  divide  the  gray  matter  of  the  cord  alone,  without  injuring,  more  or 
less,  the  white  substance;  but,  when  the  gray  matter  is  divided  with  very  slight  injury 
of  the  white  substance,  sensibility  in  the  parts  below  the  point  of  section  is  totally 
destroyed.  As  regards  the  part  of  the  gray  substance  specially  concerned  in  the  trans- 
mission of  sensory  impressions,  the  results  of  experimental  investigation  have  not  been  so 
definite ;  but  Brown-S6quard  is  of  the  opinion  that  the  transmission  takes  place  chiefly 
in  the  gray  matter  surrounding  the  central  canal,  while  it  may  also  occur  to  some  extent 
in  other  portions. 

The  answer  to  the  third  question  is  deduced  from  the  answers  to  the  first  two.  The 
gray  matter  and  the  white  substance  of  the  cord  do  not  participate  in  the  transmission 
of  sensory  impressions,  this  being  eifected  by  the  gray  substance,  especially  its  central 
portion,  to  the  exclusion  of  the  white. 

The  precise  office  of  the  posterior  white  columns  of  the  cord  is  still  a  matter  of  con- 
jecture. If  these  parts  be  insensible,  except  on  the  surface  and  near  the  posterior  roots 
of  the  nerves,  and  if  they  take  no  part  in  the  transmission  of  sensory  impressions  to  the 
brain  (which  seems  to  have  been  conclusively  proven),  what  is  their  function  ? 

The  anatomical  relations  of  the  posterior  white  columns,  the  results  of  experiments 
upon  living  animals,  and  certain  well-marked  pathological  phenomena,  point  very  strongly 
to  a  connection  between  these  columns  and  the  coordination  of  muscular  movements. 

Probable  Function  of  the  Cord  in  Connection  with  Muscular  Coordination. — Anato- 
mists have  not  been  able  to  trace  satisfactorily  the  direction  of  all  of  the  fibres  contained 
in  the  posterior  columns ;  but  it  is  probable  that  at  least  some  of  these  fibres  serve  as 
longitudinal  commissures,  and  connect  together  the  nerve-cells,  extending  for  a  greater 
or  less  distance  both  upward  and  downward  in  the  cord.  This  anatomical  arrangement 
is  rendered  probable  chiefly  by  the  results  of  experiments. 

If  the  posterior  columns  be  completely  divided,  by  two  or  three  sections  made  at  inter- 
vals of  from  three-fourths  of  an  inch  to  an  inch  and  a  quarter,  the  most  prominent  effect 
is  a  remarkable  trouble  in  locomotion,  consisting  in  a  want  of  proper  coordination  of 
movements. 

In  the  remarkable  disease  known  under  the  name  of  locomotor  ataxia,  there  is  a  very 
peculiar  condition  of  the  muscular  system,  in  which,  while  the  power  of  the  muscles  is 
but  slightly  diminished,  the  movements  of  progression  show  great  deficiency  in  coordi- 
nating power,  frequently  attended  with  more  or  less  disturbance  in  the  sensibility  of  the 
parts  affected.  These  symptoms  are  associated  with  structural  disease  of  the  cord,  gen- 
erally limited  to  the  posterior  columns  and  the  posterior  roots  of  the  spinal  nerves. 

Many  years  ago,  before  locomotor  ataxia  had  been  generally  recognized  by  patholo- 
gists,  Todd  made  the  following  remarkable  statement  with  regard  to  the  posterior  col- 
umns :  "  I  have  long  been  impressed  with  the  opinion,  that  the  office  of  the  posterior 
columns  of  the  spinal  cord  is  very  different  from  any  yet  assigned  to  them.  They  may 
be  in  part  commissural  between  the  several  segments  of  the  cord,  serving  to  unite  them 
and  harmonize  them  in  their  various  actions,  and  in  part  subservient  to  the  function  of 
the  cerebellum  in  regulating  and  coordinating  the  movements  necessary  for  perfect  loco- 
motion." Todd  farther  states  that  this  view  is  supported  by  the  phenomena  observed  in 
cases  of  disease  "  distinguished  by  a  diminution  or  total  loss  of  the  power  of  coordinating 
movements.  ...  In  two  examples  of  this  variety  of  paralysis,  I  ventured  to  predict 
disease  of  the  posterior  columns,  the  diagnosis  being  founded  upon  the  views  of  their 
functions  which  I  now  advocate  ;  and  this  was  found  to  exist  on  post-mortem  inspection  ; 
and  in  looking  through  the  accounts  of  recorded  cases  in  which  the  posterior  columns 
were  the  seat  of  lesion,  all  seemed  to  have  commenced  by  evincing  more  or  less  disturb- 
ance of  the  locomotive  powers,  sensation  being  affected  only  when  the  morbid  change 


680  NERVOUS  SYSTEM. 

of  structure  extended  to  and  more  or  less  involved  the  posterior  roots  of  the  spinal 

nerves." 

It  is  only  necessary  to  add  that  the  views  of  Todd  have  been  in  the  mam  confirmed 
in  the  numerous  cases  of  locomotor  ataxia  that  have  lately  been  so  fully  described  by 
pathologists ;  and,  from  these  facts,  it  is  more  than  probable  that  the  posterior  columns 
contain  fibres  connecting  the  different  segments  of  the  cord,  and  that  they  play  an  im- 
portant part  in  the  coordination  of  muscular  movements.  The  general  function  of  coor- 
dination will  be  considered  more  fully  in  connection  with  the  cerebellum. 

Decussation  of  the  Sensory  Conductors  of  the  Cord.— In  hemiplegia  due  to  injury  of 
the  brain,  the  paralysis  occurs  upon  the  side  of  the  body  opposite  to  the  cerebral  lesion. 
The  phenomenon  ordinarily  observed  is  simply  paralysis  of  motion ;  but  in  those  cases, 
however,  in  which  both  motion  and  sensation  are  abolished  upon  one  side  of  the  body, 
the  lesion  in  the  brain  is  also  found  to  be  upon  the  opposite  side.  It  is  evident,  there- 
fore, that  there  is  a  decussation  of  the  conductors  of  sensory  impressions  as  well  as  of 
the  conductors  of  the  motor  stimulus. 

As  early  as  1822,  Fodera  made  a  longitudinal  section  of  the  spinal  cord  in  the  lumbar 
region,  exactly  in  the  median  line.  In  this  experiment,  "  sensation  was  destroyed,  and 
in  part  motion  upon  the  two  sides.1'  Inasmuch  as  in  this  section  it  is  only  possible  to 
divide  the  fibres  passing  from  one  lateral  half  of  the  cord  to  the  other,  it  is  evident  that 
the  sensory  conductors  must  decussate  in  the  spinal  cord  itself.  As  far  as  we  know,  this 
is  the  first  experiment  pointing  to  the  decussation  of  sensory  fibres  in  the  cord,  the  ob- 
servations of  Galen,  to  which  we  have  already  referred,  being  limited  to  the  phenomena 
of  motion. 

The  next  experiments  bearing  upon  the  decussation  of  the  sensory  conductors  in  the 
cord  are  those  of  Van  Deen.  Among  the  numerous  observations  made  upon  the  spinal 
cord  by  this  physiologist,  are  one  or  two  in  which  he  noted  the  fact  that,  after  section  of 
one  lateral  half  of  the  cord  in  the  frog,  at  the  site  to  the  third  dorsal  vertebra,  "  the 
animal  had  no  real  loss  of  sensibility  in  the  posterior  extremity  on  the  side  on  which  the 
half  of  the  spinal  cord  had  been  cut."  Although  Van  Deen  did  not  distinctly  state,  as  a 
conclusion  drawn  from  these  observations,  that  there  is  decussation  of  the  sensory  con- 
ductors in  the  cord,  the  fact  of  section  of  one  lateral  half  of  the  cord  with  no  loss  of 
sensation  on  the  corresponding  side  of  the  body  remains  as  one  of  the  first  experimental 
arguments  in  favor  of  the  crossed  action. 

Experiments  upon  living  animals  as  well  as  pathological  facts  show  that,  after  section 
or  injury  confined  to  one  lateral  half  of  the  cord,  the  general  sensibility  upon  the  cor- 
responding side  of  the  body  is  very  much  exaggerated,  producing  a  condition  of  well- 
marked  hypera3sthesia.  This  remarkable  fact  was  distinctly  noted  by  Fodera,  in  1822. 
This  observation  has  been  confirmed,  and  the  experiments  very  much  extended,  by 
Brown-Sequard.  Cases  presenting  the  same  phenomena  have  also  been  observed  in  the 
human  subject,  when  one  side  of  the  cord  has  been  invaded  by  disease. 

Physiologists  are  at  a  loss  to  explain  the  hyperaesthesia  which  follows  section  of  the 
sensory  conductors  of  the  cord,  but  the  fact  nevertheless  remains.  The  exaggeration  of 
sensibility  is  not  due  to  section  of  certain  fibres,  which  might  be  supposed  to  increase  the 
impressibility  of  the  remaining  fibres,  for,  as  was  shown  by  Vulpian,  it  is  sufficient  to 
prick  with  a  pin  one  of  the  lateral  halves  of  the  cord  to  observe  these  remarkable  phe- 
nomena. With  these  few  words,  we  shall  leave  the  subject  of  hyperasthesia  from  injury 
to  the  cord,  and  pass  to  the  crossed  action  of  its  sensory  conductors. 

In  treating  of  the  cord  as  a  conductor  of  sensory  impressions,  we  have  already  shown 
that  this  function  is  performed  by  the  gray  substance  alone.  We  have  also  seen,  in  con- 
nection with  the  phenomena  of  conduction  of  the  motor  stimulus,  that  this  is  effected  by 
the  antero-lateral  columns,  which  do  not  act  as  sensory  conductors,  except  by  virtue  of 
their  gray  matter.  As  it  is  impossible  to  divide  the  gray  matter  with  certainty  without 


FUNCTIONS   OF  THE   SPINAL  CORD  AS  A   CONDUCTOR.  681 

injuring  the  white  substance,  and,  as  we  are  fully  acquainted  with  the  motor  properties 
of  the  cord,  we  are  prepared  to  comprehend  the  effects  upon  conduction  of  sensory  im- 
pressions which  follow  division  of  one  or  the  other  lateral  half.  In  our  detail  of  experi- 
ments, we  shall  not  consider  the  phenomena  of  hyperassthesia,  but  confine  ourselves  to 
the  loss  or  diminution  of  sensibility. 

Brown-Se'quard  was  the  first  to  demonstrate  decussation  of  the  sensory  conductors  in 
the  cord  itself;  and,  although  his  experiments  upon  this  subject  are  almost  innumerable, 
and  his  writings,  scattered,  voluminous,  and  sometimes  not  free  from  the  obscurity  due 
to  unnecessary  refinement  and  elaborateness  of  detail,  the  main  facts  can  be  expressed  in 
a  very  few  words;  and  he  may  justly  be  said  to  have  created  the  physiology  of  the  sen- 
sory conductors. 

Brown-Sequard  repeated  the  experiments  of  Galen  and  of  Fodera,  dividing  the  cord 
longitudinally  in  the  median  line,  producing  complete  paralysis  of  sensation  upon  both 
sides  in  all  the  parts  below  the  section.  By  this  operation,  if  the  section  had  been  made 
accurately  in  the  median  line,  the  only  fibres  that  could  be  divided  were  those  passing 
from  one  side  of  the  cord  to  the  other. 

The  second  experimental  proof  of  the  decussation  of  sensory  fibres  consists  in  trans- 
verse section  of  one  or  the  other  of  the  lateral  halves  of  the  cord.  If  one  lateral  half  of 
the  cord  be  divided,  sensibility  is  abolished  in  the  parts  below  the  section,  upon  the  oppo- 
site side  of  the  body.  In  an  article  published  in  1858,  Brown-Sequard  details  very  suc- 
cinctly an  experiment  showing  this  fact,  though  his  first  experiments  were  made  in  1849. 
He  denuded  the  cord  in  the  lumbar  region  in  a  vigorous  dog,  and  made  sections  upon  one 
side,  progressively  deeper  and  deeper,  from  without  inward.  When  the  section  included 
about  one-third  of  the  lateral  half,  the  sensibility  seemed  slightly  augmented  upon  the 
opposite  side.  This  section  involved  only  a  part  of  the  lateral  wThite  column  and  a  small 
portion  of  the  anterior  cornu  of  gray  matter.  When  the  section  was  extended  so  as  to 
involve  about  two-thirds  of  the  lateral  half,  the  sensibility  was  notably  diminished  upon 
the  opposite  side.  When  the  section  extended  to  the  median  line,  the  sensibility  was 
very  much  diminished ;  and,  when  it  extended  just  beyond  the  median  line,  it  was  entirely 
abolished  upon  the  opposite  side.  These  observations,  and  others  of  the  same  nature, 
show  conclusively  that,  in  the  animals  experimented  upon  at  least,  there  is  a  decussation 
of  the  greatest  part  of  the  sensory  conductors  in  the  cord  itself. 

The  course  of  the  fibres  in  their  decussation  is  indicated  by  farther  experiments,  which 
show  that  the  sensitive  fibres  from  ,the  posterior  roots  of  the  nerves  "  pass  along  the  pos- 
terior columns  only  a  little  way,  and  leave  them  to  enter  the  central  gray  matter."  It  is 
undoubtedly  in  this  gray  substance  that  they  pass  from  one  side  to  the  other,  probably 
through  the  cell-prolongations.  The  fact  that  the  fibres  pass  in  the  cord  a  short  distance 
before  they  decussate,  and  that  they  pass  downward  as  well  as  upward,  is  well  shown  by 
the  following  experiment : 

"  If  we  divide  transversely  a  lateral  half  of  the  spinal  cord  in  two  places,  so  as  to  have 
three  pairs  of  nerves  between  the  two  sections,  we  find  that  the  middle  pair  has  almost 
the  same  degree  of  sensibility  as  if  nothing  had  been  done  to  the  spinal  cord,  while  the 
two  other  pairs  have  a  diminished  sensibility,  the  upper  one  particularly  in  its  upper 
roots,  and  the  lower  one  in  its  lower  roots  ;  which  facts  seem  to  show  that  the  ascending 
fibres  of  the  upper  pair,  and  the  descending  fibres  of  the  lower  one,  have  been  divided 
before  they  had  made  their  decussation. 

"  If  there  is  only  one  pair  of  nerves  between  two  sections,  its  sensibility  is  almost 
entirely  lost,  as  then  the  transversal  fibres  are  almost  alone  uninjured  (most  of  the  ascend- 
ing and  descending  being  divided),  which  fibres  are  employed  for  reflex  action,  and  hardly 
for  the  transmission  of  sensitive  impressions."  (Brown-Sequard.) 

The  experimental  facts  just  cited  conclusively  show  decussation  of  sensory  conductors 
in  the  cord  in  the  animals  operated  upon ;  and  this  has  been  sufficiently  confirmed  by 
other  experimenters  to  render  the  fact  certain.  It  is  possible  that  the  crossed  action  may 


682  NERVOUS    SYSTEM. 

not  be  so  complete  in  some  other  classes  of  animals,  which  would  account  for  the  results 
obtained  by  those  who  have  denied  decussation;  but  cases  of  disease  of  the  cord  in  the 
human  subject  all  go  to  show  that  the  crossed  action  is  complete  in  man. 

Summary  of  the  Action  of  the  Spinal  Cord  as  a  Conductor. 

The  antero-lateral  columns  of  the  cord,  comprising  that  portion  included  between  the 
anterior  median  fissure  and  the  origin  of  the  posterior  roots  of  the  nerves,  are  insensible 
to  direct  irritation,  and  serve  as  conductors  of  the  motor  stimulus  from  the  brain  to  the 
anterior  roots  of  the  nerves.  If  these  columns  be  divided,  voluntary  motion  is  lost  in  all 
parts  below  the  section.  If  the  rest  of  the  cord  be  divided,  leaving  the  antero-lateral  col- 
umns intact,  the  power  of  voluntary  motion  remains.  Throughout  the  greater  part  of  the 
cord,  this  action  is  direct,  and  division  of  the  antero-lateral  columns  upon  one  side  pro- 
duces paralysis  of  motion  upon  the  corresponding  side  of  the  body.  There  is  a  decussa- 
tion of  the  motor  fibres  at  the  medulla  oblongata,  and  probably  a  partial  decussation  in 
the  cord  itself  in  the  upper  cervical  region.  In  the  dorsal  region  and  below,  the  motor 
conducting  fibres  are  situated  chiefly  in  the  anterior  columns;  but,  in  the  cervical  region, 
these  fibres  pass  to  the  sides  and  are  contained  chiefly  in  the  lateral  columns.  The  con- 
duction of  motor  stimulus  is  probably  not  effected  exclusively  by  the  white  substance, 
but  is  transmitted  in  part  by  the  gray  matter. 

The  gray  substance  of  the  cord  serves  as  the  medium  of  transmission  of  sensory  im- 
pressions to  the  brain.  This  is  effected  chiefly  by  the  gray  matter  surrounding  the  central 
canal,  but  it  may  take  place  to  some  extent  in  other  portions.  If  the  entire  gray  matter 
be  divided,  with  but  slight  injury  to  the  white  substance,  sensation  is  lost  in  all  parts 
situated  below  the  section.  The  white  substance  does  not  conduct  sensory  impressions 
to  the  brain,  either  in  the  antero-lateral  or  the  posterior  columns.  The  most  probable 
function  of  the  white  substance  of  the  posterior  columns  is  to  unite  the  different  seg- 
ments of  the  cord  together  by  longitudinal  commissural  fibres;  and  this  portion  of  the 
cord  has  an  important  influence  in  coordinating  the  muscular  movements. 

The  sensitive  nerve-fibres  from  the  posterior  roots  of  the  spinal  nerves  pass  in  the 
cord  for  a  short  distance  upward  and  downward.  They  then  penetrate  the  gray  matter 
and  decussate  throughout  the  entire  length  of  the  cord.  Division  of  one  lateral  half  of 
the  cord  is  followed  by  complete  paralysis  of  motion  upon  the  corresponding  side  of  the 
body  in  all  parts  below  the  section,  by  anaesthesia  in  all  parts  below  the  section,  upon  the 
opposite  side  of  the  body,  and  by  hypersesthesia  in  the  parts  below  the  section,  upon  the 
corresponding  side  of  the  body. 

The  anatomical  points  bearing  upon  the  physiological  action  of  the  cord  are  the  fol- 
lowing : 

^The  fibres  from  the  anterior  roots  penetrate  the  anterior  gray  cornua  directly  and  are 
in  immediate  connection  with  the  prolongations  of  the  motor  cells.  The  motor  cells  also 
have  prolongations  which  pass  to  the  brain  in  the  white  substance.  The  motor  fibres 
are  thus  directly  connected  with  the  cellular  structures  in  the  cord  (the  elements  prob- 
ably concerned  in  reflex  movements)  and  the  cells  are  in  connection  with  conducting 
fibres  to  the  brain. 

The  fibres  from  the  posterior  roots  take  several  directions.  Some  of  them  pass  to  the 
gray  substance.  A  portion  passes  to  the  posterior  columns,  some  extending  upward  and 
others  downward.  The  decussation,  which  is  rendered  certain  by  physiological  experi- 
ments, has  not  been  satisfactorily  followed  by  anatomists.  It  undoubtedly  takes  place 
chiefly  in  the  gray  substance,  probably  in  part  by  a  crossing  of  the  fibres  themselves, 
and  in  part  by  a  crossing  of  prolongations  from  the  cells  with  which  certain  fibres  from 
the  posterior  roots  are  connected. 


KEFLEX  ACTION  OF  THE  SPINAL  COED.  683 

Action  of  the  Spinal  Cord  as  a  Nerve-  Centre. 

It  has  long  been  known  that  decapitation  of  animals  does  not  immediately  arrest  mus- 
cular action  ;  and  the  movements  observed  after  this  mutilation  present  a  certain  degree 
of  regularity,  and,  of  late  years,  have  been  shown  to  be  in  accordance  with  well-defined 
laws.  Under  these  conditions,  the  regulation  of  such  movements  is  effected  through  the 
spinal  cord  and  the  nerves  connected  with  it.  If  an  animal  be  decapitated,  leaving  only 
the  cord  and  its  nerves,  there  is  no  sensation,  for  the  parts  capable  of  appreciating  sensa- 
tion are  absent ;  nor  are  there  any  true  voluntary  movements,  as  the  organ  of  the  will  is 
destroyed.  Still,  in  decapitated  animals,  the  sensory  nerves  are  for  a  time  capable  of 
conducting  impressions,  and  the  motor  nerves  can  transmit  a  stimulus  to  the  muscles ; 
but  the  only  part  capable  of  receiving  an  impression  or  of  generating  a  motor  stimulus  is 
the  gray  matter  of  the  cord.  If,  in  addition  to  the  removal  of  all  of  the  encephalic 
ganglia,  the  cord  itself  be  destroyed,  all  movements  of  voluntary  muscles  are  abolished, 
except  as  they  may  be  produced  by  direct  stimulation  of  the  muscular  tissue  or  of  indi- 
vidual motor  nerves. 

We  must  regard  the  gray  matter  of  the  brain  and  spinal  cord  as  a  connected  chain  of 
ganglia,  capable  of  receiving  impressions  through  the  sensory  nerves  and  of  generating 
the  so-called  nerve-force.  The  great  cerebro-spinal  axis,  taken  as  a  whole,  has  this  gen- 
eral function ;  but  some  parts  have  separate  and  distinct  properties  and  can  act  inde- 
pendently of  the  others.  The  cord,  regarded  as  a  conductor,  connects  the  brain  with  the 
parts  to  which  the  spinal  nerves  are  distributed.  If  the  cord  be  separated  from  the 
brain  in  a  living  animal,  it  may  act  as  a  centre,  independently  of  the  brain ;  but  the 
encephalon  has  no  communication  with  the  parts  supplied  with  nerves  from  the  cord,  and 
it  can  only  act  upon  the  parts  which  receive  nerves  from  the  brain  itself. 

It  has  been  pretty  clearly  shown  that,  when  the  cord  is  separated  from  the  encephalon, 
an  impression  made  upon  the  general  sensory  nerves  is  conveyed  to  its  gray  substance, 
and  is  transformed,  as  it  were,  into  a  stimulus,  which  is  transmitted  to  the  voluntary 
muscles,  giving  rise  to  certain  movements,  independently  of  sensation  and  volition. 
This  impression  is  said  to  be  reflected  back  from  the  cord  through  the  motor  nerves ; 
and  the  movements  occurring  under  these  conditions  are  called  reflex.  As  they  are 
movements  excited  by  stimulation  of  sensory  nerves,  they  are  sometimes  called  excito- 
motor. 

The  term  reflex  may  properly  be  applied  to  any  generation  of  nerve-force  which 
occurs  as  a  consequence  of  an  impression  received  by  a  nerve-centre ;  and  reflex  phe- 
nomena are  by  no  means  confined  to  the  action  of  the  spinal  cord.  The  movements  of 
the  iris  are  reflex,  and  yet  they  take  place  in  many  instances  without  the  intervention  of 
the  cord.  The  movements  of  respiration  are  reflex,  and  these  are  presided  over  by  the 
medulla  oblongata.  Movements  of  the  intestines  and  the  involuntary  muscles  generally 
are  reflex,  and  they  involve  the  action  of  the  sympathetic  system  of  nerves.  Impressions 
made  upon  the  nerves  of  special  sense,  as  those  of  smell,  sight,  hearing,  etc.,  give  rise  to 
certain  trains  of  thought.  These  involve  the  action  of  the  brain,  but  still  they  are  reflex. 
In  this  last  example  of  reflex  action,  it  is  sometimes  difficult  to  connect  the  operations  of 
the  mind  with  external  impressions  as  an  exciting  cause ;  but  it  is  evident,  from  a  little 
reflection,  that  this  is  often  the  case.  This  fact  is  illustrated  by  operations  of  the  brain 
which  take  place,  as  it  were,  without  consciousness,  as  in  dreams.  It  has  been  clearly 
shown  that  a  particular  direction  may  be  given  to  the  thoughts  during  sleep,  by  impres- 
sions made  upon  the  sense  of  hearing.  A  person  sleeping  may  be  made  to  dream  of 
certain  things,  as  a  consequence  of  hearing  peculiar  noises.  Examples  of  this  kind  of 
mental  reflex  action  are  sufficiently  numerous  and  well-authenticated. 

From  the  above  considerations,  it  is  evident  that  the  term  reflex  may  be  properly  used 
in  connection  with  many  phenomena  involving  the  action  of  the  sympathetic  system  and 
of  the  brain ;  but  it  is  generally  understood  as  applying  especially  to  involuntary  move- 


684  NERVOUS  SYSTEM. 

ments,  occurring  without  consciousness,  as  the  result  of  impressions  made  upon  the  affe- 
rent nerves  and  involving  the  independent  action  of  the  spinal  cord. 

Reflex  Action  of  the  Spinal  Cord.— In  1832  and  1833,  Marshall  Hall  described 
minutely  the  movements  which  take  place  in  decapitated  animals  as  a  consequence  of 
stimulation  of  the  sensory  nerves,  and  he  formularized  these  phenomena  under  the  head  of 
"  the  reflex  function  of  the  medulla  oblongata  and  medulla  spinalis."  Since  this  publica- 
tion, a  new  interest  has  been  attached  to  the  writings  of  some  of  the  older  physiologists, 
in  which  reflex  action,  as  it  is  now  understood,  had  been  mentioned  more  or  less  defi- 
nitely. In  the  history  of  important  advances  in  physiological  knowledge,  it  has  often 
been  the  case  that  discoveries  have  been  foreshadowed  by  the  earlier  writers ;  and  bibli- 
ographical research  shows  that  the  literature  of  the  cord  as  a  nerve-centre  forms  no 
exception  to  this,  which  is  almost  the  rule.  Some  of  the  allusions  to  the  cord  as  a  centre 
of  reflex  action,  made  anterior  to  1833,  are  vague  and  indefinite  ;  but,  on  the  other  hand, 
certain  excito-motor  actions  were  very  accurately  described  by  Legallois,  as  early  as 
1812.  Marshall  Hall  grouped  and  classified  these  phenomena  and  showed  their  relations 
to  the  cord  as  an  independent  centre ;  but  he  has  no  claim  to  the  title  of  the  discoverer 
of  reflex  action,  and  his  experiments  themselves  presented  little  that  was  really  new. 

The  experiments  of  Marshall  Hall,  published  in  1832  and  1833,  are  familiar  to  every 
physiologist,  as  supplying  nearly  all  of  the  omissions  of  previous  observers.  The  points 
which  he  assumed  to  have  experimentally  demonstrated  by  his  researches  are  the  follow- 
ing: A  decapitated  animal,  the  only  part  of  the  cerebro-spinal  axis  which  remains  being 
the  spinal  cord,  will  make  no  movements,  if  completely  protected  from  all  external  im- 
pressions. An  impression  made  upon  the  sensory  nerves  of  a  decapitated  animal  is 
reflected  by  the  cord,  through  the  motor  nerves,  to  the  muscles,  and  gives  rise  to  reflex 
movements.  If  the  cord  be  destroyed,  no  movements  follow  stimulation  of  the  surface. 
If  the  centripetal  and  the  centrifugal  nerves  be  divided,  no  reflex  movements  can  take 
place.  Experiments  upon  decapitated  animals  accord  with  the  results  of  observations 
upon  acephalous  foetuses  and  in  cases  of  complete  paraplegia  from  injury  to  the  cord. 
All  of  the  involuntary  movements  observed  in  the  healthy  body  are  explained  by  the 
theory  of  reflex  action.  These  observations  of  Marshall  Hall  were,  in  the  main,  con- 
firmed by  Muller,  in  the  year  succeeding  their  first  publication  ;  and,  by  some  writers, 
the  credit  of  the  discovery  of  the  mechanism  of  reflex  action  is  given  to  both  Muller  and 
Marshall  Hall. 

From  the  point  of  view  which  the  present  condition  of  science  enables  us  to  take  with 
regard  to  the  reflex  action  of  the  cord,  we  have  to  determine  the  accuracy  of  the  obser- 
vations of  Marshall  Hall,  and  to  follow  out  the  advances  that  have  been  made  by  more 
recent  observers.  It  is  important,  as  the  first  step  in  our  inquiry,  to  ascertain  the  exact 
condition  of  decapitated  animals  as  regards  their  capacity  for  muscular  movements  ;  and 
upon  this  point  there  is  somex  difference  of  opinion.  Marshall  Hall  thought  that  an 
animal  (a  frog,  for  example)  after  decapitation,  was  incapable  of  any  voluntary  move- 
ment, or  of  any  movement  which  did  not  have,  for  its  exciting  cause,  an  external 
impression.  We  take  the  example  of  frogs,  because  these  are  the  animals  most  com- 
monly used  by  experimenters. 

All  who  have  experimented  upon  frogs  have  seen  them  jump  about  vigorously  after 
decapitation ;  and  the  question  whether  these  be  spontaneous  movements,  so  called,  or 
an  excito-motor  action,  is  more  difficult  to  determine  than  would  at  first  sight  appear. 
It  would  be  unphilosophical  to  assume  that,  because  the  animal  has  been  decapitated,  the 
movements  are  due  to  external  impressions  only,  if  we  use  this  as  evidence  against  the 
possibility  of  spontaneous  movements  under  these  conditions.  The  obvious  necessity  of 
the  argument  is  to  remove  all  possibility  of  external  impressions  or  of  irritation  of  the 
cord  itself.  Upon  this  point,  we  can  only  speak  positively  from  our  own  experiments. 
If  a  frog  be  decapitated,  so  as  to  leave  only  the  spinal  cord  intact,  if  we  wait  for  from 


ACTION  OF  THE   SPINAL   CORD  AS  A  NERVE-CENTRE.  685 

one  to  three  minutes  until  the  effects  of  the  shock  and  local  irritation  have  subsided,  if 
we  then,  when  the  animal  has  become  perfectly  quiet,  cover  it  with  a  bell-glass,  and 
finally,  if  we  remove  all  possibility  of  jarring  the  table  on  which  the  animal  is  placed, 
there  is  no  movement  of  muscles.  In  making  an  experiment  of  this  kind,  we  occasionally 
see  movements  which  are  due  to  a  very  feeble  impression,  such  as  a  breath  of  air  or  a 
jar  from  the  street,  but  which  is  perfectly  evident  to  the  observer ;  and,  when  a  move- 
ment is  once  made,  this  gives  rise  to  another  impression,  and  thus,  successive  actions  of 
the  muscles  may  take  place.  The  movements  in  jumping  are  so  simple  that  they  seem, 
sometimes  under  these  conditions,  to  be  voluntary.  The  effect  of  feeble  excitations  is 
also  very  marked  in  animals  poisoned  with  strychnine ;  but,  even  here,  we  do  not  have 
movements  unless  an  impression  be  first  made  upon  the  sensory  nerves.  When  we 
come  to  experiments  upon  the  mammalia,  there  can  hardly  be  any  question  of  this  kind ; 
for  here,  as  the  rule,  no  movements  are  observed  after  the  encephalic  ganglia  have  been 
removed,  unless  the  sensory  nerves  be  pretty  strongly  stimulated.  Analogous  phenomena 
are  observed  in  the  lower  extremities,  in  cases  of  paraplegia  in  the  human  subject. 

The  next  important  question  to  determine  is  with  regard  to  the  nature  of  movements 
excited  by  external  stimulation  in  decapitated  animals,  especially  frogs ;  for  some  of  these 
movements  are  so  regular  as  to  appear  to  be  connected  with  sensation  and  volition.  The 
experiments  of  Pfluger  upon  this  point  are  very  remarkable.  These  have  been  repeatedly 
confirmed,  and  there  can  be  no  doubt  with  regard  to  their  accuracy.  Pfluger  carefully  re- 
moved from  a  frog  the  entire  encephalon,  leaving  only  the  spinal  cord.  He  then  touched 
the  surface  of  the  thigh  over  the  inner  condyle  with  acetic  acid,  to  the  irritation  of  which 
frogs  are  peculiarly  sensitive.  The  animal  thereupon  rubbed  the  irritated  surface  with  the 
foot  of  the  same  side,  apparently  appreciating  the  locality  of  the  irritation,  and  endeavor- 
ing, by  a  voluntary  effort,  to  remove  it.  The  foot  of  this  side  was  then  amputated,  and 
the  irritation  was  renewed  in  the  same  place.  The  animal  made  an  ineffectual  effort  to 
reach  the  spot  with  the  amputated  member,  and,  failing  in  this,  after  some  general  move- 
ments of  the  limbs,  rubbed  the  spot  with  the  foot  of  the  opposite  side.  Although  this 
experiment  does  not  always  progress  precisely  in  the  manner  described,  it  has  succeeded 
perfectly  in  so  many  instances  as  to  lead  some  physiologists  to  conclude  that  sensation 
and  volition  are  not  entirely  abolished  by  removal  of  the  encephalon,  at  least  in  frogs. 

The  remarkable  phenomena  just  detailed  are  to  be  regarded  from  two  points  of  view : 
first,  with  reference  to  their  bearing  upon  the  question  of  the  existence  of  perception  and 
volition  in  the  spinal  cord  of  the  frog ;  and  second,  the  question  of  the  application  of 
these  phenomena  to  the  physiology  of  the  cord  in  man  and  the  higher  classes  of  animals. 
The  conditions  of  the  experiment  in  the  frog  are  simply  these  :  Instead  of  exposing  the 
surface  to  a  single  and  instantaneous  stimulation,  the  excito-motor  effects  of  which  are 
observed  as  a  direct  response  to  the  irritation  and  immediately  cease,  we  have,  by  the 
application  of  acetic  acid  to  the  surface,  a  prolonged  impression  upon  the  sensory  nerves, 
which,  by  virtue  of  the  anatomical  connections  between  the  different  parts  of  the  cord, 
is  probably  dispersed  throughout  the  entire  spinal  axis.  That  powerful  impressions  may 
be  thus  dispersed,  there  can  be  no  doubt,  as  we  shall  see  farther  on.  The  phenomena 
under  consideration  certainly  point  to  an  appreciation  by  the  cord  of  the  locality  of  a 
powerful  impression,  and  this  could  be  manifested  in  an  animal  only  by  an  apparent 
muscular  effort  to  reach  the  irritated  spot ;  but  we  can  hardly  reason  from  this  fact  that, 
in  man  and  the  higher  animals,  the  spinal  cord  shares  with  the  brain  the  power  of  appre- 
ciating what  we  know  as  sensation  and  of  generating  the  stimulus  of  true  voluntary 
movement.  If  a  sudden  and  very  powerful  painful  impression  be  made  upon  the  surface 
in  man  under  normal  conditions,  the  hand  may  be  instantly  applied  to  the  affected  part, 
apparently  before  we  really  appreciate  the  pain  or  have  time  to  make  a  distinct  effort  of 
the  will ;  but  the  connections  between  the  different  parts  of  the  cerebro-spinal  axis  do 
not  permit  us  to  isolate  the  action  of  the  cord.  Certain  it  is  that,  in  the  higher  animals, 
after  removal  of  the  encephalon,  and  in  experiments  upon  decapitated  criminals  and 


686  NERVOUS  SYSTEM. 

patients  suffering  from  paraplegia,  there  is  no  evidence  of  true  sensation  or  volition  in  the 
spinal  cord ;  and,  in  man  and  the  higher  animals,  we  must  regard  all  muscular  movements 
which  depend  solely  upon  the  action  of  the  cord  as  a  nerve-centre  as  automatic  and 
entirely  independent  of  consciousness  and  of  the  will. 

It  is  easy  to  determine,  by  experiments  to  which  we  have  already  incidentally  alluded, 
that  the  muscular  movements  dependent  upon  nervous  action,  occurring  in  decapitated 
animals,  are  due  to  the  action  of  the  spinal  cord  as  a  nerve-centre.  In  an  animal  in  which 
the  reflex  phenomena  are  very  marked,  as  they  are  after  decapitation,  especially  if  the 
animal  be  poisoned  with  strychnine  or  opium,  all  movements  immediately  cease  when 
the  cord  is  destroyed.  That  the  gray  matter  of  the  cord  is  the  part  concerned  as  a  centre 
in  the  production  of  these  phenomena,  is  probable,  in  view  of  what  we  know  with  regard 
to  the  general  functions  and  properties  of  this  substance ;  and  experiments  have  shown 
that  this  is  the  fact.  If,  in  a  decapitated  frog,  we  make  an  incomplete  longitudinal  sec- 
tion of  the  cord  in  the  median  line,  leaving  only  a  slight  communication  between  the  two 
sides,  we  may  sometimes  succeed,  by  strongly  irritating  the  skin  of  one  leg,  in  producing 
reflex  movements,  not  only  in  the  same  leg,  but  in  the  leg  of  the  opposite  side ;  and  it  is 
reasonable  to  suppose  that  the  irritation  is  propagated  from  one  side  to  the  other  through 
the  cells  of  the  gray  matter. 

The  conditions  essential  to  the  manifestations  of  reflex  phenomena  depending  upon 
the  action  of  the  cord  are  very  simple  and  easily  understood. 

In  the  first  place,  it  is  necessary  that  one  or  more  of  the  posterior  roots  of  the  spinal 
nerves  should  be  in  communication  with  the  cord,  in  order  to  conduct  the  impression  to 
this  nerve-centre.  If  all  of  the  posterior  roots  be  divided,  there  is  no  nervous  commu- 
nication between  the  periphery  and  the  centre,  and  no  movements  follow  irritation  of  the 
surface.  When  the  excitability  of  the  cord  is  exaggerated,  as  in  poisoning  by  strychnine, 
a  single  posterior  root  is  sufficient  to  conduct  an  impression  to  the  cord,  which  will  give 
rise  to  violent  contractions  of  all  the  muscles.  This  is  due  to  a  dispersion  of  the  impres- 
sion, under  these  conditions  of  increased  excitability,  from  the  single  point  of  entrance  of 
the  posterior  root,  throughout  the  cord.  In  animals  that  have  been  simply  decapitated, 
a  similar  diffusion  of  impressions  may  also  take  place.  If  a  comparatively  feeble  single 
impression  be  made  upon  any  part  of  the  general  surface,  as  the  rule,  the  subjacent  muscles 
only  are  the  seat  of  contraction ;  but,  if  the  impression  be  more  powerful,  or  if  it  be 
prolonged,  as  when  we  apply  a  drop  of  acetic  acid  to  any  part  of  the  skin  of  a  frog,  this 
impression  may  be  diffused  throughout  the  cord,  producing  contractions  of  the  general  mus- 
cular system.  We  have  already  shown,  in  treating  of  the  general  properties  of  the 
sensory  nerves,  that  an  impression  made  at  any  point  in  the  course  of  a  nerve  is  conducted 
to  the  centre.  Reflex  movements  may,  consequently,  be  produced  by  stimulating  the 
sensory  nerves  in  their  course  or  by  irritating  the  posterior  roots  of  the  spinal  nerves. 

We  have  already  stated  that  the  cord  must  retain  its  anatomical  integrity,  in  order  to 
receive  an  impression  made  upon  the  centripetal  nerves  and  transform  it,  as  it  were,  into 
a  stimulus,  which  is  reflected  back  by  the  motor  nerves  and  produces  muscular  contrac- 
tion. It  is  also  evident  that  the  motor  nerves  must  retain  their  connection  with  the  cord 
and  be  in  a  condition  to  conduct  the  stimulus  reflected  by  the  cord  to  the  muscles. 

The  reflex  excitability  of  the  spinal  cord  is  increased  to  a  marked  degree  by  separating 
this  portion  of  the  cerebro-spinal  axis  from  the  encephalon,  and  the  same  is  true  for  the 
lower  portion  of  the  cord,  when  a  section  is  made  in  the  dorsal  or  lumbar  region.  It 
is  difficult  to  find  an  entirely  satisfactory  explanation  of  this  fact ;  and  the  phenomena 
observed  under  these  conditions  are,  in  this  regard,  like  the  exaggerated  sensibility  of 
portions  of  the  general  surface  after  section  of  certain  columns  of  the  cord. 

In  experiments  upon  the  lower  animals,  the  reflex  phenomena  are  greatly  exaggerated  in 
intensity  in  the  tetanic  condition  observed  in  poisoning  by  opium  or  strychnine.  Take,  for 
example,  a  frog  decapitated  and  poisoned  with  strychnine.  No  reflex  movements 
occur  unless  an  impression  be  made  upon  the  sensory  nerves ;  but  the  slightest  irrita- 


ACTION   OF  THE   SPINAL   CORD  AS  A  NERVE-CENTRE. 


687 


tion,  such  as  a  breath  of  air  or  a  slight  jar,  throws  the  entire  muscular  system  into  a 
condition  of  violent  tetanic  spasm.  The  same  phenomena  are  observed  in  cases  of  poison- 
ing by  strychnine  or  of  tetanus  in  the  human  subject.  This  fact  is  important  in  its  rela- 
tions to  the  treatment  of  these  conditions ;  for  it  is  evident  that, 
in  such  cases,  the  exhaustion  due  to  the  violent  spasms  may  be 
moderated  by  carefully  avoiding  all  unnecessary  irritation  of 
the  surface. 

It  was  shown  a  number  of  years  ago,  that  the  inhalation 
of  anesthetic  agents  may  abolish  all  of  the  ordinary  reflex  phe- 
nomena. Whether  this  be  due  to  an  action  upon  the  cord  itself 
or  to  a  paralysis  of  the  sensory  nerves,  it  is  difficult  to  determine. 
Ordinarily,  in  animals  rendered  insensible  by  anesthetics,  the 
reflex  acts  of  respiration  continue ;  but  these  may  also  be  arrested, 
as  has  been  observed  by  all  who  have  experimented  with  anaes- 
thetics, especially  with  chloroform.  A  common  way  of  deter- 
mining that  an  animal  is  completely  under  the  influence  of  ether 
is  by  an  absence  of  the  reflex  act  of  closing  the  eyelids  when 
the  cornea  is  touched. 

It  now  only  remains  to  show  that  the  phenomena  of  reflex 
action  observed  in  experiments  upon  the  inferior  animals,  espe- 
cially frogs,  are  applicable  to  the  human  subject,  and  to  indi- 
cate the  muscular  actions  which  depend  upon  the  cord  as  a 
nerve-centre. 

It  is  only  necessary,  after  what  has  gone  before,  to  indicate 
in  a  general  way  the  phenomena  observed  in  the  human  sub- 
ject which  illustrate  the  reflex  action  of  the  cord.  It  is  a 
common  observation,  in  cases  of  paraplegia  in  which  the  lower 
portion  of  the  cord  is  intact,  that  movements  of  the  limbs  fol- 
low titillation  of  the  soles  of  the  feet,  these  movements  taking 
place  independently  of  the  consciousness  or  the  will  of  the  subject 
experimeuted  upon.  Acephalous  foetuses  will  present  general 
reflex  movements  and  movements  of  respiration,  and  will  even 
suck  when  the  finger  is  introduced  into  the  mouth.  Observations 
FIG.  ill.— Frog  poisoned  with  of  this  kind  are  so  numerous  and  familiar  that  they  need  not  be 
me.  (Li6geois.)  cjted  in  detail.  Experiments  have  also  been  made  upon  crimi- 
nals after  decapitation ;  and,  although  the  reflex  phenomena  are  not  so  well  marked  and 
cannot  be  excited  so  long  after  death  as  in  cold-blooded  animals,  they  are  sufficiently  distinct. 
It  is  difficult,  in  studying,  in  the  human  subject,  the  ordinary  phenomena  of  move- 
ments in  the  voluntary  muscular  system,  to  isolate  the  reflex  phenomena  from  those  acts 
involving  sensation  and  volition.  In  many  persons,  titillation  of  the  soles  of  the  feet  pro- 
duces violent  contractions  of  muscles,  which  cannot  be  arrested  by  an  effort  of  the  will,  and 
this  may  even  be  followed  by  general  convulsions.  When  we  unexpectedly  touch  an  irri- 
tating surface  with  the  hand,  the  muscles  of  the  arm  act  so  quickly  that  we  may  suppose 
that  this  takes  place  before  we  really  appreciate  the  painful  sensation,  and,  if  the  impres- 
sion be  very  severe,  we  may  have  movements  more  or  less  general ;  in  operating  upon 
highly-sensitive  parts,  it  is  frequently  impossible  to  arrest  reflex  movements,  as  the  closing 
of  the  eyelids  when  the  cornea  is  touched  ;  true  reflex  movements  may  be  produced  by 
carefully-executed  experiments  upon  persons  asleep ;  we  cannot  arrest  the  act  of  vomit- 
ing induced  by  titillation  of  the  fauces  ;  and  other  instances  of  this  kind  might  be  cited. 

Most  of  the  true  involuntary  movements  are  reflex  ;  but  these  have  been  or  will  be 
considered  under  their  proper  heads.  The  movements  of  deglutition  depend  upon  an 
impression  made  upon  the  mucous  membrane  of  the  pharynx,  etc.  The  movements  of 
respiration  are  excited  by  an  impression  made  upon  the  general  sensory  nerves,  due  to 
want  of  oxygen,  as  we  have  shown  in  treating  of  respiration.  The  ejaculation  of  semen 


688  NERVOUS  SYSTEM. 

is  also  reflex.  Important  reflex  actions  take  place  through  the  sympathetic  nerves,  such 
as  the  movements  of  the  intestines,  vaso-motor  movements,  etc. ;  but  these  will  be  con- 
sidered fully  under  the  head  of  the  sympathetic  system.  Secretion,  the  action  of  the 
heart,  the  contractions  of  the  uterus,  the  action  of  the  sphincters,  the  movements  of  the 
iris,  etc.,  are  regulated  by  the  sympathetic  and  the  cerebro-spinal  system. 

As  regards  the  farther  action  of  the  cord  as  a  nerve-centre,  there  are  undoubtedly  many 
functions  which  are  influenced  more  or  less  by  this  portion  of  the  cerebro-spinal  axis ;  but 
these  have  been  treated  of  under  their  appropriate  heads  or  will  be  considered  hereafter. 


CHAPTER    XXI. 

THE    ENCEPHALIC    GANGLIA. 

Physiological  divisions  of  the  encephalon— Weight  of  different  parts  of  the  brain  and  of  the  entire  encephalon— Some 
points  in  the  physiological  anatomy  of  the  encephalon  and  its  connections — The  cerebrum— General  properties  of 
the  cerebrum— Functions  of  the  cerebrum— Extirpation  of  the  cerebrum  in  the  lower  animals— Pathological  facts 
bearing  upon  the  functions  of  the  cerebrum — Comparative  development  of  the  cerebrum  in  the  lower  animals — 
Development  of  the  cerebrum  in  different  races  of  men  and  in  different  individuals— Location  of  the  faculty  of  artic- 
ulate language  in  a  restricted  portion  of  the  anterior  cerebral  lobes — The  cerebellum — Some  points  in  the  physio- 
logical anatomy  of  the  cerebellum — Course  of  the  fibres  in  the  cerebellum — General  properties  of  the  cerebellum — 
Functions  of  the  cerebellum — Extirpation  of  the  cerebellum  in  animals — Pathological  facts  bearing  upon  the  func- 
tions of  the  cerebellum — Connection  of  the  cerebellum  with  the  generative  function — Development  of  the  cerebel- 
lum in  the  lower  animals— Ganglia  at  the  base  of  the  encephalon— Corpora  striata—  Optic  thalami— Tubercula 
quadrigemina,  or  optic  lobes — Ganglion  of  the  tuber  annulare — Medulla  oblongata — Physiological  anatomy  of  the 
medulla  oblongata — Functions  of  the  medulla  oblongata — Connection  of  the  medulla  oblongata  with  respiration- 
Vital  point — Connection  of  the  medulla  oblongata  with  various  reflex  acts — Rolling  and  turning  movements  fol- 
lowing injury  of  certain  parts  of  the  encephalon— General  properties  of  the  peduncles. 

THE  anatomy  of  the  encephalon  is  so  complex,  that  it  can  be  treated  of  with  advan- 
tage only  by  a  very  minute  and  carefully-illustrated  description,  such  as  is  to  be  found  in 
some  of  the  elaborate  anatomical  works  or  in  special  treatises  upon  the  nervous  system. 
We  shall  not  consider  under  a  distinct  head  the  general  physiological  anatomy  of  the 
brain,  for  the  reason  just  given,  and  also  because  we  are  as  yet  ignorant  of  the  exact 
connection  between  the  structure  and  arrangement  of  many  of  its  parts  and  their  physi- 
ology. We  know  that  the  gray  substance  is  capable  of  appreciating  general  and  special 
impressions  received  by  the  peripheral  nervous  system,  and  of  generating  the  so-called 
nerve-force.  Impressions  are  conveyed  to  this  portion  of  the  cerebro-spinal  axis  by  the 
sensory  conductors,  passing  to  the  brain,  either  through  the  cord  or  by  the  cranial 
nerves,  and  by  the  nerves  of  special  sense,  as  well  as  those  of  general  sensibility.  The 
stimulus  which  gives  rise  to  voluntary  movements  is  generated  in  the  brain  and  is  con- 
veyed by  the  motor  nerves  to  the  appropriate  muscles.  We  have  seen,  also,  that  the 
centres  of  the  encephalon  may  be  concerned  in  reflex  action.  In  addition,  parts  of  the 
brain  act  as  centres  of  sensation  and  volition  and  are  concerned  in  the  varied  phenomena 
of  intellection. 

The  encephalon,  or  what  is  ordinarily  known  as  the  brain,  consists  of  a  number  of 
ganglia,  or  collections  of  gray  matter,  connected  with  each  other,  and  also,  by  the  differ- 
ent columns  of  the  cord,  with  the  motor  and  sensory  nerves  of  the  general  system.  Cer- 
tain of  these  ganglia  have  separate  and  distinct  functions  which  are  more  or  less  com- 
pletely understood ;  while  there  are,  in  addition,  masses  of  gray  substance,  the  physio- 
logical relations  of  which  are  as  yet  obscure  or  entirely  unknown.  The  greatest  and 
the  most  important  of  all,  the  gray  matter  of  the  cerebral  hemispheres,  undoubtedly  has 
subdivisions  connected  with  distinct  attributes  of  the  mind  ;  but  our  positive  knowledge 
with  regard  to  these  divisions  is,  at  the  present  day,  very  meagre,  although  this  subject 
has  long  been  a  favorite  field  for  philosophical  speculation. 

Confining  ourselves  strictly  to  the  limits  of  positive  information,  we  may  recognize 


THE   CEREBRAL   HEMISPHERES.  689 

the  following  parts  of  the  encephalon  as  distinct  ganglia:  1.  The  gray  matter  of  the 
cerebral  hemispheres  ;  2.  The  gray  matter  of  the  cerebellum  ;  3.  'The  olfactory  ganglia  ; 
4.  The  gray  matter  of  the  corpora  striata ;  5.  The  gray  matter  of  the  optic  thalami ;  6. 
The  tubercula  quadrigemina  ;  7.  The  gray  matter  of  the  tuber  annulare,  or  pons  Varolii ; 
8.  The  ganglion  of  the  medulla  oblongata.  In  addition,  the  following  parts  have  been 
made  the  subject  of  physiological  investigation  or  speculation,  with  results  more  or  less 


FIG.  215.— Vertical  section  of  the  encephalon.    (Hirschfeld.) 

1,  medulla  oblongata ;  2,  tuber  annulare;  3,  cerebral  peduncle;  4,  cerebellum;  5,  aqueduct  of  Sylvius  ;  6,  valve 
of  Vieussens;  7,  tubercula  quadrigemina;  8, pineal  gland;  9,  inferior  peduncle ;  10,  superior  peduncle; 
11,  middle  portion  of  the  great  cerebral  fissure  ;  12,  optic  thalamus;  13,  13,  gray  commissure;  14,  choroid 
plexus;  15,  infundibulum  ;  1(5, pituitary  body;  17,  tuber  cinereum;  18,  bulb  of  the  fornix;  19,  anterior  per- 
forated space;  20,  root  of  the  motor  oculi  coinmunis;  21,  optic  nerve;  22,  anterior  commissure  of  the  cerebtum; 
23,  foramen  of  Monro ;  24,  section  of  the  fornix  ;  25,  septum  lucidum ;  26,  27,  28,  corpus  callosum ;  29,  30,  31, 
32,  33,  34,  convolutions  and  sulci  of  the  cerebrum.  The  olfactory  ganglia  and  corpora  striata  are  not  shown  in 
this  section. 

definite  :  The  peduncles  of  the  cerebrum  and  of  the  cerebellum  ;  the  pineal  gland  ;  the 
corpus  callosum  ;  the  septum  lucidum  ;  the  cerebral  ventricles ;  and  the  pituitary  body. 
We  have,  however,  little  if  any  positive  information  concerning  these  parts,  except  as 
regards  their  general  anatomical  relations  ;  and  their  physiology  really  amounts  to  little 
more  than  a  history  of  the  vague  speculations  of  the  ancients  or  the  fruitless  experiments 
of  modern  observers.  It  is  to  be  hoped  that  future  anatomical  investigations,  chiefly  in 
following  out  the  course  of  the  fibres  of  the  encephalon  and  their  connections  with  the 
cells  of  the  different  collections  of  gray  matter,  will  throw  light  upon  the  functions  of  this 
part  of  the  cerebro-spinal  axis  ;  but,  at  present,  all  physiologists  will  admit  that  we  have 
received  very  little  aid  from  this  source.  In  our  anatomical  descriptions,  therefore,  we 
shall  confine  ourselves  to  those  points  that  are  strictly  physiological. 

Weight  of  different  Parts  of  the  Brain  and  of  the  entire  Encephalon. — Most  of  the 
tables  of  the  weight  of  the  healthy  adult  brain  of  the  Caucasian,  given  by  different  ob- 
servers, show  essentially  the  same  results,  the  differences  amounting  to  only  one  or  two 
ounces  for  the  entire  encephalon.  The  average  given  by  Quain  is  49£  ounces,  avoirdu- 
pois, for  the  male,  and  44  ounces  for  the  female.  This  is  the  general  result  obtained  by 
combining  the  tables  published  by  Sims,  Clendinning,  Tiedemann,  and  Reid.  The  num- 
ber of  male  brains  weighed  was  278,  and  of  female  brains,  191.  In  males,  the  minimum 
weight  was  34  ounces,  and  the  maximum,  65  ounces.  In  170  cases  out  of  the  278,  the 
weight  ranged  from  46  to  53  ounces,  which  may  be  taken  as  the  general  average.  In 
females,  the  minimum  was  31  ounces,  and  the  maximum,  56  ounces.  In  125  cases  out 
of  the  191,  the  weight  ranged  from  41  to  47  ounces. 
44 


690  NERVOUS  SYSTEM. 

Qualn  assumes,  from  various  researches,  that,  in  new-born  infants,  the  brain  weighs 
11-65  ounces,  for  the  male,  and  10  ounces,  for  the  female.  In  both  sexes,  "  the  weight  of 
the  brain  generally  increases  rapidly  up  to  the  seventh  year,  then  more  slowly  to  between 
sixteen  and  twenty,  and  again  more  slowly  to  between  thirty-one  and  forty,  at  which 
time  it  reaches  its  maximum  point.  Beyond  that  period,  there  appears  a  slow  but  pro- 
gressive diminution  in  weight  of  about  one  ounce  during  each  subsequent  decennial  period ; 
thus  confirming  the  opinion,  that  the  brain  diminishes  in  advanced  life." 

The  comparative  weights  of  the  several  parts  of  the  encephalon,  calculated  from 
observations  upon  the  brains  of  fifty- three  males  and  thirty-four  females,  between  the  ages 
of  twenty-five  and  fifty-five,  are  as  follows : 


Divisions  of  the  encephalon. 

Males. 

Females. 

43'98  oz. 

38'75  oz 

Average  weight  of  the  cerebellum 

6-26    " 

4'76    " 

Average  weight  of  the  pons  and  medulla  oblongata  .  . 

0-98    " 

1-01    " 

Average  weight  of  the  entire  encephalon                  . 

50-21  oz 

44-52  oz 

The  proportionate  weight  of  the  cerebellum  to  that  of  the  cerebrum,  in  the  male,  is 
as  1  to  8^,  and  in  the  female,  as  1  to  8£. 

The  specific  gravity  of  the  whole  encephalon  is  about  1036,  that  of  the  gray  matter 
being  1034,  and  of  the  white,  1040. 

The  above  weights  are  quoted  from  Quain's  admirable  work  upon  anatomy,  and  the 
normal  range  of  variations  and  averages  only  are  given.  When  we  come  to  treat  of  the 
cerebrum  and  its  relations  to  intelligence,  we  shall  discuss  the  weights  of  the  brain  in 
idiots  and  in  persons  of  extraordinary  intellectual  power,  as  far  as  any  data  upon  these 
points  are  to  be  found. 

Some  Points  in  the  Physiological  Anatomy  of  the  Encephalon  and  its  Connections. — 
The  direction  of  the  fibres  in  the  encephalon,  their  connections  with  the  cells  of  the 
gray  substance,  the  course  of  commissural  fibres  connecting  together  the  different  parts 
of  the  gray  substance  of  the  cerebrum,  the  cerebellum,  and  the  deeper  ganglia,  and 
finally  the  avenues  of  communication  between  the  fibres  of  the  encephalon  and  the  cord, 
are  points  of  exceeding  intricacy ;  and  many  of  them  are  still  so  uncertain  and  obscure, 
that  they  cannot  as  yet  be  connected  satisfactorily  with  the  exact  results  of  physiological 
inquiry.  All  that  we  can  do  at  present,  is  to  recognize  certain  ganglionic  masses,  the 
separate  functions  of  which  have  been  more  or  less  accurately  defined,  and  to  show,  as  far 
as  possible,  their  anatomical  relations  to  each  other  and  to  the  spinal  cord. 

The  separate  collections  of  gray  matter  concerning  which  we  possess  positive  physio- 
logical knowledge  are,  the  gray  matter  of  the  cerebral  hemispheres  and  of  the  cerebellum, 
the  corpora  striata,  optic  thalami,  tuber  annulare,  or  pons,  and  the  medulla  oblongata. 
To  these  may  be  added,  the  olfactory  ganglia,  which  preside  over  the  sense  of  smell,  and 
the  tubercula  quadrigemina,  or  optic  lobes,  which  are  the  centres  connected  with  vision. 
The  minute  anatomy  of  the  nerve-fibres  and  the  nerve-cells,  with  their  mode  of  connec- 
tion with  each  other,  have  been  already  considered  with  sufficient  minuteness  under  the 
head  of  the  general  structure  of  the  nervous  system.  We  shall  here  discuss  chiefly  the 
direction  of  the  fibres  through  which  the  encephalic  ganglia  are  connected  with  the  periph- 
ery, the  fibres  connecting  the  different  ganglia  with  each -other,  and,  in  the  case  of  the 
larger  ganglia,  certain  commissural  fibres  connecting  together  their  different  parts. 

In  the  wealth  of  literature  pertaining  to  the  minute  anatomy  of  the  encephalon,  it  is 
somewhat  difficult  to  separate  and  define  the  well-established  facts  which  have  a  direct 
bearing  upon  physiology.  Perhaps  the  most  elaborate  and,  to  a  certain  extent,  the  most 
satisfactory  observations  upon  the  various  points  to  be  considered,  are  those  of  Luys ;  but 
this  author  describes  the  course  of  the  fibres  with  an  exactitude  that  seems  hardly  justi- 


THE   CEREBRAL   HEMISPHERES. 


691 


fied,  in  all  instances,  by  the  facts,  in  view  of  the  inevitable  difficulty  and  uncertainty  of 
some  of  the  processes  employed ;  and  the  graphic  and  admirable  delineations  by  which 
the  work  is  illustrated,  though  professedly  schematic,  present  a  degree  of  ideality  which 
inspires  some  distrust  with  regard  to  the  accuracy  of  the  general  conclusions.  According 
to  Luys,  the  fibres  of  the  encephalon  have  several  directions,  as  follows : 

The  gray  matter  of  the  cerebral  hemispheres,  as  we  shall  see  farther  on,  is  composed 
of  a  mass  of  nerve-cells,  connected  together  by  their  prolongations  into  a  plexus,  which, 
in  its  turn,  is  connected  with  the  fibres  of  the  white  substance.  From  this  cortical  cellu- 
lar plexus,  white  fibres  arise,  which  may  be  divided,  according  to  their  direction  and 
destination,  into  two  classes  :  The  first  class  consists  of  curved  commissural  fibres,  which 
pass  into  the  white  substance  to  a  certain  depth  and  return  to  the  gray  matter,  connect- 
ing thus  the  gray  substance  of  adjacent  convolutions.  The  existence  of  these  fibres 
and  their  direction  are  well  established.  The  second  class  consists  of  fibres  which, 
arising  from  the  gray  substance  of  the  convolutions,  connect  these  with  the  corpora 
striata  and  the  optic  thalanru  These  may  be  called  the  converging  fibres;  and  their 
general  direction,  as  far  as  it  has  been  ascertained,  is  as  follows : 


FIG.  226.— Diagrammatic  representation  of  tlie  direction  of  the  fibres  in  the  cerebrum.    (Le  Bon.) 


Arising  from  the  internal,  concave  surface  of  the  cortical  substance  of  the  cerebrum, 
the  converging  fibres,  at  first  running  side  by  side  with  the  curved  commissural  fibres, 
separate  from  the  latter  as  they  curve  backward  to  pass  again  to  the  cortical  substance, 
and  are  directed  toward  the  corpora  striata  and  the  optic  thalami.  The  limits  of  the 
irregular  planes  of  separation  of  the  commissural  and  the  converging  fibres  contribute  to 
form  the  boundaries  of  the  ventricular  cavities  of  the  brain.  If  we  study  the  course  of 
the  converging  fibres  arising  from  all  points  in  the  concave  surface  of  the  cerebral  gray 
matter,  we  find  that  they  take  various  directions.  The  fibres  from  the  anterior  region  of 
the  cerebrum  pass  backward  and  form  distinct  fasciculi  which  converge  to  the  gray  sub- 


692  NERVOUS  SYSTEM. 

stance  of  the  corpora  striata.  The  fibres  from  the  middle  portion  converge  regularly  to 
the  middle  region  of  the  external  portions  of  the  optic  thalami.  The  fibres  from  the  pos- 
terior portion  pass  from  behind  forward  and  distribute  themselves  in  the  posterior  portion 
of  the  optic  thalami.  The  fibres  from  the  convolutions  of  the  hippocampi  and  the  fascia 
dentata  are  lost  in  the  gray  substance  lining  the  internal  borders  of  the  optic  thalami.  In 
addition  to  these  converging  fibres  and  the  curved  commissural  fibres  connecting  the 
different  convolutions  of  each  hemisphere  with  each  other,  are  commissural  fibres  which 
connect  the  two  hemispheres,  as  well  as  fibres  connecting  together  the  corpora  striata 
and  the  optic  thalami  of  the  two  sides. 

Certain  of  the  fibres  converging  from  the  gray  substance  of  the  hemispheres  to  the 
corpora  striata  and  optic  thalami  are  probably  connected  with  the  cells  in  the  gray  mat- 
ter of  these  parts.  Other  fibres  pass  through  the  corpora  striata  and  optic  thalami  to 
become  finally  connected  with  the  fibres  of  the  medulla  oblongata,  and,  through  the 
medulla  oblongata,  with  the  columns  of  the  spinal  cord.  Following  the  antero-lateral 
columns  of  the  cord  from  below  upward,  they  ascend  to  the  medulla  oblongata,  decussate 
in  the  median  line,  and  pass  from  the  medulla  to  the  brain.  Certain  of  these  ascending 
fibres,  which  are  nearly  all  continuations  of  the  antero-lateral  columns  of  the  cord,  ascend 
to  the  brain  by  passing  deeply  through  the  pons  Varolii ;  other  fibres  ascend  in  the 
cerebral  peduncles,  or  crura  cerebri ;  and  other  fibres  pass  to  the  tubercula  quadrigemina. 
As  the  bundles  of  fibres  ascend  from  the  medulla  oblongata,  they  become  more  and  more 
numerous  by  reinforcements  of  fibres,  probably  derived  from  the  cells  of  the  collections 
of  gray  matter  in  their  course. 

We  have  attempted,  in  the  above  sketch  of  the  fibres  of  the  brain,  to  give  a  succinct 
account  of  the  points  that  are  most  interesting  from  their  physiological  relations,  and  to 
confine  our  description,  as  far  as  possible,  to  anatomical  facts  that  have  been  definitively 
settled  and  are  now  generally  accepted.  But,  as  we  have  betore  remarked,  the  course 
of  the  fibres  and  their  connections  are  so  exceedingly  intricate,  that  we  cannot  rely 
entirely  upon  purely  anatomical  investigations.  The  results  obtained  by  anatomists  should 
be  controlled,  as  far  as  possible,  by  physiological  and  pathological  observations.  When 
anatomical  researches  are  directly  opposed  to  the  conclusions  to  be  deduced  from  experi- 
ments upon  living  animals,  in  view  of  the  great  uncertainty  of  the  former,  it  will  generally 
be  reasonable  to  assume  that  they  are  erroneous  or  incomplete.  We  know,  as  the  results 
of  experiments  upon  animals,  that  the  motor  stimulus  is  conducted  from  the  brain  by  the 
antero-lateral  columns  of  the  cord,  and  that  the  conducting  fibres  decussate  at  the  medulla 
oblongata.  This  fact  has  been  verified  by  pathological  observations,  chiefly  in  cases  of 
injury  to  the  brain-substance  from  haemorrhage,  softening,  etc.  We  know  that  impres- 
sions are  appreciated  as  sensations  in  some  part  of  the  cerebrum,  and  that  the  sensory 
conductors  also  decussate ;  as  is  shown  by  occasional  paralysis  of  both  motion  and  sensation 
as  a  consequence  of  brain-lesions.  It  is  evident,  therefore,  that  sensory  conductors  pass  to 
the  brain,  but  their  precise  course  is  not  easy  to  determine.  We  have  seen,  in  treating  of 
the  action  of  the  cord  as  a  conductor,  that  sensory  impressions  are  transmitted  by  the  gray 
substance  alone,  and  it  is  probably  through  connections  between  the  cells  of  the  different 
centres  that  these  impressions  are  finally  carried  to  the  brain.  The  physiological  fact  of 
the  conduction  of  sensory  impressions  is  fully  confirmed  by  pathology,  but  its  mechanism 
has  been  very  little  if  at  all  elucidated  by  anatomical  researches. 

We  have  remaining  certain  anatomical  points  relating  to  the  cerebrum,  cerebellum, 
tuber  annulare,  and  medulla  oblongata,  to  be  described  separately  in  connection  with 
these  divisions  of  the  encephalon. 

TJie   Cerebrum. 

The  anatomical  description  which  we  have  just  given  of  the  encephalon  will  answer 
for  most  of  the  points  of  physiological  interest  connected  with  the  cerebrum.  As  we 
have  seen,  the  cerebrum  constitutes  more  than  four-fifths  of  the  encephalic  mass.  Its 


GENERAL  PROPERTIES  OF  THE  CEREBRUM.         693 

gray  matter,  which  is  external  and  follows  the  convolutions,  is  from  ^  to  £  of  an  inch  in 
thickness.  Writers  have  described  this  substance  as  existing  in  several  layers,  but  this 
division  is  mainly  artificial.  In  certain  parts,  however,  particularly  in  the  posterior  por- 
tion of  the  cerebrum,  the  gray  substance  is  quite  distinctly  divided  into  two  layers,  by  a 
very  delicate  intermediate  layer  of  a  whitish  color. 

There  is  a  marked  difference  in  the  appearance  of  the  cells  in  the  most  superficial  and 
in  the  deepest  portions  of  the  gray  substance.  The  superficial  cells  are  small  and  present 
a  net- work  of  delicate,  anastomosing  fibres,  resembling  the  cells  of  the  posterior  cornua 
of  the  gray  substance  of  the  cord ;  while  the  deepest  cells  are  large  and  resemble  the  so- 
called  motor  cells  of  the  cord.  Between  these  two  extremes,  in  the  intermediate  layers, 
there  is  a  gradual  transition  in  the  size  of  the  cells.  This  anatomical  fact  points  to  the 
possibility  of  distinct  functions  of  the  cells  belonging  to  the  superficial  and  the  deep  layers ; 
viz.,  that  the  larger  cells  are  for  the  generation  of  the  motor  stimulus,  while  the  smaller 
are  for  the  reception  of  sensory  impressions.  This,  however,  is  a  mere  supposition,  inca- 
pable, as  yet,  of  positive  demonstration. 

The  mode  of  connection  between  the  cellular  and  the  fibrous  elements  of  the  ner- 
vous system  has  already  been  considered  and  does  not  demand  farther  mention.  We 
shall  also  pass  over  the  amorphous  matter,  nuclei,  myelocytes,  etc.,  found  in  the  cen- 
tral nervous  matter,  as  these  points  possess  little  or  no  physiological  interest. 

General  Properties  of  the  Cerebrum. — By  the  general  properties  of  the  cerebrum, 
we  mean  the  effect,  or  the  absence  of  effect,  observed  when  the  gray  or  white  sub- 
stance is  subjected  to  direct  irritation.  While  some  of  the  older  writers  state  that  the 
brain  is  both  irritable  and  sensible,  nearly  all  authorities,  up  to  a  very  recent  date, 
have  been  agreed  that  direct  stimulation  of  the  white  or  the  gray  substance  of  the 
greatest  part  of  the  brain  produces  neither  pain  nor  convulsive  movements.  In  numer- 
ous experiments  upon  pigeons,  we  have  invariably  noted  complete  insensibility  and  inex- 
citability  of  both  the  gray  and  the  white  substance  of  the  cerebral  hemispheres.  The 
generally-accepted  view  has  been  that  a  great  part  of  the  substance  of  the  cerebrum  is 
neither  excitable  nor  sensible,  in  the  sense  in  which  these  terms  are  applied  to  the  ordi- 
nary mixed  nerves.  There  can  be  no  doubt  with  regard  to  the  conducting  properties  of 
the  white  matter  of  the  brain,  but  the  nerve-fibres  here  seem  to  conduct  impressions 
conveyed  to  them  by  the  sensory  nerves  and  the  stimulus  generated  by  the  nerve-cells, 
without  being  capable  of  receiving  or  conducting  artificial  impressions  applied  directly  to 
their  substance. 

We  have  said  that  a  great  part  of  the  cerebral  substance  seems  to  be  neither  excitable 
nor  sensible  to  direct  stimulation ;  but  we  must  make  an  exception  in  favor  of  certain 
portions  of  the  cerebrum,  which  have  lately  been  shown  to  possess  excitability,  their 
action  being  confined  to  particular  sets  of  muscles.  In  1870,  Fritsch  and  Hitzig,  expos- 
ing the  cerebral  hemispheres  in  dogs,  found  that  certain  parts  of  its  anterior  portion 
responded  to  a  feeble  galvanic  current.  Each  galvanization  produced  movements  re- 
stricted to  particular  sets  of  muscles;  but  it  was  difficult  to  say  whether  the  contractions 
were  due  to  stimulation  of  the  white  or  of  the  gray  substance.  Different  centres  for  the 
sets  of  muscles  were  accurately  determined.  The  centre  for  the  muscles  of  the  neck 
was  located  in  the  middle  of  the  frontal  convolution ;  external  to  that,  was  a  centre  for 
the  extensor  and  adductor  muscles  of  the  forelegs ;  and  so  on,  other  centres  for  sets  of 
muscles  being  found  in  the  anterior  portion  of  the  hemispheres.  By  passing  an  inter- 
rupted current  through  these  parts,  tetanus  of  particular  muscles  was  produced.  In 
other  observations,  when  the  gray  substance  was  removed  at  the  points  mentioned,  there 
was  partial  loss  of  power,  but  not  paralysis,  of  the  sets  of  muscles  corresponding  to  the 
centres  operated  upon.  The  authors  regarded  this  as  due  to  a  loss  of  "  muscular  sense." 
In  these  experiments  the  action  was  always  crossed.  It  was  also  found  that,  after  severe 
haemorrhage,  the  excitability  of  the  cerebrum  quickly  disappeared,  which  may  account 


694  NERVOUS  SYSTEM. 

for  the  negative  results  obtained  by  previous  experimenters.  No  motor  properties  were 
discovered  in  the  posterior  portion  of  the  cerebrum. 

The  experiments  just  cited  throw  a  new  light  upon  the  properties  of  the  cerebral 
substance.  It  has  always  been  found  difficult  to  experiment  upon  the  great  encephalic 
centres  without  disturbing  the  physiological  conditions  so  seriously  as  to  render  the 
results  of  direct  observations  of  this  kind  more  or  less  indefinite.  Now  that  it  is  ascer- 
tained that,  in  all  probability,  these  centres  readily  lose  their  normal  properties,  as  a  sim- 
ple consequence  of  hemorrhage  and  exposure  of  the  parts,  we  are  less  disposed  to  accept 
the  older  experiments,  in  which  the  cerebral  tissue  was  apparently  shown  to  be  inca- 
pable of  receiving  direct  artificial  impressions. 

Since  the  first  publication  of  the  remarkable  experiments  to  which  we  have  just 
referred,  the  question  of  the  excitability  of  certain  parts  of  the  cerebral  hemispheres  has 
attracted  a  great  deal  of  attention  and  has  been  made  the  subject  of  numerous  experi- 
ments. The  most  notable  of  the  later  observations  on  this  subject  are  those  of  Terrier, 
of  London,  by  whom  the  original  experiments  of  Fritsch  and  Hitzig  have  been  fully  con- 
firmed. Although  the  methods  employed  by  Terrier  were  less  delicate  and  accurate  than 
those  of  the  German  observers,  the  results  obtained  are  of  great  value.  Many  other 
physiologists  have  since  confirmed  the  essential  points  developed  in  the  original  in- 
vestigations ;  and  the  only  serious  objection  to  the  results  is  the  possibility  of  diffusion 
of  the  galvanic  current  to  recognized  motor  tracts.  This  question  is  pretty  well  settled 
by  the  following  experiment  made  by  Dr.  Putnam,  of  Boston :  Having  localized  experi- 
mentally a  distinct  motor  centre  on  the  surface  of  the  brain,  he  made  a  flap,  about  one- 
twelfth  of  an  inch  thick,  by  a  section  parallel  to  the  surface  of  the  brain  and  involving 
this  centre.  With  the  flap  in  situ,  the  current  which  had  before  excited  muscular  con- 
traction had  no  effect.  It  is  evident  that  the  section  of  the  brain-substance  would  neces- 
sarily cut  off  the  physiological  conduction  of  a  stimulus  ;  but,  with  the  flap  in  situ,  the 
section  would  probably  not  interfere  with  the  diffusion  of  the  galvanic  current  itself. 

In  the  present  condition  of  the  question,  the  above  is  all  that  it  seems  necessary  to 
say,  in  a  systematic  work  upon  physiology,  concerning  the  excitable  centres  of  the  cere- 
brum. That  these  excitable  centres  exist,  there  can  be  little  doubt ;  and  the  idea  that 
the  movements  produced  by  their  galvanization  are  reflex  is  not  justified  by  experimen- 
tal facts.  These  observations  have  been  confirmed  by  Hitzig  as  late  as  in  1874 ;  and  his 
last  experiments  fully  substantiate  the  views  advanced  in  his  first  paper,  showing  loss  of 
power  in  certain  muscles,  following  destruction  of  portions  of  the  brain-substance  cor- 
responding to  the  excitable  points. 

functions  of  the   Cerebrum. 

The  history  of  the  functions  of  the  encephalon  belongs  without  question  to  physiol- 
ogy and  is  one  of  the  most  extensive  and  interesting  of  the  subdivisions  of  the  science  ; 
but  its  range  is  so  extensive,  that  it  has  long  been  regarded  as  a  science  by  itself  and  is 
only  treated  of  exhaustively  in  special  treatises  upon  psychology.  The  study  of  psychology 
has  been  pursued  by  the  method  of  observation  much  more  than  by  direct  experiment. 
It  comprehends,  it  is  true,  the  facts  deduced  from  experiments  upon  living  animals,  but 
the  results  obtained  by  this  method  are  comparatively  few  and  their  scope  is  restricted. 
Nevertheless,  they  are  sufficiently  definite ;  and,  if  these  results  be  corrected  and  applied 
to  the  human  subject  by  a  comparison  with  pathological  facts,  there  still  remains  in  psy- 
chology much  that  may  be  regarded  as  within  the  range  of  experimental  physiology  ;  for 
pathological  cases  are  very  frequently  available  to  the  physiologist  as  accidental  experi- 
ments indicating  the  functions  of  parts  of  the  human  organism.  We  cannot  restrict 
ourselves,  however,  to  this  method  in  the  study  of  the  intellectual  phenomena ;  and  we 
must  draw  upon  facts  in  comparative  anatomy  and  physiology,  anthropology,  and,  finally, 
upon  the  direct  observation  and  classification  of  the  intellectual  processes. 

The  experimental  physiologist  has  shown  that  the  encephalon  may  receive  impressions 


FUNCTIONS   OF  THE   CEREBRUM.  695 

and  appreciate  them  as  sensations ;  that  impressions  may  be  here  connected  and  give 
rise  to  various  of  the  phenomena  of  animal  and  intellectual  existence ;  that  impressions 
are  recorded  by  the  memory ;  and,  finally,  that  certain  parts  are  endowed  with  special 
functions.  But  beyond  this,  psychology  is  a  science  mainly  of  introspective  observation, 
the  facts  contributed  by  the  experimentalist  being  few  and  barren.  The  observer  of  intel- 
lectual phenomena  studies  the  process  of  development  of  the  mind ;  he  soon  separates 
the  instinctive  phenomena,  observed  in  the  lower  animals  and  in  the  human  being  with- 
out experience,  from  the  acts  which  follow  experience,  observation,  the  recording  of  im- 
pressions by  memory,  and  the  generation  of  ideas ;  he  brings  his  perfected  intelligence 
to  bear  upon  the  process  of  development  of  the  same  kind  of  intelligence  in  the  human 
being  progressing  from  infancy  to  adult  life ;  and,  finally,  the  psychological  philosopher 
attempts,  by  introspective  observation,  to  study  the  workings  of  the  perfect  intellect,  his 
only  means  of  investigation  being  the  very  intelligence  he  is  endeavoring  to  comprehend. 

At  the  present  day,  we  are  in  possession  of  a  sufficient  number  of  positive  facts  to 
render  it  certain  that  there  is  and  can  be  no  intelligence  without  brain-substance ;  that, 
when  brain-substance  exists  in  a  normal  condition,  intellectual  phenomena  are  manifested, 
with  a  vigor  proportionate  to  the  amount  of  matter  existing ;  that  destruction  of  brain- 
substance  produces  loss  of  intellectual  power ;  and,  finally,  that  exercise  of  the  intellect- 
ual faculties  involves  a  physiological  destruction  of  nervous  substance,  necessitating 
regeneration  by  nutrition,  here,  as  in  other  tissues  in  the  living  organism.  The  brain  is 
not,  strictly  speaking,  the  organ  of  the  mind,  for  this  statement  would  imply  that  the 
mind  exists  as  a  force,  independently  of  the  brain ;  but  the  mind  is  produced  by  the 
brain- substance  ;  and  intellectual  force,  if  we  may  term  the  intellect  a  force,  can  be  pro- 
duced only  by  the  transmutation  of  a  certain  amount  of  matter.  In  view  of  these  facts, 
which  have  long  been  more  or  less  fully  recognized,  though  not,  perhaps,  very  accurate- 
ly defined  in  words  until  within  a  few  years,  it  is  not  surprising  that  attempts  have  been 
made  to  locate  the  different  mental  attributes  in  particular  portions  of  the  brain.  The 
pseudo-science  of  phrenology  is  the  most  marked  example  of  such  an  attempt;  but  this 
has  so  slight  a  basis  in  fact,  that  it  does  not,  at  the  present  day,  merit  serious  scientific 
discussion. 

In  treating  of  the  functions  of  the  cerebrum,  we  shall  not  discuss  psychology,  except 
in  so  far  as  physiologists  have  been  able  to  connect  the  mind,  taken  as  a  whole,  with  a 
distinct  division  of  the  nervous  system.  In  this  we  shall  draw  upon  experiments  on  liv- 
ing animals,  facts  in  comparative  physiology,  in  pathology,  and,  to  a  certain  extent,  the 
relations  clearly  shown  to  exist  between  the  development  of  intelligence  and  certain  of 
the  nerve-centres,  in  different  races  of  men  and  different  individuals.  With  regard  to 
the  location  of  particular  functions  in  distinct  portions  of  the  cerebrum,  we  have  but 
little  definite  knowledge,  beyond  the  experiments  already  cited  in  treating  of  the  irrita- 
bility of  the  cerebral  substance,  and  the  probable  location  of  the  faculty  of  speech.  The 
latter  point  will  be  fully  discussed  in  its  appropriate  place. 

Extirpation  of  the  Cerebrum  in  the  lower  Animals. — It  is,  perhaps,  sufficiently  evident, 
from  anthropological  and  pathological  observations  as  well  as  the  study  of  comparative 
physiology,  that  the  intellectual  faculties  reside  in  the  encephalon ;  but  these  methods  of 
investigation  do  not  clearly  indicate  the  special  functions  of  different  parts  of  the  cranial 
contents.  We  have  seen,  in  our  general  sketch  of  the  anatomy  of  the  brain,  that  this  is 
by  no  means  a  simple  organ,  and  that  certain  parts,  although  they  are  bound  together  by 
commissural  fibres,  have  sufficient  anatomical  distinctness  to  lead  the  physiologist  to  sup- 
pose that  they  may  have  separate  and  peculiar  properties  and  functions.  One  of  the 
most  valuable  methods  of  investigation  of  the  functions  of  these  separate  ganglia  is  that 
of  extirpation  of  one  or  more,  leaving  the  others,  as  far  as  possible,  intact.  This  method 
was  first  employed  with  marked  success  by  Flourens  and  has  since  been  adopted  by 
numerous  experimenters.  It  must  be  remembered,  however,  that  there  is  no  subject  of 


696  NERVOUS  SYSTEM. 

physiological  inquiry  in  which  it  is  so  difficult  to  apply  experiments  upon  the  inferior  ani- 
mals to  the  human  suhject,  and  none  in  which  the  results  of  experiments  should  be 
received  with  greater  caution.  The  reason  for  this  is  Apparent  enough.  The  brain  and 
the  intellectual  power  of  man  are  so  far  superior  to  the  development  of  this  organ  and 
its  properties  in  the  lower  animals,  that  some  philosophers  have  regarded  the  human 
intelligence  as  distinct  in  nature  as  well  as  in  amount.  Although  we  are  by  no  means 
prepared  to  accept  this  proposition,  regarding,  as  we  must,  the  intelligence  of  man  as 
simply  superior  in  development  to  that  of  the  lower  animals,  it  is  evident  that  this  differ- 
ence in  the  degree  of  development  is  so  enormous  as  to  render  the  human  mind  hardly 
comparable  with  the  intellectual  attributes  of  animals  low  in  the  scale.  But,  when  the 
human  brain  is  slightly  developed,  as  in  idiots,  or  when  the  intellectual  faculties  are 
simply  diminished  in  activity,  as  in  certain  cases  of  disease,  the  being  is  reduced  to  a  con- 
dition very  like  that  of  some  of  the  lower  animals. 

Experiments  upon  different  classes  of  animals  show  clearly  that  the  brain  is  less 
important,  as  regards  the  ordinary  manifestations  of  animal  life,  in  proportion  as  its  rela- 
tive development  is  smaller.  For  example :  if  we  remove  the  cerebral  hemispheres  in 
fishes  or  reptiles,  the  movements  which  we  call  voluntary  may  be  but  little  affected ; 
while,  if  the  same  mutilation  be  performed  in  birds  or  some  of  the  mammalia,  the 
diminished  power  of  voluntary  motion  is  much  more  marked.  It  would  be  plainly 
unphilosophical  to  assume,  because  a  fish  or  a  frog  will  swim  in  water  and  execute  move- 
ments after  removal  of  the  hemispheres  very  like  those  of  the  uninjured  animal,  that 
the  feeble  intelligence  possessed  by  these  animals  is  not  destroyed  by  the  operation.  It 
is  not  only  possible,  but  probable,  that,  in  the  very  lowest  of  the  vertebrates,  the  func- 
tions of  the  nervous  centres  are  not  the  same  as  in  higher  animals.  There  is,  for  exam- 
ple, a  fish  (the  lancet-fish,  Amphioxus  lanceolatus),  that  has  no  brain,  all  of  the  functions 
of  animal  life  being  regulated  by  the  gray  substance  of  the  spinal  cord.  It  is  essential, 
in  endeavoring  to  apply  the  results  of  experiments  upon  the  brain  in  the  lower  animals 
to  human  physiology,  to  isolate,  as  far  as  possible,  the  distinct  manifestations  of  intelli- 
gence,'from  automatic  movements.  Bearing  in  mind,  then,  the  difficulties  of  the  ques- 
tion and  the  caution  with  which  all  observations  upon  the  great  nerve-centres  of  the 
lower  animals  must  be  received  in  their  applications  to  pure  human  physiology,  we  shall 
proceed  to  discuss  the  phenomena  following  removal  or  injury  of  the  cerebrum  in  direct 
experiments. 

In  1822  and  1823,  Flourens  communicated  to  the  French  Academy  of  Sciences  his 
remarkable  observations  upon  the  different  parts  composing  the  encephalon.  His  experi- 
ments are  so  familiar  to  physiologists,  that  it  is  only  necessary  here  to  give  his  general 
conclusions.  As  regards  the  cerebral  hemispheres,  he  found  that  the  complete  removal 
of  these  parts  in  living  animals  (frogs,  pigeons,  fowls,  mice,  moles,  cats,  and  dogs),  was 
invariably  followed  by  stupor,  apparent  loss  of  intelligence,  and  absence  even  of  the 
ordinary  instinctive  acts.  Animals  thus  mutilated  retained  general  sensibility  and  the 
power  of  voluntary  movements,  but  were  thought  to  be  deprived  of  the  special  senses  of 
sight,  hearing,  smell,  and  taste.  As  regards  general  sensibility  and  voluntary  movements, 
Flourens  was  of  the  opinion  that  animals  deprived  of  their  cerebral  lobes  possessed  sen- 
sation, but  had  lost  the  power  of  perception,  and  that  they  could  execute  voluntary 
movements  when  an  irritation  was  applied  to  any  part,  but  had  lost  the  power  of  making 
such  movements  in  obedience  to  a  spontaneous  effort  of  the  will.  One  of  the  most 
remarkable  phenomena  observed  was  entire  loss  of  memory  and  of  the  power  of  connect- 
ing ideas.  ^The  voluntary  muscular  system  was  enfeebled  but  not  paralyzed.  Eemoval 
of  one  hemisphere  produced,  in  the  higher  classes  of  animals  experimented  upon,  enfee- 
blement  of  the  muscles  upon  the  opposite  side,  but  the  intellectual  faculties  were  in  part 
or  entirely  retained.  Removal  of  even  a  considerable  portion  of  both  hemispheres  was 
followed  by  no  very  marked  effect  as  regards  the  intelligence. 

The  observations  of  Flourens  have  been  repeated  by  numerous  experimentalists  and 


FUNCTIONS   OF  THE   CEREBRUM.  597 

were,  in  the  main,  confirmed,  except  as  regards  the  special  senses.  Bouillaud,  in  1826, 
made  a  large  number  of  observations  upon  pigeons,  fowls,  rabbits,  etc.,  in  which,  after 
removal  of  the  hemispheres,  he  noted  the  persistence  of  the  senses  of  sight  and  hearing. 
Longet  finally  demonstrated  the  fact  that  both  sight  and  hearing  are  retained  after  extir- 
pation of  the  hemispheres,  even  more  clearly  than  Bouillaud,  by  the  following  experi- 
ments :  He  removed  the  hemispheres  from  a  pigeon,  the  animal  surviving  the  operation 
eighteen  days.  When  this  animal  was  placed  in  a  dark  room  and  a  light  was  suddenly 
brought  near  the  eyes,  the  iris  contracted  and  the  animal  winked ;  "but  it  was  remark- 
able, that  when  a  lighted  candle  was  moved  in  a  circle,  and  at  a  sufficient  distance,  so 
that  there  should  be  no  sensation  of  heat,  the  pigeon  executed  an  analogous  movement 
of  the  head."  An  examination  after  death  showed  that  the  removal  of  the  cerebrum 
had  been  complete.  An  animal  deprived  of  the  hemispheres  also  opened  the  eyes  at  the 
report  of  a  pistol  and  gave  other  evidence  that  the  sense  of  hearing  was  retained. 

With  regard  to  the  senses  of  smell  and  taste,  it  is  more  difficult  to  determine  their 
presence  than  to  ascertain  that  the  senses  of  sight  and  hearing  are  retained.  It  is  prob- 
able, however,  that  the  sense  of  smell  is  not  abolished,  if  the  hemispheres  be  carefully 
removed,  leaving  the  olfactory  ganglia  intact ;  and  there  is  no  direct  evidence  that  extir- 
pation of  the  cerebrum  affects  the  sense  of  taste ;  indeed,  in  young  cats  and  dogs,  Longet 
has  noted  evidences  of  a  disagreeable  impression  following  the  introduction  of  a  concen- 
trated solution  of  colocynth  into  the  mouth,  as  distinctly  as  in  the  same  animals  under 
normal  conditions. 

We  shall  now  proceed  to  describe,  as  accurately  as  possible,  the  condition  of  an  ani- 
mal after  complete  extirpation  of  the  cerebrum,  as  observed  in  numerous  experiments 
that  we  have  ourselves  made  upon  this  subject,  premising  the  statement  that  these  are 
merely  repetitions  of  observations  made  by  other  physiologists. 

A  pigeon,  in  a  perfectly  normal  condition,  is  deprived  of  the  hemispheres,  by  remov- 
ing the  calvarium  and  carefully  scooping  out  the  parts  with  the  handle  of  a  scalpel. 
This  operation  is  usually  not  difficult,  and  the  haemorrhage  is  soon  arrested  spon- 
taneously. The  slit  in  the  scalp  is  closed  with  sutures,  and  the  animal  is  set  at  liber- 
ty. The  appearance  of  the  animal  after  this  mutilation  is  peculiar  and  characteristic. 
There  immediately  supervenes  a  condition  of  stupor.  There  is  usually  no  attempt  at 
movement,  and,  though  the  pigeon  stands  upon  its  feet,  the  head  is  almost  buried  in  the 
feathers  of  the  neck,  the  eyes  are  closed,  and  the  attitude  is  one  of  absolute  indifference 
to  surrounding  conditions.  The  muscles  seem  to  act  with  just  sufficient  vigor  to  main- 
tain the  standing  position.  If  we  pinch  one  of  the  toes  or  grasp  the  beak,  there  is  evi- 
dent sensation,  and  a  persistent  and  more  or  less  vigorous  effort  is  made  to  release  the 
part.  It  is  sufficiently  evident,  from  these  and  other  tests,  that  sensation  and  the  power 
of  voluntary  motion  are  retained  ;  but,  as  soon  as  the  animal  is  left  quiet,  it  relapses  into 
its  stupid  condition,  makes  no  effort  to  escape,  and  apparently  loses  immediately  all 
recollection  of  having  been  disturbed.  The  irritation  has  evidently  produced  a  sensation 
of  discomfort  and  has  given  rise  to  a  voluntary  muscular  effort ;  but  there  has  been  no 
idea  of  danger,  nor  an  intelligent  effort  to  avoid  a  repetition  of  the  disagreeable  or  pain- 
ful impression. 

It  is  easy  to  demonstrate,  by  experiments  such  as  we  have  just  detailed,  that  the 
animal  sees  and  hears  ;  but  it  connects  no  idea  with  any  thing  seen,  and  the  report  of  a 
pistol,  which,  under  natural  conditions,  would  excite  terror  and  an  idea  of  danger,  simply 
causes  the  pigeon  to  give  evidence  that  the  sound  has  been  heard.  As  we  have  already 
stated,  it  is  probable  that  the  animal  has  the  sense  of  smell,  but  it  is  difficult,  if  not  impos- 
sible, to  establish  this  point  experimentally.  The  same  remark  applies  to  the  sensations  of 
hunger  and  thirst.  The  animal  may  feel  the  want  of  water  and  food,  but  it  has  no  idea  of 
relieving  these  sensations  by  drinking  and  eating,  and,  if  left  to  itself,  will  die  of  inanition. 

Tli ere  has  been  a  great  deal  of  discussion  among  experimentalists  with  regard  to 
spontaneous  voluntary  movements  in  animals  deprived  of  the  cerebral  hemispheres.  The 


698  NERVOUS  SYSTEM. 

experimental  conditions  necessary  for  determining  this  point  are  the  following :  The 
observer  must  be  certain  that  the  removal  of  the  hemispheres  has  been  complete  ;  for  it 
has  been  clearly  shown  that,  even  when  a  small  amount  of  cerebral  substance  has  es- 
caped, the  functions  of  these  parts  are  not  entirely  abolished.  Again,  we  must  be  equally 
certain  that  movements  which  seem  to  be  due  to  a  spontaneous  act  of  volition  take  place 
when  the  animal  has  not  been  aroused  from  the  condition  of  stupor  which  results  from 
the  operation.  Generally,  when  the  animal  is  left  to  itself,  the  condition  of  stupor  per- 
sists ;  but,  when  aroused  by  artificial  means,  it  will  walk  a  few  steps,  plume  the  feathers, 
shake  its  head,  and  make  various  voluntary  movements  without  farther  irritation,  soon 
relapsing,  however,  into  somnolency.  One  of  the  most  accurate  and  reliable  of  the 
recent  observers  of  these  phenomena,  Vulpian,  asserts  without  reserve,  that  an  animal, 
deprived  completely  of  the  cerebral  hemispheres,  is  incapable  of  a  spontaneous  voluntary 
eifort ;  and  we  are  inclined  to  an  unqualified  adoption  of  this  opinion.  "With  regard  to  a 
rabbit  from  which  Vulpian  had  removed  the  cerebral  hemispheres  and  the  corpora  stri- 
ata,  he  makes  the  following  statement :  "  I  do  not  hesitate  to  say  that  this  rabbit  is 
completely  deprived  of  spontaneous  volition.  All  its  movements,  which  are,  indeed, 
much  less  varied  than  those  of  a  bird  operated  upon  in  the  same  manner,  are  exclusively 
and  directly  due  to  a  stimulation  produced  by  exterior  excitations,  or  by  interior  inclina- 
tions, such  as  fatigue,  etc." 

In  view  of  the  very  great  variety  of  movements  that  occur  in  animals  after  removal 
of  the  cerebrum,  it  is  quite  difficult  to  define  precisely  what  movements  are  due  to  volun- 
tary action  depending  upon  some  external  or  interior  impression,  which  are  really  reflex 
voluntary  movements,  and  to  distinguish  them  from  those  which  arise  from  a  spontaneous 
and,  perhaps,  an  intelligent  effort  of  the  will.  These  points  have  been  so  admirably 
described  in  a  recent  article,  by  Onimus,  that  we  quote  his  concluding  summary  : 

"  As  a  summary,  in  the  inferior  animals,  as  in  the  superior  animals,  the  removal  of  the 
cerebral  hemispheres  does  not  cause  to  disappear  any  of  the  movements  that  previously 
existed.  Only,  these  movements  assume  certain  peculiar  characters.  In  the  first  place, 
they  are  more  regular,  they  have  the  true  normal  type,  for  no  psychical  influence  inter- 
venes to  modify  them ;  the  locomotor  apparatus  is  brought  into  action  without  interfer- 
ences, and  one  could  almost  say  that  the  ensemble  of  movements  is  then  more  normal 
than  in  the  normal  condition. 

"  In  the  second  place,  the  movements  executed  take  place  inevitably  after  certain 
excitations.  It  is  a  necessity  that  the  frog  placed  in  water  should  swim,  and  that  the 
pigeon  thrown  into  the  air  should  fly.  The  physiologist  can  then,  at  will,  in  an  animal 
without  the  brain,  determine  such  and  such  an  act,  limit  it,  arrest  it ;  he  can  anticipate 
the  movements  and  affirm  in  advance  that  they  will  take  place  under  certain  conditions, 
absolutely  as  the  chemist  knows  in  advance  the  reactions  that  he  will  obtain  in  mixing 
certain  bodies. 

"Another  peculiarity  in  the  movements  that  take  place,  when  the  cerebral  lobes  are 
removed,  is  their  continuation  after  a  first  impression.  On  the  ground,  a  frog  without 
the  brain  when  irritated  makes,  in  general,  two  or  three  jumps  at  the  most ;  it  is  rare 
that  it  makes  but  one.  Placed  in  water,  it  continues  the  movement  of  natation  until  it 
meets  with  an  obstacle  ;  it  is  the  same  in  the  carp,  eel,  etc.  The  pigeon  continues  to 
fly,  the  duck  and  goose  continue  to  swim,  etc.  We  should  say  that  there  is  a  spring 
which  needs  for  its  action  a  first  impulsion,  and  which  is  stopped  by  the  slightest  resist- 
ance. But,  what  is  striking,  is  precisely  that  continuation  of  the  condition  once  deter- 
mined, and  we  cannot  refrain  from  connecting  the  facts  observed  in  an  animal  deprived 
of  the  cerebral  lobes  with  those  which  constitute  the  characteristic  properties  of  inor- 
ganic matter.  Brought  into  movement,  the  animal  without  a  brain  retains  the  move- 
ment until  there  is  exhaustion  of  the  conditions  of  movement,  or  until  it  meets  with 
resistance ;  taken  in  repose,  it  remains  in  the  state  of  inertia  until  an  exterior  cause 
intervenes  to  bring  it  out  of  this  condition.  It  is  living,  inert  matter." 


FUNCTIONS   OF  THE   CEREBRUM.  699 

There  is  now  no  room  for  discussion  with  regard  to  the  persistence  of  general  sensi- 
bility after  removal  of  the  hemispheres.  The  experiment  upon  a  pigeon  leaves  no  doubt 
upon  this  point,  but  the  susceptibility  to  pain  has  been  much  more  strikingly  illustrated 
in  other  animals.  Vulpian,  in  describing  the  condition  of  animals  operated  upon  in  this 
way,  illustrates  the  persistence  of  sensibility  in  rats  and  rabbits,  by  the  violent  cries 
which  follow  painful  impressions. 

In  concluding  our  consideration  of  the  observations  upon  inferior  animals,  it  only 
remains  for  us  to  discuss  briefly  certain  late  experiments,  which  have  attracted  a  great 
deal  of  attention  from  the  fact  that  they  seem  to  show  that  spontaneous  volition  exists 
after  complete  extirpation  of  the  cerebrum.  These  experiments  have  been  most  ably 
and  satisfactorily  analyzed  by  Vulpian.  Goltz  argues,  from  experiments  upon  frogs  and 
the  movements  executed  after  extirpation  of  the  brain,  that  these  animals  make  intelli- 
gent muscular  efforts  when  deprived  of  the  hemispheres ;  and  the  phenomena  observed 
after  this  mutilation  are  indeed  very  curious.  As  was  shown  by  Vulpian,  in  his  own 
experiments,  frogs  and  fishes  thrown  into  water  will  swim  about  and  the  frogs  will  even 
succeed  in  getting  out  of  the  water,  but  then,  they  immediately  relapse  into  a  torpid  con- 
dition. We  do  not  conceive  that  these  facts  are  in  opposition  to  the  statement  just 
made  with  regard  to  the  absence  of  spontaneous  volition  in  birds  and  the  mammalia, 
particularly  in  view  of  the  slight  importance  of  the  functions  of  the  cerebrum  as  com- 
pared with  the  spinal  cord  in  the  lower  orders  of  vertebrate  animals.  The  views  lately 
advanced  by  Yoit  are  based  upon  an  isolated  experiment  upon  a  pigeon  that  was  kept 
alive  for  five  months  after  the  cerebral  lobes  had  been,  as  stated  by  Voit,  completely 
removed.  At  first  the  pigeon  presented  the  phenomena  usually  observed  after  this  opera- 
tion ;  but  it  gradually  recovered,  until  finally  it  seemed  entirely  normal,  with  the  single 
exception  that  it  never  would  eat,  all  food  being  introduced  forcibly.  Five  months  after 
the  operation,  the  pigeon  was  killed  and  the  encephalic  cavity  was  found  filled  with  a 
white  substance  containing  dark -bordered  nerve-fibres  and  nerve-cells.  Voit  never  before 
observed  any  thing  like  regeneration  of  the  nervous  substance  or  so  complete  a  restora- 
tion of  the  cerebral  functions ;  and  he  regarded  this  as  an  instance  of  anatomical  and 
physiological  regeneration  of  the  hemispheres.  The  objections  to  accepting  this  observa- 
tion with  the  physiological  conclusions  presented  by  Voit  are,  that  it  is  not  only  possible 
but  probable,  that  the  hemispheres  were  not  entirely  removed  and  that  the  posterior 
portion  of  the  encephalon  had  advanced  to  occupy  in  part  the  space  originally  filled  by 
the  extirpated  mass.  While  we  do  not  assume  that  anatomical  and  functional  regenera- 
tion of  the  cerebrum  in  a  pigeon  is  impossible,  it  must  be  admitted  that  such  an  extraor- 
dinary statement  as  that  made  by  Voit  cannot  be  accepted  without  reserve,  merely 
upon  the  basis  of  a  single  observation. 

Pathological  Facts  bearing  upon  the  Functions  of  the  Cerebrum. — A  careful  study  of 
the  phenomena  which  attend  certain  pathological  conditions  of  the  brain  in  the  human 
subject,  such  as  laceration  or  pressure  from  effusion  of  blood,  softening  of  the  nervous 
substance,  etc.,  taken  in  connection  with  the  results  of  experiments  upon  living  animals, 
throws  considerable  light  upon  the  functions  of  certain  distinct  portions  of  the  encephalon. 
Cerebral  haemorrhage  very  commonly  involves  the  corpus  striatum,  either  directly  or 
indirectly,  and  then  we  have  paralysis  of  motion  limited  to  the  side  of  the  body  opposite 
to  the  lesion.  When  the  optic  thalamus  is  affected,  there  is  impairment  of  sensibility 
upon  the  opposite  half  of  the  body.  These  facts  illustrate  the  course  of  the  motor  and 
sensory  conductors  from  and  to  the  cerebrum.  It  is  not  very  common  to  observe  lesions 
confined  to  the  gray  or  white  substance  of  the  hemispheres,  but,  when  this  occurs  and 
when  there  is  no  pressure  upon  the  corpora  striata  or  optic  thalami,  there  is  no  paralysis 
of  motion  or  sensation,  although  there  may  be  a  certain  amount  of  weakness  of  the  muscles 
upon  the  side  of  the  body  opposite  the  injury.  Experiments  upon  the  inferior  animals 
have  confirmed  the  conclusions  to  be  drawn  from  these  pathological  facts.  In  frogs, 


700  NERVOUS   SYSTEM. 

fishes,  and  birds,  when  one  hemisphere  has  been  removed,  the  evidences  of  feebleness  of 
the  muscles  of  the  opposite  side  are  not  very  marked ;  but  they  are  quite  distinct  in  the 
adult  mammalia. 

It  is  a  fact  now  generally  admitted  in  pathology,  that  loss  of  cerebral  substance  from 
repeated  haemorrhage  is  sooner  or  later  followed  by  impairment  of  the  intellectual  facul- 
ties. This  point  it  is  frequently  difficult  to  determine  in  a  single  instance,  but  an  analysis 
of  a  sufficient  number  of  cases  shows  impaired  memory,  tardy,  inaccurate,  and  feeble 
connection  of  ideas,  abnormal  irritability  of  temper  with  a  childish  susceptibility  to  petty 
or  imaginary  annoyances,  easily- excited  emotional  manifestations,  and  a  variety  of  phe- 
nomena denoting  abnormally  feeble  intellectual  power,  following  any  considerable  disor- 
ganization of  cerebral  substance.  In  short,  pathological  conditions  of  the  brain  all  go  to 
show  that  the  intellectual  faculties  are  connected  with  the  cerebral  hemispheres. 

As  a  final  argument  drawn  from  pathology,  in  favor  of  the  view  just  stated,  we  have 
only  to  allude  to  the  size  of  the  brain  in  certain  cases  of  idiocy.  There  are  on  record 
numerous  examinations  of  the  brain  in  idiots,  in  which  this  organ  has  been  found  to  be 
less  than  one-half  of  the  ordinary  weight;  as  the  cases  reported  by  Tiedemann,  of  19f, 
25f,  and  22^  ounces,  in  three  idiots,  whose  ages  were,  respectively,  sixteen,  forty,  and 
fifty  years.  A  case  has  been  reported  by  Mr.  Gore,  of  an  idiotic  woman,  forty-two  years 
of  age,  whose  brain  weighed  ten  ounces  and  five  grains ;  and  one  by  Mr.  Marshall,  of  an 
idiotic  boy,  twelve  years  old,  whose  brain  weighed  but  8J-  ounces.  Mr.  Bradley,  in  a  late 
number  of  the  Journal  of  Anatomy  and  Physiology,  gives  an  elaborate  description  of  the 
brain  of  an  idiot,  thirty -five  years  of  age,  extremely  emaciated  at  the  time  of  his  death, 
when  he  weighed  but  sixty  pounds.  The  en^ephalon,  including  the  cerebrum,  cerebellum, 
and  pons,  weighed  twenty-eight  ounces,  ana  the  proportion  of  the  cerebellum  to  the 
cerebrum  was  as  1  to  5*5.  In  the  healthy  adult  male  of  ordinary  weight,  the  encephalcn 
weighs  fifty  ounces,  and  the  proportion  of  the  cerebellum  to  the  cerebrum  is  as  1  to  8f . 
Mr.  Bradley  calls  attention  to  the  proportion  of  the  cerebellum  to  the  cerebrum  in  this 
case,  stating  that  this  is  common  in  the  encephalon  of  idiots.  In  idiots,  the  weight  of  the 
body  is  generally  much  below  the  normal  standard  ;  and,  in  the  case  reported  by  Bradley, 
the  proportionate  weight  of  the  encephalon  to  that  of  the  entire  body  is  even  greater  than 
in  the  healthy  adult.  If,  for  example,  we  double  the  weight  of  the  body  and  the  brain, 
we  should  have,  for  one  hundred  and  twenty  pounds  of  wreight,  an  encephalon  of  fifty-six 
ounces.  This  point,  however,  cannot  be  admitted  as  an  argument  against  the  fact  that 
congenital  idiocy  is  usually  attended  with  an  abnormally  small  development  of  the  hemi- 
spheres. Most  idiots  take  little  or  no  exercise ;  they  are  under-sized,  and  have  but  little 
muscular  vigor;  and  it  is  probable  that  the  general  development  of  the  body  is  more  or 
less  a  consequence  of  the  abnormal  cerebral  condition.  We  might  compare  the  weight 
of  the  body  in  Mr.  Bradley's  case  with  that  of  a  child  from  seven  to  fourteen  years  of 
age ;  and,  at  this  period  of  life,  according  to  the  tables  compiled  by  Quain,  the  average 
weight  of  the  encephalon  is  45-96  ounces,  for  the  male,  and  40'78  ounces,  for  the 
female. 

The  statements  just  made  with  regard  to  the  brains  of  idiots  refer  to  cases  charac- 
terized by^  complete  absence  of  intelligence,  and  farthermore,  probably,  by  very  small 
development  of  th£  body.  On  the  other  hand,  there  are  instances  of  idiocy,  the  body 
being  of  ordinary  size,  in  which  the  weight  of  the  encephalon  is  little  if  any  below  the 
average.  Lelut  reports  several  cases  of  this  kind.  In  one  of  these,  a  deaf-mute  idiot, 
forty-three  years  of  age,  a  little  above  the  ordinary  stature,  presenting  "idiocy  of  the 
lowest  degree ;^  no  speech;  almost  no  sign  of  intelligence;  no  care  for  cleanliness,"  the 
encephalon  weighed  48-32  oz.  Other  cases  of  idiots  of  medium  stature  are  given,  in  which 
the  brain  weighed  but  little  less  than  the  normal  average.  These  facts  illustrate  the  diffi- 
culty of  subordinating  individual  observations  to  any  general  rule,  and  this  is  particularly 
marked  with  regard  to  the  brain,  the  structure  of  which  is  so  complex  and  difficult  of 
investigation. 


FUNCTIONS   OF  THE   CEREBRUM.  701 

Comparative  Development  of  the  Cerebrum  in  the  Lower  Animals. — It  is  only  neces- 
sary to  refer  very  briefly  to  the  development  of  the  cerebrum  in  the  lower  animals  as 
compared  with  the  human  subject,  to  show  the  connection  of  the  hemispheres  with  intel- 
ligence. In  man,  the  cerebrum  presents  an  immense  preponderance  in  weight  over  other 
portions  of  the  encephalon ;  and,  in  some  of  the  lower  animals,  the  cerebrum  is  even  less 
in  weight  than  the  cerebellum.  In  man,  also,  not  only  the  relative  but  the  absolute 
weight  of  the  brain  is  greater  than  in  lower  animals,  with  but  two  exceptions.  Todd 
cites  a  number  of  observations  made  upon  the  brains  of  elephants,  in  which  the  weights 
ranged  from  nine  to  ten  pounds.  Rudolphi  gives  the  weight  of  the  encephalon  of  a  whale, 
seventy-five  feet  long,  as  considerably  over  five  pounds.  With  the  exception  of  these 
animals,  man  possesses  the  largest  brain  in  the  zoological  scale. 

Another  interesting  point  in  this  connection  is  the  development  of  cerebral  convolu- 
tions in  certain  animals,  by  which  the  relative  amount  of  gray  matter  is  increased.  In 
fishes,  reptiles,  and  birds,  the  surface  of  the  hemispheres  is  smooth ;  but,  in  many  mam- 
malia, especially  in  those  remarkable  for  intelligence,  the  cerebrum  presents  a  greater  or 
less  number  of  convolutions,  as  it  does  in  the  human  subject. 

Comparing  the  relative  size  of  the  brain,  its  complexity  of  organization,  and  the 
increase  of  its  gray  substance  by  convolutions,  with  the  development  of  intelligence  in  the 
animal  scale,  it  is  so  evident  that  the  cerebrum  is  the  organ  presiding  over  the  intellectual 
faculties,  that  this  point  in  our  argument  seems-  to  need  no  farther  discussion. 

Development  of  the  Cerebrum  in  Different  Races  of  Men  and  in  Different  Individuals. 
— It  may  be  stated  as  a  general  proposition,  that,  in  the  different  races  of  men,  the  cere- 
brum is  developed  in  proportion  to  their  intellectual  power ;  and,  in  different  individuals 
of  the  same  race,  the  same  general  rule  obtains.  Still,  this  law  presents  marked  excep- 
tions. Certain  brains  in  an  inferior  race  may  be  larger  than  the  average  in  the  superior 
race ;  and  it  is  frequently  observed  that  unusual  intellectual  vigor  is  coexistent  with  a 
small  brain,  and  the  reverse.  These  exceptions,  however,  do  not  take  away  from  the  force 
of  the  original  proposition.  As  regards  races,  the  rule  is  found  to  be  invariable,  when  a 
sufficient  number  of  observations  are  analyzed,  and  the  same  holds  true  in  comparing  a 
large  number  of  individuals  of  the  same  race.  Average  men  have  an  advantage  over 
average  women  of  about  six  ounces  of  cerebral  substance ;  and,  while  many  women  are 
far  superior  in  intellect  to  many  men,  such  instances  are  not  sufficiently  numerous  to 
invalidate  the  general  law,  that  the  greatest  amount  of  intellectual  capacity  and  mental 
vigor  is  coincident  with  the  greatest  quantity  of  cerebral  substance.  If  we  accept  the 
view,  which  is  in  every  way  reasonable,  that  the  gray  substance  of  the  cerebral  hemi- 
spheres is  the  generator  of  the  mind,  it  would  be  necessary,  in  comparing  different  indi- 
viduals with  the  view  of  establishing  a  definite  relation  between  brain-substance  and 
intelligence,  to  estimate  the  amount  of  gray  matter;  but  it  is  not  easy  to  see  how  this  can 
be  done  with  any  degree  of  accuracy. 

It  is  undoubtedly  true  that  proper  training  and  exercise  develop  and  increase  the  vigor 
of  the  intellectual  faculties,  and  that  thereby  the  brain  is  increased  in  power,  as  are  the 
muscles  under  analogous  conditions.  This  will  perhaps  explain  some  of  the  exceptions 
above  jndicated  ;  but  an  additional  explanation  may  be  found  in  differences  in  the  quality 
of  brain-substance  in  different  individuals,  independently  of  the  size  of  the  cerebral  hem- 
ispheres. One  evidence  that  these  differences  in  the  quality  of  intellectual  working 
matter  exist  is,  that  some  small  brains  actually  accomplish  more  and  better  work  than 
some  large  brains.  This  fact  may  be  due  to  differences  in  training,  to  the  extraordinary 
development  in  some  individuals  of  certain  qualities,  to  intensity  and  pertinacity  of  pur- 
pose, capacity  for  persistent  labor  in  certain  directions,  a  fortunate  direction  of  the  men- 
tal efforts,  opportunity  and  circumstances,  etc. ;  but,  aside  from  these  considerations,  it 
is  exceedingly  probable  that  there  are  important  individual  differences  in  the  quality  of 
generating  nervous  matter. 


702 


KEKVOUS   SYSTEM. 


In  concluding  this  portion  of  our  argument,  we  present  a  table  of  an  exceedingly  inter- 
esting series  of  observations  upon  the  comparative  weights  of  the  encephalon  in  the  Cauca- 
sian, the  negro,  and  the  intermediate  grades  produced  by  the  union  of  the  two  races.  The 
observations  in  this  table  are  hardly  sufficient  in  number  to  establish  the  exact  relations 
between  the  brains  in  the  different  grades  of  color,  but  they  illustrate  points  of  peculiar 
interest  in  this  country,  where  the  blacks  are  so  numerous  and  where  the  union  of  the 
two  races,  white  and  black,  is  so  common.  We  also  give  a  list  of  some  of  the  well- 
authenticated  weights  of  the  encephalon  in  men  whose  intellectual  faculties  had  been 
observed  during  life.  This  latter  list  we  have  prepared  with  great  care  and  have  intro- 
duced some  observations  not  found  in  most  works  upon  physiology.  In  estimating  the 
intellectual  power  of  individuals,  it  is  difficult  to  arrive  at  exact  conclusions,  except  with 
regard  to  men  of  acknowledged  eminence.  Still,  the  statements  are  as  accurate  as  pos- 
sible and  must  be  taken  for  what  they  are  worth.  Several  of  the  examples  given  in  this 
list  are  marked  exceptions  to  the  general  rule,  that  the  mental  vigor  is  in  proportion  to 
the  amount  of  brain-substance. 

We  have  not  considered  it  necessary  to  enter  into  a  discussion  of  the  relations  of  the 
facial  angle  to  intelligence  in  the  lower  animals  and  in  different  races  of  men.  It  was 
proposed  by  Camper  to  take  the  angle  made  at  the  junction  of  two  lines,  one  drawn  from 
the  most  projecting  part  of  the  forehead  to  the  alveolas  of  the  teeth  of  the  upper  jaw, 
and  another  passing  horizontally  backward  from  the  lower  extremity  of  the  first  line,  as 
the  facial  angle.  This  angle  is,  to  a  certain  extent,  a  measure  of  the  projection  of  the 
anterior  lobes  of  the  brain.  Numerous  observations  upon  the  facial  angle  in  different 
races  were  made  by  Camper  and  by  other  physiologists  and  ethnologists.  They  show,  in 
general  terms,  that  the  angle  is  larger  in  man  than  in  any  of  the  inferior  animals  and  is 
largest  in  those  races  that  possess  the  greatest  development  of  intellectual  power. 

Ethnological  Table,  derived  from  405  Autopsies  of  White  and  Negro  Brains.    Made 
under  the  Direction  of  Surgeon  Ira  Russell,  llth  Massachusetts  Volunteers. 


tri 

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White 

52-06 

64 

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49-05 

51 

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1 

10 

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2 

47 

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47-07 

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2 

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19 

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46-54 

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22 

11 

6 

95 

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46-16 

57 

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15 

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21 

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A,    ' 

45-18 

50* 

40 

8 

10 

9 

141 

Black 

46-96 

56 

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5 

42 

51 

38 

3 

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405 

2 

14 

104 

171 

94 

17 

1 

Whites  col- 

Autopsies   of    Clen- 

lated  from 

dinning,  Sims,  Reid, 

various 

and  Tiedemann, 

278 

sources. 

49^ 

65 

34 

7 

28 

99 

97 

39 

7 

1 

Table  of  Weights  of  the  Encephalon,  in  ounces,  av.,  in  Individuals,  in  some  of  whom  the 
Degree  of  Intelligence  is  more  or  less  accurately  known. 

Cromwell,  aged  59  (not  accepted  by  physiologists). 82-29  oz. 

Byron,  aged  36  (not  accepted  by  physiologists) ' .' ' "        ...  79-00  " 

Bricklayer,  aged  38  ;  fair  intelligence,  but  could  neither  read  nor  write  (reported  by' Dr. 

James  Morris) 67'00  " 

Cuvier,  aged  63  (Archives  generates  de  mededne,  1832) .  64'33  " 


FUNCTIONS   OF  THE   CEREBRUM.  703 

Abercrombie,  aged  63  (reported  by  Dr.  Adam  Hunter) 63-00  oz. 

Congenital  epileptic  idiot  (reported  by  Dr.  Tuke) 60'00  " 

Ruloff,  aged  53  ;  above  medium  stature ;  executed  for  murder,  in  1871 ;  well  versed  in 
languages,  imagining  that  he  had  discovered  new  and  important  principles  in 

philology  (reported  by  Dr.  George  Burr) 59'00  " 

James  Fisk,  Jr.,  aged  37  ;  killed  in  New  York,  in  1872  ;  illiterate,  but  said  to  possess 
great  executive  ability  ;  notorious  for  colossal  and  unscrupulous  financial  specula- 
tions (reported  by  Dr.  Marsh) 58-00  " 

Boy,  aged  13  ;  healthy  and  intelligent ;  died  from  injuries  caused  by  a  fall  (British  Medi- 

'  cal  Journal,  Oct.  19,  1872) 58'00  " 

Spurzheim  ( Medico- Chirurgical  Review,  1836) 55'06  " 

Adult  man  ;  an  idiot  since  two  years  of  age  (Wagner) 54'95  " 

Laborer,  aged  22  ;  died  of  fracture  of  the  pelvis  (Wagner) 53'79  " 

Daniel  Webster,  aged  70  (reported  by  Dr.  John  Jeffries) 53'50  " 

Celebrated  mathematician,  aged  54  ;  above  the  ordinary  stature  (Wagner) 53*41  " 

Agassiz,  aged  66  (reported  by  Dr.  M.  Wyman) 53-40 

Executed  criminal,  aged  45  ;  medium  stature  ;  of  less  than  ordinary  intelligence,  and  un- 
cultivated (Lelut) 63-12  " 

Celebrated  clinical  professor,  aged  52  ;  medium  stature  (Wagner) 52*88  " 

Mathematician  of  the  first  rank,  aged  78  ;  medium  stature  (Wagner) 52'62  " 

Executed  criminal,  aged  34  ;  rather  large  in  stature ;  ordinary  intelligence,  but  singu- 
lar and  somewhat  cultivated  (Lelut) 50*09  " 

Dupuytren,  aged  58  (Cruveilhier,  Husson,  and  Bouillaud) 49"68 

Day-laborer,  aged  49  (Wagner) 48'85 

Executed  criminal,  aged   29  ;   medium  stature ;    of  scarcely  ordinary  intelligence  and 

uncultivated  (Lelut) 48'S  1  " 

Executed  criminal,  aged  42  ;  a  little  above  medium  stature ;  intelligence  fine,  devel- 
oped, and  slightly  cultivated  (Lelut) : 48-81  " 

Idiot,  of  a  very  low  degree  of  intelligence,  aged  37 ;  a  little  above  medium  stature ; 

movements  very  active  (Lelut) 48'67  " 

Deaf-mute,  aged  43 ;  a  little  above  medium  stature ;  an  idiot,  of  the  lowest  degree  of 

intelligence  (Lelut) 48'32  " 

Executed  criminal,  aged  46 ;    medium  stature ;    of  ordinary  intelligence,  uncultivated, 

but  proud  and  vivacious  (Lelut) 48-14  " 

Man,  slightly  imbecile,  aged  67 ;  medium  stature  (Lelut) 48'14  " 

Man,  about  60  years  of  age  (Wagner) 48-14  " 

Celebrated  philologist,  aged  54 ;  5  feet  7£  inches  tall  (Wagner) 47'90  " 

Executed  criminal,  aged  34  ;  small  stature  ;  intelligence  developed  and  cultivated  (Lelut).  47*79  " 

Man,  about  24  years  of  age  ;  died  of  aortic  insufficiency  (Wagner) 47*69 

Day-laborer,  aged  51  (Wagner) 47'44  " 

Man,  34  years  of  age  ;  died  of  pneumonia  (Wagner) 47*26 

Brigand  and  assassin,  aged  32  ;  beheaded  (Wagner) 46*91  " 

Idiot  of  the  lowest  degree  of  intelligence,  aged  24 ;  medium  stature  (Lelut) 46"56-  " 

Executed  crimjnal,  aged  27 ;  medium  stature  ;  of  ordinary  and  uncultivated  intelligence 

(Lelut) 46-21  " 

Executed  criminal,  aged  40;  at  least  of  medium  stature;  intelligence  developed  and 

cultivated  (Lelut) 46-21  " 

Railroad  laborer,  aged  23  (Wagner).. 46'21  " 

Executed  criminal,  aged  29  ;  intelligence  hardly  ordinary,  and  uncultivated  (Lelut) 45*50  " 

Wood-cutter,  aged  57  ;  died  of  vertebral  caries  (Wagner) 44*90  " 

Idiot,  below  the  condition  of  a  brute  ;  aged  39  (Lelut) 44*30  " 

Imbecile,  with  difficulty  in  movements;  aged  57;  intelligence  correct,  notwithstand- 
ing its  slight  development  (Lelut) 43*56  " 

Man,  34  years  of  age  ;  died  of  phthisis  (Wagner) 43*38  " 

Celebrated  mineralogist,  aged  77  ;  above  medium  stature  (Wagner).. 43*24  " 

Executed  criminal,  aged  31 ;  small  stature  ;  intelligence  mobile  and  exaggerated  (Lelut)  .  42-04  " 

Upholsterer,  aged  60  ;  died  of  phthisis  (Wagner). 40*91  " 


704  NERVOUS  SYSTEM. 

Imbecile,  aged  23  ;  large  stature  (Lelut) 38-97  oz. 

Idiot,  of  the  lowest  degree  of  intelligence  ;  aged  46  ;  medium  stature  (L61ut) 36*86  " 

Man,  46  years  of  age;  idiocy  very  profound  ;  very  large  stature  (Lelut) 36'15  " 

Man,  44  years  of  age ;  idiocy  very  profound  ;  a  little  below  medium  stature  (Lelut) 34'39  " 

In  compiling  the  foregoing  table,  we  have  in  every  instance  consulted  the  authentic 
reports  of  the  weights  of  the  brain  and  have  reduced  them  all  to  ounces  av.  with  the 
greatest  care.  This  was  found  necessary,  on  account  of  the  important  variations  in  the 
reports  quoted  by  different  physiological  authors,  especially  as  regards  the  brains  of 
Cuvier,  "Webster,  and  Dupuytren.  We  believe  that  our  figures  are  absolutely  correct. 
The  weights  of  the  brains  of  Cromwell  and  Byron  are  given,  but  there  can  be  hardly  any 
question  that  the  weights  are  grossly  exaggerated.  A  careful  study  of  the  weights  given  in 
this  table  shows  the  impossibility  of  applying  to  individuals  an  absolute  rule  that  the  great- 
est brain-power  is  connected  with  the  greatest  amount  of  brain-substance.  The  men  of 
acknowledged  intellectual  ability  in  the  table  are,  Cuvier,  Abercrombie,  Spurzheim, 
Webster,  Agassiz,  Dupuytren,  and  those  cited  by  Wagner  as  celebrated  mathematicians, 
professors,  etc.  A  bricklayer,  Cuvier,  and  Abercrombie  stand  at  the  head  of  the  list, 
as  regards  the  weight  of  the  brain ;  but  above  Webster  and  Dupuytren,  are  Ruloff,  Fisk, 
two  idiots,  a  boy  thirteen  years  old,  and  a  common  laborer.  Far  down  in  the  list,  is  a 
celebrated  mineralogist,  whose  brain  is  at  least  six  ounces  below  the  average.  The 
advanced  age  of  the  person  referred  to  (seventy-seven  years)  would  not  account  for  the 
small  weight  of  the  brain,  although  the  weight  is  undoubtedly  diminished  in  old  persons. 
We  are  not  surprised,  then,  in  the  tables  based  upon  observations  of  thousands  of  healthy 
brains  of  men  not  remarkable  for  great  intellect,  to  find  many  between  fifty-five  and  sixty 
ounces  in  weight. 

As  the  general  result  of  all  the  observations  upon  the  human  subject,  while  we  admit 
that  intellectual  vigor  is  in  general  coincident  with  large  development  of  the  cerebral 
hemispheres,  there  are  certainly  many  striking  exceptions  to  this  rule  when  it  is  applied 
to  individuals. 

Location  of  the  Faculty  of  Articulate  Language  in  a  Restricted  Portion  of  the  Ante- 
rior Cerebral  Lobes. — Physiologists  are  often  slow  to  accept  important  facts  bearing  directly 
upon  the  functions  of  parts,  drawn  exclusively  from  pathology,  especially  when  these 
facts  are  not  capable  of  demonstration  by  experiments  upon  the  lower  animals;  and  per- 
haps this  is  due  to  a  certain  distrust  of  the  accuracy  of  pathological  researches  as  com- 
pared with  the  exact  results  of  well-executed  experimental  observations.  As  regards  the 
faculty  of  speech,  however,  our  study  must  be  confined  to  man,  the  only  animal  capable 
of  articulate  language,  and  our  data  are  drawn  exclusively  from  pathology.  Some  physio- 
logical writers  are  still  disposed  to  regard  the  location  of  the  faculty  of  speech  as  not 
definitively  settled;  but,  from  a  careful  study  of  the  pathology  of  aphasia,  we  are  con- 
vinced that  there  is  no  point  in  the  physiology  of  the  brain  more  exactly  determined 
than  that  the  faculty  of  speech  is  located  in  a  well-defined  and  restricted  portion  of  the 
anterior  lobes.  This  is  the  more  interesting  and  important,  as  it  is  the  only  sharply- 
defined  faculty  that  has  been  accurately  located  in  a  distinct  portion  of  the  brain. 

Aphasia  is  a  pathological  condition  in  which  the  subject  is  deprived,  more  or  less 
completely,  of  the  power  of  language,  spoken  or  written.  This  definition  includes  not 
alone  those  cases  in  which  patients  are  unable  to  express  ideas  by  speech,  but  cases  in 
which  the  idea^of  language  is  lost  and  there  is  agraphia,  or  inability  to  express  ideas  in 
writing.  Certain  cases  of  this  disease  present  loss  of  speech  because  the  subject  is  inca- 
pable of  coordinating  the  muscles  used  in  articulation.  The  patient  has  a  clear  idea  of 
language  and  of  the  meaning  of  words  and  is  able  to  write  perfectly  well.  In  other 
cases,  the  patient  can  neither  speak  nor  express  ideas  in  writing.  In  these,  the  idea  of 
language  is  lost.  In  both  of  these  varieties  of  the  disease,  the  difficulty  is  either  in  the 
organ  presiding  over  the  faculty  of  speech  or  in  the  connections  of  this  organ  with  the 


FUNCTIONS   OF  THE   CEREBRUM.  795 

muscles  concerned  in  articulation.  Thus  regarded,  aphasia  does  not  include  aphonia  from 
laryngeal  disease,  or  loss  of  speech  such  as  is  observed  frequently  in  hysteria,  in  the  in- 
sane, who  sometimes  refuse  to  speak  from  pure  obstinacy,  or  in  cases  of  paralysis  of  the 
parts  immediately  concerned  in  articulation.  The  whole  history  of  the  disease  points  to 
a  particular  part  of  the  brain,  which  presides  over  the  faculty  of  speech. 

As  a  preliminary  to  the  location  of  the  nerve-centre  presiding  exclusively  over  speech, 
it  is  necessary  to  establish  the  existence  of  the  power  of  articulate  language  as  a  distinct 
faculty ;  and  this  is  done  by  cases  of  disease  in  which  this  faculty  seems  to  be  lost,  the 
general  mental  condition  being  unaffected.  Passing  over  the  passages  in  the  writings  of 
the  ancients,  in  which  it  is  stated  that  the  power  of  speech  is  sometimes  lost,  and  even 
some  writers  in  the  beginning  of  the  present  century,  who  connected  this  difficulty  with 
lesions  of  the  anterior  lobes  of  the  brain,  we  come  to  the  observations  of  Dr.  Marc  Dax, 
who,  in  1836,  read  a  paper  before  the  medical  congress  at  Montpellier,  in  which  he  indicat- 
ed impairment  or  loss  of  speech  in  one  hundred  and  forty  cases  of  right  hemiplegia.  Dax 
concluded,  from  these  observations,  that  the  faculty  of  articulate  language  occupies  the 
left  anterior  lobe  of  the  cerebrum.  This  memoir,  however,  attracted  but  little  attention, 
until  1861,  when  the  discussion  was  renewed  by  Broca;  and,  since  then,  numerous  cases 
of  aphasia  with  lesion  of  the  left  anterior  lobe  have  been  reported  by  various  writers.  In 
1863,  M.  G.  Dax,  a  son  of  Marc  Dax,  limited  the  lesion  to  the  anterior  and  middle  portion 
of  the  left  anterior  lobe.  It  was  farther  stated,  by  Broca  and  Hughlings  Jackson,  to  be 
that  portion  of  the  brain  nourished  by  the  left  middle  cerebral  artery.  According  to 
recent  observers,  the  most  frequent  lesion  in  aphasia  is  in  the  parts  supplied  by  the  left 
middle  cerebral  artery,  particularly  the  lobe  of  the  insula,  or  the  island  of  Reil ;  and  it  is 
a  curious  fact  that  this  part  is  found  only  in  man  and  monkeys,  being  in  the  latter 
very  slightly  developed.  While  we  must  agree  with  most  authors  in  the  statement  that 
the  organ  of  language  cannot  be  absolutely  restricted  to  these  parts,  it  is  none  the  less 
certain  that  they  are  most  frequently  the  seat  of  lesion  in  aphasia. 

While  it  is  demonstrated  that  the  cerebral  lesion  in  aphasia  involves  the  left  anterior 
lobe  in  the  great  majority  of  cases,  there  are  several  instances  in  which  the  right  lobe 
alone  is  affected ;  and  this  has  led  physiologists  and  pathologists  to  deny  the  absolute 
location  of  the  organ  of  language  upon  the  left  side.  Even  if  we  reject  a  certain  number  of 
cases  of  aphasia  with  the  brain-lesion  limited  to  the  right  side,  in  which  we  may  suppose 
that  the  post-mortem  examinations  were  incomplete,  or  the  impairment  of  speech  was 
due,  perhaps,  to  simple  paralysis  of  muscles,  we  must  admit  that,  in  a  few  instances, 
aphasia  has  followed  injury  or  disease  of  the  brain  upon  the  right  side.  Aside  from 
the  anatomical  arrangement  of  the  arteries,  which  seem  to  furnish  a  greater  amount  of 
blood  to  the  left  hemisphere,  it  is  evident  that,  as  far  as  voluntary  movements  are  con- 
cerned, the  right  ha^nd,  foot,  eye,  etc.,  are  used  in  preference  to  the  left ;  and  that  the 
motor  functions  of  the  left  hemisphere  are  superior  in  activity  to  those  of  the  right.  It 
would  be  interesting,  then,  to  note  the  physical  peculiarities  of  persons  affected  with  left 
hemiplegia  and  aphasia.  Dr.  Bateman  quotes  two  cases  of  aphasia  dependent  upon  lesion 
of  the  right  side  of  the  brain  and  consequent  left  hemiplegia,  in  which  the  persons  were 
left-handed ;  and  these,  few  as  they  are,  are  interesting,  as  showing  that  a  person  may  use 
the  right  side  of  the  brain  in  speech,  as  in  the  other  motor  functions.  In  this  connection, 
it  may  not  be  uninteresting  to  note  that,  although  most  anatomists  have  failed  to  find  any 
marked  difference  in  the  weight  of  the  two  cerebral  hemispheres,  Dr.  Boyd  has  shown 
by  an  "  examination  of  nearly  two  hundred  cases  at  St.  Marylebone,  in  which  the  hemi- 
spheres were  weighed  separately,  that  almost  invariably  the  weight  of  the  left  exceeded 
that  of  the  right  by  at  least  the  eighth  of  an  ounce."  To  conclude  our  citations  of  patho- 
logical facts  bearing  upon  the  location  in  the  brain  of  the  organ  of  speech,  we  may  refer 
to  an  account,  by  Dr.  Broadbent,  of  the  brain  of  a  deaf  and  dumb  woman.  In  this  case 
the  brain  was  found  to  be  of  about  the  usual  weight,  but  the  left  third  frontal  convolu- 
tion was  of  "  comparatively  small  size  and  simple  character." 
45 


706  NEKVOUS  SYSTEM. 

Taking  into  consideration  all  of  the  pathological  facts  bearing  upon  the  subject,  it 
seems  certain  that,  in  the  great  majority  of  persons,  the  organ  or  part  presiding  over 
the  faculty  of  articulate  language  is  situated  at  or  near  the  third  frontal  convolution 
and  the  island  of  Reil  in  the  left  anterior  lobe  of  the  cerebrum,  and  mainly  in  the 
parts  nourished  by  the  middle  cerebral  artery.  In  some  few  instances,  the  organ  seems 
to  be  located  in  the  corresponding  part  upon  the  right  side.  It  is  possible  that,  origi- 
nally, both  sides  preside  over  speech,  and  the  superiority  of  the  left  lobe  of  the  brain 
over  the  right  and  its  more  constant  use  by  preference  in  right-handed  persons  may 
lead  to  a  gradual  abolition  of  the  functions  of  the  right  side  of  the  brain,  in  connection 
with  speech,  simply  from  disuse.  This  view,  however,  is  hypothetical,  but  it  is  rendered 
probable  by  certain  considerations,  among  the  most  important  of  which  is  the  state- 
ment by  Longet,  that  "  one  cerebral  hemisphere  in  a  healthy  condition  may  suffice  for 
the  exercise  of  intelligence  and  the  external  senses."  In  support  of  this  statement, 
Longet  cites  several  cases  of  serious  injury  of  one  hemisphere  without  impairment  of 
the  intellect.  In  what  is  called  the  ataxic  form  of  aphasia,  the  idea  and  memory  of 
words  remain,  and  there  is  simply  loss  of  speech  from  inability  to  coordinate  the  mus- 
cles concerned  in  articulate  language.  Patients  affected  in  this  way  cannot  speak  but 
can  write  with  ease  and  correctness.  In  the  amnesic  form  of  the  disease,  the  idea  and 
memory  of  language  are  lost ;  patients  cannot  speak,  and  are  affected  with  agraphia,  or 
inability  to  write.  In  cases  in  which  hemiplegia  is  marked,  the  aphasia  is  usually  of  the 
ataxic  form ;  while,  in  cases  in  which  there  is  no  hemiplegia,  the  aphasia  is  generally 
amnesic. 

The   Cerebellum. 

It  is  not  necessary,  in  order  to  comprehend  the  functions  of  the  cerebellum,  as  far  as 
these  are  known,  to  enter  into  a  full  description  of  its  anatomical  characters.  The 
points,  in  this  connection,  that  are  most  interesting  to  us  as  physiologists  are  the  follow- 
ing :  the  division  of  the  substance  of  the  cerebellum  into  gray  and  white  matter ;  the 
connection  between  the  cells  and  fibres  ;  the  connection  of  the  fibres  with  the  cerebrum, 
and  with  the  prolongations  of  the  columns  of  the  spinal  cord ;  and  the  passage  of  fibres 
between  the  two  lateral  lobes.  These  points,  therefore,  will  be  the  only  ones  that  will 
engage  our  attention. 

As  we  have  seen,  in  treating  of  the  general  arrangement  of  the  encephalon,  the  cere- 
bellum, situated  beneath  the  posterior  lobes  of  the  cerebrum,  weighs  about  5*2  ounces 
av.  in  the  male,  and  4"7  ounces  in  the  female.  The  proportionate  weight  to  that  of  the 
cerebrum  is  as  1  to  8f  in  the  male,  and  as  1  to  8J-  in  the  female.  It  is  separated  from 
the  cerebrum  by  a  strong  process  of  the  dura  mater,  called  the  tentorium.  Like  the 
cerebrum,  the  cerebellum  presents  an  external  layer  of  gray  matter,  the  interior  being 
formed  of  white,  or  fibrous  nerve-tissue.  The  amount  of  the  gray  substance  is  very 
much  increased  by  numerous  fine  convolutions  and  is  farther  extended  by  the  penetra- 
tion, from  the  surface,  of  arborescent  processes  of  gray  matter.  Near  the  centre  of  each 
lateral  lobe,  embedded  in  the  white  substance,  is  an  irregularly-dentated  mass  of  cellular 
matter,  called  the  corpus  dentatum.  The  cerebellar  convolutions  are  more  numerous  and 
the  gray  substance  is  deeper  than  in  the  cerebrum  ;  and  these  convolutions  are  present  in 
many  of  the  inferior  animals  in  which  the  surface  of  the  cerebrum  is  smooth. 

The  cerebellum  consists  of  two  lateral  hemispheres,  more  largely  developed  in  man 
than  in  the  inferior  animals,  and  a  median  lobe.  The  hemispheres  are  subdivided  into 
smaller  lobes,  which  it  is  unnecessary  to  describe.  Beneath  the  cerebellum,  bounded  in 
front  and  below  by  the  medulla  oblongata  and  pons,  laterally  by  the  superior  peduncles, 
and  superiorly  by  the  cerebellum  itself,  is  a  lozenge-shaped  cavity,  called  the  fourth  ven- 
tricle. The  crura,  or  peduncles,  will  be  described  in  connection  with  the  direction  of  the 
fibres. 

The  structure  of  the  gray  substance  of  the  convolutions  presents  certain  peculiarities. 


THE   CEREBELLUM.  707 

This  portion  is  divided  quite  distinctly  into  an  internal  and  an  external  layer.  The  inter- 
nal layer  presents  an  exceedingly  delicate  net-work  of  fine  nerve-fibres,  which  pass  to 
the  cells  of  the  external  layer.  In  the  plexus  of  anastomosing  fibres,  are  found  numer- 
ous bodies  like  free  nuclei,  called  by  Kobin,  myelocytes.  The  external  layer  is  some- 
what like  the  external  layer  of  gray  substance  of  the  posterior  lobes  of  the  cerebrum 


Fra.  221.—Ce>'elellum  and  medulla  oblongata.    (Hirschfeld.) 

1, 1,  corpus  dentatum ;  2,  tuber  annulare ;  3,  section  of  the  middle  peduncle ;  4,  4,  4,  4,  4,  4,  laminae  forming  the  arbor- 
vitaa;  5,  5,  olivary  body  of  the  medulla  oblongata;  6,  anterior  pyramid  of  the  medulla  oblongata;  7,  upper  ex- 
tremity of  the  spinal  cord. 

and  is  more  or  less  sharply  divided  into  two  or  more  secondary  layers.  The  most  exter- 
nal portion  of  this  layer  contains  a  few  small  nerve-cells  and  fine  filaments  of  connective 
tissue  ;  and  the  rest  of  the  layer  contains  a  great  number  of  large  cells,  rounded  or 
ovoid,  with  two  or  three,  and  sometimes,  though  rarely,  four  prolongations.  The  mode 
of  connection  between  the  nerve-cells  and  the  fibres  has  already  been  described  under 
the  head  of  the  general  structure  of  the  nervous  system. 

Course  of  the  Fibres  in  the  Cerebellum. — Most  anatomical  writers  give  a  very  simple 
description  of  the  course  of  the  nerve-fibres  in  the  cerebellum.  From  the  gray  sub- 
stance of  the  convolutions  and  their  prolongations,  the  fibres  converge  to  form  finally  the 
three  crura,  or  peduncles  on  each  side.  The  superior  peduncles  pass  forward  and  up- 
ward to  the  crura  cerebri  and  the  optic  thalami.  These  connect  the  cerebellum  with  the 
cerebrum.  Beneath  the  tubercular  quadrigemina,  some  of  these  fibres  decussate  with  the 
corresponding  fibres  upon  the  opposite  side ;  so  that  certain  of  the  fibres  of  the  superior 
peduncles  pass  to  the  corresponding  side  of  the  cerebrum,  and  others  pass  to  the  cere- 
bral hemisphere  of  the  opposite  side. 

The  middle  peduncles  arise  from  the  lateral  hemispheres  of  the  cerebellum,  pass  to 
the  pons  Varolii,  where  they  decussate,  connecting  together  the  two  sides  of  the  cere- 
bellum. 

The  inferior  peduncles  pass  to  the  medulla  oblongata  and  are  continuous  with  the 
restiform  bodies,  which,  in  turn,  are  continuations  chiefly  of  the  posterior  columns  of  the 
spinal  cord. 

From  the  above  sketch,  the  physiological  significance  of  the  direction  of  the  fibres, 
as  it  appears  from  the  most  reliable  and  generally-accepted  anatomical  investigations,  is 
sufficiently  evident.  By  the  superior  peduncles,  the  cerebellum  is  connected,  as  are  all 


708  NERVOUS  SYSTEM. 

of  the  encephalic  ganglia,  with  the  cerebrum  ;  by  the  middle  peduncles,  the  two  lateral 
halves  of  the  cerebellum  are  intimately  connected  with  each  other ;  and,  by  the  inferior 
peduncles,  the  cerebellum  is  connected  with  the  posterior  columns  of  the  spinal  cord. 
We  shall  see,  when  we  come  to  study  the  functions  of  the  cerebellum,  that  its  connection 
with  the  posterior  white  columns  of  the  cord  is  a  point  of  great  interest  and  importance. 

General  Properties  of  the  Cerebellum. — There  is  now  no  difference  of  opinion  among 
physiologists,  with  regard  to  the  general  properties  of  the  cerebellum.  Flourens,  who 
made  the  first  elaborate  and  satisfactory  observations  upon  the  cerebellum  in  living 
animals,  noted,  in  all  of  his  experiments,  that  lesion  or  irritation  of  the  cerebellum 
alone  produced  neither  pain  nor  convulsions ;  and  the  same  results  have  followed  the 
observations  of  all  modern  physiologists  who  have  investigated  this  question  practically. 
We  have  ourselves  frequently  exposed  and  mutilated  the  cerebellum  in  pigeons  and  have 
never  observed  any  evidence  of  excitability  or  sensibility.  From  these  facts,  we  must 
conclude  that  the  cerebellum  is  inexcitable  and  insensible  to  direct  stimulation,  at  least 
as  far  as  has  been  shown  by  direct  observations.  It  is  not  impossible,  however,  that 
future  experiments  may  reverse  this  generally-received  opinion  ;  particularly  in  view  of 
the  recent  observations  of  Fritsch  and  Hitzig,  already  cited,  which  show  that  certain 
parts  of  the  cerebrum  are  excitable,  and  that  the  excitability  of  the  encephalic  centres 
rapidly  disappears  in  living  animals,  as  the  result  of  pain  and  hemorrhage.  We  should 
note,  also,  the  experiments  of  Budge,  who  observed  movements  in  the  testicles  and  vasa 
deferentia,  in  males,  and  in  the  cornua  of  the  uterus  and  in  the  Fallopian  tubes,  in  females, 
following  irritation  of  the  cerebellum. 

Functions  of  the   Cerebellum. 

There  are  still  the  widest  differences  of  opinion  among  physiologists,  with  regard  to 
the  functions  of  the  cerebellum,  mainly  for  the  reason  that  the  experiments  upon  the 
lower  animals,  though  in  themselves  sufficiently  definite,  are  apparently  contradicted  by 
pathological  observations  upon  the  human  subject.  There  should  be  no  such  discrep- 
ancy between  well-conducted  experiments  and  carefully-observed  cases  of  disease  or 
injury ;  for  it  is  certain  that  the  functions  of  the  cerebellum  present  no  essential  differ- 
ences in  different  animals,  at  least  in  man,  the  mammalia,  and  birds.  It  is  necessary, 
therefore,  for  the  physiologist,  by  carefully  analyzing  and  correcting  the  results  obtained 
by  direct  experimentation  and  by  applying  to  the  study  of  pathological  observations  the 
facts  elicited  by  these  experiments,  to  endeavor  to  harmonize  the  real  or  apparent  con- 
tradictions ;  for,  as  we  have  often  had  occasion  to  remark,  there  are  no  exceptions  to 
the  laws  to  which  the  functions  of  similar  classes  of  animals  are  subordinated ;  and 
observations  and  experiments,  apparently  discordant,  will  always  be  found,  as  our  posi- 
tive knowledge  advances,  to  present  differences  in  the  conditions  under  which  the  phe- 
nomena have  been  observed.  To  apply  this  idea  to  the  functions  of  the  cerebellum,  it  may 
be  safely  assumed  that  it  is  impossible  for  this  organ  to  preside  directly  and  exclusively 
over  muscular  coordination  in  birds  and  the  inferior  mammals,  and,  in  man,  to  pos- 
sess different  functions.  With  regard  to  the  cerebrum,  man  possesses,  not  only  a  higher 
degree  of  development  of  certain  intellectual  faculties  than  the  inferior  animals,  but  is 
endowed  with  others,  such  as  the  power  of  articulate  language.  But,  in  man  and  in  the 
higher  orders  of  animals,  the  general  properties  and  functions  of  the  muscular  system  are 
essentially  the  same.  To  take  one  of  the  most  generally-accepted  views  of  the  functions 
of  the  cerebellum,  if  this  be  the  centre  for  muscular  coordination  in  birds  and  mammals, 
it  has  the  same  office  in  man,  although  it  may  possess  additional  functions  not  found 
lower  in  the  scale  of  animal  life.  Keeping  in  view,  then,  the  desirability  of  bringing 
into  accord  the  results  of  experiments  and  of  pathological  observations,  we  shall  first 
study  carefully  the  phenomena  which  follow  injury  or  extirpation  of  the  cerebellum  in 
the  lower  animals. 


FUNCTIONS  OF  THE  CEREBELLUM.  709 

Extirpation  of  the  Cerebellum  in  the  lower  Animals. — In  birds,  and  in  certain  mam- 
mals in  which  the  operation  has  been  successful,  the  more  or  less  complete  extirpation 
of  the  cerebellum  is  followed  by  well-marked  phenomena,  which  present  always  the  same 
character  but  are  somewhat  differently  interpreted  by  various  experimenters.  Experi- 
ments of  this  kind  were  first  made  by  Flourens ;  and  the  accuracy  of  his  observations 
has  never  been  successfully  controverted,  whatever  may  have  been  said  of  his  physiolo- 
gical deductions.  Indeed,  there  are  few  if  any  important  points  in  the  phenomena  fol- 
lowing partial  or  complete  removal  of  the  cerebellum  that  escaped  the  attention  of  this 
most  accurate  observer. 

Laying  aside,  for  the  present,  the  deductions  to  be  made  from  experiments  upon  ani- 
mals, we  may  quote  the  following  phenomena  noted  by  Flourens  and  by  all  who  have 
repeated  his  observations  upon  the  cerebellum  : 

"  I  extirpated  the  cerebellum  by  successive  layers  in  a  pigeon.  During  the  removal 
of  the  first  layers,  there  only  appeared  slight  feebleness  and  want  of  harmony  in  the 
movements. 

"  At  the  middle  layers,  there  was  manifested  an  almost  universal  agitation,  although 
there  was  not  added  any  sign  of  convulsion  ;  the  animal  executed  sudden  and  disordered 
movements  ;  it  heard  and  saw. 

"  On  the  removal  of  the  last  layers,  the  animal,  the  faculty  of  jumping,  flying,  walk- 
ing, and  maintaining  the  erect  position  being  more  and  more  disturbed  by  the  preceding 
mutilations,  lost  this  faculty  entirely. 

"  Placed  on  the  back,  it  was  not  able  to  recover  itself.  Far  from  resting  calm  and 
steady,  as  occurs  in  pigeons  deprived  of  the  cerebral  lobes,  it  became  vainly  and  contin- 
ually agitated,  but  it  never  moved  in  a  firm  and  definite  manner. 

"  For  example,  it  saw  a  blow  with  which  it  was  threatened,  wished  to  avoid  it,  made 
a  thousand  efforts  to  avoid  it,  but  did  not  succeed.  If  it  were  placed  on  its  back,  it  would 
not  rest,  exhausted  itself  in  vain  efforts  to  get  up,  and  finished  by  remaining  in  that  posi- 
tion in  spite  of  itself. 

"  Finally,  volition,  sensation,  perception,  persisted  ;  the  possibility  of  making  general 
movements  persisted  also  ;  but  the  coordination  of  the  movements  in  regular  and  definite 
acts  of  locomotion  was  lost." 

The  above  are  the  phenomena  observed  after  total  extirpation  of  the  cerebellum. 
Voluntary  movement,  sensation,  general  sensibility,  and  the  special  senses,  seem  to  be 
intact ;  but  there  is  always  a  loss  of  the  power  of  equilibrium,  and  the  movements  exe- 
cuted are  never  regular,  efficient,  and  coordinate.  Flourens  farther  states  that  animals 
operated  upon  in  this  way  retain  their  intellectual  and  perceptive  faculties. 

It  is  exceedingly  important  now  to  note  the  effects  of  partial  removal  of  the  cerebel- 
lum, as  these  bear  directly  upon  cases  of  disease  or  injury  of  this  organ  in  the  human 
subject,  in  which  its  disorganization  is  very  rarely  complete.  We  may  illustrate  this, 
also,  by  citing  two  of  Flourens's  typical  experiments  : 

"  I.  I  removed  by  successive  layers,  all  of  the  upper  half  of  the  cerebellum  in  a 
young  cock. 

"  The  animal  immediately  lost  all  stability,  all  regularity  in  its  movements  ;  and  its 
tottering  and  bizarre  mode  of  progression  reminded  one  entirely  of  the  gait  in  alcoholic 
intoxication. 

"  Four  days  after,  the  equilibrium  was  less  disturbed,  and  the  progression  was  more 
firm  and  assured. 

"  Fifteen  days  after,  the  equilibrium  was  completely  restored. 

"  II.  I  removed,  in  a  pigeon,  about  the  half  of  the  cerebellum  ;  and  I  removed  this 
organ  completely  in  a  fowl. 

"  At  the  end  of  a  certain  time,  the  pigeon  had  regained  its  equilibrium ;  the  fowl 
did  not  regain  it  at  all :  the  latter  lived  nevertheless  for  more  than  four  months  after 
the  operation." 


710  NERVOUS  SYSTEM. 

These  important  observations  we  have  repeatedly  confirmed,  and  we  have  in  our  pos- 
session the  encephalon  of  a  pigeon  which  recovered  completely  after  removal  of  about 
two-thirds  of  the  cerebellum,  the  animal  first  presenting  marked  deficiency  in  coordi- 
nating power. 

Such  are  the  phenomena  observed  in  experiments  upon  the  cerebellum  in  birds,  and 
they  have  been  extended  by  Flourens  and  others  to  certain  mammals,  as  young  cats, 
dogs,  moles,  mice,  etc.  Our  own  experiments,  which  have  been  very  numerous  during 
the  last  fifteen  years,  are  simply  repetitions  of  those  of  Flourens,  and  the  results  have 
been  the  same  without  exception. 

The  only  difficulties  in  operating  upon  the  cerebellum  arise  from  haemorrhage  and 
the  danger  of  injuring  the  medulla  oblongata.  The  skull  is  exposed  by  slitting  up  the 
scalp,  and  the  calvarium  is  removed  in  its  posterior  portion,  penetrating  just  above  the 
upper  insertion  of  the  cervical  muscles.  It  is  well  to  leave  a  strip  of  bone  in  the  median 
line,  thereby  avoiding  hemorrhage  from  the  great  venous  sinus,  although  this  precaution 
is  not  essential.  The  cerebellum  is  thus  exposed  and  may  be  removed  in  part  or  entirely, 
by  a  delicate  scalpel  or  forceps,  when  the  characteristic  phenomena  just  described  are 
observed.  Animals  operated  upon  in  this  way  feel  the  sense  of  hunger  and  attempt  to 
eat,  but,  when  the  movements  are  very  irregular,  they  are  unable  to  take  food.  We 
have  frequently  compared  the  phenomena  presented  after  removal  of  the  cerebellum  with 
the  movements  of  a  pigeon  intoxicated  by  forcing  down  the  oesophagus  a  little  bread 
impregnated  with  alcohol,  and  they  present  a  striking  similarity. 

In  view  of  the  remarkable  uniformity  in  the  actual  results  obtained  by  different  experi- 
menters, it  is  hardly  necessary  to  cite  all  of  the  observations  made  upon  the  lower  animals. 
The  phenomena  observed  by  Flourens  have  been  in  the  main  confirmed  by  Fod6ra, 
Bouillaud,  Magendie,  Wagner,  Lussana,  Dalton,  Vulpian,  Mitchell,  Onimus,  and  many 
others.  Certain  of  these  authors  differ  from  Flourens  in  their  ideas  concerning  the  func- 
tions of  the  cerebellum,  while  they  admit  the  accuracy  of  his  observations. 

We  shall  eliminate  from  the  present  discussion  the  experiments  made  upon  animals  low 
in  the  scale,  such  as  frogs  and  fishes  (although,  in  some  of  these,  the  results  are  in  accord 
with  the  observations  just  cited  upon  birds  and  mammals),  and  shall  confine  ourselves  to  an 
interpretation  of  the  phenomena  observed  after  extirpation  of  the  cerebellum  in  animals 
in  which  the  muscular  and  nervous  arrangement  is  like  that  of  the  human  subject.  The 
results  of  this  mutilation  are  as  definite,  distinct,  and  invariable,  as  in  any  experiments 
upon  living  animals,  and,  taken  by  themselves,  they  lead  inevitably  to  but  one  conclusion. 

When  the  greatest  part  or  the  whole  of  the  cerebellum  is  removed  from  a  bird  or  a 
mammal,  the  animal  being,  before  the  operation,  in  a  perfectly  normal  condition  and  no 
other  parts  being  injured,  there  are  no  phenomena  constantly  and  invariably  observed 
except  certain  modifications  of  the  voluntary  movements.  The  intelligence,  general  and 
special  sensibility,  the  involuntary  movements,  and  the  simple  faculty  of  voluntary  motion, 
remain.  The  movements  are  always  exceedingly  irregular  and  incoordinate  ;  the  animal 
cannot  maintain  its  equilibrium  ;  and,  on  account  of  the  impossibility  of  making  regular 
movements,  it  cannot  feed.  This  want  of  equilibrium  and  of  the  power  of  coordinating 
the  muscles  of  the  general  voluntary  system  causes  the  animal  to  assume  the  most  absurd 
and  remarkable  postures,  which,  to  one  accustomed  to  these  experiments,  are  entirely 
characteristic.  Call  this  want  of  equilibration,  of  coordination,  of  "muscular  sense,"  an 
indication  of  vertigo,  or  what  we  will,  the  fact  remains,  that  regular  and  coordinate  mus- 
cular action  in  standing,  walking,  or  flying,  is  impossible,  although  voluntary  power 
remains.  It  is  well  known  that  many  muscular  acts  are  more  or  less  automatic,  as  in 
standing,  and,  to  a  certain  extent,  in  walking.  These  acts,  as  well  as  nearly  all  voluntary 
movements,  require  a  certain  coordination  of  the  muscles,  and  this,  and  this  alone,  is 
abolished  by  extirpation  of  the  cerebellum.  It  is  true  that  destruction  of  the  semicir- 
cular canals  of  the  internal  ear  produces  analogous  disorders  of  movement,  but  this  is  the 
only  mutilation,  except  division  of  the  anterior  white  columns  of  the  spinal  cord,  which 


FUNCTIONS   OF  THE   CEREBELLUM.  711 

produces  any  thing  resembling  the  results  of  cerehellar  injury.  Certain  important  coordi- 
nate muscular  movements  are  well  known  to  be  dependent  upon  distinct  nerve-centres. 
The  acts  of  respiration  are  presided  over  exclusively  by  the  medulla  oblongata.  Deglutition 
probably  has  its  distinct  nerve-centre,  as  well  as  the  movements  of  the  eyes.  The  centre 
regulating  the  coordinate  movements  in  speech  is  situated  in  the  anterior  cerebral  lobes. 
None  of  these  peculiar  movements  are  affected  by  extirpation  of  the  cerebellum. 

If  there  be  a  distinct  nerve-centre  which  presides  over  the  coordination  of  the  general 
voluntary  movements,  experiments  upon  the  higher  classes  of  animals  show  that  this 
centre  is  situated  in  the  cerebellum.  It  may  be  either  in  the  entire  cerebellum  or  in  a 
certain  portion  of  this  organ,  but,  if  it  be  confined  to  a  restricted  part,  this  has  not  yet 
been  determined.  If  the  cerebellum  preside  over  coordination,  as  a  physiological  neces- 
sity, the  centre  must  be  connected  by  nerves  with  the  general  muscular  system.  If  this 
connection  exist,  a  complete  interruption  of  the  avenue  of  communication  between  the 
cerebellum  and  the  muscles,  we  should  naturally  expect,  would  be  followed  by  loss  of 
coordinating  power.  From  the  anatomical  connections  of  the  cerebellum,  it  appears  that 
the  only  communication  between  this  organ  and  the  general  system  is  through  the  pos- 
terior white  columns  of  the  spinal  cord.  We  have  seen  that  these  columns  are  not  for 
the  transmission  of  the  general  sensory  impressions,  and  there  is  no  satisfactory  evidence 
that  they  convey  to  the  encephalon  the  so-called  muscular  sense.  As  regards  general 
sensibility  and  voluntary  motion,  we  cannot  ascribe  any  function  to  the  posterior  white 
columns,  except  that,  when  they  are  divided  at  several  points,  we  invariably  have  want 
of  coordination  of  the  general  muscular  system.  When  the  posterior  white  columns  are 
disorganized  in  the  human  subject,  we  have  loss  or  impairment  of  coordinating  power,  even 
though  the  general  sensibility  be  not  affected,  as  in  the  disease  called  locomotor  ataxia. 

Confining  ourselves  still  to  the  interpretation  of  experiments  upon  living  animals,  and 
leaving  for  subsequent  consideration  the  phenomena  observed  in  cases  of  disease  or  injury 
of  the  cerebellum  in  the  human  subject,  we  are  led  to  the  following  conclusions : 

There  is  a  necessity  for  coordination  of  the  movements  of  the  general  voluntary  system 
of  muscles,  by  means  of  a  nerve-centre  or  centres. 

Whatever  other  functions  the  cerebellum  may  have,  it  acts  as  the  centre  presiding 
over  equilibration  and  general  muscular  coordination. 

The  cerebellum  has  its  nervous  connections  with  the  general  muscular  system  through 
the  posterior  white  columns  of  the  spinal  cord,  a  fact  which  is  capable  both  of  anatomical 
and  physiological  demonstration. 

If  the  cerebellum  be  extirpated,  there  is  loss  of  coordinating  power ;  and,  if  the  pos- 
terior white  columns  of  the  cord  be  completely  divided,  destroying  the  communication 
between  the  cerebellum  and  the  general  system,  there  is  also  loss  of  coordinating  power. 

When  a  small  portion  only  of  the  cerebellum  is  removed,  there  is  slight  disturbance 
of  coordination,  and  the  disordered  movements  are  marked  in  proportion  to  the  extent 
of  injury  to  the  cerebellum. 

After  extirpation  of  even  one-half  or  two-thirds  of  the  cerebellum,  the  disturbances  in 
coordination  immediately  following  the  operation  may  disappear,  and  the  animal  may 
entirely  recover,  without  any  regeneration  of  the  extirpated  nerve-substance.  This  im- 
portant fact  enables  us  to  understand  how,  in  certain  cases  of  disease  of  the  cerebellum  in 
the  human  subject,  when  the  disorganization  of  the  nerve-tissue  is  slow  and  gradual,  there 
may  never  be  any  disorder  in  the  movements. 

We  present  the  above  conclusions,  as  in  our  own  mind  positive  and  definite.  It  is 
proper  to  state,  however,  that  the  definition  of  the  function  of  the  cerebellum  is  one  of 
the  points  stated  by  many  physiological  authors  as  doubtful  and  unsettled  ;  and  this  is  so, 
mainly  because  some  writers  have  been  unable  to  harmonize  the  experimental  facts  above 
detailed,  with  cases  of  disease  or  injury  of  the  cerebellum  in  the  human  subject.  We 
conceive  that  this  has  frequently  been  due  to  an  imperfect  study  of  the  pathological  facts, 
which  we  now  propose  to  discuss. 


712  NERVOUS  SYSTEM. 

Pathological  Facts  bearing  upon  the  Functions  of  the  Cerebellum. — Nearly  all  writers 
upon  the  physiology  of  the  nervous  system,  while  they  agree  that  extirpation  of  the  cere- 
bellum in  the  lower  animals  produces  irregularity  of  movements,  are  arrested,  as  it  were, 
in  their  deductions,  by  the  following  quotation  from  Andral,  in  his  report  of  ninety-three 
cases  of  disease  of  the  cerebellum  : 

"  A  more  remarkable  alteration  of  movement  is  noted  in  the  observation  of  M.  Lalle- 
mand.  The  patient  staggered  on  his  legs,  and  often  came  near  falling  forward.  In  this 
case,  the  only  one  which  tends  to  confirm  the  opinion  of  physiologists  who  regard  the 
cerebellum  as  the  organ  of  the  coordination  of  movements,  the  cerebellum  was  entirely 
transformed  into  a  sac  filled  with  pus." 

The  bare  statement,  such  as  is  generally  made,  that  Andral  collected  ninety-three 
cases  of  disease  of  the  cerebellum,  only  one  of  which  tends  to  show  that  this  is  the 
organ  of  muscular  coordination,  is  sufficient  to  arrest  any  physiologist  in  the  conclu- 
sions that  would  naturally  be  drawn  from  experimental  facts ;  and  many  writers  have 
expressed  themselves  as  uncertain  upon  the  question  of  the  function  of  the  cerebellum. 
Before  we  go  any  farther,  we  wish  to  settle,  once  for  all,  the  physiological  bearing  of 
these  cases ;  and,  with  this  end  in  view,  have  carefully  studied,  analyzed,  and  tabulated 
them.  Out  of  the  ninety-three  cases,  fifteen  were  observed  by  Andral,  and  seventy- 
eight  are  quoted  from  various  authors.  An  analysis  of  these  cases,  with  reference  to 
conditions  likely  to  complicate  the  effects  of  the  cerebellar  disease,  etc.,  is  given  in  the 
following  table : 

Analysis  of  AndraVs  Ninety-three  Cases  of  Disease  of  the  Cerebellum. 
{Six  Cases,  observed  by  Andral.1) 

Hemiplegia  ;  death  in  fifty  hours        .         .       V      -.  -.         .     '   .'-..'.  ]  case. 

Hemiplegia ;  sudden  death         .     *"•.        .        .         .        ,         .         .'       .         .         .  1       " 

Hemiplegia ;  death  in  two  days V    V:      .'-      .  1       " 

Hemiplegia ;  associated  with  cerebral  haemorrhage     .     -   .  '     .-     v.  -'.'''.         .  3       " 

(Seventy-eight  Cases,  quoted  from  various  Authors.) 

Haemorrhage  into  the  cerebellum  ;  quoted  from  Serres        .         .        ;    ;    ....'*    •+•        .     6  *  cases. 

quoted  from  Dance        .         .       r,        .    -  *  «         .     1  f  case, 
quoted  from  Bayle         .       •••'•.        .         .:       .     l:f     " 
quoted  from  Guiot         .'  .  ......  .    ..-       .    .  :  ,;       .     1  §     " 

(Serres);  hemiplegia     ;.;  ..  ./    •  „•{    -.*,     -.,,.-.     2      cases. 
(Gazes);  coma       .      /; ..        ,'.       ..       .,     .,  j  ,,..'    1      case. 

(Morgagni) ;  found  dead        .....      !„"..    .         .     1         " 

(Sedillot) ;  died  in  fifteen  minutes  .         .         .1         " 

(Cafford) ;  died  suddenly       '.  '- ;".:'  .     1 

Haemorrhage  (Michelet) ;  apoplexy  two  years  before  death ;  found  an  old  clot  in  the 

right  lobe  of  the  cerebellum     .         .        .    / 1         » 

Haemorrhage  (quoted  from  various  authors) ;  haemorrhage  into  the  cerebrum  as  well 

as  the  cerebellum     .       , ,        .         .  9     cases. 

Atrophy  of  the  left  cerebral  and  the  right  cerebellar  hemisphere         .   '  '  .*'       .         .     2 
Cases  of  disease,  with  paralysis  ;  quoted  from  various  authors    .         ...         .9 

Cases  of  abscess,  with  paralysis  ;  quoted  from  various  authors 3         " 

Cyst  (Recamier) ;  convulsions 1      case> 

Abscess  (Laugier) ;  convulsions  .  1         " 

Abscess,  involving  the  entire  cerebellum  (Lallemand);  want  of  coordination2  1 

Cases,  quoted  from  various  authors,  in  which  no  disturbance  was  noted  in  the  move- 
ments ;  the  disease  was  confined  to  one  lateral  lobe  of  the  cerebellum     .         .     5      cases, 
i  In  these  six  cases,  there  was  haemorrhage  into  the  cerebellum. 
This  is  the  single  case,  noted  by  Andral,  out  of  the  ninety-three,  the  only  one  showing  want  of  coordination. 


FUNCTIONS   OF  THE   CEREBELLUM.  713 

Cases  of  tumor,  quoted  from  various  authors,  in  which  there  was  paralysis         .         .15  cases. 

Cases  of  tumor,  associated  with  disease  of  the  cerebrum 7  " 

Cases  of  tumor,  associated  with  convulsions ;  the  descriptions  are  very  indefinite        .9  " 


(Nine  Cases,  observed  ~by  Andral.) 


case. 


Softening ;  hemiplegia  and  convulsions .,'.-.:, 

Softening;  hemiplegia  and  subsequent  haemorrhage    .         .        ."'  "•,$..     .-'.  ,    ...... 

Softening;  hemiplegia  and  haemorrhage      .         .         .        „  .      .       ;.       ........ 

Softening;  agitation,  like  convulsions,  of  the  members      .        ....-'  :  k      ,, .        .        , 

Cyst;  paralysis  and  convulsions          .       ,-.    .,-»<,       «,        .    .    .        .        

Tubercle;  hemiplegia        .         .         .        .         .         .        .'.„.«,  j    ••*' 

Five  small  tubercles  in  one  hemisphere  of  the  cerebellum ;  movements  normal  .         .1         " 
Tuberculous  mass,  the  size  of  a  hazel-nut,  on  one  side  of  the  cerebellum  ;  movements 

normal    .         .         .         .     '   .         .         .         .         .        .        .         .        .         .1         " 

Cyst,  the  size  of  a  hazel-nut,  on  one  side  of  the  cerebellum ;  movements  normal        .     1 — 9  cases. 
Add  cases  of  haemorrhage,  previously  cited,  observed  by  Andral,         ....  6     " 

Add  cases  quoted  from  various  authors .         .         t         78     " 

Total  cases  collected  by  Andral        .         .         ...         .  .         93  cases. 

In  six  cases,  quoted  from  Serres,  marked  *,  "  there  were  observed  all  the  signs  of  vio- 
lent apoplexy  ;  nothing  in  particular  is  said  with  regard  to  disorders  of  movement."  In 
the  case  quoted  from  Dance,  marked  f,  the  patient  was  struck  with  apoplexy.  In  the 
case  quoted  from  Bayle,  marked  J,  the  patient  suddenly  lost  consciousness,  had  convul- 
sive movements  on  the  third  day,  and  died  in  coma,  on  the  fifth  day.  In  the  case  quoted 
from  Guiot,  marked  §,  there  was  "  no  lesion  except  effusion  of  blood  in  the  median  lobe 
of  the  cerebellum.  The  individual  who  was  the  subject  of  this  observation  had  had  an 
attack  of  apoplexy.  Before  his  attack,  he  had  for  some  time  a  tottering  gait  (demarche 
chancelante),  and,  after  the  attack,  remained  hemiplegic  on  the  right  side." 

Let  us  now  carefully  review  these  ninety-three  cases  of  Andral,  which  have  been  held 
in  terrorem  over  those  who  have  ventured  to  argue,  from  experiments  upon  animals,  that 
the  cerebellum  is  the  coordinator  of  the  muscular  movements,  and  see  how  many  may 
properly  be  thrown  out  of  the  question ! 

We  can  discard  the  first  six  cases,  observed  by  Andral,  in  which  there  was  hemiplegia, 
speedy  death,  and  in  three  of  which  there  was  cerebral  haemorrhage;  for  we  could 
hardly  observe  want  of  coordination  in  hemiplegics  or  in  cases  complicated  with  cerebral 
disease.  We  can  discard  the  six  cases,  quoted  from  Serres,  in  which  there  was  violent 
apoplexy,  as  well  as  the  case  quoted  from  Dance,  with  apoplexy,  and  the  case  quoted 
from  Bayle,  with  coma  and  convulsions.  It  is  evident  that  these  cases  are  useless  in 
noting  the  presence  or  absence  of  coordinating  power.  We  can  discard  two  cases,  (Serres) 
with  hemiplegia ;  one,  (Cazes)  with  coma ;  one,  (Morgagni)  found  dead ;  one,  (S6 dillot)  died 
in  fifteen  minutes  ;  one,  (Cafford)  died  suddenly ;  and  one,  (Michelet)  apoplexy  two  years 
before  death,  and  an  old  clot  in  the  right  lobe  of  the  cerebellum.  This  last  case  is  in 
accord  with  experiments  on  animals ;  for  we  have  seen  that  the  coordinating  power  may 
be  restored  after  loss  of  one-half  of  the  cerebellum.  We  can  discard  nine  cases  quoted 
from  various  authors,  in  which  there  was  cerebral  as  well  as  cerebellar  hemorrhage ;  two 
cases  of  paralysis,  with  atrophy  of  one  hemisphere  of  the  cerebrum  and  one  hemis- 
phere of  the  cerebellum  ;  nine  indefinitely-described  cases,  with  paralysis  ;  three  cases  of 
abscess,  with  paralysis ;  one  case  of  cyst  and  one  of  abscess,  with  paralysis ;  fifteen  cases 
of  tumor,  with  paralysis ;  seven  cases,  associated  with  disease  of  the  cerebrum  and 
paralysis ;  and  nine  very  indefinitely  described  cases,  associated  with  convulsions.  Of  the 
remaining  cases  observed  by  Andral,  we  can  discard  one,  with  hemiplegia  and  convul- 
sions ;  one,  with  hemiplegia  and  subsequent  haamorrhage  ;  one,  with  hemiplegia ;  one  case 
of  cyst,  with  paralysis  and  convulsions  ;  and  one,  of  tubercle,  with  hemiplegia.  We  can 


714  NERVOUS  SYSTEM. 

also  discard  one  case  of  five  small  tubercles  in  one  hemisphere  of  the  cerebellum ;  one, 
of  a  tuberculous  mass,  the  size  of  a  hazel-nut,  upon  one  side  ;  and  one,  of  a  cyst,  the  size 
of  a  hazel-nut,  upon  one  side.  These  last  cases  do  not  present  sufficient  destruction  of 
the  cerebellar  substance  to  lead  us  to  expect  any  disorder  in  the  movements. 

Thus  far  we  have  discarded  eighty-five  cases,  leaving  eight  to  be  analyzed.  Of  these 
eight  cases,  in  five,  it  is  simply  stated  that  the  movements  were  unaffected,  and  that 
"  one  of  the  lateral  lobes  of  the  cerebellum  was  the  seat  of  abscess."  In  view  of  this 
bare  statement,  and  of  the  fact  that,  in  animals,  recovery  of  coordinating  power  takes  place 
when  half  of  the  cerebellum  has  been  removed,  we  may  throw  out  these  cases  as  incom- 
plete. It  must  be  remembered  that  the  abscesses  were  probably  of  slow  development ; 
and,  if  they  did  not  destroy  a  sufficiently  large  portion  of  the  cerebellum  to  influence  the 
coordinating  power  permanently,  it  is  not  probable  that  the  functions  of  this  organ  would 
be  at  all  affected,  as  there  would  be  no  shock,  such  as  occurs  in  the  sudden  removal  of 
substance  by  an  operation. 

"We  are  thus  reduced  to  three  cases ;  and,  in  all  of  these,  the  movements  were  more 
or  less  affected.  These  cases  we  shall  now  study  as  closely  as  is  possible  from  the  details 
given. 

CASE  I. — The  first  case  is  quoted  from  Guiot.  There  was  no  lesion,  except  an  effu- 
sion of  blood  in  the  median  lobe  of  the  cerebellum,  and  there  was  probably  no  pressure 
upon  the  peduncles.  "  The  individual  who  was  the  subject  of  this  observation  had  had 
an  attack  of  apoplexy.  Before  the  attack,  he  had  for  some  time  a  staggering  gait  (une 
demarche  chancelante),  and,  after  the  attack,  he  had  remained  hemiplegic  on  the  left 
side."  From  these  meagre  details,  it  seems  probable  that  there  was  a  certain  amount  of 
difficulty  of  coordination,  although  the  description  is  not  as  definite  as  could  be  desired. 

CASE  II. — The  second  case  was  observed  by  Andral.  A  groom,  not  quite  forty  years 
of  age,  was  brought  into  the  Maison  royale  de  sante,  having  suffered  from  severe  head- 
ache, vertigo,  etc.,  for  fifteen  days,  which  finally  became  fixed  at  the  occiput.  During 
the  first  three  days  in  the  hospital,  "  he  was  in  a  continual  state  of  agitation ;  the  move- 
ments of  the  members,  on  the  right  as  well  as  the  left  side,  were  sometimes  so  brusques 
and  disordered  that  they  resembled  convulsive  movements."  Soon  the  respiration  be- 
came disturbed,  and  he  died  in  asphyxia.  "  Upon  post-mortem  examination,  there  was 
found  general  injection  of  the  meninges ;  nothing  particular  in  the  cerebral  hemispheres ; 
a  moderate  quantity  of  serum  in  the  ventricles  ;  reddish  softening  of  the  left  hemisphere 
of  the  cerebellum  in  its  posterior  and  inferior  half ;  no  other  lesion." 

The  only  marked  symptom  relating  to  the  movements  in  this  case  was  a  certain 
amount  of  irregularity  and  convulsive  action  of  the  muscles,  while  the  patient  was  in 
bed.  The  case  is  not  strong  in  its  bearings,  either  for  or  against  the  coordination-theory ; 
for  there  must  have  been  a  great  amount  of  irritation  of  the  encephalic  centres,  and  it 
would  certainly  be  difficult  to  note  disturbance  of  equilibration  or  of  coordination  in  a 
patient  confined  to  the  bed. 

The  third  case  is  quoted  by  Andral  from  Lallemand,  and  is  taken  by  Lallemand  from 
Delamare. 

CASE  III. — "M.  G«e*rin,  vicar  at  Gezeville,  forty-six  years  of  age,  of  a  good  tempera- 
ment, strong,  and  corpulent,  with  a  good  appetite,  complained  of  a  dull  pain,  which 
finally  became  acute,  under  the  frontal  bone.  For  a  year  he  experienced  attacks  of  ver- 
tigo and  vomiting,  without  fever.  He  staggered  on  his  legs,  and  was  often  near  falling 
forward.  The  treatment  employed  was  antiphlogistic  and  derivative." 

On  post-mortem  examination,  the  cerebrum  was  found  entirely  healthy,  but  the  en- 
velop of  the  cerebellum  was  collapsed,  folded,  and  only  contained  about  the  half  of  an 
egg-shell  full  of  a  brown  and  fetid,  lymphatico-purulent  liquid. 

This  case,  as  far  as  the  description  goes,  shows  marked  difficulty  in  equilibration  or 
coordination. 

If  the  reader  have  carefully  studied  the  foregoing  analysis  of  Andral's  cases,  he  will 


FUNCTION'S   OF  THE  CEREBELLUM.  715 

see  that  eighty-five  may  be  thrown  out  altogether,  leaving  but  eight ;  and,  of  these  eight 
cases,  five  are  so  imperfectly  described,  and  the  disorganization  of  the  cerebellum  is  so 
restricted,  that  they  may  also  be  disregarded.  The  ninety-three  cases  are  thus  reduced 
to  three.  Of  these  three  cases,  in  two,  it  is  uncertain  whether  or  not  there  were  defi- 
ciency of  coordinating  power ;  and  in  one,  the  difficulty  in  equilibration  or  coordination 
was  distinctly  noted.  This,  we  conceive,  disposes  of  the  much-quoted  ninety-three  cases 
of  Andral ;  and  they  are  certainly  not  opposed  to  the  view  that  the  cerebellum  is  the 
organ  of  equilibration  or  muscular  coordination. 

In  addition  to  the  cases  collected  by  Andral,  there  are  numerous  other  instances  on 
record  of  disease  confined  to  the  cerebellum,  of  which  the  following  are  examples : 

CASE  IV. — In  1826,  Petiet  reported  a  case  of  disease,  in  which  the  cerebellum  was 
entirely  destroyed,  its  tissue  being  broken  down  into  a  sort  of  whitish  louillie.  The  cere- 
brum was  healthy.  The  observation  was  made  in  1796.  The  patient,  before  death,  was 
observed  to  present  a  remarkable  tendency  to  walk  backward.  He  rose  from  his  seat 
with  difficulty,  and,  once  erect,  the  first  movements  of  the  feet  were  lateral,  and  he  finally 
walked  by  moving  the  feet  from  before  backward.  His  locomotion  consisted  simply  in 
passing  from  his  own  to  an  adjoining  bed  in  the  ward,  a  distance  of  about  six  feet. 

CASE  V.— One  of  the  most  remarkable  cases,  and  the  one  most  frequently  quoted  by 
physiological  writers,  was  reported  by  Combette,  in  1831.  This  patient,  Alexandrine 
Labrosse,  in  her  seventh  year,  was  seen  by  M.  Miquel.  Since  the  age  of  five  years  only 
had  she  been  able  to  sustain  herself  on  her  feet.  M.  Miquel  was  struck  with  her  slight 
development  and  the  feebleness  of  the  extremities.  At  the  age  of  nine  and  a  half  years, 
she  was  admitted  into  the  Orphelins.  "When  spoken  to,  she  answered  with  difficulty 
and  hesitation.  Her  legs,  although  very  feeble,  enabled  her  still  to  walk,  but  she  often 
fell."  She  was  first  seen  by  M.  Combette,  in  January,  1831.  She  had  then  kept  the  bed 
for  three  months;  was  constantly  lying  on  the  back,  and  could  scarcely  move  the  legs; 
she  used  her  hands  with  ease.  She  died  of  some  intestinal  disorder,  March  25,  1831.  On 
post-mortem  examination,  "  in  place  of  the  cerebellum  there  was  a  cellular  membrane, 
gelatiniform,  semicircular,  from  eighteen  to  twenty  lines  in  its  transverse  diameter." 
There  was  no  trace  of  the  pons  Yarolii.  Combette  states  that  Alexandrine  Labrosse  was 
able  to  walk  for  several  years,  always,  it  is  true,  in  an  uncertain  manner ;  later,  her  legs 
became  more  and  more  feeble,  and  finally  she  ceased  to  be  able  to  sustain  her  weight. 
She  had  the  habit  of  masturbation.  Combette  farther  states  that  this  observation  is  not 
in  accord  "  with  the  experiments  of  Flourens,  which  tend  to  show  that  the  cerebellum  is 
the  regulator  of  movements."  The  encephalon  was  also  examined  by  Guillot,  who  noted 
absence  of  the  cerebellum  and  of  the  pons. 

This  case  is  somewhat  imperfect,  as  it  was  not  seen  by  Combette  until  the  patient  had 
kept  the  bed  for  three  months.  By  some  writers,  it  is  quoted  in  favor  of,  and  by  some, 
in  opposition  to  the  view  that  the  cerebellum  coordinates  the  muscular  movements.  It 
was  not  a  case  of  simple  disease  of  the  cerebellum,  as  the  pons  and  the  posterior  pedun- 
cles were  also  absent.  It  was  noted,  before  the  case  was  seen  by  Combette,  that  the 
patient  walked  in  an  uncertain  manner  and  often  fell. 

Several  cases  of  injury  of  the  cerebellum  are  reported  by  Larrefv. 

CASE  VI.— One  case  is  described,  in  which  the  patient  was  struck  by  a  ball  from  a 
blunderbuss,  which  grazed  the  occipital  protuberances.  There  was  no  disturbance  of 
movement.  The  patient  died  on  the  thirty-ninth  day,  in  opisthotonos.  On  post-mortem 
examination,  "  the  occipital  bone  had  sustained  a  considerable  loss  of  substance ;  the  slit 
into  the  dura  mater,  to  which  we  have  alluded,  corresponded  to  the  centre  of  the  right 
lobe  of  the  cerebellum,  which  was  sunk  downward  and  was  of  a  yellowish  color,  but  free 
from  suppuration  or  effusion.  The  medulla  oblongata  and  spinal  marrow  bore  a  dull, 
white  aspect,  were  of  greater  consistence  than  is  natural,  and  had  lost  about  a  quarter  of 
their  size ;  the  nerves  arising  from  them  appeared  to  us  also  to  be  in  a  state  of  atrophy 
near  their  origin." 


716  NERVOUS  SYSTEM. 

CASE  VII.— Another  patient  was  struck  by  a  piece  of  wood  on  the  right  side  of  the 
head.  He  was  found  dead  a  little  more  than  three  months  after  the  injury.  "  The  right 
hemisphere  of  the  cerebellum  was  entirely  disorganized  by  an  abscess  which  pervaded 
its  whole  substance."  No  disturbances  of  movement  were  noted. 

CASE  VIII.— Another  patient  had  erysipelas  following  a  fall  on  the  side  of  the  head, 
and  abscess.  He  lived  for  three  or  four  months.  Five  or  six  weeks  after  the  injury,  he 
had  severe  pains  in  the  occiput,  and,  "  when  standing,  he  could  with  difficulty  only  pre- 
serve his  equilibrium."  On  post-mortem  examination,  the  deep-seated  vessels  of  the  cere- 
brum were  found  injected.  "  We  found,  in  the  left  lobe  of  the  cerebellum,  about  three 
table-spoonfuls  of  pus  of  a  whitish  and  gelatinous  aspect,  which  had  encroached  upon,  or 
rather  displaced  entirely,  the  hemisphere  of  the  cerebellum ;  this  purulent  substance  was 
enveloped  within  the  pia  mater,  which  had  acquired  a  somewhat  firmer  consistence,  and, 
as  in  the  subject  of  the  preceding  case,  assumed  a  pearly  color.  The  other  half  of  the 
cerebellum  was  shrivelled,  and  the  medullary  substance  forming  the  arbor-vita3  was  of  a 
grayish  color  and  very  dense." 

The  first  of  these  cases  was  found  by  Larrey  to  be  associated  with  extinction  of  sexual 
appetite  and  atrophy  of  the  organs  of  generation.  In  the  first  two  cases,  judging  from 
the  results  of  experiments  on  animals,  there  was  not  enough  injury  of  the  cerebellum  to 
necessarily  influence  the  power  of  coordination.  In  the  last  case,  there  was  difficulty  in 
equilibration,  but  also  some  paralysis. 

A  number  of  cases,  which  it  is  unnecessary  to  detail  fully,  are  cited  by  Wagner,  in  the 
Journal  de  la  physiologic,  1861,  in  which  tottering  gait  and  want  of  equilibration  or  of 
muscular  coordination  were  noted,  in  connection  with  greater  or  less  disorganization  of 
the  cerebellum.  In  the  same  journal,  is  a  brief  note  of  a  case,  reported  by  Laborde,  in 
which  there  was  a  large  cyst  in  the  cerebellum,  with  incomplete  paraplegia  and  "  want 
of  coordination  of  the  movements  of  progression." 

CASE  IX. — A  most  remarkable  and  carefully-observed  case  of  atrophy  of  the  cerebel- 
lum was  reported  by  Dr.  Fiedler,  in  1861.  The  subject  of  this  observation,  a  man,  aged 
about  fifty  years,  had  remarkable  peculiarities  in  his  movements  for  thirty  years.  After 
the  age  of  twenty  years,  it  is  stated  that  "  he  could  no  longer  walk  with  as  much  cer- 
tainty as  before ;  the  gait  was  staggering  (taumelnd).  .  .  .  Not  only  in  the  house,  but 
also  in  the  street,  the  patient  often  fell,  so  that  he  was  very  frequently  taken  for  a  drunk- 
ard, and  was  either  carried  home  or  taken  to  the  police-station.  It  is  said  that  he  never 
had  drunk  spirituous  liquors. 

"  Sometimes  the  patient  walked  backward,  but  only  a  few  steps.  He  never  had  any 
turning  movements;  the  gait  was  always  tottering  (wacklig)  and  slow."  He  never  fell 
forward,  but  always  on  the  back.  On  post-mortem  examination,  the  cerebrum  was  found 
healthy,  "  but  the  cerebellum  was  atrophied,  especially  at  its  posterior  and  inferior  portion, 
and  was  reduced  in  size  at  least  one-half."  This  case  presented  the  phenomena  of  defec- 
tive coordination  to  a  marked  degree.  Nothing  is  said  of  vertigo. 

Among  the  most  striking  of  the  cases  of  disease  of  the  cerebellum,  are  two  observed 
by  Vulpian. 

CASE  X.— The  first  was  a  woman,  forty-nine  years  of  age,  in  the  hospital  of  la  Sal- 
petriere.  "  All  of  the  movements  were  preserved,  but  locomotion  was  most  irregular 
and  difficult ;  she  could  only  walk  in  the  most  Uzarre  manner,  resting  on  a  chair  which 
she  placed  before  her  at  every  step,  and,  in  spite  of  her  efforts  at  equilibration,  she  often 
This  patient,  however,  retained  great  muscular  power.  On  post-mortem  exami- 
nation, "  the  cortical  gray  substance  of  the  cerebellum  was  found  entirely  atrophied  :  all 
the  nerve-cells  of  this  layer  had  disappeared."  There  was  considerable  reduction  in  the 
size  of  the  cerebellum.  The  corpora  dentata  were  perfectly  preserved,  "  showing  that 
these  parts,  at  all  events,  have  but  a  slight  office  in  coordination." 

CASE  XI. — The  second  case  presented  an  old  softening,  about  the  size  of  a  hazel-nut, 
destroying  a  corresponding  amount  of  the  cerebellar  substance  of  one  of  the  hemi- 


FUNCTIONS  OF  THE  CEREBELLUM.  717 

spheres.  The  corpus  dentatum  was  completely  destroyed.  This  woman  "  walked  well, 
but  it  appears  nevertheless  that  she  vacillated  very  slightly  in  her  gait,  without,  how- 
ever, a  tendency  to  fall." 

We  have  thus  cited  quite  a  number  of  cases  of  disease  confined  to  the  cerebellum  in 
which  there  was  marked  disturbance  in  the  muscular  movements ;  but  there  are  others, 
in  which  the  movements  were  unaffected.  As  an  example  of  the  latter,  we  may  refer  to 
a  case  quite  fully  reported  by  Bouvier : 

CASE  XII. — "  A  man,  fifteen  years  of  age,  had  been  subject,  for  a  length  of  time,  to 
a  discharge  from  the  ear,  with  deafness  and  frequent  headache.  He  was  suddenly  seized 
with  more  severe  headache  on  the  left  side  of  the  head,  vomiting,  and  disorder  of  mind. 
His  symptoms  were,  indeed,  so  characteristic,  that  a  physician  who  was  consulted  pro- 
nounced him  to  be  laboring  under  abscess  in  the  head,  and  that  death  was  almost  certain. 

"  He  entered  the  Hotel  Lieu  on  the  15th  of  September,  three  weeks  after  the  last 
exacerbation,  when  he  complained  of  fixed  pain  in  the  head,  which  frequently  caused 
him  to  cry  out;  sensibility,  in  other  respects,  obtuse;  slow  answers;  somnolency;  face 
pale ;  features  sunken ;  look,  sad  and  anxious ;  a  copious,  purulent  discharge  from  the 
left  ear ;  deafness  of  the  same  side ;  pulse  slightly  slower ;  vomiting ;  constipation ;  the 
movements  of  the  limbs  were  preserved,  an  incomplete  paralysis  of  the  upper  eyelid 
being  alone  observed. 

"  These  symptoms  continued  for  the  following  days  without  any  marked  aggravation  ; 
and  it  seemed  probable  that  the  patient's  life  might  still  be  prolonged  for  some  time, 
when,  on  the  23d  of  September,  after  vomiting,  accompanied  by  great  agitation  and  vio- 
lent outcry,  he  suddenly  fell  into  a  state  of  complete  collapse.  Respiration  became 
embarrassed,  and  he  died  eight  days  after  his  entrance  into  the  hospital,  with  symptoms 
of  asphyxia. 

"  On  examining  the  body,  there  was  found,  as  had  been  foretold  during  life,  a  caries 
of  the  petrous  portion  of  the  temporal  bone,  and  an  abscess  in  the  interior  of  the  cra- 
nium. But  what  was  remarkable,  the  abscess  occupied  the  left  hemisphere  of  the  cere- 
bellum, although  nothing  led  to  the  suspicion  that  there  was  any  lesion  of  that  organ. 
There  was  an  extensive  cavity,  which  invaded  the  two  outer  thirds  of  the  left  lobe  of 
the  cerebellum,  and  which  contained  several  table-spoonfuls  of  pus,  somewhat  similar  to 
that  of  an  abscess.  The  substance  forming  its  parietes  were  softened  and  of  a  livid  tint. 
The  meatus  auditorius  was  filled  with  reddish  vegetations. 

"  The  caries  occupied  the  base  of  the  pars  petrosa  only— the  labyrinth  and  auditory 
nerve  were  untouched.  There  was  no  perceptible  communication  between  the  internal 
abscess  and  the  abscess  of  the  caries.  The  disease  of  the  bone,  however,  extended  to 
the  dura  mater,  in  two  very  circumscribed  points,  at  the  upper  and  hind  part  of  the  pars 
petrosa.  The  dura  mater,  opposite  these  points,  was  deeply  colored ;  an'd  its  coloration 
extended  to  its  inner  surface,  where  it  was  in  contact  with  the  cerebellum. 

"The  cerebral  ventricles  were,  moreover,  distended  by  a  limpid  fluid;  and  the  pi  a 
mater  exhibited  a  decided  injection  under  the  anterior  part  of  the  cerebral  lobes,  chiefly 
on  the  left  side. 

"  *  Two  circumstances,'  says  M.  Bouvier,  '  give  interest  to  this  case.  The  first  is  the 
almost  entire  separation,  by  means  of  the  dura  mater — which  was  scarcely  affected — 
between  two  lesions,  one  of  which  must  have  been  the  effect  of  the  other ;  so  that  it  is 
difficult  to  explain,  merely  by  continuity  of  tissue,  the  transmission  of  the  affection  from 
the  ear  to  the  cerebellum. 

"  '  The  second  is  the  absence  of  all  the  symptoms  which  have  been  of  late  regarded  as 
an  effect  of  lesions  of  the  cerebellum — such  as  augmentation  of  the  general  sensibility, 
loss  of  equilibrium,  and  excitation  of  the  genital  organs.  Could  this  peculiarity  be  owing 
to  the  slowness  of  the  affection,  or  to  its  not  having  extended  sufficiently  far  from  the 
side  of  the  medulla  oblongata? '  " 

The  interpretation  of  certain  of  the  cases  which  we  have  cited  depends  apparently 


718  NERVOUS  SYSTEM. 

upon  the  ideas  concerning  the  functions  of  the  cerebellum  with  which  they  are  regarded. 
We  should  certainly  consider  those  cases  in  which  disordered  movements  have  been 
noted,  as  very  strong  evidence,  taken  in  connection  with  the  results  of  experiments  upon 
living  animals,  that  the  cerebellum  regulates  equilibration  and  muscular  coordination. 
Some  physiologists  regard  them  as  in  accordance  with  the  view  that  injury  of  the  cere- 
bellum does  not  affect  coordination,  but  simply  produces  vertigo.  It  remains  for  the 
reader  to  judge  whether  or  not  the  phenomena  observed  in  these  cases  indicate  want  of 
coordinating  power.  In  the  case  reported  by  Bouvier,  the  lesion  of  the  cerebellum  was 
not  sufficient  to  necessarily  disturb  coordination. 

We  now  come  to  the  main  question,  whether  or  not,  in  view  of  the  results  of  experi- 
ments upon  animals  and  the  phenomena  observed  in  cases  of  disease  or  injury  of  the  cere- 
bellum, this  nerve-centre  presides  over  coordination  of  action  of  the  muscles,  which  is 
certainly  necessary  to  equilibration,  except  the  muscles  of  the  face  and  those  concerned 
in  speech.  This  question,  it  seems  to  us,  can  be  definitely  answered. 

Every  carefully-observed  case  that  we  have  been  able  to  find,  in  which  there  was 
uncomplicated  disease  or  injury  of  the  cerebellum,  provided  the  disease  or  injury  involved 
more  than  half  of  the  organ,  presented  great  disorder  in  the  general  movements,  par- 
ticularly those  of  progression.  We  have  collected  the  more  or  less  complete  reports  of 
twelve  cases.  In  Case  II.,  there  was  softening  of  one-half  of  one  hemisphere,  with 
remarkable  convulsive  movements.  In  Case  V.,  the  one  so  often  quoted  from  Combette, 
the  gait  was  uncertain,  with  frequent  failing ;  there  was  incomplete  paralysis ;  but,  in 
addition  to  the  absence  of  the  cerebellum,  there  was  no  pons  Varolii.  In  Case  VI., 
there  was  no  disturbance  of  movement,  and  there  was  partial  degeneration  of  one  lateral 
lobe  of  the  cerebellum.  In  Case  VII.,  there  was  no  disturbance  of  movement,  and  dis- 
organization of  one  lateral  lobe  of  the  cerebellum.  In  Case  XI.,  there  was  slight  loss  of 
substance  in  one  lateral  lobe  of  the  cerebellum,  and  slight  "vacillation"  in  the  move- 
ments. In  Case  XII.,  there  was  an  abscess  involving  two-thirds  of  one  lateral  lobe,  and  the 
movements  of  the  limbs  were  preserved.  In  Cases  I.,  III.,  IV.,  VIII.,  IX.,  X.,  six  out  of 
twelve,  there  was  difficulty  in  muscular  coordination,  which  was  invariably  in  direct  ratio 
to  the  amount  of  cerebellar  substance  involved  in  the  disease  or  injury.  We  do  not  make 
the  reservation,  that  more  than  half  of  the  cerebellum  must  be  destroyed  in  order  neces- 
sarily to  produce  difficulty  in  muscular  coordination,  upon  purely  theoretical  grounds,  but 
we  regard  this  point  as  positively  demonstrated  by  experiments  upon  animals.  These  ex- 
periments show  that  one-half  of  the  organ  is  capable  of  performing  the  function  of  the 
whole.  We  have  an  analogy  to  this  in  the  action  of  the  kidneys,  one  of  which  is  sufficient 
for  the  elimination  of  the  effete  constituents  of  the  urine,  after  the  other  has  been  removed. 

Notwithstanding  the  contrary  views  of  many  physiological  writers,  we  are  firmly 
convinced,  froA  experiments  and  a  careful  study  of  pathological  facts,  that  there  is  no 
one  point  in  the  physiology  of  the  nerve-centres  more  definitely  settled  than  that  the 
cerebellum  presides  over  equilibration  and  the  coordination  of  the  muscular  movements, 
particularly  those  of  progression.  In  this  statement,  we  make  exceptions  in  favor  of  the 
movements  of  respiration,  deglutition,  of  the  face,  and  of  those  concerned  in  speech,  as 
well  as  the  involuntary  movements  generally.  As  another  example  of  a  nerve-centre  pre- 
siding over  muscular  coordination,  we  have  the  instance  of  the  portion  of  the  left  anterior 
lobe  of  the  cerebrum  which  coordinates  the  action  of  the  muscles  concerned  in  speech. 

The  theory  that  the  disordered  movements  which  follow  injury  of  the  cerebellum  are 
due  simply  to  vertigo  is  not  tenable  ;  and  in  only  one  of  the  cases  cited  is  vertigo  men- 
tioned. There  is  a  disease,  involving  the  semicircular  canals  and  other  parts  of  the  inter- 
nal ear,  called  Mgniere's  disease,  in  which  there  is  marked  want  of  equilibration  and 
muscular  coordination,  attended  with,  and  probably  dependent  upon  vertigo.  The  ver- 
tigo is  always  very  distinct  and  is  mentioned  in  all  of  these  cases  ;  and,  although  it  is  less 
in  the  recumbent  posture,  it  is  never  entirely  absent.  A  careful  study  of  these  cases, 
comparing  them  with  the  cases  of  deficient  coordination  from  disease  of  the  cerebellum, 


FUNCTIONS   OF  THE   CEREBELLUM.  719 

cannot  fail  to  show  a  great  difference  between  the  phenomena  following  cerebellar  dis- 
ease and  the  muscular  phenomena  due  to  well-marked  and  persistent  vertigo. 

Connection  of  the  Cerebellum,  with  the  Generative  Function. — The  fact  that  the  cere- 
bellum is  the  centre  for  equilibration  and  the  coordination  of  certain  muscular  move- 
ments does  not  necessarily  imply  that  it  has  no  other  functions.  The  idea  of  Gall,  that 
"the  cerebellum  is  the  organ  of  the  instinct  of  generation,"  is  sufficiently  familiar;  and 
there  are  numerous  facts  in  pathology  which  show  a  certain  relation  between  this  nerve- 
centre  and  the  organs  of  generation,  although  the  idea  that  it  presides  over  the  genera- 
tive function  is  not  sustained  by  the  results  of  experiments  upon  animals  or  by  facts  in 
comparative  anatomy. 

In  experiments  upon  animals  in  which  the  cerebellum  has  been  removed,  there  is  noth- 
ing pointing  directly  to  this  part  as  the  organ  of  the  generative  instinct.  Flourens  re- 
moved a  great  part  of  the  cerebellum  in  a  cock.  The  animal  survived  for  eight  months. 
It  was  put  several  times  with  hens  and  always  attempted  to  mount  them,  but  without 
success,  from  wanf  of  equilibrium.  In  this  animal,  the  testicles  were  enormous.  This 
observation  has  been  repeatedly  confirmed,  and  there  are  no  instances  in  which  the  cere- 
bellum has  been  removed  with  apparent  destruction  of  sexual  instinct.  In  a  comparison 
of  the  relative  weights  of  the  cerebellum  in  stallions,  mares,  and  geldings,  Leuret  found 
that,  far  from  being  atrophied,  the  cerebellum  in  geldings  was  even  larger  than  in  either 
stallions  or  mares. 

In  the  numerous  cases  of  disease  or  injury  of  the  cerebellum,  to  which  we  have 
referred,  there  are  some,  in  which  irritation  of  this  part  has  been  followed  by  per- 
sistent erection  and  manifest  exaggeration  of  the  sexual  appetite,  and  others,  in  which 
its  extensive  degeneration  or  destruction  has  apparently  produced  atrophy  of  the  genera- 
tive organs  and  total  loss  of  sexual  desire.  There  are  also  certain  cases  of  this  kind 
which  we  have  not  yet  cited.  Serres  gives  the  history  of  several  cases,  in  which  irrita- 
tion of  the  cerebellum  was  followed  by  satyriasis  or  nymphomania,  but,  in  other  cases, 
there  were  no  symptoms  referable  to  the  generative  organs.  In  the  case  reported  by 
Combette,  the  patient  had  the  habit  of  masturbation.  Dr.  Fisher,  of  Boston,  reported 
(1838)  two  cases  of  diseased  or  atrophied  cerebellum,  with  absence  of  sexual  desire, 
and  one  case  of  irritation,  with  satyriasis.  Similar  instances  are  given  by  other  writers, 
which  it  is  unnecessary  to  detail.  We  have  already  cited  the  observations  of  Budge,  in 
which  mechanical  irritation  of  the  cerebellum  was  followed  by  movements  of  the  uterus, 
testicles,  etc. 

Although  there  are  many  facts  in  pathology  which  are  opposed  to  the  view  that  the 
cerebellum  presides  over  the  generative  function,  there  are  numerous  cases  which  go  to 
show  a  certain  connection  between  this  portion  of  the  central  nervous  system  and  the 
organs  of  generation  in  the  human  subject.  But  this  is  all  that  we  can  say  upon  this 
important  point ;  certain  it  is  that  the  facts  are  not  sufficiently  numerous,  definite,  and 
invariable,  to  sustain  the  doctrine  that  the  cerebellum  is  the  seat  of  the  sexual  instinct. 

Development  of  the  Cerebellum  in  the  Lower  Animals. — The  study  of  the  comparative 
anatomy  of  the  cerebellum  has  little  physiological  interest,  except  in  so  far  as  it  bears 
upon  our  knowledge  of  its  functions.  From  this  point  of  view,  there  is  little  to  be  said 
concerning  its  development  in  the  animal  scale.  We  can  hardly  establish  a  definite  rela- 
tion between  this  particular  part  of  the  encephalon  and  the  complicated  character  of  the 
muscular  movements ;  for,  as  we  pass  from  the  lower  to  the  higher  orders  of  animals,  we 
have  other  parts  of  the  brain,  as  well  as  the  cerebellum,  developed  in  proportion  to  the 
increased  complexity  of  the  muscular  system.  Nor  can  we  connect  the  comparative 
anatomy  of  the  cerebellum  with  the  ideas  of  the  functions  of  this  organ  in  connection 
with  generation.  The  amphioxus  lanciolatus  has  no  cerebellum,  and  this  organ,  there- 
fore, is  not  indispensable  to  generation.  In  some  animals  remarkable  for  salacity,  the 
cerebellum  is  not  unusually  large ;  and  facts  of  this  kind  might  be  multiplied  ad  injinitum. 


720  NERVOUS  SYSTEM. 

"We  have  thus  discussed  only  those  views  with  regard  to  the  functions  of  the  cerebel- 
lum which  are  supported  by  experimental  or  pathological  facts,  and  have  not  touched 
upon  the  vague  and  unsupported  ideas  advanced  by  various  writers  before  the  publica- 
tion of  the  remarkable  observations  of  Flourens.  There  is  no  proof  that  the  cerebellum 
is  the  organ  presiding  over  memory,  the  involuntary  movements,  general  sensibility,  or 
the  general  voluntary  movements.  The  only  view  that  has  any  positive  experimental  or 
pathological  basis  is  that  it  presides  over  equilibration  and  the  coordination  of  certain 
muscular  movements,  and  is,  perhaps,  in  some  way  connected  with  the  generative 
function. 

Ganglia  at  the  Base  of  the  Encephalon. 

At  the  base  of  the  encephalon,  are  found  several  collections  of  gray  matter,  or  gan- 
glia, some  of  which  ha»ve  functions  distinct  from  those  already  described  in  connection  with 
the  cerebrum  and  cerebellum ;  but  most  of  them  are  so  difficult  of  access  in  living  ani- 
mals, that  we  possess  very  little  definite  information,  even  with  regard  to  their  general 
properties.  We  have,  however,  a  tolerably  complete  knowledge  of  the  functions  of  the 
medulla  oblongata  and  the  tubercula  quadrigemina,  and  have  some  idea  of  the  physiology 
of  the  tuber  annulare;  but  the  functions  of  the  corpora  striata,  optic  thalami,  ventricles, 
pineal  gland,  peduncles,  etc.,  are  little  understood,  and  the  speculations  of  the  older 
writers,  with  the  indefinite  experiments  of  modern  physiologists,  upon  these  parts,  will 
be  passed  over  very  briefly. 

Corpora  Striata. 

These  bodies  are  somewhat  pear-shaped,  and  are  situated  at  the  base  of  the  brain, 
partly  without  the  cerebral  hemispheres  and  partly  embedded  in  their  white  substance. 


FIG.  228.— Corpora  striata.    (Sappey.) 

1,  fifth  ventricle ;  2,  the  two  laminae  of  the  septum  lucidum  meeting-  in  front  of  the  fifth  ventricle :  3,  hippocampus 
minor;  4  posterior  portion  of  the  corpus  callosum;  5,  middle  portion  of  the  fornix;  6  posterior  pillar  of  the 
formx;  7,  hippocampus  major;  8,  eminentia  collaterals ;  9,  lateral  portions  of  the  formx-  10  choroid  plexus- 
11,  taema  semicirculans ;  12,  corpiis  atriatum. 


OPTIC  THALAMI.  721 

Their  rounded  base  is  directed  forward,  and  the  narrower  end,  backward  and  outward. 
Their  external  surface  is  gray,  and  they  present,  on  section,  alternate  striae  of  white  and 
gray  matter,  which  appearance  has  given  them  the  name  of  corpora  striata.  Between 
the  narrow  extremities  of  these  bodies,  are  situated  the  optic  thalami. 

There  is  very  little  to  be  said  with  regard  to  the  functions  of  the  corpora  striata. 
Burdon- Sanderson  has  lately  shown  that,  when  the  corpus  striatum  on  one  side,  exposed 
by  carefully  removing  a  small  portion  of  the  anterior  lobe  of  the  cerebrum,  is  stimulated 
with  a  weak  induced  current  of  galvanism,  movements  of  the  muscles  occur  upon  the  oppo- 
site side  of  the  body.  If  the  deepest  parts  be  stimulated,  "  the  animal  opens  its  mouth, 
puts  out  its  tongue,  and  draws  it  in  again  alternately."  "When  the  corpora  striata  are 
removed,  disturbing  the  hemispheres  as  little  as  possible,  there  appears  to  be  no  paralysis, 
either  of  motion  or  sensation. 

We  have  obtained  a  little  more  information  regarding  the  functions  of  the  corpora 
striata,  from  cases  of  cerebral  haemorrhage  in  the  human  subject,  than  from  experimental 
investigations.  In  apoplexy,  when  the  corpus  striatum  on  one  side  is  alone  involved, 
there  is  paralysis  of  motion  of  the  opposite  lateral  half  of  the  body,  the  general  sensibility 
usually  being  unaffected.  Facts  of  this  kind  show  that  the  action  of  the  corpora  striata 
is  crossed ;  and  they  farther  illustrate  their  connection  with  the  motor  tract  from  the 
hemispheres. 

There  is  no  reason  to  suppose  that  the  corpora  striata  are  the  centres  of  olfaction,  as 
Avas  at  one  time  thought,  for  they  are  sometimes  absent  in  animals  possessing  very  large 
olfactory  nerves,  and  they  are  very  largely  developed  in  the  cetacea,  in  which  the  olfac- 
tory apparatus  is  rudimentary. 

Optic  Thalami. 

From  their  name,  we  should  infer  that  the  optic  thalami  have  some  important  func- 
tion in  connection  with  vision ;  but  they  serve  merely  as  beds  for  the  optic  commissures 
and  give  to  the  nerves  but  very  few  fibres.  They  are  oblong  bodies,  situated  between 
the  posterior  extremities  of  the  corpora  striata,  and  resting  upon  the  crura  cerebri  on  the 
two  sides.  They  are  white  externally,  and,  in  their  interior,  present  a  mixture  of  white 
and  gray  matter.  Longet  has  destroyed  them  upon  the  two  sides,  carefully  avoiding 
injury  of  the  optic  tracts,  and  he  noted  no  interference  with  vision  or  with  the  move- 
ments of  the  iris. 

The  optic  thalami  seem,  from  experiments  upon  animals,  to  have  a  peculiar  crossed 
action  upon  the  muscular  system.  While  their  mechanical  irritation  produces  neither 
pain  nor  convulsive  movements,  showing  that  they  are  probably  insensible  and  inexcita- 
ble,  the  extirpation  of  one  optic  thalamus  is  followed  by  enfeeblement  of  the  muscles  of 
the  opposite  lateral  half  of  the  body,  without  actual  paralysis.  When  both  have  been 
removed,  there  is  general  debility  of  the  muscular  system.  It  is  unnecessary  to  refer  to 
other  experiments  upon  these  parts,  which  have  been  very  indefinite  in  their  results,  or  to 
allude  to  the  "  circular  "  movements  produced  by  lesion  upon  one  side,  involving  also 
the  crus  cerebri ;  for,  beyond  the  statement  just  made,  the  function  of  the  optic  thalami 
is  unknown. 

We  derive  but  little  information  concerning  the  optic  thalami  from  cases  of  cerebral 
haemorrhage  in  the  human  subject ;  for  it  is  not  common  to  have  disease  involving  these 
parts  and  not  affecting  other  centres.  In  some  cases  of  lesion  limited  to  the  optic  thala- 
mus on  one  side,  there  is  paralysis  of  sensation  of  the  opposite  lateral  half  of  the  body, 
without  actual  paralysis  of  motion,  although  the  movements  are  generally  feeble.  When 
the  brain-lesion  involves  both  the  corpus  striatum  and  the  optic  thalamus  on  one  side, 
which  is  more  common,  there  is  paralysis  of  motion,  with  loss  or  disorder  of  sensibility, 
on  the  opposite  side  of  the  body.  These  facts  illustrate,  to  a  certain  extent,  the  anatomi- 
cal connection  of  the  optic  thalami  with  the  sensory  tracts,  although,  in  experiments  upon 
animals,  destruction  of  these  parts  does  not  necessarily  affect  the  general  sensibility. 
46 


722  NERVOUS   SYSTEM. 

Tubercula   Quadrigemina. 

These  little  bodies,  sometimes  called  the  optic  lobes,  are  rounded  eminences,  two 
upon  either  side,  situated  just  below  the  third  ventricle.  The  anterior,  called  the  nates, 
are  the  larger.  These  are  oblong  and  of  a  grayish  color  externally.  The  posterior, 
called  the  testes,  are  situated  just  behind  the  anterior.  They  are  rounded  and  are  rather 
lighter  in  color  than  the  anterior.  Both  contain  gray  nervous  matter  in  their  interior. 
They  are  the  main  points  of  origin  of  the  optic  nerves  and  are  connected  by  commissu- 
ral  fibres  with  the  optic  thalami.  In  birds,  the  tubercles  are  two  in  number,  instead  of 
four,  and  are  called  tubercular  bigemina. 

It  is  probable  that  the  tubercula  quadrigemina  are  inexcitable  and  insensible.  When 
pain  and  convulsive  movements  have  apparently  followed  their  mechanical  irritation  in 
living  animals,  these  phenomena  have  probably  been  due  to  excitation  or  stimulation  of 
the  motory  or  sensory  commissural  fibres  which  pass  beneath  them. 

As  regards  the  function  of  the  optic  lobes,  aside  from  their  action  as  reflex  nervous 
centres  for  the  movements  of  the  iris,  there  is  little  to  be  said,  except  that  they  preside 
over  the  sense  of  sight.  They  are  easily  reached  and  operated  upon  in  birds,  where  they 
are  very  large,  and  their  extirpation  is  followed  by  total  loss  of  sight,  as  well  as  abolition 
of  the  reflex  movements  of  the  iris.  In  birds  and  in  those  mammals  in  which  they  have 
been  operated  upon,  their  action  in  vision  is  crossed  ;  i.  e.,  when  the  lobe  is  removed  upon 
one  side,  the  sight  is  lost  in  the  opposite  eye,  vision  in  the  eye  upon  the  same  side  being 
unimpaired.  We  have  long  been  in  the  habit,  in  class-demonstrations,  of  removing  the 
optic  lobe  on  one  side  from  a  pigeon,  with  the  result  just  mentioned.  The  operation  is 
quite  simple :  A  part  of  the  skull  is  removed  by  the  side  of  one  hemisphere,  and  the 
optic  lobe  is  seen,  in  the  form  of  a  large,  white  tubercle,  between  the  posterior  portion 
of  the  cerebrum  and  the  cerebellum.  A  little  slit  is  then  made  in  its  capsule,  and  the 
interior  is  broken  up  carefully  with  a  delicate  forceps.  The  animal  generally  recovers 
from  the  operation,  blinded  in  the  eye  upon  the  opposite  side.  In  removing  the  portion 
of  the  skull,  it  is  well  not  to  go  too  far  back,  as  there  is  then  danger  of  wounding  the 
great  venous  sinus  and  complicating  the  operation  by  haemorrhage. 

In  treating  of  the  special  sense  of  sight,  we  shall  see  that  the  decussation  of  the 
optic  nerves  is  more  complex  in  man  than  in  birds,  in  which  the  nerve  from  one  optic 
lobe  passes  totally  and  exclusively  to  the  eye  upon  the  opposite  side.  In  man,  most  of 
the  fibres  of  the  optic  nerve  from  one  side  pass  to  the  eye  upon  the  opposite  side ;  but  a 
few  fibres  pass  to  the  eye  upon  the  same  side,  a  few  connect  the  tubercles  upon  the  two 
sides,  and  a  few  connect  the  two.  eyes.  It  is  not  known  whether  or  not,  in  man,  the 
action  of  the  tubercles  in  vision  is  exclusively  crossed,  as  it  appears  to  be  in  most  of  the 
inferior  animals. 

The  optic  lobes  undoubtedly  serve  as  the  sole  centres  presiding  over  the  sense  of 
sight,  and  not  merely  as  avenues  of  communication  of  this  sense  to  the  cerebral  hemi- 
spheres. A  positive  proof  of  this  proposition  lies  in  the  fact  that  the  sense  of  sight  is 
preserved  after  complete  removal  of  the  cerebrum,  provided  that  injury  of  the  tuber- 
cles have  been  carefully  avoided. 

We  shall  say  nothing,  in  this  connection,  with  regard  to  t>he  movements  of  the  iris, 
except  that  the  reflex  action  by  which  the  size  of  the  pupil  is  modified  is  effected  through 
the  optic  lobes  as  nerve-centres.  The  mechanism  of  the  movements  of  the  iris  and  their 
regulation  through  nervous  action  are  questions  of  great  interest  and  are  somewhat  com- 
plex. We  have  already  treated  of  them  to  some  extent,  in  connection  with  the  physi- 
ology of  the  third  pair  of  nerves,  and  they  will  be  considered  still  more  fully  in  the  sec- 
tion upon  the  special  sense  of  sight. 

Ganglion  of  the  Tuber  Annulare. 

The  tuber  annulare,  called  the  pons  Varolii  or  the  mesocephalon,  is  situated  at  the 
base  of  the  brain,  just  above  the  medulla  oblongata.  It  is  white  externally  and  contains 


GANGLION   OF  THE   TUBER   ANNULARE.  733 

in  its  interior  a  large  admixture  of  gray  matter.  It  presents  both  transverse  and  longi- 
tudinal white  fibres.  Its  transverse  fibres  connect  the  two  halves  of  the  cerebellum.  Its 
longitudinal  fibres  are  connected  below,  with  the  anterior  pyramidal  bodies  and  the  oli- 
vary bodies  of  the  medulla  oblongata,  the  lateral  columns  of  the  cord,  and  a  certain  por- 
tion of  the  posterior  columns.  Above,  the  fibres  are  connected  with  the  crura  cerebri 
and  pass  to  the  brain.  The  superficial  transverse  fibres  are  wanting  in  animals  in  which 
the  cerebellum  has  no  lateral  lobes. 

The  general  properties  of  the  tuber  annulare  have  been  demonstrated  in  the  most  sat- 
isfactory manner  by  Longet.  In  his  experiments,  direct  excitation  of  the  superficial 
transverse  fibres  did  not  produce  well-marked  convulsive  movements,  and  there  were  no 
convulsions  when  the  posterior  fibres  were  stimulated.  When  galvanization  was  applied 
to  the  deeper  anterior  fibres,  convulsive  movements  were  distinct  at  each  excitation. 
Stimulation  of  the  posterior  portion  always  produced  pain.  This  was  not  constantly 
observed  to  follow  irritation  of  the  anterior  portion,  and,  when  pain  occurred,  it  was 
thought  to  be  due  to  irritation  of  the  root  of  the  fifth  nerve. 

The  above  experiments,  it  is  true,  are  not  so  free  from  uncertainty  as  those  made  upon 
the  more  accessible  parts  of  the  encephalon,  but,  as  far  as  they  go,  they  tend  to  show  that 
the  tuber  annulare  is  both  insensible  and  inexcitable  in  its  superficial  anterior  portion, 
which  is  composed  chiefly  of  commissural  fibres  from  the  cerebellum ;  that  it  is  excita- 
ble and  probably  insensible  in  its  deeper  anterior  portion,  which  seems  to  be  composed 
chiefly  of  descending  motor  conductors ;  and,  finally,  that  it  is  sensible  and  probably 
inexcitable  in  its  posterior  portion. 

The  tuber  annulare  undoubtedly  acts  as  a  conductor  of  sensory  impressions  and  motor 
stimulus  to  and  from  the  cerebrum,  as  we  should  naturally  expect  from  the  direction  of 
its  fibres,  and  as  has  been  repeatedly  shown  by  cases  of  disease,  particularly  as  regards 
motion.  In  addition,  however,  judging  from  the  fact  that  it  contains  numerous  nodules 
of  gray  matter  between  fasciculi  of  white  fibres,  and  that  this  gray  matter  contains  cel- 
lular elements  similar  to  those  found  in  other  nerve-centres  and  from  which  nerve- 
fibres  undoubtedly  originate,  it  would  be  inferred  that  these  nodules  have  a  distinct 
function  and  give  to  the  tuber  annulare  the  properties  of  a  nerve-centre.  It  will  be 
interesting,  therefore,  to  follow  out  the  experiments  upon  this  part,  by  which  its  action 
as  a  centre  has  been  illustrated.  These  experiments  are  of  two  kinds :  First,  the  re- 
moval of  other  encephalic  ganglia,  leaving  only  the  tuber  annulare,  the  medulla  oblon- 
gata, and  the  cerebellum,  and  noting  the  properties  or  faculties  retained  by  animals 
under  these  conditions.  Experiments  of  this  kind  are  tolerably  definite,  as  we  already 
know  the  general  functions  of  most  of  the  other  encephalic  ganglia.  Second,  to  note 
the  effects  of  extirpation  of  the  tuber  annulare  alone. 

If  the  cerebral  hemispheres,  the  olfactory  ganglia,  the  optic  lobes,  the  corpora  striata, 
and  the  optic  thalami,  be  removed,  the  animal  loses  the  special  senses  of  smell  and  sight 
and  the  intellectual  faculties,  there  is  a  certain  amount  of  enfeeblement  of  the  muscular 
system,  but  voluntary  motion  and  general  sensibility  are  retained.  There  can  be  no 
doubt  upon  these  points.  As  far  as  voluntary  motion  is  concerned,  an  animal  oper- 
ated upon  in  this  way  is  in  nearly  the  same  condition  as  one  simply  deprived  of  the 
cerebral  hemispheres.  There  are  no  voluntary  movements  which  show  any  degree  of 
intelligence,  but  the  animal  can  stand,  and  various  consecutive  movements  are  executed, 
which  are  entirely  different  from  the  simple  reflex  acts  depending  exclusively  upon  the 
spinal  cord.  The  coordination  of  movements  is  perfect,  unless  the  cerebellum  be  re- 
moved. As  regards  general  sensibility,  an  animal  deprived  of  all  the  encephalic  ganglia 
except  the  tuber  annulare  and  the  medulla  oblongata  undoubtedly  feels  pain.  This  has 
been  demonstrated  in  the  most  conclusive  manner  by  Longet,  and  has  been  shown  even 
more  satisfactorily  by  Vulpian.  In  rabbits,  rats,  etc.,  after  removal  of  the  cerebrum, 
corpora  striata,  and  optic  thalami,  pinching  of  the  ear  or  foot  is  immediately  followed  by 
prolonged  and  plaintive  cries.  Both  of  the  experimenters  referred  to  insist  upon  the 


724  NERVOUS   SYSTEM. 

character  of  these  cries  as  indicating  the  actual  perception  of  painful  impressions,  and  as 
very  different  from  cries  that  are  purely  reflex,  according  to  the  ordinary  acceptation  of 
this  term.  Longet  alludes  to  the  voluntary  movements  and  the  cries  observed  in  persons 
subjected  to  painful  surgical  operations,  when  incompletely  under  the  influence  of  an 
anesthetic,  concerning  the  character  of  which  there  can  be  no  doubt.  He  regards  the 
movements  as  voluntary,  and  the  cries  as  evidence  of  the  acute  perception  of  pain ;  but 
it  is  well  known  that  such  patients  have  no  recollection  of  any  painful  impression, 
although  they  have  apparently  experienced  great  suffering.  As  far  as  we  can  judge 
from  what  we  positively  know  of  the  functions  of  the  encephalic  centres,  the  pain  under 
these  circumstances  is  perceived  by  some  nerve-centre,  probably  the  tuber  annulare,  but 
the  impression  is  not  conveyed  to  the  cerebrum  and  is  not  recorded  by  the  memory. 

Taking  all  the  experimental  facts  into  consideration,  the  following  seems  to  be  the 
most  reasonable  view  with  regard  to  the  function  of  the  tuber  annulare  as  a  nerve-centre  : 

It  is  an  organ  capable  of  originating  a  stimulus  giving  rise  to  voluntary  movements, 
when  the  cerebrum,  corpora  striata,  and  the  optic  thalami,  have  been  removed,  and  it 
probably  regulates  the  automatic  voluntary  movements  of  station  and  progression.  Many 
voluntary  movements,  the  result  of  intellectual  effort,  are  made  in  obedience  to  a  stimu- 
lus transmitted  from  the  cerebrum,  through  conducting  fibres  in  the  tuber  annulare,  to 
the  motor  conductors  of  the  cord  and  the  general  motor  nerves. 

The  tuber  annulare  is  also  capable  of  perceiving  painful  impressions,  which,  when  all 
of  the  encephalic  ganglia  are  preserved,  are  also  conducted  to  and  are  perceived  by  the 
cerebrum,  and  are  remembered ;  but  there  are  distinct  evidences  of  the  perception  of 
pain,  even  when  the  cerebrum  has  been  removed. 

Medulla   Oblongata. 

The  chief  points  of  interest  in  the  physiological  anatomy  of  the  medulla  oblongata 
relate  to  the  direction  of  its  fibres,  their  connection  with  the  gray  matter  embedded  in 
its  substance,  and  the  course  of  the  filaments  of  origin  of  certain  of  the  cranial  nerves. 
Concerning  the  deep  origin  of  the  large  root  of  the  fifth,  the  motor  oculi  externus,  facial, 
pneumogastric,  spinal  accessory,  and  the  sublingual,  we  shall  have  nothing  to  say  in  this 
connection,  as  we  have  already  treated  of  the  physiological  anatomy  of  these  nerves  with 
sufficient  minuteness ;  and  we  have  now  to  study  the  functions  of  the  medulla  oblongata, 
and  particularly  its  action  as  a  nerve-centre. 

Physiological  Anatomy  of  the  Medulla  Oblongata. — The  medulla  oblongata  is  the 
oblong  enlargement  which  connects  the  spinal  cord  with  the  various  encephalic  ganglia. 
It  is  about  an  inch  and  a  quarter  in  length,  and  nearly  an  inch  broad  at  its  widest  por- 
tion. It  rests  in  the  basilar  groove  of  the  occipital  bone,  extending  from  the  atlas  to  the 
lower  border  of  the  tuber  annulare,  with  its  broad  extremity  above.  Like  the  cord,  it 
has  an  anterior  and  a  posterior  median  fissure. 

Apparently  continuous  with  the  anterior  columns  of  the  cord,  are  the  two  anterior 
pyramids,  one  on  either  side.  Viewed  superficially,  the  innermost  fibres  of  these  pyra- 
mids are  seen  to  decussate  in  the  median  line ;  but,  if  these  fibres  be  traced  from  the 
cord,  it  is  found  that  they  come  from  the  white  substance  of  its  lateral  columns,  and  that 
none  of  them  are  derived  from  the  anterior  columns.  The  fibres  of  the  external  portion 
of  the  anterior  pyramids  come  from  the  anterior  columns  of  the  cord.  At  the  site  of  the 
decussation,  the  pyramids  are  composed  entirely  of  white  matter;  but,  as  the  fibres 
spread  out  to  pass  to  the  encephalon  above,  they  present  nodules  of  gray  matter  between 
the  fasciculi. 

External  to  the  anterior  pyramids,  are  the  corpora  olivaria.  These  are  oval  and  are 
surrounded  by  a  distinct  groove.  They  are  white  externally  and  contain  a  gray  nucleus, 
called  the  corpus  dentatum. 


MEDULLA   OBLONGATA. 


725 


External  to  the  corpora  olivaria,  are  the  restiform  bodies,  formed  exclusively  of 
white  matter  and  constituting  the  postero-lateral  portion  of  the  medulla.  They  are 
continuous  with  the  posterior  columns  of  the  cord.  The  restiform  bodies  spread  out 
as  they  ascend,  and  pass  to  the  cerebellum,  forming  a  great  portion  of  the  inferior 
peduncles. 

Beneath  the  olivary  bodies  and  between  the  anterior  pyramids  and  the  restiform 
bodies,  are  the  lateral  tracts  of  the  medulla,  called  by  the  French,  the  intermediary  fas- 
ciculi.    These  are  composed  of  an  intimate  mixture  of  white  and  gray  matter  and  have 
a  yellowish-gray  color.     They  receive  all  that  portion 
of  the  antero-lateral  columns  of  the  cord  which  does 
not  enter  into  the  composition  of  the  anterior  pyra- 
mids.    They  are  frequently  considered  as  parts  of  the 
restiform  bodies,  but  they  are  peculiarly  interesting, 
from  the  fact  that  they  contain  the  gray  centre  pre- 
siding over  respiration ;  and,  for  that  reason,  we  have 
described  them  as  distinct  fasciculi. 

The  posterior  pyramids  (fasciculi  graciles)  are  the 
smallest  of  all.  They  pass  upward  to  the  cerebrum, 
without  decussating,  and  are  composed  exclusively 
of  white  matter.  As  they  pass  upward,  they  diverge, 
leaving  a  space  at  the  fourth  ventricle. 

The  fourth  ventricle  is  in  the  medulla,  and  is 
bounded  above,  by  the  valve  of  Vieussens  and  the 
under  surface  of  the  cerebellum.  In  the  lower  part 
of  the  floor  of  the  fourth  ventricle,  are  several  trans- 
verse fasciculi  of  white  matter ;  but  the  greatest  part 
of  this  portion  is  composed  of  a  layer  of  gray  sub- 
stance. 

The  two  lateral  halves  of  the  posterior  portion  of 
the  medulla  are  connected  together  by  fibres  arising 
from  the  gray  matter  of  the  lateral  tracts,  or  inter- 
mediary fasciculi,  passing  obliquely,  in  a  curved 
direction  from  behind  forward,  to  the  raphe  in  the 
median  line.  There  are  also  fibres  passing  from  be- 
fore backward,  to  form  a  posterior  commissure,  and 
fibres  arising  from  the  cells  of  the  olivary  bodies, 
which  connect  the  gray  substance  of  the  lateral 
halves.  Commissural  fibres  also  connect  the  gray 
matter  of  the  lateral  tracts  with  the  corpora  dentata 
of  the  olivary  bodies,  and  the  olivary  bodies  with  the 
cerebellum,  their  fibres  forming  part  of  the  inferior 
peduncles  of  the  cerebellum.  In  addition,  it  is  prob- 
able that  fibres,  taking  their  origin  from  all  of  the 
gray  nodules  of  the  medulla,  pass  to  the  parts  of  the 
encephalon  situated  above. 

As  far  as  the  fibres  of  origin  of  the  nerves  are 
concerned,  it  may  be  stated  in  general  terms  that  a 
number  of  the  motor  roots  arise  from  the  gray  matter 

of  the  floor  of  the  fourth  ventricle,  the  roots  of  the  sensory  nerves  arising  from  gray 
matter  in  the  posterior  portions. 

Aside  from  purely  anatomical  demonstrations,  the  connection  of  the  anterior  pyra- 
mids of  the  medulla  with  the  corpora  striata  has  been  shown  by  pathological  observa- 
tions. It  is  well  known  that,  when  the  connection  between  the  nerve-centres  and  the 


FIG.  229.— Anterior  mew  of  the  medulla 
oblongata.  (Sappey.) 

1,  infundibulum ;  2,  tuber  cinereum ;  3, 
corpora  albicantia  ;  4,  cerebral  pedun- 
cle ;  5,  tuber  annulare ;  6,  origin  of  the 
middle  peduncle  of  the  cerebellum ;  7, 
anterior  pyramids  of  the  medulla  ob- 
longata ;  8,  decussation  of  the  anterior 
pyramids;  9,  olivary  bodies;  10,  resti- 
form  bodies;  11,  arciform  fibres ;  12, 
upper  extremity  of  the  spinal  cord ;  13, 
ligainentum  denticulatum ;  14, 14,  dura 
mater  of  the  cord ;  15,  optic  tracts ;  16, 
chiasm  of  the  optic  nerves;  17,  motor 
oculi  communis ;  18,  patheticus ;  19, 
fifth  nerve;  20,  motor  oculi  externus; 
21,  facial  nerve;  22,  auditory  nerve;  2=3, 
nerve  of  Wrisberg ;  24,  glosso-pharyn- 
geal  nerve ;  25,  pneumogastric  ;  26,  26, 
spinal  accessory  •  27,  sublingual  nerve ; 
28,  29,  30,  cervical  nerves. 


726  NERVOUS  SYSTEM. 

fibres  is  destroyed,  these  fibres  after  a  time  become  degenerated.  In  old  lesions  of  the 
corpora  striata,  it  has  been  shown  that,  when  the  white  substance  is  injured  upon  one 
side,  there  follow  degeneration  and  atrophy  of  the  fibres  of  the  corresponding  cerebral 
peduncle  and  anterior  pyramid  of  the  medulla,  and  of  the  lateral  portion  of  the  spinal 
cord  upon  the  opposite  side.  This  important  fact  illustrates  the  connection  between  the 
lateral  columns  of  the  cord  and  the  anterior  pyramids  of  the  medulla  oblongata,  the 
decussation  of  the  anterior  pyramids,  and  the  passage  of  fibres  from  the  anterior  pyra- 
mids to  the  corpora  striata,  in  the  substance  of  the  cerebral  peduncles. 

Functions  of  the  Medulla   Oblongata. 

It  is  hardly  necessary  to  discuss  the  functions  of  the  medulla  oblongata  as  a  conductor 
of  sensory  impressions  and  of  motor  stimulus  to  and  from  the  brain.  "We  know  that  there 
is  conduction  of  this  kind  from  the  spinal  cord  to  the  ganglia  of  the  encephalon,  and  this 
must  take  place  through  the  medulla;  a  fact  which  is  inevitable,  from  its  anatomical  rela- 
tions, and  which  is  demonstrated  by  its  section  in  living  animals.  Nor  is  it  necessary  to 
dwell  upon  its  general  properties,  in  which  it  resembles  the  spinal  cord,  at  least  as  far  as 
has  been  demonstrated  by  experiments  upon  living  animals  or  upon  animals  just  killed. 
It  is  difficult  to  expose  this  part  in  the  higher  classes  of  animals,  but  experiments  show 
that  it  is  sensitive  on  its  posterior  surface  and  insensible  in  front.  The  difficulty  of  ob- 
serving the  phenomena  which  follow  its  irritation  in  living  animals  has  rendered  it  im- 
possible to  determine  the  limits  of  its  excitability  and  sensibility  as  exactly  as  has  been 
done  for  the  different  portions  of  the  cord. 

It  is  also  somewhat  difficult  to  determine  whether  the  action  of  the  medulla  itself,  in 
its  relations  to  motion  and  sensation,  be  crossed  or  direct.  As  regards  conduction  from 
the  brain,  the  direction  is  sufficiently  well  shown  by  cases  of  cerebral  disease,  in  which 
the  paralysis,  in  simple  lesions,  is  always  on  the  opposite  side  of  the  body. 

The  action  of  the  medulla  as  a  reflex  nerve-centre  depends  upon  its  gray  matter. 
"When  this  gray  substance  is  destroyed,  certain  of  the  important  reflex  functions  are 
instantly  abolished.  From  its  connections  with  various  of  the  cranial  nerves,  we  should 
expect  it  to  play  an  important  part  in  the  movements  of  the  face,  in  deglutition,  in  the 
action  of  the  heart  and  of  various  glands,  etc.,  important  points  which  will  be  fully  con- 
sidered in  their  appropriate  place.  Its  most  striking  function,  however,  is  in  connection 
with  respiration. 

Connection  of  the  Medulla  Oblongata  with  Respiration. — In  1809,  Legallois  made  a 
number  of  experiments  upon  rabbits,  cats,  etc.,  in  which  he  showed  that  respiration 
depends  exclusively  upon  the  medulla  oblongata  and  not  upon  the  brain,  and  he  farther 
located  the  part  which  presides  over  this  function  at  the  site  of  origin  of  the  pneumogastric 
nerves.  Flourens,  in  his  elaborate  experiments  upon  the  nerve-centres,  extended  the 
observations  of  Legallois,  and  limited  the  respiratory  centre  in  the  rabbit,  between  the 
upper  border  of  the  roots  of  the  pneumogastrics  and  a  plane  situated  about  a  quarter  of 
an  inch  below  the  lowest  point  of  origin  of  these  nerves ;  these  limits,  of  course,  varying 
with  the  size  of  the  animal.  Following  these  experiments,  Longet  has  shown  that  the 
respiratory  nervous  centre  does  not  occupy  the  whole  of  the  medulla  included  between 
the  two  planes  indicated  by  Flourens,  but  that  it  is  confined  to  the  gray  matter  of  the 
lateral  tracts,  or  the  intermediary  fasciculi.  This  was  demonstrated  by  the  fact  that 
respiration  persists  in  animals  after  division  of  the  anterior  pyramids  and  the  restiform 
bodies.  Subsequently,  Flourens  still  farther  restricted  the  limits  of  the  respiratory  centre 
and  fully  confirmed  the  observations  of  Longet, 

The  portion  of  the  medulla  oblongata  above  indicated  presides  over  the  movements 
of  respiration  and  is  the  true  respiratory  nerve-centre.  Nearly  all  who  have  repeated 
the  experiments  of  Flourens  have  found  that  the  spinal  cord  may  be  divided  below  the 
medulla  oblongata,  and  that  all  of  the  encephalic  ganglia  above  may  be  removed,  re- 


FUNCTIONS   OF  THE  MEDULLA   OBLONGATA. 


727 


spiratory  movements  still  persisting.  It  is  a  very  common  thing  in  vivisections  to  kill  an 
animal  by  breaking  up  the  medulla.  In  a  dog,  for  example,  we  grasp  the  head  firmly 
with  the  left  hand,  flex  it  forcibly  upon  the  neck,  and  penetrate  with  a  stylet  a  little  behind 
the  occipital  protuberance,  entering  between  the  atlas  and  the  skull.  By 
a  rapid  lateral  motion  of  the  instrument,  the  medulla  is  broken  up,  and 
the  animal  instantly  ceases  to  breathe.  There  are  no  struggles,  no  mani- 
festations of  the  distress  of  asphyxia;  the  respiratory  muscles  simply 
cease  their  action,  and  the  animal  loses  instantly  the  sense  of  want  of 
air.  A  striking  contrast  to  this  is  presented  when  the  trachea  is  tied  or 
when  all  of  the  respiratory  muscles  are  paralyzed  without  touching  the 
medulla. 

In  another  chapter,  we  have  insisted  upon  the  mechanism  of  the  reflex 
phenomena  of  respiration.  We  have  conclusively  shown  by  experiments, 
that  an  impression  is  received  by  the  sensory  nerves  of  the  general  sys- 
tem, which  is  due  to  want  of  oxygen  and  not  to  the  irritation  produced 
by  carbonic  acid ;  and  that  this  impression  is  conveyed  to  the  medulla 
oblongata  and  gives  rise  to  the  reflex  movements  of  respiration.  If  this 
impression  be  abolished,  there  are  no  respiratory  movements ;  and  if  the 
medulla,  the  sole  centre  capable  of  receiving  this  impression  and  of  gen- 
erating the  stimulus  sent  to  the  respiratory  muscles,  be  destroyed,  respi- 
ration instantly  ceases,  without  any  sensation  of  asphyxia. 


Vital  Point  (so  called). — Since  it  has  been  definitely  ascertained  that 
destruction  of  a  restricted  portion  of  the  gray  substance  of  the  medulla 
produces  instantaneous  and  permanent  arrest  of  the  respiratory  move- 
ments, Flourens  and  others  have  spoken  of  this  centre  as  the  vital  knot, 
destruction  of  which  is  immediately  followed  by  death.  With  our 
present  knowledge  of  the  properties  and  functions  of  the  different  tissues 
and  organs  of  which  the  body  is  composed,  it  is  almost  unnecessary  to 
present  any  arguments  to  show  the  unphilosophical  character  of  such  a 
sweeping  proposition.  We  can  hardly  imagine  such  a  thing  as  instan- 
taneous death  of  the  entire  organism ;  still  less  can  it  be  assumed  that 
any  restricted  portion  of  the  nervous  system  is  the  one  essential,  vital 
point.  Probably,  a  very  powerful  electric  discharge  passed  through  the 
entire  cerebro-spinal  axis  produces  the  nearest  approach  to  instantaneous 
death  of  any  thing  of  which  we  have  any  knowledge ;  but,  even  here,  it  FIG.  230.  —  Stylet 
is  by  no  means  certain  that  some  parts  do  not  for  a  time  retain  their  so- 
called  vital  properties.  In  apparent  death,  the  nerves  and  the  heart  may 
be  shown  to  retain  their  characteristic  properties;  the  muscles  will  con- 
tract under  stimulus,  and  will  appropriate  oxygen  and  give  off  carbonic  acid,  or  respire ; 
the  glands  may  be  made  to  secrete,  etc. ;  and  no  one  can  assume  that,  under  these  con- 
ditions, the  entire  organism  is  dead.  We  really  know  of  no  such  thing  as  death,  except 
as  the  various  tissues  and  organs  which  go  to  make  up  the  entire  body  become  so  altered 
as  to  lose  their  physiological  properties  beyond  the  possibility  of  restoration  ;  and  this 
never  occurs  for  all  parts  of  the  organism  in  an  instant.  A  person  drowned  may  be  to  all 
appearances  dead,  and  would  certainly  die  without  measures  for  restoration ;  yet,  in 
such  instances,  restoration  may  be  accomplished,  the  period  of  apparent  death  being 
simply  a  blank,  as  far  as  the  recollection  of  the  individual  is  concerned.  It  is  as  utterly 
impossible  to  determine  the  exact  instant  when  the  vital  principle,  or  whatever  it  may 
be  called,  leaves  the  body  in  death,  as  to  indicate  the  time  when  the  organism  becomes 
a  living  being.  Death  is  nothing  more  than  a  permanent  destruction  of  so-called  vital 
physiological  properties ;  and  this  occurs  successively,  and  at  different  periods,  for  differ- 
ent tissues  and  organs. 


for  breaking  up 
flte  medulla  ob- 
longata. (Ber- 
nard.) 


728  NERVOUS  SYSTEM. 

When  we  see  that  frogs  will  live  for  weeks,  and  sometimes  for  months,  after  destruc- 
tion of  the  medulla  oblongata,  and  that,  in  mammals,  by  keeping  up  artificial  respiration, 
we  can  prolong  many  of  the  most  important  functions,  as  the  action  of  the  heart,  for 
hours  after  decapitation,  we  can  understand  the  physiological  absurdity  of  the  proposition 
that  there  is  any  such  thing  as  a  vital  point,  in  the  medulla  or  in  any  part  of  the  nervous 
3m. 


Connection  of  the  Medulla  Oblongata  with  Various  Reflex  Acts.— There  are  numerous 
reflex  phenomena  that  are  completely  under  the  control  of  the  medulla  oblongata  as  a 
nerve-centre.  Among  these  are  the  various  acts  connected  with  respiration,  as  yawning, 
coughing,  crying,  sneezing,  etc.  It  also  presides  over  the  coordination  of  the  muscles 
concerned  in  expression,  and  the  act  of  vomiting.  We  have  seen,  in  treating  of  the 
pneumogastric  nerves,  that  their  galvanization  arrests  the  action  of  the  heart  in  diastole. 
The  same  result  follows  galvanization  of  the  medulla  at  the  point  of  origin  of  these  nerves. 
We  have  also  fully  discussed  the  influence  of  the  medulla  upon  sugar-formation  in  the 
liver,  as  illustrated  by  the  striking  experiments  of  Bernard,  in  which  he  produced  diabetes 
in  animals  by  irritating  the  floor  of  the  fourth  ventricle,  and  the  influence  of  this  centre 
upon  the  quantity  and  the  composition  of  the  urine. 

There  is  very  little  to  be  said  concerning  certain  ganglia  and  other  parts  of  the  brain 
that  we  have  not  yet  considered.  The  olfactory  bulbs,  or  ganglia,  preside  over  olfaction 
and  will  be  treated  of  fully  in  connection  with  the  special  senses.  The  pineal  gland  and 
the  pituitary  body,  in  their  structure,  present  a  certain  resemblance  to  the  ductless  glands, 
and  then-  anatomy  has  been  considered  in  another  chapter.  Passing  over  the  purely 
theoretical  views  of  the  older  writers,  who  had  very  indefinite  ideas  of  the  functions  of 
any  of  the  encephalic  ganglia,  we  have  only  to  say  that  the  uses  of  the  pineal  gland  and 
pituitary  body  in  the  economy  are  entirely  unknown.  The  same  remark  applies  to  the 
corpus  callosum,  the  septum  lucidum,  the  ventricles,  hippocampi,  and  various  other  minor 
parts  that  are  necessarily  described  in  anatomical  works.  It  is  useless  to  discuss  the 
early  or  even  the  recent  speculations  with  regard  to  the  functions  of  these  parts,  which 
are  entirely  unsupported  by  experimental  or  pathological  facts  and  which  have  not  ad- 
vanced our  positive  knowledge.  Most  of  the  parts  just  enumerated  have  no  physiological 
history. 

Rolling  and  Turning  Movements  following  Injury  of  Certain  Parts  of  the 

Eneephalon. 

The  remarkable  movements  of  rolling  and  turning,  produced  by  section  or  injury  of 
certain  of  the  commissural  fibres  of  the  encephalon,  are  not  very  important  in  their  bearing 
upon  the  functions  of  the  brain,  and  they  are  rather  to  be  classed  among  the  curiosities  of 
experimental  physiology.  These  movements  follow  unilateral  lesions  and  are  dependent, 
to  a  certain  extent,  upon  a  consequent  inequality  in  the  power  of  the  muscles  on  one  side, 
without  actual  paralysis.  Vulpian  enumerates  the  following  parts,  injury  of  which,  upon 
one  side,  in  living  animals,  may  determine  movements  of  rotation  : 

"  1.  Cerebral  hemispheres ; 

"  2.  Corpora  striata ; 

"  3.  Optic  thalami  (Flourens,  Longet,  Schiff ) ; 

"  4.  Cerebral  peduncles  (Longet)  ; 

"5.  Pons  Varolii; 

"  6.  Tubercula  quadrigemina  or  bigemina  (Flourens)  ; 

"  7.  Peduncles  of  the  cerebellum,  especially  the  middle,  and  the  lateral  portions  of  the 
cerebellum  (Magendie) ; 

"  8.  Olivary  bodies,  restiform  bodies  (Magendie)  ; 

"  9.  External  part  of  the  anterior  pyramids  (Magendie)  ; 


ROLLING  AND   TURNING  MOVEMENTS.  729 

"  10.  Portion  of  the  medulla  from  which  the  facial  nerve  arises  (Brown-Sequard) ; 

"11.  Optic  nerves ; 

"  12.  Semicircular  canals  (Flourens)  ;  auditory  nerve  (Brown-Sequard)." 

To  the  parts  above  enumerated,  Vulpian  adds  the  upper  part  of  the  cervical  portion 
of  the  spinal  cord. 

The  movements  which  follow  unilateral  injury  of  the  parts  mentioned  above  are  of 
two  kinds ;  viz.,  rolling  of  the  entire  body  on  its  longitudinal  axis,  and  turning,  always  in 
one  direction,  in  a  small  circle,  called  by  the  French  the  movement  of  manege.  A  capital 
point  to  determine  in  these  phenomena  is,  whether  these  movements  be  due  to  paralysis 
or  enfeeblement  of  certain  muscles  upon  one  side  of  the  body,  to  a  direct  or  reflex  irrita- 
tion of  the  parts  of  the  nervous  system  involved,  or  to  both  of  these  causes  combined.  The 
experiments  of  Brown-Sequard  and  others  conclusively  show  that  the  movements  may  be 
due  to  irritation  alone,  for  they  occur  when  parts  of  the  encephalon  and  the  upper  por- 
tions of  the  cord  are  simply  pricked,  without  section  of  fibres.  When  there  is  extensive 
division  of  fibres,  it  is  probable  that  the  effects  of  the  enfeeblement  of  certain  muscles  are 
added  to  the  phenomena  produced  by  simple  irritation.  The  most  satisfactory  explana- 
tion of  these  movements  is  the  one  proposed  by  Brown-Sequard,  who  attributes  them  to 
a  more  or  less  convulsive  action  of  muscles  on  one  side  of  the  body,  produced  by  irrita- 
tion of  the  nerve-centres.  He  regards  the  rolling  as  simply  an  exaggeration  of  the  turn- 
ing movements,  and  places  both  in  the  same  category. 

We  do  not  propose  to  enter  into  an  elaborate  discussion  of  the  above  experiments,  for 
the  reason  that  they  do  not  seem  to  have  advanced  our  positive  knowledge  of  the  func- 
tions of  the  nerve-centres.  In  some  of  them,  the  movements  have  been  observed  toward 
the  side  operated  upon,  and  in  others,  toward  the  sound  side.  These  differences  probably 
depend  upon  the  fact  that,  in  certain  experiments,  the  fibres  are  involved  before  their 
decussation,  and  in  others,  after  they  have  crossed  in  the  median  line.  In  some  instances, 
the  movements  may  be  due  to  a  reflex  action,  from  .stimulation  of  afferent  fibres,  and  in 
others,  the  action  of  the  irritation  may  be  direct.  Judging  from  the  fact  that  most  of  the 
encephalic  commissural  fibres  are  apparently  insensible  and  inexcitable  under  direct 
stimulation,  it  is  probable  that  the  action  is  generally  reflex. 

In  concluding  the  physiological  history  of  the  encephalon,  we  have  only  to  refer  to 
the  general  properties  of  certain  of  the  peduncles.  Longet  found  that  direct  irritation  of 
the  superior  and  the  inferior  peduncles  of  the  cerebellum,  in  rabbits,  produced  pain,  but 
the  disturbance  consequent  upon  exposure  of  the  parts  did  not  allow  of  any  accurate 
observations  upon  the  movements.  He  says  nothing  of  the  general  properties  of  the  mid- 
dle peduncles  or  of  the  peduncles  of  the  cerebrum. 


CHAPTER    XXII. 

SYMPATHETIC  NERVOUS  SYSTEM— SLEEP. 

General  arrangement  of  the  sympathetic  system— Peculiarities  in  the  intimate  structure  of  the  sympathetic  ganglia 
and  nerves — General  properties  of  the  sympathetic  ganglia  and  nerves — Functions  of  the  sympathetic  system — 
Vaso-motor  nerves — Keflex  phenomena  operating  through  the  sympathetic  system — Trophic  centres  and  nerves 
(so  called) — Sleep — General  considerations — Condition  of  the  organism  during  sleep — Dreams — Keflex  mental  phe- 
nomena during  sleep— Condition  of  the  brain  and  nervous  system  during  sleep— Theories  of  sleep— Anaesthesia 
and  sleep  produced  by  pressure  upon  the  carotid  arteries— Differences  between  natural  sleep  and  stupor  or 
coma — Regeneration  of  the  brain-substance  during  sleep — Theory  that  sleep  is  due  to  a  want  of  oxygen — Condi- 
tion of  the  various  functions  of  the  organism  during  sleep. 

WHILE  there  are  certain  points  in  the  physiology  of  the  sympathetic  nervous  system 
that  are  perfectly  well  established,  it  must  be  admitted  that  its  functions  are,  in  many 
respects,  obscure,  and  that  our  positive  knowledge  of  its  general  properties  and  its  rela- 


730  NERVOUS   SYSTEM. 

tions  to  the  functions  of  nutrition,  secretion,  movements,  etc.,  amounts  to  comparatively 
little.  The  very  name,  sympathetic,  is  some  indication  of  our  indefinite  ideas  with  regard 
to  its  functions  ;  but  we  have  adopted  this  name,  for  the  reason  that  it  is  the  one  most 
generally  in  use,  although  it  has  no  very  exact  relation  to  the  peculiar  functions  of  the 
system.  It  is  sometimes  called  the  ganglionic  nervous  system ;  but  this  name  is  inappro- 
priate, as  it  implies  that  it  alone  possesses  ganglia.  The  name  of  the  system  of  organic, 
or  vegetative  life  is  more  in  accordance  with  its  general  functions  ;  but  this  is  not  so  com- 
monly used  as  that  of  sympathetic  system.  The  older  anatomists  and  physiologists  called 
the  great  cord  of  this  system  the  nervus  intercostalis. 

As  far  as  we  know,  there  is  no  account  of  the  sympathetic  system,  even  in  the  most 
recent  works  upon  physiology  or  in  special  treatises,  a  careful  study  of  which  does  not  con- 
vey the  idea  that  there  is  little  else  in  the  literature  of  the  subject  than  controversial 
questions  of  priority,  etc.,  in  minor  details,  and  a  few  observations,  some  of  them  quite 
unsatisfactory,  with  regard  to  the  effects  of  the  division  or  galvanization  of  sympathetic 
filaments  upon  the  functions  of  circulation,  secretion,  and  animal  heat.  It  is  unfortunate 
that  well-ascertained  facts,  which  might  be  stated  in  a  very  few  pages,  should  be  so 
largely  overshadowed  by  a  mass  of  purely  historical  details  of  no  great  interest.  Still,  we 
must  take  the  physiological  data  as  we  find  them  and  endeavor  not  to  limit  the  knowledge 
to  be  looked  for  in  the  future,  by  adopting  theories  upon  insufficient  positive  evidence. 

There  are  certain  important  anatomico-physiological  questions,  more  or  less  definitely 
determined,  that  have  a  direct  bearing  upon  the  functions  of  the  sympathetic  system. 
These  are  the  following :  Is  the  sympathetic  anatomically  and  physiologically  dependent 
upon  its  connections  with  the  cerebro-spinal  nerves  ?  What  are  the  general  properties 
of  the  sympathetic  nerves  as  regards  motion  and  sensation?  Do  the  sympathetic  ganglia 
act  as  independent  reflex  nerve-centres?  To  what  extent  and  in  what  way  do  the  sym- 
pathetic ganglia  and  nerves  influence  the  functions  of  the  various  organs  and  tissues  to 
which  their  filaments  are  distributed  ?  A  solution  of  these  questions  involves  a  careful 
and  critical  study  of  the  results  of  experiments  upon  living  animals  and  of  pathological 
facts;  and  it  is  evident  that  very  little  information  is  to  be  derived  from  observations 
made  anterior  to  the  discovery  of  the  properties  and  functions  of  the  most  important 
parts  of  the  cerebro-spinal  system.  We  shall  begin  the  study  of  these  points  with  an 
account  of  the  general  arrangement  and  the  peculiarities  of  structure  of  the  sympathetic 
ganglia  and  nerves. 

General  Arrangement  of  the  Sympathetic  System. 

Like  the  cerebro-spinal  system,  the  sympathetic  is  composed  of  centres  and  nerves, 
at  least  as  far  as  we  can  judge  from  its  anatomy.  The  centres  contain  nerve-cells,  most 
of  which  differ  but  little  from  the  cells  of  the  encephalon  and  spinal  cord.  The  nerves 
are  composed  of  fibres,  the  greater  part  of  which  are  nearly  identical  in  structure  with  the 
ordinary  motor  and  sensory  fibres.  The  fibres  are  connected  with  the  nerve-cells  in  the 
ganglia,  and  the  ganglia  are  connected  with  each  other  by  commissural  fibres.  These 
ganglia  constitute  a  continuous  double  chain,  on  either  side  of  the  body,  beginning  above, 
by  the  ophthalmic  ganglia,  and  terminating  below,  in  the  ganglion  impar.  It  is  important 
to  note,  however,  that  the  chain  of  sympathetic  ganglia  is  not  independent,  but  that  each 
ganglion  receives  motor  and  sensory  filaments  from  the  cerebro-spinal  nerves,  and  that 
some  filaments  pass  from  the  sympathetic  to  the  cerebro-spinal  system.  The  general  dis- 
tribution of  the  sympathetic  filaments  is  to  mucous  membranes— and  possibly  to  integu- 
ment—to non-striated  muscular  fibres,  and  particularly  to  the  muscular  coat  of  the 
arteries.  As  far  as  we  have  been  able  to  learn  from  anatomical  investigations,  there  are 
no  fibres  derived  exclusively  from  the  sympathetic  which  are  distributed  to  striated 
muscles,  except  those  which  pass  to  the  muscular  tissue  of  the  heart.  Near  the  terminal 
filaments  of  the  sympathetic,  in  most  of  the  parts  to  which  these  fibres  are  distributed, 
there  exist  numerous  ganglionic  cells. 


GENERAL  ARRANGEMENT  OF  THE  SYMPATHETIC   SYSTEM.       731 

The  general  arrangement  of  the  sympathetic  ganglia  and  the  distribution  of  the  nerves 
may  be  stated,  sufficiently  for  our  purposes,  very  briefly ;  still,  a  knowledge  of  certain 
anatomical  points  is  indispensable  as  an  introduction  to  an  intelligent  study  of  the  physi- 
ology of  this  system. 

In  the  cranium,  are  four  ganglia ;  the  ophthalmic,  the  spheno-palatine,  the  otic,  and 
the  submaxillary.  In  the  neck,  are  the  three  cervical  ganglia;  the  superior,  middle,  and 
inferior.  In  the  chest,  are  the  twelve  thoracic  ganglia,  corresponding  to  the  twelve  ribs. 
The  great  semilunar  ganglia,  the  largest  of  all,  sometimes  called  the  abdominal  brain,  are 
in  the  abdomen,  by  the  side  of  the  cceliac  axis.  In  the  lumbar  region,  in  front  of  the 
spinal  column,  are  the  four,  and  sometimes  five,  lumbar  ganglia.  In  front  of  the  sacrum, 
are  the  four  or  five  sacral,  or  pelvic  ganglia  ;  and  in  front  of  the  coccyx,  is  a  small,  single 
ganglion,  the  last  of  the  chain,  called  the  ganglion  impar.  Thus,  the  sympathetic  cord, 
as  it  is  sometimes  called,  consists  of  from  twenty-eight  to  thirty  ganglia  on  either  side, 
terminating  below  in  a  single  ganglion. 

Cranial  Ganglia. — The  ophthalmic,  lenticular,  or  ciliary  ganglion  is  situated  deeply 
in  the  orbit,  is  of  a  reddish  color,  and  about  the  size  of  a  pin's-head.  It  receives  a  motor 
branch  from  the  third  pair,  and  sensory  filaments  from  the  nasal  branch  of  the  ophthal- 
mic division  of  the  fifth.  It  is  also  connected  with  the  cavernous  plexus  and  with 
Meckel's  ganglion.  Its  so-called  motor  and  sensory  roots  from  the  third  and  the  fifth 
pair  have  already  been  described  in  connection  with  these  nerves.  Its  filaments  of  dis- 
tribution are  the  ten  or  twelve  short  ciliary  nerves,  which  pass  to  the  ciliary  muscle  and 
the  iris.  A  very  delicate  filament  from  this  ganglion  passes  to  the  eye  with  the  central 
artery  of  the  retina,  in  the  canal  in  the  centre  of  the  optic  nerve. 

The  functions  of  the  ophthalmic  ganglion  are  connected  exclusively  with  the  action 
of  the  ciliary  muscle  and  iris;  and  we  shall  here  merely  indicate  its  anatomical  relations, 
leaving  its  physiology  to  be  taken  up  under  the  head  of  vision. 

The  spheno-palatine  ganglion  was  first  described  by  Meckel  and  is  known  as  Meckel's 
ganglion.  This  is  the  largest  of  the  cranial  ganglia.  It  is  of  a  triangular  shape,  reddish 
in  color,  and  is  situated  in  the  spheno-maxillary  fossa,  near  the  spheno-palatine  foramen. 
It  receives  a  motor  root  from  the  facial,  by  the  Vidian  nerve.  Its  sensory  roots  are  the 
two  spheno-palatine  branches  from  the  superior  maxillary  division  of  the  fifth.  Its 
branches  of  distribution  are  quite  numerous.  Two  or  three  delicate  filaments  enter  the 
orbit  and  go  to  its  periosteum.  Its  other  branches,  which  it  is  unnecessary  to  describe 
fully  in  detail,  are  distributed  to  the  gums,  the  membrane  covering  the  hard  palate,  the 
soft  palate,  the  uvula,  the  roof  of  the  mouth,  the  tonsils,  the  mucous  membrane  of  the 
nose,  the  middle  auditory  meatus,  a  portion  of  the  pharyngeal  mucous  membrane,  and 
the  levator  palati  and  azygos  uvulae  muscles.  It  is  probable  that  the  filaments  sent  to 
these  two  striated  muscles  are  derived  from  the  facial  nerve  and  do  not  properly  belong 
to  the  sympathetic  system.  The  ganglion  also  sends  a  short  branch,  of  a  reddish-gray 
color,  to  the  carotid  plexus. 

The  otic  ganglion,  sometimes  called  Arnold's  ganglion,  is  a  small,  oval,  reddish-gray 
mass,  situated  just  below  the  foramen  ovale.  It  receives  a  motor  filament  from  the 
facial,  and  sensory  filaments  from  branches  of  the  fifth  and  the  glosso-pharyngeal.  Its 
filaments  of  distribution  go  to  the  mucous  membrane  of  the  tympanic  cavity  and  Eusta- 
chian  tube  and  to  the  tensor  tympani  and  tensor  palati  muscles.  Reasoning  from  the 
general  mode  of  distribution  of  the  sympathetic  filaments,  those  going  to  the  striated 
muscles  are  derived  from  the  facial.  It  also  sends  branches  to  the  carotid  plexus. 

The  submaxillary  ganglion,  situated  on  the  submaxillary  gland,  is  small,  rounded, 
and  of  a  reddish-gray  color.  It  receives  motor  filaments  from  the  chorda  tympani  and 
sensory  filaments  from  the  lingual  branch  of  the  fifth.  Its  filaments  of  distribution  go  to 
Wharton's  duct,  to  the  mucous  membrane  of  the  mouth,  and  to  the  submaxillary  gland. 

Cervical  Ganglia. — The  three  cervical  ganglia  are  situated  opposite  the  third,  fifth, 


732 


NERVOUS   SYSTEM. 


FIG.  231  (A).—  Cervical  and  thoracic  portion  of  the  sympathetic.    (Sappey.) 

1, 1, 1,  right  pneumogastric ;  2,  glosso-pharyngeal  ;  3,  spinal  accessory  ;  4,  divided  trunk  of  the  sublingual ; 
5,  5,  5,  chain  of  ganglia  of  the  sympathetic  ;  6,  superior  cervical  ganglion  ;  7,  branches  from  this  ganglion  to 
the  carotid  ;  «,  nerve  of  Jacobson  ;  9,  two  filaments  from  the  facial,  one  to  the,  spheno-palatine  and  the  other 
to  the  otic  ganglion  ;  10,  motor  oculi  externus  :  11,  ophthalmic  ganglion,  receiving  a  motor  filament  from 
the  motor  oculi  communis  and  a  sensory  filament  from  the  nasal  branch  of  the  fifth  ;  12,  spheno-palahne 
ganglion;  13,  otic  ganglion;  14,  lingual  branch  of  the  fifth  nerve;  15,  submaxillary  ganglion .;  16,  17. 
superior  laryngeal  nerve ;  18,  external  laryngeal  nerve ;  19,  20,  recurrent  laryngeal  nerve ;  21,  22,  23, 
anterior  branches  of  the  upper  four  cervical  nerves,  sending  filaments  to  the  superior  cervical  sympathetic 
ganglion  ;  24,  anterior  branches  of  the,  fifth  and  sixth  cervical  nerve,  sending  filaments  to  the  middle,  cervical 
ganglion  ;  25,  26,  anterior  branches  of  'the  seventh  and  eighth  cervical  and  the  first  dorsal  nerves,  sending  fila- 
ments to  the  inferior  cervical  ganglion  ;  27,  middle  cervical  ganglion  ;  28,  cord  connecting  the  two  ganglia  ; 
29,  inferior  cervical  ganglion  ;  30,  31,  filaments  connecting  this  with  the  middle  ganglion  ;  32,  superior  car- 
diac nerve  ;  33,  middle  cardiac  nerve ;  34,  inferior  cardiac  nerve  ;  35,  35,  cardiac  plexus  ;  3G,  ganglion  of 
the  cardiac  plexus  ;  37,  nerve  following  the  right  coronary  artery;  38,  38,  intercostal  nerves,  ivith  their  two 
filaments  of  communication  with  the  thoracic  ganglia  ;  39,  40, 41,  great  splanchnic  nerve  ;  42,  lesser  splanchnic 
nerve  ;  43,  43,  solar  plexus  ;  44,  left  pneumogastfic ;  45.  right  pneumo<raf?tric  ;  46,  lower  end  of  the  phrenic 
nerve  ;  47,  section  of  the  right  bronchus  ;  48,  arch  of  the  aorta  ;  49,  right  auricle  ;  50,  right  ventricle  ;  51, 
52,  pulmonary  artery ;  53.  right  half  of  the  stomach ;  54,  section  of  the  diaphragm. 


GENERAL  ARRANGEMENT  OF  THE   SYMPATHETIC   SYSTEM.       733 

and  the  seventh  cervical  vertebrae  respectively.  The  middle  ganglion  is  sometimes  want- 
ing, and  the  inferior  is  occasionally  fused  with  the  first  thoracic  ganglion.  These  ganglia 
are  connected  together  by  the  so-called  sympathetic  cord.  They  have  numerous  fila- 
ments of  communication  above,  with  the  cranial  and  the  cervical  nerves  of  the  cerebro- 
spinal  system.  Branches  from  the  superior  ganglion  go  to  the  internal  carotid,  to  form 
the  carotid  and  the  cavernous  plexus,  following  the  vessels  as  they  branch  to  their  dis- 
tribution. Branches  from  this  ganglion  pass  to  the  cranial  ganglia.  There  are  also 
branches  which  unite  with  filaments  from  the  pneumogastric  and  the  glosso-pharyngeal 
to  form  the  pharyngeal  plexus,  and  branches  which  form  a  plexus  on  the  external  carotid, 
the  vertebral,  and  the  thyroid  artery,  following  the  ramifications  of  these  vessels. 

From  the  cervical  portion  of  the  sympathetic,  the  three  cardiac  nerves  arise  and  pass 
to  the  heart,  entering  into  the  formation  of  the  cardiac  plexus.  The  superior  cardiac 
nerve  arises  from  the  superior  ganglion ;  the  middle  nerve,  the  largest  of  the  three, 
arises  from  the  middle  ganglion,  or  from  the  sympathetic  cord,  when  this  ganglion  is  want- 
ing; and  the  inferior  nerve  arises  from  the  inferior  cervical  ganglion  or  the  first  thoracic. 
These  nerves  present  numerous  communications  with  various  of  the  adjacent  cerebro- 
spinal  nerves,  penetrate  the  thorax,  and  form  the  deep  and  the  superficial  cardiac  plexus 
and  the  posterior  and  the  anterior  coronary  plexus.  In  these  various  plexuses,  are  found 
numerous  ganglioform  enlargements;  and,  upon  the  surface  and  in  the -substance  of  the 
heart,  are  numerous  collections  of  nerve-cells  connected  with  the  fibres. 

Thoracic  Ganglia. — The  thoracic  ganglia  are  situated  in  the  chest,  beneath  the  pleura, 
and  rest  on  the  heads  of  the  ribs.  They  are  usually  twelve  in  number,  but  occasionally 
two  are  fused  into  one.  They  are  connected  together  by  the  sympathetic  cord.  They 
each  communicate  by  two  filaments  with  the  cerebro-spinal  nerves.  One  of  these  is 
white,  like  the  spinal  nerves,  and  probably  passes  to  the  sympathetic,  and  the  other,  of 
a  grayish  color,  is  thought  to  contain  the  true  sympathetic  filaments.  From  the  upper 
six  ganglia,  filaments  pass  to  the  aorta  and  its  branches.  The  branches  which  form  the 
posterior  pulmonary  plexus  arise  from  the  third  and  fourth  ganglia.  The  great  splanchnic 
nerve  arises  mainly  from  the  seventh,  eighth,  and  ninth  ganglia,  receiving  a  few  filaments 
from  the  upper  six  ganglia.  This  is  a  large,  white,  rounded  cord,  which  penetrates  the 
diaphragm  and  passes  to  the  semilunar  ganglion,  sending  a  few  filaments  to  the  renal 
plexus  and  the  suprarenal  capsules.  The  lesser  splanchnic  nerve  arises  from  the  tenth 
and  eleventh  ganglia,  passes  into  the  abdomen,  and  joins  the  coeliac  plexus.  The  renal 
splanchnic  nerve  arises  from  the  last  thoracic  ganglion  and  passes  to  the  renal  plexus. 
The  three  splanchnic  nerves  present  numerous  anastomoses  with  each  other. 

Ganglia  in  the  Abdominal  and  the  Pelvic  Cavity. — The  semilunar  ganglia  on  the  two 
sides  send  off  radiating  branches  to  form  the  solar  plexus.  They  are  situated  by  the  side 
of  the  coeliac  axis  and  near  the  suprarenal  capsules.  These  are  the  largest  of  the  sym- 
pathetic ganglia.  From  these  arise  numerous  plexuses  distributed  to  various  parts  in 
the  abdomen,  as  follows :  The  phrenic  plexus  follows  the  phrenic  artery  and  its  branches 
to  the  diaphragm.  The  coeliac  plexus  subdivides  into  the  gastric,  hepatic,  and  splenic 
plexuses,  which  are  distributed  to  organs  as  their  names  indicate.  From  the  solar  plexus, 
different  plexuses  are  given  off,  which  pass  to  the  kidneys,  the  suprarenal  capsules,  the 
testes  in  the  male,  and  the  ovaries  in  the  female,  the  intestines  (by  the  superior  and  the 
inferior  mesenteric  plexuses),  the  upper  part  of  the  rectum,  the  abdominal  aorta,  and  the 
vena  cava.  The  filaments  follow  the  distribution  of  the  blood-vessels  in  the  solid  viscera. 

The  lumbar  ganglia,  four  in  number,  are  situated  in  the  lumbar  region,  upon  the 
bodies  of  the  vertebrae.  They  are  connected  with  the  ganglia  above  and1  below  and  with 
each  other  by  the  sympathetic  cord,  receiving,  like  the  other  ganglia,  filaments  from  the 
spinal  nerves.  Their  branches  of  distribution  form  the  aortic  lumbar  plexus  and  the 
hypogastric  plexus  and  follow  the  course  of  the  blood-vessels. 


734: 


NERVOUS  SYSTEM. 


The  four  or  five  sacral  ganglia  and  the  ganglion  impar  are  situated  by  the  inner  side 
of  the  sacral  foramina  and  in  front  of  the  coccyx.  These  are  connected  with  the  ganglia 
above  and  with  each  other,  and  receive  filaments  from  the  sacral  nerves,  there  being 


FIG.  231  (B).—  Lumbar  and  sacral  portions  of  the  sympathetic.    (Sappey.) 

1,  section  of  the  diaphragm ;  2,  lower  end  of  the  oasophagus ;  3,  left  half  of  the  stomach ;  4,  small  intestine ;  5,  sig- 
moid  flexure  of  the  colon  ;  6,  rectum;  7,  bladder;  8.  prostate;  9,  lower  end  of  the  left  pneumogastric ;  10,  lower 
ernl  of  the  right  pneumogastric;  11,  solar  plexus;  12,  lower  end  of  the  great  splanchnic  nerve;  13,  lower  end 
of  me  lesser  splanchnic  nerve;  14,  14,  last  two  thoracic  ganglia  ';  15, 15,  the  four  lumbar  ganglia  ;  16,  16, 17, 
i,V  ".ranches  from  the  lumbar  ganglia  ;  18,  superior  mesenteric  plexus  ;  1!>,  21,  22,  23,  aortic  lumbar  plexus  ; 
M,  inferior  mesenteric  plexus ;  24,  24,  sacral  portion  of  the  syvvpathetic ;  25,  25,  26,  26,  27,  27,  hypogastric 
ius;  28,  29,  30,  tenth,  eleventh,  and  twelfth  dorsal  nerves ;  Si,  32,  33,  34,  35,  36,  37,  38,  39.  lumbar  and  sacral 

generally  two  branches  of  communication  for  each  ganglion.  The  filaments  of  distribu- 
tion go  to  all  of  the  pelvic  viscera  and  the  blood-vessels.  The  inferior  hypogastric,  or 
pel  vie- plexus  is  a  continuation  of  the  hypogastric  plexus  above,  and  receives  a  few  fila- 
ments from  the  sacral  ganglia.  The  most  interesting  branches  from  this  plexus  are  the 


GENERAL  ARRANGEMENT   OF  THE  SYMPATHETIC   SYSTEM.       735 

uterine  nerves,  which  go  to  the  uterus  and  the  Fallopian  tubes.  In  the  substance  of  the 
uterus,  the  nerves  are  connected  with  small  collections  of  ganglionic  cells.  The  sympa- 
thetic filaments  are  undoubtedly  prolonged  into  the  upper  and  lower  extremities,  follow- 
ing the  course  of  the  blood-vessels  and  distributed  to  their  muscular  coat. 

According  to  the  latest  researches,  the  filaments  of  the  sympathetic,  at  or  near  their 
termination,  are  connected  with  ganglionic  cells,  not  only  in  the  heart  and  the  uterus, 
but  in  the  blood-vessels,  lymphatics,  coccygeal  gland,  the  submucous  and  the  muscular 
layer  of  the  entire  alimentary  canal,  the  salivary  glands,  pancreas,  excretory  ducts  of 
the  liver  and  pancreas,  the  larynx,  trachea,  pulmonary  tissue,  bladder,  ureters,  the  entire 
generative  apparatus,  suprarenal  capsules,  thyrnus,  lachrymal  canals,  ciliary  muscle,  and 
the  iris.  In  these  situations,  nerve-cells  have  been  demonstrated  by  various  observers, 
and  it  is  probable  that  they  exist  everywhere  in  connection  with  the  terminal  filaments 
of  this  system  of  nerves. 

Peculiarities  in  the  Intimate  Structure  of  the  Sympathetic  Ganglia  and  Nerves. — The 
peculiarities  in  the  structure  of  the  cells  an<J  fibres  of  the  sympathetic  system  are  not 
numerous,  nor  do  they  possess  very  great  physiological  importance.  The  free  communi- 
cations between  the  sympathetic  ganglia  and  the  cerebro-spinal  nerves,  and  the  differ- 
ences in  the  general  appearance  of  certain  of  these  anastomosing  branches,  lead  to  the 
important  question  of  their  origin.  As  a  rule,  the  sympathetic  nerves  are  softer  and 
more  grayish  in  color  than  the  spinal  nerves.  When  there  are  two  branches  of  commu- 
nication between  a  ganglion  and  a  spinal  nerve,  one  of  them  is  white  and  the  other  is 
grayish,  and  we  might  infer  from  this  that  one,  the  white,  is  derived  from  the  spinal 
system,  and  the  other,  from  the  sympathetic  ;  but  this  is  a  point  not  yet  settled  by  micro- 
scopical investigations.  It  has  been  conclusively  shown,  however,  that  the  communi- 
cating fibres  pass  in  both  directions. 

While  the  branches  of  the  sympathetic  contain  a  large  number  of  the  ordinary  medul- 
lated  fibres,  such  as  are  found  in  the  cerebro-spinal  nerves,  they  also  present  numerous 
fibres  of  Remak,  and  fine  fibres,  from  A0^06  to  ^Vs  of  an  inch  in  diameter,  which  are 
regarded  by  Kolliker  as  true  efferent  fibres  from  the  sympathetic  ganglia.  With  regard 
to  the  fibres  of  Remak,  we  have  nothing  to  add  to  what  we  have  already  stated  under 


FIG.  232.— Sympathetic  ganglion,  with  multipolar  cells  ;  highly  magnified.    (Leydig.) 

the  head  of  the  general  structure  of  the  nervous  system.  These  points,  with  the  fact 
that  most  of  the  terminal  filaments  of  the  sympathetic  are  connected  with  nerve-cells  in 
the  substance  of  the  different  tissues,  constitute  the  most  important  anatomical  pecu- 
liarities of  the  sympathetic  nerve-fibres. 

With  regard  to  the  cells,  which  constitute  the  characteristic  anatomical  element  of 
the  sympathetic  ganglia,  we  shall  have  little  to  say,  as  their  peculiarities  at  present  seem 


736  NERVOUS   SYSTEM. 

to  be  of  purely  anatomical  interest.  They  are  generally  rounded,  ovoid,  or  pear-shaped, 
with  a  nucleus,  generally  clear,  and  a  distinct  nucleolus.  They  present  a  nucleated  cap- 
sule, probably  composed  of  connective  tissue,  which  is  sometimes  lined  on  its  inner  sur- 
face with  a  single  layer  of  flattened,  polygonal  epithelium.  Some  of  the  cells  are  unipolar,' 
some  are  bipolar,  and  some  are  multipolar.  In  frogs,  Beale  and  Arnold  have  described  a 
peculiar  appearance  in  certain  cells,  there  being  a  single,  straight  prolongation,  sur- 
rounded by  a  fine,  spiral  fibre.  These  have  not  been  demonstrated  in  the  human  subject, 
and  it  is  not  necessary  to  enter  into  a  discussion  of  the  probable  origin  and  nature  of  the 
spiral  fibre.  The  connection  between  the  cells  and  fibres  of  the  sympathetic  is  probably 
the  same  as  in  the  cerebro-spinal  centres  and  is  represented  in  the  accompanying  dia- 
gram, taken  from  Leydig.  (See  Fig.  233.) 

General  Properties  of  the  Sympathetic   Ganglia  and  Nerves. 

The  older  writers  had  no  definite  ideas  with  regard  to  the  functions  of  the  sympa- 
thetic system,  and  they  were  divided,  even  6n  the  simple  question  of  its  sensibility,  some 
assuming  that  the  ganglia  were  absolutely  insensible,  while  others  noted  distinct  evi- 
dences of  pain  following  their  irritation  in  living  animals.  The  sensibility  of  the  ganglia, 
though  distinct,  is  dull  as  compared  with  that  of  the  ordinary  sensory  nerves.  We  have 
also  noted  a  dull  but  well-marked  sensibility  of  the  cervical  ganglia  in  rabbits.  In  view 
of  the  decided  and  uniform  results  of  the  most  careful  recent  experiments  upon  this  point, 
there  can  be  no  doubt  of  the  existence  of  a  certain  degree  of  sensibility  in  the  ganglia  of 
the  sympathetic  system. 

As  regards  excitability,  recent  experiments  are  quite  satisfactory.  Mtiller  exposed 
the  intestines  and  the  semilunar  ganglia  in  rabbits ;  and,  having  waited  until  the  intes- 
tines, which  generally  present  movements  upon  first  opening  the  abdomen,  had  ceased  their 
contractions,  the  peristaltic  movements  "  were  immediately  renewed  with  extraordinary 
activity  "  by  touching  the  ganglia  with  caustic  potash.  The  experiments  of  Longet  show 
that  a  feeble  continued  galvanic  current  applied  to  the  great  splanchnic  nerves  produces 
contractions  of  the  muscular  coat  of  the  intestines  when  they  contain  alimentary  mat- 
ters, but  that  no  contractions  occur  when  they  are  empty.  On  the  other  hand,  Pfliiger 
has  observed  that  galvanization  of  the  splanchnic  nerves  produces  a  passive  condition  of 
the  small  intestine ;  that  is,  arrest  of  its  movements  without  persistent  contractions  of 
its  muscular  coat.  More  recently,  in  a  series  of  very  elaborate  experiments,  by  Legros 
and  Onimus,  it  has  been  shown  that  the  induced  galvanic  current  applied  to  the  splanch- 
nic nerves  does  not  produce  peristaltic  movements,  but  that  these  movements  are  excited 
by  the  constant  current. 

Taking  into  consideration  the  most  reliable  direct  observations  upon  the  sympathetic 
ganglia  and  nerves,  the  fact  that  their  stimulation  induces  movements  in  the  non-striated 
muscles  to  which  they  are  distributed  can  hardly  be  doubted.  This  action  is  particularly 
well  marked  in  the  muscular  coat  of  the  blood-vessels;  but  here,  the  function  of  the 
nerves  is  so  important,  that  it  merits  special  consideration  and  will  be  treated  of  fully 
under  the  head  of  the  vaso-motor  nerves.  The  mechanism  of  these  movements,  however,  is 
peculiar.  The  action  does  not  immediately  follow  the  stimulation,  as  it  does  in  the  case 
of  the  cerebro-spinal  nerves  and  the  striated  muscles,  but  it  is  induced  gradually,  begin- 
ning a  few  seconds  after  the  irritation  and  enduring  for  a  time,  and  it  is  more  or  'less 
tetanic.  This  mode  of  action  is  peculiar  to  the  sympathetic  nerves  and  the  non-striated 
muscular  fibres. 

When  we  remember  the  invariable  connection  of  the  sympathetic  ganglia  with  the 
cerebro-spinal  nerves,  we  see  at  once  the  importance  of  the  question  of  the  derivation  of 
the  motor  and  sensory  properties  of  the  ganglionic  system.  Are  the  sympathetic  ganglia 
independent  nerve-centres,  or  do  they  derive  their  properties  from  the  cerebro-spinal 
system  ?  This  question  may  be  satisfactorily  answered  by  two  kinds  of  experimental 


FUNCTIONS   OF  THE   SYMPATHETIC   SYSTEM.  737 

facts :  In  the  first  place,  section  or  irritation  of  the  spinal  cord  and  certain  of  the  en- 
cephalic centres  is  capable  of  influencing  the  vaso-motor  system,  a  fact  which  will  he  dwelt 
upon  more  fully  in  another  connection.  In  the  second  place,  the  experiments  of  Bernard 
upon  the  submaxillary  ganglion  and  its  influence  on  the  secretion  of  the  submaxillary 
gland  have  demonstrated,  in  the  most  conclusive  manner,  that  this  ganglion  is  the  centre 
presiding  immediately  over  the  reflex  phenomena  of  secretion  by  the  gland ;  but  it  has 
also  been  shown  that,  when  all  of  the  connections  of  the  submaxillary  ganglion  with  the 
cerebro-spinal  system  are  divided,  after  a  few  days,  this  ganglion  loses  its  power  as  a 
reflex  nervous  centre.  In  the  chapters  upon  secretion,  we  have  given  numerous  examples 
of  reflex  action  through  the  sympathetic  system.  The  experiments  just  cited  from  Ber- 
nard show  that  individual  ganglia  belonging  to  this  system  may  act  independently  for  a 
time,  but  that  this  action  cannot  continue  indefinitely,  after  the  cerebro-spinal  branches 
have  been  divided.  It  remains,  however,  to  apply  these  experiments  to  other  sympa- 
thetic ganglia ;  but,  in  the  case  of  the  submaxillary,  they  are  very  satisfactory,  from  the 
facility  with  which  the  parts  may  be  operated  upon  and  the  certainty  with  which  the 
ganglion  may  be  separated  from  its  connections  with  the  cerebro-spinal  system.  As 
regards  the  explanation  of  the  final  loss  of  power  over  the  functions  of  the  submaxillary 
gland,  the  experiments  of  Waller  seem  to  have  escaped  the  attention  of  the  eminent 
physiologist  whom  we  have  quoted.  There  is  no  experimental  fact  more  conclusively 
demonstrated  than  that  of  the  anatomical  degeneration  and  consequent  loss  of  physio- 
logical function  of  nerve-fibres  in  a  few  days  after  they  have  been  separated  from  their 
centres  of  origin.  After  division  of  a  cerebro-spinal  nerve-trunk,  the  tubes  soon  lose 
their  anatomical  characters  and  will  no  longer  respond  to  a  galvanic  stimulus.  In  the 
case  of  the  fibres  operating  upon  the  submaxillary  gland,  the  question  of  their  degenera- 
tion after  division  of  the  cerebro-spinal  roots  was  not  submitted  to  microscopical  investi- 
gation. If  these  fibres  had  undergone  the  degeneration  which  has  so  frequently  been 
observed  in  experiments  upon  other  nerves,  their  galvanization  would  not  have  produced 
any  effect ;  which  was  precisely  the  result  obtained  by  Bernard.  In  the  absence  of 
direct  observations  upon  this  point,  it  is  the  most  reasonable  view  to  adopt,  that  the 
fibres  from  the  cerebro-spinal  nerves  had  lost  their  function,  as  a  natural  consequence  of 
separation  from  their  centres,  and  that  this  was  the  cause  of  the  absence  of  effect  upon 
the  gland  following  their  galvanization.  The  observation  of  Bernard  shows,  however, 
that  filaments  may  pass  to  special  organs  from  the  cerebro-spinal  centres  through  the 
sympathetic  ganglia. 

Functions  of  the  Sympathetic  System. 

In  the  early  part  of  the  last  century  (1712  and  1725),  Pourfour  du  Petit  demonstrated 
that  the  influence  of  the  sympathetic  nerve  in  the  neck  (the  great  sympathetic  was  fre- 
quently called  the  nervus  intercostalis)  was  propagated  from  below  upward  toward  the 
head,  and  not  from  the  brain  downward.  This  may  be  taken  as  the  starting-point  of  our 
definite  knowledge  of  the  functions  of  the  sympathetic  system,  though  the  experiments 
of  Petit  showed  only  the  influence  of  the  cervical  portion  upon  the  eye.  In  1816,  Dupuy 
removed  the  superior  cervical  ganglia  in  horses,  with  the  effect  of  producing  injection  of 
the  conjunctiva,  increase  of  temperature  in  the  ear,  and  an  abundant  secretion  of  sweat 
upon  one  side  of  the  head  and  neck.  These  experiments  showed  that  the  sympathetic 
has  an  important  influence  upon  nutrition,  calorification,  and  secretion.  In  1851,  Bernard 
repeated  the  experiments  of  Pourfour  du  Petit,  dividing  the  sympathetic  in  the  neck  on 
one  side  in  rabbits,  and  noted,  on  the  corresponding  side  of  the  head  and  the  ear,  in- 
creased vascularity,  and  an  elevation  in  temperature,  amounting  to  from  7°  to  11°  Fahr. 
This  condition  of  increased  heat  and  vascularity  continues  for  several  months  after  divi- 
sion of  the  nerve.  In  1852,  Brown-SSquard  repeated  these  experiments  and  attributed 
the  elevation  of  temperature  directly  to  an  increase  in  the  supply  of  blood  to  the  parts 
affected.  He  made  a  most  important  advance  in  the  history  of  the  sympathetic,  by 
47 


738  NERVOUS  SYSTEM. 

demonstrating  that  its  section  paralyzed  the  muscular  walls  of  the  arteries,  and,  farther, 
that  galvanization  of  the  nerve  in  the  neck  caused  the  vessels  to  contract.  This  was  the 
discovery  of  the  vaso-motor  nerves,  concerning  which  so  much  has  been  written  within 
the  past  few  years,  and  it  belongs  without  question  to  Brown-Sequard,  who  published 
his  observations  in  August,  1852.  A  few  months  later,  in  the  same  year,  Bernard  made 
analogous  experiments  and  presented  the  same  explanation  of  the  phenomena  observed. 

The  above  embraces  all  that  is  important  with  regard  to  the  history  of  experimental 
observations  upon  the  sympathetic.  It  is  evident  that  we  could  know  nothing  of  the 
functions  of  this  system  before  the  time  of  Pourfour  du  Petit,  when  the  prevailing  opin- 
ion was  that  the  nerve  originated  from  the  encephalon,  and  that  its  influence  was  propa- 
gated downward ;  and  writings  anterior  to  the  experiments  of  Bernard  and  of  Brown- 
Sequard  present  interesting  suggestions  and  theories,  but  they  contain  little  that  bears 
upon  our  positive  knowledge. 

The  important  points  developed  by  the  first  experiments  of  Bernard  and  of  Brown- 
Se*quard  were,  that  the  sympathetic  system  influences  the  general  process  of  nutrition, 
and  that  many  of  its  filaments  are  distributed  to  the  muscular  coat  of  the  blood-vessels. 
Before  these  experiments,  it  had  been  shown  that  filaments  from  this  system  influenced 
the  contractions  of  the  muscular  coats  of  the  alimentary  canal.  Leaving,  for  the  present, 
the  action  of  the  vaso-motor  nerves,  we  shall  briefly  recapitulate  some  of  the  facts  with 
regard  to  the  influence  of  the  sympathetic  upon  animal  heat  and  secretion. 

When  the  sympathetic  is  divided  in  the  neck,  the  local  increase  in  temperature  is 
always  attended  with  a  very  great  increase  in  the  supply  of  blood  to  the  side  of  the  head 
corresponding  to  the  section.  The  increased  temperature  is  due  to  a  local  exaggeration 
of  the  nutritive  processes,  apparently  dependent  directly  upon  the  hypereemia;  and  it  is 
not  probable  that  there  are  any  nerves  to  which  the  name  of  calorific,  as  distinguished 
from  vaso-motor,  can  justly  be  applied.  There  are  numerous  instances  in  pathology  of 
local  increase  in  temperature  attending  increased  supply  of  blood  to  restricted  parts.  In 
a  recent  experiment  by  Bidder,  after  excising  about  half  an  inch  of  the  cervical  sympa- 
thetic in  a  half-grown  rabbit,  the  ear  on  that  side,  in  the  course  of  about  two  weeks, 
became  distinctly  longer  and  broader  than  the  other. 

The  experiment  of  dividing  the  sympathetic  in  the  neck,  especially  in  rabbits,  is  so 
easily  performed,  that  the  phenomena  observed  by  Bernard  and  Brown-S6quard  have 
been  repeatedly  verified.  We  have  often  done  this  in  class-demonstrations.  A  very 
striking  experiment  is  the  following,  suggested  by  Bernard :  After  dividing  the  sympa- 
thetic and  exhibiting  the  increase  in  the  temperature  and  the  vascularity  of  the  ear  on 
one  side  in  the  rabbit,  if  both  ears  be  cut  off  just  above  the  head  with  a  sharp  knife,  the 
artery  on  the  side  on  which  the  sympathetic  has  been  divided  will  frequently  send  up  a 
jet  of  blood  to  the  height  of  several  feet,  while,  on  the  sound  side,  the  jet  is  always 
much  less  forcible,  and  it  may  not  be  observed  at  all.  This  experiment  succeeds  best  in 
large  rabbits. 

It  is  very  easy  to  observe  the  effects  of  dividing  the  sympathetic  in  the  neck,  but 
analogous  phenomena  have  been  noted  in  other  parts.  Among  the  most  striking  of  these 
experiments  are  those  reported  by  Samuel,  who  noted  an  intense  hyperaemia  of  the 
mucous  membrane  of  the  stomach  and  intestines  following  extirpation  of  the  coaliac 
plexus.  ^  By  comparative  experiments,  it  was  shown  that  this  did  not  result  from  the 
peritonitis  produced  by  the  operation. 

As  regards  secretion,  the  influence  of  the  sympathetic  is  very  marked.  When  the 
sympathetic  filaments  distributed  to  a  gland  are  divided,  the  supply  of  blood  is  very  much 

reased,  and  an  abundant  flow  of  the  secretion  follows.     This  point  we  have  already 

discussed  in  another  chapter,  where  we  have  referred  particularly  to  the  experiments  of 

Bernard  upon  the  salivary  glands.     In  some  recent  experiments  by  Peyrani,  it  has  been 

shown  that  the  sympathetic  has  a  remarkable  influence  upon  the  secretion  of  urine. 

When  the  nerves  are  galvanized  in  the  neck,  the  amount  of  urine  and  urea  is  increased, 


VASO-MOTOR  NERVES.  739 

and  this  increase  is  greater  with  the  induced  than  with  the  constant  current.     When  the 
sympathetic  is  divided,  the  quantity  of  urine  and  urea  sinks  to  the  minimum. 

Dr.  Moreau  has  recently  published  a  series  of  observations  on  the  influence  of  the 
sympathetic  nerves  upon  the  secretion  of  liquid  by  the  intestinal  canal,  which  are  pecul- 
iarly interesting  in  their  bearing  upon  the  sudden  occurrence  of  watery  diarrhoea.  In 
these  experiments,  the  abdomen  was  opened  in  a  fasting  animal,  and  three  loops  of  intes- 
tine, each  from  four  to  eight  inches  long,  were  isolated  by  two  ligatures.  All  of  the 
nerves  passing  to  the  middle  loop  were  divided,  taking  care  to  avoid  the  blood-vessels. 
The  intestine  was  then  replaced,  and  the  wound  in  the  abdomen  was  closed  with  sutures. 
The  next  day  the  animal  was  killed.  The  two  loops  with  the  nerves  intact  were  found 
empty,  as  is  normal  in  fasting  animals,  and  the  mucous  membrane  was  dry;  but  the  loop 
with  the  nerves  divided  was  found  filled  with  a  clear,  alkaline  liquid,  colorless  or  slightly 
opaline,  which  precipitated  a  few  flocculi  of  organic  matter  on  boiling. 

Vaso-Motor  Nerves.     * 

The  experiments  which  we  have  already  cited  demonstrate  beyond  a  doubt  the  exist- 
ence of  nerves  distributed  to  the  muscular  coats  of  the  blood-vessels  and  capable  of. 
regulating  their  caliber  and  the  quantity  of  blood  sent  to  different  parts.  These  are  the 
vaso-motor  nerves,  discovered  by  Brown-Sequard,  in  1852.  The  importance  of  nerves 
apable  of  regulating  what  we  may  call  the  local  circulations  is  sufficiently  apparent. 
The  glands,  for  example,  require  at  certain  times  an  immense  increase  in  their  supply  of 
blood,  and  the  same  is  probably  true  of  the  muscles,  brain,  and  other  parts.  It  has  been 
shown,  by  direct  experiments  upon  living  animals,  that  local  variations  in  the  circulation, 
independent  of  the  action  of  the  heart,  actually  take  place,  and  that  they  are  of  great 
importance  in  special  functions ;  and  there  are  numerous  instances  of  such  action,  which 
can  only  take  place  through  the  nervous  system.  The  phenomena  of  blushing  and  pallor, 
from  mental  emotions,  are  familiar  examples. 

There  can  be  no  doubt  of  the  fact  that  the  sympathetic  branches  contain  filaments 
capable  of  modifying  the  caliber  of  the  blood-vessels,  and  that  the  cerebro-spinal  nerves 
also  contain  elements  possessing  analogous  properties  ;  but  when  we  reflect  upon  the 
extensive  anastomoses,  in  both  directions,  between  the  sympathetic  and  the  ordinary 
motor  and  sensory  nerves,  we  can  appreciate  the  importance  of  determining  the  exact 
origin  and  course  of  these  vaso-motor  fibres.  The  first  important  question  is,  whether  the 
vaso-motor  filaments  be  derived  from  the  sympathetic  ganglia  or  from  the  cerebro-spinal 
centres. 

All  experiments  upon  the  question  just  proposed  tend  to  show  that  the  vaso-motor 
nerves  are ,  derived  exclusively  from  the  cerebro-spinal  system  and  do  not  originate  in 
the  sympathetic  ganglia.  Without  citing  the  numerous  confirmatory  observations  of  dif- 
ferent physiologists,  it  is  sufficient  to  state  that  Schiff  has  experimentally  demonstrated, 
in  the  most  conclusive  manner,  that  the  vaso-motor  nerves  are  derived  from  the  cerebro- 
spinal  centres  and  not  from  the  sympathetic  ganglia.  There  is  now  no  difference  of 
opinion  among  physiologists  upon  this  point,  the  only  question  being  the  exact  location 
of  the  vaso-motor  centres. 

As  a  summary  of  our  present  knowledge  of  the  origin  of  the  vaso-motor  nerves  in  the 
cerebro-spinal  axis,  we  may  cite  the  following  remarks,  from  a  review  of  the  experiments 
of  Schiff,  by  Brown-Sequard  :  "1.  That  if  there  are  vaso-motor  elements  which  decus- 
sate in  the  spinal  cord,  their  number  is  excessively  small.  2.  That  the  facts  observed  by 
M.  Schiff,  on  this  subject,  admit  of  a  more  simple  explanation.  3.  That  a  number  of  the 
vaso-motor  elements  stop  in  the  spinal  cord.  4.  That  a  tolerably  large  number  of  vaso- 
motor  elements,  coming  from  different  points  in  the  body,  ascend  as  far  as  the  tuber 
annulare,  and  some  as  far  as  the  cerebellum  and  to  other  parts  of  the  encephalon.  5. 
That,  consequently,  the  medulla  oblongata  is  not  the  sole  source  of  the  vaso-motor  ele- 


740  NERVOUS  SYSTEM. 

ments."  These  statements  express  pretty  much  all  that  we  know  of  the  origin  of  the 
vaso-motor  elements  and  their  decussation,  as  far  as  their  direct  action  is  concerned ;  but 
some  important  points  have  been  developed  by  observations  upon  reflex  vaso-motor  phe- 
nomena, involving  a  transmission  of  impressions  to  the  centres  through  the  nerves  of 
general  sensibility. 

Reflex  Phenomena  operating  through  the  Sympathetic  System.— We  shall  not  discuss, 
in  this  connection,  the  reflex  phenomena  of  secretion,  as  these  have  already  been  consid- 
ered with  sufficient  minuteness,  nor  again  treat  of  reflex  action,  through  the  sympathetic, 
upon  the  general  circulatory,  system,  which  has  been  taken  up  fully  under  the  head  of  the 
depressor-nerve  of  the  circulation,  but  we  shall  here  describe  certain  reflex  acts,  involv- 
ing vaso-motor  phenomena,  which  we  thus  far  have  touched  upon  very  briefly. 

As  regards  animal  heat,  the  phenomena  of  which  are  intimately  connected  with  the 
supply  of  blood  to  the  parts,  we  may  mention  the  observations  of  Brown-Sequard  and 
Lombard,  who  found  that  pinching  of  the  skin  on  one  side  was  attended  with  a  diminu- 
tion in  the  temperature  in  the  corresponding  member  of  the  opposite  side,  and  that  some- 
times, when  the  irritation  was  applied  to  the  upper  extremities,  changes  were  produced 
in  the  temperature  of  the  lower  limbs.  Tholozan  and  Brown-SSquard  found,  also,  that 
lowering  the  temperature  of  one  hand  produced  a  considerable  depression  in  the  heat  of 
the  other  hand,  without  any  notable  diminution  in  the  general  heat  of  the  body.  Brown- 
Sequard  showed  that,  by  immersing  one  foot  in  water  at  41°  Fahr.,  the  temperature  of  the 
other  foot  was  diminished  about  7°  Fahr.  in  the  course  of  eight  minutes.  These  facts 
show  that  certain  impressions  made  upon  the  sensory  nerves  affect  the  animal  heat  by 
reflex  action.  As  section  of  the  sympathetic  filaments  increases  the  heat  in  particular 
parts,  with  an  increase  in  the  supply  of  blood,  and  their  galvanization  reduces  the  quan- 
tity of  blood  and  diminishes  the  temperature,  it  is  reasonable  to  infer  that  the  reflex  action 
takes  place  through  the  vaso-motor  nerves.  If  we  assume  that  the  impression  is  conveyed 
to  the  centres  by  the  nerves  of  general  sensibility,  and  that  the  vessels  are  modified  in 
their  caliber  and  the  heat  is  affected  through  the  sympathetic  fibres,  we  have  only  to 
determine  the  situation  of  the  centres  which  receive  the  impression  and  generate  the 
stimulus.  These  centres,  as  we  have  already  seen,  are  not  situated  in  the  sympathetic 
ganglia,  but  in  the  cerebro-spinal  axis. 

The  existence  of  vaso-motor  nerves  and  their  connection  with  centres  in  the  cerebro- 
spinal  axis  are  now  sufficiently  well  established.  It  is  certain,  also,  that  centres  presiding 
over  particular  functions  may  be  distinctly  located,  as  the  genito-spinal  centre,  in  the  spinal 
cord  opposite  the  fourth  lumbar  vertebra,  and  the  cilio-spinal  centre,  in  the  cervical  region 
of  the  cord.  A  stimulus  generated  in  these  centres,  sometimes  as  the  result  of  impressions 
received  through  the  nerves  of  general  sensibility,  produces  contraction  of  the  non-striated 
muscular  fibres  of  the  iris,  vasa  deferentia,  etc.,  including  the  muscular  walls  of  the  blood- 
vessels. The  contraction  of  the  muscular  walls  of  the  vessels  is  tonic ;  and,  when  their 
nerves  are  divided,  relaxation  takes  place,  and  the  vessels  are  dilated  by  the  pressure  of 
blood.  By  this  action,  the  local  circulations  are  regulated  in  accordance  with  impressions 
made  upon  sensory  nerves,  the  physiological  requirements  of  certain  parts,  mental  emotions, 
etc.  Secretion,  the  peristaltic  movements  of  the  alimentary  canal,  the  movements  of  the 
iris,  etc.,  are  influenced  in  this  way.  This  action  is  also  illustrated  in  cases  of  reflex  pa- 
ralysis, in  inflammations  as  the  result  of  "taking  cold,1'  and  in  many  pathological  condi- 
tions, of  which  it  is  not  our  province  to  treat.  The  facts  already  noted  with  regard  to 
the  excito-motor  action  of  the  spinal  cord  in  the  functions  of  animal  life  have  their  anal- 
ogy m  the  vaso-motor  reflex  system.  When  the  centres  are  destroyed,  when  the  sensory 
nerves  are  paralyzed  by  anaesthetics,  or  when  the  true  vaso-motor  nerves  are  divided, 
reflex  vaso-motor  action  is  abolished. 

The  vaso-motor  filaments  are  not  confined  to  the  branches  of  the  sympathetic,  but 
they  exist  as  well  in  the  ordinary  cerebro-spinal  nerves.  Bernard  has  demonstrated  this 


TKOPHIO  CENTRES  AND  NERVES.  741 

fact  in  the  most  conclusive  manner.  He  divided  the  fourth,  fifth,  sixth,  seventh,  and 
eighth  pairs  of  lumbar  nerves  on  one  side  in  a  dog,  at  the  spinal  column,  and  paralyzed 
motion  and  sensation  in  the  leg  of  that  side,  hut  the  temperature  of  the  two  sides  remained 
the  same.  He  afterward  exposed  and  divided  the  sciatic  nerve  on  that  side,  and  then 
noted  a  decided  increase  of  temperature.  This  experiment,  which  is  only  one  of  a  large 
number,  shows  conclusively  that  the  ordinary  mixed  nerves  contain  vaso-motor  fibres, 
which  are  entirely  independent  of  the  nerves  of  motion  and  sensation,  a  fact  which  is 
admitted  by  all  physiologists  and  has  frequently  been  illustrated  in  cases  of  disease  in  the 
human  subject. 

It  only  remains  to  show  that  the  phenomena  following  section  of  the  sympathetic  in 
animals  are  illustrated  in  certain  cases  of  disease  or  injury  in  the  human  subject.  It  is 
excessively  rare  to  observe  traumatic  injury  confined  to  the  sympathetic  in  the  neck.  A 
single  case,  however,  apparently  of  this  kind,  has  lately  been  reported  by  Mitchell.  A 
man  received  a  gunshot-wound  in  the  neck.  Among  the  phenomena  observed  a  few 
weeks  after,  were,  contraction  of  the  pupil  on  the  side  of  the  injury,  and,  after  exercise, 
flushing  of  the  face  upon  that  side.  There  was  no  difference  in  the  temperature  upon 
the  two  sides,  during  repose,  but  no  thermometric  observations  were  made  when  half  of 
the  face  was  flushed  by  exercise.  Dr.  Bartholow  has  reported  several  cases  of  unilateral 
sweating  of  the  head  (two  observed  by  himself),  in  several  of  which  there  was  probably 
compression  of  the  sympathetic  from  aneurism.  In  those  cases  in  which  the  condition 
of  the  eye  was  observed,  the  pupil  was  found  contracted  in  some  and  dilated  in  others. 
In  none  of  these  cases  were  there  any  accurate  thermometric  observations.  In  a  series 
of  observations  by  Wagner,  upon  the  head  of  a  woman,  eighteen  minutes  after  decapita- 
tion, powerful  galvanization  of  the  sympathetic  produced  great  enlargement  of  the  pupil. 
In  such  a  case  as  this,  it  would  not  be  possible  to  make  any  observations  on  the  influence 
of  the  sympathetic  upon  the  temperature. 

Trophic   Centres  and  Nerves  (so  called). 

We  have  deferred  the  consideration  of  the  so-called  trophic  nerves  until  we  had 
treated  of  the  functions  of  the  sympathetic  system,  because  the  vaso-motor  nerves,  by 
their  influence  upon  the  circulation,  are  evidently  connected  with  the  phenomena  of 
nutrition.  It  is  not  necessary  to  dwell  very  minutely  upon  this  point;  but  cases  of 
disease,  as  well  as  experiments  upon  the  inferior  animals,  show  that,  when  a  muscle  is 
paralyzed,  as  a  result  of  the  abolition  of  nervous  influence  and  consequent  disease,  it 
becomes  atrophied,  its  fibres  lose  their  characteristic  structure  and  finally  become  inca- 
pable of  contracting  under  a  stimulus.  As  we  have  seen  that  the  cerebro-spinal 
nerves,  in  addition  to  their  motor  and  sensory  fibres,  contain  vaso-motor  elements,  it 
becomes  a  question  whether  the  muscles  be  supplied  with  special  nerves — aside  from  those 
of  motion  and  sensation  and  the  vaso-motor  nerves — which  preside  over  their  nutrition. 
Such  could  properly  be  called  trophic  nerves.  Many  pathologists,  relying  upon  the 
presence  of  certain  lesions  of  cells  in  the  cord,  in  connection  with  cases  of  progressive 
muscular  atrophy,  admit  the  existence  of  trophic  cells  and  nerves.  It  must  be  admitted, 
however,  that  these  views  rest  upon  pathological  facts  alone  and  have  not  been  demon- 
strated by  physiological  experiments  or  observations. 

After  what  we  have  said,  it  is  evident  that  proper  nutrition  of  the  muscular  system 
depends  upon  its  exercise  and  the  integrity  of  its  motor  nerves.  In  the  second  place,  the 
history  of  monsters  shows  that  the  muscular  system  may  be  developed  independently  of 
the  cerebro-spinal  centres.  In  the  admirable  work  of  Brachet,  upon  the  ganglionic  system, 
numerous  cases  of  anencephalic  monsters  are  detailed,  in  which  the  muscular  system  was 
found  more  or  less  perfectly  developed.  In  some  of  these,  the  foetus  was  delivered  at 
term  and  lived  for  several  hours.  "When  we  consider  the  great  number  of  cases  of  this 
kind  on  record,  a  few  of  which  only  are  cited  by  Brachet,  it  is  evident  that  the  cerebro- 


742  NERVOUS  SYSTEM. 

spinal  centres  are  not  absolutely  necessary  to  development  in  utero.  Some  of  the  cases 
reported  presented  spasmodic  movements  of  certain  muscles. 

"While  it  is  certain  that  a  foetus  may  become  developed  in  utero,  when  there  is  reason 
to  suppose  that  the  cerebro-spinal  influence  is  wanting  and  the  chief  nervous  operations 
are  effected  through  the  ganglionic  system,  direct  experiments  upon  the  sympathetic  in 
animals  do  not  positively  show  any  influence  upon  nutrition,  except  as  this  system  of 
nerves  affects  the  supply  of  blood  to  the  parts.  When  we  divide  a  sympathetic  nerve, 
there  is  an  apparent  exaggeration  of  the  nutritive  processes  in  particular  parts,  and  there 
may  be  inflammatory  phenomena,  but  atrophy  of  muscles  is  not  observed.  Indeed,  we 
only  have  atrophy  of  muscles  following  division  of  cerebro-spinal  nerves,  or,  as  recently- 
observed  cases  of  disease  have  shown,  after  disorganization  of  cells  belonging  to  what  we 
recognize  as  motor  centres.  As  regards  the  latter  condition,  there  can  be  no  doubt  of 
the  fact  that  progressive  muscular  atrophy  is  attended  with  disorganization  of  certain  of 
the  motor  cells  of  the  spinal  cord. 

Without  fully  discussing  this  subject,  which  belongs  to  pathology,  the  facts  may  be 
briefly  stated  as  follows :  We  may  have  progressive  atrophy  of  certain  muscles,  which 
may  be  uncomplicated  with  paralysis  except  in  so  far  as  there  is  weakness  of  these  mus- 
cles, due  to  partial  and  progressive  destruction  of  their  contractile  elements.  The  only 
pathological  condition  in  these  cases,  aside  from  the  changes  in  the  muscular  tissue,  is 
destruction  of  certain  cells  in  the  antero-lateral  portions  of  the  cord,  with  more  or  less 
atrophy  of  the  corresponding  anterior  roots  of  the  nerves.  No  one  has  pretended  to 
have  demonstrated  cells  in  the  cord,  presenting  anatomical  peculiarities  by  which  they 
may  be  distinguished  from  the  ordinary  motor  or  sensory  elements,  but  the  fact  of  the 
degeneration  of  certain  cells,  others  remaining  normal,  and  this  fact  alone,  has  led  to  the 
distinction,  by  certain  writers,  of  trophic  cells ;  and,  of  course,  these  must  be  connected 
with  the  muscles  by  trophic  nerves. 

We  shall  now  study  the  phenomena  of  progressive  muscular  atrophy  from  a  physio- 
logical point  of  view,  and  see  if  they  aiford  any  positive  evidence  of  the  existence  of 
special  cells  and  nerves  presiding  over  the  nutrition  of  the  muscular  system,  or  whether 
the  phenomena  observed  cannot  be  explained  by  the  partial  degeneration  of  the  ordinary 
motor  cells  and  nerves. 

There  can  be  no  doubt  of  the  fact  that  the  cells  of  the  antero-lateral  columns  of  the 
spinal  cord  preside  over  motion,  and  that  the  stimulus  generated  in  these  cells  is  con- 
veyed to  the  muscles  by  the  anterior  roots  of  the  spinal  nerves.  It  is  a  fact,  no  less 
definite,  that,  when  a  muscle  or  a  part  of  a  muscle  is  deprived  of  the  motor  stimulus  by 
which  it  is  brought  into  action,  its  fibres  atrophy,  become  altered  in  structure,  and  lose 
their  contractility.  Starting  with  these  two  well-defined  physiological  propositions,  and 
assuming  that  a  few  of  the  ordinary  motor  cells  of  the  cord  are  destroyed — we  will  not 
call  them  trophic  cells — what  are  the  phenomena  to  be  expected  as  a  consequence  of 
such  a  lesion  ?  Reasoning  from  what  we  know  of  the  physiology  of  the  nervous  system, 
we  should  expect  to  find  the  following  conditions : 

The  destruction  of  certain  motor  nerve-cells  would  certainly  produce  degeneration  of 
the  fibres  to  which  they  give  origin.  This  has  been  observed;  for,  in  this  condition,  the 
anterior  roots  arising  from  the  diseased  portions  of  the  cord  are  atrophied.  This  occurs 
when  any  motor  nerves  are  separated  from  their  cells  of  origin,  and  it  involves  no  neces- 
sity of  assuming  the  existence  of  special  trophic  cells  or  nerves. 

If  a  few  of  the  motor  cells  be  affected  with  disease,  and  if  the  degeneration  be  gradual 
and  progressive,  we  should  expect  progressive  and  partial  paralysis  of  the  muscles  to 
which  their  nerves  are  distributed.  This  paralysis,  confined  to  a  limited  number  of 
fibres  of  particular  muscles  or  sets  of  muscles,  would  give  the  idea  of  progressive  weak- 
ening of  the  muscles,  and  the  phenomena  would  not  be  those  observed  in  complete 
paralysis  produced  by  section  of  the  motor  nerves.  These  are  precisely  the  phenomena 
observed  in  progressive  muscular  atrophy,  preceding  the  paralysis  which  is  the  final 


SLEEP.  743 

result  of  the  disease;  and  these  do  not  involve  the  action  of  any  special  centres  or 
nerves. 

As  regards  the  muscular  atrophy  itself,  if  the  nervous  stimulus  he  progressively  de- 
stroyed, the  muscular  tissue  will  necessarily  undergo  progressive  degeneration  and 
atrophy. 

With  the  above  considerations,  we  leave  the  trophic  cells  and  nerves  to  the  patholo- 
gist ;  and  we  can  only  admit  the  existence  of  centres  and  nerves  specially  and  directly  in- 
fluencing the  nutrition  of  the  muscular  system,  when  it  has  been  demonstrated  that  there 
are  lesions  of  particular  structures  in  the  nervous  system,  which  produce  phenomena  that 
cannot  be  explained  by  our  knowledge  of  the  action  of  ordinary  motor  and  sensory  nerves 
and  of  the  vaso-motor  system. 

We  have  thus  endeavored  to  represent  what  is  actually  known  concerning  the  sym- 
pathetic system,  but  it  is  evident  that  we  have  much  to  learn  with  regard  to  its  physi- 
ology. The  great  sympathetic  ganglia  may  have  functions  of  which  we  have  no  definite 
idea ;  and  we  are  better  prepared  to  advance  our  knowledge  in  this  direction,  by  admit- 
ting our  ignorance,  than  by  attempting  to  supply  the  deficiencies  in  our  positive  infor- 
mation by  theories  unsupported  by  facts. 

Sleep. 

When  we  remember  that  about  one-third  of  our  existence  is  passed  in  sleep,  and  that, 
at  this  time,  voluntary  motion,  sensation,  the  special  senses,  and  various  of  the  functions 
of  the  organism,  are  greatly  modified,  the  importance  of  a  physiological  study  of  this 
condition  is  sufficiently  apparent.  The  subject  of  sleep  is  most  appropriately  considered 
in  connection  with  the  nervous  system,  for  the  reason  that  the  most  important  modifica- 
tions in  function  are  observed  in  the  cerebro-spinal  axis  and  nerves.  Eepose  is  as  neces- 
sary to  the  nutrition  of  the  muscular  system  as  proper  exercise  ;  but  repose  of  the  mus- 
cles relieves  the  fatigue  due  to  exercise,  without  sleep.  It  is  true  that,  after  violent  and 
prolonged  exertion,  there  is  frequently  a  desire  for  sleep,  but  simple  repose  will  often 
restore  the  muscular  power.  After  the  most  violent  effort,  a  renewal  of  muscular  vigor 
is  most  easily  and  completely  effected  by  rest  without  sleep,  a  fact  familiar  to  all  who  are 
accustomed  to  athletic  exercises.  The  glands  engaged  in  the  production  of  the  true  secre- 
tions need  certain  intervals  of  repose  ;  but  this  does  not  necessarily  involve  sleep.  After 
prolonged  and  severe  mental  exertion,  however,  or  after  long-continued  muscular  effort 
which  involves  an  excessive  expenditure  of  the  so-called  nerve-force,  sleep  becomes  an 
imperative  necessity.  If  the  nervous  system  be  not  abnormally  excited  by  effort,  sleep 
follows  moderate  exertion  as  a  natural  consequence,  and  it  is  the  only  physiological  means 
of  complete  restoration ;  but  the  two  most  important  muscular  acts,  viz.,  those  con- 
cerned in  circulation  and  respiration,  are  never  completely  arrested,  sleeping  or  waking, 
although  they  undergo  certain  modifications. 

In  infancy  and  youth,  when  the  organism  is  in  process  of  development,  sleep  is  more 
important  than  in  adult  life  or  old  age.  The  infant  does  little  but  sleep,  eat,  and  digest. 
In  adult  life,  under  perfectly  physiological  conditions,  we  require  about  eight  hours  of 
sleep ;  some  persons  need  less,  but  very  few  require  more.  In  old  age,  unless  after 
extraordinary  exertion,  less  sleep  is  required  than  in  adult  life.  Each  individual  learns 
by  experience  how  much  sleep  is  necessary  for  perfect  health,  and  there  is  nothing  which 
more  completely  incapacitates  one  for  mental  or  muscular  effort,  especially  the  former, 
than  loss  of  rest. 

Sleeplessness  is  one  of  the  most  important  of  the  predisposing  causes  of  certain  forms- 
of  brain-disease,  a  fact  which  is  well  recognized  by  practical  physicians.  One  of  the 
most  refined  and  exquisite  methods  of  torture  is  long-continued  deprivation  of  sleep ;  and 
persons  have  been  known  to  sleep  when  subjected  to  acutely  painful  impressions.  Severe 
muscular  effort,  even,  may  be  continued  during  sleep.  In  forced  marches,  regiments  have 


744    *  NERVOUS  SYSTEM. 

been  known  to  sleep  while  walking ;  men  have  slept  soundly  in  the  saddle  ;  persons  will 
sometimes  sleep  during  the  din  of  battle  ;  and  other  instances  illustrating  the  imperative 
demand  for  sleep  after  prolonged  vigilance  might  be  cited.  It  is  remarkable,  also,  how 
noises  to  which  we  Lave  become  accustomed  may  fail  to  disturb  our  natural  rest.  Those 
who  have  been  long  habituated  to  the  endless  noise  of  a  crowded  city  frequently  find 
difficulty  in  sleeping  in  the  oppressive  stillness  of  the  country.  We  must  have  sleep ; 
and  this  demand  is  so  imperious,  that  we  soon  accommodate  ourselves  to  the  most  un- 
favorable surrounding  conditions.  It  is  remarkable,  also,  that  prolonged  exposure  to 
intense  cold  induces  excessive  somnolence,  and,  if  this  be  not  resisted,  the  sleep  passes 
into  stupor,  the  power  of  resistance  to  cold  becomes  rapidly  diminished,  and  death  is  the 
inevitable  result.  Intense  heat  often  produces  drowsiness,  but,  as  is  well  known,  is  not 
favorable  to  natural  sleep.  We  generally  sleep  less  in  summer  than  in  winter,  though  in 
summer,  perhaps,  we  are  less  capable  of  protracted  mental  and  physical  exertion. 

Sleep  is  preceded  by  an  indescribable  feeling  of  drowsiness,  an  indisposition  to  mental 
or  physical  exertion,  and  a  general  relaxation  of  the  muscular  system.  It  then  requires 
a  decided  effort  to  keep  awake  ;  and,  if  we  yield  to  the  soporific  tendency,  the  voluntary 
muscles  cease  to  act,  the  lids  are  closed,  we  cease  to  appreciate  the  ordinary  impressions 
of  sound,  and  we  sometimes  pass  into  a  dreamless  condition,  in  which  we  lose  all  knowl- 
edge of  existence.  We  say  sometimes,  because  the  mind  is  not  generally  inactive  during 
what  we  may  regard  as  normal  sleep.  We  may  have  dreams  which  are  not  due,  as  far 
as  can  be  ascertained,  to  impressions  from  the  external  world  received  during  sleep. 
Ideas  in  the  form  of  dreams  may  be  generated  in  the  brain  from  impressions  previously 
received  while  awake,  or  trains  of  thought  may  be  gradually  extended  from  the  moments 
immediately  preceding  sleep  into  the  insensible  condition. 

There  may  be,  during  sleep,  mental  operations  of  which  we  have  no  consciousness  or 
recollection,  unconscious  cerebration,  as  it  is  called  by  Carpenter.  It  is  well  known  that 
we  vividly  remember  dreams  immediately  on  awakening,  but  that  the  recollection  of 
them  rapidly  fades  away,  unless  they  be  brought  to  mind  by  an  effort  to  remember  and 
relate  them.  Whatever  be  the  condition  of  the  mind  in  sleep,  if  the  sleep  be  normal, 
there  is  a  condition  of  repose  of  the  cerebro-spinal  system  and  an  absence  of  voluntary 
effort,  which  restore  the  capacity  for  mental  and  physical  exertion. 

The  impressionability  and  the  activity  of  the  human  mind  are  so  great,  most  of  the 
animal  functions  are  so  subordinate  to  its  influence,  and  we  are  so  subject  to  unusual 
mental  conditions,  that  it  is  difficult  to  determine  with  exactness  the  phenomena  of  sleep 
that  are  absolutely  physiological,  and  to  separate  those  that  are  slightly  abnormal.  We 
cannot  assert,  for  example,  that  a  dreamless  sleep,  in  which  our  existence  is,  as  it  were, 
a  blank,  is  the  only  normal  condition  of  repose  of  the  system ;  nor  can  we  determine 
what  dreams  are  due  to  previous  trains  of  thought,  to  impressions  from  the  external 
world  received  during  sleep,  and  are  purely  physiological,  and  what  are  due  to  abnormal 
nervous  influence,  disordered  digestion,  etc.  We  may  assume  that  an  entirely  refreshing 
sleep  is  normal,  and  that  is  all. 

That  reflex  ideas  originate  during  sleep,  as  the  result  of  external  impressions,  there 
can  be  no  doubt ;  and  we  have  already  alluded  to  this  point  under  the  head  of  reflex 
action.  The  most  remarkable  experiments  upon  the  production  of  dreams  of  a  definite 
character,  by  subjecting  a  person  during  sleep  to  peculiar  influences,  are  those  of  Maury. 
The  hallucinations  produced  in  this  way  are  called  hypnagogic,  and  they  occur  when 
the  subject  is  not  in  a  condition  favorable  to  sound  sleep.  The  experiments  made  by 
Maury  upon  himself  are  so  curious  and  interesting,  that  we  quote  the  most  striking  of 
them  in  full : 

FIRST  OBSERVATION.—"  I  was  tickled  with  a  feather  successively  on  the  lips  and 
inside  of  the  nostrils.  I  dreamed  that  I  was  subjected  to  a  horrible  punishment,  that  a 
mask  of  pitch  was  applied  to  my  face,  and  then  roughly  torn  off,  tearing  the  skin  of  the 
lips,  the  nose,  and  the  face. 


SLEEP.  745 

SECOND  OBSERVATION. — "  A  pair  of  pincers  is  held  at  a  little  distance  from  my  ear, 
and  rubbed  with  a  steel  scissors.  I  dreamed  that  I  heard  the  ringing  of  hells ;  this  soon 
became  the  tocsin,  and  I  imagined  myself  in  the  days  of  June,  1848. 

THIED  OBSERVATION. — "  I  was  caused  to  inhale  Cologne-water.  I  dream  that  I  am 
in  a  perfumer's  shop,  and  the  idea  of  perfumes  doubtless  awakens  the  idea  of  the  East :  I 
am  in  Cairo,  in  the  shop  of  Jean  Farina.  Many  extravagant  adventures  follow,  the  con- 
nection of  which  escapes  me. 

FOURTH  OBSERVATION. — "  I  am  caused  to  smell  a  burning  match.  I  dream  that  I  am 
at  sea  (remark  that  the  wind  was  then  blowing  in  through  the  windows),  and  that  the 
Saint-Barbe  blew  up. 

FIFTH  OBSERVATION. — "  I  am  slightly  pinched  on  the  nape  of  the  neck.  I  dream  that 
a  blister  is  applied,  which  recalls  the  recollection  of  a  physician  who  had  treated  me  in 
my  infancy. 

SIXTH  OBSERVATION. — "  A  piece  of  hot  iron  is  held  to  my  face,  keeping  it  far  enough 
removed,  so  that  the  sensation  of  heat  should  be  slight.  I  dream  of  chauffeurs,  who  enter 
houses  and  force  the  inmates,  by  putting  their  feet  to  the  fire,  to  reveal  where  their  money 
was.  The  idea  of  the  chauffeurs  immediately  suggests  that  of  the  Duchess  d'Abrantes, 
who,  I  suppose  in  my  dream,  has  taken  me  as  secretary.  I  had,  indeed,  long  ago  read  in 
the  memoirs  of  this  intelligent  woman  certain  details  concerning  the  chauffeurs. 

SEVENTH  OBSERVATION. — "  The  word  parafagaramus  is  pronounced  in  my  ear.  I  hear 
nothing,  and  awake,  having  had  rather  a  vague  dream.  The  experiment  is  repeated 
when  I  am  asleep  in  my  bed,  and  the  word  maman  is  pronounced  many  times  in  suc- 
cession. I  dream  of  different  things,  but  in  this  dream  I  heard  the  humming  of  bees. 
The  same  experiment,  repeated  several  days  after,  when  I  was  scarcely  asleep,  was  more 
conclusive.  The  words  Azor,  Castor,  Leonore,  were  pronounced  in  my  ear  ;  on  awaking, 
I  recollected  that  I  had  heard  the  last  two  words,  which  I  attributed  to  one  of  the  per- 
sons who  had  conversed  with  me  in  my  dream. 

"Another  experiment  of  the  same  kind  likewise  showed  that  the  sound  of  the  word, 
and  not  the  idea  attached  to  it,  had  been  perceived.  The  words  chandelle,  haridelle, 
were  pronounced  in  my  ear  many  times  in  succession.  I  awoke  suddenly  of  my  own 
accord,  saying,  c'est  elle.  It  was  impossible  for  me  to  recall  what  idea  I  attached  to  this 
answer. 

EIGHTH  OBSERVATION. — "  A  drop  of  water  is  allowed  to  fall  on  my  forehead.  I  dream 
that  I  am  in  Italy,  that  I  am  very  warm,  and  that  I  am  drinking  the  wine  of  Orviette. 

NINTH  OBSERVATION. —  "A  light,  surrounded  with  a  red  paper,  is  many  times  in  suc- 
cession passed  before  my  eyes.  I  dream  of  a  tempest  of  lightning,  and  all  the  remem- 
brance of  a  violent  storm  which  I  had  encountered  in  the  English  Channel,  in  going  from 
Morlaix  to  Havre,  is  present  in  my  mind." 

As  regards  dreams  due  to  external  impressions,  it  is  a  curious  fact,  which  has  been 
noted  by  many  observers  and  is  one  which  accords  with  the  personal  experience  of  all  who 
have  reflected  upon  the  subject,  that  trains  of  thought  and  imaginary  events,  which  seem 
to  pass  over  a  long  period  of  time  in  our  dreams,  actually  occur  in  the  brain  within  a  few 
seconds.  A  person  is  awakened  by  a  certain  impression,  which  undoubtedly  gives  rise 
to  a  dream  that  seems  to  occupy  hours  or  days,  and  yet  the  period  of  time  between  the 
impression  and  the  awakening  is  hardly  more  than  a  few  seconds ;  and  persons  will  drop 
asleep  for  a  very  few  minutes,  and  yet  have  dreams  with  the  most  elaborate  details  and 
apparently  of  great  length.  It  is  unnecessary  to  cite  the  numerous  accounts  of  literary 
compositions  of  merit,  the  working  out  of  difficult  mathematical  problems  in  dreams,  etc., 
some  of  which  are  undoubtedly  accurate.  If  it  be  true,  that  the  mind  is  capable  of  form- 
ing consecutive  ideas  during  sleep — which  can  hardly  be  doubted — there  is  no  good  reason 
why  these  phenomena  should  not  occur,  and  the  thoughts  should  not  be  remembered  and 
noted  immediately  on  awakening.  In  most  dreams,  however,  the  mind  is  hardly  in  a 
normal  condition,  and  the  brain  generally  loses  the  power  of  concentration  and  of  accu- 


746  NERVOUS  SYSTEM. 

rate  reasoning.  We  sometimes  commit  atrocious  crimes  in  our  dreams,  without  appre- 
ciating their  enormity,  and  we  are  often  placed  in  the  most  absurd  and  impossible  condi- 
tions, without  any  idea,  at  the  time,  of  their  extraordinary  and  unnatural  character. 
This  is  a  fact  sufficiently  familiar  to  every  one  and  is  one  which  does  not  admit  of  satis- 
factory explanation. 

We  have  made  no  attempt  to  offer  an  explanation  of  the  curious  psychological  phe- 
nomena presented  during  sleep,  and,  indeed,  we  know  little  enough  of  the  action  of  the 
mind  at  any  time;  but  we  have  merely  given  the  above  as  examples  of  what  we  may  call 
reflex  mental  phenomena.  Somnambulism,  general  anaesthesia,  sleep  from  hypnotics,  the 
so-called  magnetic  sleep,  ecstasy,  catalepsy,  trance,  etc.,  are  abnormal  conditions,  which 
we  shall  only  consider  in  so  far  as  they  resemble  natural  sleep. 

Condition  of  the  Brain  and  Nervous  System  during  /Sleep. 

As  we  have  already  seen,  during  sleep,  the  brain  may  be  in  a  condition  of  absolute 
repose — at  least,  as  far  as  we  have  any  subjective  knowledge  of  mental  operations — or  we 
may  have  more  or  less  connected  trains  of  thought.  There  is,  also,  as  a  rule,  absence  of 
voluntary  effort,  although  movements  may  be  made  to  relieve  discomfort  from  position  or 
external  irritation,  without  awakening.  The  sensory  nerves  retain  their  properties, 
although  the  general  sensibility  is  somewhat  blunted  ;  and  the  same  may  be  said  of  the 
special  senses  of  hearing,  smell,  and  probably  of  taste.  The  peculiar  dreams  induced 
in  the  case  of  Maury  by  red  lights  show  that  the  sense  of  sight  is  not  entirely  lost. 
There  is  every  reason  to  believe,  however,  that  the  functions  of  the  sympathetic  system 
are  not  disturbed  or  affected  by  sleep,  if  we  except  the  action  of  the  vaso-motor  nerves 
upon  the  circulation  in  the  brain. 

Two  opposite  theories  have  long  been  in  vogue  with  regard  to  the  immediate  cause 
of  sleep.  In  one,  this  condition  is  attributed  to  venous  congestion  and  increased  presssure 
of  blood  in  the  brain,  and  this  view  probably  had  its  origin  in  the  fact  that  cerebral 
congestion  induces  stupor  or  coma.  Stupor  and  coma,  however,  are  entirely  distinct 
from  natural  sleep ;  for  here,  the  functions  of  the  brain  are  suspended,  there  is  no  con- 
sciousness, no  dreaming,  and  the  condition  is  manifestly  abnormal.  In  animals  rendered 
comatose  by  opium,  the  brain  may  be  exposed  and  is  found  deeply  congested  with  venous 
blood.  The  same  condition  often  obtains  in  profound  anaesthesia  from  chloroform,  but  a 
state  of  the  brain  very  nearly  resembling  normal  sleep  is  observed  in  anaesthesia  from 
ether.  These  facts  have  been  positively  demonstrated  by  experiments  upon  living  ani- 
mals, and  have  been  observed  in  the  human  subject,  in  cases  of  injury  of  the  head. 
When  opium  is  administered  in  large  doses,  the  brain  is  congested  during  the  condition 
of  stupor  or  coma,  but  this  congestion  is  relieved  when  the  animal  passes,  as  sometimes 
happens,  from  the  effects  of  the  agent  into  a  natural  sleep.  In  view  of  these  facts  and 
others  which  will  be  stated  hereafter,  it  is  unnecessary  to  discuss  the  theory  that  sleep 
is  attended  with  or  is  produced  by  congestion  of  the  cerebral  vessels. 

The  idea  that  the  circulation  in  the  brain  is  diminished  during  sleep  has  long  been 
entertained  by  certain  physiologists ;  but,  until  within  a  few  years,  it  has  rested  chiefly 
upon  theoretical  considerations. 

Passing  over  arguments  by  the  older  writers  for  and  against  this  theory  of  sleep,  we 
come  to  the  researches  of  Durham,  in  1860,  in  which  it  seemed  to  be  demonstrated  that 
the  supply  of  blood  to  the  brain  is  always  greatly  diminished  during  sleep.  These  experi- 
ments were  made  upon  dogs.  A  piece  of  the  skull,  about  the  size  of  a  shilling,  was 
removed  with  a  trephine,  and  a  watch-glass  was  accurately  fitted  to  the  opening  and 
cemented  at  the  edges  with  Canada  balsam.  When  the  animals  operated  upon  in  this 
way  were  awake,  the  vessels  of  the  pia  mater  were  seen  moderately  distended,  and  the 
circulation  was  active  ;  but,  during  perfectly  natural  sleep,  the  brain  retracted  and  became 
pale.  "  The  contrast  between  the  appearances  of  the  brain  during  its  period  of  func- 


CONDITION  OF  THE  BRAIN,  ETC.,  DURING  SLEEP.  747 

tional  activity  and  during  its  state  of  repose  or  sleep  was  most  remarkable."  There 
can  be  hardly  any  doubt,  from  these  experiments,  that  the  circulation  in  the  cerebral 
substance  is  more  active  when  we  are  awake  than  during  sleep ;  but  the  question  has 
been  raised  by  Dr.  Cappie,  in  a  very  interesting  little  work  upon  the  causation  of  sleep, 
whether,  during  a  state  of  diminished  activity  of  the  capillary  circulation  in  the  brain- 
substance,  the  veins  be  not  congested,  and  sleep  be  immediately  due  to  pressure  from 
these  distended  vessels  on  the  gray  matter.  This  point  is  one  very  difficult  to  decide, 
and  it  has  not  been  made  the  subject  of  experimental  inquiry.  Dr.  Cappie  accepts,  in 
the  main,  the  experiments  of  Durham  as  accurate,  but  he  regards  his  observations  as  ap- 
plying only  to  the  circulation  in  the  arteries  and  capillaries.  His  view  is  that,  when  the 
capillary  circulation  in  the  brain-substance  is  diminished  in  sleep,  the  nervous  matter  is 
more  or  less  collapsed,  and  that  the  veins  are  necessarily  congested.  At  present,  how- 
ever, we  can  only  accept  the  experimental  results  of  Durham,  that  the  circulation  in  the 
brain  is  notably  diminished  in  sleep.  .  . 

The  influence  of  diminished  supply  of  blood  to  the  brain  has  been  Illustrated  by  com- 
pression of  both  carotid  arteries.  In  an  experiment  performed  upon  his  own  person,  Dr. 
Fleming  produced  immediate  and  profound  sleep  in  this  way,  and  this  result  invariably 
followed  in  subsequent  trials  upon  himself  and  others.  We  have,  however,  the  observa- 
tions of  Waller,  who  produced  anesthesia  in  patients  by  pressure  upon  both  pneumogas- 
tric  nerves ;  but  the  nerves  are  so  near  the  carotid  arteries  that  they  could  hardly  be 
compressed,  in  the  human  subject,  without  interfering  with  the  current  of  blood,  and 
such  experiments  do  not  positively  show  whether  the  loss  of  sensibility  be  due  to 
pressure  upon  the  nerves  or  upon  the  vessels.  In  some  rare  cases,  in  which  both  carotid 
arteries  have  been  ligatured  in  the  human  subject,  it  has  been  stated  that  there  is  an 
unusual  drowsiness  following  the  necessary  diminution  in  the  activity  of  the  cerebral 
circulation ;  but  this  result  is  by  no  means  constant,  and  the  morbid  conditions  in- 
volving so  serious  an  operation  are  usually  such  as  to  interfere  with  their  value  as  facts 
bearing  upon  the  question  under  consideration.  As  far  as  the  human  subject  is  concerned, 
the  most  important  facts  are  the  results  of  compression  of  both  carotids  in  healthy  per- 
sons. These,  as  well  as  experiments  on  animals,  all  go  to  show  that  the  supply  of  blood 
to  the  brain  is  very  much  diminished  during  natural  sleep,  and  that  sleep  may  be  induced 
by  retarding  the  cerebral  circulation  by  compressing  the  vessels  of  supply.  When  the 
circulation  is  interfered  with  by  compressing  the  veins,  congestion  is  the  result,  and  we 
have  stupor  or  coma. 

If  diminished  flow  of  blood  through  the  cerebral  vessels  be  the  cause  of  natural  sleep, 
it  becomes  important  to  inquire  how  this  condition  of  physiological  anasmia  is  brought 
about.  It  must  be  that,  when  the  system  requires  sleep,  the  vessels  of  the  brain  contract 
in  obedience  to  a  stimulus  received  through  the  sympathetic  system  of  nerves,  diminish- 
ing the  supply  of  blood,  here,  as  in  other  parts  under  varied  physiological  conditions. 
The  vessels  of  the  brain  are  provided  with  vaso-motor  nerves,  and  it  is  sufficient  to  have 
noted  that  the  arteries  are  contracted  during  sleep,  the  mechanism  of  this  action  being 
well  established  by  observations  upon  other  parts  of  the  circulatory  system.  Contraction 
of  the  vessels  of  the  pia  mater  has  been  observed,  although  there  is  some  discussion  with 
regard  to  its  exciting  cause. 

It  must  be  acknowledged  that  we  know  but  little  of  the  intimate  nature  of  the  pro- 
cssses  of  nutrition  of  the  brain  during  its  functional  activity  and  in  repose;  but  there 
can  be  no  doubt  of  the  fact  that  there  is  more  or  less  cerebral  action  at  all  times  when 
we  are  awake.  Although  the  mental  processes  are  much  less  active  during  sleep,  even  at 
this  time,  the  operations  of  the  brain  are  not  always  suspended.  It  is  equally  well  estab- 
lished, that  exercise  of  the  brain  is  attended  with  physiological  waste  of  nervous  sub- 
stance, and,  like  other  parts  of  the  organism,  its  tissue  requires  periodic  repose  to  allow 
of  the  regeneration  of  the  substance  consumed.  Analogies  to  this  are  to  be  found  in 
parts  that  are  more  easily  subjected  to  direct  observation.  The  muscles  require  repose 


748  NEKVOUS  SYSTEM. 

after  exertion,  and  the  glands,  when  not  actively  engaged  in  discharging  their  secretions, 
present  intervals  of  rest.  As  regards  the  glands,  during  the  intervals  of  repose,  the  sup- 
ply of  blood  to  their  tissue  is  very  much  diminished.  It  is  probable,  also,  that  the  mus- 
cles in  action  receive  more  blood  than  during  rest;  but  it  is  mainly  when  these  parts  are 
not  active,  and  when  the  supply  of  blood  is  smallest,  that  the  processes  of  regeneration 
of  tissue  seem  to  be  most  efficient.  As  a  rule,  the  functional  activity  of  parts,  while  it  is 
attended  with  an  increased  supply  of  blood,  is  a  condition  more  or  less  opposed  to  the 
process  of  repair,  the  hyperaemia  being,  apparently,  a  necessity  for  the  marked  and 
powerful  manifestations  of  their  peculiar  functions.  When  the  parts  are  in  active  func- 
tion, the  blood  seems  to  be  required  to  keep  at  the  proper  standard  the  so-called  irri- 
tability of  the  tissues  and  to  increase  their  power  of  action  under  proper  stimulus. 
Exercise  increases  the  power  of  regeneration  and  favors  full  development,  in  the  repose 
which  follows ;  but,  during  rest,  the  tissues  have  time  to  appropriate  new  matter,  and 
this  does  not  seem  to  involve  a  large  supply  of  blood.  A  muscle  is  exhausted  by  pro- 
longed exertion ;  and  the  large  quantity  of  blood  passing  through  it  carries  away  carbonic 
acid,  urea,  and  other  products  of  disassimilation,  which  are  all  increased  in  amount,  until 
it  gradually  uses  up  its  capacity  for  work.  Then  follows  repose ;  the  supply  of  blood  is 
reduced,  but,  under  normal  conditions,  the  tissue  repairs  the  waste  which  has  been 
excited  by  action,  the  blood  furnishing  nutritive  matter  and  carrying  away  a  compara- 
tively small  amount  of  effete  products. 

We  may  safely  assume  that  processes  analogous  to  those  just  decribed  take  place  in 
the  brain.  By  absence  of  voluntary  effort,  we  allow  the  muscles  time  for  rest  and  for  the 
repair  of  physiological  waste,  and  their  active  function  is  for  the  time  suspended.  As 
the  activity  of  the  brain  involves  consciousness,  volition,  the  generation  of  thought,  and, 
in  short,  the  mental  condition  observed  while  awake,  complete  repose  of  the  brain  is 
characterized  by  the  opposite  conditions.  It  is  true  that  we  rest  the  brain  without  sleep, 
by  abstaining  from  mental  effort,  by  the  gratification  of  certain  of  the  senses,  and  by  men- 
tal distraction  of  various  kinds,  and  that  the  mind  may  work  to  some  degree  during  sleep ; 
but,  during  the  period  of  complete  repose — that  condition  which  is  so  necessary  to  perfect 
health  and  full  mental  vigor — we  lose  consciousness  and  volition,  there  is  no  thought, 
and  the  brain,  which  does  not  receive  blood  enough  to  stimulate  it  to  action,  is  simply 
occupied  in  the  insensible  repair  of  its  substance  and  is  preparing  itself  for  future  work. 
The  exhaustion  of  the  muscles  produces  a  sense  of  fatigue  of  the  muscular  system,  indis- 
position to  muscular  exertion,  and  a  desire  for  rest,  not  necessarily  involving  drowsiness. 
Fatigue  of  the  brain  is  manifested  by  indisposition  to  mental  exertion,  dulness  of  the 
special  senses,  and  a  desire  for  sleep.  Simple  repose  will  relieve  physiological  fatigue  of 
muscles;  and,  when  a  particular  set  of  muscles  has  been  used,  the  fatigue  disappears 
when  these  muscles  alone  are  at  rest,  though  others  be  brought  into  action.  Sleep,  and 
sleep  alone,  relieves  fatigue  of  the  brain.  When  the  sleep  has  continued  long  enough  for 
the  rest  of  the  brain  and  the  repair  of  its  tissue,  we  awake,  prepared  for  new  effort. 

We  have  now  only  to  refer  to  a  new  theory  of  sleep,  proposed  by  Sommer.  Taking 
as  a  basis  the  researches  of  Pettenkofer  and  Voit  upon  respiration,  Sommer  advances  the 
idea  that,  when  the  brain  is  active,  or  while  we  are  awake,  the  system  appropriates  but 
a  small  quantity  of  oxygen  in  respiration  and  eliminates  a  relatively  large  proportion  of 
carbonic  acid;  after  a  time,  the  oxygen  thus  appropriated  is  consumed,  and  the  system 
demands  a  new  supply;  and,  during  sleep,  the  organism  appropriates  oxygen  largely  and 
eliminates  a  relatively  small  amount  of  carbonic  acid.  When  the  elimination  of- carbonic 
acid  at  the  expense  of  the  oxygen  stored  up  reaches  a  certain  point,  the  necessity  for  a 
farther  supply  of  oxygen  induces  sleep  ;  and  when,  during  sleep,  oxygen  has  been  appro- 
priated in  sufficient  quantity,  the  system  awakes,  prepared  for  a  new  period  of  activity 
of  the  animal  functions. 

By  reference  to  the  researches  of  Pettenkofer  and  Yoit,  we  find  that  these  observers, 
in  experiments  upon  a  man  confined  in  a  chamber  in  which  the  interchanges  of  gases  in 


CONDITION  OF  THE  BRAIN,  ETC.,  DURING  SLEEP.  749 

respiration  could  be  estimated,  noted,  in  twenty-four  hours,  that  the  subject  of  the  observa- 
tion, awake  but  in  a  condition  of  complete  repose,  appropriated  sixty-seven  per  cent,  of 
the  entire  amount  of  oxygen  of  the  twenty-four  hours  during  the  night,  and  thirty-three 
per  cent,  during  the  day,  while  he  eliminated  fifty-eight  per  cent,  of  the  entire  amount 
of  carbonic  acid  excreted,  during  the  day,  and  forty-two  per  cent.,  during  the  night. 
When  the  subject  of  the  experiment  worked  during  the  day,  by  turning  a  heavy  wheel, 
the  appropriation  of  oxygen  was  thirty-one  per  cent,  for  the  day,  and  sixty-nine  per  cent, 
for  the  night ;  and  the  elimination  of  carbonic  acid  was  sixty-nine  per  cent,  for  the  day,  and 
thirty-one  per  cent,  for  the  night.  According  to  these  observations,  the  system  stores  up 
oxygen  at  night  for  use  during  the  day,  at  this  time  eliminating  a  relatively  small  quan- 
tity of  carbonic  acid ;  and,  during  the  day,  it  excretes  more  carbonic  acid  than  during 
sleep,  appropriating  then  a  relatively  small  amount  of  oxygen. 

This  theory  of  sleep  seems  to  rest  upon  observations  too  restricted  to  be  adopted 
without  reserve.  It  is  stated,  indeed,  that  the  first  experiments  of  Pettenkofer  and  Yoit 
were  not  confirmed  in  other  observations  made  upon  the  same  person.  It  is  hardly  pos- 
sible, with  our  present  information,  to  assume  that  sleep  is  due  simply  to  want  of  oxygen, 
and  it  is  more  in  accordance  with  well-established  physiological  facts  to  attribute  it  to  a 
necessity  for  the  general  regeneration  of  the  nervous  tissue,  though  into  this,  the  neces- 
sity for  oxygen  may  enter  as  one  element  in  the  physiological  repair. 

During  sleep,  nearly  all  of  the  functions,  except  those  directly  under  the  control  of  the 
sympathetic  nervous  system,  are  diminished  in  activity.  The  circulation  is  slower,  and 
the  pulsations  of  the  heart  are  less  frequent,  as  well  as  the  respiratory  movements.  These 
points  have  already  been  considered  under  the  heads  of  circulation  and  respiration.  "We 
have  but  little  positive  information  with  regard  to  the  relative  activity  of  the  processes 
of  digestion,  absorption,  and  secretion,  during  sleep.  The  drowsiness  which  many  per- 
sons experience  after  a  full  meal  is  probably  due  to  a  determination  of  blood  to  the  ali- 
mentary canal  and  a  consequent  diminution  in  the  supply  to  the  brain. 


CHAPTER    XXIII. 

SPECIAL  SENSES-TOUCH,   OLF ACTION,  AND  GUSTATION. 

General  characters  of  the  special  senses — Muscular  sense  (so  called) — Appreciation  of  weight— Sense  of  touch — Varia- 
tions in  tactile  sensibility  in  different  parts — Table  of  variations  measured  by  the  aesthesiometer — Connection 
between  the  variations  in  tactile  sensibility  and  the  distribution  of  the  tactile  corpuscles— Titillation— Apprecia- 
tion of  temperature — Venereal  sense — Olfaction — Nasal  fossae — Schneiderian  and  olfactory  membrane — Physio- 
logical anatomy  of  the  olfactory  nerves— Olfactory  bulbs— Olfactory  cells  and  terminations  of  the  olfactory  nerve- 
fibres — Properties  and  functions  of  the  olfactory  nerves — Mechanism  of  olfaction— Eelations  of  olfaction  to  the 
sense  of  taste — Reflex  acts  through  the  olfactory  nerves— Gustation — Savory  substances — Eelations  between 
gustation  and  olfaction — Taste  and  flavor — Modifications  of  the  sense  of  taste — Nerves  of  taste — Chorda  tympani 
— Facial  paralysis  with  impairment  of  taste — Paralysis  of  general  sensibility  of  the  tongue  without  impairment  of 
taste— Glosso-pharyngeal  nerve  (first  division  of  the  eighth)— Physiological  anatomy— General  properties  of  the 
glosso-pharyngeal — Relations  of  the  glosso-pharyngeal  nerves  to  gustation — Mechanism  of  gustation — Physiolo- 
gical anatomy  of  the  organ  of  taste — Papillae  of  the  tongue — Taste-buds,  or  taste-beakers — Connections  of  the 
nerves  with  the  organs  of  taste. 

OUK  study  of  the  nervous  system  thus  far  has  involved  simply  motion  and  what  is 
known  as  general  sensibility ;  and  almost  all  our  positive  knowledge  of  these  properties 
has  been  derived  from  experiments  upon  the  inferior  animals.  As  regards  sensation,  the 
experiments  have  referred  to  impressions  recognized  as  painful ;  and  we  have  seen  that 
these  are  conveyed  to  the  centres  by  nerve-filaments,  anatomically  as  well  as  physiologi- 
cally distinct  from  those  which  convey  to  the  contractile  parts  the  stimulus  that  gives  rise 
to  motion.  As  far  as  we  have  studied  the  sensory  nerves,  we  have  alluded  to  simple  im- 


750  SPECIAL  SENSES. 

pressions  only ;  but  it  is  evident  that  the  filaments  of  peripheral  distribution  of  these 
nerves  are  capable  of  receiving  a  variety  of  impressions,  by  which  we  determine,  to  a  cer- 
tain extent,  the  form,  size,  character  of  surface,  density,  and  temperature  of  objects.  We 
also  have  a  general  appreciation  of  heat  and  cold  ;  a  sense  of  resistance,  which  gives  an 
idea  of  weight ;  and,  finally,  there  are  nerves  of  peculiar  properties,  terminating  in  organs 
calculated  to  receive  the  impressions  of  smell,  taste,  sight,  and  hearing. 

The  senses  of  olfaction,  gustation,  vision,  and  audition,  belong  to  peculiar  organs,  pro- 
vided with  nerves  of  special  properties,  which  are  usually  not  endowed  with  general  sen- 
sibility. These  nerves  have  been  omitted  in  our  general  study  of  the  nervous  system ; 
and  the  accessory  organs  to  which  they  are  distributed  are  so  important  and  intricate  in 
their  structure  as  to  demand  extended  description. 

The  senses  of  touch,  titillation,  temperature,  and  pain  are  all  conveyed  to  the  nerve- 
centres  by  what  we  have  described  as  ordinary  sensory  nerves ;  the  touch  being  perfected 
in  certain  parts  by  peculiar  arrangements  of  the  terminal  nerve-fibres.  Although  it  be 
possible  that  each  one  of  these  impressions  may  be  transmitted  by  special  and  distinct 
fibres,  this  has  not  yet  approached  a  positive  demonstration.  The  so-called  muscular 
sense,  by  which  we  appreciate  weight,  resistance,  etc.,  undoubtedly  depends,  to  a  great 
extent  if  not  entirely,  upon  the  muscular  nerves. 

Muscular  Sense  (so  called). 

It  is  difficult  to  define  exactly  what  is  meant  by  the  term  muscular  sense,  as  it  is  used 
by  many  physiologists.  In  all  probability,  the  sense  which  enables  us  to  appreciate  the 
resistance,  immobility,  and  elasticity  of  substances  that  are  grasped,  on  which  we  tread, 
or  which,  by  their  weight,  are  opposed  to  the  exertion  of  muscular  power,  is  immensely 
modified  by  education  and  habit.  Still,  it  is  undoubtedly  true  that  the  general  sensibility 
regulates  the  action  of  muscles  to  a  very  great  extent.  If,  for  example,  the  lower  extremi- 
ties be  paralyzed  as  regards  sensation,  the  muscular  power  remaining  intact,  the  person 
affected  cannot  walk,  unless  he  be  able  to  see  the  ground.  In  these  cases,  the  individual 
often  falls  when  blindfolded,  for  the  simple  reason  that  his  limbs  have  lost  the  sense  of 
contact  with  the  ground,  which  is  nothing  more  nor  less  than  loss  of  general  sensibility. 
Many  curious  examples  of  this  kind  are  to  be  found  in  works  upon  diseases  of  the  nervous 
system.  One  of  the  most  striking  is  a  case  communicated  to  Sir  Charles  Bell  by  Dr.  Ley. 
The  patient  was  afflicted  with  partial  loss  of  sensibility  upon  one  side  of  the  body,  "  with- 
out, however,  any  corresponding  diminution  of  power  in  the  muscles  of  volition,  so  that 
she  could  hold  her  child  in  the  arm  of  that  side  so  long  as  her  attention  was  directed  to 
it ;  but,  if  surrounding  objects  withdrew  her  from  the  notice  of  the  state  of  her  arm,  the 
flexors  gradually  relaxed,  and  the  child  was  in  hazard  of  falling."  This  is  something  like 
the  phenomena  ordinarily  described  under  the  head  of  locomotor  ataxia.  In  this  disor- 
der, there  is  disease  of  the  posterior  columns  of  the  spinal  cord,  with  progressive  loss  of 
general  sensibility,  the  muscular  power,  in  some  instances,  being  intact.  Patients  affected 
in  this  way  are  sometimes  unable  to  walk  or  stand  unless  they  supply  the  sense  of  contact 
by  the  sight.  One  of  the  most  characteristic  phenomena  is  inability  to  stand  when  blind- 
folded ;  although,  with  the  aid  of  the  sight,  the  muscles  can  be  made  by  the  will  to  act 
with  great  power. 

Without  entering  into  a  full  discussion  of  the  various  arguments  used  for  and  against 
the  existence  of  a  special  "muscular  sense,"  it  is  sufficient  to  state  that,  in  those  cases 
in  which  general  sensibility  is  lost  or  seriously  impaired,  the  brain  has  no  exact  apprecia- 
tion of  the  action  of  the  muscles,  except  as  regards  the  sense  of  fatigue.  This  question 
is  of  great  importance  in  connection  with  the  pathology  of  the  nervous  system  ;  and  it 
seems  that  the  weight  of  evidence  is  decidedly  in  favor  of  the  view  that  there  is  no  dis- 
tinct perception  of  muscular  action— aside  from  general  sensibility — that  can  properly  be 
called  a  muscular  sense. 


SENSE  OF  TOUCH.  751 

Habit  and  education  enable  us  to  appreciate  with  great  nicety  differences  in  weight ; 
but  this  is  chiefly  due  to  the  sense  of  resistance  to  muscular  effort  and  has  little  depend- 
ence upon  the  sense  of  touch.  In  the  elaborate  and  classical  experiments  of  Weber,  this 
point  was  very  strikingly  illustrated.  The  observations  of  this  physiologist  upon  the 
sense  of  touch  and  general  sensibility  were  very  varied  and  extensive  ;  and,  among  the 
most  important  of  the  results  with  regard  to  the  appreciation  of  pressure  and  weight, 
are  the  following : 

In  general,  those  parts  which  are  most  sensitive  to  the  impressions  of  touch,  as  the 
fingers,  enable  us  to  appreciate  differences  in  pressure  and  weight  with  the  greatest  accu- 
racy. The  sense  of  simple  pressure,  unaided  by  the  estimation  of  weight  by  muscular 
effort,  is  generally  more  acute  upon  the  left  side,  probably  because  the  integument  of  the 
left  hand  is  thinner  than  that  of  the  right  hand.  Differences  in  weight  can  be  accurately 
distinguished,  when  they  amount  to  only  one-sixteenth,  by  employing  muscular  effort  in 
lifting,  as  well  as  the  sense  of  pressure ;  but  the  sensa  of  pressure  alone  enables  us  to 
appreciate  a  difference  of  not  less  than  one-eighth.  When  weights  are  tested  by  lifting 
with  the  hand,  the  appreciation  of  slight  differences  is  more  delicate  when  the  weights 
are  successively  tested  with  the  same  hand  than  when  two  weights  are  placed,  one  on 
either  hand.  When  the  interval  between  the  two  trials  amounts  to  more  than  forty  sec- 
onds, slight  differences  in  weight — the  difference  between  fourteen  and  a  half  and  fifteen 
ounces,  for  example — cannot  be  accurately  appreciated.  In  such  trials,  it  is  necessary 
to  have  the  metals  used  of  the  same  temperature,  for  cold  metals  seem  heavier  than 
warm. 

These  observations  formularized  some  of  the  facts,  sufficiently  evident  to  every  one, 
relating  to  the  appreciation  of  slight  differences  in  weight.  It  is  well  known  that  experts 
acquire,  in  this  regard,  wonderful  delicacy  and  accuracy.  Those  who  are  in  the  daily 
habit  of  handling  coins  not  only  count  with  astonishing  rapidity,  but  are  able  to  detect 
and  throw  out  a  light  piece  instantly  and  with  unerring  certainty. 

Sense  of  Touch. 

We  have  already  considered,  in  connection  with  the  nervous  system,  the  modes  of 
termination  of  the  sensory  nerves ;  and,  in  many  instances,  it  is  possible  to  explain,  by 
the  anatomical  characters  of  the  nerves,  the  great  differences  that  have  been  observed  in 
the  delicacy  of  the  tactile  sensibility  in  different  parts — differences  which  are  exceedingly 
important,  pathologically  as  well  as  physiologically,  and  which  have  been  studied  by 
Weber,  Valentin,  and  others,  with  great  minuteness. 

Variations  in  the  Tactile  Sensibility  in  Different  Parts. — In  certain  parts  of  the  cuta- 
neous surface,  the  general  sensibility  is  much  more  acute  than  in  others.  For  example, 
a  sharp  blow  upon  the  face  is  more  painful  than  a  similar  injury  to  other  parts ;  and  the 
eye,  as  is  well  known,  is  most  exquisitely  sensitive.  The  appreciation  of  temperature  also 
varies  in  different  parts,  this  probably  depending  to  a  great  extent  upon  habitual  exposure. 
Some  parts,  as  the  soles  of  the  feet  or  the  axilla,  are  peculiarly  sensitive  to  titillation. 
The  sense  of  touch,  however,  by  which  we  appreciate  the  size,  form,  character  of  the 
surface,  consistence,  etc.,  of  objects,  is  developed  to  a  greater  degree  in  some  parts  than 
in  others;  a  fact  which  can  be  very  readily  explained,  in  some  instances,  by  the  ana- 
tomical arrangements  of  the  peripheral  sensory  nerves.  When  we  wish  to  ascertain 
those  properties  of  objects  revealed  by  the  sense  of  touch,  we  generally  employ  the  fin- 
gers. This  sense  is  capable  of  education  and  is  almost  always  extraordinarily  developed 
in  persons  who  are  deprived  of  other  special  senses,  as  sight  or  hearing.  The  blind  learn 
to  recognize  individuals  by  feeling  of  the  face.  A  remarkable  instance  of  this  is  quoted 
in  works  on  physiology,  of  the  blind  sculptor,  Giovanni  Gonelli,  who  was  said  to  model 
the  most  striking  likenesses  entirely  by  the  sense  of  touch.  Other  instances  of  this  kind 


752  SPECIAL  SENSES. 

are  on  record.  The  blind  have  been  known  to  become  proficients  in  conchology  and 
botany,  guided  simply  by  the  sense  of  touch.  It  is  related  of  a  blind  botanist,  that  he 
was  able  to  distinguish  ordinary  plants  by  the  fingers  and  by  the  tip  of  the  tongue.  It 
is  well  known  that  the  blind  learn  to  read  with  perfect  facility,  by  passing  the  fingers 
over  raised  letters  but  little  larger  than  the  letters  in  an  ordinary  folio  Bible.  Eudolphi 
cites  the  remarkable  faculty  acquired  by  Baczko,  of  distinguishing  the  colors  of  fabrics  by 
the  sense  of  touch  alone. 

An  exceedingly  ingenious  and  accurate  method  of  determining  the  relative  delicacy 
of  the  tactile  sensibility  of  different  portions  of  the  cutaneous  surface  was  devised  a 
number  of  years  ago  (1829)  by  E.  H.  Weber,  whose  researches  upon  this  subject,  which 
have  been  repeatedly  confirmed  by  other  observers,  are  still  the  most  careful  and  reliable 
on  record.  This  method  consists  in  the  application  to  the  skin,  of  two  fine  but  blunt 
points,  separated  from  each  other  by  a  known  distance.  The  individual  experimented 
upon  should  be  blindfolded,  and  the  points  applied  to  the  skin  simultaneously.  By  care- 
fully adjusting  the  distance  between  the  points,  a  limit  will  be  reached  where  the  two 
impressions  upon  the  surface  are  appreciated  as  one ;  i.  e.,  by  gradually  approximating 
them,  the  subject  will  suddenly  feel  both  points  as  one,  when,  an  instant  before,  with  the 
points  a  little  farther  removed  from  each  other,  he  distinctly  felt  two  impressions.  This 
gives  a  very  accurate  measure  of  the  delicacy  of  the  tactile  as  distinguished  from  the 
general  sensibility  of  different  parts,  and  it  has  lately  been  found  a  most  important  guide 
in  the  investigation  of  diseases  of  the  nervous  system  attended  with  partial  anaesthesia 
of  the  surface.  Of  course,  the  instrument  used  may  be  very  simple  (a  pair  of  ordinary 
dividers  will  answer),  but  it  is  convenient  to  have  some  ready  means  of  ascertaining  the 
distances  between  the  points.  An  instrument,  consisting  simply  of  a  pair  of  dividers, 
with  a  graduated  bar  giving  a  measure  of  the  separation  of  the  points,  is  the  best,  as  it 
combines  simplicity,  convenience  of  use,  and  portability.  This  instrument  is  called  the 
sesthesiometer. 

The  experiments  of  Weber  were  made  upon  his  own  person,  and,  of  course,  they  do  not 
show  the  variations  that  may  occur  in  different  individuals  in  health,  a  point  of  consider- 
able importance  in  estimating  the  extent  of  anaesthesia  in  disease.  His  observations  also 
showed  some  slight  variations  with  the  direction  of  the  line  of  the  two  points,  but  these 
are  not  important.  Valentin  repeated  the  experiments  of  Weber,  and,  in  addition,  took 
the  maximum,  minimum,  and  mean,  in  six  persons.  Aside  from  these  observations,  the 
repetition  of  Weber's  experiments  has  done  little  more  than  confirm  the  original  facts. 
The  table  upon  the  next  page,  taken  from  the  article  on  "Touch  "  by  Dr.  W.  B.  Carpen- 
ter in  the  Cyclopedia,  of  Anatomy  and  Physiology,  London,  1849-1852,  vol.  iv.,  part  ii., 
p.  1169,  gives  the  results  obtained  by  Weber  and  by  Valentin. 

If  we  note  the  distribution  of  the  tactile  corpuscles  in  connection  with  this  table,  it 
will  be  seen  that  the  sense  of  touch  is  most  acute  in  those  situations  in  which  the  cor- 
puscles are  most  abundant.  In  the  space  of  about  one-fiftieth  of  a  square  inch  on  the 
palmar  surface  of  the  third  phalanx  of  the  index-finger,  Meissner  counted  the  greatest 
number  of  corpuscles,  viz.,  one  hundred  and  eight.  In  this  situation,  the  tactile  sensi- 
bility is  more  acute  than  in  any  other  part  of  the  skin,  the  mean  distance  indicated  by 
the  sesthesiometer  being  0'603  of  a  line.  In  the  same  space  on  the  second  phalanx,  forty 
corpuscles  were  counted,  the  sesthesiometer  marking  1  -558  line,  this  part  ranking  next  in 
tactile  sensibility  after  the  red  surface  of  the  lips.  We  can  readily  understand  how  the 
tactile  corpuscles,  embedded  in  the  amorphous  substance  of  the  cutaneous  papillae,  might 
increase  the  power  of  appreciation  of  delicate  impressions  by  presenting  hard  surfaces 
against  which  the  delicate  nerve-filaments  can  be  pressed. 

As  regards  those  portions  of  the  general  cutaneous  surface  in  which  no  tactile  corpus- 
cles have  been  demonstrated,  it  is  not  easy  to  connect  the  variations  in  the  tactile  sen- 
sibility with  the  nervous  distribution,  as  we  know  little  or  nothing  of  the  comparative 
richness  of  the  terminal  nervous  filaments  in  these  situations. 


SENSE   OF  TOUCH. 


753 


Table  of  Variations  in  the  Tactile  Sensibility  of  Different  Portions  of  the 
Skin  (Weber  and  Valentin). 

The  tactile  sensibility  is  measured  by  the  greatest  distance  between  two  points  at  which  they  convey  a  single 
impression  when  applied  simultaneously.    The  measurements  are  given  in  lines  (^  of  an  inch). 


PART  OF  SURFACE. 

WEBEE. 

VALENTIN. 

Tip  of  the  tongue  

0-50 
1-00 

Max. 
0-50 
1-00 
1-00 
1-00 
1-00 
1-00 
2-00 
2-00 
2-00 
1-75 
4-00 
8-00 
4-00 
8-00 
4-00 
4-00 
8-00 
5-00 
4-50 
5-00 
5-00 
5-50 
5-50 
5-50 
5-50 
5-50 
6-CO 
9-00 
5-00 
7-00 
7-00 
6-00 
8-00 

10-00 

7-00 

10-00 

14-00 
12-00 
15-00 

10-00 

14-00 
15-00 
16-00 
20-00 
18-00 
14-00 
18-00 
24-00 
18-00 
18-00 
18-00 
18-00 
20-00 
18-00 
30-00 
30-00 
80-00 
24-00 
24-00 
30-00 

Min. 
0-40 
0-50 
0-37 
0-60 
0-50 
0-50 
0-50 
0-50 
1-25 
1-50 
1-50 
1-75 
1-50 
0-50 
1-50 
1-50 
1-75 
8-00 
2-00 
2-50 
8-00 
2-75 
2-75 
2-75 
2-50 
2-75 
2-00 
2-00 
3-25 
8-00 
4-00 
4-00 
3-25 
3-00 
5-00 
4-00 
3-50 
6  00 
8-00 
8-00 
3-00 
5-50 
6-00 
9-50 
7-50 
12-00 
7-00 
8-00 
9-00 

10-00 

6-00 
7-50 
8-00 
10-50 
8-75 
9-00 
7-00 
11-00 
11-50 
11-00 

Mean. 
0-488 
0-603 
0-706 
0-723 
0-725 
0-738 
1-500 
1-520 
1-558 
1-650 
1-916 
2-125 
2-208 
2-250 
2-478 
2-500 
2-625 
3-250 
8-333 
8-888 
8-883 
8-893 
8-898 
8-900 
8-948 
3-971 
•042 
•125 
•541 
•620 
•917 
5-100 
5-250 
5-286 
5-875 
6-000 
6-966 
8-292 
8-292 
9-000 
9-200 
9-563 
10-208 
12-066 
12-525 
13-000 
13-292 
13-292 
18-708 
18-650 
13-886 
14-958 
15-875 
16-625 
17-083 
17-683 
18-542 
19-000 
19-912 
24-208 

Relative 
acuteness. 
1-000 
0-802 
0-685 
0-669 
0-667 
0-659 
0-322 
0-318 
0-310 
0-293 
0-252 
0-227 
0-219 
0-215 
0-195 
0-193 
0-184 
0-149 
0-145 
0-126 
0-126 
0-124 
0-124 
0-124 
0-122 
0-121 
0-120 
0-117 
0-106 
0-105 
0-098 
0-095 
0-092 
0-091 
0-082 
0-081 
0-069 
0-058 
0-058 
0-054 
0-052 
0-050 
0-047 
0-040 
0-039 
0-037 
0-036 
0-036 
0-085 
0-034 
0-034 
0-032 
0-030 
0-029 
0-028 
0-027 
0-026 
0-025 
0-022 
0-020 

Relative 
obtuseness. 
1-000 
1-248 
1-461 
1-496 
1-500 
1-517 
3-130 
8-145 
8-223 
8-414 
8-964 
4-397 
4-568 
4-655 
5-127 
5-172 
5-431 
6-724 
6-896 
7-930 
7-930 
8-054 
8-054 
8-069 
8-158 
8-216 
8-363 
8-535 
9-395 
9-559 
10-173 
10-552 
10-862 
10-936 
12-155 
12-414 
14-412 
17-156 
17-156 
18-621 
19-C35 
19-827 
21-120 
24-964 
25-914 
26-897 
27-501 
27-501 
28-361 
28-655 
28-688 
30-948 
82-845 
34-397 
35-344 
86-482 
38-362 
39-310 
44-758 
50-086 

Palmar  surface  of  third  phalanx  of  forefinger 

do.                     do.                  middle  finger  

do.                      do.                  ring-finger  ^ 

do.                      do.                  thumb  

do.                      do.                  little  finger  ! 

Red  surface  of  under  lip  

2-00 

do.              upper  lip  

Palmar  surface  of  second  phalanges  of  fingers  

2-00 

do.                first                         do.    "      

Middle  of  the  dorsum  of  the  tongue  

4-00 
8-00 
4-00 
8-00 

Dorsal  surface  of  the  third  phalanges  of  fingers 

Portion  of  the  lips  not  red.  

Tip  of  the  nose                 

Edge  of  the  tongue  an  inch  from  the  tip  

Lateral  surface  of  the  dorsum  of  the  tongue  '• 

Palmar  surface  of  the  metacarpus  

8-00 
5-00 
4-00 
5-00 
5-00 
5-00 

End  of  the  great-toe  

Metacarpal  joint  of  the  thumb  

External  surface  of  the  eyelids  

Palm  of  the  hand 

Dorsal  surface  of  second  phalanx  of  thumb 

do.                       do.                  forefinger  

do.                       do.                  middle  finger  

do.                       do.                  little  finger  

do.                       do.                  ring-finger  

Centre  of  the  hard  palate  

6-00 
9-00 
5-00 
7-00 
7-00 

Mucous  membrane  of  lips  close  to  the  gum  

Skin  of  the  cheek  over  buccinator 

do.           over  anterior  part  of  malar  bone  
Dorsal  surface  of  first  phalanges  of  fingers. 

Prepuce  :  

Dorsal  surface  of  heads  of  metacarpal  bones  .... 

8-00 

10-00 

Skin  of  cheek  over  posterior  part  of  malar  bone  
Plantar  surface  of  metacarpal  bone  of  great-toe  

Lower  part  of  forehead  

10-00 

14-00 
12-00 
15-00 

10-00 

Back  of  the  hand  

Lower  part  of  hairy  scalp  in  occipital  region  
Surface  of  the  throat  beneath  lower  jaw  

Back  of  the  heel  

Pubes  

Crown  of  the  head  

15-00 
16-00 

Patella  and  surrounding  part  of  thigh 

Areola  around  nipple  

Dorsum  of  foot  near  the  toes  

18-00 

Axilla  

Upper  and  lower  extremities  of  forearm 

18-00 
24-00 
18-00 
18-00 
18-00 
18-00 
20-00 
18-00 
30-00 
30-00 
30-00 
24-00 
24-00 
30-00 

Back  of  the  neck  near  the  occiput  

Upper  and  lower  extremities  of  leg 

Penis  i 

Acromion  and  upper  part  of  arm.. 

Sternum  

Gluteal  region  and  neighboring  part  of  thigh  
Middle  of  forearm  where  its  circumference  is  greatest  
Middle  of  thigh                              do.                             
Middle  of  cervical  vertebrae  

Five  upper  dorsal  vertebrae. 

Lower  part  of  thorax  and  over  lumbar  vertebras  
Middle  of  dorsal  vertebrae  I 

Titillation. — The  sensation  experienced  when  certain  parts  of  the  general  surface  are 
subjected  to  titillation  cannot  easily  be  described,  although  it  is  sufficiently  familiar.  This 
sensation  is  due  simply  to  delicate  impressions  made  in  unusual  situations  and  is  remark- 
able chiefly  on  account  of  the  reflex  movements  which  it  occasions.  If  the  soles  of  the 
feet  be  tickled,  it  is  almost  impossible  to  avoid  movements  of  the  limbs.  These  are  not 
due  entirely  to  the  peculiar  sensation  appreciated  by  the  brain,  for  the  same  stimulus,  in 
persons  suffering  from  complete  paralysis  of  sensation  and  voluntary  motion  of  the  lower 
extremities,  may  produce  even  violent  action  of  the  paralyzed  muscles.  The  peculiar 
48 


754 


SPECIAL  SENSES. 


nature  of  the  sensation  is  due  to  the  unusual  character  of  the  impression,  and  it  does  not 
involve  the  action  of  special  nerve-fibres  as  conductors. 

Appreciation  of  Temperature.— It  is  not  known  that  the  sense  of  temperature,  either 
of  the  surrounding  medium  or  of  bodies  applied  to  different  parts  of  the  skin,  is  appreci- 
ated through  any  nerves  other  than  those  of  general  sensibility,  or  that  there  is  any  special 
arrangement  of  the  terminations  of  certain  of  the  nerves  connected  with  this  sense.  As 
regards  the  general  temperature,  the  sense  is  relative  aud  is  much  modified  by  habit. 
This  statement  needs  no  explanation.  As  is  well  known,  what  is  cold  for  an  inhabitant 
of  the  torrid  zone  would  be  warm  for  one  accustomed  to  an  excessively  cold  climate. 
Habitual  exposure  also  modifies  the  sense  of  temperature.  Many  persons  not  in  the  habit 
of  dressing  warmly  suffer  but  little  in  extremely  cold  weather.  Those  who  habitually 
expose  the  hands,  or  even  the  feet,  to  cold,  render  these  parts  quite  insensible  to  tempera- 
ture ;  and  the  same  is  true  of  those  who  often  expose  the  hands,  face,  etc.,  to  heat. 

The  variations  in  the  sensibility  of  different  parts  of  the  surface  to  temperature  depend, 
as  we  have  just  indicated,  to  a  great  extent  upon  habit,  exposure,  etc.,  but  also  upon 
special  properties  of  the  parts  themselves.  The  differences,  however,  are  not  so  marked 
as  to  be  of  any  great  importance,  and  the  experiments  made  upon  this  point  are  simply 
curious.  It  is  remarkable,  however,  to  note  the  exquisite  sensibility  to  variations  in  tem- 
perature sometimes  presented  by  those  who  are  deprived  of  other  senses.  The  example 
is  quoted  by  DungHson,  of  Dr.  Saunderson,  formerly  Professor  of  Mathematics  at  Cam- 
bridge, England,  who,  "  when  some  of  his  pupils  were  engaged  in  taking  the  altitude  of 
the  sun,  could  tell,  by  the  slight  modification  in  the  temperature  of  the  air,  when  very 
light  clouds  were  passing  over  the  sun's  disk." 

The  experiments  of  Weber  show  conclusively  that  the  skin  is  the  main  organ  for  the 
appreciation  of  temperature,  if  we  except  the  mouth,  palate,  vagina,  and  rectum,  by  which 
the  difference  between  warm  and  cold  substances  is  readily  distinguished.  In  several 
instances  in  which  large  portions  of  the  skin  were  destroyed  by  burns  and  other  injuries, 
experiments  have  been  made  by  applying  spatulas  of  different  temperatures.  At  one  time 
a  spatula  plunged  in  water  at  from  48°  to  55°  Fahr.  was  applied  to  a  denuded  surface, 
and  again,  a  spatula  at  from  113°  to  122°  Fahr.  When  the  patient  was  requested  to  tell 
which  was  the  warmer,  the  answers  were  as  frequently  incorrect  as  they  were  correct ; 
but  the  discrimination  was  easy  and  certain  when  the  applications  were  made  to  the  sur- 
rounding healthy  skin.  When  applications  at  a  higher  temperature  were  made  to  the 
denuded  part,  the  patient  suffered  only  pain. 

The  venereal  sense,  which  we  shall  not  attempt  to  describe,  is  unlike  any  other  sensa- 
tion, and  is  general,  as  well  as  referable  to  the  organs  of  generation.  In  this  connection, 
however,  it  is  interesting  to  note  that  the  tactile  sensibility  of  the  palmar  surface  of  the 
third  phalanx  of  the  fingers,  measured  by  the  aBsthesioraeter,  compared  with  the  sensi- 
bility of  the  penis,  is  as  0-802  to  0-034,  or  between  twenty-three  and  twenty-four  times 
greater. 

Olfactory  Nerves. 

The  nerves  directly  connected  with  the  senses  of  olfaction,  vision,  and  audition,  are 
but  slightly  if  at  all  endowed  with  general  sensibility.  As  regards  the  olfactory  nerves, 
the  parts  to  which  they  are  distributed  are  so  fully  supplied  with  branches  from  the  fifth, 
that  it  is  difficult  to  determine  the  fact  of  their  sensibility  or  insensibility  to  ordinary 
impressions.  The  olfactory  nerves,  however,  are  distributed  to  the  mucous  membrane 
of  that  portion  of  the  nasal  cavity  endowed  with  the  special  sense  of  smell.  Before 
taking  up  their  physiological  anatomy,  we  shall  describe  briefly  the  parts  to  which  the 
olfactory  sense  is  probably  confined. 

Nasal  Fosses.—  The  two  irregularly-shaped  cavities  in  the  middle  of  the  face,  opening 
in  front  by  .the  anterior  nares  and  connected  with  the  pharynx  by  the  posterior  nares, 


OLFACTOKY  NERVES.  755 

are  called  the  nasal  fossae.  The  membrane  lining  these  cavities  is  generally  called  the 
Schneiderian  mucous  membrane,  and  sometimes,  particularly  by  the  French,  the  pituitary 
membrane.  This  membrane  is  closely  adherent  to  the  fibrous  coverings  of  the  bones 
and  cartilages  by  which  the  nasal  fossae  are  bounded,  and  it  is  thickest  over  the  turbinated 
bones.  It  is  continuous  with  the  membrane  lining  the  pharynx,  the  nasal  duct  and  lach- 
rymal cauals,  the  Eustachian  tube,  the  frontal,  ethmoidal,  and  sphenoidal  sinuses,  and 
the  antrum.  There  are  openings  leading  from  the  nasal  fossae  to  all  of  these  cavities. 

The  essential  organ  of  olfaction  is  the  mucous  membrane  lining  the  upper  half  of  the 
nasal  fossae.  Not  only  has  it  been  shown  anatomically  that  this  part  only  of  the  mem- 
brane receives  the  terminal  filaments  of  the  olfactory  nerves,  but  physiological  experi- 
ments have  demonstrated  that  it  is  the  only  part  capable  of  receiving  odorous  impressions. 
If  a  tube  be  introduced  into  the  nostril,  placed  horizontally  over  an  odorous  substance  so 
that  the  emanations  cannot  penetrate  its  caliber,  no  odor  is  perceived,  though  the  parts 
below  the  end  of  the  tube  might  receive  the  emanations;  but,  if  the  tube  be  now  directed 
toward  the  odorous  substance,  so  that  the  emanations  can  penetrate  to  the  upper  portion 
of  the  nares,  the  odor  is  immediately  appreciated. 

That  portion  of  the  lining  of  the  nasal  fossae  properly  called  the  olfactory  membrane 
extends  from  the  cribriform  plate  of  the  ethmoid  bone  downward  a  little  less  than  an 
inch.  It  is  exceedingly  soft  and  friable,  very  vascular,  thicker  than  the  rest  of  the 
Schneiderian  membrane,  and,  in  man,  has  rather  a  yellowish  color.  It  is  covered  by 
long,  delicate,  columnar  cells,  nucleated,  each  one  provided  with  from  three  to  eight  cili- 
ary processes,  their  movement  being  from  before  backward.  The  mucous  glands  of  the 
olfactory  membrane  are  numerous,  long,  and  racemose.  They  secrete  a  fluid  which  keeps 
the  surface  moist,  a  condition  essential  to  the  accurate  perception  of  odorous  impressions. 

Physiological  Anatomy  of  the  Olfactory  Nerves. — The  apparent  origin  of  the  olfactory 
nerve  is  by  three  roots,  from  the  inferior  and  internal  portion  of  the  anterior  lobe  of  the 


FIG.  233.— Olfactory  ganglion  and  nerves.    (Hirschfeld.) 

1,  olfactory  ganglion  and  nerves ;  2,  branch  of  the  nasal  nerve;  3,  spheno-palatine  ganglion ;  4,  7,  branches  of  the 
great  palatine  nerve;  5,  posterior  palatine  nerve;  6,  middle  palatine  nerve;  8,  9,  branches  from  the  spheno-pala- 
tine ganglion ;  10, 11, 12,  Vidian  nerve  and  its  branches ;  13,  external  carotid  branch  from  the  superior  cervical 
ganglion. 

cerebrum,  in  front  of  the  anterior  perforated  space.  The  three  roots  are  an  external  and 
an  internal  white  root,  and  a  middle  root  composed  of  gray  matter.  The  external  white 
root  is  long  and  delicate,  passing  outward  across  the  fissure  of  Sylvius  to  the  middle  lobe 
of  the  cerebrum.  The  internal  white  root  is  thicker  and  shorter  than  the  external  root, 


756 


SPECIAL  SENSES. 


and  it  arises  from  the  most  posterior  portion  of  the  anterior  lobe.  The  middle,  or  gray 
root  arises  from  a  little  eminence  of  gray  matter  situated  on  the  posterior  and  inner  por- 
tion of  the  inferior  surface  of  the  anterior  lobe. 

The  deep  origin  of  these  three  roots  of  the  olfactory  nerves  is  still  a  matter  of  discus- 
sion. The  external  root  is  stated  by  various  anatomists  to  originate  from  the  corpus 
striatum,  the  optic  thalamus,  the  anterior  commissure,  and  the  island  of  Eeil;  but 
researches  upon  this  point  have  been  by  no  means  satisfactory.  The  same  uncertainty 
exists  with  regard  to  the  deep  origin  of  the  internal  white  root  and  the  gray  root. 

The  three  roots  of  the  olfactory  converge  to  form  a  single  nervous  cord  at  the  inner 
boundary  of  the  fissure  of  Sylvius.  This  passes  forward  and  slightly  inward  in  a  deep 
groove  between  two  convolutions  on  the  under  surface  of  the  anterior  lobe,  covered  by 
the  arachnoid  membrane,  to  the  ethmoid  bone.  This  portion  of  the  nerve  is  exceedingly 
soft  and  friable.  It  is  composed  of  both  white  and  gray  matter,  the  proportions  being 
about  two-thirds  of  the  former  to  one-third  of  the  latter.  The  gray  substance,  derived 
from  the  gray  root,  is  situated  at  the  upper  portion  of  the  nerve,  the  white  substance 
occupying  the  inferior  and  the  lateral  portions. 

By  the  side  of  the  crista  galli  of  the  ethmoid  bone,  the  nerve-trunk  expands  into  an 
oblong  ganglion,  called  the  olfactory  bulb.  This  is  grayish  in  color,  excessively  soft,  and 
contains  the  ordinary  ganglionic  elements.  From  the  olfactory  bulb,  from  fifteen  to 
eighteen  nervous  filaments  are  given  off,  which  pass  through  the  foramina  in  the  cribriform 
plate  of  the  ethmoid  bone.  These  filaments  are  composed  entirely  of  nerve-fibres  and  are 
quite  resisting,  owing  to  fibrous  elements  prolonged  from  the  dura  mater.  It  is  strictly 

proper,  perhaps,  to  regard  these  as  the  true  olfactory 
nerves,  the  cord  leading  from  the  olfactory  bulb  to  the 
cerebrum  being  more  properly  a  commissure.  Having 
passed  through  the  cribriform  plate,  the  olfactory  nerves 
are  distributed  to  the  olfactory  membrane  in  three  groups : 
an  inner  group,  distributed  to  the  mucous  membrane  of 
the  upper  third  of  the  septum ;  a  middle  group,  to  the 
upper  portion  of  the  nasal  fossae ;  and  an  outer  group,  to 
the  mucous  membrane  covering  the  superior  and  middle 
turbinated  bones  and  a  portion  of  the  ethmoid. 

The  mode  of  termination  of  the  olfactory  nerves  differs 
from  that  of  the  ordinary  sensory  nerves,  and  is  peculiar 
and  characteristic,  as  it  is  in  the  other  organs  of  special 
sense.     According  to  recent  observations,   the  olfactory 
mucous  membrane  contains  peculiar  terminal  nerve-cells, 
FIG.  234.— Terminal  filaments  of  the  ca^e^  tne  olfactory  cells,  which  are  situated  between  the 
olfactory  nerves;  magnified  30  cells  of  epithelium.      These  are  long,   delicate,  spindle- 

diametera.    (Kolliker.) 

1,  from  the  frog.-a,  epithelial  cells  of  snaPed  structures,  varicose,  each  one  containing  a  clear, 
the  olfactory  region;  b  olfactory  round  nucleus.     The  appearance  of  these,  which  are  con- 
cells.    2.  small  branch  of  the  olfac-  .  , 
tory  nerve  of  the  frog,  separating  at  sidered  as  the  true  olfactory  organs,  is  represented  in  Fig. 

one  end  into  a  brush  of  varicose    r»o/<       T    J.-L.     /?          .LI  i±        i     •     TI  •      j.- 

fibrils.  3,  olfactory  cell  of  the  sheep.  234-    In  tne  fr°S> tnere  1S  a  nne>  hair-like  process  projecting 
from  each  cell  beyond  the  mucous  membrane,  which  has 

not  been  observed  in  man  or  the  mammalia.  The  great  delicacy  of  the  structures  enter- 
ing into  the  composition  of  the  olfactory  membrane  renders  the  investigation  of  the  ter- 
mination of  its  nervous  filaments  exceedingly  difficult. 

Properties  and  Functions  of  the  Olfactory  Nerves.— It  is  almost  certain  that  the  olfac- 
tory nerves  possess  none  of  the  general  properties  of  the  ordinary  nerves  belonging  to  the 
cerebro-spinal  system,  but  that  they  are  endowed  with  the  special  sense  of  smell  alone. 
As  far  as  we  know,  no  one  has  exposed  and  operated  upon  the  filaments  coming  from  the 
olfactory  bulbs  and  distributed  to  the  pituitary  membrane  in  living  animals;  but  experi- 


OLFACTORY   NERVES.  757 

ments  upon  the  nerves  behind  the  olfactory  bulbs  show  that  they  are  entirely  insensible 
to  ordinary  impressions.  Attempts  have  been  made  to  demonstrate,  in  the  human  sub- 
ject, the  special  properties  of  these  nerves,  by  passing  a  galvanic  current  through  the 
nostrils ;  but  the  situation  of  the  nerves  is  such  that  these  observations  are  of  necessity 
indefinite  and  unsatisfactory.  On  one  or  two  occasions,  in  witnessing  surgical  operations 
upon  the  upper  part  of  the  nasal  fossae,  we  have  been  struck  with  the  exceedingly  dull 
sensibility  of  its  mucous  membrane. 

The  question  as  to  whether  or  not  the  olfactory  nerves  endow  the  membrane  of  the 
nasal  fossse  with  the  sense  of  smell  hardly  demands  discussion  at  the  present  day.  It 
must  be  evident  to  any  one  who  reads  the  experiments  of  Magendie,  in  which  he  at- 
tempted to  show  that  the  sense  of  smell  was  retained  after  division  of  these  nerves,  that 
he  confused  the  general  sensibility  of  the  parts  with  the  peculiar  impressions  of  odors; 
and  the  cases,  especially  the  one  reported  by  Bernard,  in  the  human  subject,  in  which  it 
was  supposed  that  the  olfactory  sense  existed  notwithstanding  congenital  absence  of  the 
olfactory  nerves  and  bulbs,  are  by  no  means  satisfactory,  in  view  of  the  numerous  in- 
stances in  which  precisely  the  opposite  has  been  observed. 

Among  the  numerous  experiments  upon  the  higher  orders  of  animals,  in  which  the 
olfactory  nerves  have  been  divided,  we  may  cite,  as  open  to  no  objections,  those  of  Vul- 
pian  and  Philipaux,  upon  dogs.  It  is  well  known  that  the  sense  of  smell  is  usually  very 
acute  in  these  animals.  Upon  dividing  or  extirpating  the  olfactory  bulbs,  "  after  the 
animal  had  completely  recovered,  it  was  deprived  of  food  for  thirty-six  or  forty-eight 
hours ;  then,  in  its  absence,  a  piece  of  cooked  meat  was  concealed  in  a  corner  of  the 
laboratory.  Animals,  successfully  operated  upon,  then  taken  into  the  laboratory,  never 
found  the  bait ;  and  nevertheless,  care  had  been  taken  to  select  hunting-dogs."  This 
experiment  is  absolutely  conclusive ;  more  so  than  those  in  which  animals  deprived  of 
the  olfactory  bulbs  were  shown  to  eat  fa3ces  without  disgust,  for  this  sometimes  occurs  in 
dogs  that  have  not  been  mutilated. 

Comparative  anatomy  shows  that  the  olfactory  bulbs  are  generally  developed  in  pro- 
portion to  the  acuteness  of  the  sense  of  smell.  Pathological  facts  also  show,  in  the 
human  subject,  that  impairment  or  loss  of  the  olfactory  sense  is  coincident  with  injury 
or  destruction  of  these  ganglia.  Numerous  cases  have  been  reported  in  which  the  sense 
of  smell  was  lost  or  impaired  from  injury  to  the  olfactory  nerves.  In  nearly  all  of  the 
cases  on  record,  the  general  sensibility  of  the  nostrils  was  not  affected.  In  1864,  we  had 
an  opportunity  of  examining  the  following  very  remarkable  case  of  gunshot  wound  of  the 
head,  in  which,  among  other  injuries,  the  sense  of  smell  was  destroyed : 

The  patient  was  a  soldier,  twenty-three  years  of  age,  who  was  shot  through  the  head 
with  a  rifle-ball,  May  3,  1863.  The  ball  entered  on  the  left  side,  1£  inch  behind  and  £ 
of  an  inch  below  the  outer  canthus  of  the  eye,  emerging  at  nearly  the  corresponding 
point  on  the  opposite  side.  Small  pieces  of  bone  were  discharged  from  time  to  time  for 
three  months  from  openings  in  the  posterior  nares  and  the  throat.  He  was  examined 
May  10,  1864,  when  the  wounds  had  healed  with  falling  in  of  the  face  over  the  left 
malar  and  nasal  bones.  He  had  then  entirely  lost  the  power  of  distinguishing  odors. 
Upon  applying  acetic  acid  to  the  nostrils,  he  stated  that  he  felt  a  prickling  sensation,  but 
no  odor.  Dilute  ammonia  produced  a  warm  sensation.  Chloroform  gave  no  sensation. 
He  had  no  sensation  from  the  emanations  of  flowers.  There  was  loss  of  general  sensi- 
bility of  the  nasal  mucous  membrane  on  the  left  side,  with  diminished  sensibility  on  the 
right  side.  He  had  a  sensation,  not  very  definite,  when  in  water-closets,  where  (as  he 
was  told)  the  odor  was  very  offensive,  but  he  experienced  no  sensation  unless  the  emana- 
tions were  very  powerful.  Before  entering  the  army,  he  was  a  photographer  by  trade 
and  was  familiar  with  the  odors  of  acetic  acid  and  ammonia.  In  this  case,  it  is  almost 
certain  that  the  olfactory  nerves  had  been  divided,  although  other  injuries  undoubtedly 
existed. 


758  SPECIAL  SENSES. 

Mechanism  of  Olfaction. 

There  can  be  no  doubt  at  the  present  day  with  regard  to  the  mechanism  of  the  sense 
of  smell.  Substances  endowed  with  odorous  properties  give  off  material  emanations, 
which  must  come  in  contact  with  the  olfactory  membrane  before  their  peculiar  odor  is 
appreciated.  As  we  have  seen,  this  membrane  is  situated  high  up  in  the  nostrils,  is 
peculiarly  soft,  is  provided  with  numerous  glands,  by  the  secretions  of  which  its  surface 
is  kept  in  proper  condition,  and  it  possesses  the  peculiar  nerve-terminations  of  the  olfac- 
tory filaments. 

In  experimenting  upon  the  sense  of  smell,  it  has  been  found  quite  difficult  to  draw  the 
exact  line  of  distinction  between  impressions  of  general  sensibility  and  those  which  attack 
the  special  sense,  or,  in  other  words,  between  irritating  and  odorous  emanations;  and 
the  vapors  of  ammonia,  acetic  acid,  nitric  acid,  etc.,  undoubtedly  possess  irritating 
properties  which  greatly  overshadow  their  odorous  qualities.  It  is  unnecessary,  in  this 
connection,  to  discuss  the  different  varieties  of  odors  recognized  by  some  of  the  earlier 
writers,  as  the  fragrant,  aromatic,  fetid,  nauseous,  etc.,  distinctions  sufficiently  evident 
from  their  mere  enumeration ;  and  it  is  plain  enough  that  there  are  emanations,  like 
those  from  delicately-scented  flowers,  which  are  easily  recognizable  by  the  sense  of 
smell  while  they  make  no  impression  upon  the  ordinary  sensory  nerves.  The  very 
marked  individual  differences  in  the  delicacy  of  the  olfactory  organs  in  the  human  sub- 
ject and  in  different  animals  is  an  evidence  of  this  fact.  Hunting-dogs  recognize  odors 
to  which  we  are  absolutely  insensible ;  and  certain  races  of  men  are  said  to  possess  a 
wonderful  delicacy  of  the  sense  of  smell.  Like  all  of  the  other  special  senses,  olfaction 
may  be  cultivated  by  attention  and  practice,  as  is  exemplified  in  the  delicate  discrimina- 
tion of  wines,  qualities  of  drugs,  etc.,  by  experts. 

After  what  we  have  said  concerning  the  situation  of  the  true  olfactory  membrane  in 
the  upper  part  of  the  nasal  fossa3  and  the  necessity  of  particles  impinging  upon  this  mem- 
brane in  order  that  their  odorous  properties  may  be  appreciated,  it  is  almost  unnecessary 
to  state  that  the  passage  of  odorous  emanations  to  this  membrane  by  inspiring  through 
the  nostrils  is  essential  to  olfaction,  so  that  animals  or  men,  after  division  of  the  tracheci, 
being  unable  to  pass  the  air  through  the  nostrils,  are  deprived  of  the  sense  of  smell.  The 
act  of  inhalation  through  the  nose,  when  we  wish  to  appreciate  a  particular  odor,  is  an 
illustration  of  the  mechanism  by  which  the  odorous  particles  may  be  brought  at  will  in 
contact  with  the  olfactory  membrane. 

It  is  a  curious  point  to  determine  whether  the  sense  of  smell  be  affected  by  odors 
passing  from  within  outward  through  the  nasal  fossae.  Persons  who  have  offensive  ema- 
nations from  the  respiratory  organs  usually  are  not  aware,  from  their  own  sensations, 
of  any  disagreeable  odor.  This  fact  is  explained  by  Longet  on  the  supposition  that  the 
olfactory  membrane  becomes  gradually  accustomed  to  the  odorous  impression,  and  there- 
fore it  is  not  appreciated.  This  is  an  apparently  satisfactory  explanation,  for  we  could 
hardly  suppose  that  the  direction  of  the  emanations,  provided  they  came  in  contact  with 
the  membrane,  could  modify  their  effects.  He  cites  a  case  of  cancer  of  the  stomach, 
in  which  the  vomited  matters  were  exceedingly  fetid.  At  first,  the  patient,  when  he 
expired  the  gases  from  the  stomach  through  the  nostrils,  perceived  a  disagreeable  odor  at- 
each  expiration ;  but  little  by  little  this  impression  disappeared. 

Relations  of  Olfaction  to  the  Sense  of  Taste. — The  relations  of  the  sense  of  smell  to 
gustation  are  very  intimate.  In  the  appreciation  of  delicate  shades  of  flavor,  it  is  well 
known  that  the  sense  of  olfaction  plays  so  important  a  part,  that  it  can  hardly  be  sepa- 
rated from  gustation.  The  common  practice  of  holding  the  nose  when  disagreeable 
remedies  are  swallowed  is  another  illustration  of  the  connection  between  the  two  senses. 
In  most^  cases  of  anosmia,  there  is  inability  to  distinguish  delicate  flavors ;  and  patients 
can  distinguish  by  the  taste  only  sweet,  saline,  acid,  and  bitter  impressions. 


GUSTATION.  759 

It  is  undoubtedly  true  that  we  lose  the  delicacy  of  the  sense  of  taste  when  the  sense 
of  smell  is  abolished.  The  experiment  of  tasting  wines  blindfolded  and  with  the  nostrils 
plugged,  and  the  partial  loss  of  taste  during  a  severe  coryza,  are  sufficiently  familiar  illus- 
trations of  this  fact.  In  the  great  majority  of  cases,  when  there  is  complete  anosmia,  the 
taste  is  sensibly  impaired;  and,  in  cases  in  which  this  does  not  occur,  it  is  probable 
that  the  savory  emanations  pass  from  the  mouth  to  the  posterior  portion  of  the  nasal 
fossas,  and  that  here  the  mucous  membrane  is  not  entirely  insensible  to  special  impres- 
sions. 

It  is  unnecessary,  in  this  connection,  to  describe  fully  the  reflex  phenomena  which  fol- 
low impressions  made  upon  the  olfactory  membrane.  The  odor  of  certain  sapid  sub- 
stances, under  favorable  conditions,  will  produce  an  abundant  secretion  of  saliva  and  even 
of  gastric  juice,  as  has  been  shown  by  experiments  upon  animals.  Other  examples  of  the 
effects  of  odorous  impressions  of  various  kinds  are  sufficiently  familiar. 
. 

Gustation. 

The  special  sense  of  taste  enables  us  to  appreciate  what  is  known  as  the  savor  of  cer- 
tain substances  introduced  into  the  mouth ;  and  this  sense  exists,  in  general  terms,  in 
parts  supplied  by  filaments  from  the  lingual  branch  of  the  fifth  and  the  glosso-pharyngeal 
nerves. 

It  is  somewhat  difficult  to  define  precisely  what  is  meant  by  savory  substances.  The 
word  savory  is  frequently  used  so  as  to  include  the  quality  of  odor ;  and,  indeed,  the 
senses  of  gustation  and  olfaction  are  quite  closely  connected.  Almost  all  substances  that 
affect  the  sense  of  taste  possess  a  certain  odor,  and  taste  and  smell  are  thus  simultaneously 
impressed.  Medicinal  articles  of  a  disagreeable  taste  may  sometimes  be  swallowed  with- 
out making  a  very  disagreeable  impression,  if  the  nares  be  closed.  Again,  when  the 
nares  are  closed  or  when  the  sense  of  smell  is  rendered  obtuse  by  an  affection  of  the 
Schneiderian  membrane,  it  is  difficult  to  distinguish  delicate  shades  of  flavor,  as  the  differ- 
ences in  wines.  This  is  a  matter  of  common  observation  and  remark.  There  are,  also, 
certain  articles  which  have  a  repulsive  odor,  the  taste  of  which  is  not  disagreeable,  such 
as  some  varieties  of  old  cheese.  As  a  rule,  however,  articles  agreeable  to  the  taste  pos- 
sess an  agreeable  odor,  and  the  senses  of  taste  and  smell  are  not  easily  separated  from 
each  other.  These  facts  have  led  to  a  distinction — which  cannot,  however,  be  always 
made  with  accuracy — between  true  tastes  and  flavors.  It  is  assumed  by  some  physiolo- 
gists, that  the  true  tastes  are  quite  simple,  presenting  the  qualities  which  we  recognize  as 
sweet,  acid,  saline,  and  bitter ;  while  the  more  delicate  shades  of  what  are  called  flavors 
nearly  always  involve  olfactory  impressions,  which  it  is  difficult  to  separate  entirely  from 
^station. 

If  we  apply  the  term  savor  exclusively  to  the  quality  which  makes  an  impression  upon 
the  sense  of  taste,  we  recognize  that  the  sensation  is  special  in  its  character  and  different 
from  the  tactile  sensibility  of  the  parts  involved  and  from  the  sensation  of  temperature. 
The  terminal  filaments  of  the  gustatory  nerves  are  impressed  by  the  actual  contact  of 
savory  substances,  which  must,  of  necessity,  be  soluble.  To  a  certain  extent,  there  is  a 
natural  classification  of  savors,  some  of  which  are  agreeable,  and  others  disagreeable ;  but 
even  this  distinction  is  modified  by  habit,  education,  and  various  other  circumstances. 
Articles  that  are  unpleasant  in  early  life  often  become  agreeable  in  later  years.  Inasmuch 
as  the  taste  is,  to  some  extent,  an  expression  of  the  nutritive  demands  of  the  system,  it  is 
found  to  vary  under  different  conditions.  Chlorotic  females,  for  example,  frequently 
crave  the  most  unnatural  articles,  and  these  morbid  tastes  may  disappear  under  appro- 
priate treatment.  Inhabitants  of  the  frigid  zones  seem  to  crave  fatty  articles  and  will 
even  drink  rancid  oils  with  avidity.  Patients  often  become  accustomed  to  the  most  dis- 
agreeable remedies  and  take  them  without  repugnance.  Again,  the  most  savory  dishes 
may  even  excite  disgust,  when  the  sense  of  taste  has  become  cloyed,  while  abstinence 


760  SPECIAL  SENSES. 

sometimes  lends  a  delicious  flavor  to  the  simplest  articles  of  food.  The  taste  for  certain 
articles  is  certainly  acquired,  and  this  is  almost  always  true  of  tobacco,  now  so  largely 
used  in  civilized  countries. 

Any  thing  more  than  the  simplest  classification  of  savors  is  difficult,  if  not  impossible. 
We  recognize  that  certain  articles  are  bitter  or  sweet,  empyreumatic  or  insipid,  acid  or 
alkaline,  etc.,  but,  beyond  these  simple  distinctions,  the  shades  of  difference  are  closely 
connected  with  olfaction  and  are  too  delicate  and  numerous  for  detailed  description. 
Many  persons  are  comparatively  insensible  to  nice  distinctions  of  taste,  while  others  recog- 
nize with  facility  the  most  delicate  differences.  Strong  impressions  may  remove,  for  a 
time,  the  appreciation  of  less  powerful  and  decided  flavors.  The  tempting  of  the  appetite 
by  a  proper  gradation  of  gustatory  and  odorous  impressions  is  illustrated  in  the  modern 
cuisine,  which  aims  at  an  artistic  combination  and  succession  of  dishes  and  wines,  so  that 
the  agreeable  sensations  are  prolonged  to  the  utmost  limit.  This  may  often  be  regarded 
as  a  violation  of  strictly  hygienic  principles,  but  it  none  the  less  exemplifies  the  cultiva- 
tion of  the  sense  of  taste. 

In  discussing  the  physiology  of  taste,  we  shall  avoid  an  elaborate  and  artificial  classi- 
fication of  savory  articles,  and  shall  use  the  terms  sweet,  acid,  bitter,  etc.,  as  they  are 
commonly  understood.  We  shall  first  describe  the  physiological  anatomy  and  properties 
of  the  gustatory  nerves,  and  then  consider  the  mechanism  of  gustation,  the  special  organs 
of  taste,  and  the  probable  mode  of  connection  between  the  organs  of  taste  and  the  nerves. 

Nerves  of  Taste. — Two  nerves,  the  chorda  tympani  and  the  glosso-pharyngeal,  preside 
over  the  sense  of  taste.  These  nerves  seem  to  be  distributed  to  distinct  portions  of  the 
gustatory  apparatus  and  to  have  somewhat  different  functions.  The  chorda  tympani  has 
already  been  referred  to  as  one  of  the  branches  of  the  facial ;  the  glosso-pharyngeal,  one 
of  the  nerves  of  the  eighth  pair,  has  not  yet  been  described. 

Chorda  Tympani. — In  the  description  we  have  given  of  the  facial,  the  chorda  tympani 
is  spoken  of  as  the  fourth  branch.  It  passes  through  the  tympanum,  between  the  ossicles 
of  the  ear,  and  joins  the  inferior  maxillary  division  of  the  fifth,  at  an  acute  angle,  between 
the  two  pterygoid  muscles,  becoming  so  closely  united  with  it  that  it  cannot  be  followed 
farther  by  ordinary  dissection.  (See  Fig.  202,  p.  622.)  It  is  impossible  to  determine  with 
certainty  from  what  root  the  filaments  of  this  branch  derive  their  origin,  whether  from 
the  main  trunk  or  the  intermediary  nerve  of  Wrisberg;  but  experiments  have  shown  that 
it  possesses  functions  entirely  distinct  from  those  of  the  other  branches  of  the  facial.  The 
lingual  branch  of  the  inferior  maxillary  division  of  the  fifth  has  been  called  the  gustatory 
branch  ;  but  this  is  an  error ;  for,  as  we  shall  see,  the  fifth  has  nothing  to  do  with  gusta- 
tion, except  that  it  is  joined  with  filaments  of  the  chorda  tympani,  which  reach  the  tongue 
through  the  lingual  branch. 

As  regards  the  course  of  the  filaments  of  the  chorda  tympani  after  this  nerve  has  joined 
the  fifth,  there  can  be  no  doubt,  both  from  the  effect  upon  taste  and  the  alteration  of 
the  nerve-fibres  following  its  division.  Vulpian  and  Prevost,  by  the  so-called  Wallerian 
method,  after  dividing  the  chorda  tympani,  found  degenerated  fibres  at  the  terminations 
of  the  lingual  branch  of  the  fifth  in  the  mucous  membrane  of  the  tongue,  the  fibres  being 
examined  ten  days  or  more  after  the  section.  It  is  well  known  that,  a  number  of  days 
after  the  section  of  a  nerve,  its  fibres  of  distribution  undergo  change,  and  these  observa- 
tions leave  no  doubt  of  the  fact  that  the  chorda  tympani  is  really  distributed  to  the  lingual 
mucous  membrane.  Observations  upon  the  sense  of  taste  show  that  the  chorda  tympani 
is  distributed  to  about  the  anterior  two-thirds  of  the  tongue. 

The  general  properties  of  the  chorda  tympani  have  only  been  ascertained  by  observa- 
tions made  after  its  paralysis  or  division.  All  experiments  in  which  excitation  has  been 
applied  directly  to  the  nerve  in  living  animals  have  been  negative  in  their  results. 
Longet  states  that,  when  the  nerve  has  been  isolated  as  completely  as  possible  and  all 
reflex  action  is  excluded,  its  galvanization  produces  no  movement  in  the  tongue. 


GUSTATION.  761 

It  is  now  established  beyond  question  that,  in  cases  of  facial  palsy  in  which  the  lesion 
affects  the  root  so  deeply  as  to  involve  the  chorda  tympani,  there  is  loss  of  taste  in  the 
anterior  two-thirds  of  the  tongue,  tactile  sensibility  being  unaffected;  and  numerous 
cases  illustrating  this  fact  have  been  cited  by  various  authors.  Aside  from  cases  of 
paralysis  of  the  facial  with  impairment  of  taste,  in  which  the  general  sensibility  of  the 
tongue  is  intact,  numerous  instances  are  on  record  of  affections  of  the  fifth  pair,  in  which 
the  tongue  is  absolutely  insensible  to  ordinary  impressions,  the  sense  of  taste  being  pre- 
sarved.  A  number  of  such  cases  have  been  reported,  which  show  conclusively  that  the 
fifth  pair  presides  over  general  sensibility  only,  and  that  it  is  not  a  gustatory  nerve,  except 
by  virtue  of  filaments  derived  from  the  chorda^  tympani. 

Passing  from  the  consideration  of  pathological  cases  to  experiments  upon  living  ani- 
mals, the  results  are  equally  satisfactory.  Although  it  is  somewhat  difficult  to  observe 
impairment  of  taste  in  animals,  Bernard  and  others  have  succeeded  in  training  dogs  and 
cats  so  as  to  observe  the  effects  of  colocynth  and  various  sapid  substances  applied  to  the 
tongue.  In  a  great  number  of  experiments  of  this  kind,  it  has  been  observed  that,  after 
section  of  the  chorda  tympani  or  of  the  facial  so  as  to  involve  the  chorda  tympani,  the 
sense  of  taste  is  abolished  in  the  anterior  two-thirds  of  the  tongue  on  the  side  of  the  sec- 
tion. However  this  result  may  be  explained,  the  fact  remains,  that  section  of  the  nerve 
in  the  lower  animals  is  followed  by  the  same  results  as  those  observed  in  pathological 
observations.  In  a  remarkable  case  reported  by  Moos,  the  introduction  of  an  artificial 
membrana  tympani  was  followed  by  loss  of  taste  upon  the  corresponding  side  of  the 
tongue,  and  upon  both  sides,  when  a  membrane  was  introduced  into  each  ear.  This  dis- 
appeared when  the  membranes  were  removed,  and  the  phenomena  were  referred  to 
pressure  upon  the  chorda  tympani.  Experimenters  are  somewhat  at  variance  with 
regard  to  the  effects  observed  upon  animals,  some  asserting  that  the  sensations  of  taste 
are  simply  delayed  in  their  manifestation  ;  but  we  must  remember  the  difficulty  of  such 
observations,  and  we  are  to  rely  mainly  upon  the  unmistakable  phenomena  noted  in 
cases  of  affection  of  the  chorda  tympani  in  the  human  subject. 

It  seems  tolerably  certain,  first,  that  the  gustatory  filaments  of  the  lingual  branch  of 
the  fifth  are  derived  exclusively  from  the  chorda  tympani ;  second,  that  the  chorda  tym- 
pani, viewed  as  a  gustatory  nerve,  is  really  a  branch  of  the  facial ;  third,  that  many  cases 
of  paralysis  of  the  entire  large  root  of  the  fifth,  in  the  human  subject,  present  loss  of 
general  sensibility  in  the  tongue  and  no  alteration  of  taste ;  and  fourth,  that  paralysis  ot 
the  facial,  behind  the  origin  of  the  chorda  tympani,  is  attended  with  loss  of  taste  in  the 
anterior  two-thirds  of  the  tongue,  without  any  affection  of  the  general  sensibility  of  this 
organ. 

As  a  summary  of  our  knowledge  regarding  the  gustatory  properties  of  the  anterior 
two-thirds  of  the  tongue,  certainly  in  the  human  subject,  it  may  be  stated  without 
reserve,  that  these  properties  depend  upon  the  chorda  tympani,  its  gustatory  filaments 
being  derived  from  the  facial  and  taking  their  course  to  the  tongue  with  the  lingual 
branch  of  the  inferior  maxillary  division  of  the  fifth.  In  addition,  the  lingual  branch  of 
the  fifth  contains  filaments,  derived  from  the  large  root  of  this  nerve,  which  endow  the 
mucous  membrane  with  general  sensibility. 

Glosso-Pharyngeal  Nerve  (First  Division  of  the  Eighth}. — The  glosso-pharyngeal  is 
distributed  to  those  portions  of  the  gustatory  mucous  membrane  not  supplied  by  filaments 
from  the  chorda  tympani.  It  is  undoubtedly  a  nerve  of  taste ;  and  the  question  of  its 
other  functions  will  be  fully  considered  in  connection  with  its  general  properties,  as  well 
as  the  differences  between  this  nerve  and  the  chorda  tympani.  We  have  mentioned  this 
nerve  in  another  chapter  as  the  first  division  of  the  eighth  pair  according  to  the  classifi- 
cation of  Willis,  but  we  have  to  treat  of  its  physiological  anatomy  in  this  connection,  as 
its  most  important  function  is  in  connection  with  gustation. 

Physiological  Anatomy  of  the  Glosso-Pharyngeal. — The  apparent  origin  of  the  glosso- 
pharyngeal  is  from  the  groove  between  the  lateral  tracts  of  the  medulla  oblongata  and 


762 


SPECIAL  SENSES. 


the  inferior  peduncle  of  the  cerebellum,  between  the  roots  of  the  auditory  nerve  above 
and  the  pneumogastric  below.  A  number  of  its  filaments  of  origin  come  from  the 
medulla  and  a  portion  from  the  peduncle.  The  deep  origin  is  nearly  the  same  as  that  of 
the  pneumogastric,  its  filaments  arising  primarily  from  the  gray  substance  of  the  medulla 
oblongata.  From  this  origin,  the  filaments  pass  forward  and  outward  to  the  posterior 
foramen  lacerum,  which  the  nerve  enters  in  company  with  the  pneumogastric,  the  spinal 
accessory,  and  the  internal  jugular  vein.  At  the  upper  portion  of  the  foramen,  is  a  small 
ganglion,  the  jugular  ganglion,  including  only  a  portion  of  the  root.  Within  the  foramen, 
is  the  main  ganglion,  including  aU  of  the  filaments  of  the  trunk,  called  the  petrous  gan- 
glion, or  the  ganglion  of  Andersch,  after  the  anatomist  by  whom  it  was  first  described. 

At  or  near  the  ganglion  of  Andersch,  the  glosso-pharyngeal  usually  receives  a  delicate 
filament  from  the  pnenmogastric.  This  communication  is  sometimes  wanting.  The 
same  may  be  said  of  a  small  filament  passing  to  the  glosso-pharyngeal  from  the  facial, 
which  is  not  constant.  Branches  from  the  glosso-pharyngeal  go  to  the  otic  ganglion  and 
to  the  carotid  plexus  of  the  sympathetic. 


FIG.  235. — Glosso-pharyngeal  nerve.      (Sappey.) 

1.  large  root  of  the  fifth  nerve ;  2,  ganglion  of  Gasser ;  3,  ophthalmic  division  of  the  fifth ;  4,  superior  maxillary  division ; 
5,  inferior  maxillary  division ;  6, 10,  lingual  branch  of  the  fifth,  containing  the  filaments  of  the  chorda  tym- 
pani  ;  7,  branch  from  the  sublingual  to  the  lingual  branch  of  the  fifth ;  8,  chorda  tympani  ;  9,  inferior  dental 
nerve;  11,  submaxillary  ganglion;  12,  mylo-hyoid  branch  of  the  inferior  dental  nerve;  13,  anterior  belly  of  the 
digastric  muscle ;  14,  section  of  the  mylo-hyoid  muscle ;  15,  18,  glosso-pharyngeal  nerve;  16,  ganglion  of  An- 
dersch ,'  17,  branches  from  tlw,  glosso-pharyngeal  to  the  sti/lo-glossus  and  the  stylo-pharyngeus  muscles ; 
19, 19.  pneumogastric ;  20,  21,  ganglia  of  the  pneumogastric ;  22,  22,  superior  laryngeal  nerve ;  23,  spinal  accessory ; 
24,  25,  26,  27,  28,  sublingual  nerve  and  branches. 

The  distribution  of  the  glosso-pharyngeal  is  quite  extensive.  The  tympanic  branch, 
the  nerve  of  Jacobson,  arises  from  the  anterior  and  external  part  of  the  ganglion  of 
Andersch,  and  enters  the  cavity  of  the  tympanum,  where  it  divides  into  six  branches. 
Of  these  six  branches,  two  posterior  are  distributed  to  the  mucous  membrane  of  the 
fenestra  rotunda  and  the  membrane  surrounding  the  fenestra  ovalis ;  two  anterior  are 


GUSTATION.  763 

distributed,  one  to  the  carotid  canal,  where  it  anastomoses  with  a  hranch  from  the  supe- 
rior cervical  ganglion,  and  the  other  to  the  mucous  membrane  of  the  Eustachian  tube  ; 
two  superior  branches  are  distributed  to  the  otic  ganglion  and,  as  is  stated  by  some  anat- 
omists, to  the  spheno-palatine  ganglion. 

A  little  below  the  posterior  foramen  lacerum,  the  glosso-pharyngeal  sends  branches 
to  the  posterior  belly  of  the  digastric  and  to  the  stylo-hyoid  muscle.  There  is  also  a 
branch  which  joins  a  filament  from  the  facial  to  the  stylo-glossus. 

Opposite  the  middle  constrictor  of  the  pharynx,  three  or  four  branches  join  branches 
from  the  pneumogastric  and  the  sympathetic  to  form  together  the  pharyngeal  plexus. 
This  plexus  contains  numerous  ganglionic  points,  and  filaments  of  distribution  from  the 
three  nerves  go  to  the  mucous  membrane  and  to  the  constrictors  of  the  pharynx.  Prob- 
ably, the  mucous  membrane  is  supplied  by  the  glosso-pharyngeal.  As  we  have  stated  in 
another  chapter,  it  is  probable  that  the  muscles  of  the  pharynx  are  supplied  by  filaments 
from  the  pneumogastric,  which  are  originally  derived  from  the  spinal  accessory. 

Near  the  base  of  the  tongue,  branches  are  sent  to  the  mucous  membrane  covering  the 
tonsils  and  the  soft  palate. 

The  lingual  branches  penetrate  the  tongue  about  midway  between  its  border  and 
centre  and  are  distributed  to  the  mucous  membrane  at  its  base,  being  probably  connected 
with  the  papillsB. 

General  Properties  of  the  Glosso- Pharyngeal. — As  in  the  case  of  other  sensory  nerves 
emerging  from  the  cranial  cavity,  it  is  important,  in  studying  the  general  properties  of 
the  glosso-pharyngeal,  to  make  our  observations  under  certain  conditions.  First,  it  must 
be  remembered  that  this  nerve  contracts  anastomoses  a  short  distance  from  its  origin. 
As  we  desire  to  know  the  properties  of  the  original  filaments  of  the  nerve,  we  must 
operate  upon  it  before  it  has  received  communicating  fibres.  Next,  in  irritating  sensory 
nerves,  we  are  liable  to  produce  reflex  contractions.  To  avoid  this,  the  nerve  must  be 
divided,  when  the  reflex  contractions  will  only  follow  stimulation  of  the  central  end.  It 
is  probably  from  a  neglect  of  these  essential  experimental  conditions,  that  the  results  of 
direct  observation  have  been  so  discordant  in  the  hands  of  different  physiologists. 

To  begin  with,  we  shall  assume  that  the  glosso-pharyngeal  nerve  must  be  irritated  be- 
tween its  origin  and  the  ganglion  of  Andersch,  in  order  to  avoid  anastomosing  filaments 
from  motor  nerves,  and  that  the  nerve  must  be  divided  and  irritation  be  applied  to  its 
peripheral  end,  to  avoid  reflex  movements.  Assuming  these  conditions  as  essential,  we 
can  discard  most  of  the  earlier  experiments,  as  open  to  the  objections  we  have  mentioned. 
Longet,  operating  upon  horses  and  dogs,  after  removal  of  the  cerebral  lobes  and  division  of 
the  glosso-pharyngeal,  found  that  galvanization  of  the  peripheral  extremity  of  the  nerve 
did  not  produce  movements  of  the  palate  or  pharynx ;  and,  from  these  experiments,  he 
concludes  that  the  nerves  are  exclusively  sensory  at  their  roots,  or,  at  least,  that  they  do 
not  contain  motor  filaments.  In  another  chapter,  under  the  head  of  movements  of  the 
palate  and  uvula,  we  have  cited  in  detail  a  series  of  experiments  which  illustrate  the 
reflex  movements  of  the  velum  palati  through  the  facial,  produced  by  galvanization  of 
the  glosso-pharyngeal.  As  a  complement  to  the  first  experiments  of  Longet,  just  cited, 
the  same  observer  noted  contractions  of  the  pharyngeal  muscles  following  galvanization 
of  the  peripheral  end  of  the  divided  nerve  in  the  neck,  which  could  only  be  produced  by 
the  action  of  motor  anastomosing  filaments. 

As  regards  general  sensibility,  there  can  be  no  doubt  of  the  fact  that  the  glosso- 
pharyngeal  is  sensory,  although  its  sensibility  is  somewhat  obtuse.  In  the  experiments  in 
which  the  nerve  has  seemed  to  be  insensible  to  ordinary  impressions,  it  is  probable  that 
the  animals  operated  upon  had  been  exhausted  more  or  less  by  pain  and  loss  of  blood  in 
the  operation  of  exposing  the  nerve,  which,  it  is  well  known,  abolish  the  sensibility  of 
some  of  the  nerves.  Longet  states  distinctly  that,  unless  the  animals  (dogs)  be  already 
exhausted  by  resistance  during  the  operation,  they  have  always  appeared  to  suffer  pain 
on  pinching  or  dividing  the  glosso-pharyngeal. 


764  SPECIAL  SENSES. 

Experiments  upon  the  glosso-pharyngeal  are  not  very  definite  and  satisfactory  in  their 
results  as  regards  the  general  sensibility  of  the  base  of  the  tongue,  the  palate,  and  the 
pharynx.  The  sensibility  of  these  parts  seems  to  depend  chiefly  upon  branches  of  the  fifth 
passing  to  the  mucous  membrane  through  MeckeFs  ganglion.  Experiments  show,  also, 
that  the  reflex  phenomena  of  deglutition  take  place  mainly  through  these  branches  of  the 
fifth,  and  that  the  glosso-pharyngeal  has  little  or  nothing  to  do  with  the  process.  In  fact, 
after  division  of  both  glosso-pharyngeal  nerves,  deglutition  does  not  seem  to  be  affected. 

With  these  remarks,  we  dismiss  the  functions  of  the  glosso-pharyngeals  as  nerves  of 
general  sensibility  and  shall  consider  in  detail  their  relations  to  the  sense  of  taste. 

Relations  of  the  Glosso-Pharyngeal  Nerves  to  Gustation.— Relying  upon  experiments 
on  the  inferior  animals,  particularly  dogs,  it  seems  pretty  certain  that  there  are  two 
nerves  presiding  over  the  sense  of  taste :  The  chorda  tympani  gives  this  sense  to  the 
anterior  portion  of  the  tongue  exclusively,  probably  the  anterior  two-thirds ;  the  glosso- 
pharyngeal  supplies  this  sense  to  the  posterior  portion  of  the  tongue  ;  the  chorda  tympani 
seems  to  have  nothing  to  do  with  general  sensibility ;  while  the  glosso-pharyngeal  is  an 
ordinary  sensory  nerve,  as  well  as  a  nerve  of  special  sense. 

Where  there  are  such  differences  in  the  delicacy  of  the  sense  of  taste  as  exist  usually 
in  different  individuals,  it  must  be  difficult  to  describe  with  accuracy  delicate  shades  of 
savor,  particularly  in  alimentary  substances ;  but  the  distinct  impressions  of  acidity  or 
bitter  quality  are  easily  recognizable.  It  is  certain,  however,  that  saline,  acid,  and  styptic 
tastes  are  best  appreciated  through  the  chorda  tympani,  and  that  sweet,  alkaline,  bitter, 
and  metallic  impressions  are  received  mainly  by  the  glosso-pharyngeal. 

Mechanism  of  Gustation. — The  mode  in  which  sapid  substances  are  brought  in  con- 
tact with  the  organ  of  taste  is  so  simple,  that  we  need  only  allude  to  it,  before  we  study 
the  anatomy  of  the  parts  directly  concerned  and  their  connections  with  the  terminal 
filaments  of  the  gustatory  nerves.  In  the  first  place,  the  articles  which  make  the  special 
impression  are  in  solution ;  introduced  into  the  mouth,  they  increase  the  flow  of  saliva, 
the  reflex  action  involving  chiefly  the  submaxillary  and  sublingual  glands ;  there  is  usu- 
ally more  or  less  mastication,  which  increases  the  flow  of  the  parotid  saliva  ;  and,  during 
the  acts  of  mastication  and  the  first  stages  of  deglutition,  the  sapid  substances  are  dis- 
tributed over  the  gustatory  membrane,  so  much  so,  indeed,  that  it  is  difficult  to  exactly 
locate  the  seat  ot  the  special  impression.  In  this  way,  by  the  movements  of  the  tongue, 
aided  by  an  increased  flow  of  saliva,  the  actual  contact  of  the  savory  articles  is  rapidly 
effected.  The  thorough  distribution  of  these  substances  over  the  tongue  and  the  mucous 
membrane  of  the  general  buccal  cavity  leads  to  a  certain  amount  of  confusion  in  our 
appreciation  of  the  special  impressions ;  and,  in  order  to  ascertain  if  different  portions 
of  the  membrane  possess  different  properties,  it  is  necessary  to  make  careful  experiments, 
limiting  the  points  of  contact  as  closely  as  possible.  This  has  been  done,  with  the  result 
of  showing  that  the  true  gustatory  organ  is  quite  restricted  in  its  extent,  and,  as  such,  it 
demands  special  anatomical  description. 

Physiological  Anatomy  of  the  Organ  of  Taste. — Recent  anatomical  and  physiological 
researches  have  shown  that,  at  least  in  the  human  subject,  the  organ  of  taste  is  probably 
confined  to  the  dorsal  surface  of  the  tongue.  When  we  examine  the  structure  of  the 
mucous  membrane  of  the  mouth,  tongue,  and  palate,  we  find  that  the  upper  surface  of 
the  tongue  presents  numerous  papillae,  called,  in  .contradistinction  to  the  filiform  papilla?, 
fungiform  and  circumvallate.  These  are  not  found  on  its  under  surface  or  anywhere 
except  on  the  superior  portion.  It  is  now  pretty  well  established  that  the  circumvallate 
and  fungiform  papillae  alone  are  the  organs  of  taste.  Camerer,  in  some  recent  experi- 
ments upon  the  gustatory  organs  by  the  application  of  solutions  to  different  parts  through 
fine  glass  tubes,  concluded  that  the  parts  around  a  papilla  have  no  gustatory  sensibility,  but 
that  different  savors  can  be  distinguished  when  a  single  papilla  is  touched.  These  obser- 
vations give  a  new  importance  to  the  peculiar  papillae  of  the  tongue,  and  we  therefore 
present  a  description  of  their  arrangement  and  structure. 


GUSTATION. 


765 


In  Fig.  236,  which  represents  the  dorsal  surface  of  the  tongue,  the  large,  circumvallate 
papillae,  which  usually  number  from  seven  to  twelve,  are  seen  in  the  form  of  a  V,  occu- 
pying the  base  of  the  tongue.  The  fungiform  papillae  are  scattered  over  the  surface  but 
are  most  numerous  at  the  point  and  near  the  borders.  Both  of  these  varieties  of  papillaa 
are  distinguishable  by  the  naked  eye. 

The  circumvallate  papillae  are  simply  enlarged  fungiform  papillae,  each  one  surrounded 
by  a  circular  ridge,  or  wall,  and  covered  by  numerous  small,  secondary  papillaa.  The 
fungiform  papillae  have  a  short,  thick  pedicle  and  enlarged,  rounded  extremities.  Accord- 


FIG.  236.— Papillae,  of  the  tongue,    (Sappey.) 

1, 1,  circumvallate  papillae;  2,  median  circumvallate  papilla,  which  entirely  fills  the  foramen  caecum;  3,  3,  3,  3,  fungi- 
form  papillae ;  4,  4,  filiform  papillae ;  5, 5,  vertical  folds  and  furrows  of  the  border  of  the  tongue ;  6,  6,  6,  6,  glands  at 
the  base  of  the  tongue  ;  7,  7,  tonsils ;  8,  epiglottis ;  9,  median  glosso-epiglottidean  fold. 


ing  to  Sappey,  from  one  hundred  and  fifty  to  two  hundred  of  these  can  easily  be  counted. 
These,  also,  present  secondary  papillae  on  their  surface.  When  the  mucous  membrane  of 
the  tongue  is  examined  with  a  low  magnifying  power,  particularly  after  maceration  in 
acetic  or  dilute  hydrochloric  acid,  their  structure  is  readily  observed.  They  are  abun- 
dantly supplied  with  blood-vessels  and  nerves. 

Taste- Buds,  or  Taste- Beakers. — A  few  years  ago,  Loven  and,  a  little  later,  Schwalbe 
described,  under  these  names,  peculiar  structures,  which  are  supposed  to  be  the  true 


766 


SPECIAL  SENSES. 


organs  of  taste.  They  are  found  on  the  lateral  slopes  of  the  circumvallate  papillaa  and 
occasionally  on  the  fungiform  papillse.  The  structure  of  these  organs  is  very  simple. 
They  consist  of  flask-like  collections  of  spindle-shaped  cells,  which  are  received  into  little 
excavations  in  the  epithelial  covering  of  the  mucous  membrane,  the  bottom  resting  upon 
the  connective-tissue  layer.  Their  form  is  ovoid,  and,  at  the  neck  of  the  flask,  is  a 


FIG.  237.  FKJ.  238. 

Varieties  ofpapillce,  of  the  tongue.    (Sappey.) 

Fig.  237.—  Medium-sized  circumvallate  papilla:  1,  papilla,  the  base  only  being  apparent:  it  is  seen  that  the  base  is 
covered  with  secondary  papillae  ;  2,  groove  between  the  papilla  and  the  surrounding  wall  ;  3,  3,  wall  of  the  papilla. 
Fig.  238.—  Fungiform,  filiform,  and  hemispherical  papillae  :  1,1,  two  fungiform  papillae,  covered  with  secondary  pa- 
pillae; 2,2,  2,  filiform  papillae;  8,  a  filiform  papilla,  the  prolongations  of  which  are  turned  outward;  4.  a  filiform 
papilla,  with  vertical  prolongations  ;  5,  5,  small  filiform  papillae,  with  the  prolongations  turned  inward  ;  6,  6,  fili- 
form papillae,  with  striations  at  their  bases  ;  7,  7,  hemispherical  papillae,  slightly  apparent,  situated  between  the 
fungiform  and  the  filiform  papillae. 

rounded  opening,  called  the  taste-pore.  Their  length  is  from  ^7  to  -g^-,  and  their  trans- 
verse diameter,  about  -^  of  an  inch.  The  cavity  of  the  taste-beakers  is  filled  with  cells, 
of  which  two  kinds  are  described.  The  first  variety,  the  outer  cells,  or  the  cover-cells, 
are  spindle-shaped,  and  curved  to  correspond  to  the  wall  of  the  beaker.  These  come  to 
a  point  at  the  taste-pore.  In  the  interior  of  the  beaker,  are  elongated  cells,  with  large, 
clear  nuclei,  which  are  called  taste-cells.  It  is  supposed  that  nerve-fibrils  are  connected 

directly  with  these  cells.  As  far  as  we 
can  learn,  the  only  reason  why  these 
structures  are  connected  with  the  physi- 
ology of  gustation  is  on  account  of  their 
anatomical  relations  to  the  gustatory 
papillae. 

It  now  remains  only  to  note  the  ulti- 
mate distribution  of  the  nerves  in  the 
gustatory  organ.  Upon  this  point,  ana- 
tomical researches  are  not  entirely  sat- 
isfactory. However,  the  following  de- 
scription, by  Elin,  may  be  regarded  as 


—•    l 


FIG.  239.—  Taste-buds  from  the  lateral  taste-organ  of  the 
rabbit.   (Engelmann.) 


probably    correct,    although     the    facts 

'    , 

have  not  been  absolutely  demonstrated. 
According  to  this  authority,  from  the  submucous  tissue,  small  nerve-branches  pass  per- 
pendicularly to  the  upper  layer  of  the  membrane.  These  fibres  have  a  varicose  appear- 
ance. In  the  most  superficial  layer  of  the  mucous  membrane,  there  is  a  net-work  of  fine, 
non-medullated  fibres  ;  and,  from  this  net-work,  branches  follow  the  blood-vessels  into  the 
papillae  and  penetrate  the  epithelium.  Sometimes,  though  more  seldom,  they  pass  into 
the  epithelium  lying  between  the  papillse.  In  this  layer,  there  are  branches  which  end, 
some  in  nerve-cells,  and  some  taking  a  winding  course  and  passing  into  neighboring 


PHYSIOLOGICAL  ANATOMY   OF  THE   OPTIC  NEKVES.  767 

fibres.     These  descriptions  are  from  preparations  made  with  chloride  of  gold ;  but  the 
plates  by  which  they  are  illustrated  are  somewhat  unsatisfactory. 

According  to  the  views  of  those  who  have  described  the  so-called  taste-beakers,  sapid 
solutions  find  their  way  into  the  interior  of  these  structures  through  the  taste-pores  and 
come  in  contact  with  what  have  been  called  the  taste-cells,  these  structures  being  directly 
connected  with  the  terminal  filaments  of  the  gustatory  nerves. 


CHAPTER    XXIV. 
VISION. 

General  considerations — Physiological  anatomy  and  general  properties  of  the  optic  nerves— Physiological  anatomy  of 
the  eyeball — Sclerotic  coat— Cornea — Membrane  of  Descemet,  or  of  Demours — Ligamentum  iridis  pectinatum — 
Choroid  coat— Ciliary  processes— Ciliary  muscle— Iris— Pupillary  membrane— Ketina— Crystalline  lens— Aqueous 
humor— Chambers  of  the  eye— Vitreous  humor— Summary  of  the  anatomy  of  the  globe— The  eye  as  an  optical 
instrument — Laws  of  refraction,  dispersion,  etc.,  bearing  upon  the  physiology  of  vision — Theories  of  light — Ke- 
fraction  by  lenses— Myopia  and  hypermetropia— Formation  of  images  in  the  eye— Mechanism  of  refraction  in  the 
eye — Astigmatism — Movements  of  the  iris — Direct  action  of  light  upon  the  iris — Action  of  the  nervous  system  upon 
the  iris — Mechanism  of  the  movements  of  the  iris — Accommodation  of  the  eye  to  vision  at  different  distances — 
Changes  in  the  crystalline  lens  in  accommodation— Action  of  the  ciliary  muscle— Changes  in  the  iris  in  accom- 
modation— Erect  impressions  produced  by  images  inverted  upon  the  retina — Single  vision  with  both  eyes — Cor- 
responding points — The  horopter — Appreciation  of  distance  and  of  the  form  of  objects — Mechanism  of  the  stereo- 
scope—Duration of  luminous  impressions— Irradiation— Movements  of  the  eyeball— Muscles  of  the  eyeball— Parts 
for  the  protection  of  the  eyeball — Eyelids — Muscles  which  open  and  close  the  eyelids — Conjunctival  mucous 
membrane— Lachrymal  apparatus— Composition  of  the  tears. 

THE  chief  important  points  to  be  considered  in  the  physiology  of  vision  are  the  fol- 
lowing : 

1.  The  physiological  anatomy  and  the  general  properties  of  the  optic  nerves. 

2.  The  physiological  anatomy  of  the  parts  essential  to  correct  vision. 

3.  The  laws  of  refraction,  diffusion,  etc.,  bearing  upon  the  physiology  of  vision. 

4.  The  action  of  the  different  parts  of  the  eye  in  the  production  and  appreciation  of 
correct  images. 

5.  Binocular  vision. 

6.  The  physiological  anatomy  and  the  functions  of  accessory  parts,  as  the  muscles 
which  move  the  eyeball. 

7.  The  physiological  anatomy  and  the  functions  of  the  parts  which  protect  the  eye,  as 
the  lachrymal  glands,  eyelids,  etc. 

Physiological  Anatomy  of  the  Optic  Nerves. — The  optic  nerves,  or  optic  tracts,  take 
their  origin,  each  by  two  principal  roots  of  white  matter  and  a  few  filaments  from  what  is 
described  as  the  gray  root,  chiefly  from  the  tubercula  quadrigemina,  but  in  part  from 
those  portions  of  the  encephalon  over  which  the  nerves  pass  to  go  to  the  eyes.  The 
internal  white  root  arises  from  the  posterior,  and  the  external  white  root,  which  is  the 
larger,  from  the  anterior  tuberculum.  The  gray  root  is  situated  in  front  of  and  above 
the  optic  commissure  and  is  a  dependence  of  the  gray  matter  which  covers  the  internal 
surface  of  the  optic  thalamus.  It  arises  from  the  gray  matter  which  constitutes  the  ante- 
rior floor  of  the  third  ventricle,  in  the  form  of  delicate  filaments  which  join  the  optic 
nerves  at  this  point. 

The  apparent  origin  of  the  optic  nerves  is  from  the  tubercula  quadrigemina,  receiving 
filaments  from  the  corpora  geniculata,  the  optic  thalami,  the  peduncles  of  the  cerebrum, 
the  anterior  substantia  perforata,  the  tuber  cinereum,  and  the  lamina  terminalis.  It  has 
thus  far  been  found  impossible  to  trace  all  these  roots  to  their  true  origin  in  the  cerebral 
substance ;  but  experiments  upon  the  lower  animals,  in  which  it  has  been  shown  that 


768 


SPECIAL  SENSES. 


the  sense  of  sight  is  completely  abolished  by  destruction  of  the  tubercula  quadrigemina 
(called  bigemina,  in  birds),  show  that  the  origin  of  the  filaments  that  preside  over  vision 
is,  in  all  probability,  from  these  bodies. 

The  two  principal  roots  of  the  optic  nerves  unite 
above  the  external  corpus  geniculatum,  forming  a 
flattened  band,  .which  takes  an  oblique  course  around 
the  under  surface  of  the  crus  cerebri  to  the  optic 
commissure.  This  is  usually  called  the  optic  tract, 
in  contradistinction  to  the  optic  nerve,  which  is  de- 
scribed as  arising  from  the  optic  commissure. 

The  optic  commissure,  or  chiasm,  is  situated  just  in 
front  of  the  corpus  cinereum,  resting  upon  the  olivary 
process  of  the  sphenoid  bone.  As  its  name  implies, 
this  is  the  point  of  union  between  the  nerves  of  the 
two  sides.  At  the  commissure,  the  fibres  from  the 
optic  tracts  take  three  directions ;  and,  in  addition, 
the  commissure  contains  filaments  passing  from  one 
eye  to  the  other,  which  have  no  connection  with  the 
optic  tracts.  The  four  sets  of  fibres  in  the  optic 
commissure  are  the  following: 

1.  Decussating    fibres,   passing  from    the    optic 
tract  upon  either  side  to  the  eye  of  the   opposite 
side.     The  greatest  part  of  the  fibres  take  this  direc- 
tion.    Their  relative  situation  is  internal. 

2.  External  fibres,  much  less  numerous  than  the 
preceding,  which  pass  from  the  optic  tract  to  the  eye 
upon  the  same  side. 

3.  Fibres,  situated  on  the  posterior  boundary  of 
the  commissure,  which  pass  from  one  optic  tract  to 
the  other  and  do  not  go  to  the  eyes.     These  fibres 
are  scanty  and  are  sometimes  wanting. 

4.  Fibres,  situated  on  the  anterior  border  of  the  commissure,  more  numerous  than  the 
preceding,  which  pass  from  one  eye  to  the  other  and  which  have  no  connection  with  the 
optic  tracts. 

It  is  probable,  reasoning  chiefly  from  cases  of  cerebral  injury  or  disease,  that  the  fila- 
ments from  the  optic  tracts  upon  the  two  sides  are  connected  with  distinct  portions  of 
the  retina ;  and  two  pathological  cases  have  lately  been  reported  by  Drs.  Keen  and 

Thomson,  of  Philadelphia,  which  go  to  show  that  this  is 
the  fact,  and  which  illustrate  certain  interesting  points 
in  connection  with  the  decussation  of  the  nerves.  One 
was  a  case  of  gunshot-wound  of  the  head,  with  severe 
injury  of  the  brain-substance.  This  case  presented,  im- 
mediately after  the  injury,  unconsciousness  and  partial 
paralysis  of  the  right  arm  and  right  leg,  which  lasted  two 
or  three  months.  About  a  year  after,  the  paralysis  had 
almost  entirely  disappeared,  but  the  memory  was  some- 
what impaired.  Upon  careful  examination  of  the  eyes,  it 
was  ascertained  that  the  field  of  vision  was  divided  in 
each  eye  by  a  vertical  line  passing  through  its  centre. 
In  the  right  eye,  the  inner  half  of  the  retina,  beginning  on 
a  line  with  the  inner  border  of  the  macula  lutea,  was  entirely  insensible  to  light.  In 
the  left  eye,  the  outer  half  of  the  retina,  beyond  the  macula,  was  insensible  to  light.  No 
pathological  appearances  were  observed  upon  examining  the  retinas  with  the  ophthalmo- 


FIG.  240. — Optic  tracts,  commissure,  and 
nerves.  (Hirschfeld.) 

1,  infundibulum ;  2,  corpus  cinereum ;  3, 
corpora  albicantia;  4,  cerebral  pedun- 
cle ;  5,  tuber  annulare ;  6,  optic  tracts 
and  nerves,  decussating  at  the  commis- 
sure, or  chiasm;  7,  motor  oculi  com- 
munis ;  8,  patheticus ;  9,  fifth  nerve ;  10, 
motor  oculi  externus;  11,  facial  nerve; 
12,  auditory  nerve ;  13,  nerve  of  Wris- 
berg;  14,  glosso-pharyngeal  nerve;  15, 
pnemnogastric;  16,  spinal  accessory;  17, 
sublingual  nerve. 


FIG.  241.— Diagram  of  the  decussation 

at  the  optic  commissure. 
The  dotted  lines  show  the  four  direc- 
tions of  the  fibres. 


GENERAL  PROPERTIES   OF  THE   OPTIC  NERVES.  769 

scope.  The  second  case,  reported  by  Dr.  W.  Thomson,  presented  the  same  condition 
following  partial  heiniplegia,  the  result  of  sunstroke.  The  peculiar  affection  of  vision  in 
these  cases,  called  hemiopsia,  especially  as  illustrated  in  the  first  case,  reported  by  Dr. 
Keen,  can  be  explained  by  assuming  the  following  as  the  course  of  the  decussating  fibres 
of  the  optic  tracts :  From  the  left  side  of  the  encephalon,  visual  fibres  pass  to  the  right 
eye,  supplying  the  inner  mathematical  half  of  the  retina,  from  a  vertical  line  passing 
through  the  macula  lutea.  Visual  fibres  also  pass  to  the  left  eye,  supplying  the  outer 
half  of  the  retina,  beginning  at  the  macula  lutea.  The  macula  lutea,  then,  and  not  the 
point  of  entrance  of  the  optic  nerve,  is  in  the  line  of  division  of  the  visual  field.  The 
outer  half  of  the  left  and  the  inner  half  of  the  right  retina  are  supplied  by  fibres  from  the 
left  side  ;  and  the  outer  half  of  the  right  and  the  inner  half  of  the  left  retina  are  sup- 
plied from  the  right  side.  Although  this  anatomical  arrangement  has  not  been  actually 
demonstrated,  it  is  rendered  exceedingly  probable  by  pathological  cases  like  those  just 
cited.  In  the  case  reported  by  Dr.  Keen,  the  left  side  of  the  brain  was  injured,  as  the 
paralysis  occurred  in  the  right  leg  and  arm. 

With  the  exception  of  the  few  filaments  derived  from  what  have  been  described  as  the 
gray  roots,  the  fibres  of  the  optic  tracts  and  the  optic  nerves  are  of  the  inedullated  variety, 
and  they  present  no  differences  in  structure  from  the  ordinary  cerebro-spinal  nerves. 

The  optic  commissure  is  covered  with  a  fibrous  membrane  and  is  consequently  more 
resisting  than  the  optic  tracts.  From  its  anterior  and  outer  border,  arise  the  optic  nerves, 
which  take  a  curved  direction  to  the  eyes.  The  nerves  are  rounded  and  are  enclosed  in 
a  double  fibrous  sheath  derived  from  the  dura  mater  and  the  arachnoid.  They  pass  into 
the  orbit  upon  the  two  sides  by  the  optic  foramina  and  penetrate  the  sclerotic  at  the 
posterior,  inferior,  and  internal  portion  of  the  globe.  As  the  nerves  enter  the  globe,  they 
lose  their  coverings  from  the  dura  mater  and  arachnoid.  The  sheath  derived  from  the 
dura  mater  is  adherent  to  the  periosteum  of  the  orbit  at  the  foramen  opticum,  and,  when 
it  reaches  the  globe,  it  fuses  with  the  sclerotic  coat.  Just  before  the  nerves  penetrate  the 
globe,  they  each  present  a  well-marked  constriction.  At  the  point  of  penetration,  there 
is  a  thin  but  strong  membrane,  presenting  numerous  perforations  for  the  passage  of  the 
nervous  filaments.  This  membrane,  the  lamina  cribrosa,  is  in  part  derived  from  the 
sclerotic,  and  in  part,  from  the  coverings  of  the  individual  nerve-fibres,  which  lose  their 
investing  membranes  at  this  point.  In  the  interior  of  each  eye,  there  is  a  little,  mammil- 
lated  eminence,  formed  by  the  united  fibres  of  the  nerve.  The  retina,  with  which  the 
optic  nerve  is  connected,  will  be  described  as  one  of  the  coats  of  the  eye. 

In  the  centre  of  the  optic  nerve,  is  a  minute  canal,  lined  by  fibrous  tissue,  in  which  are 
lodged  the  central  artery  of  the  retina  and  its  corresponding  vein,  with  a  delicate  nervous 
filament  from  the  ophthalmic  ganglion.  The  vessels  penetrate  the  optic  nerve  a  short 
distance  (from  %  to  £  of  an  inch)  behind  the  globe.  The  central  canal  does  not  exist 
behind  these  vessels. 

General  Properties  of  the  Optic  Nerves. — There  is  very  little  to  be  said  regarding  the 
general  properties  of  the  optic  nerves,  except  that  they  are  undoubtedly  the  only  nerves 
capable  of  conveying  to  the  cerebrum  the  special  impressions  of  sight,  and  that  they  are 
not  endowed  with  general  sensibility. 

That  the  optic  nerves  are  the  only  nerves  of  sight,  there  can  be  no  doubt.  Their 
division  or  injury  always  involves  loss  or  impairment  of  vision,  directly  corresponding 
with  the  lesion.  It  is  interesting,  however,  to  note  that  they  are  absolutely  insensible  to 
ordinary  impressions.  "We  can,  in  a  living  animal,  pinch,  cauterize,  cut,  destroy  in  any 
way  the  optic  nerve  without  giving  rise  to  the  slightest  painful  sensation  ;  whether  it  be 
taken  before  or  after  its  decussation,  it  seems  completely  insensible  in  its  entire  length." 
(Longet.) 

Not  only  are  the  optic  nerve  and  retina  insensible  to  pain,  but  any  irritation  produces 
the  impression  of  light.  This  was  stated  in  the  remarkable  paper,  Idea  of  a  New  Anatomy 
49 


770  SPECIAL  SENSES. 

of  the  Brain,  printed  by  Charles  Bell,  in  1811.  A  few  years  later,  Magendie,  in  operating 
for  cataract,  passed  the  needle  to  the  bottom  of  the  eye  and  irritated  the  retina,  in  two 
persons.  The  patients  experienced  no  pain  but  merely  an  impression  of  flashes  of  light. 
The  insensibility  of  the  optic  nerves  has  also  been  repeatedly  noted  in  surgical  operations 
in  which  the  nerves  have  been  exposed.  If  a  current  of  galvanism  be  passed  through  the 
optic  nerves,  a  sensation  of  light  is  experienced.  The  same  phenomenon  is  observed  when 
the  eyeball  is  pressed  upon  or  contused,  a  fact  which  is  sufficiently  familiar. 

Physiological  Anatomy  of  the  Eyeball. 

The  eyeball  is  a  spheroidal  body,  partially  embedded  in  a  cushion  of  fat  in  the  orbit, 
protected  by  the  surrounding  bony  structures  and  the  eyelids,  its  surface  bathed  by  the 
secretion  of  the  lachrymal  gland,  and  movable  in  various  directions  by  the  action  of  cer- 
tain muscles.  When  the  axis  of  the  eye  is  directed  forward,  the  globe  has  the  form  of  a 
sphere  in  its  posterior  five-sixths,  with  the  segment  of  a  smaller  sphere  occupying  its 
anterior  sixth.  The  segment  of  the  smaller  sphere,  bounded  externally  by  the  cornea,  is 
more  prominent  than  the  rest  of  the  surface. 

The  eyeball  is  made  up  of  several  coats  enclosing  certain  refracting  media.  The  exter- 
nal coat  is  the  sclerotic,  covering  the  posterior  five-sixths  of  the  globe,  which  is  continuous 
with  the  cornea,  covering  the  anterior  sixth.  This  is  a  dense,  opaque,  fibrous  membrane, 
for  the  protection  of  the  inner  coats  and  the  contents  of  the  globe.  The  cornea  is  dense, 
resisting,  and  perfectly  transparent.  The  muscles  that  move  the  globe  of  the  eye  are 
attached  to  the  sclerotic  coat. 

Were  it  not  for  the  prominence  of  the  cornea,  the  eyeball  would  present  very  nearly 
the  form  of  a  perfect  sphere,  as  will  be  seen  by  the  following  measurements  of  its  various 
diameters;  but  the  prominence  of  its  anterior  sixth  gives  the  greatest  diameter  in  the 
antero-posterior  direction. 

The  form  and  dimensions  of  the  globe  are  subject  to  considerable  variations  after 
death,  by  evaporation  of  the  humors,  emptying  of  vessels,  etc.,  and  there  is  no  way  in 
which  the  normal  conditions  can  be  restored.  The  most  exact  measurements  are  those 
made  by  Sappey.  As  an  illustration  of  the  post-mortem  changes  in  the  eye,  Sappey  men- 
tions comparative  measurements  made  three  hours  and  twenty -four  hours  after  death,  the 
results  of  which  presented  very  considerable  differences. 

In  measurements  made  by  Sappey,  apparently  with  great  care  and  accuracy,  from  one 
to  four  hours  after  death,  of  the  eyes  of  twelve  adult  females  and  fourteen  adult  males  of 
different  ages,  the  following  mean  results  were  obtained  : 


Subjects  examined. 

Diameters  (Inch). 

Ant.-post. 

Transverse. 

Vertical.               Oblique. 

Mean  of  12  females,  from  18  to  81  years  of  age 

0-941 
0-968 

0-911 
0-941 

0-905 
0-925 

0-93T 
0-949 

Mean  of  14  males,  from  20  to  79  years  of  age  

From  these  results,  it  is  seen  that  all  the  diameters  are  less  in  the  female  than  in  the 
male.  The  antero-posterior  diameter  is  the  greatest  of  all,  and  the  vertical  diameter  is 
the  shortest.  The  measurements  at  different  ages,  not  cited  in  the  table  just  given,  show 
that  the  excess  of  the  antero-posterior  diameter  over  the  others  is  diminished  by  age. 

Sclerotic  Coat. — The  sclerotic  is  the  dense,  opaque,  fibrous  covering  of  the  posterior 
five-sixths  of  the  eyeball.  Its  thickness  is  different  in  different  portions.  At  the  point 
of  penetration  of  the  optic  nerve,  it  measures  -fa  of  an  inch.  It  is  thinnest  at  the  middle 
portion  of  the  eye,  measuring  about  -^  of  an  inch,  and  is  a  little  thicker  again  near  the 
cornea.  This  membrane  is  composed  chiefly  of  bundles  of  ordinary  connective  tissue. 


PHYSIOLOGICAL  ANATOMY   OF   THE  EYEBALL.  77! 

The  fibres  are  slightly  wavy,  and  arranged  in  flattened  bands,  which  are  alternately  longi- 
tudinal and  transverse,  giving  the  membrane  a  lamellated  appearance,  although  it  cannot 
be  separated  into  distinct  layers.  Mixed  with  these  bands  of  connective-tissue  fibres,  are 
numerous  small  fibres  of  elastic  tissue.  The  vessels  of  the  sclerotic  are  scanty.  They  are 
derived  from  the  ciliary  vessels  and  the  vessels  of  the  muscles  of  the  eyeball.  The  tissue 
of  the  sclerotic  yields  gelatine  on  boiling. 

Cornea. — The  cornea  is  the  transparent  membrane  which  covers  about  the  anterior 
sixth  of  the  globe  of  the  eye.  As  before  remarked,  this  is  the  most  prominent  portion  of 
the  eyeball.  It  is  in  the  form  of  a  segment  of  a  sphere  attached  by  its  borders  to  the 
segment  of  the  larger  sphere  formed  by  the  sclerotic.  The  thickness  of  the  cornea  is 
about  jV  °f  an  m°h  m  its  central  portion,  and  about  fa  of  an  inch  near  its  periphery.  Its 
substance  is  composed  of  transparent  fibres,  arranged  in  incomplete  layers,  something  like 
the  layers  of  the  sclerotic.  It  yields  chondrine,  instead  of  gelatine,  on  boiling. 

Upon  the  external,  or  convex  surface  of  the  cornea,  are  several  layers  of  delicate, 
transparent,  nucleated  epithelium.  The  most  superficial  cells  are  flattened,  the  middle 
cells  are  rounded,  and  the  deepest  cells  are  elongated  and  arranged  perpendicularly. 
These  cells  become  slightly  opaque  and  whitish  after  death.  Just  beneath  the  epithelial 
covering  of  the  cornea,  is  a  very  thin,  transparent  membrane,  described  by  Bowman 
under  the  name  of  the  "  anterior  elastic  lamella."  This  membrane,  with  its  cells,  is  a 
continuation  of  the  conjunctiva. 

The  proper  corneal  membrane  is  composed  of  excessively  pale,  flattened  bundles  of 
fibres,  interlacing  with  each  other  in  every  direction.  Their  arrangement  is  lamellated, 
although  they  cannot  be  separated  into  complete  and  distinct  layers.  Between  the  bun- 
dles of  fibres,  lie  a  great  number  of  stellate,  anastomosing,  connective-tissue  corpuscles. 
In  these  cells  and  in  the  intervals  between  the  fibres,  there  is  a  considerable  quantity  of 
transparent  liquid.  The  fibres  constituting  the  substance  of  the  cornea  are  continuous 
with  the  fibrous  structure  of  the  sclerotic,  from  which  they  cannot  be  separated  by 
maceration.  At  the  margin  of  the  cornea,  the  opaque  fibres  of  the  sclerotic  abruptly 
become  transparent.  The  corneal  substance  is  very  tough,  and  it  will  resist  a  pressure 
sufficient  to  rupture  the  sclerotic. 

Upon  the  posterior,  or  concave  surface  of  the  cornea,  is  the  membrane  of  Descemet, 
or  of  Demours.  This  is  elastic,  transparent,  structureless,  rather  loosely  attached,  and 
covered  with  a  single  layer  of  regularly  polygonal,  nucleated  epithelium.  At  the  circum- 
ference of  the  cornea,  a  portion  of  this  membrane  passes  to  the  anterior  surface  of  the 
iris,  in  the  form  of  numerous  processes  which  constitute  the  ligamentum  iridis  pectinatum, 
a  portion  passes  into  the  substance  of  the  ciliary  muscle,  and  a  portion  is  continuous 
with  the  fibrous  structure  of  the  sclerotic. 

In  the  adult,  the  cornea  is  almost  without  blood-vessels,  but  in  foetal  life  it  presents 
a  rich  plexus  extending  nearly  to  the  centre.  These  disappear,  however,  before  birth, 
leaving  a  very  few  delicate,  looped  vessels  at  the  extreme  edge. 

A  great  deal  of  anatomical  interest  has  lately  been  attached  to  the  cornea,  from 
researches  showing  the  termination  of  the  fine  nerve-fibres  in  the  nuclei  of  the  posterior 
layer  of  the  epithelium  of  its  convex  surface  and  the  investigation  of  the  "  lymph-spaces" 
by  the  use  of  certain  reagents,  the  demonstration  of  the  so-called  u  wandering  cells," 
etc.,  points  that  we  do  not  propose  to  consider.  It  is  well  known  that  the  surface  of  the 
cornea  is  exquisitely  sensitive. 

Choroid  Coat. — Calling  the  sclerotic  and  the  cornea  the  first  coat  of  the  eyeball,  the 
second  is  the  choroid,  with  the  ciliary  processes,  the  ciliary  muscle,  and  the  iris.  This 
was  called  by  the  older  anatomists  the  uvea,  a  name  which  was  later  applied,  sometimes 
to  the  entire  iris,  and  sometimes  to  its  posterior,  or  pigmentary  layer.  We  shall  describe, 
however,  the  choroid  and  ciliary  processes  together  as  the  second  coat,  and  then  take  up 
the  ciliary  muscle  and  the  iris. 


772  SPECIAL  SENSES. 

The  choroid  is  distinguished  from  the  other  coats  of  the  eye  by  its  dark  color  and  its 
great  vascularity.  It  occupies  that  portion  of  the  eyeball  corresponding  to  the  sclerotic. 
It  is  perforated  posteriorly  by  the  optic  nerve  and  is  connected  in  front  with  the  iris. 
It  is  very  delicate  in  its  structure  and  is  composed  of  two  or  three  distinct  layers.  Its 
thickness  is  from  -^  to  ^V  °f  an  mcn-  Its  thinnest  portion  is  at  about  the  middle  of  the 
eye.  Posteriorly  it  is  a  little  thicker.  Its  thickest  portion  is  at  its  anterior  border. 

The  external  surface  of  the  choroid  is  connected  with  the  sclerotic  by  vessels,  nerves 
(the  long  ciliary  arteries  and  the  ciliary  nerves),  and  very  loose  connective  tissue.  This 
is  sometimes  called  the  membrana  fusca,  although  it  can  hardly  be  called  a  distinct  layer. 
It  contains,  in  addition  to  the  vessels,  nerves,  and  fibrous  tissue,  a  few  irregularly-shaped 
pigment-cells. 


FIG.  242.— Choroid  coat  of  the  eye.    (Sappey.) 

1,  optic  nerve ;  2,  2,  2,  2, 3,  3,  3,  4,  sclerotic  coat,  divided  and  turned  back  to  show  the  choroid ;  5,  5,  5,  5,  the  cornea, 
divided  into  four  portions  and  turned  back ;  6,  6,  canal  of  Schlemm ;  7,  external  surface  of  the  choroid,  traversed 
by  the  ciliary  nerves  and  one  of  the  long  ciliary  arteries ;  8,  central  vessel  into  which  open  the  vasa  vorticosa ;  9, 
9, 10, 10,  choroid  zone ;  11,  11,  ciliary  nerves;  12,  long  ciliary  artery ;  13, 13, 13, 13,  anterior  ciliary  arteries ;  14,  iris ; 
15, 15,  vascular  circle  of  the  iris ;  16,  pupil. 

The  rest  of  the  choroid  is  composed  of  two  distinct  layers ;  viz.,  an  external,  vascular, 
and  an  internal,  pigmentary  layer.  The  vascular  layer  consists  of  numerous  arteries,  veins, 
and  capillaries,  arranged  in  a  peculiar  manner.  The  layer  of  capillary  vessels,  which  is 
internal,  is  sometimes  called  the  middle  layer  of  the  choroid,  or  the  tunica  Euyschiana. 
The  arteries,  which  are  derived  from  the  posterior  short  ciliary  arteries  and  are  connected 
with  the  capillary  plexus,  lie  just  beneath  the  pigmentary  layer.  The  plexus  of  capilla- 
ries is  closest  at  the  posterior  portion  of  the  membrane.  The  veins  are  external  to  the 
other  vessels.  They  are  very  numerous  and  are  disposed  in  curves  converging  to  four 
trunks.  This  arrangement  gives  the  veins  a  very  peculiar  appearance,  and  they  have 
been  called  the  vasa  vorticosa.  The  pigmentary  portion  is  composed,  over  the  greatest 
part  of  the  choroid,  of  a  single  layer  of  regularly  polygonal  cells,  somewhat  flattened, 
measuring  from  ^^  to  ^fa  of  an  inch  in  diameter.  These  cells  are  filled  with  pig- 
mentary granulations  of  uniform  size,  and  they  give  to  the  membrane  its  characteristic 
dark-brown  or  chocolate  color.  The  pigmentary  granules  in  the  cells  are  less  numerous 
near  their  centre,  where  a  clear  nucleus  can  readily  be  observed.  In  the  anterior  por- 
tion of  the  membrane,  in  front  of  the  anterior  limit  of  the  retina,  the  cells  are  smaller, 
more  rounded,  more  completely  filled  with  pigment,  and  present  several  layers.  Beneath 
the  layer  of  hexagonal  pigment-cells,  the  intervascular  spaces  of  the  choroid  are  occupied 
by  stellate  pigment-cells. 


PHYSIOLOGICAL  ANATOMY   OF  THE  EYEBALL. 


773 


Ciliary  Processes. — The  anterior  portion  of  the  choroid  is  arranged  in  the  form  of 
folds  or  plaits  projecting  internally,  called  the  ciliary  processes.  The  largest  of  these 
folds  are  about  -^  of  an  inch  in  length.  They  are  from  sixty  to  eighty  in  number.  The 
larger  folds  are  of  nearly  uniform  size  and  are  regularly  arranged  around  the  margin  of 
the  crystalline  lens.  Between  these  folds,  which  constitute  about  two-thirds  of  the  entire 
number,  are  smaller  folds,  lying,  without  any  regular  alternation,  between  the  larger. 
Within  the  folds,  are  received  corresponding  folds  of  the  thick  membrane,  continuous  an- 
teriorly with  the  hyaloid  membrane  of  the  vitreous  humor,  called  the  zone  of  Zinn. 

The  ciliary  processes  present  blood-vessels,  which  are  somewhat  larger  than  those  of 
the  rest  of  the  choroid.  The  pigmentary  cells  are  smaller  and  are  arranged  in  several 
layers.  The  anterior  border  of  the  processes  is  free  and  contains  little  or  no  pigment. 

Ciliary  Muscle. — This  muscle,  formerly  known  as  the  ciliary  ligament  and  now 
sometimes  called  the  tensor  of  the  choroid,  is  almost  universally  recognized  by  physi- 


FIG.  243. — Ciliary  muscle;  magnified  10  diameters.    (Sappey.) 

1,  1.  crystalline  lens-  2,  hyaloid  membrane;  3,  zone  of  Zinn;  4,  iris;  5,  5,  one  of  the  ciliary  processes ;  6,  6,  radiating 
fibres  of  the  ciliary  muscle;  7,  section  of  the  circular  portion  of  the  ciliary  muscle;  8.  venous  plexus  of  the  ciliary 
process;  9, 10,  sclerotic  coat;  11, 12,  cornea  ;  13,  epithelial  layer  of  the  cornea;  14,  membrane  of  Descemet;  15, 
tig-amentum  iridis  pectinatum ;  16,  epithelium  of  the  membrane  of  Descemet ;  17,  union  of  the  sclerotic  coat 
with  the  cornea ;  18,  section  of  the  canal  of  Schlemm. 


ologists  as  the  agent  for  the  accommodation  of  the  eye  to  vision  at  different  distances. 
Under  this  view,  the  ciliary  muscle  is  an  organ  of  great  importance,  and  it  is  essential, 
in  the  study  of  accommodation,  to  have  an  exact  idea  of  its  relations  to  the  coats  of  the 
eye  and  to  the  crystalline  lens.  For  this  reason,  we  shall  describe  its  arrangement  as 
exactly  as  possible. 

The  form  and  situation  of  the  ciliary  muscle  are  as  follows  :  It  surrounds  the  anterior 
margin  of  the  choroid,  in  the  form  of  a  ring  about  £  of  an  inch  wide  and  -^  of  an  inch 
in  thickness  at  its  thickest  portion,  which  is  its  anterior  border.  It  becomes  thinner 


774  SPECIAL  SENSES. 

from  before  backward,  until  its  posterior  border  apparently  fuses  with  the  fibrous  struct- 
ure of  the  choroid.  It  is  semitransparent  and  of  a  grayish  color.  Its  situation  is  just 
outside  of  the  ciliary  processes,  these  processes  projecting  in  front  of  its  anterior  border 
about  ¥V  of  an  incn-  Regarding  the  anterior  border  of  this  muscle  as  its  origin  and  the 
posterior  border  as  its  insertion,  it  arises  in  front  from  the  circular  line  of  junction  of  the 
cornea  and  sclerotic,  from  the  border  of  the  membrane  of  Descemet,  and  the  ligamentum 
iridis  pectinatum.  Its  fibres,  which  are  chiefly  longitudinal,  pass  backward  and  are 
lost  in  the  choroid,  extending  somewhat  farther  back  than  the  anterior  limit  of  the 
retina.  In  addition,  a  net-work  of  circular  muscular  fibres  has  been  described  lying  over 
the  anterior  portion  of  the  ciliary  body,  at  the  periphery  of  the  iris,  beneath  the  longitu- 
dinal fibres.  Some  of  these  fibres  have  an  oblique  direction. 

Although  there  was  formerly  considerable  discussion  with  regard  to  the  structure  of 
the  ciliary  ligament,  or  muscle,  there  can  now  be  scarcely  any  doubt  of  the  fact  that  it  is 
composed  mainly  of  muscular  fibres.  These  fibres,  anatomically  considered,  belong  to  the 
non-striated,  or  involuntary  variety.  They  are  pale,  present  numerous  oval,  longitudinal 
nuclei,  and  have  no  striae. 

It  is  evident,  from  the  arrangement  of  the  fibres  of  the  ciliary  muscle,  that  its  action 
must  be  to  approximate  the  border  of  connection  of  the  sclerotic  and  cornea  and  the  cir- 
cumference of  the  choroid,  compressing  the  vitreous  humor  and  relaxing  the  suspensory 
ligament  of  the  crystalline  lens.  We  shall  see  farther  on  that  this  action  enables  the  lens 
to  change  its  form,  and  probably  it  adapts  the  curvature  of  the  lens  to  vision  at  different 
distances.  The  nerves  of  the  ciliary  muscle  are  derived  from  the  long  and  the  short 
ciliary. 

Iris. — The  iris  corresponds  to  the  diaphragm  of  optical  instruments,  except  that  its 
orifice  is  capable  of  dilatation  and  contraction.  It  is  a  circular  membrane,  situated  just 
in  front  of  the  crystalline  lens,  with  a  round  perforation,  the  pupil,  near  its  centre.  It  is 
called  the  uvea  by  some  anatomists,  a  name  that  was  formerly  applied  to  the  iris  and 
choroid  together. 

The  attachment  of  the  greater  circumference  of  the  iris  is  to  the  line  of  junction  of 
the  cornea  and  sclerotic,  near  the  origin  of  the  ciliary  muscle,  the  latter  passing  back- 
ward to  be  inserted  into  the  choroid,  and  the  former  passing  directly  over  the  crystalline 
lens.  The  diameter  of  the  iris  is  about  half  an  inch.  T^he  pupil  is  subject  to  considerable 
variations  in  size.  When  at  its  medium  of  dilatation,  the  diameter  of  the  pupil  is  from  £ 
to  £  of  an  inch.  The  pupillary  orifice  is  not  in  the  mathematical  centre  of  the  iris  but  is 
situated  a  little  toward  the  nasal  side.  The  thickness  of  the  iris  is  a  little  greater  than 
that  of  the  choroid,  but  it  is  unequal  in  different  parts,  the  membrane  being  thinnest  at 
its  great  circumference  and  its  pupillary  border,  and  thickest  at  about  the  junction  of  its 
inner  third  with  the  outer  two-thirds.  It  slightly  projects  anteriorly  and  divides  the  space 
between  the  lens  and  the  cornea  into  two  chambers,  anterior  and  posterior,  the  anterior 
chamber  being  much  the  larger.  Taking  advantage  of  a  property  of  the  crystalline  lens, 
called  fluorescence,  which  enables  us,  by  concentrating  upon  it  a  blue  light,  to  see  the 
boundaries  in  the  living  eye,  Helmholtz  has  demonstrated  that  the  posterior  surface  of 
the  iris  and  the  anterior  surface  of  the  lens  are  actually  in  contact,  except,  perhaps,  for  a 
certain  distance  near  the  periphery  of  the  iris.  This  being  the  case,  the  posterior  cham- 
ber is  very  small  and  only  exists  near  the  margins  of  the  lens  and  the  iris. 

The  color  of  the  iris  is  very  different  in  different  individuals.  Its  anterior  surface  is 
generally  very  dark  near  the  pupil  and  presents  colored  radiations  toward  its  periphery. 
Its  posterior  surface  is  of  a  dark-purple  color  and  is  covered  with  pigmentary  cells. 

The  entire  iris  presents  three  layers.  The  anterior  layer  is  continuous  with  the  mem- 
brane of  the  aqueous  humor.  At  the  great  circumference,  it  presents  little  fibrous  pro- 
longations, forming  a  delicate  dentated  membrane,  called  the  ligamentum  iridis  pectina- 
tum. The  membrane  covering  the  general  anterior  surface  of  the  iris  is  extremely  thin 


PHYSIOLOGICAL  ANATOMY   OF  THE  EYEBALL.  775 

and  is  covered  by  cells  of  tessellated  epithelium.  Just  beneath  this  membrane,  are  a 
number  of  irregularly-shaped  pigmentary  cells. 

The  posterior  layer  of  the  iris  is  very  thin,  easily  detached  from  the  middle  layer,  and 
contains  numerous  small  cells  exceeding  rich  in  pigmentary  granules.  Some  anatomists 
recognize  this  membrane  only  as  the  uvea.1 

The  middle  layer  constitutes  by  far  the  greatest  part  of  the  substance  of  the  iris.  It 
is  composed  of  connective  tissue,  muscular  fibres  of  the  non-striated  variety,  numerous 
blood-vessels,  and,  probably,  nerve-terminations.  From  a  physiological  point  of  view, 
the  arrangement  of  the  muscular  fibres  is  the  most  interesting.  Directly  surrounding 
the  pupil,  forming  a  band  about  ¥4¥  of  an  inch  in  width,  is  a  layer  of  non-striated  muscu- 
lar fibres,  called  the  sphincter  of  the  iris.  The  existence  of  these  fibres  is  admitted  by 
all  anatomists.  It  is  different,  however,  for  the  radiating  muscular  fibres.  Most  anato- 
mists describe,  in  addition  to  the  sphincter,  fibres  of  the  same  variety,  which  can  be 
traced  from  near  the  great  circumference  of  the  iris  almost  to  its  pupillary  border,  lying 
both  in  front  of  and  behind  the  circular  fibres,  which  are,  as  it  were,  enclosed  between 
them.  A  few  observers  deny  that  these  fibres  are  muscular ;  but  they  recognize  a  thick 
muscular  layer  surrounding  the  arteries  of  the  iris.  This  is  merely  a  question  of  observa- 
tion ;  but  the  weight  of  anatomical  authority  is  greatly  in  favor  of  the  existence  of  the 
radiating  fibres,  and  their  presence  explains  certain  of  the  phenomena  of  dilatation  of 
the  iris  which  would  otherwise  be  difficult  to  understand. 

The  blood-vessels  of  the  iris  are  derived  from  the  arteries  of  the  choroid,  from  the 
long  posterior  ciliary,  and  from  the  anterior  ciliary  arteries.  The  long  ciliary  arteries  are 
two  branches,  running  along  the  sides  of  the  eyeball  between  the  sclerotic  and  choroid,  to 
form,  finally,  a  circle  surrounding  the  iris.  The  anterior  ciliary  arteries  are  derived  from 
the  muscular  branches  of  the  ophthalmic.  They  penetrate  the  sclerotic  a  little  behind 
the  iris  and  join  the  long  ciliary  arteries  in  the  vascular  circle.  From  this  circle,  the 
vessels  branch  and  pass  into  the  iris,  to  form  a  smaller  arterial  circle  around  the  pupil. 
The  veins  from  the  iris  empty  into  a  circular  sinus  situated  at  the  junction  of  the  cornea 
with  the  sclerotic.  This  is  sometimes  spoken  of  as  the  circular  venous  sinus,  or  the  canal 
of  Schlemm. 

The  nerves  of  the  iris  are  the  long  ciliary,  from  the  fifth  cranial,  and  the  short  ciliary, 
from  the  ophthalmic  ganglion. 

Pupillary  Membrane. — At  a  certain  period  of  foetal  life,  the  pupil  is  closed  by  a  mem- 
brane connected  with  the  lesser  circumference  of  the  iris,  called  the  pupillary  membrane. 
This  is  not  distinct  during  the  first  months ;  but,  between  the  third  and  the  fourth  months, 
it  is  readily  seen.  It  is  most  distinct  at  the  sixth  month.  The  membrane  is  thin  and  trans- 
parent, and  it  completely  separates  the  anterior  from  the  posterior  chamber  of  the  eye.  It 
is  provided  with  vessels  derived  from  the  arteries  of  the  iris,  anastomosing  with  each 
other  and  turning  back  in  the  form  of  loops  near  the  centre.  At  about  the  seventh 
month,  it  begins  to  give  way  at  the  centre,  gradually  atrophies,  and  generally  scarcely  a 
trace  of  it  can  be  seen  at  birth. 

Retina. — The  retina  is  described  by  anatomists  as  the  third  tunic  of  the  eye.  It  is 
closely  connected  with  the  optic  nerve,  and  the  most  important  structures  entering  into 
its  composition  are  probably  continuous  with  prolongations  from  the  nerve-cells.  This 
is  the  membrane  endowed  with  the  special  sense  of  sight,  the  other  structures  in  the  eye 
being  accessory. 

If  the  sclerotic  and  choroid  be  removed  from  the  eye  under  water,  the  retina  is  seen, 
in  perfectly  fresh  specimens,  in  the  form  of  an  exceedingly  delicate  and  transparent  mem- 
brane covering  the  posterior  portion  of  the  vitreous  humor.  A  short  time  after  death,  it 
becomes  slightly  opaline.  It  extends  over  the  posterior  portion  of  the  eyeball  to  a  dis- 

1  The  name  uvea  was  applied,  at  one  time,  to  the  choroid  with  the  iris,  again  to  the  iris  alone,  and  again  to  the 
posterior,  or  pigmentary  layer  of  the  iris.    To  avoid  confusion,  this  term  will  not  be  again  used. 


776  SPECIAL  SENSES. 

tance  of  about  ^  of  an  inch  behind  the  ciliary  processes.  When  torn  from  its  anterior 
attachment,  it  presents  a  finely-serrated  edge,  called  the  ora  serrata.  This  edge  adheres 
very  closely,  by  mutual  interlacement  of  fibres,  to  the  zone  of  Zinn.  In  the  middle  of 
the  membrane,  its  thickness  is  about  T-|7  of  an  inch.  It  becomes  thinner  near  the  ante- 
rior margin,  where  it  measures  only  about  ^  of  an  incn-  Its  external  surface  is  in  con- 
tact with  the  choroid,  and  its  internal,  with  the  hyaloid  membrane  of  the  vitreous  humor. 

The  optic  nerve  penetrates  the  retina  about  %  of  an  inch  within  and  T^  of  an  inch  be- 
low the  antero-posterior  axis  of  the  globe,  presenting,  at  this  point,  a  small,  rounded 
elevation  upon  the  internal  surface  of  the  membrane,  perforated  in  its  centre  for  the  pas- 
sage of  the  centra]  artery  of  the  retina.  At  from  T^  to  %  of  an  inch  external  to  the  point 
of  penetration  of  the  nerve,  is  an  elliptic  spot,  its  long  diameter  being  horizontal,  about 
£  of  an  inch  long  and  -fa  of  an  inch  broad,  called  the  yellow  spot  of  Sommerring,  or  the 
macula  lutea.  In  the  centre  of  this  spot,  is  a  depression,  called  the  fovea  centralis.  This 
depression  is  exactly  in  the  axis  of  distinct  vision.  The  yellow  spot  exists  only  in  man 
and  the  quadrumana. 

The  structures  in  the  retina  which  present  the  greatest  physiological  interest  are  the 
external  layer,  formed  of  rods  and  cones,  the  layer  of  nerve-cells,  and  the  filaments  which 
connect  the  rods  and  cones  with  the  cells.  These  are  the  only  anatomical  elements  of 
the  retina,  as  far  as  we  know,  that  are  directly  concerned  in  the  reception  of  optical  im- 
pressions, and  they  will  be  described  rather  minutely,  while  the  intermediate  layers  will 
be  considered  more  briefly. 

Most  modern  anatomists  recognize  eight  distinct  layers  in  the  retina,  as  follows: 

1.  An  external  layer,  situated  next  the  choroid,  called  Jacob's  membrane,  the  bacillar 
membrane,  or  the  layer  of  rods  and  cones. 

2.  The  external  granule-layer. 

3.  The  inter-granule  layer  (cone-fibre  plexus,  of  Hulke). 

4.  The  internal  granule-layer. 

5.  The  granular  layer. 

6.  The  layer  of  nerve-cells  (ganglion-layer). 

7.  The  expansion  of  the  fibres  of  the  optic  nerve. 

8.  The  limitary  membrane. 

The  layer  of  rods  and  cones  is  composed  of  rods,  or  cylinders,  extending  through  its 
entire  thickness,  closely  packed,  and  giving  to  the  external  surface  a  regular,  mosaic  ap- 
pearance ;  and,  between  these,  are  a  greater  or  less  number  of  flask-shaped  bodies,  the 
cones.  This  layer  is  about  ^^  of  an  inch  in  thickness  at  the  middle  of  the  retina;  ^-^ 
of  an  inch,  about  midway  between  the  centre  and  the  periphery ;  and,  near  the  periphery, 
about  4-^  of  an  inch.  At  the  macula  lutea,  the  rods  are  wanting,  and  the  layer  is  com- 
posed entirely  of  cones,  which  are  here  very  much  elongated.  Over  the  rest  of  the  mem- 
brane, the  rods  predominate,  and  the  cones  become  less  and  less  numerous  toward  the- 
periphery. 

The  rods  are  regular  cylinders,  their  length  corresponding  to  the  thickness  of  the 
layer,  terminating  above  in  truncated  extremities,  and  below  in  points,  which  are  prob- 
ably continuous  with  the  filaments  of  connection  with  the  nerve-cells,  though  they  have 
been  actually  traced  only  into  the  external  granule-layer.  Their  diameter  is  about  T^IT 
of  an  inch.  They  are  clear,  of  rather  a  fatty  lustre,  soft  and  pliable,  but  somewhat  brittle, 
and  so  alterable  that  they  are  with  difficulty  seen  in  a  natural  state.  They  should  be 
examined  in  perfectly  fresh  preparations,  moistened  with  liquid  from  the  vitreous  humor 
or  with  serum.  Their  intimate  structure,  as  well  as  that  of  the  cones,  has  recently 
been  very  closely  studied,  especially  by  German  anatomists.  When  perfectly  fresh,  it 
is  difficult  to  make  out  any  thing  but  an  entirely  homogeneous  structure ;  but,  shortly  after 
death,  each  rod  seems  to  be  divided  by  a  delicate  line  into  an  outer  and  an  inner  segment, 
the  outer  being  a  little  the  longer.  At  the  upper  extremity  of  the  inner  segment,  is  a 
hemispherical  body,  with  its  convexity  presenting  inward,  called  the  lentiform  body  (Lin- 


PHYSIOLOGICAL  ANATOMY   OF  THE  EYEBALL. 


777 


FIG.  14±.-Rods  of  the  retina. 

(Schultze.) 

From  the  monkey. — A.  Kods,  after  ma- 
ceration in  iodized  serum,  the  outer 
segment  (li)  truncated,  the  inner 
segment  (a)  coagulated,  granular, 
and  somewhat  swollen ;  c,  filament 
of  the  rods ;  rf,  nucleus.  B.  Kods 
from  the  frog:  1.  Fresh,  magnified 
500  diameters;  «,  inner  segment; 
&,  outer  segment ;  c,  lentiform  body ; 
d,  nucleus.  2.  Treated  with  di- 
lute acetic  acid  and  broken  up  into- 
plates. 


senformiger  Korper).  The  entire  inner  segment  is  somewhat  granular,  and  it  often  pre- 
sents a  granular  nucleus  at  its  inner  extremity.  The  outer  segment  apparently  differs 
in  its  constitution  from  the  inner  segment  and  is  not  similarly  affected  by  reagents. 
Treated  with  dilute  acetic  acid,  the  outer  segment  becomes 
broken  up  transversely  into  thin  disks.  These  points  in 
the  anatomy  of  the  rods  are  referred  to  particularly,  for 
the  reason  that  they  have  lately  been  used  as  an  anatomi- 
cal basis  for  a  theory  of  the  perception  of  colors.  They 
can  be  readily  understood  by  reference  to  Fig.  244. 

The  cones  are  probably  of  the  same  constitution  as  the 
rods,  but  that  portion  called  the  inner  segment  is  pyri- 
form.  The  straight  portion  above  (the  outer  segment)  is 
sometimes  called  the  cone-rod.  The  entire  cones  are 
about  half  the  length  of  the  rods  and  occupy  the  inner 
portion  of  the  layer.  The  outer  segment  is,  in  its  consti- 
tution, precisely  like  the  outer  segment  of  the  rods.  The 
inner  segment  is  slightly  granular  and  contains  a  nucleus. 
The  cones  are  connected  below  with  filaments  passing 
into  the  deeper  layers  of  the  retina.  The  arrangement  of 
the  rods  and  cones  is  seen  in  Fig.  245,  which  shows  the 
different  layers  of  the  retina. 

At  the  fovea  centralis,  the  external  layer  is  composed 
entirely  of  immensely  elongated  cones,  with  no  rods. 
These  are  slightly  increased  in  thickness  at  the  macula 
lutea,  but  are  diminished  again  in  thickness,  by  about 
one-half,  at  the  fovea  centralis.  At  the  fovea,  the  optic 
nerve-fibres  are  wanting;  and  the  ganglion-cells,  which  exist  in  a  single  layer  over 
other  portions  of  the  retina,  here  present  from  six  to  eight  layers,  except  at  the  very 
centre,  where  there  are  but  three  layers.  Of  the  layers  between  the  cones  and  the 
ganglion -cells,  the  external  granule-layer  and  the  inter-granule  layer  (cone-fibre  plexus) 
remain,  in  the  fovea,  while  the  internal  granule-layer  and  the  granular  (molecular)  layer 
are  wanting.  At  the  fovea,  indeed,  those  elements  of  the  retina  which  may  be  regarded 
as  purely  accessory  seem  to  disappear,  leaving  only  the  structures  that  are  concerned 
directly  in  the  reception  of  visual  impressions. 

The  external  granule-layer  is  composed  of  large  granules,  looking  like  cells,  which  are 
each  nearly  filled  with  a  single  nucleus.  These  are  connected  with  the  filaments  from  the 
rods  and  cones.  They  are  rounded  or  ovoid  and  measure  from  T^^-g-  to  ^^Vo  of  an  ^ncn 
in  diameter.  The  inter-granule  layer  (cone-fibre  plexus)  is  composed  apparently  of  mi- 
nute fibrillse  and  a  few  nuclei.  The  internal  granule-layer  is  composed  of  cells  nearly 
like  those  of  the  external  granule-layer,  but  a  little  larger,  and  probably  connected  with 
the  filaments  of  the  rods  and  cones.  The  granular  (molecular)  layer  is  situated  next  the 
layer  of  ganglion -cells. 

The  layer  of  ganglion-cells  is  composed  of  multipolar  cells,  like  those  in  the  brain, 
measuring  from  ^Vjr  to  T^-g-  of  an  inch  in  diameter.  In  the  centre  of  the  retina,  at  the 
macula  lutea,  the  cells  present  eight  layers,  and  they  diminish  to  a  single  layer  near  the 
periphery.  The  smaller  cells  are  situated  near  the  centre,  and  the  larger,  near  the  periph- 
ery. Each  cell  sends  off  several  filaments  (from  two  to  twenty-five)  probably  going  to 
the  layer  of  rods  and  cones,  and  a  single  filament,  which  becomes  continuous  with  one 
of  the  filaments  of  the  optic  nerve. 

The  layer  formed  by  the  expansion  of  the  optic  nerve  is  composed  of  pale,  transparent 
nerve-fibres,  from  5o^60  to  g-gooo  °f  an  in°h  in  diameter.  These  do  not  call  for  special 
description. 

The  limitary  membrane  is  a  delicate  structure,  with  fine  strife  and  nuclei,  composed 


778  SPECIAL  SENSES. 

of  connective-tissue  elements.  It  is  about  -^^  of  an  inch  in  thickness.  From  this 
membrane,  connective-tissue  elements  are  sent  into  the  various  layers  of  the  retina, 
where  they  form  a  framework  for  the  support  of  the  other  structures. 

As  we  before  remarked,  the  retina  becomes  progressively  thinner  from  the  centre  to 
the  periphery.  The  granular  layers  and  the  nervous  layers  rapidly  disappear  in  the 
anterior  half  of  the  membrane. 


FIG.  245  (A).—  Vertical  section  of  the  retina.  FIG.  245  (B).— Connection  of  the  rods  and  cones 

(H.  Muller.)  of  the  retina  with  the   nervous  elements. 

(Sappey.) 

FIG.  245  (A). — 1, 1,  layer  of  rods  .and  cones;  2,  rods;  8,  cones;  4,  4,  5,  (5,  external  granule-layer;  7,  inter-granule  layer 
(cone-fibre  plexus);  8,  internal  granule-layer;  9,  10,  finely  granular  gray  layer;  11,  layer  of  nerve-cells;  12, 12, 
12,  12,  14,  14,  fibres  of  the  optic  nerve ;  18,  membrana  limitans. 

FIG.  245  (B).— 1, 1,  2,  3,  rods  and  cones,  front  view ;  4,  5,  6,  rods,  side  view ;  7, 7,  8,  8,  cells  of  the  external  and  internal 
granule-layers ;  9,  cell,  connected  by  a  filament  with  subjacent  cells ;  10, 18,  nerve-cells,  connected  with  cells  of  the 
granule-layers ;  11,  21,  filaments  connecting  cells  of  the  external  and  internal  granule-layers  (12  is  not  in  the  figure) ; 
14, 15,  16,  17, 18,  19,  20,  22,  23,  24.  25,  26,  a  rod  and  a  cone,  connnected  with  the  cells  of  the  granule-layers,  with  the 
nerve-cells,  and  with  the  nerve-fibres. 


The  connection  between  the  rods  and  cones  and  the  ganglion-cells  may  be  readily 
understood  if  we  accept  the  following  explanation:  The  filaments  from  the  bases  of  the 
rods  and  cones  pass  inward,  presenting,  in  their  course,  the  corpuscles  which  we  have 
described  in  the  granule-layers,  and  finally  become,  as  is  thought,  directly  continuous 
with  the  poles  of  the  ganglion-cells.  The  cells,  in  their  turn,  send  filaments  to  the  layer 
formed  by  the  expansion  of  the  optic  nerve,  which  are  continuous  with  the  nerve-fibres. 
This  arrangement  is  shown  in  Tig.  245  (B). 

The  arteries  of  the  retina  branch  from  the  arteria  centralis,  presenting  a  beautifully 
arborescent  appearance  when  viewed  with  the  ophthalmoscope.  They  pass  into  the  layer 
of  gray  nervous  matter  and  send  their  branches  to  the  periphery,  where  they  supply  a 
wide  plexus  of  very  small  capillaries  in  the  ora  serrata.  The  capillaries  empty  into  an 


PHYSIOLOGICAL  ANATOMY  OF  THE  EYEBALL. 


779 


incomplete  venous  circle,  branches  from  which  pass  back  by  the  sides  of  the  arteries  to 
the  vena  centralis.    The  macula  lutea  is  provided  with  a  rich  plexus  of  minute  capillaries. 

Crystalline  Lens. — The  anatomy  of  the  crystalline  lens,  as  far  as  it  bears  upon  the 
physiology  of  vision,  is  very. simple.  It  is  a  double-convex  lens,  transparent,  and  exceed- 
ingly elastic.  It  has  a  function  in  the  refraction  of  the  rays  of  light  analogous  to  the 
action  of  convex  lenses  in  optical  instruments.  When  we  come  to  study  its  exact  struct- 
ure, however,  we  shall  find  many  points  that  are  still  undetermined  and  somewhat 
obscure ;  but,  fortunately,  these  are  not,  as  far  as  we  now  know,  of  much  physiological 
importance.  In  treating  of  the  anatomy  of  the  lens,  we  shall  simply  describe  the  most 
prominent  and  the  well-determined  points  in  its  structure.  A  complete  account  of  the 
arrangement  of  its  component  parts  would  necessitate  very  full  and  minute  descriptions, 
which  could  only  be  elucidated  by  numerous  illustrative  figures. 

The  lens  is  situated  behind  the  pupil,  in  what  is  called  the  hyaloid  fossa  of  the  vitre- 
ous humor,  which  is  exactly  moulded  to  its  posterior  convexity.  In  the  foetus,  the  cap- 
sule of  the  lens  receives  a  branch  from  the  arteria  centralis,  but  it  is  non-vascular  in  the 
adult.  The  anterior  convexity  of  the  lens  is  just  behind  the  iris,  and  its  borders  are  in 
relation  with  what  is  known  as  the  suspensory  ligament.  The  convexities  do  not  present 
regular  curves,  and  they  are  so  subject  to  variations  after  death  that  the  measurements, 
post-mortem,  are  of  little  value.  During  life,  however,  they  have  been  measured  very 
exactly  in  the  various  conditions  of  accommodation.  These  measurements  will  be  dis- 
cussed fully  in  connection  with  the  physiology  of  the  lens. 


FIG.  ^^.—Crystalline  lens,  anterior  view.     (Babuchin.) 

The  diameters  of  the  lens  in  the  adult  are  about  £  of  an  inch  transversely  and  £  of  an 
inch  antero-posteriorly.  The  convexity  is  greater  on  its  posterior  than  on  its  anterior 
surface.  In  foetal  life,  the  convexities  of  the  lens  are  much  greater  than  in  the  adult  and 
its  structure  is  much  softer.  In  old  age,  the  convexities  are  diminished  and  the  lens 
becomes  harder  and  quite  inelastic,  which  accounts  for  the  progressive  diminution  in  the 
power  of  accommodation. 

The  important  physiological  points  in  the  structure  of  the  lens  are  that  it  presents  an 
investing  membrane,  the  capsule,  the  lens  itself  being  composed  of  layers  of  fibres  of  dif- 
ferent degrees  of  density. 


780 


SPECIAL  SENSES. 


The  capsule  of  the  lens  is  an  exceedingly  thm>  transparent  membrane,  very  elastic,  so 
that,  when  it  is  torn,  the  force  of  its  contraction  frequently  expels  its  contents.  This 
membrane  is  generally  from  ^Vo  to  ^7  of  an  inch  thick ;  but  it  is  very  thin  at  the 
periphery,  measuring  here  only  ^  of  an  inch.  Its  thickness  is  increased  in  old  age. 
On  the  anterior  portion,  the  capsule  is  lined  with  a  layer  of  exceedingly  delicate,  nucle- 
ated epithelial  cells.  These  are  situated  on  the  inner  surface  of  the  membrane.  The 
posterior  half  of  the  capsule  has  no  epithelial  lining.  The  cells  are  regularly  polygonal, 
measuring  from  ^Vo  to  T1JVs  of  an  inch  in  diameter,  with  large,  round  nuclei.  After 
death  they  are  said  to  break  down  into  a  liquid,  known  as  the  liquid  of  Morgagni,  though 
by  some  this  liquid  is  supposed  to  be  exuded  from  the  substance  of  the  lens.  At  all 
events,  the  cells  disappear  soon  after  death. 

If  the  lens  be  viewed  entire  with  a  low  magnifying  power,  it  presents,  upon  either  of 
its  surfaces,  a  star  with  from  nine  to  sixteen  radiations  extending  from  the  centre  to 


FIG.  247.—  Crystalline  lens,  posterior  view.    (Babuchin.) 

about  half  or  two-thirds  of  the  distance  to  the  periphery.  The  stars  seen  upon  the  two 
surfaces  are  not  coincident,  the  rays  of  one  being  situated  between  the  rays  of  the  other. 
In  the  foetus,the  stars  are  more  simple,  presenting  only  three  radiations  upon  either  sur- 
face. These  stars  are  not  fibrous,  like  the  rest  of  the  lens,  but  are  composed  of  a  homo- 
geneous substance,  which  extends,  also,  between  the  fibres. 

The  greatest  part  of  the  substance  of  the  lens  is  composed  of  very  delicate,  soft,  and 
pliable  fibres,  which  are  transparent,  but  perfectly  distinct.  These  fibres  are  flattened, 
six-sided  prisms,  closely  packed  together,  so  that  their  transverse  section  presents  a  regu- 
larly-tesselated  appearance.  They  are  from  T-gVo  to  ^Vs  of  an  incn  broad  and  from 
TTOTO  to  -roV?  °f  an  mch  in  thickness.  Their  flat  surfaces  are  parallel  with  the  surface 
of  the  lens.  The  direction  of  the  fibres  is  from  the  centre  and  from  the  rays  of  the 
stellate  figures  to  the  periphery,  where  they  turn  and  pass  to  the  star  upon  the  opposite 
side.  The  outer  layers  of  fibres,  near  the  equator,  or  circumference  of  the  lens,  are  pro- 
vided with  exceedingly  distinct,  oval  nuclei,  with  one  or  two  nucleoli.  These  become 
smaller  as  we  pass  deeper  into  the  substance  of  the  lens,  and  gradually  they  disappear. 

The  regular  arrangement  of  the  fibres  of  the  lens  makes  it  possible  to  separate  its 
substance  into  lamina,  which  have  been  compared  by  anatomists  to  the  layers  of  an 
onion ;  but  this  separation  is  entirely  artificial,  and  the  number  of  apparent  layers  depends 


PHYSIOLOGICAL   ANATOMY   OF   THE  EYEBALL. 


781 


upon  the  dexterity  of  the  manipulator.  It  is  to  be  noted,  however,  that  the  external 
portions  of  the  lens  are  soft,  even  gelatinous,  and  that  the  central  layers  are  much 
harder,  forming  a  sort  of  central  kernel,  or  nucleus. 

The  lens  is  composed  of  a  peculiar  organic  nitro- 
genized  substance,  very  analogous  to  globuline,  called 
crystalline,  combined  with  various  inorganic  salts. 
One  of  the  peculiar  constituents  of  this  body  is  choles- 
terine.  In  an  examination  of  four  fresh  crystalline 
lenses  of  the  ox,  we  found  cholesterine,  in  the  pro- 
portion of  0-907  of  a  part  per  1,000.  In  some  cases 
of  cataract,  cholesterine  exists  in  the  lens  in  a  crys- 
talline form ;  but,  under  normal  conditions,  it  is  united 
with  the  other  constituents. 


FIG.  248.— Section  of  the  crystalline  lens. 
(Babuchin.) 


Suspensory  Ligament  of  the  Lens  (Zone  of  Zinri). — 
When  we  come  to  the  description  of  the  vitreous  hu- 
mor, we  shall  see  that  it  occupies  about  the  posterior 
two-thirds  of  the  globe,  and  is  enveloped  in  a  delicate 
capsule,  called  the  hyaloid  membrane.  In  the  region 
of  the  ora  serrata  of  the  retina,  this  membrane  di- 
vides into  two  layers.  The  posterior  layer  lines  the 
depression  in  the  vitreous  humor  into  which  the  lens 
is  received.  The  anterior  layer  passes  forward  toward 
the  lens  and  divides  into  two  secondary  layers,  one  of 
which  passes  forward  to  become  continuous  with  the 
anterior  portion  of  the  capsule  of  the  lens,  while  the  other  passes  to  the  posterior  surface 
of  the  lens  to  become  continuous  with  this  portion  of  its  capsule.  The  anterior  of  these 
layers  is  corrugated,  or  thrown  into  folds  which  correspond  with  the  ciliary  processes, 
with  which  it  is  in  contact.  This  corrugated  portion  is  called  the-  zone  of  Zinn. 
The  two  layers  thus  surround  the  lens  and  are  properly  called  its 
suspensory  ligament.  As  the  two  layers  of  the  suspensory  ligament 
separate  at  a  certain  distance  from  the  lens,  one  passing  to  the  ante- 
rior and  the  other  to  the  posterior  portion  of  the  capsule,  there 
remains  a  triangular  canal,  about  -^  of  an  inch  wide,  surrounding 
the  border  of  the  lens,  called  the  canal  of  Petit.  Under  natural 
conditions,  the  walls  of  this  canal  are  nearly  in  apposition  and  it 
contains  a  very  small  quantity  of  clear  liquid. 

As  we  have  already  remarked  in  describing  the  retina,  at  the   FlG"  249^ap™y.f  Zinn' 


1,  crystalline  lens;  2, 2,  vit- 
reous humor ;  3,  3,  zone 
of  Zinn ;  4,  4,  posterior 
portion  of  the  zone  of 
Zinn,  thrown  into  folds  ; 
5,  6,  6,  anterior  and  mid- 
dle portions  of  the  zone 
of  Zinn. 


ora  serrata,  the  membrane  is  closely  connected,  by  a  mutual  inter- 
lacement of  fibres,  with  the  suspensory  ligament.  It  is  important 
to  appreciate  clearly  the  relations  of  the  suspensory  ligament,  in 
order  to  understand  the  mechanism  of  accommodation  of  the  lens 
to  vision  at  different  distances.  The  ciliary  muscle  being  in  repose, 
during  what  is  termed  the  indolent  condition  of  the  eye,  when  it  is 
adapted  to  vision  at  long  distances,  the  tension  of  the  parts  flattens  the  lens ;  but,  in  the 
effort  of  accommodation  for  near  objects,  the  ciliary  muscle  contracts,  compresses  the 
contents  of  the  globe,  relaxes  the  suspensory  ligament,  and  the  inherent  elasticity  of  the 
lens  renders  it  more  convex.  It  is  by  a  delicate  use  of  this  muscle,  that  the  proper  adap- 
tation of  the  curvatures  of  the  lens  is  obtained. 

The  membrane  forming  the  suspensory  ligament  is  composed  of  pale  longitudinal  and 
transverse  fibres  of  rather  a  peculiar  appearance,  which  are  much  less  affected  by  acetic 
acid  than  the  ordinary  fibres  of  connective  tissue. 

Aqueous  Humor. — The  space  bounded  in  front  by  the  cornea,  posteriorly  by  the  crys- 


782  SPECIAL  SENSES. 

talline  lens  and  the  anterior  face  of  its  suspensory  ligament,  and,  at  its  circumference,  by 
the  tips  of  the  ciliary  processes,  is  known  as  the  aqueous  chamber.  This  contains  a  clear 
liquid,  called  the  aqueous  humor.  The  iris  separates  this  space  into  two  divisions,  which 
communicate  with  each  other  through  the  pupil ;  viz.,  the  anterior  chamber,  situated  be- 
tween the  anterior  face  of  the  iris  and  the  cornea,  and  the  posterior  chamber,  between  the 
posterior  face  of  the  iris  and  the  crystalline.  It  is  evident,  from  the  position  of  the  iris, 
that  the  anterior  chamber  is  much  the  larger ;  and,  indeed,  the  posterior  surface  of  the 
iris  and  the  anterior  surface  of  the  lens  are  in  contact,  except,  perhaps,  near  their  pe- 
riphery or  when  the  iris  is  very  much  dilated.  The  liquid  filling  the  chambers  of  the  eye 
is  said  to  be  secreted  by  the  blood-vessels  of  the  ciliary  processes ;  at  all  events,  it  is  rap- 
idly reproduced  after  it  has  been  evacuated,  as  occurs  in  many  surgical  operations  upon 
the  eye. 

There  is  very  little  to  be  said  concerning  the  properties  and  composition  of  the  aque- 
ous humor.  It  is  perfectly  colorless  and  transparent,  faintly  alkaline,  of  a  specific  gravity 
of  about  1005,  and  possesses  the  same  index  of  refraction  as  the  cornea  and  the  vitreous 
humor.  As  we  should  infer  from  its  low  specific  gravity,  the  aqueous  humor  is  composed 
chiefly  of  water.  It  contains  a  small  quantity  of  an  albuminoid  matter,  but  it  is  not  ren- 
dered turbid  by  heat  or  other  agents  which  coagulate  albumen.  Various  inorganic  salts 
(the  chlorides,  sulphates,  phosphates,  and  carbonates)  exist  in  this  liquid,  in  small  propor- 
tion. It  contains  also  traces  of  urea  and  glucose. 

Vitreous  Humor. — The  vitreous  humor  is  a  clear,  glassy  substance,  occupying  about 
the  posterior  two-thirds  of  the  globe.  It  is  enveloped  in  an  exceedingly  delicate,  struct- 
ureless capsule,  called  the  hyaloid  membrane,  which  is  about  ^Vfr  °f  an  inch  m  thick- 
ness. This  membrane  adheres  pretty  strongly  to  the  limitary  membrane  of  the  retina. 
In  front,  at  the  ora  serrata,  as  we  have  already  seen,  the  hyaloid  membrane  is  thickened 
and  becomes  continuous  with  the  suspensory  ligament  of  the  lens. 

The  vitreous  humor  itself  is  gelatinous,  of  feeble  consistence,  slightly  alkaline  in  its 
reaction,  with  a  specific  gravity  of  about  1005.  Upon  section,  there  oozes  from  it  a 
watery  fluid  of  a  slightly  mucilaginous  consistence.  This  humor  is  not  affected  by  heat  or 
alcohol,  but  it  is  coagulated  by  certain  mineral  salts,  more  especially  the  acetate  of  lead. 
When  thus  solidified,  it  presents  regular  layers,  like  the  white  of  an  egg  boiled  in  its 
shell ;  but  these  are  artificial.  In  the  embryon,  the  vitreous  humor  is  divided  into  numer- 
ous little  cavities  and  contains  cells  and  leucocytes.  It  is  also  penetrated  by  a  branch  from 
the  central  artery  of  the  retina,  which  passes  through  its  centre  to  ramify  on  the  poste- 
rior surface  of  the  crystalline  lens.  This  structure,  however,  is  not  found  in  the  adult, 
the  vitreous  humor  being  then  entirely  without  blood-vessels. 

There  is  still  considerable  difference  of  opinion  with  regard  to  the  structure  of  the 
vitreous  humor  in  the  adult,  some  anatomists  believing  that  it  is  perfectly  homogeneous 
and  that  the  so-called  laminae  are  produced  only  by  the  action  of  reagents,  while  others 
state  that  it  is  divided  into  compartments,  by  processes  penetrating  from  and  connected 
with  the  hyaloid  membrane.  The  weight  of  authority  is  decidedly  in  favor  of  a  sub- 
division of  the  humor  into  compartments  formed  by  delicate  membranes  radiating  from 
the  point  of  penetration  of  the  optic  nerve  to  the  anterior  boundary  where  the  hyaloid 
membrane  is  in  contact  with  the  capsule  of  the  lens.  In  this  way,  the  humor  is  divided 
up,  something  like  the  half  of  an  orange,  by  about  one  hundred  and  eighty  membranous 
processes  of  extreme  delicacy,  which  do  not  interfere  with  its  transparency. 

Summary  of  the  Anatomy  of  the  Globe  of  the  Eye. 

For  the  intimate  structure  of  the  various  coats  of  the  eye,  their  dimensions,  etc.,  the 
reader  is  referred  to  the  descriptions  just  given  of  these  parts.  In  this  summary,  we 
propose  simply  to  show  the  relations  of  the  various  parts,  giving  at  the  same  time  a 
brief  statement  of  their  physiological  importance.  This  end  will  be  attained  by  a  full 


SUMMARY   OF  THE   ANATOMY   OF  THE   GLOBE   OF  THE  EYE.      783 

explanation  of  Fig.  250,  which  represents  a  section  of  the  human  eye  and  shows  the 
relations  of  its  various  coats,  humors,  etc. 

The  eyeball  is  nearly  spherical  in  its  posterior  five-sixths,  its  anterior  sixth  being 
formed  of  the  segment  of  a  smaller  sphere,  which  is  slightly  projecting.  In  its  posterior 
five-sixths,  it  presents  the  following  coats,  indicated  in  the  figure  : 

S.  The  sclerotic ;  a  dense,  fibrous  membrane,  chiefly  for  the  protection  of  the  more 
delicate  structures  of  the  globe,  and  giving  attachment  to  the  muscles  which  move  the 
eyeball.  Attached  to  the  sclerotic,  are  the  tendons  of  R,  R,  the  recti  muscles. 


...CKo. 


Cor. 


FIG.  250.— Section  of  the  human  eye,  copied  from  Helmholtz  and  slightly  modified, 

Cor.  The  cornea ;  a  transparent  structure,  forming  the  anterior,  projecting  sixth  of 
the  globe ;  dense  and  resisting,  allowing,  however,  the  passage  of  light ;  covered,  on  its 
convex  surface,  with  several  layers  of  transparent  epithelial  cells,  and,  on  its  posterior 
surface,  with  the  membrane  of  the  aqueous  humor. 

Oho.  The  choroid  coat,  lining  the  sclerotic  and  extending  only  as  far  forward  as  the 
cornea  ;  connected  with  the  sclerotic  by  loose  connective  tissue,  in  which  ramify  blood- 
vessels and  nerves,  and  presenting  an  external,  vascular  layer  and  an  internal,  pigmentary 
layer,  which  latter  gives  its  characteristic  dark-brown  color. 

0.  P.,  0.  P.  The  ciliary  processes ;  peculiar  folds  of  the  choroid,  which  form  its  ante- 
rior border,  and  which  embrace  the  folds  of  the  suspensory  ligament  of  the  lens. 

0.  M.,  C.  M.  The  ciliary  muscle,  formerly  called  the  ciliary  ligament ;  a  muscular  ring, 
situated  just  outside  of  the  ciliary  processes,  arising  from  the  circular  line  of  junction  of 
the  sclerotic  with  the  cornea,  and  passing  over  the  ciliary  processes,  to  become  lost  in 
the  fibrous  tissue  of  the  choroid.  This  is  sometimes  called  the  tensor  of  the  choroid.  Its 
action  is  to  tighten  the  choroid  over  the  vitreous  humor  and  to  relax  the  ciliary  processes 
and  the  suspensory  ligament  of  the  lens,  when  the  lens,  by  virtue  of  its  elasticity,  becomes 
more  convex.  The  ciliary  muscle  is  the  active  agent  in  accommodation.  In  the  figure, 
the  mechanism  of  accommodation  is  shown  by  the  dotted  lines,  which  represent  the  sus- 


784  SPECIAL  SENSES. 

pensory  ligament  relaxed  by  the  contraction  of  the  ciliary  muscle,  and  the  lens,  increased 
in  its  convexity,  pushing  forward  the  iris. 

I.,  I.  The  iris  ;  dividing  the  space  in  front  of  the  lens  into  two  chambers  occupied  by 
the  aqueous  humor :  (A)  The  anterior  chamber  is  much  the  larger.  The  iris,  in  its  cen- 
tral portion  surrounding  the  pupil  (P),  is  in  contact  with  the  lens.  Its  circumference  is 
just  in  front  of  the  line  of  origin  of  the  ciliary  muscle. 

Ret.,  Ret.  The  retina ;  an  exceedingly  delicate,  transparent  membrane,  lining  the 
choroid  and  extending  to  about  TV  of  an  inch  behind  the  ciliary  processes,  the  anterior  mar- 
gin forming  the  ora  serrata.  O.  The  optic  nerve  penetrating  the  retina  a  little  internal  to 
and  below  the  antero-posterior  axis.  The  layer  of  rods  and  cones  is  situated  externally, 
next  the  choroid.  Internal  to  the  layer  of  rods  and  cones,  are  the  four  granular  layers  ; 
next,  the  layer  of  nerve-cells ;  next,  the  expansion  of  the  fibres  of  the  optic  nerve ;  and 
next,  in  apposition  with  the  hyaloid  membrane  of  the  vitreous  humor,  is  the  limitary 
membrane.  The  layer  of  rods  and  cones  is  supposed  to  be  the  portion  which  receives 
visual  impressions,  the  rods  and  cones  being  connected  with  the  nerve-cells,  and  through 
them  with  the  fibres  of  the  optic  nerve,  by  delicate  filaments.  The  macula  lutea  and  the 
fovea  centralis  are  exactly  in  the  axis  of  distinct  vision. 

C.  The  crystalline  lens ;  elastic,  transparent,  enveloped  in  its  capsule  and  surrounded 
by  S.  L.,  S.  L.,  the  suspensory  ligament. 

S.  L.,  S.  L.  The  suspensory  ligament ;  the  anterior  layer  connected  with  the  anterior 
portion  of  the  capsule  of  the  lens,  and  the  posterior,  with  the  posterior  portion  of  the 
capsule.  The  folded  portion  of  this  ligament,  which  is  received  between  the  folds  of  the 
ciliary  processes,  is  called  the  zone  of  Zinn.  The  triangular  canal  between  the  anterior 
and  the  posterior  layers  of  the  suspensory  ligament  and  surrounding  the  equator  of  the 
lens  is  called  the  canal  of  Petit. 

V.  The  vitreous  humor ;  enveloped  in  the  structureless  hyaloid  membrane,  which 
membrane  is  continuous  in  front  with  the  suspensory  ligament  of  the  lens. 

Refraction  in  the  Eye. 

It  is  simply  impossible  to  obtain  a  clear  idea  of  the  physiology  of  vision  without  hav- 
ing carefully  studied  the  physiological  anatomy  of  the  visual  organs ;  and,  for  this  rea- 
son, we  have  been  as  exact  as  possible  and  somewhat  minute  in  our  description  of  the 
structure  of  the  eye.  If  the  student  will  carefully  study  the  anatomy  of  the  parts,  a 
very  succinct  statement  of  some  of  the  well-established  laws  of  refraction  will  render 
the  physiology  so  simple  that  it  will  follow  almost  without  explanation. 

In  applying  the  laws  of  the  refraction  of  light  to  the  transparent  media  of  the  eye, 
it  is  necessary  to  bear  in  mind  certain  general  facts  with  regard  to  vision,  that  have  as 
yet  been  referred  to  either  very  briefly  or  not  at  all. 

The  eye  is  not  by  any  means  a  perfect  optical  instrument,  looking  at  it  from  a  purely 
physical  point  of  view.  This  statement,  however,  should  not  be  understood  as  implying 
that  the  arrangement  of  the  organs  of  vision  is  not  such  as  to  adapt  them  perfectly  to  the 
functions  which  they  have  to  perform  in  connection  with  the  proper  appreciation  of 
visual  impressions.  By  physical  tests,  it  can  be  demonstrated  that  the  eye  is  not  entirely 
achromatic ;  but,  in  ordinary  vision,  the  dispersion  of  colors  is  not  appreciated.  There 
is  but  a  single  point  in  the  retina,  the  fovea  centralis,  where  vision  is  absolutely  distinct ; 
and  it  is  upon  this  point  that  images  are  made  to  fall  when  the  eye  is  directed  toward 
any  particular  object. 

It  is  curious  to  note,  however,  that  the  refracting  apparatus  is  not  exactly  centred,  a 
condition  so  essential  to  the  satisfactory  performance  of  our  most  perfect  optical  instru- 
ments. For  example,  in  a  compound  microscope  or  a  telescope,  the  centres  of  the  differ- 
ent lenses  entering  into  the  construction  of  the  instrument  are  all  situated  in  a  straight 
line.  Were  the  eye  a  perfect  optical  instrument,  the  line  of  vision  would  coincide  ex- 


REFRACTION   IN   THE  EYE.  785 

actly  with  the  axis  of  the  cornea ;  but  this  is  not  the  ease.  The  visual  line  (a  line  drawn 
from  an  object  to  its  image  on  the  fovea  centralis)  deviates  from  the  axis  of  the  cornea, 
in  normal  eyes,  to  the  nasal  side.  The  visual  line,  therefore,  forms  an  angle  with  the 
axis  of  the  cornea.  This  is  known  as  the  angle  alpha.  This  deviation  of  the  visual 
line  from  the  mathematical  centre  of  the  eye  is  observed  both  in  the  horizontal  and  in 
the  vertical  planes.  "  The  horizontal  deviation  varies  from  two  to  eight  degrees  (Schuer- 
mari),  the  vertical,  from  one  to  three  degrees  (Mandelstamm).'1'1  Of  course,  this  want  of 
exact  centratiou  of  the  optical  apparatus,  in  normal  eyes,  does  not  practically  affect  dis- 
tinct vision,  for,  when  the  eyes  are  directed  toward  any  object,  this  object  is  brought  in 
the  line  of  the  visual  axis ;  but  the  angle  alpha  is  an  important  element  to  be  taken  into 
account  in  various  mathematical  calculations  connected  with  the  physics  of  the  eye. 

The  field,  or  area  of  distinct  vision,  is  quite  restricted ;  but,  were  it  larger,  it  is  proba- 
ble that  the  mind  would  become  confused  with  the  extent  and  variety  of  the  impressions, 
and  that  we  should  be  unable  so  easily  to  observe  minute  details  and  fix  the  attention 
upon  small  objects. 

While  we  see  certain  objects  with  absolute  distinctness  in  a  restricted  field,  the  angle 
of  vision  is  very  wide,  and  rays  of  light  are  admitted  from  an  area  equal  nearly  to  the 
half  of  a  sphere.  Such  a  provision  is  eminently  well  adapted  to  our  requirements.  We 
direct  the  eyes  to  a  particular  point  and  see  a  certain  object  distinctly,  getting  the  advan- 
tage of  an  image  in  the  two  eyes  exactly  at  the  points  of  distinct  vision ;  the  rays  com- 
ing from  without  the  area  of  distinct  vision  are  received  upon  different  portions  of  the 
surface  of  the  retina  and  produce  an  impression  more  or  less  indistinct,  not  interfering 
with  the  observation  of  the  particular  object  to  which  the  attention  is  for  the  moment 
directed ;  but,  even  while  looking  intently  at  any  object,  the  attention  may  be  attract- 
ed by  another  object  of  an  unusual  character,  which  might,  for  example,  convey  an  idea 
of  danger,  and  the  point  of  distinct  vision  can  be  turned  in  its  direction.  Thus,  while 
we  see  distinctly  but  few  objects  at  one  time,  the  area  of  indistinct  vision  is  immense  ; 
and  our  attention  may  be  readily  directed  to  unexpected  or  unusual  objects  that  may 
come  within  any  portion  of  the  field  of  view.  The  small  extent  of  the  area  of  distinct 
vision,  especially  for  near  objects,  may  be  readily  appreciated  if  we  watch  a  person 
attentively  reading  a  book,  when  the  eyes  will  be  seen  to  follow  the  lines  from  one  side 
of  the  page  to  the  other  with  perfect  regularity.  When  we  consider  that,  in  addition  to 
these  remarkable  qualities,  which  are  never  thought  of  in  artificial  optical  instruments, 
the  eye  may  be  accommodated  at  will,  with  the  most  exquisite  nicety,  to  vision  at  differ- 
ent distances,  and  that  we  possess  correct  appreciation  of  form,  etc.,  by  the  use  of  the 
two  eyes,  it  is  evident  that  the  organ  of  vision  gains  rather  than  loses  in  comparison  with 
the  most  perfect  instruments  that  have  ever  been  or  probably  ever  will  be  constructed. 

Laws  of  Refraction,  Dispersion,  etc.,  bearing  upon  the  Physiology  of  Vision. — In 
the  present  state  of  physiological  science,  we  have  little  to  do  with  the  theory  of 
light,  except  as  regards  the  modifications  of  luminous  rays  in  passing  through  the  re- 
fracting media  of  the  eye.  It  will  be  sufficient  to  state  that  nearly  all  physicists  of  the 
present  day  agree  in  accepting  what  is  known  as  the  theory  of  undulation,  rejecting  in 
toto  the  emission-theory  proposed  by  Newton.  It  is  necessary  to  the  theory  of  undula- 
tion to  assume  that  all  space  and  all  transparent  bodies  are  permeated  with  what  has  been 
called  a  luminiferous  ether ;  and  that  light  is  propagated  by  a  vibration  or  an  undulation 
of  this  hypothetical  substance.  This  theory  assimilates  light  to  sound,  in  the  mechanism 
of  its  propagation  ;  but,  in  sound,  the  waves  are  supposed  to  be  longitudinal,  or  to  fol- 
low the  line  of  propagation,  while  in  light  the  particles  are  supposed  to  vibrate  trans- 
versely, or  at  right  angles  to  the  line  of  propagation.  It  must  be  remembered,  however, 
that  the  undulatory  theory  of  sound  is  capable  of  positive  demonstration,  and  that  the 
propagation  of  sound  by  waves  can  only  take  place  through  ponderable  matter,  the 
vibrations  of  which  can  always  be  observed ;  while  luminous  vibrations  involve  the 
50 


786  SPECIAL  SENSES. 

existence  of  an  imponderable  and  a  purely  hypothetical  ether.  It  is  possible,  indeed,  that 
scientific  facts  may,  in  the  future,  render  the  existence  of  such  an  ether  improbable  or  its 
supposition  unnecessary ;  but,  at  present,  all  we  can  say  is  that  the  theory  of  luminous 
undulation  is  entirely  in  accord  with  the  optical  phenomena  that  have  thus  far  been  rec- 
ognized. 

The  different  calculations  of  physicists  with  regard  to  the  velocity  of  light  have  been 
remarkably  uniform  in  their  results.  The  lowest  calculations  put  it  at  about  185,000 
miles  in  a  second,  and  the  highest,  at  about  195,000  miles.  The  rate  of  propagation  is 
usually  assumed  to  be  about  192,000  miles. 

The  intensity  of  light  is  in  proportion  to  the  amplitude  of  the  vibrations.  The  inten- 
sity diminishes  as  the  distance  of  the  luminous  body  increases,  and  is  in  inverse  ratio  to 
the  square  of  the  distance. 

In  the  theory  of  the  colors  into  which  pure  white  light  may  be  decomposed  by  prisms, 
it  is  assumed,  as  a  matter  of  demonstration,  that  the  waves  of  the  different  colors  of  the 
solar  spectrum  are  not  of  the  same  length.  The  decomposition  of  light  is  produced  by 
differences  in  the  refrangibility  of  the  different  colored  rays  as  they  pass  through  a  denser 
medium  than  the  air.  The  differences  in  the  wave-lengths  for  different  colors  is  very 
simply  set  forth  by  Tyndall  as  follows  : 

"  The  color  of  light  is  determined  solely  by  its  wave-length.  The  ether-waves  grad- 
ually diminish  in  length  from  the  red  to  the  violet.  The  length  of  a  wave  of  red  light  is 
about  Tj^fjnr  of  an  inch  ;  that  of  the  wave  of  violet  light  is  about  -^-^  of  an  inch.  The 
waves  which  produce  the  other  colors  of  the  spectrum  lie  between  these  extremes. 

"  The  velocity  of  light  being  192,000  miles  in  a  second,  if  we  multiply  this  number 
by  39,000,  we  obtain  the  number  of  waves  of  red  light  in  192,000  miles  ;  the  product  is 
474,439,680,000,000.  All  of  these  waves  enter  the  eye  in  a  second.  In  the  same  inter- 
val 699,000,000,000,000  waves  of  violet  light  enter  the  eye.  At  this  prodigious  rate  is 
the  retina  hit  by  the  waves  of  light. 

"  Color,  in  fact,  is  to  light,  what  pitch  is  to  sound.  The  pitch  of  a  note  depends 
solely  on  the  number  of  aerial  waves  which  strike  the  ear  in  a  second.  The  color  of 
light  depends  on  the  number  of  ethereal  waves  which  strike  the  eye  in  a  second. 
Thus  the  sensation  of  red  is  produced  by  imparting  to  the  optic  nerve  four  hundred  and 
seventy-four  millions  of  millions  of  impulses  per  second,  while  the  sensation  of  violet  is 
produced  by  imparting  to  the  nerve  six  hundred  and  ninety-nine  millions  of  millions  per 
second."  In  this  way  the  scale  of  colors  in  the  solar  spectrum  is  compared  to  the  scale 
of  musical  notes  and  intervals.  Indeed,  Helmholtz  has  constructed  a  theoretical  scale 
of  colors  to  correspond  with  musical  tones  and  semitones. 

The  analysis  of  white  light  into  the  different  colors  of  the  spectrum  shows  that  it  is 
compound ;  and,  by  synthesis,  the  colored  rays  may  be  brought  together,  producing 
white  light.  Colors  may  be  obtained  by  decomposition  of  light  by  transparent  bodies, 
the  different  colored  rays  being  refracted,  or  bent  by  a  prism  at  different  angles.  It  is 
not  in  this  way,  however,  that  the  colors  of  different  objects  are  produced.  Certain 
objects  have  the  property  of  reflecting  the  rays  of  light.  A  perfectly  smooth,  polished 
surface,  like  a  mirror,  may  reflect  all  of  the  rays  ;  and  the  object  then  has  no  color,  the 
reflected  light  only  being  appreciated  by  the  eye.  Certain  other  objects  do  not  reflect 
all  of  the  rays  of  light,  some  of  them  being  lost  to  view  or  absorbed.  When  an  object 
absorbs  all  of  the  rays,  it  has  no  color  and  is  called  black.  When  an  object  absorbs  the 
rays  equally  and  reflects  a  portion  of  these  rays  without  decomposition,  it  is  gray  or 
white.  There  are  many  objects,  however,  that  decompose  white  light,  absorbing  certain 
rays  of  the  spectrum  and  reflecting  others.  The  rays  not  absorbed,  but  returned'  to 
the  eye  by  reflection,  give  color  to  the  object.  Thus,  if  an  object  absorb  all  of  the  rays 
of  the  spectrum  except  the  red,  the  red  rays  strike  the  eye,  and  the  color  of  the  object 
is  red.  So  it  is  with  objects  of  different  shades,  the  colors  of  which  are  given  simply 
by  the  unabsorbed  rays. 


REFRACTION   IN   THE  EYE.  737 

It  is  a  curious  fact  that  the  mixture  of  different  colors  in  certain  proportions  will 
result  in  white.  Two  colors,  which,  when  mixed,  result  in  white,  are  called  complemen- 
tary. The  following  colors  of  the  spectrum  bear  such  a  relation  to  each  other : 

Red  and  greenish -blue. 

Orange  and  cyanogen-blue. 

Yellow  and  indigo-blue. 

Greenish-yellow  and  violet. 

The  fact  that  impressions  made  upon  the  retina  persist  for  an  appreciable  length  of 
time  enables  us  to  illustrate  the  law  of  complementary  colors.  If  a  disk,  presenting 
divisions  with  two  complementary  colors,  be  made  to  revolve  so  rapidly  that  the  impres- 
sions made  by  the  two  colors  are  blended,  the  resulting  color  is  white. 

It  is  almost  useless,  with  our  present  knowledge,  to  speculate  with  regard  to  the  prob- 
able mechanism  of  the  appreciation  of  colors  in  vision.  The  facts  just  stated  are  suffi- 
ciently clear,  showing  that  the  number  of  ethereal  vibrations  is  different  for  different 
colors  ;  but  it  is  by  no  means  determined  that  differences  in  the  amplitude  of  the  vibra- 
tions are  in  direct  relation  with  the  arrangement  of  the  disks  of  the  rods  and  cones  in 
different  portions  of  the  retina,  a  theory  lately  proposed  by  Zenker.  The  curious  phe- 
nomena of  color-blindness  depend  upon  an  abnormal  condition  of  the  visual  apparatus. 
Persons  possessing  this  peculiarity — called  sometimes  Daltonism,  after  the  celebrated 
English  chemist,  who  described  this  infirmity  as  it  existed  in  his  own  person — although 
vision  may  be  normal  in  other  respects,  cannot  distinguish  certain  colors,  will  mistake  red 
for  green,  etc.,  and  some  can  only  distinguish  black  and  white.  It  is  a  curious  fact,  also, 
that  persons  affected  with  color-blindness  (Daltonism,  or  achromatopsia)  are  sometimes 
incapable  of  distinguishing  different  musical  tones.  Although  often  congenital  and  irre- 
mediable, it  is  now  known  that  color-blindness  is  sometimes  produced  by  the  excessive 
use  of  alcohol  and  tobacco,  exposure  to  cold  and  wet,  etc.,  and  is  amenable  to  treatment. 

Refraction  ly  Lenses. — A  ray  of  light  is  an  imaginary  pencil,  so  small  as  to  present 
but  a  single  line ;  and  the  light  admitted  to  the  interior  of  the  eye  by  the  pupil  is  sup- 
posed to  consist  of  an  infinite  number  of  such  rays.  In  studying  the  physiology  of 
vision,  it  is  important  to  recognize  the  laws  of  refraction  of  rays  by  transparent  bodies 
bounded  by  curved  surfaces,  with  particular  reference  to  the  action  of  the  crystalline  lens. 


FIG.  251. — Refraction  by  prisms. 

The  action  of  a  double-convex  lens,  like  the  crystalline,  in  the  refraction  of  light, 
may  be  readily  understood  if  we  simply  apply  the  well-known  laws  of  refraction  by 
prisms.  A  ray  of  light  falling  upon  the  side  of  a  prism  at  an  angle  is  deviated  toward 
a  line  perpendicular  to  the  surface  of  the  prism.  As  the  ray  passes  from  the  prism  to 


7gg  SPECIAL  SENSES. 

the  air,  it  is  again  refracted,  but  then  the  deviation  is  from  the  perpendicular  of  the  sec- 
ond  surface  of  the  prism.  If  we  imagine  two  prisms  placed  together,  as  in  Fig.  251,  the 
ray  A  B  will  be  bent  toward  the  perpendicular  G  B  to  M.  As  it  passes  from  the  prism, 
it  will  be  refracted  from  the  perpendicular  H  M  and  take  the  direction  M  I.  Correspond- 
ing refraction  takes  place  in  the  ray  N"  O  falling  upon  the  lower  prism.  These  two  rays 
will  cross  each  other  at  the  point  L. 

A  circle  is  supposed  to  be  equivalent  to  a  polygon  with  an  infinite  number  of  sides. 
A  regular  double-convex  lens  is  a  transparent  body  bounded  by  portions  of  a  sphere,  and 
it  may  be  assumed  to  be  composed  of  an  infinite  number  of  prisms.  The  action  of  a  con- 
vex lens  is  to  converge  the  rays  of  light  falling  upon  different  portions  of  their  surface  so 
that  they  cross  at  a  certain  distance  behind  the  lens.  If  we  imagine  the  lens  A  B  (Fig. 
252)  to  be  free  from  spherical  aberration,  the  rays  C  D  and  C  E,  from  the  point  C,  will 


FIG.  252.— Refraction  by  convex  lenses. 

be  refracted  and  brought  to  a  focus  at  the  point  F.  In  the  same  way.  the  rays  from  the 
point  K  will  be  brought  to  a  focus  at  the  point  L,  the  two  sets  of  rays  crossing  at  G. 
The  same  is  true  for  all  the  rays  from  the  object  C  K,  which  strike  the  lens  at  an  angle  ; 
but  the  ray  H  I,  which  is  perpendicular  to  the  lens,  is  not  deviated.  The  line  H  I  is 
called  the  axis  of  the  lens.  These  facts  may  be  applied  to  the  crystalline  lens.  The  rays 
from  an  object  C  K  fall  upon  the  lens  and  are  brought  to  a  focus  so  as  to  produce  the 
image  L  F.  The  retina  is  supposed  to  be  at  such  a  distance  from  the  lens  that  the  rays 
are  brought  to  a  focus  exactly  at  its  surface.  Inasmuch  as  the  rays  cross  each  other  at 
the  point  G,  the  image  is  always  inverted. 

Supposing  the  crystalline  lens  to  be  free  from  spherical  and  chromatic  aberration,  the 
formation  of  a  perfect  image  depends  upon  the  following  conditions : 

The  object  must  be  at  a  certain  distance  from  the  lens.  If  the  object  be  too  near,  the 
rays,  as  they  strike  the  lens,  are  too  divergent  and  are  brought  to  a  focus  beyond  the 
plane  L  I  F,  or  behind  the  retina ;  and,  as  a  consequence,  the  image  is  confused.  In 
optical  instruments,  the  adjustment  is  made  for  objects  at  different  distances  by  moving 
the  lens  itself.  In  the  eye,  however,  the  adjustment  is  effected  by  increasing  or  dimin- 
ishing the  curvatures  of  the  lens,  so  that  the  rays  are  always  brought  to  a  focus  at  the 
visual  surface  of  the  retina.  The  faculty  of  thus  changing  the  curvatures  of  the  crys- 
talline lens  is  called  accommodation.  This  power,  however,  is  restricted  within  certain 
well-defined  limits. 

In  some  individuals,  the  antero-posterior  diameter  of  the  eye  is  too  long,  and  the 
rays,  for  most  objects,  come  to  a  focus  before  they  reach  the  retina.  This  defect  may  be 
remedied  by  placing  the  object  very  near  the  eye,  so  as  to  increase  the  divergence  of  the 
rays  as  they  strike  the  crystalline.  Such  persons  are  said  to  be  near-sighted  (myopic), 
and  objects  are  seen  distinctly  only  when  very  near  the  eye.  This  defect  may  be  reme- 


REFRACTION   IN  THE   EYE.  789 

died  for  distant  objects  by  placing  concave  lenses  before  the  eyes,  by  which  the  rays 
falling  upon  the  crystalline  are  diverged.  The  opposite  condition,  in  which  the  antero- 
posterior  diameter  is  too  short  (hypermetropia),  is  such  that  the  rays  are  brought  to  a 
focus  behind  the  retina.  This  is  corrected  by  converging  the  rays  of  incidence  by  plac- 
ing convex  lenses  before  the  eyes.  In  old  age,  the  crystalline  lens  becomes  flattened,  its 
elasticity  is  diminished,  and  the  power  of  accommodation  is  lessened  ;  conditions  which 
also  tend  to  bring  the  rays  to  a  focus  -behind  the  retina.  This  condition  is  called  pres- 
byopia. To  render  near  vision,  as  in  reading,  distinct,  objects  are  placed  farther  from 
the  eye  than  under  normal  conditions.  The  defect  may  be  remedied,  as  in  hypermetro- 
pia, by  placing  convex  lenses  before  the  eyes,  by  which  the  rays  are  converged  before 
they  fall  upon  the  crystalline  lens. 

The  mechanism  of  accommodation  will  be  fully  considered  in  connection  with  the 
physiology  of  the  crystalline  lens  ;  and  at  present,  it  is  sufficient  to  state  that,  in  looking  at 
distant  objects,  the  rays,  as  they  fall  upon  the  lens,  are  nearly  parallel.  The  lens  is  then 
in  repose,  or  "  indolent."  It  is  only  when  an  effort  is  made  to  see  near  objects  distinctly, 
that  the  agents  of  accommodation  are  called  into  action  ;  and  then,  very  slight  changes 
in  the  curvature  of  the  lens  are  sufficient  to  bring  the  rays  to  a  focus  exactly  on  the 
visual  surface  of  the  retina. 

Spherical  Aberration. — In  a  convex  lens,  with  its  surfaces  consisting  of  portions  of  a 
perfect  sphere,  the  rays  of  light  from  any  object  are  not  converged  to  a  uniform  focus, 
and  the  production  of  an  absolutely  distinct  image  is  impossible.  For  example,  if  we 
suppose  the  crystalline  lens  to  present  regular  curvatures,  the  rays  refracted  by  its  periph- 
eral portion  would  be  brought  to  a  focus  in  front  of  the  retina ;  the  focus  of  the  rays 
converged  by  the  lens  near  its  centre  would  be  behind  the  retina  ;  a  few,  only,  of  the 
rays  would  have  their  focus  at  the  retina  itself;  and,  as  a  consequence,  the  image  would 
appear'confused.  This  is  illustrated  in  imperfectly-corrected  lenses  and  is  called  spherical 
aberration.  For  example,  in  examining  an  object  with  an  imperfectly-corrected  objec- 
tive under  the  microscope,  it  is  evident  that  the  field  of  view  is  not  uniform,  and  that 
there  is  a  different  focal  adjustment  for  the  central  and  the  peripheral  portions  of  the 
lens.  In  the  construction  of  optical  instruments,  this  difficulty  may  be  in  part  corrected 
if  the  rays  of  light  be  cut  off  from  the  periphery  of  the  lens  by  a  diaphragm,  which  is 
an  opaque  screen  with  a  circular  perforation  allowing  the  rays  to  pass  to  a  restricted  por- 
tion of  the  lens  near  its  centre.  The  iris  corresponds  to  the  diaphragm  of  optical  instru- 
ments, and  it  corrects  the  spherical  aberration  of  the  crystalline  in  part,  by  eliminating  a 
portion  of  the  rays  that  would  otherwise  fall  upon  its  peripheral  portion.  But  this  cor- 
rection is  not  sufficient  for  high  magnifying  powers ;  and  it  is  only  by  the  more  or  less 
perfect  correction  of  this  kind  of  aberration  by  other  means,  that  powerful  lenses  have 
been  rendered  available  in  optics. 

The  spherical  aberration  of  lenses  which  diverge  the  rays  of  light  is  precisely  opposite 
to  the  aberration  of  converging  lenses.  If,  therefore,  we  construct  a  compound  lens,  it 
is  possible  to  fulfil  the  conditions  necessary  to  the  convergence  of  all  the  incident  rays  to 
a  focus  on  -a  uniform  plane,  so  that  the  image  produced  behind  the  lens  is  not  distorted. 
Given,  for  example,  a  double-convex  lens,  by  which  the  rays  are  brought  to  innumerable 
focal  points  situated  in  different  planes.  The  fact  that  but  a  few  of  these  focal  points  are 
in  the  plane  of  the  retina  renders  the  image  indistinct.  If  we  place  behind  this  convex 
lens  a  concave  lens,  by  the  action  of  which  the  rays  are  more  or  less  diverged,  the  ine- 
quality of  the  divergence  by  different  portions  of  the  second  lens  will  have  the  following 
effect :  As  the  angle  of  divergence  gradually  increases  from  the  centre  toward  the  periph- 
ery, the  rays  near  the  periphery,  which  are  most  powerfully  converged  by  the  convex 
lens,  will  be  most  widely  diverged  by  the  peripheral  portion  of  the  concave  lens;  so  that, 
if  the  opposite  curvatures  be  accurately  adjusted,  the  aberrant  rays  may  be  blended.  It 
is  evident  that,  if  all  of  the  rays  were  equally  converged  by  the  convex  lens  and  equally 


790  SPECIAL  SENSES. 

diverged  by  the  concave  lens,  the  action  of  the  latter  would  be  simply  to  elongate  the 
focal  distance ;  and  it  is  equally  evident  that,  if  the  aberration  of  the  one  be  exactly  oppo- 
site to  the  aberration  of  the  other,  there  will  be  perfect  correction.  Mechanical  art  has 
not  enabled  us  to  effect  correction  of  every  portion  of  very  powerful  convex  lenses  in  this 
way;  but,  by  a  combination  of  lenses  and  diaphragms  together,  highly-magnified  images, 
nearly  perfect,  have  been  produced. 

It  is  evident  that,  for  distinct  vision  at  different  distances,  the  crystalline  lens  must  be 
nearly  free  from  spherical  aberration.  This  is  not  effected  by  a  combination  of  lenses,  as 
in  ordinary  optical  instruments,  but  by  the  curvatures  of  the  lens  itself,  and  by  certain 
differences*  in  the  consistence  of  different  portions  of  the  lens,  which  will  be  fully  con- 
sidered hereafter. 

Chromatic  Aberration. — We  have  already  alluded  to  the  fact  that  a  refracting  medium 
does  not  act  equally  upon  the  different  colored  rays  into  which  pure  white  light  may  be 
decomposed  ;  in  other  words,  as  the  pure  ray  falling  upon  the  inclined  surface  of  a  glass 
prism  is  bent,  it  is  decomposed  into  the  colors  of  the  spectrum.  As  a  convex  lens  is 
practically  composed  of  an  infinite  number  of  prisms,  the  same  effect  would  be  expected. 
Indeed,  a  simple  convex  lens,  even  if  the  spherical  aberration  be  corrected,  always 
produces  more  or  less  decomposition  of  light.  The  image  formed  by  such  a  lens  will 
consequently  be  colored ;  and  this  defect  in  simple  lenses  is  called  chromatic  aberration. 
At  the  same  time,  it  is  evident  that  the  centre  of  the  different  rays  from  an  object  will  be 
composed  of  all  the  colors  of  the  spectrum  combined,  producing  the  effect  of  white  light ; 
but,  at  the  borders,  the  different  colors  will  be  separate  and  distinct,  and  an  image  pro- 
duced by  a  simple  convex  lens  will  thils  be  surrounded  by  a  circle  of  colors  like  a  rain- 
bow. 

In  prisms,  the  chromatic  dispersion  may  be  corrected  by  allowing  the  colored  rays 
from  one  prism  to  fall  upon  a  second  prism,  which  is  inverted,  so  that  the  colors  will  be 
brought  together  and  produce  white  light.  Two  prisms  thus  applied  to  each  other  con- 
stitute, in  fact,  a  flat  plate  of  glass,  and  the  rays  of  light  pass  without  deviation.  If  this 
law  be  applied  to  lenses,  it  is  evident  that  the  dispersive  power  of  a  convex  lens  may  be 
exactly  opposite  to  that  of  a  concave  lens.  By  the  convex  lens,  the  colored  rays  are 
separated  by  convergence  and  cross  each  other ;  while,  in  the  concave  lens,  the  colored 
rays  are  dispersed  in  the  opposite  direction.  If,  then,  we  combine  a  convex  with  a  con- 
cave lens,  the  white  light  decomposed  by  the  one  will  be  recomposed  by  the  other,  and 
the  chromatic  aberration  will  thus  be  corrected.  But,  in  using  a  convex  and  a  concave 
lens  composed  of  the  same  material,  the  convergence  by  the  one  will  be  neutralized  by 
the  dispersion  of  the  other,  and  there  will  be  no  amplification  of  the  object. 

In  the  construction  of  optical  instruments,  the  chromatic  aberration  is  corrected,  with 
but  slight  diminution  in  the  amplification,  by  combining  lenses  made  of  different  material, 
as  of  flint-glass  and  crown-glass.  Flint-glass  has  a  much  greater  dispersive  power  than 
crown-glass.  If,  therefore,  we  use  a  convex  lens  of  crown-glass  combined  with  a  concave 
lens  of  flint-glass,  the  chromatic  aberration  of  the  convex  lens  may  be  corrected  by  a  con- 
cave lens  with  a  curvature  which  will  take  but  little  from  the  magnifying  power.  A  com- 
pound lens,  with  the  spherical  aberration  of  the  convex  element  corrected  by  the  curvature 
of  a  concave  lens,  and  the  chromatic  aberration  corrected  by  the  curvature,  in  part,  and 
m  part  by  the  superior  refractive  power  of  flint-glass  over  crown-glass,  will  produce 
a  perfect  image. 

Although  the  eye  is  not  absolutely  achromatic,  the  dispersion  of  light  is  not  sufficient 
to  interfere  with  distinct  vision.  "We  can  understand  how  the  chromatic  aberration  is 
practically  corrected  in  the  crystalline  lens,  when  we  remember  that  its  various  layers 
are  of  different  consistence  and  of  different  refractive  power. 


FORMATION   OF  IMAGES  IN  THE  EYE.  791 

Formation  of  Images  in  the  Eye. 

It  is  only  necessary  to  call  to  mind  the  general  arrangement  of  the  different  structures 
in  the  eye  and  to  apply  the  simple  laws  of  refraction,  to  comprehend  precisely  how  images 
are  formed  upon  the  retina. 

The  eye  corresponds  to  a  camera  obscura.  Its  interior  is  lined  with  a  dark,  pigment- 
ary membrane  (the  choroid),  the  function  of  which  is  to  prevent  the  confusion  of  images 
by  internal  reflection.  The  rays  of  light  are  admitted  through  a  circular  opening  (the 
pupil),  the  size  of  which  is  regulated  by  the  movements  of  the  iris.  The  pupil  is  contracted 
when  the  light  striking  the  eye  is  intense  and  is  dilated  as  the  amount  of  light  is  dimin- 
ished. In  the  accommodation  of  the  eye,  the  pupil  is  dilated  for  distant  objects  and  con- 
tracted for  near  objects ;  for,  in  looking  at  near  objects,  the  aberrations  of  sphericity  and 
achromatism  in  the  lens  are  more  marked,  and  the  peripheral  portion  is  cut  off  by  the 
action  of  this  movable  diaphragm,  thus  aiding  the  correction.  The  rays  of  light  from  an 
object  pass  through  the  cornea,  the  aqueous  humor,  the  crystalline  lens,  and  the  vitreous 
humor,  and  they  are  refracted  with  so  little  spherical  and  chromatic  aberration,  that  the 
image  formed  upon  the  retina  is  practically  perfect.  The  layer  of  rods  and  cones  of  the 
retina  is  the  only  portion  of  the  eye  endowed  directly  with  special  sensibility,  the  impres- 
sions of  light  being  conveyed  to  the  brain  by  the  optic  nerves.  This  layer  is  situated 
next  the  choroid,  but  the  other  layers  of  the  retina,  through  which  the  light  passes  to 
reach  the  rods  and  cones,  are  perfectly  transparent. 

It  has  been  positively  demonstrated  that  the  rods  and  cones  are  the  only  structures 
capable  of  directly  receiving  visual  impressions,  by  the  following  interesting  experiment, 
first  made  by  Purkinje:  We  concentrate  upon  the  sclerotic,  with  a  convex  lens  of  short 
focus,  an  intense  light,  at  a  point  as  far  as  possible  removed  from  the  cornea.  This  passes 
through  the  translucent  coverings  of  the  eye  at  this  point,  and  the  image  of  the  light 
reaches  the  retina.  If  we  then  look  at  a  dark  surface,  we  have  the  field  of  vision  present- 
ing a  reddish-yellow  illumination,  with  a  dark,  arborescent  appearance  produced  by  the 
shadow  of  the  large  retinal  vessels ;  and,  as  we  move  the  lens  slightly,  the  shadow  of  the 
vessels  moves  with  it.  Without  going  elaborately  into  the  mechanism  of  this  remarkable 
phenomenon,  it  is  sufficient  to  state  that  Heinrich  Miiller  has  arrived  at  an  absolute  mathe- 
matical demonstration  that  the  shadows  of  the  vessels  are  formed  upon  the  layer  of  rods 
and  cones,  and  that  this  layer  alone  is  capable  of  receiving  impressions  of  light.  His  ex- 
planation is  accepted  by  all  writers  at  the  present  day  and  is  regarded  as  positive  proof 
of  the  peculiar  sensibility  of  this  portion  of  the  retina.  In  carefully-conducted  observa- 
tions of  this  kind,  a  spot  is  seen  in  which  no  vessels  appear,  which  corresponds  to  the 
fovea  centralis.  When  the  experiment  is  prolonged,  the  vessels  disappear,  as  the  sensi- 
bility of  the  retina  becomes  diminished  by  fatigue. 

Theoretically,  an  illuminated  object  placed  in  the  angle  of  vision  would  form  upon  the 
retina  an  image,  diminished  in  size  and  inverted.  This  fact  is  capable  of  actual  demon- 
stration by  means  of  the  ophthalmoscope.  With  this  instrument,  the  retina  and  the  im- 
ages formed  upon  it  may  be  seen  during  life  with  perfect  distinctness. 

All  parts  of  the  retina,  except  the  point  of  entrance  of  the  optic  nerve,  are  sensitive  to 
light ;  and  the  arrangement  of  the  cornea  and  pupil  is  such,  that  the  field  of  vision  is,  at 
the  least  estimate,  equal  to  the  half  of  a  sphere.  If  a  ray  of  light  fall  upon  the  border  of 
the  cornea  at  a  right  angle  to  the  axis  of  the  eye,  it  is  refracted  by  its  surface  and  will 
pass  through  the  pupil  to  the  border  of  the  retina  upon  the  opposite  side.  Above  and 
below,  the  circle  of  vision  is  cut  off  by  the  overhanging  arch  of  the  orbit  and  the  malar 
prominence ;  but  externally  the  field  is  free.  With  the  two  eyes,  therefore,  the  lateral 
field  of  vision  must  be  equal  to  at  least  one  hundred  and  eighty  degrees.  It  is  easy  to 
demonstrate,  however,  by  the  ophthalmoscope,  as  well  as  by  taking  cognizance  of  the 
impressions  made  by  objects  far  removed  from  the  axis  of  distinct  vision,  that  images 
formed  upon  the  lateral  and  peripheral  portions  of  the  retina  are  confused  and  imperfect. 


792  SPECIAL  SENSES. 

We  have  a  knowledge  of  the  presence  and  an  indefinite  idea  of  the  general  form  of  large 
objects  situated  outside  of  the  area  of  distinct  vision ;  but,  when  we  wish  to  note  such 
objects  exactly,  the  eyeball  is  turned  by  muscular  effort,  so  as  to  bring  them  at  or  very 
near  the  axis  of  the  globe.  This  fact,  with  what  we  know  of  the  mechanism  of  refraction 
by  the  cornea  and  lens,  makes  it  evident  that  the  area  of  the  retina  upon  which  images 
are  formed  with  perfect  distinctness  is  quite  restricted.  A  moment's  reflection  is  sufficient 
to  convince  any  one  that,  in  order  to  see  any  object  distinctly,  we  must  look  at  it,  or 
bring  the  axis  of  the  eye  to  bear  upon  it  directly.  Let  us  see,  now,  how  far  this  fact  is 
capable  of  positive  demonstration. 

If  we  examine  the  bottom  of  the  eye  with  the  ophthalmoscope,  we  can  see  the  yellow 
spot  with  the  fovea  centralis,  apparently  free  from  blood-vessels,  and  composed,  as  we 
know,  chiefly  of  those  elements  of  the  retina  which  are  sensitive  to  light.  If,  at  the 
same  time,  we  examine  an  image  for  which  the  eye  is  perfectly  adjusted,  it  will  be  seen 
that  this  image  is  perfect  only  at  the  fovea  centralis  ;  and,  if  the  object  be  removed  from 
the  axis  of  vision,  we  see  a  confused  image  upon  the  retina  removed  from  the  fovea,  at 
the  same  time  that  the  subject  is  conscious  of  indistinct  vision.  In  the  words  of  Helm- 
holtz,  "It  is  only  in  the  immediate  vicinity  of  the  ocular  axis  that  the  retinal  image  pos- 
sesses entire  distinctness ;  beyond  this,  the  contours  are  less  defined.  It  is  in  part  for 
this  reason  that  in  general  we  see  distinctly  in  the  field  of  vision,  only  the  point  that  we 
fix.  All  the  others  are  seen  vaguely.  This  lack  of  distinctness  in  indirect  vision,  in 
addition,  depends  also  upon  diminished  sensibility  of  the  retina  :  at  a  slight  distance  from 
the  fixed  point,  the  distinctness  of  vision  has  diminished  much  more  than  the  objective 
distinctness  of  retinal  images." 

At  the  point  of  penetration  of  the  optic  nerve,  the  retina  is  insensible  to  luminous 
impressions ;  at  least,  its  sensibility  is  here  so  obtuse  as  to  be  entirely  inadequate  for 
the  purposes  of  vision.  This  point  is  called  the  punctum  caecum ;  and  its  want  of 
sensibility  was  demonstrated  many  years  ago  (1668)  by  Mariotte.  The  classical  ex- 
periment by  which  this  important  fact  was  positively  ascertained,  which  is  gener- 
ally known  to  physiologists  as  Mariotte's  experiment,  is  so  curious  that  we  quote  it 
verbatim : 

"  I  fasten1  d  on  an  obscure  Wall  about  the  hight  of  my  Eye,  a  small  round  paper,  to 
serve  me  for  a  fixed  point  of  Vision ;  and  I  fastened  such  an  other  on  the  side  thereof 
towards  my  right  hand,  at  the  distance  of  about  2.  foot ;  but  somewhat  lower  than  the 
first,  to  the  end  that  it  might  strike  the  OpUck  Nerve  of  my  Eight  Eye,  whilst  I  kept  my 
Left  shut.  Then  I  plac'd  myself  over  against  the  First  paper,  and  drew  back  by  little 
and  little,  keeping  my  Eight  Eye  fixt  and  very  steddy  upon  the  same  ;  and  being  about 
10.  foot  distant,  the  second  paper  totally  disappear'd." 

In  this  experiment,  the  rays  of  light  from  the  paper  which  has  disappeared  from  view 
are  received  upon  the  punctum  caecum,  at  the  point  of  entrance  of  the  optic  nerve.  If 
the  observer  withdraw  himself  still  farther,  the  second  circle  will  reappear,  as  the  rays 
are  removed  from  the  punctum  caecum.  With  the  ophthalmoscope,  the  point  of  penetra- 
tion of  the  optic  nerve  may  be  readily  seen  in  the  living  eye.  If  the  image  of  a  flame 
be  directed  upon  this  point,  the  sensation  of  light  is  either  not  perceived  or  it  is  very 
faint  and  indefinite,  and  it  is  then  probably  due  to  diffusion  to  other  portions  of  the 
retina. 

The  relative  sensibility  of  different  portions  of  the  retina  has  been  accurately  meas- 
ured by  Volkmann  and  has  been  found  to  be  in  an  inverse  ratio  equal  to  about  the  square 
of  the  distance  from  the  axis  of  most  perfect  vision.  This  observer  calculated  the  dis- 
tance between  the  sensitive  elements  of  the  retina  at  which  he  supposed  that  two  par- 

1  lines  would  appear  as  one.  In  the  axis  of  vision,  the  distance  was  0-00029",  and,  at 
i  deviation  inward  of  8°,  it  was  0-03186",  a  diminution  of  acuteness  of  more  than  a  hun- 
dred times.  The  following  table  gives  the  results  of  these  experiments  : 


MECHANISM   OF  REFRACTION  IN   THE  EYE. 


793 


Angle  of  deviation  of  the 
object  seen,  from  the  vis- 
ual axis  inward. 

Calculated  distance,  for  the  retinal 
elements,  of  the  parallel  lines. 

0° 

0-00029" 

1° 

0-00055" 

2° 

0-00091" 

3° 

0-00141" 

4° 

0-00153" 

5° 

0-00180" 

6° 

0-00383" 

T 

0-01527" 

8° 

0-03186" 

This  table  illustrates,  with  great  exactness,  the  gradual  diminution  in  the  acuteness 
of  vision  as  the  impressions  are  made  farther  and  farther  from  the  visual  axis.  The 
experiments  were  made  upon  the  same  principle*  as  that  of  observations  upon  the  tactile 
sensibility  of  different  portions  of  the  skin  by  testing  the  power  of  distinguishing  the  two 
points  of  the  sesthesiometer. 

The  fact  of  the  formation  of  images  upon  the  retina,  which  are  exact  only  at  or  imme- 
diately surrounding  the  fovea  centralis,  being  settled,  it  remains  to  see  how  these  images 
are  rendered  perfect,  and  to  study  the  mechanism  of  refraction  by  the  transparent  media 
of  the  eye. 

Mechanism  of  Refraction  in  the  Eye. 

A  visible  object  sends  rays  from  every  point  of  its  surface  to  the  cornea.  If  the 
object  be  near,  the  rays  from  each  and  every  point  are  divergent  as  they  strike  the  eye. 
Rays  from  distant  objects  are  practically  parallel.  It  is  evident  that  the  refraction  for 
diverging  rays  must  be  greater  than  for  parallel  rays,  as  a  necessity  of  distinct  vision ;  in 
other  words,  the  eye  must  be  accommodated  for  vision  at  different  distances.  Leaving, 
however,  the  mechanism  of  accommodation  for  future  consideration,  we  shall  endeavor 
to  sho\v  how  the  rays  of  light  as  they  penetrate  the  eye  are  refracted  and  brought  to  a 
focus  at  the  retina. 

The  important  agents  in  refraction  in  the  eye  are  the  surfaces  of  the  cornea  and  the 
crystalline  lens.  Careful  calculations  have  shown  that  the  index  of  refraction  of  the 
aqueous  humor  is  sensibly  the  same  as  that  of  the  substance  of  the  cornea,  so  that,  prac- 
tically, the  refraction  is  the  same  as  if  the  cornea  and  the  aqueous  humor  were  one  and 
the  same  substance.  The  index  of  refraction  of  the  vitreous  humor  is  practically  the 
same  as  that  of  the  aqueous  humor,  both  being  about  equal  to  the  index  of  refraction  of 
pure  water.  Refraction  by  the  crystalline  lens,  however,  is  more  complex  in  its  mechan- 
ism ;  depending,  first,  upon  the  curvatures  of  its  two  surfaces,  and,  again,  upon  the  differ- 
ences in  the  consistence  of  different  portions  of  its  substance.  In  view  of  these  facts, 
we  may  simplify  the  conditions  of  refraction  in  the  eye  by  assuming  the  following 
arrangement : 

The  cornea  presents  a  convex  surface  upon  which  the  rays  of  light  are  received.  At 
a  certain  distance  behind  its  anterior  border,  is  the  crystalline,  a  double-convex  lens, 
corrected,  sufficiently  for  all  practical  purposes,  both  for  spherical  and  chromatic  aberra- 
tion. This  lens  is  practically  suspended  in  a  liquid  with  an  index  of  refraction  equal  to 
that  of  pure  water  ;  as  both  the  aqueous  humor  in  front  and  the  vitreous  humor  behind 
have  the  same  refractive  power.  Behind  the  lens,  in  its  axis  and  exactly  in  the  plane  upon 
which  the  rays  of  light  are  brought  to  a  focus  by  the  action  of  the  cornea  and  the  lens, 
is  the  fovea  centralis,  which  is  the  centre  of  distinct  vision.  The  anatomical  elements  of 
the  fovea  are  capable  of  receiving  visual  impressions,  which  are  conveyed  to  the  brain 
by  the  optic  nerves.  All  impressions  made  upon  other  portions  of  the  retina  are  com- 
paratively indistinct ;  and  the  point  of  entrance  of  the  optic  nerve  is  insensible  to  light. 
Inasmuch  as  the  punctum  caBcum  is  situated  in  either  eye  upon  the  nasal  side  of  the  retina, 


794 


SPECIAL   SENSES. 


in  normal  vision,  rays  from  the  same  object  cannot  fall  upon  both  points  at  the  same  time. 
Thus,  in  binocular  vision,  the  insensibility  of  the  punctum  caecum  does  not  interfere  with 
sight ;  and  the  movements  of  the  globe  prevent  any  notable  interference  in  vision,  even 
with  one  eye.  The  sclerotic  coat  is  for  the  protection  of  its  contents  and  for  the  inser- 
tion of  muscles.  The  iris  has  an  action  similar  to  that  of  the  diaphragm  in  optical  instru- 
ments. The  suspensory  ligament  of  the  lens,  the  ciliary  body,  and  the  ciliary  muscle,  are 
for  the  fixation  of  the  lens  and  its  accommodation  to  distinct  vision  at  different  distances. 
The  choroid  is  a  dark  membrane  for  the  absorption  of  light,  preventing  confusion  of  vision 
from  reflection  within  the  eye. 

Refraction  by  the  cornea  is  effected  simply  by  its  external  surface.  The  rays  of  light 
from  a  distant  point  are  deviated  by  its  convexity  so  that,  if  they  were  not  again  refracted 
by  the  crystalline  lens,  they  would  be  brought  to  a  focus  at  a  point  situated  about  T\  of 
an  inch  behind  the  retina.  Without  the  crystalline  lens,  therefore,  -distinct,  unaided 
vision  is  generally  impossible,  although  the  sensation  of  light  is  appreciated.  In  cases  of 
extraction  of  the  lens  for  cataract,  the  crystalline  is  supplied  by  a  convex  lens  placed 
before  the  eye. 

The  rays  of  light,  refracted  by  the  anterior  surface  of  the  cornea,  are  received  upon 
the  anterior  surface  of  the  crystalline  lens,  by  which  they  are  still  farther  refracted. 
Passing  through  the  substance  of  the  lens,  they  undergo  certain  modifications  in  refrac- 
tion dependent  upon  the  differences  in  the  various  strata  of  the  lens.  These  modifica- 
tions have  not  been  accurately  calculated ;  but  it  is  sufficient  to  state  that  they  contribute 
to  the  accuracy  of  the  formation  of  the  retinal  image  and  to  the  production  of  an  image 
practically  free  from  chromatic  dispersion.  As  the  rays  pass  out  of  the  crystalline  lens, 
they  are  again  refracted  by  its  posterior  curvature  and  are  brought  to  a  focus  at  the  area 
of  distinct  vision. 

The  rays  from  all  points  of  an  object  distinctly  seen  are  brought  to  a  focus,  if  the 
accommodation  of  the  lens  be  correct,  upon  a  restricted  surface  in  the  macula  lutea ;  but 
the  rays  from  different  points  cross  each  other  before  they  reach  the  retina,  and  the 
image  is  consequently  inverted.  This  is  a  fact  capable  of  actual  demonstration,  as  we 
have  shown  in  treating  of  the  formation  of  images  in  the  eye. 

Calculating  the  curvatures  of  the  refracting  surfaces  in  the  eye  and  the  indices  of 
refraction  of  its  transparent  media,  it  has  been  pretty  clearly  shown,  by  mathematical 
formula,  that  the  eye,  viewed  simply  as  an  optical  instrument,  and  not  practically,  as  the 
organ  of  vision,  presents  a  certain  degree  of  spherical  and  chromatic  aberration;  but  with 
these  formula  we  have  little  to  do  in  our  purely  physiological  consideration  of  vision. 

In  most  calculations  of  the  size  of  images,  the  positions  of  conjugate  foci,  etc.,  in  nor- 
mal and  abnormal  eyes,  a  schematic  eye  reduced  by  Bonders,  after  the  example  of  List- 
ing, is  regarded  as  sufficiently  exact  for  all  practical  purposes.  This  simple  scheme 
represents  the  eye  as  reduced  to  a  single  refracting  surface,  the  cornea,  and  a  single  liquid 
assumed  to  have  an  index  of  refraction  equal  to  that  of  pure  water.  The  distance  between 
what  are  called  the  two  nodal  points  and  between  the  two  principal  points  of  the  dioptric 
system  of  the  eye  is  so  small,  amounting  to  hardly  Tfo.  of  an  inch,  that  it  can  be  neglected. 
In  this  simple  eye,  we  assume  a  radius  of  curvature  of  the  cornea  of  about  |  of  an  inch, 
and  have  a  single  optical  centre  situated  |  of  an  inch  back  of  the  cornea,  the  "  principal 
point "  being  in  the  cornea,  at  the  axis  of  vision.  The  posterior  focal  distance,  that  is, 
the  focus,  at  the  bottom  of  the  eye;  for  rays  that  are  parallel  in  the  air,  is  about  f  of  an 
inch.  The  anterior  focal  distance,  that  is,  for  rays  parallel  in  the  vitreous  humor,  is  about 
I  of  an  inch.  The  measurements  in  this  simple  schematic  eye  can  be  easily  remembered 
and  used  in  calculations. 

Astigmatism. 

^     We  have  already  alluded  to  an  important  peculiarity  in  the  optical  apparatus;  which 
i  that  the  visual  line  does  not  coincide  exactly  with  the  axis  of  the  eye.     There  is  still 


ASTIGMATISM. 


795 


another  normal  deviation  from  mathematical  exactness  in  the  refraction  of  rays  by  the 
cornea  and  the  crystalline  lens,  which  is  of  considerable  importance.  If  we  place  before 
the  eyes  two  threads  crossing  each  other  at  right  angles  in  the  same  plane,  one  of  these 
threads  being  vertical,  and  the  other,  horizontal,  when  the  optical  apparatus  is  adjusted 
so  that  one  line  is  seen  with  perfect  distinctness,  the  other  is  not  well  defined.  In  other 
words,  when  we  accommodate  for  the  vertical  thread,  the  horizontal  is  indistinct,  and 
vice  versa.  If  the  horizontal  line  be  seen  distinctly,  in  order  to  see  the  vertical  without 
modifying  the  accommodation,  it  must  be  removed  to  a  greater  distance.  This  depends 
chiefly  upon  a  difference  in  the  vertical  and  the  horizontal  curvatures  of  the  cornea,  so 
that  the  horizontal  meridian  has  a  focus  slightly  different  from  the  focus  of  the  vertical 
meridian.  A  condition  opposite  to  that  observed  in  the  cornea  usually  exists  in  the 
crystalline  lens ;  that  is,  the  difference  which  exists  between  the  curvatures  of  the  lens 
in  the  vertical  and  the  horizontal  meridians  is  such  that  the  deepest  curvature  in  the  lens 
is  situated  in  the  meridian  of  the  shallowest  curvature  of  the  cornea.  In  this  way,  in 
normal  eyes,  the  aberration  of  the  lens  has  a  tendency  to  correct  the  aberration  in  the 
cornea  ;  but  this  correction  is  incomplete,  and  there  still  remains,  in  all  degrees  of  tension 
of  accommodation,  a  marked  difference  in  the  vision  as  regards  vertical  and  horizontal 
lines. 

The  condition  just  described  is  known  under  the  name  of  normal,  regular  astigmatism ; 
but  the  aberration  is  not  sufficiently  great  to  interfere  with  distinct  vision.  The  degree 
of  regular  astigmatism  presents  normal  variations  in  different  eyes.  In  some  eyes  there 
is  no  astigmatism  ;  but  this  is  rare.  According  to  Bonders,  if  the  astigmatism  amount  to 
4^  or  more,  it  is  to  be  considered  abnormal ;  which  simply  means  that,  beyond  this  point, 
the  aberration  interferes  with  distinct  vision. 

From  the  mere  definition  of  regular  astigmatism,  it  is  evident  that  this  condition  and 
the  degree  to  which  it  exists  may  easily  be  determined  by  noting  the  differences  in  the 
foci  for  vertical  and  horizontal  lines,  and  it  may  be  exactly  corrected  by  the  application 
of  cylindrical  glasses  of  proper  curvature.  Indeed,  the  curvature  of  a  cylindrical  glass 
which  will  enable  a  person  to  distinguish  vertical  and  horizontal  lines  with  perfect  dis- 
tinctness at  the  same  time  is  an  exact  indication  of  the  degree  of  aberration.  Kegular 
astigmatism,  such  as  we  have  described,  may  be  so  exaggerated  as  to  interfere  very 
seriously  with  vision,  when  it  becomes  abnormal.  This  kind  of  aberration,  however, 
which  is  dependent  upon  an  abnormal  condition  of  the  cornea,  is  remediable  by  the 
use  of  properly-adjusted  cylindrical  glasses. 

Irregular  astigmatism,  excluding  cases  of  pathological  deformation,  opaque  spots,  etc.r 
in  the  cornea,  depends  upon  irregularity  in  the  different  sectors  of  the  crystalline  lens. 
Instead  of  a  simple  and  regular  aberration,  consisting  in  a  difference  between  the  depth 
of  the  vertical  and  the  horizontal  curvatures  of  the  cornea  and  lens,  we  have  irregular 
variations  in  the  curvatures  of  different  sectors  of  the  lens.  As  a  consequence  of  this, 
when  the  irregularities  are  very  great,  there  is  impairment  of  the  sharpness  of  vision. 
The  circles  of  diffusion,  which  are  regular  in  normal  vision,  become  irregularly  radiated, 
and  single  points  appear  multiple,  an  irregularity  described  under  the  name  of  polyopia 
monocularis.  Accurate  observations  have  shown  that  this  condition  exists  to  a  very 
moderate  degree  in  normal  eyes  \-  but  it  is  so  slight  as  not  to  interfere  with  ordinary  vision. 
In  what  is  called  normal,  irregular  astigmatism,  the  irregularity  depends  entirely  upon 
the  crystalline  lens.  If  we  place  before  the  eye  a  card  with  a  very  small  opening,  and 
move  this  before  the  lens,  so  that  the  pencil  of  light  falls  successively  upon  different  sec- 
tors, it  can  be  shown  that  the  focal  distance  is  different  for  different  portions.  The  radi- 
ating lines  of  light  observed  in  looking  at  remote  luminous  points,  as  the  fixed  stars,  are 
produced  by  this  irregularity  in  the  curvatures  of  the  different  sectors  of  the  lens. 

While  regular  astigmatism,  both  normal  and  abnormal,  may  be  perfectly  corrected 
by  placing  cylindrical  glasses  before  the  eyes,  it  is  impossible,  in  the  great  majority  of 
cases,  to  construct  glasses  which  will  remedy  the  irregular  form. 


796  SPECIAL   SENSES. 

Movements  of  the  Iris. 

The  movements  of  the  iris  are  sufficiently  simple,  as  well  as  the  physiological  con- 
ditions under  which  they  take  place ;  and  it  is  only  when  we  come  to  study  the  exact 
mechanism  of  the  production  of  these  movements  through  the  nervous  system,  that  the 
subject  becomes  complex,  and,  to  a  certain  extent,  obscure.  As  regards  the  movements 
themselves,  the  simple  facts  are  as  follows  : 

There  are  two  physiological  conditions  under  which  the  size  of  the  pupil  is  modified  : 
The  first  of  these  depends  upon  the  amount  of  light  to  which  the  eye  is  exposed.  When 
the  quantity  of  light  is  small,  the  pupil  is  widely  dilated,  so  as  to  admit  as  much  as  pos- 
sible to  the  retina.  When  the  eye  is  exposed  to  a  bright  light,  the  retina  is  protected  by 
contraction  of  the  iris.  The  muscular  action  by  which  the  iris  is  contracted  is  character- 
istic of  the  smooth  muscular  fibres,  as  can  be  readily  seen  by  exposing  an  eye,  in  which 
the  pupil  is  dilated,  to  a  bright  light.  Contraction  does  not  take  place  instantly,  but  an 
appreciable  interval  elapses  after  the  exposure,  and  a  more  or  less  gradual  diminution  in 
the  size  of  the  pupil  is  observed.  This  is  seen  both  in  solar  and  in  artificial  light.  The 
second  of  these  conditions  depends,  indirectly,  upon  the  voluntary  action  of  muscles. 
We  have  already  seen,  in  connection  with  the  physiology  of  the  third  pair  of  nerves,  that 
the  effort  of  converging  the  axes  of  the  eyes  by  looking  at  a  very  near  object  contracts 
the  pupils.  We  shall  see,  also,  that  the  effort  of  accommodation  of  the  eye  for  near 
objects  produces  the  same  effect,  even  when  the  eyes  are  not  converged.  This  action 
will  be  fully  considered  under  the  head  of  accommodation. 

One  point  relating  to  the  anatomy  of  the  iris  is  of  great  importance  in  connection  with 
the  physiology  of  its  movements ;  and  that  is  the  question  of  the  existence  of  dilator 
fibres.  Upon  this  point  there  is  some  difference  of  opinion  ;  but,  as  we  stated  in  treating 
of  the  structure  of  the  eye,  the  weight  of  anatomical  authority  is  decidedly  in  favor  of 
the  existence  of  radiating  fibres. 

Direct  Action  of  Light  upon  the  Iris. — The  variations  in  the  size  of  the  pupil  under 
different  physiological  conditions  are  effected  almost  exclusively  through  the  nervous 
system,  either  by  reflex  action  from  variations  in  the  intensity  of  light,  or  by  a  direct 
influence,  as  in  accommodation  for  distances ;  but  it  is  nevertheless  true  that  the  muscu- 
lar tissue  of  the  iris  will  respond  directly  to  the  stimulus  of  light.  Harless  noted,  in  sub- 
jects dead  of  various  diseases,  from  five  to  thirty  hours  after  death,  that  the  iris  con- 
tracted under  the  stimulus  of  light ;  and  he  justly  remarks  that  this  is  probably  due  to 
direct  action  upon  its  muscular  tissue,  and  that  it  is  not  reflex,  for  the  reason  that  the 
irritability  of  the  nerves  in  warm-blooded  animals  disappears  certainly  in  twenty  hours 
after  death.  The  experiments  of  Harless  were  made  upon  the  two  eyes,  one  being 
exposed  to  the  light,  while  the  other  was  closed.  The  contraction,  however,  took  place 
very  slowly,  requiring  an  exposure  of  several  hours.  This  mode  of  contraction  is  very 
different  from  the  action  of  the  iris  during  life,  but  it  is  precisely  like  the  contraction 
observed  after  division  of  the  motor  oculi  communis,  which  is  slow  and  gradual  and 
undoubtedly  depends  upon  the  direct  action  of  light  upon  the  muscular  fibres. 

Action  of  the  Nervous  System  upon  the  Iris. — This  subject,  as  far  as  it  relates  to  the 
third  pair,  has  been  pretty  fully  considered  in  connection  with  the  physiology  of  these 
nerves ;  and  it  is  unnecessary  to  refer  again  in  detail  to  the  experiments  which  have 
already  been  cited.     The  reflex  phenomena  observed  are  sufficiently  distinct.    When  light 
admitted  to  the  retina,  the  pupil  contracts,  and  the  same  result  follows  mechanical 
irritation  of  the  optic  nerves.     When  the  third  pair  of  nerves  has  been  divided,  no  such 
eflex  phenomena  are  observed.     It  is  well  known,  also,  that  division  of  the  third  nerves 
m  the  lower  animals  or  their  paralysis  in  the  human  subject  produces  permanent  dilata- 
tion of  the  pupil,  the  iris  responding,  only  in  the  slow  and  gradual  manner  already  indi- 
cated, to  the  direct  action  of  light. 


MOVEMENTS   OF  THE   IRIS.  797 

Taking  all  the  experimental  facts  into  consideration,  it  is  certain  that  the  third  nerve 
has  an  important  intiuence  upon  the  iris.  Filaments  from  the  ophthalmic  ganglion  animate 
the  circular  fibres,  or  sphincter,  and  these  filaments  derive  their  power  from  the  third 
cranial  nerve.  If  this  nerve  be  divided,  the  iris  becomes  permanently  dilated  and  is  im- 
movable, except  that  it  responds  very  slowly  to  the  direct  action  of  light.  The  reflex 
action  by  which  the  pupil  is  contracted  under  the  stimulus  of  light  operates  through  the 
third  nerve,  and  no  such  action  can  take  place  after  this  nerve  has  been  divided.  In  view 
of  these  facts,  there  can  be  no  doubt  with  regard  to  the  nervous  action  upon  the  sphincter 
of  the  pupil,  this  muscle  being  animated  exclusively  by  filaments  from  the  motor  oculi 
communis,  coming  through  the  ophthalmic  ganglion. 

We  admit,  with  most  modern  anatomists,  the  existence  of  radiating  muscular  fibres  in 
the  iris,  the  action  of  which  is  antagonistic  to  the  circular  fibres,  and  which  dilate  the 
pupil.  That  these  fibres  are  subjected  to  nervous  influence  is  rendered  certain  by  experi- 
ments upon  the  sympathetic  system. 

The  effects  of  division  of  the  sympathetic  in  the  neck  have  been  treated  of  fully  in 
connection  with  the  general  functions  of  these  nerves.  It  will  be  sufficient  for  our  present 
purposes  to  state,  in  a  general  way,  the  influence  of  these  nerves  upon  the  movements  of 
the  iris.  There  can  be  no  doubt  that  the  action  of  the  sympathetic  upon  the  pupil  is 
directly  antagonistic  to  that  of  the  third  pair,  the  former  presiding  over  the  radiating,  or 
dilating  muscular  fibres ;  and  the  only  question  to  determine  is  the  course  taken  by  the 
sympathetic  filaments  to  the  iris.  Experiments  on  the  influence  of  the  fifth  pair  upon  the 
pupil  have  been  somewhat  contradictory  in  different  animals.  In  rabbits,  section  of  this 
nerve  in  the  cranial  cavity  produces  contraction  of  the  pupil ;  but  in  dogs  and  cats  the 
same  operation  produces  dilatation.  In  the  human  subject,  of  course,  it  is  impossible  to 
determine  this  point  by  direct  experiment ;  and  the  varying  results  obtained  in  observa- 
tions upon  different  animals  probably  depend  upon  differences  in  the  anatomical  relations 
of  the  nerves.  It  is  probable,  however,  that  the  filaments  of  the  sympathetic  which  ani- 
mate the  dilator  fibres  join  the  fifth  nerve  near  the  ganglion  of  Gasser  and  from  this 
nerve  pass  to  the  iris. 

There  seem  to  be  two  distinct  nerve-centres  corresponding  to  the  two  sets  of  nerves 
which  regulate  the  movements  of  the  iris.  One  of  these  centres  presides  over  the  reflex 
contractions  of  the  iris,  and  the  other  is  the  centre  of  origin  of  the  nervous  influence 
through  which  the  pupil  is  dilated. 

The  mechanism  of  reflex  contraction  of  the  iris  under  the  stimulus  of  light  is  suffi- 
ciently simple.  An  impression  is  made  upon  the  retina,  which  is  conveyed  by  the  optic 
nerves  to  the  centre  of  vision,  and,  in  obedience  to  this  impression,  the  sphincter  of  the 
iris  contracts.  If  the  optic  nerves  be  divided,  so  that  the  impression  cannot  be  conveyed 
to  the  centre,  or  if  we  divide  the  third  pair,  through  which  the  motor  stimulus  is  con- 
veyed to  the  muscular  fibres,  no  movements  of  the  iris  can  take  place.  The  centres 
which  preside  over  these  reflex  phenomena  are  situated  in  the  tubercula  quadrigemina. 
In  the  remarkable  experiments  of  Flourens  upon  the  encephalic  centres,  it  was  shown 
that  the  iris  loses  its  mobility  after  destruction  of  the  tubercula.  This  fact  has  been 
repeatedly  confirmed  by  later  experimenters.  In  birds,  in  which  the  decussation  of  the 
optic  nerves  is  complete,  this  action  is  crossed,  destruction  of  the  tubercle  upon  one  side 
producing  immobility  of  the  iris  upon  the  opposite  side  ;  but  in  man,  where  the  anatomi- 
cal relations  of  the  optic  nerves  upon  the  two  sides  are  more  complex,  the  crossed  action 
is  probably  not  so  complete.  In  man,  the  axes  of  both  eyes  are  habitually  brought 
to  bear  upon  objects,  and  it  is  well  known  that  there  is  a  physiological  unity  in  the 
action  of  the  two  eyes  in  ordinary  vision.  We  also  observe  that,  when  one  eye  only 
is  exposed  to  light,  the  pupil  becoming  contracted  under  this  stimulus,  the  pupil  of 
the  other  eye  also  contracts.  There  is,  indeed,  a  direct  contraction  and  dilatation 
of  the  pupil  of  the  eye  which  is  exposed  to  the  light,  and  an  indirect,  or  "consen- 
sual "  movement  of  the  iris  upon  the  opposite  side.  The  consensual  contraction  occurs 


798  SPECIAL  SENSES. 

about  |  of  a  second  later  than  the  direct  action,  and  the  consensual  dilatation,  about  £ 
of  a  second  later.  (Bonders.) 

Budge  and  Waller  have  shown  that  the  filaments  of  the  sympathetic  which  produce 
dilatation  of  the  pupil  take  their  origin  from  the  spinal  cord.  In  the  spinal  cord,  between 
the  sixth  cervical  and  the  second  thoracic  nerves,  is  situated  the  inferior  cilio-spinal 
centre.  When  the  spinal  cord  is  stimulated  in  this  situation,  both  pupils  become  dilated. 
If  the  cord  be  divided  longitudinally  and  the  two  halves  be  separated  from  each  other  by 
a  glass  plate,  stimulation  of  the  right  half  produces  dilatation  of  the  right  pupil,  and  vice 
versa.  This  does  not  occur  when  the  sympathetic  in  the  neck  has  been  divided.  In 
addition  to  the  inferior  cilio-spinal  centre,  there  is  a  superior  centre,  which  is  in  com- 
munication with  the  superior  cervical  ganglion  and  is  situated  near  the  sublingual  nerve. 
The  influence  of  this  centre  over  the  pupil  cannot  be  demonstrated  by  direct  stimulation, 
because  it  is  too  near  the  origin  of  the  fifth,  irritation  of  which  has  an  influence  over  the 
iris;  but  it  is  shown  by  division  of  its  filaments  of  communication  with  the  iris. 

Section  and  galvanization  of  the  different  nerves  which  regulate  the  movements  of  the 
iris  have  a  certain  influence  upon  its  vascularity ;  and,  indeed,  it  has  been  thought  that 
contraction  is  in  a  measure  due  to  congestion  of  its  vessels,  and  dilatation,  to  an  opposite 
condition.  This  view  is  adopted  by  some  of  those  who  deny  the  existence  of  the  radi- 
ating muscular  fibres  of  the  iris.  Assuming  that  the  size  of  the  pupil  is,  to  a  certain 
extent,  affected  by  the  condition  of  the  vessels,  it  is  evident  that  the  more  extensive  move- 
ments of  the  iris  are  due  mainly  to  muscular  action.  It  has  been  also  shown  that  the 
changes  in  the  iris  produced  by  injection  of  its  vessels  are  not  to  be  compared  in  their 
extent  with  its  physiological  movements.  The  changes  in  vascularity  produced  by  divid- 
ing or  galvanizing  the  sympathetic  do  not  differ  from  the  phenomena  noted  in  experi- 
ments upon  other  portions  of  the  sympathetic  system. 

Accommodation  of  the  Eye  to  Vision  at  Different  Distances. 

The  mechanism  by  which  the  eye  is  adjusted  for  distinct  vision  at  different  distances 
is  one  of  the  most  interesting  and  important  points  connected  with  the  physiology  of  the 
sight.  At  the  present  day,  this  point  may  be  regarded  as  definitely  settled,  particularly 
since  the  variations  in  the  thickness  and  the  curvatures  of  the  crystalline  lens  have  been 
so  accurately  measured  by  Helmholtz.  We  shall  have  little  to  say  with  regard  to  the 
various  theories  of  accommodation  advanced  by  the  older  physiologists,  except  to  indicate, 
in  a  very  general  way,  the  most  plausible  views  that  have  been  adopted  from  time  to  time 
by  physiological  writers.  In  the  first  place,  we  shall  note  certain  physical  laws  and  their 
application  to  the  eye,  which  show  the  necessity  for  accommodation. 

Supposing  the  eye  to  be  adapted  to  vision  at  an  infinite  distance,  in  which  the  rays 
from  an  object,  as  they  strike  the  cornea,  are  practically  parallel,  it  is  evident  that  the 
foci  of  the  rays,  as  they  form  a  distinct  image  upon  the  retina,  are  all  situated  at  the 
proper  plane.  Under  these  conditions,  in  a  perfectly  normal  eye,  the  image,  appreciated 
by  the  individual  or  seen  by  means  of  the  ophthalmoscope,  is  perfectly  clear  and  distinct. 
If  the  foci  be  situated  in  front  of  the  retina,  the  rays,  instead  of  coming  to  a  focus  upon  a 
point  in  the  retina,  will  cross,  and,  from  their  diffusion  or  dispersion,  will  produce  indis- 
tinct vision.  Under  these  circumstances,  a  distinct  point  is  not  perceived,  but  every  point 
in  the  image  is  surrounded  by  an  indistinct  circle.  These  are  called  "  circles  of  diffusion." 
If,  now,  the  eye,  adjusted  for  vision  at  an  infinite  distance,  be  brought  to  bear  upon  a 
near  object,  the  rays  from  which  are  divergent  as  they  strike  the  cornea,  the  image  will 
>e  no  longer  distinct,  but  will  be  obscured  by  circles  of  diffusion.  It  is  the  adjustment  by 
which  these  circles  of  diffusion  are  removed  that  constitutes  accommodation.  This  fact 
has  been  demonstrated  by  Helmholtz  by  means  of  the  ophthalmoscope.  "  If  the  eye  be 

isted  to  the  observation  of  an  object  placed  at  a  certain  distance,  it  is  found  that  the 
image  of  a  flame,  placed  at  the  same  distance,  is  produced  with  perfect  distinctness  upon 


ACCOMMODATION   OF  THE  EYE. 


799 


the  retina,  and,  at  the  same  time,  upon  the  illuminated  plane  of  the  image,  the  vessels  and 
the  other  anatomical  details  of  the  retina  are  seen  with  equal  distinctness.  But,  when 
the  flame  is  brought  considerably  nearer,  its  image  becomes  confused,  while  the  details 
of  the  structure  of  the  retina  remain  perfectly  distinct." 

It  is  evident  that  there  is  a  certain  condition  of  the  eyes  adapted  to  vision  at  an  infi- 
nite distance,  and  that,  for  the  distinct  perception  of  near  objects,  the  transparent  media 
must  be  so  altered  in  their  arrangement  or  in  the  curvatures  of  their  surfaces,  that  the 
refraction  will  be  greater ;  for,  without  this,  the  rays  would  be  brought  to  a  focus  be- 
yond the  retina. 

The  changes  in  the  eye  by  which  accommodation  is  effected  are  now  known  to  con- 
sist mainly  in  an  increased  convexity  of  the  lens  for  near  objects;  and  the  only  points  in 
dispute  are  a  few  unimportant  details  in  the  mechanism  of  this  action.  The  simple  facts 
to  be  borne  in  mind  in  studying  this  question  are  the  following  : 

When  the  eye  is  accommodated  to  vision  at  an  infinite  distance,  the  parts  are  passive. 

In  the  adjustment  of  the  eye  for  near  objects,  the  convexities  of  the  lens  are  increased 
by  muscular  action. 

In  accommodation  for  near  objects,  the  pupil  is  contracted;  but  this  action  is  merely 
accessory  and  is  not  essential. 

The  ordinary  range  of  accommodation  varies  between  a  distance  of  about  five  inches 
and  infinity. 

Changes  in  the  Crystalline  Lens  in  Accommodation. — It  is  important  to  determine 
first  the  extent  and  nature  of  the  changes  of  the  lens  in  accommodation ;  and,  by  the 
ingenious  experiments  of  the  German  physiologists,  particularly  those  of  Helmholtz, 
these  changes  have  been  accurately  measured  in  the  living  subject.  As  the  general  result 
of  these  measurements,  it  was  ascertained  that  the  lens  becomes  increased  in  thickness 
in  accommodation  for  near  objects,  chiefly  by  an  increase  in  its  anterior  curvature,  by 
which  this  surface  of  the  lens  is  made  to  project  toward  the  cornea.  As  the  iris  is  in 
contact  with  the  anterior  surface  of  the  lens,  this  membrane  is  made  to  project  in  the  act 
of  accommodation.  The  posterior  curvature  of  the  lens  is  also  increased,  but  this  is  slight 
as  compared  with  the  increase  of  the  curvature  of  its  anterior  surface.  The  distance 
between  the  posterior  surface  of  the  lens  and  the  cornea  is  not  sensibly  altered.  It  is 
unnecessary  to  describe  minutely  the  methods  employed  in  making  these  calculations, 
and  it  is  sufficient  for  our  purposes  to  state  that  it  is  done  by  accurately  measuring  the 
comparative  size  of  images  formed  by  reflection  from  the  anterior  surface  of  the  lens. 
The  results  obtained  by  Helmholtz  in  observations  upon  three  different  persons  are  as 
follows : 


Persons  examined. 

Eadius  of  curvature  of  the  anterior  surface 
of  the  lens. 

Displacement  of  the  pup 
for  near  o 

il  in  accommodation 
yects. 

Distant  vision. 

Near  vision. 

O.K. 
B.  P. 
J.  H. 

0-4641  of  an  inch. 
0-3432         " 
0-4056         " 

0-3354  of  an  inch. 
0-2701         " 

0-0140  of  an  inch. 
0-0172 

The  mechanism  of  the  changes  in  the  thickness  and  in  the  curvatures  of  the  lens  in 
accommodation  can  only  be  understood  by  keeping  clearly  in  mind  the  physical  proper- 
ties of  the  lens  itself  and  its  anatomical  relations.  In  situ,  in  what  has  been  called  the 
indolent  state  of  the  eye,  the  lens  is  adjusted  to  vision  at  an  infinite  distance  and  is  flat- 
tened by  the  tension  of  its  suspensory  ligament.  After  death,  indeed,  it  is  is  easy  to  pro- 
duce changes  in  its  form  by  applying  traction  to  the  zone  of  Zinn.  If  we  remember, 


800 


SPECIAL  SENSES. 


now 


. ..,  the  exact  relations  of  the  suspensory  ligament,  the  ciliary  muscle,  and  the  lens,  and 
keep  in  mind  the  tension  within  the  globe,  it  is  evident  that,  when  the  ciliary  muscle  is  in 
repose,  the  capsule  will  compress  the  lens,  increasing  its  diameter  and  diminishing  its 
convexity.  It  is  in  this  condition  that  the  eye  is  adapted  to  vision  at  an  infinite  distance. 
It  is  evident,  also,  that  very  slight  changes  in  the  convexity  of  the  lens  will  be  sufficient 
for  the  range  of  accommodation  required.  If  we  fix  with  the  eye  any  near  object  we  are 
conscious  of  an  effort,  and  the  prolonged  vision  of  near  objects  produces  a  sense  of  fatigue. 
This  may  be  illustrated  by  the  very  familiar  experiment  of  looking  at  a  distant  object 
through  a  gauze.  When  the  object  is  seen  distinctly,  the  gauze  is  scarcely  perceived ; 
but  by  an  effort  we  can  bring  the  eye  to  see  the  meshes  of  the  gauze  distinctly,  when  the 
impression  of  the  distant  object  is  either  lost  or  becomes  very  indistinct. 

Our  knowledge  of  the  action  of  the  ciliary  muscle  is  only  to  be  arrived  at  theoretically 
and  by  studying  the  effects  produced  upon  the  lens.  This  muscle,  it  will  be  remembered, 
arises  from  the  circular  line  of  junction  of  the  cornea  and  sclerotic,  which  is  undoubtedly 
its  fixed  point,  passes  backward,  and  is  lost  in  the  tissue  of  the  choroid,  extending  as  far 
back  as  the  anterior  border  of  the  retina.  Most  of  the  fibres  pass  directly  backward,  but 
some  become  circular  or  spiral.  When  this  muscle  contracts,  the  choroid  is  drawn  for- 
ward, with,  probably,  a  slightly  spiral  motion  of  the  lens,  the  contents  of  the  globe  situ- 
ated posterior  to  the  lens  are  compressed,  and  the  suspensory  ligament  is  relaxed.  The 
lens  itself,  the  compressing  and  flattening  action  of  the  suspensory  ligament  being  dimin- 
ished, becomes  thicker  and  more  convex,  by  virtue  of  its  own  elasticity,  in  the  same  way 
that  it  becomes  thicker  after  death  when  the  tension  of  the  ligament  is  artificially  dimin- 
ished. 


FIG.  253.— Section  oftfte  lens,  etc.,  showing  the  mechanism  of  accommodation.     (Fick.) 

The  left  side  of  the  figure  (F)  shows  the  lens  adapted  to  vision  at  infinite  distances ;  the  right  side  of  the  figure  (N) 
shows  the  lens  adapted  to  the  vision  of  near  objects,  the  ciliary  muscle  being  contracted  and  the  suspensory  liga- 
ment of  the  lens  consequently  relaxed. 

This  is,  in  brief,  the  mechanism  of  accommodation.  Near  objects  are  seen  distinctly 
by  a  voluntary  contraction  of  the  ciliary  muscle,  the  action  of  which  is  adapted  to  the 
requirements  of  vision  with  exquisite  nicety.  In  early  life,  the  lens  is  soft  and  elastic, 
and  the  accommodating  power  is  at  its  maximum ;  but  in  old  age  the  lens  becomes  flat- 
tened, harder,  and  less  elastic,  and  the  power  of  accommodation  is  necessarily  diminished. 

Changes  in  the  Iris  in  Accommodation. — The  size  of  the  pupil  is  sensibly  diminished 
in  accommodation  of  the  eye  for  near  objects.  Although  the  movements  of  the  iris  are 
directly  associated  with  the  muscular  effort  by  which  the  form  of  the  lens  is  modified, 
the  contraction  of  the  pupil  is  not  one  of  the  essential  conditions  of  accommodation. 
Helmholtz  cites  a  case  in  which  the  iris  was  completely  paralyzed,  the  power  of  accom- 
modation remaining  perfect ;  and  he  mentions  another  case,  reported  by  Yon  Graefc,  in 
which  accommodation  was  not  disturbed  after  loss  of  the  entire  iris. 

We  have  already  noted  the  fact  that  the  pupil  contracts  when  the  eyes  are  made  to 
converge  by  the  action  of  the  muscles  animated  by  the  third  pair  of  nerves ;  and  it  is  evi- 


EKECT   IMPRESSIONS  PRODUCED   BY  INVERTED  IMAGES.         801 

dent  that  convergence  of  the  eyes  always  occurs  in  looking  at  very  near  objects.  It 
becomes  a  question,  then,  whether  the  contraction  of  the  pupil  in  accommodation  for  near 
objects  be  associated  with  the  action  of  the  third  nerves,  or  with  filaments  from  the 
ophthalmic  ganglion,  which  supplies  the  nervous  influence  to  the  ciliary  muscle.  This 
seems  to  have  been  definitively  settled  by  Donders,  who  demonstrated  two  important 
points:  First,  that  increased  convergence  of  the  visual  lines  without  change  of  accommo- 
dation makes  the  pupil  contract,  as  is  easily  proven  by  simple  experiments  with  prismatic 
glasses.  Second,  that  when  accommodation  is  effected  without  converging  the  visual 
axes,  "each  stronger  tension  is  combined  with  contraction  of  the  pupil." 

The  action  of  the  iris,  as  is  evident  from  the  facts  just  stated,  is  to  a  certain  extent 
under  the  control  of  the  will ;  but  it  cannot  be  disassociated,  first,  from  the  voluntary 
action  of  the  muscles  which  converge  the  visual  axes,  and  second,  from  the  action  of  the 
ciliary  muscle.  Donders  states  that,  by  alternating  the  accommodation  for  a  remote  and 
a  near  object,  he  could  voluntarily  contract  and  dilate  the  pupil  more  than  thirty  times 
in  the  minute.  Brown-Sequard,  in  discussing  the  voluntary  movements  of  the  iris,  men- 
tions a  case  in  which  "  the  pupil  could  be  contracted  or  dilated  without  changing  the 
position  of  the  eye  or  making  an  effort  of  adaptation  for  a  long  or  a  short  distance." 
As  a  farther  evidence  of  the  connection  of  accommodation  with  muscular  action,  cases 
are  cited  in  works  on  ophthalmology,  in  which  there  is  paralysis  of  the  ciliary  mus- 
cle as  well  as  cases  in  which  the  act  of  accommodation  is  painful. 

An  interesting  phenomenon  connected  with  accommodation  is  observed  in  looking  at 
a  near  object  through  a  very  small  orifice,  like  a  pinhole.  The  shortest  distance  at 
which  we  can  see  a  small  object  distinctly  is  about  five  inches ;  but,  if  we  look  at  the 
same  object  through  a  pinhole  in  a  card,  it  can  be  seen  distinctly  at  the  distance  of  about 
one  inch,  and  it  then  appears  considerably  magnified.  In  this  experiment,  the  card  serves 
as  a  diaphragm  with  a  very  small  opening,  so  that  the  centre  of  the  lens  only  is  used ; 
and  the  apparent  increase  in  the  size  of  the  object  is  probably  due  to  the  fact  that  its  dis- 
tance from  the  eye  is  many  times  less  than  the  distance  at  which  distinct  vision  is  possible 
under  ordinary  conditions.  It  is  well  known  that  myopic  persons,  by  being  able  to  bring 
the  eye  nearer  to  objects  than  is  possible  in  ordinary  vision,  can  see  minute  details  with 
extraordinary  distinctness. 

Erect  Impressions  produced  by  Images  inverted  upon  the  Retina. 

If  we  have  become  thoroughly  acquainted  with  the  mechanism  of  the  formation  of 
images  upon  the  retina  and  the  physiological  action  of  the  different  parts  of  the  optical 
apparatus,  it  will  be  sufficient  to  note  the  action  of  both  eyes,  as  contrasted  with  the 
action  of  one,  in  normal  vision,  without  discussing  fully  the  multitude  of  curious  observa- 
tions made  with  the  stereoscope  ;  and  we  can  readily  comprehend  the  action  of  muscles  by 
which  the  axis  of  vision  is  directed  toward  different  objects,  without  entering  into  a  discus- 
sion of  abstruse  mathematical  calculations  with  regard  to  the  exact  centre  of  rotation,  the 
law  of  torsions,  and  other  points  connected  with  physiological  optics.  These  are  ques- 
tions, however,  of  great  interest  to  ophthalmologists  and  are  fully  discussed  in  elaborate 
special  treatises. 

We  shall  allude  briefly,  in  this  connection,  to  a  question  which  has  long  engaged  the 
attention  of  physiologists,  and  one  which,  we  cannot  but  think,  has  been  made  the  sub- 
ject of  much  unprofitable  speculation.  It  is  a  matter  of  positive  demonstration  that  the 
images  of  objects  seen  are  inverted  as  they  appear  upon  the  retina.  Why  is  it,  however, 
that  objects  are  appreciated  as  erect,  when  their  images  are  thus  inverted  ?  With  a 
knowledge  of  the  fact  that  the  appreciation  of  impressions  made  upon  the  nerves  of 
special  sense  is  capable  of  education  and  is  corrected  by  experience,  it  seems  hardly 
necessary  to  enter  into  an  elaborate  discussion  of  this  point.  We  appreciate  with  accu- 
racy the  density  of  objects,  the  direction  of  sounds,  differences  in  musical  tones,  the 
51 


SPECIAL  SENSES. 

taste  of  sapid  substances,  odors,  etc.,  as  the  result,  to  a  great  degree,  of  education.  In 
the  same  way,  probably,  we  acquire  the  power  of  noting  the  position  of  objects  m  vision  ; 
but  even  this  supposition  is  not  necessary  to  explain  the  phenomenon  of  direct  vision  by 
means  of  inverted  images.  The  following  paragraph,  quoted  from  Giraud-Teulon,  is  a 
simple  expression  of  facts  and  shows  the  absurdity  of  the  elaborate  theoretical  explana- 
tions made  by  many  of  the  earlier  writers : 

"  If  the  objects  seen  mark  their  image  upon  the  retina,  each  one  in  a  proper  second- 
ary axis ;  if,  on  the  other  hand,  the  retina  appreciates  these,  independently  of  ourselves, 
in  these'  same  secondary  axes,  which  all  cross  at  the  same  point,  it  is  evident  that  an 
exact  or  erect  sensation,  as  well  as  the  object  which  produces  it,  should  necessarily  corre- 
spond to  an  inverted  or  reversed  image.  But  it  is  neither  habit,  education,  nor  informa- 
tion derived  from  the  sense  of  touch,  that  enables  us,  as  it  is  said,  to  see  objects  erect 
by  means  of  reversed  images.  The  retina  sees  or  localizes  objects  where  they  are  ;  that  is 
what  we  call  '  erect.'  If  the  picture  be  reversed,  it  is  a  mere  matter  of  geometry." 

In  discussing  the  same  question,  Helmholtz  says  that  "  our  natural  consciousness  is 
completely  ignorant  even  of  the  existence  of  the  retina  and  of  the  formation  of  images  : 
how  should  it  know  any  thing  of  the  position  of  images  formed  upon  it  ? " 

J3inocular  Vision. 

We  have  thus  far  considered  the  mechanism  of  the  eye  and  its  action  as  an  optical  instru- 
ment, in  simple,  or  monocular  vision.  It  is  evident,  however,  that  we  habitually  use  both 
eyes,  and  that  their  axes  are  practically  parallel  in  looking  at  distant  objects  and  are  con- 
verged when  objects  are  approached  to  the  nearest  point  at  which  we  have  distinct  vision. 
In  fact,  an  image  is  formed  simultaneously  upon  the  retina  of  each  eye,  but  it  is  neverthe- 
less appreciated  as  a  unit.  If  the  axis  of  one  eye  be  slightly  deviated  by  pressure  upon 
the  globe,  so  that  the  images  are  not  formed  upon  corresponding  points  upon  the  retina 
of  each  eye,  our  vision  is  more  or  less  indistinct  and  is  double.  In  strabismus,  when  this 
condition  is  recenf,  temporary,  or  periodical,  as  in  recent  cases  of  paralysis  of  the  exter- 
nal rectus  muscle,  when  both  eyes  are  normal,  there  is  double  vision.  "When  the  strabis- 
mus is  permanent  and  has  existed  for  a  long  time,  double  vision  may  not  be  observed, 
unless  the  subject  direct  the  attention  strongly  to  this  point.  As  it  is  usual,  in  such 
cases,  for  one  eye  to  be  much  superior  to  the  other  in  acuteness  of  vision,  an  object  is 
fixed  with  the  better  eye,  and  its  image  is  formed  upon  the  fovea.  The  image  formed 
upon  the  retina  of  the  other  eye  is  indistinct,  and  in  many  instances  it  is  habitually  disre- 
garded ;  so  that,  practically,  the  subject  uses  but  one  eye,  and  presents  the  errors  of 
appreciation  which  attend  monocular  vision,  such  as  a  want  of  accurate  estimation  of 
the  solidity  and  distance  of  objects.  It  is  stated  as  the  rule  that,  when  strabismus  of 
long  standing  is  remedied,  as  far  as  the  axes  of  the  eyes  are  concerned,  by  an  operation, 
binocular  vision  is  not  restored ;  but  the  experiments  necessary  to  the  accurate  determi- 
nation of  this  point  are  exceedingly  delicate  and  must  be  made  with  great  care.  This  is 
explained  upon  the  supposition  that  the  functional  power  of  the  retina  of  the  affected 
eye  has  been  gradually  and  irrecoverably  lost  from  disuse.  In  normal  binocular  vision, 
the  images  are  formed  upon  the  fovea  centralis  of  each  eye  ;  that  is,  upon  corresponding 
points,  which  are,  for  each  eye,  the  centres  of  distinct  vision. 

It  is  hardly  necessary  to  speculate  with  regard  to  the  reason  why  two  images,  one 
upon  each  retina,  convey  the  impression  of  a  single  object.     We  appreciate  a  sound  with 
both  ears;  the  impression  of  a  single  object  is  received  by  the  sensory  nerves  of  two. or 
more  fingers;  the  olfactory  nerves  upon  the  two  sides  are  simultaneously  concerne 
olfaction ;  and,  in  the  same  way,  when  we  look  at  a  single  object  with  both  eyes,  the 
brain  appreciates  a  single  image.     We  shall  see,  however,  that  the  concurrence  of  both 
eyes  is  necessary  to  the  exact  appreciation  of  distance  and  form  ;  and,  when  the  two  iir 
are  formed  upon  corresponding  points,  the  brain  receives  a  correct  impression  of  a  . 


BINOCULAR  VISION.  803 

object.  When  our  vision  is  perfectly  normal,  the  sensation  of  the  situation  of  any  single 
object  is  referred  to  one  and  the  same  point ;  and  we  cannot  receive  the  impression  of  a 
double  image  unless  the  conditions  of  vision  be  abnormal. 

Corresponding  Points. — While  it  requires  no  argument,  after  the  statements  we  have 
just  made,  to  show  that  an  image  must  be  formed  upon  the  fovea  of  each  eye  in  order 
to  produce  the  effect  of  a  single  object,  it  becomes  important  to  ascertain  how  far  it  is 
necessary  that  the  correspondence  of  points  be  carried  out  in  the  retina.  This  leads  to 
considerations  of  very  great  interest  and  importance.  It  is  almost  certain  that,  for  abso- 
lutely perfect,  single  vision  with  the  two  eyes,  the  impressions  must  be  made  upon  ex- 
actly corresponding  points,  even  to  the  ultimate  sensitive  elements  of  the  retina.  We 
may  suppose,  indeed,  that  each  rod  and  each  cone  of  one  eye  has  its  corresponding  rod 
and  cone  in  the  other,  situated  at  exactly  the  same  distance  in  corresponding  directions 
from  the  visual  axis.  When  the  two  images  of  an  object  are  formed  upon  these  correspond- 
ing points,  they  appear  as  one  ;  but,  when  the  images  do  not  correspond,  the  impression 
is  as  though  the  images  were  formed  upon  different  points  in  one  retina,  and,  of  neces- 
sity, they  appear  double. 

The  effect  of  a  slight  deviation  from  the  corresponding  points  may  be  illustrated  by 
the  following  experiment :  We  fix  a  small  object,  like  a  lead-pencil,  held  at  a  distance  of 
a  few  inches,  with  the  eyes,  and  see  it  distinctly  as  a  single  object ;  we  hold  in  the  same 
line,  a  few  inches  farther  removed,  another  small  object ;  when  the  first  is  seen  distinctly, 
the  second  appears  double  ;  we  fix  the  second  with  the  eyes,  and  the  first  appears  double. 
It  is  evident  here,  that,  when  the  axes  of  the  eyes  bear  upon  one  of  these  objects,  the 
images  of  the  other  must  be  formed  at  a  certain  distance  from  the  corresponding  retinal 
points. 

The  Horopter. — The  above-mentioned  experiment  enables  us  to  understand  the  situa- 
tion of  the  horopter.  If  we  fix  both  eyes  upon  any  object  directly  in  front  and  keep 
them  in  this  position,  a  similar  object  moved  to  one  side  or  the  other,  within  a  certain 
area,  may  be  seen  without  any  change  in  the  direction  of  the  axis  of  vision ;  but  the  dis- 
tance from  the  eye  at  which  we  have  single  vision  of  this  second  object  is  fixed,  and,  at 
any  other  distance,  the  object  appears  double.  The  explanation  of  this  is,  that,  at  a  cer- 
tain distance  from  the  eye,  the  images  are  formed  upon  corresponding  points  in  the  retina ; 
but,  at  a  shorter  or  longer  distance,  this  cannot  occur.  This  illustrates  the  fact  that  there 
are  corresponding  points  throughout  the  sensitive  layer  of  the  retina,  as  well  as  in  the 
fovea  centralis.  By  these  experiments,  the  following  facts  have  been  ascertained :  With 
both  eyes  fixed  upon  an  object,  another  object  moved  to  one  side  or  the  other  can  be 
distinctly  seen  only  when  it  is  carried  in  a  certain  curved  line.  On  either  side  of  this  line, 
the  object  appears  double.  This  line,  or  area,  for  the  line  may  have  any  direction,  is 
called  the  horopter.  It  was  supposed  at  one  time  to  be  a  regular  curve,  a  portion  of  a 
circle  drawn  through  the  fixed  point  and  the  points  of  intersection  of  the  rays  of  light  in 
each  eye.  Although  it  has  been  ascertained  that  the  line  varies  somewhat  from  a  regular 
curve,  and  also  varies  in  different  meridians,  this  is  due  to  differences  in  refraction,  etc., 
and  the  principle  is  not  altered. 

It  is  undoubtedly  true  that  education  and  habit  have  a  great  deal  to  do  with  the  cor- 
rection of  visual  impressions  and  the  just  appreciation  of  the  size,  form,  and  distance  of 
objects.  If  we  may  credit  the  account  of  the  remarkable  case  of  Caspar  Hauser,  who  is 

d  to  have  been  kept  in  total  darkness  and  seclusion,  from  the  age  of  five  months  until 
he  was  nearly  seventeen  years  old,  the  appreciation  of  size,  form,  and  distance  is  acquired 
by  correcting  and  supplementing  the  sense  of  sight  by  experience,  even  in  binocular  vision. 

:s  boy  at  first  had  no  idea  of  the  form  of  objects,  or  of  distance,  until  he  had  learned 
ouch,  by  walking,  etc.,  that  certain  objects  were  round,  others  square,  and  had  actually 


804  SPECIAL  SENSES. 

traversed  the  distance  from  one  object  to  another.  At  first,  all  objects  appeared  to  be,  as 
it  were,  painted  upon  a  screen.  Such  points  as  these  it  would  be  impossible  for  us  to. 
accurately  observe  in  infants ;  but  we  have  all  seen  young  children  grasp  at  remote 
objects,  apparently  under  the  impression  that  they  were  within  reach.  It  must  be  ad- 
mitted,'however,  that  the  case  of  Casper  Hauser  is  rather  indefinite;  but  it  is  certain 
that,  even  in  the  adult,  education  and  habit  enable  us  to  greatly  improve  the  faculty  of 
estimating  distances. 

The  important  questions  for  us  now  to  determine  relate  to  the  differences  between 
monocular  and  binocular  vision  in  the  adult.  We  may  see  an  object  distinctly  with 
one  eye ;  but  are  we  able,  from  an  image  made  upon  one  retina,  to  appreciate  all  its 
dimensions  and  its  exact  locality  ? 

Accurate  observations  bearing  upon  this  question  leave  no  doubt  of  the  fact  that 
monocular  vision  is  incomplete  and  inaccurate,  and  that  it  is  only  when  two  images  are 
formed,  one  upon  each  retina,  that  vision  is  perfect.  We  cannot  better  illustrate  the 
truth  of  this  proposition  and  the  exact  condition  of  our  positive  knowledge  upon  this 
important  point,  than  by  quoting  in  full  the  facts  and  arguments  advanced  by  Giraud- 
Teulon : 

"  Monocular  vision  only  indicates  to  us  immediately  visual  direction,  and  not  precise 
locality.  At  whatever  distance  a  luminous  point  may  be  situated  in  the  line  of  direction, 
it  forms  its  image  upon  the  same  point  in  the  retina. 

"  In  the  physiological  action  of  a  single  eye,  in  order  to  arrive  at  an  idea  of  the  dis- 
tance of  a  point  in  a  definite  direction,  we  have  only  the  following  elements : 

"  1.  The  consciousness  of  an  effort  of  accommodation. 

"  2.  Our  own  movement  in  its  relations  to  the  point  observed. 

"  3.  Facts  brought  to  bear  from  recollection,  education,  our  acquired  knowledge  with 
regard  to  the  form  and  size  of  objects :  in  a  word,  experience. 

"  4.  The  geometric  perspective  of  form  and  position. 

"  5.  Aerial  perspective. 

"  All  these  are  elements  wanting  in  precision  and  leaving  the  problem  without  a 
decisive  solution. 

"  And,  indeed : 

"We  place  before  one  of  our  eyes,  the  other  being  closed,  the  excavated  mould  of  a 
medallion :  we  do  not  hesitate,  after  a  few  seconds,  to  mistake  it  for  the  relief  of  the 
medallion.  This  illusion  ceases  at  the  instant  that  both  eyes  are  opened. 

"  Or  again : 

"  A  miniature,  a  photograph,  a  picture,  produces  for  a  single  eye  a  perfect  illusion  ; 
but,  if  both  eyes  be  open,  the  picture  becomes  flat,  the  prominences  and  the  depressions 
are  effaced. 

"  We  may  repeat  the  following  experiment  described  by  Malebranche :  '  Suspend  by 
a  thread  a  ring,  the  opening  of  which  is  not  directed  toward  us  ;  step  back  two  or  three 
paces ;  take  in  the  hand  a  stick  curved  at  the  end ;  then,  closing  one  eye  with  the  hand^ 
endeavor  to  insert  the  curved  end  of  the  stick  within  the  ring,  and  we  shall  be  surprised 
at  being  unable  to  do  in  a  hundred  trials  what  we  should  believe  to  be  very  easy.  If, 
indeed,  we  abandon  the  stick  and  endeavor  to  pass  one  of  the  fingers  through  the  ring, 
we  shall  experience  a  certain  amount  of  difficulty,  although  it  is  very  near.  This  diffi- 
culty ceases  at  the  instant  that  both  eyes  are  opened.' 

As  regards  precision,  exactitude  of  information  concerning  the  relative  distance 
of  objects,  that  is  to  say,  the  idea  of  the  third  dimension  or  of  depth,  there  is  then  a 
notable  difference  between  binocular  vision  and  that  which  is  obtained  by  means  of  one 
eye  alone." 

It  is  evident  that  •  n  accurate  idea  of  the  distance  of  near  objects  cannot  be  obtained 
except  by  the  use  of  both  eyes,  and  this  fact  will  explain,  in  part,  the  errors  of  monocu- 
lar vision,  when  we  look  with  one  eye  upon  objects  in  relief ;  for,  under  these  conditions, 


BINOCULAR  VISION.  805 

•we  cannot  determine  with  accuracy  whether  the  points  in  relief  be  nearer  or  farther 
from  the  eye  than  the  plane  surface.  This  will  not  fully  explain,  however,  the  idea  of 
solidity  of  objects  which  we  obtain  by  the  use  of  both  eyes ;  for  the  estimation  of  dis- 
tance is  obtained  by  bringing  the  axes  of  both  eyes  to  bear  upon  a  single  object,  be  it 
near  or  remote.  The  fact  is,  as  was  distinctly  stated  by  Galen,  in  the  second  century 
that,  when  we  look  at  any  solid  object  not  so  far  removed  as  to  render  the  visual  axes, 
practically  parallel,  we  see  with  the  right  eye  a  portion  of  the  surface  which  is  not  seen 
with  the  left  eye,  and  vice  versa.  The  two  impressions,  therefore,  are  not  identical  for 
each  retina ;  the  image  upon  the  left  retina  including  a  portion  of  the  left  side  of  the 
object  not  seen  by  the  right  eye,  the  right  image  in  the  same  way  including  a  portion  of 
the  right  surface  not  seen  by  the  left  eye.  These  slightly  dissimilar  impressions  are 
fused,  as  it  were,  produce  the  impression  of  a  single  image,  when  vision  is  perfectly 
normal,  and  this  gives  the  idea  of  relief  or  solidity,  enabling  us  to  appreciate  exactly  the 
form  of  objects,  when  they  are  not  too  remote. 

The  fact  just  stated  is  of  course  a  mathematical  necessity  in  binocular  vision  for  near 
objects ;  but  the  actual  demonstration  of  the  fusion  of  two  dissimilar  images  and  the  con- 
sequent formation  of  a  single  image  giving  the  impression  of  solidity  was  made  by  the 
invention  of  the  stereoscope,  by  Wheatstone.  The  principle  of  this  instrument  is  very 
simple.  Two  pictures  are  made,  representing  a  solid  object,  one  viewed  slightly  from 
the  right  side,  and  the  other,  slightly  from  the  left,  so  as  to  imitate  the  differences  in 
the  images  formed  upon  the  two  retinae.  These  pictures  are  so  placed  in  a  box  that  the 
image  of  one  is  formed  upon  the  right  retina,  and  the  other,  upon  the  left.  When  these 
conditions  are  accurately  fulfilled,  we  see  but  a  single  image,  and  this  conveys  to  the 
mind  the  perfect  illusion  of  a  solid  object.  Experiments  with  the  stereoscope  are  so 
familiar  that  they  need  hardly  be  dwelt  upon.  With  most  persons,  an  apparatus  is 
necessary  to  shut  off  disturbing  visual  impressions ;  but  some  individuals  are  able  to 
fuse  two  images  in  this  way,  placed  in  proper  position,  without  the  aid  of  an  instrument, 
by  a  simple  effort  of  the  will. 

The  invention  of  the  stereoscope  has  led  to  many  curious  and  interesting  experiments, 
especially  since  the  art  of  photography  has  enabled  us  to  produce  pictures  in  any  position 
with  absolute  accuracy  ;  but  a  simple  statement  of  the  principle  upon  which  the  instru- 
ment is  constructed  illustrates  the  mechanism  of  binocular  vision  in  the  appreciation  of 
the  form  of  objects.  Experience,  the  aid  of  the  sense  of  touch,  etc.,  enable  persons  with 
but  one  eye  to  get  a  notion  of  form,  but  the  impressions  are  never  entirely  accurate  in 
this  regard,  although,  from  habit,  this  defect  occasions  little  or  no  inconvenience.  A 
striking  illustration  of  these  points  is  afforded  by  the  binocular  microscope,  which, 
especially  with  low  magnifying  powers,  produces  a  startling  impression  of  relief. 

As  we  have  just  remarked,  the  stereoscope  affords  a  satisfactory  explanation  of  the 
mechanism  of  the  eye  in  the  appreciation  of  the  form  of  objects ;  but,  notwithstanding 
this,  a  theory  has  been  proposed,  and  is  adopted  by  some  writers,  that  we  obtain  an  idea 
of  form  by  rapidly  and  insensibly  directing  the  eyes  successively  toward  different  points 
on  the  surface  of  objects.  It  is  difficult  to  understand  how  the  eye  can  make  these  rapid 
movements,  but  the  question  is  definitively  settled  by  a  very  simple  fact  demonstrated 
by  Dove,  Helmholtz,  and  others.  In  an  article  on  visual  perception,  by  Helmholtz,  it  is 
stated  that  stereoscopic  effect  is  recognized  when  two  pictures  are  seen  illuminated  by 
an  electric  spark,  the  duration  of  which  does  not  amount  to  the  four-thousandth  part  of 
a  second,  so  short,  indeed,  that  a  falling  body  appears  absolutely  motionless.  Under 
these  conditions,  displacement  of  the  line  of  vision  would  seem  to  be  impossible. 

We  shall  conclude  our  discussion  of  binocular  vision  and  the  stereoscope  with  a  brief 
account  of  some  experiments  upon  the  binocular  fusion  of  colors,  which  are  very  curious, 
although  they  have  no  very  important  bearing  upon  the  physiology  of  the  eye  in  ordinary 
vision.  Though  an  opposite  opinion  is  held  by  some  experimenters,  Helmholtz,  with 
many  others,  states  that,  when  one  color  is  seen  with  one  eye  and  another  color  with  the 


806  SPECIAL  SENSES. 

other  eye,  in  the  stereoscope,  the  impression  is  not  of  a  single  color  resulting  from  the 
combination  of  the  two.  It  is  true  that  there  is  an  imperfect  mingling  of  the  two  colors, 
but  this  is  very  different  from  the  resulting  color  produced  by  the  actual  fusion  of  the 
two.  There  is,  in  other  words,  a  sort  of  confusion  of  colors,  without  the  complete  com- 
bination with  which  we  are  familiar  in  ordinary  experiments.  One  additional  point  of 
interest,  however,  is  that  the  binocular  fusion  of  two  pictures,  unequally  illuminated  or 
of  different  colors,  produces  a  single  image  of  a  peculiar  lustre,  even  when  both  surfaces 
are  dull.  This  may  be  very  strikingly  shown  by  making  a  stereoscopic  combination  of 
images  of  crystals,  one  witli  black  lines  on  a  white  ground,  and  the  other  with  white  lines 
on  a  black  ground.  The  resulting  image  has  then  the  appearance  of  dark,  brilliant  crys- 
tals, like  graphite. 

Duration  of  Luminous  Impressions. 

The  time  necessary  for  vision  is  exceedingly  short ;  so  short,  indeed,  that  it  almost 
passes  our  powers  of  comprehension.  Taking  advantage  of  the  very  delicate  methods  of 
chronometric  observations  now  employed  by  physicists,  it  has  been  shown  by  Prof.  Rood, 
of  New  York,  that  the  letters  on  a  printed  page  are  distinctly  seen  when  illuminated  by 
an  electric  spark,  the  duration  of  which  was  measured  and  found  to  be  not  more  than 
forty  billionths  of  a  second.  Inasmuch  as  the  waves  of  light  strike  the  eye  at  the  rate  of 
over  five  hundred  millions  of  millions  in  a  second,  it  is  evident  that,  even  in  the  period 
indicated  by  Prof.  Eood,  an  immense  number  of  waves  have  time  to  impinge  upon  the 
retina. 

We  have  long  been  familiar  with  the  fact  that  an  impression  made  upon  the  retina 
endures  for  a  length  of  time  that  can  readily  be  measured,  and  that  its  duration  bears  a 
certain  degree  of  relation  to  the  intensity  of  the  luminous  excitation.  If,  after  looking 
fixedly  at  a  very  bright  object,  we  suddenly  produce  complete  obscurity,  the  object  is 
more  or  less  distinctly  seen  after  the  rays  have  ceased  to  pass  to  the  eye,  and  the  image 
fades  away  gradually.  When  we  produce  a  rapid  succession  of  images,  they  may  be,  as 
it  were,  fused  into  one,  as  the  spokes  of  a  rapidly-revolving  wheel  are  indistinct  and 
produce  a  single  impression.  This  is  due  to  the  persistence  of  the  successive  retinal 
impressions ;  for,  if  a  revolving  wheel,  or  even  a  falling  body,  be  illuminated  for  the  brief 
duration  of  an  electric  spark,  it  appears  absolutely  stationary,  as  the  period  of  time  neces- 
sary for  perfectly  distinct  vision  and  the  duration  of  the  illumination  are  so  short,  that 
there  is  no  time  for  any  appreciable  movement  of  the  object.  The  familiar  experiments 
made  with  revolving  disks  strikingly  illustrate  these  points.  In  a  disk  marked  with 
alternate  radiating  lines  of  black  and  white,  the  rays  become  entirely  indistinguishable 
during  rapid  revolution,  and  the  disk  appears  of  a  uniform  color,  such  as  would  be  pro- 
duced by  a  combination  6*f  the  black  and  white.  Very  beautiful  effects  of  artificial  com- 
bination of  colors  may  be  produced  in  this  way,  the  resultant  color  appearing  precisely 
as  if  the  individual  colors  had  been  ground  together.  It  is  also  interesting,  in  this  con- 
nection, to  note  that  the  duration  of  retinal  impressions  varies  considerably  for  the 
different  colors.  According  to  Emsmann,  the  duration  for  yellow  is  0'25  of  a  second ; 
for  white,  0'25  of  a  second  ;  for  red,  0-22  of  a  second ;  and  for  blue,  0'21  of  a  second. 

It  is  unnecessary  to  describe  farther  in  detail  the  well-known  phenomena  which 
illustrate  the  point  under  consideration.  The  circle  of  light  produced  by  rapidly  revolving 
a  burning  coal,  the  track  of  a  meteor,  and  other  illustrations,  are  sufficiently  familiar,  as 
well  as  many  scientific  toys  producing  optical  illusions  of  various  kinds. 

Irradiation.— It  has  been  observed  that  luminous  impressions  are  not  always  confined 

the  elements  of  the  retina  directly  involved,  but  are  sometimes  propagated  to  those 

immediately  adjacent.    This  gives  to  objects  a  certain  degree  of  amplification,  which  is 

generally  in  proportion  to  their  brightness.     An  illustration  of  this  is  afforded  by  the 

imple  experiment  of  looking  at  two  circles,  one  black  on  a  white  ground,  and  the  other 


MOVEMENTS   OF  THE  EYEBALL.  807 

white  on  a  black  ground.  Although  the  actual  dimensions  of  the  two  circles  are  iden- 
tical, the  irradiation  of  rays  from  the  white  circle  makes  this  appear  the  larger.  In  a 
circle  with  one  half  black  and  the  other  white,  the  white  portion  will  appear  larger,  for 
the  same  reason.  This  deception  increases  sensibly  when  we  look  steadily  at  the  object. 
These  phenomena  are  due  to  what  has  been  called  by  physiologists  irradiation ;  and  their 
explanation  is  very  simple.  It  is  probable  that  luminous  impressions  are  never  confined 
absolutely  to  those  parts  of  the  retina  upon  which  the  rays  of  light  directly  impinge,  but 
that  the  sensitive  elements  immediately  contiguous  are  always  more  or  less  involved. 
In  looking  at  powerfully-illuminated  objects,  the  irradiation  is  considerable,  as  compared 
with  objects  which  send  fewer  luminous  rays  to  the  eye. 

In  experiments  analogous  to  those  just  described,  made  with  strongly  colored  objects, 
it  has  been  observed  that  the  border  of  irradiation  takes  a  color  complementary  to  that 
of  the  object  itself.  This  is  particularly  well  marked  when  the  objects  are  steadily  looked 
at  for  some  time.  Illustrations  of  this  point  also  are  very  simple.  If  we  looked  fixedly 
at  a  red  spot  or  figure  on  a  white  ground,  we  soon  see  surrounding  the  red  object  a  faint 
areola  of  a  pale  green ;  or,  if  the  image  be  yellow,  the  areola  will  appear  pale  blue. 
These  appearances  have  been  called  accidental  areolse. 

Movements  of  the  Eyeball. 

The  eyeball  nearly  fills  the  cavity  of  the  orbit,  resting,  by  its  posterior  portion, 
upon  a  bed  of  adipose  tissue,  which  is  never  absent,  even  in  extreme  emaciation.  Out- 
side of  the  sclerotic,  is  a  fibrous  membrane,  the  tunica  vaginalis  oculi,  or  capsule  of 
Tenon,  which  is  useful  in  maintaining  the  equilibrium  of  the  globe.  This  fibrous  mem- 
brane surrounds  the  posterior  two-thirds  of  the  globe  and  is  loosely  attached  to  the 
sclerotic.  It  is  perforated  by  the  optic  nerve  posteriorly,  and  by  the  tendons  of  the 
recti  and  oblique  muscles  of  the  eyeball  in  front,  being  reflected  over  these  muscles.  It 
is  also  continuous  with  the  palpebral  ligaments  and  is  attached  by  two  tendinous  bands 
to  the  border  of  the  orbit  at  the  internal  and  the  external  angles  of  the  lids. 

The  muscles  which  move  the  globe  are  six  in  number  for  each  eye.  These  are,  the 
external  and  internal  recti,  the  superior  and  inferior  recti,  and  the  two  oblique  muscles. 
The  four  recti  muscles  and  the  superior  oblique  arise  posteriorly  from  the  apex  of  the 
orbit.  The  recti  pass  directly  forward  by  the  sides  of  the  globe  'and  are  inserted  by 
short,  tendinous  bands  into  the  sclerotic,  at  a  distance  of  from  one-fourth  to  one-third  of 
an  inch  from  the  margin  of  the  cornea.  The  superior  oblique,  or  trochlearis  muscle 
passes  along  the  upper  and  inner  wall  of  the  orbit  to  a  point  near  the  inner  angle.  It 
here  presents  a  rounded  tendon,  which  passes  through  a  ring,  or  pulley  of  fibro-cartilage ; 
and  it  is  from  this  point  that  its  action  is  exerted  upon  the  globe.  From  the  pulley,  or 
trochlea,  the  tendon  becomes  flattened,  passes  outward  and  backward  beneath  the  supe- 
rior rectus,  and  is  inserted  into  the  sclerotic,  about  midway  between  the  superior  and  the 
external  rectus  and  just  behind  the  equator  of  the  globe.  The  inferior  oblique  muscle 
arises  just  within  the  anterior  margin  of  the  orbit,  near  the  inner  angle  of  the  eye,  and 
passes  around  the  anterior  portion  of  the  globe,  beneath  the  inferior  rectus  and  between 
the  external  rectus  and  the  eyeball,  taking  a  direction  outward  and  slightly  backward. 
Its  tendon  is  inserted  into  the  sclerotic,  a  little  below  the  insertion  of  the  superior 
oblique.  The  general  arrangement  of  these  muscles  is  shown  in  Fig.  254. 

The  various  movements  of  the  eyeball  are  easily  understood  by  a  study  of  the  asso- 
ciated movements  of  the  muscles  just  enumerated,  at  least,  as  far  as  is  necessary  to  the 
comprehension  of  the  mechanism  by  which  the  eyes  are  directed  toward  any  particular 
object.  We  have  already*  seen  that  the  centre  of  exact  vision  is  in  the  fovea;  and  it  is 
evident  that,  in  order  to  see  any  object  distinctly,  it  is  necessary  to  bring  it  within  the 
axes  of  vision  of  both  eyes.  As  the  globe  is  so  balanced  in  the  orbit  as  to  be  capable  of 
rotation,  within  certain  limits,  in  every  direction,  we  have  only  to  note  the  exact  mode 


808  SPECIAL  SENSES. 

of  action  of  each  of  the  muscles,  in  order  to  comprehend  how  the  different  movements 
are  accomplished  ;  and  it  is  sufficient  for  our  purposes  to  admit  that,  approximative^, 
there  is  a  common  axis  of  rotation  for  each  pair  of  muscles. 

Under  ordinary  conditions,  in  the  human  subject,  the  action  of  the  six  ocular  muscles 
is  confined  to  the  movements  of  rotation  and  torsion  of  the  globe.  It  is  said  that,  in  the 
human  subject,  there  is  no  such  thing  as  protrusion  of  the  eye  from  general  relaxation 
of  these*  muscles,  and  that  it  is  impossible,  by  a  combined  action  of  the  four  recti  muscles 
to  retract  the  globe  in  the  orbit ;  but  those  who  have  operated  upon  the  eyes  assert  posi- 
tively that  this  statement  is  erroneous,  and  that  the  globe  is  almost  always  suddenly  and 
powerfully  drawn  within  the  orbit  when  a  painful  impression  is  made  upon  the  cornea. 
This  is  stated  as  a  matter  of  common  observation  by  ophthalmic  surgeons. 


FIG.  254.— Muscles  of  the  eyeball.    (Sappey.) 

1,  attachment  of  the  tendon  connected  with  the  inferior  rectus,  internal  rectus,  and  external  rectus  ;  2,  external  rectus 
divided  and  turned  downward  to  expose  the  inferior  rectus  ;  8,  internal  rectus ;  4,  inferior  rectus  ;  5,  superior 
rectus;  6  superior  oblique;  7,  pulley  and  reflected  portion  of  the  superior  oblique;  8,  inferior  oblique :  9,  leva- 
tor  palpebn  superioris;  10, 10,  middle  portion  of  the  levator  palpebri  superioris ;  11,  optic  nerve. 

The  extent  to  which  the  line  of  vision  may  be  turned  by  a  voluntary  effort  varies  in 
different  individuals,  even  when  the  eyes  are  perfectly  normal.  In  myopic  eyes,  the  centre 
of  rotation  is  deeper  in  the  orbit  than  normal,  and  the  extent  of  the  possible  deviation  of 
the  visual  line  is  correspondingly  diminished.  Helmholtz  states  that,  in  his  own  person, 
with  the  greatest  effort  that  he  is  capable  of  making,  he  can  move  the  line  of  vision  in 
the  horizontal  plane  to  the  extent  of  about  fifty  degrees,  and,  in  the  vertical  plane,  about 
forty-five  degrees ;  but  he  adds  that  these  extreme  rotations  are  very  forced,  and  that 
they  cannot  be  sustained  for  any  length  of  time.  It  is  probable  that  we  seldom  move  the 
eyeball  in  any  direction  to  an  angle  of  forty-five  degrees,  the  direction  of  the  visual  line 
>emg  more  easily  accomplished  by  movements  of  the  head. 

Action  of  the  Recti  Muscles.— The  action  of  the  recti,  particularly  of  the  internal  and 
external,  is  quite  simple. 

The  internal  and  the  external  recti  rotate  the  globe  upon  a  vertical  axis,  which  is  per- 
icular  to  the  axis  of  the  eye.     The  isolated  action  of  these  muscles,  particularly  of  the 
rnal  rectus,  is  often  illustrated  in  certain  forms  of  paralysis,  which  have  been  alluded 
o  in  connection  with  the  history  of  the  cranial  nerves. 

The  superior  and  the  inferior  recti  rotate  the  globe  upon  a  horizontal  axis,  which  is 


MOVEMENTS   OF  THE  EYEBALL. 


809 


not  at  right  angles  with  the  axis  of  the  eye,  but  is  inclined  from  the  nasal  side  slightly 
backward.  The  line  which  serves  as  the  axis  of  rotation  for  these  muscles  forms  an  angle 
of  about  seventy  degrees  with  the  axis  of  the  globe ;  and,  as  a  consequence  of  this  arrange- 
ment, their  action  is  not  so  simple  as  that  of  the  internal  and  external  recti.  The  inser- 
tion of  the  superior  rectus  is  such,  that,  when  it  contracts,  the  pupil  is  directed  upward 
and  inward,  the  inferior  rectus  directing  the  pupil  downward  and  inward. 

The  above  represents  the  simple,  isolated  action  of  each  pair  of  recti  muscles ;  but  it 
is  easy  to  see  how,  without  necessarily  involving  the  action  of  the  oblique  muscles,  the 
globe  may  be  made  to  perform  an  immense  variety  of  rotations,  and  the  line  of  vision  may 
be  turned  in  nearly  every  direction,  by  the  action  of  the  recti  muscles  alone. 

Action  of  the  Oblique  Muscles. — Although  there  has  been  considerable  discussion  con- 
cerning the  exact  mode  of  action  of  the  oblique  muscles,  their  mechanism  may  now  be 
regarded  as  pretty  well  settled,  at  least  as  regards  the  human  subject.  In  the  first  place, 
it  is  sufficient  for  all  practical  purposes,  to  assume  that  the  superior  and  the  inferior 
oblique  muscles  act  as  direct  antagonists  to  each  other.  The  next  point  to  determine  is 
the  direction  of  the  axis  of  rotation  of  the  globe  with  reference  to  the  action  of  these 
muscles.  The  most  exact,  recent  measurements  show  that  this  axis  is  horizontal  and 
that  it  has  an  oblique  direction  from  before  backward  and  from  without  inward.  The 
angle  formed  by  the  axis  of  rotation  of  the  oblique  muscles  with  the  axis  of  the  globe  is 
thirty-five  degrees;  and  the  angle  be- 
tween the  axis  of  the  oblique  muscles 
and  the  axis  of  the  superior  and  inferior 
recti  muscles  is  seventy-five  degrees. 

Given  the  direction  of  the  axis  of 
rotation  and  the  direction  of  the  supe- 
rior oblique  muscle,  it  is  easy  to  under- 
stand the  effects  of  its  contraction.  As 
this  muscle,  passing  obliquely  backward 
and  forward  over  the  globe,  acts  from 
the  pulley  near  the  inner  angle  of  the 
eye  to  its  insertion  just  behind  the  an- 
terior half  of  the  globe  on  its  external 
and  superior  surface  (7,  Fig.  254),  it 
must  rotate  the  globe  so  as  to  direct  the 
pupil  downward  and  outward. 

The  inferior  oblique,  passing  outward 
and  slightly  backward  under  the  globe, 
acts  from  its  origin  at  the  margin  of  the 
orbit  near  the  inner  angle  of  the  eye  to 
its  insertion,  which  is  just  below  the  in- 
sertion of  the  superior  oblique.  This 
muscle  rotates  the  globe  so  as  to  direct 
the  pupil  upward  and  outward. 

The  action  of  the  oblique  muscles 
seems  to  be  specially  connected  with 
the  movements  of  torsion  of  the  globe. 
It  is  necessary  to  distinct,  single  vision 
with  both  eyes,  that  the  images  should 
be  formed  upon  exactly  corresponding  points  on  the  retina,  and  that  they  should  bear, 
for  the  two  eyes,  corresponding  relations  to  the  perpendicular.  Thus  it  is  that,  when  the 
head  is  inclined  to  one  side,  the  eyes  are  twisted  upon  an  oblique,  antero-posterior  axis ; 
as  can  be  readily  observed  if  we  watch  little  spots  upon  the  iris  during  these  movements. 


next. 


FIG.  255. — Diagram  illustrating  the  action  of  the  muscles  of 

the  eyeball.    (Fick.) 
The  dark  lines  represent  the  muscles  of  the  eyeball,  and  the 

dotted  lines,  the  axis  of  the  superior  and  the  inferior  rectus 

and  the  axis  of  the  oblique  muscles. 


310  SPECIAL  SENSES. 

The  superior  oblique  muscle  is  supplied  by  a  single  nerve,  the  patheticus.  When  this 
muscle  is  paralyzed,  the  inferior  oblique  acts  without  its  antagonist,  and  the  eyeball  is 
immovable,  as  far  as  the  twisting  of  the  globe,  just  described,  is  concerned.  When 
the  head  is  moved  toward  the  shoulder,  the  globe  cannot  rotate  to  maintain  a  position 
corresponding  to  that  of  the  other  eye,  and  we  have  double  vision.  This  point  has 
already  been  touched  upon  in  connection  with  the  physiology  of  the  nerves  of  the  eye- 
ball and  the  situation  of  corresponding  points  in  the  retina. 

Associated  Action  of  the  Different  Muscles  of  the  Eyeball. — It  is  almost  unneces- 
sary to  add,  after  the  description  just  given  of  the  actions  of  the  individual  muscles  of 
the  globe,  that  their  contractions  may  be  associated,  so  as  to  produce  an  infinite  variety 
of  movements.  We  have  no  consciousness,  under  ordinary  circumstances,  of  the  muscular 
action  by  which  the  globe  is  rotated  and  twisted  in  various  directions,  except  that,  by  an 
eifort  of  the  will,  we  direct  the  visual  line  toward  different  objects.  By  a  strong  effort, 
we  can  make  the  eyes  converge  by  contracting  both  internal  recti,  and  some  persons  can 
produce  extreme  divergence  by  using  both  external  recti ;  but  this  is  abnormal. 

In  looking  at  distant  objects,  the  axes  of  vision  are  practically  parallel.  When  we 
look  at  near  objects,  the  effort  of  accommodation  is  attended  with  the  amount  of  con- 
vergence necessary  to  bring  the  visual  axes  to  bear  upon  identical  points.  In  looking 
around  at  different  objects,  we  move  the  head  more  or  less,  rotating  and  twisting  the 
globes  in  various  directions.  In  the  movements  of  the  globes  vertically,  the  axes  are 
kept  parallel,  or  at  the  proper  angle,  by  the  internal  and  external  recti,  and  the  superior 
and  inferior  recti  upon  the  two  sides  act  together.  In  rotating  the  globe  from  one  side 
to  the  other,  upon  a  vertical  axis,  the  external  rectus  upon  one  side  acts  with  the  internal 
rectus  upon  the  other.  In  the  movements  of  torsion  upon  an  antero-posterior  axis,  there 
must  be  an  associated  action  of  the  oblique  muscles  and  the  recti.  We  quote  from  Longet 
the  following,  as  illustrative  of  this  combination  of  action  : 

u  If  the  eyes  be  directed  obliquely  upward  and  to  the  left,  the  vertical  meridians  of 
the  two  eyes  are  parallel  and  inclined  from  left  to  right,  for  the  left  eye,  outward,  and  for 
the  right  eye,  inward.  The  movement  of  the  left  eye  upward  and  to  the  left,  or  outward, 
necessitates  a  contraction  of  the  superior  rectus,  the  external  rectus,  and  the  inferior 
oblique  muscles.  As  regards  the  right  eye,  also  directed  upward  and  to  the  left,  that  is 
to  say,  inward,  this  is  moved  by  the  simultaneous  action  of  the  superior  rectus,  the  inter- 
nal rectus,  and  the  inferior  oblique." 

We  have  given  the  above  quotation  simply  to  illustrate  a  combination  of  action  of 
three  muscles  for  each  eye,  the  only  difference  in  binocular  vision  being  that  in  one  eye 
the  external  rectus  is  brought  into  play,  while  the  internal  rectus  acts  upon  the  opposite 
side.  Reversing  this  action  of  the  internal  and  external  recti,  we  have  the  action  which 
directs  the  pupil  upward  and  to  the  right.  If  we  substitute  for  the  superior  rectus  and 
the  inferior  oblique,  the  inferior  rectus  and  the  superior  oblique,  we  have  the  pupil  directed 
downward,  and  either  to  the  right  or  left,  as  the  internal  or  external  rectus  upon  either 
side  is  brought  into  action. 

One  important  point,  never  to  be  lost  sight  of  in  our  study  of  the  associated  action 
of  the  muscles  of  ths  globe,  relates  to  the  associated  movements  of  the  two  eyes.  We 
have  already  seen  that  perfect  binocular  vision  is  possible  only  when  impressions  are 
made  upon  exactly  corresponding  points  in  the  retina  of  each  eye.  If  one  eye  be  deviated 
in  the  horizontal  plane,  the  points  no  longer  correspond,  and  there  is  double  vision,  the 
same  as  if  two  impressions  were  made  upon  one  retina ;  for,  when  the  impressions 
exactly  correspond,  the  two  retina?  act  practically  as  a  single  organ.  The  same  is  true 
in  deviation^  the  globe  in  the  vertical  plane.  If  we  suppose,  for  the  sake  of  argument, 
that  the  retina  is  square,  it  is  evident  that  a  torsion,  or  twisting  of  one  globe  upon  an 
antero-posterior  axis  must  be  attended  with  an  analogous  movement  of  the  other  globe, 
in  order  to  bring  the  visual  rays  to  bear  upon  the  corresponding  points  ;  in  other  words, 


PARTS  FOR  THE  PROTECTION"  OF  THE  EYEBALL.       811 

the  obliquity  of  the  assumed  square  of  the  retina  must  be  exactly  the  same  for  the  two 
eyes,  or  the  coincidence  of  the  corresponding  points  would  be  disturbed  and  we  should 
have  double  vision.  When  we  clearly  understand  that  deviation  of  one  eye  in  the  hori- 
zontal or  the  vertical  plane  disturbs  the  relation  of  the  corresponding  points,  which  is 
sufficiently  easy  of  comprehension,  and  that  a  deviation  from  exact  coincidence  of  action 
in  torsion  of  the  globes  twists,  as  it  were,  the  corresponding  points,  so  that  their  rela- 
tion is  also  disturbed,  we  can  see  that  the  varied  movements  of  the  globes,  by  the  com- 
bined action  of  the  recti  and  oblique  muscles,  must  correspond  for  each  eye,  in  the  move- 
ments of  torsion  upon  an  antero-posterior  axis,  as  well  as  in  movements  of  rotation  upon 
the  horizontal  or  the  vertical  axis. 

Parts  for  the  Protection  of  the  Eyeball. 

The  orbit,  formed  by  the  union  of  certain  of  the  bones  of  the  face,  receives  the  eyeball, 
the  ocular  muscles,  the  muscle  of  the  upper  lid,  blood-vessels,  nerves,  part  of  the  lachry- 
mal apparatus,  and  contains,  also,  a  certain  amount  of  adipose  tissue,  which  latter  never 
disappears,  even  in  extreme  marasmus.  The  bony  walls  of  this  cavity  protect  the  globe 
and  lodge  the  parts  above  enumerated.  The  internal,  or  nasal  wall  of  the  orbit  projects 
considerably  beyond  the  external  wall,  so  that  the  extent  of  vision  is  far  greater  in  the 
outward  than  in  the  inward  direction.  As  the  globe  is  more  exposed  to  accidental  injury 
from  an  outward  direction,  the  external  wall  of  the  orbit  is  stroog,  while  the  bones  which 
form  its  internal  wall  are  comparatively  fragile.  The  upper  border  of  the  orbit  (the 
superciliary  ridge)  is  provided  with  short,  stiff  hairs  (the  eyebrows)  which  serve  to  shade 
the  eye  from  excessive  light  and  to  protect  the  eyelids  from  perspiration  from  the  fore- 
head. 

The  eyelids  are  covered  by  a  very  thin  integument  and  are  lined  by  the  conjunctival 
mucous  membrane.  The  subcutaneous  connective  tissue  is  thin  and  loose  and  is  entirely 
free  from  fat.  The  skin  presents  numerous  short  papilla  and  small  sudoriparous  glands. 
At  the  borders  of  the  lids,  are  short,  stiff,  curved  hairs,  arranged  in  two  or  more  rows, 
called  the  eyelashes  or  cilia.  Those  of  the  upper  lid  are  longer  and  more  numerous  than 
the  lower  cilia.  The  curve  of  the  lashes  is  from  the  eyeball.  They  serve  to  protect  the 
globe  from  dust,  and,  to  a  certain  extent,  to  shade  the  eye. 

The  tarsal  cartilages  are  small,  elongated,  semilunar  plates,  extending  from  the  edges 
of  the  lids  toward  the  margin  of  the  orbit,  between  the  skin  and  the  mucous  membrane. 
Their  length  is  about  an  inch.  The  central  portion  of  the  upper  cartilage  is  about  one- 
third  of  an  inch  broad,  and  the  corresponding  part  of  the  lower  cartilage  measures  about 
one-sixth  of  an. inch.  At  the  inner  canthus,  or  angle  of  the  eye,  is  a  small,  delicate  liga- 
ment, or  tendon,  the  tendo  palpebrarum,  which  is  attached  to  the  lachrymal  groove 
internally,  passes  outward,  and  divides  into  two  lamella,  which  are  attached  to  the  two 
tarsal  cartilages.  At  the  outer  canthus,  the  cartilages  are  attached  to  the  malar  bone  by 
the  external  tarsal  ligament.  The  tarsal  cartilages  receive  additional  support  from  the 
palpebral  ligament,  a  fibrous  membrane  attached  to  the  margin  of  the  orbit  and  the  con- 
vex border  of  the  cartilages  and  lying  beneath  the  orbicularis  muscle.  This  membrane  is 
strongest  near  the  outer  angle  of  the  eye. 

On  the  posterior  surface  of  the  tarsal  cartilages,  partly  embedded  in  them  and  lying 
just  beneath  the  conjunctiva,  are  the  Meibomian  glands.  The  structure  and  functions 
of  these  glands  have  already  been  considered  in  connection  with  secretion.  They  pro- 
duce an  oily  fluid,  which  smears  the  edges  of  the  eyelids  and  prevents  the  overflow  of 
tears. 

Muscles  which  open  and  close  the  Eyelids. — Leaving  out  the  corrugator  supercilii, 
which  draws  the  skin  of  the  forehead  downward  and  inward,  we  have  the  orbicularis 
palpebrarum,  which  closes  the  lids,  and  the  levator  palpebraa  superioris,  which  raises  the 
upper  lid.  The  tensor  tarsi,  called  the  muscle  of  Horner,  is  a  very  thin,  delicate  muscle, 


812  SPECIAL  SENSES. 

which  is  regarded  by  some  anatomists  as  a  deep  portion  of  the  orbicularis.  Considering 
this  as  a  distinct  muscle,  it  consists  of  two  delicate  slips,  which  pass  from  either  eyelid 
behind  the  lachrymal  sac,  uniting  here  to  go  to  its  attachment  at  the  posterior  portion  of 
the  lachrymal  bone.  When  this  acts  with  the  orbicularis,  it  compresses  the  lachrymal  sac. 

The  orbicularis  palpebrarum  is  a  broad,  thin  muscle,  closely  attached  to  the  skin, 
surrounding  the  free  margin  of  the  lids,  and  extending  a  short  distance  over  the  bones, 
beyond  the  margin  of  the  orbit.  This  muscle  may  be  described  as  arising  from  the  tendo 
palpebrarum,  the  surface  of  the  nasal  process  of  the  superior  maxiliary  bone,  and  the 
internal  angular  process  of  the  os  frontis.  From  this  origin  at  the  inner  angle  of  the 
eye,  its  fibres  pass  elliptically  around  the  fissure  of  the  lids,  as  above  indicated.  Its 
action  is  to  close  the  lids.  In  the  ordinary,  moderate  contraction  of  this  muscle,  only 
the  upper  lid  is  moved ;  but,  in  forcible  contraction,  the  lower  lid  moves  slightly  and  the 
lids  are  drawn  toward  the  nose.  In  facial  palsy,  or  when  the  temporo-facial  branch  of 
the  portio  dura  of  the  seventh  nerve  is  paralyzed,  this  muscle  cannot  act,  and  it  is  impos- 
sible to  close  the  eye. 

The  levator  palpebraB  superioris  is  situated  within  the  orbit.  It  arises  from  a  point 
a  little  above  and  in  front  of  the  optic  foramen  at  the  apex  of  the  orbit,  passes  forward 
above  the  eyeball,  and  spreads  into  a  thin  tendon,  which  is  inserted  into  the  anterior 
surface  of  the  superior  tarsal  cartilage.  Its  evident  action  is  to  raise  the  upper  lid.  It  is 
animated  by  filaments  from  the  third  pair  of  cranial  nerves ;  and,  when  this  nerve  is 
paralyzed,  we  have  permanent  falling  of  the  upper  lid,  or  blepharoptosis.  This  muscle 
and  its  relations  are  shown  in  Fig.  254  (9,  10,  10),  page  808. 

In  the  act  of  opening  the  eyes,  the  levator  muscles  alone  are  brought  into  play. 
Closing  of  the  lids  is  accomplished  by  the  orbicular  muscles.  Both  of  these  sets  of  mus- 
cles act  to  a  great  extent  without  the  intervention  of  the  will.  The  eyes  are  kept  open 
almost  involuntarily,  except  in  extreme  fatigue ;  although,  when  the  will  ceases  to  act, 
the  lids  are  closed.  Nevertheless,  we  are  hardly  conscious  of  an  effort  in  keeping  the 
eyes  open,  in  our  waking  moments,  and  we  require  an  effort  to  close  the  eyes.  During 
sleep,  the  eyes  are  closed  and  the  globes  are  turned  upward.  The  contractions  of  the 
orbicular  muscles  which  take  place  in  winking  are  usually  involuntary.  This  act  occurs 
at  short  intervals,  and  it  is  useful  in  spreading  the  lachrymal  secretion  over  the  exposed 
portions  of  the  globes.  The  action  of  both  sets  of  muscles  is  usually  simultaneous,  although 
we  may  educate  them  so  as  to  close  one  eye  while  the  other  is  kept  open.  The  action 
of  the  orbicularis  is  so  far  removed  from  the  control  of  the  will,  that,  when  the  surface 
of  the  globe  is  touched  or  irritated  or  when  the  impression  of  light  produces  intense 
pain,  it  is  impossible  to  keep  the  eye  open. 

Oonjunctival  Mucous  Membrane. — The  entire  inner  surface  of  the  upper  and  lower 
eyelids  is  lined  by  a  mucous  membrane,  which  is  reflected  forward  from  the  inner  periph- 
ery of  the  lids  over  the  eyeball.  The  membrane  lining  the  lids  is  called  the  palpebral 
conjunctiva,  and  that  covering  the  eyeball,  the  ocular  conjunctiva.  The  latter  presents 
a  sclerotic  and  a  corneal  portion.  The  membrane  presents  a  superior  and  an  inferior 
fold,  where  it  is  reflected  upon  the  globe.  In  the  superior  conjunctival  fold,  are  numer- 
ous glandular  follicles,  or  accessory  lachrymal  glands,  which  secrete  a  certain  portion  of 
the  fluid  which  moistens  the  surface  of  the  eyeball.  These  are  generally  described  as 
forming  a  part  of  the  lachrymal  gland.  At  the  inner  canthus,  there  is  a  vertical  fold 
(the  plica  semilunaris)  with  a  reddish,  spongy  elevation  at  its  inner  portion,  called  the 
caruncula  lacrymalis.  The  caruncula  presents  a  collection  of  follicular  glands,  with  a 
few  delicate  hairs  on  its  surface.  The  conjunctiva  is  continuous  with  the  membrane  of 
the  Jachrymal  ducts,  of  the  puncta  lacrymalia,  and  of  the  Meibomian  glands.  Beneath  the 
conjunctiva,  except  in  the  corneal  portion,  is  a  loose  connective  tissue. 

The  palpebral  conjunctiva  is  reddish,  thicker  than  the  ocular  portion,  furrowed,  and 
presents  small,  isolated  papilla  near  the  borders  of  the  lids,  which  increase  in  number 


PARTS  FOR  THE  PROTECTION  OF  THE  EYEBALL.       813 

and  size  toward  the  folds.  This  portion  of  the  membrane  presents  large  capillary  blood- 
vessels an ck lymphatics  and  is  covered  with  a  layer  of  cells  of  flattened  epithelium.  The 
sclerotic  portion  is  thinner,  less  vascular,  and  has  no  papillae.  It  is  covered  by  conical 
and  rounded  epithelial  cells,  which  present  from  two  to  four  layers.  Over  the  cornea, 
the  epithelium  of  the  sclerotic  portion  is  continued  in  delicate,  transparent  layers,  without 
a  distinct  basement-membrane. 

The  Lachrymal  Apparatus. — The  eyeball  is  constantly  bathed  in  a  thin,  watery  fluid 
which  is  secreted  by  the  lachrymal  gland,  is  spread  over  the  globe  by  the  movements  of 
the  lids  and  of  the  eyeball,  and  is  prevented,  under  ordinary  conditions,  from  overflowing 
upon  the  cheek,  by  the  Meibomian  secretion.  The  excess  of  this  fluid  is  collected  into 
the  lachrymal  sac  and  is  carried  into  the  nose  by  the  nasal  duct.  The  lachrymal  gland, 
the  lachrymal  canals,  duct,  and  sac,  and  the  nasal  duct,  constitute  the  lachrymal  appa- 
ratus. 

The  lachrymal  gland  is  an  ovoid,  flattened  gland  of  the  racemose  variety,  resembling 
the  salivary  glands  in  its  general  structure.  It  is  about  the  size  of  a  small  almond  and  is 
lodged  in  a  shallow  depression  in  the  bones  of  the  orbit  at  its  upper  and  outer  portion. 
It  is  closely  attached  to  the  periosteum  by  its  upper  surface  and  is  moulded  below  to  the 
convexity  of  the  globe.  Its  anterior  portion  is  separated  from  the  rest  by  a  well-marked 
groove,  is  comparatively  thin,  and  adheres  to  the  upper  lid.  It  presents  from  six  to  eight 
(usually  seven)  ducts,  which  form  a  row  of  openings  into  the  conjunctival  fold.  Five  or 
six  of  these  orifices  are  situated  above  the  outer  canthus  and  two  or  three  open  below. 
In  its  minute  structure,  this  gland  presents  no  points  of  special  physiological  interest  as 
distinguished  from  the  ordinary  racemose  glands.  It  receives  nervous  filaments  from  the 
fifth  cranial  nerve  and  the  sympathetic. 


FIG.  256.— Lachrymal  and  Meibomian  glands.    (Sappey.) 

1, 1,  internal  wall  of  the  orbit;  2,  2,  internal  portion  of  the  orbicularis  palpebrarum;  3,  3,  attachment  of  this  muscle  to 
the  orbit;  4,  orifice  for  the  passage  of  the  nasal  artery;  5,  muscle  of  Horner;  6,  6.  posterior  surface  of  the  eyelids, 
with  the  Meibomian  glands;  7,  T,  8,  8,  9,  9, 10,  lachrymal  gland  and  ducts;  11,  openings  of  the  lachrymal  ducts. 

The  apparatus  by  which  the  excess  of  tears  is  conducted  into  the  nose  begins  by  two 
little  points,  situated  on  the  margin  of  the  upper  and  the  lower  lid,  near  the  inner  canthus, 
called  the  puncta  lacpymalia,  which  present  each  a  minute  orifice.  These  orifices  open 
respectively  into  the  upper  and  the  lower  lachrymal  canals,  which  together  surround  the 
caruncula  lacrymalis.  At  the  inner  angle,  just  beyond  the  caruncula,  the  two  canals 
join,  to  empty  into  the  lachrymal  sac,  which  is  the  dilated  upper  extremity  of  the  nasal 
duct.  The  duct  is  about  half  an  inch  in  length  and  empties  into  the  inferior  meatus  of  the 
nose,  taking  a  direction  nearly  vertical,  and  inclined  slightly  outward  and  backward.  This 


814 


SPECIAL  SENSES. 


portion  of  the  lachrymal  apparatus  is  fibrous  and  is  lined  by  a  reddish  mucous  membrane, 
which  presents  several  well-marked  folds.  Near  the  puncta,  are  two  folds,  one  for  each 
lachrymal  canal.  Another  pair  of  folds  exists  near  the  horizontal  portions  of  the  canals. 
At  the  opening  of  the  duct  into  the  nose,  is  an  overhanging  fold  of  the  nasal  mucous 
membrane.  These  folds  are  supposed  to  prevent  the  reflux  of  fluid  from  the  lachrymal 
canals  and  the  entrance  of  air  from  the  nose.  The  mucous  membrane  of  the  lachrymal 
canals  is  covered  by  a  flattened  epithelium,  like  that  of  the  conjunctiva.  The  lachrymal 
sac  and  duct  are  lined  by  a  continuation  of  the  ciliated  epithelium  of  the  nose.  The  dis- 
position of  the  apparatus  just  described  is  shown  in  Fig.  257. 

The  Tears. — The  secretion  of  the  lachrymal  glands  is  constant,  although  the  quantity  of 
fluid  may  be  increased  under  various  conditions.  The  actual  amount  of  the  secretion  has 
never  been  estimated.  During  sleep  it  is  much  diminished ; 
and,  when  the  eyes  are  open,  the  quantity  is  just  sufficient  to 
moisten  the  eyeball,  the  excess  being  carried  into  the  nose  so 
gradually  that  this  process  is  not  appreciated.  That  this  drain- 
age of  the  excess  of  tears  takes  place  is  shown  by  cases  of  ob- 
struction of  the  nasal  duct,  when  the  liquid  constantly  over- 
flows upon  the  cheeks,  producing  considerable  inconvenience. 

The  mechanism  of  the  action  of  the  excretory  lachrymal 
apparatus  is  quite  simple,  though  it  has  been  the  subject  of  a 
good  deal  of  discussion.  It  is  probable  that  the  openings  at 
the  puncta  lacrymalia  take  up  the  liquid  like  delicate  pipettes, 
this  action  being  aided  by  the  movements  in  winking,  by 
which,  when  the  lids  are  closed,  the  points  are  compressed  and 
turned  backward,  opening  and  drawing  in  the  tears  when  the 
lids  are  opened.  It  is  possible  that  the  lachrymal  sac  is  com- 
pressed in  the  act  of  winking,  by  the  contractions  of  the  muscle 
of  Homer,  and  that  this,  while  it  empties  the  sac,  may,  in  the 
subsequent  relaxation,  assist  the  introduction  of  liquid  from  the 
orbit. 

We  know  very  little  with  regard  to  the  chemical  compo- 
sition of  the  tears,  beyond  the  analysis  made  many  years  ago 
by  Frerichs.  According  to  this  observer,  the  following  is  the  composition  of  the  lachry- 
mal secretion : 


FIG.  257.— Lachrymal  canals, 
lachrymal  sac,  and  nasal 
canal,  opened  by  their  ante- 
rior portion.  (Sappey.) 

1,  walls  of  the  lachrymal  pas- 
sages, smooth  and  adherent; 
2,  2,  walls  Of  the  lachrymal  sac, 
presenting  delicate  folds  of  the 
mucous  membrane;  3,  a  simi- 
lar fold  belonging  to  the  nasal 
mucous  membrane. 


Composition  of  the  Tears. 

Water 990'60    to 

Epithelium 1-40     " 

Albumen 0'80     " 

Chloride  of  sodium, 
Alkaline  phosphates, 

Earthy  phosphates,       \ 7-20 

Mucus, 
Fat, 


1,000-00 


987*00 
3-20 
1-00 


8-80 


1,000-00 


The  specific  gravity  of  the  tears  has  never  been  ascertained.  The  liquid  is  perfectly 
clear,  colorless,  of  a  saltish  taste  and  a  feebly  alkaline  reaction.  The  albumen  given  in 
the  table  is  called  by  some  authors,  lachrymine,  thr&nine,  or  dacryoline.  This  substance, 
whatever  it  may  be  called,  resembles  mucus  in  many  regards  and  is  probably  secreted  by 
the  conjunctiva  and  not  by  the  lachrymal  glands.  It  differs  from  ordinary  mucus  in  being 
coagulated  by  water. 

The  secretion  of  tears  is  readily  influenced  through  the  nervous  system.     Aside  from 


AUDITORY  KERVES.  815 

the  increased  flow  of  this  secretion  from  emotional  causes,  which  probably  operate  through 
the  sympathetic,  a  hypersecretion  almost  immediately  follows  irritation  of  the  mucous 
membrane  of  the  conjunctiva  or  of  the  nose.  The  same  result  follows  violent  muscular 
effort,  laughing,  coughing,  sneezing,  etc.  The  secretion  of  tears  under  stimulation  of  the 
mucous  membrane  is  reflex. 


CHAPTER    XXY. 

A  UDITION. 

Physiological  anatomy  of  the  auditory  nerves— General  properties  of  the  auditory  nerves— Topographical  anatomy 
of  the  parts  essential  to  the  appreciation  of  sound — The  external  ear — General  arrangement  of  the  parts  composing 
the  middle  ear — Anatomy  of  the  tympanum — Arrangement  of  the  ossicles  of  the  ear — Muscles  of  the  middle  ear 
— Mastoid  cells— Eustachian  tube— Muscles  of  the  Eustachian  tube— Mucous  membrane  of  the  middle  ear  and  of 
the  Eustachian  tube— General  arrangement  of  the  bony  labyrinth — Laws  of  sonorous  vibrations — Noise  and  musi- 
cal sounds— Intensity,  pitch,  and  quality  of  musical  sounds— Musical  scale— Harmonics,  or  overtones— Eesonators 
of  Helmholtz — Kesultant  tones— Summation  tones — Harmony — Discord— Tones  by  influence  (consonance) — Uses 
of  different  parts  of  the  auditory  apparatus— Uses  of  the  external  ear— Structure  of  the  membrana  tympani— Uses 
of  the  membrana  tympani — Vibrations  of  the  membrane  by  influence — Appreciation  of  the  pitch  of  tones — Mech- 
anism of  the  ossicles  of  the  ear — Physiological  anatomy  of  the  internal  ear — General  arrangement  of  the  mem- 
branous labyrinth— Vestibule— Semicircular  canals— Cochlea— Liquids  of  the  labyrinth— Distribution  of  nerves  in 
the  cochlea — Organ  of  Corti — Functions  of  different  parts  of  the  internal  ear — Functions  of  the  semicircular  canals 
— Functions  of  the  parts  contained  in  the  cochlea — Summary  of  the  mechanism  of  audition. 

THE  general  considerations  introductory  to  the  study  of  vision  are  equally  applicable 
to  the  physiology  of  hearing.  The  impressions  of  sound  are  conveyed  to  the  brain  by 
special  nerves  ;  but,  in  order  that  these  impressions  shall  reach  these  nerves  so  as  to  be 
properly  appreciated,  a  complex  accessory  apparatus  is  required,  the  integrity  of  which  is 
essential  to  perfect  audition.  The  study  of  the  arrangement  and  action  of  these  accessory 
parts  is  even  more  important  and  is  far  more  intricate  than  the  physiology  of  the  auditory 
nerves.  The  latter  simply  convey  the  impressions  to  the  brain,  by  a  mechanism  analogous 
to  that  of  general  nervous  conduction,  the  essential  character  of  which  is  not  fully  under- 
stood. The  auditory  nerves  conduct  impressions  of  sound,  as  the  optic  nerves  conduct 
impressions  of  light ;  and  this  statement  expresses  the  extent  of  our  positive  knowledge ; 
but  there  is  an  elaborate  apparatus  by  which  the  waves  are  collected,  conveyed  to  a 
membrane  capable  of  vibration,  and  finally  carried  to  the  nerves,  by  which  we  are  enabled 
to  appreciate  the  intensity  and  the  varied  qualities  of  sound. 

Our  positive  and  definite  knowledge  of  the  structure  and  arrangement  of  the 'auditory 
apparatus  is  by  no  means  so  complete  as  it  is  with  regard  to  the  eye,  nor  do  we  as  yet 
understand  so  clearly  the  physiological  relations  of  many  points  developed  by  late  ana- 
tomical researches ;  and,  for  this  reason,  it  does  not  seem  desirable  to  consider  the  struct- 
ure of  the  ear  as  fully  as  we  have  the  anatomy  of  the  eye,  restricting  ourselves,  as  we 
have  done,  to  the  physiological  anatomy  of  parts.  With  this  end  in  view,  we  shall  take 
up  fully  the  following  points : 

1.  The  physiological  anatomy  and  the  general  properties  of  the  auditory  nerves. 

2.  The  physiological  anatomy  of  the  parts  essential  to  the  correct  appreciation  of 
sound. 

3.  The  laws  of  the  propagation  of  sonorous  vibrations,  as  far  as  they  are  applicable 
to  audition. 

4.  The  physiological  action  of  different  parts  of  the  auditory  apparatus. 

Physiological  Anatomy  of  the  Auditory  Nerves. — The  auditory  nerve  constitutes  the 
portio  mollis  of  the  seventh  pair  of  Willis.  The  origin  of  this  nerve  can  easily  be  traced 
to  the  floor  of  the  fourth  ventricle,  where  it  presents  two  roots.  The  external,  or  super- 


816  SPECIAL  SENSES. 

ficial  root,  sometimes  called  the  posterior  root,  can  be  seen  usually  without  preparation. 
This  consists  of  from  five  to  seven  grayish  filaments,  which  decussate  in  the  median  line, 
and  pass  outward,  winding  from  the  fourth  ventricle  around  the  restiform  body.  The 
deep  root  consists  of  numerous  distinct  filaments,  arising  from  the  gray  matter  of  the 
fourth  ventricle,  two  or  three  of  which  pass  to  the  median  line  to  decussate  with  corre- 
sponding filaments  from  the  opposite  side.  This  root  passes  around  the  restiform  body 
inward,  so  that  this  portion  of  the  medulla  is  encircled,  as  it  were,  by  the  two  roots. 
Passing  from  the  superior  and  lateral  portion  of  the  medulla  oblongata,  the  trunk  of  the 
nerve  is  applied  to  the  superior  and  anterior  surface  of  the  facial.  It  then  passes  around 
the  middle  peduncle  of  the  cerebellum,  and  receives  a  process  from  the  arachnoid  mem- 
brane, which  envelops  it  in  a  common  sheath  with  the  facial.  It  then  penetrates  the 
internal  auditory  meatus.  In  its  course,  it  receives  filaments  from  the  restiform  body, 
and  possibly  from  the  pons  Varolii.  Within  the  meatus,  the  nerve  divides  into  an  ante- 
rior and  a  posterior  branch,  the  anterior  being  distributed  to  the  cochlea,  and  the  poste- 
rior, to  the  vestibule  and  semicircular  canals.  The  distribution  of  these  branches  will  be 
fully  described  in  connection  with  the  anatomy  of  the  internal  ear. 

The  color  of  the  auditory  nerves  is  grayish,  and  their  consistence  is  soft,  thus  differing 
from  the  ordinary  cerebro-spinal  nerves,  and  resembling,  to  a  certain  extent,  the  other 
nerves  of  special  sense.  On  the  external,  or  superficial  root,  is  a  small  ganglioform  en- 
largement, containing  fusiform  nerve-cells.  According  to  the  latest  researches,  the  fila- 
ments of  the  trunk  of  this  nerve  consist  of  very  large  axis-cylinders,  surrounded  by  a 
medullary  sheath,  but  having  no  tubular  membrane.  In  the  course  of  these  fibres,  are 
found  small,  nucleated  ganglionic  enlargements. 

General  Properties  of  tJie  Auditory  Nerves. — There  can  be  no  doubt,  as  regards  the 
portio  mollis  of  the  seventh,  that  it  is  the  only  nerve  capable  of  receiving  and  conveying 
to  the  brain  the  special  impressions  produced  by  waves  of  sound ;  but  it  is  an  interesting 
question  to  determine,  whether  this  nerve  be  endowed  also  with  general  sensibility. 
Analogy  with  most  of  the  other  nerves  of  special  sense  would  indicate  that  the  auditory 
nerves  are  insensible  to  ordinary  impressions;  and  this  view  is  sustained  by  direct  experi- 
ments, made  many  years  ago. 

The  phenomena  observed  during  the  passage  of  galvanic  currents  through  the  audi- 
tory nerves  have,  of  late  years,  been'the  subject  of  much  discussion.  The  old  experiment 
of  Volta,  which  was  almost  immediately  confirmed  by  Kitter,  is  sufficiently  familiar  and 
is  often  quoted  as  showing  that  galvanic  stimulation  of  these  nerves  produces  a  sensation 
of  sound ;  but  the  facts  ascertained  leave  room  for  doubt  with  regard  to  the  precise  mode 
of  action  of  the  current.  A  careful  study  of  recent  observations  upon  this  point  renders 
the  question  even  more  obscure  ;  but,  from  a  purely  physiological  point  of  view,  we  have 
only  to  do  with  the  effects  of  stimulating  the  auditory  nerves  in  health.  Leaving  the 
therapeutic  and  diagnostic  uses  of  galvanism  out  of  the  question,  we  find  that  there  is 
considerable  uncertainty  with  regard  to  the  fact  of  direct  stimulation  of  the  auditory 
nerves,  in  the  recent  experiments  with  the  galvanic  current.  Brenner  observed  strong 
sensations  of  sound  with  one  of  the  poles  of  a  battery  in  the  auditory  passage  filled  with 
water  and  the  other  connected  with  different  parts  of  the  body.  When  the  cathode  was 
placed  in  the  ear,  the  sound  was  heard  at  the  making  of  the  current.  With  the  anode  in 
the  ear,  there  was  no  sound  at  the  making  of  the  current  or  during  its  passage,  but  a 
slight  sound  was  heard  at  the  breaking  of  the  current.  These  phenomena  closely  resem- 
ble those  produced  by  the  galvanic  current  applied  to  ordinary  motor  nerves,  in  so  far 
as  the  action  seemed  to  be  most  vigorous  at  the  making  of  the  circuit,  with  the  direct 
current,  and  at  the  breaking  of  the  circuit,  with  the  inverse  current;  for,  when  the 
cathode  is  placed  in  the  ear,  the  current  is  direct,  following  the  course  of  the  nerve  from 
the  centre  to  the  periphery,  and  vice  versa.  Without  following  out  the  discussion  of  this 
question  in  detail,  it  seems  only  necessary  to  study  the  very  clear  and  satisfactory  experi- 


THE   EXTERNAL  EAR.  817 

ments  of  Wreden,  to  become  convinced  that  the  subjective  auditory  phenomena,  attrib- 
uted by  Brenner  and  others  to  irritation  of  the  auditory  nerves,  are  due  to  contraction 
of  the  muscles  of  the  middle  ear,  particularly  the  stapedius.  The  facts,  clinical  and  ex- 
perimental, upon  which  this  view  is  based,  are  the  following :  In  cases  of  clonic  spasm  of 
the  stapedius,  sensations  of  sound  have  been  observed,  exactly  like  those  produced  by  an 
induced  current.  In  cases  of  complete  facial  paralysis  from  otitis,  in  which  paralysis  of 
the  auditory  nerve  could  be  positively  excluded,  it  was  not  possible  to  produce  subjective 
auditory  sensations,  even  by  powerful  galvanization  by  a  catheter  passed  through  the 
Eustachian  tube  into  the  tympanic  cavity,  or  by  the  external  meatus.  In  addition,  there 
are  other  well-established  clinical  observations,  mentioned  by  Wreden,  which  sustain  the 
theory  of  muscular  contraction  and  are  opposed  to  the  idea  of  direct  stimulation  of  the 
auditory  nerves. 

The  facts  just  stated  show  that  there  is  no  positive  evidence  of  the  production  of  im- 
pressions of  sound  by  galvanic  stimulation  of  the  auditory  nerves  ;  while  it  appears  from 
experiments,  that  these  nerves  are  not  endowed  with  general  sensibility.  The  results, 
then,  as  regards  the  auditory  nerves,,  are  simply  negative.  Were  it  possible  to  subject 
these  nerves  to  mechanical  or  galvanic  stimulation,  in  the  human  subject,  without  involv- 
ing other  parts,  we  might  arrive  at  £ome  definite  conclusion ;  but  the  difficulties  in  the 
way  of  such  an  experiment,  it  must  be  admitted,  have  thus  far  proved  insurmountable. 

Topographical  Anatomy  of  the  Parts  essential  to  the  Appreciation  of  Sound. 

Perfect  audition  requires  the  anatomical  integrity  of  a  very  complex  apparatus,  which, 
for  convenience  of  anatomical  description,  may  be  divided  into  the  external,  middle,  and 
internal  ear.  A  correct  appreciation  of  the  physiology  of  these  parts  demands,  as  a  neces- 
sary preparation,  a  knowledge  of  their  physiological  anatomy : 

1.  The  external  ear  includes  the  pinna  and  the  external  auditory  meatus,  which  is 
closed  internally  by  the  membrana  tympani. 

2.  The  middle  ear  includes  the  cavity  of  the  tympanum,  or  drum,  with  its  boundaries. 
The  parts  here  to  be  described  are,  the  membrana  tympani,  the  form  of  the  tympanic 
cavity,  its  openings,  its  lining  membrane,  and  the  small  bones  of  the  ear,  or  ossicles,  with 
their  ligaments,  muscles,  and  nerves.     The  cavity  of  the  tympanum  communicates,  by 
the  Eustachian  tube,  with  the  pharynx  and  also,  presents  openings  into  the  mastoid  cells. 

3.  The  internal  ear  contains  the  terminal  filaments  of  the  auditory  nerve.     It  includes 
the  vestibule,  the  three  semicircular  canals,  and  the  cochlea,  which  together  form  the 
labyrinth. 

The  pinna  and  the  external  meatus  simply  conduct  the  waves  of  sound  to  the  tym- 
panum. The  parts  entering  into  the  structure  of  the  middle  ear  are  accessory,  and  are 
analogous  in  their  functions  to  the  refracting  media  of  the  eye.  Structures  contained 
in  the  labyrinth  constitute  the  true  sensory  organ  ;  and  these  bear  the  same  relations  to 
the  auditory  apparatus  as  the  retina  to  the  eye. 

The  External  Ear. — It  is  hardly  necessary  to  our  purpose  to  describe  very  minutely 
the  external  ear.  The  pinna,  or  auricle  is  that  portion  projecting  from  the  head,  which 
first  receives  the  waves  of  sound.  Beginning  externally,  we  have  the  helix,  which  is  the 
outer  ridge  of  the  pinna.  Just  within  this,  is  a  groove,  called  the  fossa  of  the  helix.  This 
fossa  is  bounded  anteriorly  by  a  prominent  but  shorter  ridge,  called  the  antihelix ;  and 
above  the  concha,  between  the  superior  portion  of  the  antihelix  and  the  anterior  portion 
of  the  helix,  is  a  shallow  fossa,  called  the  fossa  of  the  antihelix.  The  deep  fossa,  imme- 
diately surrounding  the  opening  of  the  meatus,  is  called  the  concha.  A  small  lobe  pro- 
jects posteriorly,  covering  the  anterior  portion  of  the  concha,  which  is  called  the  tragus ; 
and  the  projection  at  the  lower  extremity  of  the  antihelix  is  called  the  antitragus.  The 
fleshy,  dependent  portion  of  the  pinna  is  called  the  lobule  of  the  ear. 
52 


818  SPECIAL  SENSES. 

The  form  of  the  pinna  and  its  consistence  depend  upon  the  presence  of  fibro-cartilage, 
which  occupies  the  whole  of  the  external  ear  except  the  lobule.  This  structure  has 
already  been  described  in  another  chapter. 

The  integument  covering  the  ear  does  not  vary  much  from  the  integument  of  the 
general  surface.  It  is  thin,  closely  attached  to  the  subjacent  parts,  and  possesses  small, 
rudimentary  hairs,  with  sudoriparous  and  sebaceous  glands. 

The  muscles  of  the  ear  are  not  important  in  the  human  subject ;  and,  excluding  a 
few  exceptional  cases,  they  are  not  under  the  control  of  the  will.  The  extrinsic  muscles 
are  the  superior,  or  attollens,  the  anterior,  or  attrahens,  and  the  posterior,  or  retrahens 
aurem.  In  addition,  there  are  the  six  small  intrinsic  muscles,  situated  between  the  ridges 
upon  the  cartilaginous  surface.  The  pinna  is  attached  to  the  sides  of  the  head  by  two 
distinct  ligaments  and  a  few  delicate  ligamentous  fibres. 

The  external  auditory  meatus  is  about  an  inch  and  a  quarter  in  length  and  extends 
from  the  concha  to  the  membrana  tympani.  Its  course  is  somewhat  tortuous.  Passing 
from  without  inward,  its  direction  is  at  first  somewhat  upward,  turning  abruptly  over  a 
bony  prominence  near  the  middle,  from  which  it  has  a  slightly  downward  direction  to 
the  membrana  tympani.  Its  general  course  is  from  without  inward  and  slightly  forward. 
The  inner  termination  of  the  canal  is  the  membrana  tympani,  which  is  quite  oblique,  the 
upper  portion  being  inclined  outward,  so  that  the  inferior  wall  of  the  meatus  is  consid- 
erably longer  than  the  superior. 

The  walls  of  the  external  meatus  are  partly  cartilaginous  and  fibrous,  and  partly  bony. 
The  cartilaginous  and  fibrous  portion  occupies  a  little  less  than  one-half  of  the  entire 
length  and  consists  of  a  continuation  of  the  cartilage  of  the  pinna,  with  fibrous  tissue. 
About  the  lower  two-thirds  of  this  portion  of  the  canal  is  cartilaginous,  the  upper  third 
being  fibrous.  The  rest  of  the  tube  is  osseous  and  is  a  little  longer  and  narrower  than 
the  cartilaginous  portion.  Around  the  inner  extremity  of  the  canal,  with  the  exception 
of  its  superior  portion,  is  a  narrow  groove,  which  receives  the  greater  portion  of  the 
margin  of  the  membrana  tympani. 

The  skin  of  the  external  meatus  is  continuous  with  the  integument  covering  the 
pinna.  It  is  very  delicate,  becoming  thinner  from  without  inward.  In  the  osseous  por- 
tion, it  adheres  very  closely  to  the  periosteum,  and,  at  the  bottom  of  the  canal,  it  is 
reflected  over  the  membrana  tympani,  forming  its  outer  layer.  In  the  cartilaginous  and 
fibrous  portion,  are  numerous  short,  stiff  hairs,  with  sebaceous  glands  attached  to  their 
follicles,  and  the  coiled  tubes  known  as  the  ceruminous  glands.  The  structure  of  these 
glands  and  the  properties  and  composition  of  the  cerumen  have  already  been  described 
under  the  head  of  secretion. 

General  Arrangement  of  the  Parts  composing  the  Middle  Ear.— Without  a  very  elabo- 
rate and  minute  anatomical  description,  fully  illustrated  by  plates,  it  is  difficult  to  give  a 
clear  idea  of  the  structure  and  relations  of  the  very  complex  apparatus  of  the  middle  and 
the  internal  ear.  Such  a  minute  and  purely  anatomical  description  would  be  out  of 
place  in  this  work,  where  it  is  desired  only  to  give  such  an  account  of  the  anatomy  as 
will  enable  the  student  to  comprehend  the  physiology  of  the  ear,  reserving  for  special 
description  certain  of  the  most  important  structures.  In  beginning  the  difficult  task  of 
describing  the  physiological  anatomy  of  the  middle  and  internal  ear,  it  will  be  convenient 
to  give  a  general  outline  of  the  different  parts,  with  their  names.  This,  with  a  careful 
study  of  Figs.  258,  259,  260,  and  261,  can  hardly  fail  to  greatly  facilitate  the  closer  in- 
vestigation of  the  more  important  structures. 

The  arrangement  of  the  parts  constituting  the  external  ear  is  sufficiently  simple.    The 

middle  ear  presents  a  narrow  cavity  (Fig.  258,  11),  of  irregular  shape,  situated  between 

ie  external  ear  and  the  labyrinth,  in  the  substance  of  the  temporal  bone.     The  general 

arrangement  of  its  parts  is  shown  in  Fig.  258.     The  outer  wall  of  the  tympanic  cavity  is 

formed  by  the  membrana  tympani  (Fig.  258,  6).     This  membrane  is  concave,  its  concav- 


THE   MIDDLE   EAR. 


819 


ity  looking  outward,  and  oblique,  inclining  usually  at  an  angle  of  forty-five  degrees  with 
the  perpendicular.  This  angle,  however,  varies  considerably  in  different  individuals. 
The  roof  is  formed  by  an  exceedingly  thin  plate  of  bone.  The  floor  is  bony  and  is  much 
narrower  than  the  roof.  The  inner  wall,  separating  the  tympanic  cavity  from  the  laby- 
rinth, is  irregular,  presenting  several  small  elevations  and  foramina.  The  fenestra  ovalis, 
an  ovoid  opening  near  its  upper  portion,  leads  to  the  cavity  of  the  vestibule.  This  is 


FIG.  258.— General  view  of  the  organ  of  hearing.    (Sappey.) 

1,  pinna ;  2,  cavity  of  the  concha,  on  the  walls  of  which  are  seen  the  orifices  of  a  great  number  of  sebaceous  glands ; 
8,  external  auditory  meatus ;  4,  angular  projection  formed  by  the  union  of  the  anterior  portion  of  the  concha 
with  the  posterior  wall  of  the  auditory  canal ;  5,  openings  of  the  ceruminous  glands,  the  most  internal  of  which 
form  a  curved  line  which  corresponds  with  the  beginning  of  the  osseous  portion  of  the  external  meatus ;  6, 
membrana  tympani  and  the  elastic  fibrous  membrane  which  forms  its  border;  7,  anterior  portion  of  the  incus; 
8,  malleus ;  9.  handle  of  the  malleus  applied  to  the  internal  surface  of  the  membrana  tympani,  which  it  draws 
inward  toward  the  projection  of  the  promontory  ;  10,  tensor  tympani  muscle,  the  tendon  of  which  is  reflected  at 
a  right  angle  to  become  attached  to  the  superior  portion  of  the  handle  of  the  malleus ;  11,  tympanic  cavity ;  12; 
Eustachian  tube,  the  internal,  or  pharyngeal  extremity  of  which  has  been  removed  by  a  section  perpendicular 
to  its  curve;  13,  superior  semicircular  canal;  14,  posterior  semicircular  canal;  15,  external  semicircular  canal, 
16,  cochlea;  IT,  internal  auditory  canal;  18,  facial  nerve;  19,  large  petrosal  branch,  given  off  from  the  ganglio- 
form  enlargement  of  the  facial  and  passing  below  the  cochlea  to  go  to  its  distribution ;  20,  vestibular  branch  of 
the  auditory  nerve ;  21,  cochlear  branch  of  the  auditory  nerve. 

closed,  in  the  natural  state,  by  the  base  of  the  stapes  and  its  annular  ligament.  Below, 
is  a  smaller,  ovoid  opening,  the  fenestra  rotunda,  which  leads  to  the  cochlea.  This  is 
closed,  in  the  natural  state,  by  a  membrane,  called  the  secondary  membrana  tympani. 
In  addition,  the  posterior  wall  presents  several  small  foramina  leading  to  the  mastoid 
cells,  which  are  lined  by  a  -continuation  of  the  mucous  membrane  of  the  tympanic 
cavity.  The  tympanic  cavity  also  presents  an  opening  leading  to  the  Eustachian  tube, 
and  a  small  foramen,  which  gives  passage  to  the  tendon  of  the  stapedius  muscle.  The 
Eustachian  tube  extends  from  the  upper  part  of  the  pharynx  to  the  tympanum. 

The  small  bones  of  the  ear  are  three  in  number;  the  incus,  the  malleus,  and  the 
stapes,  forming  a  chain,  connected  together  by  ligaments  (Fig.  259).  These  bones  are 
situated  in  the  upper  part  of  the  tympanic  cavity.  The  handle  of  the  malleus  (A,  2, 
Fig.  259)  is  closely  attached  to  the  membrana  tympani,  and  the  long  process  (A,  3,  Fig. 
259)  is  attached  to  the  Glasserian  fissure  of  the  temporal  bone.  The  malleus  is  articu- 
lated with  the  incus.  The  incus  (B,  Fig.  259)  is  connected  with  the  posterior  wall 
of  the  tympanic  cavity,  near  the  openings  of  the  mastoid  cells.  It  is  articulated  with 
the  malleus,  and,  by  the  extremity  of  its  long  process  (B,  2,  Fig.  259),  with  the  stapes. 
The  stapes  (0,  Fig.  259)  is  the  most  internal  bone  of  the  middle  ear.  It  is  articulated 


820 


SPECIAL  SENSES. 


by  its  smaller  extremity  with  the  long  process  of  the  incus.     Its  base  is  oval  (0*,  Fig. 

259)  and,  with  its  annular  ligament,  is  applied  to  the  fenestra  ovalis.     The  direction  of 

the  stapes  is  nearly  at  a  right  angle  with  the 
long  process  of  the  incus  in  the  natural  state 
(8,  Fig.  260). 

There  are  three  well-defined  muscles  con- 
nected with  the  middle  ear.  Of  these,  two  are 
attached  to  the  malleus,  and  one,  to  the  stapes. 
The  largest  of  the  three  muscles  is  the  tensor 
tympani,  called  sometimes  the  internal  muscle 
of  the  malleus.  Its  fibres  arise  from  the  carti- 
laginous portion  of  the  Eustachian  tube,  the 
spinous  process  of  the  sphenoid  bone,  and  the 
adjacent  portion  of  the  temporal.  From  this 
origin,  it  passes  backward,  almost  horizontally, 
to  the  tympanic  cavity.  In  front  of  the  fenes- 
tra ovalis,  it  turns,  nearly  at  a  right  angle,  over 
a  bony  process,  and  its  tendon  is  inserted  into 

FIG.  259.— Ossicles  of  tht '•tympanum  of  the  right  *  . 

tide ;  magnified  2  diameters.   (Arnold.)          the  handle  of  the  malleus  at  its  inner  surface 
A,  malleus;  i,  its  head;  2,  the  handle;  3,  long,  or   near  the  root.     The  tendon  is  very  delicate, 

slender  process;  4,  short  process;  B,  incus;  1,  its  J 

body;  2,  the  long  process  with  the  orbicular  pro-    and  the  muscular  portion  is  about  halt  an  inch 

in  length  (10,  Fig.  258).  The  muscle  and  its 
tendon  are  enclosed  in  a  distinct  fibrous  sheath. 
The  action  of  this  muscle  is  to  draw  the  handle 
of  the  malleus  inward,  pressing  the  base  of  the 
stapes  against  the  membrane  of  the  fenestra  ovalis  and  producing  tension  of  the  inem- 
brana  tympani.  The  fibres  of  this,  and  of  all  the  muscles  of  the  middle  ear,  are  of  the 
striated  variety.  The  tensor  tympani  is  supplied  with  motor  filaments  from  the  otic 
ganglion,  which  are  probably  derived  from  the  facial  nerve. 


cess ;  3,  short,  or  posterior  process ;  4,  articular 
surface  receiving  the  head  of  the  malleus;  C, 
stapes;  1,  head;  2,  posterior  crus;  3,  anterior 
crus ;  4,  base ;  C*,  base  of  the  stapes ;  D,  the  three 
bones  in  their  natural  connection  as  seen  from  the 
outside;  a,  malleus;  &,  incus;  c,  blcpes. 


FIG.  260.— The  right  temporal  bone,  the  petrosal  portion  removed^  showing  the  ossicles  seen  from  within.    From 

a  photograph.    (Rudinger.) 

inSi^frpp0-    *?  Pr°CeS8of  whichis  directed  nearly  in  an  horizontal  direction  backward;  5,  the  long  processor  the 

ono^raM  \  of •«, tymPamc  o^ty,  articulated  with  the  stapes;  6,  the  malleus,  articulated  with  the  incus;  7,  the 

I  the  malleus  in  the  Glasserian  fissure ;  8.  the  stapes,  articulated  with  the  incus.     This  is  drawn 

SESiji  ?th.trwise' the  base  of  the  8taPes  alone  would  be  visible.    This  figure  shows  the  handle  of 

ic  malleus  attached  to  the  membrana  tympani. 

The  laxator  tympani,  the  external  muscle  of  the  malleus,  arises  from  the  spiaous  pro- 
cess of  the  sphenoid  bone  and,  by  a  few  filaments,  from  the  cartilaginous  portion  of  the 


THE   MIDDLE   EAR.  821 

Eustachian  tube.  It  passes  backward,  through  the  Glasserian  fissure,  to  be  inserted  into 
the  neck  of  the  malleus,  being  enclosed,  in  its  course,  in  a  fibrous  sheath.  The  laxator 
tympani  is  generally  believed  to  be  muscular,  though  some  authorities  deny  that  it  is 
composed  of  true  muscular  fibres.  Its  action  would  be  to  draw  the  malleus  forward  and 
outward,  producing  relaxation  of  the  membrana  tympani.  It  is  not  definitely  known  from 
what  nerve  this  muscle  derives  its  motor  filaments. 

The  stapedius  muscle  is  situated  in  the  descending  portion  of  the  aqueductus  Fallopii 
and  in  the  cavity  of  the  pyramid  on  the  posterior  wall  of  the  tympanic  cavity.  Its  ten- 
don emerges  from  a  foramen  at  the  summit  of  the  pyramid.  In  the  canal  in  which  this 
muscle  is  lodged,  its  direction  is  upward  and  vertical.  At  the  summit  of  the  pyramid,  it 
turns  at  nearly  a  right  angle,  its  tendon  passing  horizontally  forward  to  be  attached  to 
the  head  of  the  stapes.  Like  the  other  muscles  of  the  ear,  this  is  enveloped  in  a  fibrous 
sheath.  Its  action  is  to  draw  the  head  of  the  stapes  backward,  relaxing  the  membrana 
tympani.  This  muscle  receives  filaments  from  the  facial  nerve  by  a  distinct  branch,  the 
tympanic. 

The  posterior  wall  of  the  tympanic  cavity  presents  several  foramina  which  open 
directly  into  numerous  irregularly-shaped  cavities,  communicating  freely  with  each  other, 
in  the  mastoid  process  of  the  temporal  bone.  These  are  called  the  mastoid  cells.  They 
are  lined  by  a  continuation  of  the  mucous  membrane  of  the  tympanum.  There  is,  under 
certain  conditions,  a  free  circulation  of  air  between  the  pharynx  and  the  cavity  of  the 
tympanum  through  the  Eustachian  tube,  and  from  the  tympanum  to  the  mastoid  cells. 

The  Eustachian  tube  (12,  Fig.  258)  is  partly  bony  and  partly  cartilaginous.  Following 
its  direction  from  the  tympanic  cavity,  it  passes  forward,  inward,  and  slightly  downward. 
Its  entire  length  is  about  an  inch  and  a  half.  Its  caliber  gradually  contracts  from  the 
tympanum  to  the  spine  of  the  sphenoid,  and  from  this  constricted  portion  it  gradually 
dilates  to  its  opening  into  the  pharynx,  the  entire  canal  presenting  the  appearance  of  two 
cones.  The  osseous  portion  extends  from  the  tympanum  to  the  spine  of  the  sphenoid  bone. 
The  cartilaginous  portion  is  an  irregularly  triangular  cartilage,  bent  upon  itself  above, 
forming  a  furrow,  with  its  concavity  presenting  downward  and  outward.  The  fibrous 
portion  occupies  about  half  of  the  tube  beyond  the  osseous  portion,  and  completes  the 
canal,  forming  its  inferior  and  external  portion.  In  its  structure,  the  cartilage  of  the 
Eustachian  tube  is  intermediate  between  the  hyaline  and  the  fibro-cartilage. 

The  circumflexus,  or  tensor  palati  muscle,  which  has  already  been  described  in  connec- 
tion with  deglutition,  is  attached  to  the  anterior  margin,  or  the  hook  of  the  cartilage.  The 
attachments  of  this  muscle  have  lately  been  accurately  described  by  Riidinger,  who  calls 
it  the  dilator  of  the  tube.  The  following  excellent  summary  of  the  action  of  the  muscles 
upon  the  tube  is  taken  from  the  report  on  otology,  by  Dr.  J.  Orne  Green,  contained  in 
the  Transactions  of  the  American  Otological  Society,  1870 : 

"The  tensor  palati  muscle  is  a  dilator  of  the  tube;  it  is  inserted  along  the  whole 
length  of  the  hook  of  the  cartilage,  passing  forward,  inward,  and  slightly  downward,  and 
its  fibres  spread  out  along  the  edge  of  the  soft  palate  and  on  the  side  of  the  pharynx.  In 
contracting,  it  draws  the  hook  of  the  cartilage  forward  and  a  little  downward,  thus  en- 
larging the  caliber  of  the  tube.  The  levator  palati  takes  its  origin  from  the  temporal 
bone  just  below  the  osseous  tube,  and  passes  along  the  floor  of  the  tube,  some  of  its  fibres 
arising  from  the  lower  end  of  the  cartilage ;  it  is  inserted  in  the  uvula,  and,  in  contracting 
the  belly  of  the  muscle  which  lies  along  the  floor  of  the  tube,  becomes  thicker :  the  floor 
of  the  tube  is  raised,  and  the  fibres  arising  from  the  cartilage  serve  to  draw  the  lower  end 
of  this  away  from  the  opposite  wall. 

"  The  palato-pharyngeus  rises  from  the  posterior  part  of  the  lower  end  of  the  cartilage, 
passes  backward,  and  is  inserted  on  the  posterior  wall  of  the  pharynx.  Its  action  would 
be  to  draw  the  posterior  wall  of  the  tube  backward ;  but,  as  it  is  often  but  slightly  de- 
veloped, it  probably  onlj  serves  to  fix  the -cartilage,  so  that  the  other  muscles  can  act 
more  effectively. 


822  NERVOUS   SYSTEM. 

"  The  opening  of  the  tube  is  thus  the  result  of  the  action  of  these  three  muscles:  the 
tensor  palati,  or  dilator  tubae,  draws  the  hook  of  the  cartilage  outward,  the  cartilage 
becomes  less  curved  and  the  tube  is  widened ;  the  levator  palati  in  contracting  becomes 
more  horizontal,  and  draws  the  lower  end  of  the  cartilage  inward  and  upward,  thus 
enlarging  the  pharyngeal  orifice  more  than  3'".  As  soon  as  these  muscles  cease  acting, 
the  elasticity  of  the  cartilage  restores  the  canal  to  its  former  condition." 

It  is  thus  that  the  action  of  certain  of  the  muscles  of  deglutition  dilates  the  pharyngeal 
opening  of  the  Eustachian  tube.  If  we  close  the  mouth  and  nostrils  and  make  several 
repeated  acts  of  deglutition,  we  draw  the  air  from  the  tympanic  cavity,  and  the  atmos- 
pheric pressure  renders  the  membrane  of  the  tympanum  tense,  increasing  its  concavity. 
By  one  or  two  lateral  movements  of  the  jaws,  we  open  the  tube,  the  pressure  of  air  is 
equalized,  and  the  ear  returns  to  its  normal  condition.  The  nerves  animating  the  dilator 
tuba3  come  from  the  pneumogastric  and  are  derived  from  the  spinal  accessory. 

A  smooth  mucous  membrane  forms  a  continuous  lining  for  the  Eustachian  tube,  the 
cavity  of  the  tympanum,  and  the  mastoid  cells.  In  all  parts,  it  is  closely  adherent  to  the 
subjacent  tissues,  and,  in  the  cavity  of  the  tympanum,  it  is  very  thin.  In  the  cartilaginous 
portion  of  the  Eustachian  tube,  there  are  numerous  mucous  glands,  which  are  most 
abundant  near  the  pharyngeal  orifice,  and  gradually  diminish  in  number  toward  the 
osseous  portion,  in  which  there  are  no  glands.  Throughout  the  tube,  the  surface  of  the 
mucous  membrane  is  covered  with  conoidal  cells  of  ciliated -epithelium.  The  mucous 
membrane  of  the  tympanic  cavity  is  very  thin,  consisting  of  little  more  than  epithelium 
and  a  layer  of  connective  tissue.  It  lines  the  walls  of  the  cavity,  the  inner  surface  of  the 
membrana  tympani,  is  prolonged  into  the  mastoid  cells,  and  covers  the  ossicles  and  those 
portions  of  the  muscles  and  tendons  which  pass  through  the  tympanum.  On  the  floor  of 
the  tympanic  cavity  and  on  its  anterior,  inner,  and  posterior  walls,  the  epithelium  is  of 
the  conoidal,  ciliated  variety.  On  the  promontory,  roof,  ossicles,  and  muscles,  the  cells 
are  of  the  pavement- variety  and  not  ciliated,  the  transition  from  one  form  to  the  other 
being  gradual.  The  entire  mucous  membrane  contains  numerous  lymphatics,  a  plexus 
of  nerve-fibres  and  nerve-cells,  with  some  peculiar  cells,  the  physiology  of  which  is  not 
understood. 

We  have  thus  given  a  general  sketch  of  the  physiological  anatomy  of  the  middle  ear, 
and  shall  not  find  it  necessary  to  treat  more  fully  of  the  cavity  of  the  tympanum,  the 
mastoid  cells,  or  the  Eustachian  tube,  except  as  regards  certain  points  in  their  physiology. 
The  minute  anatomy  of  the  membrana  tympani  and  the  articulations  of  the  ossicles  can 
be  more  conveniently  considered  in  connection  with  the  physiology  of  these  parts. 

General  Arrangement  of  the  Bony  Labyrinth. — The  internal  portion  of  the  auditory 
apparatus  is  contained  in  the  petrous  portion  of  the  temporal  bone.  It  consists  of  an 
irregular  cavity,  called  the  vestibule,  the  three  semicircular  canals  (13,  14,  15,  Fig.  258), 
and  the  cochlea  (16,  Fig.  258).  The  general  arrangement  of  these  parts  in  situ  and  their 
relations  to  the  adjacent  structures  are  shown  in  Fig.  258.  Fig.  261,  showing  the  bony 
labyrinth  isolated,  is  taken  from  the  beautiful  photograph  contained  in  Eudinger's  atlas. 

The  vestibule  is  the  central  chamber  of  the  labyrinth,  communicating  with  the  tympanic 
cavity  by  the  fenestra  bvalis,  which  is  closed  in  the  natural  state  by  the  base  of  the  stapes. 
This  is  the  central,  ovoid  opening  shown  in  Fig.  261.  The  inner  wall  of  the  vestibule 
presents  a  small,  round  depression  (the  fovea  hemispherica)  perforated  by  numerous  small 
foramina,  through  which  pass  nervous  filaments  from  the  internal  auditory  meatns. 
Behind  this  depression,  is  the  opening  of  the  aqueduct  of  the  vestibule.  In  the  posterior 
wall  of  the  vestibule,  are  five  small,  round  openings  leading  to  the  semicircular  canals, 
with  a  larger  opening  below,-  leading  to  the  cochlea. 

The  general  arrangement  of  the  semicircular  canals  is  shown  in  Fig.  261  (6,  7,  8.  9, 

The  arrangement  of  the  cochlea  (the  anterior  division  of  the  labyrinth)  is  shown  in 


THE   INTERNAL   EAR.  823 

Fig.  261  (1,  3,  4).  This  is  a  spiral  canal,  about  an  inch  and  a  half  long,  and  one-tenth  of 
an  inch  wide  at  its  commencement,  gradually  tapering  to  the  apex,  and  making,  in  its 
course,  two  and  a  half  turns.  Its  interior  presents  a  central  pillar,  around  which  winds 
a  spiral  lamina  of  bone.  The  fenestra  rotunda  (2,  Fig.  261),  closed  in  the  natural  state 
by  a  membrane  (the  secondary  membrana  tympani),  lies  between  the  lower  portion  of  the 
cochlea  and  the  cavity  of  the  tympanum. 


FIG.  261. — The  left  bony  labyrinth  of  a  new-born  child,  forward  and  outward  view.  From  a  photograph. 

(Rudinger.) 

1,  the  wide  canal,  the  beginning  of  the  spiral  canal  of  the  cochlea;  2,  the  fenestra  rotunda:  3.  the  second  turn  of  the 
cochlea ;  4,  the  final  half-turn  of  the  cochlea ;  5,  the  border  of  the  bony  wall  of  the  vestibule,  situated  between  the 
cochlea  and  the  semicircular  canals;  6,  the  superior,  or  sagittal  semicircular  canal;  7,  the  portion  of  the  superior 
semicircular  canal  bent  outward ;  8,  the  posterior,  or  transverse  semicircular  canal ;  9,  the  portion  of  the  posterior 
connected  with  the  superior  semicircular  canal;  10,  point  of  junction  of  the  superior  and  the  posterior  semicircu- 
lar canal;  11,  the  ampulla  ossea  externa;  12,  the  horizontal,  or  external  semicircular  canal.  The  explanation  of 
this  Figure  has  been  modified  and  condensed  from  Rudinger. 

What  is  called  the  membranous  labyrinth  is  contained  within  the  bony  parts  just 
described.  Its  structure,  and  the  ultimate  distribution  and  connections  of  the  auditory 
nerve,  which  penetrates  by  the  internal  auditory  meatus,  involve  some  of  the  most  intri- 
cate and  difficult  points  in  the  whole  range  of  minute  anatomy.  Some  of  these  have 
direct  and  important  relations  to  the  physiology  of  hearing,  while  many  are  of  purely 
anatomical  interest.  Such  facts  as  bear  directly  upon  physiology  will  be  considered  fully 
in  connection  with  the  functions  of  the  internal  ear. 

Physics  of  Sound. 

The  sketch  that  we  have  given  of  the  general  anatomical  arrangement  of  the  auditory 
apparatus  conveys  an  idea  of  the  uses  of  the  different  parts  of  the  ear.  The  waves  of 
sound  must  be  transmitted  to  the  terminal  extremities  of  the  auditory  nerve  in  the 
labyrinth.  These  waves  are  collected  by  the  pinna,  are  conducted  to  the  membrana 
tympani  through  the  external  auditory  meatus,  produce  vibrations  of  the  membrana 
tympani,  are  conducted  by  the  chain  of  ossicles  to  the  openings  in  the  labyrinth,  and 
are  communicated  through  the  fluids  of  the  labyrinth  to  the  ultimate  nervous  filaments. 
The  free  passage  of  air  through  the  external  meatus  and  the  communications  of  the  cavity 
of  the  tympanum  with  the  mastoid  cells,  and,  by  the  Eustachian  tube,  with  the  pharynx, 
are  necessary  to  the  proper  vibration  of  the  membrana  tympani ;  the  integrity  of  the 


824  SPECIAL  SENSES. 

ossicles  and  of  their  ligaments  and  muscles  is  essential  to  the  proper  conduction  of  sound 
to  the  labyrinth ;  the  presence  of  liquid  in  the  labyrinth  is  a  condition  essential  to  the 
conduction  of  the  waves  to  the  filaments  of  distribution  of  the  auditory  nerves ;  and, 
finally,  from  the  labyrinth,  the  nerves  pass  through  the  internal  auditory  meatus  to  the 
brain,  where  the  auditory  impressions  are  appreciated. 

Most  of  the  points  in  acoustics  which  are  essential  to  the  comprehension  of  the  physi- 
ology of  audition  are  definitely  settled.  The  theories  of  the  propagation  of  sound  involve 
wave-action,  concerning  which  there  is  no  dispute  among  physicists.  For  the  conduc- 
tion of  sound,  a  ponderable  medium  is  essential ;  and  it  is  not  necessary,  as  in  the  case 
of  the  undulatory  theory  of  light,  to  assume  the  existence  of  an  imponderable  ether. 
The  human  ear,  although  perhaps  not  so  acute  as  the  auditory  apparatus  of  some  of  the 
inferior  animals,  not  only  appreciates  irregular  waves,  such  as  produce  noise  as  distin- 
guished from  sounds  called  musical,  but  is  capable  of  distinguishing  regular  waves,  as  in 
simple  musical  sounds,  and  harmonious  combinations. 

In  music,  certain  successions  of  regular  sounds  are  agreeable  to  the  ear  and  constitute 
what  we  call  melody.  Again,  we  are  able  to  appreciate,  not  only  the  intensity  of  sounds, 
both  noisy  and  musical,  but  we  recognize  pitch  and  different  qualities,  particularly  in 
music.  Still  farther,  we  find  that  musical  notes  may  be  resolved  into  certain  invariable 
component  parts,  such  as  the  octave,  the  third,  fifth,  etc.  These  components  of  what 
are  usually  supposed  to  be  simple  sounds — which  may  be  isolated  by  artificial  means,  to 
be  described  farther  on — are  called  tones ;  while  the  sounds  themselves,  produced  by  the 
union  of  the  different  tones,  are  called  notes,  which  may  themselves  be  combined  to  form 
chords. 

The  quality  of  musical  sounds  may  be  modified  by  the  simultaneous  production  of 
others  which  correspond  to  certain  of  the  components  of  the  predominating  note.  For 
example,  if  we  add  to  a  single  note,  the  third,  fifth,  and  octave,  we  produce  a  major 
chord,  the  sound  of  which  is  very  different  from  that  of  a  single  note  or  of  a  note  with 
its  octave.  If  we  diminish  the  third  by  a  semitone,  we  have  a  different  quality,  which 
is  peculiar  to  minor  chords.  In  this  way,  we  can  form  an  immense  variety  of  musical 
sounds  upon  a  single  instrument,  as  the  piano.  And  still  farther,  by  the  harmonious 
combinations  of  the  notes  of  different  instruments  and  of  different  registers  of  the 
human  voice,  as  in  grand  choral  and  orchestral  compositions,  shades  of  effect,  almost 
innumerable,  may  be  produced.  The  modification  of  tones  in  this  way  constitutes  har- 
mony ;  and  an  educated  ear,  not  only  experiences  pleasure  from  these  musical  combina- 
tions, but  can  distinguish  their  different  component  parts. 

A  chord  may  convey  to  the  ear  the  sensation  of  completeness  in  itself  or  it  may  lead 
to  a  succession  of  notes  before  this  sense  of  completeness  is  attained.  Different  chords 
of  the  same  key  may  be  made  to  follow  each  other,  or  we  may,  by  transition-notes,  pass 
to  the  chords  of  other  keys.  Each  key  has  its  fundamental  note,  and  the  transition  from 
one  key  to  another,  in  order  to  be  agreeable  to  the  ear,  must  be  made  in  certain  well- 
defined  and  invariable  ways.  These  regular  transitions  constitute  modulation.  The  ear 
becomes  fatigued  by  long  successions  of  notes  always  in  one  key,  and  modulation  is  essen- 
tial to  the  enjoyment  of  elaborate  musical  compositions  ;  otherwise,  the  notes  would  not 
only  become  monotonous,  but  their  correct  appreciation  would  be  impaired,  as  the  ap- 
preciation of  colors  becomes  less  distinct  after  looking  for  a  long  time  at  an  object  pre- 
senting a  single  vivid  tint. 

Laws  of  Sonorous  Vibrations. 

As  we  have  already  remarked,  sound  is  produced  by  vibrations  in  a  ponderable  me- 
dium. The  sounds  ordinarily  heard  are  transmitted  to  the  ear  by  means  of  vibrations 
of  the  atmosphere.  A  simple  and  very  common  illustration  of  this  fact  is  afforded  by 
the  experiment  of  striking  a  bell  carefully  arranged  in  vacuo.  Although  the  stroke  and 
the  vibration  can  readily  be  seen,  there  is  no  sound  ;  and,  if  air  be  gradually  introduced. 


LAWS  OF  SONOROUS   VIBRATIONS.  825 

the  sound  will  become  appreciable  and  progressively  more  intense  as  the  surrounding 
medium  is  increased  in  density. 

If  we  produce  a  single  sound,  or  shock,  in  a  free  atmosphere,  we  may  suppose  that 
the  waves  are  transmitted  equally  in  every  direction ;  and  this  is  accomplished  in  the 
following  manner :  An  imaginary  sphere  of  air  receives  an  impulse,  or  shock,  from  the 
body  which  produces  the  sound.  This  shock  is,  in  its  turn,  communicated  to  another 
spherical  stratum  of  air  ;  this,  to  a  third,  and  so  on.  The  elasticity  of  the  air,  however, 
produces  a  recoil  of  each  imaginary  sphere  of  air,  and  it  is  a  portion  of  the  last  stratum 
which  strikes  the  tympanum,  throwing  it  into  vibration.  If  but  a  single  impulse  be 
given  to  the  air,  we  may  suppose  that  all  of  the  different  strata,  after  a  single  oscillation, 
return  to  their  original  quiescent  condition.  The  first  stratum  receives  the  shock,  and 
the  last  communicates  the  shock  to  the  ear.  The  oscillations  of  sound,  produced  in  this 
way,  are  to  and  fro  in  the  direction  of  the  line  of  conduction  and  are  said  to  be  longi- 
tudinal. In  the  undulatory  theory  of  light,  the  vibrations  are  supposed  to  be  at  right 
angles  to  the  line  of  propagation,  or  transversal.  A  complete  oscillation  to  and  fro  is 
called  a  sound-wave. 

It  is  evident  that  vibrating  bodies  may  be  made  to  perform  and  impart  to  the  atmos- 
phere oscillations  of  greater  or  less  amplitude.  The  intensity  of  the  sound  is  in  propor- 
tion to  the  amplitude  of  the  vibrations.  If  we  cause  a  tuning-fork  to  vibrate,  the  sound 
is  at  first  loud,  or  intense ;  but  the  amplitude  gradually  diminishes,  and  the  sound  dies 
away  until  it  is  lost.  In  a  vibrating  body  capable  of  producing  a  definite  number  of 
waves  of  sound  in  a  second,  it  is  evident  that,  the  greater  the  amplitude  of  the  wave,  the 
greater  is  the  velocity  of  the  particles  thrown  into  vibration.  It  has  been  ascertained  by 
experiment,  that  there  is  an  invariable  mathematical  relation  between  the  intensity  of 
sound,  the  velocity  of  the  conducting  particles,  and  the  amplitude  of  the  waves ;  and 
this  is  expressed  by  the  formula,  that  the  intensity  is  proportional  to  the  square  of  the 
amplitude.  It  is  evident,  also,  that  the  intensity  of  sound  is  diminished  by  distance,  as 
the  amplitude  of  the  waves  and  the  velocity  of  the  vibrating  particles  become  weaker, 
the  farther  we  are  removed  from  the  sonorous  body.  The  sound,  as  the  waves  recede 
from  the  sonorous  body,  becomes  distributed  over  an  increased  area.  The  propagation 
of  sound  has  been  reduced  also  to  the  formula,  that  the  intensity  diminishes  in  propor- 
tion to  the  square  of  the  distance. 

Sonorous  vibrations  are  subject  to  many  of  the  laws  of  reflection  which  we  have 
studied  in  connection  with  light.  Sound  may  be  absorbed  by  soft  and  non-vibrating 
surfaces,  in  the  same  way  that  certain  surfaces  absorb  the  rays  of  light.  It  is  in  this  way 
that  we  explain  the  deadening  of  sound  in  apartments  furnished  with  carpets,  curtains, 
etc.,  and  its  reflection  from  smooth,  hard  surfaces.  By  carefully-arranged  convex  sur- 
faces, the  waves  of  sound  may  be  readily  collected  to  a  focus.  These  laws  of  the  reflec- 
tion of  sonorous  waves  explain  echoes  and  the  conduction  of  sound  by  confined  strata  of 
air,  as  in  tubes.  We  thus  explain  the  mechanism  of  speaking-trumpets,  the  collection  of 
the  waves  by  the  pavilion  of  the  ear,  and  their  transmission  to  the  tympanum  by  the 
external  auditory  meatus.  To  make  the  parallel  between  sonorous  and  luminous  trans- 
mission more  complete,  it  has  been  ascertained  that  the  waves  of  sound  may  be  refracted 
to  a  focus  by  being  made  to  pass, through  an  acoustic  lens,  as  a  balloon  filled  with  car- 
bonic-acid gas.  The  waves  of  sound  may  also  be  deflected  around  solid  bodies,  when 
they  produce  what  have  been  called  by  Tyndall,  shadows  of  sound. 

Any  one  observing  the  sound  produced  by  the  blow  of  an  axe  can  note  the  important 
fact  that  sound  is  transmitted  with  much  less  rapidity  than  light.  At  a  short  distance, 
our  view  of  the  body  is  practically  instantaneous ;  but  there  is  a  considerable  interval 
between  the  blow  and  the  sound.  This  interval  represents  the  velocity  of  the  sonorous 
conduction.  This  fact  is  also  illustrated  by  the  interval  between  a  flash  of  lightning  and 
the  sound  of  thunder.  The  velocity  of  sound  depends  upon  the  density  and  elasticity  of 
the  conducting  medium.  The  rate  of  conduction  of  sound  by  atmospheric  air  at  the 


g26  SPECIAL  SENSES. 

freezing-point  of  water  is  about  1,090  feet  per  second.  This  rate  presents  comparatively 
slight  variations  for  the  different  gases,  but  it  is  very  much  more  rapid  in  liquids  and  in 
solids.  In  ordinary  water,  it  is  4,708  feet  per  second ;  in  iron  or  steel  wire,  about  16,000 
feet ;  and  in  most  woods,  in  the  direction  of  the  fibre,  about  the  same. 

Noise  and  Musical  Sounds.— There  is  a  well-defined  physical  as  well  as  an  aesthetic 
distinction  between  noise  and  music.  Taking,  as  examples,  single  sounds,  a  sound  be- 
comes noise  when  the  air  is  thrown  into  confused  and  irregular  vibrations.  A  noise  may 
be  composed  of  a  few  musical  sounds,  when  these  are  not  in  accord  with  each  other,  and 
sounds  called  musical  are  not  always  entirely  free  from  discordant  vibrations,  as  we  shall 
see  in  studying  musical  sounds,  properly  so  called.  A  noise  possesses  intensity,  varying 
with  the  amplitude  of  the  vibrations,  and  it  may  have  different  qualities,  depending  upon 
the  form  of  its  vibrations.  We  may  call  a  noise  dull,  sharp,  ringing,  metallic,  hollow, 
etc.,  thus  expressing  qualities  that  are  readily  understood.  In  percussion  of  the  chest, 
the  resonance  is  called  vesicular,  tympanitic,  etc.,  distinctions  in  quality  that  are  quite 
important.  A  noise  may  also  be  called  sharp  or  low  in  pitch,  as  the  rapid  or  slow  vibra- 
tions predominate,  without  answering  the  requirements  of  musical  sounds.  These  expla- 
nations, with  the  definition  that  a  noise  is  a  sound  that  is  not  musical,  will  be  better 
understood  after  we  have  described  some  of  the  characters  of  musical  vibrations. 

A  pure  and  simple  musical  sound  consists  of  vibrations  following  each  other  at  regular 
intervals,  provided  that  the  succession  of  waves  be  not  too  slow  or  too  rapid.  When  the 
vibrations  are  too  slow,  we  have  an  appreciable  succession  of  impulses,  and  the  sound  is 
not  musical.  When  they  are  too  rapid,  we  recognize  that  the  sound  is  excessively  sharp, 
but  it  is  then  painfully  acute  and  has  no  pitch  that  can  be  accurately  determined  by  the 
auditory  apparatus.  Such  sounds  may  be  occasionally  employed  in  musical  compositions, 
but,  in  themselves,  they  are  not  strictly  musical. 

In  musical  sounds,  we  recognize  duration,  intensity,  pitch,  and  quality.  The  duration 
depends  simply  upon  the  length  of  time  during  which  the  vibrating  body  is  thrown  into 
action.  The  intensity  depends,  as  we  have  already  stated,  upon  the  amplitude  of  the 
vibrations,  and  it  has  no  relation  whatsoever  to  pitch.  Pitch  depends  absolutely  upon  the 
rapidity  of  the  regular  vibrations,  and  quality,  upon  the  combinations  of  different  tones 
in  harmony,  the  character  of  the  harmonics  of  fundamental  tones,  and  the  form  of  the 
vibrations. 

Pitch  of  Musical  Sounds. — In  discussing  the  pitch  of  musical  sounds,  we  shall  leave 
out  of  the  question,  for  the  present,  the  harmonics,  which  exist  in  nearly  all  musical  notes 
and  affect  their  quality,  and  confine  ourselves  to  the  study  of  simple  vibrations.  Such 
tones  are  those  of  great  organ-pipes,  which  are  deficient  in  harmonics  and  in  overtones, 
and  are  almost  entirely  pure. 

Pitch  depends  upon  the  number  of  vibrations.  A  musical  sound  may  be  of  greater  or 
less  intensity ;  it  may  at  first  be  quite  loud  and  gradually  die  away;  but  the  number  of 
vibrations  in  a  definite  tone  is  invariable,  be  it  weak  or  powerful.  The  rapidity  of  the 
conduction  of  sound  does  not  vary  with  its  intensity  or  pitch,  and,  in  the  harmonious 
combination  of  the  sounds  of  different  instruments,  be  they  high  or  low  in  pitch,  intense 
or  feeble,  it  is  always  the  same  in  the  same  conducting  medium.  Distinct  musical  notes 
may  present  an  immense  variety  of  qualities,  but  all  tones  of  the  same  pitch  have  abso- 
lutely equal  rates  of  vibration.  Tones  equal  in  pitch  are  said  to  be  in  unison.  This  fact, 
though  simple,  has  a  most  important  physiological  bearing.  In  the  first  place,  an  edu- 
cated ear  can,  without  difficulty,  distinguish  slight  differences  in  pitch  in  ordinary  musical 
tones.  Again,  we  ascertain  by  experiment  that  this  power  of  appreciation  of  tones  is 
restricted  within  well-defined  limits,  which  vary  slightly  in  different  individuals.  With- 
out citing  all  of  the  numerous  observations  upon  this  point,  we  may  state  that  Helmholtz, 
whose  authority  is  the  very  highest,  gives,  as  the  range  of  sounds  that  can  be  legitimately 


LAWS   OF  SONOROUS  VIBRATIONS.  827 

employed  in  music,  those  of  from  40  to  4,000  vibrations  in  a  second,  embracing  about 
seven  octaves.  In  an  orchestra,  the  double  bass  gives  the  lowest  note,  which  has  40*25 
vibrations  in  a  second,  and  the  highest  note,  given  by  the  small  flute,  has  4,752  vibrations. 
In  grand  organs,  there  is  a  pipe  which  gives  a  note  of  16'5  vibrations,  and  the  deepest 
note  of  modern  pianos  has  27'5  vibrations ;  but  delicate  shades  of  pitch  in  these  low  notes 
are  not  appreciable  to  most  persons.  Sounds  above  the  limits  just  indicated  are  painfully 
sharp,  and  their  pitch  cannot  be  exactly  appreciated  by  the  ear.  The  physiological  inter- 
est connected  with  these  facts  is,  that  the  limits  of  the  appreciation  of  musical  sounds  are 
probably  due  to  the  anatomical  arrangement  of  the  auditory  apparatus,  as  we  have  a 
limit  to  the  acuteness  of  vision,  which  can  be  explained  by  the  structure  of  the  eye.  This 
fact  is  the  basis  of  the  accepted  theories  of  the  appreciation  of  musical  sounds. 

Musical  Scale. — We  have  thus  far  considered  musical  sounds,  without  any  reference 
to  the  relations  of  different  notes  to  each  other.  A  knowledge  of  these  relations  lies  at 
the  foundation  of  the  science  of  music;  and,  without  a  clear  idea  of  certain  of  the  funda- 
mental laws  of  music,  we  cannot  thoroughly  comprehend  the  mechanism  of  audition. 

It  requires  very  little  cultivation  of  the  ear  to  enable  us  to  comprehend  the  fact,  that 
the  successions  and  combinations  of  tones  must  obey  certain  fixed  laws;  and,  long  before 
these  laws  were  the  subject  of  mathematical  demonstration,  the  relations  of  the  different 
notes  of  the  scale  were  established,  merely  because  certain  successions  and  combinations 
were  agreeable  to  the  ear,  while  others  were  discordant  and  apparently  unnatural.  Now 
that  Ave  are  pretty  thoroughly  acquainted  with  the  laws  of  vibrations,  we  can  study  the 
scale  from  a  scientific,  as  well  as  from  an  aesthetic  point  of  view. 

The  most  convenient  notes  for  our  study  are  those  produced  by  vibrating  strings,  and 
the  phenomena  here  observed  are  essentially  the  same  for  all  musical  sounds;  for  it  is 
by  means  of  vibrations  communicated  to  the  air  that  the  waves  of  sound  find  their 
way  to  the  auditory  apparatus.  Let  us  take,  to  begin  with,  a  string  vibrating  24 
times  in  a  second.  If  this  string  be  divided  into  two  equal  parts,  each  part  will  vibrate 
48  times  in  a  second.  The  note  thus  produced  is  the  octave,  or  the  8th  of  the  primary 
note,  called  the  8th,  because  the  natural  scale,  as  we  shall  see,  contains  eight  notes,  of 
which  the  first  is  the  lowest  and  the  last,  the  highest.  We  may  divide  the  half  again, 
producing  a  second  octave,  and  so  on,  within  the  limits  of  our  appreciation  of  musical 
sounds.  If  we  divide  the  string  so  that  £  of  its  length  will  vibrate,  we  have  36  vibrations 
in  a  second,  and  this  note  is  the  5th  in  the  scale.  If  we  divide  the  string  again,  so  as  to 
leave  f  of  its  length,  we  have  30  vibrations,  which  gives  the  3d  note  in  the  scale.  These 
are  the  most  natural  subdivisions  of  the  note;  and  the  1st,  3d,  5th,  and  8th,  when  sound- 
ed together,  make  what  is  known  as  the  common  major  chord.  Three-fourths  of  the 
length  of  the  original  string  makes  32  vibrations,  and  gives  the  4th  note  in  the  scale.  If 
we  take  f  of  the  string,  we  have  27  vibrations,  and  the  note  is  the  2d  in  the  scale.  With 
f  of  the  string,  we  have  40  vibrations  in  a  second,  or  the  6th  note  in  the  scale.  With  T8y 
of  the  string,  we  have  45  vibrations  in  a  second,  or  the  7th  note  in  the  scale. 

It  will  be  observed  that  we  have  started  with  a  note,  which  we  may  call  0.  This  is 
the  key-note,  or  the  tonic.  In  this  scale,  which  is  called  the  natural,  or  diatonic  key,  we 
have  a  regular  mathematical  progression  from  the  1st  to  the  8th.  This  is  called  the 
major  key  of  0.  Melody  consists  in  an  agreeable  succession  of  notes,  which  we  may 
assume,  for  sake  of  simplicity,  to  be  pure.  We  cannot,  in  a  simple  melody,  sound  any 
note  but  one  of  those  in  the  scale.  When  a  different  note  is  sounded,  we  pass  into  a  key 
which  has  a  different  fundamental  note,  or  tonic,  with  a  different  succession  of  3ds,  5ths, 
etc.  Every  key,  therefore,  has  its  1st,  3d,  5th,  and  8th,  as  well  as  the  intermediate 
notes.  If  we  substitute  for  the  3d  a  note  formed  by  a  string  £  the  length  of  the  tonic 
instead  of  f ,  we  have  the  key  converted  into  the  minor.  The  minor  chord,  consisting  of  the 
1st,  the  diminished  3d,  the  5th,  and  the  8th,  is  perfectly  harmonious,  but  it  has  a  quality 
quite  different  from  that  of  the  major  chord.  The  notes  of  a  melody  may  progress  in  the 


SPECIAL  SENSES. 

minor  key  as  well  as  in  the  major.     Taking  the  small  numbers  of  vibrations  merely  for 
convenience,  the  following  is  the  mode  of  progression  in  the  natural  scale  of  0  major: 

1st.  2d.  3d.  4th.  5th  Cth.  7th.  8th. 

Note C  D  E        F         G  B  C 

Lengths  of  the  string 1  f         s         i           t  f  fs  k 

Number  of  vibrations 24  27  30  32  36  40  45  48 

The  intervals  between  the  notes  of  the  scale,  it  is  seen,  are  not  equal.  The  smallest, 
between  the  3d  and  4th  and  the  7th  and  8th,  are  called  semitones.  The  other  intervals 
are  either  full  perfect  tones  or  small  perfect  tones.  Although  there  are  semitones,  not 
belonging  to  the  key  of  C,  between  0  and  D,  D  and  E,  F  and  G,  G  and  A,  and  A  and 
B,  these  intervals  are  not  all  composed  of  exactly  the  same  number  of  vibrations ;  so 
that,  taking  the  notes  on  a  piano,  if  we  have  D  as  the  tonic,  its  5th  would  be  A.  We 
assume  that  D  has  27  vibrations,  and  A,  40,  giving  a  difference  of  13.  With  C  as  the 
tonic  and  G  as  the  5th,  we  have  a  difference  of  12.  It  is  on  account  of  these  differences 
in  the  intervals,  that  each  key  in  music  has  a  peculiar  and  an  individual  character. 

In  tuning  a  piano,  which  is  the  single  instrument  most  commonly  used  for  accompani- 
ment and  the  general  interpretation  of  musical  compositions,  the  ordinary  method  is  by 
the  5ths.  We  bring  the  5th  of  0  in  exact  accord  with  the  tonic ;  then  the  5th  of  D  ; 
then  the  5th  of  E,  and  finally  the  5th  of  F.  The  5th  of  F  should  be  the  octave  of  C, 
but,  by  progressing  in  this  way,  the  last  note  (0)  is  too  sharp  and  is  not  the  octave  of 
the  lower  C.  If  this  progression  were  continued  higher  and  higher,  the  octaves  would 
become  more  and  more  out  of  tune  ;  and,  to  avoid  this,  the  octaves  are  made  perfect  and 
the  5ths  and  3ds  are  tuned  down,  so  that  the  inequality  is  distributed  throughout  the 
scale.  This  is  called  tempering  the  scale,  and,  with  this  "  temperament,"  the  notes  are 
not  exactly  true ;  still,  musicians  are  accustomed  to  this,  and  they  fail  to  recognize  the 
mathematical  defect. 

Even  in  melody,  and  still  more  in  harmony,  in  long  compositions,  the  ear  becomes 
fatigued  by  a  single  key,  and  it  is  necessary,  in  order  to  produce  the  most  pleasing  effects, 
to  change  the  tonic,  by  what  is  called  modulation,  returning  afterward  to  the  original  key. 

Quality  of  Musical  Sounds. — By  appropriate  means,  we  can  analyze  or  decompose 
white  light  into  prismatic  colors;  and,  in  the  same  way,  nearly  all  musical  sounds,  which 
seem  at  first  to  be  simple,  can  be  resolved  into  certain  well-defined  constituents.  There 
are  few  absolutely  simple  sounds  used  in  music.  We  may  take  an  example,  however,  in 
the  notes  of  great  stopped-pipes  in  the  organ.  These  are  simple,  but  are  of  an  unsatis- 
factory quality  and  wanting  in  richness.  Almost  all  other  musical  sounds,  however, 
have  a  fundamental  tone,  which  we  recognize  at  once ;  but  this  tone  is  accompanied 
by  harmonics  caused  by  secondary  vibrations  of  subdivisions  of  the  sonorous  body. 
The  number,  pitch,  and  intensity  of  these  harmonic,  or  aliquot  vibrations  affect  what 
is  called  the  quality,  or  timbre  of  musical  notes,  by  modifying  the  form  of  the  sonorous 
waves.  This  fact,  which  we  shall  discuss  more  elaborately  farther  on,  requires  little 
argument  for  its  support.  If  we  suppose  a  string  vibrating  a  certain  number  of  times  in 
a  second,  the  vibrations  being  perfectly  simple,  we  should  have,  according  to  the  laws 
of  vibrating  bodies,  a  simple  musical  tone ;  but,  if  we  suppose  that  the  string  subdivides 
itself  into  different  segments,  one  of  which  gives  the  3d,  another,  the  5th,  and  so  on,  of  the 
fundamental  tone,  it  is  evident  that  the  form  of  the  vibrations  must  be  considerably 
modified.  This  is  the  fact ;  and,  with  these  modifications  in  form,  the  quality,  or  timbre 
of  the  note  is  changed.  We  can  illustrate  this  roughly  on  the  piano.  If  we  strike  the 
note  0,  we  have  a  certain  quality  of  sound.  We  may  assume,  for  sake  of  argument, 
that  this  is  a  simple  tone,  although  in  reality  it  is  complex.  We  now  strike  simultaneously 
the  fundamental  note,  its  3d,  5th,  and  8th,  making  the  common  chord  of  C  major.  The 
predominant  note  is  still  C,  but  the  addition  of  the  harmonious  notes  modifies  its  quality. 


LAWS   OF   SONOROUS   VIBRATIONS.  829 

If  we  diminish  the  third  by  a  semitone,  we  still  have  0  for  the  predominant  note,  but 
the  quality  of  the  chord  is  changed  to  the  minor.  In  this  rough  illustration,  the  ear  can 
readily  detect  the  harmonious  tones ;  but,  in  the  note  of  a  single  string,  this  cannot  be 
done  without  practice  and  close  attention.  Still,  in  the  notes  of  single  strings,  the  ear 
can  distinguish  the  harmonics ;  and,  what  is  more  satisfactory,  the  existence  of  harmon- 
ics can  be  actually  demonstrated  in  various  ways. 

From  what  we  have  just  stated,  it  follows  that  nearly  all  musical  tones  consist,  not 
only  of  a  fundamental  sound,  but  of  harmonic  vibrations,  subordinate  to  the  fundamental 
and  qualifying  it  in  a  particular  way.  These  harmonics  may  be  feeble  or  intense  ;  cer- 
tain of  them  may  predominate  over  others ;  some,  that  are  usually  present,  may  be 
eliminated  ;  and,  in  short,  there  may  be  a  great  diversity  in  their  arrangement,  and  thus 
the  timbre  may  present  an  infinite  variety.  This  is  one  of  the  elements  entering  into  the 
composition  of  notes,  and  it  affords  a  partial  explanation  of  quality. 

Another  element  in  the  quality  of  notes  depends  upon  their  reinforcement  by  reso- 
nance. The  vibrations  of  a  stretched  string,  not  connected  with  a  resonant  body,  are 
almost  inaudible.  In  musical  instruments,  we  have  the  sound  taken  up  by  some  mechani- 
cal arrangement,  as  the  sound-board  of  the  organ,  piano,  violin,  harp,  guitar,  etc.  In 
the  violin,  for  example,  the  sweetness  of  the  tone  depends  chiefly  upon  the  construction 
of  the  resonant  part  of  the  instrument,  and  but  little  upon  the  strings  themselves,  which 
are  frequently  changed.  The  same  is  true  of  the  human  voice,  of  wind-instruments,  etc. ; 
but  we  could  not  discuss  these  points  elaborately,  without  giving  a  full  description  of  the 
various  musical  instruments  in  common  use,  which  would  be  out  of  place  in  a  work  upon 
physiology. 

In  addition  to  the  harmonic  tones  of  sonorous  bodies,  various  discordant  sounds  are 
generally  present,  which  modify  the  timbre,  producing,  usually,  a  certain  roughness, 
such  as  the  grating  of  a  violin-bow,  the  friction  of  the  columns  of  air  against  the  angles 
in  wind-instruments,  etc.  All  of  these  conditions  have  their  effect  upon  the  quality  of 
tones ;  and  these  discordant  sounds  may  exist  in  infinite  number  and  variety.  These 
sounds  are  composed  of  irregular  vibrations  and  are  consequently  inharmonious.  Nearly 
all  notes  that  we  speak  of  in  general  terms  as  musical  are  composed  of  musical,  or  har- 
monic aliquot  tones  with  the  discordant  elements  to  which  we  just  alluded. 

Aside  from  the  relations  of  the  various  component  parts  of  musical  notes,  the  quality 
depends  largely  upon  the  form  of  the  vibrations.  To  quote  the  words  of  Helmholtz,  u  the 
more  uniformly  rounded  the  form  of  the  wave,  the  softer  and  milder  is  the  quality  of  the 
sound.  The  more  jerking  and  angular  the  wave-form,  the  more  piercing  the  quality. 
Tuning-forks,  with  their  rounded  forms  of  wave,  have  an  extraordinarily  soft  quality ; 
and  the  qualities  of  sound  generated  by  the  zither  and  violin  resemble  in  harshness  the 
angularity  of  their  wave-forms." 

Harmonics,  or  Overtones. — As  we  have  stated  in  the  foregoing  discussion,  nearly  all 
sounds  are  composite,  but  some  contain  many  more  aliquot,  or  secondary  vibrations  than 
others.  The  notes  of  vibrating  strings  are  peculiarly  rich  in  harmonics,  and  these  may 
be  used  for  illustration,  remembering  that  the  phenomena  here  observed  have  their  analo- 
gies in  nearly  all  varieties  of  musical  sounds.  If  a  stretched  string  be  made  to  vibrate, 
the  secondary  tones,  which  qualify,  as  it  were,  the  fundamental,  are  called  harmonics,  or, 
in  German,  overtones,  a  term  which  is  now  much  used  by  English  writers. 

While  it  is  difficult  at  all  times  to  distinguish  by  the  ear  the  individual  overtones  of 
vibrating  strings,  their  existence  can  be  demonstrated  by  a  few  simple  experiments.  Let 
us  suppose,  for  example,  that  we  have  a  string,  the  fundamental  tone  of  which  is  0.  We 
damp  this  string  with  a  feather  at  one-fourth  of  its  length  and  draw  a  violin-bow  across 
the  smaller  section.  We  then  sound,  not  only  the  fourth  part  of  the  string  across  which 
the  bow  is  drawn,  but  the  remaining  three-fourths ;  but,  if  we  have  placed  little  riders  of 
paper  upon  the  longer  segment,  at  distances  equal  to  one-fourth  the  entire  string,  they 


83o  SPECIAL  SENSES. 

will  remain  undisturbed,  while  riders  placed  at  any  other  portion  of  the  string  will  be 
thrown  off.  This  experiment  shows  that  the  three-fourths  of  the  string  have  been  di- 
vided, as  we  have  sounded  the  second  octave  above  the  fundamental  tone.  This  may  be 
illustrated  by  connecting  one  end  of  the  string  with  a  tuning-fork.  When  this  is  done, 
and  the  string  is  brought  to  the  proper  degree  of  tension,  it  will  first  vibrate  as  a  whole, 
then,  when  a  little  tighter,  will  spontaneously  divide  into  two  equal  parts,  and,  under 
increased  tension,  into  three,  four,  and  so  on.  By  damping  a  string  with  the  light  touch 
of  a  feather,  we  suppress  the  fundamental  tone  and  bring  out  the  overtones,  which  exist 
in  all  vibrating  strings,  but  are  usually  concealed  by  the  fundamental.  The  points  which 
mark  the  subdivisions  of  the  string  into  segments  of  secondary  vibrations  are  called 
nodes.  When  we  damp  the  string  at  its  centre,  we  quench  the  fundamental  tone  and 
have  overtones  an  octave  above;  damping  it  at  a  distance  of  one-fourth,  we  have  the 
second  octave  above,  and  so  on.  When  we  damp  it  at  a  distance  of  one-fifth  from  the 
end,  we  have  the  four-fifths  sounding  the  3d  of  the  fundamental,  with  the  second  octave 
of  the  3d.  If  we  damp  it  at  a  distance  of  two-thirds,  we  have  the  5th  of  the  fundamen- 
tal, with  the  octave  of  the  5th. 

Every  vibrating  string  possesses,  thus,  a  fundamental  tone  and  overtones.  We  have, 
qualifying  the  fundamental,  first,  as  the  most  simple,  a  series  of  octaves ;  next,  a  series 
of  5ths  of  the  fundamental  and  their  octaves ;  and  next,  a  series  of  3ds.  These  are  the 
most  powerful  overtones,  and  they  form  the  common  chord  of  the  fundamental ;  but  they 
are  so  far  concealed  by  the  greater  intensity  of  the  fundamental,  that  they  cannot  be  easily 
distinguished  by  the  unaided  ear,  unless  the  fundamental  be  quenched  in  some  such  way 
as  we  have  indicated.  In  the  same  way,  the  harmonic  5ths  and  8ds  overpower  other 
overtones ;  for  we  have  the  string  subdividing  again  and  again  into  overtones,  which  are 
not  harmonious  like  the  notes  of  the  common  chord  of  the  fundamental. 

The  presence  of  overtones,  resultant  tones,  and  additional  tones,  which  latter  will  be 
described  hereafter,  can  be  demonstrated,  without  damping  the  strings,  by  the  resonators, 
invented  by  Helmholtz.  It  is  well  known  that,  if  a  glass  tube,  closed  at  one  end,  which 
contains  a  column  of  air  of  a  certain  length,  be  brought  near  a  resounding  body  emitting 
a  note  identical  with  that  produced  by  the  vibrations  of  the  column  of  air,  the  air  in  the 
tube  will  resound  in  consonance  with  the  note.  If,  for  example,  we  have  a  tube  sounding 
C,  a  tuning-fork  of  the  same  pitch  sounded  near  the  tube  will  throw  the  air  in  the  tube 
into  action  and  will  produce  a  powerful  sound,  while  no  other  note  will  have  this  effect. 
The  resonators  of  Helmholtz  are  constructed  upon  this  principle.  A  glass  globe  or  tube 
(Fig.  262)  is  constructed  so  as  to  produce  a  certain  note.  This  has  a  larger  opening  (a) 
and  a  smaller  opening  (b)  which  latter  is  fitted  in  the  ear  by  warm  sealing-wax,  the  other 
ear  being  closed.  When  the  proper  note  is  sounded,  it  is  reenforced  by  the  resonator 
and  is  greatly  increased  in  intensity,  while  all  other  notes  are  heard  very  faintly.  Sup- 
pose, now,  that  we  apply  this  to  the  detection  of  overtones.  We  fix  in  the  ear  a  resonator 
adjusted  to  G,  and  sound  the  fundamental  (C).  The  fundamental  (C)  is  imperfectly  heard, 
but  the  overtone  (G)  is  reenforced,  and  we  have  a  loud  and  distinct  sound  of  the  5th.  By 
using  resonators  graduated  to  the  musical  scale,  we  can  easily  analyze  a  note  and  distin- 
guish the  overtones.  In  the  same  way,  if  we  place  in  the  ear  a  resonator  tuned  to  a  par- 
ticular note  and  strike  a  succession  of  chords  on  the  piano,  the  general  sound  is  imper- 
fectly heard ;  but,  whenever  we  strike  the  note  of  the  resonator,  this  is  clearly  distin- 
guished, to  the  practical  exclusion  of  all  others ;  and  we  can  thus  analyze  complicated 
chords  into  each  of  their  constituent  parts.  This  experiment  shows  the  similarity  between 
chords,  resolved  into  their  constituent  parts,  and  single  notes,  resolved  into  their  harmonics, 
or  overtones.  The  resonators  of  Helmholtz,  which  are  open  at  the  larger  extremity,  are 
infinitely  more  delicate  than  those  in  which  this  is  closed  by  a  membrane. 

A  very  striking  and  instructive  point  in  the  present  discussion  is  the  following :  All 
the  overtones  are  produced  by  vibrations  of  segments  of  the  string  included  between  the 
comparatively  still  points,  called  nodes ;  and,  if  we  cause  a  string  to  vibrate  by  plucking 


LAWS   OF  SONOROUS   VIBRATIONS.  831 

or  striking  it  at  one  of  these  nodal  points,  we  abolish  the  overtones  which  vibrate  from  this 
node  at  a  fixed  point.  For  example,  if  we  pluck  the  string  at  its  exact  centre,  we  sound 
the  fundamental ;  but  we  then  have  a  dull  tone,  which  is  deficient  in  the  overtones  of  the 
octaves.  We  can  demonstrate  the  fact  that  these  overtones  are  absent,  for,  if  we  damp 
the  string  at  its  centre,  the  fundamental  is  quenched,  but  we  have  no  octaves,  which  are 
always  heard  on  damping  the  centre  when  the  string  is  plucked  at  other  points.  In  the 
same  way,  by  plucking  the  string  at  different  points,  we  can  abolish  the  overtones  of 


FIG.  262  b. 
FIG.  262.— Resonators  of  Helniholtz. 

5ths,  3ds,  etc.  It  is  readily  understood  that,  when  a  string  is  plucked  at  any  point,  it 
will  vibrate  so  vigorously  at  this  point  that  no  node  can  be  formed.  This  fact  has  long 
been  recognized  by  practical  musicians,  although  many  are  probably  unacquainted  with 
its  scientific  explanation.  Performers  upon  stringed  instruments  habitually  attack  the 
strings  near  their  extremities.  In  the  piano,  where  the  strings  may  be  struck  at  almost 
any  point,  the  hammers  are  placed  at  from  \  to  \  of  their  extremities ;  and  it  has  been 
ascertained  by  experience  that  this  gives  the  richest  notes.  The  nodes  formed  at  these 
points  would  produce  the  Tths  and  9ths  as  overtones,  which  do  not  belong  to  the  perfect 
major  chord,  while  the  nodes  for  the  harmonious  overtones  are  undisturbed.  The  reason, 
then,  why  the  notes  are  richer  and  more  perfect  when  the  strings  are  attacked  at  this 
point,  is  that  the  harmonious  overtones  are  full  and  perfect,  and  certain  of  the  discordant 
overtones  are  suppressed. 

When  two  harmonious  notes  are  produced  under  favorable  conditions,  we  can 
hear,  in  addition  to  the  two  sounds,  a  sound  differing  from  both  and  much  lower  than 
the  lower  of  the  two.  This  sound  is  too  low  for  an  harmonic,  and  it  has  been  called  a 
resultant  tone.  The  formation  of  a  new  sound  by  combining  two  sounds  of  different 
pitch  is  analogous  to  the  blending  of  colors  in  optics,  except  that  the  primary  sounds  are 
not  lost.  The  laws  of  the  production  of  these  resultant  sounds  are  very  simple.  When 
two  notes  in  harmony  are  sounded,  the  resultant  tone  is  equal  to  the  difference  between 
the  two  primaries.  For  example,  if  we  sound  0,  with  48  vibrations,  and  its  5th,  with  72 
vibrations  in  a  second,  the  resultant  tone  is  equal  to  the  difference,  which  is  24  vibrations, 
and  it  is  consequently  the  octave  below  0  ;  or,  if  we  sound  0,  with  48  vibrations,  and  its 
3d,  with  60,  we  have  a  resultant  tone  two  octaves  below  0,  the  number  of  vibrations 
being  12.1  These  resultant  tones  are  very  feeble  as  compared  with  the  primary  tones,  and 

1  These  numbers  are  used  merely  in  illustration.    A  sound  of  12  vibrations  does  not  come  within  the  musical  scale. 


832  SPECIAL  SENSES. 

they  can  be  heard  only  under  the  most  favorable  experimental  conditions.  In  addition  to 
these  sounds,  Helmholtz  has  discovered  sounds,  even  more  feeble,  which  he  calls  addi- 
tional, or  summation  tones.  The  value  of  these  is  equal  to  the  sum  of  vibrations  of  the 
primary  tones.  For  example,  0  (24)  and  its  5th  (36)  would  give  a  summation  tone  of  60 
vibrations,  or  the  octave  of  the  3d ;  and  0  (24)  with  its  3d  (30)  would  give  54  vibrations, 
the  octave  of  the  2d.  These  tones  can  readily  be  distinguished  by  means  of  the  reso- 
nators already  described. 

It  is  thus  seen  that  musical  sounds  are  excessively  complex.  With  single  sounds,  we 
have  an  infinite  variety  and  number  of  harmonics,  or  overtones,  and  in  chords,  which 
will  be  treated  of  more  fully  under  the  head  of  harmony,  we  have  a'  series  of  resultants, 
which  are  lower  than  the  primary  tones,  and  a  series  of  additional,  or  summation  tones, 
which  are  higher ;  but  both  the  resultant  and  the  summation  tones  bear  an  exact  mathe- 
matical relation  to  the  primary  tones  of  the  chord. 

Harmony. — We  have  discussed  the  overtones,  resultant  tones,  and  summation  tones 
of  strings  rather  fully,  for  the  reason  that,  in  the  physiology  of  audition,  we  shall  see  that 
the  ear  is  capable  of  recognizing  single  sounds  or  successions  of  single  sounds ;  but,  at 
the  same  time,  certain  combinations  of  sounds  are  appreciated  and  are  even  more  agree- 
able than  those  which  are  apparently  produced  by  simple  vibrations.  Combinations  of 
tones  which  thus  produce  an  agreeable  impression  are  called  harmonious.  They  seem  to 
become  blended  with  each  other  into  a  complete  sound  of  peculiar  quality,  all  of  the  dif- 
ferent vibrations  entering  into  their  composition  being  simultaneously  appreciated  by  the 
ear.  From  what  we  have  learned  of  overtones,  it  is  evident  that  few  musical  sounds  are 
really  simple,  and  that  those  which  are  simple  are  wanting  in  richness,  while  they  are  per- 
fectly pure.  The  blending  of  tones  which  bear  to  each  other  a  certain  mathematical  rela- 
tion is  called  harmony  ;  but  two  or  more  tones,  though  each  one  be  musical,  are  not  neces- 
sarily harmonious.  The  most  prominent  overtone,  except  the  octave,  is  the  5th,  with  its 
octaves,  and  this  is  called  the  dominant.  The  next  is  the  3d,  with  its  octaves.  The 
other  overtones  are  comparatively  feeble.  Reasoning,  now,  from  our  knowledge  of  the 
relations  of  overtones,  we  might  infer  that  the  reinforcement  of  the  5th  and  3d  by  other 
notes  bearing  similar  relations  to  the  tonic  would  be  agreeable.  This  is  the  fact,  and  it 
was  ascertained  empirically  long  before  the  pleasing  impression  produced  by  such  com- 
binations was  explained  mathematically.  We  do  not  propose  to  enter  into  a  full  discus- 
sion of  the  laws  of  harmony,  but  a  knowledge  of  certain  of  these  laws  is  essential  to  the 
comprehension  of  the  physiology  of  audition.  These  are  very  simple,  now  that  we  have 
analyzed  the  sound  of  a  single  vibrating  body. 

It  is  a  law  in  music,  that  the  more  simple  the  ratio  between  the  number  of  vibrations 
in  two  sounds,  the  more  perfect  is  the  harmony.  The  simplest  relation,  of  course,  is 
1  :  1,  when  the  two  sounds  are  said  to  be  in  unison.  The  next  in  order  is  1  :  2.  If  we 
sound  C  and  its  8th,  we  have,  for  example,  24  vibrations  of  one  to  48  of  the  other. 
These  sounds  can  produce  no  discord,  because  the  waves  never  interfere  with  each  other, 
and  the  two  sounds  can  be  prolonged  indefinitely,  always  maintaining  the  same  relations. 
The  combined  impression  is  therefore  continuous.  The  next  in  order  is  the  1st  and  5th, 
their  relations  being  2:3.  In  other  words,  with  the  1st  and  5th,  for  two  waves  of  the 
1st  we  have  three  waves  of  the  5th.  The  two  sounds  may  thus  progress  indefinitely, 
for  the  waves  coincide  for  every  second  wave  of  the  1st  and  every  third  wave  of  the  5th. 
The  next  in  order,  if  we  sound  at  the  same  time  the  1st,  5th,  and  8th,  is  the  3d.  The  3d 

3  has  the  8th  of  0  for  its  5th,  and  the  5th  of  C  for  its  minor  3d.  The  1st,  3d,  5th, 
3th  form  the  common  major  chord;  and  the  waves  of  each  tone  blend  with  each 
other  at  such  short  intervals  of  time  that  the  ear  experiences  a  continuous  impression, 
and  no  discord  is  appreciated.  This  explanation  of  the  common  major  chord  illustrates 
the  law  that,  the  smaller  the  ratio  of  vibration  between  different  tones,  the  more  perfect 
is  their  harmony.  Sounded  with  the  1st,  the  4th  is  more  harmonious  than  the  3d  ;  but 


USES   OF  DIFFERENT   PARTS   OF  THE  AUDITORY  APPARATUS.    835 

When  arranged  in  this  way,  the  membrane  can  be  made  to  sound  its  fundamental  note 
by  influence.  In  addition,  the  membrane,  like  a  string,  will  divide  itself  so  as  to  sound  the 
harmonics  of  the  fundamental,  and  it  will  likewise  be  thrown  into  vibration  by  the  5th 
3d,  etc.,  of  its  fundamental  tone,  thus  obeying  the  laws  of  vibrations  of  strings,  though 
the  harmonic  sounds  are  produced  with  greater  difficulty. 

Uses  of  Different  Parts  of  the  Auditory  Apparatus. 

The  uses  of  the  pavilion  of  the  ear  and  of  the  external  auditory  meatus  are  sufficiently 
apparent.  The  pavilion  serves  to  collect  the  waves  of  sound,  and  probably  it  inclines  them 
toward  the  external  meatus  as  they  come  from  various  directions.  Although  this  action 
is  simple,  it  undoubtedly  has  a  certain  degree  of  importance,  and  the  various  curves  of 
the  concavity  of  the  pavilion  tend  more  or  less  to  concentrate  the  sonorous  vibrations. 
Such  has  long  been  the  opinion  of  physiologists,  and  this  seems  to  be  carried  out  by 
experiments  in  which  the  concavities  of  the  external  ear  have  been  obliterated  by  wax. 
There  is,  probably,  no  resonance  or  vibration  of  much  importance  until  the  waves  of 
sound  strike  the  membrana  tympani.  The  same  remarks  may  be  made  with  regard  to 
the  external  auditory  meatus.  We  do  not  know  precisely  how  the  obliquity  and  the 
curves  of  this  canal  affect  the  waves  of  sound,  but  we  may  suppose  that  the  deviation 
from  a  straight  course  protects,  to  a  certain  degree,  the  tympanic  membrane  from  im- 
pressions that  might  otherwise  be  too  violent. 

Structure  "of  the  Membrana  Tympani. — The  general  arrangement  of  the  membrana 
tympani  has  already  been  described  in  connection  with  the  topographical  anatomy  of  the 
auditory  apparatus.  This  structure,  which  is  of  great  importance  in  the  physiology  of 
hearing,  is  delicate,  elastic,  about  the  thickness  of  ordinary  gold-beater's  skin,  and  is 
subject  to  various  degrees  of  tension,  from  the  action  of  the  muscles  of  the  middle  ear 
and  different  conditions  of  atmospheric  pressure  within  and  without  the  cavity  of  the 
tympanum.  Its  form  is  nearly  circular.  From  a  number  of  accurate  measurements  of 
its  diameter  in  the  adult,  by  Sappey,  we  may  assume  that  its  ring  measures  a  little  more 
than  f  of  an  inch  vertically  and  about  f  of  an  inch  antero-posteriorly.  The  excess  of  the 
vertical  over  the  horizontal  diameter  is  about  -^  of  an  inch.  Notwithstanding  the  asser- 
tion of  some  of  the  older  anatomists,  that  the  tympanic  membrane  presents  one  or  two 
small  perforations,  it  is  now  almost  universally  regarded  as  forming  a  complete  division, 
without  openings,  between  the  external  meatus  and  the  middle  ear ;  or,  if  any  openings 
exist,  they  are  exceedingly  minute. 

The  periphery  of  the  tympanic  membrane  is  received  into  a  little  ring  of  bone,  which 
may  be  separated  by  maceration  in  early  life,  but  which  is  consolidated  with  the  adja- 
cent bony  structures  in  the  adult.  This  bony  ring  is  incomplete  at  its  superior  portion, 
but,  aside  from  this,  it  resembles  the  groove  which  receives  the  crystal  of  a  watch.  At  the 
periphery  of  the  membrane,  is  a  ring  of  condensed  fibrous  tissue,  which  is  received  into 
the  bony  ring.  This  ring  also  presents  a  break  at  its  superior  portion. 

The  concavity  of  the  membrana  tympani  presents  outward,  and  it  may  be  increased  or 
diminished  by  the  action  of  the  muscles  of  the  middle  ear.  The  point  of  greatest  con- 
cavity, where  the  extremity  of  the  handle  of  the  malleus  is  attached,  is  called  the  umbo. 
Upon  the  inner  surface  of  the  membrane  are  two  pouches,  or  pockets.  One  is  formed  by 
a  small,  irregular,  triangular  fold,  situated  at  the  upper  part  of  its  posterior  half  and  con- 
sisting of  a  process  of  the  fibrous  layer.  This,  which  is  called  the  posterior  pocket,  is  open 
below  and  extends  from  the  posterior  upper  border  of  the  membrane  to  the  handle  of 
the  malleus,  which  it  assists  in  holding  in  position.  "  After  it  has  been  divided,  the  bone 
is  much  more  movable  than  before."  (Troltsch.)  The  anterior  pocket  is  lower  and  shorter 
than  the  posterior.  It  is  formed  by  a  small  bony  process  turned  toward  the  neck  of  the 
malleus,  by  the  mucous  membrane,  by  the  bony  process  of  the  malleus,  by  its  anterior 


836  SPECIAL  SENSES. 

ligament,  the  chorda  tympani,  and  the  anterior  tympanic  artery.  The  handle  of  the 
malleus  is  inserted  between  the  two  layers  of  the  fibrous  structure  of  the  membrana 
tympani  and  occupies  the  upper  half  of  its  vertical  diameter,  extending  from  the  periph- 
ery to  the  umbo. 

The  membrana  tympani,  though  thin  and  translucent,  presents  three  distinct  layers. 
Its  outer  layer  is  an  excessively  delicate  prolongation  of  the  integument  lining  the  exter- 
nal meatus,  presenting,  however,  neither  papillae  nor  glands.  The  inner  layer  is  a  deli- 
cate continuation  of  the  mucous  membrane  lining  the  tympanic  cavity  and  is  covered  by 


FIG.  263.  —  Right  membrana  tympani,  seen  from  vtithin.    From  a  photograph,  and  somewhat  reduced. 

(Kudinger.) 

1,  head  of  the  malleus,  divided  ;  2,  neck  of  the  malleus;  3,  handle  of  the  malleus,  with  the  tendon  of  the  tensor  tym- 
pani muscle;  4,  divided  tendon  of  the  tensor  tympani;  5,  6,  portion  of  the  malleus  between  the  layers  of  the 
membrana  tympani ;  7,  outer  (radiating)  and  inner  (circular)  fibres  of  the  membrana  tympani ;  8,  fibrous  ring  of 
the  membrana  tympani;  9,  14, 15,  dentated  fibres,  discovered  by  Gruber  ;  10,  posterior  pocket;  11,  connection 
of  the  posterior  pocket  with  the  malleus ;  12,  anterior  pocket ;  13,  chorda  tympani  nerve. 

tessellated  epithelial  cells.  The  fibrous  portion,  or  lamina  propria,  is  formed  of  two 
layers.  The  outer  layer  consists  of  fibres,  radiating  from  the  handle  of  the  malleus  to 
the  periphery.  These  are  best  seen  near  the  centre.  The  inner  layer  is  composed  of 
circular  fibres,  which  are  most  abundant  near  the  periphery  and  diminish  in  number 
toward  the  centre. 

The  color  of  the  membrana  tympani,  when  it  is  examined  with  an  aural  speculum  by 
daylight,  is  peculiar,  and  it  is  rather  difficult  to  describe,  as  it  varies  in  the  normal  ear  in 
different  individuals.  Politzer  describes  the  membrane,  examined  in  this  way,  as  trans- 
lucent, and  of  a  color  which  "  most  nearly  approaches  a  neutral  gray,  mingled  with  a 
weaker  tint  of  violet  and  light  yellowish-brown.  This  color  is  modified,  in  certain  por- 
tions of  the  membrane,  by  the  chorda  tympani  and  the  bones  of  the  ear,  which  produce 
some  opacity.  The  entire  membrane  in  health  has  a  soft  lustre.  In  addition,  there  is 


USES   OF   DIFFERENT   PARTS   OF  THE  AUDITORY   APPARATUS.   837 

seen,  with  proper  illumination,  a  well-marked,  triangular  cone  of  light,  with  its  apex  at 
the  end  of  the  handle  of  the  malleus,  spreading  out  in  a  downward  and  forward  direc- 
tion, and  from  T\  to  TV  of  an  inch  broad  at  its  base.  This  appearance  is  regarded  by 
pathologists  as  very  important,  as  indicating  a  normal  condition  of  the  membrane.  It  is 
undoubtedly  due  to  reflection  of  light,  depending  upon  three  factors,  indicated  by  Roosa 
as  follows :  "  First,  the  inclination  of  the  membrana  tympani  to  the  auditory  canal  • 
second,  the  traction  of  the  malleus,  which  renders  it  concave  at  the  centre ;  third,  its 
polish  or  brilliancy."  With  this  explanation,  it  is  not  admitted  that  the  light  spot  is  due 
to  a  peculiar  structure  of  that  portion  of  the  membrane  upon  which  it  is  seen. 

Uses  of  the  Membrana,  Tympani. — It  is  unquestionable  that  the  membrana  tympani  is 
very  important  in  audition.  In  cases  of  disease  in  which  the  membrane  is  thickened, 
perforated,  or  destroyed,  the  acuteness  of  hearing  is  always  more  or  less  affected.  That 
this  is  in  great  part  due  to  the  absence  of  a  vibrating  surface  for  the  reception  of  waves 
of  sound,  is  shown  by  the  relief  which  is  experienced  by  those  patients  who  can  tolerate 
the  presence  of  an  artificial  membrane  of  rubber,  when  this  is  introduced.  As  regards 
the  mere  acuteness  of  hearing,  aside  from  -the  pitch  of  sounds,  the  explanation  of  the 
action  of  the  membrane  is  very  simple.  Sonorous  vibrations  are  not  readily  transmitted 
through  the  atmosphere  to  solid  bodies,  like  the  bones  of  the  ear ;  and  when  they  are 
thus  transmitted  they  lose  considerably  in  intensity.  When,  however,  the  aerial  vibra- 
tions are  received  by  a  delicate  membrane,  under  the  conditions  of  the  membrana  tym- 
pani, they  are  transmitted  with  very  little  loss  of  intensity ;  and,  if  this  membrane  be 
connected  with  solid  bodies,  like  the  bones  of  the  middle  ear,  the  vibrations  are  readily 
conveyed  to  the  sensory  portions  of  the  auditory  apparatus.  The  parts  composing  the 
middle  ear  are  thus  admirably  adapted  to  the  transmission  of  sonorous  waves  to  the 
auditory  nerves.  The  membrane  of  the  tympanum  is  delicate  in  structure,  stretched  to 
the  proper  degree  of  tension,  and  vibrates  under  the  influence  of  the  waves  of  sound. 
Attached  to  this  membrane,  is  the  chain  of  bones,  which  conducts  its  vibrations,  like 
the  bridge  of  a  violin,  to  the  liquid  of  the  labyrinth.  The  membrane  is  fixed  at  its 
periphery  and  has  air  upon  both  sides,  so  that  it  is  under  the  most  favorable  conditions 
for  vibration. 

A  study  of  the  mechanism  of  the  ossicles  and  muscles  of  the  middle  ear  shows  that 
the  membrana  tympani  is  subject  to  certain  physiological  variations  in  tension,  due  to 
contraction  of  the  tensor  tympani.  It  is  also  evident  that  this  membrane  may  be  drawn 
in  and  rendered  tense  by  exhausting  or  rarefying  the  air  in  the  drum.  If  the  mouth  and 
nose  be  closed  and  we  attempt  to  breathe  forcibly  by  expanding  the  chest,  the  external 
pressure  tightens  the  membrane.  In  this  condition,  the  ear  is  rendered  insensible  to 
grave  sounds,  but  high-pitched  sounds  appear  to  be  more  intense.  If  the  tension  be  re- 
lieved, as  may  be  done  by  an  act  of  swallowing,  the  grave  sounds  are  heard  with  normal 
distinctness.  This  experiment,  tried  at  a  concert,  produces  the  curious  effect  of  abolish- 
ing a  great  number  of  the  lowest  tones,  while  the  shrill  sounds  are  heard  very  acutely. 
The  same  phenomena  are  observed  when  the  external  pressure  is  increased  by  descent  in 
a  diving-bell. 

Undoubted  cases  of  voluntary  contraction  of  the  tensor  tympani  have  been  observed 
by  otologists ;  and  in  these,  by  bringing  this  muscle  into  action,  the  limit  of  the  perception 
of  high  tones  is  greatly  increased.  In  two  instances  of  this  kind,  recorded  by  Dr.  Blake, 
of  Boston,  the  ordinary  limit  of  perception  was  found  to  be  three  thousand  single  vibra- 
tions ;  and,  by  contraction  of  the  muscle,  this  was  increased  to  five  thousand  single  vibra- 
tions. 

The  membrana  tympani  undoubtedly  vibrates  by  influence,  when  it  is  brought  in 
accord  with  a  given  note.  In  other  words,  this  membrane  obeys  the  laws  of  consonance 
and  vibrates  strongly  by  the  influence  of  sounds  in  unison  or  in  harmony  with  its  funda- 
mental tone.  The  laws  of  vibrations  by  influence  have  already  been  fully  discussed ; 


SPECIAL  SENSES. 

and  it  remains  for  us  now  to  determine  how  far  these  laws  are  applicable  to  the  physi- 
ology of  the  vibrations  of  the  membrana  tympani  and  the  action  of  these  vibrations  in 
the  accurate  perception  of  musical  sounds. 

There  are  certain  phenomena  of  vibration  of  the  membrana  tympani  that  must  occur, 
as  a  physical  necessity,  under  favorable  conditions,  which  it  is  important  to  note  in  this 
connection ;  and  these  have  hardly  attracted  sufficient  attention  at  the  hands  of  physio- 
logical writers.  In  the  first  place,  this  membrane  must  obey  the  laws  of  vibration  by 
influence.  It  is  undoubtedly  thrown  into  vibration  by  irregular  waves  of  noise,  as  contra- 
distinguished from  musical  tones ;  but,  when  a  tone  is  sounded  in  unison  with  its  funda- 
mental tone,  or  when  the  tone  sounded  is  one  of  the  octaves  of  its  fundamental,  it  must 
undergo  a  vibration  by  influence,  like  an  artificial  membrane.  If  we  suppose  the  mem- 
brane to  be  tuned  in  unison  with  a  certain  note,  it  will  not  only  return  this  note  by  influ- 
ence, but  it  will  repeat  its  quality.  Not  only  this,  when  a  combination  of  harmonious 
tones  is  sounded,  the  combined  sound  will  be  returned,  with  all  the  shades  in  quality 
which  the  combined  tones  produce.  On  account  of  its  small  size,  the  sound  produced  by 
the  exposed  membrane  itself  cannot  be  heard ;  but  that  the  membrane  does  vibrate  by 
influence,  has  been  proven  by  experiments  with  small  particles  of  sand  on  its  surface. 

We  are  certainly  justified  in  supposing  that  vibrations  of  the  membrana  tympani,  too 
delicate  to  be  revealed  to  the  eye  or  the  ear  in  objective  experiments,  may  be  appreciated 
by  the  auditory  nerves  as  a  subjective  phenomenon.  In  other  words,  we  can  probably  ap- 
preciate vibrations  in  our  own  tympanic  membrane,  when  these  would  be  too  delicate  to 
be  observed  by  the  eye  or  ear,  in  a  membrane  exposed  and  subjected  to  similar  influences. 
This  point  must  be  accepted  as  probable ;  and  it  cannot  be  proven  by  direct  experiment. 
If  this  be  true,  the  most  complex  combinations  of  sound  produced  by  an  orchestra  might 
be  actually  reproduced  by  the  tympanic  membrane,  if  this  membrane  were  accurately 
tuned  to  the  fundamental  tone. 

The  arrangement  of  the  muscles  and  bones  of  the  middle  ear  admits  of  the  possibility 
of  tuning  the  membrana  tympani  with  exquisite  nicety.  These  muscles  are  sometimes  so 
far  under  the  control  of  the  will  that  we  can  tighten  the  membrane  to  its  limit  by  a  vol- 
untary effort ;  the  muscles  are  of  the  striated  variety,  and  are  capable  of  rapid  action ; 
they  are  supplied  with  motor  filaments  from  the  cerebro-spinal  system ;  the  ear  is  fatigued 
by  long  attention  to  particular  tones ;  persons  not  endowed  with  what  is  termed  a  musical 
ear  cannot  appreciate  slight  distinctions  between  different  tones ;  the  ear  is  capable  of 
education  in  the  appreciation  of  pitch  and  in  following  rapid  successions  of  tones;  and,  in 
short,  there  are  many  points  in  the  mechanism  of  the  transmission  of  musical  sounds  in 
the  ear  that  seem  to  involve  muscular  action.  In  the  larynx,  we  are  conscious  of  differ- 
ences in  the  tension  of  the  vocal  chords  only  from  differences  in  the  character  and  pitch 
of  the  sounds  produced  ;  in  the  eye,  we  are  conscious  of  the  contraction  of  the  muscle  of 
accommodation  from  the  fact  that  an  effort  enables  us  to  see  objects  distinctly  at  differ- 
ent distances ;  and  it  is  not  impossible  that,  under  ordinary  conditions,  the  consciousness 
of  contractions  of  the  muscles  of  the  middle  ear  may  be  revealed  only  by  the  fact  of  the 
correct  appreciation  of  certain  musical  tones.  Some  persons  can  educate  the  ear  so  as  to 
acquire  what  is  called  the  faculty  of  absolute  pitch ;  that  is,  without  the  aid  of  a  tuning- 
iork  or  any  musical  instrument,  they  can  give  the  exact  musical  value  of  any  given  tone. 
A  possible  explanation  of  this  is  that  such  persons  may  have  educated  the  muscles  of  the 
ear^so  as  to  put  the  tympanic  membrane  in  such  a  condition  of  tension  as  to  respond  to 
a  given  note  and  to  recognize  the  position  of  this  note  in  the  musical  scale.  Finally,  an 
complished  musician,  in  conducting  an  orchestra,  can,  by  a  voluntary  effort,  direct  his 
attention  to  certain  instruments,  and  hear  their  notes  distinctly,  separating  them,  as  it 
were,  from  the  general  mass  of  sound,  can  distinguish  the  faintest  discords,  and  immedi- 
ately designate  a  single  instrument  making  a  false  note. 

The  fact  that  rapid  successions  of  notes  are  readily  appreciated  does  not  of  necessity 
argue  against  the  possibility  of  following  these  notes  with  the  muscles  of  the  ear ;  for  the 


USES   OF  DIFFERENT  PARTS   OF  THE   AUDITORY   APPARATUS.    839 

muscles  of  the  larynx  may  act  so  as  to  produce  successions  of  notes  as  rapidly  as  they  can 
be  correctly  appreciated.  Nor  does  the  fact  that  we  must  prepare  the  tympanic  mem- 
brane for  certain  notes  militate  against  the  theory  we  have  just  given,  for  musical  com- 
positions present  melodious  successions  in  a  certain  scale,  the  notes  of  which  bear  well- 
defined  harmonious  relations  to  each  other,  and  we  immediately  appreciate  a  change  in 
the  key,  which  is  simply  a  change  in  the  fundamental.  These  changes  in  the  key  must 
be  made  in  accordance  with  the  laws  of  modulation ;  otherwise  they  are  harsh  and  grat- 
ing. Modulation  in  music  is  simply  a  mode  of  passing  from  one  key  to  another  by  certain 
transition-notes  or  chords,  which  seem  ine\7itably  to  lead  to  a  certain  key,  and  to  no 
other.  Finally,  the  laws  of  vibration  by  influence  show  that  a  single  vibrating  membrane 
returns  the  quality  as  well  as  the  pitch  of  tones  and  of  combinations  of  tones  as  well. 

The  theory  we  have  just  given  of  the  possible  action  of  the  membrana  tympani  is  an 
elaboration  of  the  view  advanced  by  Everard  Home.  Unfortunately  for  the  simplicity  of 
the  mechanism  of  hearing  and  the  idea  of  division  and  isolation  of  function  in  different 
parts,  which  is  so  seductive  to  physiologists,  there  are  certain  facts  and  considerations 
which  may  prevent  some  from  adopting  it  absolutely  and  exclusively  as  an  explanation 
of  the  mechanism  of  the  appreciation  of  musical  sounds.  These  are  the  following : 

Destruction  of  both  menibranso  tympani  does  not  necessarily  produce  total  deafness, 
although  this  condition  involves  considerable  impairment  of  hearing.  So  long  as  there 
is  simple  destruction  of  these  membranes,  the  bones  of  the  middle  ear  and  the  other 
parts  of  the  auditory  apparatus  being  intact,  the  waves  of  sound  are  conducted  to  the 
auditory  nerves,  though  imperfectly.  In  a  remarkable  case  reported  by  Sir  Astley 
Cooper,  which  is  cited  by  most  writers  upon  physiology,  one  membrana  tympani  was  en- 
tirely destroyed,  and  the  other  was  nearly  gone,  there  being  some  parts  of  its  periphery 
remaining.  In  this  person,  the  hearing  was  somewhat  impaired,  although  he  could  dis- 
tinguish ordinary  conversation  pretty  well.  Fortunately,  he  had  considerable  musical 
taste,  and  it  was  ascertained  that  his  musical  ear  was  not  seriously  impaired ;  "for  he 
played  well  on  the  flute  and  had  frequently  borne  a  part  in  a  concert.  I  speak  this,  not 
from  his  authority  only,  but  also  from  that  of  his  father,  who  is  an  excellent  judge  of 
music,  and  plays  well  on  the  violin :  he  told  me,  that  his  son,  besides  playing  on  the 
flute,  sung  with  much  taste,  and  perfectly  in  tune."  This  single  case,  if  its  details  be 
accurate — which  we  have  no  reason  to  doubt — shows  conclusively  that  the  correct  appre- 
ciation of  musical  sounds  may  exist  independently  of  the  action  of  the  membrana  tym- 
pani. 

There  is  one  consideration,  of  the  greatest  importance,  that  must  be  kept  in  view 
in  studying  the  functions  of  any  distinct  portion  of  the  auditory  apparatus,  like  the 
membrana  tympani.  This,  like  all  other  parts  of  the  apparatus,  except  the  auditory 
nerves  themselves,  has  simply  an  accessory  function.  If  the  regular  waves  of  a  musical 
tone  be  conveyed  to  the  terminal  filaments  of  the  auditory  nerves,  these  waves  make 
their  impression  and  the  tone  is  appreciated.  It  makes  no  difference,  except  as  regards 
intensity,  how  these  waves  are  conducted ;  the  tone  is  appreciated  by  the  impression 
made  upon  the  nerves,  and  the  nerves  only.  The  waves  of  sound  are  not  like  the  waves 
of  light,  refracted,  decomposed,  perhaps,  and  necessarily  brought  to  a  focus  as  they  im- 
pinge upon  the  retina ;  as  far  as  the  action  of  the  accessory  parts  of  the  ear  are  concerned, 
the  waves  of  sound  are  unaltered  ;  that  is,  the  rate  of  their  succession  remains  absolutely 
the  same,  though  they  be  reflected  by  the  concavities  of  the  concha  and  repeated  by  the 
tympanic  membrane.  Even  if  we  assume  that  the  membrane,  under  normal  conditions, 
repeats  musical  sounds  by  vibrations  produced  by  influence,  and  that  this  membrane  is 
tuned  by  voluntary  muscular  action  so  that  tones  are  exactly  repeated,  the  position  of 
these  tones  in  the  musical  scale  is  not  and  cannot  be  altered  by  the  action  of  any  of  the 
accessory  organs  of  hearing.  The  fact  that  a  person  may  retain  his  musical  ear  with 
both  membranes  destroyed  is  not  really  an  argument  against  the  view  that  the  membrane 
repeats  tones  by  influence ;  for,  if  musical  tones  or  noisy  vibrations  be  conducted  to  the 


84Q  SPECIAL  SENSES. 

auditory  nerves,  the  impression  produced  must  of  necessity  be  dependent  exclusively 
upon  the  character,  regularity,  and  number  of  the  sonorous  vibrations.  And,  again,  the 
physical  laws  of  sound,  which  are  fixed  and  unchangeable,  teach  us  that  a  membrane, 
like  the  membrana  tympani,  must  return  or  reproduce  sounds  which  are  in  unison  or  are 
harmonious  with  its  fundamental  tone,  much  more  perfectly  than  discordant  or  irregular 
vibrations.  In  a  loud  confusion  of  noisy  sounds,  we  can  readily  distinguish  pure  melody 
or  harmony,  even  when  the  vibrations  of  the  latter  are  comparatively  feeble.  In  follow- 
ing with  the  ear  any  piece  of  music,  reasoning  from  purely  physical  considerations,  it 
must  at  times  occur  that  the  tones  are  in  exact  unison  or  in  harmony  with  the  funda- 
mental tone  of  the  membrana  tympani.  Supposing  the  fundamental  tone  of  the  mem- 
brane to  be  constant  and  invariable,  such  tones  would  be  heard  much  more  distinctly 
than  others,  as  a  physical  necessity.  Such  a  difference  in  the  appreciation  of  certain 
notes  in  melody  does  not  occur ;  and  the  only  reasonable  explanation  of  this  is  that  the 
tension  of  the  membrane  is  altered.  It  is  shown  by  anatomical  researches  that  the  ten- 
sion can  be  altered  by  muscular  action,  and,  as  the  muscles  are  striated,  we  may  suppose 
that  it  may  be  modified  rapidly.  Physiological  observations  show  that  such  modifica- 
tions in  tension  do  occur ;  and  there  are  on  record  unquestionable  instances  in  which  the 
membrana  tympani  is  tightened  by  a  voluntary  contraction  of  the  tensor  tympani  muscle. 

Another  important  point  to  note  in  this  connection  is  the  following :  Can  it  be 
shown  that  the  appreciation  of  the  pitch  of  tones  bears  any  relation  to  the  degree  of  ten- 
sion of  the  tympanic  membrane  ?  We  can  answer  this  question  unreservedly  in  the 
affirmative.  When  the  membrane  is  rendered  tense,  there  is  insensibility  to  low  tones. 
When  the  membrane  is  brought  to  the  highest  degree  of  tension  by  voluntary  contrac- 
tion of  the  tensor  tympani,  the  limit  of  appreciation  of  high  tones  may  be  raised  from 
three  thousand  to  five  thousand  vibrations.  It  is  a  fact  in  the  physics  of  the  membrana 
tympani,  that  the  vibrations  are  more  intense  the  nearer  the  membrane  approaches  to  a 
vertical  position.  It  has  also  been  shown  that  the  membrane  has  a  strikingly  vertical 
position  in  musicians,  and  that  the  position  is  very  oblique  in  persons  with  an  imperfect 
musical  ear.  This  fact  has  a  most  important  bearing  upon  the  probable  relation  between 
the  membrana  tympani  and  the  correct  appreciation  of  musical  sounds. 

In  view  of  all  facts  and  considerations  for  and  against  the  theory  which  we  have 
given  of  the  action  of  the  tympanic  membrane  in  the  appreciation  of  musical  sounds, 
does  it  not  seem  probable  that  there  are,  acting  upon  this  membrane,  muscles  of  auditory 
accommodation,  analogous  in  their  operation  to  the  muscle  of  visual  accommodation  ? 
We  have  carefully  studied  this  subject  in  all  its  bearings,  and,  if  the  reader  follow  closely 
our  process  of  reasoning,  it  must  seem  probable  that  the  muscles  of  the  middle  ear  are 
muscles  of  auditory  accommodation  ;  but  it  should  be  remembered  that  the  action  of  the 
membrane  is  not  absolutely  essential,  and  that  musical  tones,  however  conducted,  must 
of  necessity  be  correctly  appreciated,  whenever  and  however  they  find  their  way  to  the 
auditory  nerves. 

Experiments  have  shown  pretty  conclusively  that  the  tympanic  membrane  vibrates 
more  forcibly  when  relaxed  than  when  it  is  tense.  It  is  evident  that  the  relaxed  mem- 
brane must  undergo  vibrations  of  greater  amplitude  than  when  it  is  under  strong  tension. 
In  certain  cases  of  facial  palsy,  in  which  it  is  probable  that  the  branch  of  the  facial  going 
to  the  tensor  tympani  was  affected,  the  ear  became  painfully  sensitive  to  powerful  impres- 
sions of  sound.  This  probably  has  no  relation  to  pitch,  and  most  sounds  that  are  pain- 
fully loud  are  comparatively  grave.  The  tension  of  the  membrane  may  be  modified  as  a 
means  of  protection  of  the  ear,  but  the  facts  belonging  to  cases  of  facial  palsy  are  all 
that  we  have  bearing  upon  this  point.  Artillerists  are  in  danger  of  rupture  of  the  mem- 
brana tympani  from  sudden  concussions.  To  guard  against  this  injury,  it  is  recom- 
mended to  stop  the  ear,  draw  the  shoulder  up  against  the  ear  most  in  danger,  and  parti- 
cularly to  inflate  the  middle  ear  after  Valsalva's  method.  "This  method  consists  in 
making  a  powerful  expiration,  with  the  mouth  and  nostrils  closed." 


USES   OF  DIFFERENT  PARTS  OF  THE  AUDITORY  APPARATUS.    841 

Mechanism  of  the  Ossicles  of  the  Ear. — The  ossicles  of  the  middle  ear,  in  connection 
with  the  muscles,  have  a  twofold  function :  First,  by  the  action  of  the  muscles,  the 
membrana  tympani  may  be  brought  to  different  degrees  of  tension.  Second,  the  chain 
of  bones  serves  to  conduct  sonorous  vibrations  to  the  labyrinth.  It  must  be  remembered 
that  the  handle  of  the  malleus  is  closely  attached  to  the  membrana  tympani,  especially 
near  its  lower  end.  Near  the  short  process,  the  attachment  is  looser  and  there  is  even 
an  incomplete  joint-space  at  this  point.  The  long  process  is  attached  closely  to  the 
Glasserian  fissure  of  the  temporal  bone. 

The  malleus  is  articulated  with  the  incus  by  a  very  peculiar  joint,  which  has  been 
accurately  described  by  Helmholtz.  This  joint  is  so  arranged,  presenting  a  sort  of  cog, 
that  the  handle  of  the  malleus  can  rotate  only  outward ;  and,  when  a  force  is  applied 
which  would  have  a  tendency  to  produce  a  rotation  inward,  the  malleus  must  carry  the 
incus  with  it.  This  mechanism  has  been  aptly  compared  by  Helmholtz  to  that  of  a 
watch-key  with  cogs  which  are  fitted  together  and  allow  the  whole  key  to  turn  in  one 
direction,  but  are  separated  so  that  only  the  upper  portion  of  the  key  turns  when  the  force 
is  applied  in  the  opposite  direction.  In  the  articulation  between  the  malleus  and  the 
incus,  the  only  difference  is  that  there  is  but  one  cog  ;  but  this  is  sufficient  to  prevent  an 
independent  rotation  of  the  malleus  inward.  This  enables  us  to  understand  the  action 
of  the  tensor  tympani  muscle.  By  the  contraction  of  this  muscle,  "  all  the  bands  which 
give  firmness  to  the  position  of  the  ossicles  are  rendered  tense.  This  muscle,  in  the  first 
place,  draws  the  handle  of  the  hammer  inward,  and  with  it  the  membrana  tympani.  At 
the  same  time  it  pulls  upon  the  axis-band  of  the  hammer,  drawing  it  inward  and  putting 
it  upon  the  stretch.  Another  effect,  as  we  have  shown,  is  to  draw  the  head  of  the  ham- 
mer away  from  the  tympano-incudal  joint,  to  tighten  all  the  ligaments  of  the  anvil,  those 
toward  the  hammer  as  well  as  those  at  the  end  of  its  short  process,  and  to  lift  the  latter 
up  from  its  bony  bed.  In  this  way  the  anvil  is  brought  into  the  position  where  the  cogs 
of  the  malleo-incudal  joint  fit  into  one  another  the  tightest.  Finally,  the  long  process 
of  the  anvil  is  compelled  to  form  a  rotation  inward  in  company  with  the  handle  of  the 
hammer ;  in  so  doing,  as  we  shall  see  further  on,  it  presses  upon  the  stirrup  and  drives 
it  into  the  oval  window  against  the  fluid  of  the  labyrinth. 

"In  this  respect  the  construction  of  the  ear  is  very  remarkable.  By  the  contraction 
of  the  single  mass  of  elastic  fibres  constituting  the  tensor  tyinpani  (whose  tension,  besides, 
is  variable  and  may  be  adapted  to  the  wants  of  the  ear)  all  the  inelastic  tendinous  liga- 
ments of  the  ossicles  are  simultaneously  put  upon  the  stretch."  (Helmholtz.) 

The  body  of  the  incus  is  attached  to  the  posterior  bony  wall  of  the  tympanic  cavity. 
Its  articulation  with  the  malleus  has  just  been  indicated.  By  the  extremity  of  its  long 
process,  it  is  also  articulated  with  the  stapes,  which  completes  the  chain.  In  situ,  the 
stapes  forms  nearly  a  right  angle  with  the  long  process  of  the  incus. 

The  stapes  is  articulated  with  the  incus,  as  indicated  above,  and  its  oval  base  is  applied 
to  the  fenestra  ovalis.  Surrounding  the  base  of  the  stapes,  is  a  ring  of  elastic  fibro-carti- 
lage,  which  is  closely  united  to  the  bony  wall  of  the  labyrinth,  by  an  extension  of  the 
periosteum  over  the  base  of  the  stapes. 

"The  relation  of  the  stirrup  to  the  anvil  is  such  that,  if  the  handle  of  the  hammer  be 
drawn  inward,  the  long  process  of.the  anvil  presses  firmly  against  the  knob  of  the  stirrup; 
the  same  takes  places  if  the  capsular  ligament  between  both  be  cut  through."  (Helm- 
holtz.) 

The  articulations  between  the  malleus  and  the  incus  and  between  the  incus  and  the 
stapes  are  so  arranged  that,  when  the  membrana  tympani  is  forced  outward,  as  it  may 
be  by  inflation  of  the  tympanic  cavity,  there  is  no  danger  of  tearing  the  stapes  from  its 
attachment  to  the  fenestra  ovalis  ;  for,  when  the  handle  of  the  malleus  is  drawn  outward, 
the  cog-joint  between  the  malleus  and  the  incus  is  loosened  and  no  great  traction  can  be 
exerted  upon  the  stapes. 

Although  experiments  have  demonstrated  pretty  conclusively  the  mechanism  of  the 


843  SPECIAL  SENSES. 

ossicles  and  the  action  of  the  tensor  tympani  muscle,  both  as  regards  the  chain  of  bones 
and  the  membrana  tyrapani,  direct  observations  are  wanting  to  show  the  exact  relations 
of  these  different  conditions  of  the  ossicles  and  of  the  membrane  to  the  physiology  of 
audition.  One  very  important  physical  point,  however,  which  has  been  the  subject  of 
much  discussion,  is  settled.  The  chain  of  bones  acts  as  a  single  solid  body  in  conducting 
vibrations  to  the  labyrinth.  It  is  a  matter  of  physical  demonstration  that  vibrations  of 
the  bones  themselves  would  be  infinitely  rapid  as  compared  with  the  highest  tones  which 
can  be  appreciated  by  the  ear,  if  it  were  possible  to  induce  in  these  bones  regular  vibra- 
tions. Practically/then,  the  ossicles  have  no  independent  vibrations  that  we  can  appre- 
ciate. This  being  the  fact,  the  ossicles  simply  conduct  to  the  labyrinth  the  vibrations 
induced  in  the  membrana  tympani  by  sound-waves ;  and  their  arrangement  is  such  that 
these  vibrations  lose  very  little  in  intensity.  While  it  has  been  shown  experimentally 
that  the  amplitude  of  vibration  in  the  membrana  tympani  and  the  ossicles  diminishes 
with  the  tension  of  the  membrane,  it  would  seem  that,  when  the  tensor  tympani  con- 
tracts, it  must  render  the  conduction  of  sound-waves  to  the  labyrinth  more  delicate  than 
when  the  auditory  apparatus  is  in  a  relaxed  condition,  which  we  may  compare  with  the 
"indolent"  condition  of  the  apparatus  of  accommodation  of  the  eye.  When  the  mem- 
brana tympani  is  relaxed  and  the  cog-like  articulation  between  the  malleus  and  the  incus 
is  loosened,  the  vibrations  of  the  membrane  and  of  the  malleus  may  have  a  greater  ampli- 
tude ;  but,  when  the  malleo-incudal  joint  is  tightened  and  the  stapes  is  pressed  against 
the  fenestra  ovalis,  the  loss  of  intensity  of  vibration  in  conduction  through  the  bones  to 
the  labyrinth  must  be  reduced  to  the  minimum.  With  this  view,  the  tensor  tympani 
muscle,  while  it  contracts  to  secure  for  the  membrana  tympani  the  degree  of  tension 
most  favorable  for  vibration  under  the  influence  of  certain  tones,  puts  the  chain  of  bones 
in  the  condition  best  adapted  to  the  conduction  of  the  vibrations  of  the  membrane  to  the 
labyrinth,  with  the  smallest  possible  loss  of  intensity. 

Physiological  Anatomy  of  the  Internal  Ear. 

The  internal  ear  consists  of  the  labyrinth,  which  is  divided  into  the  vestibule,  semi- 
circular canals,  and  cochlea.  The  general  arrangement  of  these  parts  has  already  been 
described ;  and  it  remains  for  us  only  to  study  the  structures  contained  within  the  bony 
labyrinth,  in  so  far  as  their  anatomy  bears  upon  the  physiology  of  audition.  The  most 
delicate  and  complicated  points,  by  far,  in  the  anatomy  of  the  auditory  apparatus  are 
connected  with  the  histology  of  the  internal  ear,  which,  since  the  researches  of  Corti,  has 
been  studied  very  closely,  particularly  in  Germany.  We  shall  avoid,  however,  the  dis- 
cussion of  histological  questions  of  purely  anatomical  interest  and  confine  ourselves  to 
those  points  which  have  a  direct  bearing  upon  physiology. 

Passing  inward  from  the  tympanum,  the  first  division  of  the  internal  ear  is  the  ves- 
tibule. This  cavity  communicates  with  the  tympanum  by  the  fenestra  ovalis,  which  is 
closed  in  the  natural  state  by  the  base  of  the  stapes.  It  communicates,  also,  with  the 
semicircular  canals  and  with  the  cochlea. 

General  Arrangement  of  the  Membranous  Labyrinth. — The  bony  labyrinth  is  lined 
by  a  moderately  thick  periosteum,  consisting  of  connective  tissue,  a  few  delicate  elastic 
fibres,  numerous  nuclei,  and  blood-vessels,  with  spots  of  calcareous  concretions.  This 
membrane  adheres  closely  to  the  bone  and  extends  over  the  fenestra  ovalis  and  the  fenes- 
tra rotunda.  Its  inner  surface  is  smooth  and  covered  with  a  single  layer  of  cells  of  pave- 
ment-epithelium, which  in  some  parts  is  segmented  and  in  others  forms  a  continuous 
nucleated  sheet.  In  certain  portions  of  the  vestibule  and  semicircular  canals,  the  perios- 
teum is  united  to  the  membranous  labyrinth,  more  or  less  closely,  by  fibrous  bands, 
which  have  been  called  ligaments  of  the  labyrinth.  The  fenestra  rotunda,  which  lies 
between  the  cavity  of  the  tympanum  and  the  cochlea,  is  closed  by  a  membrane  formed 


PHYSIOLOGICAL   ANATOMY   OF   THE  INTERNAL  EAR.  843 

by  an  extension  of  the  periosteum  lining  the  cochlea,  on  the  one  side,  and  the  mucous 
membrane  lining  the  tympanic  cavity,  on  the  other. 

In  the  bony  vestibule,  occupying  about  two-thirds  of  its  cavity,  are  two  distinct  sacs ; 
a  large,  ovoid  sac,  the  utricle,  situated  in  the  upper  and  posterior  portion  of  the  cavity, 
and  a  smaller,  rounded  sac,  the  saccule,  situated  in  its  lower  and  anterior  portion.  The 


FIG.  2&1.— Diagram  of  the  labyrinth,  vestibule,  and  semicircular  canals.    From  a  photograph,  and  somewhat 

reduced.  ,  (Kudinger.) 

Upper  figure:  1,  utricle;  2,  saccule;  8,  5,  membranous  cochlea;  4,  canalis  reunions  ;  6,  semicircular  canals. 
Lower  figure:  1,  utricle  ;  2,  saccule ;  3,  4,  6,  ampullae  ;  5,  7,  8,  9,  semicircular  canals  ;  10,  auditory  nerve  (partly  dia- 
grammatic) ;  1 1, 12, 13, 14, 15,  distribution  of  the  branches  of  the  nerve  to  the  vestibule  and  the  semicircular  canals ; 
16,  ganglioform  enlargement. 

utricle  communicates  with  the  semicircular  canals;  and  the  saccule  opens  into  the  mem- 
branous canal  of  the  cochlea  by  the  canalis  reuniens.  At  a  point  in  the  utricle  corre- 
sponding to  the  entrance  of  a  branch  of  the  auditory  nerve,  is  a  round,  whitish  spot,  called 
the  acoustic  spot  (macula  acustica),  containing  otoliths,  or  otoconia,  which  are  attached 
to  the  inner  surface  of  the  membrane.  A  similar  spot,  containing  otoliths,  exists  in  the 
saccule  at  the  point  of  entrance  of  its  nerve.  Otoliths  are  also  found  in  the  ampullae  of  the 
semicircular  canals.  These  calcareous  masses  are  composed  of  crystals  of  carbonate  of  lime, 
which  are  hexagonal  and  pointed  at  their  extremities.  Nothing  definite  is  known  of  the 
function  of  these  calcareous  bodies,  which  exist  in  man.  mammals,  birds,  and  reptiles. 

The  membranous  semicircular  canals  occupy  about  one-third  of  the  cavity  of  the  bony 
canals.  They  present  little  ovoid  dilatations,  called  ampullae,  corresponding  to  the  ampul- 
lary  enlargements  of  the  bony  canals. 

The  membrane  of  the  cochlea,  including  the  lining  periosteum,  occupies  the  spiral 
canal  of  the  cochlea,  which  it  fills  completely.  Viewed  externally,  it  appears  as  a  single 


844 


SPECIAL  SENSES. 


tube,  following  the  turns  of  the  bony  cochlea,  beginning  below,  at  the  first  turn,  by  a 
blind  extremity,  and  terminating  in  a  blind  extremity  at  the  summit  of  the  cochlea.  If 
we  make  a  section  of  the  cochlea  in  a  direction  vertical  to  its  coils,  it  will  be  seen  that 
this  canal  is  divided,  partly  by  bone  and  partly  by  membrane,  into  an  inferior  portion,  a 
superior  portion,  and  a  triangular  canal,  lying  between  the  two,  which  is  external.  The 
bony  septum  is  in  the  form  of  a  spiral  plate,  extending  from  the  central  column  (the 
modiolus)  into  the  cavity  of  the  cochlea,  about  half-way  to  its  external  wall,  and  termi- 
nating above  in  a  hook-shaped  extremity,  called  the  hamulus.  The  free  edge  of  this 
bony  lamina  is  thin  and  dense.  Near  the  central  column,  it  divides  into  two  plates, 
with  an  intermediate  spongy  structure  in  which  are  lodged  vessels  and  nerves.  The 
surface  of  the  bony  lamina  looking  toward  the  base  of  the  cochlea  is  marked  by  numer- 
ous regular,  transverse  ridges,  or  striae. 


FIG.  265.— Otolithsfrom  various  animals.     (Rudinger.) 

1,  from  tfce  goat ;  2,  from  the  herring  ;  3,  from  the  devil-fish  ;  4,  from  the  mackerel;  5,  from  the  flying-fish  ;  6,  from 
the  pike  ;  7,  from  the  carp ;  8,  from  the  ray ;  9,  from  the  shark  ;  10,  from  the  grouse. 

Attached  to  the  free  margin  of  the  bony  lamina,  is  a  membrane  (the  membrana  basi- 
laris)  which  extends  to  the  outer  wall  of  the  cochlea.  In  this  way,  the  canal  of  the  cochlea 
is  divided  into  two  portions,  one  above  and  the  other  below  the  septum.  The  portion 
below  begins  at 'the  fenestra  rotunda  and  is  called  the  scala  tympani.  The  portion 
above,  exclusive  of  the  triangular  canal  of  the  cochlea,  communicates  with  the  vestibule 
and  is  called  the  scala  vestibuli. 

Above  the  membrana  basilaris,  is  a  membrane  (the  limbus  laminae  spiralis)  the  external 
continuation  of  which  is  called  the  membrana  tectoria,  or  the  membrane  of  Corti.  Be- 
tween the  membrana  tectoria  and  the  membrana  basilaris,  is  the  organ  of  Corti.  The 
membrane  of  Eeissner  extends  from  the  inner  portion  of  the  limbus  upward  and  outward 
to  the  outer  wall  of  the  cochlea.  This  divides  the  portion  of  the  cochlea  situated  above 
the  scala  tympani  into  two  portions ;  an  internal  portion,  the  scala  vestibuli,  and  an 
external,  triangular  canal,  called  the  canalis  cochleas,  or  the  membranous  cochlea. 

In  the  anatomical  description  of  the  contents  of  the  bony  cochlea,  the  membranous 
parts  may  be  designated  as  follows : 

I.  The  portion  below  the  bony  and  membranous  septum,  called  the  scala  tympani. 
This  is  formed  by  the  periosteum  lining  the  corresponding  portion  of  the  cochlea  and  the 
under  surface  of  the  bony  lamina,  and  the  membrana  basilaris. 


PHYSIOLOGICAL   ANATOMY   OF  THE  INTERNAL  EAR. 


845 


2.  The  scala  vestibuli.     This  is  formed  by  the  periosteum  lining  the  corresponding 
portion  of  the  bony  cochlea  and  the  upper  surface  of  the  bony  septum  and  is  bounded 
externally  by  the  membrane  of  Reissner. 

3.  The  true  membranous  cochlea.     This  is  the  spiral  triangular  canal,  bounded  ex- 
ternally by  the  periosteum  of  the  corresponding  portion  of  the  wall  of  the  cochlea, 


FIG.  266.— Section  of the  first  turn  of 'the  spiral  canal  of  a  cat  newly-born— Section  of  the  cochlea  of  a  human 
fcctus  at  the  fourth  month.  From  a  photograph,  and  somewhat  reduced.  (Kiidinger.) 

Upper  figure  :  1,  2,  6,  lamina  spiralis ;  2,  lower  plate  ;  8, 4,  5,  5,  nervus  cochlearis  ;  7,  membrane  of  Keissner ;  8,  mem- 
brana tectoria;  9,  epithelium  ;  10, 11,  pillars  of  Corti;  12,  inner  hair-cells;  13,  outer  hair-cells ;  14, 16,  membrana 
basilaris;  15,  epithelium  in  the  sulcus  spiralis;  IT,'  18, 19,  ligamentum  spirale;  20,  spiral  canal  below  the  membrana 
basilaris. 

Lower  figure:  S  T,  8  T,  5,  5,  7,  7,  8,  8,  scala  tympani ;  S  V,  8  V,  9,  9,  scala  vestibuli;  1,  base  of  the  cochlea ;  2,  apex ; 
3,  4,  central  column;  10,  10,  10,  10,  ductus  cochlearis;  11,  branches  of  the  nervus  cochlearis;  12,12,12,  spiral 
ganglion;  13,  14,  limbus  laminse  spiralis;  15,  membrane  of  Eeissner;  16,  epithelium  ;  17,  outer  hair-cells;  18, 
epithelium  of  the  membrana  basilaris ;  19,  nervous  filaments ;  20,  union  of  the  membrana  basilaris  with  the 
ligamentum  spirale  ;  21,  epithelium  of  the  peripheral  wall  of  the  ductus  cochlearis;  22,  23,  membrana  tectoria ; 
24,  spiral  canal  below  the  membrana  basilaris. 

internally,  by  the  membrane  of  Reissner,  and,  on  the  other  side,  by  the  membrana  basi- 
laris.1 What  we  thus  call  the  membranous  cochlea  is  divided  by  the  limbus  lamina  spi- 
ralis and  the  membrana  tectoria  into  two  portions ;  a  triangular  canal  above,  which  is  the 

1  Some  anatomists  include  this  canal  in  the  scala  vestibuli.    For  the  sake  of  clearness,  we  describe  it  by  itself,  as  a 
distinct  canal. 


846  SPECIAL  SENSES. 

larger,  and  a  quadrilateral  canal  below,  between  the  limbus  and  membrana  tectoria  and 
the  membrana  basilaris.  The  quadrilateral  canal  contains  the  organ  of  Corti  and  various 
structures  of  a  very  complicated  character.  The  relations  of  these  divisions  of  the  cochlea, 
a  knowledge  of  which  is  essential  to  the  comprehension  of  the  physiological  anatomy  of 
this  portion  of  the  auditory  apparatus,  are  shown  in  Fig.  266. 

The  membranous  cochlea,  as  described  above,  follows  the  spiral  course  of  the  cochlea, 
terminates  superiorly  in  a  blind,  pointed  extremity  at  the  cupola,  beyond  the  hamulus, 
and  is  connected  below  with  the  saccule  of  the  vestibule  by  the  canalis  reuniens.  The 
relations  of  the  different  portions  of  the  membranous  cochlea  to  each  other  and  to  the 
scalae  of  the  cochlea  are  shown  in  Fig.  266. 

We  shall  now  describe,  as  possessing  the  most  physiological  interest,  the  liquids  of  the 
labyrinth,  the  distribution  and  connections  of  the  nerves  in  the  labyrinth,  and  the  organ 
of  Corti. 

Liquids  of  the  Labyrinth. — The  labyrinth  contains  a  certain  quantity  of  a  clear, 
watery  liquid,  called  the  humor  of  Cotugno,  or  of  Valsalva.  A  portion  of  this  liquid 
surrounds  the  membranous  sacs  of  the  vestibule,  the  semicircular  canals,  and  the  mem- 
branous cochlea,  and  this  is  known  as  the  perilymph  of  Breschet.  Another  portion  of 
the  liquid  fills  the  membranous  labyrinth.  This  is  sometimes  called  the  humor  of  Scarpa, 
but  it  is  known  more  generally  as  the  endolymph  of  Breschet.  The  perilymph  occupies 
about  one-third  of  the  cavity  of  the  vestibule,  of  the  semicircular  canals,  and  of  both  scales 
of  the  cochlea.  Both  this  liquid  and  the  endolymph  are  clear  and  watery,  becoming 
somewhat  opalescent  on  the  addition  of  alcohol.  The  perilymph  seems  to  be  secreted 
by  the  periosteum  lining  the  osseous  labyrinth.  As  far  as  we  know,  the  uses  of  the 
liquid  of  the  internal  ear  are  to  sustain  the  delicate  structures  contained  in  this  portion 
of  the  auditory  apparatus  and  to  conduct  sonorous  vibrations  to  the  terminal  filaments 
of  the  auditory  nerves  and  the  parts  with  which  they  are  connected. 

Distribution  of  the  Nerves  in  the  Labyrinth. — As  the  auditory  nerves  enter  the  inter- 
nal auditory  meatus,  they  divide  into  an  anterior,  or  cochlear,  and  a  posterior,  or  vestib- 
ular  branch.  The  vestibular  branch  divides  into  three  smaller  branches,  a  superior  and 
anterior,  a  middle,  and  a  posterior  branch.  The  superior  and  anterior  branch,  the  largest 
of  the  three,  is  distributed  to  the  utricle,  the  superior  semicircular  canal,  and  the  external 
semicircular  canal.  The  middle  branch  is  distributed  to  the  saccule.  The  posterior 
branch  passes  to  the  posterior  semicircular  canal.  The  nerves  distributed  to  the  utricle 
and  saccule  penetrate  at  the  points  occupied  by  the  otoliths,  and  the  nerves  going  to  the 
semicircular  canals  pass  to  the  ampulla),  which  also  contain  otoliths.  (See  Fig.  264.)  In 
each  ampulla,  at  the  point  where  the  nerve  enters,  is  a  transverse  fold,  projecting  into 
the  canal  and  occupying  about  one-third  of  its  circumference,  called  the  septum  trans- 
versum. 

The  nerves  terminate  in  essentially  the  same  way  in  the  sacs  of  the  vestibule  and  the 
ampullae  of  the  semicircular  canals.  At  the  points  where  the  nerves  enter,  in  addition 
to  the  otoliths,  are  cells  of  cylindrical  epithelium,  of  various  forms,  which  pass  gradually 
into  the  general  pavement-epithelium  of  the  cavities.  In  addition  to  these  cells,  are  fusi- 
form, nucleated  bodies,  the  free  ends  of  which  are  provided  with  hair-like  processes, 
called  fila  acustica.  These  are  about  ¥^  of  an  inch  in  length  and  are  distributed  in 
quite  a  regular  manner  around  the  otoliths.  The  nerves  form  an  anastomosing  plexus 
beneath  the  epithelium,  and  they  probably  terminate  in  the  fusiform  bodies  just  described 
as  presenting  the  fila  acustica  at  their  free  extremities.  In  the  sacs  of  the  vestibule 
and  in  the  semicircular  canals,  nerves  exist  only  in  the  macula  acustica  and  the 
ampullae. 

The  cochlear  division  of  the  auditory  nerve  breaks  up  into  numerous  small  branches, 
which  pass  through  foramina  at  the  base  of  the  cochlea,  in  what  is  called  the  tractus 


PHYSIOLOGICAL   ANATOMY   OF  THE   INTERNAL  EAR. 


847 


spiralis  foraminulentus.  These  follow  the  axis  of  the  cochlea  and  pass  in  their  course 
toward  the  apex,  between  the  plates  of  the  bony  spiral  lamina.  Between  these  plates  of 
bone,  the  dark-bordered  nerve- 
fibres  pass  each  one  through  a 
bipolar  cell,  these  cells  together 
forming  a  spiral  ganglion,  known 
as  the  ganglion  of  Corti.  Beyond 
this  ganglion,  the  nerves  form  an 
anastomosing  plexus  and  finally 
enter  the  quadrilateral  canal,  or 
the  canal  of  Corti.  As  they  pass 
into  this  canal,  they  suddenly  be- 
come pale  and  exceedingly  fine, 
and  probably  they  are  connected 
finally  with  the  organ  of  Corti, 
although  their  exact  mode  of  ter- 
mination has  not  yet  been  deter- 
mined. The  course  of  the  nerve- 
fibres  to  their  distribution  in  the 
cochlea  is  shown  in  Fig.  267. 


FIG.  267. — Distribution  of  the  cochlear  nerve  in  the  spiral  lamina 
of  the  cochlea  (the  cochlea  is  from  the  right  side  and  is  seen 
from  its  antero-inferior  part).  (Sappey.) 

1,  trunk  of  the  cochlear  nerve  ;  2,  2,  2,  membranous  zone  of  the  spiral 
lamina ;  8,  3,  3,  terminal  expansion  of  the  cochlear  nerve  exposed  in 
its  whole  extent  by  the  removal  of  the  superior  plate  of  the  lamina 
spiralis ;  4,  orifice  of  communication  of  the  scala  tympani  with  the 
scala  vestibuli. 


Organ  of  Corti.— Qi  all  the 
parts  contained  within  the  bony 
labyrinth,  the  organ  of  Corti  pos- 
sesses the  greatest  physiological  interest ;  for  it  is  this  organ  which  is  supposed  to  receive 
the  sonorous  vibrations  and  communicate  them  directly  to  the  terminal  filaments  of  the 
auditory  nerves.  Although  this  view  has  not  received  the  support  of  actual  demonstra- 
tion, it  affords  an  explanation,  more  or  less  plausible,  of  the  mechanism  of  audition,  car- 
ried to  the  point  of  the  actual  reception  of  impressions  by  the  nerves.  In  view  of  this, 
it  is  important  to  have  a  clear  comprehension  of  the  arrangement  of  those  parts  which 
are  supposed  to  receive  the  sonorous  vibrations ;  and  we  shall,  for  the  sake  of  simplicity, 
eliminate  from  our  description  certain  accessory  structures,  the  functions  of  which  are 
obscure. 

In  the  quadrilateral  canal,  bathed  in  the  endolymph,  throughout  its  entire  spiral 
course,  is  an  arrangement  of  pillars,  or  rods,  regular,  like  the  strings  of  a  harp  in  minia- 
ture, which  are  supposed  to  repeat  the  varied  vibrations  of  sound.  These  are  the  pillars 
of  Corti. 

The  structures  contained  in  the  quadrilateral  canal  are  so  delicate  that  their  investi- 
gation presents  great  difficulty ;  but  the  arrangement  of  the  pillars,  or  rods  of  Corti  is 
pretty  well  understood.  These  pillars  are  external  and  internal,  with  their  bases  attached 
to  the  basilar  membrane,  and  their  summits  articulated  above,  so  as  to  form  a  regular, 
spiral  arcade,  enclosing  a  triangular  space,  which  is  bounded  below  by  the  basilar  mem- 
brane. The  number  of  the  elements  of  the  organ  of  Corti  is  estimated  at  about  3,500,  for 
the  outer,  and  5,200,  for  the  inner  rods,  the  proportion  of  inner  rods  to  the  outer  being 
about  three  to  two.  The  relations  of  these  structures  to  the  membranous  labyrinth  are 
seen  in  Fig.  266.  The  external  pillar  is  longer,  more  delicate  and  rounded,  and  is  also 
attached  to  the  basilar  membrane.  The  form  of  the  pillars  is  more  exactly  shown  in 
Figs.  268  and  269,  the  latter  figure,  however,  exhibiting  other  structures  which  enter 
into  the  constitution  of  the  organ  of  Corti.  It  will  be  remarked  that  a  small  nucleated 
body  is  attached  to  the  base  of  each  pillar.  At  the  summit,  where  the  internal  and  the 
external  pillars  are  joined  together,  is  a  delicate  prolongation,  directed  outward,  which 
is  attached  to  the  covering  of  the  quadrilateral  canal. 

The  above  description  comprises  about  all  that  is  definitely  known  of  the  arrangement 


848 


SPECIAL  SENSES. 


of  the  pillars,  or  rods  of  Corti.  They  are  nearly  homogeneous,  except  when  treated  with 
reagents,  and  are  said  to  be  of  about  the  consistence  of  cartilage.  They  are  closely  set 
together,  with  very  narrow  spaces  between  them,  and  it  is  difficult  to  see  how  they  can 
be  stretched  to  any  considerable  degree  of  tension.  The  arch  is  longer  at  the  summit 


FIG.  268. —  The  two  pillars  of  the  organ  of  Corti.    (Sappey.) 

A,  external  pillar  of  the  organ  of  Corti :  1,  body,  or  middle  portion ;  2,  posterior  extremity,  or  base ;  3,  cell  on  its  in- 

ternal side ;  4,  anterior  extremity ;  5,  convex  surface  by  which  it  is  joined  to  the  internal  pillar ;  6,  prolongation 
of  this  extremity. 

B,  internal  pillar  of  the  organ  of  Corti :  1,  body,  or  middle  portion ;  2,  posterior  extremity ;  3,  cell  on  its  external  side; 

4,  anterior  extremity ;  5,  concave  surface  by  which  it  is  joined  to  the  external  pillar ;  6,  prolongation,  lying  above 
the  corresponding  prolongation  of  the  external  pillar. 

€,  the  two  pillars  of  the  organ  of  Corti,  united  by  their  anterior  extremity,  and  forming  an  arcade,  the  concavity  of 
which  presents  outward :  1,  1,  body,  or  middle  portion  of  the  pillars ;  2,  2,  posterior  extremities ;  3,  3,  cells  at- 
tached to  the  posterior  extremities;  4,  4,  anterior  extremities  joined  together;  5,  terminal  prolongation  of  this 
extremity. 

than  at  the  base  of  the  cochlea,  the  longest  rods,  at  the  summit,  measuring  about  ^^  of 
an  inch,  and  the  shortest,  at  the  base,  about  -^  of  an  inch.  As  we  before  remarked,  the 
relations  between  the  pillars  and  the  terminal  filaments  of  the  auditory  nerves  are  not 
definitely  settled. 

In  addition  to  the  pillars  just  described,  various  cellular  elements  enter  into  the  struct- 
ure of  the  organ  of  Corti.     The  most  important  of  these  are  the  inner  and  the  outer  hair- 


Fro.  269.—  Vertical  section  of  the  organ  of  Corti  of  the  dog ;  magnified  800  diameters.    (Waldeyer.) 


cpn- 
c?,  spiral 
I,  head- 


r>iafa    Wu    •  '  •' '    '  uuuulc  «*  nerves ,  j/.  epimeuuui :  z, inner  nair-cen,  wun  its  oasuar  process,  K,  v. 

ontPr  i T-innen  pill?l;  m'  union  of  the  two  Pillars  ?  ""  base  of  the  inner  pillar;  o,  base  of  the  outer  pillar; 
««m,i«  .nair"cells'  Wlth  traces  of  the  cilia;  t,  bases  of  two  other  hair-cells;  *.  Hensen's  prop-cell;  «.,  1 
ins,  w,  nerve-fibre  passing  to  the  first  hair-cell,  p. 

cells.  The  inner  hair-cells  are  arranged  in  a  single  row,  and  the  outer  hair-cells,  in  three 
rows.  Nothing  definite  is  known  of  the  function  of  these  cells.  The  relations  of  these 
parts  are  shown  in  Fig.  269,  which  is  rather  complex,  but,  on  careful  study,  gives  a  good 


FUNCTIONS  OF  DIFFERENT  PARTS  OF  THE  INTERNAL  EAR.     849 

idea  of  the  arrangement  of  all  of  the  structures  which  compose  the  organ  of  Corti.  It  is 
supposed  by  some  anatomists  that  the  filaments  of  the  auditory  nerves  terminate  in  the 
cells  above  described ;  but  this  point  is  not  definitively  settled. 

Functions  of  Different  Parts  of  the  Internal  Ear. 

The  precise  function  of  the  different  parts  which  are  found  in  the  internal  ear  is 
obscure,  notwithstanding  the  careful  researches  that  have  been  made  into  the  anatomy 
and  the  physiology  of  the  labyrinth.  There  are  several  points,  however,  bearing  upon 
the  physiology  of  this  portion  of  the  auditory  apparatus,  concerning  which  there  can  be 
no  doubt : 

First,  it  is  certain  that  impressions  of  sound  are  received  by  the  terminal  filaments  of 
the  auditory  nerves  and  by  these  nerves  are  conveyed  to  the  brain. 

Second,  the  functions  of  the  parts  composing  the  external  and  the  middle  ear  are 
simply  accessory.  The  sonorous  waves  are  collected  by  the  pavilion  and  are  conveyed 
by  the  external  meatus  to  the  middle  ear ;  the  membrana  tympani  vibrates  under  their 
influence ;  and  they  are  thus  collected,  repeated,  and  transmitted  to  the  internal  ear, 
under  the  most  favorable  conditions  for  producing  a  proper  impression  upon  the  auditory 
nerves. 

In  view  of  these  facts,  we  must  look  to  the  functions  of  semicircular  canals  and  the 
cochlea,  for  an  elucidation  of  the  problem  of  the  mechanism  of  the  final  process  of  audi- 
tion ;  and,  in  doing  this,  we  come  at  once  to  the  question  of  the  relative  importance  of 
different  divisions  of  the  internal  ear. 

Functions  of  the  Semicircular  Canals.— In  a  memoir  presented  to  the  French  Acad- 
emy of  Sciences,  in  1824,  Flourens  detailed  a  number  of  experiments  upon  pigeons  and  rab- 
bits, in  which  he  destroyed  different  portions  of  the  internal  ear.  In  these  experiments, 
the  results  of  which  were  very  definite,  it  was  shown  that  destruction  of  the  semicircular 
canals  had  apparently  no  effect  upon  the  sense  of  hearing,  while  destruction  of  the  coch- 
lea upon  both  sides  produced  complete  deafness.  In  addition,  it  was  observed  that 
destruction  of  the  semicircular  canals  on  both  sides  was  followed  by  remarkable  dis- 
turbances in  equilibration.  The  animals  could  maintain  the  standing  position,  but,  as 
soon  as  they  made  any  movements,  u  the  head  commenced  to  be  agitated ;  and  this 
agitation  increasing  with  the  movements  of  the  body,  walking  and  all  regular  move- 
ments finally  became  impossible,  in  nearly  the  same  way  as  when  equilibrium  and  stabil- 
ity of  movements  are  lost  after  turning  several  times  or  violently  shaking  the  head.1' 
These  observations  of  Flourens,  at  least  as  far  as  regards  the  influence  of  the  semicircular 
canals  upon  equilibration,  have  been  confirmed  by  Goltz  and  are  sustained  by  observa- 
tions upon  the  human  subject  in  the  condition  known  as  Meniere's  disease.  In  some  more 
recent  experiments,  however,  Boettcher  assumes  to  have  demonstrated  that  the  semi- 
circular canals  have  nothing  to  do  with  equilibration ;  but  all  of  his  observations  were 
made  upon  frogs,  in  which  deficiency  of  equilibration  and  of  hearing  would  be  very  diffi- 
cult to  determine.  As  far  as  we  can  judge  from  experimental  data,  it  does  not  seem 
probable  that  the  nerves  directly  concerned  in  audition  are  distributed  to  any  consid- 
erable extent  in  the  semicircular  canals.  Indeed,  the  function  of  these  parts  is  exceed- 
ingly obscure ;  for  we  can  hardly  admit,  upon  purely  anatomical  grounds,  that  they  are 
concerned  in  the  discrimination  of  the  direction  of  sonorous  vibrations,  an  idea  which 
has  been  advanced  by  some  physiologists. 

Functions  of  the  Parts  contained  in  the  Cochlea.— There  can  be  no  doubt  with  regard 
to  the  capital  point  in  the  physiology  of  the  cochlea ;  namely,  that  those  branches  of  the 
auditory  nerve  which  are  essential  to  the  sense  of  hearing  and  which  receive  the  impres- 
sions of  sound  are  distributed  mainly  in  the  cochlea.  When  we  come  to  analyze  sonorous 
impressions,  we  find  that  they  possess  various  attributes,  such  as  intensity,  quality,  and 
54 


85o  SPECIAL   SENSES. 

pitch,  which  have  been  discussed  rather  fully  under  the  head  of  the  physics  of  sound. 
As  far  as  the  terminal  filaments  of  the  auditory  nerve  are  concerned,  it  is  evident  that 
the  intensity  of  sound  is  appreciated  in  proportion  to  the  power  of  the  impression  made 
upon  these  nerves,  and  this  point  does  not  demand  elaborate  discussion.  With  regard  to 
quality  of  sound,  we  have  seen  that  this  is  due  to  the  form  of  sonorous  vibrations,  and 
that  most  musical  tones  are  compound,  their  quality  depending  largely  upon  the  relative 
power  of  the  harmonics,  partial  tones,  etc.  We  have  also  seen  that  consonating  bodies 
repeat  by  influence,  not  only  the  actual  pitch  of  tones,  but  their  quality.  If  there  be  in 
the  cochlea  an  anatomical  arrangement  of  rods  or  fibres  by  which  the  sonorous  vibra- 
tions, conveyed  to  the  ear  by  the  atmosphere,  are  repeated,  there  is  reason  to  believe 
that  the  quality,  as  well  as  the  pitch,  is  reproduced.  Narrowing  down  the  question, 
then,  to  its  most  interesting  and  important  point,  viz.,  the  appreciation  of  differences  in 
the  pitch  of  musical  tones,  we  inquire  whether  there  be  in  the  cochlea  any  arrangement 
by  which  the  pitch  can  be  repeated.  This  inquiry  can  only  be  answered  by  a  study  of 
the  anatomical  arrangement  of  the  structures  connected  with  the  terminal  filaments  of 
the  nerves,  and  by  the  application  of  physical  laws. 

The  arrangement  of  the  rods  which  enter  into  the  structure  of  the  organ  of  Corti  has 
afforded  a  theoretical  explanation  of  the  final  mechanism  of  the  appreciation  of  pitch. 
Until  we  come  to  the  internal  ear,  the  action  of  different  portions  of  the  auditory  appa- 
ratus is  simply  to  conduct  and  repeat  sonorous  vibrations ;  and  the  sole  function  of  these 
accessory  parts,  aside  from  the  protection  of  the  organs,  is  to  convey  the  vibrations  to 
the  terminal  nervous  filaments.  Whatever  be  the  functions  of  the  membrana  tympani  in 
repeating  sounds  by  influence,  it  is  certain  that  this  membrane  possesses  no  true  auditory 
nerves,  and  that  the  auditory  nerves  only  are  capable  of  receiving  impressions  of  sound. 
Thus,  hearing,  and  even  the  appreciation  of  pitch,  is  not  necessarily  lost  after  destruction 
of  the  membrana  tympani;  and,  if  sonorous  vibrations  reach  the  auditory  nerves,  they 
will  be  appreciated  and  appreciated  correctly.  With  this  point  clearly  understood,  we 
are  prepared  to  study  the  probable  functions  of  the  organ  of  Corti. 

When  we  consider  the  organ  of  Corti,  with  its  eight  thousand  or  more  rods  of  differ- 
ent lengths  arranged  with  a  certain  degree  of  regularity,  a  number  more  than  sufficient 
to  represent  all  the  tones  of  the  musical  scale,  we  are  not  surprised  that  eminent  physi- 
ologists regard  them  as  capable  of  repeating  all  the  shades  of  tone  heard  in  music. 
Helmholtz  formularizes  this  idea  in  the  theory  that  tones  conveyed  to  the  cochlea  throw 
into  vibration  those  elements  of  the  organ  of  Corti  which  are  tuned,  so  to  speak,  in  unison 
with  them.  According  to  this  hypothesis,  the  rods  of  Corti  constitute  a  harp  of  several 
thousand  strings,  played  upon,  as  it  were,  by  the  sonorous  vibrations. 

It  would  be  difficult  to  imagine  any  thing  more  satisfactory  and  simple  than  such  an 
hypothesis  as  we  have  just  quoted.  Attention  and  education  enable  persons  endowed 
with  what  is  called  a  musical  ear  to  discriminate  between  different  tones  with  great 
accuracy.  Experiments  have  shown  that  the  situation  of  the  actual  appreciation  of 
tones  may  be  restricted  to  the  cochlea ;  and,  in  the  cochlea,  the  only  anatomical  arrange- 
ment, as  far  as  we  know,  which  points  toward  an  appreciation  of  the  pitch  of  different 
tones  is  that  of  the  rods  x>f  Corti.  Still,  it  must  be  remembered  that  the  cochlea  is  so 
situated  as  to  be  removed  from  the  possibility  of  experimental  investigation  to  prove  the 
theory;  and  we  must  carefully  study  the  anatomical  arrangement  of  the  parts  and  the 
possible  application  of  physical  laws  to  the  supposed  vibration  of  the  rods. 

Viewing  the  question  from  its  anatomical  aspect,  it  is  by  no  means  certain  that  the 
rods  of  Corti  are  so  attached  and  stretched  that  they  are  capable  of  separate  and  indi- 
vidual vibrations.  It  has  not  been  demonstrated  that  certain  of  these  rods  vibrate  under 
the  influence  of  certain  tones  or  that  they  are  tuned  in  accord  with  certain  tones.  Hensen, 
who  has  written  elaborately  upon  the  very  question  under  consideration,  denies  the  accu- 
racy of  the  theory  of  Helmholtz,  basing  his  opinion  upon  the  anatomical  arrangement  of 
the  rods  of  Corti,  and  he  assumes  that  it  is  a  physical  impossibility  for  the  different  rods 


SUMMARY   OF  THE  MECHANISM  OF  AUDITIOK  851 

to  vibrate  individually,  and  that  it  is  not  certain  that  they  are  tuned  in  accord  with  differ- 
ent tones.  Hensen  makes,  upon  this  point,  the  following  statement : 

41  It  is  now  my  conviction,  that  by  the  hypothesis  '  more  and  more  corroborated '  that 
the  fibres  of  Corti  constitute  the  organ  of  the  labyrinth  tuned  to  the  appreciation  of 
tones,  our  comprehension  and  the  investigation  of  the  internal  ear  have  taken  a  false 
direction. 

"  I  assert,  next,  that  the  rods  of  Corti  cannot  play  the  important  part  in  the  appreci- 
tion  of  tones,  whicli  has  been  attributed  to  them  in  the  hypothesis  of  Helmholtz." 

It  is  pretty  evident  that,  although  the  theory  of  Helmholtz  is  undoubtedly  the  only 
one  affording  any  reasonable  explanation  of  the  appreciation  of  tones,  it  lacks  positive 
anatomical  confirmation.  And,  farthermore,  we  do  not  even  know  the  anatomical  con- 
nections between  the  rods  of  Corti  and  the  filaments  of  the  auditory  nerves. 

In  view  of  the  considerations  just  given,  we  have  simply  recited  the  theory  of  Du 
Yerney,  Le  Cat,  and  Helmholtz,  as  one  which  may  or  may  not  be  sustained  hereafter  by 
more  exact  researches ;  but  at  present  it  must  be  acknowledged  that  there  is  no  more 
satisfactory  explanation  of  the  mechanism  of  the  final  appreciation  of  musical  tones. 

Summary  of  the  Mechanism  of  Audition. 

The  waves  of  sound  are  simply  collected  by  the  pavilion  of  the  ear  and  are  conveyed, 
through  the  external  meatus,  to  the  membrana  tympani.  The  membrana  tympani,  a 
delicate,  rounded,  concave  membrane,  receives  these  waves  and  is  thrown  into  vibration. 

The  arrangement  of  the  bones  and  muscles  of  the  middle  ear  admits  of  variations  in 
the  tension  of  the  membrana  tympani.  By  increasing  the  tension  of  this  membrane,  the 
ear  may  be  rendered  insensible  to  grave  sounds,  while  high-pitched  sounds  become  more 
intense ;  and,  in  cases  of  voluntary  tension,  the  limit  of  perception  of  high  tones  may  be 
greatly  extended.  The  membrana  tympani  obeys  the  laws  of  consonance  and  vibrates 
strongly  under  the  influence  of  sounds  in  unison  or  in  harmony  with  its  fundamental 
tone,  returning,  in  this  way,  not  only  the  pitch,  but  the  quality  of  tones  and  combina- 
tions of  tones  in  harmony.  Destruction  of  the  membrane  does  not  necessarily  of  itself 
destroy  hearing,  or  even  the  appreciation  of  tones,  for  the  impressions  may  be  conduct- 
ed to  the  cochlea  by  the  chain  of  ossicles. 

The  arrangement  of  the  ossicles  and  muscles  of  the  middle  ear  is  such  that  contrac- 
tion of  the  tensor  tympani  renders  the  articulations  firm,  tightens  the  little  ligaments, 
and  presses  the  stapes  against  the  liquid  of  the  labyrinth,  so  that  the  chain  resembles,  in 
its  action,  a  solid  and  continuous  bony  rod.  By  this  arrangement,  the  sonorous  vibra- 
tions are  conducted  to  the  labyrinth  with  very  little  loss  of  intensity. 

The  cavity  of  the  tympanum  is  filled  with  air,  communicates  with  the  mastoid  cells, 
and  with  the  pharynx  by  means  of  the  Eustachian  tube ;  and,  by  this  means,  the  press- 
ure of  air  in  its  interior  is  regulated.  The  labyrinth,  consisting  of  the  vestibule,  semi- 
circular canals,  and  cochlea,  is  filled  with  liquid,  and  the  different  cavities  communicate 
with  each  other.  The  vibrations,  repeated  by  the  membrana  tympani,  are  conveyed  by 
the  chain  of  bones  to  the  liquid  of  the  labyrinth,  and  by  it  to  the  terminal  filaments  of 
the  auditory  nerves. 

The  vestibule  and  semicircular  canals  seem  to  possess  much  less  importance  in  the 
appreciation  of  sound  than  the  cochlea.  In  the  cochlea,  throughout  the  entire  extent  of 
the  spiral  canal,  is  the  organ  of  Corti,  presenting,  among  other  structures,  about  8, TOO 
rods,  varying  in  length,  called  the  rods  of  Corti.  But  little  is  known  of  the  anatomical 
relations  between  the  auditory  nerves  and  the  organ  of  Corti ;  still,  it  is  thought,  as  a 
matter  of  pure  theory,  that  the  rods  of  Corti  are  tuned  in  unison  with  different  tones, 
that  they  repeat  the  tones  conveyed  to  the  cochlea,  and  that  we  are  thus  enabled  to  dis- 
tinguish the  different  tones  in  music. 

We  have  no  very  definite  knowledge  of  the  functions  of  the  cells  of  the  organ  of  Cor- 


852  GENERATION. 

ti  of  the  otoliths,and  of  various  other  structures  in  the  auditory  apparatus.  Soun,!* 
may  be  conducted  to  the  auditory  nerves  through  the  bones  of  the  head  and  the  Eus- 
tachian  tube,  as  is  shown  by  the  simple  and  familiar  apenment  of  placmg  a  tunmg-fork 
in  vibration  in  contact  with  the  head  or  between  the  teeth. 


CHAPTER    XXVI. 

ORGANS  AND  ELEMENTS  OF  GENERATION. 

General  considerations— Sexual  generation— Spontaneous  generation  (so  called)— Female  organs  of  generation— Gen- 
eral arrangement  of  the  female  organs— External  and  internal  organs— The  ovaries— Development  of  the  Graa- 
flan  follicles— The  parovarium— The  uterus— The  Fallopian  tubes— Structure  of  the  ovum— Vitelline  membrane— 
Vitellus— Germinal  vesicle  and  germinal  spot— Discharge  of  the  ovum— Puberty  and  menstruation— Descrip- 
tion of  a  menstrual  period— Characters  of  the  menstrual  flow— Changes  in  the  uterine  mucous  membrane  during 
menstruation— Changes  in  the  Graaflan  follicle  after  its  rupture  (corpus  luteum)— The  testicles— Tunica  vagi- 

nalis Tunica  albuginea— Tunica  vasculosa — Seminiferous  tubes — Epididymis— Vas  deferens — Yesicul*  seminales 

—Prostate— Glands  of  the  urethra— Semen — Secretions  mixed  with  the  products  of  the  testicles—  Sperrnatozoids — 
Development  of  the  spermatozoids — Seminal  fluid  in  advanced  age. 

A  REVIEW  of  the  physiological  processes  which  we  have  thus  far  studied  shows  that 
the  functions  of  the  perfected  organism  are  divided  into  two  great  classes: 

The  first  class  of  functions  may  be  grouped  under  the  general  head  of  nutrition, 
taken  in  its  widest  sense.  Nutrition  is  common  to  animal  and  vegetable  life,  and  this  is 
sometimes  called  a  vegetative  process. 

The  study  of  nutrition  involves  the  following  considerations :  First,  the  blood,  which 
is  the  great  nutritive  fluid,  contained  in  the  innumerable  vessels  which  penetrate  nearly 
all  of  the  tissues  and  organs  of  the  body  and  are  connected  with  the  system  of  lymphatic 
and  lacteal  vessels.  Second,  the  process  by  which  the  blood  is  circulated,  sent  by  the 
heart  to  all  parts  in  the  capillary  system,  used  by  the  tissues  for  their  nutrition,  then  los- 
ing oxygen,  gaining  carbonic  acid,  and  being  returned  by  the  veins.  Third,  respiration, 
the  blood  being  freed  from  carbonic  acid  and  getting  a  new  supply  of  oxygen  in  the 
lungs,  by  which  it  is  rendered  capable  of  again  circulating  through  the  general  system. 
Fourth,  as  the  blood,  in  its  passage  through  the  capillary  vessels,  not  only  loses  oxygen, 
but  is  more  or  less  impoverished  by  the  assimilation  of  its  nutritive  constituents  by  the 
tissues,  it  is  necessary  to  keep  it  up  to  the  proper  nutritive  standard  ;  and  this  is  effected 
by  alimentation,  digestion,  and  absorption.  Fifth,  we  have  certain  secretions,  necessary 
to  the  above-mentioned  processes  ;  and  the  products  of  physiological  waste  or  decay  of 
the  tissues  are  removed  by  excretion.  Sixth,  the  processes  of  vegetative  life  involve  the 
production  of  heat  and  are  regulated  and  coordinated  by  the  nervous  system. 

The  second  class  of  functions  relates  to  animal  life,  and  these  are  called  the  functions 
of  relation.  In  this  class,  are  included  movements,  voice  and  speech,  the  functions  of 
the  cerebro-spinal  nervous  system,  and  the  operation  of  the  special  senses. 

In  studying  the  processes  of  nutrition  of  the  general  system,  we  observe  that  certain 

tituents  of  the  organism,  which  contain  nitrogen  and  are  exclusively  of  organic  ori- 

the  property,  in  the  living  body,  of  self-regeneration ;  i.  e.,  when  these  parts 

t  in  contact  with  nutritive  matter  in  proper  form,  as  it  exists  in  the  blood, 

is  appropriated  and  transformed  into  the  substance  of  each  tissue  and  organ. 

8  way  that,  during  adult  life,  the  different  parts  of  the  organism  are  maintained 

y  uniform  condition.     In  the  absence  of  an  exact  knowledge  of  the  cause 

these  assimilative  processes,  we  call  them  vital;  which  term  is  applied  to 

it  property  of  living,  organized  parts.     Physiologists  have  ascertained  that  each 

in  of  the  body  possesses  one  or  more  characteristic  organic  nitrogenized 

uents  which  are  possessed  of  this  so-called  vital  property.     But,  at  the  same  time 


GENERAL  CONSIDERATIONS.  853 

it  is  always  observed  that  the  organic  nitrogenized  constituents  of  the  organism  are 
combined  most  intimately  with  a  tolerably  definite  quantity  of  inorganic  matter,  which 
latter  regulates,  to  a  certain  extent,  nutritive  processes,  and  constitutes,  also,  an  impor- 
tant component  part  of  the  tissues.  It  is  observed,  in  addition,  that,  during  early  life, 
when  the  system  is  proceeding  toward  its  perfect  development  by  growth,  the  proportion 
of  inorganic  matter  is  less  than  in  the  adult,  and  that  the  process  of  nutrition  is  then  at 
its  maximum  of  activity,  the  regeneration  being  superior  to  the  waste.  During  the  adult 
period,  repair  and  physiological  decay  are  nearly  balanced  ;  but,  in  the  decline  of  life, 
there  seems  to  be  a  gradual  accumulation  of  inorganic  matter,  and  this  continues  until 
the  so-called  vital  properties  of  some  important  organ  become  so  feeble  that  its  func- 
tions cease,  and  we  have  physiological  death.  This  regeneration  of  the  tissues  is  a  neces- 
sary consequence  of  the  constant  waste  or  decay  of  every  part  of  the  organism,  resulting 
in  a  change  of  constituents  into  effete  matters,  which  are  discharged ;  there  being,  during 
life,  a  constant  waste  and  repair.  If  no  new  matter  be  introduced  as  food,  the  system 
wastes  to  a  point  which  is  incompatible  with  life,  and  death  results  from  inanition. 

With  some  very  insignificant  exceptions,  we  cannot  conceive  that  living  tissues  exist 
in  an  absolutely  stationary  condition.  The  organized  parts  of  the  body  are  undergoing 
constant  molecular  destruction  and  repair.  Again,  the  so-called  vital  properties  of  the 
tissues,  which  involve  self-regeneration,  seem  to  have  certain  limits.  We  cannot  intro- 
duce nutritive  matter  in  sufficient  quantity  to  produce  growth  beyond  a  certain  point, 
although  we  may  limit  development  and  growth  by  deficient  supply.  When  we  ask  why 
the  organs  develop  with  fixed  regularity,  why,  when  an  occasional  excess  of  nutritive 
matter  is  presented,  this  excess  is  not  used,  we  must  confess  our  ignorance  or  say  that 
the  parts  are  endowed  with  vital  properties.  We  also  find,  to  come  to  the  most  impor- 
tant point  of  this  discussion,  that,  however  carefully  we  may  supply  nutritive  matter  to 
the  system,  we  cannot  arrest  the  gradual  enfeeblement  of  the  assimilative  powers  of  the 
tissues,  which  occurs  in  old  age.  In  short,  as  we  cannot  conceive  of  a  living  tissue 
without  decay  and  regeneration  of  its  substance,  so  it  is  impossible  for  the  organism  to 
last  for  an  indefinite  period.  A  necessary,  invariable,  and  inevitable  consequence  of 
individual  life  is  death.  The  constant  molecular  death — if  we  can  apply  this  term  to  the 
transformation  of  living  into  effete  matter — of  every  tissue  of  the  body  is  always,  in  the 
end,  superior  to  the  power  of  repair.  There  seems,  indeed,  to  be  an  antagonism  of  pro- 
cesses during  life ;  a  view  which  was  so  fully  adopted  by  Bichat,  that  it  led  to  his  cele- 
brated definition  of  life  ;  "  the  ensemble  of  functions  which  resist  death.1'  Although  death 
is  thus  inevitable,  and,  in  the  circulation  of  material  in  Nature,  the  organic  parts  of  the 
body  become  changed  in  the  arrangement  of  their  ultimate  elements  and  appropriated  by 
the  vegetable  kingdom,  during  adult  life,  certain  anatomical  elements,  male  and  female,  are 
formed  in  the  human  subject,  which,  when  they  come  together  under  proper  conditions, 
develop  into  new  beings,  which  pass  through  the  same  course  of  existence  as  the  parents. 
By  the  concourse  of  two  beings,  new  organisms  come  into  life,  which  perpetuate  exist- 
ence and  preserve  species.  The  function  by  which  this  is  accomplished  is  called  genera- 
tion, or  reproduction. 

In  o"ur  study  of  generation,  we  shall  confine  ourselves  as  closely  as  possible  to  the 
process  as  it  takes  place  in  the  human  subject.  There  are  many  considerations  of  great 
interest  connected  with  the  generation  of  the  lowest  orders  of  animal  organization, 
among  the  most  prominent  of  which  is  the  question  of  so-called  spontaneous  generation. 
While  this  may  have  a  certain  bearing  upon  the  genesis  of  anatomical  elements,  it  has 
little  or  nothing  to  do  with  the  development  of  the  fecundated  human  ovum,  and  will, 
therefore,  receive  little  more  than  an  incidental  consideration.  For  similar  reasons,  we 
shall  not  engage  in  a  discussion  of  the  development-theory  applied  to  the  origin  of  spe- 
cies, which  is  exciting  so  much  controversy  at  the  present  day,  nor  shall  we  treat  of  gen- 
eration in  the  lower  animals,  except  to  illustrate  the  history  of  development  in  man. 


854  GENERATION. 

The  study  of  human  generation  will  naturally  assume  the  following  course:  First, 
the  female  organs  of  generation  and  the  formation  of  the  female  element,  the  ovum  ; 
second  the  discharge  of  the  ovum  and  the  phenomena  which  attend  this  process  ;  third, 
the  male  organs  and  the  development  and  discharge  of  the  male  elements,  the  spermato- 
zoids;  fourth,  the  union  of  the  two  elements  of  generation,  or  fecundation;  fifth,  the 
development  of  the  fecundated  ovum  into  the  fetus  at  term ;  sixth,  the  development 
of  the  body  after  birth  and  at  different  ages,  or  stages  of  existence ;  finally,  the  natural 
cessation  of  the  so-called  vital  functions,  or  physiological  death. 

Sexual  Generation. 

Before  we  describe  the  actual  phenomena  of  sexual  generation,  as  they  are  observed 
in  man  and  the  mammalia,  it  will  be  interesting  to  note  some  of  the  salient  points  in  the 
history  of  our  knowledge  of  this  process  in  the  inferior  animals.  This  we  can  do,  with- 
out exceeding  the  limits  we  have  laid  down  in  our  general  remarks. 

In  the  history  of  sexual  generation,  there  seems  to  have  been  a  limiting  line  between 
the  production  of  animals  from  preexisting  organisms  and  of  those  produced  in  some 
unknown  manner,  or,  as  it  has  been  said,  spontaneously.  This  line  of  distinction  has 
always  receded  toward  organisms  lower  and  lower  in  the  scale  of  being,  with  our  advance 
in  positive  knowledge.  The  ancients  understood  that  the  higher  animals  required  for 
their  production  a  concourse  of  the  sexes;  but  they  thought  that  many  fishes,  reptiles, 
insects,  worms,  etc.,  were  produced  spontaneously.  Indeed,  with  the  limited  knowledge 
of  natural  history  possessed  by  Aristotle  and  those  who  succeeded  him  for  many  hun- 
dred years,  the  classes  of  animals  said  to  be  produced  spontaneously  represented  simply 
those,  the  generation  of  which  was  not  understood.  But,  as  the  habits  of  many  animals 
became  better  understood,  more  and  more  of  them  were  observed  to  lay  eggs,  which 
were  found  to  undergo  development. 

Dating  from  Aristotle,  who  lived  between  three  and  four  hundred  years  B.  c.,  it  was 
nearly  two  thousand  years  before  any  thing  was  known  of  the  generation  of  insects ; 
the  difficulty  here  being  that  the  young  are  first  in  a  larval  state  and  bear  no  resem- 
blance to  the  parents.  Anterior  to  the  experiments  of  Eedi,  it  was  thought  that  certain 
organic  matters  in  course  of  putrefaction  developed  living  organisms,  as  maggots  in  meat 
and  the  larvae  in  cheese. 

We  refer  to  the  experiments  of  Redi,  made  about  the  year  1668,  for  the  reason  that 

these  mark  an  era  in  our  knowledge  of  the  process  of  generation.     This  observer,  noting 

that  flies  frequently  lighted  upon  meat  when  it  was  exposed,  simply  protected  it  by 

gauze  and  found  that  no  maggots  were  developed,  while  other  pieces  of  meat,  placed 

under  the  same  conditions,  except  that  the  flies  had  free  access  to  them,  developed  mag- 

\  m  great  numbers.    By  this  simple  experiment,  Redi  showed  that  the  maggots  in 

putrefying  meat  were  produced  by  insects  and  not  by  the  meat ;  but  it  remained  for 

Swammerdam  and  Vallisneri  to  study  the  metamorphoses  of  insects,  and  to  show  how 

he  eggs  were  developed,  first  into  sexless  larvae,  and  finally  into  perfect  beings  resembling 

le  parents.    It  is  curious  to  note  the  condition  of  science  anterior  to  Redi  and  Vallis- 

and  compare  it  with  the  ideas  that  are  current  at  the  present  day.     When  -maggots 

red  in  putrefying  meat,  they  were  thought  to  be  produced  by  a  spontaneous  aggre- 

orgamc  particles,  simply  because  observers  knew  of  no  other  way  in  which 

?s  could  come  into  existence.     Now,  the  advocates  of  spontaneous  generation 

»  same  ideas  as  those  advanced  anterior  to  1668  ;  but,  in  the  place  of  meat,  they 

»  infusions,  and  for  maggots,  they  substitute  infusorial  animalcules.     It  is 

that  the  discussion  of  the  question  then  was  as  energetic  as  it  is  now  ;  but  the 

of    uoh  d     anC-6S  m  a,kn°wled^  of  the  generation  of  insects  has  swept  away  the  memorv 

.scions,  if  they  existed,  as  future  advances  may  possibly  cause  many  of  the 

controversial  writings  of  the  present  day  to  pass  into  oblivion 


SEXUAL  GENERATION.  855 

For  a  time  after  the  researches  to  which  we  have  just  alluded  had  taken  their  place 
in  the  history  of  science,  there  was  little  written  about  spontaneous  generation.  Redi 
had  satisfactorily  described  the  mode  of  generation  of  many  of  the  entozoa,  the  origin 
of  which  had  been  obscure ;  Harvey  had  enunciated,  in  substance,  his  famous  axiom, 
"  omne  animal  ex  ovo  ;  "  Regnerus  de  Graaf  had  described,  in  the  ovaries,  the  vesicles 
which  have  since  borne  his  name ;  and  the  knowledge  of  ovulation  and  development 
began  to  make  definite  progress,  the  important  fact  having  been  ascertained,  that  vivipa- 
rous, as  well  as  oviparous  animals,  are  produced  from  ova. 

With  the  discovery,  by  Leeuwenhoek,  of  living  beings  in  water,  called  by  him  ani- 
malcules, but  since  known  as  infusoria,  a  new  problem  was  presented  to  students  of 
natural  history.  Here  were  animal  organisms,  so  small  as  to  be  invisible  to  the  naked 
eye,  existing  in  great  variety  and  in  infinite  numbers,  the  mode  of  generation  of  which 
was  not  understood.  As  these  organisms  were  studied  more  closely,  their  multiplication 
by  segmentation  and  by  budding  became  known,  and  these  have  since  been  described  as 
processes  of  generation  peculiar  to  some  of  the  lower  orders  of  beings;  but,  at  the  same 
time,  some  writers  revived  the  theory  of  spontaneous  generation,  to  account  for  the 
original  appearance  of  animalcules  in  water,  and  this  idea  has  its  advocates  at  the  pres- 
ent day.  If,  however,  we  follow  out  the  history  of  the  spontaneous-generation  theory, 
we  find  that  the  different  epochs  have  repeated  themselves ;  that  the  theory  took  its 
origin  from  an  ignorance  of  the  mode  of  generation  of  organisms  quite  high  in  the  scale 
of  being ;  that  the  progress  of  exact  knowledge  gradually  restricted  the  theory  to  lower  and 
lower  organisms,  until,  by  this  rigid  process,  it  became  extinct,  simply  from  want  of  ma- 
terial ;  that  its  application  to  entozoa  was  eliminated  in  the  same  way ;  that  it  was  revived 
by  the  discovery  of  infusoria ;  and  that  now  its  limits  have  been  restricted  by  positive 
advances  in  knowledge,  it  being  demonstrated,  by  Balbiani  and  others,  that  many  varie- 
ties of  infusoria  present  the  phenomena  of  sexual  generation. 

Of  the  advocates  of  spontaneous  generation  within  a  comparatively  recent  period, 
perhaps  the  most  prominent  has  been  Pouchet ;  but  modern  researches  have  shown 
pretty  clearly  that  the  infusoria  produced  in  organic  infusions  are  due,  in  all  probability, 
to  the  introduction  of  ova  or  spores  floating  in  the  air,  which  are  developed  when  they 
meet  with  proper  conditions  of  heat  and  moisture.  In  numerous  experiments  by  differ- 
ent observers,  which  it  is  not  necessary  to  cite  in  detail,  it  appeared  that,  when  organic 
infusions  had  been  exposed  to  a  degree  of  heat  sufficient  to  destroy  germs,  and  the  intro- 
duction of  new  germs  from  the  air  was  prevented,  no  infusoria  were  developed  ;  and  this 
was  the  case  when  air  was  admitted  to  the  infusions,  care  being  taken  to  pass  the  air 
through  heated  tubes  or  sulphuric  acid,  so  as  to  destroy  all  organic  matter.  The  present 
aspect  of  the  question  of  spontaneous  generation  is  the  following : 

First,  it  is  reduced  to  the  very  lowest  orders  of  infusoria,  such  as  vibriones  and  bac- 
teria, which  simply  present  movement,  have  no  distinguishable  internal  structure,  and 
are  exceedingly  minute. 

Second,  the  question  is  discussed  as  to  what  degree  of  temperature  and  length  of 
exposure  to  heat  are  necessary  in  order  to  destroy  preexisting  germs  in  organic  infu- 
sions ;  for  the  idea  that  living  organisms  ever  result  from  an  aggregation  of  inorganic 
particles  has  been  generally  abandoned,  and  the  so-called  spontaneous  production  of 
animals  has  been  reduced  to  a  coming  together  of  organic  molecules. 

It  is  at  once  apparent  to  the  rigidly  scientific  mind  that  the  second  division  of  the 
question  presents  great  difficulties  in  the  way  of  its  positive  solution.  It  is  granted,  for 
example,  that  vibriones  and  bacteria  are  living,  animal  organisms.  It  is  proposed  by  the 
advocates  of  the  theory  of  spontaneous  generation,  that  these  beings  arise  without  pre- 
existing germs,  by  an  aggregation  of  organic  particles.  The  opponents  of  this  view  assert 
that,  when  the  air  admitted  to  organic  infusions  is  freed  from  germs  or  organic  particles, 
and  when  the  organic  infusions  are  subjected  to  a  high  temperature  for  a  time  sufficient 
to  destroy  all  possible  preexisting  germs,  no  generation  of  infusoria  can  take  place. 


Q-A  GENERATION, 

bob 

Now  what  degree  of  temperature  is  required,  what  is  the  duration  of  exposure  to  heat 
necessary  to  destroy  germs,  and  how  are  the  limits  of  these  conditions  to  be  ascertained  < 
The  only  answer  to  this  question  lies  in  the  experimental  test.  When  infusoria  make 
their  appearance  in  solutions  that  have  been  exposed  to  heat  and  protected  from  the 
entrance  of  germs,  it  is  said  that  the  heat  has  not  been  sufficiently  high  or  the  exposure 
has  been  of  too  short  duration.  When  infusoria  do  not  appear,  the  conditions  are 
assumed  to  have  been  fulfilled.  This  mode  of  reasoning  assumes  the  fact,  from  the  begin- 
ning that  there  is  no  such  thing  as  spontaneous  generation.  Suppose,  now,  we  start 
with  the  contrary  assumption,  that  there  may  be  spontaneous  generation  in  an  organic 
infusion.  We  admit  to  such  an  infusion,  air,  carefully  purified  from  germs,  which  is 
logically  an  essential  experimental  condition;  we  have. previously  exposed  the  infusion 
to  a  high  temperature  for  a  certain  period.  Under  these  conditions,  no  infusoria  appear. 
It  may  then  be  assumed  that  the  heat  has  destroyed  the  properties  of  the  organic  mole- 
cules, so  that  they  cannot  come  together  and  generate  new  beings. 

Under  these  circumstances,  all  that  we  can  do  is  to  argue  logically  from  such  facts  as  ' 
have  been  positively  established,  and  to  take  the  most  reasonable  view  of  other  points, 
that  are  not  as  yet  capable  of  satisfactory  and  definite  explanation. 

We  shall  assume  that  it  has  been  demonstrated,  beyond  a  reasonable  doubt,  that,  in 
organic  infusions,  subjected  to  a  temperature  somewhat  above  that  of  boiling  water,  and 
supplied  with  air  that  has  been  effectually  deprived  of  organic  matter,  ova,  spores,  or 
whatever  it  may  be,  no  living  organisms  make  their  appearance  so  long  as  these  experi- 
mental conditions  are  maintained.  We  also  assume  that  simple  boiling,  at  212°  Fahr., 
does  not  necessarily  destroy  all  germs,  which  excludes  experiments  made  in  this  way. 
This  reduces  the  question  to  a  single,  simple  point :  In  infusions  in  which  the  organic 
matter  has  not  been  destroyed  by  heat,  do  the  living  organisms  come  from  a  spontaneous 
aggregation  of  organic  molecules,  or  are  they  the  result  of  the  development  of  ova  ? 

In  the  case  of  the  very  lowest  organisms  making  their  appearance  under  these  con- 
ditions, they  are  themselves  so  small,  that  it  would  be  reasonable  to  suppose  that  we 
might  be  unable  to  see  the  ova,  assuming  that  they  exist.  The  organic  particles  that  are 
supposed  to  come  together  spontaneously  are  also  invisible,  even  under  the  highest  mag- 
nifying powers  at  our  command.  If  we  come  to  an  exact  definition  of  the  term  spon- 
taneous, we  may  say  that  it  means  an  action  "  arising  or  existing  from  natural  inclination, 
disposition,  or  tendency,  or  without  external  cause  "  (Worcester).  With  this  definition, 
the  statement  that  a  living  organism  is  generated  spontaneously  can  only  mean  that  there 
is  no  cause  that  can  be  assigned  for  its  production.  In  point  of  fact,  we  simply  acknowl- 
edge that  the  mode  and  cause  of  generation  of  certain  infusoria  are  unknown,  and  the 
history  of  our  knowledge  of  generation  shows  that  the  term  spontaneous  generation  has 
always  been  applied  to  the  production  of  beings  in  a  manner  that  is  incapable  of  satis- 
factory explanation.  What  we  actually  know  of  the  mode  of  generation  of  animal  organ- 
isms teaches  us  that  all  beings  are  produced  and  multiplied  by  ova,  or  by  processes  of 
segmentation  or  budding  of  preexisting  organisms ;  and  our  knowledge  of  these  processes 
now  extends  to  all  except  the  most  minute  infusoria,  which  have  no  apparent  structure. 
We  know,  also,  that  such  organisms  may  develop  in  pure  water  from  particles  floating  in 
the  atmosphere ;  and  that  particles  in  the  air,  singly  invisible,  may  be  developed  into 
infusoria  that  are  quite  highly  organized.  If  we  reason  that  the  products  of  so-called 
spontaneous  generation  are  formed  by  the  fortuitous  aggregation  of  organic  molecules, 
we  assume  a  fact  of  which  we  have  no  other  example  in  Nature;  and  we  assume,  also, 
that  such  an  aggregation  of  particles  produces  beings  of  a  definite  and  uniform  character. 
For  such  a  supposition,  we  have  no  basis  in  analogy.  If,  on  the  other  hand,  we  regard 
these  low  orders  of  beings  as  produced  by  the  development  of  invisible  germs,  which 
have  found  favorable  conditions  of  heat  and  moisture,  we  rest  upon  a  basis  of  reasonable 
analogy,  and  we  merely  confess  that  this  is  a  form  of  generation,  the  processes  of  which 
are  not  as  yet  capable  of  demonstration. 


FEMALE  OKGANS  OF  GENERATION.  857 

As  the  only  true  philosophic  view  to  take  of  the  question,  we  shall  assume,  in  common 
with  nearly  all  modern  writers  upon  physiology,  that  there  is  no  such  thing  in  Nature 
as  spontaneous  generation ;  admitting  that  the  exact  mode  of  production  of  some  of  the 
infusoria,  lowest  in  the  scale  of  being,  is  not  understood. 

Female   Organs  of  generation. 

An  accurate  knowledge  of  certain  points  in  the  anatomy  of  the  female  organs  of  gen- 
eration is  essential  to  the  comprehension  of  the  most  important  of  the  processes  of  repro- 
duction. Following  a  fruitful  intercourse  of  the  sexes,  the  function,  as  regards  the  male, 
ceases  with  the  comparatively  simple  process  of  penetration  of  the  male  element  through 
the  protective  covering  of  the  ovum  and  its  fusion  with  the  female  element.  The  fecun- 
dated ovum  then  passes  through  certain  changes,  which  are  the  first  processes  of  its 
development,  forms  its  attachments  to  the  body  of  the  mother,  continues  its  develop- 
ment, materials  being  derived  from  the  mother,  is  nourished  and  grows,  until  the  foetus 
at  term  is  brought  into  the  world.  An  exact  knowledge  of  the  mechanism  of  these  com- 
plicated processes  can  only  be  obtained  after  a  careful  study  of  the  anatomy  of  the  female 
organs.  We  must  know  precisely  how  the  ovum  is  developed  in  the  ovary  and  how  it 
is  discharged ;  how,  after  its  discharge,  it  is  received  by  the  oviduct  and  carried  to  the 
uterus ;  if  fecundation  dosnot  take  place,  there  is  nothing  more  to  study,  as  the  ovum  is 
lost ;  but,  as  the  fecundated  ovum  must  form  certain  attachments  within  the  uterus,  we 
must  be  acquainted  with  the  anatomy  of  this  organ,  before  we  can  comprehend  its  devel- 
opment. Again,  we  have  to  study  the  phenomena  which  attend  the  discharge  of  ova, 
and  the  changes  which  take  place  in  the  ovaries,  anterior  to,  during,  and  subsequent  to 
ovulation.  It  will  not  be  essential  for  us  to  study  very  closely  the  anatomy  of  the  exter- 
nal parts,  as  these  are  only  concerned  in  sexual  intercourse  and  in  parturition ;  which 
latter,  though  a  purely  physiological  process,  forms  the  greatest  part  of  the  science  of 
obstetrics,  is  considered  elaborately  in  treatises  on  this  subject,  and  is  not  usually  treated 
of,  to  any  great  extent,  in  works  upon  physiology. 

The  female  organs  of  generation  are  divided  anatomically  into  internal  and  external. 
The  external  organs  are  the  vulva,  the  adjacent  parts,  and  the  vagina ;  the  internal 
organs  are  the  uterus,  Fallopian  tubes,  and  ovaries.  When  we  come  to  study  the  func- 
tions of  the  internal  parts,  we  shall  see  that  the  ovaries  are  the  true  female  organs,  in 
which,  and  in  which  alone,  the  female  element  can  be  produced.  The  Fallopian  tubes 
jmd  the  uterus  are  accessory  in  their  functions,  the  female  element  (the  ovum)  passing 
through  the  Fallopian  tubes  to  the  uterus,  where  it  forms  the  attachments  to  the  body 
of  the  mother  which  are  essential  to  its  nourishment  and  full  development  after  fecun- 
dation. 

Before  we  proceed  to  study  the  structure  of  any  of  the  female  organs,  it  is  important 
to  have  a  clear  idea  of  the  general  arrangement  and  the  relations  of  these  parts ;  for, 
without  this,  we  shall  be  constantly  in  the  dark  as  to  the  bearing  of  certain  important 
anatomical  points  that  have  been  brought  forward  within  the  last  few  years. 

The  vagina  has  a  direction,  slightly  curved  anteriorly,  which  is  nearly  coincident  with 
the  axis  of  the  outlet,  or  the  inferior  strait  of  the  pelvis.  Projecting  into  the  vagina,  at 
its  upper  extremity,  is  the  lower  part  of  the  neck  of  the  uterus.  The  uterus  extends  from 
the  vagina  nearly  to  the  brim  of  the  pelvis.  It  is  situated  between  the  bladder  and  the 
rectum,  and  has  an  antero-posterior  inclination,  when  the  bladder  is  moderately  distended, 
which  brings  its  axis  nearly  coincident  with  that  of  the  superior  strait  of  the  pelvis.1 
Supposing  the  body  to  be  erect,  the  angle  of  the  uterus  with  the  perpendicular  would 
be  about  forty-five  degrees.  These  details  with  regard  to  the  position  of  the  uterus 

1  The  statements  given  above,  with  regard  to  the  position  of  the  uterus,  are  very  general.  The  uterus  is  exceed- 
ingly movable  nntero-posteriorly,  and  the  direction  of  its  axis  is  largely  dependent  upon  the  condition  of  the  other 
pelvic  organs.  When  the  bladder  is  distended,  the  fundus  is  moved  upward ;  and,  when  the  bladder  is  empty,  the 
axis  of  the  uterus  may  be  inclined  forward  so  as  to  become  nearly  horizontal. 


858 


GENEKATION. 


are  essential  to  a  comprehension  of  the  situation  and  relations  of  the  ovaries  and  Fallo- 
pian tubes. 

The  uterus  is  held  in  place  by  ligaments,  certain  of  which  are  formed  of  folds  of  the 
peritoneum.  The  anterior  ligament  is  reflected  from  the  anterior  surface  to  the  bladder ; 
the  posterior  ligament  extends  from  the  posterior  surface  to  the  rectum  ;  the  round  liga- 
ments extend  from  the  upper  angle  of  the  uterus,  on  either  side,  between  the  folds  of  the 
broad  ligament  and  through  the  inguinal  canal,  to  the  symphysis  pubis ;  the  broad  liga- 
ments, which  extend  from  the  sides  of  the  uterus  to  the  walls  of  the.  pelvis,  are  the  most 
interesting  of  all,  as  they  lodge  the  ovaries  and  the  Fallopian  tubes. 

If  we  imagine  the  uterus,  occupying,  as  it  does,  the  upper  part  of  the  pelvis,  and 
remember  its  angle  of  inclination,  it  is  evident  that  it,  with  the  broad  ligaments,  must 
partially  divide  the  pelvis  into  two  portions  ;  and  these  ligaments,  which  are  formed  of 
a  double  fold  of  peritoneum,  present  a  superior,  or  posterior  surface,  and  an  inferior,  or 
anterior  surface.  The  superior,  or  anterior  border  of  this  fold  is  occupied  by  the  Fallopian 
tubes,  the  peritoneum  constituting  their  outer  coat.  Laterally,  at  the  free  extremities  of 
the  tubes,  the  peritoneum  ceases,  and  there  is  an  actual  opening  of  each  Fallopian  tube 
into  the  peritoneal  cavity.  Attached  to  the  broad  ligament  and  projecting  upon  its  pos- 
terior surface,  is  the  ovary.  This  little,  almond-shaped  body  is  connected  with  the  fibrous 
tissue  between  the  two  layers  of  the  ligament,  and  has  no  proper  peritoneal  investment ; 
so  that  it  is  actually  within  the  peritoneal  cavity.  If  we  look  at  the  ovary  from  the 
front,  we  simply  see  the  rounded  prominence  which  marks  the  point  of  its  attachment  to 
the  broad  ligament ;  but,  if  we  look  from  behind,  the  projecting  surface  is  seen,  and  we 


n  mt"H-  Faa°fian  <"»««.  a**  maries  ;  posterior  tiew.    (Sapper  ) 


dema]rcati°nat  the  base'  whicb  indicato  ^ere  the  tessellated, 
d  Wh6re  the  Pr°per  columnar  «P^elium  of  the  ovary  begins. 

rn  ?,:  surface  °f  the  °™ry'  its  e°ntent9  -5*  «*  be 

the  uter  by  ,gen  1±  '  t  S  ""TV"  *""  ^^  ^  °™?  '"  attached  to 
ovary  This  it™  '  7  g  J  b°neath  the  Peritoneum,  called  the  ligament  of  the 

of  th'e  bro;  f;arnVSaCre°Z°Sn,0f  n°n-striated  mus™'»  fi"res.  Between  the  folds 
blood-vessels  SS^^^'*.*11*1?8  the  ^^  ligament  of  the  uterus, 
the  superficial  ^S*  ™^  fib-8' 


FEMALE  ORGANS  OF  GENERATION.  859 

"We  are  now  prepared  to  study  Fig.  270,  which  shows  the  general  arrangement  of 
these  parts,  viewed  from  behind.  A  portion  of  the  figure  which,  in  the  original,  shows 
the  external  parts,  is  cut  off,  to  avoid  complicating  our  description.  A  careful  examina- 
tion of  Fig.  270  will  give  a  general  idea  of  the  relations  of  the  different  parts  and  enable 
us  to  study  intelligently  their  minute  anatomy. 

The  Ovaries. — The  situation  of  these  bodies  has  already  been  indicated.  Attached, 
as  they  are,  to  the  broad  ligament,  and  projecting  from  its  posterior  surface,  they  lie 
nearly  horizontally  in  the  pelvic  cavity,  on  either  side  of  the  uterus.  They  are  of  a 
whitish  color,  and  their  form  is  ovoid  and  flattened,  with  the  anterior  border,  sometimes 
called  the  base,  attached  to  the  broad  ligament.  If  we  closely  examine  their  mode  of 
connection  with  the  broad  ligament,  it  is  seen  that,  at  the  margin  of  the  attached  surface 
of  the  ovary,  the  posterior  layer  of  the  ligament  ceases,  and  that  the  fibrous  stroma  of 
the  medullary  portion  of  the  ovary  is  continuous  with  the  fibrous  tissue  lying  between 
the  two  layers.  It  is  at  this  portion  of  the  ovary,  called  the  hilum,  that  the  vessels  pene- 
trate, to  be  distributed  in  its  substance. 

Each  ovary  is  about  an  inch  and  a  half  in  length,  half  an  inch  in  thickness,  and  three- 
quarters  of  an  inch  in  width  at  its  broadest  portion.  The  outer  extremity  is  somewhat 
rounded  and  is  attached  to  one  of  the  fimbrias  of  the  Fallopian  tube.  The  inner  extremi- 
ty is  more  pointed  and  is  attached  to  the  side  of  the  uterus  by  means  of  the  ligament  of 
the  ovary.  This  ligament  is  shown  in  Fig.  270  (7,  7).  It  is  a  rounded  cord,  composed 
of  non-striated  muscular  fibres  spread  out  upon  the  attached  extremity  of  the  ovary  and 
the  posterior  surface  of  the  uterus,  and  is  covered  by  peritoneum.  The  weight  of  each 
ovary  is  from  sixty  to  one  hundred  grains,  and  these  organs  are  largest  in  the  adult  virgin. 
Its  attached  border  is  called  the  hilum;  and,  at  this  portion,  the  vessels  and  nerves  pene- 
trate. The  surface  is  marked  by  rounded,  translucent  elevations,  produced  by  distended 
Graafian  follicles ;  and  we  frequently  see  here  little  cicatrices,  indicating  the  situation  of 
ruptured  follicles.  We  may  also  see,  between  the  distended  follicles,  corpora  lutea  in 
various  stages  of  atrophy. 

Within  the  last  few  years,  anatomical  researches  have  shown  that  the  surface  of  the 
ovaries  does  not  present  the  appearance  of  a  continuation  of  the  peritoneum.  At  the 
base,  is  a  distinct  line,  surrounding  the  hilum,  which  indicates  where  the  peritoneum 
ceases  and  where  the  proper  epithelial  covering  of  the  ovary  begins;  and  there  is  a  well- 
marked  and  abrupt  distinction  between  the  tessellated  epithelium  of  the  serous  surface 
and  the  layer  of  cylindrical  cells  covering  the  ovary  itself.  This  peculiarity  has  led 
to  the  idea  that  the  ovary  is  really  covered  by  a  mucous  membrane.  Indeed,  there 
seems  to  be  little  difference  between  the  cells  covering  the  ovaries  and  those  lining  the 
Fallopian  tubes,  except  that  the  latter  are  provided  with  cilia. 

Most  anatomists  describe  a  proper  fibrous  membrane  investing  the  ovaries,  which 
they  call  the  tunica  albuginea,  and  which  is  compared  to  the  fibrous  covering  of  the 
testes.  This,  however,  is  not  a  proper  term.  Sappey  denies  the  existence  of  a  tunica 
albuginea;  and,  indeed,  in  the  sense  in  which  it  was  formerly  described,  such  a  membrane 
cannot  be  demonstrated.  On  making  a  section  of  the  ovary,  it  is  readily  seen  by  the 
naked  eye  that  the  organ  is  composed  of  two  distinct  structures ;  a  cortical  substance, 
formerly  called  the  tunica  albuginea,  which  is  about  -fa  of  an  inch  in  thickness,  and  a 
medullary  substance,  containing  a  large  number  of  blood-vessels.  The  cortical  substance 
alone  contains  the  Graafian  follicles.  The  external  layer  of  this  may  be  a  little  denser 
than  the  deeper  portion,  but  there  is  no  distinct  fibrous  membrane. 

The  structure  of  the  cortical  substance  of  the  ovary  is  very  simple.  It  consists  of  con- 
nective tissue  in  several  layers,  the  fibres  of  which  are  continuous  with  the  looser  fibres 
of  the  medullary  portion.  In  the  substance  of  this  layer,  are  embedded  the  ova,  enclosed 
in  the  sacs  called  Graafian  follicles.  This  layer  contains  a  few  blood-vessels,  coming 
from  the  medullary  portion,  which  surround  the  follicles. 


860  GENERATION. 

The  medullary  portion  of  the  ovary  is  exceedingly  vascular  and  is  composed  of  numer- 
ous small  bands,  or  trabecul*  of  connective  tissue,  with  smooth  muscular  fibres.  The 
blood-vessels,  which  penetrate  at  the  hilum,  are  large  and  convoluted,  especially  at  the 
hilum  itself  where  there  is  a  mass  of  convoluted  veins,  forming  a  sort  of  vascular  bulb, 
w  hich  has  been  described  particularly  by  Eouget.  In  the  medullary  portion  of  the  ovary, 
which  is  sometimes  called  the  vascular  zone,  the  muscular  fibres  follow  the  vessels,  m  the 
form  of  muscular  sheaths.  According  to  Rouget,  the  mass  of  vessels  at  the  hilum  con- 
stitutes a  true  erectile  organ. 

In  addition  to  the  blood-vessels,  the  ovary  receives  nerves  from  the  spermatic  plexus 
of  the  sympathetic,  the  exact  mode  of  termination  of  which  has  not  been  ascertained. 
Lymphatics  have  also  been  demonstrated  at  the  hilum. 

Graafian  Follicles.— These  vesicles,  or  follicles,  were  described  and  figured  by  De 
Graaf  and  are  known  by  his  name.  They  contain  the  ova.  undergo  a  series  of  interest- 
ing changes,  enlarge,  approach  the  surface  of  the  ovary,  and  finally  are  ruptured,  dis- 
charging their  contents  into  the  fimbriated  extremity  of  the  Fallopian  tube. 

It  was  formerly  supposed  that  the  smallest  Graafian  follicles  were  situated  deeply  in 
the  medullary  portion  of  the  ovaries,  approaching  the  surface  gradually,  as  they  became 
larger;  but  it  is  now  known  that  they  are  developed  exclusively  in  the  cortical  substance. 
If,  indeed,  we  examine  the  ovary  at  any  period  of  life,  we  find  no  follicles  properly  in  the 
medullary  substance;  but  a  few  of  the  larger  may  project  downward,  so  as  to  encroach 
somewhat  upon  it,  being  actually  of  a  diameter  greater  than  the  thickness  of  the  cortex. 

The  earlier  anatomists  supposed  that  the  Graafian  follicles  were  few  in  number,  fifteen 
or  twenty,  but  they  counted  those  only  that  were  readily  seen  with  the  naked  eye.  When, 
however,  it  was  calculated  that  ova  might  be  discharged  every  month  during  a  period  of 
about  forty  years,  it  became  evident  that  the  follicles  must  either  be  quite  numerous  or 
become  successively  and  constantly  developed.  This  led  some  anatomists,  who  believed 
that,  at  the  age  of  puberty,  the  ovaries  contained,  either  partially  or  fully  developed,  all 
the  follicles  that  ever  existed  in  these  organs,  to  increase  their  estimates  of  the  number 
of  follicles.  Sappey,  from  a  series  of  careful  observations  on  this  point,  puts  the  number 
of  follicles  at  from  600,000  to  700,000.  We  cannot  but  regard  this  estimate  as  very  much 
exaggerated.  According  to  the  table  of  measurements  given  by  Waldeyer,  the  primor- 
dial follicles  in  the  human  embryo,  at  the  seventh  month,  measure  from  ^  to  ^  of  an 
inch,  and  the  primordial  ova,  from  T1^  to  j^Vo  of  an  mch.  From  what  has  been  written 
on  this  point,  it  seems  difficult,  if  not  impossible,  to  give  an  approximation,  even,  of  the 
number  of  follicles  in  the  ovaries,  but  there  certainly  must  be  several  thousands,  many 
of  which  may  never  become  fully  developed. 

Within  the  last  few  years,  very  important  advances  have  been  made  in  our  knowledge 
of  the  mode  of  development  of  the  ova  and  ovaries,  which  will  be  more  fully  considered 
hereafter;  but  we  must  here  refer  to  these  points  briefly,  in  order  to  give  a  clear  idea  of 
the  relations  of  the  Graafian  follicles,  in  the  different  forms  which  they  present  under 
varied  conditions  of  development. 

The  ovary  appears,  particularly  from  observations  upon  the  development  of  the  chick, 

ery  early  in  embryonic  life,  in  the  form  of  a  cellular  outgrowth  from  the  Wolffian  body. 

ts  cells  are  small,  but,  as  early  as  the  fourth  or  fifth  day,  some  of  them  are  to  be 

ished  by  their  large  size,  their  rounded  form,  and  the  presence  of  a  large  nucleus. 

Is  are  supposed  to  be  primordial  ova.     In  the  process  of  development  of  the 

wy,  some  of  the  peripheral  cells  penetrate  in  the  form  of   tubes  (the  so-called  ova- 

s)  and,  at  the  same  time,  delicate  processes,  formed  of  connective  tissue  and 

essels  extend  from  the  fibrous  stroma  underlying  the  epithelium  and  enclose  col- 

:  cells.     It  is  probable  that  we  have  these  two  modes  of  formation  of  follicles  ; 

md  J  %**  V™^™  °f  ePithelial  tabes  from  the  surface,  which  become  constricted 

r  into  closed  cavities,  and  the  other,  by  the  extension  of  fibrous  processes 


FEMALE  OKGANS  OF  GENERATION. 


861 


from  below,  which  enclose  little  collections  of  cells.  By  both  of  these  processes,  little 
cavities  are  formed,  which  contain  a  number  of  cells.  In  each  of  these  cavities,  we 
observe  a  single,  large,  rounded  cell,  with  a  large  nucleus,  this  cell  being  a  primordial 
ovum ;  and,  in  addition,  we  have  in  the  same  cavity,  other  cells,  which  are  the  cells  of 
the  Graafian  follicle.  The  exact  nature  of  the  processes  we  have  just  described  has  been 
studied  in  the  fowl,  but  it  is  probable  that  the  same  kind  of  development  occurs  in  mam- 
malia and  in  the  human  female. 

From  birth  until  just  before  the  age  of  puberty,  the  cortical  substance  of  the  ovary 
contains  thousands  of  what  are  termed  primordial  follicles,  enclosing  the  primordial  ova; 
and  it  is  probable  that,  after  the  ovaries  are  fully  developed  at  birth,  no  additional  ova 
or  Graafian  follicles  make  their  appearance.  The  prevailing  idea  is,  indeed,  that  the 
great  majority  of  these  never  arrive  at  maturity,  and  that  they  undergo  atrophy  at  vari- 


FIG.  Ml.— Portion  of  a  sagittal  section,  of  tlie,  ovary  of  an  old  bitch     (Waldeyer.) 

a,  ovarian  epithelium;  5,  &,  ovarian  tubes;  c,  c,  younger  follicles;  d,  older  follicle;  e,  discus  proligerus,  with  the 
ovum  ;  /;  epithelium  of  a  second  ovum  in  the  same  follicle  ;  g,  fibrous  coat  of  the  follicle ;  ft,  proper  coat  of  the 
follicle;  *,  epithelium  of  the  follicle  (membrana  granulosa) ;  k,  collapsed,  atrophied  follicle ;  £,  blood-vessels ;  m, »?, 
cell-tubes  of  the  parovarium,  divided  longitudinally  and  transversely  ;  y,  tubular  depression  of  the  ovarian  epi- 
thelium in  the  tissue  of  the  ovary  ;  2,  beginning  of  the  ovarian  epithelium  close  to  the  lower  border  of  the  ovary. 

ous  stages  of  their  development.  According  to  the  table  of  measurements  given  by  Wal- 
deyer, the  primordial  follicles  of  the  human  embryo,  at  the  seventh  month,  are  from 
about  3-^-5-  to  2^5  of  an  inch  in  diameter,  and  the  primordial  ova,  from  -j-sV^  to  y^Vrr  °f  an 
inch.  In  the  adult,  the  smallest  follicles  measure  from  about  ^|^  to  -^  of  an  inch,  and 


862  GENERATION. 


the  smallest  ova,  a  little  more  than  J^TT  of  an  inch.  The  primordial  ova  have  the  form 
of  rounded  cells,  each  with  a  large,  clear  nucleus,  and  a  nucleolus.  Other  structures  are 
developed  in  and  surrounding  these  cells,  as  they  arrive  at  their  full  development. 

The  most  interesting  stage  in  the  development  of  the  ova  and  Graafian  follicles  is 
observed  at  about  the  period  of  puberty.  At  this  time,  a  number  of  follicles  (twelve, 
twenty,  thirty,  or  even  more)  enlarge,  so  that  we  have  all  sizes,  between  the  smallest 
primordial  follicles,  -^  of  an  inch,  and  the  largest,  nearly  £  an  inch  in  diameter.  In 
follicles  that  have  attained  any  considerable  size,  we  have  the  fully-developed  ova,  one  in 
each  follicle,  except  in  very  rare  instances,  when  there  are  two,  and  these  ova  have  a 
pretty  uniform  diameter  of  about  y^y  of  an  inch.  In  the  process  which  culminates  in 
the  discharge  of  the  ovum  into  the  fiinbriated  extremity  of  the  Fallopian  tube,  the  Graa- 
fian follicle  gradually  enlarges,  becomes  distended  with  liquid,  and  finally  breaks  through 
and  ruptures  upon  the  surface  of  the  ovary.  It  becomes  necessary,  then,  to  study  the 
structure  of  these  large  follicles  and  their  relations  to  the  ova  ;  but,  before  we  do  this, 
we  can  review,  with  advantage,  the  relations  of  the  different  portions  of  the  ovary  and 
the  follicles  and  ova  of  various  sizes,  by  an  examination  of  Fig.  271. 

Fig.  271  shows  the  follicles  and  ova  of  various  sizes.  It  is  observed  that  the  larger 
follicles  contain  fully-formed  ova  and  have  a  proper  fibrous  coat.  The  ova  here  present 
an  epithelial  covering  and  are  embedded  in  a  mass  of  the  epithelial  lining  of  the  follicle 
(membrana  granulosa),  this  mass  being  called  the  discus  or  cumulus  proligerus. 

According  to  the  measurements  given  by  Waldeyer,  the  smallest  Graafian  follicles  are 
from  s-fg-  to  5^5-  of  an  inch  in  diameter,  while  the  largest  measure  from  f  to  \  an  inch. 
At  or  near  the  period  of  their  maturity,  the  follicles  present  several  coats  and  are  filled 
with  an  albuminous  liquid.  The  mature  follicles  project  just  beneath  the  surface  and 
form  little,  rounded,  translucent  elevations.  The  smallest  follicles  are  near  the  surface, 
and,  as  they  enlarge,  at  first  become  deeper,  as  is  seen  in  Fig.  271,  becoming  superficial 
only  as  they  approach  the  period  of  fullest  distention. 


Fio.  272.—  Graafian  follicle;  magnified  30  diameters.    (Luschka.) 

1,  1,  stroma  of  the  ovary;  2,  2.  convoluted,  cork-screw  blood-vessels ;  3,  fibrous  wall  of  the  follicle ;  4,  membrana 
granulosa ;  5.  cumulus  proligerus  ;  6,  zona  pellucida  of  the  ovum ;  7,  vitellus  of  the  ovum  ;  8,  germinal  vesicle 
with  the  germinal  spot. 

Taking  one  of  the  largest  follicles  as  an  example,  two  fibrous  layers  can  be  distin- 
guished ;  an  outer  layer,  of  ordinary  connective  tissue,  and  an  inner  layer,  the  tunica 
propria,  formed  of  the  same  kind  of  tissue,  with  the  difference  that,  as  the  follicle  en- 


FEMALE  ORGANS  OF  GENERATION. 


863 


larges,  the  inner  layer  becomes  vascular.  The  vascular  tunica  propria  is  lined  by  cells 
of  epithelium,  forming  the  so-called  membrana  granulosa.  At  a  certain  point  in  this 
membrane,  is  a  mass  of  cells,  called  the  discus  or  cumulus  proligerus,  in  which  the  ovum 
is  embedded.  The  situation  of  the  discus  proligerus  and  the  ovum  has  been  a  subject  of 
discussion.  Some  anatomists  describe  it  in  the  most  superficial  portion,  and  others,  in 
the  deepest  part  of  the  follicle.  Waldeyer  states  that  he  has  observed  it  in  both  situa- 
tions ;  and  it  is  probable  that  its  position  is  not  invariable. 

The  liquid  of  the  Graafian  follicle  is  alkaline,  slightly  yellowish,  not  viscid,  and  it  con- 
tains a  small  quantity  of  albuminoid  matter  coagulable  by  heat,  alcohol,  and  acids.  This 
liquid  is  supposed  to  be  secreted  by  the  cells  lining  the  inner  membrane  of  the  follicle. 

It  is  important  to  remember  that  the  ovum  is  not  a  product  of  secretion,  nor  can  the 
ovary  be  properly  considered  as  a  glandular  organ.  The  ovum  is  an  anatomical  ele- 
ment ;  and  the  ovary  is  the  only  organ  in  which  this  anatomical  element  can  be  devel- 
oped. The  only  process  of  secretion  which  takes  place  in  the  ovary  is  the  production, 
probably  by  the  cells  of  the  membrana  grnnulosa,  of  the  liquid  of  the  Graafian  follicles. 

The  Parovarium. — The  parovarium,  or  organ  of  Rosenmtiller,  is  simply  the  remains 
of  the  Wolffian  body,  lying  in  the  folds  of  the  broad  ligament,  between  the  ovary  and 
the  Fallopian  tube.  It  consists  of  from  twelve  to  fifteen  tubes  of  fibrous  tissue,  lined  by 
ciliated  epithelium,  and  it  has  no  physiological  importance.  The  Wolffian  bodies  will  be 
fully  described  in  connection  with  the  development  of  the  genito-urinary  system. 

The  Uterus. — The  form,  situation,  and  relations  of  the  uterus  and  Fallopian  tubes 
have  already  been  indicated  and  are  shown  in  Fig.  270. 

The  uterus  is  a  pear-shaped  body,  somewhat  flattened  antero-posteriorly,  presenting 
a  fundus,  a  body,  and  a  neck.  At  its  lower  extremity,  is  an  opening  into  the  vagina, 


FIG.  273.  —  Virgin  uterus.    A..— anterior  view.    B. — median  section.    C.— -transverse  section.    (Sappey.) 

A.  1,  body  ;  2,  2,  angles ;  3,  cervix  ;  4,  site  of  the  os  internum  ;  5.  vaginal  portion  of  the  cervix  ;  6,  external  os ;  7,  7. 

vagina. 

B.  1,  1,  profile  of  the  anterior  surface;  2,  vesico-uterine  cul-rle-toe ;  3.  3,  profile  of  the  posterior  surface;  4,  body; 

5,  neck;  6,  isthmus;   7,  cavity  of  the  body;    8,  cavity  of  the  cervix;   9,  os  internum;  10,  anterior  lip  of  the 
os  externum  ;  11.  posterior  lip  ;  12.  12.  vagina. 

C.  1.  cavitv  of  the  body;  2.  lateral  wall:  3,  superior  will ;  4,  4,  cornua;  5,  os  internum;  6,  cavity  of  the  cervix; 

7,  arbor  vitae  of  the  cervix  ;  8,  os  externum  ;  9,  9,  vagina. 

called  the  os  externum.    At  the  upper  portion  of  the  neck,  is  a  constriction,  which  indicates 
the  situation  of  the  os  internum.     The  form  of  the  uterus  is  shown  in  Fig.  273  (A).     It  is 


864 


GENERATION. 


usually  about  three  inches  in  length,  two  in  breadth,  at  its  widest  portion,  and  one  inch  in 
thickness.  Its  weight  is  from  one  and  a  half  to  two  and  a  half  ounces.  It  is  somewhat 
loosely  held  in  place  by  the  broad  and  round  ligaments  and  by  the  folds  of  the  peritoneum 
in  front  and  behind.  The  delicate  layer  of  peritoneum  which  forms  its  external  covering 
extends  behind  as  far  down  as  the  vagina,  where  it  is  reflected  back  upon  the  rectum,  and 
anteriorly,  a  little  below  the  upper  extremity  of  the  neck  (os  internum),  where  it  is  re- 
flected upon  the  urinary  bladder.  At  the  sides  of  the  uterus,  the  peritoneal  covering,  a  lit- 
tle below  the  entrance  of  the  Fallopian  tubes,  becomes  loosely  attached  and  leaves  a  line 
for  the  penetration  of  the  vessels  and  nerves.  Fig.  273  (C),  giving  a  view  of  the  interior 


Fm.  111.— Muscular  fibres  of  the  uterus.    (Sappey.) 
A,  fibres  of  the  uterus  of  the  foetus  at  term  ;  B,  of  a  woman  twenty  years  of  age ;  C,  of  a  woman  just  delivered, 

of  the  uterus,  shows  a  triangular  cavity,  with  two  cornua,  corresponding  to  the  openings 
of  the  Fallopian  tubes,  and  exceedingly  thick  walls,  the  greatest  part  of  which  is  com- 
posed of  layers  and  bands  of  non-striated  muscular  fibres. 

The  muscular  walls  of  the  uterus  are  composed  of  fibres  of  the  involuntary  variety, 
arranged  in  several  layers.  These  fibres  are  spindle-shaped,  always  nucleated,  the  nu- 
cleus presenting  one  or  two  large  granules,  which  have  been  taken  for  nucleoli.  They 
are  closely  bound  together,  so  that  they  are  isolated  with  great  difficulty.  In  addition  to 
an  amorphous  adhesive  substance  between  the  muscular  fibres,  we  find  numerous  round- 
ed and  spindle-shaped  cells  of  connective  tissue  of  the  variety  called  embryonic,  and  a 
few  elastic  fibres.  The  muscular  tissue  of  the  uterus  is  remarkable  from  the  fact  that 
the  fibres  enlarge  immensely  during  gestation,  becoming,  at  that  time,  ten  or  fifteen 
times  as  long  and  five  or  six  times  as  broad  as  they  are  in  the  unimpregnated  state.  They 
are  united  into  bundles,  or  fasciculi,  which,  in  certain  of  the  layers,  interlace  with  each 
other  in  every  direction. 

It  is  quite  difficult  to  follow  out  the  course  of  the  fasciculi  of  the  muscular  tissue  of 
the  uterus,  and  the  layers  of  fibres  are  described  somewhat  differently  by  different 
writers.  All  agree,  however,  that  there  is  a  superficial  layer,  tolerably  distinct,  very 
thin,  resembling  the  platysma  myoides,  which  is  sometimes  called  the  platysma  of  the 
uterus.  In  addition  to  this  layer,  we  shall  describe  two,  making,  in  all,  three  layers,  an 
external,  middle,  and  internal,  although  this  division  is  somewhat  arbitrary. 


FEMALE   ORGANS   OF  GENERATION.  865 

The  external  muscular  layer,  which  is  very  thin  but  distinct,  is  closely  attached  to  the 
peritoneum.  When  the  uterus  is  somewhat  enlarged  after  impregnation,  we  observe 
oblique  and  transverse  superficial  fibres  passing  over  the  f  undus  and  the  anterior  and  pos- 
terior surfaces  to  the  sides.  Here  they  are  prolonged  upon  the  Fallopian  tubes,  the  round 
ligament,  and  the  ligament  of  the  ovary,  and  also  extend  between  the  layers  of  the  broad 
ligament.  This  external  layer  is  so  thin  that  it  cannot  be  very  efficient  in  the  expulsive 
contractions  of  the  uterus ;  but,  from  its  connections  with  the  Fallopian  tubes  and  the 
ligaments,  it  is  useful  in  holding  the  uterus  in  place.  It  does  not  extend  entirely  over 
the  sides  of  the  uterus.  Rouget,  who  has  given  a  very  elaborate  description  of  the  ex- 
ternal layer  in  the  human  subject  and  in  various  classes  of  animals,  has  found  it  prolonged 


f 


b 


FIG.  275.— Superficial  muscular  fibres  of  the  anterior  surface  of  the  uterus.    (LiSgeois.) 
a,  a,  round  ligaments ;  &,  &,  Fallopian  tubes  ;  c,  c,  e,  e,  transverse  fibres ;  c?,  /,  longitudinal  fibres. 

into  the  ligaments  and  extending  to  the  ovaries  and  Fallopian  tubes.  He  regards  the 
uterus  and  its  so-called  appendages  as  lying  between  two  thin,  muscular  sheets,  and  con- 
siders the  action  of  the  muscular  fibres  as  very  efficient  in  producing  an  engorgement  of 
the  erectile  tissue  of  the  internal  organs,  by  constriction  of  the  veins.  Erection,  accord- 
ing to  this  observer,  occurs  at  the  period  of  menstruation,  determines  the  application  of 
the  fimbriated  extremity  of  the  Fallopian  tubes  to  the  surface  of  the  ovary,  and  assists 
in  the  expulsion  of  the  ovum.  These  points  will  be  more  fully  considered  under  the  head 
of  ovulation. 

The  middle  muscular  layer  is  the  one  most  efficient  in  the  parturient  contractions  of 
the  uterus.  It  is  composed  of  a  thick  and  complicated  net-work  of  fasciculi  interlacing 
with  each  other  in  every  direction. 

The  inner  muscular  layer  is  arranged  in  the  form  of  broad  rings,  which  surround  the 
Fallopian  tubes,  become  larger  as  they  extend  over  the  body  of  the  uterus,  and  meet  at 
the  centre  of  the  organ  near  the  neck. 

The  mucous  membrane  of  the  uterus  is  of  a  pale,  reddish  color ;  and  that  portion 
lining  the  body  is  smooth,  and  so  closely  attached  to  the  subjacent  structures,  that  it 
cannot  be  separated  to  any  great  extent  by  dissection.  There  is,  however,  no  proper 
55 


866 


GENERATION. 


submucous  areolar  tissue,  the  membrane  being  applied  directly  to  the  uterine  walls.  It  is 
covered  by  a  single  layer  of  cylindrical  epithelial  cells  with  delicate  cilia,  the  movements 
of  which  are  from  without  inward,  toward  the  openings  of  the  Fallopian  tubes.  Ex- 
amination of  the  surface  of  the  membrane 
with  a  low  magnifying  power  shows  the 
openings  of  numerous  tubular  glands. 
These  glands  are  usually  simple,  some- 
times branched,  dividing,  about  midway 
between  the  opening  and  the  lower  ex- 
tremity, into  two  and,  very  rarely,  into 
three  secondary  tubules.  Their  course  is 
generally  tortuous,  so  that  their  length 
frequently  exceeds  the  thickness  of  the 
mucous  membrane.  The  openings  of  these 
tubes  are  about  ^^  of  an  inch  in  diameter. 
The  uterine  tubes  are  of  considerable 
physiological  interest  and  have  been  the 
subject  of  much  discussion.  Their  secre- 
tion, which  forms  a  thin  layer  of  mucus 
on  the  surface  of  the  membrane  in  health, 
is  grayish,  viscid,  and  feebly  alkaline.  The 
tubes  themselves  have  exceedingly  thin, 
structureless  walls,  and  are  lined  with 
cylindrical  ciliated  epithelial  cells. 

The  changes  which  the  mucous  mem- 
brane of  the  body  of  the  uterus  undergoes 

Un- 
der ordinary  conditions,  its  thickness  is 
from  FV  to  TV  of  an  inch  ;  but  it  measures,  during  the  menstrual  period,  from  |  to  i  of 
an  inch. 

In  the  cervix,  the  mucous  membrane  is  paler,  firmer,  and  thicker  than  the  mem- 
brane of  the  body  of  the  uterus,  and  between  these  two  surfaces,  there  is  a  distinct 
line  of  demarkation.  It  is  here  more  loosely  attached  to  the  subjacent  tissue  in  the 
cervix,  and  the  anterior  and  posterior  surfaces  of  the  neck  present  an  appearance  of 
folds  radiating  from  the  median  line,  forming  what  has  been  called  the  arbor  vitse  uteri, 
or  plicsB  palmatae.  These  so-called  folds  are  supposed  by  some  anatomists  to  be  formed 
by  rows  of  large,  papillary  elevations  of  the  membrane.  Throughout  the  entire  cervical 
membrane,  are  numerous  mucous  glands,  and,  in  addition,  in  the  lower  portion,  are  a 
few  rounded,  semitransparent,  closed  follicles,  called  the  ovules  of  Naboth,  which  are 
probably  cystic  enlargements  of  obstructed  follicles.  The  upper  half  of  the  cervical 
membrane  is  smooth,  but  the  lower  half  presents  numerous  villi.  The  epithelium  of 
the  cervix  presents  great  variations  in  its  character  in  different  individuals.  Before  the 
time  of  puberty,  the  entire  membrane  of  the  cervix  is  covered  with  ciliated  epithelium. 
After  puberty,  however,  the  epithelium  of  the  lower  portion  changes  its  character,  and 
we  have  cylindrical  cells  above,  with  squamous  cells  in  the  inferior  portion.  The  latter 
extend  upward  in  the  neck  to  a  variable  distance. 

The  blood-vessels  of  the  uterus  are  very  large  and  present  certain  important  peculi- 
arities in  their  arrangement.  The  uterine  arteries  pass  between  the  layers  of  the  broad 
ligament  to  the  neck,  and  then  ascend  by  the  sides  of  the  uterus,  presenting  an  exceed- 
ingly rich  plexus  of  convoluted  vessels,  anastomosing  above  with  branches  from  the 
ovarian  arteries,  sending  branches  over  the  body  of  the  uterus,  and  finally  penetrating 
the  organ,  to  be  distributed  mainly  in  the  middle  layer  of  muscular  fibres.  In  their 
course,  these  vessels  present  the  convoluted  arrangement  characteristic  of  erectile  tissue 


FIG.  2T6. — Inner  layer  of  muscular  fibres  of  the  uterus. 
(Liegeois.) 

a,  a,  rings  around  the  openings  of  the  Fallopian  tubes ;  &,  &,   during  menstruation  are  remarkable. 

circular  fibres  of  the  cervix. 


FEMALE  ORGANS  OF  GENERATION.  867 

and  form  a  sort  of  mould  of  the  body  of  the  uterus.  Rouget  calls  this  the  erectile  tissue 
of  the  internal  generative  organs.  By  placing  the  pelvis  in  a  bath  of  warm  water  and 
injecting  what  he  calls  the  spongy  bodies  of  the  ovaries  and  uterus  by  the  ovarian  veins, 
he  produced  a  distention  of  the  vessels  and  a  true  erection,  the  uterus  executing  a  move- 
ment analogous  to  that  of  the  penis  during  venereal  excitement. 


FIG.  277.— Blood  -vessels  of  the  uterus  and  ovaries  ;  posterior  view.   ^Rouget.) 

T,  T,  Fallopian  tubes  ;  O,  O,  ovaries ;  U,  uterus ;  V,  vagina ;  P,  pubis ;  L,  anterior  round  ligament ;  1,  2,  muscular 
fibres  of  the  vagina ;  3,  4,  ligament  of  the  ovary ;  5,  superior  round  ligament ;  6,  ovarian  artery;  7,  ovarian  vein ; 
8,  uterine  artery ;  9,  uterine  vein ;  10, 11,  uterine  plexus ;  12,  vaginal  plexus. 

In  addition  to  the  erectile  action  above  described,  Wernich  has  lately  noted  a  true 
erection  of  the  lower  portion  of  the  uterus,  particularly  the  neck,  which  he  believes  to 
be  very  efficient  in  aiding  the  penetration  of  spermatozoids.  In  several  observations,  he 
noticed,  during  a  vaginal  examination  by  the  touch,  that  the  neck  of  the  uterus,  which 
at  first  was  soft  and  flaccid,  became  elongated,  hardened,  and  apparently  in  a  condition 
of  erection,  giving  an  impression  to  the  finger  comparable  to  the  hardened  glans  penis. 
As  an  anatomical  explanation  of  the  phenomena  observed,  Wernich  quotes  from  Henle 
an  account  of  the  arrangement  of  the  blood-vessels  of  the  cervix  and  his  physiological 
deductions  from  the  presence,  in  this  portion  of  the  uterus,  of  a  true  erectile  tissue. 
This  question  will  be  considered  more  fully  under  the  head  of  the  mechanism  of  fecun- 
dation. 

In  the  muscular  structure  of  the  uterus,  are  numerous  large  veins,  the  walls  of  which 
are  closely  adherent  to  the  uterine  tissue.  During  gestation,  these  vessels  become  en- 
larged, forming  the  so-called  uterine  sinuses. 

Lymphatics  are  not  very  numerous  in  the  unimpregnated  uterus,  but  they  become 
largely  developed  during  gestation.  They  exist  in  a  superficial  and  a  deep  layer,  the 
deeper  vessels  coming  from  the  muscular  substance  and  probably  also  from  the  mucous 
membrane. 

The  uterine  nerves  are  derived  from  the  inferior  hypogastric  and  the  spermatic  plex- 
uses, and  the  third  and  fourth  sacral.  In  the  substance  of  the  uterus,  they  present  in 
their  course  small  collections  of  ganglionic  cells  and  it  is  said  that  the  nerves  pass  finally 
to  the  nucleoli  of  the  muscular  fibres. 


868  GENERATION.. 

The  Fallopian  Tubes.— The  Fallopian  tubes,  or  oviducts,  lead  from  the  ovaries  to  the 
uterus.  They  are  shown  in  Fig.  270.  These  tubes  are  from  three  to  four  inches  long, 
but  their  length  is  not  always  equal  upon  the  two  sides.  They  lie  between  the  folds  of 
the  broad  ligament  at  its  upper  border.  Opening  into  the  uterus  upon  either  side  at  the 
cornua,  they  present  a  small  orifice,  about  -fa  of  an  inch  in  diameter.  From  the  cornua, 
they  take  a  somewhat  undulatory  course  outward,  gradually  increasing  in  size,  so  that 
they  are  rather  trumpet-shaped.  Near  the  ovary,  they  turn  downward  and  backward. 
The  extremity  next  the  ovary  is  marked  by  from  ten  to  fifteen  fimbrise,  or  fringes,  which 
has  given  this  the  name  of  the  fimbriated  extremity,  or  morsus  diaboli.  All  of  these 


Fio.  278.— Fallopian  tube.    (Liegeois.) 


fringe-like  processes  are  free,  except  one  ;  and  this  one,  which  is  longer  than  the  others, 
is  attached  to  the  outer  angle  of  the  ovary  and  presents  a  little  gutter,  or  furrow,  ex- 
tending from  the  ovary  to  the  opening  of  the  tube.  At  this  extremity,  is  the  abdominal 
opening  of  the  tube,  which  is  two  or  three  times  as  large  as  the  uterine  opening.  Pass- 
ing from  the  uterus,  the  caliber  of  the  tube  gradually  increases  as  the  tube  itself  en- 
larges, and  there  is  an  abrupt  constriction  at  the  abdominal  opening. 

Beneath  the  peritoneal  coat,  which  is  formed  by  the  layers  of  the  broad  ligament,  is 
a  layer  of  connective  tissue,  containing  a  rich  plexus  of  blood-vessels.  This  constitutes 
the  proper  fibrous  coat  of  the  Fallopian  tubes. 

The  muscular  layer  is  composed  mainly  of  circular  fibres  of  the  non-striated  variety, 
with  a  few  longitudinal  fibres  prolonged  over  the  tube  from  the  external  muscular  layer 
of  the  uterus.  This  coat  is  quite  thick  and  sends  bands  between  the  layers  of  the  broad 
ligament  to  the  ovary,  which  are  supposed  to  act  in  adapting  the  fimbriated  extremity  of 
the  tube  to  the  surface  of  the  ovary. 

The  mucous  membrane  of  the  tube  is  thrown  into  folds,  which  are  longitudinal  and 
transverse  near  the  uterus,  and  are  more  complicated  at  the  dilated  portion.  In  this 
portion,  next  the  ovary,  embracing  about  the  outer  two-thirds,  the  folds  project  far  into 
the  caliber  of  the  tube.  These  are  sometimes  simple,  but  more  frequently  they  present 
secondary  folds,  often  meeting  as  they  project  from  opposite  sides.  This  arrangement 
gives  an  arborescent  appearance  to  the  membrane  on  transverse  section  of  the  tube. 
The  mucous  membrane  is  covered  by  cylindrical  ciliated  epithelium,  the  movement  of 
the  cilia  being  from  the  ovary  toward  the  uterus.  At  the  margins  of  the  fimbriae,  the 
ciliated  epithelium  is  continuous  with  the  epithelium  of  the  peritoneum,  presenting  the 
exceptional  example  of  an  opening  of  a  mucous-lined  tube  into  the  cavity  of  the  perito- 
neum. The  membrane  of  the  tubes  has  no  mucous  glands. 

It  is  not  necessary  to  enter  into  a  minute  description  of  the  external  organs  of  the 
female.  Opening  by  the  vulva,  externally,  and  terminating  at  the  neck  of  the  uterus,  is 
a  membranous  tube,  the  vagina.  This  lies  between  the  bladder  and  the  rectum.  It  has 


STRUCTURE   OF  THE   OVUM.  869 

a  curved  direction,  being  about  four  inches  long  in  front,  and  five  or  six  inches  long  pos- 
teriorly. There  is  a  constricted  portion  at  the  outer  opening,  where  we  have  a  muscle, 
called  the  sphincter  vagina,  and  the  tube  is  somewhat  narrowed  at  its  upper  end,  where 
it  embraces  the  cervix  uteri.  The  inner  surface  presents  a  mucous  membrane,  marked  by 
transverse  rugae,  with  papilla  and  mucous  glands.  Its  surface  is  covered  with  flattened 
epithelium.  The  vagina  is  quite  extensible,  as  it  must  be  during  parturition,  to  allow 


FIG.  279. — External  erectile  organs  of  the  female.    (Liegeois.) 

A,  pubis;  B,  B,  ischium ;  C,  clitoris  ;  D,  gland  of  the  clitoris ;  E,  bnlb ;  F,  constrictor  muscle  of  the  vulva ;  G,  left 
pillar  of  the  clitoris  ;  H,  dorsal  vein  of  the  clitoris ;  I,  intermediary  plexus ;  J,  vein  of  communication  with  the 
obturator  vein ;  K,  obturator  vein ;  M,  labia  minora. 

the  passage  of  the  child.  It  presents  a  proper  coat  of  dense  fibrous  tissue,  with  longi- 
tudinal and  circular  muscular  fibres  of  the  non-striated  variety.  We  have,  also,  sur- 
rounding it,  a  rather  loose  erectile  tissue,  which  is  most  prominent  at  its  lower  portion. 

The  parts  composing  the  external  organs  are  abundantly  supplied  with  vessels  and 
nerves.  In  the  clitoris,  which  corresponds  to  the  penis  of  the  male,  and  on  either  side 
of  the  vestibule,  we  find  a  true  erectile  tissue. 

Structure  of  the   Ovum. 

The  ripe  ovum  lies  in  the  Graafian  follicle,  embedded  in  the  mass  of  cells  which  con- 
stitutes the  discus  proligerus.  Within  the  discus,  surrounding  the  ovum,  there  seem  to 
be  two  kinds  of  cells ;  first,  cells  evidently  belonging  to  the  Graafian  follicle  and  similar 
to  the  cells  in  other  parts  of  the  membrana  granulosa ;  second,  a  single  layer  of  columnar 
cells  belonging  to  the  ovum  and  probably  concerned  in  the  production  of  the  proper 
membrane  of  the  ovum,  the  vitelline  membrane.  Regarding  the  vitelline  membrane  as 
the  external  covering,  we  can  see,  in  the  ovum,  a  clear,  transparent  membrane,  a  granu- 
lar mass  (the  vitellus)  filling  this  membrane  completely,  a  large,  clear  nucleus,  called  the 
germinal  vesicle,  and  a  nucleolus,  called  the  germinal  spot. 

The  size  of  the  ripe  ovum,  in  the  human  subject  and  in  mammals,  is  about  T£T  of  an 
inch,  and  its  form  is  globular. 

The  external  membrane  of  the  ovum  is  clear,  apparently  structureless,  quite  strong 
and  resisting,  and  it  measures  about  -^^  of  an  inch  in  thickness.  As  it  forms  a  trans- 
parent ring  in  the  mass  of  cells  in  which  the  ovum  is  embedded,  this  is  sometimes  called 
the  zona  pellucida.  According  to  recent  researches,  it  seems  that  the  primordial  ovum 
has  at  first  no  special  investing  membrane ;  as  it  develops,  it  presents,  surrounding  the 


870  GENERATION. 

vitellus,  a  single  layer  of  columnar  cells ;  at  the  deepest  portion  of  these  cells,  a  homo- 
geneous basement-membrane  is  gradually  formed  ;  and  the  cells  undergo  a  sort  of  cuticu- 
lar  transformation,  becoming  finally  the  vitelline  membrane. 

An  important  point,  in  this  connection,  is  the  question  of  the  existence  of  pores,  or  per- 
forations in  the  vitelline  membrane.  As  we  shall  see  farther  on,  there  can  be  no  doubt 
with  regard  to  the  actual  penetration  of  the  spermatozoids  through  this  membrane,  so 
that  they  come  in  contact  with  the  vitellus ;  and  it  is  in  this  way  that  the  ovum  is  fecun- 
dated. In  the  osseous  fishes  and  in  mollusks,  there  seems  to  be  no  question  with  regard 
to  the  existence  of  numerous  pores  in  the  vitelline  membrane  ;  but  these  are  not  so  easily 
demonstrated  in  the  ova  of  mammals.  Admitting  the  existence  of  a  micropyle  and  pores 
in  the  vitelline  membrane  in  fishes  and  mollusks,  it  is  certain  that  openings  are  very 
much  more  indistinct,  if  they  can  be  seen  at  all,  in  the  ova  of  mammals ;  still,  the  fact 
of  the  actual  penetration  of  spermatozoids  almost  of  necessity  presupposes  the  presence 
of  orifices.  We  have  often  thought,  in  studying  this  subject,  that  it  must  be  difficult, 
examining  a  perfectly  transparent  and  homogeneous  membrane  in  water,  which  would 
fill  up  all  pores,  to  distinguish  any  openings,  and  we  have  been  disposed  to  admit  their 
presence,  mainly  because  the  spermatozoids  are  known  to  pass  through.  The  idea  of 
their  existence  in  mammals  certainly  receives  support  from  analogy  with  the  lower 
orders  of  animals. 

The  vitellus,  called  the  principal  yolk  or  the  formative  yolk,  contains  the  elements 
which  are  to  undergo  development  into  the  embryon.  It  is  composed  of  a  semifluid 
mass,  containing,  in  addition  to  the  germinal  vesicle,  numerous  granules.  Some  of  these 
granules  are  large,  strongly-refracting,  globular  bodies,  which  are  so  bright  and  so  numer- 
ous, that  they  obscure  the  other  parts  of  the  vitellus.  Between  these,  are  numerous  albu- 
minoid granules,  which  are  much  smaller  and  not  so  distinct. 

The  germinal  vesicle,  sometimes  called  the  vesicle  of  Purkinje,  is  the  enlarged  nucleus 
of  the  primordial  ovum.  It  is  a  clear,  globular  vesicle,  about  7^  of  an  inch  in  diameter, 
embedded  in  the  vitellus,  its  position  varying  in  different  ova.  It  presents  in  its  interior 
a  number  of  fine  granules,  and  a  large,  dark  spot,  called  the  germinal  spot,  or  the  spot 
of  Wagner,  which  measures  about  ^gV?  of  an  inch  in  diameter.  This  spot  corresponds 
to  the  nucleolus  of  the  primordial  ovum.  In  mammals,  the  mature  ovum  contains  but 
one  germinal  vesicle  and  one  germinal  spot.  The  various  points  we  have  described  are 
illustrated  in  Fig.  280. 

Discharge  of  the    Ovum. 

A  ripe  Graafian  follicle  measures  from  f  to  \  of  an  inch  in  diameter  and  presents  a 
rounded  elevation,  containing  a  plexus  of  blood-vessels,  upon  the  surface  of  the  ovary. 
At  its  most  prominent  portion,  is  an  ovoid  spot,  in  which  the  membranes  are  entirely  free 
from  blood-vessels.  At  this  spot,  which  is  called  the  macula  folliculi,  the  coverings  finally 
give  way,  and  the  contents  of  the  follicle  are  discharged.  For  a  short  time  anterior  to 
the  rupture  of  the  follicle,  important  changes  have  been  going  on  in  its  structure.  In 
the  first  place,  the  non- vascular  portion,  situated  at  the  very  surface  of  the  ovary,  under- 
goes fatty  degeneration,  by  which  this  part  of  the  wall  becomes  gradually  weakened.  At 
the  same  time,  at  the  other  portions  of  the  follicle,  there  is  a  growth  of  cells,  which  pro- 
ject into  the  interior,  and  an  extension,  into  the  interior,  of  blood-vessels  in  the  form  of 
loops.  These  changes,  with  an  increase  in  the  pressure  of  liquid  and  the  fatty  degen- 
eration of  the  macula,  cause  the  follicle  to  burst ;  and,  with  the  liquid,  the  discus  prolige- 
rus  and  the  ovum  are  expelled.  The  formation  of  a  cell-growth  in  the  interior  of  the 
follicle  is  really  the  beginning  of  the  corpus  luteum  ;  and  this  occurs  some  time  before 
the  discharge  of  the  ovum  takes  place.  It  is  a  disputed  question  whether  or  not  a 
hemorrhage  occurs  into  the  follicle  at  the  time  of  its  rupture.  This  may,  and  undoubtedly 
does  sometimes  occur,  but  it  cannot  be  regarded  as  constant  and  has  been  denied  by 
many  observers. 


DISCHARGE   OF  THE   OVUM. 


871 


The  time  at  which  the  follicle  ruptures,  particularly  with  reference  to  the  menstrual 
period,  is  probably  not  definite ;  but  it  is  certain  that,  while  sexual  excitement  may 
hasten  the  discharge  of  an  ovum  by  producing  a  greater  or  less  tendency  to  congestion 
of  the  internal  organs,  ovulation  takes  place  independently  of  the  action  of  coition.  The 
opportunities  for  determining  this  fact  in  the  human  female  are  not  frequent ;  but  it  has 
been  fully  demonstrated  by  observations  upon  the  inferior  animals,  and  there  is  now  no 
doubt  with  regard  to  the  identity  of  the  phenomena  of  rut  and  of  menstruation.  It  is 
useless,  at  the  present  day,  to  enter  into  an  elaborate  discussion  of  this  point,  which 
occupied  so  much  the  attention  of  the  earlier  writers.  From  the  earliest  times,  it  was 
recognized,  not  only  that  women  became  fruitful  only  after  the  appearance  of  the  menses, 
but  that  sexual  intercourse  was  most  likely  to  be  followed  by  conception  when  it 
occurred  near  the  periods  ;  a  point  which  we  shall  discuss  more  fully  under  the  head  of 
fecundation.  When  it  was  recognized  that  rupture  of  Graafian  follicles  was  followed  by 
the  formation  of  corpora  lutea,  it  became  easy  to  verify  the  supposition  that  the  ova 
were  discharged  at  regular  intervals,  by  an  examination  of  the  ovaries  in  women  who 
had  died  suddenly;  and  such  observations,  showing  corpora  lutea  in  virgins,  demon- 
strated that  ovulation  was  not  necessarily  dependent  upon  coitus. 


FIG.  280.— Ovum  of  the  rabbit,  from  a  Graafian  follicle  fa  of  an  inch  in  diameter.    (Waldeyer.) 
a,  epithelium  of  the  ovum ;  £>,  zona  pellucida,  with  radiating  Btriations  (vitelline  membrane)  ;  c,  germinal  vesicle ; 

tf,  germinal  spot ;  e,  vltellus. 

Observations  upon  the  lower  animals  have  shown,  notwithstanding  the  fact  of  dis- 
charge of  ova  without  copulation  or  even  the  sight  of  the  male,  that  sexual  excitement 
has  a  certain  influence  upon  ovulation.  The  experiments  of  Coste  upon  this  point  are 
very  interesting.  This  observer  noted  that,  in  rabbits  killed  from  ten  to  fifteen  hours 
after  copulation,  there  was  evidence  of  the  recent  discharge  of  ova.  In  two  experiments, 
however,  he  took  female  rabbits  in  heat  and  manifesting  the  greatest  ardor  for  the  male, 
presented  them  to  the  male,  in  order  to  show  that  they  were  really  in  heat,  but  care- 
fully prevented  copulation.  This  was  done  for  three  days  in  succession,  there  being,  on 
each  occasion,  a  manifest  desire  for  the  approach  of  the  male.  One  rabbit  was  killed  on 
the  third  day,  while  still  in  heat ;  and  six  distended  Graafian  follicles  were  found  in  one 


872  GENEKATIOK 

ovary  and  two  in  the  other ;  but  there  was  no  trace  of  ruptured  follicles.  The  other 
rabbit  ceased  to  be  in  heat  on  the  fourth  day  and  was  killed  on  the  fifth.  This  animal 
presented  seven  distended  follicles  on  one  side,  and  one  on  the  other,  but  no  ruptured 
follicles.  From  these  and  other  experiments  upon  the  lower  animals,  there  seems  to  be 
no  doubt  that  copulation  hastens  the  rupture  of  ripe  Graafian  follicles;  but,  on  the  other 
hand,  it  is  equally  true  that  follicles  rupture  independently  of  the  sexual  act. 

To  return  to  the  phenomena  which  attend  ovulation  in  the  human  subject,  there  is 
every  reason  to  suppose,  at  least  from  analogy,  that  the  excitement  of  the  genital  organs 
during  sexual  intercourse  may  determine  the  rupture  of  a  ripe  Graafian  follicle.  At 
stated  periods,  marked  by  the  phenomena  of  menstruation,  one,  and  sometimes  more 
Graafian  follicles  become  distended  and  usually  rupture  and  discharge  their  contents  into 
the  Fallopian  tubes.  This  discharge  of  an  ovum  or  ova  may  occur  at  the  beginning,  at 
the  end,  or  at  any  time  during  the  continuance  of  the  menstrual  flow.  Upon  this 
point,  the  observations  of  Coste,  which  were  made  many  years  ago,  seem  entirely  con- 
clusive. In  a  woman  who  died  on  the  first  day  of  menstruation,  he  found  a  recently- 
ruptured  follicle ;  in  other  instances,  at  a  more  advanced  period  and  toward  the  decline 
of  the  menstrual  flow,  he  found  evidences  that  the  rupture  had  occurred  later ;  in  the 
case  of  a  female  who  drowned  herself  four  or  five  days  after  the  cessation  of  the  menses, 
a  follicle  was  found  in  the  right  ovary,  so  distended  that  it  was  ruptured  by  very  slight 
pressure ;  and  other  instances  were  observed  in  which  follicles  were  not  ruptured  during 
the  menstrual  period.  The  most  striking  case  of  this  kind  was  of  a  young  girl,  nineteen 
years  of  age,  who  committed  suicide  fifteen  days  after  the  menstrual  period.  The  ovaries 
were  examined  with  the  greatest  care.  "By  the  side  of  the  Graafian  vesicles  largely 
developed,  were  found  traces  of  ruptured  vesicles ;  but  the  corpora  lutea  were  evidently 
too  old  to  be  reasonably  referred  to  the  last  menstruation ;  the  Graafian  vesicle,  conse- 
quently, had  not  matured,  or  at  least  had  been  arrested  in  its  development." 

In  conclusion,  remembering  that  coitus  may  hasten  the  rupture  of  ripe  follicles,  we 
quote  from  Coste  the  following  as  representing  what  we  know  of  the  relations  between 
ovulation  and  menstruation : 

"  As  a  summary,  then,  of  all  the  facts  that  I  have  observed,  I  believe  it  to  be  con- 
clusive, that,  in  the  human  female,  there  is  always,  at  each  menstrual  period,  as  during 
the  condition  of  rut  in  animals,  a  vesicle  of  the  ovary  which  has  a  marked  preponder- 
ance over  the  others;  that  it  spontaneously  arrives  at  maturity,  and,  most  generally,  is 
ruptured  at  some  time  during  this  period  to  give  issue  to  the  ovum  which  it  contains; 
but  there  are  cases,  also,  in  which,  in  the  absence  of  sufficiently  favorable  conditions, 
this  distended  vesicle  cannot  accomplish  this  end,  and,  as  in  mammals  again,  may  remain 
stationary  or  be  entirely  reabsorbed." 

Passage  of  Ova  into  the  Fallopian  Tubes. 

The  fact  that  the  ova,  in  the  great  majority  of  instances,  pass  into  the  Fallopian 
tubes,  is  sufficiently  evident.  The  fact,  also,  that  ova  may  fall  into  the  cavity  of  the 
peritoneum  is  shown  by  the  occasional  occurrence  of  extra-uterine  pregnancy,  a  rare 
accident,  which  shows  that,  in  all  probability,  the  failure  of  unimpregnated  ova  to  enter 
the  tubes  is  exceptional.  When  we  come,  however,  to  the  mechanism  of  the  passage 
of  the  ova  into  the  tubes,  the  explanation  is  difficult.  At  the  present  time  there  are  two 
theories  with  regard  to  this  process ;  one,  in  which  it  is  supposed  that  the  fimbriated 
extremities  of  the  Fallopian  tubes,  at  the  time  of  rupture  of  the  Graafian  follicles,  be- 
come adapted  to  the  surface  of  the  ovaries;  and  the  other,  that  the  ova  are  carried  to 
the  openings  of  the  tubes  by  ciliary  currents.  Neither  of  these  theories  is  capable  of 
actual  demonstration  ;  and  we  can  only  judge  of  their  probable  correctness  from  ana- 
tomical facts.  Kouget,  an  earnest  advocate  of  the  first-mentioned  theory,  has  given  an 
exact  description  of  the  muscular  structures  connected  with  the  tubes  and  ovaries.  "We 


PASSAGE  OF  OVA  INTO  THE  FALLOPIAN  TUBES.  873 

have  already  seen  that  one  of  the  fimbriaa  of  the  tube  is  longer  than  the  others  and  is 
attached  to  the  outer  angle  of  the  ovary.  The  other  fimbriae  are  unattached  and  are 
distant  from  about  half  an  inch  to  an  inch  from  the  ovarian  surface.  According  to  this 
observer,  there  is  a  double  layer  of  muscular  fibres,  passing  from  the  lumbar  region  of 
the  uterus  and  embracing  the  whole  of  the  dilated  portion  of  the  tube  ;  and  the  action  of 
these  fibres  must  draw  the  extremity  of  the  tube  toward  the  ovary  and  apply  it  to  its  sur- 
face. That  the  muscular  fibres  described  by  Rouget  exist,  there  can  be  scarcely  a  doubt ; 
but  that  their  action  is  essential  to  the  passage  of  ova  into  the  Fallopian  tubes,  is  a  ques- 
tion for  discussion.  If  we  could  assume  with  certainty  that  the  ova  are  discharged  only 
during  sexual  intercourse,  or  that  follicles  are  usually  ruptured  as  a  consequence  of 
pressure  exerted  by  the  muscular  action  described  by  Rouget,  this  theory  would  be  ren- 
dered exceedingly  probable,  to  say  the  least ;  but  the  facts  do  not  admit  of  this  exclusive 
view.  However,  observations  upon  the  lower  animals,  particularly  rabbits,  have  shown 
that  copulation  actually  hastens  the  discharge  of  ova  from  ripe  Graafian  follicles ;  but  it 
must  be  a  question  of  theory  simply,  whether  the  act  be  attended  with  the  muscular 
contraction  indicated  by  Rouget,  or  whether  there  be  a  determination  of  blood  to  the 
ovary,  which  produces  an  additional  tendency  to  rupture  at  this  time.  We  can  hardly 
adopt  unreservedly  the  theory  of  Rouget,  unless  it  be  evident  that  there  is  no  other  way 
in  which  the  ova  can  enter  the  tubes.  The  fact  is  that,  in  the  human  female,  an  ovum 
may  be  discharged  at  the  beginning  of  menstruation,  at  any  time  during  the  flow,  or 
even  after  the  flow  has  ceased ;  and  it  is  more  than  probable  that  pressure  within  the 
follicle  alone  may  cause  its  rupture,  and  that  this  may  occur  independently  of  sexual 
excitement.  In  view  of  these  facts,  while  we  cannot  deny  that  the  firnbriated  extrem- 
ities of  the  tubes  may,  by  muscular  action,  be  drawn  toward  the  surface  of  the  ovary, 
we  cannot  admit  that  such  an  action  is  constant,  or  that  it  is  necessary  to  the  passage 
of  ova  into  the  tubes,  though  the  theory  of  Rouget  has  been  adopted,  entirely  or  in 
part,  by  some  writers  of  authority. 

If  we  take  into  account  the  situation  of  the  ovaries  and  the  relations  of  the  Fallopian 
tubes,  we  can  understand  how  an  ovum  may  pass  into  the  tube,  without  invoking  the  aid 
of  muscular  action.  Let  us  suppose,  for  example,  that  a  Graafian  follicle  be  ruptured 
when  the  fimbriated  extremity  of  the  tube  is  not  applied  to  the  surface  of  the  ovary.  One 
of  the  fimbriae,  longer  than  the  others,  is  attached  to  the  outer  angle  of  the  ovary  and 
presents  a  little  furrow,  or  gutter,  leading  to  the  opening  of  the  tube.  This  furrow  is 
lined  by  ciliated  epithelium,  as  indeed,  is  the  mucous  membrane  of  all  of  the  fimbria3,  the 
movements  of  which  produce  a  current  in  the  direction  of  the  opening,  which  we  might 
suppose  would  be  sufficient  to  carry  a  little  globule,  only  y^-j-  of  an  inch  in  diameter,  into 
the  tube.  At  the  same  time,  there  is  probably,  as  has  been  suggested  by  Becker,  a  con- 
stant flow  of  liquid  over  the  ovarian  surface,  directed  by  the  ciliary  current  toward  the 
tube ;  and  when  the  liquid  of  the  ruptured  follicle  is  discharged,  this,  with  the  ovum, 
takes  the  same  course. 

In  all  probability,  what  we  have  just  described  is  the  mechanism  of  the  passage  of  the 
ova  into  the  Fallopian  tubes ;  and  it  is  possible  that  the  fimbriated  extremity  may  be 
drawn  toward  the  ovarian  surface,  though  we  can  hardly  understand  how  it  can  be  closely 
applied  to  the  ovary  and  exert  any  considerable  pressure  upon  the  distended  follicle.  It 
is  proper  to  note,  also,  that  the  conditions  dependent  upon  the  currents  of  liquid  directed 
by  the  movements  of  cilia,  are  constant  and  could  influence  the  passage  of  an  ovum  at 
whatever  time  it  might  be  discharged,  while  a  muscular  action  would  be  more  or  less 
intermittent. 

It  is  somewhat  difficult  to  understand  the  exact  mechanism  of  the  passage  of  an  ovum 
discharged  from  an  ovary  into  the  Fallopian  tube  upon  the  opposite  side,  although  it  cannot 
be  doubted  that  this  sometimes  occurs.  Schroeder  has  collected,  from  various  authors,  the 
reports  of  several  cases,  in  which  an  ovum  has  been  discharged,  has  found  its  way  into 
the  uterus,  and  has  undergone  development,  one  tube  being  closed  and  the  corpus  luteum 


874  GENERATION. 

existing  upon  the  side  on  which  the  tube  was  impervious.  In  some  instances  in  which 
the  corpus  luteum  has  been  found  on  the  side  on  which  the  tube  was  closed,  tubal  preg- 
nancy has  occurred  upon  the  opposite  side.  In  these  cases,  the  ovum  must  have  passed 
across  the  uterus.  It  is  possible  that,  the  subject  lying  upon  one  side,  a  current  of  liquid 
may  have  taken  a  direction  from  the  ovary  to  the  opposite  tube,  but  this  can  be  only  a 
matter  of  conjecture. 

Puberty  and  Menstruation. 

At  a  certain  period  of  life,  usually  between  the  age  of  thirteen  and  of  fifteen  years, 
the  human  female  undergoes  a  remarkable  change  and  arrives  at  what  is  termed  the  age 
of  puberty.  At  this  time,  there  is  a  marked  increase  in  the  general  development  of  the 
body ;  the  limbs  become  fuller  and  more  rounded ;  a  growth  of  hair  makes  its  appearance 
upon  the  mons  veneris ;  the  mammary  glands  increase  in  size  and  take  on  a  new  stage  of 
development ;  Graafian  follicles  enlarge,  and  one  or  more  approach  the  condition  favor- 
able to  rupture  and  the  discharge  of  ova.  At  this  time,  also,  certain  changes  are  observed 
in  the  moral  as  well  as  in  the  physical  attributes  of  the  female.  There  is  then  a  sort  of 
indefinite  consciousness  of  a  capacity  for  new  functions,  with  an  indescribable  change  in 
feeling  for  the  opposite  sex,  due  to  the  first  development  of  sexual  instincts.  The  female 
becomes  capable  of  impregnation,  and  continues  so,  in  the  absence  of  pathological  condi- 
tions, until  the  cessation  of  the  menses. 

It  is  a  commonly-recognized  fact  that  the  age  of  puberty  is  earlier  in  warm  than  in 
cold  climates;  and  numerous  instances  are  on  record,  in  which  the  menses  have  appeared 
exceptionally,  much  before  the  usual  period.  Generally,  at  the  age  of  forty  or  forty-five, 
the  menstrual  flow  becomes  irregular,  occasionally  losing  its  sanguineous  character,  and 
it  usually  ceases  at  about  the  age  of  fifty  years.  Sometimes  it  is  said  that  the  menses 
return,  with  a  second  period  of  fecundity,  though  this  is  rare.  According  to  most  writers, 
while  climate  has  a  certain  influence  over  the  time  of  cessation  as  well  as  the  first  appear- 
ance of  the  menses,  this  is  not  very  marked.  When  the  menses  appear  early  in  life,  they 
usually  cease  at  a  correspondingly  early  period ;  but  this  is  by  no  means  constant.  There 
are,  also,  numerous  exceptions  to  the  ordinary  limits  to  the  period  of  fecundity.  Haller 
observed  a  case  of  a  young  girl,  nine  years  of  age,  who  had  menstruated  for  several  years, 
and  others,  who  had  become  pregnant  at  nine,  ten,  and  twelve  years.  He  also  quotes 
cases  of  women  who  have  been  fruitful  at  from  fifty -four  to  seventy  years  of  age.  Other 
instances  of  this  kind  are  on  record,  which  it  is  unnecessary  to  quote.  The  occurrence 
of  pregnancy  after  the  age  of  fifty  or  fifty-five  is  certainly  doubtful. 

Menstruation. 

It  is  unnecessary  to  discuss  farther  the  correspondence  between  menstruation  in  the 
human  female  and  the  condition  of  heat  in  the  lower  animals,  as  we  have  already  seen, 
under  the  head  of  ovulation,  that  these  two  conditions  are  essentially  identical.  In  the 
lower  animals,  the  female  will  admit  the  male  only  at  the  period  of  heat ;  and,  in  some 
animals  in  the  savage  state,  it  is  only  at  this  time  that  the  male  is  capable  of  copulation. 
The  variations  in  sexual  temperament  in  the  human  female  are  so  considerable,  and  the 
sentiments  toward  the  opposite  sex  are  so  subordinate  to  artificial  conditions  of  society 
and  civilization,  that  it  is  difficult  to  establish  a  parallel,  in  this  regard,  between  her  and 
the  lower  animals.  Some  females  rarely  or  never  experience  sexual  excitement  and  have 
no  orgasm  during  intercourse ;  while  others  seem  to  be  capable  of  sexual  ardor  at  any  time. 
Women  who  are  in  the  habit  of  promiscuous  relations  with  the  other  sex  frequently  lose 
the  sexual  feeling  and  simulate  excitement  during  coitus.  It  is  very  difficult,  indeed,  to 
say  positively  how  far  the  facts  observed  in  the  lower  animals  are  applicable  to  the  human 
subject,  as  we  must  depend  largely  upon  statements  which,  of  themselves,  are  entitled  to 
but  little  consideration.  It  is  nevertheless  true  that,  in  some  women,  sexual  desire  is 


MENSTRUATION".  875 

decidedly  marked  just  after  the  cessation  of  the  menses,  and  in  many,  it  really  exists  at 
no  other  time.  -  Still,  mercenary  or  other  considerations  may  induce  women  to  admit 
intercourse  at  any  time,  and  the  sexual  orgasm,  and  even  fecundation,  may  at  any  time 
occur.  As  a  rule,  the  female  yields  to  advances  made  by  the  male  and  is  reputed  to 
experience  a  less  degree  of  sexual  desire  and  ardor,  although  this  has  marked  exceptions. 
It  is  probably  true  that,  eliminating,  as  far  as  we  can,  all  considerations  except  those 
of  a  purely  sexual  character,  there  is  less  of  a  promiscuous  feeling  for  the  opposite  sex  in 
females  than  in  males,  and  that  sexual  desire,  aside  from  feelings  of  fatigue  or  satiety,  is 
sometimes  markedly  periodical  in  women.  If  we  may  take  certain  individual  cases  as 
representing  physiological  conditions,  it  appears  that,  in  some  women,  there  is  a  period 
of  comparative  indifference  to  the  opposite  sex;  as  the  menses  approach,  there  is  more 
or  less  irritability  of  temper  and  disinclination  for  society,  which  disappear  as  the  flow  is 
established ;  and,  at  or  following  the  cessation  of  the  menses,  sexual  desire  is  manifested 
to  an  unusual  degree,  this  continuing  for  only  a  few  days. 

Although  there  is  a  periodical  condition  of  heat  in  the  lower  animals,  connected  with 
ovulation,  a  sanguineous  discharge  from  the  genital  organs  is  not  often  observed.  It  is 
only  in  monkeys  that  we  have  a  counterpart  of  what  occurs  in  the  human  female ;  and 
observations  upon  these  animals  have  shown  that  they  are  subject  to  a  monthly  discharge 
of  blood,  at  this  time  giving  evidence  of  unusual  salacity. 

In  the  human  female,  near  the  time  of  puberty,  there  is  sometimes  a  periodical  sero- 
mucons  discharge  from  the  genital  organs,  preceding,  for  a  few  months,  the  regular  estab- 
lishment of  the  menstrual  flow.  Sometimes,  also,  after  the  first  discharge  of  blood,  the 
female  passes  several  months  without  another  period,  when  the  second  flow  takes  place, 
and  the  menses  then  become  regular.  In  a  condition  of  health,  the  periods  recur  every 
month,  until  they  cease,  at  what  is  termed  the  change  of  life.  In  the  majority  of  cases, 
the  flow  recurs  on  the  twenty-seventh  or  the  twenty-eighth  day;  but  sometimes  the 
interval  is  thirty  days.  As  a  rule,  also,  utero-gestation,  lactation,  and  most  severe  dis- 
eases, acute  and  chronic,  suspend  the  periods ;  but  this  has  exceptions,  as  some  females 
menstruate  regularly  during  pregnancy,  and  it  is  not  very  uncommon  for  the  menses  to 
appear  during  lactation. 

As  we  should  naturally  expect,  from  the  connection  between  menstruation  and  ovu- 
lation, removal  of  the  ovaries,  especially  when  this  occurs  before  the  age  of  puberty,  is 
usually  followed  by  arrest  of  the  menses.  It  is  a  well-known  fact  that  animals  do  not 
present  the  phenomena  of  heat  after  extirpation  of  the  ovaries.  Eaciborski  has  quoted 
cases  of  this  operation  in  the  human  subject,  in  which  the  menses  were  arrested ;  but 
this  rule  does  not  appear  to  be  absolute,  as  Dr.  H.  E.  Storer  reports  at  least  one  case,  in 
which  menstruation  continued  with  regularity  for  more  than  a  year  after  removal  of  both 
ovaries.  Dr.  T.  Gr.  Thomas,  of  New  York,  in  three  cases  of  removal  of  both  ovaries 
from  menstruating  women,  which  he  followed  for  from  five  and  a  half  months  to  two 
years  and  eleven  months  after  the  operation,  noted  no  return  of  menstruation.  In  one 
case,  nearly  six  months  after  the  operation,  the  patient  had  "  a  bloody  discharge  from 
the  vagina  and  all  the  symptoms  accompanying  the  menstrual  function."  When  a  cow 
brings  forth  twins,  one  a  male  and  the  other  apparently  a  female,  the  latter  is  called  a 
free-martin  and  generally  has  no  ovaries.  Hunter,  in  his  paper  on  the  free-martin, 
gives  a  full  description  of  this  anomalous  animal  and  states  that  it  does  not  breed  or 
show  any  inclination  for  the  bull.  In  1868,  we  had  an  opportunity  of  examining  the 
generative  organs  of  a  free-martin  raised  and  killed  by  Prof.  James  E.  Wood.  In 
this  animal,  the  uterus  was  rudimentary  and  there  were  no  ovaries. 

A  menstrual  period  usually  presents  three  stages  :  first,  invasion  ;  second,  a  sanguine- 
ous discharge ;  third,  cessation. 

The  stage  of  invasion  is  variable  in  different  females.  There  is  usually,  anterior  to 
the  establishment  of  the  flow,  more  or  less  of  a  feeling  of  general  malaise,  a  sense  of  ful- 
ness and  weight  in  the  pelvic  organs,  accompanied  with  a  greater  or  less  increase  in  the 


876  GENERATION". 

quantity  of  vaginal  mucus,  which  becomes  brownish  or  rusty  in  color.  It  is  probable 
that,  at  this  time,  the  discharge  has  a  peculiar  odor,  though  this  point  is  somewhat  diffi- 
cult to  determine.  In  the  lower  animals,  at  least,  there  is  certainly  a  characteristic  odor 
during  the  rutting  period,  which  attracts  the  male.  At  this  time,  also,  the  breasts  be- 
come slightly  enlarged  in  the  human  female,  showing  the  connection  between  these 
organs  and  the  organs  of  generation.  This  stage  may  continue  for  one  or  two  days, 
although,  in  many  instances,  the  first  evidence  of  the  access  of  a  period  is  a  discharge 
of  blood. 

When  the  general  symptoms  above  indicated  occur,  the  sense  of  uneasiness  is  usually 
relieved  by  the  discharge  of  blood.  During  this,  the  second  stage,  blood  flows  from  the 
vagina  in  variable  quantity,  and  the  discharge  continues  for  from  three  to  five  days. 
With  regard  to  the  duration  of  the  flow,  there  are  great  variations  in  different  individu- 
als. Some  women  present  a  flow  of  blood  for  only  one  or  two  days ;  while,  in  others, 
the  flow  continues  for  from  five  to  eight  days,  within  the  limits  of  health.  A  fair  aver- 
age, perhaps,  is  four  days.1  It  is  also  difficult  to  arrive  at  an  approximation,  even,  of  the 
total  quantity  of  the  menstrual  flow.  Burdach  estimated  it  at  from  five  to  six  ounces. 
According  to  Longet,  this  estimate  is  rather  low,  the  quantity  ordinarily  ranging  from 
ten  to  twelve  ounces,  occasionally  amounting  to  seventeen  ounces,  or  even  more.  It  is 
well  known  that  the  quantity  is  exceedingly  variable,  as  is  the  duration  of  the  flow, 
and  the  difficulties  in  the  way  of  collecting  and  estimating  the  total  discharge  are 
evident.  • 

The  characters  of  the  menstrual  flow  are  sufficiently  simple.  Supposing  the  discharge 
to  continue  for  four  days,  on  the  first  day,  the  quantity  is  comparatively  small ;  on  the 
second  and  third,  the  flow  is  at  its  height ;  and  the  quantity  is  diminished  on  the  fourth 
day.  During  this,  the  second  stage,  the  fluid  has  the  appearance  of  pure  arterial  blood, 
not  coagulated,  and  mixed,  as  has  been  shown  by  microscopical  examination,  with  pave- 
ment-epithelium from  the  vagina,  cylindrical  cells  from  the  uterus,  leucocytes,  and  a 
certain  amount  of  sero-mucous  secretion.  Chemical  examination  of  the  fluid  does  not 
show  any  marked  peculiarities,  except  that  the  quantity  of  fibrin  is  either  not  estimated 
or  is  given  as  much  less  than  in  ordinary  blood. 

The  mechanism  of  the  haemorrhage,  which  will  be  considered  more  fully  when  we 
come  to  study  the  changes  in  the  uterine  mucous  membrane  during  menstruation, 
is  probably  the  same  as  in  epistaxis.  There  is  a  rupture  of  small  blood-vessels,  prob- 
ably capillaries,  and  blood  is  thus  exuded  from  the  entire  surface  of  the  membrane 
lining  the  uterus,  and  sometimes  from  the  membrane  of  the  Fallopian  tubes.  The 
blood  is  then  discharged  into  the  vagina  and  is  kept  fluid  by  the  vaginal  mucus. 
The  mucus  of  the  body  of  the  uterus  is  viscid  and  alkaline;  the  mucus  secreted  at 
the  neck  is  gelatinous,  viscid,  tenacious,  and  also  alkaline ;  the  vaginal  mucus  is  decid- 
edly acid,  creamy,  and  not  viscid,  containing  numerous  cells  of  scaly  epithelium,  and 
leucocytes. 

The  third  stage,  that  of  cessation  of  the  menses,  is  very  simple.  During  the  latter 
part  of  the  second  stage,  the  flow  of  blood  gradually  diminishes  ;  the  discharge  becomes 
rusty,  then  lighter  in  color ;  and,  in  the  course  of  about  twenty-four  hours,  it  assumes 
the  characters  observed  in  the  intermenstrual  period. 

When  the  menstrual  flow  has  become  fully  established,  there  is  no  very  marked  gen- 
eral disturbance,  except  a  sense  of  lassitude,  which  may  become  exaggerated  if  the  dis- 
charge be  unusually  abundant.  It  has  been  noted,  however,  by  Eabuteau,  that,  during 
the  menstrual  period,  the  production  of  urea  is  diminished  more  than  twenty  per  cent., 
that  the  pulse  becomes  slower,  and  that  the  temperature  falls  at  least  one  degree  (half 
a  degree,  centigrade). 

1  Burdach  makes  the  following1  statement  with  regard  to  certain  conditions  capable  of  modifying  the  menstrual 
flow:  "The  flow  is  more  abundant  in  the  indolent  than  in  women  accustomed  to  labor;  in  those  of  feeble  con- 
stitution than  hi  those  who  enjoy  robust  health ;  in  inhabitants  of  cities  than  in  inhabitants  of  villages." 


MENSTKUATIOK 


877 


Changes  in  the  Uterine  Mucous  Membrane  during  Menstruation. — If  the  mucous  mem- 
brane of  the  uterus  be  examined  during  the  menstrual  flow,  it  is  found  smeared  with 
blood,  which  sometimes  extends  into  the  Fallopian  tubes.  It  is  then  much  thicker  and 
softer  than  during  the  intermenstrual  period.  Instead  of  measuring  about  -fa  of  an  inch 
in  thickness,  as  it  does  under  ordinary  conditions,  its  thickness  is  from  $•  to  i  of  an  inch. 
It  becomes  more  loosely  attached  to  the  subjacent  parts,  is  somewhat  rugous,  and  the 
glands  are  very  much  enlarged.  At  the  same  time,  there  are  developed,  in  the  substance 
of  the  membrane,  numerous  spherical  and  fusiform  cells.  According  to  the  recent  and 
very  striking  researches  of  Kundrat  and  Engelmann,  this  condition  probably  precedes  the 
discharge  of  blood  by  several  days,  during  which  time,  the  membrane  is  gradually  pre- 
paring for  the  reception  of  the  ovum.  One  of  the  most  important  points  in  these  re- 
se-arches  is  that  there  is  a  fatty  degeneration  of  the  different  elements  entering  into  the 
structure  of  the  mucous  membrane,  including  the  blood-vessels,  this  change  being  most 
marked  at  the  surface;  and  it  is  on  account  of  the  weakened  condition  of  the  vascular 
walls  that  the  hemorrhage  takes  place.  A  short  time  after  the  flow  has  ceased,  the 
mucous  membrane  returns  to  its  ordinary  condition. 

We  have  already  noted  that  there  is  a  considerable  desquamation  of  epithelium  from 
the  uterus  with  the  flow  of  blood,  during  the  menstrual  period.  Sometimes,  in  normal 
menstruation,  the  epithelium  is  in  the  form  of  patches ;  and,  in  certain  cases  of  dysmen- 
orrhea,  there  is  a  membranous  exfoliation,  which  has  led  to  the  idea  that  the  mucous 
membrane  is  actually  thrown  off.  In  normal  menstruation,  there  is  no  true  exfoliation 
of  the  membrane,  and,  even  in  what  is  called  membranous  dysmenorrhea,  the  so-called 
membrane  is  usually  nothing  more  than  a  membraniform 
exudation,  secreted  by  the  mucous  surface. 


Changes  in  the  Graafian  Follicles  after  their  Rupture 
(Corpus  Luteum).  —  After  the  discharge  of  an  ovum,  its 
Graafian  follicle  undergoes  certain  retrograde  changes,  in- 
volving the  formation  of  what  is  called  the  corpus  luteum. 
Even  when  the  discharged  ovum  has  not  been  fecundated, 
the  corpus  luteum  persists  for  several  weeks,  so  that,  ovu- 
lation  occurring  every  month,  several  of  these  bodies,  in 
various  stages  of  retrogression,  may  sometimes  be  seen  in  the 
ovaries. 

For  a  certain  time  anterior  to  the  discharge  of  the  ovum, 
there  is  a  cell-growth  from  the  proper  coat  of  the  Graafian  fol- 
licle, and  probably  from  the  membrana  granulosa,  with  a  pro-  FIQ 
jection  of  looped  blood-vessels  into  the  interior  of  the  follicle, 
which  is  the  first  formation  of  the  corpus  luteum.  At  the 
time  of  rupture  of  the  follicle,  the  ovum,  with  a  great  part 
of  the  membrana  granulosa,  is  discharged.  Sometimes,  at  the 
time  of  rupture  of  the  follicle,  there  is  a  discharge  of  blood 


of  two  cor- 
natural    size. 


eight  days  after 
conception :  a,  external  coat 
of  the  ovary ;  J,  stroma  of  the 
ovary;  c,  convoluted  wall  of 
Graafian  follicle;  d,  clot  of 
blood. 


into  its  interior;  but  this  is  not  constant,  though  we  usually   2,  corpus  o}.uterumnajjt  * 
have  a  gelatinous  exudation,  more  or  less  colored  with  blood.       ma  of  the  ovary;  c,  convo- 


fibrous  envelope  of  the  corpus 


At  the  same  time,  the  follicular  wall  undergoes  hypertrophy, 
and  it  becomes  convoluted,  or  folded,  and  highly  vascular. 
This  convoluted  wall,  formed  by  the  proper  coat  of  the  fol- 
licle, is  surrounded  by  the  fibrous  tunic,  and  its  thickening  is  most  marked  at  the  deep- 
est portion  of  the  follicle.  At  the  end  of  about  three  weeks,  the  body—  which  is  now 
called  the  corpus  luteum,  on  account  of  its  yellowish  or  reddish-yellow  color  —  has  arrived 
at  the  height  of  its  development  and  measures  about  half  an  inch  in  depth  by  about 
three-quarters  of  an  inch  in  length,  its  form  being  ovoid.  The  convoluted  wall  then 
contains  a  layer  of  large,  pale,  finely  granular  cells,  which  are  internal  and  are  sup- 


878  GENEKATIOK 

posed  to  be  the  remains  of  the  epithelium  of  the  follicle.  The  great  mass  of  this  wall, 
however,  is  composed  of  large  nucleated  cells,  containing  fatty  globules  and  granules 
of  reddish  or  yellowish  pigmentary  matter.  The  thickness  of  the  wall  is  about  one- 
eighth  of  an  inch,  at  its  deepest  portion. 

After  about  the  third  week,  the  corpus  luteum  begins  to  retract ;  its  central  portion 
and  the  convoluted  wall  become  paler,  and,  at  the  end  of  seven  or  eight  weeks,  a  small 
cicatrix  marks  the  point  of  rupture  of  the  follicle. 

The  above  are  the  changes  which  occur  in  the  Graafian  follicles  after  their  rupture 
and  the  discharge  of  ova,  when  the  ova  have  not  been  fecundated  ;  and  the  bodies  thus 
produced  are  called  false  corpora  lutea,  as  distinguished  from  corpora  lutea  found  after 
conception,  which  are  called  true  corpora  lutea. 

Corpus  Luteum  of  Pregnancy. — Before  the  process  of  spontaneous  ovulation  and  its 
connection  with  menstruation  were  understood,  anatomists  were  unable  to  make  a  defi- 
nite distinction  between  the  corpus  luteum  following  the  discharge  of  an  ovum  without 
fecundation,  called  the  corpus  luteum  of  menstruation,  and  the  corpus  luteum  of  preg- 
nancy. Coste  exactly  described  the  various  points  of  distinction  between  them ;  and 
his  account  of  the  differences  in  the  development  of  these  bodies,  dependent  upon  the 
non-fecundation  or  the  fecundation  of  the  ovum,  is  still  regarded  as  entirely  accurate  and 
answers  the  requirements  of  science  at  the  present  day,  even  in  its  medico-legal  aspects, 
as  well  as  in  1847,  when  his  observations  were  published. 

When  a  discharged  ovum  has  been  fecundated,  the  corpus  luteum  passes  through  its 
various  stages  of  development  and  retrogression  much  more  slowly  than  the  ordinary 
corpus  luteum  of  menstruation.  It  is  then  called,  to  distinguish  it  from  the  latter,  the 
true  corpus  luteum.  We  cannot  do  better  than  to  quote,  in  the  words  of  Coste,  the 
description  of  the  changes  which  this  body  undergoes  in  pregnancy  : 

"  I  have  followed,  with  the  greatest  care,  in  the  pregnant  female,  all  the  phases  of 
this  retrogression.  This  commences  to  be  really  appreciable  toward  the  end  of  the  third 
month.  During  the  fourth  month,  the  corpus  luteum  diminishes  by  nearly  a  third,  and 
toward  the  end  of  the  fifth,  it  is  ordinarily  reduced  one-half.  It  still  forms,  however, 
during  the  first  days  after  parturition,  and  in  the  greatest  number  of  cases,  a  tubercle 
which  has  a  diameter  of  not  less  than  from  f  to  £  of  an  inch.  The  tubercle  afterward 
diminishes  quite  rapidly ;  but  it  is  nearly  a  month  before  it  is  reduced  to  the  condition 
of  a  little,  hardened  nucleus,  which  persists  more  or  less  as  the  last  vestige  of  a  process 
so  slow  in  arriving  at  its  final  term.  Nevertheless,  there  is  nothing  absolute  in  the  retro- 
grade progress  of  this  phenomenon.  I  have  seen  women,  dead  at  the  sixth  and  even  the 
eighth  month  of  pregnancy,  present  corpora  lutea  as  voluminous  as  others  at  the  fourth 
month. 

u  Although  it  may  not  be,  in  general,  that,  after  parturition,  the  corpora  lutea  dis- 
appear, it  is  nevertheless  not  without  examples  that  they  disappear  much  more  prompt- 
ly. I  have  had  the  opportunity  of  examining  the  body  of  a  woman,  dead  in  the  course 
of  the  eighth  month  of  pregnancy,  in  whom  the  absorption  was  already  complete. 
Facts  of  this  kind  are  doubtless  very  rare,  as  only  one  has  occurred  in  my  observa- 
tions, notwithstanding  the  numerous  researches  to  which  I  have  devoted  myself  for  a 
long  time.  .  .  . 

"  There  exists  a  notable  difference  between  the  corpora  lutea  which  are  formed  as 
the  sequence  of  conception,  and  those  which  occur  aside  from  the  conditions  developed 
by  impregnation.  The  duration  of  the  former  is  much  longer  than  that  of  the  latter, 
and  the  volume  becomes,  also,  much  more  considerable,  although  their  nature  is,  in 
truth,  identical.  I  have  too  often  had  occasion  to  remark  this,  in  the  ovaries  of  suicides, 
to  retain  the  slightest  doubt  in  this  regard." 

The  following  table,  q.uoted  from  Coste,  shows  the  different  stages  of  the  corpus 
luteum  of  pregnancy.  It  will  be  remembered  that  the  corpus  luteum  of  menstruation  is 
at  its  maximum  of  development  at  the  end  of  about  three  weeks,  when  it  measures  half 


MALE   ORGANS  AND  ELEMENTS   OF  GENERATION. 


879 


an  inch  in  depth 'by  three-quarters  of  an  inch  in  length,  that  it  then  begins  to  retract, 
and  becomes  a  small  cicatrix  at  the  end  of  seven  or  eight  weeks.1 

Dimensions  of  the   Corpus  Luteum  at  different  Stages. 


Corpora  lutea. 

Observations. 

Long  diameter. 

Short  diameter. 

a 
£  ^ 

CO 

f  25  to  30  days  

f  in 
1 
1 

1 

1 
| 

1 

1 

1 
1 

1 

'i 
I 

ah. 

3 

i 

j 

' 
3 

. 

I 

1 

in( 

.     * 
« 
i 
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i 

< 

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i 

i  ! 
v  ; 

i  * 
t> 

:h. 

It  is  rare  that  a  corpus  lu- 
teum  assumes  a  spherical  form, 
and  that,  whatever  be  the  sec- 
tion, its  diameters  are  equal,  or 
nearly  so.  It  generally  under- 
goes, in  its  development,  a  sort 
of  compression  in  the  same 
way  as  does  the  ovary.  Here, 
only  the  long  and  the  short 
diameters,  taken  from  a  section 
of  the  copora  lutea,  have  been 
measured,  the  ovary  being  di- 
vided longitudinally,  and,  as 
it  is,  generally  figured  in  the 
plates  of  the  atlas. 

t  Double  gestation. 
(•  Double  gestation. 

About  40  days 

2  months                      .... 

3  months                    .      .  . 

In  the  4th  month  

Idem  

Idem                      .    . 

In  the  5th  month  
5  months 

In  the  6th  month 

7  months  

In  the  9th  month  

120  hours  after 

3  days  after  •] 

Idem                                -j 

7  days  after 

Male   Organs  and  Elements  of  Generation. 

There  is  not  the  same  physiological  interest  attached  to  the  anatomical  study  of  the 
male  genitalia,  particularly  the  external  organs,  as  there  is  to  the  corresponding  parts 
in  the  female,  for  the  reason  that  the  function  of  the  spermatozoids  is  accomplished 
within  the  female  organs,  where  they  unite  with  the  ovum  and  where  the  processes  of 
development  take  place.  The  anatomy  of  the  penis  and  urethra  has  a  more  exclusively 
surgical  interest.  As  physiologists,  we  have  to  study  the  testicles  (organs  which  cor- 
respond to  the  ovaries,  and  in  which  the  male  generative*  element  is  developed),  the 
various  glandular  structures  which  secrete  fluids  forming  a  part  of  the  ejaculated  semen, 
the  mechanism  of  erection,  by  which  penetration  of  the  male  organ  into  the  vagina  is 
rendered  possible,  the  composition  of  the  seminal  fluid  and  the  mechanism  of  its  ejac- 
ulation, and  the  course  of  the  semen  in  the  generative  passages  of  the  fe*nale  until  it  is 
brought  in  contact  with  and  fecundates  the  ovum.  As  regards  the  penis,  it  will  be  suffi- 
cient to  describe,  as  we  shall  under  the  head  of  coitus,  the  mechanism  of  erection  and 
of  the  ejaculation  of  semen.  It  will  be  necessary,  however,  to  study  the  structure  of 
the  testicles  and  of  the  various  glandular  organs  connected  with  the  urethra,  in  order 
to  understand  the  development  of  the  spermatozoids  and  the  composition  of  the  seminal 
fluid. 

The  Testicles. — The  testicles  are  two  symmetrical  organs,  situated,  during  a  certain 
portion  of  intra-uterine  life,  in  the  abdominal  cavity,  but  finally  descending  into  the 
scrotum.  Within  the  scrotum,  which  is  a  pouch-like  process  of  integument,  are  the 

1  In  1851,  Dr.  J.  C.  Dalton  published  an  essay  on  the  "  Corpus  Luteum  of  Menstruation  and  Pregnancy,"  in  which 
he  pointed  out  very  accurately  the  different  points  of  distinction  between  what  had  been  known  as  the  false  and  the 
true  corpora  lutea.  These  observations  it  is  unnecessary  to  quote  in  detail,  as  the  results  were  almost  identical  with 
those  obtained  by  Coste ;  but  they  are  peculiarly  interesting,  not  only  from  the  accuracy  of  the  descriptions,  but  as 
they  were  made  independently,  and  without  any  knowledge  of  the  publication  by  Coste  four  years  before. 


880  GENERATION. 

two  testicles,  with  their  coverings,  vessels,  nerves,  etc.  The  skin  of  the  scrotum  encloses 
both  testicles,  but  is  marked  by  a  median  raphe.  Immediately  beneath  the  skin,  is  a 
loose,  reddish,  contractile  tissue,  called  the  dartos,  which  forms  two  distinct  sacs,  one 
enveloping  each  testicle,  the  inner  portion  of  these  sacs  fusing  in  the  median  line,  to  form 
the  septum.  Within  these  two  sacs,  the  coverings  of  each  testicle  are  distinct.  These 
organs  are,  as  it  were,  suspended  in  the  scrotum  by  the  spermatic  cords,  the  left  usually 
hanging  a  little  lower  than  the  right.  The  coverings  for  each  testicle,  in  addition  to 
those  just  mentioned,  are  the  intercolumnar  fascia,  the  cremaster  muscle,  the  infundi- 
buliform  fascia,  the  tunica  vaginalis,  and  the  proper  fibrous  coat. 

The  tunica  vaginalis  is  a  shut  sac  of  serous  membrane,  covering  the  testicle  and  epi- 
didymis,  and  reflected  from  the  posterior  border  of  the  testicle  to  the  wall  of  the  scrotum, 
lining  the  cavity  occupied  by  the  testicle  on  either  side,  and  also  extending  over  the 
spermatic  cord.  This  tunic  is  really  a  process  of  peritoneum,  which  has  become  shut  off 
from  the  general  lining  of  the  abdominal  cavity.  The  spermatic  cord  is  composed  of 
the  vas  deferens,  blood-vessels,  lymphatics,  and  nerves,  with  the  various  coverings  already 
described,  which  expand  and  surround  the  testicle. 

Beneath  the  tunica  vaginalis,  are  the  testicles,  with  their  proper  fibrous  coat.  These 
organs  are  ovoid,  and  flattened  laterally  and  posteriorly.  "  They  are  from  an  inch  and 
a  half  to  two  inches  long,  about  an  inch  and  a  quarter  from  the  anterior  to  the  posterior 
border,  and  nearly  an  inch  from  side  to  side.  The  weight  of  each  varies  from  three- 
quarters  of  an  ounce  to  an  ounce,  and  the  left  is  often  a  little  the  larger  of  the  two." 
(Quain.)  The  proper  fibrous  coat  is  everywhere  covered  by  the  closely  adherent  tunica 
vaginalis,  except  at  the  posterior  border,  where  the  vessels  enter  and  the  duct  passes 
out.  At  the  outer  edge  of  this  border,  is  the  epididymis,  formed  of  convoluted  tubes,  pre- 
senting a  superior  enlargement,  called  the  globus  major,  a  long  mass  running  the  length 
of  the  testicle,  called  the  body,  and  a  smaller  enlargement  inferiorly,  called  the  globus 
minor.  This,  too,  is  covered  with  the  tunica  vaginalis.  Between  the  membrane  cover- 
ing the  testicle  and  epididymis  and  the  layer  lining  the  scrotal  cavity,  is  a  small  quan- 
tity of  serum,  just  enough  to  moisten  the  serous  surfaces.  At  the  superior  portion 
of  the  testicle,  we  usually  find  one  or  more  small,  ovoid  bodies,  each  attached  to  the 
testicle  by  short,  constricted  processes,  which  are  called  the  hydatids  of  Morgagni. 
These  have  no  physiological  importance  and  are  supposed  to  be  the  remains  of  foetal 
structures. 

The  proper  fibrous  coat  of  the  testicle  is  called  the  tunica  albuginea.  It  is  white, 
dense,  inelastic,  measures  about  ^  of  an  inch  in  thickness,  and  is  simply  for  the  protec- 
tion of  the  contained  structures.  Sections  of  the  testicle,  made  in  various  directions, 
show  an  im complete  vertical  process  of  the  tunica  albuginea,  called  the  corpus  Highmo- 
rianum,  or  the  mediastinum  testis.  This  is  wedge-shaped,  about  •£  of  an  inch  wide  at 
its  superior  and  thickest  portion,  is  pierced  by  numerous  openings,  and  lodges  blood- 
vessels and  seminiferous  tubes.  From  the  mediastinum,  numerous  delicate,  radiating 
processes  of  connective  tissue  pass  to  the  inner  surface  of  the  tunica  albuginea,  dividing 
the  substance  of  the  testicle  into  imperfect  lobules,  which  lodge  the  seminiferous  tubes. 
The  number  of  these  lobules  has  been  estimated  at  from  one  hundred  and  fifty  to  two 
hundred.  Their  shape  is  pyramidal,  the  larger  extremities  presenting  toward  the  sur- 
face, and  the  pointed  extremities  situated  at  the  mediastinum. 

Lining  the  tunica  albuginea  and  following  the  mediastinum  and  the  processes  which . 
penetrate  the  testicle,  is  a  tunic,  composed  of  blood-vessels  and  delicate  connective  tissue, 
called  the  tunica  vasculosa,  or  pia  mater  testis. 

Lodged  in  the  cavities  formed  by  the  trabeculse  of  connective  tissue,  are  the  semi- 
niferous tubes,  in  which  the  male  elements  of  generation  are  developed.  These  tubes 
exist  to  the  number  of  about  eight  hundred  and  forty  in  each  testicle  and  constitute 
almost  the  entire  substance  of  the  lobules.  The  larger  lobules  contain  five  or  six  tubes, 
the  lobules  of  medium  size,  three  or  four,  and  the  smallest  frequently  enclose  but  a  single 


MALE   ORGANS  AND   ELEMENTS   OF   GENERATION. 


881 


tube.  Each  tube  presents  a  convoluted  mass,  which  can  frequently  be  disentangled  under 
water,  particularly  if  the  testicle  be  macerated  for  several  months  in  water  with  a  little 
nitric  acid.  The  entire  length  of  the  tube,  when  thus  unravelled,  is  about  thirty  inches, 
and  its  diameter  is  from  -^  to  Tf^  of  an  inch.  It  begins  by  from  two  to  seven  short, 
blind  extremities  and  sometimes  by  anastomosing  loops.  The  caeca!  diverticula  are  found 
usually  in  the  external  half  of  the  tube,  and  their  length  is  from  -fa  to  %  of  an  inch.  The 
anastomoses  are  sometimes  between  the  tubes  of  different  lobules,  sometimes  between 
tubes  in  the  same  lobule,  and  sometimes  between  different  points  in  the  same  tube.  As 
the  tubes  pass  toward  the  posterior  portion  of  the  testicle,  they  unite  into  about  twenty 
straight  canals,  called  the  vasa  recta,  about  -fa  of  an  inch  in  diameter,  which  penetrate 
the  mediastinum  testis.  In  the  mediastinum,  the  tubes  form  a  close  net-work,  called  the 
rete  testis;  and,  at  the  upper  portion  of  the  posterior  border,  they  pass  out  of  the 
testicle,  by  from  twelve  to  fifteen  openings,  and  are  here  called  the  vasa  efferentia. 

Having  passed  out  of  the  testicle,  the 
vasa  efferentia  form  a  series  of  small,  con- 
ical masses,  which  together  constitute  the 
globus  major,  or  head  of  the  epididymis. 
Each  of  these  tubes,  when  unravelled,  is 
from  six  to  eight  inches  long,  gradually 
increasing  in  diameter,  until  they  all  unite 
into  a  single,  convoluted  tube,  which  forms 
the  body  and  the  globus  minor  of  the  epi- 
didymis. This  single  tube  of  the  epididy- 
mis, when  unravelled,  is  about  twenty  feet 
in  length. 

The  walls  of  the  seminiferous  tubes  in 
the  testicle  itself  are  composed  of  connec- 
tive tissue,  a  basement-membrane,  and  a 
lining  of  granular,  nucleated  cells.  In  the 
rete  testis,  it  is  uncertain  whether  the  tubes 
have  a  special  fibrous  coat  or  are  simple 
channels  in  the  fibrous  structure.  They 
are  here  lined  with  pavement-epithelium. 
In  the  vasa  efferentia  and  the  epididymis, 
we  have  a  fibrous  membrane,  with  longi- 
tudinal and  circular  fibres  of  involuntary 
muscular  tissue  and  a  lining  of  ciliated 
epithelium.  The  movement  of  the  cilia  is 
toward  the  vas  deferens.  In  the  lower 
portion  of  the  epididymis,  the  cilia  are  ab- 
sent. The  tubular  structures  of  the  testicle, 
the  epididymis,  and  the  commencement  of 
the  vas  deferens  are  shown  in  Fig.  282. 

At  the  lower  portion  of  the  epididymis,  communicating  with  the  canal,  there  is 
usually  found  a  small  mass,  formed  of  a  convoluted  tube  of  variable  length,  called  the 
•vas  aberrans  of  Haller.  (i,  Fig.  282.)  This  is  sometimes  wanting,  and  its  function, 
which  cannot  be  very  important,  is  unknown. 

Vas  Deferens. — The  excretory  duct  of  the  testicle  extends  from  the  epididymis  to  the 
prostatic  portion  of  the  urethra  and  is  a  continuation  of  the  single  tube  which  forms  the 
body  and  globus  minor  of  the  epididymis.  It  is  somewhat  tortuous  near  its  origin  and 
becomes  larger  at  the  base  of  the  bladder,  just  before  it  is  joined  by  the  duct  of  the  semi- 
nal vesicle.  Near  its  point  of  junction  with  this  duct,  it  becomes  narrower.  Its  entire 
length  is  nearly  two  feet. 

56 


FIG.  282.—  Testicle  and  epididymis  of  the  human  sub- 
ject. (Arnold.) 

a,  testicle  ;  6,  &,  ?>,  &.  lobules  of  the  testicle ;  c,  c,  vasa  rec- 
ta; d,  d,  rete  testis  ;  e,  e,  vasa  efferentia ;  f,f,f,  cones 
of  the  globus  major  of  the  epididymis;  g,  g,  epi- 
didymis ;  h,  ^,  vas  deferens  ;  i,  vas  aberrans  ;  m,  m, 
branches  of  the  spermatic  artery  to  the  testicle  and 
epididymis  ;  n,  «.,  w,  ramification  of  the  artery  upon 
the  testicle :  o,  deferential  artery ;  p,  anastomosis  of 
the  deferential  with  the  spermatic  artery. 


882 


GENERATION. 


The  course  of  the  vas  deferens  is  in  the  spermatic  cord  to  the  external  abdominal 
ring,  through  the  inguinal  canal  to  the  internal  ring,  where  it  leaves  the  blood-vessels, 
passes  beneath  the  peritoneum  to  the  side  of  the  bladder,  then  along  the  base  of  the 
bladder  by  the  inner  side  of  the  seminal  vesicle,  finally  joining  the  duct  of  the  seminal 
vesicle,  the  common  tube  forming  the  ejaculatory  duct,  which  opens  into  the  prostatic 
portion  of  the  urethra. 

The  walls  of  the  vas  deferens  are  thick,  abundantly  supplied  with  vessels  and  nerves, 
and  provided  with  an  external  fibrous,  a  middle  muscular,  and  an  internal  mucous  coat. 
The  greater  part  of  that  portion  of  the  tube  which  is  connected  with  the  bladder  is  dilated 
and  sacculated.  The  fibrous  coat  is  composed  of  strong  connective  tissue.  The  muscular 
coat  presents  three  layers  ;  an  external,  rather  thick  layer  of  longitudinal  fibres,  a  thin, 
middle  layer  of  circular  fibres,  and  a  thin,  internal  layer  of  longitudinal  fibres,  all  of  the 
non-striated  variety.  By  the  action  of  these  fibres,  the  vessel  may  be  made  to  undergo 
energetic  peristaltic  movements,  and  this  has  followed  galvanization  of  that  portion  of 
the  spinal  cord  corresponding  to  the  fourth  lumbar  vertebra,  which  is  described  by  Budge 
as  the  genito-spinal  centre. 

The  mucous  membrane  of  the  vas  deferens  is  pale,  thrown  into  longitudinal  folds  in 
the  greatest  part  of  the  canal,  and  presents  numerous  additional  rugae  in  the  sacculated 
portion,  these  rugae  enclosing  little,  irregular,  polygonal  spaces.  The  membrane  is  cov- 
ered with  columnar  epithelium,  which  is  not  ciliated.  In  the  sacculated  portion,  are 
numerous  mucous  glands. 

Attached  to  the  vas  deferens,  near  the  head  of  the  epididymis,  is  a  little  mass  of  con- 
voluted and  saccnlated  tubes,  called  the  organ  of  Giraldes,  or  the  corpus  innominatum. 

This  body  is  from  ^  to  £  of  an  inch  long  and 
•^  of  an  inch  broad.  Its  tubes  are  lined  with 
cells  of  pavement-epithelium,  which  are  often 
filled  with  fatty  granules.  Generally,  the  tubes 
present  only  blind  extremities,  but  some  of 
them  occasionally  communicate  with  the  tubes 
of  the  epididymis.  This  organ  has  no  physio- 
logical importance.  It  is  regarded  by  Giraldes 
as  a  remnant  of  the  Wolffian  body,  analogous 
to  the  parovarium. 


Vesiculm  Seminales. — Attached  to  the  base 
of  the  bladder  and  situated  externally  to  the 
vasa  deferentia,  are  the  two  vesiculse  semi- 
nales.  These  bodies  are  each  composed  of  a 
coiled  and  sacculated  tube,  from  four  to  six 
inches  in  length  when  unravelled,  and  some- 
what convoluted,  in  the  natural  state,  into  an 
ovoid  mass  which  is  firmly  bound  to  the  vesical 
wall.  The  structure  of  the  seminal  vesicles  is 
not  very  unlike  that  of  the  sacculated  portion 
of  the  vasa  deferentia.  They  have  an  external 
fibrous  coat,  a  middle  coat  of  muscular  fibres, 
and  a  mucous  lining.  Muscular  fibres  pass 
over  these  vesicles  from  the  bladder,  both  in  a  longitudinal  and  in  a  circular  direction, 
and  serve  as  compressors,  by  the  action  of  which  their  contents  may  be  discharged.  The 
mucous  coat  is  pale,  finely-reticulated,  and  is  covered  with  cells  of  polygonal  epithelium, 
nucleated  and  containing  brownish  granules.  No  mucous  glands  have  been  found  in  its 
substance. 

The  vesiculos  seminales  undoubtedly  serve,  in  part  at  least,  as  receptacles  for  the 


FIG.  283. —  Vas  deferetv*,  vesiculce  seminales,  and 

ejaculatory  fact*.    (Liegeois.) 
«,  vas  deferens ;   &,  seminal  vesicle  ;   c,  ejaculatory 

duct ;    d,  termination  of  the  ejaculatory  duct ; 

e,  opening  of  the  prostatic  utricle  ;  /,  g,  veru 

montanum  ;  h,  I,  prostate. 


MALE  ELEMENTS   OF  GENERATION. 

seminal  fluid,  as  their  contents  often  present  a  greater  or  less  number  of  sperm atozoids. 
Although  the  mucous  membrane  of  the  vesicles  seems  to  produce  an  independent  secre- 
tion, the  presence  of  glands  has  not  been  demonstrated.  The  fact  that  the  fluid  capable 
of  fecundating  the  ovum  is  produced  only  by  the  testicles,  that  the  spermatozoids  are 
the  true  fecundating  elements  of  the  male,  and  that  these  are  developed  in  the  testicles, 
shows  that  the  spermatozoids  found  in  the  seminal  vesicles  pass  into  their  cavity  from  the 
vasa  deferentia. 

The  ejaculatory  ducts  are  formed  by  the  union  of  the  vasa  deferentia  with  the  ducts 
of  the  vesiculae  seminales  on  either  side  and  open  into  the  prostatic  portion  of  the  urethra. 
Except  that  their  coats  are  much  thinner,  they  have  essentially  the  same  structure  as  the 
vasa  deferentia. 

Prostate. — Surrounding  the  inner  extremity  of  the  urethra,  including  what  is  known 
as  its  prostatic  portion,  is  the  prostate  gland  or  body.  This  organ,  except  as  it  secretes 
a  fluid  which  forms  a  part  of  the  ejaculated  semen,  has  chiefly  a  surgical  interest,  so  that 
it  is  unnecessary  to  describe  minutely  its  form  and  relations.  It  is  enveloped  in  an 
exceedingly  dense,  fibrous  coat,  contains  numerous  glandular  structures  opening  into  the 
urethra,  and  presents  a  great  number  of  non-striated,  with  a  few  striated  muscular  fibres, 
some  just  beneath  the  fibrous  coat  and  others  penetrating  its  substance  and  surrounding 
the  glands. 

The  glands  of  the  prostate  are  most  distinct  at  that  portion  which  lies  behind  the 
urethra.  In  the  posterior  portion  of  this  canal,  are  found  about  twenty  openings,  which 
lead  to  tubes  ramifying  in  the  glandular  substance.  These  tubes  are  formed  of  a  struct- 
ureless membrane,  branching  as  it  penetrates  the  gland.  They  present  hemispherical 
diverticula  in  their  course,  and  terminate  in  dilated  extremities,  which  are  looped  and 
coiled.  In  the  deeper  portions  of  the  tubes,  the  epithelium  is  columnar  or  cubical,  becom- 
ing tesselated  near  their  openings,  and  sometimes  laminated. 

The  prostatic  fluid  is  probably  secreted  only  at  the  moment  of  ejaculation.  Its  char- 
acters will  be  considered  under  the  head  of  the  seminal  fluid ;  but  we  may  here  note 
that  it  has  been  thought  by  Kraus,  that  the  prostatic  fluid  has  the  important  function  of 
maintaining  the  vitality  of  the  spermatozoids.  "The  spermatozoa,  in  the  absence  of  the 
prostatic  fluid,  cannot  live  in  the  mucous  membrane  of  the  uterus  of  mammalia ;  but 
with  its  aid  they  may  live  for  a  long  time  in  the  uterine  mucus,  often  more  than  thirty- 
six  hours." 

Glands  of  the  Urethra. — In  front  of  the  prostate,  opening  into  the  bulbous  portion  of 
the  urethra,  are  two  small  racemose  glands,  called  the  glands  of  M6ry  or  of  Cowper. 
These  have  each  a  single  excretory  duct,  are  lined  throughout  with  cylindrical  epithe- 
lium, and  secrete  a  viscid,  mucus-like  fluid,  which  forms  a  part  of  the  ejaculated  semen. 
Sometimes  there  exists  only  a  single  gland,  and  occasionally,  though  rarely,  both  are 
absent.  Their  function  is  probably  not  very  important. 

The  glands  of  Littre,  found  throughout  the  entire  urethra  and  most  abundant  on  its 
anterior  surface,  are  simple  racemose  glands,  extending  beneath  the  mucous  membrane 
into  the  muscular  structure,  presenting  here  four  or  five  acini.  As  these  acini  are 
surrounded  by  muscular  fibres,  we  can  readily  understand  how  their  secretion  may  be 
pressed  out  during  erection  of  the  penis.  They  are  lined  throughout  with  columnar 
or  conoidal  epithelium,  and  secrete  a  clear  and  somewhat  viscid  mucus,  which  is  mixed 
with  the  ejaculated  semen. 

Male  Elements  of  Generation. 

The  ejaculated  seminal  fluid  contains  the  male  elements  of  generation ;  but  it  must 
be  remembered  that  the  complex  fluid  known  as  the  semen  is  composed  of  anatomical 
elements  developed  in  the  testicle  itself,  mixed  with  the  secretion  of  the  vasa  deferentia, 


884  GENERATION. 

of  the  vesicular  seininales,  of  the  glands  of  the  prostate,  and  of  the  glands  of  the  urethra. 
As  we  shall  see  when  we  come  to  discuss  the  mechanism  of  fecundation  of  the  ovum,  the 
spermatozoids  are  the  essential  male  elements,  and  these  are  produced  in  the  substance 
of  the  testicle,  by  a  process  analogous  to  that  of  the  development  of  other  true  anatomi- 
cal elements,  and  not  by  the  mechanism  with  which  we  are  familiar  in  secreting  glands. 
The  testicles  cannot  be  regarded  strictly  as  glandular  organs.  They  are  analogous  to  the 
ovaries,  and  they  are  the  only  organs  in  which  spermatozoids  can  be  developed,  as  the 
ovaries  are  the  only  organs  in  which  the  ovum  can  be  formed.  If  the  testicles  be  absent, 
the  power  of  fecundation  is  lost,  none  of  the  fluids  secreted  by  the  accessory  organs  of 
generation  being  able  to  perform  the  functions  of  the  true  fecundating  elements. 

In  the  healthy  male,  at  the  climax  of  a  normal  venereal  orgasm,  from  half  a  drachm 
to  a  drachm  of  seminal  fluid  is  ejaculated  with  considerable  force  from  the  urethra,  by  an 
involuntary  muscular  spasm.  This  fluid  is  slightly  mucilaginous,  grayish  or  whitish, 
streaked  with  lines  more  or  less  opaque,  and  it  evidently  contains  various  kinds  of  mucus. 
It  has  a  faint  and  peculiar  odor,  sui  generis,  which  is  observed  only  in  the  ejaculated 
fluid  and  not  in  any  of  its  constituents  examined  separately.  It  is  a  little  heavier  than 
water  and  does  not  mix  with  it  or  dissolve.  After  ejaculation,  it  becomes  jelly-like  and 
dries  into  a  peculiar,  hard  mass,  which  may  be  softened  by  the  application  of  appropriate 
liquids.  The  liquid  is  not  coagulated  by  heat  and  does  not  contain  albumen.  Its  reac- 
tion is  faintly  alkaline.  It  contains,  in  the  human  subject,  from  100  to  120  parts  of  solid 
matter  per  1,000. 

The  chemical  constitution  of  the  semen  has  not  been  very  thoroughly  investigated 
and  does  not  present  the  same  physiological  interest  as  its  anatomical  characters.  Aside 
from  the  anatomical  elements  derived  from  the  testicles  and  the  genital  passages,  it  pre- 
sents an  organic  principle  (spermatine)  which  has  nearly  the  same  chemical  characters  as 
ordinary  mucosine.  It  also  contains  a  considerable  quantity  of  phosphates,  particularly 
the  phosphate  of  magnesia.  During  desiccation,  the  characteristic  crystals  of  this  salt 
usually  make  their  appearance  ;  and,  in  the  decomposed  fluid,  we  frequently  find  crystals 
of  the  triple  phosphates. 

The  composite  character  of  the  seminal  fluid  will  be  better  understood  if  we  examine 
briefly  the  properties  of  the  different  mucous  secretions  which  enter  into  its  composition. 

In  the  dilated  portion  of  the  vasa  deferentia,  the  mucous  glands  secrete  a  fluid  which  is 
the  first  that  is  added  to  the  spermatozoids  as  they  come  from  the  testicles.  This  fluid  is 
brownish  or  grayish.  It  contains  epithelium,  and  small,  rounded  granulations,  which  are 
dark  and  strongly  refractive.  The  liquid  itself  is  very  slightly  viscid.  In  the  vesicula3  semi- 
nales,  there  is  a  more  abundant  secretion  of  a  grayish  fluid,  with  epithelium,  little  color- 
less concretions  of  nitrogenized  matter,  called  by  Robin,  sympexions,  and  a  few  leucocytes. 
The  glandular  structures  of  the  prostate  produce  a  creamy  secretion,  which  contains  nu- 
merous fine  granulations.  It  is  chiefly  to  the  admixture  of  this  fluid  that  the  semen  owes 
its  whitish  appearance.  Finally,  as  the  semen  is  ejaculated,  it  receives  the  exceedingly 
viscid  secretion  of  the  glands  of  Oowper,  a  certain  amount  of  stringy  mucus  from  the 
follicles  of  the  urethra,  with,  perhaps,  a  little  of  the  urethral  epithelium. 

Anatomically  considered,  the  seminal  fluid  contains  no  important  elements  except  the 
spermatozoids,  the  various  secretions  we  have  mentioned  serving  simply  as  a  vehicle  for 
the  introduction  of  these  bodies  into  the  generative  passages  of  the  female.  "We  shall 
therefore  consider  only  the  structure  of  the  spermatozoids,  their  movements,  and  the  pro- 
cess of  their  development. 

Spermatozoids. — In  August,  1677,  a  German  student,  named  Von  Hammen.  discov- 
ered the  spermatozoids  in  the  human  semen,  and  exhibited  them  to  Leeuwenhoek,  who 
studied  them  as  closely  as  was  possible  with  the  instruments  at  his  command.  For  a  long 
time,  they  were  regarded  as  living  animalcules ;  though  now  they  are  considered  simply 
as  peculiar  anatomical  elements,  endov/ed  with  movements,  like  ciliated  epithelium. 


MALE   ELEMENTS   OF  GENERATION. 


885 


These  elements  are  developed  within  the  seminiferous  tubes ;  and  they  differ,  not  so  much 
in  their  mode  of  development,  as  in  their  form,  in  different  animals.  We  shall  describe, 
however,  only  the  spermatozoids  of  the  human  subject. 

If  we  examine  a  specimen  of  the  fluid  taken  from  the  vesiculae  seminales  of  an  adult 
who  has  died  suddenly,  or  the  ejaculated  semen,  we  find  that  it  contains,  in  addition  to 
the  various  accidental  or  unimportant  anatomical  elements  which  we  have  mentioned, 
innumerable  bodies,  resembling  animalcules,  which  present  a  flattened,  conoidal  head  and 
a  long,  tapering,  filamentous  tail.  The  caudate  appendage  is  in  active  motion,  and  the 
spermatozoids  move  about  the  field  of  view  with  considerable  rapidity  and  force,  pushing 
aside  little  corpuscles  or  grannies  with  which  they  come  in  contact.  This  is  supposed  to 
be  an  indication  of  the  vitality  of  the  spermatozoids,  which  are  not  thought  to  be  capable 
of  fecundating  the  ovum  after  their  movements 
have  ceased.  Under  favorable  conditions,  par- 
ticularly in  the  generative  passages  of  the  fe- 
male, the  movements  continue  for  days;  and 
this  fact  is  important,  as  we  shall  see  here- 
after, in  its  bearing  upon  the  limits  of  the  time 
of  fecundation. 

Microscopical  examination  does  not  reveal 
any  very  distinct  structure  in  the  substance 
of  the  spermatozoids.  The  head  is  about 
suW  °f  an  incn  long,  ^Vo  °f  an  inch  broad, 
an(l  T3TOT  ot  an  inch  in  thickness.  The  tail 
is  about  T$T  of  an  inch  in  length.  La  Vallette 
St.  George  has  found,  in  man  and  many  of  the 
inferior  animals,  the  ''intermediate  segment" 
described  first  by  Schweigger-Seidel,  though 
he  does  not  agree  with  Schweigger-Seidel  that 
this  portion  is  motionless.  The  length  of  the 
intermediate  segment  is  about  ^Yo  °f  an  inch.  It  is  usually  described  as  the  beginning 
of  the  tail ;  and  the  only  difference  between  this  and  other  portions  is  that  it  is  a  little 
thicker. 

Water  speedily  arrests  the  movements  of  the  spermatozoids,  which  may  be  restored 
by  the  addition  of  dense  saline  and  other  solutions.  All  of  the  alkaline  animal  fluids  of 
moderate  viscidity  favor  the  movements,  while  the  action  of  acid  or  of  very  dilute  solu- 
tions is  unfavorable.  The  movements  are  suspended  by  extreme  cold,  but  they  return 
when  the  ordinary  temperature  is  restored. 

Before  the  age  of  puberty,  the  seminiferous  tubes  are  much  smaller  than  in  the  adult, 
and  they  contain  small,  transparent  cells,  which,  in  their  form  and  arrangement,  resemble 
epithelium.  As  puberty  approaches,  however,  the  tubes  become  larger,  and  the  cell-con- 
tents increase  in  size.  At  this  time,  there  seem  to  be  two  kinds  of  cells ;  an  epithelium, 
in  the  form  of  irregularly-shaped  cells,  lining  the  tubes,  and  rounded  cells,  containing  one 
or  more  nuclei,  some  of  the  cells  appearing  to  be  in  process  of  segmentation.  Many  of 
the  cells  lining  the  tubes  present  a  rounded  portion,  with  a  large,  clear  nucleus  applied  to 
the  tube-wall,  each  with  a  caudate  prolongation  projecting  into  the  tube.  Sometimes 
the  projections  from  the  different  cells  anastomose  with  each  other,  forming  a  kind  of  net- 
work. In  the  central  portions  of  the  tubes  of  the  adult,  are  rounded  vesicles,  from  -^^  to 
¥fo  of  an  inch  in  diameter,  each,  containing  from  two  to  twenty  transparent  nuclei  meas- 
uring from  y-gVff  t°  WOT>  °f  an  inch.  In  these,  which  are  called  the  seminal  cells,  amoe- 
boid movements  have  been  observed.  The  large  vesicles  with  multiple  nuclei  are  the  seat 
of  development  of  the  spermatozoids.  The  nuclei  of  the  vesicles  appear  to  be  trans- 
formed into  the  heads  of  the  spermatozoids,  and  the  filamentous  appendages,  which  are 
seen  in  the  vesicles  in  various  stages  of  formation,  are  developed  gradually.  It  often 


FIG.  2M.— Human  spermatosoid* ;  magnified  800 
diameters.    (Luschka.) 


886 


GENERATION. 


occurs  that,  when  from  ten  to  twenty  spermatozoids  are  developed  in  a  single  vesicle,  the 
heads  and  tails  are  arranged  regularly,  side  by  side ;  but,  when  only  two  or  three  are  ob- 
served, their  arrangement  is  irregular.  The  vesicular  envelopes  finally  disappear  and  the 
spermatozoids  are  liberated ;  but  this  occurs  only  in  the  rete  testis  and  in  the  epididymis. 
In  the  epididymis  and  the  vasa  deferentia,  the  spermatozoids  are  motionless,  though  they 
are  not  enclosed  in  vesicles,  apparently  from  the  density  of  the  substance  in  which  they 
are  embedded ;  for  movements  are  sometimes  presented  when  the  contents  of  the  vasa 
deferentia  are  examined  with  the  addition  of  water  or  saline  solutions.  Once  in  the 
vesiculce  seminales,  or  after  ejaculation,  the  spermatozoids  are  invariably  in  active  motion. 


FIG.  2S5.— Development  of  the  spermatozoids  in  the  rabbit.     (Liegeois.) 

a,  «,  spermatozoids  ;  b,  spermatic  cell  containing  thirteen  nuclei,  two  of  which  contain  each  a  head  of  a  spermatozoid 
developed ;  c,  spermatic  cell  containing  two  secondary  cells,  each  one  provided  with  a  nucleus  from  which  two 
spermatozoids  are  to  be  developed;  d,f,  spermatic  cells,  each  with  one  nucleus;  e,  spermatic  cell  containing  a 
secondary  cell  with  a  nucleus ;  /t,  bundle  of  spermatozoids. 

The  semen,  thus  developed  and  mixed  with  the  various  secretions  before  mentioned,  is 
found  during  adult  life  and  even  at  an  advanced  age  ;  and,  under  physiological  condi- 
tions, it  contains  innumerable  spermatozoids  in  active  movement.  But  if  sexual  inter- 
course be  frequently  repeated  at  short  intervals,  the  ejaculated  fluid  becomes  more  and 
more  transparent,  homogeneous,  and  scanty,  and  it  may  consist  of.  a  small  amount  of  secre- 
tion from  the  vesiculse  seminales  and  the  glands  opening  into  the  urethra,  without  sper- 
matozoids, and  consequently  deprived  of  fecundating  properties. 

In  old  men,  the  seminal  vesicles  may  not  contain  spermatozoids ;  but  this  is  not  always 
the  case,  even  in  very  advanced  life.  Instances  are  constantly  occurring  of  men  who 
have  children  in  their  old  age,  in  which  the  paternity  of  the  offspring  can  hardly  be 
doubted.  Duplay,  in  1852,  examined  the  semen  of  a  number  of  old  men,  and  found,  in 
about  half  the  number,  spermatozoids,  normal  in  appearance  and  quantity,  though,  in 
some,  the  vesiculse  seminales  contained  either  none  or  very  few.  Some  of  the  individu- 
als in  whom  the  spermatozoids  were  normal  were  between  seventy-three  and  eighty -two 
years  of  age.  More  recently,  M.  A.  Dieu  has  investigated  the  same  question.  In  his 
conclusions,  adding  to  his  own  observations  the  fifty-one  cases  noted  by  Duplay,  he  gives 
the  following  results,  in  one  hundred  and  fifty-six  old  men  : 

"  25  sexagenarians  gave  a  proportion,  still  presenting  spermatozoids,  of  68*5  per  100. 


MECHANISM   OF  FECUNDATION. 


895 


This  history  was  accompanied  by  an  excellent  photograph  of  the  mother  and  the  two- 
children,  a  copy  of  which  is  given  in  Fig.  286.  One  of  the  children  has  the  color  and  all 
characteristics  of  the  negro,  and  the  other  looks  like  a  white  child.  "  The  mother  and 
children  were  inmates  of  Howard  Grove  Hospital  near  this  city  (Richmond),  where  the 
picture  was  taken,  and  I  saw  them  frequently.  Both  children  are  now  dead.  The  black 
one  died  first,  teething,  the  other  was  killed  by  a  tobacco-plaster  applied  to  its  abdomenT 
it  is  supposed  by  its  mother. 


FIG.  280). — Mulatto  mother  with  twins,  one  white  and  tlie  other  black.    From  a  photograph. 

u  The  only  negro  feature  in  the  white  child  was  its  nose.  There,  its  resemblance  to 
its  mother  was  perfect.  Its  hair  was  long,  light,  and  silky.  Complexion  brilliant.'" 

We  have  already  referred  to  the  curious  fact  that,  when  a  cow  gives  birth  to  twins, 
one  male  and  the  other  female,  the  female,  which  is  called  the  free-martin,  is  sterile  and 
presents  an  imperfect  development  of  the  internal  organs  of  generation.  This  has  led  to 
the  idea  that  possibly  the  same  law  may  apply  to  the  human  subject,  in  cases  of  twins, 
one  male  and  the  other  female  ;  but  numerous  observations  are  recorded  in  gynaecologi- 
cal works,  showing  the  incorrectness  of  this  view,  to  which  we  may  add  the  following : 
The  author  of  the  report  on  Rinderpest  to  the  New  York  State  Agricultural  Society, 
1867,  stated  that  his  father  was  one  of  twins,  male  and  female,  and  that  his  father's  twin 
sister  had  borne  several  children. 

It  has  long  been  a  question  whether  impressions  made  upon  the  nervous  system  of  the 
mother  can  exert  an  influence  upon  the  foetus  in  utero.  While  many  authors  admit  that 
violent  emotions  experienced  by  the  mother  may  affect  the  nutrition  and  the  general 
development  of  the  foetus,  some  writers  of  high  authority  deny  that  the  imagination  can 
have  any  influence  in  producing  deformities.  It  must  be  admitted  that  many  of  the 


896  GENERATION. 

remarkable  cases  recorded  in  works  upon  physiology  as  instances  of  deformity  due  to  the 
influence  of  the  maternal  mind  are  not  reliable.  It  is  often  the  case  that,  when  a  child 
is  born  with  a  deformity,  the  mother  imagines  she  can  explain  it  by  some  impression 
received  during  pregnancy,  which  she  only  recalls  after  she  knows  that  the  child  is 
deformed.  Still,  there  are  cases  which  cannot  be  doubted,  but  which,  in  the  present 
state  of  our  knowledge  of  development  and  the  connection  between  the  mother  and  the 
foetus,  we  cannot  attempt  to  explain. 

Union  of  the  Male  with  the  Female  Element  'of  Generation. — The  first  important  step 
in  our  positive  knowledge  of  the  mechanism  of  fecundation  was  the  discovery  of  the 
spermatozoids,  in  1677,  to  which  we  have  already  referred ;  the  second  was  the  demon- 
stration, by  Spallanzani,  in  his  experiments  upon  artificial  fecundation,  that,  when  the 
seminal  fluid  is  carefully  filtered,  the  liquid  which  passes  through  has  no  fecundating 
properties,  the  male  element  remaining  on  the  filter ;  and  the  third  was  the  demonstra- 
tion of  the  presence  of  spermatozoids  within  the  vitelline  membrane,  showing  that  fecun- 
dation consists  in  a  direct  union  of  the  male  with  the  female  element. 

As  to  the  mechanism  of  the  penetration  of  spermatozoids  to  the  vitellus,  we  can  only 
refer  to  the  micropyle  discovered  in  the  ova  of  fishes  and  rnollusks,  which  we  have 
already  described.  In  the  ova  of  the  Nephelis,  a  small  species  of  leech,  Robin  has  seen 
spermatozoids,  to  the  number  of  several  hundreds,  penetrate  the  vitelline  membrane, 
always  at  one  point,  continuing  their  movements  upon  the  surface  of  the  vitellus. 
"  Almost  always,  when  the  penetration  has  ceased,  a  bundle  of  spermatozoids  are 
arrested  in  the  micropyle."  We  had  an  opportunity  of  witnessing  a  demonstration  of 

these  phenomena  by  Prof.  Robin,  in  1861,  in  the  ova 
of  the  Limnteus  stagnalis,  and  actually  saw  a  sper- 
matozoid  half-way  through  the  vitelline  membrane. 
According  to  numerous  direct  observations,  the  sper- 
matozoids move  actively  around  the  ovum,  collect 
toward  a  certain  point,  and  there  penetrate  the  vitel- 
line membrane.  Coste,  and  many  other  observers 
whom  it  is  unnecessary  to  quote,  have  seen  the  sper- 
matozoids within  the  vitelline  membrane,  in  the  ovum 
of  the  rabbit ;  and,  more  recently,  Weil  has  seen  sper- 
matozoids wedged  in  the  substance  of  the  zona  pellu- 
cida,  has  added  blood  to  the  specimen  under  observa 
tion,  and  has  restored  the  movements  of  the  sperma- 
FIG.  287.— Penetration  of  spermatozoids  tozoids  while  in  this  position.  He  has  also  seen,  in 

through    the     vitelline     membrane.  •  n     ,-\      «  j  .         •  j     •      ,-\ 

(Haeckoi.)  some  instances,  perfectly-formed  spermatozoids  m  the 

very  substance  of  the  vitellus. 

All  direct  observations  upon  the  lower  orders  of  animals  have  shown  that  several  sper- 
matozoids are  necessary  for  the  fecundation  of  a  single  ovum;  but  we  have  no  definite 
idea  of  the  number  required  in  mammals,  much  less  in  the  human  subject.  Nor  do  we 
know  what  becomes  of  the  spermatozoids  after  they  have  come  in  contact  with  the  vitel- 
lus. All  that  we  can  say  upon  this  point  is,  that  there  is  probably  a  molecular  union 
between  the  two  generative  elements,  soon  to  be  followed  by  the  remarkable  series  of 
changes  involved  in  the  first  processes  of  development. 

Segmentation  of  the   Vitellus. 

As  we  have  already  stated,  it  is  probable  that  tlje  ovum  is  fecundated,  either  just  as 
it  enters  the  Fallopian  tube  or  in  the  dilated  portion  near  the  ovary.  As  it  passes  down 
the  tube,  whether  it  be  or  be  not  fecundated,  it  becomes  covered  with  an  albuminous 
layer.  This  layer  probably  serves  to  protect  the  fecundated  ovum,  and,  when  the  sper- 
matozoids do  not  penetrate  the  vitelline  membrane  near  the  ovary,  it  presents  an  obstacle 


SEGMENTATION  OF  THE    VITELLUS. 


897 


to  their  passage.  Shortly  after  fecundation,  the  germinal  vesicle  disappears ;  but  this 
occurs  in  ova  that  have  not  been  fecundated.  Soon  after  ovulation,  also,  the  vitellus 
gradually  withdraws  itself  from  certain  portions  of  the  vitelline  membrane,  or  becomes 
deformed,  and  then  often  rotates  upon  itself;  a  phenomenon  which  has  long  been  observed 
in  the  ova  of  some  of  the  lowest  orders  of  animals  and  of  rabbits.  The  deformation 
and  gyration  of  the  vitellus,  however,  have  been  observed  in  ova  before  fecundation  and 
have  nothing  to  do  with  the  process  of  development.  They  are  of  the  class  of  move- 
ments called  amoeboid. 

After  the  penetration  of  spermatozoids  and  their  union  with  the  vitellus,  at  least  in 
many  of  the  lowest  orders  of  animals,  the  appearance  of  the  vitellus  undergoes  a  remark- 
able change,  by  which  ova  that  are  about  to  pass  through  the  first  processes  of  develop- 
ment may  be  readily  distinguished  from  those  which  have  not  been  fecundated.  This 
change  consists  in  an  enlargement  of  the  granules  and  their  more  complete  separation 
from  the  clear  substance  of  the  vitellus.  The  granules  then  refract  light  more  strongly 
than  before,  so  that  the  fecundated  ova  are  distinctly  brighter  than  the  others.  This  is 
the  first  appearance  that  is  distinctive  of  fecundation. 

Polar  Globule. — The  next  process  observed  in  the  ovum  is  the  separation  from  the 
vitellus  of  a  comparatively  clear,  rounded  mass,  called  by  Robin  the  polar  globule.  This 
body  has  been  observed  before  by  various  anatomists  and  described  under  different 
names.  The  exact  mode  of  its  formation  has  been  studied  by  Robin  in  some  of  the  lower 


FIG.  288.— Formation  of  the  polar  globules  in  the  ova  of  the  Nephelis  octoculata.    (Bobin.) 

orders  of  animals.     We  shall  describe  briefly  this  process  as  it  was  demonstrated  to  ns  by 
Robin,  in  1861,  the  description  being  taken  from  notes  made  at  that  time  : 

Five  hours  after  the  entrance  of  the  spermatozoids,  we  see  a  little  elevation  at  one 
point  in  the  vitellus.     This  is  the  beginning  of  the  polar  globule.     It  increases  in  size 
gradually,  and  becomes  constricted  at  its  base,  until  it  is  attached  to  the  vitellus  by  a 
57 


898 


GENERATION. 


*$? 


little  pedicle.  There  is  then,  usually,  a  second  globule 
formed  just  behind  the  first,  in  the  same  manner  ;  and 
sometimes  a  third  makes  its  appearance.  As  soon  as 
the  globules  are  perfectly  formed,  they  all  become  de- 
tached from  the  vitellus,  but  remain  adherent  to  each 
other,  gradually  fusing  to  form  a  single,  rounded,  very 
faintly  granular  mass  ;  and  it  is  opposite  this  globule 
that  the  first  furrow  of  segmentation  of  the  vitellus  is 
observed.  The  complete  formation  of  the  polar  globules 
and  their  fusion  into  one  occupy  three  hours.  It  is  prob- 
able that  the  polar  globule  is  formed  in  the  mammalia  in 
the  manner  above  indicated.  Sometimes  the  polar  glob- 
ule is  formed  in  ova  that  have  not  been  fecundated. 

Vitelline  Nucleus.  —  A  short  time  after  the  complete 
formation  of  the  polar  globule,  the  germinal  vesicle  hav- 
ing disappeared,  the  deformed  vitellus  resumes  its  original 
rounded  appearance  and  fills  again  the  cavity  of  the  vi- 
telline  membrane.  At  this  time,  the  extreme  periphery 
of  the  vitellus  becomes  clearer,  the  granules  collect  in  a 
large  zone  around  the  centre,  and,  in  the  centre  itself,  a 
clear,  rounded  body  makes  its  appearance,  which  is  called 
the  nucleus  of  the  vitellus.  This  mass  is  viscid,  amorphous, 
without  granules,  and  is  entirely  different  from  the  germi- 
nal vesicle,  having  no  nucleus  at  first,  a  nucleolus,  how- 
ever, appearing  in  each  of  the  numerous  nuclei  which  re- 
sult from  its  segmentation.  The  formation  of  the  nucleus 
of  the  vitellus  is  a  positive  evidence  of  fecundation. 
It  appears  from  fifteen  to  thirty  hours  after  fecundation. 


FIG.  289.—  Segmentation  of  the  vitel- 
Iw.  (Liegeois.) 

a,  a,  a,  «,  a,  spermatozoids.  The  four 
upper  figures  represent  the  progres- 
sive segmentation  of  the  vitellus. 
The  lowest  figure  shows  the  cells  of 
the  'blastoderm. 


Segmentation  of  the  Vitellus.  —  Almost  immediately 
following  the  phenomena  we  have  just  described,  the 
vitellus  begins  to  undergo  the  remarkable  process  of 
segmentation,  by  which  it  is  divided  into  numerous 
small  cells.  This  process  may  take  place  to  a  limited 
extent  in  non-fecundated  ova  ;  but  in  this  case  the 
cells  soon  disappear,  as  the  disintegration  of  the  ovum 
advances.  The  true  segmentation  of  the  vitellus,  how- 
ever, results  in  the  formation  of  what  are  called  the 
blastodermic  cells.  As  segmentation  has  been  studied 
in  the  inferior  animals,  there  appears  first  a  furrow  in 
the  vitellus,  at  the  site  of  the  polar  globule,  and  there 
is  then  a  furrow  on  the  opposite  side,  both  deepening 
until  the  entire  vitellus  is  divided  into  two  globes.  These 
are  at  first  spherical  ;  but  they  soon  become  flattened 
upon  each  other  into  two  hemispheres.  There  follows 
then  a  similar  division  into  four,  another  into  eight,  and 
so  on,  until  the  entire  vitellus  is  divided  into  numerous 
cells,  each  with  a*  clear  nucleus  resulting  from  the  seg- 
mentation of  the  original  nucleus  of  the  vitellus.  It  is 
probable  that,  at  first,  the  cells  of  the  vitellus  have  no 
membrane  ;  but  a  membrane  is  soon  formed,  a  nucleus 
appears,  and  the  cells  are  perfect. 


PRIMITIVE  TRACE   OF  THE  EMBRYON.  899 

Most  of  the  phenomena  of  segmentation  have  been  observed  in  the  lower  orders  of 
animals ;  but  there  can  be  no  doubt  that  analogous  processes  take  place  in  the  human 
ovum.  In  the  rabbit,  Weil  observed,  forty-five  and  a  half  hours  after  copulation,  an 
ovum,  with  sixteen  segmentations,  situated  in  the  lower  third  of  the  Fallopian  tube. 
Ninety-four  hours  after  copulation,  he  observed  an  ovum,  with  a  delicate  mosaic  appear- 
ance, presenting  a  small,  rounded  eminence  on  its  surface. 

It  is  impossible  to  say  how  long  the  process  of  segmentation  continues  in  the  human 
ovum.  It  is  stated  that  it  is  completed  in  rabbits  in  a  few  days,  and,  in  dogs,  that  it  occu- 
pies more  than  eight  days.  When  the  cells  of  the  blastoderm  are  completely  formed, 
they  present  a  polygonal  appearance  as  they  are  pressed  against  the  vitelline  membrane, 
their  inner  surface  being  rounded.  The  ovum  then  contains,  within  the  external  layer 
of  cells,  a  small  quantity  of  liquid.  It  is  probably  in  this  condition  that  the  ovum  passes 
from  the  Fallopian  tube  into  the  uterus,  at  about  the  eighth  day  after  fecundation. 

Primitive  Trace  of  the  Embryon. — The  cells  formed  by  the  segmentation  of  the  vitel- 
1ns,  after  this  process  is  completed,  are  arranged  in  the  form  of  a  membrane  (the  blasto- 
dermic  membrane)  which  is  farther  subdivided,  as  development  advances,  into  layers, 
which  will  be  fully  described  hereafter.  The  albuminous  covering  which  the  ovum  has 
received  in  the  upper  part  of  the  Fallopian  tube  gradually  liquefies  and  penetrates  the 
vitelline  membrane,  furnishing,  it  is  thought,  matter  for  the  nourishment  and  develop- 


FIG.  290. — Primitive  trace  of  the  enibryon.     (Liegeois.) 

«,  primitive  trace ;  6,  area  pellucida;  c,  area  obscura;  <?,  blastodennic  cells;  e,  villi  beginning  to  appear  on  the  vitel- 
line membrane. 

ment  of  the  vitellus. .  In  the  Fallopian  tube,  indeed,  the  adventitious  albuminous  cover- 
ing of  the  ovum  presents  an  analogy  to  the  albuminous  coverings  which  the  eggs  of 
oviparous  animals  receive  in  the  oviducts ;  with  the  difference  that  this  albuminous 
matter  is  almost  the  sole  source  of  nourishment  in  the  latter,  and  exists  in  large  quantity, 
while,  in  viviparous  animals,  the  quantity  is  small,  is  generally  consumed  as  the  ovum 
passes  into  the  uterus,  and,  in  the  uterus,  the  ovum  forms  attachments  to  and  draws  its 
nourishment  from  the  vascular  system  of  the  mother. 

At  the  period  when  the  fecundated  ovum  enters  the  uterus,  it  has  increased  in  size 
about  five  times.  It  is  then  composed  of  an  external  covering  (the  vitelline  membrane) 
with  a  cellular  membrane  internal  to  this  (the  blastodermic  membrane)  and  a  certain 
amount  of  liquid  in  its  interior. 

Soon  after  the  formation  of  the  single  blastodermic  membrane,  at  a  certain  point  on 


900  GENERATION. 

its  surface,  there  appears  a  rounded  elevation  or  heap  of  smaller  cells,  forming  a  distinct 
spot,  called  the  embryonic  spot.  As  development  advances,  this  spot  becomes  elongated 
and  oval.  It  is  then  surrounded  by  a  clear,  oval  area,  called  the  area  pellucida,  and  the 
area  pellucida  is  itself  surrounded  by  a  zone  of  cells,  more  granular  and  darker  than  the 
rest  of  the  blastoderm.  The  elongated  line  thus  formed  and  surrounded  by  the  area 
pellucida  is  called  the  primitive  trace.  It  has  been  shown,  however,  that  this  primitive 
trace,  or  primitive  groove,  is  a  temporary  structure  and  has  nothing  to  do  with  the 
development  of  the  neural  canal.  After  the  groove  is  formed,  there  appears  in  front  of, 
but  not  continuous  with  it,  a  new  fold  and  a  groove  leading  from  it.  This  is  the  "  head- 
fold,"  and  the  groove  is  the  true  medullary  groove,  which  is  subsequently  developed  into 
the  neural  canal.  If  we  adopt  this  view — and  the  difference  is  not  very  important — we 
simply  substitute  the  new  trace,  which  is  the  seat  of  the  development  of  the  neural  canal, 
for  the  original  primitive  trace,  which  is  temporary.  It  is  probable  that  embryologists 
have  heretofore  noted  the  so-called  primitive  trace  and  studied  subsequently  the  develop- 
ment of  the  true  medullary  groove,  supposing  that  they  were  identical  structures  in  dif- 
ferent stages  of  formation,  and  not  observing  that  the  first  trace  disappears. 

Blastodermic  Layers. — Shortly  after  the  appearance  of  the  primitive  trace,  the  blasto- 
dermic  cells,  which  are  at  first  arranged  so  as  to  form  a  single  membrane,  separate  into 
layers.  These  layers  have  been  differently  described  by  various  observers,  and  there  is 
some  uncertainty  with  regard  to  the  application  of  direct  researches  made  upon  the  chick, 
in  which  most  of  these  early  processes  of  development  have  been  studied,  to  the  mam- 
malia and  the  human  subject.  We  shall  endeavor  to  describe  the  different  layers  in  as 
simple  a  manner  as  is  consistent  with  our  positive  knowledge,  omitting  all  points  that  are 
unsettled  or  which  seem  to  be  of  minor  importance. 

The  blastodermic  cells,  resulting  originally  from  the  segmentation  of  the  vitellus,  are 
first  apparently  split  into  two  layers,  which  may  be  termed  the  external  and  the  internal 
blastodermic  membranes.  According  to  the  most  recent  observations,  the  main  portion 
of  the  external  layer,  sometimes  called  the  serous  layer,  simply  forms  a  temporary  invest- 
ment for  the  rest  of  the  vitellus  and  is  not  developed  into  any  part  of  the  embryon.  The 
internal  layer,  called  the  mucous  layer,  is  developed  into  nothing  but  the  epithelial  lining 
of  the  alimentary  canal.  There  is  a  thickening  of  both  of  these  layers  at  the  line  of  devel- 
opment of  the  cerebro-spinal  system,  with  a  furrow,  which  is  finally  enclosed  by  an  ele- 
vation of  the  ridges  and  their  union  posteriorly,  forming  the  canal  for  the  spinal  cord. 

As  the  spinal  canal  is  thus  developed,  a  new  layer  is  formed,  by  a  genesis  of  cells  from 
the  internal  surface  of  the  original  external  layer  and  the  opposite  surface  of  the  internal, 
or  mucous  layer.  This  layer  of  new  cells  may  be  termed  the  intermediate  layer ;  and  it 
is  from  this  that  nearly  all  the  parts  of  the  embryon  are  developed. 

To  summarize  the  development  of  the  layers  just  mentioned,  we  may  state  that  the 
external  layer  is  a  temporary  structure ;  the  internal  layer  is  very  thin  and  is  for  the 
development  of  the  epithelial  lining  of  the  alimentary  canal ;  the  most  important  structure 
is  a  thick  layer  of  cells,  developed  from  the  opposite  surfaces  of  the  external  and  the 
internal  layer  and  situated  between  them,  called  the  intermediate  layer ;  and  it  is  from 
these  cells  that  the  greatest  part  of  the  embryon  is  formed. 

Formation  of  the  Membranes. 

The  brief  description  we  have  just  given  of  the  formation  of  the  blastodermic  layers 
seemed  necessary  as  an  introduction  to  the  study  of  the  membranes ;  and  we  shall  defer, 
for  the  present,  the  description  of  their  development  into  the  different  parts  of  the 
embryon. 

In  the  mammalia,  a  portion  of  the  blastoderm  is  developed  into  membranes,  by  which 
a  communication  and  union  are  established  between  the  ovum  and  the  mucous  membrane 
of  the  uterus.  From  the  ovum,  two  membranes  are  developed;  one  non-vascular,  the 


FORMATION  OF  THE  MEMBRANES.  901 

amnion,  and  another  vascular,  the  allantois.  From  the  mucous  membrane  of  the  uterus, 
are  developed. the  two  layers  of  the  decidua.  At  a  certain  part  of  the  uterus,  a  vascular 
connection  is  established  between  the  mucous  membrane  and  the  allantois,  and  the  union 
of  these  two  structures  forms  the  placenta.  The  foetal  portion  of  the  placenta  is  con- 
nected with  the  foetus  by  the  vessels  of  the  umbilical  cord  ;  and  the  maternal  portion  is 
connected  with  the  great  uterine  sinuses.  Development  takes  place  from  material  sup- 
plied to  the  foetus  by  the  blood  of  the  mother. 

The  external  covering  of  the  ovum,  during  the  first  stage  of  its  development,  is  the 
vitelline  membrane.  As  the  ovum  is  received  into  the  uterus,  the  vitelline  membrane 
develops  upon  its  surface  little  villosities,  which  are  non- vascular  and  are  formed  of  amor- 
phous matter  with  granules.  These  are  the  first  villosities  of  the  ovum,  and  they  assist 
in  fixing  the  egg  in  the  uterine  cavity.  They  are  not  permanent,  they  do  not  become 
developed  into  the  vascular  villosities  of  the  chorion,  and  they  disappear  as  the  true 
membranes  of  the  embryon  are  developed  from  the  blastodermic  layers.  It  is  probable 
that  the  vitelline  membrane  disappears  about  the  fourth  or  fifth  day,  when  it  is  replaced 
by  the  anmion. 

Formation  of  the  Amnion, — As  the  ovum  advances  in  its  development,  it  is  observed 
that  a  portion  of  the  blastoderm  becomes  thickened,  to  form  the  first  trace  of  the  embryon. 
At  this  portion,  where  the  body  of  the  embryon  subsequently  makes  its  appearance,  as 
we  have  already  seen,  we  have  the  external  layer,  the  internal  layer,  and  a  thick,  inter- 
mediate layer  of  cells,  which  are  developed  from  the  opposite  surfaces  of  the  external  and 
the  internal  layer,  called  the  middle  layer.  At  nearly  the  time  when  this  thickening  begins, 
a  fold  of  the  external  layer  makes  its  appearance,  surrounding  the  thickened  portion,  and 
most  prominent  at  the  cephalic  and  the  caudal  extremity  of  the  furrow  for  the  neural  canal. 
This  fold  increases  in  extent  as  development  advances,  passes  over  the  dorsal  surface  of 
the  embryon,  and  finally  meets  so  as  to  enclose  the  embryon  completely.  We  can  readily 
figure  to  ourselves  this  process  and  understand  how,  at  a  certain  period  of  the  develop- 
ment of  the  amnion,  this  membrane  consists  of  an  external  layer,  formed  of  the  external 
layer  of  the  fold,  and  an  internal  layer ;  the  point  of  union  of  the  two  layers,  or  the  point 
of  meeting  of  the  fold,  being  marked  by  a  membranous  septum. 

The  two  amniotic  layers  are  formed  in  the  way  that  we  have  just  described,  and  a 
complete  separation  finally  takes  place,  by  a  disappearance  of  the  septum  formed  by  the 
meeting  of  the  folds  over  the  back  of  the  embryon.  This  process  occupies  four  or  five 
days  in  the  human  ovum.  The  point  where  the  folds  meet  is  called  the  amniotic  umbili- 
cus. When  the  amnion  is  thus  completely  formed,  the  vitelline  membrane  has  been 
encroached  upon  by  the  external  amniotic  layer  and  disappears,  leaving  this  layer  of  the 
amnion  as  the  external  covering  of  the  ovum.  At  this  time,  there  is  a  growth  of  villosi- 
ties upon  the  surface  of  the  external  amniotic  layer,  which,  like  the  villosities  of  the  vitel- 
line membrane,  are  not  vascular. 

Soon  after  the  development  of  the  amnion,  the  allantois  is  formed.  This  membrane 
is  vascular,  encroaches  upon  and  takes  the  place  of  the  external  amniotic  membrane, 
becomes  villous,  and  its  villosities  take  the  place  of  those  of  the  amnion.  Over  a  certain 
portion  of  the  membrane,  the  villosities  are  permanent.  The  mode  of  development  of  the 
amnion,  as  we  have  described  it,  is  illustrated  by  the  diagrammatic  Fig.  291.  This  figure 
illustrates  the  formation  of  the  amnion,  the  umbilical  vesicle,  and  the  allantois.  The  last  two 
structures  are  not  derived  from  the  external  blastodermic  layer,  and  they  will  be  described 
farther  on,  after  we  have  studied  the  full  development  of  the  amnion  and  its  relations. 

When  the  allantois  has  become  the  chorion,  or  the  external  membrane  of  the  ovum, 
having  taken  the  place  of  the  external  layer  of  the  amnion,  the  structures  of  the  ovum 
are  the  following:  1.  The  chorion,  formed  of  the  two  layers  of  the  allantois,  derived  from 
the  internal  blastodermic  membrane,  and  penetrated  by  blood-vessels.  2.  The  umbilical 
cord,  which  connects  the  embryon  with  the  placental  portion  of  the  chorion,  and  the  um- 


902 


GENERATION. 


bilical  vesicle,  formed  from  the  same  layers  as  the  allantois.  8.  The  amnion,  which  is  the 
internal  layer  of  the  amniotic  fold,  persisting  throughout  the  whole  of  foetal  life.  4.  The 
embryon  itself. 

During  the  early  stages  of  development  of  the  umbilical  vesicle  and  the  allantois,  the 


FIG.  291. — Five  diagrammatic  representations  of  the  formation  of  the  membranes  in  the  mammalia.    (Kolliker.) 

FIG.  1 :  «,  a',  external  layer  of  the  blastoderm;  d,  vitelline  membrane;  d',  villi  on  the  vitelline  membrane ;  i,  inter- 
nal layer  of  the  blastoderm ;  m,  m',  middle  layer. 

FIG.  2:  a',  external  layer  of  the  amnion;  d,  d',  vitelline  membrane;  e,  embryon;  dt*,  umbilical  vesicle;  vl,  £*,  ss, 
folds  of  the  amnion;  dd,  m',  st,  internal  layer  of  the  blastoderm  ;  dd,  connection  of  the  embryon  with  the  um- 
bilical vesicle. 

FIG.  3:  d,  d',  vitelline  membrane;  vl,  internal  amniotic  layer;  e,  embryon;  ah.  amniotic  cavity;  sh,  s 7i,  external 
amniotic  layer ;  a  m,  space  between  the  two  layers  of  the  amnion  ;  d  d,  internal  layer  of  the  blastoderm  ;df,  *  t,  i, 
walls  of  the  umbilical  vesicle  ;  d g,  omphalo-mesenteric  canal;  d s,  cavity  of  the  umbilical  vesicle ;  a  I,  first  ap- 
pearance of  the  allantois. 

FIG.  4:  s/t,  external  layer  of  the  amnion ;  ss,  villi  of  the  external  layer  of  the  amnion,  which  has  now  become  the 
chorion,  the  yitellirie  membrane  having1  disappeared;  /*//-,  am,  internal  layer  of  the  amnion;  e,  embryon;  ah. 
amniotic  cavity :  d  fl,  omphalo-mesenteric  canal ;  d  s,  cavity  of  the  umbilical  vesicle  ;  a  I,  allantois ;  r,  space  be- 
tween the  two  layers  of  the  amnion. 

FIG.  5:  ch,8h,ch,  a  I,  allantois  (which  has  now  become  the  chorion,  the  external  amniotic  layer  having  disap- 
peared), with  its  villi;  am,  amnion;  as,  amniotic  covering:  of  the  umbilical  cord;  r,  space  between  the  amnion 
and  the  allantois;  aft,  amniotic  cavity;  d  s,  umbilical  vesicle;  d  g,  omphalo-mesenteric  canal. 


AMNIOTIC  FLUID.  903 

internal  amniotic  layer,  or  the  true  aniniotic  membrane,  is  closely  applied  to  the  surface 
of  the  embryon  and  is  continuous  with  the  epidermis  at  the  umbilicus.  It  is  then  sepa- 
rated from  the  allantois  by  a  layer  of  gelatinous  matter ;  and  in  this  layer,  between  the 
amnion  and  the  allantois,  is  embedded  the  umbilical  vesicle.  At  this  time,  the  umbilical 
cord  is  short  and  not  twisted.  As  development  advances,  however,  the  inter-membra- 
nous gelatinous  matter  gradually  disappears ;  the  cavity  of  the  amnion  is  enlarged  by  the 
production  of  a  liquid  between  its  internal  surface  and  the  embryon ;  and,  at  about  the 
end  of  the  fourth  month,  the  amnion  comes  in  contact  with  the  internal  surface  of  the 
chorion.  At  this  time,  the  embryon  floats,  as  it  were,  in  the  amniotic  cavity,  surrounded 
by  the  amniotic  fluid.  The  amnion  forms  a  lining  membrane  for  the  chorion;  by  its 
gradual  enlargement  it  has  formed  a  covering  for  the  umbilical  cord  ;  and,  between  it  and 
the  cord,  is  the  atrophied  umbilical  vesicle.  The  amnion  then  resembles  a  serous  mem- 
brane, except  that  it  is  non-vascular.  It  is  lined  by  a  single  layer  of  pale,  delicate  cells 
of  pavement-epithelium,  which  contain  a  few  fine,  fatty  granulations.  At  term,  the  am- 
nion adheres  to  the  chorion,  though  it  may  be  separated,  with  a  little  care,  as  a  distinct 
membrane,  and  may  be  stripped  from  the  cord.  From  its  arrangement  and  from  the 
absence  of  blood-vessels,  it  is  evident  that  this  membrane  is  simply  for  the  protection  of 
the  foetus  and  is  not  directly  concerned  in  its  nutrition  and  development.  (See  Plate 
III.,  Fig.  2,  facing  page  922.)  The  gelatinous  mass  referred  to  above,  situated,  during 
the  early  periods  of  intra-uterine  life,  between  the  amnion  and  the  chorion,  presents  a 
semifluid  consistence,  and  it  is  marked  by  the  presence  of  numerous  very  delicate,  inter- 
lacing fibres  of  young  connective  tissue  and  fine  grayish  granulations  scattered  through  its 
substance.  These  fibres  gradually  develop  as  the  quantity  of  gelatinous  matter  diminishes 
and  the  amnion  approaches  the  chorion,  until,  finally,  it  forms  a  rather  soft,  reticulated 
layer,  which  is  sometimes  called  the  membrana  media. 

Amniotic  Fluid. — The  process  of  enlargement  of  the  amnion  shows  that  the  amniotic 
fluid  gradually  increases  in  quantity  as  the  development  of  the  foetus  progresses.  At 
term,  the  entire  quantity  is  variable,  being  rarely  more  than  two  pints  or  less  than  one 
pint.  In  the  early  periods  of  utero-gestation,  it  is  clear,  slightly  yellowish  or  greenish, 
and  perfectly  liquid.  Toward  the  sixth  month,  its  color  is  more  pronounced,  and  it  be- 
comes slightly  mucilaginous.  Its  reaction  is  usually  neutral  or  faintly  alkaline,  though 
sometimes  it  is  feebly  acid  in  the  latest  periods.  It  sometimes  contains  a  small  quantity 
of  albumen,  as  determined  by  heat  and  nitric  acid;  and  there  is  generally  a  gelatinous 
precipitate  on  the  addition  of  acetic  acid.  The  following  table,  compiled  by  Robin,  gives 
its  chemical  composition : 

Composition  of  the  Amniotic  Fluid. 

Water 991*00  to  975-00 

Albumen  and  mucosine 0'82  "     10'77 

Urea 2'00  "       3'50 

Creatine  and  creatinine  (Scherer.  Robin  and  Verdeil) not  estimated 

Lactate  of  soda  (Vogt,  Regnauld) a  trace 

Fatty  matters  (Rees,  Mack) 0-13  to      T25 

Glucose  (Cl.  Bernard) not  estimated 

Chloride  of  sodium  and  chloride  of  potassium 2-40  to      5'95 

Chloride  of  calcium a  trace 

Carbonate  of  soda a  trace 

Sulphate  of  soda a  trace 

Sulphate  of  potassa  (Rees) a  trace 

Calcareous  and  magnesian  phosphates  and  sulphates 1'14  to      1'72 

The  presence  of  certain  of  the  urinary  constituents  in  the  amniotic  fluid  has  led  to  the 
view  that  the  urine  of  the  foetus  is  discharged,  in  greater  or  less  quantity,  into  the  am- 


904  GENERATION. 

niotic  cavity.  Bernard,  who  is  cited  in  the  above  table  as  having  determined  the  pres- 
ence of  sugar  in  the  araniotic  fluid,  has  shown  that,  in  animals  with  a  multiple  placenta, 
the  amnion  has  a  glycogenic  function  during  the  early  part  of  intra-uterine  existence. 

With  regard  to  the  origin  of  the  arnniotic  fluid,  it  is  impossible  to  say  how  much  of  it 
is  derived  from  the  general  surface  of  the  foetus,  how  much  from  the  urine,  and  how 
much  from  the  amnion  itself,  by  transudation  from  the  vascular  structures  beneath  this 
membrane.  The  quantity  is  apparently  too  great,  especially  in  the  early  months,  to  be 
derived  entirely  from  the  urine  of  the  foetus,  and  there  is  probably  an  exudation  from  the 
general  surface  of  the  foetus  and  from  the  membranes.  After  the  third  month,  the  seba- 
ceous secretion  from  the  skin  of  the  foetus  prevents  the  absorption  of  any  of  the  liquid. 

An  important  property  of  the  amniotic  fluid  is  that  of  resisting  putrefaction  and  of 
preserving  dead  tissues.  It  is  stated  by  Robin  to  be  the  best  fluid  for  the  preservation 
of  the  embryonic  tissues,  when  it  is  desired  to  keep  them  for  examination. 

Formation  of  the  Umbilical  Vesicle. — As  the  visceral  plates,  which  will  be  described 
hereafter,  close  over  the  front  of  the  embryon,  that  portion  of  the  blastoderm  from  which 
the  intestinal  canal  is  developed  presents  a  vesicle,  which  is  cut  off,  as  it  were,  from  the 
abdominal  cavity,  but  which  still  communicates  freely  with  the  intestine.  This  is  the  um- 
bilical vesicle.  On  its  surface,  is  a  rich  plexus  of  blood-vessels ;  and  this  is  a  very  important 
organ  in  birds  and  in  many  of  the  lower  orders  of  animals.  In  the  human  subject  and  in 
mammals,  however,  the  umbilical  vesicle  is  not  so  important,  as  nutrition  is  effected  by 
means  of  vascular  connections  between  the  chorion  and  the  uterus.  The  vesicle  becomes 
gradually  removed  farther  and  farther  from  the  embryon,  as  development  advances,  by 
the  elongation  of  its  pedicle,  and  it  is  compressed  between  the  amnion  and  the  chorion  as 
the  former  membrane  becomes  distended. 

When  the  umbilical  vesicle  is  formed,  in  the  way  which  we  have  indicated,  it  receives 
two  arteries  from  the  two  aortae,  and  the  blood  is  returned  to  the  embryon  by  two  veins, 
which  open  into  the  vestibule  of  the  heart.  These  are  called  the  omphalo-mesenteric 
vessels.  At  about  the  fortieth  day,  one  artery  and  one  vein  disappear,  and,  soon  after, 
all  vascular  connection  with  the  embryon  is  abolished.  At  first  there  is  a  canal  of  com- 
munication with  the  intestine,  called  the  omphalo-mesenteric  canal.  This  is  gradually 
obliterated,  and  it  closes  at  the  thirtieth  or  the  thirty -fifth  day.  The  point  of  communica- 
tion of  the  vesicle  with  the  intestine  is  called  the  intestinal  umbilicus ;  and,  early  in  the 
process  of  development,  there  is  here  a  true  hernia  of  a  loop  of  intestine.  The  umbilical 
vesicle  remains  as  a  tolerably  prominent  structure  as  late  as  the  fourth  or  fifth  month, 
but  it  may  often  be  discovered  at  the  end  of  pregnancy. 

The  umbilical  vesicle  presents  three  coats;  an  external,  smooth  membrane,  formed 
of  connective  tissue,  a  middle  layer  of  transparent,  polybedric  cells,  and  an  internal  layer 
of  spheroidal  cells.  The  membrane,  composed  of  these  layers,  encloses  a  pulpy  mass, 
composed  of  a  liquid  containing  cells  and  yellowish  granulations. 

Formation  of  the  Allantois  and  the  Permanent  Chorion. — During  the  early  stages  or 
development  of  the  umbilical  vesicle,  and  while  it  is  being  shut  off  from  the  intestine, 
there  appears  an  elevation  at  the  posterior  portion  of  the  intestine,  which  rapidly  in- 
creases in  extent,  until  it  forms  a  membrane  of  two  layers,  which  is  situated  between 
the  internal  and  the  external  layer  of  the  amnion.  This  membrane  becomes  vascular 
early  in  the  progress  of  its  development,  increases  in  size  quite  rapidly,  and  finally  com- 
pletely encloses  the  internal  layer  of  the  amnion  and  the  embryon,  the  gelatinous  mass 
already  described  being  situated  between  it  and  the  internal  amniotic  layer,  before  this 
membrane  becomes  enlarged.  While  the  formation  of  the  two  layers  of  the  allantois  is 
quite  distinct  in  certain  of  the  lower  orders  of  animals,  in  the  human  subject  and  in  mam- 
mals, it  is  not  so  easily  observed ;  still  there  can  be  no  doubt  as  to  the  mechanism  of  its 
formation,  even  in  the  human  ovum.  Here,  however,  the  allantois  soon  becomes  a  single 


FORMATION   OF  THE  ALLANTOIS  AND   PERMANENT   CHORION.    905 


membrane,  the  two  original  layers  of  which  cannot  be  separated  from  each  other.  The 
process  of  the  development  of  the  allantois  is  shown  in  the  diagrammatic  Figure  291 
(3,4,5). 

It  is  the  vascularity  of  the  allantois  which  causes  the  rapid  development  by  which  it 
invades  and  finally  supersedes  the  external  layer  of  the  amnion,  becoming  the  permanent 
chorion,  or  external  membrane  of  the  ovum.  At  first  there  are  two  arteries  extending 
into  this  membrane  from  the  lower  portion  of  the  aorta,  and  two  veins.  The  two  arte- 
ries persist  and  form  the  two  arteries  of  the  umbilical  cord,  coming  from  the  internal 
iliac  arteries  of  the  foetus ;  and  the  two  veins  are  reduced  to  one,  the  umbilical  vein, 
which  returns  the  blood  from  the  placenta  to  the  foetus.  These  vessels  are  connected 
with  the  permanent  vascular  tufts  of  the  chorion. 

The  development  of  the  allantois  cannot  be  well  observed  in  human  ova  before  the 
fifteenth  or  the  twenty-fifth  day.  We  have  already  noted  the  formation  of  villosities, 

first  upon  the  vitelline  membrane,  and 
next  upon  the  external  amniotic  mem- 
brane, and  we  have  seen  that  both  of 
these  membranes  are  temporary  struct- 
ures. As  the  vascular  allantois  en- 
croaches upon  the  external  amniotic 
layer,  the  villosities  become  vascular; 
and,  when  the  allantois  becomes  the  per- 
manent chorion,  it  is  marked  by  a  mul- 
titude of  compound  villi  over  its  entire 
surface,  which  give  the  ovum  a  shaggy 
appearance.  It  is  difficult  to  say  whether 
new  villi  appear  upon  the  allantois,  or 
whether  the  villi  of  the  amnion  are  pene- 
trated by  the  vessels  of  the  allantois ; 
but  it  is  certain  that  the  true  or  perma- 
nent chorion  presents  upon  its  surface 
vascular  villi.  As  the  ovum  enlarges, 
over  a  certain  area  surrounding  the  point 
»f  attachment  of  the  pedicle  which  con- 
nects  it  with  the  embryon,  the  villi  are 
developed  more  rapidly  than  over  the  rest  of  the  surface.  Indeed,  as  the  egg  becomes 
larger  and  larger,  the  villi  of  the  surface  outside  of  this  area  become  more  and  more 
scanty,  lose  their  vascularity,  and  finally  disappear.  That  portion  upon  which  the  villi 
persist  and  increase  in  length  and  in  the  number  of  their  branches  is  destined  to  form 
connections  with  the  mucous  membrane  of  the  uterus,  and  it  constitutes  the  foetal  portion 
of  the  placenta.  This  change  begins  at  about  the  end  of  the  second  month,  and  the  pla- 
centa becomes  distinctly  limited  at  about  the  end  of  the  third  month. 

It  must  be  remembered  that,  as  the  changes  progress  which  result  in  the  formation  of 
the  permanent  chorion  and  the  limitation  of  the  foetal  portion  of  the  placenta,  the  forma- 
tion of  the  umbilical  vesicle  and  the  enlargement  of  the  amnion  are  also  going  on.  The 
amnion  is  gradually  becoming  distended  by  the  increase  in  the  quantity  of  amniotic 
fluid.  It  reaches  the  internal  surface  of  the  chorion  at  about  the  end  of  the  fourth  month, 
extends  over  the  umbilical  cord  to  form  its  external  covering,  including  the  cord  of  the 
umbilical  vesicle,  and  the  umbilical  vesicle  itself  lies  in  the  gelatinous  matter  between 
the  two  membranes. 

At  about  the  beginning  of  the  fifth  month,  then,  the  ovum  is  constituted  as  follows : 
The  foetus  floats  freely  in  the  amniotic  fluid,  attached  to  the  placenta  by  the  umbili- 
cal cord  ;  the  chorion  presents  a  highly-vascular,  thickened,  and  villous  portion,  the  foetal 
portion  of  the  placenta ;  the  rest  of  the  chorion  is  a  simple  membrane,  without  villi  and 


906  GENERATION. 

without  blood-vessels ;  the  amnion  lines  the  internal  surface  of  the  chorion  and  also 
forms  the  external  covering  of  the  umbilical  cord ;  the  umbilical  vesicle  has  become 
atrophied  and  has  lost  its  vascularity ;  the  hernia  at  the  point  of  connection  of  the  um- 
bilical vesicle  with  the  intestine  of  the  fcetus  has  closed ;  and,  finally,  the  foetus  has  under- 
gone a  considerable  degree  of  development. 

It  now  remains  for  us  to  study  the  structure  of  the  umbilical  cord,  the  membranes 
formed  from  the  mucous  membrane  of  the  uterus,  or  the  membrane  deciduse,  and  the 
mode  of  development  and  the  structure  of  the  placenta. 

Umbilical  Cord. — From  the  description  we  have  given  of  the  mode  of  development 
of  the  chorion  and  the  amnion,  it  is  evident  that  the  umbilical  cord  is  nothing  more  than 
the  pedicle  which  connects  the  embryon  with  that  portion  of  the  chorion  which  enters 
into  the  structure  of  the  placenta.  It  is,  indeed,  a  process  of  the  allantois,  in  which  the 
vessels  eventually  become  the  most  important  structures.  The  cord  is  distinct  at  about 
the  end  of  the  first  month ;  and,  as  development  advances,  the  vessels  consist  of  two 
arteries  coming  from  the  body  of  the  fcetus,  which  are  usually  twisted  from  left  to  right 
around  the  single  umbilical  vein.  In  addition  to  the  spiral  turns  of  the  arteries  around 
the  veins,  the  entire  cord  may  be  more  or  less  twisted,  probably  from  the  movements  of 
the  foetus. 

The  fully-developed  cord  extends  from  the  umbilicus  of  the  fcetus  to  the  central  por- 
tion of  the  placenta,  in  which  its  insertion  is  usually  oblique ;  though  it  may  be  inserted 
at  other  points,  and  even  outside  of  the  border  of  the  placenta,  its  vessels  penetrating 
this  organ  from  the  side.  Its  usual  length,  which  varies  very  considerably,  is  about 
twenty  inches.  It  has  been  observed  as  long  as  sixty,  and  as  short  as  seven  inches. 
When  the  cord  is  very  long,  it  sometimes  presents  knots,  or  it  may  be  wound  around  the 
neck,  the  body,  or  any  of  the  members  of  the  foetus ;  and  this  can  only  be  accounted  for 
by  the  movements  of  the  foetus  in  utero. 

The  external  covering  of  the  cord  is  a  process  of  the  amnion,  which,  as  it  extends 
over  the  vessels,  includes  a  gelatinous  substance  (the  gelatine  of  Wharton)  which  sur- 
rounds the  vessels  and  protects  them  from  compression.  This  gelatinous  substance  is 
identical  with  the  so-called  membrana  intermedia,  or  the  substance  included  between  the 
amnion  and  the  chorion.  The  entire  cord,  covered  with  the  gelatine  of  Wharton  and 
the  amnion,  is  usually  about  the  size  of  the  little  finger.  According  to  Robin,  the  nor- 
mal cord  will  sustain  a  weight  of  from  ten  pounds  and  ten  ounces  to  twelve  pounds  and 
twelve  ounces  avoirdupois.  As  the  amniotic  fluid  accumulates  and  distends  the  amniotic 
membrane,  it  becomes  more  and  more  closely  applied  to  the  cord.  This  pressure  extends 
from  the  placental  attachment  of  the  cord  toward  the  foetus  and  gradually  forces  into 
the  abdomen  of  the  foetus  the  loop  of  intestine,  which,  in  the  early  periods  of  intra- 
uterine  life,  forms  an  umbilical  hernia. 

It  is  generally  stated  by  writers  upon  embryology  that  the  vessels  of  the  cord  present 
no  valves ;  but  recent  observations  have  demonstrated  the  presence  of  semilunar  folds, 
both  in  the  vein  and  in  the  arteries.  These  are  simple  inversions  of  the  walls  of  the  ves- 
sels ;  and  they  do  not  exist  in  pairs,  nor  do  they  seem  to  influence  the  current  of  blood. 
In  the  arteries,  these  folds  are  situated  at  intervals  of  from  half  an  inch  to  two  inches, 
and  they  are  more  abundant  where  the  vessels  are  very  contorted.  In  the  vein,  the  folds 
are  most  abundant  near  the  placenta ;  they  are  very  irregularly  placed,  and,  in  a  length  of 
four  inches,  fifteen  folds  were  found.  It  is  not  apparent  that  these  folds  have  any  physio- 
logical importance. 

As  the  allantois  is  developed,  it  presents,  in  the  early  stages  of  its  formation,  three 
portions ;  an  external  portion,  which  becomes  the  chorion,  an  internal  portion,  enclosed 
in  the  body  of  the  embryon,  and  an  intermediate  portion.  The  intermediate  portion,  as 
we  have  seen,  becomes  the  umbilical  cord.  As  the  umbilicus  of  the  foetus  closes  around 
the  cord,  it  shuts  off  a  portion  of  the  allantois  contained  in  the  abdominal  cavity,  which 


MEMBRANE  DECIDUA.  907 

becomes  the.  urinary  bladder ;  but  there  is  a  temporary  communication  between  the  inter- 
nal portion  and  the  lower  portion  of  the  cord,  which  is  called  the  urachus.  This  is  gen- 
erally obliterated  before  birth  and  is  reduced  to  the  condition  of  an  impervious  cord ; 
but  it  may  persist  during  the  whole  of  intra-uterine  life,  in  the  form  of  a  narrow  canal, 
extending  from  the  bladder  to  the  umbilicus,  which  is  closed  soon  after  birth. 

Meiribrance  Deciduce. — In  addition  to  the  two  membranes  connected  with  the  foetus, 
there  are  two  membranes  formed  from  the  mucous  membrane  of  the  uterus,  which  are 
derived  from  the  mother  and  which  serve  still  farther  to  protect  the  ovum.  The  cho- 
rion,  as  we  have  just  seen,  is  for  the  protection  of  the  foetus ;  but  a  portion  of  this 
membrane,  about  one-third  of  its  surface,  becomes  closely  united  with  a  corresponding 
portion  of  the  uterine  mucous  membrane,  to  form  the  placenta.  This  organ,  which 
serves  for  the  nutrition  of  the  fcetus,  will  be  described  by  itself ;  but,  before  we  can 
thoroughly  comprehend  its  structure  and  the  process  of  its  development,  we  must  study 
carefully  the  formation  of  the  membranae  deciduse. 

As  the  fecundated  ovum  descends  into  the  uterus,  it  is  usually  invested  with  a  shaggy 
covering,  which  is  either  the  permanent  chorion  or  one  of  the  membranes  which  invests 
the  ovum  previous  to  the  complete  development  of  the  allantois.  At  this  time,  the 
mucous  membrane  of  the  uterus  has  undergone  certain  changes  by  which  it  is  prepared 
for  the  reception  of  the  ovum.  The  changes  which  this  membrane  undergoes  in  men- 
struation have  already  been  studied.  It  has  been  seen  that,  during  an  ordinary  men- 
strual period,  the  membrane  has  been  increased  three  or  four  times  in  thickness  and  has 
become  more  or  less  rugous.  Without  being  able  to  state  from  positive  observation  the 
character  of  the  first  changes  in  the  uterine  mucous  membrane  preceding  the  descent  of 
the  fecundated  ovum — for  the  opportunities  for  direct  inspection  of  these  parts  after 
fecundation  and  before  the  arrival  of  the  ovum  are  not  frequent — it  is  almost  certain 
that  this  hypertrophy  occurs  and  progresses.  One  of  the  most  favorable  occasions  for 
observing  these  early  changes  in  the  human  subject  lately  presented  itself,  and  the  ap- 
pearances were  minutely  described  by  Reichert.  In  this  case,  the  ovum  was  lenticular, 
measuring  nearly  one-fourth  of  an  inch  in  its  long  and  about  one-sixth  of  an  inch  in 
its  short  diameter.  It  was  covered  with  simple,  empty,  cylindrical  villi,  and  was  esti- 
mated to  be  at  from  the  twelfth  to  the  thirteenth  day  of  its  development,  dating  from 
fecundation.  It  was  enclosed  in  the  decidua  reflexa,  and  it  was  thought  that  this 
had  been  accomplished  from  twenty-four  to  forty-eight  hours  before  the  death  of  the 
mother. 

According  to  Reichert,  the  thickening  of  the  mucous  membrane  of  the  uterus  which 
occurs  at  each  menstrual  period,  in  case  the  ovum  be  not  fecundated,  is  relieved  by  a  flow 
of  blood  and  disappears ;  but,  if  fecundation  take  place,  the  membrane  continues  to  hyper- 
trophy and  to  prepare  itself  to  enclose  the  ovum.  In  this  process,  when  an  ovum  has 
been  fecundated,  there  are  formed,  upon  the  surface  of  the  mucous  membrane,  little  ele- 
vations, or  islands,  provided  with  primary  and  secondary  papillae  everywhere  except  at 
their  borders,  where  the  membrane  is  smooth  and  presents  the  enlarged  orifices  of  the 
uterine  follicles.  The  ovum  observed  by  Reichert  was  found  embedded  in  the  parenchyma 
of  one  of  these  islands ;  and,  as  it  was  detached,  several  villi  were  drawn  immediately  out 
from  the  uterine  tubules. 

It  is  now  well  known  that  the  mucous  membrane  lining  the  gravid  uterus  forms  what 
has  been  called  the  decidua  vera,  and  that  a  portion  is  reflected  over  the  ovum,  to  form 
the  decidua  reflexa.  Reichert  is  of  the  opinion  that  the  view  entertained  by  most  ob- 
servers, that  the  fecundated  ovum  lodges  itself  in  one  of  the  furrows  of  the  hypertrophied 
membrane  and  is  finally  enclosed  by  an  elevation  of  the  walls  of  the  furrow,  cannot  be 
sustained.  He  thinks  that  the  ovum  first  becomes  attached  to  one  of  the  " islands;  "  at 
the  point  of  attachment,  the  island  does  not  increase  in  size  as  rapidly  as  at  other  por- 
tions, so  that  the  ovum  rests  in  a  cup-shaped  depression  ;  and,  finally,  a  growth  takes  place 


908  GENERATION. 

from  the  margin  of  this  depression,  which  extends  around  and  encloses  the  ovum,  pre- 
senting a  spot  where  the  final  closure  takes  place,  called  the  decidual  umbilicus. 

We  have  given  the  recent  views  of  Reichert  thus  fully,  for  the  reason  that  they  are 
ba.sed  upon  the  study  of  a  remarkably  young  ovum  and  appear  to  be  more  exact  and 
definite  than  any  observation  hitherto  recorded ;  and  we  shall  adopt  this  description  as 
representing  the  early  stages  of  the  formation  of  the  membrane  decidua3. 

According  to  Reichert,  the  ovum  is  completely  enclosed  at  the  twelfth  or  the  thir- 
teenth day.  The  mucous  membrane  lining  the  uterus  becomes  the  decidua  vera,  and  the 
border  from  which  the  new  growth  is  formed  which  covers  the  ovum  is  the  boundary 
between  this  and  the  decidua  reflexa.  The  new  growth,  springing  from  this  border,  en- 
velops the  ovum  completely  and  is  called  the  decidua  reflexa ;  and,  in  this  membrane, 
there  is  no  trace  of  the  uterine  tubules. 

As  development  advances,  a  portion  of  the  decidua  vera — the  description  of  which  we 
reserve  for  the  present — undergoes  development  into  the  maternal  portion  of  the  placenta. 
The  rest  of  the  decidua  vera  becomes  extended,  loses  its  vessels  and  glands,  and  is  reduced 
to  the  condition  of  a  simple  membrane.  The  cylindrical  epithelial  cells  of  the  mucous 
membrane  of  the  body  of  the  uterus,  soon  after  fecundation,  become  gradually  exfoliated, 
and  their  place  is  supplied  by  flattened  epithelial  scales,  of  the  pavement-variety.  This 
change  is  effected  at  from  the  sixth  to  the  eighth  week,  and  the  pavement-cells  are  then 
founol  covering  both  the  decidua  vera  and  the  reflexa.  The  epithelium  of  the  cervix 
retains  its  cylindrical  character,  but  most  of  the  cells  lose  their  cilia. 

During  the  first  periods  of  utero-gestation,  the  two  layers  of  decidua  are  separated  by 
a  small  amount  of  an  albuminous  and  sometimes  a  sanguinolent  fluid  ;  but  this  disappears 
at  about  the  end  of  the  fourth  month,  and  the  membranes  then  come  in  contact  with  each 
other.  They  soon  become  so  closely  adherent  as  to  form  a  single  membrane,  which  is  in 
contact  with  the  chorion.  Sometimes,  at  full  term,  the  membranes  of  the  foetus  can  be 
separated  from  the  decidua ;  but  frequently  all  of  the  different  layers  are  closely  adherent 
to  each  other. 

The  changes  we  have  just  described  are  not  participated  in  by  the  mucous  membrane 
of  the  neck  of  the  uterus.  The  glands  in  this  situation  secrete  a  semisolid,  transparent, 
viscid  mucus,  which  closes  the  os  and  is  sometimes  called  the  uterine  plug. 

Toward  the  fourth  month,  a  very  delicate,  soft,  homogeneous  layer  appears  over  the 
muscular  fibres  of  the  uterus,  beneath  the  decidua  vera,  which  is  the  beginning  of  a  new 
mucous  membrane.  This  is  developed  very  gradually,  and  the  membrane  is  completely 
restored  about  two  months  after  parturition. 

Development  and  Structure  of  the  Placenta. — In  describing  the  formation  of  the  mem- 
brane decidua  and  of  the  chorion,  we  have  necessarily  hinted  at  the  mode  of  development 
of  the  placenta.  Although  there  is  considerable  difference  of  opinion  among  anatomists 
with  regard  to  the  exact  relations  between  the  vessels  of  the  mother  and  of  the  foetus  in 
utero,  it  is  admitted  by  all  that  the  foetus  derives  its  nourishment  from  the  maternal  blood, 
and  that  the  placenta  is,  in  addition,  a  respiratory  organ.  Reasoning  from  what  we 
should  consider  to  be  the  requirements  of  the  foetus,  it  would  be  natural  to  suppose  that 
the  foetal  vessels  are  bathed  in  maternal  blood ;  and  it  is  certain  that  the  two  sets  of 
vessels  have  no  direct  communication  with  each  other.  It  is  also  well  known  that  the 
foetus  has  an  independent  circulation,  its  heart  beating  about  twice  as  fast  as  the  heart  of 
the  mother.  In  our  description  of  the  placenta,  we  shall  first  give  the  views  which  we 
conceive  to  be  correct,  and  then  advance  the  facts  and  arguments  by  which  these  views 
are  apparently  supported. 

Beginning  with  the  first  development  of  the  placenta,  the  observation  which  we  have 
quoted  from  Reichert,  in  which,  it  will  be  remembered,  the  tufts  of  the  foetal  chorion 
were  actually  drawn  out  of  the  tubules  of  the  uterine  mucous  membrane,  seems  to  de- 
monstrate beyond  question  the  fact  of  penetration  of  the  villi  of  the  chorion  into  the 


DEVELOPMENT   AND   STRUCTURE  OF  THE  PLACENTA.  909 

maternal  tubes.  This  is  a  capital  point  in  our  view  of  the  mode  of  development  of  the 
placenta;  and  this  cannot  be  questioned,  if  we  admit  the  accuracy  of  Reichert's  descrip- 
tion. It  is  certain  that  the  portion  of  the  chorion  which  eventually  becomes  attached  to 
the  uterus  undergoes  a  much  greater  degree  of  development  than  the  rest  of  the  mem- 
brane. The  villi  in  this  situation  become  branched  and  arborescent;  they  are  filled  with 
blood-vessels,  while  the  vascularity  in  other  parts  of  the  chorion  disappears ;  the  mucous 
membrane  corresponding  to  this  portion  of  the  chorion  also  becomes  thickened ;  the  tubes 
in  which  the  villi  have  penetrated  are  correspondingly  enlarged  and  branched,  and  the 
vessels  which  surround  them  are  increased  in  size  ;  and,  finally,  the  union  between  the  villi 
and  the  tubes  becomes  so  close  that  they  cannot  be  separated  from  each  other.  It  is 
evident  that,  if  this  be  the  mode  of  development  of  the  placenta,  the  maternal  portion  is 
formed  from  a  restricted  and  an  hypertrophied  part  of  the  mucous  membrane  of  the  uterus, 
and  the  foetal  portion  is  simply  an  exceedingly  vascular  and  villous  part  of  the  chorion. 

As  development  advances,  the  vessels  of  the  maternal  portion  of  the  placenta  coalesce 
into  great  lakes,  which  communicate  freely  with  the  uterine  sinuses.  In  these  great 
cavities,  we  find  the  vascular  foetal  tufts ;  and  it  is  easy  to  understand  how  transudation 
of  nutritive  material  and  gases  can  take  place  from  the  blood  of  the  mother  to  the  vascular 
system  of  the  foetus. 

If  the  above  description  be  correct,  we  should  be  able  to  pass  an  injection  from  the 
uterine  sinuses  into  the  maternal  portion  of  the  placenta,  even  as  far  as  its  foetal  surface ; 
but  this  is  '&  point  concerning  which  there  has  been  a  great  deal  of  discussion. 

In  injected  specimens  of  the  placenta,  when  an  attempt  has  been  made  to  fill  the 
maternal  as  well  as  the  foetal  vessels,  the  material  injected  into  the  uterine  vessels  has 
sometimes  passed  through  the  entire  thickness  of  the  placenta  and  appeared  just  beneath 
the  transparent  chorion  at  the  foetal  surface  of  the  organ.  This  appearance,  however, 
has  been  thought  by  some  writers  to  be  due  to  extravasation ;  and  many  physiologists 
are  of  the  opinion  that  the  placenta  has  no  maternal  portion,  that  it  is  entirely  a  foetal 
organ,  and  that  the  maternal  vessels  do  not  pass  beyond  the  surface  by  which  it  is 
attached  to  the  walls  of  the  uterus.  This  opinion,  however,  we  believe  to  be  erroneous. 

The  important  point  in  the  determination  of  the  connection  of  what  may  be  termed 
the  placental  maternal  sinuses  with  the  vessels  of  the  uterus  can  be  settled  by  injection 
of  the  uterine  vessels  in  cases  in  which  the  observation  can  be  made  while  the  placenta 
is  still  attached  to  the  uterine  walls.  Dalton,  since  1853,  has  examined  the  parts  in  situ 
in  four  cases  of  women  who  died  undelivered  at  or  near  the  full  term  of  pregnancy,  and 
he  adopted  the  ingenious  expedient  of  filling  the  uterine  vessels  with  air,  by  which  the 
course  of  the  injection  could  be  directly  observed.  This  operation  is  performed  in  the 
following  manner  :  The  uterus,  with  its  contents,  is  removed  from  the  body,  is  carefully 
opened,  and  the  foetus  is  taken  out,  after  dividing  the  umbilical  cord.  The  parts  are 
then  placed  under  water,  the  end  of  a  blow-pipe  is  introduced  into  one  of  the  divided 
vessels  of  the  uterine  walls,  and  air  is  forced  in  by  gentle  insufflation.  By  this  process, 
the  venous  sinuses  of  the  uterus  itself  are  first  filled,  next,  the  deeper  portions  of  the 
placenta,  and  finally,  "  the  bubbles  of  air  insinuate  themselves  everywhere  between  the 
foetal  tufts,  and  appear  in  the  most  superficial  portions  of  the  placenta,  immediately 
underneath  the  transparent  chorion.  If  the  chorion  be  now  divided  at  any  point  by  an 
incision,  passing  merely  through  its  own  thickness,  the  air,  which  was  confined  beneath 
it  in  the  placental  sinuses,  will  escape,  and  rise  in  bubbles  to  the  surface  of  the  water. 
Such  an  experiment  shows  conclusively  that  the  placental  sinuses  communicate  freely 
with  the  uterine  vessels,  occupy  the  entire  thickness  of  the  placenta,  and  are  equally 
extensive  with  the  tufts  of  the  foetal  chorion."  Dalton  farther  states  that  the  uterine 
vessels,  as  they  penetrate  the  placenta,  have  an  exceedingly  oblique  direction,  and  that 
their  orifices  may  be  easily  overlooked,  but  can  be  seen  by  careful  inspection. 

We  have  no  doubt  with  regard  to  the  accuracy  of  the  observations  of  Dalton,  and  we 
conceive  that  they  have  settled  the  question  of  the  existence  of  a  true  maternal  portion 


910 


GENERATION. 


of  the  placenta.  In  corroboration  of  this,  in  1864,  we  examined  the  uterus,  with  the 
placenta  attached,  of  a  woman  who  died  in  the  latter  months  of  pregnancy,  in  the  pres- 
ence of  the  late  Prof.  G.  T.  Elliot  and  Prof.  J.  P.  White,  and  forced  air  from  the  uterine 
sinuses  throughout  the  entire  thickness  of  the  placenta,  between  the  foetal  tufts.  In 
view  of  these  facts,  concerning  which  there  can  be  no  doubt,  it  seems  unnecessary  to 
discuss  the  more  or  less  theoretical  views  of  writers  who  have  not  made  injections  of  the 
uterus  with  the  placenta  attached.  The  observations  of  Dalton  have  since  been  con- 
firmed by  numerous  anatomists,  so  that  we  must  consider  the  fact  of  an  intra-placental 
circulation  of  maternal  blood  as  definitively  established. 

Structure  of  the  Fully-developed  Placenta. — The  placenta  of  the  human  subject  pre- 
sents certain  differences  in  its  structure  at  various  periods  of  utero-gestation,  most  of 
which  have  been  indicated  in  treating  of  its  development.  At  about  the  end  of  the  third 
month,  the  limits  of  the  placenta  become  distinct,  and  the  organ  rapidly  assumes  the  ana- 
tomical characters  observed  after  it  may  be  said  to  be  fully  developed.  It  then  occupies 


FIG.  293.— Diagrammatic  figure,  showing  the  placenta  and  deciduce.    (Liegeois.) 

c,  embryon  ;  *,  intestine ;  p,  pedicle  of  the  umbilical  vesicle ;  o,  umbilical  vesicle  ;  m,  m,  m,  amnion ;  a',  chorion  ; 
a,  lower  end  of  tbe  umbilical  cord  ;  q,  q,  vascular  tufts  of  the  chorion,  constituting  the  foetal  portion  of  the  pla- 
centa ;  «',  n,  maternal  portion  of  the  placenta  ;  «,  re,  decidua  vera  ;  *,  decidua  reflexa. 

about  one-third  of  the  uterine  mucous  membrane,  and  it  is  generally  rounded  or  ovoid  in 
form,  with  a  distinct  border  connected  with  the  decidua  and  the  chorion.  It  is  from 
seven  to  nine  inches  in  diameter,  a  little  more  than  an  inch  in  thickness  at  the  point  of 
penetration  of  the  umbilical  cord,  slightly  attenuated  toward  the  border,  and  weighs 
from  fifteen  to  thirty  ounces.  Its  fcetal  surface  is  covered  with  the  smooth  amniotic 
membrane,  and  its  uterine  surface,  when  detached,  is  rough,  and  divided  into  numerous 
irregular  lobes  or  cotyledons,  from  half  an  inch  to  an  inch  and  a  half  in  diameter.  Be- 
tween these  lobes,  are  membranes,  called  dissepiments,  which  penetrate  into  the  sub- 
stance of  the  organ,  frequently  as  far  as  the  foatal  surface. 


DEVELOPMENT  OF  THE  EMBRYON.  911 

Upon  the  uterine  surface  of  the  placenta,  is  a  thin,  soft  membrane,  sometimes  called 
the  decidua  serotina.  This  is  merely  a  portion  of  the  mucous  membrane  of  the  uterus 
situated  next  the  muscular  walls,  the  greater  part  of  it  not  being  thrown  off  with  the  pla- 
centa. It  is  composed  of  amorphous  matter,  numerous  granulations,  and  colossal  cells  with 
enlarged  and  multiple  nuclei.  If  we  scrape  the  uterine  surface  of  a  fresh  placenta,  these 
cells  appear,  upon  microscopical  observation,  very  much  like  the  so-called  cancer-cells. 
There  has  been  and  is  now  considerable  difference  of  opinion  with  regard  to  the  formation 
of  the  decidua  serotina.  Some  writers,  who  do  not  admit  that  the  placenta  has  any  true 
maternal  portion,  regard  it  as  the  portion  of  decidua  imprisoned  between  the  chorion 
and  the  muscular  walls  of  the  uterus ;  but,  if  we  adopt  the  view  that  the  placenta  ia 
formed  in  part  of  the  uterine  mucous  membrane,  we  must  regard  the  serotina,  so  called, 
as  simply  the  deeper  portion  of  this  membrane. 

Blood-vessels  of  the  Placenta. — The  two  arteries  of  the  umbilical  cord  branch  upon 
the  foetal  surface  of  the  placenta  beneath  the  amnion  and  finally  penetrate  the  substance 
of  the  organ.  The  branches  of  the  veins,  which  are  about  sixteen  in  number,  converge 
toward  the  cord  and  unite  to  form  the  umbilical  vein.  Upon  the  uterine  surface  of  the 
placenta,  are  numerous  oblique  openings  of  the  veins  which  return  the  maternal  blood  to 
the  uterine  sinuses.  There  are  also  numerous  small  spiral  arteries,  which  pass  into  the 
substance  of  the  organ  to  supply  blood  to  the  maternal  portion.  These  are  the  "  curling 
arteries,"  described  by  John  Hunter. 

If  we  inject  the  umbilical  arteries,  the  fluid  is  returned  by  the  umbilical  vein,  having 
passed  through  the  vascular  tufts  of  the  fcetal  portion  of  the  placenta.  According  to 
Farre,  the  small  arteries  and  the  veins  of  the  villi  at  first  communicate  through  a  true 
capillary  plexus ;  but,  toward  the  end  of  pregnancy,  the  capillaries  disappear,  leaving 
loops  of  vessels,  "  simple,  compound,  wavy,  or  much  contorted,  and  in  parts  varicose." 

According  to  the  recent  researches  of  Winkler,  there  are  three  kinds  of  foetal  villi : 
1.  Those  which  terminate  just  beneath  the  chorion,  without  penetrating  the  vascular 
lacunae.  2.  Longer  villi,  which  hang  free  in  the  lacunae.  3.  Long,  branching  villi,  which 
penetrate  more  deeply  into  the  placenta,  some  extending  as  far  as  its  uterine  surface. 

The  formation  of  the  great  vascular  lakes  of  the  maternal  portion  of  the  placenta  has 
already  been  described.  These,  according  to  Winkler,  present  numerous  trabeculse, 
which  extend  from  the  uterine  to  the  foetal  surface ;  and,  between  these  trabeculae,  are 
numerous  exceedingly  delicate  transverse  and  oblique  secondary  trabecular  processes. 
The  chorionic  villi  contain  blood-vessels,  which  we  have  already  described,  surrounded 
by  a  gelatinous,  connective-tissue  structure  {Schlewigewebe),  and  are  generally  covered 
with  a  layer  of  nucleated  cells  of  pavement-epithelium. 

In  parturition,  the  curling  arteries  and  the  veins  on  the  uterine  surface  of  the  pla- 
centa are  torn  off,  and  the  placenta  then  consists  of  the  parts  we  have  just  described ; 
the  torn  ends  of  these  vessels  attached  to  the  uterus  are  closed  by  the  contractions  of  the 
surrounding  muscular  fibres  ;  and  the  blood  which  is  discharged  is  mainly  derived  from 
the  placenta  itself.  Thus  the  very  contractions  which  expel  the  contents  of  the  uterus 
close  the  vessels  and  prevent  loss  of  blood  by  the  mother. 

Development  of  the  Embryon. 

The  product  of  generation  retains  the  name  of  ovum  until  the  form  of  the  body  begins 
to  be  apparent,  when  it  is  called  the  embryon.  At  the  fourth  month,  about  the  time  of 
quickening,  it  is  called  the  foetus,  a  name  which  it  retains  during  the  rest  of  intra-uterine 
life.  The  membranes  which  we  have  described  are  appendages  developed  for  the  pur- 
poses of  protection  and  nutrition  ;  and  the  embryon  itself,  in  the  mammalia,  is  developed 
from  a  restricted  portion  of  the  layers  of  cells  resulting  from  the  segmentation  of  the 
vitellus. 

We  have  already  described  the  formation  of  the  blastodermic  cells  and  the  appearance 


912  GENERATION. 

of  the  groove  which  is  subsequently  developed  into  the  neural  canal.  At  this  portion  of 
the  ovuin,  there  is  a  thickening  of  the  blastoderm,  which  then  presents  three  layers,  the 
middle  layer,  the  thickest  and  most  important,  being  developed  from  the  opposite  sur- 
faces of  the  external  and  the  internal  layer.  We  have  to  study,  then,  the  changes  which 
take  place  in  three  layers  of  cells,  which  we  shall  call  the  external,  the  intermediate, 
and  the  internal  blastodermic  membranes.  The  earliest  stages  of  development  have  been 
studied  almost  exclusively  in  the  chick,  and  the  processes  here  observed  cannot  be  as- 
sumed to  represent  exactly  the  mode  of  development  of  the  human  subject.  For  this 
reason,  we  feel  justified  in  adopting  the  simplest  division  of  layers,  which  is  into  three, 
and  shall  not  attempt  to  follow  the  excessively  minute  descriptions  of  the  early  arrange- 
ment of  cells,  given  by  some  recent  observers. 

A  general  idea  of  the  development  of  certain  of  the  important  parts  of  the  embryon  will 
aid  us  in  comprehending  the  more  minute  processes  and  the  formation  of  special  organs ; 
and  this  we  can  give  without  reference  to  the  various  divisions  of  the  blastodermic  layers 
adopted  by  different  writers.  It  makes  very  little  difference,  indeed,  as  regards  our  actual 
knowledge  of  development,  whether  we  restrict  the  external  blastodermic  membrane  to 
the  development  of  the  epidermis,  or  whether  we  assume  that  a  portion  of  it  forms  the 
walls  of  the  neural  canal.  In  the  latter  case,  we  simply  make  a  thicker  external  layer 
at  the  expense  of  a  portion  of  the  intermediate  layer.  It  is  the  discussion  of  such  minor 
points  as  this,  which  depend  mainly  upon  observations  made  upon  the  chick,  that  we 
propose  to  avoid,  in  our  endeavor  to  make  the  description  of  the  first  processes  of  devel- 
opment as  simple  as  possible. 

We  may  assume  that  the  furrow  for  the  spinal  canal  and  its  dilated  superior  portion, 
the  head,  have  been  closed  over  by  the  union  of  the  dorsal,  or  medullary  plates  behind. 
At  a  later  period,  there  has  been  a  growth  of  the  abdominal,  or  visceral  plates,  which 
finally  close  over  the  front  of  the  embryon.  Now,  to  adopt,  with  slight  modifications,  a 
simile  given  by  Hermann,  we  may  imagine  a  young  mammal,  with  a  short,  straight  ali- 
mentary canal,  taking  no  account,  for  the  present,  of  its  glandular  appendages.  We  take 
the  entire  body  as  a  tube,  the  caliber  of  which  is  the  alimentary  canal,  with  walls  formed 
of  concentric  layers.  Counting  these  layers  from  within  outward,  we  have  first,  the 
mucous  membrane ;  next,  the  muscular  coat  of  the  intestine ;  then,  the  visceral  serous 
membrane,  the  parietal  serous  membrane,  the  muscles  of  the  trunk,  with  the  bones ;  and 
finally,  the  integument.  All  of  these  layers  are  developed,  to  a  greater  or  less  degree, 
simultaneously,  from  different  layers  of  the  blastodermic  cells.  With  the  view  that  we 
shall  adopt,  the  external  blastodermic  membrane  becomes  the  epidermis,  and  the  internal 
blastodermic  membrane,  the  epithelium  of  the  alimentary  canal.  The  intermediate  mem- 
brane splits  into  two  layers;  the  outer  layer  becoming  attached  to  the  external  blasto- 
dermic membrane  and  forming  the  muscular  layer  of  the  trunk,  while  the  inner  layer  is 
connected  with  the  internal  blastodermic  membrane  and  contributes  to  the  formation  of 
the  viscera.  At  a  later  period,  the  extremities  are  developed,  as  solid  processes  con- 
nected with  the  outer  layer  of  the  intermediate  membrane  and  covered  by  a  prolonga- 
tion of  the  external  blastodermic  membrane. 

Development  of  the  Cavities  and  Layers  of  the  Trunk  in  the  Chicle. — As  an  intro- 
duction to  a  description  of  the  development  of  special  organs  in  the  human  subject  and 
in  mammals,  it  will  be  found  very  useful  to  study  the  first  stages  of  development  in  the 
chick,  by  which  we  can  get  an  idea  of  the  arrangement  of  the  different  blastodermic 
layers,  and  the  way  in  which  they  are  developed  into  the  different  parts  of  the  trunk, 
with  the  mode  of  formation  of  the  great  cavities.  In  doing  this,  we  shall  endeavor  to 
describe  the  figures  given  by  Briicke,  which  were  photographed  on  wood  from  large  dia- 
grams, made  from  actual  preparations,  by'Seboth.  In  this  description,  we  shall  take  no 
account  of  the  formation  of  the  membranes. 

Fig.  294  illustrates  one  of  the  earliest  stages  of  development  in  the  chick.     In  this 


DEVELOPMENT   OF  THE   EMBRYON. 


913 


figure,  the  superior  layer  of  dark  cells  (5,  &)  represents  the  external  blastodermic  mem- 
brane. The  inferior  layer  of  dark  cells  (d,  d)  represents  the  internal  blastodermic  mem- 
brane. The  middle  layer  of  lighter  cells  is  the  intermediate  membrane,  which,  toward 


FIG.  294. 

the  periphery,  is  split  into  two  layers.  This  figure  represents  a  transverse  section.  At 
«,  is  a  transverse  section  of  the  groove  which  is  subsequently  developed  into  the  canal 
for  the  spinal  cord.  Beneath  this  groove,  is  a  section  of  a  rounded  cord  (e),  the  chorda 
dorsalis.  The  openings  (^,  g)  represent  the  situation  of  the  two  aortae.  The  other  cavities 
are  as  yet  indistinct  in  this  figure. 


FIG.  295. 

Fig.  295  shows  the  same  structures  at  a  more  advanced  stage  of  development.  The 
dorsal,  or  vertebral  plates,  which  bound  the  furrow  (a)  in  Fig.  294,  are  closed  above, 
and  include  (a)  the  neural  canal.  The  chorda  dorsalis  (e)  is  separated  from  the  cells  sur- 
rounding it  in  Fig.  294.  "We  have  still  the  external  blastodermic  membrane  (5,  J)  and  the 
internal  blastodermic  membrane  (d,  d),  presenting  various  curves  which  follow  the  arrange- 
ment of  the  cells  of  the  intermediate  layer.  By 
the  sides  of  the  boundaries  of  the  neural  canal, 
are  two  distinct  masses  of  cells  (c,  c),  which  are 
developed  into  the  vertebrae.  Outside  of  these 
masses  of  cells,  are  two  smaller  collections  of 
cells,  afterward  developed  into  the  Wolffian 
bodies,  which  will  be  described  farther  on. 
Beneath  those  two  masses,  are  two  large  cavi- 
ties (gr,  g),  the  largest  cavities  shown  in  Fig. 
295,  presenting  an  irregular  form,  which  are 
sections  of  the  two  primitive  aortas.  The  two 
openings  (A,  7i)  become  afterward  the  pleuro- 
peritoneal  cavity. 

In  Fig.  296,  the  parts  are  still  farther  de- 
veloped. The  neural  canal  is  represented  (a) 
nearly  the  same  as  in  Fig.  295,  with  the  chorda 
dorsalis  (e)  just  beneath  it.  A  groove,  or  gutter 
(d)  has  been  formed  in  front,  which  is  the  groove  of  the  intestinal  canal.  This  remains 
open  at  this  time  and  is  lined  by  the  internal  blastodermic  membrane.  Just  above  d,  is 
58 


ff 

FIG.  296. 


914  GENERATION. 

a  single  opening  (#),  which  is  formed  by  the  union  of  the  two  openings  (</,  g)  in  Figs. 
294  and  295,  and  this  is  the  abdominal  aorta,  which  has  here  become  single.  The  two 
openings  (h,  h)  represent  a  section  of  the  pleuro-peritoneal  cavity.  The  outer  wall  of 
this  cavity  is  the  outer  visceral  plate,  which  is  developed  into  the  muscular  walls  of  the 
abdomen.  The  lower  and  inner  wall  is  the  inner  visceral  plate,  which  forms  the  main 
portion  of  the  intestinal  walh  The  outer  wall  is  the  outer  layer  of  the  intermediate 
membrane,  and  the  inner  wall  is  the  inner  layer  of  the  same  membrane.  The  two  round 
orifices  (*',  i)  are  sections  of  the  Wolffian  ducts. 

The  figures  we  have  just  described,  it  must  be  borne  in  mind,  represent  transverse  sec- 
tions of  the  body  of  the  chick,  made  through  the  middle  portion  of  the  abdomen.  In  our 
explanations  of  these  figures,  we  have  not  adhered  absolutely  to  the  text  of  Brticke,  but 
have  made  use  of  the  very  elegant  semi-diagrammatic  illustrations  by  Waldeyer,  whose 
explanations  are  remarkably  clear  and  satisfactory.  Our  explanations,  however,  particu- 
larly those  of  Fig.  296,  are  sufficiently  extended  to  enable  us  to  study  the  development 
of  special  organs.  The  posterior  parts,  it  is  seen,  are  developed  first,  the  situation  of  the 
vertebral  column  being  marked  soon  after  the  enclosure  of  the  neural  canal  by  the  verte- 
bral plates ;  and,  at  about  the  same  time,  the  two  aortae  make  their  appearance,  with  the 
first  traces  of  the  pleuro-peritoneal  cavity.  The  next  organs  in  the  order  of  development, 
after  the  vascular  system,  are  the  Wolffian  bodies,  which  are  so  large  and  important  in 
the  early  life  of  the  embryon.  The  intestinal  canal  is  then  a  simple  groove,  and  the  em- 
bryon  is  entirely  open  in  front.  Were  we  now  to  follow  the  process  of  development  far- 
ther, we  should  see  that  the  visceral  plates  advance  and  close  over  the  abdominal  cavity, 
as  the  medullary  plates  have  closed  over  the  neural  canal.  Thus  there  would  be  formed  a 
closed  tube,  the  intestine,  lined  by  the  thin,  internal  blastodermic  membrane,  the  walls  of 
the  intestine  being  formed  of  the  inner  layer  of  the  intermediate  membrane.  This  would 
bring  the  external  layer  of  the  intermediate  membrane  around  the  intestine  to  form  the 
muscular  walls  of  the  abdomen,  the  cavity  (Fig.  296,  ^,  A)  being  the  peritoneal  cavity,  and 
the  external  covering  being  the  external  blastodermic  membrane.  At  this  time,  the  great 
Wolifian  bodies  lie  next  the  spinal  column,  between  the  intestine  and  the  abdominal 
walls,  with  the  single  abdominal  aorta  situated  behind  the  intestine. 

Development  of  the  Skeleton,  Muscular  System,  and  Skin. 

Chorda  Dorsalis. — One  of  the  earliest  structures  observed  in  the  developing  embryon  ' 
is  the  chorda  dorsalis.  This  is  situated  beneath  the  neural  canal  and  extends  the  entire 
length  of  the  body.  It  is  formed  of  a  cord  of  simple  cells,  and  marks  the  situation  of  the 
vertebral  column,  though  itself  it  is  not  developed  into  the  vertebras,  which  grow  around 
it  and  encroach  upon  its  substance,  until  it  finally  disappears.  This  structure  has  been 
very  minutely  described  by  Robin,  under  the  name  of  the  notocorde.  In  many  mam- 
mals, the  notocorde  presents  a  slight  enlargement  at  the  cephalic  extremity,  which  ex- 
tends to  the  auditory  vesicles  and  it  is  somewhat  diminished  in  size  at  the  caudal  extrem- 
ity. By  the  sides  of  this  cord,  are  the  masses  of  cells  which  are  eventually  developed 
into  the  vertebra.  The  vertebrae,  as  they  are  developed,  are  formed  of  temporary  car- 
tilaginous structure,  gradually  extending  around  the  chorda  dorsalis,  which  then  occupies 
the  axis  of  the  spinal  column.  Between  the  bodies  of  the  vertebras,  the  chorda  dorsalis 
presents  regular  enlargements,  surrounded  by  a  delicate  membrane.  As  ossification  of 
the  spinal  column  advances,  that  portion  of  the  chorda  dorsalis  which  is  surrounded  by 
the  bodies  of  the  vertebrae  disappears,  leaving  the  enlargements  between  the  vertebrae 
distinct.  These  enlargements,  which  are  not  permanent,  are  gradually  invaded  by  fibrous 
tissue,  their  gelatinous  contents  disappear,  and  the  intervertebral  disks,  composed  of  fibro- 
cartilaginous  structure,  remain.  These  disks  are  permanent  between  the  cervical,  the 
dorsal,  and  the  lumber  vertebrae ;  but  they  eventually  disappear  from  between  the  dif- 
ferent parts  of  the  sacrum  and  coccyx,  as  these  are  consolidated,  this  occurring,  in  the 


DEVELOPMENT  OF  THE  SKELETON,  MUSCULAR  SYSTEM,  AND  SKIN.  9i5 


human  subject,  at  from  the  ninth  to  the  twelfth  year, 
just  described  are  represented  in  Fig.  297. 


The  processes  of  development 


Vertebral  Column,  etc. — In  Figs.  295  and  296  (c,  c),  are  seen  the  two  masses  of  cells, 
situated  by  the  sides  of  the  neural  canal,  which  are  destined  to  be  developed  into  the 
vertebrae.  These  cells  extend  around  and  encroach  upon  the  chorda  dorsalis  and  form 

the  bodies  of  the  vertebrae.  They  also  ex- 
tend over  the  neural  canal,  closing  above, 
and  these  processes  are  called  the  medul- 
lary, or  dorsal  plates.  Sometimes  the  dorsal 
plates  fail  to  close  at  a  certain  point  in  the 
spinal  column,  and  this  constitutes  the  mal- 
formation known  as  spina  bifida.  From  the 
sides  of  the  bodies  of  the  vertebras,  the  va- 
rious processes  of  these  bones  are  formed. 
As  the  spinal  column  is  developed,  its  lower 
portion  presents  a  projection  beyond  the 
pelvis,  which  constitutes  a  temporary  caudal 
appendage,  curved  toward  the  abdomen ;  but 
this  no  longer  projects  after  the  bones  of  the 
pelvis  are  fully  developed.  At  the  same  time, 
the  entire  vertebral  column  is  curved  toward 
the  abdomen,  and  it  is  twisted  upon  its  axis 
from  left  to  right,  so  that  the  anterior  face 
of  the  pelvis  presents  a  right  angle  to  the 


FIG.  297. —  The  first  six  cervical  vertebra  of  the  embryon 
of  a  rabbit  one  inch  in  length.  (Robin.) 

rt,  &,  cephalic  portion  of  the  notocorde  exposed  by  the  re- 
moval of  the  cartilage ;  b,  portion  of  the  chorda  dor- 
salis slightly  enlarged,  which,  in  this  embryon,  was 
situated  between  the  atlas  and  the  occipital  bone ;  c, 
odontoid  process  ;  d,  base  of  the  odontoid  process;  e, 
inferior,  or  second  part  of  the  body  of  the  axis ;  /,  k, 
enlargements  of  the  chorda  dorsalis  between  the  ver- 
tebrae ;  ff,  cartilage  of  the  lateral  portion  of  the  atlas ; 
h,  lateral  portion  of  the  axis ;  *,  *',  transverse  apophy- 
ses  of  vertebrae. 


FIG.  298. — Human  embryo,  about  one  month  old,  show- 
ing the  large  size  of  the  head  and  upper  parts  of 'the 
body,  the  twisted  form  of  the  spinal  column,  tfie 
rudimentary  condition  of  the  upper  and  lower 
extremities,  and  the  rudimentary  tail  at  tfie  end 
of  the  spinal  column.  (Dalton.) 


upper  part  of  the  body ;  but,  as  the  inferior  extremities  and  the  pelvis  become  developed, 
the  spine  becomes  straight.  The  vertebrae  make  their  appearance  first  in  the  middle  of 
the  dorsal  region,  from  which  point,  they  rapidly  extend  upward  and  downward,  until 
the  spinal  column  is  complete. 

At  the  base  of  the  skull,  on  either  side  of  the  superior  prolongation  of  the  chorda  dor- 
salis, are  two  cartilaginous  processes,  which  are  developed  into  the  so-called  cranial  ver- 
tebrae. In  this  cartilaginous  mass,  three  ossific  points  appear,  one  behind  the  other. 
The  posterior  point  of  ossification  is  for  the  basilar  portion  of  the  occipital  bone,  which 
is  developed  in  the  same  way  as  one  of  the  vertebrae  ;  the  middle  point  is  for  the  poste- 
rior portion  of  the  sphenoid ;  and  the  anterior  point  is  for  the  anterior  portion  of  the 
sphenoid.  The  frontal  bone,  the  parietal  bone,  the  temporal  bone,  and  a  portion  of  the 
occipital  bone  are  developed  from  the  connective  tissue,  without  the  intervention  of  pre- 


91 G  GENERATION". 

existing  cartilaginous  structure.  The  development  of  the  face  will  be  described  separately. 
At  the  time  when  the  vertebrae  are  being  developed,  with  their  laminae  and  their  spinous 
and  transverse  processes,  the  ribs  extend  over  the  thorax,  and  the  clavicle,  scapula,  and 
sternum  make  their  appearance. 

At  about  the  beginning  of  the  second  month,  four  papillary  prominences,  which  are 
the  first  traces  of  the  arms  and  legs,  appear  on  the  body  of  the  embryon.  These  progres- 
sively increase  in  length,  the  arms  appearing  near  the  middle  of  the  embryon,  and  the 
legs,  at  the  lower  portion.  Each  extremity  is  divided  into  three  portions,  the  arm,  fore- 
arm, and  hand,  for  the  upper  extremities,  and  the  thigh,  leg,  and  foot,  for  the  lower  ex- 
tremities. At  the  end  of  eacli  extremity,  there  are,  finally,  divisions  into  the  fingers  and 
toes,  wTith  the  various  cartilages  and  bones  of  all  of  these  parts,  and  their  articulations. 
(See  Plates  I.  and  II.,  Figs.  D  and  II,  facing  page  920.) 

Very  early  in  intra-uterine  life,  the  skeleton,  which  is  at  first  entirely  cartilaginous, 
begins  to  ossify,  from  little  bony  points  which  appear  in  the  cartilaginous  structure.  The 
first  points  appear  at  nearly  the  same  time  (about  the  beginning  of  the  second  month)  in 
the  clavicle  and  the  upper  and  the  lower  jaw.  Similar  ossific  points,  which  gradually 
extend,  are  also  seen  in  other  parts,  the  head,  ribs,  pelvis,  scapula,  metacarpus,  and  meta- 
tarsus, and  the  phalanges  of  the  fingers  and  toes.  At  birth,  the  carpus  is  entirely  cartila- 
ginous, and  it  does  not  begin  to  ossify  until  the  second  year.  The  same  is  true  of  the 
tarsus,  except  the  calcaneum  and  astragalus,  which  ossify  just  before  birth.  The  pisiform 
bone  of  the  carpus  is  the  last  to  take  on  osseous  transformation,  this  occurring  at  from 
the  twelfth  to  the  fifteenth  year.  As  ossification  progresses,  the  deposits  in  the  various 
ossific  points  gradually  extend  until  they  reach  the  joints,  which  remain  incrusted  with 
the  permanent  articular  cartilage. 

While  the  skeleton  is  being  thus  developed,  the  muscles  are  formed  from  the  outer 
layer  of  the  intermediate  blastodermic  membrane,  and  the  visceral  plates  close  over  the 
thorax  and  abdomen  in  front,  leaving  an  opening  for  the  umbilical  cord.  The  various 
tissues  of  the  external  parts,  particularly  the  muscles,  begin  to  be  distinct  at  the  end  of 
the  second  month.  The  deep  layers  of  the  dorsal  muscles  are  the  first  to  be  distin- 
guished ;  then,  successively,  the  long  muscles  of  the  neck,  the  anterior  straight  muscles 
of  the  head,  the  straight  and  transverse  muscles  of  the  abdomen,  the  muscles  of  the  ex- 
tremities, the  superficial  muscles  of  the  back,  the  oblique  muscles  of  the  abdomen,  and 
the  muscles  of  the  face. 

The  skin  appears  at  about  the  beginning  of  the  second  month,  when  it  is  very  delicate 
and  transparent.  At  the  end  of  the  second  month,  the  epidermis  may  be  distinguished. 
The  sebaceous  follicles  are  developed  at  the  third  month ;  and,  at  about  the  fifth  month, 
the  surface  is  covered  with  their  secretion  mixed  with  desquamated  epithelium.  This 
cheesy  substance  constitutes  the  vernix  caseosa.  At  the  third  month,  the  nails  make 
their  appearance,  and  the  hairs  begin  to  grow  at  about  the  fifth  month.  The  sudoripa- 
rous glands  first  appear  at  about  the  fifth  month,  by  the  formation  of  flask -like  processes 
of  the  true  skin,  which  are  gradually  elongated  and  convoluted,  until  they  are  fully 
developed  only  a  short  time  before  birth. 

Development  of  the  Nervous  System. 

We  have  seen,  in  studying  the  development  of  the  spinal  column,  how  the  dorsal,  or 
medullary  plates  close  over  the  groove  for  the  neural  canal.  In  the  interior  of  this 
canal,  the  cerebro-spinal  axis  is  developed,  by  cells,  which  gradually  encroach  upon  its 
caliber,  until  we  have  remaining  only  the  small  central  canal  of  the  spinal  cord,  commu- 
nicating with  the  ventricles  of  the  brain.  As  the  nervous  tissue  is  developed  in  the  inte- 
rior of  the  neural  canal,  there  is  a  separation  of  the  histological  elements  at  the  surface, 
to  form  the  membranes.  The  dura  mater  'and  the  pia  mater  are  formed  first,  appearing 
at  about  the  end  of  the  second  month,  while  the  arachnoid  is  not  distinct  until  the  fifth 


DEVELOPMENT   OF   THE   NERVOUS   SYSTEM.  917 

month.  The  nerves  are  not  produced  as  prolongations  from  the  cord  into  the  various 
tissues,  nor  do  they  extend  from  the  tissues  to  the  cord ;  but  they  are  developed,  in  each 
tissue,  by  a  separation  of  histological  elements  from  the  cells  of  which  the  parts  are 
originally  constituted,  which  at  first  appear  to  be  identical  in  their  morphological  char- 
acters. The  nerves  of  the  sympathetic  system  are  developed  in  the  same  way. 

The  mode  of  development  of  the  spinal  cord  is  thus  sufficiently  simple ;  but,  with  the 
growth  of  the  embryon,  we  observe  dilatations  at  the  superior  and  at  the  inferior  extrem- 
ities of  the  neural  canal.  The  cord  is  uniform  in  size  in  the  dorsal  region,  marked  only 
by  the  regular  enlargements  at  the  sites  of  origin  of  the  spinal  nerves ;  but  we  soon 
observe  an  ovoid  dilatation  below,  which  forms  the  lumbar  enlargement,  from  which  the 
nerves  are  given  off  to  the  inferior  extremities,  and  the  brachial  enlargement  above,  where 
the  nerves  of  the  superior  extremities  take  their  origin.  At  the  same  time,  there  is  a 
more  marked  dilatation  of  the  canal  at  its  cephalic  extremity.  Here,  a  single  enlargement 
appears,  which  is  soon  divided  into  three  vesicles,  called  the  anterior,  middle,  and  poste- 
rior cerebral  vesicles.  These  become  more  and  more  distinct  as  development  advances. 
The  formation  of  these  parts  is  illustrated  in  Fig.  299,  taken  from  Wagner,  and  made 
more  distinct  by  Longet,  as  they  are  drawn  upon  a  black  ground.  This  figure,  in  C, 
shows  the  projections,  on  either  side,  of  the  vesicles  which  are  eventually  developed 
into  the  nervous  portions  of  the  organ  of  vision. 


FIG.  299. — Development  of  the  nervous  system  of  the  chick.    (Longet.) 

A.  the  two  primitive  halves  of  the  nervous  system,  twenty-four  hours  after  incubation ;  B,  the  same,  thirty-six  hours 
after ;  C,  the  same,  at  a  more  advanced  stage,  c,  the  two  primitive  halves  of  the  vertebrae ;  d,  anterior  dilata- 
tion of  the  neural  canal ;  ft,  posterior  dilatation  (the  lumbar  enlargement) ;  1,  2,  8,  anterior,  middle,  and  inferior 
cerebral  vesicles;  a,  slight  flattening  of  the  anterior  cerebral  vesicle;  o,  formation  of  the  ocular  vesicles. 

The  three  cerebral  vesicles  now  undergo  farther  changes.  The  superior,  which  we 
may  call  the  first  primitive  vesicle,  enumerating  them  from  above  downward,  is  soon 
divided  into  two  secondary  vesicles,  the  anterior  of  which  becomes  the  cerebral  hemi- 
spheres, and  the  posterior,  the  optic  thalami,  which  are  eventually  covered,  by  the  great- 
er relative  development  of  the  hemispheres.  The  middle,  or  second  primitive  vesicle, 
does  not  undergo  division  and  is  developed  into  the  tubercula  quadrigemina,  or  centres 
of  vision.  The  posterior,  or  third  primitive  vesicle,  is  divided  into  two  secondary  vesi- 
cles, the  anterior  of  which  becomes  the  cerebellum,  and  the  posterior,  which  is  covered 
by  the  anterior,  the  medulla  oblongata  and  the  pons  Varolii.  While  this  division  of  the 
primitive  cerebral  vesicles  is  going  on,  the  entire  chain  of  encephalic  ganglia  becomes 
curved  from  behind  forward,  forming  three  prominent  angles.  The  first  of  these  angles 
or  prominences  (e,  Fig.  300,  A,  B,  C),  counting  from  before  backward,  is  formed  by  a 
projection  of  the  tubercula  quadrigemina,  which,  at  this  time,  constitute  the  most  pro- 
jecting portion  of  the  encephalic  mass ;  the  second  prominence  (c,  Fig.  300),  situated 
behind  the  tubercula  quadrigemina,  is  formed  by  the  projection  of  the  cerebellum  ;  the 


918  GENERATION. 

third  (d,  Fig.  300,  A,  B,  C),  is  the  bend  of  the  superior  portion  of  the  spinal  cord. 
These  projections  and  the  early  formation  of  certain  parts  of  the  encephalon  in  the 
human  subject  are  illustrated  in  Fig.  300. 

The  cerebrum,  as  we  have  just  seen,  is  developed  from  the  anterior  division  of  the 
first  primitive  cerebral  vesicle.  The  development  of  this  part  is  more  rapid  in  its  lateral 
portions  than  in  the  median  line,  which  divides  the  cerebrum  imperfectly  into  two  lateral 
halves,  forming,  in  this  way,  the  great  longitudinal  fissure.  At  the  same  time,  by  the 
rapid  development  of  the  posterior  portion,  it  extends  over  the  optic  thalami,  the  cor- 
pora quadrigemina,  and  the  cerebellum.  Up  to  the  end  of  the  fourth  month,  the  hemi- 
spheres are  smooth  on  their  surface ;  but  they  then  begin  to  present  large  depressions, 
following  folds  of  the  pia  mater,  which  .are  the  first  convolutions,  these  increasing  rap- 


FIG.  300.— Development  of  the  spinal  cord  and  brain  of  the  human  subject.    (Longet.) 

A,  brain  and  spinal  cord  of  an  embryon  of  seven  weeks ;  lateral  view. 

B,  the  same,  from  an  embryon  farther  advanced  in  development;  £,  spinal  cord;  d,  enlargement  of  the  spinal  cord 

with  its  anterior  curvature ;  c,  cerebellum ;  e,  tubercula  quadrigemina ;  /,  optic  thalamus ;  #,  cerebral  hemi- 
spheres. 

C,  brain  and  spinal  cord  of  an  embryon  of  eleven  weeks ;  6.  spinal  cord  ;  d,  enlargement  of  the  spinal  cord,  with 

its  anterior  curvature ;  c,  cerebellum ;  e,  tubercula  quadrigemina ;  gr,  cerebral  hemispheres  ;  o,  optic  nerve  of 
the  left  side. 

C',  the  same  parts  in  a  vertical  section  in  the  median  line  from  before  backward  ;  5,  membrane  of  the  spinal  cord 
turned  backward ;  d,  second  curvature  of  the  upper  portion  of  the  spinal  cord,  which  has  become  thickened  and 
constitutes  the  peduncles  of  the  cerebrum ;  c,  tubercula  quadrigemina  ;  /J  optic  thalami  covered  by  the  hemi- 
spheres. 

idly  in  number  and  complexity,  especially  after  the  seventh  month.  The  septum  lucidum 
is  then  formed  by  an  elevation  of  nervous  matter  from  the  base,  which  divides  the  lower 
portion  of  the  space  left  between  the  hemispheres  as  they  ascend,  and  forms  the  two 
lateral  ventricles.  At  the  base  of  these,  are  developed  the  corpora  striata.  The  septum 
lucidum  is  formed  of  two  laminae,  with  a  small  space  between  them,  which  is  the  cavity 
of  the  fifth  ventricle.  The  posterior  division  of  this  first  primitive  vesicle  forms  the 
optic  thalami.  These  become  separated  in  front  into  two  lateral  halves,  but  they  remain 
connected  together  at  their  posterior  portion,  which  becomes  the  posterior  commissure. 
The  central  canal  of  the  cord  is  prolonged  upward  between  the  optic  thalami,  and  forms 
the  third  ventricle,  which  is  covered  by  the  hemispheres. 

The  second,  or  middle  cerebral  vesicle  becomes  filled  with  medullary  substance,  ex- 
tends upward,  and  forms  the  peduncles  of  the  cerebrum,  the  upper  portion  being  divided 
to  form  the  tubercula  quadrigemina. 

The  anterior  portion  of  the  third  primitive  vesicle  is  developed  into  the  cerebellum, 
the  convolutions  of  which  appear  at  about  the  fifth  month.  Its  posterior  portion  forms 
the  medulla  oblongata,  in  the  substance  of  which  is  the  fourth  ventricle,  communicating 
with  the  third  ventricle  by  a  little  canal,  the  aqueduct  of  Sylvius,  which  is  left  in  the 
development  of  the  middle  vesicle.  At  about  the  fourth  month,  there  is  a  deposition  of 
nervous  matter  in  front  and  above,  forming  the  pons  Yarolii. 

In  Fig.  299  (C,  0),  it  is  seen  that  the  vesicles  for  the  organs  of  vision  appear  very  early, 
as  lateral  offshoots  of  the  anterior  cerebral  vesicle.  These  gradually  increase  in  size  and 
advance  anteriorly,  as  development  of  the  other  parts  progresses.  We  shall  see,  when 
we  come  to  study  the  development  of  the  face,  that  the  eyes  are  situated  at  first  at  the 
sides  of  the  head,  gradually  approaching  the  anterior  portion.  At  the  extremity  of  each 
of  these  lateral  prolongations,  a  rounded  mass  appears,  which  becomes  the  globe  of  the 


DEVELOPMENT   OF  THE  ALIMENTARY   SYSTEM.  919 

«ye.  The  superficial  portions  of  the  globe  are  developed  into  the  sclerotic  and  the  cornea, 
which  seem  to  be  formed  of  a  process  from  the  dura  mater.  The  pedicle  attached  to  the 
globe  becomes  the  optic  nerve.  The  iris  is  developed  at  about  the  seventh  week,  and  is 
at  first  a  simple  membrane,  without  any  central  opening.  As  the  pupil  appears,  it  is 
closed  by  a  vascular  membrane — which  probably  belongs  to  the  capsule  of  the  crystal- 
line lens — called  the  pupillary  membrane.  This  membrane  gradually  disappears  by  an 
atrophy  extending  from  the  centre  to  the  periphery.  It  attains  its  maximum  of  develop- 
ment at  the  sixth  month  and  disappears  at  the  seventh  month.  The  vitreous  humor  is 
formed  of  the  fluid  contents  of  the  optic  vesicle.  The  crystalline  lens  is  regarded  as  a 
product  of  the  tegumentary  layer.  At  the  tenth  week,  we  observe  the  beginning  of  the 
formation  of  the  eyelids.  These  meet  at  about  the  fourth  month  and  adhere  together  by 
their  edges.  In  many  mammals,  the  eyelids  remain  closed  for  a  few  days  after  birth ;  but 
they  become  separated  in  the  human  subject  in  the  later  periods  of  fcetal  life. 

It  is  probable  that  the  vesicle  which  becomes  developed  into  the  internal  ear  is  formed 
independently ;  at  least,  cases  have  been  observed  in  which  there  was  congenital  absence 
of  the  auditory  nerves,  the  parts  of  the  internal  ear  being  perfect.  Soon  after  the  forma- 
tion of  the  auditory  vesicle,  however,  it  communicates  with  the  third  primitive  cerebral 
vesicle,  the  filament  of  communication  being  developed  into  the  auditory  nerve. 

The  auditory  vesicle,  which  appears  subsequently  to  the  organ  of  vision,  is  eventually 
developed  into  the  vestibule.  The  next  formations  are  the  arches,  or  diverticula,  which 
constitute  the  semicircular  canals.  The  membranous  labyrinth  appears  long  before  the 
osseous  labyrinth ;  and  it  has  been  found  perfectly  developed  at  three  months.  The  bones 
of  the  middle  ear,  which  have  no  connection,  in  their  development,  with  the  nervous 
system,  but  which  it  is  convenient  to  mention  here,  are  remarkable  for  their  early  appear- 
ance. They  appear  at  the  beginning  of  the  third  month  and  are  as  large  in  the  foetus  at 
term  as  in  the  adult.  A  remarkable  anatomical  point  with  relation  to  these  structures  is 
the  existence  of  a  cartilage,  attached  to  the  malleus  on  each  side  and  extending  from  this 
bone  along  the  inner  surface  of  the  lower  jaw,  the  two  cartilages  meeting  and  uniting  in 
the  median  line  to  form  a  single  cord.  "  This  cartilage  now  ossifies,  although,  in  the 
commencement,  it  forms  most  of  the  mass  of  the  bone ;  it  disappears  at  the  eighth  month." 
(Meckel.)  This  curious  structure  is  known  as  the  cartilage  of  Meckel. 

There  are  no  special  points  for  description  in  the  development  of  the  olfactory  lobes, 
which  is  very  simple.  These  are  offshoots  from  the  first  cerebral  vesicle,  appearing  at  the 
inferior  and  anterior  part  of  the  cerebral  hemispheres,  a  little  later  than  the  parts  con- 
nected with  vision  and  audition.  The  vesicles  themselves  become  filled  with  ganglionic 
matter,  and  constitute  the  olfactory  bulbs,  their  pedicles  being  the  so-called  olfactory 
nerves,  or  commissures.  The  development  of  some  of  the  parts  of  the  central  nervous 
system  is  illustrated  in  Plates  I.  and  II.,  facing  page  920. 

As  far  as  the  functions  of  the  nervous  system  of  the  foetus  are  concerned,  it  is  probable 
that  they  are  restricted  mainly  to  reflex  phenomena  depending  upon  the  action  of  the 
spinal  cord,  and  that  perception  and  volition  hardly  exist.  It  is  probable  that  many  reflex 
movements  take  place  in  utero.  When  a  foetus  is  removed  from  the  uterus  of  an  animal, 
even  during  the  early  periods  of  pregnancy,  movements  of  respiration  occur,  a  fact  which 
we  have  often  demonstrated  to  medical  classes ;  and  it  is  well  known  that  efforts  of  respi- 
ration sometimes  occur  within  the  uterus.  This  we  believe  to  be  a  reflex  action  excited 
by  the  want  of  oxygen  in  the  tissues,  when  the  placental  circulation  is  interrupted.  "We 
have  already  discussed  these  phenomena  in  connection  with  the  subject  of  respiration. 

Development  of  the  Alimentary  System. 

The  intestinal  canal  is  the  first  formation  of  the  alimentary  system.  As  we  have 
already  seen,  this  is  at  first  open  in  the  greatest  part  of  its  extent,  presenting,  at  either 
extremity  of  the  longitudinal  gutter,  in  front  of  the  spinal  column,  a  rounded,  blind  ex- 


920  GENERATION. 

tremity,  which  is  closed  over  in  front  for  a  short  distance.  The  closure  of  the  abdominal 
plates  then  extends  laterally  and  from  the  two  extremities  of  the  intestine,  until  we  have 
only  the  opening  remaining  for  the  passage  of  the  umbilical  cord  and  the  pedicle  of  the 
umbilical  vesicle.  There  is  at  first  an  open  communication  between  the  lower  part  of  the 
intestinal  tube  and  the  allantois,  which  forms  the  canal  known  as  the  urachus ;  but  that 
portion  of  this  communication  which  remains  enclosed  in  the  abdominal  cavity  becomes 
separated  from  the  urachus,  is  dilated,  and  eventually  forms  the  urinary  bladder.  When 
the  bladder  is  first  shut  off,  it  communicates  with  the  lower  portion  of  the  intestine,  which 
is  called  the  cloaca ;  but  it  finally  loses  this  connection  and  presents  a  special  opening? 
the  urethra. 

As  development  advances,  the  intestine  grows  rapidly  in  length  and  becomes  convo- 
luted.    It  is  held  loosely  to  the  spinal  column  by  the  mesentery,  a  fold  of  the  peritoneum, 

this  membrane  being  reflected  along  the  walls  of  the  ab- 
dominal cavity.  In  the  early  stages  of  development,  a  por- 
tion of  the  intestine  protrudes  at  the  umbilicus,  where  the 
first  intestinal  convolution  appears ;  and  sometimes  there 
is  a  congenital  hernia  of  this  kind  at  birth,  which  usually 
disappears  under  the  influence  of  gentle  and  continued 
pressure.  An  illustration  of  this  is  given  in  Fig.  301.  This 
protrusion,  in  the  normal  process  of  development,  is  grad- 
ually returned  into  the  abdomen,  as  the  cavity  of  the  pedi- 
cle of  the  umbilical  vesicle  is  obliterated,  at  about  the  tenth 
week. 

At  the  upper  part  of  the  abdominal  cavity,  the  aliment- 
i  pig,  showing  a  loop   arv  canal  presents  two  lateral   projections,  or  pouches. 
of  intestine,  farming  an  umUii-   The  one  on  the  left  side,  as  it  increases  in  size,  becomes  the 

eat  herma.    From  a  specimen  in 

the  possession  of  Prof.  Daiton.        greater  pouch  of  the  stomach,  and  the  one  on  the  right 

From  the  convexity  of  the  loop  a  thin     sjde    the  lesser  pouch, 
filament  is  seen  passing  to  the 

umbilical  vesicle,  "which  is  here         At  a  short  distance  below  the  attachment  of  the  pedicle 
of  the  umbilical  vesicle  to  the  intestine,  there  appears  a 

rounded  diverticulum,  which  is  eventually  developed  into  the  caecum,  or  the  commence- 
ment of  the  larger  intestine.  The  caecum  gradually  recedes  from  the  neighborhood  of  the 
umbilicus,  which  is  its  original  situation,  and  finally  becomes  fixed,  by  a  shortening  of  the 
mesentery,  in  the  right  iliac  region.  As  the  caecum,  or  caput  coli,  is  developed,  it  presents 
a  conical  appendage,  which  is  at  first  fully  as  large  as  the  small  intestine  and  is  relatively 
longer  than  in  the  adult.  During  the  fourth  week,  this  appendage  becomes  relatively  smaller 
and  more  or  less  twisted,  forming  the  appendix  vermiformis.  At  the  second  month,  the 
caecum,  or  caput  coli,  as  we  have  seen,  is  at  the  umbilicus,  and  the  large  intestine  extends 
in  a  straight  line  toward  the  anus  ;  at  the  third  month,  it  is  situated  at  about  the  middle 
of  the  abdomen ;  and  it  gradually  descends,  until  it  reaches  the  right  iliac  region  at  about 
the  seventh  month.  Thus,  at  the  second  month,  there  is  only  a  descending  colon ;  the 
transverse  colon  is  formed  at  the  third  month ;  and  the  ascending  colon,  at  the  fifth 
month.  The  ileo-caecal  valve  appears  at  the  third  month ;  the  rectum,  at  the  fourth 
month;  and  the  sigmoid  flexure  of  the  colon,  at  the  fifth  month.  During  this  time,  the 
large  intestine  increases  more  rapidly  in  diameter  than  the  small  intestine,  while  the  latter 
develops  more  rapidly  in  its  length. 

In  the  early  stages  of  development,  the  surface  of  the  intestines  is  smooth  ;  but  villi 
appear  upon  its  mucous  membrane  during  the  latter  half  of  intra-uterine  existence. 
These  are  found  at  first  both  in  the  large  and  the  small  intestine.  At  the  fourth  month, 
they  become  shorter  and  less  numerous  in  the  large  intestine,  and  they  are  lost  at  about 
the  eighth  month,  when  the  projections  which  bound  the  sacculi  of  this  portion  of  the 
intestinal  canal  make  their  appearance.  The  valvulae  conniventes  appear,  in  the  form  of 
slightly-elevated,  transverse  folds,  in  the  upper  portion  of  the  small  intestine.  The  villi 
of  the  small  intestine  are  permanent. 


P1.I. 


Germs  or  Embryos 


n  a    l 


Fios.  A,  B,  E,  F.—v,  anterior  cerebral  hemispheres ;  2,  optic  thalaini,  m,  tnbercula  qnadri- 

gernina  ;  /%,  cerebellum ;  w,  pons  Varolii ;  r,  spinal  cord ;  w,  spine ;  *,  tail ;  a,  eyes ; 

r  r ,  we,  nose ;  q>,  ^aij;  5fcf,X,  ^,  visceral  arches ;  bv,  anterior  extremity ;  bh,  posterior  ex- 

ttfMrity.  '( 


of  four  Vertebrates. 


PI.  IT. 


FIG*.  (7,  A  £,  #.— P,  anterior  cerebral  hemispheres ;  z,  optic  thalami ;  w,  tubercula  quadri- 
gemina;  ^cerebellum;  w,  pons  Varolii;  r,  spinal  cord;  w,  spine;  «,  tail;  a,  eyes 
n«,  nose ;  o,  ear;  tj,  #2,  *8,  visceral  arches ;  bv,  anterior  eitreraU^;;^,  posterior ,ex;<  ^ 
tremity.    (Haeckel.)  ,  •*•  2 


DEVELOPMENT   OF   THE   ALIMENTARY   SYSTEM.  921 

The  mesentery  is  first  formed  of  two  perpendicular  folds,  attached  to  the  sides  of  the 
spinal  column.  As  the  intestine  undergoes  development,  a  portion  of  the  peritoneal 
membrane  extends  in  a  quadruple  fold  from  the  stomach  to  the  colon,  to  form  the  great 
omentum,  which  covers  the  small  intestine  in  front. 

As  the  head  undergoes  development,  a  large  cavity  appears,  which  is  eventually 
bounded  by  the  arches  that  are  destined  to  form  the  different  parts  of  the  face.  This  is 
the  pharynx.  It  is  entirely  independent,  in  its  formation,  of  the  intestinal  canal,  the 
latter  terminating  in  a  blind  extremity  at  the  stomach ;  and,  between  the  pharynx  and 
the  stomach,  there  is  at  first  no  channel  of  communication.  The  anterior  portion  of  the 
pharynx  presents,  during  the  sixth  week,  a  large  opening,  which  is  afterward  partially 
closed  in  the  formation  of  the  face.  The  rest  of  this  cavity  remains  closed  until  a  com- 
munication is  effected  with  the  oesophagus.  The  oesophagus  appears  in  the  form  of  a 
tube,  which  finally  opens  into  the  pharynx  above  and  into  the  stomach  below.  At  this 
time,  there  is  really  no  thoracic  cavity,  the  upper  part  of  the  stomach  is  very  near  the 
pharynx,  the  a>sophagus  is  short,  the  rudimentary  lungs  appear  by  its  sides,  and  the  heart 
lies  just  iii  front.  As  the  thorax  is  developed,  however,  the  oesophagus  becomes  longer, 
the  lungs  increase  in  size,  and  finally  the  diaphragm  shuts  off  its  cavity  from  the  cavity 
of  the  abdomen.  The  growth  of  the  diaphragm  is  from  its  periphery  to  the  central  por- 
tion, which  latter  gives  passage  to  the  vessels  and  the  oesophagus.  Sometimes,  when  this 
closure  is  incomplete,  we  have  the  malformation  known  as  congenital  diaphragmatic 
hernia. 

The  development  of  the  anus  is  sufficiently  simple.  At  first,  as  we  have  seen,  the 
intestine  terminates  below  in  a  blind  extremity ;  but,  at  about  the  seventh  week,  a  lon- 
gitudinal slit  appears  below  the  external  organs  of  generation,  by  which  the  rectum 
opens.  This  is  the  anus.  It  is  not  very  unusual  to  observe  an  arrest  in  the  development 
of  this  opening,  the  intestine  terminating  in  a  blind  extremity,  a  short  distance  beneath 
the  integument.  This  constitutes  the  malformation  known  as  imperforate  anus,  a  de- 
formity which  can  usually  be  relieved,  without  much  difficulty,  by  a  surgical  operation,  if 
the  distance  between  the  rectum  and  the  skin  be  not  too  great.  The  opening  of  the  anus 
appears  about  a  week  after  the  opening  of  the  mouth,  at  or  about  the  seventh  week. 

The  rudiments  of  the  liver  appear  very  early,  and,  indeed,  at  the  end  of  the  first 
month,  this  organ  has  attained  an  enormous  size.  Two  projections,  or  buds,  appear  on 
either  side  of  the  intestine,  which  form  the  two  principal  lobes  of  the  liver.  This  organ 
is  at  first  symmetrical,  the  two  lobes  being  of  nearly  the  same  size,  with  a  median  fis- 
sure. One  of  these  prolongations  from  the  intestine  becomes  perforated  and  forms  the 
excretory  duct,  of  which  the  gall-bladder,  with  its  duct,  is  an  appendage.  During  the 
early  part  of  fcatal  life,  the  liver  occupies  the  greatest  part  of  the  abdominal  cavity. 
According  to  Burdach,  its  weight,  in  proportion  to  the  weight  of  the  body  at  different 
ages,  is  as  follows :  At  the  end  of  the  first  month,  1  to  3 ;  at  term,  1  to  18 ;  in  the 
adult,  1  to  36.  Its  structure  is  very  soft  during  the  first  months,  and  it  is  only  at  about 
the  fourth  or  fifth  month  that  it  assumes  one  of  its  most  important  functions,  viz.,  the 
production  of  sugar.  As  development  advances,  and  as  the  relative  size  of  the  liver 
gradually  diminishes,  its  tissue  becomes  more  solid. 

The  pancreas  appears  at  the  left  side  of  the  duodenum,  by  the  formation  of  two  ducts 
leading  from  the  intestine,  which  branch  and  develop  glandular  structure  at  their  ex- 
tremities. The  spleen  is  developed,  about  the  same  time,  at  the  greater  curvature  of  the 
stomach.  This  organ  is  abundantly  supplied  with  blood-vessels,  but  it  has  no  excretory 
duct.  The  spleen  becomes  distinct  during  the  second  month. 

There  is  no  reason  to  believe  that  any  of  the  digestive  fluids  are  secreted  during 
intra-uterine  life.  The  stomach,  at  least,  never  contains,  at  this  time,  an  acid  secretion. 
At  birth,  the  intestine  contains  a  peculiar  substance,  called  meconinm,  which  will  be 
described  farther  on.  Cholesterine,  an  important  constituent  of  the  bile,  is  found  in  the 
meconium  in  large  quantity,  but  its  function  is  connected  exclusively  with  excretion. 


922  GENERATION. 

Development  of  the  Respiratory  System. 

On  the  anterior  surface  of  the  membranous  tube  which  becomes  the  oesophagus,  an 
elevation  appears,  which  soon  presents  an  opening  into  the  resophagus,  the  projection 
forming,  at  this  time,  a  single,  hollow  cul-de-sac.  This  opening  becomes  the  rima  glotti- 
dis,  and  the  single  tube  with  which  it  is  connected  is  developed  into  the  trachea.  At  the 

lower  extremity  of  this  tube,  a  bifurca- 
tion appears,  terminating  first  in  one. 
and  afterward,  in  several  culs-de-sac. 
The  bifurcated  tube  constitutes,  after 
the  lungs  are  developed,  the  primitive 
bronchi,  at  the  extremities  of  which  are 
the  branches  of  the  bronchial  tree.  As 
the  bronchi  branch  and  subdivide,  they 
extend  downward  into  what  becomes 
eventually  the  cavity  of  the  thorax. 

FIG.  302. — Formation  of  the  bronchial  ramifications  and    _. 

of  the  pulmonary  cells.- A,  £,  development  of  the  lungs,    The    pulmonary    vesicles,    according    to 
after  Rathke;    C,  D,  histological  development  of  the    T>np^Qni>    Qro   /Wolnr^rl    l^fn™  the  +™ 

lungs,  after  J.  Mulier.   (Longet.)  .Buidacu,  are  developed  before  tne  tra- 

chea.    The  lungs  contain  no  air  at  any 

period  of  intra-uterine  life,  and  receive  but  a  small  quantity  of  blood  ;  but,  at  birth, 
they  become  distended  with  air,  are  increased  thereby  in  volume,  and  receive  all  the 
blood  from  the  right  ventricle.  This  process  of  development  is  illustrated  in  Fig.  302. 
The  lungs  appear,  in  the  human  embryon,  during  the  sixth  week.  The  two  portions  into 
which  the  original  bud  is  bifurcated  constitute  the  true  pulmonary  structure,  and  the 
formation  of  the  trachea  and  bronchial  tubes  occurs  afterward  and  is  secondary.  We 
have  indicated  the  pulmonary  structure  as  branching  processes  from  the  bronchial  tubes, 
merely  for  convenience  of  description. 

Development  of  the  Face. 

The  development  of  the  face  in  the  embryon  of  mammals  is  somewhat  complex,  but 
it  is  peculiarly  interesting,  as  its  study  enables  us  to  comprehend  the  manner  in  which 
various  very  common  malformations  of  the  face  and  palate  are  produced.  The  anterior 
portion  of  the  embryon,  as  we  have  seen  in  studying  the  development  of  the  trunk,  re- 
mains open  in  front  long  after  the  medullary  plates  have  met  at  the  back  and  enclosed 
the  neural  canal.  The  common  cavity  of  the  thorax  and  abdomen  is  closed  by  the 
growth  of  the  visceral  plates,  which  meet  in  front.  These  are  projecting  plates  of  the 
intermediate  blastodermic  layer,  which  gradually  extend  forward  from  the  vertebral  col- 
umn. At  the  same  time  that  the  visceral  plates  are  thus  closing  over  the  thorax  and 
abdomen,  four  distinct,  tongue-like  projections  appear,  one  above  the  other,  by  the  sides 
of  the  neck.  These  are  called  the  visceral  arches,  and  the  slits  between  them  are  called 
the  visceral  clefts.1  The  first  three  arches,  enumerating  them  from  above  downward,  cor- 
respond, in  their  origin,  to  the  three  primitive  cerebral  vesicles.  The  fourth  arch,  which 
is  not  enumerated  by  some  authors,  who  recognize  but  three  arches,  corresponds  to  the 
superior  cervical  vertebrae.  Of  these  four  arches,  the  first  is  the  most  important,  as  its 
development,  in  connection  with  that  of  the  frontal  process,  forms  the  face  and  the  mal- 
leus and  incus  of  the  middle  ear.  The  second  arch  forms  the  lesser  cornua  of  the  hyoid 
bone,  the  stapes,  and  the  styloid  ligament.  The  third  arch  forms  the  body  and  the  greater 
cornua  of  the  hyoid.  The  fourth  arch  forms  the  larynx.  The  first  cleft,  situated  be- 
tween the  first  and  the  second  arch,  becomes  obliterated  in  front  by  a  deposition  of 
plastic  matter,  but  an  opening  remains  by  the  side,  which  forms,  externally,  the  external 

1  These  arches  correspond  to  the  branchial  vascular  arc-lies,  which  will  be  fully  described  in  connection  with  the 
development  of  the  circulatory  system. 


PI,  111. 


FIG.  1.— Human  erribryon,  at  the  ninth  week,  removed  from  the  membranes ;  three  times  the 
natural  size.    (Erdl . ) 

FTG,  2.— Human  embryon,  at  the  twelfth  week,  enclosed  in  the  amnion;  natural  size.  (Erdl.) 


2' : 


DEVELOPMENT  OF  THE  FACE.  923 

auditory  meatus,  and  internally,  the  tympanic  cavity  and  the  Eustachian  tube.  The 
other  clefts  become  obliterated  as  the  arches  advance  in  their  development. 

From  the  above  sketch,  it  is  seen  that  the  face  and  the  neck  are  formed  by  the 
advance  and  closure  in  front  of  projections  from  behind,  in  the  same  way  as  the  cavities 
of  the  thorax  and  abdomen  are  closed;  but  the  closure  of  the  first  visceral  arch  is 
complicated  by  the  projection,  from  above  downward,  of  the  frontal,  or  intermaxillary 
process,  and  by  the  formation  of  several  secondary  projections,  which  leave  certain  per- 
manent openings,  forming  the  mouth,  nose,  etc.  These  processes  of  development,  we 
shall  now  attempt  to  follow. 

In  the  very  first  stages  of  development  of  the  head,  there  is  no  appearance  of  the 
face.  The  cephalic  extremity  consists  simply  of  the  cerebral  vesicles,  the  surface  of  this 
enlarged  portion  of  the  embryon  being  covered,  in  front  as  well  as  behind,  by  the  exter- 
nal blastodermic  membrane.  During  the  sixth  week,  after  the  cavity  of  the  pharynx 
has  appeared,  the  membrane  gives  way  in  front,  forming  a  large  opening,  which  may  be 
called  the  first  opening  of  the  mouth.  At  this  time,  however,  the  face  is  entirely  open 
in  front  as  far  back  as  the  ears.  The  first,  or  the  superior  visceral  arch,  now  appears 
as  a  projection  of  the  middle  blastodermic  layer,  extending  forward.  This  is  soon  marked 
by  two  secondary  projections,  the  upper  projection  forming  the  superior  maxillary  por- 
tion of  the  face,  and  the  lower,  the  inferior  maxilla.  The  two  projections  which  form 
the  lower  jaw  soon  meet  in  the  median  line,  and  their  superior  margin  is  the  lower  lip. 
At  the  same  time  there  is  a  projection  from  above,  extending  between  the  two  superior 
projections,  which  is  called  the  frontal,  or  intermaxillary  process.  This  extends  from 
the  forehead  (that  portion  which  covers  the  front  of  the  cerebrum)  downward.  The 
superior  maxillary  projections  then  advance  forward,  gradually  passing  to  meet  the 
frontal  process,  but  leaving  two  small  openings  on  either  side  of  the  median  line,  which 
are  the  openings  of  the  nostrils.  The  upper  portion  of  the  frontal  process  thus  forms 
the  nose ;  but  below,  is  the  lower  end  of  this  process,  which  is  at  first  split  in  the  median 
line,  projects  below  the  nose,  and  forms  the  incisor  process,  at  the  lower  border  of  which 
are  finally  developed  the  incisor  teeth.  As  the  superior  maxillary  processes  advance 
forward,  the  eyes  are  moved,  as  it  were,  from  the  sides  of  the  head  and  present  anteriorly, 
until  finally  their  axes  become  parallel.  These  processes  advance  from  the  two  sides, 
come  to  the  sides  of  the  incisor  process  beneath  the  nose,  unite  with  the  incisor  process 
on  either  side,  and  their  lower  margin,  with  the  lower  margin  of  the  incisor  process, 
forms  the  upper  lip ;  but,  before  this,  the  two  lateral  halves  of  the  incisor  process  have 
united  in  the  median  line.  At  the  bottom  of  the  cavity  of  the  mouth,  a  small  papilla 
makes  its  appearance,  which  gradually  elongates  and  forms  the  tongue. 

While  this  process  of  development  of  the  anterior  portion  of  the  first  visceral  arch 
is  going  on,  at  its  posterior  portion,  we  have  developing,  the  malleus  and  incus,  the 
former  being  at  first  connected  with  the  cartilage  of  Meckel,  which  extends  along  the 
inner  surface  of  the  inferior  maxilla,  the  cartilages  from  either  side  meeting  at  the  chin. 
The  cleft  between  the  first  and  the  second  visceral  arch  has  closed,  except  at  its  posterior 
portion,  where  an  opening  is  left  for  the  external  auditory  meatus,  the  cavity  of  the 
tympanum,  and  the  Eustachian  tube. 

At  the  same  time,  the  second  visceral  arch  advances  and  forms  the  stapes,  the  styloid 
ligament,  and  the  lesser  cornua  of  the  hyoid  bone.  The  third  arch  advances  in  the  same 
way ;  and  the  arches  from  the  two  sides  meet,  become  united  in  the  median  line,  and 
form  the  body  and  the  greater  cornua  of  the  hyoid.  The  clefts  between  the  second  and 
the  third  and  between  the  third  and  fourth  arches  become  obliterated  by  the  deposition 
of  plastic  matter. 

The  fourth  arch  forms  the  sides  of  the  neck  and  the  larynx,  the  arytenoid  cartilages 
being  developed  first.  In  front  of  the  larynx  and  just  behind  the  tongue,  is  a  little  ele- 
vation, which  is  developed  into  the  epiglottis.  The  openings  of  the  nostrils  appear  during 
the  second  half  of  the  second  month.  A  little  elevation,  the  nose,  appears  between  these 


924 


GENERATION. 


\ 


openings,  and  the  nasal  cavity  begins  to  be  separated  from  the  mouth.  The  lips  are 
distinct  during  the  third  month,  and  the  tongue  first  appears  in  the  course  of  the 
seventh  week. 

The  above  sketch  of  the  mode  of  develop- 
ment of  the  face  enables  us  to  understand  the 

/Si  origin  of  certain  of  the  more  common  malfor- 

mations of  this  part.  When,  by  an  arrest  of 
development,  the  superior  maxilla  on  one  side 
fails  to  unite  with  the  side  of  the  incisor 
process,  we  have  the  very  common  deformity 
known  as  single  hare-lip.  If  this  union  fail  on 
both  sides,  we  have  double  hare-lip,  when  the 
incisor  process  is  usually  more  or  less  project- 
ing. As  a  very  rare  deformity,  it  is  sometimes 
observed  that  the  two  sides  of  the  incisor  pro- 
cess have  failed  to  unite  with  each  other,  leav- 
ing a  fissure  in  the  median  line. 

It  is  somewhat  difficult  to  comprehend  the 
exact  mode  of  development  of  the  face  by  ver- 
bal description  alone;  but  it  will  be  readily 
understood,  after  the  account  we  have  just 
given,  by  studying  Figs.  303,  304,  and  305, 
copied  from  the  great  atlas  of  Coste,  and  plates 
I.  and  II.,  Figs.  A,  B,  C,  and  D,  facing  page 
920. 

The  palatine  arch  is  developed  by  two  pro- 
cesses, which  arise  on  either  side  from  the  in- 
cisor process,  pass  backward  and  upward,  and 
finally  meet  and  unite  in  the  median  line.  The 
union  of  these  forms  the  plane  of  separation 
between  the  mouth  and  the  nares  ;  and  want 
of  fusion  of  these  processes,  from  arrest  of  de- 
velopment, produces  the  malformation  known  as  cleft  palate,  in  which  the  fissure  is 
always  in  the  median  line.  At  the  same  time,  a  vertical  process  forms  in  the  median 
line,  between  the  palatine  arch  and  the  roof  of  the  nasal  cavity,  which  separates  the 
two  nares. 

Development  of  the  Teeth. — Recent  enibryological  researches  have  shown  that  the  old 
idea  of  the  development  of  the  dental  papilla  in  the  bottom  of  a  gutter  formed  at  the 
border  of  either  jaw  is  erroneous.  According  to  the  most  recent  observers,  the  first 
appearance  of  the  organs  for  the  development  of  the  teeth  is  marked  by  the  formation 
of  a  cellular  projection  extending  the  entire  length  of  the  rounded  border  of  each  jaw, 
which  forms  a  rounded  band  above  and  dips  down  somewhat  into  the  subjacent  struct- 
ure. This  band  is  readily  separated  by  maceration,  and  the  removal  of  the  portion  that 
dips  into  the  maxilla  leaves  a  groove,  which  is  thought  to  be  the  explanation  of  the 
description  of  a  groove  by  the  earlier  writers.  This  band  extends  the  entire  length  of 
the  jaws  without  interruption.  Its  superior  surface  is  rounded,  and  that  portion  which 
dips  into  the  subjacent  mucous  structure  is  wedge-shaped,  so  that  its  section  has  the 
form  of  a  V. 

As  soon  as  this  primitive  band  is  formed,  which  occurs  at  the  sixth  or  seventh  week, 
a  flat  band  projects  from  its  internal  surface,  near  the  mucous  structure,  which  is  called 
the  epithelial  band.  This  also  extends  over  the  entire  length  of  the  jaws.  It  is  thin, 
flattened,  with  its  free  edge  curved  inward  and  toward  the  jaw,  and  is  composed,  at 
first,  of  a  central  layer  of  polygonal  cells,  covered  by  a  layer  of  columnar  epithelium. 


FIG.  80S.— Mouth  of  a  human  embryon  of  from 
twenty-five  to  twenty-eight  days ;  magnified  \f> 
diameters.  (Coste.) 

1,  median  or  frontal  process,  the  inferior  portion  of 
which  is  considerably  enlarged ;  2,  right  nostril ; 
3.  left  nostril;  4,  4,  inferior  maxillary  processes, 
already  united  in  the  median  line ;  5,  5,  superior 
maxillary  processes,  which  have  become  quite 
prominent  and  have  descended  to  the  level  of  the 
slope  of  the  frontal  process  ;  6,  mouth ;  7,  first  vis- 
ceral arch;  8,  second  visceral  arch  ;  9,  third  visceral 
arch;  10,  eye;  11,  ear. 


DEVELOPMENT   OF  THE   FACE. 


925 


At  certain  points— these  points  corresponding  to  the  situation  of  the  true  dental 
bulbs— there  appear  rounded  enlargements  at  the  free  margin  of  the  epithelial  band 
just  described.  Each  one  of  these  is  developed  into  one  of  the  structures  of  the  perfect 
tooth.  The  mechanism  of  the  formation  of  this,  which  is  called  the  enamel-organ,  and 
of  the  dental  bulb  is  as  follows : 


FIG.  304. — Mouth,  of  a  human  embryon  of  thirty-five 
days.  (Coste.) 

1,  frontal  process  widely  sloped  at  its  inferior  portion  ; 
2,  2,  incisor  processes  produced  by  this  sloping;  8,  8, 
nostrils;  4,  lower  lip  and  maxilla,  formed  by  the 
union  of  the  inferior  maxillary  processes;  5,  5, 'supe- 
rior maxillary  processes  contiguous  to  the  incisor 
process;  6,  niouth,  still  confounded  with  the  nasal 
fossae ;  7,  first  appearance  of  the  closure  of  the  nasal 
fossae ;  8,  8,  first  appearance  of  the  two  halves  of 
the  palatine  arch;  9,  tongue ;  10,  10,  eyes;  11,12, 
13,  visceral  arches. 


FIG.  305.— Mouth  of  an  embryon  of  forty  days.  (Coste.) 
1,  first  appearance  of  the  nose;  2.  2,  first  appearance  of 
the  alaa  of  the  nose ;  8,  appearance  of  the  closure  be- 
neath the  nose ;  4,  middle,  or  median  portion  of  the  up- 
per lip,  formed  by  the  approach  and  union  of  the  two 
incisor  processes,  a  little  notch  in  the  median  line  still 
indicating  the  primitive  separation  of  the  two  processes ; 
5,  5,  superior  maxillary  processes,  forming  the  lateral 
portions  of  the  upper  lip ;  6,  6,  groove  for  the  develop- 
ment of  the  lachrymal  sac  and  the  nasal  canal ;  7,  lower 
lip;  8,  mouth;  9,  9,  the  two  lateral  halves  of  the  pala- 
tine arch,  already  nearly  approximated  to  each  other 
in  front,  but  still  widely  separated  behind. 


A  rounded  enlargement  appears  at  the  margin  of  the  epithelial  band.  This  soon  be- 
comes directed  downward  (adapting  our  description  to  the  lower  jaw)  and  dips  into  the 
mucous  structure,  being  at  first  connected  with  the  epithelial  band  by  a  narrow  pedicle, 
which  soon  disappears,  leaving  the  enlargement  enclosed  completely  in  a  follicle.  This 
is  the  dental  follicle,  and  it  has  no  connection  with  the  wedge-shaped  band  which  we  de- 
scribed first.  While  this  process  is  going  on,  a  conical  bulb  appears  at  the  bottom  of  the 
follicle.  The  enamel-organ,  formed  from  the  epithelial  band,  becomes  excavated  or;«up- 
shaped  at  its  under  surface  and  fits  over  the  dental  bulb,  becoming  united  to  it. 

The  tooth,  at  this  time,  consists  of  the  dental  bulb,  with  the  enamel-organ  closely 
fitted  to  its  projecting  surface.  The  enamel-organ  is  developed  into  the  enamel ;  the 
dental  bulb,  which  is  provided  with  vessels  and  nerves,  becomes  the  tooth-pulp ;  and, 
upon  the  surface  of  the  dental  bulb,  the  dentine,  or  ivory,  is  developed  in  successive 
layers.  The  cement  is  developed  by  successive  layers  upon  that  portion  of  the  dentine 
which  forms  the  root  of  the  tooth.  As  these  processes  go  on,  the  tooth  projects  more 
and  more,  the  upper  part  of  the  wall  of  the  follicle  gives  way,  and  the  tooth  finally 
appears  at  the  surface. 

1  The  periods  of  development  indicated  for  these  diagrams  are  somewhat  earlier  than  those  which  we  have 
noted  in  the  text ;  but  it  is  impossible  to  fix  these  with  absolute  accuracy,  and  all  the  estimates  given  by  authors  are 
understood  to  be  merely  approximative. 


926 


GENERATION. 


The  permanent  teeth  are  developed  beneath  the  follicles  of  the  temporary,  or  milk- 
teeth.  The  first  appearance  is  a  prolongation  or  diverticulum  from  the  enamel-organ  of 
the  temporary  tooth,  which  dips  more  deeply  into  the  mucous  structure.  This  becomes 
the  enamel-organ  of  the  permanent  tooth ;  and  the  successive  stages  of  development  of 
the  dental  follicles  and  the  dental  pulp  progress  in  the  same  way  as  in  the  temporary 
teeth.  As  the  permanent  teeth  increase  in  size,  they  gradually  encroach  upon  the  roots 
of  the  temporary  teeth.  The  roots  of  the  latter  are  absorbed,  the  permanent  teeth  ad- 


FIG.  306. —  Temporary  and  permanent  teeth.    (Sappey.) 

1, 1,  temporary  central  incisors  ;  2,  2,  temporary  lateral  incisors  ;  8,  3,  temporary  canines  :  4,  4,  temporary  anterior 
molars;  5,  5,  temporary  posterior  molars;  6,6.  permanent  central  incisors;  7,7,  permanent  lateral  incisors; 
8,  8.  permanent  canines  ;  9,  9,  permanent  first  bicuspids  ;  10,  10,  permanent  second  bicuspids;  11,  II,  first  molars. 


vance  more  and  more  toward  the  surface,  and  the  crown  of  each  temporary  tooth  is 
finally  pushed  out.  The  number  of  the  temporary  teeth  is  twenty,  while  there  are 
thirty-two  permanent  teeth.  Thus  there  are  three  permanent  teeth  on  either  side  of 
both  jaws,  which  are  developed  de  novo  and  are  not  preceded  by  temporary  structures. 

The  first  dental  follicles  usually  appear  in  regular  succession.  The  follicles  for  the 
internal  incisors  of  the  lower  jaw  appear  first,  this  occurring  at  about  the  ninth  week. 
All  of  the  follicles  for  the  temporary  teeth  are  completely  formed  at  about  the  eleventh 
or  the  twelfth  week. 

The  temporary  teeth  appear  successively,  the  corresponding  teeth  appearing  a  little 
earlier  in  the  lower  jaw.  The  usual  order,  subject  to  certain  exceptional  variations, 
according  to  Sappey,  is  as  follows  : 

The  four  central  incisors  appear  from  six  to  eight  months  after  birth. 

The  four  lateral  incisors  appear  from  seven  to  twelve  months  after  birth. 

The  four  anterior  molars  appear  from  twelve  to  eighteen  months  after  birth. 

The  four  canines  appear  from  sixteen  to  twenty-four  months  after  birth. 

The  four  posterior  molars  appear  from  twenty-four  to  thirty-six  months  after  birth. 


DEVELOPMENT   OF  THE   GENITO-URINARY   SYSTEM.  927 

The  order  of  eruption  of  the  permanent  teeth  is  as  follows  : 

The  two  central  incisors  of  the  lower  jaw  appear  from  the  sixth  to  the  eighth  year. 

The  two  central  incisors  of  the  upper  jaw  appear  from  the  seventh  to  the  eighth  year. 

The  four  lateral  incisors  appear  from  the  eighth  to  the  ninth  year. 

The  four  first  bicuspids  appear  from  the  ninth  to  the  tenth  year. 

The  four  canines  appear  from  the  tenth  to  the  eleventh  year. 

The  four  second  bicuspids  appear  from  the  twelfth  to  the  thirteenth  year. 

The  above  are  the  permanent  teeth  which  replace  the  temporary  teeth,  The  per- 
manent teeth  which  are  developed  de  novo  appear  as  follows  : 

The  first  molars  appear  from  the  sixth  to  the  seventh  year. 

The  second  molars  appear  from  the  twelfth  to  the  thirteenth  year. 

The  third  molars  appear  from  the  seventeenth  to  the  twenty-first  year. 

Development  of  the  Genito  -  Urinary  System. 

The  genital  and  the  urinary  organs  are  developed  together  and  are  both  preceded  by 
the  appearance  of  two  large,  symmetrical  structures,  known  as  the  Wolffian  bodies,  or 
the  bodies  of  Oken.  These  are  sometimes  called  the  false  or  the  primordial  kidneys. 
They  appear  at  about  the  thirtieth  day,  develop  very  rapidly  on  either  side  of  the  spinal 
column,  and  are  so  large  as  to  almost  fill  the  cavity  of  the  abdomen.  Fig.  307,  rep- 
resenting a  specimen  in  the  possession  of  Prof.  Dalton,  shows  how  large  these  bodies 
are  in  the  early  life  of  the  embryon,  at  which  time  their  function  is  undoubtedly  very 
important. 

Very  soon  after  the  Wolffian  bodies  have  made  their  appearance,  we  can  distinguish, 
at  their  inner  borders,  two  ovoid  bodies,  which  are  finally  developed  into  the  testicles, 
for  the  male,  or  the  ovaries,  for  the  female.  At  their  external  borders,  are  two  ducts, 
on  either  side,  one  of  which,  the  internal,  is  called  the  duct  of  the  Wolffian  body.  This- 
finally  disappears,  in  the  female,  but  it  is  developed  into  the  vas 
deferens,  in  the  male.  The  other  duct,  which  is  external  to 
the  duct  of  the  Wolffian  body,  disappears,  in  the  male,  but  it 
becomes  the  Fallopian  tube,  in  the  female.  This  is  known  as 
the  duct  of  Muller.  Behind  the  Wolffian  bodies,  are  devel- 
oped the  kidneys  and  the  suprarenal  capsules. 

As  the  development  of  the  Wolffian  bodies  attains  its  maxi- 
mum, their  structure  becomes  somewhat  complex.  From  their 
proper  ducts,  which  are  applied  directly  to  their  outer  bor- 
ders, tubes  make  their  appearance  at  right  angles  to  the 
ducts,  which  extend  into  the  substance  of  the  bodies  and  be-  FIG.  sot.—  Fatal  pig,  %  of  an 
come  somewhat  convoluted  at  their  extremities.  These  tubes  ?n  the  possession™  f^roTSa" 
communicate  directly  with  the  ducts,  and  the  ducts  them-  *  .  2  anterior  extremity  . 


selves  open  into  the  lower  part  of  the  intestinal  canal,  oppo-     '  3,   posterior   extremity; 
site  to  the  point  of  its  communication  with  the  allantois.   The        inai  wails  have'  been  cut  away" 
tubes  of  the  Wolffian  bodies  are  simple,  terminating  in  single,        SthfwoVtnbo^s1'08^011 
somewhat  dilated,  blind  extremities,  are  lined  with  epithe- 

lium, and  are  penetrated,  at  their  extremities,  by  blood-vessels,  which  form  coils  or  con- 
volutions in  their  interior.  These  are  undoubtedly  organs  of  depuration  for  the  embryon 
and  take  on  the  function  to  be  subsequently  assumed  by  the  kidneys  ;  but,  in  the  female, 
they  are  temporary  structures,  disappearing  as  development  advances,  and  having  noth- 
ing to  do  with  the  development  of  the  true  urinary  organs. 

The  testicles  or  ovaries  are  developed  at  the  internal  and  anterior  surface  of  the  Wolf- 
fian bodies,  first  appearing  in  the  form  of  small,  ovoid  masses.  Beginning  just  above 
and  passing  along  the  external  borders  of  the  Wolffian  bodies,  are  the  tubes  called  the 
ducts  of  Muller.  These  at  first  open  into  the  intestine,  near  the  point  of  entrance  of  the 


928  GENERATION. 

Wolffian  ducts.  In  the  female,  their  upper  extremities  remain  free,  except  the  single 
fimbria  which  is  connected  with  the  ovary.  Their  inferior  extremities  unite  with  each 
other,  and,  at  their  point  of  union,  they  form  the  uterus.  When  this  union  is  incomplete, 
we  have  the  malformation  known  as  double  uterus,  which  may  be  associated  with  a 
double  vagina.  The  Wolffian  bodies  and  their  ducts  disappear,  in  the  female,  at  about 
the  fiftieth  day.  A  portion  of  their  structure,  however,  persists,  in  the  form  of  a  col- 
lection of  closed  tubes,  constituting  the  parovarium,  or  organ  of  Rosenmtiller. 

In  the  female,  the  ovaries  pass  down  no  farther  than  the  pelvic  cavity  ;  but  the  testi- 
cles, which  are  at  first  in  the  abdomen  of  the  male,  finally  descend  into  the  scrotum. 
As  the  testicles  descend,  they  carry  with  them  the  Wolffian  duct,  that  portion  of  the 
Wolffian  body  which  is  permanent  constituting  the  head  of  the  epididymis.  At  the 
same  time,  a  cord  appears,  attached  to  the  lower  extremity  of  the  testicle  and  extending 
to  the  symphysis  pubis.  This  is  called  the  gubernaculum  testis.  It  is  at  first  muscular, 
but  the  muscular  fibres  disappear  during  the  later  periods  of  utero-gestation.  It  is  not 
known  that  its  muscular  structure  takes  any  part,  by  contractile  action,  in  the  descent 
of  the  testicle  in  the  human  subject.  The  epididymis  and  the  vas  deferens  are  formed 
from  the  Wolffian  body  and  the  Wolffian  duct. 

At  about  the  end  of  the  seventh  month,  the  testicle  has  reached  the  internal  abdom- 
inal ring ;  and,  at  this  time,  a  double  tubular  process  of  peritoneum,  covered  with  a  few 
fibres  from  the  lower  portion  of  the  internal  oblique  muscle  of  the  abdomen,  gradually 
extends  into  the  scrotum.  The  testicle  descends,  following  this  process  of  peritoneum, 
which  latter  becomes  eventually  the  visceral  and  parietal  portion  of  the  tunica  vaginalis. 
The  canal  of  communication  between  the  abdominal  cavity  and  the  cavity  of  the  scrotum 
is  finally  closed,  and  the  tunica  vaginalis  is  separated  from  the  peritoneum.  The  fibres 
derived  from  the  internal  oblique  constitute  the  cremaster  muscle. 

At  the  eighth  or  the  ninth  month,  the  testicles  have  reached  the  external  abdominal 
ring  and  then  soon  descend  into  the  scrotum.  The  vas  deferens,  as  we  have  seen,  passes 
from  the  testicle,  along  the  base  of  the  bladder,  to  open  into  the  prostatic  portion  of 
the  urethra;  and,  as  development  advances,  two  sacculated  diverticula  from  these  tubes 
make  their  appearance,  which  are  attached  to  the  bladder  and  constitute  the  vesicular 
seminal  es. 

As  the  ovaries  descend  to  their  permanent  situation  in  the  pelvic  cavity,  there  appears, 
attached  to  the  inner  extremity  of  each,  a  rounded  cord,  analogous  to  the  gubernaculum 
testis.  A  portion  of  this,  connecting  the  ovary  with  the  uterus,  constitutes  the  ligament 
of  the  ovary ;  and  the  inferior  portion  forms  the  round  ligament  of  the  uterus,  which 
passes  through  the  inguinal  canal  and  is  attached  to  the  symphysis  pubis. 

The  development  of  the  external  organs  of  generation  will  be  studied  after  we  have 
described  the  development  of  the  urinary  apparatus. 

Development  of  the  Urinary  Apparatus. — Behind  the  Wolffian  bodies,  and  developed 
entirely  independently  of  them,  the  kidneys,  suprarenal  capsules,  and  ureters  make  their 
appearance.  The  kidneys  are  developed  in  the  form  of  little,  rounded  bodies,  composed 
of  short,  blind  tubes,  all  converging  toward  a  single  point,  which  is  the  hilum.  These  tubes 
increase  in  length,  branch,  become  convoluted  in  a  certain  portion  of  their  extent,  and 
finally  assume  the  structure  and  arrangement  of  the  renal  tubules,  with  their  Malpighian 
bodies,  blood-vessels,  etc.  They  all  open  into  the  hilum.  At  the  same  time  that  the  kid- 
neys are  undergoing  development,  the  suprarenal  capsules  are  formed  at  their  superior 
extremities.  These  bodies,  the  function  of  which  is  unknown,  are  relatively  so  much 
larger  in  the  foetus  than  in  the  adult,  that  they  have  been  supposed  to  be  peculiarly 
important  in  intra-uterine  life,  though  nothing  definite  is  known  upon  this  point.  The 
kidneys  are  relatively  very  large  in  the  foetus.  Their  proportion  to  the  weight  of  the 
body,  iii  the  fcetus,  is  1  to  80,  and,  in  the  adult,  1  to  240.  The  ureters  are  undoubtedly 
developed  as  tubular  processes  from  the  kidneys,  which  finally  extend  to  open  into  the 


DEVELOPMENT  OF  THE   GENITO-UKINARY  SYSTEM. 


929 


bladder.     This  fact  is  shown  "by  certain  cases  of  malformation,  in  which  the  ureters  have 
not  reached  the  bladder,  but  terminate  in  blind  extremities.     The  development  of  the 


FIG.  W&.— Diagrammatic  representation  of  t/te  genito-urinary  system.    (Henle.) 

A,  embryonic  condition,  in  which  there  is  no  distinction  of  sex  ;  B,  female  form;  C,  male  form.  The  dotted  lines  in 
B  and  C  represent  the  situations  which  the  male  and  female  genital  organs  assume  after  the  descent  of  the  ovaries 
and  testicles.  Tho  small  letters  in  B  and  C  correspond  to  the  capital  letters  in  A. 

Fig.  308  A.— A,  kidney;  B,  ureter;  C,  bladder;  D,  urachus,  developed  into  the  median  ligament  of  the  bladder;  E, 
constriction  which  becomes  the  urethra  ;  F',  Wolffian  body;  G,  Wolffian  duct,  with  its  opening  below,  G';  II, 
duct  of  Miiller,  united  below,  from  the  two  sides,  into  a  single  tube,  J,  which  presents  a  single  opening,  J', 
between  the  openings  of  the  Wolffian  ducts ;  I£,  ovary  or  testicle ;  L,  gubernaculum  testis  or  round  ligament  of 
the  uterus :  M,  genito-urinary  sinus ;  N,  O,  external  genitalia. 

Fig.  808,  B  (female). — a,  kidney;  b,  ureter;  c.  bladder;  d,  urachus;  e,  urethra;  f,  remains  of  the  Wolffian  body  (paro- 
varium)  ;  g,  remnant  of  the  Wolffian  duct;  h,  Fallopian  tube  ;  i,  uterus  ;  i',  vagina  ;  k,  ovary;  1,  round  ligament 
of  the  uterus;  m,  extremity  of  the  urethra;  n,  clitoris;  n'  corpus  cavernosum  of  the  clitoris;  n",  bulb  of  the 
vestibule  ;  o.  external  genital  opening ;  p,  excretory  duct  of  the  gland  of  Bartholinus. 

Fig.  308.  C  (male). — a,  kidney ;  b,  ureter ;  c,  bladder  ;  d,  urachus ;  e,  m.  urethra ;  f,  epididymis ;  g,  vas  deferens ;  g', 
seminal  vesicle;  g",  ejaculatory  duct;  h,  i,  remains  of  the  duct  of  Miiller ;  k,  testicle;  1,  gubernaculum  testis ;  n, 
n',  n".  urethra  and  penis;  o,  scrotum;  p,  gland  of  Cowper;  q,  prostate. 

59 


930  GENERATION. 

genitourinary  system  can  be  readily  understood,  after  the  description  we  have  just- 
given,  by  a  study  of  Fig.  308. 

External  Organs  of  Generation. — The  external  organs  of  generation  begin  to  be 
developed  at  about  the  fifth  week.  At  the  inferior  extremity  of  the  body  of  the  embryon, 
a  small,  ovoid  eminence  appears  in  the  median  line,  at  the  lower  portion  of  which  there 
is  a  longitudinal  slit,  which  forms  the  common  opening  of  the  anus  and  the  genital  and 
urinary  passages.  This  is  the  cloaca.  There  is  soon  developed,  internally,  a  septum, 
which  separates  the  rectum  from  the  vagina,  the  urethra  of  the  female  opening  above. 
In  the  male,  this  septum  is  developed  between  the  rectum  and  the  urethra,  the  gener- 
ative and  the  urinary  passages  opening  together.  From  this  median  prominence,  two 
lateral,  rounded  bodies  make  their  appearance.  These  are  developed,  with  the  median 
elevation,  into  the  glans  penis  and  corpora  cavernosa  of  the  male,  or  into  the  clitoris  and 
the  labia  minora  of  the  female.  In  the  male,  these  two  lateral  prominences  unite  in  the 
median  line  and  enclose  the  spongy  portion  of  the  urethra.  When  there  is  a  want  of 
union  in  the  cavernous  bodies  in  the  male,  we  have  the  malformation  known  as  hypospa- 
dias.  In  the  female,  there  is  no  union  in  the  median  line,  and  an  opening  remains 
between  the  two  labia  minora.  The  scrotum  in  the  male  is  analogous  to  the  labia 
majora  of  the  female;  the  distinction  being  that  the  two  sides  of  the  scrotum  unite 
in  the  median  line,  while  the  labia  majora  remain  permanently  separated.  This  anal- 
ogy is  farther  illustrated  by  the  anatomy  of  inguinal  hernia,  in  which  the  intestine 
descends  into  the  labia,  in  the  female,  and  into  the  scrotum,  in  the  male.  It  sometimes 
occurs,  also,  that  the  ovaries  descend,  very  much  as  the  testicles  pass  down  in  the  male, 
and  pass  through  the  external  abdominal  ring. 

From  the  above  description,  it  is  easy  to  imagine  how  malformation  and  malposition 
of  the  genital  organs  may  occur,  so  that  it  is  difficult  to  determine  the  sex  of  the  indi- 
vidual. We  may  have,  in  a  male,  absence  of  beard  and  a  certain  degree  of  development 
of  the  mammary  glands,  with  a  pelvic  conformation  approximating,  more  or  less,  that  of 
the  female  ;  and,  on  the  other  hand,  a  female  may  have  a  beard,  slight  mammary  devel- 
opment, and  a  general  conformation  of  the  body  resembling  that  of  a  male.  This  may 
be  associated  with  corresponding  malformations  of  the  genital  organs.  We  may,  for 
example,  have  a  large  development  of  the  clitoris,  descent  of  the  ovaries,  more  or  less 
complete  occlusion  of  the  vagina,  and  union  of  the  labia  majora,  so  that  it  is  difficult  to 
determine  the  sex  from  an  external  examination ;  and  opposite  vices  of  formation  may 
occur  in  the  male,  the  testicles  remaining  in  the  pelvic  cavity.  It  is  not  surprising, 
therefore,  that  beings  have  existed  of  undetermined  sex,  and  many  cases  of  this  kind  are 
on  record.  Two  cases  have  been  reported  in  which,  apparently,  the  two  sexes  were 
combined.  The  first  case  was  presented  to  the  Medical  Society  of  Vienna,  by  Koki- 
tansky,  in  1869.  This  case  presented,  on  post-mortem  examination,  two  ovaries  with 
their  Fallopian  tubes,  a  rudimentary  uterus,  a  testicle,  and  a  vas  deferens  containing 
spermatozoids.  This  individual  menstruated,  had  an  imperfect  penis,  and  a  bifid  scro- 
tum. The  sexual  indifference  was  absolute.  The  second  case  was  published  by  Hepp- 
ner,  in  1872.  This  was  a  child,  six  weeks  old,  which  had  been  preserved  in  alcohol  for 
several  years.  It  presented  ovaries,  Fallopian  tubes,  a  uterus,  and  a  vagina  opening  into 
the  urethra.  There  were  also  two  bodies  which  were  shown,  upon  microscopical  examina- 
tion, to  be  testicles,  a  penis  with  hypospadia,  and  a  prostate ;  but  there  were  neither 
vesiculee  seminales  nor  vasa  deferentia. 

Development  of  the   Circulatory  System. 

The  blood  and  the  blood-vessels  are  developed  very  early  in  the  life  of  the  ovum  and 
make  their  appearance  nearly  as  soon  as  the  primitive  trace.  The  mode  of  development 
of  the  first  vessels  differs  from  that  of  vessels  formed  later,  as  they  appear  de  *iovo  in  the 
blastodermic  layers,  while  afterward,  vessels  are  formed  as  prolongations  of  preexisting 


DEVELOPMENT  OF  THE  CIRCULATORY  SYSTEM.  931 

tubes.  Soon  after  the  external  and  the  internal  blastodermic  membranes  have  become 
separated  from  each  other,  and  the  intermediate  membrane  has  been  formed  at  the 
thickened  portion  of  the  ovum  which  is  destined  to  be  developed  into  the  embryon,  cer- 
tain of  the  blastodermic  cells  undergo  a  transformation  into  blood-corpuscles.  These  are 
larger  than  the  blood-corpuscles  of  the  adult  and  are  generally  nucleated.  At  about  the 
same  time  (it  may  be  before  or  after  the  appearance  of  the  corpuscles,  for  this  point  is 
undetermined)  certain  of  the  blastodermic  cells  fuse  with  each  other  and  arrange  them- 
selves so  as  to  form  vessels.  Leucocytes  are  probably  developed  in  the  same  way  as  the 
red  corpuscles.  The  vessels  thus  formed  constitute  the  area  vasculosa,  which  is  the 
beginning  of  what  is  known  as  the  first  circulation. 

It  is  evident  that  the  relations  of  the  embryon  at  different  stages  of  development  must 
require  certain  variations  in  the  arrangement  of  the  circulatory  system.  The  ovum  nas, 
of  course,  no  vascular  connection  with  the  mother  before  the  formation  of  the  allantois, 
It  has  undergone,  however,  a  certain  degree  of  development,  and  presents  a  circulator^ 
system,  which  extends  over  the  umbilical  vesicie.  This  stage  of  development  of  the  vas- 
cular system  constitutes  what  is  known  as  the  first  circulation.  As  the  allantois  is  devel- 
oped, the  circulation  over  tne  umbilical  vesicle  becomes  unimportant,  and  its  vessels  disap- 
pear. Vessels  then  extend  into  the  allantois,  are  finally  developed  into  the  foetal  portion 
of  the  placenta,  and  what  is  known  as  the  second  circulation  is  established.  This  circu- 
lation continues  throughout  intra-uterine  life,  and,  as  we  know,  the  embryon  and  foetus 
depend  entirely  upon  the  placenta  for  materials  for  respiration,  nutrition,  and  growth. 
At  birth,  the  requirements  are  again  changed.  The  placental  circulation  is  then  abol- 
ished, and  the  arrangement  of  vessels  peculiar  to  it  disappears.  Now,  for  the  first 
time,  the  pulmonary  circulation  becomes  important.  All  the  blood  passes  through  the 
lungs  before  it  is  sent  to  the  general  system,  the  two  sides  of  the  heart  become  com- 
pletely separated  from  each  other,  and  the  third,  the  pulmonary,  or  adult  circulation,  is 
established. 

The  First,  or  Vitelline  Circulation. — In  the  development  of  oviparous  animals,  the 
first,  or  vitelline  circulation  is  very  important ;  for,  by  these  vessels,  the  contents  of  the 
nutritive  yolk  are  taken  up  and  carried  to  the  embryon,  constituting  the  only  source  of 
material  for  its  nutrition  and  growth.  In  mammals,  however,  nutritive  matter  is  ab- 
sorbed almost  exclusively  from  the  mother,  by  simple  endosmosis,  before  the  placental 
circulation  is  established,  and  by  the  placental  vessels,  at  a  later  period.  The  vitelline 
circulation  is  therefore  not  important,  and  the  vessels  disappear  with  the  atrophy  of  the 
umbilical  vesicle. 

The  area  vasculosa,  in  mammals,  consists  of  vessels  coming  from  the  body  of  the 
embryon,  forming  a  nearly  circular  plexus  in  the  substance  of  the  vitellus,  around  the 
embryon.  The  vessels  of  this  plexus  open  into  a  sinus  at  the  border  of  the  area,  called 
the  sinus  terminalis.  It  is  probable  that  these  vessels  are  developed  de  novo  in  the  inter- 
mediate blastodermic  layer  and  are  not  preceded  by  a  distinct  membrane ;  but  such  a 
membrane  has  been  described  under  the  name  of  the  vascular  blastodermic  layer. 

If  we  examine  the  ovum  when  the  area  vasculosa  is  first  formed,  we  see  the  embryon 
lying  in  the  direction  of  the  diameter  of  the  nearly  circular  plexus  of  blood-vessels.  The 
plexus  surrounds  the  embryon,  except  at  the  cephalic  extremity,  where  the  terminal 
sinuses  of  the  two  sides  curve  downward  toward  the  head,  to  empty  into  the  omphalo- 
mesenteric  veins.  As  the  umbilical  vesicle  is  separated  from  the  body  of  the  embryon, 
it  carries  the  plexus  of  vessels  of  the  area  vasculosa  with  it,  the  vessels  of  communication 
with  the  embryon  being  the  omphalo-mesenteric  arteries  and  veins.  As  these  processes 
are  going  on,  the  great  central  vessel  of  the  embryon  becomes  enlarged  and  twisted  upon 
itself,  at  a  point  just  below  the  cephalic  enlargement  of  the  embryon,  between  the  inferior 
extremity  of  the  pharynx  and  the  superior  cul-de-sac  of  the  intestinal  canal.  The  exca- 
vation which  receives  this  vessel  is  called  the  fovea  cardiaca.  The  different  stages  of 


932  GENERATION.   . 

development  of  the  heart,  which  is  formed  of  the  twisted  portion  of  the  central  vessel, 
will  be  described  farther  on.  Simple,  undulatory  movements  take  place  in  the  heart  of 
the  chick  at  about  the  middle  of  the  second  day ;  but  there  is  not,  at  that  time,  any 
regular  circulation.  At  the  end  of  the  second  day  or  the  beginning  of  the  third,  the  cur- 
rents of  the  circulation  are  established.  The  time  of  the  first  appearance  of  the  circula- 
tion in  the  human  embryon  has  not  been  accurately  determined. 


FIG.  309.— Area  vasculosa.    (Bischoff.) 
«,  cr,  &,  sinus  terminalis;  c,  omphalo-mesenteric  vein;  c7,  heart;  e,f,f,  posterior  vertebral  arteries. 

In  the  arrangement  of  the  vessels  for  the  first  circulation  of  the  embryon,  the  heart  is 
situated  exactly  in  the  median  line  and  gives  off  two  arches  which  curve  to  either  side 
and  unite  into  a  single  central  trunk  at  the  spinal  column  below.  These  are  the  two  aorta3, 
and  the  single  trunk  formed  by  their  union  becomes  the  abdominal  aorta.  The  two  aortic 
arches,  one  of  which  only  is  permanent,  are  sometimes  called  the  inferior  vertebral  arteries. 
These  vessels  give  off  numerous  branches,  which  pass  into  the  area  vasculosa.  Two  of 
these  branches,  however,  are  larger  than  the  others,  pass  to  the  umbilical  vesicle,  and  are 
called  the  omphalo-mesenteric  arteries.  In  the  embryon  of  mammals,  there  are,  at  first, 
four  omphalo-mesenteric  veins,  two  superior,  which  are  the  larger,  and  two  inferior ; 
but,  as  development  advances,  the  two  inferior  veins  are  closed,  and  we  then  have  two 
omphalo-mesenteric  arteries  and  two  omphalo-mesenteric  veins.  At  about  the  fortieth 
day,  one  artery  and  one  vein  disappear,  and  we  have  then  but  one  omphalo-mesenteric 
artery  and  one  vein.  Soon  after,  as  the  circulation  becomes  established  in  the  allantois, 
the  vessels  of  the  umbilical  vesicle  and  the  omphalo-mesenteric  vessels  are  obliterated, 
and  the  first  circulation  is  superseded  by  the  second. 

As  the  septum  between  the  two  ventricles  makes  its  appearance,  that  division  of  the 
right  aortic  arch  which  constitutes  the  vascular  portion  of  one  of  the  branchial  arches  dis- 
appears and  loses  its  connection  with  the  abdominal  aorta;  a  branch,  however,  persists 
during  the  whole  of  intra-uterine  life  and  constitutes  the  ductus  arteriosus,  and  another 
branch  is  permanent,  forming  the  pulmonary  artery. 


DEVELOPMENT   OF  THE   CIRCULATORY   SYSTEM. 


The  Second,  or  Placental  Circulation. — As  the  omphalo-mesenteric  vessels  disappear, 
and  as  the  allantois  is  developed  to  form  the  chorion,  two  vessels  (the  hypogastric  arte- 
ries) are  given  off,  first  from  the  abdominal  aorta;  but  afterward,  as  the  vessels  going  to 
the  lower  extremities  are  developed,  the  branching  of  the  abdominal  aorta  is  such  that 
the  vessels  become  connected  with  the  internal  iliac  arteries.  The  hypogastric  arteries 
pass  to  the  chorion  through  the  umbilical  cord  and  constitute  the  two  umbilical  arteries. 
At  first,  there  are  two  umbilical  veins;  but  one  of  them  afterward  disappears,  and  there 
is  finally  but  one  vein  in  the  umbilical  cord.  It  is  in  this  way — the  umbilical  arteries  car- 
rying the  blood  to  the  tufts  of  the  foetal  placenta,  which  is  returned  by  the  umbilical 
vein — that  the  placental  circulation  is  established. 

Corresponding  to  the  four  visceral  arches,  which  we  have  described  in  connection  with 
the  development  of  the  face,  are  four  vascular  arches.  One  of  these  disappears,  and  the 
remaining  three  undergo  certain  changes,  by  which  they  are  converted  into  the  vessels 
going  to  the  head  and  the  superior  extremities.  The  anterior  arches  on  the  two  sides 
are  converted  into  the  carotids  and  subclavians ;  the  second,  on  the  left  side,  is  converted 
into  the  permanent  aorta,  and  the  right  is  obliterated ;  the  third,  on  either  side,  is  con- 
verted into  the  right  and  left  pulmonary  arteries.  In  the  early  stages  of  the  develop- 
ment of  the  vascular  system  of  mammals,  the  conditions  have  been,  compared  to  the  per- 
manent arrangement  of  the  circulatory  system  in  fishes.  The  heart  of  fishes  remains 
single ;  and  the  heart  of  mammals  is  at  first  single,  but  afterward  it  becomes  divided  by  the 
development  of  the  intra-ventricular  septum.  The  branchial  arches  in  fishes  are  perma- 
nent, they  receive  all  the  blood  from  the  aortic  bulb,  and  the  blood 
from  these  arches  then  passes  into  the  dorsal  aorta.  This  is  very 
nearly  the  condition  of  the  vascular  system  when  the  branchial 
arches  first  appear  in  the  embryon  of  mammals. 

The  changes  of  the  branchial  arches  which  we  have  described 
are  illustrated  in  the  diagrammatic  Fig.  310.  In  this  figure,  the 
three  branchial  arches  that  remain  and  participate  in  the  devel- 
opment of  the  upper  portion  of  the  vascular  system  are  1,  2,  3, 
on  either  side.  The  two  anterior  (3,  3)  become  the  carotids  (c,  c) 
and  the  subclavians  («,  *).  The  second  (2,  2)  is  obliterated  on  the 
right  side,  and  becomes  the  arch  of  the  aorta  on  the  left  side. 
The  third  (1,  1),  counting  from  above  downward,  is  converted 
into  the  pulmonary  arteries  of  the  two  sides.  Upon  the  left  side, 
there  is  a  large  anastomosing  vessel  (ca),  between  the  pulmonary 
artery  of  that  side  and  the  arch  of  the  aorta,  which  is  the  ductus 
arteriosus.  The  anastomosing  vessel  (cd)  between  the  right  pul- 
monary artery  and  the  aorta,  is  obliterated. 

The  mode  of  development  of  the  veins  is  very  simple.  Two 
venous  trunks  make  their  appearance  by  the  sides  of  the  spinal 
column,  which  are  called  the  cardinal  veins,  and  run  parallel  with 
the  superior  vertebral  arteries,  or  the  two  aortaB,  emptying  finally 
into  the  auricular  portion  of  the  heart  by  two  canals,  which  are 
called  the  canals  of  Cuvier.  These  veins  change  their  relations 
and  connections  as  the  first  circulation  is  replaced  by  the  second. 
The  omphalo-mesenteric  vein  opens  into  the  heart  between  the 
two  canals  of  Cuvier.  As  development  advances,  the  liver  is 
formed  in  the  course  of  this  vessel,  a  short  distance  below  the 
heart,  and  the  vein  ramifies  in  its  substance ;  so  that  the  blood  of 
the  omphalo-mesenteric  vein  passes  through  the  liver  before  it 
gets  to  the  heart.  We  have  seen  that  the  omphalo-mesenteric  vein  is  obliterated  as  the 
umbilical  vein  makes  its  appearance.  The  blood  from  the  umbilical  vein  is  at  first 
emptied  directly  into  the  heart ;  but  this  vessel  soon  establishes  the  same  relations 


FIG.  310.  —  Transformation 
of  the  system  of  aortic 
arches  into  permanent 
arterial  trunks,  in  the 
mammalia.  (Von  Baer.) 

B,  aortic  bulb :  1,  2,  3,  4,  5,  on 
either  side,  the  five  pairs  of 
aortic  arches ;  5, 5,  the  earli- 
est in  their  appearance ;  1. 1, 
the  most  recent;  c,  c,  the 
two  carotids,  still  united, 
which  are  separated  at  a 
later  period;  s,  *,  the  two 
subclavians,  the  right  aris- 
ing from  the  arteria  innomi- 
nata  ;  a,  a,  the  aorta;  p,p< 
the  pulmonary  arteries ;  cor, 
the  ductus  arteirosus ;  cd, 
the  left  artieral  canal,  which 
is  finally  obliterated. 


934  GENERATION. 

with  the  liver  as  the  omphalo-mesenteric  vein,  and  its  blood  passes  through  the  liver 
before  it  reaches  the  central  organ  of  the  circulation.  As  the  omphalo-mesenteric  vein 
atrophies,  the  mesenteric  vein,  bringing  the  blood  from  the  intestinal  canal,  is  developed, 
and  this  penetrates  the  liver,  becoming,  finally,  the  portal  vein. 

As  the  lower  extremities  are  developed,  the  inferior  vena  cava  makes  its  appearance 
between  the  two  inferior  cardinal  veins.  This  vessel  receives  an  anastomosing  branch 
from  the  umbilical  vein,  before  it  penetrates  the  liver,  and  this  branch  is  the  ductus 
venosus.  As  the  inferior  vena  cava  increases  in  size,  it  communicates  below  with  the 
two  inferior  cardinal  veins ;  and  that  portion  of  the  two  inferior  cardinal  veins  which 
remains  constitutes  the  two  iliac  veins.  The  inferior  cardinal  veins,  between  that  portion 
which  forms  the  iliac  veins  and  the  heart,  finally  become  the  right  and  the  left  azygos 
veins. 

The  right  canal  of  Cuvier,  as  the  upper  extremities  are  developed,  enlarges  and  be- 
comes the  vena  cava  descendens,  receiving,  finally,  all  the  blood  from  the  head  and  the 
superior  extremities.  The  left  canal  of  Cuvier  undergoes  atrophy  and  finally  disappears. 
The  upper  portion  of  the  superior  cardinal  veins  is  developed  into  the  jugulars  and  sub- 
clavians  on  the  two  sides.  As  the  lower  portion  of  the  left  cardinal  vein  and  the  left 
canal  of  Cuvier  atrophy,  a  venous  trunk  appears,  connecting  the  left  subclavian  with  the 
right  canal  of  Cuvier.  This  increases  in  size  and  becomes  the  left  vena  innominata,  which 
connects  the  left  subclavian  and  internal  jugular  with  the  vena  cava  descendens. 

Development  of  the  Heart. — The  central  enlargement  of  the  vascular  system  in  the 
first  circulation,  which  becomes  the  heart,  is  twisted  upon  itself  by  a  single  turn.  The 
portion  connected  with  the  cephalic  extremity  of  the  embryon  gives  origin  to  the 
arterial  system,  and  the  portion  connected  with  the  caudal  extremity  receives  the  tilood 
from  the  venous  system.  The  walls  of  the  arterial  portion  of  the  heart  soon  become 
thickened,  while  the  walls  of  the  venous  portion  remain  comparatively  thin.  There  then 
appears  a  constriction,  which  partly  separates  the  auricular  from  the  ventricular  portion. 
At  a  certain  period  of  development,  the  heart  presents  a  single  auricle  and  a  single  ven- 
tricle. 

The  division  of  the  heart  into  two  ventricles  appears  before  the  two  auricles  are  sepa- 
rated. This  is  effected  by  a  septum,  which  gradually  extends  from  the  apex  of  the  heart 
upward  toward  the  auricular  portion.  At  the  seventh  week,  there  is  a  large  opening  be- 
tween the  two  ventricles.  This  gradually  closes  from  below  upward,  the  heart  becomes 
more  pointed,  and  the  separation  of  the  two  ventricles  is  complete  at  about  the  end  of  the 
second  month. 

At  about  the  end  of  the  second  month,  a  septum  begins  to  be  formed  between  the 
auricles.  This  extends  from  the  base  of  the  heart  toward  the  ventricles,  but  it  leaves  an 
opening  between  the  two  sides  (the  foramen  ovale,  or  the  foramen  of  Botal)  which  per- 
sists during  the  whole  of  foetal  life.  At  the  anterior  edge  of  the  opening  of  the  vena 
cava  ascendens  into  the  right  auricle,  there  is  a  membranous  fold,  which  projects  into 
the  auricle.  This  is  the  valve  of  Eustachius,  and  it  divides  the  right  auricle  incompletely 
into  two  portions. 

During  the  sixth  week,  the  heart  is  vertical  and  situated  in  the  median  line,  with  the 
aorta  arising  from  the  centre  of  its  base.  At  the  end  of  the  second  month,  it  is  raised 
up  by  the  development  of  the  liver,  and  its  point  presents  forward.  During  the  fourth 
month,  it  is  twisted  slightly  upon  its  axis,  and  the  point  presents  to  the  left.  At  this 
time,  the  auricular  portion  is  larger  than  the  ventricles ;  but  the  auricles  diminish  in  their 
relative  capacity  during  the  latter  half  of  intra-uterine  life.  The  pericardium  makes  its 
appearance  during  the  ninth  week. 

Early  in  intra-uterine  life,  the  relative  size  of  the  heart  is  very  great.  At  the  second 
month,  its  weight,  in  proportion  to  the  weight  of  the  body,  is  1  to  50.  This  proportion, 
however,  gradually  diminishes  until,  at  birth,  the  ratio  is  1  to  120.  The  proportionate 


DEVELOPMENT  OF  THE   CIRCULATORY   SYSTEM.  935 

weight  in  the  adult  is  about  1  to  160.  During  about  the  first  half  of  intra-uterine  life, 
the  thickness  of  the  two  ventricles  is  nearly  the  same ;  but,  after  that  time,  the  relative 
thickness  of  the  left  ventricle  gradually  increases. 

Peculiarities  of  the  Festal  Circulation. — In  studying  the  complete  course  of  the  blood 
in  the  foetus,  which  constitutes  the  second,  or  the  placental  circulation,  we  note  peculiari- 
ties in  two  portions  of  the  circulatory  system.  In  the  one,  a  peculiar  arrangement  is 
necessitated  by  the  passage  of  blood  to  and  from  the  placenta ;  and  in  the  other,  the  char- 
acter of  the  blood  coming  from  the  placenta  necessitates  a  peculiar  arrangement  of  the 
heart  and  the  great  vessels. 

The  branches  from  the  internal  iliac  arteries,  which  pass  to  the  foetal  tufts  of  the  pla- 
centa, do  not  exist  in  the  adult.  The  ductus  venosus,  which  conveys  a  portion  of  the 
blood  of  the  umbilical  vein  to  the  vena  cava  ascendens,  and  the  umbilical  vein  itself  do 
not  exist  in  the  adult. 

The  Eustachian  valve,  situated  at  the  inner  margin  of  the  vena  cava  ascendens  as  it 
opens  into  the  right  auricle,  does  not  exist  in  the  adult.  The  foramen  ovale,  or  the  open- 
ing between  the  right  and  the  left  auricle,  through  which  the  blood  from  the  vena  cava 
ascendens  is  directed  into  the  left  auricle,  does  not  exist  in  the  adult.  The  ductus  arte- 
riosus,  which  conveys  the  blood  from  the  left  pulmonary  artery  to  the  arch  of  the  aorta, 
does  not  exist  in  the  adult.  In  the  adult,  the  pulmonary  arteries  receive  all  the  blood 
from  the  right  ventricle.  In  the  foetus,  the  pulmonary  arteries  receive  a  small  quantity 
of  blood,  as  compared  with  that  which  passes  to  the  aorta  through  the  ductus  arteriosus. 
Keeping  in  view  these  peculiarities  of  the  circulatory  apparatus,  the  entire  course  of  the 
blood,  during  foetal  life,  is  as  follows  : 

Beginning  with  the  abdominal  aorta,  we  follow  the  course  of  blood  into  the  two 
primitive  iliacs,  and  thence  into  the  internal  iliacs.  From  the  two  internal  iliacs,  the  two 
hypogastric  arteries  arise,  which  ascend  along  the  sides  of  the  bladder  to  its  fundus,  thence 
pass  to  the  umbilicus  and  go  to  the  placenta,  forming  the  two  umbilical  arteries.  In  this 
way,  the  blood  of  the  foetus  goes  to  the  placenta. 

The  umbilical  vein  enters  the  body  of  the  foetus  at  the  umbilicus ;  it  passes  along  the 
margin  of  the  suspensory  ligament  to  the  under  surface  of  the  liver ;  it  gives  off  one 
branch  of  large  size,  and  one  or  two  smaller  branches  to  the  left  lobe ;  it  sends  a  branch 
each  to  the  lobus  quadratus  and  the  lobus  Spigelii ;  and  the  vessel  reaches  the  transverse 
fissure.  At  the  transverse  fissure,  it  divides  into  two  branches,  the  larger  of  which  joins 
the  portal  vein  and  enters  the  liver;  and  the  smaller,  which  is  the  ductus  venosus, 
passes  to  the  vena  cava  ascendens,  at  the  point  where  it  receives  the  left  hepatic  vein. 
Thus,  the  greater  part  of  the  blood  returned  to  the  foetus  from  the  placenta  passes 
through  the  liver,  a  relatively  small  quantity  being  emptied  into  the  vena  cava  by  the 
ductus  venosus. 

The  vena  cava  ascendens,  containing  the  placental  blood  which  has  passed  through 
the  liver,  the  blood  conveyed  directly  from  the  umbilical  vein  by  the  ductus  venosus,  and 
the  blood  from  the  lower  extremities,  passes  to  the  right  auricle.  As  the  blood  enters 
the  right  auricle,  it  is  directed  by  the  Eustachian  valve,  passing  behind  the  valve,  through 
the  foramen  ovale,  into  the  left  auricle.  At  the  same  time,  the  blood  from  the  "head  and 
the  superior  extremities  passes  down,  by  the  vena  cava  descendens,  in  front  of  the  Eusta- 
chian valve,  through  the  right  auricle,  into  the  right  ventricle.  The  arrangement  of  the 
Eustachian  valve  is  such,  that  the  right  auricle  simply  affords  a  passage  for  the  two  cur- 
rents of  blood ;  the  one,  from  the  vena  cava  ascendens,  through  the  foramen  ovale,  passes 
into  the  left  auricle  and  the  left  ventricle ;  and  the  other,  from  the  vena  cava  descendens, 
passes  through  the  right  auriculo-ventricular  opening,  into  the  right  ventricle.  It  is 
probable,  indeed,  that  there  is  very  little  admixture  of  these  two  currents  of  blood  in  the 
natural  course  of  the  foetal  circulation.  Reid  injected  the  vena  cava  ascendens  with  red, 
and  the  vena  cava  descendens  with  yellow,  in  a  foetus  of  seven  months,  and  he  found  very 


936  GENERATION. 

little  mixture  of  the  two  colors  in  the  passage  of  the  injected  material  through  the  right 
auricle. 

The  blood  poured  into  the  left  auricle  from  the  vena  cava  ascendens  through  the  fora- 
men ovale  passes  from  the  left  auricle  into  the  left  ventricle.  The  left  auricle  and  the 
left  ventricle  also  receive  a  small  quantity  of  blood  from  the  lungs,  by  the  pulmonary 
veins.  Thus  the  left  ventricle  is  filled.  At  the  same  time,  the  right  ventricle  is  tilled 
with  blood  which  has  passed  through  the  right  auricle,  in  front  of  the  Eustachian  valve. 
The  two  ventricles,  thus  distended,  then  contract  simultaneously.  The  blood  from  the 
right  ventricle  passes  in  small  quantity  to  the  lungs,  the  greater  part  passing  through  the 
ductus  arteriosus  into  the  descending  portion  of  the  arch  of  the  aorta.  This  duct  is  short 
(half  an  inch  in  length)  and  about  the  size  of  a  goose-quill.  The  blood  from  the  left  ven- 
tricle passes  into  the  aorta  and  goes  to  the  system.  The  vessels  of  the  head  and  superior 
extremities  being  given  off  from  the  aorta  before  it  receives  the  blood  from  the  ductus 
arteriosus,  these  parts  receive  almost  exclusively  the  pure  blood  from  the  vena  cava 
ascendens,  the  only  mixture  with  the  placental  blood  being  the  blood  from  the  lower 
extremities,  the  blood  from  the  portal  system,  and  the  small  amount  of  blood  received 
from  the  lungs.  After  the  aorta  has  received  the  blood  from  the  ductus  arteriosus,  how- 
ever, it  is  mixed  blood;  and  it  is  this  which  supplies  the  trunk  and  lower  extremities. 
This  is  one  of  the  reasons  assigned  by  physiologists  for  the  greater  relative  development 
of  the  upper  parts  of  the  foetus. 

In  Fig.  311,  which  is  partly  diagrammatic,  the  foatal  circulation  is  illustrated.  In 
endeavoring,  in  this  figure,  to  give  a  clear  idea  of  the  second  circulation,  we  have  not 
attempted  to  preserve  the  exact  relations  or  the  relative  size  of  the  organs.  We  have 
endeavored  to  represent,  by  dotted  lines,  the  Eustachian  valve,  the  foramen  ovale,  and 
the  two  auriculo- ventricular  orifices.  The  liver,  which  is  smaller  in  the  diagram  than  it 
really  is,  and  the  bladder,  are  represented  by  dotted  lines. 

There  can  be  no  doubt  that  the  foetus  derives  materials  for  its  nutrition  and  growth 
from  the  placenta,  and  that  this  also  serves  as  a  respiratory  organ.  In  another  chapter, 
under  the  head  of  respiration  before  birth,  we  have  stated  that  "  Legallois  frequently 
observed  a  bright-red  color  in  the  blood  of  the  umbilical  vein ;  and,  on  alternately  com- 
pressing and  releasing  the  vessel,  he  saw  the  blood  change  in  color  successively  from  red 
to  dark  and  from  dark  to  red."  This  difference  in  color  between  the  blood  of  the  umbili- 
cal arteries  and  of  the  umbilical  vein  has,  however,  been  denied  by  some  authors,  who 
state  that  all  of  the  foetal  blood,  while  it  is  of  nearly  a  uniform  color,  is  lighter  than  the 
venous  blood  of  the  adult ;  but  Dalton,  in  a  direct  observation  upon  a  cat,  "nearly  arrived 
at  the  term  of  pregnancy,"  noted  that  "  the  difference  in  color  between  the  umbilical 
arteries  and  veins  was  very  distinct.  They  were  both  dark,  but  the  color  of  the  veins 
was  very  decidedly  more  ruddy  than  that  of  the  arteries ;  i.  e.,  the  blood  in  the  umbilical 
arteries  was  of  the  color  of  the  ordinary  venous  blood,  while  that  of  the  umbilical  veins 
had  a  color  midway  between  the  ordinary  venous  and  arterial  hues.  All  the  foetuses 
were  healthy,  and  moved  briskly  after  being  taken  out  of  the  uterus." 

There  are  numerous  observations  showing  that  the  foetus  in  utero  makes  respiratory 
efforts  when  the  umbilical  vessels  are  compressed.  We  believe  that  these,  as  well  as  the 
first  respiration  after  birth,  are  due  to  a  want  of  oxygen  in  the  general  system  of  the 
foetus,  and  we  think  that  we  have  demonstrated  this  fact  by  experiments.  This  point  has 
already  been  elaborately  discussed  in  another  chapter.  If  our  experiments  and  the  deduc- 
tions drawn  from  them  be  correct,  there  can  be  no  doubt  with  regard  to  the  respiratory 
function  of  the  placenta,  although,  as  far  as  we  know,  there  has  never  been  an  accurate 
comparison  of  the  gases  contained  in  the  blood  of  the  umbilical  arteries  and  the  umbilical 
vein. 

The  Third,  or  Adult  Circulation. — When  the  child  is  born,  the  placental  circulation 
is  suddenly  arrested.  After  a  short  time,  the  sense  of  want  of  air  becomes  sufficiently 


DEVELOPMENT   OF  THE   CIRCULATORY   SYSTEM. 


937 


intense  to  give  rise  to  an  inspiratory  effort,  and  the  first  inspiration  is  made.     The  pul- 
monary organs  are  then,  for  the  first  time,  distended  with  air,  the  pulmonary  arteries 


Pulmonary  Art. 


Foramen  Ovale. /— 

Eustachian  Valve.—- 
Right  Auric.  -Vent.  Opening. 


ry  Art. 
Left  Auricle. 
r Left  Auric.  -  Vent 


Bladder 


Hepatic  Vein.*. 

Branches  of  the 
Umbilical 'Vein-*., 
to  the  Liver. 


Internal  Mac  Arteries. 
FIG.  311. — Diagram  of  the  foetal  circulation. 

carry  the  greatest  part  of  the  hlood  from  the  right  ventricle  to  the  lungs,  and  a  new  cir- 
culation is  established.  During  the  later  periods  of  foetal  life,  the  heart  is  gradually  pre- 
pared for  the  new  currents  of  blood.  The  foramen  ovale,  which  is  largest  at  the  sixth 


938  GENERATION. 

month,  after  that  time,  is  partly  occluded  by  the  gradual  growth  of  a  valve,  which  extends 
from  below  upward  and  from  behind  forward,  upon  the  side  of  the  left  auricle.  The 
Eustachian  valve,  which  is  also  largest  at  the  sixth  month,  gradually  atrophies  after  this 
time,  and,  at  full  term,  it  has  nearly  disappeared.  At  birth,  then,  the  Eustachian  valve  is 
practically  absent;  and,  after  pulmonary  respiration  becomes  established,  the  foramen 
ovale  has  nearly  closed.  The  arrangement  of  the  valve  of  the  foramen  ovale  is  such,  that, 
at  birth,  a  small  quantity  of  blood  may  pass  from  the  right  to  the  left  auricle,  but  none 
oan  pass  in  the  opposite  direction.  The  situation  of  the  Eustachian  valve,  on  the  right 
side  of  the  inter-auricular  septum,  is  marked  by  an  oval  depression,  called  the  fossa  ovalis. 

As  a  congenital  malformation,  the  foramen  ovale  may  remain  open,  producing  the 
condition  known  as  cyanosis  neonatorum.  This  may  continue  into  adult  life,. and  it  is  then 
attended  with  more  or  less  disturbance  of  respiration  and  difficulty  in  maintaining  the 
normal  heat  of  the  body.  Usually,  the  foramen  ovale  is  completely  closed  at  about  the 
tenth  day  after  birth.  The  ductus  arteriosus  begins  to  contract  at  birth,  and  it  is  occluded, 
being  reduced  to  the  condition  of  an  impervious  cord,  at  from  the  third  to  the  tenth  day. 

When  the  placental  circulation  is  arrested  at  birth,  the  hypogastric  arteries,  the  um- 
bilical vein,  and  the  ductus  venosus  contract,  and  they  become  impervious  at  from  the 
second  to  the  fourth  day.  The  hypogastric  arteries  remain  pervious  at  their  lower  por- 
tion and  constitute  the  superior  vesical  arteries.  A  rounded  cord,  which  is  the  remnant 
of  the  umbilical  vein,  forms  the  round  ligament  of  the  liver.  A  slender  cord,  the  rem- 
nant of  the  ductus  venosus,  is  lodged  in  a  fissure  of  the  liver,  called  the  fissure  of  the 
ductus  venosus. 

A  history  of  the  development  of  the  various  tissues  of  the  body  belongs  really  to  gen- 
eral anatomy  and  is  usually  given  in  works  specially  devoted  to  that  subject.  We  have 
only  treated  of  it  incidentally,  in  our  account  of  the  development  of  the  various  organs 
.and  systems. 


CHAPTER    XXVIII. 

F(ETAL    LIFE— DEVELOPMENT  AFTER   BIRTH-DEATH. 

Enlargement  of  the  uterus  in  pregnancy— Duration  of  pregnancy— Size,  weight,  and  position  of  the  foetus— The  foetus 
at  different  stages  of  intra-uterine  life — Multiple  pregnancy — Cause  of  the  first  contractions  of  the  uterus  in  nor- 
mal parturition— Involution  of  the  uterus— Meconium— -Dextral  preeminence— Development  after  birth— Ages- 
Death— Cadaveric  rigidity— Putrefaction. 

As  the  development  of  the  ovum  advances,  the  uterus  is  enlarged  and  its  walls  are 
thickened.  The  form  of  the  organ,  also,  gradually  changes,  as  well  as  its  position.  Im- 
mediately after  birth,  its  weight  is  about  a  pound  and  a  half,  while  the  virgin  uterus 
weighs  less  than  two  ounces.  It  is  a  remarkable  fact,  demonstrated  upon  the  living  sub- 
ject, by  Prof.  I.  E.  Taylor,  of  New  York,  that  the  neck  of  the  uterus,  while  it  becomes 
softer  and  more  patulous  during  pregnancy,  does  not  change  its  length,  even  in  the  very 
latest  stages  of  utero-gestation.  This  fact  is  in  opposition  to  the  statements  of  most 
obstetricians,  who  believe  that  the  os  internum  dilates,  and  that  the  neck  is  gradually 
absorbed,  as  it  were,  by  the  body  of  the  uterus,  during  the  later  months  of  pregnancy. 

We  have  already  studied  the  remarkable  changes  which  take  place  in  the  mucous 
membrane  of  the  uterus  during  pregnancy  and  the  mode  of  formation  of  the  decidua, 
and  we  have  seen  that  the  mucous  membrane  of  the  neck  does  not  participate  in  these 
changes  and  is  not  thrown  off  in  parturition.  The  only  change,  indeed,  which  we  note 
in  the  neck,  aside  from  the  softening  of  its  texture,  is  the  secretion  of  the  plug  of  mucus 
which  closes  the  os. 


DURATION   OF  PREGNANCY.  939 

The  changes  in  the  walls  of  the  uterus  during  pregnancy  are  very  important.  The 
blood-vessels  become  much  enlarged,  and  the  muscular  fibres  increase  immensely  in  size, 
so  that  their  contractions  are  very  powerful  when  the  foetus  is  expelled. 

It  is  evident  that,  on  account  of  the  progressive  increase  in  the  size  of  the  uterus  dur- 
ing pregnancy,  it  cannot  remain  in  the  cavity  of  the  pelvis  at  the  later  months.  During 
the  first  three  months,  however,  when  it  is  not  too  large  for  the  pelvis,  it  sinks  back  into 
the  hollow  of  the  sacrum,  the  fundus  being  directed  somewhat  backward,  with  the  neck 
presenting  downward,  forward,  and  a  little  to  the  left.  After  this  time,  however,  the 
increased  size  of  the  organ  causes  it  to  extend  into  the  abdominal  cavity,  so  that  its 
fundus  eventually  reaches  the  epigastric  region.  Its  axis  then  has  the  general  direction 
of  the  axis  of  the  superior  strait  of  the  pelvis. 

The  enlargement  of  the  uterus  and  the  necessity  of  carrying  on  a  greatly-increased 
circulation  in  its  walls  during  pregnancy  are  attended  with  a  temporary  hypertrophy  of 
the  heart.  According  to  Robin,  it  is  mainly  the  left  ventricle  which  is  thickened  during 
utero-gestation,  and  the  increase  in  the  weight  of  the  heart  at  full  term  amounts  to  more 
than  one-fifth.  After  delivery,  the  weight  of  the  heart  soon  returns  to  nearly  the  nor- 
mal standard. 

Duration  of  Pregnancy. — The  duration  of  pregnancy,  dating  from  a  fruitful  inter- 
course, must  be  considered  as  variable,  within  certain  limits.  The  method  of  calculation 
most  in  use  by  obstetricians  is,  to  date  from  the  end  of  the  last  menstrual  period.  Dr. 
Matthews  Duncan,  who  has  made  quite  a  number  of  observations  upon  this  point,  states 
that  the  278th  day  after  the  end  of  the  last  menses  is  the  average  day  of  delivery ;  but 
he  admits  that  his  method  of  calculation  is  rough,  though  he  cannot  find  any  that  is  more 
reliable.  The  observations  upon  which  this  opinion  is  based  are  the  following :  The  day 
was  predicted  in  153  cases ;  in  10  cases,  confinement  occurred  on  the  exact  day ;  in  80 
cases,  the  confinement  occurred  sooner,  presenting  an  average  of  7  days  for  each  case ; 
arid,  in  63  cases,  the  confinement  occurred  later,  presenting  an  average  of  8  days  for  each 
case.  The  great  difficulty  in  predicting  the  exact  time  of  confinement,  which  is  very 
important  in  practice,  is  mainly  due  to  the  comparatively  small  number  of  reliable  obser- 
vations in  which  the  pregnancy  can  be  dated  from  a  single  intercourse  or  from  intercourse 
occurring  within  two  or  three  days.  We  have  received  from  Prof.  Fordyce  Barker  the 
following  very  interesting  account  of  a  case  in  which  this  observation  was  made  in  his 
own  practice :  A  lady,  concerning  whom  there  could  be  no  suspicion  of  inaccuracy,  resid- 
ing in  New  York,  received  a  visit  from  her  husband,  after  a  long  interval  of  absence. 
He  arrived  in  this  city  from  New  Orleans,  remained  thirty-six  hours,  and  then  went  to 
Europe,  where  he  remained  for  four  months.  Exactly  298  days  from  the  date  of  the 
first  visit  of  the  husband,  the  lady  was  confined  and  delivered  by  Prof.  Barker.  This 
occurred  in  1852.  Taking  into  account  the  various  cases  which  are  quoted  by  authors, 
in  which  conception  has  been  supposed  to  follow  a  single  coitus,  there  appears  to  be  a 
range  of  variation  in  the  duration  of  pregnancy  of  no  less  than  40  days,  the  extremes 
being  260  and  300  days. 

In  the  very  interesting  observations  of  Kundrat  and  Engelmann,  upon  the  changes  of 
the  uterine  mucous  membrane  during  menstruation,  to  which  we  have  already  referred, 
the  idea  is  advanced  that  pregnancy  dates  really  from  a  menstrual  period  which  is  pre- 
vented, as  far  as  a  discharge  of  blood  is  concerned,  by  fecundation  of  an  ovum,  and  not 
from  the  period  immediately  preceding,  in  which  the  flow  takes  place.  If  we  adopt  this 
view,  the  changes  in  the  mucous  membrane  of  the  uterus  ordinarily  terminate  in  a  fatty 
degeneration  of  the  vascular  walls,  which  results  in  a  capillary  haemorrhage ;  if,  how- 
ever, an  ovum  be  fecundated,  these  changes  do  not  pass  into  fatty  degeneration,  but 
advance  to  an  hypertrophy,  which  is  the  first  stage  in  the  formation  of  the  decidua.  The 
arguments  in  opposition  to  this  method  of  calculating  the  duration  of  pregnancy  are  the 
following :  The  time,  with  relation  to  the  menstrual  flow,  at  which  an  ovum  is  discharged 


940  GENERATION. 

has  not  been  accurately  determined ;  and  it  is  certain  that  ovulation  frequently  does  not 
take  place  until  after  the  flow  of  blood  has  been  established.  This  question  we  have 
fully  considered  in  a  previous  chapter.  It  is  probable,  also,  that  intercourse  is  most  liable 
to  be  followed  by  fecundation,  when  it  occurs  just  after  the  cessation  of  a  menstrual 
period,  and  when  the  female  often  presents  unusual  sexual  excitement;  but  it  is  true  that 
fecundation  may  follow  intercourse  at  any  time.  If  we  admit  that  fecundation  dates 
more  nearly  from  a  menstrual  period  prevented  than  from  the  last  appearance  of  the 
flow,  it  would  be  necessary  to  assume  that  ovulation  usually  takes  place  before  tbe  flow, 
and  fecundation  would  be  most  liable  to  follow  intercourse  occurring  at  that  time;  for 
we  could  hardly  admit  that  an  ovum,  fecundated  at  the  cessation  of  a  menstrual  period, 
could  remain  in  the  generative  passage  of  the  female  for  two  or  three  weeks,  before  the 
mucous  membrane  of  tbe  uterus  is  prepared  for  its  reception.  Tbese  facts  are  so  strong, 
that  the  view  entertained  by  Kundrat  and  Engelmann  cannot  yet  be  adopted  without 
reserve. 

As  regards  the  practical  applications  of  calculations  of  the  probable  duration  of  preg- 
nancy in  individual  cases,  we  must  recognize  the  fact  that  the  duration  is  variable.  If 
we  date  from  the  end  of  the  last  menstrual  period,  we  may  adopt  the  average  of  278 
days,  a  little  more  than  nine  calendar  months.  If  we  adopt  the  view  that  pregnancy 
dates  from  a  menstrual  period  which  has  been  prevented,  the  duration  of  intra-uterine 
life  would  be  about  250  days. 

Size,  Weight,  and  Position  of  the  Fffitus. — The  estimates  of  writers  with  regard  to  the 
size  and  weight  of  the  embryon  and  foetus  at  different  stages  of  intra-uterine  life  present 
very  wide  variations ;  still,  it  is  important  to  have  an  approximate  idea,  at  least,  upon 
these  points,  and  we  shall  adopt  the  figures  given  by  Scanzoni,  as  presenting  fair  aver- 
ages. As  the  measurements  and  weights  are  simply  approximative,  the  slight  differ- 
ences between  the  German  and  the  English  standards  are  not  important.  It  will  be 
useful,  also,  to  give,  as  is  done  by  Scanzoni,  a  review  of  the  general  development  of  the 
organs  at  different  stages. 

At  the  third  week,  the  embryon  is  from  two  to  three  lines  in  length.  This  is  about 
the  earliest  period  at  which  measurements  have  been  taken  in  the  normal  state. 

At  the  seventh  week,  the  embryon  measures  about  nine  lines.  Points  of  ossification 
have  appeared  in  the  clavicle  and  the  lower  jaw  ;  the  Wolffian  bodies  are  large ;  the 
pedicle  of  the  umbilical  vesicle  is  very  much  reduced  in  size  ;  the  internal  organs  of  gen- 
eration have  just  appeared;  the  liver  is  of  large  size  ;  the  lungs  present  several  lobules. 

At  the  eighth  week,  the  embryon  is  from  ten  to  fifteen  lines  in  length.  The  lungs 
begin  to  receive  a  small  quantity  of  blood  from  the  pulmonary  arteries;  the  external 
organs  of  generation  have  appeared,  but  it  is  difficult  to  determine  the  sex  ;  the  abdomi- 
nal walls  have  closed  over  in  front. 

At  the  third  month,  the  embryon  is  from  two  to  two  and  a  half  inches  long  and 
weighs  about  one  ounce.  The  amniotic  fluid  is  then  more  abundant,  in  proportion  to  the 
size  of  the  embryon,  than  at  any  other  period.  The  umbilical  cord  begins  to  be  twisted ; 
the  various  glandular  organs  of  the  abdomen  appear  ;  the  pupillary  membrane  is  formed ; 
the  limitation  of  the  placenta  has  become  distinct.  At  this  time,  the  upper  part  of  the 
embryon  is  relatively  much  larger  than  the  lower  portion. 

At  the  end  of  the  fourth  month,  the  embryon  becomes  the  foetus.  It  is  then  from 
four  to  five  inches  long  and  weighs  about  five  ounces.  The  muscles  begin  to  manifest 
contractility ;  the  eyes,  mouth,  and  nose  are  closed  ;  the  gall-bladder  is  just  developed  ; 
the  fontanelles  and  sutures  are  wide. 

At  the  fifth  month,  the  foetus  is  from  nine  to  twelve  inches  long  and  weighs  from 
five  to  nine  ounces.  The  hairs  begin  to  appear  on  the  head  ;  the  liver  begins  to  secrete 
bile,  and  the  meconium  appears  in  the  intestinal  canal ;  the  amnion  is  in  contact  with 
the  chorion. 


MULTIPLE   PREGNANCY.  941 

At  the  sixth  month,  the  foetus  is  from  eleven  to  fourteen  inches  long  and  weighs 
from  one  and  a  half  to  two  pounds.  If  the  foetus  be  delivered  at  this  time,  life  may  con- 
tinue for  a  few  moments;  the  bones  of  the  head  are  ossified,  but  the  fontanelles  and 
sutures  are  still  wide  ;  the  prepuce  has  appeared  ;  the  testicles  have  not  descended. 

At  the  seventh  month,  the  foetus  is  from  fourteen  to  fifteen  inches  long  and  weighs 
from  two  to  three  pounds.  The  hairs  are  longer  and  darker  ;  the  pupillary  membrane 
disappears,  undergoing  atrophy  from  the  centre  to  the  periphery ;  the  relative  quantity 
of  the  amniotic  fluid  is  diminished,  and  the  foetus  is  not  so  free  in  the  cavity  of  the 
uterus  ;  the  foetus  is  now  viable. 

At  the  eighth  month,  the  foetus  is  from  fifteen  to  sixteen  inches  long  and  weighs  from 
three  to  four  pounds.  The  eyelids  are  opened  and  the  cornea  is  transparent ;  the  pupil- 
lary membrane  has  disappeared ;  the  left  testicle  has  descended ;  the  umbilicus  is  at 
about  the  middle  of  the  body,  the  relative  size  of  the  lower  extremities  having  increased. 

At  the  ninth  month,  the  foetus  is  about  seventeen  inches  long  and  weighs  from  five  to 
six  pounds.  Both  testicles  have  usually  descended,  but  the  tunica  vaginalis  still  commu- 
nicates with  the  peritoneal  cavity. 

At  birth,  the  infant  weighs  a  little  more  than  seven  pounds,  the  usual  range  being 
from  four  to  ten  pounds,  though  these  limits  are  sometimes  exceeded. 

The  position  of  the  foetus,  in  the  great  majority  of  cases,  excluding  abnormal  presenta- 
tions, is  with  the  head  downward  ;  and  why  this  is  the  usual  and  the  normal  position,  is  a 
question  which  has  been  the  subject  of  much  discussion.  As  we  have  just  seen,  in  the 
early  stages  of  pregnancy,  the  foetus  floats  quite  freely  in  the  amniotic  fluid.  Upon  this 
point,  Dr.  Matthews  Duncan  has  made  the  following  interesting  experiments :  Securing 
the  limbs  of  the  foetus  in  the  natural  position  which  it  assumes  in  utero,  by  means  of 
threads,  and  immersing  it  in  a  solution  of  salt  of  nearly  its  own  specific  gravity,  he  found 
that  it  naturally  gravitated  to  nearly  the  normal  position,  with  the  head  downward.  It 
is  probable,  judging  from  these  observations,  that  the  natural  gravitation  of  the  head  and 
of  the  upper  part  of  the  foetus  is  the  determining  cause  of  the  ordinary  position  in  utero. 

The  shape  of  the  uterus  at  full  term  is  ovoid,  the  lower  portion  being  the  narrower. 
The  foetus  has  the  head  slightly  flexed  upon  the  sternum,  the  arms  flexed  upon  the  chest 
and  crossed,  the  spinal  column  curved  forward,  the  thighs  flexed  upon  the  abdomen,  the 
legs  slightly  flexed  and  usually  crossed  in  front,  and  the  feet  flexed  upon  the  legs,  with 
their  inner  margin  drawn  toward  the  tibia.  This  is  the  position  in  which  the  foetus  is 
best  adapted  to  the  size  of  the  uterine  cavity,  and  in  which  the  expulsive  force  of  the 
uterus  can  be  most  favorably  exerted,  both  as  regards  the  foetus  and  the  generative  pas- 
sages of  the  mother. 

Multiple  Pregnancy. — It  is  not  very  rare  to  observe  two  children  at  a  birth,  and  cases 
are  on  record  where  there  have  been  four  and  even  fiv^,  though  in  these  latter  instances 
the  children  generally  survive  but  a  short  time,  or,  as  is  more  common,  abortion  takes 
place  during  the  first  months.  Three  at  a  birth,  though  rare,  has  been  often  observed  ; 
and  we  have  in  mind  at  this  moment  a  case  of  three  females,  triplets,  all  of  whom  lived 
past  middle  age. 

In  cases  of  twins,  it  is  an  interesting  question  to  determine  whether  the  development 
always  takes  place  from  two  ova,  or  whether  a  single  ovum  may  be  developed  into  two 
beings.  In  the  majority  of  cases,  twins  are  of  the  same  sex,  though  sometimes  they  are 
male  and  female.  In  some  cases,  there  are  two  full  sets  of  membranes,  each  foetus  hav- 
ing its  distinct  decidua,  placenta,  and  chorion  ;  in  others,  there  is  a  single  chorion  and  a 
double  amnion  ;  but,  in  some,  both  foetuses  are  enclosed  in  the  same  amnion.  As  a  rule, 
the  two  placentae  are  distinct ;  but  sometimes  there  is  a  vascular  communication  between 
them,  or  what  appears  to  be  a  single  placenta  may  give  origin  to  two  umbilical  cords. 
If  there  be  but  a  single  chorion  and  amnion  and  a  single  placenta,  it  has  been  thought 
that  the  two  beings  are  developed  from  a  single  ovum ;  otherwise,  it  would  be  necessary 


943 


GENERATION. 


to  assume  that  there  were  originally  two  sets  of  membranes,  which  had  become  fused 
into  one.  The  instances  on  record,  one  of  which  we  have  given,  of  twins,  one  white  and 
the  other  black,  show  conclusively  that  two  ova  may  be  developed  in  the  uterus  at  the 
same  time.  While  there  can  be  no  doubt  upon  this  point,  the  question  of  the  possibility 
of  the  development  of  two  beings  from  a  single  ovum  remains  unsettled.  It  is  thought 
to  be  more  difficult  to  understand  how  two  conjoined  monsters,  like  the  celebrated 
Siamese  twins,  who  died  in  1874  at  the  age  of  sixty-three  years,  could  be  developed 


CNG 


CHANG. 


FIG.  312.—  The  Siamese  twins. 

V  V,  vena  cava  ;  V  P,  V  P.  portal  vein ;  </,  upper  hepatic  pouch  of  Chang ;  &,  peritoneal,  or  umbilical  pouch  of  Eng  ;  c, 
lower  peritoneal,  or  umbilical  pouch  of  Chang ;  D,  D,  connecting  liver-band  ;  e,  lower  border  of  the  band  ;  /;  upper 
border  of  the  band. 

from  two  ova  which  became  fused,  than  to  imagine  the  development  of  two  beings  from 
a  single  ovum.  This  question,  however,  belongs  to  teratology  and  could  be  settled  only 
by  observations  of  conjoined  monsters  very  early  in  their  development,  which  do  not 
exist  in  literature. 

As  pathological  conditions,  we  have  extra-uterine  pregnancies,  in  which  the  fecun- 
dated ovum,  forming  its  attachments  in  the  Fallopian  tube  (Fallopian  pregnancy)  or  within 
the  abdominal  cavity  (abdominal  pregnancy),  undergoes  a  certain  degree  of  development. 
The  uterus  usually  enlarges,  in  these  instances,  and  forms  an  imperfect  decidua. 

Came  of  the  First  Contractions  of  the  Uterus  in  Normal  Parturition. — The  cause 
of  the  first  contraction  of  the  uterus  in  normal  parturition  is  undoubtedly  referable  to 
some  change  in  the  attachmect  of  its  contents,  which  causes  the  foetus  and  its  membranes 
to  act  as  a  foreign  body.  When,  for  any  reason,  it  is  advisable  to  cause  the  uterus  to 
expel  its  contents  before  the  full  term  of  pregnancy,  the  most  physiological  method  of 
bringing  on  the  contractions  of  this  organ  is  to  cautiously  separate  a  portion  of  the  mem- 
branes, as  is  often  done  by  introducing  an  elastic  catheter  between  the  ovum  and  the 
uterine  wall.  A  certain  time  after  this  operation,  the  uterus  contracts  to  expel  the  ovum, 
which  then  acts  as  a  foreign  body. 

In  the  normal  state,  toward  the  end  of  pregnancy,  the  cells  of  the  decidua  vera  and 
of  that  portion  of  the  placenta  which  is  attached  to  the  uterus  undergo  fatty  degenera- 
tion, and,  in  this  way,  there  is  a  gradual  separation  of  the  outer  membrane,  so  that  the 


INVOLUTION   OF  THE  UTERUS— MECONIUM.  943 

contents  of  the  uterus  gradually  lose  their  anatomical  connection  with  the  mother.  When 
tliis  change  has  progressed  to  a  certain  extent,  the  uterus  hegins  to  contract;  each  con- 
traction then  separates  the  membranes  more  and  more,  the  most  dependent  part  pressing 
upon  the  os  internum ;  and  the  subsequent  contractions  are  probably  due  to  reflex  action. 
The  first  "  pain  "  is  induced  by  the  presence  of  the  foetus  and  its  membranes  as  a  foreign 
body,  a  mechanism  similar  to  that  which  obtains  when  premature  labor  has  been  brought 
on  by  separation  of  the  membranes. 

We  shall  not  describe  the  mechanism  of  parturition,  although  this  is  entirely  a  physi- 
ological process,  for  the  reason  that  it  is  necessarily  considered  elaborately  in  works  upon 
obstetrics.  The  first  contractions  of  the  uterus,  by  pressing  the  bag  of  waters  against 
the  os  internum,  gradually  dilate  the  cervix ;  the  membranes  usually  rupture  when  the  os 
is  pretty  fully  dilated,  and  the  amniotic  fluid  is  discharged  ;  the  head  then  presses  upon  the 
outlet;  and,  the  uterine  contractions  becoming  more  and  more  vigorous  and  efficient,  the 
child  is  brought  into  the  world,  this  being  followed  by  the  expulsion  of  the  membranes  and 
placenta.  There  then  follows  a  tonic  contraction  of  the  muscular  walls  of  the  uterus, 
which  becomes  a  hard,  globular  mass,  easily  felt  through  the  flaccid  abdominal  walls. 
The  very  contractions  of  the  muscular  fibres  of  the  uterus  which  expel  the  foetus  close 
the  vessels  ruptured  by  the  separation  of  the  placenta  and  arrest  the  haemorrhage  from 
the  mother.  The  changes  which  then  take  place  in  the  respiration  and  the  circulation 
of  the  infant  have  been  fully  considered  in  connection  with  the  development  of  the  circu- 
latory system. 

Involution  of  the  Uterus. — At  from  four  to  six  days,  and  seldom  later  than  eight  days 
after  parturition,  the  uterus  has  sensibly  advanced  in  the  process  of  involution ;  and  it  is 
then  gradually  reduced  to  the  size  and  structure  which  it  presents  during  the  non-preg- 
nant condition,  though  it  never  becomes  quite  as  small  as  in  the  virgin  state.  The  new 
mucous  membrane,  which  has  been  developing  during  the  latest  periods  of  pregnancy, 
becomes  perfect  at  about  the  end  of  the  second  month  after  delivery.  It  has  then  united, 
at  the  os  internum,  with  the  mucous  membrane  of  the  neck,  which  does  not  participate 
in  the  formation  of  the  decidua.  The  muscular  fibres,  after  parturition,  present  granules 
and  globules  of  fat  in  their  substance,  and  are  gradually  reduced  in  size,  as  the  uterus 
becomes  smaller.  Their  involution  is  complete  at  about  the  end  of  the  second  month. 
During  the  first  month,  and  particularly  within  the  first  two  weeks  after  delivery,  there 
is  a  sero-sanguinolent  discharge  from  the  uterus,  which  is  due  to  disintegration  of  the 
blood  and  of  the  remains  of  the  membranes  in  its  cavity,  this  debris  being  mixed  with  a 
certain  amount  of  sero-mucous  secretion.  This  discharge  constitutes  the  lochia,  which 
are  at  first  red,  but  become  paler  as  they  are  reduced  in  quantity  and  disappear. 

During  lactation,  the  processes  of  ovulation  and  menstruation  are  usully  arrested, 
though  this  is  not  always  the  case.  In  treating  of  secretion,  we  have  given  a  full  descrip- 
tion of  the  vernix  caseosa,  and  we  have  also  stated  what  is  known  with  regard  to  the 
properties  and  composition  of  the  urine  of  the  foetus. 

Meconium.— M  about  the  fifth  month,  there  appears  a  certain  amount  of  secretion  in 
the  intestinal  canal,  which  becomes  more  abundant,  particularly  in  the  large  intestine,  as 
development  advances.  This  is  rather  light-colored  or  grayish  in  the  upper  portion  of 
the  small  intestine,  becoming  yellowish  in  the  lower  portion,  and  is  of  a  dark-greenish 
color  in  the  colon.  The  dark,  pasty,  adhesive  matter,  which  is  discharged  from  the  rec- 
tum soon  after  birth,  is  called  the  meconium. 

The  meconium  appears  to  consist  of  a  thick,  mucous  secretion,  with  numerous  grayish 
granules,  a  few  fatty  granules,  intestinal  epithelium,  and,  frequently,  crystals  of  choleste- 
rine.  The  color  seems  to  be  due  to  granulations  of  the  coloring  matter  of  the  bile,  but 
the  biliary  salts  cannot  be  detected  in  the  meconium  by  Pettenkofer's  test.  The  con- 
stituent of  the  meconium  which,  in  our  own  observations,  we  have  found  to  possess  the 


944 


GENERATION. 


greatest  physiological  importance,  is  cholesterine.     Although  but  few  crystals  of  cho- 

lesterine  are  found  upon  microscopical  examination,  the  simplest  processes  for  its  ex- 
traction will  reveal  the  presence  of  this 
principle  in  large  quantity.  In  a  specimen 
of  ineconium  in  which  we  made  a  quantita- 
tive examination,  the  proportion  of  choles- 
terine was  6-245  parts  per  1,000.  It  is  a 
significant  fact,  that  the  meconium  contains 
cholesterine  and  no  stercorine,  the  sterco- 
rine,  in  the  adult,  resulting  from  a  trans- 
formation of  cholesterine  by  the  digestive 
fluids,  which  are  probably  not  secreted  dur- 
ing intra-uterine  life. 

None  of  the  secretions  concerned  in  di- 
gestion appear  to  be  produced  in  utero,  and 
it  is  also  probable  that  the  true  biliary  salts 
are  not  formed  at  that  time  ;  but  we  know 
that  the  processes  of  disassimilation  and 
excretion  are  then  active,  and  the  choles- 
terine of  the  meconium  is  the  product  of  the 
excretory  action  of  the  liver.  The  relations 

of  cholesterine  as  an  excrementitious  principle  have  already  been  very  fully  discussed,  in 

connection  with  the  bile  and  with  excretion. 


FIG.  313. — Cholesterine  extracted  from  meconium 
inch  objective. 


Dextral  Preeminence. — The  curious  fact,  that  most  persons  by  preference  use  the 
right  arm,  leg,  eye,  etc.,  instead  of  the  left,  while,  as  exceptions,  some  use  the  left  in 
preference  to  the  right,  has  excited  a  great  deal  of  discussion,  even  among  the  earlier 
writers.  There  can  be  no  doubt  with  regard  to  the  fact  of  a  natural  dextral  pre- 
eminence; and,  also,  that  left-handedness  is  congenital,  difficult,  if  not  impossible,  to 
correct  entirely,  and  not  due  simply  to  habit.  It  would  appear  that  there  must  be  some 
condition  of  organization,  which  produces  dextral  preeminence  in  the  great  majority  of 
persons,  and  left-handedness,  as  an  exception ;  but  what  this  condition  is,  it  is  very  diffi- 
cult to  determine.  An  explanation,  very  often  offered  by  anatomists,  is,  that  the  right 
subclavian  artery  arises  nearer  the  heart  than  the  left,  that  the  right  arm  is  therefore 
better  supplied  with  arterial  blood,  develops  more  fully,  and  is,  consequently,  generally 
used  in  preference  to  the  left ;  but  we  cannot  explain  the  exceptional  predominance  of 
the  left  hand  by  an  inversion  of  this  arrangement  of  vessels. 

The  most  important  anatomical  and  pathological  facts  bearing  upon  the  question 
under  consideration  are  the  following:  Dr.  Boyd  has  shown  that  the  left  side  of  the  brain 
almost  invariably  exceeds  the  right  in  weight,  by  about  one-eighth  of  an  ounce.  In 
aphasia,  the  lesion  is  almost  always  on  the  left  side  of  the  brain.  These  facts  point  to  a 
predominance  of  the  left  side  of  the  brain,  which  presides  over  the  movements  of  the 
right  side  of  the  body.  Again,  a  few  cases  of  aphasia  with  left  hemiplegia,  the  lesion 
being  on  the  right  side  of  the  brain,  have  been  reported  as  occurring  in  left-handed  per- 
sons. These  points  we  have  noted  in  treating  of  the  nervous  system. 

Dr.  Ogle,  in  a  recent  paper  on  right-handedness,  gives  several  instances  of  aphasia  in 
left-handed  persons,  in  which  the  brain-lesion  was  on  the  right  side.  In  two  left-handed 
individuals,  the  brain  was  examined  and  compared  with  the  brain  of  right-handed  per- 
sons. It  was  found  that  the  brain  was  more  complex  on  the  left  side  in  the  right- 
handed,  and  on  the  right  side  in  the  left-handed.  In  the  discussion  which  followed  the 
presentation  of  this  paper,  Dr.  Charlton  Bastion  stated  that  he  had  found  the  gray  mat- 
ter of  the  brain  to  be  generally  heavier  on  the  left  than  on  the  right  side.  With  regard 
to  the  cause  of  the  superior  development  of  the  left  side  of  the  brain,  the  only  explana- 


DEVELOPMENT  AFTEK  BIRTH,  AGES,  AND  DEATH.  945 

tion  offered  was  the  fact  that  the  arteries  going  to  the  left  side  are  usually  larger  than 
those  on  the  right.  There  were  no  observations  with  regard  to  the  comparative  size  of 
the  arteries  upon  the  two  sides  in  left-handed  persons. 

Eeasoning  from  the  facts  just  stated,  Dr.  Ogle  conceives  that  dextral  preeminence 
depends  upon  a  natural  predominance  of  the  left  side  of  the  brain,  the  reverse  obtaining 
in  the  left-handed.  This  view  seems  to  afford  the  most  rational  explanation  of  dextral 
preeminence.  It  is  generally  true  that  the  members  on  the  right  side  are  stronger  than 
the  left,  particularly  the  arm  ;  but  this  is  not  always  the  case,  even  in  the  right-handed. 
A  not  inconsiderable  practical  experience  in  athletic  exercises  has  led  us  to  observe  that 
the  right  hand  is  more  conveniently  and  easily  used  than  the  left,  from  which  fact  we 
derive  the  term  dexterity;  but  that  the  left  arm  is  often  stronger  than  the  right.  In 
many  feats  of  strength,  the  left  arm  appears  less  powerful  than  the  right,  because  we 
have  less  command  over  the  muscles.  As  a  single  illustration  of  this,  we  may  mention 
the  feat  of  drawing  the  body  up  with  one  arm,  which  requires  unusual  strength,  but  very 
little  dexterity.  In  a  number  of  right-handed  persons,  we  find  many  who  perform  this 
feat  more  easily  with  the  left  arm,  and  not  a  few  who  can  accomplish  it  with  the  left 
arm  and  not  with  the  right.  When  we  come  to  the  cause  of  the  superior  development 
of  the  left  side  of  the  brain,  we  must  confess  that  the  anatomical  explanation  is  not 
entirely  satisfactory.  We  can  only  say  that  the  two  sides  of  the  brain  are  generally  not 
exactly  equal  in  their  development,  the  left  side  being  usually  superior  to  the  right,  and 
that  we  ordinarily  use  the  muscles  of  the  right  side  of  the  body  in  preference  to  those 
of  the  left  side. 

.Development  after  Birth^  Ages,  and  Death. 

When  the  child  is  born,  the  organs  of  special  sense  and  the  intelligence  are  dull ; 
there  is  then  very  little  muscular  power;  and  the  new  being,  for  several  weeks,  does  lit- 
tle more  than  eat  and  sleep.  The  natural  food  at  this  time  is  the  milk  of  the  mother,  and 
the  digestive  fluids  do  not,  for  some  time,  possess  the  varied  solvent  properties  that  we 
find  in  the  adult,  though  observations  upon  the  secretions  of  the  infant  are  few  and 
rather  unsatisfactory.  The  full  activity  of  pulmonary  respiration  is  gradually  and  slowly 
established.  Young  animals  appropriate  a  comparatively  small  quantity  of  oxygen,  and, 
just  after  birth,  they  present  a  much  greater  power  of  resistance  to  asphyxia  than  the  adult. 
The  power  of  maintaining  the  animal  temperature  is  also  much  less  in  the  newly-born. 
The  process  of  ossification,  development  of  the  teeth,  etc.,  have  already  been  considered. 
The  hairs  are  shed  and  replaced  by  a  new  growth  a  short  time  after  birth.  The  fonta- 
nelles  gradually  diminish  in  size  after  birth,  and  they  are  completely  closed  at  the  age  of 
about  four  years. 

The  period  of  life  which  dates  from  birth  to  the  age  of  two  years  is  called  infancy 
At  the  age  of  two  years,  the  transition  takes  place  from  infancy  to  childhood.  The 
child  is  now  able  to  walk  without  assistance,  the  food  is  more  varied,  and  the  digestive 
operations  are  more  complex.  The  special  senses'  and  the  intelligence  become  more 
acute,  and  the  being  begins  to  learn  how  to  express  ideas  in  language.  The  child  gradu- 
ally develops,  and  the  milk-teeth  are  replaced  by  the  permanent  teeth.  At  puberty, 
which  begins  at  from  the  fourteenth  to  the  seventeenth  year — a  little  earlier  in  the 
female — the  development  of  the  generative  organs  is  attended  with  important  physical 
and  moral  changes. 

The  different  ages  recognized  by  the  older  writers  were  as  follows :  Infancy,  from 
birth  to"  the  age  of  five  years ;  adolescence,  or  youth,  to  the  twenty-fifth  year ;  adult 
age,  to  the  thirty-fifth  year ;  middle  life,  to  the  fiftieth  year ;  old  age,  to  the  sixtieth 
yeaf ;  and  then,  extreme  old  age.  A  man  may  be  regarded  at  his  maximum  of  intellect- 
ual and  physical  development  at  about  the  age  of  thirty-five,  and  he  begins  to  decline 
after  the  sixtieth  year,  although  such  a  rule,  as  regards  intellectual  vigor,  would  cer- 
tainly meet  with  numerous  exceptions. 
60 


946  GENERATION. 

We  do  not  propose  to  consider,  in  this  connection,  the  psychological  variations  which 
occur  at  different  ages,  but,  as  regards  the  general  process  of  nutrition,  it  may  be  stated, 
in  general  terms,  that  the  appropriation  of  new  matter  is  a  little  superior  to  disassimila- 
tion  up  to  about  the  age  of  twenty-five  years ;  between  twenty -five  and  forty -five,  these 
two  processes  are  nearly  equal ;  and,  at  a  later  period,  the  nutrition  does  not  completely 
supply  the  physiological  waste  of  the  tissues,  the  proportion  of  organic  to  inorganic 
matter  gradually  diminishes,  and  death  follows,  as  an  inevitable  consequence  of  life.  In 
old  age,  the  muscular  movements  gradually  become  feeble ;  the  bones  contain  an  excess 
of  inorganic  matter ;  the  ligaments  become  stiff;  the  special  senses  are  usually  obtuse  ; 
and  there  is  a  diminished  capacity  for  mental  labor,  with  more  or  less  loss  of  the  memory 
and  of  intellectual  vigor.  It  is  a  curious  fact  that  remote  events  are  more  clearly  and 
easily  recalled  to  the  mind  in  old  age,  than  those  of  recent  occurrence ;  and,  indeed, 
early  impressions  and  prejudices  then  appear  to  be  unusually  strong. 

It  frequently  happens,  in  old  age,  that  some  organ  essential  to  life  gives  way,  and  that 
this  is  the  immediate  cause  of  death ;  or  that  an  old  person  is  stricken  down  by  some 
disease  to  which  his  age  renders  him  peculiarly  liable.  It  is  so  infrequent  to  observe  a 
perfectly  physiological  life,  continuing  throughout  the  successive  ages  of  man,  that  it  is 
almost  impossible  to  present  a  picture  of  physiological  death  ;  but  we  sometimes  observe 
a  gradual  fading  away  of  vitality  in  old  persons,  who  die  without  being  affected  with  any 
special  disease.  It  is  also  difficult  to  fix  the  natural  period  of  human  life.  Some  per- 
sons die,  apparently  of  old  age,  at  seventy,  and  it  is  rare  that  life  is  preserved  beyond 
one  hundred  years.  In  treating  of  the  so-called  vital  point,  we  have  stated  that  there 
does  not  seem  to  be  any  such  occurrence,  except  under  conditions  of  most  extraordinary 
external  violence,  as  instantaneous  death  of  all  parts  of  the  organism.  If  we  confine 
ourselves  to  physiological  facts,  we  cannot  admit  the  existence  of  a  single  vital  principle 
which  animates  the  entire  organism.  Each  tissue  appears  to  have  its  peculiar  property, 
dependent  upon  its  exact  physiological  constitution,  which  we  call  vitality;  a  term 
which  really  explains  nothing.  The  tissues  usually  die  successively,  and  not  simulta- 
neously, nearly  all  of  them  being  dependent  upon  the  circulating,  oxygen-carrying  blood 
for  'the  maintenance  of  their  physiological  properties.  It  has  been  demonstrated,  in- 
deed, that  the  so-called  vital  properties  of  tissues  may  be  restored,  after  apparent  death, 
by  the  injection  of  blood  into  their  vessels. 

After  death,  there  is  often  a  discharge  of  the  contents  of  the  rectum  and  bladder, 
and  parturition,  even,  has  been  known  to  take  place.  The  appearance  which  indicates 
growth  of  the  beard  after  death  is  probably  due  to  shrinking  of  the  skin  and,  perhaps, 
contraction  of  the  smooth  muscular  fibres  attached  to  the  hair-follicles.  The  most 
important  phenomenon,  however,  which  is  observed  before  putrefaction  begins,  is  a  gen- 
eral rigidity  of  the  muscular  system. 

Cadaveric  Rigidity. — At  a  variable  period  after  death,  ranging  usually  from  five  to 
seven  hours,  all  of  the  muscles  of  the  body,  involuntary  as  well  as  voluntary,  become 
rigid  and  can  only  be  stretched  by  the  application  of  considerable  force.  Sometimes, 
especially  after  long-continued  and  exhausting  diseases,  this  rigidity  appears  as  soon  as  a 
quarter  of  an  hour  after  death.  In  the  case  of  persons  killed  suddenly,  while  in  full  health, 
it  may  not  be  developed  until  twenty  or  thirty  hours  after  death,  and  it  then  continues 
for  six  or  seven  days.  Its  average  duration  is  from  twenty-four  to  thirty-six  hours ; 
and,  as  a  rule,  it  is  more  marked  and  lasts  longer,  the  later  it  appears.  In  warm  weather, 
cadaveric  rigidity  appears  early  and  continues  for  a  short  time.  When  the  contraction 
is  overcome  by  force,  after  the  rigidity  has  been  completely  established  and  has  continued 
for  some  time,  it  does  not  reappear.  The  rigidity  of  the  muscular  system  extends  to  the 
muscular  coats  of  the  arteries  and  the  lymphatics.  It  is  for  this  reason  that  the  arterial 
system  is  usually  found  empty  after  death.  The  rigidity  first  appears  in  the  muscles 
which  move  the  lower  jaw ;  then  it  is  noted  in  the  muscles  of  the  trunk  and  neck,  ex- 


CADAVERIC  RIGIDITY.  947 

tends  to  the  arms,  and  finally,  to  the  legs,  disappearing  in  the  same  order  of  succession. 
The  stiffening  of  the  muscles  is  due  to  a  sort  of  coagulation  of  their  substance,  analogous 
to  the  coagulation  of  the  blood,  and  is  probably  attended  with  some  shortening  of  the 
fibres ;  at  all  events,  the  fingers  and  thumbs  are  generally  flexed.  That  the  rigidity  is 
not  due  to  coagulation  of  the  blood,  is  shown  by  the  fact  that  it  occurs  in  animals  killed 
by  hemorrhage. 

According  to  John  Hunter,  the  blood  does  not  coagulate  nor  do  the  muscles  become 
rigid  in  animals  killed  by  lightning  or  hunted  to  death ;  but  it  is  a  question,  in  these 
instances,  whether  the  rigidity  does  not  begin  very  soon  after  death  and  continue  for 
a  brief  period,  so  that  it  may  escape  observation.  As  a  rule,  rigidity  is  less  marked  in 
very  old  and  in  very  young  persons  than  in  the  adult.  It  occurs  in  paralyzed  muscles, 
provided  they  have  not  undergone  extensive  fatty  degeneration. 

Under  ordinary  conditions  of  heat  and  moisture,  as  the  rigidity  of  the  muscular  sys- 
tem disappears,  the  processes  of  putrefaction  commence.  The  various  tissues,  with  the 
exception  of  certain  parts,  such  as  the  bones  and  teeth,  which  contain  a  large  proportion 
of  inorganic  matter,  gradually  decompose,  forming  water,  carbonic  acid,  ammonia,  etc., 
which  pass  into  the  earth  and  the  atmosphere.  The  products  of  decomposition  of  the 
organism  are  then  in  a  condition  in  which  they  may  be  appropriated  by  the  vegetable 
kingdom. 


INDEX. 


PAGE 

Abdominal  plates 914,  916,  920 

Abdominal  salivary  gland 269 

Abducens  (see  Motor-oculi  externus) 614 

Abercrombie,  brain  of. 708 

Absorption 800 

by  blood-vessels 801 

by  the  mucous  membrane  of  the  mouth 801 

by  the  stomach  301 

of  fats 801 

by  the  intestinal  mucous  membrane 302 

of  biliary  salts 284,  302 

of  gases  in  the  intestines 302 

by  lacteal  and  lymphatic  vessels 802 

of  albuminoids  by  the  lacteals 818 

of  glucose  and  salts  by  the  lacteals 313 

of  water  by  the  laoteals 314 

by  parts  not  connected  with  the  digestive  sys- 
tem  314 

by  the  skin 814 

by  the  respiratory  surface 816 

of  substances  by  the  lungs,  in  contagious  diseases  316 

by  closed  cavities,  reservoirs  of  glands,  etc 817 

of  fats  and  insoluble  substances 817,  326 

variations  and  modifications  of 819 

of  fluids  of  greater  density  than  the  blood. . .  819, 827 

of  woorara,  venoms,  etc 819, 327,  358 

of  substances  which  disorganize  the  tissues 320 

influence  of  the  condition  of  the  blood  and  of  the 

vessels  upon 820 

influence  of  the  nervous  system  upon 820,  827 

—  passage  of  liquids  through  membranes  (see  En- 
dosmosis) '. f.  821 

—  application  of  physical  laws  to  the  process  of 826 

Accidental  areolae 807 

Accommodation,  auditory 840 

Accommodation  of  the  eye 798 

changes  of  the  crystalline  lens  in 799 

action  of  the  ciliary  muscle  in 773,  800 

changes  of  the  iris  in 800 

Achromatopsia 787 

Acid  of  the  gastric  juice 238 

Acid  phosphate  of  lime  in  the  gastric  juice 240 

Acoustic  spot 843 

Addison's  disease 481 

Additional  tones 832 

Adipose  tissue 183,  503 

Adolescence 945 

^Esthesiometer 752 

Agassiz,  brain  of 703 

Age,  influence  of,  upon  the  pulse 52 

influence  of,  upon  the  respiratory  movements . . .  132 

influence  of,  upon  the  consumption  of  oxygen. . .  148 

influence  of,  upon  the  exhalation  of  carbonic  acid  147 

influence  of,  upon  the  power  to  resist  depriva- 
tion of  food 172 


Age,  influence  of,  upon  digestion 251 

influence  of,  upon  the  urine 426 

variations  in  the  animal  heat  dependent  upon. . .  510 

Ages  (infancy,  childhood,  youth,  adult  age,  middle 

age,  and  old  age) 945 

Agminated  glands  of  the  small  intestine 263 

Air,  composition  of 140 

proper  allowance  of,  in  hospitals,  prisons,  etc.. . .  142 

in  the  veins  (see  Veins) 108 

Air-cells  of  the  lungs 120 

Air-swallowing 225 

Album  Grsecum 292 

Albumen 177 

action  of  the  gastric  juice  upon 245 

comparative  action  of  the  gastric  juice  upon  raw 

and  coagulated 245 

not  coagulated  by  the  gastric  juice 245 

Albumen-peptone 245 

Albumen,  vegetable 178 

Albuminoids,  action  of  the  intestinal  juice  upon 267 

action  of  the  pancreatic  juice  upon 277,  286 

absorption  of,  by  the  lacteals 813 

Albuminose 246 

Alcohol,  action  of.  in  alimentation  and  nutrition. .  185,  18C 

elimination  of 185 

influence  of,  upon  endurance,  the  power  of  resist 

ance  to  cold,  etc 187,  512 

influence  of,  upon  lactation 870 

influence  of,  upon  the  elimination  of  urea 428 

Alcoholic  beverages,  influence  of,  upon  the  exhalation 

of  carbonic  acid 149 

Aliment  (see  Food) 176 

Alimentation,  general  considerations 171, 176 

Allantois,  formation  of. -. 904 

first  villosities  of. 901 

•  vascularity  of 905 

vascular  villosities  of 905 

Alternate  paralysis 618 

Amandine 179 

Amoeboid  movements 522 

of  the  vitellus 897 

Ammonia,  exhalation  of,  by  the  lungs 154 

Ammonia-theory  of  the  coagulation  of  the  blood 29 

Amnesia 706 

Amnion,  formation  of 901 

villosities  of. 901 

enlargement  of. 908,  905 

Amniotic  fluid 908 

origin  of. 904 

antiseptic  properties  of 904 

Amniotic  umbilicus 901 

Amphioxus  lanceolatus,  an  animal  without  a  brain. . .  696 

Amputation,  sensation  in  members  after 598 

Amyloid  corpuscles 468 

Ana?mia...  185 


INDEX. 


949 


PAGE 

Anaesthesia 746 

Anaesthetics,  influence  of,  upon  glycogenesis 471 

influence  of,  upon  the  sensory  nerves 596,  687 

abolition  of  the  reflex  excitability  ol  the  spinal 

cord  by 687 

Andersen,  ganglion  of. 762 

Anelectrotonus 605 

Angle  alpha 785 

Antihelix  of  the  ear 817 

Animal  food 177 

Animal  heat 506 

limits  of  variation  in  the  normal  temperature  in 

man 507 

variations  of,  with  external  temperature 507 

variations  of,  in  different  parts  of  the  body 508 

variations  of,  at  different  periods  of  life 510 

in  the  newly -born 510 

diurnal  varieties  of 511 

relations  of  digestion  to 511 

in  inanition-. 511 

influence  of  alcohol  upon 512 

—  influence  of  exercise  upon 513 

influence  of  mental  exertion  upon  514 

influence  of  the  nervous  system  upon 514 

influence  of  the  circulation  upon 514 

sources  of. 515 

seat  of  the  production  of. 515 

relations  of,  to  nutrition 516 

relations  of  non-nitrogenized  and   nitrogenized 

food  to 517 

—  relations  of,  to  respiration 5i8 

relations  of,  to  the  consumption  of  oxygen  and 

the  production  of  carbonic  acid 519 

effects  of  division  of  the  sympathetic  nerve  in 

the  neck  upon 514,  519,  737 

intimate  nature  of  processes  giving  rise  to 520 

equalization  of 520 

uses  of  clothing  in  the  equalization  of 520 

equalization  of,  by  cutaneous  transpiration 521 

influence  of  menstruation  upon 876 

Antiperistaltic  movements  of  the  small  intestine 286 

Anti-scorbutics 198 

Antitragus  of  the  ear 817 

Anus,  retractors  of 290 

sphincters  of 291,  297,  298 

development  of 921 

imperforate 921 

Aorta,  development  of 932,  933 

Aortas,  primitive 913,  932,  933 

Aortic  plexus 733 

Aortic  valves 39,  48 

Aphasia 704 

—  cases  of,  in  left  hemiplegia  in  left-handed  per- 
sons    705 

Appendices  epiploicae ., 289 

Appendix  vermiformis 288 

development  of 920 

Appetite  for  food 172 

influence  of  climate  and  season  upon 172 

influence  of  vegetable  bitters  upon 172 

perversion  of,  after  extirpation  of  one  kidney 404 

modifications  of,  by  extirpation  of  the  spleen 478 

—  modifications  of.  by  extirpation  of  one  kidney  and 

in  cases  of  biliary  fistula 479 

Aqueous  humor  of  the  eye 781 

composition  of 782 

restoration  of,  after  its  evacuation 782 

refraction  by 793 

Arachnoid. . .  667 


PAGE 

Arachnoid,  first  appearance  of. 916 

Arantius,  corpuscles  of. 89 

Arbor  vitse  uteri 866 

Arctic  regions,  diet  in 512 

Area  vasculosa  of  the  ovum 981 

Areolar  tissue,  absorption  from 817 

Arms,  development  of 915,  910 

Arnold's  ganglion 731 

Arrow-root 181 

Arseniuretted  hydrogen,  effects  of. 141 

Arteries,  physiological  anatomy  of 64 

mode  of  branching  of G4 

anastomoses  of. 65 

anatomical  divisions  of. 65 

coats  of. 65 

muscular  fibres  of. 66 

vasa  vasorum  of. 67 

nerves  of 67 

lymphatics  not  found  in  the  walls  of. 67 

course  of  the  blood  in 67 

elasticity  of. 67 

gradual  diminution  of  the  intermittency  of  the 

current  in 68 

contractility  of 69 

influence  of  the  sympathetic  nerves  upon 69 

irritability  of. 69 

influence  of  temperature  upon  the  size  of 70 

influence  of  the  resiliency  of,  upon  the  circulation  70 

influence  of  the  contractility  of  the  small  vessels 

upon  the  distribution  of  blood  in  the  tissues 70 

locomotion  of,  and  production  of  the  pulse 70 

tonicity  of 74 

variations  in  the  diameter  of,  at  different  periods 

of  the  day 74 

pressure  of  blood  in 74 

pressure  in  different  vessels 77 

influence  of  respiration  upon  the  pressure  of 

blood  in 77 

—  influence  of  muscular  effort  upon  the  pressure  of 

blood  in 73 

influence  of  haemorrhage  upon  the  pressure  of 

blood  in 78 

rapidity  of  the  flow  of  blood  in 79 

reason  why  they  are  found  empty  after  death.. .  114 

Articular  cartilage 351 

Ary^enoid  muscle 552,  557 

Asphyxia,  influence  of,  upon  the  circulation,  54,  89, 110, 169 

arrest  of  the  action  of  the  heart  in 54, 110, 169 

power  of  resistance  to,  in  the  newly-born,  143, 169, 510 

phenomena  of 168 

influence  of  various  conditions  of  the  system  upon 

the  power  of  resistance  to 170 

Associated  movements 592 

Astigmatism 794 

Atmosphere,  composition  of. 140 

Attollens  aurem 818 

Attrahens  aurem 818 

Audition,  general  considerations 815 

topographical  anatomy  of  the  parts  connected 

with  817 

physics  of  sound  (see  Sound) 853 

function  of  the  external  ear  in 835,  849 

function  of  the  membrana  tympani  in 887 

accommodation  in 840 

action  of  the  ossicles  of  the  ear  in 841 

functions  of  the  semicircular  canals  in 849 

functions  of  parts  contained  in  the  cochlea  in ...  849 

functions  of  the  organ  of  Corti  in 850 

summary  of  the  mechanism  of 851 


950 


INDEX. 


PAGE 

Audition,  development  of  the  organs  of. 919 

A  uditory  meatus,  external 818 

external,  development  of 923 

—  internal 815,  846 

Auditory  nerves,  physiological  anatomy  of. 815 

general  properties  of 816 

galvanization  of. 816 

distribution  of 846 

development  of '. 919 

Auditory  vesicles 919 

Auricle,  of  the  ear 817 

Auricles  of  the  heart 35 

Auriculo-ventricular  valves,  action  of 47 

Autolaryngoscopy  in  the  study  of  the  mechanism  of 

deglutition 223 

in  the  study  of  phonation 554 

Axis-cylinder . .  567 

Azygos  uvulae 217 

Bacillar  membrane 776 

Bacteria 855 

Banting > 502 

Bartholinus,  glands  of. 890 

Barytone' 556 

Bass  voice 556 

Baths,  Turkish  and  Russian 521 

Beard,  apparent  growth  of,  after  death 946 

Boats,  a  cause  of  discord 833 

Beaumont's  table  of  digestibility  of  various  alimentary 

substances  in  the  stomach 250 

Beet-root  sugar 181 

Bellini,  tubes  of 396 

Bertin,  columns  of. 396,  400 

.De^oin  de  respirer 1C4,  660,  727 

Bicarbonate  of  soda 497 

Bicuspid  teeth 201 

Bile,  action  of,  in  digestion 277 

—  color,  reaction,  and  specific  gravity  of 230 

•  influence  of,  upon  the  faeces  and  upon  the  peri- 
staltic movements  of  the  intestine 2S3,  236 

influence  of,  upon  the  digestion  and  absorption 

of  fats 283 

absorption  of  the  salts  of,  by  the  intestinal  canal.  2S4 

variations  in  the  flow  of 234 

resorption  of. 317,  327 


— -  coloring  matter  of. 448 

mechanism  of  the  secretion  and  discharge  of 439 

secretion  of,  by  the  liver-cells 439 

secretion  of,  from  venous  or  arterial  blood 440 

quantity  of 441* 

variations  in  the  flow  of 441 

influence  of  digestion  upon  the  flow  of. 441 

excretory  function  of 450 

general  properties  of 442 

color,  reaction,  and  specific  gravity  of 442 

composition  of 442,  443 

: excretory  and  secretory  constituents  of 443 

inorganic  salts  of. 443 

fatty  and  saponaceous  constituents  of 443 

cholesterine  of 446 

—  organic  salts  of. 280,  444 

tests  for 449 

Biliary  acids 444 

Biliary  fistula 278,  281 

nutrition  in  a  case  of 173 

influence  of,  upon  the  appetite 479 

Biliary  salts 280,  444 

absorption  of,  by  the  intestinal  canal 284,  302 


Biliary  salts,  origin  of 440 

—  test  for 449 

Biliverdine 448 

—  test  for 449 

Binocular  vision 802. 

fusion  of  colors 805 

Bitters,  influence  of,  upon  the  appetite 172 

"Black-hole"  of  Calcutta 170 

Bladder,  urinary,  physiological  anatomy  of 407 

—  muscular  coats  of 408 

sphincter  of. 408 

corpus  trigonum 408 

uvula  of 408 

—  blood-vessels  of 408 

lymphatics  of 409 

contractions  of 409 

absorption  by 317 

mucus  of 357 

first  appearance  of 907,  920 

Blastoderm,  formation  of  the  cells  of 899 

Blastodermic  membranes 900,  913 

Blepharoptosis 611,  812 

Blind  spot  of  the  retina 792 

Blood,  general  considerations 1 

extra-vascular"  tissues 1 

effects  of  abstraction  and  subsequent  return  of. .      1 

transfusion  of 2 

quantity  of 2 

relative  quantity  of,  in  animals  during  digestion 

and  fasting 4 

influence  of  abstinence  from  food  upon  the  quan- 
tity of 4 

opacity  of 4 

odor  of,  and  development  of  odor  of,  by  sul- 
phuric acid 4 

taste  of 4 

reaction  of 4 

— r-  specific  gravity  of 4 

temperature  of. 5 

color  of 5, 155 

variations  in  the  color  of,  in  the  vascular  system  5,  155 

color  of,  in  veins  coming  from  glands 6,  344,  347 

anatomical  elements  (corpuscles)  of 6 

plasma  of,  or  liquor  sanguinis 6 

specific  gravity  of  the  plasma  of 7 

red  corpuscles  of $ 

specific  gravity  of  the  red  corpuscles  of 7 

discovery  of  the  red  corpuscles  of 8 

size  of  the  red  corpuscles  of 8 

relations  of  the  size  of  the  red  corpuscles  of,  to 

muscular  activity  in  different  animals 9 

table  of  measurements  of  the  red  corpuscles  of, 

in  different  animals 9 

enumeration  of  the  red  corpuscles  of 10 

post-mortem  changes  in  the  red  corpuscles  of. . .     11 

method  for  restoring  the  form  of  the  red  cor- 
puscles of,  after  their  desiccation 11 

structure  of  the  red  corpuscles  of. 12 

development  of  the  red  corpuscles  of 12.  931 

red  corpuscles  of,  in  the  foetus 12,  931 

nucleated  corpuscles  of 12,  931 

relations  of  leucocytes  to  the  development  of  the 

red  corpuscles  of 12 

thebry  of  destruction  of  the  red  corpuscles  of, 

for  the  production  of  pigment 12 

relations  of  the  spleen  to  the  blood-corpuscles. . .     13 

function  of  the  red  corpuscles  of 13, 156, 160 

capacity  of  the  red  corpuscles  of,  for  the  absorp- 
tion of  oxygen,  as  compared  with  the  plasma,  13, 156, 160 


INDEX. 


951 


PAGE 

Blood,  action  of  the  red  corpuscles  of,  as  respiratory 

organs 13 

leucocytes,  or  white  corpuscles  of 13 

— —  situations  in  which  leucocytes  are  found 14 

appearance  and  characters  of  leucocytes 14 

—  quantity  of  leucocytes  as  compared  with  that  of 
the  red  corpuscles 14 

—  variations  in  the  proportions  of  leucocytes 14  j 

proportion  of  leucocytes  in  the   blood  of  the 

splenic  veins 15 

—  specific  gravity  of  the  leucocytes  of 15 

development  of  leucocytes 15 

elementary  corpuscles  of . 15 

composition  of  the  red  corpuscles  of : 16 

analysis  of : 19 

table  of  composition  of  the  blood-plasma 19 

proximate  principles  of. 20 

inorganic  principles  of 21 

functions  of  water  in 21 

functions  of  chloride  of  sodium  in 21 

functions  of  other  inorganic  salts  in  21 

organic  saline  principles  in 21 

—  organic  non-nitrogenized  principles  in 21 

excreinentitious  matters  in 21 

fats  and  sugars  in „ 22 

organic  nitrogenized  principles  in 22 

plasnaine,  fibrin,  metalbumen,  and  serine  in 22 

peptones  in 23 

coloring  matter  of  the  plasma  of 23 

coagulation  of. 24 

clot  and  serum  of 24 

: J'ormation  of  the  clot  in 24 

proportions  of  clot  and  serum 24 

characters  of  the  clot  of 25 

characters  of  the  serum  of. 25 

coagulatory  principle  of 25 

circumstances  which  modify  coagulation  of,  out 

of  the  body 26 

influence  of  temperature,  chemicals,  etc.,  upon 

the  coagulation  of 26 

coagulation  of,  in  the  organism 26 

coagulation  of,  in  animals  killed  by  lightning  or 

hunted  to  death 26 

coagulation  of,  in  the  heart  and  vessels 27 

coagulation  of,  in  the  serous  cavities  and  in  tha 

Graafian  follicles 27 

office  of  the  coagulation  of,  in  the  arrest  of 

haemorrhage 27 

cause  of  the  coagulation  of 28 

theory  that  coagulation  of,  is  due  to  the  evapora-  • 

tion  of  ammonia 28 

other  theories  of  the  coagulation  of 28 

decomposition  of  plasmine  into  fibrin  and  metal- 
bumen    29 

non-coagulation  of,  when  drawn  by  tire  leech ...  30 

fibrillation  of  fibrin  in  coagulation  of 30 

non-coagulation  of,  in  the  renal  and  hepatic  veins 

and  in  the  capillaries 30, 472 

circulation  of  (see  Circulation) 31 

function  of,  in  respiration 115 

"changes  in,  in  respiration  (see  Respiration) 155 

difference  in  color  between  arterial  and  venous. .  155 

absorption  of  oxygen  by  the  red  corpuscles  of. .  156 

gases  of. 156 

nitrogen  in 1 60 

condition  of  the  gases  in 160 

general  differences  in  the  composition  of  arterial 

and  venous 161 

influence  of  the  condition  of,  upon  absorption . . .  320 


PAGE 
Blood,  influence  of  the  composition  and  pressure  of, 

upon  secretion ,   . .  34(5 

changes  of,  in  passing  through  the  kidneys 4C6 

changes  in  the  albuminoid  and  corpuscular  con- 
stituents of,  in  passing  through  the  liver 472 

changes  in,  in  passing  through  the  spleen 477 

relations  of,  to  muscular  irritabilit/ 587 

Blood-corpuscles,  development  of,  in  the  ovum 631 

Blood-vessels,  absorption  by ,. . .  301 

first  formation  of,  in  the  blastodermic  layers 930 

Bones,  action  of  the  gastric  juice  upon 249 

anatomy  of 543 

fundamental  substance  of 544 

Haversian  rods  of 544 

Haversian  canals  of 544 

Iacuna3  of 545 

—  osteoplasts  and  canaliculi  of 545 

marrow  of 546 

blood-vessels  of 547 

periosteum  547 

regeneration  of,  by  transplantation  of  periosteum  547 

Bone-corpuscles 545 

Botal,  foramen  of 934 

Boys,  voice  of 556 

Brain,  circulation  in 100 

•  contraction  and  expansion  of,  with  the  acts  of 

respiration '.  107,  668 

peculiarity  of  the  small  vessels  of 107,  583,  668 

lymphatics  of 306 

variations  in  the  quantity  of  blood  in 667 

ganglia  of 688,  690 

—  weight  of  different  parts  of 6S9 

difference  in  the  weight  of,  in  the  sexes 689 

differences  in  the  weight  of,  at  different  ages —  690 

specific  gravity  of 690 

some  pouits  in  the  physiological  anatomy  of 690 

directions  of  the  fibres  in 601 

table  of  weights  of,  in  white  and  black  races 702 

table  of  weights  of,  in  various  individuals 702 

state  of  knowledge  concerning  the  functions  of 

the  piueal  gland,  pituitary  body,  corpus  callosurn, 

septum  lucidum,  ventricles,  and  hippocampi  of 728 

rolling  and  turning  movements  following  injury 

of  certain  parts  of 728 

Branchial  arches £33 

Bread,  made  from  gluten 179 

Bread,' digestibility  of 251 

Breathing  capacity,  extreme 187 


846 
121 
866 
118 
922 


Breschet,  perilymph  and  endolymph  of. 

Bronchial  arteries 

mucus 

tubes 

tubes,  development  of. . . 

Bronzed  skin 481 

Brunner,  glands  of 260,  267 

Buccal  glands 209 

Buccinator  nluscle,  action  of,  in  mastication 205 

Bursae  mucosae 351 

synovial 851 

Butter 1S3 

composition  of 874 

Butyrine 375 

Byron,  brain  of 702 

Cadaveric  rigidity 946 

Caecum 280 

development  of 920 

Caffeine 189 

Calorification  (see  Animal  heat) 596 


952 


INDEX. 


PAGE 

Canals  of  Cuvier 933 

Cane-sugar 180 

Canine  teeth •. 201 

Calcutta,  "black-hole"  of 170 

•Capillaries,  circulation  in 81 

physiological  anatomy  of 82 

epithelium  of 82 

stomata  in  the  walls  of 82 

size  of 82 

capacity  of  the  system  of. 84 

course  of  blood  in 84, 87 

study  of  the  circulation  in,  with  the  microscope 

(note) 85 

"  still  layer"  in 86 

circulation  in,  in  the  lungs * 88 

rapidity  of  the  flow  of  blood  in 89 

relations  of  the  circulation  in,  to  respiration 89 

causes  of  the  circulation  in 90 

Capillary  attraction 323 

blood,  non-coagulation  of. 30 

power,  so-called 90 

influence  of  temperature  upon  the  circulation  in    91 

influence  of  direct  irritation  upon  the  circula- 
tion in 91 

phenomena  of  inflammation  observed  in 92 

Capriline 875 

Caprine 375 

Caproi'ne 375 

Capsicum 190 

Caput  coli 288 

Carbon,  quantity  of,  necessary  to  nutrition 192 

Carbonate  of  lime 495 

table  of  quantities  of 496 

origin  and  discharge  of 496 

of  magnesia 497 

of  potassa 497 

of  soda,  function  of 496 

of  soda,  origin  and  discharge  of 496 

Carbonic  acid,  small  proportion  of,  in  the  air 140 

relations  of  the  consumption  of  oxygen  to  the 

production  of 143, 152 

exhalation  of,  in  respiration  (see  Kespiration) 144 

sources  of,  in  the  expired  air 153 

analysis  of  the  blood  for 157 

proportion  of,  in  the  blood 159 

disengagement  of,  by  the   action  of  pneumic 

acid 153, 160 

condition  of,  in  the  blood 160 

sources  of,  In  the  blood 160 

action  of  the  phosphate  of  soda  upon  the  capacity 

of  absorption  of,  by  the  blood 160 

effects  of  accumulation  of,  in  the  atmosphere 169 

in  milk 375 

relations  of  the  production  of,  to  animal  heat 519 

Carbonic  oxide,  effects  of. 141, 167, 169 

use  of,  in  analysis  of  the  blood  for  oxygen. 

158,  160 

Cardiac  plexus 733 

Cardinal  veins 933 

Cardiometer 46,  76 

Carotid  plexus 733 

Carotids,  development  of. 933 

Cartilage 548 

articular 351 

cells  and  cavities 549 

of  Meckel 919,  923 

Cartilagine 177 

Caruncula 812 

•Caseine 177,  374 


PAGE 

Caseine,  vegetable 179 

action  of  the  gastric  juice  upon 246 

action  of  reagents  upon 874 

coagulation  of,  by  the  mucous  membrane  of  the 

stomach 374 

Caseine-peptone 246 

Casper  Hauser,  case  of 803 

Castration,  effects  of,  upon  the  voice 556 

Catelectrotonus 605 

Cavernous  plexus 733 

Cellulose 182 

Cement  of  the  teeth 199,  925 

Cephalo-rachidian  fluid 107,  667,  668 

situation  of 107 

quantity,  properties,  composition,  and  functions 

of. 668 

effects  of  removal  of. 668 

Cereals 179, 1S1,  183 

proportion  of  fat  in 183 

Cerebellum,  weight  of 690,  706 

physiological  anatomy  of 706 

comparative  weight  of,  in  the  sexes 706 

course  of  the  fibres  in 707 

general  properties  of. 708 

functions  of. 708 

extirpation  of,  in  animals 709 

influence  of,  upon  muscular  coordination 709 

recovery  of  coordinating  power  after  removal  of 

a  portion  of. 710 

pathological  facts  bearing  upon  the  function  of. .  712 

analysis  of  Andral's  ninety -three  cases  of  disease 

of.. 712 

additional  cases  of  disease  of 715 

connection  of,  with  the  generative  function 719 

comparative  size  of,  in  stallions,  mares,  and  geld- 
ings   719 

movements  of  the  uterus,  testicles,  etc.,  follow- 
ing irritation  of 719 

comparative  development  of,  in  the  lower  ani- 
mals   719 

development  of 917 

Cerebral  vesicles,  formation  of. 917 

Cerebrate  of  soda 584 

Cerebric  acid 584 

Cerebrine 584 

Cerebro-spinal  axis,  general  arrangement  of. 666 

Cerebro-spinal  fluid  (see  Cephalo-rachidian  fluid).  667,  668 

Cerebrum,  case  of  supposed  regeneration  of 585 

weight  of. 690 

physiological  anatomy  of  (see  Brain) 692 

motor  and  sensory  cells  of 693 

general  properties  of 693 

motor  centres  in  693 

functions  of. 694 

extirpation  of,  in  animals 695 

absence  of,  in  the  amphioxus  lanceolatus 696 

absence  of  intellectual  faculties  in  animals  after 

removal  of 697 

pathological  facts  bearing  upon  the  functions  of  699 

in  idiots 700 

comparative  development  of,  in  the  lower  ani- 
mals    701 

—  comparative  development  of,  in  different  races  of 

men  and  in  different  individuals 701 

location  of  the  faculty  of  articulate  language  in. .  704 

development  of 917 

development  of  the  convolutions  of 918 

development  of  the  ventricles  of 918 

Cervix  uteri,  mucous  membrane  of 865 


INDEX. 


953 


PAGE    I 

Cervix  uteri,  erectile  tissue  of. 86T 

action  of,  in  coitus 890 

production  of  mucus  by,  in  coitus 891 

Cerumen 363 

Ceruminous  glands 360 

Cheeks,  action  of,  in  mastication 204,  205 

Cheese 17T 

from  peas 179 

Chest-register 559 

Chick,  development  of. 912 

Childhood 945 

Chloride  of  potassium 494 

Chloride  of  sodium,  function  of,  in  alimentation. .  184,  191 

table  of  quantities  of. 492 

general  functions  of 492 

effects  upon  animals  of  deprivation  of 493 

origin  and  discharge  of 493 

Chlorides,  diminution  of,  in  the  urine 422 

Chocolate 190 

Choleic  acid 280, 444 

Cholesteriue 280 

transformation  of,  into  stercorine 295 

in  the  faeces  of  animals  in  starvation,  in  hibernat- 
ing animals,  and  in  the  meconium 295 

in  the  bile 446 

extraction  of 447 

origin  of,  by  disassimilation  of  the  nervous  tissue  451 

comparative  quantity  of,  in  the  bood  going  to 

and  coming  from  the  brain 451 

comparative  quantity  of,  in  the  blood  upon  the 

two  sides  of  the  body,  in  cases  of  hemiplegia 453 

elimination  of,  by  the  liver 454 

comparative  quantity  of,  in  the  blood  going  to 

and  coming  from  the  liver 455 

proportion  of,  in  the  blood  in  cases  of  grave  and 

of  simple  icterus 457 

proportion  of,  in  the  blood  in  cases  of  cirrhosis.  457 

poisoning  by  injection  of,  into  the  blood 458 

Cholesteraemia 458 

Cholic  acid 280,  444 

Chondrine 177,  548 

Chorda  dorsalis 913, 914 

Chorda  tympani 622,  760 

influence  of,  upon  gustation 622,  761 

influence  of,  upon  the  submaxillary  gland 623 

general  properties  of 760 

Chords  in  music 832 

Chorion  of  the  ovum,  formation  of 901,  904 

disappearance  of  villi  from  a  portion  of 905 

Choroid 771 

vasa  vorticosa  of 772 

Chromatic  aberration 790 

Chyle 334 

specific  gravity  of 335 

coagulation  of. 835 

table  of  composition  of 336 

urea  in ". 336 

comparison  of  constituents  of,  with  those  of 

lymph 837 

microscopical  characters  of 337 

—  movements  of  (see  Lymph) 337 

Chyle-corpuscles 13 

Cilia , 523 

Cilia  (eyelashes) 811 

Ciliary  ganglion 731 

Ciliary  movements ^23 

Ciliary  muscle f  73 

Ciliary  nerves ?31 

Ciliary  processes 773 


PAGE 

Ciliated  epithelium 354 

Cilio-spinal  centre 793 

Circulation  of  the  blood 81 

discovery  of gl 

action  of  the  heart  in  (see  Heart) 40 

in  the  arteries  (see  Arteries) 64 

depressor-nerve  of 78,  655 

in  the  capillaries  (see  Capillaries) 81 

in  the  veins  (see  Veins) 92 

in  the  cranial  cavity 106 

derivative 108 

pulmonary 109 

in  the  walls  of  the  heart 110 

general  rapidity  of HO 

- —  relations  of  the  frequency  of  the  heart's  action 

to  the  rapidity  of 112 

phenomena  of,  after  death 113 

influence  of,  upon  the  movements  of  the  small 

intestine 287 

influence  of,  upon  absorption 320 

influence  of,  upon  animal  heat 514 

effects  of  section  of  the  pneumogastrics  upon . .  653 

effects  of  galvanizing  the  pneumogastrics  or  then- 
branches  upon 654 

i —  reflex  influence  upon,  through  the  pneumogas- 


trics , 


influence  of  the  sympathetic  system  upon 788 

first  appearance  of,  in  the  embryon 932 

foetal  (see  Foetal  circulation) 985 

Circulation  of  the  lymph  and  chyle  (see  Lymph) 338 

Circulatory  system,  development  of 980 

Circumflexus,  or  tensor-palati  muscle 821 

Cirrhosis,  proportion  of  cholesterine  in  the  blood  in 

cases  of 457 

Cleft  palate 562,924 

Climate,  influence  of,  upon  the  diet 172, 193,  512 

Clitoris 869 

development  of 980 

Cloaca 920,  930 

Clot  of  blood  (see  Blood) 24 

non-organization  of 27,  80 

Clothing,  uses  of. 520 

Coagulation  of  the  blood  (see  Blood) . .. 24 

Coccyx,  consolidation  of 914 

Cochlea,  bony 

bony,  modiolus  of 

bony,  hamulus  of 823,  844 

membranous 844 

membrana  basilaris  of. 844 

scala  tympani  and  scala  vestibuli  of 844 

limbus  laminae  spiralis  of 844 

membrana  tectoria  (membrane  of  Corti)  of 844 

membrane  of  Eeissner  of 844 

the  true  membranous 845 

quadrilateral  canal  of 846 

cupola  of 846 

distribution  of  the  nerves  in 846 

functions  of,  in  audition 849 

Cocoa I90 

Cocoa-shells 190 

Coffee,  influence  of,  upon  the  exhalation  of  carbonic 

acid 149 

composition  of 187 

influence  of,  upon  nutrition 188 

influence  of,  upon  the  elimination  of  urea.. .  188, 428 

Coitus,  influence  of,  upon  the  rupture  of  Graafian  fol- 
licles   872 

action  of  the  male  in 888 

physiological  frequency  of 888 


954 


INDEX. 


PAGE 

Coitus,  action  of  the  female  in 889 

action  of  the  cervix  and  ps  uteri  in 890 

production  of  mucus  in  the  cervix  uteri  in 891 

establishment  of  a  "  continuous  canal  "in 891 

Colon 283 

development  of 920 

Colors 186 

complementary 787 

theory  of  the  appreciation  of. 787 

inability  to  distinguish 787 

binocular  fusion  of 805 

fusion  of,  in  vision 806 

duration  of  impressions  of. 806 

Colostrum 376 

cream  from *. 377 

relations  of  the  subsequent  secretion  of  milk  to 

the  quantity  of 378 

Colostrum-corpuscles 377 

Columnar  epithelium 354 

Combustion,  definition  of,  as  it  occurs  in  the  organism  515 

Combustion-theory  of  respiration 163 

Complemental  air 137 

Concha  of  the  ear 817 

Condiments 190 

Cone-fibre  plexus 777 

Cones  of  the  retina 776,791 

Conjunctiva 812 

mucus  of 357 

Connective  tissue 531 

relations  of  the  lymphatics  to 310 

Conoidal  epithelium 354 

Consonance 834,  837 

Consonants 562 

Contagious  diseases,  absorption  of  agents  producing, 

from  the  respiratory  surface 316 

Continuous  canal,  establishment  of,  in  coitus 891 

Contractility 535 

Contralto 556 

Cooking,  development  of  savors  in 177 

Coordination  of  muscular  action,  connection  of  the 

posterior  white  columns  of  the  spinal  cord  with  679,  711 
connection  of  the  cerebellum  with  (see  Cerebel- 
lum)    709,  718 

Copulation  (see  Coitus) 837 

influence  of,  upon  the  ruptus-e  of  Graafian  folli- 
cles   ' 871,  872 

Corium  (see  Skin) 331 

Cornea 771 

anterior  elastic  lamella  of 771 

membrane  of  Descemet  or  of  Demours 771 

blood-vessels  of. 771 

lymph-spaces  of 771 

wandering  cells  of. 771 

terminations  of  the  nerves  in 771 

refraction  by 793 

development  of. 919 

Corneal  corpuscles 771 

Coronary  arteries,  arrest  of  the  action  of  the  heart  by 

ligation  of. 57 

Corpora  amylacea 535 

Corpora  striata,  physiological  anatomy  of. 720 

functions  of , 721 

development  of 918 

Corpulence,  effect  of  diet  upon 502 

Corpus  dentatum  of  the  cerebellum , 706 

- —  of  the  medulla  oblongata 724 

Corpus  Highmorianum 880 

Corpus  innominatum  (organ  of  Giraldes) 882 

Corpus  luteum,  first  appearance  of. 870 


PAGE 

Corpus  luteum,  general  characters  of 877 

in  pregnancy 878 

measurements  of,  in  menstruation  and  in  preg- 
nancy   879 

Corpus  trigonum 408 

Corpuscles  of  Arantius 39 

Corpuscles  of  the  blood  (see  Blood) , 6 

Corresponding  points  in  vision 802,  803,  610 

Corti,  membrane  of 844 

ganglion  of 847 

organ  of 847 

rods,  or  pillars  of 847 

function  of  the  organ  of 850 

Cotugno,  humor  of 846 

Cotyledons  of  the  placenta 910 

Coughing 134 

Cowper,  glands  of 883 

Cranial  nerves ...  608 

anatomical  classification  of 608 

physiological  classification  of. 609 

Cranium,  circulation  in 106 

development  of. 915 

Cream 371 

from  colostrum 377 

Creatine 418 

change  of,  into  urea  and  sarcosine 419 

Creatinine 419 

Cremaster  muscle 880,  928 

Crico-arytenoid  muscles •. 551,  557 

lateral 551,  553,  557 

posterior 552 

Crico-thyroid  muscles 552,  557 

Cromwell,  brain  of. 702 

Crusta  petrosa  of  the  teeth 199 

Crying 125 

Crystalline  (organic  substance  of  the  lens) 781 

Crystalline  lens 779 

suspensoiy  ligament  of 773,  779,  781 

capsule  of 780 

liquid  of  Morgagni  of. 780 

stars  of. 780 

refraction  by 793 

changes  of,  in  accommodation , . .  799 

development  of 919 

Cumulus  proligerus 863 

Cupola  of  the  cochlea 846 

Curare  (see  Woorara) 595 

Curling  arteries  of  the  placenta 911 

Cuticle  (see  Skin'' 381 

Cutis  vera  (see  Skin) 881 

Cuvier,  brain  of 702 

canals  of 9S3 

Cyanosis 938 

Cystine 421 

in  the  fa?ces 293 

Dacryoline 814 

Daltonism 787 

Dartoic  fibres 525 

Dartos 880 

Death,  definition  of,  etc 946 

discharge  of  contents  of  the  bladder  and  rectum 

1    after 946 

Apparent  growth  of  the  beard  after. . .  .• 946 

after  breaking  up  the  medulla  oblongata 727 

parturition  after 946 

Decidua  vera 907 

reflexa 907 

serotina 911 


INDEX. 


955 


PAGE 

Decidme,  formation  of 90T 

Defalcation 296 

conditions  which  precede  the  desire  for 29T 

muscular  action  in 29T,  298 

Deglutition,  uses  of  the  epiglottis  in 117 

action  of  the  tongue  in 204,  219 

—  influence  of  the  saliva  upon 214 

physiological  anatomy  of  the  parts  concerned  in.  215 

mechanism  of 218 

—  first  period  of 218 

effects  of  section  of  the  sublingual  nerves  upon. .  219 

in  cases  of  absence  of  the  tongue 219 

—  second  period  of 219 

action  of  the  constrictors  of  the  pharynx  in  the 

second  period  of 220 

protection  of  the  posterior  nares  during 220 

•  protection  of  the  opening  of  the  larynx  dur- 
ing   220,  224 

relations  of,  to  respiration 220 

action  of  the  epiglottis  in 221 

influence  of  the  sensibility  of  the  top  of  the 

larynx  in  protecting  the  opening  during 221 

study  of,  by  autolaryngoscopy 223 

third  period  of 224 

action  of  the  oesophagus  in. 224 

length  of  time  occupied  in 224 

character  of  the  movements  of 225 

—  in  the  inverted  posture 225 

of  air 225 

influence  of  the  pneumogastric  nerves  upon. . . .  252 

influence  of  the  spinal  accessory  nerves  upon. . .  631 

influence  of  the  sublingual  nerves  upon 684 

influence  of  the  superior  laryngeal  branches  of 

the  pneumogastrics  v.pon 651 

influence  of  the  inferior  laryngeal  branches  of  the 

pneumogastrics  upon 653 

Demours,  membrane  of 771 

Dental  bulb 925 

follicle 925 

Dentine 199,  925 

Depressor-nerve  of  the  circulation 78,  655 

Derivative  circulation 108 

Derma  (see  Skin) 381 

Descemet,  membrane  of 771 

Development  of  the  embryon  (see  Embryon) 911 

after  birth 945 

Dextral  preeminence 944 

Dextrine 182 

Diabetes,  artificial 405,  470,  663 

Diaphragm 121, 123 

action  of,  in  inspiration 124 

influence  of  contraction  of,  upon  the  size  of  the 

opening  for  the  oesophagus 125 

development  of 921 

Diaphragmatic  hernia,  congenital -. 921 

Diastase 182 

animal,  action  of,  upon  starch 214 

Dicrotism  of  the  pulse 73,  74 

Diet  (see  Food) 191 

regulation  of,  in  hospitals,  etc 192 

influence  of,  upon   the  development  of  power 

and  endurance 498 

variations  in,  in  different  climates. 512 

in  arctic  regions 512,  518 

Diffusion  of  liquids 324,  326 

Digestion,  influence  of,  upon  the  proportion  of  leuco- 
cytes in  the  blood 15 

influence  of,  upon  the  pulse : .    52 

influence  of,  upon  the  exhalation  of  carbonic  acid .  148 


PAGE 

Digestion,  general  considerations 195 

duration  of 195 

general  view  of  the  organs  of 195 

successive  action  of  the  various  digestive  fluids 

in 242 

action  of  the  saliva  in  (see  Saliva) 206 

action  of  the  gastric  juice  in  (see  Gastric  juice). .  242 

of  nitrogenized  alimentary  principles. . .  243,  267,  277 

duration  of,  in  the  stomach 249 

circumstances  which  influence 251 

influence  of  exercise  upon 251 

influence  of  sleep  upon 251 

influence  of  haemorrhage  upon .. 251 

influence  of  inanition  upon 251 

influence  of  age  upon 251 

in  the  small  intestine 257,  267,  273 

action  of  the  intestinal  juice  in  (see  Intestinal 

juice) 267 

action  of  the  pancreatic  juice  in  (see  Pancreatic 

juice) 273 

action  of  the  bile  in  (see  Bile) 277 

influence  of,  upon  the  quantity  of  lymph 329 

influence  of,  upon  the  flow  of  bile 441 

influence  of,  upon  the  glycogenic  function  of  the 


liver 


469 

-  influence  of,  upon  the  volume  of  the  spleen.  .  .'.  .  477 

-  influence  of,  upon  animal  heat  .................  511 

Digestive  fluids  in  the  foetus  ....................  921,  944 

Digitalis,  want  of  action  of,  upon  the  heart,  after  sec- 

tion of  the  pneumogastrics  ...................  654,  665 

Dilator  tubse  muscle  ..............................  821 

Disassimilation,  products  of  ........................  505 

-  table  of  products  of  ...........................  506 

Discords  ..........................................  833 

Discus  proligerus  ..................................  863 

Dissepiments  of  the  placenta  .......................  910 

Diurnal  variations  in  the  urine  ......................  427 

Dorsal  plates  ..................................  913,  915 

Double  vision  .....................................  802 

Dreams  ...........................................  744 

Drinking,  mechanism  of  ...........................  197 

Drinks  ............................................  184 

-  influence  of,  upon  the  urine  ....................  427 

Duct  of  Muller,  development  of,  Into  the  Fallopian 

tube  ............................................  927 

Ductless  glands  ....................................  472 

-  enumeration  of  ...............................  473 

Ductus  arteriosus  ..............................  932,  933 

-  closure  of  .....................................  938 

-  venosus,  closure  of  ............................  9§ 

Duodenum  .........................................  257 

-  glands  of  ......................................  260 

Dupuytren,  brain  of  ................................  703 

Dura  mater  ........................................  667 

-  first  appearance  of  ............................  916 

Ear,  glanda  of  .....................................  360 

-  uses  of  the  hairs  at  the  opening  of.  .............  390 

-  disease  of  the  semicircular  canals  of  ............  718 

-  lobule  of.  .................  ....................  817 

Ear,  external  ......................................  817 

-  uses  of.  ..................................  835,  849 

-  muscles  of.  ...................................  818 

Ear,  middle,  general  arrangement  of  the  parts  in  ....  818 

--  arrangement  of  the  ossicles  of  .................  819 

-  fenestra  ovalis  and  fenestra  rotunda  of.  .........  819 

-  muscles  of  ..............  *  .....................  820 

-  arrangement  of  the  tympanic  membrane  in  (see 
Tympanic  membrane)  ...........................  835 


956 


INDEX. 


Ear,  middle,  development  of 919,  923 

Ear,  internal 822 

physiological  anatomy  of. 842 

distribution  of  the  nerves  in 846 

liquids  of. 846 

hair-cells  of. 848 

Ear,  functions  of  different  parts  of 849 

Ear,  internal,  development  of 919 

Effort,  muscular 54^ 

Eggs,  digestibility  of 251 

Eighth  cranial  nerve,  third  division  of  (see  Spinal  ac- 
cessory nerve) 627 

second  division  of  (see  Pneumogastric) 644 

first  division  of  (sse  Glosso-pharyngeal) 761 

Ejaculatory  ducts 883 

Elastic  tissue 525 

Electric  current  in  muscles 542 

Electricity,  action  of,  upon  the  nerves 599 

action  of  direct  and  inverse  currents  of,  upon  the 

nerves 600 

action   of   a   constant    current   of,   upon    the 

nerves 600,  603 

Electrotonus 603 

Embryon,  primitive  trace  of. 899,  900 

development  of. 911 

time  when  it  becomes  the  fetus 911,  940 

general  view  of  the  development  of 912 

size,  weight,  and  development  of,  at  different 

stages  of  utero-gestation 940 

Embryonic  spot 900 

Embryo-plastic  elements 532 

Enamel  of  the  teeth 199 

Enamel-organ 925 

Encephalic  circulation 106 

Encephalon  (see  Brain) 6SS 

development  of 917 

Endocardium 35 

Endolymph  of  the  labyrinth 846 

Endosmometer 323 

Endosmosis 321 

influence  of  membranes  upon 323,  325 

through  porous  septa 828 

influence  of  different  liquids  upon 825 

Epidermis  (see  Skin) 332 

first  appearance  of 916 

Epididyinis 880,  881 

development  of,  from  a  portion  of  the  Wolffian 

body... 928 

Epiglottis,  uses  of,  in  deglutition 117 

cases  of  loss  of 118 

action  of,  in  deglutition 221 

removal  of,  from  the  lower  animals 222 

cases  of  loss  of,  in  the  human  subject 222 

action  of,  in  phonation 553 

development  of 923 

Epithelium,  action  of,  in  the  absorption  of  fats 318 

glandular 343 

pavement,  mucous  membranes  covered  with 353 

columnar,  or  conoidal,  mucous  membranes  cov- 
ered with „ 354 

ciliated,  mucous  membranes  covered  with. .  354,  523 

mixed,  mucous  membranes  covered  with 354 

influence  of,  upon  the  absorption  of  venoms 357 

Erect  impressions  of  images  inverted  on  the  retina. . .  801 

Erectile  organs,  structure  of 108 

tissues,  circulation  in 107 

tissue  of  the  uterus  and  ovaries 666 

of  the  external  female  organs  of  generation 869 

Erection,  mechanism  of 108 


PAGE 

Erection,  of  the  penis S89 

mechanism  of. , 889 

nerve  of 889 

of  the  cervix  uteri  in  coitus 890 

Eructation 256 

Eunuchs,  voice  of 556 

Eustachian  tube 821 

muscular  action  in  dilatation  of 821 

Eustachian  valve .36,  934 

disappearance  of 988 

Excito-motor  action 683 

Excrementitious  matters  in  the  blood. . ., 22 

Excrementitious  principles 505 

table  of 506 

Excretine 293 

Excretion,  distinction  of,  from  secretion 342,  346 

mechanism  of. 346 

general  considerations 379 

Excretoleic  acid. . , 293 

Excretory  function  of  the  liver 450 

Exercise,  influence  of,  upon  the  pulse 53 

influence  of,  upon  the  exhalation  of  carbonic 

acid 150 

influence  of,  upon  digestion 251 

influence  of,  upon  the  urine 428 

development  of  power  and  endurance  by 498 

influence  of,  upon  animal  heat 513 

Exosmosis 322 

Expiration 128 

action  of  the  elasticity  of  the  parenchyma  of  the 

lungs  in 129 

action  of  the  elasticity  of  the  thoracic  walls  in. . .  129 

tabte  of  muscles  of 130 

action  of  the  abdominal  muscles  in 131 

relations  of,  to  inspiration 133 

duration  of 133 

Expression,  nerve  of  (see  Facial  nerve) 618 

Eye,  physiological  anatomy  of. 770 

form  and  dimensions  of  the  globe  of. 770 

sclerotic  coat  of 770 

cornea  of 771 

anterior  elastic  lamella  of 771 

membrane  of  Descemet  or  of  Demours. . . , 771 

choroid  coat  of. 771 

tunica  Euschiana  of 772 

vasa  vorticosa  of 772 

ciliary  processes  of 773 

zone  of  Zinn 773,  779,  781 

iris  of...  ..  774 


ligamentum  iridis  pectinaturn  of 774 

pupil  of 774 

pupillary  membrane  of 775 

canal  of  Schlemm 775 

retina  of  (see  Eetina) 775 

macula  lutea  of 776 

fovea  centralis  of. 776 

- —  crystalline  lens  of 779 

liquid  of  Morgagni 7SO 

aqueous  humor  of. 781 

chambers  of 782 

vitreous  humor  of  (see  Vitreous  humor) 782 

hyaloid  membrane  of. 782 

summary  of  the  anatomy  of  the  globe  of 7S2 

refraction  in  (see  Vision) 784 

considered  as  an  optical  instrument 784 

axis  of 785,  792 

angle  alpha  of. 785 

p'unctum  caecum,  or  blind  spot  of 792 

mechanism  of  refraction  in 793 


INDEX. 


957 


Eye,  simple  schematic 794 

astigmatic 794 

•  movements  of  the  iris 796 

accommodation  of,  to  vision  at  different  distances  798 

corresponding  points  in  the  retinae  of. .  .802,  803,  810 

movements  of 807 

muscles  of. 807 

protrusion  and  retraction  of,  by  muscular  action  808 

action  of  the  recti  muscles  of 808 

action  of  the  oblique  muscles  of 809 

axes  of  rotation  of 808,  809 

movements  of  torsion  of. 809 

associated  action  of  the  muscles  of 810 

parts  for  the  protection  of 811 

tarsal  cartilages  of. 811 

— -  development  of 918 

Eyebrows 390,  811 

Eyelashes 390,  811 

Eyelids '. 811 

glands  of 861 

muscles  of. 811 

development  of 919 

time  of  separation  of,  in  the  foetus 941 

Face,  development  of 922 

Facial  angle 702 

Facial  nerve 618 

physiological  anatomy  of 618 

decussation  of  the  roots  of. 618 

branches  of,  within  the  aquaeductus  Fallopii 620 

external  branches  of. 621 

summary  of  the  anastomoses  and  distribution  of  621 

properties  and  functions  of 621 

influence  of,  upon  taste  and  upon  the  submaxil- 

lary  gland  (see  Chorda  tympani) 622,  623 

influence  of,  upon  the  movements  of  the  palate, 

uvula,  and  tongue 623,  624 

functions  of  the  external  branches  of 625 

effects  of  stimulation  of  branches  of 626 

influence  of,  upon  mastication,  through  the  buc- 
cinator muscle 626 

Facial  palsy,  symptoms  of 625 

Faeces,  influence  of  the  bile  upon 283 

quantity  of 292 

analysis  of 293 

cholesterine  in,  in  starvation,  in  hibernating  ani- 
mals, and  in  meconium 295 

"  figured  " 296,  297 

stercorine  in 456 

Fallopian  tubes 868 

fimbriaa  of 668 

mucous  membrane  of 868 

opening  of,  into  the  peritoneal  cavity 868 

—  supposed  influence  of,  upon  the  rupture  of  Graa- 

fian  follicles 872 

passage  of  the  semen  through 892 

development  of,  from  the  ducts  of  Muller 927 

Fallopian  pregnancy 892,  942 

Falsetto-register 559 

Falx  cerebelli 667 

Falx  cerebri 667 

Fats  in  the  blood 22 

Fats,  composition  of 1£ 

saponification  of. 184 

emulsification  of 184 

as  a  single  article  of  diet 1£ 

action  of  the  gastric  juice  upon 248 

not  acted  upon  by  the  intestinal  juice 268 

action  of  the  pancreatic  juice  upon 273 


PAGE 

Fats,  influence  of  the  bile  upon  the  digestion  and  ab- 
sorption of 2S3 

absorption  of  (see  Absorption) 301 

absorption  of,  by  the  lacteals 802,  317,  326 

alleged  production  of,  by  the  liver 472 

relations  of,  to  nutrition 501 

formation  and  deposition  of 501 

disappearance  of,  in  inanition 502 

condition  of,  in  the  organism 503 

anatomy  of  adipose  tissue ' 503 

Fatty  acids  and  salts  in  the  blood 21 

Fatty  degeneration  or  substitution 501 

Fatty  diarrhoea,  cases  of 275 

Fatty  matters  of  the  nervous  system 584 

Fatty  and  saponaceous  constituents  of  the  bile 443 

Fauces,  pillars  of 216 

isthmus  of 216 

Fecundation,  situation  of.  892,  896 

time  when  it  is  most  likely  to  occur 893 

mechanism  of. 893 

Fecundity,  limits  of,  as  regards  age 874 

Fehling's  test  for  sugar 461 

Female  organs  of  generation,  internal 857 

Female  organs  of  generation,  external 868 

Female,  action  of,  in  coitus 889 

Female,  orgasm  in 890 

Fenestra  ovalis 819,  822 

Fenestra  rotunda 819,  822, 842 

Fenestrated  membranes 526 

Ferrein,  pyramids  of. 896,  400 

Fibrin 177 

concrete  and  dissolved 23 

of  the  clot 25 

non-organization  of 27,  80 

formation  of,  by  decomposition  of  plasmine 29 

fibrillation  of,  in  coagulation 30 

vegetable ....  179 

action  of  the  gastric  juice  upon 245 

action  of  dilute  acids  upon 246 

Fibrin-factors 29 

Fibrinogen 29 

Fibrinoplastic  matter 29 

Fibrin-peptone 246 

Fibro-cartilage ^9 

Fibro-plastic  elements 532 

Fibrous  tissue,  white,  or  inelastic 531 

Fifth  cranial  nerve,  small  root  of  (see  Mastication, 

nerve  of) 615 

Fifth  cranial  nerve,  large  root  of 68 

physiological  anatomy  of. 635 

ganglion  of  Gasser 635 

branches  of 686 

properties  and  functions  of 638 

operation  for  the  division  of,  within  the  cranial 

cavity 689 

immediate  effects  of  division  of. 64 

influence  of,  upon  deglutition 641 

remote  effects  of  division  of. 641 

different  remote  effects  of  division  of,  before  and 

behind  the  ganglion  of  Gasser 642 

effects  of  division  of,  upon  the  nutrition  of  the 

organs  of  special  sense 642 

relations  of,  to  the  sympathetic  system 643 

cases  of  paralysis  of,  in  the  human  subject 643 

Fila  acustica 846 

Fish,  digestibility  of 251 

Fisk,  James,  Jr.,  brain  of. 70S 

Flax-seed 182 

Foetal  circulation 935 


958 


INDEX. 


PAGE 

Fcetal  circulation,  change  of,  into  the  adult   circu- 
lation   936 

Fcetus  blood-corpuscles  of 12 

respiratory  efforts  by 1*>7 

urine  of 426 

glycogenesis  in 469 

influence  of  the  maternal  mind  upon  the  develop- 
ment of 8y3<895 

determination  of  the  sex  of 8£ 

at  the  fifth  month 905 

time  when  this  name  is  applied  to  the  product  of 

fecundation 911' 94° 

functions  of  the  nervous  system  ia  919 

ot  G 

reflex  movements  in 

respiratory  efforts  by ^ 

digestive  fluids  in 921)  944 

size,  weight,  and  development  of,  at  different 

stages  of  utero-gestation 940 

when  viable 941 

weight  of,  at  term 941 

position  of,  in  the  uterus 941 

Food,  influence  of  climate  and  season  upon  the  quan- 
tity of. 1T2,  193 

definition  of 176 

nitrogenized  principles  of 176 

animal 177 

vegetable 178 

—  non-nitrogenized  principles  of 180 

inorganic  principles  of  184 

quantity  and  variety  of,  necessary  to  nutrition  . .  191 

regulation  of,  in  hospitals,  etc 192 

influence  of,  upon  the  capacity  for  labor 192 

necessity  of  a  varied  diet 193 

influence  upon   nutrition  of  single  articles   of, 

when  taken  alone 194 

—  influence  of,  upon  lactation 369 

influence  of,  upon  the  urine 427 

influence  of  different  kinds  of,  upon  the  glyco- 

genic  function  of  the  liver '. 470 

Foramen  ovale 36,  934 

closure  of 937 

Fossa  ovalis  in  the  heart 938 

Fourth  cranial  nerve  (see  Patheticus) C13 

Fourth  ventricle 706 

Fovea  cardiaca 931 

centralis 776 

hemispherica 822 

Free-martin 875,  895 

Frontal  process,  in  the  development  of  the  face 923 

Gall-bladder 433 

mucus  of 857 

development  of 921 

Galactophorous  ducts 366,  367 

Galvanic  current  in  muscles 542 

Ganglia  in  the  substance  of  the  heart 56  (note),  59 

Ganglionic  nervous  system  (see  Sympathetic) 729 

Gargling 223 

Gases  of  the  blood 156 

in  the  blood  in  different  parts  of  the  system 159 

mechanism  of  the"  interchange  of,  between  the 

blood  and  the  air  in  the  lungs 161 

of  the  small  intestine,  uses  of. 286,  299 

of  the  stomach 293 

of  the  large  intestine 299 

—  origin  of,  in  the  intestines 299 

absorption  of,  in  the  intestines  302 

of  the  milk 375 

of  the  urine ...  . .  425 


PAGE 

Gases  in  the  body 489 

Gasser,  ganglion  of. 635 

Gasterase 237 

Gastric  fistula  in  the  lower  animals 231 

in  the  human  subject 232 

Gastric  glands 229 

Gastric  juice 230 

mode  of  collecting 232 

secretion  of 234 

modifications  of  the  secretion  of 235 

artificial,  made  by  infusion  of  the  mucous  mem- 
brane of  the  stomach 235 

quantity  of  * 23o 

composition  of 236 

reaction  of 2i>6 

specific  gravity  of 286 

does  not  decompose  by  keeping 286 

antiseptic  properties  of 237,  247 

table  of  composition  of .' 237 

organic  principle  of > . . .  237 

source  of  the  acidity  of 233,  241 

substitution  of  other  acids  for  the  normal  acid 

of 241,  242 

ordinary  saline  constituents  of 241 

action  of,  in  digestion 242 

action  of,  upon  meats,  or  muscular  tissue 243 

—  action  of,  upon  albumen 245 

—  action  of,  upon  fibrin 245 

action  of,  upon  caseine 246 

action  of,  upon  vegetable  nitrogenized  principles, 

such  as  gluten 246 

action  of,  upon  non-nitrogenized  alimentary  prin- 
ciples   248 

—  action  of,  upon  fats 248 

action  of,  upon  sugars 248 

action  of,  upon  carbonate  and  phosphate  of  lime 

and  upon  bones 249 

influence  of  the  pneumogastric  nerves  upon  the 

secretion  of 252 

Gastric  plexus 733 

Gelatine 177 

French  committee  on 178, 179, 194 

Gelatine  of  Wharton 906 

Generation,  general  considerations 852 

spontaneous 854 

sexual. 854 

female  organs  of,  internal 857 

female  organs  of,  external 868 

male  organs  of 879 

development  of  the  internal  organs  of 927 

development  of  the  external  organs  of. 930 

Genito-spinal  centre 410,  882 

Genito-urinary  system,  development  of 927 

Germinal  spot 870 

Germinal  vesicle 870 

disappearance  of 897 

Giraldes,  organ  of 882 

Glands,  color  of  the  blood  in  the  veins  of 6,  344,  347 

comparative  quantity  of  blood  in,  during  activ- 
ity and  repose 69 

—  lymphatics  of 306 

absorption  from  the  reservoirs  and  ducts  of. 317 

variations  in  the  circulation  in 344 

irritability  of 345,  535 

• elimination  of  foreign  substances  by 346 

influence  of  nerves  upon 347 

general  structure  of 348 

anatomical  classification  of 349 

sebaceous  ...                    358 


INDEX. 


959 


PAGE 

Glands,  of  Tyson 359 

of  the  ear  (ceruminous) 360 

Meiboruian 361 

ductless,  or  blood-glands 472 

terminations  of  nerves  in 572 

Glandular  epithelium 343 

Glisson,  capsule  of 431,  432 

Globuline 17, 177 

Globulins  of  the  lymph  and  chyle 333,  337 

Glosso-pharyngeal  nerves 761 

—  physiological  anatomy  of 7til 

general  properties  of 763 

relatiftns  of,  to  gustation 764 

Glottis,  movements  of,  in  respiration 116,  553 

influence  of  the  inferior  laryngeal  nerves  upon 

the  movements  of 116,  553 

appearance  of,  as  seen  with  the  laryngoscope. . .  554 

development  of 922 

Glucose  (see  Sugars) 22, 180, 182 

Gluten 179 

bread  made  from 179 

action  of  the  gastric  juice  upon 246 

Glutine 179 

Glycine 280 

Glycocholate  of  soda 280,  444,  446 

Glycocholie  acid 280,  444,  446 

Glycocolle 178 

Glycogenic  function  of  the  liver  (see  Liver) 458 

Glycogenic  matter 467 

mode  of  extraction  of 467 

Goose-flesh 381 

Graafian  follicles 859,  860 

number  of 860 

mode  of  formation  of 860 

size  of 862 

coats  of 862 

membrana  granulosa  of 863 

discus,  or  cumulus  proligerus  in 863 

situation  of  the  ovum  in 863 

rupture  of 870,  871 

macula  of 870 

influence  of  copulation  upon  the  rupture  of.  .871,  872 

relations  of  rupture  of,  to  menstruation 872 

changes  in,  after  their  rupture  (see  Corpus  lu- 

teum) 877 

Grape-sugar 180 

Gubernaculum  testis 928 

Gums 182 

Gustation,  relations  of,  to  olfaction 758 

general  considerations  of 759 

nerves  of 760 

functions  of  the  chorda  tympani  in 761 

functions  of  the  glosso-pharyngeal  nerve  in 764 

mechanism  of 764 

physiological  anatomy  of  the  organ  of. 764 

influence  of  the  chorda  tympani  upon 622 

Gutturals 562 

Hsernadrorneter 79 

Hsemadynamometer 75 

Hzemagiobine 17,.185 

—  absorption  of  oxygen  by 160 

Haemaglobuline 17 

Haematine 17,  IS 

Hasmatocrystalline 17 

Hsematoidine IS 

Hasmatosis 155 

Haemorrhage,  difference  in  the  effects  of,  during  diges- 
tion and  fasting 4 


PAGE 

Haemorrhage,  influence  of,  upon  the  arterial  pressure .     78 

effects  of,  upon  the  sense  of  thirst 174 

influence  of,  upon  digestion 251 


27 
848 
887 
576 


Haernorrhagic  diathesis 

Hair-cells  of  the  internal  ear 

Hair-follicles 

terminat.ons  of  nerves  in. . . 

Hairs,  varieties  of 

size  of,  in  different  parts 355 

number  of 386 

hygrometricity  of 886 

roots  of . .  386 

structure  of. 335 

color  of 3S9 

growth  of 389 

development  of 389 

shedding  of,  in  the  infant 389 

sudden  blanching  of 889 

uses  of 390 

first  appearance  of 916 

—  shedding  and  replacing  of 945 

Haller,  vas  aberrans  of 881 

Hamulus  of  the  cochlea 823,  844 

Hare-lip 562,  924 

Harmonics,  or  overtones 829 

Harmony 832 

Hauser,  Caspar,  case  of 803 

Haversian  canals 544 

Haversian  rods '. 544 

Head-fold  of  the  neural  canal 900 

Head-register 559 

Hearing  (see  Audition) 815 

Heart,  description  of  the  action  of,  by  Harvey 82 

general  description  of  the  action  of 34 

physiological  anatomy  of 85 

pericardium  of 85 

weight  of 35 

auricles  of 35 

foramen  ovale  of 36 

Eustachian  valve  of 36 

ventricles  of 86 

—  comparative  capacity  of  the  right  and  the  left 
ventricle  of. 36 

muscular  tissue  of 35,  87 

comparative  thickness  of  the  ventricles  of 38 

valves  of 88,  39,  47,  48 

demonstration    of    the    action   of    the   valves 

of. 39,46 

movements  of. 40 

complete  revolution  of 40 

demonstration  of  the  action  of 40 

action  of  the  auricles  of 40 

action  of  the  ventricles  of 41 

locomotion  of 41 

twisting  of 42 

hardening  of 42 

shortening  and  elongation  of 42 

impulse  of 4 

succession  of  the  movements  of 43 

relative  time  occupied  by  the  auricular  and  the 

ventricular  contractions  of '. 44 

force  of 46 

sounds  of 48,  49 

frequency  of  the  action  of  (see  Pulse) 51 

-, —  influence  of  respiration  upon  the  action  of 54 

arrest  of  the  action  of,  in  asphyxia 54 

arrest  of  the  action  of,  by  voluntary  arrest  of 

respiration 55 

cause  of  the  rhythmical  contractions  of 55,  58 


960 


INDEX. 


PAGE 

Heart,  pulsation  of,  when  removed  from  the  body. . .     56 

pulsation  of,  in  animals  poisoned  with  woora- 

ra 56,59,61 

ganglia  in  the  substance  of 56  (note)  59 

arrest  of  the  action  of,  by  ligation  of  the  coronary 

arteries 57 

contractions  of,  produced  by  irritation  during  its 

repose 57 

influence  of  the  blood  in  its  cavities  upon  the 

contractions  of. 57,  58 

influence  of  the  density  of  its  contents  upon  the 

contractions  of 58 

irritability  of  the  muscular  tissue  of 58 

irritability  of  the  lining  membrane  of. 58 

influence  of  the  nervous  system  upon 58 

insensibility  of 58 

arrest  of  the  action  of,  by  sudden  destruction  of 

the  spinal  cord 59 

influence  of  the  pneumogastrics  upon 59,  60,  631 

influence  of  the  sympathetic  nerves  upon 60 

influence  of  the  spinal  accessory  nerves  upon  61,  631, 

655,  658 

palpitation  of 59,  61 

influence  of  mental  emotions  upon 62 

summary  of  causes  of  arrest  of  the  action  of. . .     62 

death  from  distention  of 63 

death  from  a  blow  upon  the  epigastrium 63 

relations  of  the  force  of,  to  the  frequency  of  its 

pulsations , 78, 112 

circulation  in  the  walls  of 110 

time  required  for  the  passage  of  the  entire  mass 

of  blood  through 112 

quantity  of  blood  discharged  by  each  ventricular 

systole  of 112 

relation  of  the  frequency  of  the  action  of,  to  the 

rapidity  of  the  circulation 112 

respiratory  efforts  after  excision  of 166 

temperature  of  the  blood  in  the  two  sides  of. .  5,  509 

want  of  action  of  digitalis  upon,  after  section  of 

the  pneumogastrics 654,  665 

effects  of  galvanization  of  the  pneumogastrics 

upon 654,  658 

development  of 932,  934 

relative  size  of,  in  the  foetus  and  at  different  peri- 
ods of  life 934 

enlargement  of,  in  pregnancy 939 

Heart-clots 26,  27 

Heat,  animal  (see  Animal  heat) 506 

Heat,  power  of  resistance  of  the  body  to 521 

Helix  of  the  ear 817 

Hemiopsia 769 

Hemiplegia,  comparative  quantity  of  cholesterine  in 
the  blood  upon  the  two  sides  of  the  body  in  cases 

of 453 

Hemp-seed 183 

Henle,  tubes  of 399 

Hepatic  artery,  influence  of  ligation  of,  upon  the  secre- 
tion of  bile 440 

Hepatic  cells 435 

Hepatic  ducts 435 

Hepatic  plexus 733 

Hepatic  veins,  non -coagulation  of  the  blood  of 30 

arrangement  of  (see  Liver) 434 

temperature  of  the  blood  in 5,  509 

Hereditary  transmission 894 

Hermaphroditism 930 

Hernia  at  the  umbilicus,  in  the  foetus 904,  920 

diaphragmatic 921 

Hibernation,  consumption  of  oxygen  in 143 


PAGE 

Hibernation,  cholesterine  in  the  faeces  in 295 

Hiccough 125,  135 

Hippuric  acid  and  its  compounds 417 

amount  of  daily  excretion  of 417 

Homer,  muscle  of. 811 

Horopter 803 

Hunger 172 

seat  of  the  sense  of 178 

in  diabetes 173 

after  section  of  both  pneumogastric  nerves. .  174,  664 

after  section  of  the  hypoglossal  and  lingual 

nerves 174 

Hunted  animals,  coagulation  of  the  blood  in 26 

Hyaloid  membrane  of  the  vitreous  humor 782 

Hydatids  of  Morgagni 880 

Hydro-carbons 180 

relations  of,  to  nutrition 500 

Hydrochlorate  of  ammonia 497 

Hydrochloric  acid,  action  of,  upon  cane-sugar 248 

Hydrogen,  effects  of  confining  au  animal  in  a  mixture 

of  with  oxygen 143 

Hygrometricity 824 

Hyoid  bone,  development  of 922,  923 

Hypermetropia 789 

Hypnagogic  hallucinations 744 

Hypodermic  administration  of  remedies 317 

Hypogastric  arteries 983 

closure  of 938 

Hypogastric  plexus 733,  734 

Hypoglossal  nerve  (see  Sublingual  nerve) 632 

Hypospadias 930 

Hypoxanthine 421 


Icterus,  cholesterine  in  the  blood  in  grave  and  in  sim- 
ple cases  of. 

Idiots,  cerebrum  of 

Ileo-csecal  valve 

development  of 

Ileum 

Iliac  veins,  development  of 

Imbibition 321, 

Imperforate  anus 

Impotence,  apparent 

Inanition,  influence  of,  upon  the  exhalation  of  carbonic 
acid 

influence  of  age  upon  the  power  of  resistance  to . 

phenomena  attending 

duration  of  life  in 

influence  of,  upon  digestion 

quantity  of  lymph  in 

influence  of,  upon  the  glycogenic  function  of  the 

liver 

disappearance  of  fat  in 

animal  heat  in 

Incisor  process,  in  the  development  of  the  face 

Incisor  teeth 

Incus  

development  of 

Induced  muscular  contraction 

Inelastic  fibrous  tissue 

Infancy 

— «-  secretion  of  milk  in 

Inferior  laryngeal  nerves  (see  Pneumogastric) 

Inflammation,  phenomena  of,  studied  in  the  capilla- 
ries   

after  section  of  the  fifth  nerve 

Infracostalis,  action  of,  in  expiration 

Infundibuliform  fascia 

Infusoria 


457 

700 

288 


934 
324 

921 

888 

148 
172 
175 

175 
251 


470 
502 
511 


819 
922 
602 
531 
965 
378 


92 
643 
130 

880 
855 


INDEX. 


961. 


PAGE 

Innominate  vein,  development  of 934 

Inorganic  principles,  in  the  blood 21 

alimentary,  union  of,  with  organic  principles 184 

absorption  of,  by  the  lacteals 814 

in  the  urine 421 

action  of,  in  nutrition 488 

table  of 4S9 

Inosates  in  the  urine 418 

Insalivation 205 

entanglement  of  bubbles  of  air  in  the  alimentary 

mass  during 214 

Inspiration .122 

table  of  muscles  of 123 

auxiliary  muscles  of 127 

relations  of,  to  expiration 133 

duration  of 133 

Insula. . . , 705 

Intelligence,  absence  of,  in  animals  deprived  of  the 

cerebrum 697 

Intercolumnar  fascia 880 

Intercostal  muscles 122, 125, 130 

action  of,  in  inspiration 125 

action  of,  in  expiration 130 

Intermaxillary  process,  in  the  development  of  the 


face. 


Intervertebral  discs,  formation  of 914 

Intestinal  canal,  first  appearance  of 914 

Intestinal  digestion 257 

Intestinal  fistula,  hunger  in  a  case  of 178 

case  of,  in  the  human  subject 266 

Intestinal  gases,  origin  of 299 

Intestinal  juice 265,  267 

action  of,  upon  starch  and  albuminoids 267 

Intestinal  villi,  development  of 920 

Intestine,  small,  physiological  anatomy  of 257 

length  of 257 

divisions  of 257 

peritoneal  coat  of 258 

muscular  coat  of 258 

valvulae  conniventes  of 259,  802 

mucous  membrane  of 259 

villi  of 261,  263,  302 

lacteals  in  the  villi  of 263 

patches  of  Peyer  of 263,265,  267 

solitary  glands  of. 264,  265,  267 

movements  of 285,  286 

uses  of  the  gases  in 286,  299 

influence  of  the  circulation  upon  the  movements 

of , 287 

— -  influence  of  the  nervous  system  upon  the  move- 
ments of 287,  665 

action  of  the  epithelium  of,  in  the  absorption  of 

fats 318 

distribution  of  the  pneumogastric  to 665 

influence  of  the  pneumogastric  upon 665 

development  of r. 920 

Intestine,  large,  physiological  anatomy  of 287 

peritoneal  coat  of 289 

muscular  coat  of 289 

mucous  coat  of , 290 

follicles  of 290 

solitary  glands  of 291 

digestion  and  absorption  in 291 

contents  of  (see  Faeces) 292 

movements  of 296 

gases  of 299 

development  of 92° 

Intestines,  influence  of  the  bile  upon  the  peristaltic 
movements  of 

<      61 


PACK. 

Intestines,  influence  of  the  sympathetic  system  up- 
on   739,  797 

Intoxication,  alcoholic 186 

Inuline 182, 

Involuntary  muscular  tissue  and  movements. . .  527,  528 

Involution  of  the"  uterus 948 

Iodine,  test  for  starch 181 

Iris,    influence     of     the    motor    oculi    communis 

upon 611,  796 

— —  reflex    action    of  the    tubercula    quadrigemina 

upon 722,  797 

influence  of  the  sympathetic  nerves  upon 741 

anatomy  of 774 

—  ligamentum  iridis  pectinatum 774 

layers  of 774 

arrangement  of  the  muscular  fibres  of 775 

blood-vessels  and  nerves  of 775 

movements  of 796 

direct  action  of  light  upon 796 

—  action  of  the  nervous  system  upon 796 

consensual  contraction  of 797 

influence  of  the  cilio-spinal  centre  upon 798 

variations  in  the  vascularity  of 798 

action  of,  in  accommodation 800 

movements  of,  in  converging  the  axes  of  vision . .  801 

voluntary  contraction  of 801 

development  of. 919 

Iron,  function  of,  in  the  organism 185 

in  milk 375 

Irradiation 806 

Irritability,  muscular 56,  59 

of  the  muscular  tissue  of  the  heart 58,  59 

action  of  sulpho- cyanide  of  potassium  upon 59 

distinction  between  muscular  and  nervous 59,  536 

of  the  arteries •  •     69 

oftheveins 96 

of  muscles. . . : 535 

of  glands 535 

distinction  between  muscular  and  nervous 536 

of  nerves  (see  Nervous  irritability) 594 

Island  of  Eeil T05 

Jacobson,  nerve  of 672 

Jacob's  membrane 776 

Jaundice  (see  Icterus) 457 

Jaws,  physiological  anatomy  of 2( 

articulations  of 202 

Jejunum 259 

Jugular  veins,  development  of 934 

Kidneys,  effects  of  destruction  of  the  nerves  of. .  848,  405 

physiological  anatomy  of 895 

hilum  and  pelvis  of 395 

calices  of 395 

infundibula  of 395 

divisions  of  the  substance  of 896 

cortical  substance  of 896,  398 

columns  of  Bertin 896,  400 

pyramids  of  Malpighi 396 

pyramids  of  Ferrein 896,  400 

pyramidal  substance  of 896 

tubes  of  Bellini 396 

Malpighian  bodies 398,  399 

capsule  of  Muller 399 

varieties  of  cells  in  the  Malpighian  bodies 39 

convoluted  tubes  of 899 

tubesofHenle 399 

intermediate,  or  communicating  tubes 899 

distribution  of  blood-vessels  in 400 


962 


INDEX. 


PAGE 

Kidneys,  arterial  arcade  of. 400 

arteriolse  recite  of 400 

plexus  of  vessels  around  the  convoluted  tubes  of  400 

portal  system  of 401 

stars  of  Verheyn 401 

venous  arcade  of 401 

lymphatics  of 401 

nerves  of 401 

extirpation  of 403 

extirpation  of,  upon  one  side 404 

alternate  action  of,  upon  the  two  sides 406 

changes  in  the  blood  in  passing  through 406 

influence  of  extirpation  of  one,  upon  the   ap- 
petite  4T9 

development  of 928 

Krause,  corpuscles  of . .  575 

Labia  majora,  development  of 930 

Labia  minora,  smegma  of. 363 

Labial  glands 209 

Labials ..  562 

Labyrinth,  bony 822 

membranous 842 

ligaments  of 842 

utricle  and  saccule  of 843 

liquids  of 846 

distribution  of  the  nerves  in 846 

development  of 919 

Lachrymal  apparatus 813 

Lachrymal  fluid 814 

Lachrymal  glands 813 

Lachrymal  points 813 

Lachrymal  sac  and  ducts 813 

Lachiymine 814 

Lactates  in  the  blood 21 

in  the  urine 418 

Lactation,  duration  of 369 

modifications  of  (see  Milk) 369 

influence  of,  upon  menstruation 875 

Lacteals,  in  the  intestinal  villi 263 

situation  of 802 

discovery  of 302 

absorption  by 302 

course  of 306,  311 

structure  of 808 

absorption  of  albuminoids  by 318 

absorption  of  glucose  and  salts  by 313 

absorption  of  water  by 814 

Lactiferous  ducts 366,  367 

Lactine 875 

Lactometers 871 

Lacto-proteine 374 

Lactose 375 

Lamellar  elastic  tissue 526 

Lancet-fish,  an  animal  without  a  brain 696 

Language 550,  560 

centre  presiding  over 704 

Laryngoscope 554,  559 

Larynx,  physiological  anatomy  of 116,  550 

muscles  of  (see  names  of  the  muscles) 551 

action  of,  in  respiration 553 

action  of,  in  phonation 558 

influence  of  the  inferior  laryngeal  branches  of 

the  pneumogastrics  upon  the  movements  of 652 

development  of 922,  923 

Laughing , 125, 135 

Laxator  tympani  muscle 820 

Lecithene 21,  584,  585 

in  the  bile...  ..  443 


PAGE 

Leech-drawn  blood,  non-coagulation  of 30 

Left-handedness  (see  Dextral  preeminence) 944 

Legs,  development  of 915,  916 

Legumine 1 79 

Lenses,  refraction  by 787 

• spherical  aberration  of. 789 

chromatic  aberration  of. 790 

correction  of 790 

Lenticular  ganglion. 731 

Leucine 421 

Leucocytes  (see  Blood) 6,  18 

relations  of,  to  the  development  of  the  blood-cor- 
puscles      12 

development  of 15 

in  the  lymph 332,  837 

development  and  function  of,  in  the  lymph 833 

in  colostrum 377 

development  of,  in  the  ovum 931 

Levator  anguli  scapulae,  action  of,  in  respiration 128 

Levator  palati 217 

Levator  palpebrae  superioris  812 

Levatores  costarum,  action  of,  in  respiration 126, 127 

Lichenine 1S2 

Lichens,  edible 182 

Lieberkuhn,  follicles  of 260,  267 

Life,  definition  of. 437,  504,  853 

duration  of,  in  man 946 

Ligamentum  denticulatum 667 

Ligamentum  iridis  pectinatum 774 

Light,  theory  of  the  propagation  of: 785 

velocity  of 786 

decomposition  of 786 

refraction  of,  by  lenses 787 

Lightning,  coagulation  of  the  blood  in  animals  killed 

by. 26 

Limbus  lamina?  spiralis  of  the  cochlea 844 

Limitary  membrane  of  the  retina 777 

Lingual  glands 209 

Linseed-oil 183 

Lips,  action  of,  in  speech 562 

development  of .928 

Liquids,  influence  of  the  ingestion  of,  upon  lactation . .  370 

Liquids  (division  of  consonants) 562 

Liquor  sanguinis  (see  Blood) 6 

Littre,  glands  of 888 

Liver,  circulation  in  the  veins  of 102 

formation  of  urea  in 415 

physiological  anatomy  of 431 

weight  of. 431 

capsule  of  Glisson 431,  432 

blood-vessels  of. 432 

attachment  of  the  walls  of  the  hepatic  vein  to  the 

substance  of 432 

vaginal  plexus  of 432 

interlobular  vessels  of 433 

lobular  vessels  of. 433 

intralobular  veins  of. 434 

sublobular  veins  of 434 

anatomy  of  a  lobule  of. 435 

accessory  portal  veins  of. 435 

arrangement  of  the  bile-ducts  in  the  lobules  of. .  435 

anatomy  of  the  excretory  biliary  passages  of 436 

racemose  glands  attached  to  the  ducts  of. 437 

vasa  aberrantia  of 437 

gall-bladder,  hepatic,  cystic,  and  common  ducts 

of. 437 

nerves  and  lymphatics  of 439 

excretory  function  of 450 

extirpation  of 457 


963T- 


PAGE 

Liver,  production  of  sugar  by 458 

evidences  of  the  glycogenic  function  of 459 

examination  of  the  blood  of  the  portal  system  for 

sugar 461 

examination  of  the  blood  of  the  hepatic  veins  for 

sugar 462 

examination  of  the  blood  from  the  right  side  of 

the  heart  for  sugar 462,  468 

does  the  liver  normally  contain  sugar  during  life  ?  464 

formation  of  sugar  in  the  li ver  during  life,  which 

is  washed  out  by  the  current  of  blood 466 

characters  of  the  sugar  produced  by 466 

mechanism  of  the  production  of  sugar  in 46T 

glycogenic  matter  of. 467 

ferment  produced  by,  which  is  capable  of  chang- 
ing glycogenic  matter  into  sugar 468 

variations  in  the  glycogenic  function  of. 469 

glycogenesis  in  the  foetus 469 

influence  of  digestion  upon  the  glycogenic  func- 
tion of 469 

influence  of  different  kinds  of  food  upon  the  gly- 
cogenic function  of.  469 

influence  of  the  nervous  system  upon  the  pro- 
duction of  sugar  by 470,  662 

influence  of  the  inhalation  of  anaesthetics  and  ir- 
ritating vapors  upon  the  production  of  sugar  by. .    471 

alleged  production  of  fat  by 472 

changes  in  the  albuminoid  and  corpuscular  con- 
stituents of  the  blood  in '.  . .  472 

influence  of  the  pneumogastrics  upon 662 

development  of 921 

proportionate  weight  of,  at  different  periods  of 

life 921 

first  circulation  in 933 

Lochia 943 

Locomotion,  passive  organs  of 543 

Locomotor  ataxia 679 

Lungs,  capillary  circulation  in 88,  110 

circulation  through 109 

parenchyma  of 119 

air-cells  of 120 

action  of  the  elasticity  of  the  parenchyma  of,  in 

expiration 129 

capacity  of. 135 

vital  capacity  of. 138 

diffusion  of  air  in 138 

lymphatics  of 306 

absorption  by  the  respiratory  surface 316 

development  of. 922 

Lunula  of  the  nail 384 

Lymph 328 

mode  of  collecting .*. 828 

quantity  of. 829 

influence  of  digestion  upon  the  quantity  of. 329 

properties  and  composition  of 329 

color  of 329 

specific  gravity  of 330 

coagulation  of. 330 

tables  of  composition  of 831 

presence  of  glucose  and  urea  in 332 

corpuscular  elements  of 332,  337 

globulins  of 833,  337 

origin  and  function  of. 334 

comparison  of  constituents  of,  with   those  of 

chyle 337 

circulation  of. 338 

causes  of  the  movements  of. 838 

influence  of  the  force  of  endosmosis  upon  the 

movements  of . . .  . .  389 


Lymph,  influence  of  the  contractile  walls  of  the  vessels 

upon  the  movements  of 339 

influence  of  pressure  from  surrounding    parts 

upon  the  movements  of §39 

influence  of  respiration  upon  the  movements  of  340 

Lymphatic  glands 306 

function  of. 313 

Lymphatic  trunk,  right 306 

Lymphatics,  not  found  in  the  coats  of  the  blood-ves- 
sels      gj 

discovery  of 302 

anatomy  of 303 

injection  of. 303 

mode  of  origin  of 803 

valves  of 303,  809,  840 

course  and  anastomoses  of 304 

—  parts  provided  with 805 

structure  of. 80S 

question  of  orifices  in  the  walls  of. 809,  318 

relations  of,  to  connective  tissue 810 

of  the  liver 439 

of  the  muscular  tissue 533 

Lymph-corpuscles 13 


Macula  acustica 848 

Macula  folliculi 870 

Macula  lutea 776 

Male  organs  of  generation 879 

Male,  action  of,  in  coitus 888 

erection  in 889 

orgasm  in 889 

Malleus 819 

development  of 922 

Malpighi,  pyramids  of 896 

Malpighian  bodies  of  the  kidney 398,  399 

arrangement  of  blood-vessels  in 400 

bodies  of  the  spleen 474 

Mammary  secretion  (see  Milk) 864 

Mammary  glands 365 

condition  of,  during  the  intervals  of  lactation 365 

structure  of,  during  lactation 366 

acini  of 366 

Manage,  movements  of. 729 

Manna 182 

Mannite 182 

Maranta  arundinacea 181 

Margaric  acid 188 

Margarine 183,  504 

Mariotte,  experiment  of 792 

Marrow 546 

Mastication 197 

table  of  muscles  of 202 

action  of  the  muscles  which  depress  the  lower 

jaw 208 

action  of  the  muscles  which  elevate  the  lower 

jaw  and  move  it  laterally  and  antero-posteriorly. . .  203 

action  of  the  tongue,  lips,  and  cheeks  in 204 

action  of  the  orbicularis  oris  and  buccinator  in . .  205 

function  of  the  sensibility  of  the  teeth  to  hard 

and  soft  substances  in 205 

influence  of,  upon  the  flow  of  the  parotid  saliva. .  207 

nerve  of 615 

physiological  anatomy  of  the  nerve  of 615 

properties  and  functions  of  the  nerve  of. 617 

influence  of  division  of  the  nerve  of,  upon  the 

teeth,  in  the  rabbit 617 

Mastoid  cells 821 

Maternal  mind,  influence  of,  upon  the  development  of 

the  foetus... 


964 


INDEX. 


,  PAGE 

Maxilla,  superior,  development  of 923 

Maxilla,  inferior,  development  of 923 

Maxillary  bones,  physiological  anatomy  of 201 

articulations  of 202 

Meats 176 

action  of  the  gastric  juice  upon 243 

digestibility  of 251 

action  of  the  intestinal  juice  upon 2GT 

action  of  the  pancreatic  juice  upon 2T7 

Meckel,  cartilage  of 919,923 

MeckePs  ganglion • 731 

Meconium 295,  921,  943 

Medulla  oblongata,  decussation  of  motor  conductors 

in •. 6T7 

physiological  anatomy  of T24 

general  properties  of 726 

functions  of. 726 

connection  of,  with  respiration 726 

vital  point  in 727 

action  of,  in  the  reflex  acts  of  yawning,  coughing, 

crying,  sneezing,  vomiting,  etc 728 

influence  of,  upon  glycogenesis 728 

influence  of,  upon  the  heart 728 

development  of 917 

Medulla  oblongata  and  pons  Varolii,  weight  of. 690 

Medullary  plates 913,  915 

Medullocells 546 

Meibomian  glands 361 

secretion  of. 364 

Membrana  basilaris  of  the  cochlea 844 

Membrana  granulosa  of  the  Graafian  follicle 863 

Membrana  media  of  the  ovum 903 

Membrana  tectoria  (membrane  of  Corti)  of  the  cochlea  844 

Membranse  deciduse  (see  Deciduse) 907 

Membranes  of  the  foetus,  formation  of 900 

Meniere's  disease 718,  849 

Mental  emotions,  influence  of,  upon  lactation 370,  376 

Mental  exertion,  influence  of,  upon  the  urine 430 

influence  of,  upon  animal  heat 514 

Menstruation,  influence  of,  upon  the  exhalation  of 

carbonic  acid 148 

influence  of,  upon  lactation 370,  376 

•  enlargement  of  the  thyroid  gland  in 483 

variations  in  the  thickness  of  the  mucous  mem- 
brane of  the  uterus  in 866,  876 

identity  of,  with  rut 871,  875 

relations  of,  to  the  discharge  of  ova 872,  875 

phenomena  of. 874 

supposed  appearance  of,  after  extirpation  of  the 

ovaries 875 

influence  of  pregnancy,  lactation,  and  diseases 

upon 875 

stages  of. 875 

stage  of  invasion  of. 875 

duration  of 876 

characters  of  the  flow  in 876 

cessation  of 876 

diminution  in  the  excretion  of  urea  in 876 

influence  of,  upon  the  pulse 876 

influence  of,  upon  the  temperature 876 

Mercury,  absorption  of  minute  particles  of. 318 

Mery,  glands  of. , 883 

Mesenteric  plexus 733 

Mesenteric  vein,  development  of. 934 

Mesentery 257 

development  of. 921 

Mesocaecum 289 

Mesocephalon  (see  Tuber  annulare) 722 

Mesocolon. . .  . .  289 


PAGE 

Metalbumen 23 

formation  of,  by  decomposition  of  plasmine 29 

Mezzo-soprano 556 

Micropile 870,  896 

Micturition 409 

Milk 177,  364 

digestibility  of 251 

mechanism  of  the  secretion  of 368 

modifications  of. 369 

influence  of  diet  upon 369 

influence  of  liquids  upon 869 

influence  of  alcohol  upon 370 

influence  of  mental  emotions  upon 370,  376 

influence  of  the  nervous  system  upon 370,  376 

quantity  of 870 

influence  of  pregnancy  upon 370,  376 

influence  of  menstruation  upon 370,  376 

general  properties  of 371 

specific  gravity  and  reaction  of. 371 

coagulation  of 871,  374 

formation  of  cream  upon 371 

— — -  microscopical  characters  of 371 

table  of  composition  of 373 

nitrogenized  constituents  of 374 

albumen  in 374 

comparison  of,  from  the  cow  and  from  the  human 

subject 374 

fatty  matters  of. 374 

sugar  of 375 

fermentation  of 375 

inorganic  constituents  of 375 

iron  in 875 

gases  in 375 

a  typical  food 375 

variations  in  the  composition  of. 375 

variations  in,  at  different  periods  of  lactation 375 

relations  of  the  quantity  of,  to  the  previous  se- 
cretion of  colostrum 378 

of  the  infant 378 

Milk-fever 378 

Milk-globules 372 

action  of  reagents  upon 372 

structure  of 373 

Milk-sugar 180 

Mitral  valve 39,  47 

Modiolus  of  the  cochlea 823,  844 

Modulation 839 

Moisture  and  temperatiire,  influence  of,  upon  the  ex- 
halation of  carbonic  acid 151 

Molarglands 209 

Molar  teeth 201 

Monocular  vision 804 

Morgagni,  liquid  of 780 

hydatids  of 880 

Mosses,  edible 182 

Motor  nerves,  action  of 591 

disappearance  of  irritability  of 596 

Motor-oculi  communis 4509 

physiological  anatomy  of 610 

properties  and  functions  of 610 

— -  influence  of,  upon  the  iris 611,  796 

Motor-oculi  externus 614 

physiological  anatomy  of 614 

properties  and  functions  of 614 

Mouth,  absorption  by  the  mucous  membrane  of 801 

action  of,  in  phonation 558 

action  of,  in  speech 562 

first  appearance  of 923 

Movements 522 


INDEX. 


965 


PAGE 

Movements,    of  amorphous    contractilo    substance 

(amoeboid) 522 

ciliary 523 

due  to  elasticity 524 

muscular 526 

associated 592 

Mucilages 182 

Mucosine 356 

Mucous  membranes,  lymphatics  of 306 

varieties  of 353 

Mucus 354 

varieties  of 355 

nasal 356 

bronchial  and  pulmonary 356 

of  the  alimentary  canal 35T 

of  the  gall-bladder 357 

of  the  urinary  passages 85T 

of  the  generative  passages 357 

conjunctiva! 357 

virulent 357 

general  function  of 357 

influence  of,  upon  the  absorption  of  venoms 858 

Muller,  capsule  of 399 

Miiller,  duct  of  (see  Duct  of  Muller) ; 927 

Muscles,  connection  of,  with  the  tendons 533 

voluntary,  terminations  of  nerves  in 570 

involuntary,  terminations  of  nerves  in 571 

lymphatics  of. 306 

Muscular  atrophy,  progressive 742 

Muscular  coat  of  the  arteries 66 

Muscular  contraction,  influence  of,  upon  the  venous 

circulation.. 101 

influence  of,  upon  the  circulation  of  lymph 340 

Muscular  current 542 

Muscular  effort 542 

influence  of,  upon  the  arterial  pressure 78 

Muscular  exercise  (see  Exercise)  53, 150,  251,  428,  498,  513 

Muscular  fibres,  involuntary 227,  527 

characteristic  mode  of  contraction  of 253,  528 

Muscular  movements  (see  Movements) 526 

Muscular  sense T50 

'  Muscular  system,  development  of 916 

Muscular  tissue  of  the  heart 35,  37 

Muscular  tissue,  involuntary 527 

contraction  of. 528 

voluntary 528 

development  of,  by  exercise 529 

anatomical  elements  of 530 

sarcolemma,  or  myolemma  of 530 

reactions  of. 533 

physiological  properties  of. 533 

elasticity  of. 534 

tonicity  of. 534 

sensibility  of. 534 

contractility,  or  irritability  of 535 

irritability  of,  distinguished  from  nervous  irrita- 
bility   59,  536 

influence  of  the  blood  upon  the  irritability  of. ...  537 

restoration  of  irritability  of,  by  injection  of  blood  537 

contraction  of. 538 

no  change  in  the  volume  of,  in  contraction 538 

changes  in  the  form  of,  during  contraction 538 

duration  of  contraction  of,  under  artificial  excita- 


Muscular  tissue,  action  of  the  gastric  juice  upon 243 

blood-vessels  of • 532 

lymphatics  of 533 

chemical  composition  of 533 

Muscular  wave 549 

Musculine 176,  533 

Mushrooms jgj 

Musical  sounds  (see  Sound) §26 

Melody. S27 

Mustache,  uses  of 390 

Mustard 190 

Mutes : 552 

Myeline 566 

Myelocytes 583 

Myeloplaxes 547 

Myolemma 530 

Myopia 788 

Myosine. 533  • 

Naboth,  ovules  of y . .  866 

Nails,  physiological  anatomy  of 383 

connections  of,  with  the  skin 885 

growth  of 385 

development  of ' 385 

first  appearance  of 916 

Nares,  posterior,  development  of 924 

Nasal  duct 813 

Nasal  fossae 754 

action  of,  in  phonation 558 

Nasal  mucus 356 

Nasals 562 

Negative  variation 606 

Negro,  brain  of 702 

Nerve-cells 576 

varieties  of 576 

striation  of,  by  the  action  of  nitrate  of  silver 578 

connections  of,  with  the  fibres  and  with  each 

other 579 

Nerve-centres,  structure  of 576 

accessory  anatomical  elements  of 583 

connective  tissue  of 583 

blood-vessels  of 583 


of  (perivascular  canals) . 


tion. 


artificial  spasm  of 53 

prolonged  contraction  of  (tetanus) 540 

sound  produced  by  contraction  of. 541 

fatigue  of. 541 

electric  phenomena  in 541 


583 
565 
566 
566 
566 


lymphati 

Nerve-fibres 

classification  of 

medullated 

tubular  membrane  of, 

medullary  substance  of,  or  white  substance  of 

Schwann • 566 

axis-cylinder  of 567 

simple,  or  non-medullated 567 

gelatinous,  or  fibres  of  Kemak 568,  735 

striation  of,  by  the  action  of  nitrate  of  silver 567 

Nerve-force 597 

non-identity  of,  with  electricity 597 

rapidity  of  conduction  of 597 

Nerves,  of  the  arteries 67 

vaso-motor 67 

of  the  liver & 

structure  of , 565 

accessory  anatomical  elements  of. 568 

perinevre  of. 569 

blood-vessels  of 569 

branching  and  course  of 569 

terminations  of,  in  the  voluntary  muscles 570 

terminations  of,  in  the  involuntary  muscles 571 

terminations  of,  in  glands 572 

sensory,  terminations  of 572,  575 

terminations  of,  in  the  hair-follicles 576 

reunion  of 585 


'966 


INDEX. 


PAGE 

Nerves,  motor  and  sensory 586 

motor,  action  of 591 

sensory,  action  of 592 

general  properties  of 594 

irritability  of  (see  Nervous  irritability) 594 

—  disappearance  of  the  sensory  properties  of 596 

action  of  electricity  upon  (see  Electricity) 599 

process  of  dying  of 601 

galvanic  current  from  the  exterior  to  the  cut  sur- 
face of . .   603 

cranial  (see  Cranial  nerves) 608 

sympathetic  (see  Sympathetic) 729 

vaso-motor  (see  Vaso-motor  nerves) 739 

development  of 916 

Nervous  conduction,  rapidity  of 597 

Nervous  irritability  distinct  from  muscular  irritability 

59,  536 

description  of. 594 

distinct  in  motor  and  sensory  nerves 595 

influence  of  woorara  upon 595 

process  of  disappearance  of,  in  motor  nerves  ...  596 

momentary  destruction  of,  by  severe  shock 596 

destruction  of,  by  a  powerful  galvanic  shock 597 

Nervous  system,  influence  of,  upon  the  heart 58 

influence  of,  upon  absorption 320,  327 

influence  of,  upon  secretion 347 

influence  of,  upon  lactation 370,  376 

influence  of,  upon  the  secretion  of  sweat 393 

influence  of,  upon  the  secretion  of  urine 405 

origin  of  cholesterine  in 451 

influence  of,  upon  the  glycogenic  function  of  the 

liver 470 

influence  of,  upon  animal  heat 514 

general  considerations 503 

divisions  of. . .  564 

physiological  anatomy  of  the  tissue  of 5(55 

anatomical  divisions  of 565 

development  of 916 

functions  of,  in  the  foetus 919 

Nervous  tissue,  composition  of 583 

fatty  constituents  of. 584 

Nervus  intercostalis . . ,~ 730 

Neural  canal 900, 918 

head-fold  of. 900 

Neurilemma  of  the  spinal  cord. 667 

Neurine 584 

Neutrafp jint 605 

Ninth  cranial  nerve  (see  Sublinguai  nerve) 632 

Nipple,  sebaceous  glands  of 862,  366 

structure  of 366 

Nitrogen,  proportion  of,  in  the  air 140 

exhalation  of,  in  respiration 154 

in  the  blood 160 

quantity  of,  necessary  to  nutrition 192 

in  milk 375 

Nitrogenized  alimentary  principles 176 

digestion  of 243,  267,  277 

Nitrogenized  food,  influence  of,  upon  the  elimination 

of  urea 428 

relations  of,  to  animal  heat 518 

Nitrogenized  principles,  action  of  the  gastric  juice 

upon 245 

action  of  the  intestinal  juice  upon 267 

action  of  the  pancreatic  juice  upon 277  i 

action  of,  in  nutrition .' .  498  | 

Nitrous  oxide,  effects  of,  when  respired 141  I 

Nodes  in  vibrating  strings 830  ' 

Non-nitrogenized  alimentary  principles 180 

action  of  the  gastric  juice  upon 248  ! 


Non-nitrogenized  alimentary  principles,  action  of  the 

intestinal  juice  upon 267 

relations  of,  to  animal  heat 517 

—  action  of  the  pancreatic  juice  upon  274,  275 

Non-nitrogenized  principles  in  the  blood 21 

action  of,  in  nutrition 500 

Non-striated  muscular  fibres 527 

Nose,  uses  of  the  hairs  in  the  nostrils 390 

- —  development  of 928 

Notocorde 914 

Nutrition,  relations  of  respiration  to 161 

quantity  and  variety  of  food  necessary  to 191 

general  consideration 486 

action  of  inorganic  principles  in 488 

principles  consumed  by  the  organism 497 

action  of  nitrogenized  principles  in 498 

development  of  power  and  endurance  by  exercise 

and  diet 498 

action  of  non-nitrogenized  principles  in 500 

^  modifications  of,  by  various  conditions "504 

relations  of,  to  animal  heat 516 

O'Beirne,  sphincter  of 297 

Obliquus  externus,  action  of,  in  expiration 131 

internus,  action  of,  in  expiration 131 

(Esophagus,  influence  of  contraction  of  the  diaphragm 

upon 125 

structure  of. 218 

glands  of 218 

action  of,  in  deglutition 224 

alternate  contraction  and  relaxation  of 224 

effects  of  division  of  the  pneumogastrics  u;,on. .  662 

development  of 921 

Oils  (see  Fats) 183 

Oken,  bodies  of 927 

Oleine 183,  504 

Oleo-phosphoric  acid 5S5 

Olfaction,  mechanism  of 758 

relations  of,  to  gustation 758 

Olfactory  ganglia,  or  bulbs 756 

Olfactory  commissures  and  nerves,  development  of. .  919 

Olfactory  nerves 754 

physiological  anatomy  of 755 

general  properties  of 756 

functions  of 757 

Olivary  bodies 724 

Olive-oil 1S3 

Omentum 2S9 

development  of 921 

Omphalo-mesenteric  vessels 904,  931,  932 

Ophthalmic  ganglion 731 

Ophthalmoscope 791 

Opium,  exaggeration  of  the  reflex  excitability  of  the 

spinal  cord  by 686 

Optic  commissure 768 

Optic  lobes  (see  Tubercula  quadrigemina) 722 

Optic  nerves,  physiological  anatomy  of 767 

decussation  of 722,  768 

general  properties  of 769 

effects  of  stimulation  of 770 

expansion  of,  in  the  retina 777 

development  of. 919 

Optic  thalami,  physiological  anatomy  of 721 

functions  of 721 

development  of 917 

Ora  serrata  of  the  retina 776 

Orbicularis  oris,  action  of,  in  mastication 205 

Orbicularis  palpebrarum 812 

Organic  matter,  exhalation  of,  by  the  lungs 154 


INDEX. 


967 


PAGE 

Organic  nervous  system  (see  Sympathetic) 729 

Organic  non-nitrogenized  principles  in  the  blood 21 

Organic  saline  principles  in  the  blood 21 

Organic  nitrogenized  principles  in  the  blood 22 

Orgasm,  in  the  male 889 

in  the  female 890 

Osmazome ITS 

Osmosis 321 

Ossicles  of  the  ear 819,  841 

mechanism  of  the  action  of 841 

Ossification  of  the  skeleton 915 

time  of,  for  various  bones 916 

Osteine ITT,  544 

Osteoplasts 545 

Os  uteri 864 

action  of,  in  coitus 890 

Otic  ganglion T31 

Otoconia,  or  otoliths 843,  846 

Ovarian  tubes 860 

Ovaries,  situation  of 858 

ligament  of 858,  859 

structure  of 859 

cortical  and  medullary  substance  of 859 

Graaflan  follicles  of 859 

blood-vessels,  nerves,  and  lymphatics  of 860 

development  of 860 

passage  of  spermatozoids  to 892 

first  appearance  of 92T 

development  of  the  ligament  of 928 

Overtones 829 

Ovules  of  Naboth 866 

Ovum,  primordial 860,  869 

Ovum,  situation  of,  in  the  Graafian  follicle 863 

structure  of 869 

zona  pellucida  of 869 

vitelline  membrane  of STO 

micropile  of STO,  896 

vitellus  of 8TO 

discharge  of,  from  the  Graafian  follicle STO 

influence  of  copulation  upon  the  discharge  of 

871,  8T2 

relations  of  the  discharge  of,  to  menstruation  ST2, 8T5 

passage  of,  into  the  Fallopian  tube 8T2 

passage  of,  into  the  Fallopian  tube  upon  the  op- 
posite side 8T3 

duration  of  vitality  of. 892 

coating  of,  with  albumen,  in  the  Fallopian  tube 

892,  899 

union  of  spermatozoids  with 896 

membrana  media  of 903 

Oxalate  of  lime 420 

formation  of,  from  urate  of  ammonia 421 

Oxaluria 420 

Oxygen,  absorption  of,  by  the  blood-corpuscles 

13,  156,  160 

proportion  of,  in  the  air 140 

minimum  proportion  of,  in  the  air,  capable  of 

supporting  life 140 

—  effects  of  respiration  of  pure 141 

consumption  of  (see  Kespiration) 141 

relations  of  the  consumption  of,  to  the  exhalation 

of  carbonic  acid 143,  152 

analysis  of  the  blood  for 158 

proportion  of,  in  the  blood 158 

in  milk 375 

relations  of  the  consumption  of,  to  animal  heat. .  519 

Oxyhajmaglobine 17,  160 

Oysters,  digestibility  of 251 

Ozone...  140 


PAGE 

Pacini,  corpuscles  of 573 

Palatals 562 

Palate 216 

muscles  of 21T 

action  of,  in  protecting  the  posterior  nares  dur- 
ing deglutition 220 

action  of  the  velum  of,  in  phonation 55S 

action  of,  in  speech 562 

influence  of  the  facial  nerves  upon  the  move- 
ments of 623 

development  of 924 

Palato-glossus 217 

Palato-pharyngeus 217,  821 

Palpitation  of  the  heart 59,  61 

Pancreas,  physiological  anatomy  of 268 

extirpation  of 2T4 

development  of 921 

Pancreatic  fistula 269 

Pancreatic  juice 268 

mode  of  secretion  of 271 

general  properties  of 271 

reaction  and  specific  gravity  of 272 

composition  of 272 

quantity  of 272 

alterations  of 273 

action  of,  in  digestion 273 

action  of,  upon  fats 273 

action  of,  upon  starchy  and  saccharine   prin- 
ciples   275 

action  of,  upon  albuminoids 277 

Pancreatine 272 

Panniculus  adiposus 881 

Paraglobuline 29 

Parotid  saliva  (see  Saliva)  206 

Parovarium 863,  928 

Parturition,  separation  of  the  placenta  in  v 911,  942 

cause  of  the  first  contractions  of  the  uterus  in...  942 

arrest  of  hemorrhage  after 943 

after  death 946 

Par  vagum  nerve  (see  Pneumogastric) 644 

Patheticus 613 

physiological  anatomy  of 613 

properties  and  functions  of 613 

Pavement-epithelium 350,  353 

Pectine 182 

Pectoralis  major,  action  of  the  inferior  portion  of,  in 

respiration : 128 

Pectoralis  minor,  action  of,  in  respiration 128 

Pectose 182 

Penis,  erection  of 889 

development  of 930 

Pepper 190 

Pepsin 287 

Peptic  glands 229 

Peptone,  albumen 245 

fibrin 246 

caseine 246 

Peptones 23,  246 

Pericardial  secretion 852 

Pericardium 35 

development  of 934 

Perilymph  of  the  labyrinth 846 

Perimysium 531 

Perinevre 569 

Peristaltic  movements  of  the  small  intestine .'....' 285 

influence  of  the  bile  upon 283,  286 

influence  of  the  nervous  system  upon 287 

Peritoneal  cavity,  first  appearance  of 914 

Peritoneal  secretion 852 


968 


INDEX. 


PAGE 

Perivascular  canals 107,  583,  668 

Perspiration  (see  Sweat) 391 

Pettenkofer's  chamber  for  studying  the  processes  of 

respiration 142 

Pettenkofer's  test  for  bile 449 

Peyer,  patches  of 263,  267 

Pharyngeal  glands • 209 

Pharyngeal  plexus 738,  763 

Pharynx,  physiological  anatomy  of 215 

muscles  of 217 

mucous  membrane  of 217 

action  of  the  muscles  of,  in  deglutition 220 

action  of,  in  phonation 558 

development  of 921 

Phonation  (see  Voice) 554 

Phosphate  of  lime,  function  of,  in  alimentation 185 

table  of  quantities  of 495 

general  function  of 495 

origin  and  discharge  of 495 

Phosphate  of  magnesia 497 

Phosphate  of  potassa 497 

Phosphate  of  soda 497 

influence  of,  upon  the  capacity  of  the  blood  for 

absorbing  carbonic  acid 160 

Phosphates,  elimination  of,  in  the  urine  (see  Urine)..  423 
proportion  of,  in  the  blood  of  herbivora  and  car- 

nivora 423 

Phosphorized  fats 5S4,  535 

Phrenic  nerve 125 

Phrenic  plexus 733 

Pia  mater  cerebri 667 

first  appearance  of! 916 

Pia  mater  testis 880 

Picromel 444 

Pineal  gland 485 

Pinna  of  the  ear 817 

Pitch  of  musical  sounds 826 

Pituitary  body 485 

Pituitary  membrane 755 

Placenta,  glycogenic  function  of 469 

first  appearance  of 905,  90S 

development  and  structure  of 908 

maternal  portion  of 909 

injection  of,  from  the  sinuses  of  the  uterus 909 

connection  of  the  maternal  and  foetal  portions 

of 910 

structure  of,  fully  developed 910 

cotyledons,  or  lobes  of 910 

dissepiments  of , 910 

blood-vessels  of 911 

curling  arteries  of 911 

villi  of 911 

separation  of,  in  parturition. 911,  942 

Placental  circulation 933 

Plasma  of  the  blood,  (see  Blood) 6 

coloring  matter  of 23 

Plasmine 22 

decomposition  of,  into  fibrin  and  metalbumen  in 

coagulation  of  the  blood 29 

Platysma  of  the  uterus 864 

Pleural  secretion 852 

Pleuro-peritoneal  cavity,  first  appearance  of 914 

Plica  semilunaris 812 

Pneumate  of  soda  in  the  blood 21 

Pneumic  acid 21 

action  of,  upon  the  alkaline  carbonates  and  bi- 

carbonates  in  the  blood 153, 160 

Pneumogastric  nerves,  influence  of,  upon  the  action 

of  the  heart 59,  60 


PAGE 

Pneumogastric  nerves,  hunger  after  section  of. .  .174,  664 
influence  of,  upon  the  movements  of  the  small 

intestine 287 

physiological  anatomy  of 644 

deep  origin  of 644 

ganglia  of 645 

anastomoses  of 645 

distribution  of 646 

difference  in  the  distribution  of  the  nerves  of 

the  two  sides,  to  the  abdominal  organs 648 

—  properties  and  functions  of 648 

general  properties  of  the  roots  of. 649 

—  properties  and  functions  of  the  auricular  branch 

of. 650 

properties  and  functions  of  the  superior  laryngeal 

branch  of 651 

— —  influence  of  the  superior  laryngeal  branch  of, 
upon  the  voice 651 

influence  of  the  superior  laryngeal  branch  of, 

upon  deglutition 651 

influence  of  the  superior  laryngeal  branch  of, 

upon  respiration 652 

properties  and  functions  of  the  inferior,  or  recur- 
rent laryngeal  branch  of. 652 

influence  of  the  inferior  laryngeal  branch  of,  upon 

the  movements  of  the  larynx 116,  652 

influence  of  the  inferior  laryngeal  branch  of,  upon 

respiration 653 

influence  of  the  inferior  laryngeal  branch  of,  upon 

deglutition 653 

effects  of  section  of,  upon  the  circulation 653 

effects  of  section  of,  upon  the  respiratory  move- 
ments   653,  659 

want  of  action  of  digitalis  upon  the  heart  after 

section  of ; 654,  665 

effects  of  galvanization  of,  upon  the  circula- 
tion   654,658 

direct  influence  of,  upon  the  heart 654,  65S 

condition  of  the  lungs  after  death  following  sec- 
tion of 659 

effects  of  galvanization  of,  upon  respiration 661 

properties  and  functions  of  the  oesophageal 

branches  of 662 

effects  of  division  of,  upon  the  oesophagus . .  252,  662 

—  properties    and   functions   of   the   abdominal 
branches  of. : 662 

influence  of,  upon  the  liver 471,  662 

influence  of,  upon  the  stomach 252,  663 

effects  of  galvanization  of,  upon  the  stomach 663 

effects  of  section  of,  upon  the  movements  of  the 

stomach  and  the  secretion  of  gastric  juice 252,  664 

distribution  of,  to  the  intestinal  canal 665 

want  of  action  of  purgatives,  after  section  of 665 

Polar  globule  of  the  vitellus 897 

Pons  Yarolii  and  medulla  oblongata,  weight  of. 690 

Pons  Varolii  (see  Tuber  annulare) 722 

development  of. 917,  918 

Portal  system  of  the  kidney 401 

Portal  vein,  distribution  of  (see  Liver) 432 

influence  of  obliteration  of,  upon  the  secretion 

of  bile 440 

temperature  of  the  blood  in 5 

Portio  dura  of  the  seventh  cranial  nerve  (see  Facial 

nerve) 618 

Pregnancy,  influence  of,  upon  lactation 370,  876 

influence  of,  upon  menstruation 875 

— -  influence  of,  upon  the  corpus  luteum 878 

Fallopian 892,  942 

abdominal 


INDEX. 


969 


PAGE 

Pregnancy,  influence  of,  upon  subsequent  offspring.. .  894 

enlargement  of  the  uterus  in 938 

enlargement  of  the  heart  in 939 

duration  of 939 

multiple 941 

extra-uterine 942 

Prehension  of  solids  and  liquids 197 

Prepuce,  smegnia  of 862 

Presbyopia 789 

Primitive  trace  of  the  embryon 899,  900 

Prisms,  action  of,  upon  light 786 

Progressive  muscular  atrophy 742 

Prostate 883 

Prostatic  fluid,  uses  of 888 

Protagon 29,  584,  585 

Protoplasm 522 

Proximate  principles 20 

Ptosis  (see  Blepharoptosis) 611,  812 

Ptyaline 211 

action  of,  upon  starch 214 

Puberty,  influence  of,  upon  the  exhalation  of  carbonic 

acid  in  the  female 148 

period  of 874,  945 

Pulmonary  artery,  pressure  of  blood  in 109 

development  of 932,  933 

Pulmonary  circulation 109 

Pulmonary  mucus 356 

Pulmonic  semilunar  valves 88,  48 

safety-valve  function  Of. 48, 109 

Pulp-cavity  of  the  teeth 199 

Pulse,  frequency  of,  at  different  ages 52 

in  the  sexes 52 

influence  of  digestion  upon  the  frequency  of 52 

influence  of  muscular  exertion  upon  the  fre- 
quency of. 52,  53 

comparative  frequency  of,  in  sitting  and  standing    52 

influence  of  temperature  upon  the  frequency  of.    53 

influence  of  sleep  upon  the  frequency  of 53 

production  of,  and  locomotion  of  the  arteries;. . .     70 

investigation  of,  by  the  finger 71 

gradual  delay  of,  receding  from  the  heart 71 

pathological  varieties  of 71,  74 

form  of. 71 

movements  of,  in  the  foot  when  the  legs  are 

crossed 71 

traces  of 72,  73 

influence  of  temperature  upon  the  form  of. ...  73,  74 

dicrotism  of ' 73,  74 

in  the  veins 99, 106 

relation  of  the  frequency  of,  to  the  respiratory  acts  132 

influence  of  menstruation  upon 876 

Punctum  ca3cum  of  the  retina 792 

Pupil 774,  919 

Pupillary  membrane 775.  919 

Purgatives,  want  of  action  of,  after  section  of  the 

pneumogastrics 66 

Purkinje,  vesicle  of. 870 

Pus-corpuscles 13 

Putrefaction  of  the  body  after  death 947 

Pyloric  muscle 227 

Quickening 911 

Quince-seeds 182 

Rape-seed  oil 183 

Receptaculum  chyli 302,  307 

Rectum,  muscular  coat  of. 290 

physiological  anatomy  of 291 

development  of 920 


PAGE 

Recurrent  laryngeal  nerves  (see  Pneumogastric) 652 

Recurrent  sensibility 590 

Reflex  action  in  respiration 166,  G60,  727 

Reflex  action,  time  occupied  by 599 

definition  of 683 

of  the  spinal  cord 684 

conditions  necessary  to  the  manifestations  of. . .  686 

exaggeration  of,  by  poisoning  with  opium  or 

strychnine 6S6 

abolition  of,  by  anaesthetics 687 

examples  of. 687 

operating  through  the  sympathetic  system 740 

in  the  foetus 919 

Refraction  (see  Light  and  Eye) 787,  798 

Reil,  island  of. 705 

Reissner,  membrane  oT 844 

Remak,  fibres  of. 568,  735 

Renal  veins,  color  of  the  blood  in 5 

non-coagulation  of  the  blood  of. 30 

Reproduction  (see  Generation) 852 

Reserve  air 186 

Residual  air 186 

Resonators  of  Helmholtz 881 

Respiration,  relations  of  the  blood-corpuscles  to 13 

influence  of,  upon  the  action  of  the  heart 54, 110 

voluntary  arrest  of,  with  arrest  of  the  action  of 

the  heart 55 

influence  of,  upon  the  arterial  pressure 78 

relations  of,  to  the  capillary  circulation 89 

relations  of,  to  the  venous  circulation 105 

general  considerations  and  definition  of 114 

function  of  the  blood  in 115 

essential  conditions  in 115 

physiological  anatomy  of  the  organs  of. 116 

movements  of. -121 

ribs,  arrangement  of. 122 

table  of  muscles  of,  used  in  inspiration 123 

auxiliary  muscles  of,  used  in  inspiration 127 

table  of  muscles  of,  used  in  expiration 130 

action  of  the  abdominal  muscles  in 131 

types  of 131 

differences  in  types  of,  in  the  sexes  and  at  differ- 
ent ages 132 

frequency  of  the  movements  of 132 

relations  of  the  frequency  of  the  movements  of,  to 

the  pulse 132 

influence  of  age  upon  the  frequency  of  the  move- 
ments of 132 

relations  of  inspiration  and  expiration  to  each 

other 133 

arrest  of,  in  straining,  etc 133 

stethoscopic  sounds  of. 133 

extreme  breathing  capacity 137 

relations  in  the  volume  of  the  expired  to  the 

inspired  air 138 

diffusion  of  gases  in 189 

of  pure  oxygen 141 

consumption  of  oxygen 141 

variations  in  the  consumption  of  oxygen  with 

muscular  activity,  external  temperature,  and  diges- 
tion   142 

variations  in  the  consumption  of  oxygen,  sleeping 

and  waking 143 

variations  in  the  consumption  of  oxygen  with 

age 143 

variations  in  the  consumption  of  oxygen  in  lean 

and  fat  animals 143 

relations  of  the  consumption  of  oxygen  to  the 

production  of  carbonic  acid 143, 152 


970 


IM)EX. 


Respiration,  effects  upon  the  consumption  of  oxygen 

of  increasing  its  proportion  in  the  air 143 

effects  upon  the  consumption  of  oxygen  of  con- 
fining an  animal  in  a  mixture  of  oxygen  and  hy- 
drogen    143 

quantity  of  oxygen  consumed  per  hour  in 144 

changes  in  the  air  in  passing  through  the  lungs  144 

elevation  in  temperature  in  the  air  in  passing 

through  the  lungs 144 

exhalation  of  carbonic  acid  in 144 

variations  in  the  exhalation  of  carbonic  acid  with 

the  frequency  and  extent  of  the  acts  of. 145 

—  quantity  of  carbonic  acid  exhaled  per  hour  in. . .  146 
influence  of  sleep  upon  the  exhalation  of  car- 
bonic acid  in 146, 150 

influence  of  age  upon  the  exhalation  of  carbonic 

acid  in 147 

influence  of  sex  upon  the  exhalation  of  carbonic 

acid  in 147 

influence  of  digestion  upon  the  exhalation  of  car- 
bonic acid  in 143 

influence  of  inanition  upon  the  exhalation  of  car- 
bonic acid  in 148 

influence  of  diet  upon  the  exhalation  of  carbonic 

acid  in 148 

influence  of  alcoholic  beverages,  tea,  and  coffee 

upon  the  exhalation  of  carbonic  acid  in 149 

influence  of  tea,  coffee,  and  tobacco  upon  the  ex- 
halation of  carbonic  acid  in 149 

influence  of  mental  depression  upon  the  exhala- 
tion of  carbonic  acid  ini 150 

influence  of  exercise  upon  the  exhalation  of  car- 
bonic acid  in 150 

influence  of  moisture  and  temperature  upon  the 

exhalation  of  carbonic  acid  in 151 

influence  of  season  upon  the  exhalation  of  car- 
bonic acid  in -. 151 

relations  between  the  quantity  of  oxygen  con- 
sumed and  the  quantity  of  carbonic  acid  exhaled . . .  152 

sources  of  the  carbonic  acid  exhaled  in 153 

exhalation  of  watery  vapor  in 153 

exhalation  of  ammonia,  organic  matter,  etc.,  in. .  154 

exhalation  of  nitrogen  in 154 

changes  in  the  blood  in 155 

mechanism  of  the  interchange  of  gases  between 

the  blood  and  the  air  in 161 

relations  of,  to  nutrition 161 

essential  processes  of 162 

combustion -theory  of. 163 

cutaneous 168 

in  a  confined  space  170 

relations  of,  to  deglutition 220 

connection  of  the  medulla  oblongata  with 726 

influence  of,  upon  the  circulation  of  lymph 840 

relations  of,  to  animal  heat 518 

influence  of  the  superior  laryngeal  branches  of 

the  pneumogastrics  upon 652 

influence  of  the  inferior  laryngeal  branches  of 

the  pneumogastrics  upon 653 

effects  of  section  of  the  pneumogastrics  upon  653, 659 

effects  of  galvanization  of  the  pneumogastrics 

upon 661 

movements  of  the  brain  with 668 

Eespiratory  efforts  before  birth 167,  919 

Respiratory  excitants 149 

Respiratory  movements,  reflex  character  of,  and  cause 

of  these  movements 166,  660,  727 

Respiratory  movements  of  the  glottis 558 

Respiratory  non-exciters 149 


PAGE 

Respiratory  sense 164,  660,  727 

Restiform  bodies 725 

Resultant  tones 831 

Rete  testis 881 

Retina 775 

ora  serrata  of 776 

macula  lutea  of 776,  791 

fovea  centralis  of 776,  791 

layers  of. 776 

layer  of  rods  and  cones  of 776,  791 

external  granule-layer  of. 777 

inter-granule  layer  (cone-fibre  plexus)  of 777 

- —  internal  granule  layer  of 777 

— —  granular  (molecular)  layer  of. 777 

layer  of  ganglion-cells  of 777 

expansion  of  the  optic  nerve  in 777 

limitary  membrane  of 777 

connective  tissue  of 778 

connection  between  the  rods  and  cones  and  the 

ganglion -cells  of 778 

blood-vessels  of 778 

sensibility  of  the  layer  of  rods  and  cones  of  —  791 

shadows  of  the  vessels  of 791 

relative  sensibility  of  different  parts  of 792 

corresponding  points  in 802,  803,  810 

Retractors  of  the  anus 290 

Retrahens  aurem 81 8 

Right-handedness  (see  Dextral  preeminence) 944 

Rigor  mortis  (see  Cadaveric  rigidity) 946 

Rima  glottidis 116 

Rods  of  the  retina 776,  791 

Rolling  movements  following  injury  of  certain  parts 

of  the  encephalon,  etc : 728 

Rosenmuller,  organ  of 863,  928 

Ruloff,  brain  of W3 

Rumination 255 

Russian  baths 521 

Rut,  identity  of,  with  menstruation 871,  875 

Ruysch,  tunic  of 772 

Saccule  of  the  internal  ear 843 

distribution  of  the  nerves  in 846 

Sacro-lumbalis,  action  of,  in  expiration 131 

Sacrum,  consolidation  of 914 

..  181 


Sago. 


205 


Saliva 

Saliva,  parotid 206 

secretion  of 206 

action  of,  upon  starch 206 

relations  of  the  flow  of,  to  mastication 207,  214 

alternation  in  the  secretion  of,  upon  the  two 

sides 207 

Saliva,  submaxillary 208 

influence  of  sapid  substances  upon  the  secre- 
tion of 208 

Saliva,  sublingual 203 

influence  of  sapid  substances  upon  the  secretion 

of 209 

Saliva,  fluids  from  the  smaller  glands  of  the  mouth, 

tongue,  and  pharynx 209 

Saliva,  mixed 210 

influence  of  matters  introduced  into  the  stomach     ^ 

through  a  gastric  fistula  upon  the  secretion  of 210 

influence  of  the  sight,  odor,  or  thought  of  food 

upon  the  secretion  of 210 

quantity  of 210 

reaction  of 210 

quantity  of,  secreted  during  the  intervals  of  mas- 
tication...  210 


INDEX. 


971 


PAGE 

Saliva,  mixed,  general  properties  and  composition  of  210 

specific  gravity  of. 210 

sulpho-cyanide  in 211 

table  of  the  composition  of 211 

organic  principle  of. , 211 

functions  of 212 

action  of,  upon  starch 212 

influence  of,  upon  deglutition 214 

mechanical  functions  of. 214 

Salivary  fistula 206 

Salivary  glands 205 

Saponification 184 

Sarcode 522 

Sarcolactates 418 

Sarcolemma 530 

Savors 759 

Scala  tympani  of  the  cochlea 844 

Scala  vestibuli  of  the  cochlea 844 

Scalene  muscles,  action  of,  in  respiration 125 

Scarf-skin  (see  Skin) 881 

Scarpa,  humor  of 846 

Schlemm,  canal  of 775 

Schneiderian  mucous  membrane 755 

Schwann,  sheath  of 566 

white  substance  of 566 

Sclerotic  coat  of  the  eye 770 

development  of 919 

Scrotum 880 

development  of 930 

Scurvy 193 

Season,  influence  of,  upon  the  exhalation  of  carbonic 

acid 151 

influence  of,  upon  the  diet 172, 193 

influence  of,  upon  the  urine 427 

Sebaceous  glands 358 

first  appearance  of 916 

Sebaceous  matter. 358,  361 

of  the  nipple 362 

Secreted  fluids,  tabular  view  of 850 

Secreting  organs,  general  structure  of. 34S 

Secretion,  general  considerations 341 

mechanism  of 312 

classification  of  the  products  of 342 

distinction  of,  from  excretion 342 

mechanism  of,  as  distinguished  from  excretion. .  843 

action  of  glandular  epithelium  in 343 

intermittency  of,  as  distinguished  from  excretion  844 

—  influence  of  the  composition  and  pressure  of  the 
blood  upon 346 

influence  of  the  nervous  system  upon 347,  738 

centres  presiding  over 347 

influence  of  the  sympathetic  system  upon 738 

Segmentation  of  the  vitellus 896 

Semen . 833 

quantity  of 884 

general  characters  of  884 

chemical  constitution  of 884 

mucous  secretions  mixed  with 884 

in  advanced  age 836 

ejaculation  of 889 

penetration  of,  into  the  uterus 891 

passage  of,  through  the  Fallopian  tubes 892 

—  time  occupied  by  passage  of,  to  the  ovaries 892 

Semicircular  canals,  bony 822 

Semicircular  canals,  membranous 843 

ampullae  of 843 

distribution  of  the  nerves  in 846 

septum  transversum  of. 846 

functions  of. ..  849 


PAGE 

Semicircular  canals,  influence  of,  upon  equilibration. .  849 

disease  of  (Meniere's  disease) 718,  849 

development  of 919 

Semilunar  ganglia 733 

Semilunar  valves,  pulmonic 88,  48 

pulmonic,  safety-valve  function  oi 48, 109 

aortic...  ..  ao  40 


Seminal  vesicles. . g82 

Seminiferous  tubes §80,  885 

Semivowels 532 

Sensation  in  amputated  members,  etc 593 

Sensory  nerves,  action  of 592 

disappearance  of  the  physiological  properties  of  596 

effects  of  anaesthetics  upon 596 

Septum  lucidum,  development  of. 918 

Serine 23 

Seroline 295 

Serotina,  cells  of 911 

Serous  cavities,  absorption  from 317 

Serous  fluids 351 

Serous  membranes 850 

Serratus  magnus,  action  of,  in  respiration 128 

Serratus  posticus  superior,  action  of,  in  respiration. . .  127 

Serum  of  the  blood  (see  Blood) 24 

Seventh  cranial  nerve,  portio  dura  of  (see  Facial  nerve)  618 

portio  mollis  of  (see  Auditory  nerves) 815 

Sex,  influence  of,  upon  the  pulse 52 

influence  of,  upon  the  exhalation  of  carbonic 

acid 147,  150 

influence  of,  upon  the  urine 426 

determination  of,  hi  the  foetus 893 

Sexual  intercourse  (see  Coitus) 887 

Shells  of  cocoa 190 

Sighing 134,  167 

Sinus  terminalis  of  the  area  vasculosa 931 

Sinuses  of  Valsalva 39,  64 

Sixth  cranial  nerve  (see  Motor  oculi  externus) 614 

Skeleton,  ossification  of. 915 

Skin,  respiration  by 168 

effects  of  an  impermeable  coating  applied  to  168,  891 

distribution  of  lymphatics  in 305 

absorption  by 314 

physiological  anatomy  of. 880 

extent  and  thickness  of 880 

layers  of. 881 

layer  of  corium 881 

reticulated  layer  of 381 

papillary  layer  of. 331 

epidermis 

rete  mucosum,  or  Malpighian  layer  of 

of  the  negro .*.... 

horny  layer  of. 

general  uses  of 

amount  of  exhalation  from 

development  of . . .  / 

action  of,  in  the  equalization  of  the  animal  heat. , 

Skull,  development  of 915 

Sleep,  influence  of,  upon  the  pulse 53 

influence  of,  upon  the  consumption  of  oxygen . . .  143 

influence  of,  upon  the  exhalation  of  carbonic  acid  146 

influence  of,  upon  digestion 251 

phenomena  of. 743 

condition  of  the  brain  and  nervous  system  in 746 

produced  by  pressure  on  the  carotids 747 

theories  of. 747,  749 

conditions  of  various  functions  in 749 

Smegma  of  the  prepuce  and  of  the  labia  minora 3G2 

Smell  (see  Olfaction) 758 

Sneezing 134 


382 
382 


916 
521 


973 


INDEX. 


PAGE 

Snoring 133 

Sobbing 125,135 

Solar  plexus 733 

Solitary  glands  of  the  intestine 264,  267,  291 

Sommering,  yellow  spot  of 776 

Soprano 556 

Sound,  physics  of 823 

laws  of  vibrations  of. 824 

propagation  of 825 

reflection  of. 825 

refraction  of 825 

shadows  of 8£5 

>  rapidity  of  transmission  of. 825 

noisy  and  musical 826 

pitch  of. 826 

range  of,  in  music 826 

musical  scale  of 827 

quality  of. 828 

harmonics,  or  overtones « 829 

resultant  tones 831 

summation  tones 832 

harmony 832 

chords 832 

discords 833 

beats 833 

to'nes  by  influence  (consonance) 834,  837 

Sounds  of  the  heart 48 

Soups,  digestibility  of. 251 

Spasm,  artificial 539 

Speech,  mechanism  of 560 

action  of  the  mouth,  teeth,  lips,  tongue,  and  pal- 
ate in 562 

modifications  of,  in  cases  of  cleft  palate  or  hare- 
lip   562 

Spermatic  cells 886 

Spermatic  cord • 880 

Spermatiue 884 

Spermatozoids 884 

discovery  of 884 

movements  of. 885 

intermediate  segment  of 885 

action  of  water,  reagents,  cold,  heat,  etc.,  upon . .  885 

—  development  of 885 

in  advanced  age 886 

duration  of  the  vitality  of,  in  the  female  genera- 
tive passages 893 

penetration  of,  through  the  vitelline  membrane. .  896 

Spheno-palatine  ganglion 731 

Spherical  aberration 789 

Sphygmograph 72 

Sphincter  of  the  bladder 408 

Sphincters  of  the  anus 296-298 

Spices ...  190 

Spina  bifida 915 

Spinal  accessory  nerve 627 

physiological  anatomy  of.  627 

small,  internal,  or  communicating  branch  of,  to 

the  pneumogastric 628 

properties  and  functions  of. ; 628 

functions  of  the  internal  branch  of 629 

extirpation  of,  in  living  animals 629 

influence  of,  upon  phonation 629 

influence  of,  upon  deglutition 631 

influence  of,  upon  the  heart 631,  655,  658 

functions  of  the  external,  or  muscular  branch 

of,  going  to  the  sterno-cleido  mastoid  and  trapezius 

muscles 631 

Spinal  column,  development  of.  915 

twisting  of,  in  the  embryon 915 


PAGE 
Spinal  column,  temporary  caudal  appendage  of  ......  915 

Spinal  cord,  arrest  of  the  action  of  the  heart  by  sud- 
den destruction  of  ...............................     59 

—  lymphatics  of  .................................  306 

-  regeneration  of.  ...............................  586 

-  neurilemma  of  ................................  667 

—  physiological  anatomy  of.  .....................  668 

-  filum  terminale  of.  ...............  .  ............  669 

—  proportion  of  white  to  gray  substance  in  differ- 
ent  portions  of.  .................................  669 

—  direction  of  the  fibres  in  .......................  671 

-  connections  of,  with  the  roots  of  the  nerves  .....  672 

—  general  properties  of  ..........................  673 

—  excitable  and  sensible  portions  of.  .............  674 

-  transmission  of  motor  stimulus  in  ..............  676 

-  direction  of  motor  conductors  in  ................  676 

-  decussation  of  the  motor  conductors  of  .........  676 

—  transmission  of  sensory  impressions  in  .........  677 

—  the  posterior  white  columns  of,  do  not  serve  as 
conductors  of  sensory  impressions  ................  678 

—  conduction  of  sensory  impressions  by  the  gray 
substance  of  ____  ..................................  678 

—  function  of,  in  connection  with  muscular  coordi- 
nation ......................................  679,  711 

-  decussation  of  the  sensory  conductors  of.  .......  680 

—  hyperaesthesia  due  to  injury  of  portions  of.  ......  6SO 

-  summary  of  the  action  of,  as  a  conductor  .......  682 

—  action  of,  as  a  nerve-centre  .....................  6S3 

—  reflex  action  of  (see  Keflex  action)  ...............  684 

-  dispersion,  or  diffusion  of  impressions  in  ........  655 

--  development  of.  ...............................  917 

Spinal  nerves,  distinction  between  motor  and  sensory 

roots  of  ........................................  587 

-  properties  of  the  posterior  roots  of  .............  589 

-  properties  of  the  anterior  roots  of  .............  590 

-  distribution  of  ................................  606 

-  connections  of,  with  the  spinal  cord  ............  672 

Splanchnic  nerves  ...............................  ...  733 

Spleen,  relations  of,  to  the  blood  -corpuscles  ..........     13 

-  proportion  of  leucocytes  in  the  blood  of  the  veins 

of.  ..............................................     15 

--  physiological  anatomy  of  .......................  473 

-  fibrous  structure  of  (trabecula?)  ................  474 

-  Malpighian  bodies  of  ..........................  474 

-  spleen-pulp  ____  ...............................  475 

-  blood-corpuscle-containing  cells  of.  .............  475 

-  blood-vessels  and  nerves  of  ..............  •  ......  475 

-  contractility  of  ................................  476 

-  chemical  constitution  of  .......................  476 

-  functions  of.  ..................................  477 

--  changes  in  the  constitution  of  the  blood  by  .....  477 

-  variations  in  the  volume  of.  ....................  477 

-  extirpation  of.  ................................  478 

-  influence  of  extirpation  of,  upon  the  appetite  and 
disposition  ......................................  478 

-  development  of  ...............................  921 

Splenic  plexus  .....................................  733 

Spores  ..........  .................................  856 


Spurzheim,  brain  of 
Stapedius  muscle 
Stapes 


703 
...  821 
819 
Starch  ............................................  181 

-  iodine-test  for  .................................  181 

-  proportion  of,  in  different  vegetables  ............  181 

-  action  of  the  parotid  saliva  upon  ................  206 

-  general  action  of  the  saliva  upon  ................  212 

-  action  of  the  gastric  juice  upon,  by  hydration.  .  .  248 

-  action  of  the  intestinal  juice  upon  ..............  267 

-  action  of  the  pancreatic  juice  upon  .............  275 


INDEX. 


973 


PAGE 

Starvation  (see  Inanition) 148,  1T5 

Stearic  acid 183 

Stearine 183,  504 

Steno,  duct  of 206 

Stercorine 294 

.  formation  of,  from  cbolesterine 295 

in  the  faeces 456 

Stereoscope 805 

Sterno-mastoideus,  action  of,  in  respiration 127 

St.  Martin,  case  of 232 

Stomach,  physiological  anatomy  of 226 

capacity  of. 226 

peritoneal  coat  of. 226 

muscular  coat  of 226 

blood-vessels  of 223 

mucous  coat  of. 228 

pits  of 228 

glandular  apparatus  of. 229 

gastric,  or  peptic  glands 229 

mucous  glands  of 229 

closed  follicles  of 229 

secretion  of  (see  Gastric  juice) 230 

changes   in    the   appearance    of    the    mucous 

membrane    of,    during    the    secretion    of    gastric 

juice : . .  234 

secretion  in  different  parts  of. 235 

infusions  of  the  mucous  membrane  of 235 

duration  of  digestion  in 249 

digestibility  of  different  aliments  in 249 

influence  of  the  pneumogastrics  upon 252,  663 

influence  of  the  nervous  sj'stem  upon 252 

movements  of. 253 

division  of,  into  two  compartments,  by  contrac- 
tions of  circular  fibres  during  digestion 254 

regurgitation  of  food  from 255 

gases  of. 298 

absorption  by 301 

development  of 920 

Stomata  in  the  walls  of  the  capillaries 82 

Strabismus,  external 611 

internal 615 

Striated  muscular  fibres 529 

Strychnine,  exaggeration  of  the  reflex  excitability  of 

the  spinal  cord  by 686 

Styloid  ligament,  development  of 922 

Subareolar  muscle 366 

Subclavian  arteries,  development  of 933 

Subclavian  veins,  development  of , 934 

Sublingual  nerves,  effects  of  section  of,  upon  deglu- 
tition   219 

effects  of  section  of,  upon  mastication 204 

physiological  anatomy  of 632 

properties  and  functions  of 633 

influence  of,  upon  the  tongue  and  upon  degluti- 
tion   634 

Sublingual  saliva  (see  Saliva) 208 

Submaxillary  ganglion T31 

Submaxillary  glands,  variations  in  the  color  of  the 

blood  in 5,  844,  347 

influence  of  the  chorda  tympani  upon 623 

Submaxillary  saliva  (see  Saliva) 208 

Sucking,  mechanism  of 197 

action  of  the  tongue  in 204 

Sudoric  acid  and  sudorates 395 

Sudoriparous  glands  (see  Sweat) 391 

first  appearance  of 916 

Suffocation,  sense  of 166 

Sugar  in  the  blood 22 

Sugar,  characters  of 180 


PAGE 

Sugar,  action  of  the  gastric  juice  upon 248 

not  acted  upon  by  the  intestinal  juice 267 

action  of  the  pancreatic  juice  upon 276 

absorption  of,  by  the  lacteals 313 

presence  of,  in  the  lymph 332 

presence  of,  in  the  chyle 837 

of  milk 875 

production  of,  by  the  liver  (see  Liver) 458 

process  for  the  determination  of 460 

Trommer's  test  for 461 

Fehling's  test  for 461 

character  of,  produced  by  the  liver 466 

rapidity  with  which  the  different  varieties  of, 

(cane-sugar,  milk-sugar,  glucose,  and  liver-sugar) 

are  destroyed  in  the  system 467 

destination  of,  in  the  economy 471 

relations  of,  to  nutrition 500 

Sulphate  of  lime 497 

Sulphate  of  potassa 497 

Sulphate  of  soda! 497 

Sulphates,  elimination  of,  in  the  urine 423 

Sulpho-cyanide  in  the  saliva 207,  208,  211,  212 

Sulpho-cyanide  of  potassium,  action  of,  upon  mus- 
cular irritability 59 

Sulphuretted  hydrogen,  exhalation  of,  by  the  lungs, 

when  injected  into  the  venous  system 154 

Summation  tones 832 

Superfecundation 894 

Superfcetation 894 

Superior  laryngeal  nerves  (see  Pneumogastric) 651 

Suprarenal  capsules,  development  of 928 

weight  of,  compared  with  the  kidneys,  in  the 

fostus  and  adult 928 

structure  of 479,  480 

chemical  reactions  of.  .* 481 

functions  of. 481 

extirpation  of 482 

Suspensory  ligament  of  the  crystalline  lens 779 

Sweat 391 

Sweat-glands 391 

number  of,  in  different  parts  of  the  surface . . .  392 

Sweat,  mechanism  of  the  secretion  of 393 

influence  of  the  nervous  system  upon  the  secre- 
tion of 893 

quantity  of 393 

influence  of  exercise  upon 894 

influence  of  temperature  upon 394 

properties  and  composition  of 894 

urea  in 894 

peculiarities  of,  in  certain  parts 395 

odor  of,  in  certain  parts 395 

equalization  of  animal  heat  by 521 

Sympathetic  nerves,  influence  of,  upon  the  color  of 

the  blood  in  the  veins C 

action  of,  upon  the  heart 59,  60 

— —  influence  of,  upon  the  arteries 69 

influence  of,  upon  the  movements  of  the  small 

intestine 287 

influence  of,  upon  animal  heat 514,  519 

Sympathetic  system 729 

general  arrangement  of. 730 

distribution  of 730 

cranial  ganglia  of 731 

cervical  ganglia  of 781 

thoracic  ganglia  of 733 

abdominal  and  pelvic  ganglia  of 733 

parts  in  which  the  terminal  nerves  of,  are  con- 
nected with  ganglionic  cells 735 

structure  of  the  nerves  and  ganglia  of. 735 


974 


INDEX. 


PAGE 

Sympathetic  system,  general  properties  of. . .   736 

connection  of,  with  the  cerebro-spinal  system..  736 

functions  of 737 

influence  of  division  of  nerves  of,  upon  animal 

heat : 737 

influence  of,  upon  the  circulation 738 

influence  of,  upon  secretion 733 

influence  of,  upon  the  urine 738 

influence  of,  upon  the  intestines 739 

reflex  phenomena  in 740 

influence  of,  upon  the  iris 741,  797 

Sympexions 884 

Syncope 62 

Synovial  bursse 351 

Synovial  fluid 352 

composition  of 353 

variations  of,  with  use  of  the  joints 353 

Synovial  fringes 351,  353 

Synovial  membranes 351 

absorption  by 317 

Synovial  sheaths 351 

Synovine 352 

Tactile  corpuscles 574 

Tao-foo 179 

Tapioca 181 

Taste  (see  Gustation) 759 

—  action  of  the  glosso-pharyngeal  nerve  in 764 

influence  of  the  chorda  tympani  upon 622 

Taste-buds,  or  taste-beakers 765 

Taste-cells 766 

Taste-pores 766 

Tastes  and  flavors 759 

Taurine 280,  421 

Taurocholic  acid  and  taurocholate  of  soda 280,  444 

Tea 189 


of,   upon  the  exhalation  of  carbonic 


influence 

acid 149 

influence  of,  upon  the  elimination  of  urea 428 

Tears 814 

Teeth,  physiological  anatomy  of 198 

enamel  of 199 

dentine  of 199 

cement  of. 199 

pulp-cavity  of 199 

varieties  of 200 

function  of  the  sensibility  of,  to  hard  substances, 

in  mastication 205 

action  of,  hi  speech 562 

Teeth,  temporary,  development  of. 924 

primitive  band  for  the  development  of. 924 

epithelial  band  for  the  development  of. 924 

enamel-organ  of. 925 

bulb  of 925 

follicle  of 925 

dentine,  or  ivory  of 925 

cement  of 925 

order  of  eruption  of 926 

Teeth,  permanent,  development  of. 926 

order  of  eruption  of 927 

Temperament,  in  musical  instruments 828 

Temperature  of  the  blood 5 

Temperature,  influence  of,  upon  the  pulse 53,  73,  74 

influence  of,  upon  the  size  of  the  arteries 70 

influence  of,  upon  the  capillary  circulation 91 

influence  of,  upon  the  exhalation  of  carbonic 

acid 151 

—  appreciation  of 754 

Temporo-maxillary  articulation 202 


PAGE 

Tendons,  sheaths  of 851 

connection  of,  with  the  muscles 533 

Tenesmus 297 

Tenor- voice 555 

Tensor  palati 217,  821 

Tensor  tympani 820,  837 

Tentorium 667,  706 

Tesselated  epithelium 350,  353 

Testicles 879 

tunica  vaginalis  of 880,  928 

tunica  albuginea  of 880 

corpus  Highmorianum  of,  or  mediastinum  tes- 

tis 880 

lobules  of 880 

tunica  vasculosa  of,  or  pia  mater  testis 880 

seminiferous  tubes  of 880 

vasa  recta  of 881 

rete  of 881 

vasa  efferentia  of 881 

vas  aberrans  of  Haller '. 881 

first  appearance  of 927 

descent  of 928 

gubernaculum  of 928 

Tetanic  contraction 540 

Tetanus 6S7 

Theine '. 189 

Theobromine 190 

Third  cranial  nerve  (see  Motor  oculi  communis) 60 J 

Thirst 174 

effects  of  haemorrhage  upon 174 

seat  of  sense  of 175 

—  relief  of,  by  absorption  of  water  by  the  skin 316 

Thoracic  duct 302,  806,  307 

fistula  into 328,335 

Thorax,  form  of 121 

action  of  the  elasticity  of  the  walls  of,  in  expira- 
tion   129 

Thraenine 814 

Thymus  gland 4S3 

Thyroid  gland 482 

structure  of 488 

functions  of 4S3 

enlargement  of,  during  menstruation 483 

Thyro-arytenoid  muscles 553,  557 

Tidal  air 136 

Titillation 753 

Tobacco,  influence  of,  upon  the  exhalation  of  carbonic 

Mfcid 149 

Tones  (see  Sound) 826 

Tongue,  action  of,  hi  mastication 204 

action  of  the  muscles  of 204 

action  of,  in  sucking 204 

action  of,  in  deglutition 204,  219 

mechanism  of  the  protrusion  of 204 

action  of,  in  phonation 558 

action  of,  in  speech ........  562 

influence  of  the  facial  nerve  upon 624 

influence  of  the  sublingual  nerve  upon 634 

papilhe  of 765,  766 

development  of 923 

Tonicity  of  muscles 534 

Tonsils 209,216 

Touch,  sense  of 751 

variations  in  the  sense  of,  in  different  parts 751 

extraordinary  development  of  the  sense  of 751 

— —  table  of  variations  in  the  sense  of,  in  different 

parts..' T53 

Townshenrt,  Colonel,  voluntary  arrest  of  respiration 
and  the  action  of  the  heart  by 55 


INDEX. 


975 


PAGE 

Trachea 118,119 

action  of,  in  phonation 557 

development  of. 922 

Trachealis  muscle 119 

Tractus  spiralis  foraminulentus 847 

Tragus  of  the  ear 817 

Training 498 

Transfusion  of  blood 2 

Transudations 348 

Transversalis,  action  of,  in  expiration 131 

Trapezius,  action  of  the  superior  portion  of,  in  respi- 
ration   128 

Triangularis  sterni,  action  of,  in  expiration 130 

Tricuspid  valve .- 38,  47 

safety-valve  function  of. 47, 109 

Trifacial,  or  trigeminal  nerve  (see  Fifth  cranial  nerve, 

large  root  of) 634 

Trigone 408 

Triphthongs 561 

Triplets 941 

Trochlearis  nerve  (see  Patheticus) 613 

Trommer's  test  for  sugar 461 

Trophic  centres  and  nerves 741 

Truffles 191 

Tuber  annulare,  physiological  anatomy  of 722 

function  of. 723 

development  of 917,  918 

Tubercula  quadrigemina,  physiological  anatomy  of. . .  722 

functions  of. ; 722 

reflex  action  of,  upon  the  iris 722,  797 

development  of 917,  918 

Turkish  baths 521 

Turning  movements  following  injury  of  certain  parts 

of  the  encephalon 728 

Twins,  one  white  and  the  other  black 894 

one  male  and  the  other  female 895 

question  of  development  of,  from  a  single  ovum 

or  from  two  ova 941 

Siamese 942 

Tympanic  membrane,  physiological  anatomy  of 835 

— -  pockets  in 835 

connection  of,  with  the  ossicles 835 

color  of 836 

cone  of  light  in 837 

uses  of 837 

vibration  of,  by  influence 837 

tension  of,  by  muscular  action 820,  837,  838- 

theory  of  the  action  of,  in  the  appreciation  of 

musical  sounds 838 

protection  of,  from  concussion 840 

Tympanum 818 

development  of '. 923 

Tyrosine 421 

Tyson,  glands  of 359 

Umbilical  arteries  and  vein 905,  933 

Umbilical  cord 90 

valves  in  the  vessels  of 906 

Umbilical  hernia  in  the  foetus 904,  920 

Umbilical  vein,  closure  of. 938 

Umbilical  vesicle .' 904 

Umbilicus,  amniotic 901 

decidual 908 

intestinal 904 

Unconscious  cerebration 744 

Unison 826 

Urachus 907,  920 

Ursemic  poisoning 403 

Urea,  influence  of  coffee  upon  the  elimination  of  188,  428 


Urea,  presence  of,  in  the  lymph 832 

presence  of,  in  the  chyle 836 

accumulation  of,  in  the  blood,  after  extirpation 

of  the  kidneys 403 

effects  of  injection  of,  into  the  blood-vessels,  after 

extirpation  of  the  kidneys 403 

vicarious  elimination  of,  after  extirpation  of  the 

kidneys 403 

characters  of. 413 

where  found  in  the  economy 414 

artificial  formation  of 414 

— —  decomposition  of 414 

crystals  of 414 

origin  of. 414 

detection  of,  in  the  blood 415 

production  of,  in  the  liver 415 

theory  of  production  of,  from  uric  acid,  crea- 

tine,  etc 415 

amount  of  daily  excretion  of 416 

influence  of  nitrogenized  food  upon  the  elimina- 
tion of 428 

influence  of  alcohol,  tea,  and  coffee  upon  the 

elimination  of. 188,  428 

influence  of  muscular  exercise  upon  the  elimina- 
tion of 428 

influence  of  the  sympathetic  system  upon  the 

elimination  of 788 

diminished  excretion  of,  during  menstruation . . .  876 

Ureters,  physiological  anatomy  of 407 

contractions  of,  produced  by  stimulation  of  the 

eleventh  dorsal  nerves 409 

development  of 928 

Urethra,  physiological  anatomy  of 409 

glands  of 883 

development  of 920 

Uric  acid  and  its  compounds 416 

amount  of  daily  excretion  of 417 

Influence  of  muscular  exercise  upon  the  elimina- 
tion of 429 

Urinary  organs,  development  of 928 

Urine,  absorption  of  the  watery  portion  of,  by  the 

bladder 817 

mechanism  of  the  production  of 401 

influence  of  the  nervous  system  upon  the  secre- 
tion of 405 

influence  of  blood-pressure  upon  the  secretion  of  405 

effects  of  destruction  of  the  nerves  of  the  kid- 
neys upon  the  secretion  of. 405 

alternate  action  of  the  kidneys  in  the  secre- 
tion of 406 

mechanism  of  the  discharge  of. 409 

properties  and  composition  of. 410 

color  and  odor  of 410 

temperature  of 410 

quantity  and  variations  of 411 

specific  gravity  and  reaction  of .'  —  411 

cause  of  the  acidity  of 412 

composition  of 412 

table  of  constituents  of 413 

fatty  matters  in 421 

Inorganic  constituents  of 421 

chlorides  of. 422 

sulphates  of 423 

phosphates  of. 423 

derivation  of  the  phosphates  of,  from  food  and 

from  the  tissues 428 

relation  of  the  proportion  of  phosphates  in,  to 

the  condition  of  the  brain 424 

variations  in  the  phosphates  of. 424 


976 


INDEX. 


PAGE   i  PAGE 

Urine,  coloring  matter  and  mucus  of.  424     Valentin,  limiting  membrane  of. 566 

- —  gases  of 425     Valsalva,  sinuses  of 89,  64 

variations  in  the  composition  of 426     -  —  humor  of. 846 

variations  of,  with  age  and  sex 426  Valsalva's  method  for  protection  of  the  membrana 

of  the  foetus 426         tympani  from  concussion 840 

variations  of,  at  different  seasons  and  at  different  Valve,  tricuspid 38,  47 

periods  of  the  day 427        —  pulmonic 38,  48 

variations  of,  produced  by  food 427        —mitral 39,47 

influence  of  nitrogenized  food  upon 428        —  aortic 39,  48 

influence  of  muscular  exercise  upon  the  quantity  Valves  of  the  veins,  discovery  of. 32 

of. 428        —  uses  of,  described  by  Harvey 33,  96 

influence  of  muscular  exercise  upon  the  inorganic  Valves  of  the  heart,  action  of. 46 

constituents  of 429     Valves  of  the  lymphatics 303,  309,  340 

influence  of  mental  exertion  upon 430     Valvulae  conniventes 259,  302 

influence  of  the  sympathetic  system  upon 738     -  —  development  of 920 

Urrosacine 424  I  Vas  deferens 880,881 

Uterine  plug  of  mucus 908,  938     movements  of,  produced  by  galvanization  of  the 

Uterus,  mucus  of 357         lumbar  portion  of  the  spinal  cord 882 

situation  and  position  of. 857        —  development  of,  from  the  Wolffian  duct 928 

—  ligamentsof 858,864     Vasa  vasorum 67,94 

parts  and  structures  contained  in  the  broad  liga-  Vasa  vorticosa 772 

ment  of. 858     Vascular  arches,  in  the  embryon 933 

physiological  anatomy  of 863  !  Vascular  blastodermic  layer 931 

—  muscular  fibres  of. 864     Vaso-motor  nerves  and  centres 67,  739 

arrangement  of  the  muscular  layers  of. 864     Vater,  corpuscles  of 573 

platysma  of. 864  I  Vegetable  albumen 178 

—  mucous  membrane  of  the  body  of 864  I  Vegetable  caseine 179 

—  mucous  membrane  of  the  cervix  of 865,  866  !  Vegetable  fibrin 179 

—  tubules  of  the  mucous  membrane  of. 866  I  Vegetable  food : 178 

variations  in  the  thickness  of  the  mucous  mem-  Vegetables,  digestibility  of 251 

brane  of,  with  menstruation 866     Veins,  variations  in  the  color  of  the  blood  in 5 

ovules  of  Naboth  of 866  j  -  —  renal,  color  of  the  blood  in 5 

arbor  yitse  of. 866     discovery  of  valves  of 32 

blood-vessels  of 866  !  uses  of  the  valves  of,  described  by  Harvey .      33,  96 

erectile  tissue  of 866     circulation  in 92,  98 

erectile  tissue  of  the  cervix  of 867     capacity  of,  as  compared  with  that  of  the  arte- 

nerves  of. 867        ries 93 

changes  in  the  mucous  membrane  of,  during            anastomoses  of 94 

menstruation 866,  876  I  structure  and  properties  of 94 

action  of  the  cervix  and  os  of,  in  coitus 890     coats  of 94 

penetration  of  the  semen  into 891     vasa  vasorum  of 94 

—  production  of  mucus  in  the  neck  of,  in  coitus ...  891 strength  of  the  walls  of 95 

formation  of  the  membranse  deciduae  from  the            elasticity  and  contractility  of. 96 

mucous  membrane  of 907     valves  of 96, 104 

—  secretion  of  mucus  by  the  cervix  of,  in  preg-          j  those  in  which  there  are  no  valves 98 

nancy 908,938  '  course  of  the  blood  in 98 

—  first  appearance  of  the  new  mucous  membrane  —  pulse  in. 99, 106 

of,  in  pregnancy 908  !  >—  pressure  of  blood  in .99 

development  of 928  !  rapidity  of  the  flow  of  blood  in 100 

—  double 928     causes  of  the  circulation  in 100 

development  of  the  round  ligament  of 928     obstacles  to  the  flow  of  blood  in 101, 105 

enlargement  of,  in  pregnancy 938     influence  of  muscular  contraction  upon  the  flow 

cause  of  the  first  contraction  of,  in  normal  par-  of  blood  in 101 

turition 942     influence  of  the  force  of  aspiration  from  the 

involution  of. 943         thorax  upon  the  circulation  in 102 

restoration  of  the  mucous  membrane  of,  after  of  the  liver,  circulation  in 102 

parturition 943     entrance  of  air  into 103 

Utricle  of  the  internal  ear 843     influence  of  gravity  upon  the  circulation  in .  103, 106 

—  distribution  of  the  nerves  in 846     influence  of  a  suction  force  exerted  by  larger 

Uvea 775        upon  smaller  vessels  upon  the  circulation  in 104 

Uvula 216     relations  of  respiration  to  the  circulation  in 105 

—  influence  of  the  facial  nerve  upon 623     •  —  regurgitant  pulse  in 106 

Uvula  vesicse 408     -  —  development  of 933 

Velum  pendulum  palati 216 

Vagina 857,  868     action  of,  in  phonation 55S 

—  sphinctcrof 869     influence  of  the  facial  nerve  upon  the  movements 

structure  of 869         of 624 

—  double 928     Vena  innominata,  development  of 934 

Vaginal  mucus 357     Vense  cavse,  development  of 934 


INDEX. 


977.^ 


PAGE 

Venereal  orgasm,  in  the  male 889 

in  the  female 891 

Venereal  sense , 754 

Venoms,  absorption  of 319,  327,  35S 

Venous  sinuses 95 

Ventilation  of  hospitals,  prisons,  etc 142 

Ventricles  of  the  heart 36 

comparative  capacity  of  right  and  left 36 

comparative  thickness  of  right  and  left 88 

shortening  and  elongation  of 42 

Venules,  or  venous  radicles 93 

Verheyn,  stars  of 401 

Vermiform  appendix 288 

Vernix  caseosa ~ 363,  916 

Vertebra?,  first  appearance  of. 914,  915 

Vertebral  arteries,  development  of 932 

Vertebral  column  (see  Spinal  column) 915 

Vertebral  plates 913,  915 

Vertigo 718 

Vesiculse  seminales 882 

development  of 928 

Vessels,  coagulation  of  the  blood  in 27 

Vestibule  of  the  ear 822,  842 

Vibriones 855 

Villi  of  the  small  intestine 261,  302 

development  of . 920 

Villi  of  the  vitelline  membrane 901 

Villi  of  the  amnion 901 

Villi  of  the  allantois 901,  905 

Villi  of  the  chorion 905 

Villi  of  the  placenta 911 

Vinegar 190 

Visceral  arches 922 

Visceral  clefts 922 

Visceral  plates 914,  916,  920 

Vision,  physiological  anatomy  of  the  organs  of  (see 

Optic  nerves  and  Eye) 767 

area  of 785,  791 

laws  of  refraction,  dispersion,  etc.,  bearing  upon 

the  physiology  of 785 

refraction  by  lenses 787 

myopic 788 

hypermetropic 789 

presbyopic 789 

formation  of  images  in 791 

demonstration  of  the  fact  that  the  layer  of  rods 

and  cones  is  the  seat  of  visual  impressions 791 

area  of  distinct .- , 792 

blind  spot  in  the  retina 792 

mechanism  of  refraction  in 793 

astigmatic 794 

movements  of  the  iris  in 796 

accommodation  in 798 

through  a  small  orifice,  like  a  pinhole 801 

erect,  although  the  images  on  the  retina  are  in- 
verted   801 

binocular 802 

double 802 

corresponding  points  on  the  retina  in. .  802,  803,  810 

horopter  of 803 

monocular 804 

estimation  of  distance,  the  form  and  solidity  of 

objects,  etc 804 

with  the  stereoscope 805 

binocular  fusion  of  colors 805 

duration  of  luminous  impressions  in 806 

fusion  of  colors  in 806 

irradiation  in 806 

accidental  areola?  in 807 

62 


PAGE  : 

Vision,  development  of  the  organs  of 918 

Vital  capacity  of  the  lungs 188  . 

—  variations  in,  with  stature 138 

Vital  point 727 

Vitelline 177 

Vitelline  circulation 931 

Vitelline  membrane  of  the  ovum 870  • 

disappearance  of,  after  fecundation 901 

villosities  of. 901 

Vitellus 870 

deformation  and  gyration  of 897 

bright  appearance  of,  after  fecundation 897 

formation  of  the  polar  globule  of. '897 

formation  of  the  nucleus  of 897 

segmentation  of 896,  897 

Vitreous  humor 782 

hyaloid  membrane  of 782 

in  the  embryon 782 

blood-vessels  of 782 

refraction  by.  793 

Vocal  chords 116,  550 

—  action  of,  in  phonation 555 

Vocal  registers 558 

Voice  and  speech 549 

Voice,  mechanism  of  the  production  of 558 

action  of  the  vocal  chords  in 555 

variations  in  the  quality  of 555 

varieties  of 556 

in  boys 556 

range  of 556 

action  of  the  accessory  organs  of 557 

action  of  the  trachea  in 557 

action  of  the  larynx  and  epiglottis  in 558 

action  of  the  pharynx  in 558 

action  of  the  mouth  in 558 

action  of  the  nasal  fossae  in , 558 

action  of  the  tongue  in 558 

action  of  the  velum  palati  in 558 

different  registers  of 558 

influence  of  the  spinal  accessory  nerve  upon 629 

influence  of  the  superior  laryngeal  branches  of 

the  pneumogastrics  upon 651 

Voluntary  muscular  tissue  (see  Muscular  tissue) 528 

Vomiting,  mechanism  of 256 

Vowels , 560 

Vowel-sounds,  mechanism  of 561 

Wagner,  spot  of 870 

Wandering  cells  of  the  cornea 771 

Water,  functions  of,  in  the  blood 21 

functions  of,  in  alimentation 184, 191 

quantity  of,  necessary  to  nutrition 191 

quantity  of,  eliminated  by  the  organism 191 

absorption  of,  by  the  lacteals 314 

absorption  of,  by  the  skin 315 

condition  of,  in  the  economy 490 

general  functions  of 490 

table  of  quantities  of,  in  different  tissues 491 

origin  and  discharge  of 492 

Watery  vapor,  exhalation  of,  by  the  lungs 153 

Webster,  brain  of 70S 

Weight,  appreciation  of 751 

Wharton,  duct  of 208 

gelatine  of 906 

Whey 871 

Wisdom-teeth 201 

Wolflian  bodies 913 

structure  of 927 

time  of  disappearance  of,  in  the  female 928 


978 


INDEX. 


PAGE 

V.'olffian  bodies,  development  of  the  epididymis  from  928 

Wolfflan  ducts 914,  927 

development  of  the  vasa  deferentia  from 928 

Woorara,  pulsation  of  the  heart  in  animals  poisoned 

by 56,  59,  61 

absorption  of 319,  827 

influence  of,  upon  nervous  irritability 595 

Wrisberg,  nerve  of 620,  621,  760 


PAGE 
Xanthine 420 

Yawning 134 

Yolk,  principal,  or  formative 870 

Youth 945 

Zona  pellucida 869 

Zone  of  Zinn 778,  779,  7S1 


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